A Small Molecule NNMT Inhibitor Puts Aged Stem Cells Back to Work to Improve Muscle Regeneration in Old Mice

In old tissues, stem cell activity is much reduced relative to youthful activity. This is thought to be the most important contribution to loss of muscle mass and strength with age, leading to the condition known as sarcopenia. It also diminished the ability to regenerate after muscle injury. Numerous studies in the regenerative medicine community have demonstrated that while this loss of stem cell function may be a defense against cancer, reducing the activity of cells that may bear potentially dangerous molecular damage, there appears to be a fair amount of room to push the balance towards greater activity without large increases in cancer risk. In mice, anyway.

Researchers here demonstrate a novel way of increasing muscle stem cell activity, to add to a number of others that have been shown to work to some degree in animal studies. The mechanism is arguably somewhat related to work on ways to increase levels of NAD+ so as to enhance mitochondrial activity in old tissues. Here the effect size on muscle regeneration in mice is certainly large enough to be interesting. We'll no doubt see what it does in humans fairly soon, even ahead of human trials, as the self-experimentation community decides to try this out. One would hope they would go about it more carefully than is usually the case in body building circles.

Aging is accompanied by progressive declines in skeletal muscle mass and strength and impaired regenerative capacity, predisposing older adults to debilitating age-related muscle deteriorations and severe morbidity. Muscle stem cells (muSCs) that proliferate, differentiate to fusion-competent myoblasts, and facilitate muscle regeneration are increasingly dysfunctional upon aging, impairing muscle recovery after injury. While regulators of muSC activity can offer novel therapeutics to improve recovery and reduce morbidity among aged adults, there are no known muSC regenerative small molecule therapeutics.

We recently developed small molecule inhibitors of nicotinamide N-methyltransferase (NNMT), an enzyme overexpressed with aging in skeletal muscles and linked to impairment of the NAD+ salvage pathway, dysregulated sirtuin 1 activity, and increased muSC senescence. We hypothesized that NNMT inhibitor (NNMTi) treatment will rescue age-related deficits in muSC activity to promote superior regeneration post-injury in aging muscle.

24-month old mice were treated with saline (control), and low and high dose NNMTi for 1-week post-injury, or control and high dose NNMTi for 3-weeks post-injury. In vivo contractile function measurements were conducted on the injured tibialis anterior (TA) muscle and tissues collected for ex-vivo analyses, including myofiber cross-sectional area (CSA) measurements to assess muscle recovery. Results revealed that muscle stem cell proliferation and subsequent fusion were elevated in NNMTi-treated mice, supporting nearly 2-fold greater CSA and shifts in fiber size distribution to greater proportions of larger sized myofibers and fewer smaller sized fibers in NNMTi-treated mice compared to controls.

Prolonged NNMTi treatment post-injury further augmented myofiber regeneration evinced by increasingly larger fiber CSA. Importantly, improved muSC activity translated not only to larger myofibers after injury but also to greater contractile function, with the peak torque of the TA increased by ∼70% in NNMTi-treated mice compared to controls. Taken together, these results provide the first clear evidence that NNMT inhibitors constitute a viable pharmacological approach to enhance aged muscle regeneration by rescuing muSC function.

Link: https://doi.org/10.1016/j.bcp.2019.02.008

A Study of Cell Size in the Context of Cellular Senescence

Senescent cells are a major problem in our bodies, in that their growing presence over the years is an important cause of degenerative aging. Unfortunately, the research community can't just prevent cells from ever becoming senescent, even were the capacity to do that in hand today, because transient senescence serves many useful, even necessary purposes in our biochemistry. It is only the lingering senescent cells that are the problem. Periodically removing these unwanted, harmful cells is a very viable way forward, however, and a new biotechnology industry is springing up to do just that.

One very interesting point about senescent cells is that they are notably larger than normal cells. One research group has produced a way of counting senescent immune cells from a blood sample based on sorting by size. Another measured the sizes of cells in old hearts, before and after clearing out senescent cells with a senolytic treatment, showing that the senescent cells were larger. I have to think that there is something useful, potentially even important, that can be done with this feature of senescent cells - the clever implementation just hasn't arrived yet.

In multicellular organisms, cell size ranges over several orders of magnitude. This is most extreme in gametes and polyploid cells but is also seen in diploid somatic cells and unicellular organisms. While cell size varies greatly between cell types, size is narrowly constrained for a given cell type and growth condition, suggesting that a specific size is important for cell function. Indeed, changes in cell size are often observed in pathological conditions such as cancer, with tumor cells frequently being smaller and heterogeneous in size. Cellular senescence in human cell lines and budding yeast cells is also associated with a dramatic alteration in size: senescing cells become exceedingly large. Cell size control has been studied extensively in a number of different model organisms, but why cell size may need to be tightly regulated is not known.

Several considerations argue that altering cell size is likely to have a significant impact on cell physiology. Changes in cell size affect intracellular distances, surface to volume ratio and DNA:cytoplasm ratio. It appears that cells adapt to changes in cell size, at least to a certain extent. During the early embryonic divisions in C. elegans, as cell size decreases rapidly, spindle size shrinks accordingly. Other cellular structures such as mitotic chromosomes, the nucleus and mitochondria have also been observed to scale with size in various organisms. Similarly, gene expression scales with cell size in human cell lines as well as in yeast.

However, not all cellular pathways can adapt to changes in cell size. For example, signaling through the spindle assembly checkpoint, a surveillance mechanism that ensures that cells enter anaphase only after all chromosomes have attached to the mitotic spindle, is less efficient in large cells in C. elegans embryos. In human cell lines, maximal mitochondrial activity is only achieved at an optimal cell size. Finally, large cell size has been shown to impair cell proliferation in budding yeast and human cell lines.

Here we identify the molecular basis of the defects observed in cells that have grown too big. We show that in large yeast and human cells, RNA and protein biosynthesis does not scale in accordance with cell volume, effectively leading to dilution of the cytoplasm. This lack of scaling is due to DNA becoming rate-limiting. We further show that senescent cells, which are large, exhibit many of the phenotypes of large cells. We conclude that maintenance of a cell type-specific DNA:cytoplasm ratio is essential for many, perhaps all, cellular processes and that growth beyond this cell type-specific ratio contributes to senescence.

Link: https://doi.org/10.1016/j.cell.2019.01.018

Harmful Signals Secreted by Senescent Cells Depend on the Presence of Senescence-Associated Heterochromatin Foci

Now that senescent cells are widely acknowledged as a cause of aging and age-related disease, and now that a large industry is forming to find ways to destroy or otherwise render harmless these cells, a great deal more investigative work into the biochemistry of senescence is taking place than was the case in earlier years. While destruction is very straightforward, and certainly easier to engineer at the present time, a sizable faction of scientists are interested in finding ways to turn off the harmful signals secreted by senescent cells. It is this signaling, the senescence-associated secretory phenotype (SASP), that causes all of the damage: chronic inflammation; destructive remodeling of the surrounding tissue structure; encouraging nearby cells to also become senescent; and so forth.

