Cytomegalovirus Presence Expands Considerably in Old Age
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The open access paper referenced here expands the picture of cytomegalovirus and the aging immune system with additional data. Cytomegalovirus (CMV) is a common herpesvirus present in near everyone by the time old age rolls around. In the majority of people it presents no symptoms, but it is apparently an important factor in the age-related decline of the immune system. Like all herpesviruses it cannot be effectively cleared from the body, and over the years the immune system devotes ever more of its limited resources to uselessly fighting it. An old immune system contains legions focused on cytomegalovirus and all too few cells capable of responding to other pathogens. This is one of the contributing causes of immunosenescence, the progressive failure of the immune system with age.

The best approaches to solving this problem actually involve expanding the population of useful immune cells rather than getting rid of cytomegalovirus. Clearing it doesn't fix the damage done: the specialized cells are already specialized. So possible treatments might involve delivering infusions of immune cells grown from the patient's own stem cells, selectively destroying cytomegalovirus-targeted immune cells to free up space for replacement with new immune cells, or restoring the thymus to increase the pace at which new immune cells are created.

Cytomegalovirus infection has been associated with a variety of health problems in elderly people and there is increasing interest in the mechanisms that underlie this association. A key determinant in this regard will be greater understanding of the balance of the viral load and the host immune response during healthy ageing. In this study we report, for the first time, that the level of cytomegalovirus viral load within the blood increased markedly in elderly people. A novel feature of our work was the use of digital droplet PCR (ddPCR) to provide an accurate quantitative measure of latent viral DNA. Previous methods for detection of CMV generally relied on nested PCR techniques, which made quantification challenging and also raised substantial problems with reproducibility.

Our work was performed using DNA isolated from monocytes, which are established as the most important haemopoietic site of viral latency. The first interesting finding was the observation that CMV was detectable in only a minority of donors, as 64% of people remained negative by ddPCR despite the presence of chronic infection as confirmed by CMV-specific IgG positivity. Indeed, in younger people below the age of 50 years, the detection of CMV load in the blood was uncommon, being observed in only 13% of donors tested. The lower limit of detection provided by ddPCR in our assay was for a single copy of virus within the total reaction volume and as such a negative result indicated absent or extremely low levels of virus. This low level carriage may reflect a lower intrinsic probability of viral reactivation in younger donors but is perhaps more likely to reflect the consequence of effective immune surveillance of viral replication in younger individuals.

The frequency of viral detection increased markedly with each decade above the age of 50 years to 37.5% and 50% and finally became positive in every donor who was older than 70. Interestingly the amount of viral DNA detected within the blood also increased substantially with age with a 29 fold increase observed between donors aged less than 70 and those over this age. The use of nested PCR also detected viral DNA within the majority of healthy elderly donors. These data indicate that a gradual impairment in the ability to control CMV load within blood starts around the age of 50 years and then deteriorates markedly beyond the age of 70. In conclusion, these data reveal the delicate balance that has evolved between chronic CMV infection and the host immune response and indicate that this symbiosis can break down during ageing, where an increase in CMV viral load occurs as the attritional effects of chronic surveillance and the impact of immune senescence become more apparent. It is likely that increased understanding of the clinical importance of chronic viral infection on human health will become an important health consideration in future years.

Link: http://dx.doi.org/10.1186/s12979-015-0056-6

Poor Fitness Correlates with Later Smaller Brain Volume
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The results of this study can be added to the many reasons to keep up with a decent level of exercise. A sedentary lifestyle has costs, most of which manifest as a greater risk of age-related disease in later later:

Poor physical fitness in middle age may be linked to a smaller brain size 20 years later. "We found a direct correlation in our study between poor fitness and brain volume decades later, which indicates accelerated brain aging." For the study, 1,583 people enrolled in the Framingham Heart Study, with an average age of 40 and without dementia or heart disease, took a treadmill test. They took another one two decades later, along with MRI brain scans. The researchers also analyzed the results when they excluded participants who developed heart disease or started taking beta blockers to control blood pressure or heart problems; this group had 1,094 people.

Exercise capacity was estimated using the length of time participants were able to exercise on the treadmill before their heart rate reached a certain level. For every eight units lower a person performed on the treadmill test, their brain volume two decades later was smaller, equivalent to two years of accelerated brain aging. When the people with heart disease or those taking beta blockers were excluded, every eight units of lower physical performance was associated with reductions of brain volume equal to one year of accelerated brain aging. The study also showed that people whose blood pressure and heart rate went up at a higher rate during exercise also were more likely to have smaller brain volumes two decades later. People with poor physical fitness often have higher blood pressure and heart rate responses to low levels of exercise compared to people with better fitness.

