Iron Deposition in the Aging Brain Correlates with Glymphatic System Function

Evidence to date suggests that disruption of the pathways by which fluid clears from the brain is important in the development of neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, and many others. These conditions are associated with raised amounts of specific forms of metabolic waste in the brain, including aggregates of amyloid-β, that are harmful to cell function. In a young brain, drainage of cerebrospinal fluid from the brain carries away some fraction of these wastes. As drainage pathways are disrupted with age, however, the balance between processes of creation and removal is altered in favor of an ever-increasing presence of amyloid-β and other metabolic byproducts in brain tissue.

One drainage pathway for cerebrospinal fluid is the cribriform plate, behind the nose. This structure ossifies with age, reducing fluid flow. When permeable, the cribriform plate route allows drainage from the olfactory bulb region of the brain, and the company Leucadia Therapeutics is founded on the thesis that loss of cribriform plate drainage is exactly why Alzheimer's pathology, and the buildup of amyloid-β, first appears in the olfactory bulb. Studies conducted by Leucadia staff have recreated this process in ferrets, and the company plans to develop a therapy based on implanting a small device into the cribriform plate in order to restore drainage of cerebrospinal fluid.

Another interesting discovery of recent years, and the subject of today's open access paper, is the existence of the glymphatic system. This is a more general drainage route for cerebrospinal fluid. The glymphatic system, like the cardiovascular system and lymphatic system, also declines in function with age. This decline may well contribute to rising levels of metabolic waste throughout the brain. The evidence for this proposition is still in the early stages of assembly, but is so far fairly convincing.

Dysfunction of the Glymphatic System Might Be Related to Iron Deposition in the Normal Aging Brain

Iron is an electron facilitator and is involved in many brain functions, including oxygen transport, myelin production, electron transfer, and neurotransmitter synthesis. Both imaging and postmortem analyses have shown that the concentration of iron in the brain is not uniform. Previous studies have demonstrated that iron accumulates in the normal aging brain, which might damage cognitive function. However, the exact mechanism of iron deposition in the aging brain remains unclear.

Recent work has led to the discovery of the "glymphatic system," which is a coined phrase that combines "gl" for glia cell with "lymphatic system". Within the glymphatic system, cerebrospinal fluid enters the brain via peri-arterial spaces, passes into the interstitium via astrocytic aquaporin-4, and then drives the peri-venous drainage of interstitial fluid and its solute. Evidence suggests that the glymphatic system is an important fluid clearance system in the brain. Numerous neurological disorders have been found to be closely related to the dysfunction of the glymphatic system, including Alzheimer's disease and Parkinson's disease.

Evidence also revealed that iron deposition was one of the most important underlying mechanisms in Alzheimer's disease and Parkinson's disease. Some scholars also believe that the glymphatic system may be the major contributory factor to the deposition and clearance of iron in brain tissue, but evidence is still lacking. In this study, we recruited 213 healthy participants. We evaluated the function of the glymphatic system using the index for diffusivity along the perivascular space (ALPS-index), assessed iron deposition on quantitative susceptibility mapping (QSM), and analyzed their relationship. The main finding of the current study is that the regional brain iron deposition was related to the function of the glymphatic system.

Previously, the glymphatic system has been speculated to be responsible for the clearance and homeostasis of waste in the brain. Our results support that in a healthy aging brain, the glymphatic system might also be involved in the clearance of iron, suggesting that iron metabolism shared the same pathway as other waste metabolisms. Moreover, a study has demonstrated that injury of the microvasculature and capillary-level microhemorrhages coincided with amyloid beta (Aβ) deposits in senile plaques. Iron deposition plays an important role in cerebral small vessel diseases. Therefore, we inferred that dysfunction of the glymphatic system might lead to the damage of microvasculature via deposition of Aβ, then leading to iron deposition.

The Mitochondrial Transition Pore in Aging

A few papers in recent years have reviewed what is known of the role of the mitochondrial permeability transition pore in aging. Mitochondria are the power plants of the cell, and mitochondrial function is vital to cell and tissue function. Unfortunately, mitochondria become dysfunctional with age, for a variety of reasons that have yet to be firmly traced back to specific root causes. Researchers are engaged in the exploration of proximate causes, such as changing mitochondrial dynamics and loss of mitophagy, the quality control mechanism responsible for removing worn and damaged mitochondria. Changes in the activity of mitochondrial permeability transition pores are also on the list, though as for many of these mechanisms, it is yet to be determined where it fits exactly in the hierarchy of proximate cause and proximate consequence in the final stages of the path to mitochondrial failure in aging.

The mitochondrial permeability transition pore (mPTP) is a mitochondrial inner membrane multicomponent mega-channel that is activated by calcium, oxidative stress, and membrane depolarization. The channel exhibits several conductance states with variable duration. When activated, protons flow into the matrix, while calcium, superoxide, hydrogen peroxide, and other ions flow out of the matrix, thus inhibiting oxidative phosphorylation.