Because the SASP is complicated and poorly mapped, and no doubt depends on the operation of scores of interacting mechanisms inside a cell, and few of those mechanisms are particularly well mapped in this context, it seems to me that investigating ways to modulate the SASP is more of an academic exercise than a road to therapies at the present time. It cannot possibly compare in efficiency to destroying senescent cells. The only reason to avoid destroying these cells would be the discovery of essential senescent populations, such as neurons in the brain that are both senescent and carrying out vital functions, perhaps. So far that hasn't been the case: old mice do just fine when given senolytic therapies to destroy senescent cells throughout the body, including the brain.

Nonetheless, we might ask whether or not there are master regulators of the SASP yet to be discovered. If so, their existence might make SASP suppression a more viable proposition in the future. The open access research results below may represent a step in that direction. The researchers have found what looks like a fairly important point of control for the SASP, or at least a point of dependency, and that suggests the possibility of a master regulator, even if the exact mechanism examined here turns out to be infeasible as the basis for a point of intervention (which seems quite likely to be the case at first glance).

Study sheds light on damage linked to ageing

Some of the damaging cell effects linked to ageing could be prevented by manipulating tiny parts of cells, a study shows. Scientists have shed light on how the harm caused by senescence - a vital cell process that plays a key role in diseases of ageing - could be controlled or even stopped. Researchers say the findings could have relevance for age-related diseases, although they caution that further research is needed.

During senescence, cells stop dividing. This can be beneficial in assisting wound-healing and preventing excessive growth. Some aspects of senescence are also harmful and can lead to tissue damage and the deterioration of cell health as seen in diseases of older age. Researchers focused on a chain of harmful processes triggered by senescence, known as the senescence-associated secretory phenotype (SASP). The SASP is a cascade of chemical signals that can promote damage to cells through inflammation. The researchers showed that manipulating a cell's nuclear pores - gateways through which molecules enter the heart of the cell - prevented triggering of the SASP. Findings also show that DNA had to be reorganised in space within in the cell nucleus in order for the SASP to be triggered.

Nuclear pore density controls heterochromatin reorganization during senescence

Three-dimensional (3D) genome organization is governed by a combination of polymer biophysics and biochemical interactions, including local chromatin compaction, long-range chromatin interactions, and interactions with nuclear structures. One such structure is the nuclear lamina (NL), which coats the inner nuclear membrane and is composed of lamins and membrane-associated proteins, such as Lamin B receptor (LBR). Large blocks of heterochromatin are associated with the nuclear periphery, and mapping genome interactions with laminB1 identifies more than 1000 lamina-associated domains (LADs).

One situation in which there is a dramatic reorganization of heterochromatin is in oncogene-induced senescence (OIS) - a cell cycle arrest program triggered by oncogenic signaling. OIS cells undergo striking chromatin reorganization with loss of heterochromatin and constitutive LADs from the nuclear periphery and the appearance of internal senescence-associated heterochromatin foci (SAHFs). SAHFs are not observed in nontransformed replicating cells.

The nuclear envelope is perforated by nuclear pores that control transport between the cytoplasm and nucleus. The nuclear pore complex (NPC) is a large transmembrane complex consisting of ∼30 proteins called nucleoporin. The nuclear area underneath nuclear pores is devoid of heterochromatin. The nucleoporin TPR has been shown to be responsible for heterochromatin exclusion zones at the NPC.

The composition and density of the NPC change during differentiation and tumorigenesis. We therefore hypothesized that the NPC could contribute to global chromatin organization and that, specifically, heterochromatin organization could result from a balance of forces attracting heterochromatin to the NL and forces repelling it away from the NPC. In support of this hypothesis, we show here that nuclear pore density increases during OIS and that this increase is necessary for heterochromatin reorganization into SAHFs. We identified TPR as a key player in this reorganization. Furthermore, we demonstrated the functional consequences of heterochromatin reorganization in OIS for the programmed activation of inflammatory cytokine gene expression: the senescence-associated secretory phenotype (SASP).

Interviewing Kelsey Moody of Ichor Therapeutics at the Longevity Leaders Conference

Ichor Therapeutics, led by Kelsey Moody, was one of the first companies to emerge from the core SENS Research Foundation community. The company has grown over the years and is now at the head of a collection of spin-out startups focused on a variety of approaches to aging, such as senolytic therapies to destroy senescent cells (Antoxerene), and clearance of a form of metabolic waste that contributes to macular degeneration (LysoClear). The influx of funding in this field that has taken place over the past couple of years is now powering Ichor Therapeutics forward towards the clinic.

Ichor and its portfolio companies have been very busy over the last year, so I thought it was time that we caught up on progress. Can you tell us how things are going for the Ichor group?

Ichor really had a good year in 2018. We raised over $16 million across our portfolio, and that's allowed us to scale up all aspects of our operations. We're at over 50 employees now, mostly bench scientists and research technicians, and we're really delivering on our goal of being a vertically integrated biopharmaceutical company. What that means is we want to be able to take any idea, regardless of what it is, such as a type of compound or therapeutic indication, and rapidly turn it from the discovery stage, through the pipeline, into the first demand studies. The additional capital that we've raised and the infrastructure that we're putting online are really allowing us to put that all together to support the field of longevity.

Juvenescence and you made a collaborative project called FoxBio. How's that going?

Unfortunately, I can't say a whole lot about the progress on FoxBio, except to say that I'm very, very bullish on it and very excited about the prospects and implications. We are very excited to partner with Juvenescence due to the depth of experience that they bring to the drug discovery process and the insights that they have about creating not just strong drug development and discovery programs but also company structures and platforms that allow entities to raise the large amount of capital that is necessary for clinical trials, as it's just a huge value add to the core portfolio. We found them to be great to work with, and we're really excited to expand the scope of that relationship over time.

What's the news on Lysoclear, the therapy for adult age-related adult blindness?

Again, I can't talk a whole lot about the specifics, but we did close a financing round in December of 2018 to move from our proof-of-concept lead drug candidate to a clinical candidate that would be suitable for first-demand studies. We're in the process of putting together our plan to reach IND (investigational new drug) status. IND in the US system is the point at which you're able to go into human trials for the first time. That requires all kinds of backend support, from manufacturing your product under good manufacturing processes (GMP) to toxicology studies and so forth. We were very fortunate last year to recruit a chief medical officer who has a lot of experience in drug development and discovery. He's got about 12 drugs and medical devices under his belt and about 185 clinical trials in the macular degeneration space. We're very enthusiastic to have someone with that depth of expertise, really taking the reins on our clinical planning and making sure that when we're ready with our candidate to pull the trigger, we're able to navigate clinical and regulatory issues that might arise.