Link: https://www.aan.com/PressRoom/Home/PressRelease/1432

A Study Suggesting that Dementia Incidence is Declining
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The research noted here stands in opposition to the present consensus on dementia, which is that incidence will increase as other age-related diseases are increasingly controlled. Many people avoid dementia because other conditions kill them first, particularly heart disease. If given additional years of life thanks to improved therapies, then some will later suffer dementia. However, it appears that the improvements in vascular health in old age that have reduced the impact of heart disease also have the effect of significantly reducing dementia incidence. A large fraction of the causes of dementia is a matter damage and dysfunction of the blood vessels in the brain, leading to slow, incremental structural damage to brain tissue.

Despite the concern of an explosion of dementia cases in an aging population over the next few decades, a new study, based on data from the Framingham Heart Study (FHS), suggests that the rate of new cases of dementia actually may be decreasing. It is believed that the number of Americans with Alzheimer's disease and other dementias will grow each year as the size and proportion of the U.S. population age 65 and older continues to increase. By 2025 the number of people age 65 and older with Alzheimer's disease is estimated to reach 7.1 million - a 40 percent increase from the 5.1 million aged 65 and older affected in 2015. By 2050, the number of people in this age population with Alzheimer's disease may nearly triple, from 5.1 million to a projected 13.8 million, barring the development of medical breakthroughs to prevent or cure the disease.

FHS participants have been continuously monitored for the occurrence of cognitive decline and dementia since 1975. Thanks to a rigorous collection of information, FHS researchers have been able to diagnose Alzheimer's disease and other dementias using a consistent set of criteria over the last three decades. Researchers looked at the rate of dementia at any given age and attempted to explain the reason for the decreasing risk of dementia over a period of almost 40 years by considering risk factors such as education, smoking, blood pressure and medical conditions including diabetes, high blood pressure or high cholesterol among many others.

Looking at four distinct periods in the late 1970s, late 1980s, 1990s and 2000s, the researchers found that there was a progressive decline in incidence of dementia at a given age, with an average reduction of 20 percent per decade since the 1970s, when data was first collected. The decline was more pronounced with a subtype of dementia caused by vascular diseases, such as stroke. There also was a decreasing impact of heart diseases, which suggests the importance of effective stroke treatment and prevention of heart disease. Interestingly, the decline in dementia incidence was observed only in persons with high school education and above.

Link: http://www.eurekalert.org/pub_releases/2016-02/bumc-nsr020916.php

Long-Term Benefits of Senolytic Drugs on Vascular Health
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Senolytic treatments are those that at least partially clear senescent cells, producing a narrow form of rejuvenation, enhanced longevity, and improvement in long-term health. One of the fortuitous discoveries of recent years was that a combination of the drugs dasatinib and quercetin can clear enough senescent cells in a single treatment in mice to demonstrate that doing so is beneficial. The research noted here extends that result to investigate some of the outcomes of a series of treatments over time.

It is unfortunately unlikely that the same degree of clearance will happen in humans via the use of these particular drugs, but people are certainly going to try anyway. The real value of this research lies in the ability to prove that getting rid of these cells is robustly beneficial in mammals. This will result in increased support for the clinical development of methods that will work in humans. Some of those methods already exist in prototype form and work is presently underway on these approaches at Oisin Biotechnology and Unity Biotechnology, for example.

Cells become senescent in response to stress or damage, irreversibly removing themselves from the cycle of division and replication. This most likely initially serves to reduce risk of cancer by suppressing the ability of the most vulnerable cells to become cancerous, but as the number of senescent cells rises, they have a growing detrimental effect on tissue function. Senescent cells secrete signals that produce chronic inflammation, haphazardly remodel surrounding tissue structures, and encourage bad behavior in neighboring cells. In short, senescent cells are one of the causes of aging, and therapies under development to remove them are the first practical rejuvenation biotechnologies after the SENS model.