It is now recognized that mitochondrial dysfunction is a major contributor to aging and aging-driven degenerative disease, such as diabetes, heart diseases, cancer, Alzheimer's disease, and Parkinson's disease. Mitochondrial dysfunction in aging is often manifested as the excess production of mitochondrial reactive oxygen species (mROS), calcium overloading, and membrane depolarization. Since these dysfunctions are known to activate mPTP, it can be expected that mPTP activity will be enhanced in dysfunctional mitochondria in aging. Indeed, direct evidence for enhanced mPTP activation in aging and neurodegenerative disease is extensive.

mPTP activity accelerates aging by releasing large amounts of cell-damaging reactive oxygen species, Ca2+, and NAD+. The various pathways that control the channel activity, directly or indirectly, can therefore either inhibit or accelerate aging or retard or enhance the progression of aging-driven degenerative diseases and determine lifespan and healthspan. Autophagy, a catabolic process that removes and digests damaged proteins and organelles, protects the cell against aging and disease. However, the protective effect of autophagy depends on mTORC2/SKG1 inhibition of mPTP. Autophagy is inhibited in aging cells. Mitophagy, a specialized form of autophagy, which retards aging by removing mitochondrial fragments with activated mPTP, is also inhibited in aging cells, and this inhibition leads to increased mPTP activation, which is a major contributor to neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases.

The increased activity of mPTP in aging turns autophagy/mitophagy into a destructive process leading to cell aging and death. Several drugs and lifestyle modifications that enhance healthspan and lifespan enhance autophagy and inhibit the activation of mPTP. Therefore, elucidating the intricate connections between pathways that activate and inhibit mPTP, in the context of aging and degenerative diseases, could enhance the discovery of new drugs and lifestyle modifications that slow aging and degenerative disease.

Link: https://doi.org/10.3390/cells10010079

Partial Inhibition of Mitochondrial Complex I is Neuroprotective

Mitochondria are the power plants of the cell, packaging chemical energy store molecules through the activities of electron transport chain protein complexes. Some forms of interference in the operation of these complexes can be beneficial, causing mild stress that provokes the cell into greater maintenance activities. This usually results in better cell function, greater cell resilience, and so forth, leading to better organ function and a slowing of the aging process. Researchers here demonstrate that this sort of approach is beneficial in a mouse model of Alzheimer's disease, reducing the damage done to neurons. It is, nonetheless, a compensatory approach, not a form of repair that addresses underlying issues. The utility is necessarily limited, as those underlying issues remain in place, still causing all the other downstream harms they are capable of.

Recent studies demonstrated that altered energy homeostasis associated with reduced cerebral glucose uptake and utilization, altered mitochondrial function and microglia and astrocyte activation might underlie neuronal dysfunction in Alzheimer's disease (AD). Intriguingly, accumulating evidence suggests that non-pharmacological approaches, such as diet and exercise, reduce major AD hallmarks by engaging an adaptive stress response that leads to improved metabolic state, reduced oxidative stress and inflammation, and improved proteostasis. While mechanisms of the stress response are complex, AMP-activated protein kinase (AMPK)-mediated signaling has been directly linked to the regulation of cell metabolism, mitochondrial dynamics and function, inflammation, oxidative stress, protein turnover, Tau phosphorylation, and amyloidogenesis. However, the development of direct pharmacological AMPK activators to elicit beneficial effects has presented multiple challenges.

We recently demonstrated that mild inhibition of mitochondrial complex I (MCI) with the small molecule tricyclic pyrone compound CP2 blocked cognitive decline in transgenic mouse models of AD when treatment was started in utero through life or at a pre-symptomatic stage of the disease. Moreover, in neurons, CP2 restored mitochondrial dynamics and function and cellular energetics. However, it was unclear whether MCI inhibition would elicit similar benefits if administered at the advanced stage of the disease, after the development of prominent Aβ accumulation, brain hypometabolism, cognitive dysfunction, and progressive neurodegeneration. As a proof of concept, we demonstrate that partial inhibition of MCI triggers stress-induced AMPK-dependent signaling cascade leading to neuroprotection and a reversal of behavior changes in symptomatic APP/PS1 female mice, a translational model of AD. Beneficial effect of treatment could be monitored using translational biomarkers currently utilized in clinical trials.

Link: https://doi.org/10.1038/s42003-020-01584-y

A Few More Mammalian Species Found to Exhibit Amyloid-β and Tau Pathology

The primary challenge in Alzheimer's disease research has long been that short-lived laboratory species do not naturally exhibit any of the features of the condition. Thus all mouse models of the condition are highly artificial genetic constructs, and potential treatments and relevant mechanisms in these models have a high chance of being irrelevant to Alzheimer's disease as it exists in humans. Up until fairly recently it could be argued that humans were in fact the only species to exhibit full blown Alzheimer's disease, involving a lengthy increase in amyloid-β aggregation in the brain, followed by neuroinflammation, tau aggregation, and widespread cell death.

However, in recent years the study of chimpanzee brains - as well as a variety of other species - suggests that some might exhibit enough of the mechanisms of Alzheimer's disease to be said to suffer from it in old age. This is also the case in the aging of dolphins. In today's open access paper, researchers report on more signs of Alzheimer's mechanisms in the brains of sea lions, seals, and walrus. This is all interesting, but doesn't much help the state of Alzheimer's research in practice. None of these large mammal species are likely to be used in laboratories any time soon. Even if they were, it would not be for early stage discovery and exploration.

