Fight Aging! Newsletter, November 26th 2018

When cellular senescence was first characterized in in vitro cell culture, links to tissue and organismal aging were proposed. Critics of cellular senescence questioned its relevance to in vivo aging, their possibility of being an artefact and the inevitable lack of senescence despite normal aging in lower organisms. Senescence as a pro-aging phenomenon gained popularity with the discovery of biomarkers such as p16 and beta-galactosidase in multiple aged tissues. Mechanistically, the idea of senescent cells being causal in chronic inflammation characteristic of aging, also gained momentum with the discovery of the senescence-associated secretory phenotype (SASP).

The senescence field came of age with four major milestones, (a) two proof-of-concept studies showed major improvement in healthspan and lifespan in mice by the targeted ablation of senescent cells, (b) development of small molecule senolytics as a therapeutic strategy for clearing senescent cells, (c) demonstration that senolytics improve physiological function and lifespan in aged mice and (d) the success of senolytics in pre-clinical studies of a range of age-related conditions. Below, we discuss potential alternatives to senolytics that can deploy epigenetic proteins as "switches" to turn on/off specific pathways in senescent cells for their effective elimination.

SASP inhibitors

Despite the overwhelming success of senolytics, fundamental concerns about specificity and safety prevail. Additionally, the potential benefit of senolytics in treating age-related disease remains to be tested. A second class of molecules that have shown promise in anti-aging rejuvenation therapies is SASP inhibitors. The concept of annihilating the pro-aging arm of senescent cells while preserving the anti-tumor arm is a very attractive treatment option in the elderly who have a high incidence of cancer. Both rapamycin and metformin have shown anti-SASP effects and are on the road to clinical trial for aging. Alternatively, epigenetic enzymes that play a key role in turning on SASP genes (MLL1 and BRD4) can be inhibited by small molecules to prevent its deleterious effects.

Autophagy activation

Autophagy is a self-degenerative process that clears and recycles damaged cellular components. In a seminal publication, it was reported that basal autophagy is essential to maintain the stem-cell quiescent state while preventing senescence of muscle satellite cells in mice. Furthermore, autophagy declines during aging, calorie restriction activates autophagy, and dysfunctional autophagy is evident in Alzheimer's disease pathology. Thus, boosting general macroautophagy (non-selective) is a viable anti-aging avenue. The challenge of autophagy-promoting strategies however comes from observations that autophagy of "nuclear" substrates might in fact contribute to senescence, aging, and inflammation.

Immune-mediated clearance

Senescent cells are naturally cleared by innate immune mechanisms with the macrophage playing a central role. However, immune cells themselves undergo progressive decline in function (termed immunosenescence) that actively contributes to senescent cell accumulation. Furthermore, it has been proposed that subsets of senescent cells become resistant to immune-mediated clearance. Therefore, epigenetic interventions that boost immune surveillance in aged tissues or antibody-based therapies that revert the immune-resistance of senescent cells may also be future rejuvenation strategies.

Rejuvenation therapy

The principles of regenerative medicine can be applied in aging and age-related disease. Expression of pluripotency factors in senescent cells have been shown to allow cell cycle entry with reset telomere size, gene expression profiles, oxidative stress, and mitochondrial metabolism. Additionally, their expression in mice has also shown amelioration of a panel of age-related phenotypes. Epigenetic factors that can potentiate reprogramming can be used to rejuvenate senescent/aged cells. However, it is important to be cautious with regenerative therapy in the elderly because of its potential to be pro-tumorigenic.

Other potential epigenetic therapies

The emerging conceptual themes that arise from the observations are (a) a gradual euchromatinization of the genome, (b) loss or disorganization of constitutive heterochromatin due to (c) breakdown of the nuclear lamina and changes in nuclear morphology and (d) loss of spatial organization of the genome. These large-scale changes manifest in profound transcriptional alterations that ultimately activate programs such as SASP and contribute to transcriptional noise. Systematic screens for epigenetic factors will likely yield potential candidates that can be targeted to prevent or reverse the detrimental effects of senescence.