Building on previous studies, researchers have demonstrated significant health improvements in the vascular system of mice following repeated treatments to remove senescent cells. They say this is the first study to show that regular and continual clearance of senescent cells improves age-related vascular conditions - and that the method may be a viable approach to reduce cardiovascular disease and death. "Cardiovascular disease remains the leading cause of death in our population today, and disability related to heart disease and stroke has a tremendous impact on our aging population. This is the first evidence that longer term use of senolytic drugs to clear these damaged cells from the body can have a preventative impact against vascular diseases."

Senescent cells are damaged cells that no longer function properly, but remain in the body and contribute to frailty and many of the other health conditions associated with aging. Prior studies showed chronic removal of the cells from genetically-altered mice can alter or delay many of these conditions, and short-term treatment with drugs that remove senescent cells can improve the function of the endothelial cells that line the blood vessels. This study, however, looked at the structural and functional impacts of cell clearance using a unique combination of drugs on blood vessels over time. Mice were 24 months old when the drugs - a cocktail of dasatinib and quercetin - were administered orally over a three-month period following those initial two years. A separate set of mice with high cholesterol was allowed to develop atherosclerotic plaques for 4 months and were then treated with the drug cocktail for two months.

The research showed that senescent cell clearance in either naturally-aged or atherosclerotic mice alleviated vascular dysfunction. Although it did not reduce the size of plaques in mice with high cholesterol, it did reduce calcification of existing plaques on the interior of vessel walls. "Our finding that senolytic drugs can reduce cardiovascular calcification is very exciting, since blood vessels with calcified plaques are notoriously difficult to reduce in size, and patients with heart valve calcification currently do not have any treatment options other than surgery. While more research is needed, our findings are encouraging that one day removal of senescent cells in humans may be used as a complementary therapy along with traditional management of risk factors to reduce surgery, disability, or death resulting from cardiovascular disease."

Link: http://newsnetwork.mayoclinic.org/discussion/mayo-clinic-aging-researchers-show-long-term-benefits-of-senolytic-drugs-on-vascular-health-in-mice/

Tuning Macrophages in Cancer Immunotherapy
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Immunotherapy is a broad category, and covers many very different strategies for tackling cancer and other conditions by engineering immune cells or adjusting the behavior of the immune system as a whole. In this case, researchers have found a novel and interesting approach:

Similar to stem cells differentiating to make your body's tissues, the immune system's macrophages pick a life path, differentiating into macrophages that recruit resources for wound repair or macrophages that recruit resources for wound sterilization. Cancers encourage macrophages to pick the path of wound-repair, making what are called "M2" or "repair-type" macrophages. Cancers use these M2 macrophages to promote their own growth. However, researchers can now successfully flip M2 macrophages into their wound-sterilizing cousins, called "M1" or "kill-type" macrophages, which, contrary to promoting the growth of new tissue, may aid the immune system in clearing the body of cancer.

Previous work has shown that people with a naturally high ratio of M1 to M2 macrophages are less prone to develop cancer. And in mouse models of the disease, encouraging a high M1-to-M2 ratio can "slow or stop cancer growth." In fact, there are two schools of thought describing how, exactly, to change a population of M2 macrophages into a population of M1 macrophages. In the first school of thought, M2 macrophages can reverse their differentiation to become briefly more "stem-like" before being encouraged to use their second chance to pick the more beneficial M1/kill-type phenotype. In the second school of thought, as macrophages naturally die out, they could be replaced by a new population dominated by M1 macrophages. The paper describes a way to accomplish the second: In the presence of the cytokine interferon gamma, macrophages take on the M1 phenotype.

"Interferon gamma has been explored as a possible therapeutic agent, but there are problems with it. Interferon gamma mediates hundreds of effects and some of them aren't very comfortable." Instead, one idea is to improve the sensitivity of cells to the interferon gamma that already exists in the body. "In the right context, macrophages lose their sensitivity to interferon gamma and we want to prevent that." Another approach seeks to augment interferon gamma only in tumor tissue, keeping its effects localized. "The immune system's killer cells produce interferon gamma and one promising strategy is to get them to the tumor and activated in the right way." In fact, existing immunotherapies seek to recruit the body's killer cells, especially cytotoxic T cells, to recognize and attack tumor tissue. A byproduct of this activation is the production of interferon gamma at the tumor site, which causes macrophages to take the M1 and not M2 phenotype. "Cytotoxic T cells can directly kill tumor cells. But they also produce interferon gamma. Both are likely contributing to the anti-tumor effect. By devising approaches to tune macrophages in the right way, we hope to further improve immunotherapies."