Amyloid β and tau pathology in brains of aged pinniped species (sea lion, seal, and walrus)

Alzheimer's disease (AD) is the most prevalent age-related neurodegenerative disorder and is characterized by the pathological aggregation of the amyloid-β (Aβ) and hyperphosphorylated tau (hp-tau) proteins in the form of senile plaques (SPs) and neurofibrillary tangles (NFTs), respectively. The accumulation of Aβ in the blood vessels of the brain, a condition known as cerebral amyloid angiopathy (CAA), is also detected in more than 80% of patients with AD. Humans appear to be uniquely susceptible to AD, potentially due to genetic differences, changes in cerebral structures and functions during evolution, and an increased lifespan. In the "amyloid hypothesis", the most acknowledged explanation for the pathogenesis of AD, the age-dependent accumulation of fibrillar insoluble Aβ peptides in the brain is considered to be the central and triggering event in AD pathology. Based on this hypothesis, various transgenic mouse models that produce human Aβ beyond physiological levels have been generated and exhibit the massive formation of SPs. However, they fail to develop NFTs and neuronal loss unless mutant tau is simultaneously introduced.

While AD appears to be a human-specific disease, age-dependent SP formation has been reported in several non-human primates, including chimpanzees, orangutans, and gorillas. The concomitant pathology with the formation of a small amount of NFTs was found in chimpanzees and rhesus macaques, while the oligodendroglial tau pathology was also detected in cynomolgus monkeys. Therefore, an AD-like pathology may occur during aging in primates. In contrast, non-primate animals, particularly Carnivora species, have exhibited species-specific patterns of Aβ and hp-tau accumulation. In the suborder Caniformia, aged dogs and bears developed SPs in their brains, but not NFTs, even in the oldest subjects. On the other hand, Feliformia species, such as cats, leopard cats, and cheetahs, exhibit NFTs without SP formation, although small granular deposits of Aβ were detected in the cerebral cortex.

Pinnipeds are semiaquatic carnivorans that spend most of their lives in water, and use coastal terrestrial environments and ice packs to breed, molt, and rest. They are currently classified into three families: Phocidae (seals), Otariidae (fur seals and sea lions), and Odobenidae (walruses). We herein describe the Aβ and hp-tau pathology in the brains of aged pinniped species. Molecular analyses revealed that the sequence of pinniped Aβ was identical to that of human Aβ. Histopathological examinations detected argyrophilic plaques composed of Aβ associated with dystrophic neurites in the cerebral cortex of aged pinnipeds. Astrogliosis and microglial infiltration were identified around Aβ plaques. Aβ deposits were observed in the blood vessel walls of the meninges and cerebrum.

Histopathological examinations revealed argyrophilic fibrillar aggregates composed of phosphorylated tau (hp-tau) in the neuronal somata and neurites of aged pinniped brains. Furthermore, the activation of GSK-3β was detected within cells containing hp-tau aggregates, and activated GSK-3β was strongly expressed in cases with severe hp-tau pathologies. The present results suggest that, in association with Aβ deposition, the activation of GSK-3β contributes to hp-tau accumulation in pinniped brains.

Klotho Links Inflammation, Salt Sensitivity, Hypertension and Mortality in Aging

Klotho is one of the few robustly demonstrated longevity-associated genes. Greater expression extends life in mice, while reduced expression shortens life. Present investigations of the mechanisms by which klotho produces effects on life span are largely focused on the direct actions of klotho in the kidney, and then the effects of kidney function on broader health. Kidney function influences cardiovascular decline and the aging of other organs through a variety of mechanisms. While klotho level is well known to correlate with the degree of cognitive decline with age, this is most likely a demonstration of the importance of kidney function and cardiovascular function on overall health. The brain suffers when its supporting organ systems suffer.

Klotho is a membrane-bound protein acting as an obligatory coreceptor for fibroblast growth factor 23 (FGF23) in the kidney and parathyroid glands. The extracellular portion of its molecule may be cleaved and released into the blood and produces multiple endocrine effects. Klotho exerts anti-inflammatory and antioxidative activities that may explain its ageing suppression effects evidenced in mice; it also modulates mineral metabolism and FGF23 activities and limits their negative impact on cardiovascular system.

Clinical studies have found that circulating Klotho is associated with myocardial hypertrophy, coronary artery disease, and stroke, and may also be involved in the pathogenesis of salt-sensitive hypertension with a mechanism sustained by inflammatory cytokines. As a consequence, patients maintaining high serum levels of Klotho not only show decreased cardiovascular mortality but also non-cardiovascular mortality.

These findings suggest that Klotho may represent a bridge between inflammation, salt sensitivity, hypertension and mortality. This may be particularly relevant in patients with chronic kidney disease who have decreased Klotho levels in tissues and blood.

Link: https://doi.org/10.1093/ckj/sfaa100

A Hypoxia Mimetic Drug Improves the Bone Marrow Environment to Treat Osteoporosis

Researchers here show that an iron chelation drug (deferoxamine, brand name desferal) triggers a portion of the cellular reaction to hypoxia in bone marrow. Hypoxia is one of the many types of stress that, when mild, induces cells to greater efforts in maintenance and repair, resulting in a net gain in cell function. In the rats treated with deferoxamine in this study, the hypoxia mimetic acts to reduce the burden of cellular senescence, and otherwise shift the behavior of cells in the direction of slowing the onset of osteoporosis.