The thymus undergoes age-related involution, that includes progressive loss of thymic epithelial and hematopoietic lineage cellularity, an increase in adiposity, and reduced T-cell output. In the periphery, fewer naïve T cells are available, and the old T-cell compartment is less able to respond to infections and cancer. This is believed to contribute to increased vulnerability of older adults to emerging and reemerging infections. More recent evidence suggests that secondary lymphoid organ (SLO) organization and structure also undergo changes with increased age, and the impact of these changes upon naïve T-cell survival and function is beginning to be understood.

A "holy grail" of T-cell aging research is to achieve functional rejuvenation of T-cell function. Early experiments with surgical castration have shown that transient thymic rejuvenation is possible, as measured by increased thymic volume and cellularity. Similar results have since been obtained using pharmacological sex steroid blockade as well as injection of growth factors. While some of these studies have shown some improvement in peripheral immune function in treated mice, the ultimate tests of functional immunity in the face of microbial challenge were not performed. Therefore, the question remains how well thymic rejuvenation improves the peripheral T-cell pool with aging, and whether it confers improved protection against infection.

To address this question, we examined the effects of (a) keratinocyte growth factor (KGF) administration in mice and nonhuman primates, or (b) sex steroid ablation (SSA) in mice using an antagonist of the luteinizing hormone-releasing hormone receptor, degarelix (Firmagon). Despite robust thymic rejuvenation in response to both interventions, we found no evidence of improved peripheral T-cell maintenance. KGF-treated old mice were not more effective at mounting CD8 T-cell responses to, or clearance of, Listeria monocytogenes. Similarly, degarelix did not improve CD8 T-cell responses to, or survival of old mice following challenge with, West Nile virus (WNV).

While rejuvenated thymi produced substantial numbers of recent thymic emigrants (RTE), these RTE did not significantly contribute to T-cell populations in the SLO of old mice compared to adults. We further found that old lymph nodes exhibited considerable fibrosis and degeneration of structure. These data indicate that restoration of thymic function by itself may not be sufficient to improve the immune response in elderly and suggest that interventions to simultaneously alleviate defects in aging SLO may need to be considered when designing strategies to improve immune response in older organisms.

Here we report an epigenetic mechanism by which mitochondrial dysfunction plays a role in inducing telomere attrition through acetyltransferase activity of hnRNPA2. Our results show that hnRNPA2 mediated H4K8 acetylation is a signal for telomere shortening. Additionally we provide evidence that alterations in the telomere length in response to mitochondrial dysfunction is dependent on histone acetylation status because mutant hnRNPA2 proteins, which show vastly reduced histone acetylation activity, cause a rescue of telomere length. This is in agreement with previous reports in cancer cells where telomere histone acetylation has been shown to correlate with telomere length. While our results show the causal role of mitochondrial dysfunction in telomere length maintenance by a novel epigenetic mechanism, prior studies have reported mitochondrial dysfunction as the result of telomere attrition, providing evidence for the close association between mitochondrial functions and telomere dynamics.

Mitochondria are highly susceptible to damage from numerous factors including free radicals, environmental chemicals, radiation exposure, and lipid peroxides produced by defective electron transport chain, the hypoxic environment prevalent in solid tumors and defective mtDNA transcription and replication machinery. These cellular and environmental stressors can cause mitochondrial defects such as reduction in mtDNA copy number, mtDNA mutations/deletions and impaired electron transport chain activity. In fact, defects in OXPHOS and accumulating mtDNA mutations are associated with aging and age-associated cancers. A common pathological feature of both of these diseases is shortened telomere DNA leading to DNA damage.

The consequence of telomere shortening in aging and cancer remains unclear. The prevailing view is that in aging, telomere shortening continues until cells senesce and finally die, while in cancer, the attrition stops when the telomere DNA reaches a critical length, and cells continue to divide and proliferate. It is suggested that induced telomerase activity in cancer cells is a critical factor, which prevents cell senescence and promotes tumor proliferation. It may be seemingly contradictory that mitochondrial dysfunction in immortalized cancer cells induces a proliferative phenotype in spite of mitochondrial stress induced telomere attrition. In a recent study tested the telomerase activity in these cell lines and found that mitochondrial stress induced signaling simultaneously activates telomerase in these cells. This provides a plausible explanation for these cells to maintain the critical telomere length for resisting senescence. In support, in IMR-90 cells, which do not express telomerase, we show that induction of mtDNA depletion results in hnRNPA2 activation and telomere shortening resulting in senescence. This suggests that the rescue of telomere length is possibly attributable to the reduced telomere histone acetylation but not due to activation of telomerase.