Link: http://www.coloradocancerblogs.org/tuning-macrophages-a-breakthrough-in-cancer-immunotherapy/

On Building Measures to Link Aging and Disease
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In this popular science article on the relationship between aging and age-related disease, a researcher discusses one of a number of approaches to producing a biomarker of aging, a sensitive measure of the degree to which an individual is impacted by the cell and tissue damage of aging. A good biomarker should predict the onset of disease and remaining life expectancy to the degree that these are determined by damage:

In epidemiological studies, particular those focused on the molecular mechanisms of 'growing older', loss of function and the emergence of 'biomarkers' of disease, even in young middle-aged 'healthy' adults, are often presented as diagnostics for human ageing. From my perspective, this is almost certainly misleading as it implies that health, disease and longevity are all interchangeable synonyms for ageing. If we wish to identify a definitive 'ageing' molecular programme (e.g. biological age), one that is independently informative for future health and life span then it is critical that we clearly define what is meant by the term 'ageing' and appropriately develop an assay that measures this parameter. We also have to consider if the developed diagnostic, while statistically significantly related to biological age, is sufficiently sensitive and specific enough to be considered a useful diagnostic (most will fail this final criteria e.g. telomere assays).

The other major consideration relates to how a novel diagnostic of 'biological age' would be used. If it were to be used as an independent diagnostic of longevity then it would be combined with other factors and behaviours that determine life-span, such as smoking and obesity. One could imagine the generation of an integrated risk 'score' utilised to determine insurance premiums for healthcare or to calculate pension requirements. These may seem controversial examples, but in reality our chronological age (birth year) and behaviours are already judged and used for these purposes. Why not have a more accurate 'diagnosis' of the contribution 'age' makes to these decisions? For example, if you are a poor 'biological age' (for your chronological age) then your breast-cancer or prostate-cancer screening might be scheduled 5-10 yr earlier than average.

Variation in the human transcriptome (RNA) has proven particularly powerful for identifying the huge variations in human physiology and physiological responses to environmental influences. So it is not surprising it has been used to develop diagnostics of human ageing, including our own model. While you can't use chronological age to diagnose the health status of an individual - the relationship between chronological age and disease is an epidemiological one - existing RNA or DNA methylation assays represent composites of ageing, disease and drug-treatment and not chronological age. We believe that 'biological' age will determine when you show clinical symptoms of disease and that we need an assay which accurately reflects your underlying 'rate of ageing' or 'biological age'. Which 'age associated' disease an individual then develops will depend on their genetic, epigenetic and environmental risks factors (and stochasticity).

To produce this new diagnostic of 'biological age' we had the hypothesis that we can find a set of RNAs in the tissue that was diagnostic for telling tissue from healthy old from healthy young people apart. In our study healthy old people were living a normal sedentary lifestyle, did not have type II diabetes and importantly had good fitness levels. By applying machine learning to this 'special' healthy ageing cohort, we found 150 RNA markers. In fact we could see that these 150 RNAs were either up or down regulated in tissue from healthy old people and we reasoned that activation of this gene expression 'programme' may help explain why these 65 year old people achieved good health despite living a sedentary life style. In fact, when we then applied the 150 RNA assay to a group of 70 year old people (people with the same chronological age) we found that their 'biological age' score varied dramatically and for those that failed to switch the gene expression pattern "on" as much died sooner and had a greater decline in organ function (kidney).

Link: http://www.labnews.co.uk/features/ageing-become-disease-08-02-2016/

In Search of the Genetics of Longevity in Sea Urchins
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Comparative biology is an important tool in aging research, as the analysis of similar species with widely divergent life spans can in theory point out the more important mechanisms of aging. The more similar the species the better, and so here researchers investigate the genetics of two sea urchin species that exhibit a twenty-fold difference in life span. This is a preliminary set of data, absent any rigorous analysis, but even at the outset it doesn't exactly fit the expected picture. There is no real reason to expect a universality of relative importance of mechanisms across diverse species, so things that have proved to be important in well-studied species such as flies, mice, and people may well turn out to have little relevance to more distant branches of the tree of life. As a general rule, we should always expect biology to be more complex and varied rather than less so:

Sea urchins have attracted attention due to the extreme longevity of some of their species. Red sea urchin, S. franciscanus, populating cold waters of Pacific coast of North America, was demonstrated to survive over a century. Although S. franciscanus could not be cultivated in the lab for a century for direct observation, deposition pattern of radioactive carbon released to the Pacific upon nuclear tests and skeleton growth rate studies using tetracycline labeling allowed red sea urchin to climb the pedestal of the most long-lived marine animals. At the same time, green sea urchin, L. variegatus, populating warm Caribbean sea hardly survive over four years. Although direct difference in the senescence rates between red and green sea urchins is hard to demonstrate directly on the sole basis of field studies, these two related species might be the a convenient pair for comparative genetics of longevity. In this report we aimed to obtain draft genome assemblies of S. franciscanus and L. variegatus and compare the sequence of their proteins related to longevity with longevity related proteins of other species.