Bone marrow stromal cells (BMSCs) exist in the bone marrow with multi-potency and have a broad application prospect in the field of cell therapy and regenerative medicine thanks to their accessibility and expansion potential. Previous study showed a high potential association between BMSC senescence and age-related bone loss. Several studies have documented that age drives the intrinsic alterations of BMSCs, including decreased proliferation and osteogenic differentiation potential, as well as increased senescence-associated gene expression and β-galactosidase-positive staining. It also reported that the viability of aged BMSCs decreased, and senescent BMSCs were more likely to differentiate into adipocytes. These changes led to the decrease in quantity and quality of BMSCs, which together contributed to age-related bone loss.

Oxygen is a fundamental element of the bone marrow niche, and a hypoxic environment in the bone marrow is generally considered to be indispensable for retaining normal physiological function and self-renewal of stromal cells. As the key transcription factor response to hypoxia stress, hypoxia-induced factor 1α (HIF-1α) is a highly unstable protein in normoxic conditions. However, under hypoxic conditions, the catalytic activity of prolyl hydroxylases (PHD) is inhibited, leading to the stabilized expression of HIF-1α. Some small molecules, such as deferoxamine (DFO), are known as hypoxia mimics, which can elevate HIF-1α levels by blocking PHD activity even in normoxic conditions.

In this study, Desferal, deferoxamine mesylate for injection, which is approved for the treatment of acute iron intoxication and chronic iron overload, was used to explore the beneficial effects on preventing aging-induced bone loss and mitigating dysfunction of aged BMSCs. High-dose Desferal significantly prevented bone loss in aged rats. Compared with controls, the ex vivo experiments showed that short-term Desferal administration could promote the potential of BMSC growth and improve the rebalance of osteogenic and adipogenic differentiation, as well as rejuvenate senescent BMSCs and revise the expression of stemness/senescence-associated genes. The potential of BMSCs from the Desferal group at least partly revised to the level close to that of the 2-month-old group.

Link: https://doi.org/10.1186/s13287-020-02112-9

The 2020 Year End Fundraiser Brought in More than $2 Million for the SENS Research Foundation

The SENS Research Foundation represents the best of charitable organizations working on the treatment of aging as a medical condition. It is well run, focuses on approaches capable of rejuvenation rather than merely modestly slowing aging, devotes funds and attention towards those projects in rejuvenation research that most need support in order to advance, and has a great track record when it comes to helping development programs to make the leap from academic laboratories to commercial development in startup biotech companies.

The SENS Research Foundation is near entirely supported by philanthropy, including the donations of a community of thousands of everyday visionaries, people just like you and I who want to see meaningful progress towards therapies capable of sizable degrees of human rejuvenation. For some years now, the SENS Research Foundation has run an annual year end fundraiser, bringing in millions in funding. Those funds were used well in helping to advance the state of the art in rejuvenation research.

On that topic, I'm pleased to note that last year's fundraiser, concluding a few short weeks ago, succeeded in raising more than $2 millon to help fund the rejuvenation-focused projects of 2021. From the latest SENS Research Foundation newsletter:

SENS Research Foundation supporters, thank you for going above and beyond with your generosity, especially at the end of such a difficult year. Your commitment to helping #UnlockLongevity brought in $2,355,443.46 - more than doubling our end of year campaign fundraising goal of $1M! Special thanks to Michael Antonov, Brendan Iribe, Karl Pfleger, Jim Mellon, Cameron Bloomer, Dave Fisher, Christophe Cornuejols, Didier Coeurnelle, and Larry Levinson for their matching grants during the campaign, as well as to all of you who donated at every level.

Your support means SENS Research Foundation can hit the ground running as we start 2021, with exciting research progress, facility upgrades, and more on the horizon. It means so much to us to have a community behind us that truly shares our vision of a world free of age-related disease, and is willing to help do what it takes to make such a world a reality sooner rather than later.

A Continued Focus on Metformin, a Demonstrably Poor Approach to Treating Aging

Metformin is a poster child for the way in which much of the aging research community is focused on approaches to aging that cannot possibly achieve more than a very modest slowing of degeneration, and where the existing evidence strongly suggests that those tiny positive outcomes will be unreliable at best. Metformin is a way to tinker with the operation of a damaged metabolism, not a way to repair that damage. As a calorie restriction mimetic, the animal data shows that it compares very poorly to calorie restriction itself. We know that calorie restriction doesn't do anywhere near enough for human longevity. This is not the way forward to human rejuvenation.

Although current research gives promise to metformin as an anti-aging drug, there are still concerns that need to be highlighted, and they apply not only to research into metformin but to other anti-aging mechanisms and drug research as well. First, despite the positive outcomes from many studies, it is not uncommon to find a change in dosage turning the result from life-extending to life-ending. When a low dose of metformin (0.1%) was given to middle-aged male mice with their diet, their lifespans were extended by 5.83% on average, but a higher concentration (1%) became toxic.

Another issue standing in the way relates to the side effects associated with chronic use of drugs. About 25% of patients treated with metformin have gastrointestinal side effects. Besides, chronic use of metformin can cause dose-dependent vitamin B12 deficiency, increasing the risk for anemia and neuropathy. Future research should also work to elucidate how gender influences drug effectiveness. Metformin increased mean lifespan of female mice by 4.4% while decreasing that of male mice by 13.4%. Male pre-diabetic patients who received metformin had a significantly lower coronary calcium score compared with control, while the female group did not.