One of the downsides to getting older is that skeletal muscle loses its ability to heal after injury. New research implicates Klotho, both as culprit and therapeutic target. In young animals, Klotho expression soars after a muscle injury, whereas in old animals, it remains flat. By raising Klotho levels in old animals, or by mitigating downstream effects of Klotho deficiency, the researchers could restore muscle regeneration after injury. "We found that we were able to rescue, at least in part, the regenerative defect of aged skeletal muscle. We saw functional levels of muscle regeneration in old animals that paralleled those of their young counterparts, suggesting that this could potentially be a therapeutic option down the road."

Suspecting that Klotho acts through mitochondria dysfunction, the researchers gave Klotho-deficient animals a mitochondria-targeting drug called SS-31, which currently is in phase III clinical trials. Treated animals grew more new muscle tissue at the site of injury compared to untreated controls, and their strength after recovery rivaled that of genetically normal mice. Similarly, injecting Klotho into older animals a few days after injury resulted in greater muscle mass and better functional recovery than their saline-treated counterparts. Normal, healthy mice did not benefit from SS-31 after injury. Clinically, these findings could translate to older adults who either sustained a muscle injury or underwent muscle-damaging surgery. Giving them Klotho at the appropriate timepoint could boost their muscle regeneration and lead to a more complete recovery.

In this study, we tested the hypothesis that age-related declines in α-Klotho drive dysfunctional muscle progenitor cell (MPC) mitochondrial bioenergetics, ultimately resulting in an impaired tissue regeneration. Our findings demonstrate that young skeletal muscle displays a robust increase in local α-Klotho expression following an acute muscle injury with transient demethylation of the Klotho promoter. However, aged muscle displays no change in Klotho promoter methylation and no increase in α-Klotho expression following injury.

Levels of α-Klotho in MPCs derived from aged mice are decreased relative to those of young animals, and genetic knockdown of α-Klotho in young MPCs confers an aged phenotype with pathogenic mitochondrial ultrastructure, decreased mitochondrial bioenergetics, mitochondrial DNA damage, and increased senescence. Further supporting a role for α-Klotho in skeletal muscle vitality, mice heterozygously deficient for Klotho (Kl+/-) have impaired MPC bioenergetics that is consistent with a defective regenerative response following injury, but the regenerative defect of Kl+/- mice is rescued at the cellular and organismal level when mitochondrial ultrastructure is restored through treatment with the mitochondria-targeted peptide, SS-31.

Finally, we demonstrate that systemic delivery of exogenous α-Klotho rejuvenates MPC bioenergetics and enhances functional myofiber regeneration in aged animals in a temporally dependent manner. Together, these findings reveal a role for α-Klotho in the regulation of MPC mitochondrial function and skeletal muscle regenerative capacity.

Lifting weights for less than an hour a week may reduce your risk for a heart attack or stroke by 40 to 70 percent, according to a new study. Spending more than an hour in the weight room did not yield any additional benefit, the researchers found. The results - some of the first to look at resistance exercise and cardiovascular disease - show benefits of strength training are independent of running, walking, or other aerobic activity. In other words, you do not have to meet the recommended guidelines for aerobic physical activity to lower your risk; weight training alone is enough.

Reseaerchers analyzed data of nearly 13,000 adults in the Aerobics Center Longitudinal Study. They measured three health outcomes: cardiovascular events such as heart attack and stroke that did not result in death, all cardiovascular events including death and any type of death. Resistance exercise reduced the risk for all three.

Much of the research on strength training has focused on bone health, physical function and quality of life in older adults. When it comes to reducing the risk for cardiovascular disease, most people think of running or other cardio activity. Weight lifting is just as good for your heart, and there are other benefits. Using the same dataset, researchers looked at the relationship between resistance exercise and diabetes as well as hypercholesterolemia, or high cholesterol. The two studies found resistance exercise lowered the risk for both. Less than an hour of weekly resistance exercise (compared with no resistance exercise) was associated with a 29 percent lower risk of developing metabolic syndrome, which increases risk of heart disease, stroke and diabetes. The risk of hypercholesterolemia was 32 percent lower. The results for both studies also were independent of aerobic exercise.