An area that has been problematic in the past has been taking the research from a basic stage to a translational point where it can then go to market. Has that improved in the last few years?

Yeah, I think so. I think there's a lot of academic labs in particular now that have an eye for spinning out companies, particularly with new groups emerging in the area. Juvenescence, of course, is licensing different types of technology and having a partnership with the Buck Institute, for example, and Life Biosciences, a new player in the space, is bringing in substantial amounts of capital to assist academic labs with translating programs. What's really exciting about all of this is when you bring these sophisticated drug developers into this space, you're adding a certain level of robustness to the discovery process that might not necessarily exist in a traditional academic setting. It really allows you to combine the best of both worlds.

How did you develop your career from someone who was a high school and college athlete to where you are now?

Well, like a lot of people that are really trying to start companies and do things in this space, I started by reading a book, Aubrey de Grey's book, in fact, Ending Aging, which I think was published a little over a decade now. I told myself that I'm going to switch to biochemistry as a major, and I'm going to pursue this line of work until I am certain that Aubrey is wrong. Despite my very best efforts, I have not been able to get to any sort of definitive conclusion on that. He still might be, and many have tried to prove him wrong, but the trend is in his favor. That, of course, took me to work with Aubrey at SENS Research Foundation and various startups in Silicon Valley and then eventually become a medical student where I currently am.

One of the really interesting things that I think is underappreciated about the SENS paradigm, and is a central component to how we're structuring our companies, is really this damage repair approach. A lot of people like the SENS damage repair approach that Aubrey put forth because it's something that we can understand and the whole argument of sidestepping the ignorance of metabolism, and so forth. What's underappreciated by most people that do drug development, that I think is worth highlighting here, is that the sorts of therapies that would emerge from this line of thinking are therapies that are going to be used intermittently, and that is hugely beneficial from a development perspective. That creates a huge opportunity for drug developers to bring in whole new classes of drugs that are actually able to mitigate many of these diseases of aging in a way that's rather unprecedented and very much defies the chronic-administration sort of model that we're familiar with in this space.

Link: https://www.leafscience.org/an-interview-with-kelsey-moody-developing-a-company-to-end-age-related-diseases/

White Blood Cells Degrade Capillary Blood Flow to Contribute to Age-Related Neurodegeneration

Researchers here outline a new discovery regarding the origin of reduced blood flow in the aging brain; white blood cells are clogging up capillaries. It is well known that the supply of blood is reduced in tissues with age; this is studied in muscles and the brain, among other tissue types. Some researchers blame a reduction in capillary density in later life, others consider reduced capacity of the heart to pump blood uphill to the brain. A lesser flow of blood in any specific tissue will affect its function, especially in energy-hungry tissues such as the brain, as the supply of oxygen and nutrients is reduced.

In the case of the results reported here, I have to wonder whether this might tie in some way to the observed reduction in capillary density with age; does blockage by white blood cells result in significant capillary atrophy at the smallest scale of blood vessels? There are certainly other mechanisms by which that outcome could occur, and this may not be an important contribution even it does produce atrophy to some degree.

The existence of cerebral blood flow reduction in Alzheimer's patients has been known for decades, but the exact correlation to impaired cognitive function is less understood. "People probably adapt to the decreased blood flow, so that they don't feel dizzy all of the time, but there's clear evidence that it impacts cognitive function." A new study offers an explanation for this dramatic blood flow decrease: white blood cells stuck to the inside of capillaries, the smallest blood vessels in the brain. And while only a small percentage of capillaries experience this blockage, each stalled vessel leads to decreased blood flow in multiple downstream vessels, magnifying the impact on overall brain blood flow.

The work began with a study in which researchers were attempting to put clots into the vasculatures of Alzheimer's mouse brains to see their effect. "It turns out that the blockages we were trying to induce were already in there. It sort of turned the research around - this is a phenomenon that was already happening." The researchers determined that only about 2 percent of brain capillaries had "stalls" (blockages), but the cumulative effect of that small number of stalls was an approximately 20 percent overall decrease in brain blood flow, due to the slowing of downstream vessels by the capillaries that were stalled.

Recent studies suggest that brain blood flow deficits are one of the earliest detectable symptoms of dementia. To test the effect of the stalls on performance of memory tasks in Alzheimer's mice, they were given an antibody that interfered with the adhesion of white blood cells to capillary walls, which caused the stalled capillaries to start flowing again and thus increased overall brain blood flow. Memory function was improved within a few hours, even in aged mice with more advanced stages of Alzheimer's disease.

Link: http://news.cornell.edu/stories/2019/02/brain-blood-flow-finding-gives-hope-alzheimers-therapy

Trends in Human Mortality in Very Late Life May be Illusions Resulting from Bad Data

To my mind far too much effort is expended on trying to figure out the epidemiology of the tiny fraction of humans who manage to live a fair way past one hundred years of age. For one, there just aren't enough of them to generate truly robust data from which conclusions can be drawn. People are still arguing over the legitimacy of many of the cases, including Jeanne Calment. Gathering and vetting data on the age of very old people is inherently challenging in its own ways. As the authors of today's paper point out, we should be more suspicious than we are of claims of extreme longevity. You might compare their position with another recent discussion on this topic that presents similar conclusions - the quality of the data on ages of extremely old people just isn't great. But beyond legitimacy, small data sets naturally come with all sorts of other problems. The law of small numbers applies: a low number of data points tends to exhibit false trends that will vanish given more data points.

The more important issue here, however, is that this simply doesn't matter! It really is of little importance as to the statistics of how the small number of oldest humans age to death in the absence of rejuvenation therapies. It is unimportant because rejuvenation therapies will soon arrive in the clinic. The first experimental rejuvenation therapies worthy of the name are available now for the adventurous to try. It won't be long before near everyone who reaches old age will have undergone one or more forms of treatment to slow or reverse the progression of aging. The world of natural aging, in which there were no deliberate attempts to intervene in the mechanisms that cause aging, is soon to vanish. In this environment of rapid progress in biotechnology, the demographics of unmodified aging are of increasingly little importance. Instead, the focus must be on forging ahead with the development of rejuvenation biotechnology, the means to prevent and reverse the suffering and disease of aging.