Analysis revealed several aminoacid positions that co-vary with longevity. Although this approach is not guaranteed from mistakes originated from misalignment, identification of related proteins that have different function, it could present a framework of further hypothesis-driven experiments on longevity. Our analysis revealed highly uneven distribution of proteins having aminoacid residues that co-vary with longevity among functional categories. Surprisingly, several categories of proteins were completely devoid of such positions. For example, nuclear encoded mitochondrial proteins and proteins involved in reactive oxygen species inactivation. Minimum of such aminoacids were found in the components of insulin/IGF1 pathway. Particularly enriched in positions that vary in coordination with longevity are categories of mitochondrial proteins encoded in mitochondrial genome, lipid transport proteins, proteins involved in amyloidogenesis and system of telomere maintenance. Among other, catalytic subunit of telomerase, telomerase reverse transcriptase (TERT) holds absolute record of the frequency of such positions. Despite the fact, that somatic telomerase activity could be detected in short and long living sea urchins, TERT might be involved in longevity due to more intricate mechanisms, such as maintaining the balance between support of tissue renovation and simultaneous restriction of unwanted proliferation of cancerous cells.

Link: http://www.impactaging.com/papers/v8/n2/full/100889.html

Protecting Osteoblasts to Enhance Bone Mass and Strength
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Bone is constantly remodeled at the small scale, created by cells called osteoblasts and destroyed by cells called osteoclasts. One of the proximate causes of osteoporosis, age-related loss of bone mass and strength, is a growing imbalance between these two cell populations. Any of a range of approaches that can tilt the balance back towards osteoblasts and bone creation is likely to slow skeletal degeneration, and that is demonstrated in mice in the study linked here. As a matter of interest note that this particular approach is the exact opposite of that used in the first senolytic drugs: inhibiting cell self-destruction rather than encouraging it via the same target of Bcl2 proteins.

The Bcl2 family proteins, Bcl2 and BclXL, suppress apoptosis by preventing the release of caspase activators from mitochondria through the inhibition of Bax subfamily proteins. We reported that BCL2 overexpression in osteoblasts increased osteoblast proliferation, failed to reduce osteoblast apoptosis, inhibited osteoblast maturation, and reduced the number of osteocyte processes, leading to massive osteocyte death. We generated BCLXL transgenic mice using the same promoter in order to investigate BCLXL functions in bone development and maintenance.

Bone mineral density in the trabecular bone of femurs was increased, whereas that in the cortical bone was similar to that in wild-type mice. Osteocyte process formation was unaffected and bone structures were similar to those in wild-type mice. A micro-CT analysis showed that trabecular bone volume in femurs and vertebrae and the cortical thickness of femurs were increased. Analysis revealed that the mineralizing surface was larger in trabecular bone, while the bone formation rate was increased in cortical bone. The three-point bending test indicated that femurs were stronger in BCLXL transgenic mice than in wild-type mice.

The frequency of TUNEL-positive primary osteoblasts was lower in BCLXL transgenic mice than in wild-type mice during cultivation, and osteoblast differentiation was enhanced, but depended on cell density, indicating that enhanced differentiation was mainly due to reduced apoptosis. Increased trabecular and cortical bone volumes were maintained during aging in male and female mice. These results indicate that BCLXL overexpression in osteoblasts increased the trabecular and cortical bone volumes with normal structures and maintained them majorly by preventing osteoblast apoptosis, implicating BCLXL as a therapeutic target of osteoporosis.