Aging in most species, including humans, manifests itself as a progressive functional decline leading to the exponential increase in death risk from all causes. The mortality rate doubling time is approximately 8 years. Age-independent mortality mostly associated with violent death and infectious diseases has been progressively declining over the last century, mainly due to universal access to modern medicine and sanitation. The risks of death associated with the most prevalent age-related diseases remain very low at first, increase exponentially and dominate after the age of about 40. The incidence rates of the specific diseases, such as cancer or stroke, also accelerate after this age and double at a rate that closely tracks mortality acceleration. It is therefore, entirely plausible to think there is a single underlying driving force behind the progressive accumulation of health deficits, leading to the increased susceptibility to disease and death. This force is aging.

Although we have come to expect that physical decline is a natural consequence of aging, there is no natural law that dictates the exponential morbidity and mortality increase we observe among human populations. It is possible for death risks to increase very slowly, stay constant for extended periods, or even decline with age. Naked mole rats and the growing number of bat species are now recognized as examples of mammals that exhibit the lack of detectable mortality acceleration, or negligible senescence. Formally, this means that the mortality rate doubling time could be arbitrarily large.

We have suggested that the mortality acceleration may vanish depending on modifiable parameters, such as DNA repair or protein homeostasis maintenance efficiency, and should be, in principle, subject to manipulation. We propose to combine big data from large prospective observational studies with analytical tools borrowed from the physics of complex dynamic systems to "reverse engineer" the underlying biology behind the Gompertz law of mortality variables. This approach may yield mechanistic predictive models of aging for systematic discovery of biomarkers of aging and identification of novel therapeutic targets for future anti-aging therapies.

Occluding junctions play critical roles in epithelial barrier function, restricting the free diffusion of solutes between cells, as well as in the regulation of paracellular transport. In vertebrates, the occluding junctions are called tight junctions and their functional roles are well characterized. A functionally analogous structure, called the septate junction (SJ), exists in invertebrates, such as the smooth SJs (sSJs) of Drosophila, which are found in endodermally derived epithelia, such as the midgut.

Age-related alterations in intestinal epithelial junction expression and localization have been observed in flies and mammals, yet the causal relationships between changes in occluding junction function, intestinal homeostasis, and organismal aging are only beginning to be understood. Age-onset microbial dysbiosis is tightly linked to intestinal barrier dysfunction in both flies and mice. Critically, however, the question of whether manipulating intestinal occluding junction expression can delay age-onset dysbiosis and/or positively affect lifespan has not been addressed in any organism.

In this study, we show that Snakeskin (Ssk), an sSJ-specific protein, plays an important role in controlling the density and composition of the gut microbiota and that upregulation of Ssk during aging can prolong Drosophila lifespan. More specifically, loss of intestinal Ssk in adults leads to rapid-onset intestinal barrier dysfunction, changes in gut morphology, altered expression of antimicrobial peptides (AMPs), and microbial dysbiosis. Critically, we show that these phenotypes, including intestinal barrier dysfunction and dysbiosis, can be reversed upon restored Ssk expression.

Consistent with a critical role for intestinal junction proteins in organismal viability, loss of intestinal Ssk in adult animals leads to the rapid depletion of metabolic stores and rapid death. Importantly, restoring Ssk expression in flies showing intestinal barrier dysfunction prevents early-onset mortality. Moreover, intestinal upregulation of Ssk in normal flies protects against microbial translocation, limits age-onset dysbiosis, and prolongs lifespan. Our findings support the idea that occluding junction modulation could prove an effective therapeutic approach to prolong both intestinal and organismal health during aging in other species, including mammals.

The worldwide increase in life expectancy has not been paralleled by an equivalent increase in healthy aging. Developed and developing countries are facing social and economic challenges caused by disproportional increases in their elderly populations and the accompanying burden of chronic diseases. The primary goal of aging research is to improve the health of older persons and to design and test interventions that may prevent or delay age-related diseases. Although environmental quality and genetics are not under our direct control, energy intake is. Both hypo- and hypernutrition have the potential to increase the risk of chronic disease and premature death. Manipulation of a nutritionally balanced diet, whether by altering caloric intake or meal timing, can lead to a delay of the onset and progression of diseases and to a healthier and longer life in most organisms.