Late-life mortality is underestimated because of data errors

The world longevity record for Jeanne Calment (122 years) is widely cited with great pride as the gold standard of the highest data quality for many decades. Yet even for this best documented longevity claim, some early doubts were expressed of her suspicious extremely outlying age. Still, most scientists and the public believe in the validity of the Calment longevity record. The situation is even more serious-our studies found that many longevity records for ages 105 years and older are often incorrect (see later). After age 105 years, longevity claims should be considered as extraordinary claims that require extraordinary evidence. Traditional methods of data cleaning and data quality control are just not sufficient. New, more strict methodologies of data quality control need to be developed and tested. Before this happens, all mortality estimates for ages above 105 years should be treated with caution.

Knowledge of true mortality trajectory at extreme old ages is important not only for actuaries but also for biologists who test their theories of aging with demographic data. Studies conducted in the 1990s suggest that the exponential growth of human mortality with age (the Gompertz law) is followed by a period of deceleration, with slower rates of mortality increase. These early studies, as well as studies on insects, convinced researchers of the universality of the mortality deceleration phenomenon, and until recently, there was no doubt among biodemographers and gerontologists that mortality slows down after the age of 80 years. At that time, several biological explanations of mortality deceleration and late-life mortality plateau were suggested. Reliability models of aging also suggest mortality plateau at advanced ages when assuming random loss of functional cells and other essential elements over time.

Recently, the common view about mortality deceleration at advanced ages has been challenged using both theoretical and empirical considerations. It was found that mortality of US extinct cohorts born after 1889 demonstrated the Gompertz-like trajectory in the age interval 85 to 106 years. In the study of old-age mortality in 15 low-mortality countries, Gompertz-like mortality growth was found at older ages for Australia, Canada, and the US and mortality deceleration for other studied countries.

It should be noted that hazard rate estimation at very old ages faces difficulties because of very small number of survivors to these ages, and age misreporting by older persons. Age misreporting is a big problem affecting estimates of mortality at advanced ages. It was found that even a small percentage of inaccurate data can greatly distort mortality trajectories at advanced ages and that age misreporting at older ages results in mortality underestimation. Taking into account that the accuracy of age reporting is positively correlated with education, it is reasonable to expect improvement in age reporting over time and less prevalent mortality underestimation or mortality deceleration at older ages for more recent birth cohorts. Indeed, it was found that late-life mortality in historically older US birth cohorts demonstrates stronger mortality deceleration compared to more recent birth cohorts. These results suggest that mortality deceleration observed in early studies of old-age mortality may be caused by age misreporting at older ages.

Announcing the Academy for Health and Lifespan Research

Funding is pouring into the commercial development of the first rejuvenation therapies, largely meaning senolytic treatments at the present time, alongside various ways of upregulating beneficial stress responses in order to modestly slow aging. As this progresses, we will see an accompanying growth in advocacy for the treatment of aging as a medical condition. The announcement noted here is an example of the type, somewhat analogous to the Longevity Dividend initiative of the past decade, but hopefully more energetic and more focused on strategies such as clearance of senescent cells that are likely to produce larger gains in human health and life span.

A group of leading scientists devoted to research on the mechanisms of biological aging today announced the formation of the Academy for Health and Lifespan, the first global non-profit group focused on accelerating breakthroughs in the expansion of the human health span. The Academy's mission is to set the public stage for the transformation society must make, as health span extension means a growing population fully able to live healthier lives longer. The group's plan is to accomplish its goals through awareness and education, by giving new research a platform for dissemination, and by organizing conferences and forums where the world's leaders in the study of health span and longevity will gather and share research and insights. Ultimately, the Academy will provide grants to fund promising research from established and emerging scientists.

"We believe we are at a threshold moment in the research of age-related decline, which is the timing that inspired the creation of the Academy. Our shared belief is that science shows that we can age later. The Academy is a think tank seeking to speed the rate of discoveries to expand our health spans. Our 16 founders are among the leading geroscientists in the world. In addition to raising awareness of research advances among the general public, we will encourage increased public and private investment in health span and longevity research throughout the globe."

The Academy embraces a 4C mission: First to Catalyze the world's ongoing research to accelerate the development of life-changing enhancements of healthy aging. Second to Connect our founders to each other through the auspices of the academy. The third C: Convene experts and authorities around the world to advance their missions and that of the Academy's in public and private settings. Finally, we shall Communicate with the public at large to educate them about this new generation of health span and longevity research, what it means and what it doesn't mean, and to engage in constructive conversations. "As founders of AHLR, we believe that, as the field rapidly advances, we must help bridge the gap between science and public understanding. We believe that while death is inevitable, aging need not be."

Link: https://www.ahlresearch.org/news/2019/2/13/16-longevity-scientists-have-a-valentines-day-message-for-the-world-announcing-thenbspacademy-fornbsphealth-and-lifespan-researchnbsp

BHB Therapeutics Launched to Develop Ketosis Mimetics

Since ketosis is argued to be a component of the effects of calorie restriction, responsible in some part for the reliable benefits to health and longevity that result, some research groups have investigated ways to induce ketosis via treatment rather than via diet. This is a subset of broader efforts to produce calorie restriction mimetic drugs that mimic some of the effects of a low calorie diet on cellular metabolism. With the funding now pouring into the biotech startup arena, it was inevitable that some of it would make its way towards work on aspects of calorie restriction that was ready to make the leap to commercial development, and here Juvenescence and the Buck Institute have chosen to wrap a company around some of their work on ketosis.

I will say that I think the scope of benefits that can be produced via calorie restriction mimetic development is limited. We know what calorie restriction itself does in humans: it is significantly beneficial for long-term health, reduces risk of age-related disease, but doesn't extend human life span by more than a few years. We don't know just how many years, but we do know that it can't be a very large number of years, because otherwise that outcome would have been discovered long ago. Further, mimetics only capture a fraction of the benefits; calorie restriction works through countless changes to the operation of metabolism.

Thus I believe that working in this field will do little to nothing to change the shape of human life. It will produce only an incremental improvement above the state of medicine and aging that presently exists - and is unlikely to produce a larger effect than the actual practice of calorie restriction. In an age of biotechnology, with clear guides to ways in which to produce reversal of aging via repair of molecular damage, we can and should aim to achieve far more than mimicking the effects of a good diet.

Jim Mellon's crew at Juvenescence has found its latest venture idea in a popular diet making its rounds in biotech circles. Once again teaming up with the Buck Institute for Research on Aging, Juvenescence has launched BHB Therapeutics to explore preventative medicines that have potential to protect against age-related disease by inducing a state of ketosis, where the body burns fat instead of carbohydrates, spurring the production of anti-inflammatory ketone bodies. In particular, the biotech startup will focus on the ketone body beta-hydroxybutyrate, or - you guessed it - BHB.