The issues of dosage, side effects, sexual dimorphism, and genetic regulatory mechanisms all point to the need for large-scale clinical trials. The Metformin in Longevity Study (MILES) involved 14 older than 70 year-old people who were randomized to take metformin and placebo in either order each for six weeks with a two-week washout period in between. As the number of subjects was small and the duration short, MILES effectively revealed many transcriptomic and metabolomic changes in the muscle and adipose tissue. The Glucose Lowering In Non-diabetic hyperglycaemia Trial (GLINT) is intended to evaluate the performance of metformin in reducing CVD risks by following 20,000 hyperglycemic but non-diabetic patients for five years. A one-year feasibility RCT enrolling 249 elderly, obese, and with high CVD risk (mean 28.8%, SD 8.5%) participants was concluded in 2018, and metformin improved several CVD risk indicators and decreased vitamin B12 levels. However, it also revealed problems such as a high rate of trial discontinuation (30% by six months).

The Targeting Aging with Metformin (TAME) trial is a large placebo-controlled trial that is designed to enroll 3000 subjects to test whether metformin delays age-related diseases. The TAME trial received FDA approval in 2015, and after receiving all the required budget in 2019, it was set to start at the end of the same year. The TAME trial may make metformin the first approved drug for anti-aging, but, more importantly, since it is not testing metformin against a single disease but a collection of age-related ones, it establishes aging as a medical condition that can be intervened or treated instead of an irreversible process outside human control. The shift in the notion of aging will enable future anti-aging clinical to trials proceed with much more ease.

Link: https://doi.org/10.1002/agm2.12135

Senescent Cells Provoke Excessive Sympathetic Nerve Fiber Growth, with Harmful Consequences

Senescent cells are created constantly throughout life in response to a range of circumstances, but only begin to accumulate in later life, once there is an imbalance between processes of creation (as a response to cell damage, for example) and processes of destruction (such as immune surveillance of senescent cells). Senescent cells secrete a potent mix of signals that, when sustained over time, provokes chronic inflammation and alters nearby cell behavior and tissue structure in detrimental ways. Researchers are only now attempting to catalog exactly how senescent cells cause harm, given the advent of senolytic therapies that allow a good assessment of the degree to which senescent cell accumulation contributes to specific degenerative processes in aging.

The sympathetic nervous system (SNS) is involved in a multitude of biological phenomena including stress, energy utilization, and physical activity; crucial physical functions that are regulated by the SNS include hemodynamics, temperature regulation, and metabolism. Overactivity of the SNS can result in types of chronic diseases, including cardiovascular disorders and hypertension. Multiple lines of evidence have demonstrated that sympathetic nerve density increases in tumor tissues.

Cellular senescence is implicated in several lines of aging-related disorders. However, the potential molecular mechanisms by which cellular senescence modulates age-related pathologies remain largely unexplored. Herein, we report that the density of sympathetic fibers (SFs) is significantly elevated in naturally aged mouse tissues and human colon adenoma tissues compared to the SFs densities in the corresponding young mouse tissues and human non-lesion colon tissues.

A dorsal root ganglion (DRG) and human diploid fibroblast co-culture assay revealed that senescent cells promote the outgrowth of SFs, indicating that the senescent cells induce recruitment of SFs in vitro. Additionally, subcutaneous transplantation of fibroblasts in nude mice shows that transplanted senescent fibroblasts promote SFs infiltration. Intra-articular senolytic molecular injection can reduce SFs density and inhibit SFs infiltration caused by senescent cells in osteoarthritis (OA), suggesting senescent cells promote the infiltration of SFs in vivo in aged tissues. Notably, the elevated level of SFs contributes to impaired cognitive function in naturally aged mice, which can be reversed by treatment with propranolol hydrochloride, a non-selective β receptor blocker that inhibits sympathetic nerve activity (SNA) by blocking non-selective β receptors.

Taken together, this study concludes that senescent cells secrete netrin-1 that mediates SFs outgrowth and infiltration, which contributes to aging-related disorders. This suggests that clearing senescent cells or inhibiting SNA is a promising therapeutic strategy for improving sympathetic nervous system (SNS) hyperactivity-induced aging-related pathologies.

Link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7772213/

KAT7 Inhibition via Gene Therapy Reduces Cellular Senescence in the Liver and Extends Life in Mice

Since the confirmation of cellular senescence as an important contributing cause of aging, a great many research initiatives have focused on the biochemistry of senescent cells, in search of new approaches to rejuvenation therapies. A common strategy in the life sciences is to deactivate genes one by one and observe the results, in search of suitable regulators to change cell behavior. In today's open access paper, researchers report on the results of such a screen of gene functions, identifying KAT7 as a gene important in the regulation of cellular senescence in at least the liver.

The researchers screened for gene function in cell cultures, but they used gene therapy in mice to demonstrate that KAT7 knockdown via CRISPR methods reduces cellular senescence in the liver, improves liver function, and extends mouse life span. They did not comment on other organ systems. The liver is the focus of this study most likely because it is the easiest organ to target via present gene therapy vectors. Something like 80% to 90% of any vector that is injected intravenously will end up in the liver. It is not completely clear how KAT7 reduces senescence, whether it is involved in more efficient destruction of senescent cells, or lowers the number of cells that become senescent in response to damage or signaling.