An emerging area of research is the investigation of the independent consequences of variations in meal size (through the control of energy intake) and meal frequency (by controlling the time of feeding and fasting) on the incidence or amelioration of multiple age-related diseases, including cardiovascular disease, diabetes, cancer, and dementia. These studies are starting to reveal that health-span and life-span extension can be achieved by interventions that do not require an overall reduction in caloric intake.

We discuss four experimental strategies aimed at altering energy intake or the duration of fasting and feeding periods that result in improved aspects of health in mammals. These are (i) classical caloric restriction, in which daily caloric intake is typically decreased by 15 to 40%; (ii) time-restricted feeding (TRF), which limits daily intake of food to a 4- to 12-hour window; (iii) intermittent or periodic full or partial fasting, that is a periodic, full- or multiday decrease in food intake; and (iv) fasting-mimicking diets (FMDs) that use a strategy to maintain a physiological fasting-like state by reducing caloric intake and modifying diet composition but not necessarily fasting. We also summarize the metabolic and cellular responses triggered by these feeding regimens and their impact on physiology, focusing on studies in rodents, monkeys, and humans.

Although the specific mechanisms are far from being fully understood, this periodic absence of energy intake appears to improve multiple risk factors and, in some cases, reverse disease progression in mice and humans. Thus, the time is ripe to add to our understanding of the molecular mechanisms of action and efficacy of these dietary interventions to the foundation for future clinical trials. We expect that these dietary interventions combined with classical pharmacology and clinical practice will yield interventions that will improve human health and enhance health span and quality of life as we grow old.

The people participating in this research participated in a controlled, personalised programme of strength, balance, and walking exercises adapted to their possibilities, even during the acute phase of their diseases. Depending on the status of each patient, training intensity ranging between 30% and 60% of their muscular capacity was specified, so they did leg and arm exercises. These sessions lasted twenty minutes twice a day (morning and afternoon), over between five and seven consecutive days (including weekends and public holidays) under the individual supervision of experts in the field of physical exercise for the elderly.

The results of the study show that when discharged from hospital, the group that had participated in the prescribed programme of exercise achieved, in comparison with those who had not done it, a total of 2.2 points above the average on a maximum score of 12 in the SPPB (Short Physical Performance Battery) functional assessment tool, which measures balance, walking speed and leg strength, and 6.9 points above the average score in the Barthel Functional Index for Activities of Daily Living, which has a maximum score of 100 points. "Until now, no one had suggested that patients of this type (elderly people with a range of diseases) could benefit in just five days from a personalised exercise programme far removed from the usual message of 'get up and walk along the corridor a little' or 'rest in bed or in an armchair.´"

Significant benefits of the intervention from the cognitive and life quality perspective were also found. These improvements were achieved without any side effects or increase in hospital stay. "Nevertheless, this intervention did not change the rate of re-admittance or mortality three months later. In such an elderly population as those in the study and with a theoretically short life expectancy following hospitalisation, the aim of our intervention was not to increase the quantity but the quality of life. Sometimes we believe that improvements in technologies or the latest innovative treatment can provide all the solutions for our problems, but we are not aware that disability generated by hospitalisation may exert a greater impact than the very disease that prompted admittance in the first place. In this respect the hugely positive effect that physical exercise can have on disease prevention and treatment is reiterated."

Postmortem data clearly shows that Alzheimer's disease (AD) pathology rarely occurs in isolation. Most AD patients harbor more than one pathology in the brain, with cerebrovascular disease being the most common coexisting pathology. Furthermore, the frequency of both cerebrovascular and Alzheimer's disease increases with age. However, in what way cerebrovascular disease and AD pathology act in synergy leading to downstream neurodegeneration and dementia is still unknown.

Cerebral amyloid angiopathy (CAA), a form of cerebrovascular disease resulting from amyloid deposition in vessel walls, may be the link between these two frequently coexisting pathologies. It is interesting that anti-amyloid therapy has been reported to increase the incidence of microbleeds, potentially due to removal of amyloid through vessel walls. The big question is whether CAA is just a passenger on the AD train. How does CAA interact with amyloid and tau pathology? For instance, does CAA come in early on in disease pathogenesis by affecting the spread of neurofibrillary tangles across the brain? Or is CAA an event occurring in later stages, acting downstream to amyloid and tau pathology thus mostly contributing to neurodegeneration and brain atrophy? All these questions remain largely unanswered.