Eric Verdin, the Buck president and CEO whose research inspired another Juvenescence spinout, has discovered that BHB helps the body respond to stress. A ketogenic diet - which has been heralded for its effects in weight loss, hunger suppression as well as concentration - and the consequent long-term exposure to ketone bodies can also extend healthy lifespan in model systems. Buck researchers have generated "hard scientific data" in mice that show ketosis can be cardio-protective. "The reason we think that cardio-protection may translate to humans is because if given sugar or ketones, many people's hearts prefer ketones, whereas the brain is the opposite. If given the option between sugar or ketones, the brain will take sugar. Unfortunately, individuals when they hit 50 (plus or minus a couple years) they become insulin resistant - and then the sugar can go seriously high in a variety of organs and that leads to a variety of different pathologies."

Just days ago, Juvenescence unveiled the first $46 million tranche of a promised $100 million raise that's designed to bankroll longevity projects with the collective goal of extending the human lifespan to 150 years. So far, it's ticked off stem cell tech and organ regeneration among the fields it's established itself through joint ventures with AI groups - Insilico and Netramark - and controlling interests in AgeX and LyGenesis. The goal is to have 18 projects underway by the end of the year. Look for two or three of them to be announced over the next few weeks.

Link: https://endpts.com/keto-in-a-pill-juvenescence-debuts-anti-aging-joint-venture-with-the-buck-dedicated-to-inducing-ketosis/

The Vicious Cycles of Aging

Today's open access paper is well worth reading through completely; the middle sections are a good consideration of how specific mechanisms and diseases in aging feed upon themselves to progress ever faster over time. Aging is a process of damage accumulation. The damage itself is comparatively simple; aging is complex because cellular biology is complex, not because its causes are complex. Consider rust in a baroque metal structure of many parts. Rust is very simple, but the way in which the structure falls apart over time is not simple. That is a function of the structure, not the rust. This is why I favor developing means to repair damage, as close to the root causes of aging as possible, rather than trying to adjust the operation of metabolism to resist the damage. Repair is an easier task, and should also be more effective when successful.

Anyone who has owned, used, and maintained machines has a good idea of the pattern of aging of any complicated system. Wear is slow at the outset, and then it accelerates into consequences and dysfunction quite quickly at the end of the machine's working life. Damage causes further damage, and different types of damage interact to produce a worse outcome than would be the case for either on its own. Aging is a feedback loop, an accelerating process of breakage causing further breakage. This is true in something as simple as a hammer. It is true in something as complex as our bodies, capable of self-repair.

Beyond the conclusion that addressing damage through repair is better than trying to compensate for damage, another obvious consequence of this view of aging is that prevention in the early stages is far better as a strategy than waiting until matters progress. Since damage spawns further, more complicated forms of damage, and the process accelerates, then it will be many times more costly and challenging to reverse later stages of aging. Start the repair therapies early. That is easier said than done in the present stage of development of rejuvenation therapies, of course. The first treatments worthy of the name are still uncertain, where they exist at all. Early treatment even with highly effective rejuvenation therapies means small benefits, hard to measure, and for most intents and purposes it will be indistinguishable from a treatment that didn't work at all.

Molecular mechanisms behind the rapid progression of age-related diseases

Statistical data indicate that the mortality rates due to all major age-related diseases increase exponentially with age. Researchers have hypothesized that the reason behind this self-aggravating disease progression is the indefinite repetition of reaction cycles, which increases the harm from the initially noncritical changes in the body manyfold. It is these cycles that prospective therapies might address. "Investigating the mechanisms behind age-related disease progression, one concludes that by the time the disease has been diagnosed, it is too late to address the triggering factors. Apparently the most effective strategy is to interrupt the known vicious cycles by blocking certain stages in them. Drugs doing just that are already being developed."

Researchers examined the mortality rates of patients with five most widespread diseases that tend to affect elderly people more often, leading these diseases to be widely regarded as age-related: atherosclerosis, hypertension, diabetes, Alzheimer's, and Parkinson's diseases. Mortality statistics are the most powerful and least biased tool for studying diseases, since they account for the natural progression of a disease under various life conditions across a large population. A detailed analysis of age-related diseases revealed that they progress exponentially due to reactions on the molecular or cellular level producing pathogenic products which in turn initiate the very reactions that produced them. That way the harmful products quickly multiply, and the disease progresses at an ever increasing rate, like an avalanche.

For example, nerve cells in the brain contain a small amount of a protein called alpha synuclein, which is involved in nerve impulse transmission. It may happen that the gene encoding alpha synuclein is mutated, duplicated, or triplicated in a genome. This leads to multiple protein molecules sticking to one another, forming so-called toxic oligomers, which then grow in size by attaching other alpha synuclein molecules. This process produces fibrils, which from time to time break up into oligomers, each of which eventually grows into a new fibril, etc. This chain reaction causes the number of toxic alpha synuclein oligomers to grow exponentially.

Age-related diseases as vicious cycles

Nationwide mortality and disease incidence statistics are perhaps the most powerful and least biased datasets on human diseases that we currently have. These data are derived from humans living in the complex environment and developing diseases naturally, and not from distantly related animals contained in laboratory conditions under disease-inducing regimens. I decided to use disease statistics to elucidate the underlying nature of five major ARDs: atherosclerosis, hypertension, diabetes, Alzheimer's and Parkinson's. As large-scale incidence data for these diseases is not readily available, I have instead evaluated the age distribution of mortality.

It can be seen that the exponential function provides a reasonable approximation for mortality from atherosclerosis, diabetes and Alzheimer's, but is inadequate for mortality from essential hypertension and Parkinson's. The slightly more complex but mathematically correct logistic function provides the fits that are at least as good as for the exponential function, and in addition provides the perfect fit for Parkinson's disease mortality. Finally, the sum of two logistic functions is required for the adequate fit to mortality from essential hypertension. This may indicate that essential hypertension is a heterogeneous disease composed of two major subtypes with different mortality kinetics.

This study showed that potential vicious cycles underlying ARDs are quite diverse and unique, triggered by diverse and unique factors that do not usually progress with age, thus casting doubts on the possibility of discovering the single molecular cause of aging and developing the single anti-aging pill. Rather, each disease appears to require an individual approach. However, it still cannot be excluded that some or all of these cycles are triggered by fundamental processes of aging, such as chronic inflammation or accumulation of senescent cells. Nevertheless, experimental data showing clear cause and effect relationships between fundamental aging processes and ARDs are still missing.

It could also be that the above-mentioned fundamental aging processes themselves are mediated by positive feedback loops. For example, chronic inflammation can amplify itself similarly to autoimmune diseases via cytokines and epitope spreading. Cellular senescence can propagate from cell to cell in a chain-reaction fashion via cytokines and reactive oxygen species. DNA damage may amplify by affecting the genes of more and more DNA repair enzymes. Accumulating intracellular garbage may impair the lysososmal function, leading to ever-accelerating garbage accumulation. However, to test these propositions, longitudinal data on the kinetics of corresponding processes should be obtained.