Link: http://dx.doi.org/10.1002/jbmr.2808

Aging Hair Follicles Change to Become Skin
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An interesting mechanism that appears to contribute to age-related hair loss was recently identified. It is unusual in that cells of one tissue structure are changing to cells of another as a result of age-related damage:

Scientists have uncovered a new mechanism behind hair loss: When stem cells in hair follicles are damaged by age, they turn themselves into skin. Over time, this happens to more and more stem cells, causing hair follicles to shrink and eventually disappear. This is the first time such a switch has been associated with aging in any tissue. Stem cells - precursor cells that can give rise to specialized cells like skin and hair - regenerate throughout the life of an organism and are located all over the body. But unlike stem cells in the blood or intestinal lining, hair follicle stem cells regenerate on a cyclical basis. Their active growth phase is followed by a dormant phase, in which they stop producing hair. These discrete on-off periods make hair follicle stem cells a useful model for studying stem cell regulation - and hair loss.

To figure out why hair thins in old age, researchers looked at hair follicle stem cell growth cycles in live animals - a daunting task - and found that age-related DNA damage triggers the destruction of a protein called Collagen 17A1. That in turn triggers the transformation of stem cells into epidermal keratinocytes. In their new state, the damaged stem cells slough off easily from the skin's surface. "When damaged cells deplete that niche of collagen 17A1, they alter their own signaling environment. It is interesting that these damaged cells change their fate rather than committing suicide through apoptosis (programmed cell death) or stopping cell division through senescence."

To see whether their results carried over to people, the researchers analyzed hair follicles in scalps from women aged 22 to 70. They found that follicles in people over 55 were smaller, with lower levels of Collagen 17A1. "We assume that ... aging processes and mechanisms similar to those in the mice explain the human age-associated hair thinning and hair loss." Stem cell depletion is unlikely to be the only factor behind the condition, however.

Link: http://www.sciencemag.org/news/2016/02/one-reason-your-hair-thinning-some-it-turns-skin

How Do Stem Cell Transplants Produce Heart Regeneration?
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Stem cell transplants spur greater regeneration in an injured heart that would normally be the case, and so far it appears to be the case that this is a matter of signaling that changes the behavior of native cells rather than the transplanted stem cells integrating with native tissue and generating new cells. Past studies have shown that the stem cells don't last long following transplant. Nonetheless the beneficial effects do last quite a while, and this is presently a mystery - what mechanisms are mediating this result? This is the latest in a line of studies that examine this question, and the novel finding here is that the transplanted cells do leave behind a lingering population of new cells in the heart, but the nature of those cells is unexpected, which is perhaps why past studies have missed them:

In numerous clinical trials, researchers have injected patients with various types of progenitor cells to help heal injured hearts. In some cases, subjects have ended up with better cardiac function, but exactly how has been a subject of disagreement among scientists. According to study on rats, the introduced cells themselves don't do the job by proliferating to create new muscle. "These cells do not become adult cardiac myocytes. So the mechanism is clearly a paracrine action, where the cells release 'something' which makes the heart better. And the million-dollar question now is, 'What is the something?'"

Researchers investigated the fate of so-called c-kit+ cells, progenitors harvested from the heart and named for the presence of a particular kinase. These cells have been the source of a long debate about their role in building cardiac muscle, with some studies finding no evidence of them producing new cardiomyocytes in vivo and others concluding that, if the conditions are right, c-kit cells do indeed make heart muscle. C-kit cells have also been deployed in a clinical trial on heart attack patients. Studies on a variety of cardiac cell therapies have found that the vast majority of the cells don't stick around in the heart for much longer than a few weeks, suggesting that their mode of action is likely not based on the cells themselves producing new muscle tissue directly. To test whether that's the case with c-kit cells, researchers harvested c-kit cells from healthy male rats' hearts and injected them into female rats who had been made to have a heart attack.

Compared to controls, the treated rats had smaller scars, more muscle in their hearts, and improvements in cardiac function. To follow what had happened to the injected c-kit cells, the researchers picked out cells with Y chromosomes, finding that they made up 4 percent to 8 percent of the nuclei in the heart. Many of them had lost c-kit positivity, and it was clear from their morphology that these cells are not heart muscle and don't contribute to cardiac contraction. "Honestly, I do not know what they are. That's what we're trying to figure out." It appeared that the treated animals did have more cell proliferation, which researchers attributes to the cell therapy. "Pretty amazingly, it lasts up to 12 months after transplantation, which is another thing I cannot explain. How can the transplantation, done only once, stimulate a proliferative response for 12 months?"

Link: http://www.the-scientist.com/?articles.view/articleNo/45254/title/Mysterious-Mechanisms-of-Cardiac-Cell-Therapy/