We recently conducted a comprehensive characterization of these AD subtypes in terms of cerebrovascular disease. We concluded that CAA seems to make a stronger contribution to hippocampal-sparing and minimal atrophy AD, whereas hypertensive arteriopathy, another form of cerebrovascular disease, may make a stronger contribution to typical and limbic-predominant AD. Evidence suggests that neurodegeneration can be expressed differently across different AD subtypes. Future research will also have to answer why amyloid pathology starts, what is triggering the cascade, and whether this differs in the different subtypes. Current data shows that dementia in AD is a downstream event that can be reached along different pathways. These different pathways may necessitate their own specific therapeutic strategies.

Neurologists can get a ballpark estimate of a patient's risk of Alzheimer's dementia using the Mini-Mental State Examination questionnaire, or by testing for the high-risk form of the gene ApoE, which increases a person's risk of Alzheimer's by up to 12-fold. Both tests were about 70 to 80 percent accurate in this study. Other assessments, such as PET scans for plaques of Alzheimer's proteins in the brain, are good at detecting early signs of Alzheimer's disease, but available to few patients. PET scans are expensive and require radioactive materials not found in a typical hospital.

In a small study, researchers have shown that MRI brain scans predict with 89 percent accuracy who would go on to develop dementia within three years. MRI brain scans are widely available and give doctors a glimpse into what's going on inside a person's brain. The researchers used a technique called diffusion tensor imaging to assess the health of the brain's white matter, which encompasses the cables that enable different parts of the brain to talk to one another. Diffusion tensor imaging is a way of measuring the movement of water molecules along white matter tracts. If water molecules are not moving normally it suggests damage to white tracts that can underlie problems with cognition.

Researchers identified 10 people whose cognitive skills declined over a two-year period and matched them by age and sex with 10 people whose thinking skills held steady. The average age of people in both groups was 73. Then, the researchers analyzed diffusion tensor MRI scans taken just before the two-year period for all 20 people. The researchers found that people who went on to experience cognitive decline had significantly more signs of damage to their white matter. The researchers repeated their analysis in a separate sample of 61 people, using a more refined measure of white matter integrity. With this new analysis, they were able to predict cognitive decline with 89 percent accuracy when looking at the whole brain. When the researchers focused on specific parts of the brain most likely to show damage, the accuracy rose to 95 percent.

A DNA vaccine tested in mice reduces accumulation of both types of toxic proteins associated with Alzheimer's disease. The vaccine is delivered to the skin, prompting an immune response that reduces buildup of harmful tau and beta-amyloid - without triggering severe brain swelling that earlier antibody treatments caused in some patients. "This study is the culmination of a decade of research that has repeatedly demonstrated that this vaccine can effectively and safely target in animal models what we think may cause Alzheimer's disease. I believe we're getting close to testing this therapy in people."

Although earlier research established that antibodies significantly reduce amyloid buildup in the brain, researchers needed to find a safe way to introduce them into the body. A vaccine developed elsewhere showed promise in the early 2000s, but when tested in humans, it caused brain swelling in some patients. The new idea was to start with DNA coding for amyloid and inject it into the skin rather than the muscle to produce a different kind of immune response. The injected skin cells make a three-molecule chain of beta-amyloid (Aβ42), and the body responds by producing antibodies that inhibit the buildup of amyloid and indirectly also of tau.

The latest study - consisting of four cohorts of between 15 and 24 mice each - shows the vaccine prompted a 40 percent reduction in beta-amyloid and up to a 50 percent reduction in tau, with no adverse immune response. If amyloid and tau are indeed the cause of Alzheimer's disease, achieving these reductions in humans could have major therapeutic value. The study is the latest contribution to decades of research focusing on clearing toxic proteins in hopes of preventing or slowing the progression of Alzheimer's disease.

The soft tissues in the spinal column, the intervertebral discs, are essential for the motions of daily life, such as turning your head to tying your shoes. At any given time, however, about half the adult population in the United States is suffering from back or neck pain, for which treatment and care place a significant economic burden on society - an estimated 195 billion a year. While spinal disc degeneration is often associated with that pain, the underlying causes of disc degeneration remain less understood. Today's approaches, which include spinal fusion surgery and mechanical replacement devices, provide symptomatic relief, but they do not restore native disc structure, function, and range of motion, and they often have limited long-term efficacy. Thus, there is a need for new therapies.