Oglionucleotides that Interfere in Telomerase Activity Without Killing Cells

It seems reasonable to think that sabotaging the lengthening of telomeres might prove to be the basis for a universal cancer therapy, capable of shutting down all cancers. Unfettered telomere lengthening is required by all cancers in order to permit rampant replication and growth. Without that capability, the cancer will wither. Telomere length is a part of the mechanism limiting cell replication; cells lose a little of that length with each cell division, and short telomeres force senescence or self-destruction via programmed cell death. In normal tissues only stem cells use telomerase in order to maintain lengthy telomeres. Cancer cells abuse telomerase and the normally silent alternative lengthening of telomeres (ALT) mechanisms in order to bypass the usual restrictions on cell replication. Given this, we should all be most interested in any signs of a way to safely suppress telomerase, as in the research reported here.

The ends of chromosomes are covered with a kind of safety caps - telomeres. These are compact DNA sequences that stabilize chromatin structure. With each cell division telomeres become shorter, and the older a cell, the shorter are the telomeres of its chromosomes. However, certain types of cells (e.g. germ cells, stem cells, and lymphocytes) have an active immortality enzyme called telomerase. It compensates for the shortening of telomeres and allows the cells to divide practically endlessly. The highest telomerase activity is observed in cancer cells - this is one of the factors that makes them malignant.

Biochemists have now demonstrated that the activity of telomerase may be reduced using specific oligonucleotides (short DNA fragments). "We wanted to find out whether the oligonucleotides in charge of splicing shift (splicing is the process of cutting and reattaching of mRNA segments) are able to slow down the activity of telomerase. We studied it on the example of human T-lymphocytes. As a result, we managed to find an oligonucleotide able to actively suppress telomerase and slow down cell proliferation without killing the cells."

The main way of influencing the activity of telomerase is associated with the inducing of alternative splicing of its mRNA. As a result of this process several non-active protein forms are synthesized in a cell. The biochemists affected the alternative splicing using three types of oligonucleotides specific for different regulatory areas of telomerase mRNA. They were injected into human T-lymphocyte cells, and the activity of telomerase was measured after one day. It turned out that individual oligonucleotides did not influence the enzyme considerably, but the combination had a profound effect: the activity of telomerase reduced to 50% within the first 24 hours, to 18% - within the second, and to 10% - within the third.

Link: https://www.eurekalert.org/pub_releases/2019-02/ru-rbf021119.php

CD117 Antibodies for Low-Impact Selective Destruction of Hematopoietic Stem Cells

Hematopoietic stem cell transplant (HSCT) is, in essence, a way to replace a person's immune system. These stem cells give rise to all of the immune cells in the body. There are numerous reasons why HSCT is a traumatic procedure, with a comparatively high risk of death, and thus only widely used for very severe diseases. One of them is the struggle to rebuild the immune system rapidly enough for the patient not to succumb to infection; this is particularly challenging in old patients, where the thymus is much diminished and the pace of T cell creation is slowed in comparison to youth. The thymus is where thymocytes produced by hematopoietic stem cells go to mature into T cells, and the rate of production depends on the amount of active thymic tissue that remains. Another issue is the need for aggressive chemotherapy to clear out the existing population of hematopoietic stem cells prior to transplantation, which in and of itself bears risk, particularly to older, frail individuals.

Nonetheless, swapping out the existing immune system for a new one is has many potential uses, far more than are presently actively addressed by the medical community. It is a way to control autoimmunity, suppressing that condition for years, based on results from trials against type 1 diabetes. Of greater interest to our community, rebuilding the damaged immune system of an older person via HSCT should be capable of reversing many of the issues associated with immune aging. (Though it really should be combined with some way of restoring the thymus to greater levels of T cell production). If there was a way to make HSCT safer, to remove the risk and side-effects, then many more people could undergo the procedure whenever issues of aging or autoimmunity made it beneficial.

An antibody-based treatment can gently and effectively eliminate diseased blood-forming stem cells in the bone marrow to prepare for the transplantation of healthy stem cells. The researchers believe the treatment could circumvent the need to use harsh, potentially life-threatening chemotherapy or radiation to prepare people for transplant, vastly expanding the number of people who could benefit from the procedure.

The study is one of two indicating that an antibody targeting a protein called CD117 on the surface of blood-forming, or hematopoietic, stem cells can efficiently and safely eliminate the cells in mice and non-human primates. CD117 is a protein found on the surface of the stem cells. It regulates their growth and activity; the antibody, called SR1, binds to the protein and prevents its function. The results of these studies set the stage for a clinical trial of the antibody in children with an immune disorder called severe combined immunodeficiency.

Often the best chance for a cure for this and other diseases originating in the bone marrow is to eliminate the patient's own defective hematopoietic stem cells and replace them with healthy stem cells from a closely matched donor. But in order to do so, the patient must be able to withstand the pre-treatment, known as conditioning. Most conditioning regimens consist of a combination of chemotherapy and radiation in doses high enough to kill stem cells in the marrow. The researchers studied a mouse model of a class of human diseases called myelodysplastic syndromes, or MDS. People with MDS are unable to make mature, properly functioning blood cells and the only cure is a stem cell transplant. The disease primarily affects older adults, who are more likely than younger people to have additional, complicating medical factors and who are less likely to withstand the conditioning regimen.

The anti-CD117 antibody SR1 recognizes CD117 on the surface of hematopoietic stem cells isolated from either healthy donors or from patients with MDS. The researchers found that the antibody blocked the growth of both healthy and diseased stem cells in a laboratory setting. Then, the researchers investigated the effect of SR1 treatment on mice that were engineered to have a hybrid blood systems consisting of both human and mouse hematopoietic stem cells. They found in the mice that SR1 quickly and efficiently eliminated both healthy human hematopoietic stem cells and cells isolated from low-risk MDS patients. In those animals with diseased human stem cells, SR1 pre-treatment significantly improved the ability of healthy hematopoietic stem cells to engraft after transplantation.

Link: http://med.stanford.edu/news/all-news/2019/02/antibody-could-increase-cure-rate-for-blood-immune-disorders.html

The Prospect of Growing Human Organs in Animals as a Source of Transplants

Farming animals is morally dubious, to say the least, but we live in a world in which most people are accepting of this practice. That doesn't make it right, and I think that this will change in the future. For now, however, anyone who finds farming animals for meat ethical should also consider it ethical to create genetically altered animals that contain either human organs or organs that can be humanized. The purpose in doing this is to provide a large supply of organs for transplantation, alleviating the present shortage of organs for that purpose. This is not the only approach, of course. Many research groups are working towards the growth of new organs from tissue samples, where the creation of blood vessel networks sufficient to support larger tissue sections is the biggest challenge. Others are investigating the use of decellularization to expand the pool of donor organs by recovering those that are damaged and would normally be discarded.