The question with all novel approaches to reducing the burden of senescence is whether they will do more harm than good - which is why it is important to check on longer term health and life span outcomes when conducting animal studies. Selectively destroying senescent cells is confirmed to be beneficial, increasing mouse health and life span. Preventing cells from becoming senescent, on the other hand, is beneficial in the short term, lowering the burden of inflammatory signaling generated by senescent cells, but could in principle raise the risk of cancer and other issues in the longer term, by allowing damaged cells to continue replicating. In the KAT7 work, the treated mice lived longer, an interesting outcome.

A genome-wide CRISPR-based screen identifies KAT7 as a driver of cellular senescence

Cellular senescence, a state of permanent growth arrest, has recently emerged as both a hallmark of aging and a fundamental driver of the aging processes. Senescent cells accumulate in tissues over time, triggering natural features of organismal aging and contributing to aging-related diseases (for example, hepatic steatosis and osteoarthritis). Prophylactic ablation of senescent cells expressing the senescence marker p16INK4A mitigates tissue degeneration and extends the health span in mice, indicating that senescent cells play a causative role in organismal aging. For example, senescent cells gradually accumulate in the degenerated liver, whereas clearing senescent cells from the liver attenuates the development of hepatic steatosis.

Understanding the genetic and epigenetic bases of cellular senescence is instrumental in developing interventions to slow aging. We performed genome-wide CRISPR-Cas9-based screens using two types of human mesenchymal precursor cells (hMPCs) exhibiting accelerated senescence. The hMPCs were derived from human embryonic stem cells carrying the pathogenic mutations that cause the accelerated aging diseases Werner syndrome and Hutchinson-Gilford progeria syndrome. Genes whose deficiency alleviated cellular senescence were identified, including KAT7, a histone acetyltransferase, which ranked as a top hit in both progeroid hMPC models.

Inactivation of KAT7 decreased histone H3 lysine 14 acetylation, repressed p15INK4b transcription, and alleviated hMPC senescence. Moreover, lentiviral vectors encoding Cas9/sg-Kat7, given intravenously, alleviated hepatocyte senescence and liver aging and extended life span in physiologically aged mice as well as progeroid Zmpste24-/- mice that exhibit a premature aging phenotype. KAT7 may represent a therapeutic target for developing aging interventions.

Targeting TGFβ to Treat Fibrotic Disease

TGFβ is an important component of the inflammatory signaling of senescent cells, and cellular senescence is involved in the progression of numerous fibrotic and age-related conditions. Chronic inflammation causes tissue maintenance processes to run awry, and fibrosis, the inappropriate deposition of scar-like collagen structures that disrupt tissue function, is one of the possible outcomes. Here, researchers use an established class of compound to target this form of inflammatory signaling, finding that the treatment has a positive impact on fibrotic disease in animal models. This is consistent with other studies that have found that TGFβ is a useful target, in that suppressing TGFβ signaling can limit the harms done by senescent cells.

Fibrotic disease is a major cause of mortality worldwide, with fibrosis arising from prolonged inflammation and aberrant extracellular matrix dynamics. Compromised cellular and tissue repair processes following injury, infection, metabolic dysfunction, autoimmune conditions, and vascular diseases leave tissues susceptible to unresolved inflammation, fibrogenesis, loss of function and scarring.

There has been limited clinical success with therapies for inflammatory and fibrotic diseases such that there remains a large unmet therapeutic need to restore normal tissue homoeostasis without detrimental side effects. We investigated the effects of a newly formulated low molecular weight dextran sulfate (LMW-DS), termed ILB, to resolve inflammation and activate matrix remodelling in rodent and human disease models. We demonstrated modulation of the expression of multiple pro-inflammatory cytokines and chemokines in vitro together with scar resolution and improved matrix remodelling in vivo.

Of particular relevance, we demonstrated that ILB acts, in part, by downregulating transforming growth factor (TGF)β signalling genes and by altering gene expression relating to extracellular matrix dynamics, leading to tissue remodelling, reduced fibrosis, and functional tissue regeneration. These observations indicate the potential of ILB to alleviate fibrotic diseases.

Link: https://doi.org/10.1038/s41536-020-00110-2

Predicting Alzheimer's Disease via Detection of Misfolded Amyloid-β in a Blood Sample

The research community is making progress towards forms of low cost testing for Alzheimer's disease risk. At present, the well established tests are invasive or expensive. The very early stages of Alzheimer's disease, in which symptoms are mild or absent, are characterized by increasing levels of amyloid-β in the brain. However, amyloid-β in the brain is in a state of dynamic equilibrium with amyloid-β in the bloodstream, and in principle a suitable sensitive test can use a blood sample to assess the relevant aspects of amyloid-β burden. It takes years to validate predictions of Alzheimer's risk of course, and here researchers report on a lengthy but successful validation of one particular blood sample assay.

Using a blood test, a research team has predicted the risk of Alzheimer's disease in people who were clinically diagnosed as not having Alzheimer's disease but who perceived themselves as cognitively impaired. The cohort included 203 individuals. Using a test called the Immuno-Infrared Sensor, they identified all 22 subjects at study entry who developed Alzheimer's dementia, thus the clinical symptoms, within six years.