Tissue engineering holds great promise. It involves combining the patients' or animals' own stem cells with biomaterial scaffolds in the lab to generate a composite structure that is then implanted into the spine to act as a replacement disc. For the last 15 years, a team has been developing a tissue engineered replacement disc, moving from in vitro basic science endeavors to small animal models to larger animal models with an eye towards human trials. Past studies from the team successfully demonstrated the integration of their engineered discs, known as disc-like angle ply structures (DAPS), in rat tails for five weeks. This latest research extended that time period in the rat model - up to 20 weeks - but with revamped engineered discs, known as endplate-modified DAPS, or eDAPS, to mimic the structure of the native spinal segment. The addition of the endplates helped to retain the composition of the engineered structure and promote its integration into the native tissue.

MRI, along with histological, mechanical, and biochemical analyses, showed that the eDAPS restored native disc structure, biology, and mechanical function in the rat model. Building off that success, the researchers then implanted the eDAPS into the cervical spine of goats. They chose the goat because its cervical spinal disc dimensions are similar to humans' and goats have the benefit of semi-upright stature. Researchers demonstrated successful total disc replacement in the goat cervical spine. After four weeks, matrix distribution was either retained or improved within the large-scale eDAPS. MRI results also suggest that disc composition at eight weeks was maintained or improved, and that the mechanical properties either matched or exceeded those of the native goat cervical disc.

Atherosclerosis is a complex disease characterized by smooth muscle cell proliferation, cholesterol deposition, and the infiltration of mononuclear cells. The formation and progression of atherosclerotic plaques result in the disruption of organ perfusion, causing cardiovascular and cerebrovascular diseases. It has been proved that immune responses participate in every phase of atherosclerosis. There is increasing evidence show that both adaptive and innate immunity tightly regulate the development and progression of atherosclerosis.

Atherosclerosis is considered as an immune inflammatory disease, and the T cell-mediated immune inflammatory response plays an important role in the pathogenesis of atherosclerosis. T cells mature in the thymus and are involved in the process of atherosclerosis induced by inflammation and immune response. Inflammatory mechanisms and immune system mechanisms are crucially involved in the pathophysiology of atherosclerosis and cardiovascular disease. T lymphocytes are involved and play an important role in both the inflammatory response and the immune response. An imbalance of the degree of activation of the protective Treg lymphocytes, the pro-inflammatory and cytotoxic macrophages and T-effector lymphocytes could thus be at the origin of the triggering or not of progression of vascular injury. However, all of these processes are closely associated with thymus function. In other words, changes in the function of thymus will be deeply affecting the process.

Based on previous research, we can speculate that the changes of thymus function may have an impact on the process of atherosclerosis. The mechanism of thymus involvement in the process of atherosclerosis is assumed as follows: Low density lipoprotein or cholesterol reduces the expression of the thymus transcription factor Foxn1 via low density lipoprotein receptors (LDLR) on the membrane surface and low density lipoprotein receptor-related proteins on the cell surface, which cause the thymus function decline or degradation. The imbalance of T cell subgroups and the decrease of naive T cells due to thymus dysfunction cause the increase or decrease in the secretion of various inflammatory factors, which in turn aggravates or inhibits atherosclerosis progression and cardiovascular events. NK T cell, dendritic cells, and macrophages can affect the process of atherosclerosis by affecting the production of naive T cells through the thymus. Furthermore, these cells can also participate in the progression of atherosclerosis via the direct secretion of cytokines or inducing other cells to secrete cytokines.

According to our hypothesis, various biotechnologies can be selected to improve aging thymus function in animal experiments. In the clinical treatment of atherosclerosis, and even other immune-related diseases, we may consider improving the expression of foxn1 in the human body, thereby improving or restoring aging thymus function and resisting the related-diseases caused by the decline of immunity. Further investigation on changes of thymus function will help to develop new therapeutic targets that may improve outcomes in atherosclerosis and cardiovascular disease and discover novel approaches in the treatment of atherosclerosis and vascular disease.