But back to sourcing organs from animals, there are a number of ways to obtain organs for transplantation in this way. The first is to use decellularization with an appropriately sized organ, and pigs are a useful species in this respect. The pig cells are stripped away, leaving the extracellular matrix and its biochemical cues. Human cells of the necessary types, derived from the transplant recipient, are introduced to repopulate the organ. This line of development is still somewhere in progress, as other species have a handful of problematic proteins in the extracellular matrix. At least one group is farming genetically engineering pigs that lack these proteins.

The other approach is noted in the research materials here, which is to create animal lineages in which human organs are growing. This may also require some additional work to remove problem proteins before an organ can be transplanted, and is further behind the decellularization and genetically engineered pigs approach. Nonetheless, it seems equally viable. It is an open question as to which of these various lines of research and development will prosper in the clinic, and when, in the years ahead. Still, I would say that farming organs is a stop-gap technology, something that will be replaced with the creation of organs from patient cells.

Researchers one step closer to growing made-to-order human kidneys

For patients with end-stage renal disease, a kidney transplant is the only hope for regaining quality of life. Yet many of these patients will never undergo transplant surgery thanks to a chronic shortage of donor kidneys. But researchers have been working on ways to grow healthy organs outside the human body. One such method, called blastocyst complementation, has already produced promising results. Researchers take blastocysts, the clusters of cells formed several days after egg fertilization, from mutant animals missing specific organs and inject them with stem cells from a normal donor, not necessarily of the same species. The stem cells then differentiate to form the entire missing organ in the resulting animal. The new organ retains the characteristics of the original stem cell donor, and can thus potentially be used in transplantation therapy.

Initial attempts by the researchers to grow rat kidneys in mice proved unsuccessful, as rat stem cells did not readily differentiate into the two main types of cells needed for kidney formation. However, when the reverse scenario was attempted, mouse stem cells efficiently differentiated inside rat blastocysts, forming the basic structures of a kidney. After being implanted into pseudo-pregnant rats, the complemented blastocysts matured into normal fetuses. Remarkably, more than two thirds of the resulting rat neonates contained a pair of kidneys derived from the mouse stem cells. Further screening showed that all of the kidneys were structurally intact, and at least half could potentially produce urine. "Our findings confirm that interspecific blastocyst complementation is a viable method for kidney generation. In the future, this approach could be used to generate human stem cell-derived organs in livestock, potentially extending the lifespan and improving the quality of life of millions of people worldwide."

Generation of pluripotent stem cell-derived mouse kidneys in Sall1-targeted anephric rats

Regeneration of human kidneys in animal models would help combat the severe shortage of donors in transplantation therapy. Previously, we demonstrated by interspecific blastocyst complementation between mouse and rats, generation of pluripotent stem cell (PSC)-derived functional pancreas, in apancreatic Pdx1 mutant mice. We, however, were unable to obtain rat PSC-derived kidneys in anephric Sall1 mutant mice, likely due to the poor contribution of rat PSCs to the mouse metanephric mesenchyme, a nephron progenitor.

Here, conversely, we show that mouse PSCs can efficiently differentiate into the metanephric mesenchyme in rat, allowing the generation of mouse PSC-derived kidney in anephric Sall1 mutant rat. Glomerular epithelium and renal tubules in the kidneys are entirely composed of mouse PSC-derived cells expressing key functional markers. Importantly, the ureter-bladder junction is normally formed. This data provides proof-of-principle for interspecific blastocyst complementation as a viable approach for kidney generation.

Centenarians Have Lipid Profiles More Resistant to Peroxidation

The role of oxidized lipids in aging is often studied in the context of comparative biology, comparing different species with divergent life spans in order to try to identify the properties of cellular metabolism that are most influential on life span. It appears that the degree to which lipids are resistant to oxidative reactions is an important factor, and this has given rise to the membrane pacemaker hypothesis. There is something in mitochondrial function and resilience of lipids in mitochondrial membranes to forms of damage that is important in life span, at least at the scale of differences between species. Do lipid variations have a noteworthy effect on aging and longevity within a species, however? The evidence here suggests that there is an effect, but says little about the size of the effect.

Maximum lifespan (MLSP) is a species-specific feature that may differ more than 5000-fold among animal species being about 120 years in humans. Centenarians are considered an exceptional human model of healthy aging and extreme longevity. Available evidences reveal the existence of a link between MLSP and lipids. Thus, the findings from several studies demonstrate that the membrane fatty acid profile differs between animal species (including vertebrates, invertebrates, and exceptionally long-lived animal species) and that cell membrane susceptibility to lipid peroxidation is inversely related to MLSP. Furthermore, a recent phylogenomic approach showed that genes involved in lipid metabolism have undergone an increased selective pressure in long-lived species, reinforcing the idea that cell membrane lipid profile has been an optimized evolutionary adaption.

The physiological role of ether lipids, and specially plasmalogens, is essentially linked to their function as membrane components. Thus, plasmalogens seem to play a key role in specific properties of cell membrane. Interestingly, an antioxidant effect has also been ascribed to plasmalogens. Effectively, the vinyl-ether linkage of the plasmalogens is particularly susceptible to oxidation by reactive species such as reactive oxygen species and hypochlorous acid, and thus, like a scavenger, could protect unsaturated membrane lipids (as well as lipoproteins) against oxidation.

Consequently, plasmalogens could have a modulatory effect on oxidative stress, lipid-derived inflammation and cell signalling mechanisms. Lipidomic studies reveal that ether lipids are inversely associated with genetic peroxisomal disorders, and also suggest that they are negatively associated with prevalent disease states such as obesity, prediabetes, type 2 diabetes mellitus, cardiovascular disease, cancer and Alzheimer's disease, among others. Notably, these pathological states share as common trait an increased oxidative stress, and a potential mechanistic role for plasmalogens.

Although the fact that systems biology-based approaches allow a comprehensive molecular characterization of complex biological systems, up to date no targeted lipidomic studies investigating differences in plasma of exceptionally long-lived humans have been reported. To this end, we have designed a study that represents the most detailed lipidomic analysis of plasma ether lipids associated with human longevity. We discovered a particular ether lipid signature related to the condition of extreme longevity, allowing the identification of potential mechanisms and biomarkers of healthy aging.