At study entry, blood samples were taken from all the participants and analyzed using the patented immuno-infrared sensor that detects misfolding of the amyloid-beta (Aβ) peptide, which is a biomarker for Alzheimer's disease. In addition, the subjects underwent extensive Alzheimer's disease diagnostic testing; at study entry, this did not provide a diagnosis of Alzheimer's disease in any of the subjects studied. The immuno-infrared sensor, on the other hand, detected misfolded Aβ peptides at study entry in all 22 subjects who developed the clinical disease in the following six years. In subjects who showed mild misfolding, it took on average longer (3.4 years) for conversion to clinical Alzheimer than in subjects with severe Aβ misfolding (2.2 years).

In addition, the team checked whether the combination of two different measurement methods in the plasma biomarker panel could further improve the prediction of disease risk. For this purpose, they combined the misfolding of all Aβ isoforms with a concentration decrease for Aβ42 as ratio to Aβ40 in plasma. This increased the assay accuracy. Such a blood test, which can detect the onset of Alzheimer's dementia even in the asymptomatic state, would be particularly useful if a drug were available to treat the disease.

Link: https://news.rub.de/english/press-releases/2021-01-06-protein-research-prognostic-alzheimers-disease-blood-test-symptom-free-stage

Looking Forward to the Longevity Industry in 2021

Having written retrospectives for 2020, longevity industry observers are now looking forward to what we might expect in 2021. This survey of companies and projects in the longevity industry is unbiased from the point of view of whether or not the treatments under development are expected to have a sizable effect on human aging. Can they slow aging or actually reverse aging meaningfully? It is more focused on progress on startups, business matters, and potential for profit.

One of the many issues with the highly regulated medical development market is that success in investment is only somewhat connected to success in generating a therapy. Liquidity events for investors in early stage biotech companies occur well before clinical approval by regulators, and thus incentives are not completely aligned. Merely fleshing out animal data and applying hype to a given mechanism (see the Sitris Pharmaceuticals story, for example) can work just as well as actually setting out to build a viable therapy that can have sizable effects on aging, when it comes to giving investors a sizable return on investment.

Further, the market values (a) incremental, modest advances that are easier to explain to regulators, and that fit in existing frameworks for evaluation over (b) radical, ambitious advances based on entirely new approaches that will require greater effort to obtain approval. In the treatment of aging as a medical condition, we need those radical, ambitious advances. The incremental, modest advances (such as yet another way to mimic calorie restriction, as if we need more of those) are not going to move the needle all that much on human life span. People will still be aging and dying in much the same way as their parents and grandparents did.

Top 10 Things to Watch in the Longevity Industry in 2021

Jim Mellon, billionaire patron saint of longevity investing, announced in September 2020 that he would take his longevity portfolio company, Juvenescence, public within 6-12 months. Juvenescence's diversified portfolio of 11 assets spans the gamut of senolytics, AI companies, regenerative medicine, and nutraceutical products. The Juvenescence IPO will be the biggest development in public market longevity investing since Unity Biotechnology went public in 2018. And because Juvenescence is a diversified portfolio of longevity companies it best represents the entire industry going forward.

Kristen Fortney's AI / computational drug discovery company BioAge recently closed a Series C round and will use the funds to initiate Phase 2 clinical trials this year. BioAge uses AI, machine learning, and systems biology models to mine multi-omics patient datasets and identify existing drugs that are likely to treat age-related disease. Since BioAge's strategy is to repurpose existing drugs they are able to go straight to Phase 2 trials.

Nir Barzilai recently gave an online talk with the Foresight Institute. In the talk he mentioned that an unnamed wealthy individual was in the process of setting up a longevity foundation that would invest $1 billion into anti-aging research and companies per year. Barzilai said the foundation would be announced in January of this year. Who could be the mysterious donor? Nir Barzilai indicated it is the same mysterious person that is funding the TAME trial and is a well known tech billionaire. My guess: It's Larry Ellison, founder of Oracle. He has a net worth of $88 billion and is 76 years old. Ellison has also donated to longevity causes in the past through the Ellison Medical Foundation. My second guess is Sergey Brin of Google.

2020 was a disastrous year for Unity Biotechnology. But 2021 could be a year of redemption for Unity. Their new Phase 1 trial for UBX1325, a Bcl-xL inhibitor to treat Diabetic Macular Edema (DME), will be completed in the first half of this year, with a proof of concept trial to follow shortly afterwards. I am cautiously optimistic for Unity Biotechnology. But I am also totally unworried if they fail, as there are many many other senolytics companies preparing for clinical trials - many with 2nd generation targeted approaches that may prove superior to Unity's.

2021 will be the year that more senolytics companies finally join Unity in the clinical race. And many of these companies are using 2nd gen targeted approaches to clear senescent cells. FoxBio, a Juvenescence and Ichor Therapeutics senolytics joint venture, is planning Phase 1 trials for an osteoarthritis drug this year. Numeric Biotech, a spin out from Erasmus Medical Center in the Netherlands, is planning to test the FOXO4-DRI peptide. Senolytic Therapeutics, one of David Sinclair's Life Biosciences daughter companies, has two mature assets that should be close to ready for clinical trials - although there is no set date.