Link: https://doi.org/10.1016/j.redox.2019.101127

More on Fibrinogen and Blood-Brain Barrier Leakage in the Aging Brain

The blood-brain barrier lines the blood vessels of the brain, and only very selectively allows passage of molecules to and from the brain. As is the case for all tissue structures, it fails with age. Molecular damage and cell dysfunction causes it to become leaky, and as a consequence all sorts of cells and proteins make their way into the brain to cause damage. One of these is fibrinogen, which appears toxic to brain cells. Here, researchers elaborate on previous findings, suggesting that this is an immune activation problem, and may be a significant cause of neurodegenerative conditions that exhibit significant loss of synapses, such as Alzheimer's disease.

Researchers used state-of-the-art imaging technology to study both mouse brains and human brains from patients with Alzheimer's disease. They also produced the first three-dimensional volume imaging showing that blood-brain barrier leaks occur in Alzheimer's disease. They found that fibrinogen, after leaking from the blood into the brain, activates the brain's immune cells and triggers them to destroy important connections between neurons. These connections, called synapses, are critical for neurons to communicate with one another.

Previous studies have shown that elimination of synapses causes memory loss, a common feature in Alzheimer's disease and other dementias. Indeed, the scientists showed that preventing fibrinogen from activating the brain's immune cells protected mouse models of Alzheimer's disease from memory loss. "We found that blood leaks in the brain can cause elimination of neuronal connections that are important for memory functions. This could change the way we think about the cause and possible cure of cognitive decline in Alzheimer's disease and other neurological diseases."

The team showed that fibrinogen can have this effect even in brains that lack amyloid plaques, which are the focus of diverse treatment strategies that have failed in large clinical trials. The researchers showed that injecting even extremely small quantities of fibrinogen into a healthy brain caused the same kind of immune cell activation and loss of synapses they saw in Alzheimer's disease. Interestingly, researchers recently developed an antibody that blocks the interaction between fibrinogen and a molecule on the brain's immune cells. In a previous study, they showed this antibody protected mouse models of Alzheimer's disease from brain inflammation and neuronal damage.

Link: https://gladstone.org/about-us/press-releases/new-culprit-cognitive-decline-alzheimers-disease

Better Understanding the Origins of Fibroblasts Found in Healing Wounds Might Lead to Regeneration Without Scarring

Scarring is an unfortunate fact of mammalian life, both following injury and throughout inner organs in old age, when the processes of regeneration and tissue maintenance run awry. Wound healing, or indeed any form of regeneration, is enormously complex. It is a dance of signals and actions carried out between numerous cell populations: various stem cells and progenitor cells; immune cells; somatic cells. These processes are similar at the high level in different tissues, but the details vary. It is far from completely mapped by the research community, as is true of most of cellular metabolism, particularly when multiple cell types are coordinating with one another.

Today's research is a good illustration of the complexities of regenerative biochemistry. When focusing down on even one class of cell in one tissue, fibroblasts in the skin, a wide variety of phenotypes and activities is revealed. Some of these apparently similar cells have arrived from far away in the body, and have very different roles from their peers of a similar type. If the mechanisms of scarring can be more carefully mapped in this way, there is perhaps the potential to reduce or prevent scars from forming. That would be a powerful technology, and probably more so for the ability to ameliorate some of the downstream damage of aging in organs rather than allowing better healing of injuries.

Study Reveals How Blood Cells Help Wounds Heal Scar-Free

Skin injuries activate rapid wound repair, which often culminates with the formation of scars. Unlike normal skin, scars are devoid of hair follicles and fat cells, and creating new hair and fat is necessary for regenerating an equivalent of normal skin. In 2017 researchers identified that adult mice can naturally regenerate nearly normal-looking skin when new hair follicles and fat cells form in healing wounds. New fat cells regenerate from myofibroblasts, a type of wound fibroblast that was previously not thought to be capable of converting into other cell types. This discovery brought renewed attention to wound fibroblasts as attractive targets for anti-scarring therapies. In the current study, the research team sought to further characterize wound fibroblasts and determine if they're all the same and equally capable of regenerating new fat cells.

"We saw that wound fibroblasts are surprisingly very diverse and that there are as many as twelve different cell sub-types. We understand their molecular signatures and are beginning to learn about their unique biology. For example, we already know that distinct fibroblast sub-types 'prefer' only certain parts of the wound. This suggests that they play specific roles in different locations within the wound, and possibly at different times during the repair process. Molecular profiling of wound fibroblasts strongly suggests that as many as 13% of them at some point in their past were blood cells that converted into collagen-producing fibroblasts, but kept residual blood-specific genes still turned on."

"What is truly novel about our observation is that these fibroblast-making blood cells, which are called myeloid cells, can reprogram into new fat cells. In essence, we observed that for wounds to achieve scar-less regeneration, the body must mobilize multiple cellular resources, which includes remotely circulating blood progenitors." Because myeloid cells can be fairly easy to harvest and enrich using existing techniques, the new findings open the exciting possibility that the skin's healing ability can be enhanced via delivery of regeneration-competent blood-derived progenitors to the site of the wound.

Single-cell analysis reveals fibroblast heterogeneity and myeloid-derived adipocyte progenitors in murine skin wounds

Traditionally, adult mammals are considered to have limited regenerative abilities and scarring is thought to be the default repair response. The notable exceptions to this rule are digit tip regeneration after amputation and neogenesis of hair follicles and fat in the center of large excisional wounds. Intriguingly, lineage studies reveal important differences in the regenerative strategies between these two systems. Epithelial and mesenchymal structures in the digit tip regenerate from several types of fate-restricted progenitors and no multipotent progenitors or lineage reprogramming events are observed. In contrast, large skin wounds demonstrate broadened lineage plasticity. Although progeny of preexisting hair-fated bulge stem cells migrate into wound epidermis, they do not partake in hair follicle neogenesis. Instead, new hair follicles regenerate from non-bulge epithelial stem cells, among other sources. Fat neogenesis is driven by lineage reprogramming of non-adipogenic wound myofibroblasts. Dermal papilla neogenesis also likely relies on myofibroblast reprogramming strategy.

Are all wound myofibroblasts identical or heterogeneous in terms of their origin, properties, and morphogenetic competence? Here, we studied fibroblast heterogeneity in the mouse model for wound-induced regeneration at 12 days post-wounding when wound re-epithelialization is completed and preceding hair follicle neogenesis. We show that wound fibroblasts can be broadly classified into two major populations on the basis of their transcription factor signatures and PDGF receptor expression patterns. Prominent additional heterogeneity exists within both populations.

Bone-marrow-derived progenitors, including myeloid cells, endothelial progenitors, and circulating mesenchymal stem cells can contribute new stromal cells toward injured tissues in various organs. In skin, studies document bone marrow giving rise to fibroblasts at the injury sites. Our data from large excisional wounds shows that the contribution from myeloid cells to wound fibroblasts is small yet significant, between 6% and 11.3%, depending on the assessment method. We also showed that at least a portion of these cells can convert into de novo adipocytes around neogenic hair follicles.