Thoughts on the Road to Greater Human Longevity

I recently noticed this scientific commentary, published in a journal not specifically focused on aging. The author is far from the only person to have noticed that priorities in medical research and development do not seem to match up with the major causes of death all that well. It can't hurt to keep on pointing out that research into the most harmful biological processes in the world, meaning the mechanisms that cause aging, is very poorly funded and investigated in comparison to the vast and ongoing toll of death that results. Until aging is defeated, more funding for research into rejuvenation therapies will continue to be the most cost-effective way to improve the human condition.

Longevity means living a long life, nowadays often considered a life span over 85 to 100 years. More and more people reach this limit in modern welfare societies, and citizens aged 90 years and over are said to be the fastest increasing group of people. This is a reality, but what are the background factors for this development? Many scholars think that it is mostly due to societal factors like improved hygiene, proper diet and safer environment. These are important but have mainly established the sine qua non for reaching old age through living past dangerous childhood and earlier adult life and becoming old. In modern societies, reaching longevity is jeopardized more by chronic non-communicable diseases which have replaced infectious diseases as primary causes of morbidity and mortality. By the way, according to the latest Global Health Estimates by the World Health Organization, during the first half of 2020, non-communicable diseases killed approximately 25 times more people than the ongoing COVID-19 pandemic.

According to the Bible, 'The days of our years are threescore years and ten (70 years); and if by reason of strength they be fourscore years (80 years), yet is their strength labour and sorrow; for it is soon cut off...'(Psalm 90:10). This well accords with the thoughts of biogerontologists: the warranty period of homo sapiens is 65 years, where after on the average 20 years can be attained, mainly depending on life-course factors. Whilst age 85 years is an upper limit to life expectancy at the population level, ca. 40% of the original birth cohort nevertheless can reach 90 years, 5-6% 100 years, few 100-115 years, and only a handful of individuals over that.

The most common non-communicable diseases are cardiovascular diseases, chronic obstructive pulmonary diseases, cancer, and degenerative diseases. Many risk factors for them have been identified. Overall, it seems feasible that health span - healthy years of life - extension and successful ageing can be promoted with better and long-term cardiovascular risk factor control. However, for reaching 100 years and over the role of genetic factors affecting longevity strengthens. For most of the population, extending life span and especially health span over 90 years requires new methods to control the biological ageing processes, currently investigated in the realms of Geroscience, the Longevity Dividend, and the Global Roadmap for Healthy Longevity.

Link: https://doi.org/10.1111/joim.13211

Immunosenescence in Alzheimer's Disease

Researchers here catalog the various mechanisms known to be involved in the development of Alzheimer's disease that occur as a result of the aging of the immune system. The immune system becomes less effective with age, but also constantly overactive. It generates constant and unresolved inflammatory signaling that damages tissue structure and disrupts tissue function. All of the common age-related conditions are accelerated and worsened by the chronic inflammation resulting from the age-damaged immune system.

Alzheimer's disease (AD) is the most common type of dementia characterized by progressive memory loss, visual-spatial impairment, executive dysfunction, and personality and behavioral changes. The pathological features of AD are neuritic plaques, neurofibrillary tangles, neuronal and synaptic loss, and the activation of microglia. Over the past few decades, the amyloid cascade hypothesis has dominated the field of AD research, suggesting that amyloid-β (Aβ) deposition is the central event in AD pathology. However, recent findings have challenged this hypothesis and argue that Aβ protects the brain from infection, and its aggregation promotes microglia-mediated neuroinflammation. The viewpoint that altered immune and inflammatory responses may play the main role in the progression of AD has increasingly been recognized.

In recent years, research is making significant progress and proposes that immunosenescence actively participates in the pathogenesis of AD and mediates inflammatory damage. Microglia are innate immune cells that reside in the brain and play an important role in maintaining homeostasis and immune defense. Microglia undergo significant changes in the aging brain. Morphologically, aged microglia exhibit cytoplasmic hypertrophy and branch reduction. Functionally, senescent microglia show higher proliferative capacity and production of proinflammatory cytokines, but reduced chemotaxis and ability to clear Aβ. Activated and proliferated microglia surround amyloid plaques in the AD brain and participate in the clearance of Aβ. Aβ binds to TLRs, RAGE, and other receptors on the surface of microglia membranes, transducing intracellular signaling pathways, then leading to the synthesis and release of pro-inflammatory factors. In the aging brain, the phagocytic capacity of microglia is weakened, which leads to the accumulation of Aβ. Microglia continue to activate, leading to chronic inflammation, increased oxygen free radicals, mitochondrial damage, and ultimately neuronal death.

Inflammation, a normal repair response, is crucial to combat pathogens and clear dead cells. Once the inflammation is dysregulated, it will cause tissue damage. Inflammaging refers to a state of chronic pro-inflammatory response in the process of aging, which is considered to be a part of immunosenescence. AD is also considered to be a chronic inflammatory disease. The inflammatory response of AD is not limited in the brain, but also exists in peripheral tissues, which is considered to be part of the systemic inflammatory response. The chronic inflammatory state in aging individuals may be associated with long-term chronic microbial infections, which may be a driver of cognitive decline and possibly dementia in the elderly.

Link: https://doi.org/10.14336/AD.2020.0205