Muscle-derived stem/progenitor cell dysfunction limits healthspan and lifespan in a murine progeria model

Mouse Models to Disentangle the Hallmarks of Human Aging

Model organisms have provided fundamental evidence that aging can be delayed and longevity extended. These findings gave rise to a new era in aging research aimed at elucidating the pathways and networks controlling this complex biological process. The identification of 9 hallmarks of aging has established a framework to evaluate the relative contribution of each hallmark and the interconnections among them. In this review, we revisit these hallmarks with the information obtained exclusively through the generation of genetically modified mouse models that have a significant impact on the aging process. We discuss within each hallmark those interventions that accelerate aging or that have been successful at increasing lifespan, with the final goal of identifying the most promising antiaging avenues based on the current knowledge provided by in vivo models.

Osteosarcopenia: A case of geroscience

Many older persons lose their mobility and independence due to multiple diseases occurring simultaneously. Geroscience is aimed at developing innovative approaches to better identify relationships among the biological processes of aging. Osteoporosis and sarcopenia are two of the most prevalent chronic diseases in older people, with both conditions sharing overlapping risk factors and pathogenesis. When occurring together, these diseases form a geriatric syndrome termed "osteosarcopenia," which increases the risk of frailty, hospitalizations, and death. Findings from basic and clinical sciences aiming to understand osteosarcopenia have provided evidence of this syndrome as a case of geroscience. Genetic, endocrine, and mechanical stimuli, in addition to fat infiltration, sedentarism, and nutritional deficiencies, affect muscle and bone homeostasis to characterize this syndrome. However, research is in its infancy regarding accurate diagnostic markers and effective treatments with dual effects on muscle and bone. To date, resistance exercise remains the most promising strategy to increase muscle and bone mass, while sufficient quantities of protein, vitamin D, calcium, and creatine may preserve these tissues with aging. More recent findings, from rodent models, suggest treating ectopic fat in muscle and bone marrow as a possible avenue to curb osteosarcopenia, although this needs testing in human clinical trials.

Divide and conquer: two stem cell populations in squamous epithelia, reserves and the active duty forces

Stem cells are of great interest to the scientific community due to their potential role in regenerative and rejuvenative medicine. However, their role in the aging process and carcinogenesis remains unclear. Because DNA replication in stem cells may contribute to the background mutation rate and thereby to cancer, reducing proliferation and establishing a relatively quiescent stem cell compartment has been hypothesized to limit DNA replication-associated mutagenesis. On the other hand, as the main function of stem cells is to provide daughter cells to build and maintain tissues, the idea of a quiescent stem cell compartment appears counterintuitive. Intriguing observations in mice have led to the idea of separated stem cell compartments that consist of cells with different proliferative activity. Some epithelia of short-lived rodents appear to lack quiescent stem cells. Comparing stem cells of different species and different organs (comparative stem cell biology) may allow us to elucidate the evolutionary pressures such as the balance between cancer and longevity that govern stem cell biology (evolutionary stem cell biology). The oral mucosa and its stem cells are an exciting model system to explore the characteristics of quiescent stem cells that have eluded biologists for decades.

Murine models of accelerated aging and musculoskeletal disease

The primary risk factor for most musculoskeletal diseases, including osteoarthritis, osteoporosis and sarcopenia, is aging. To treat the diverse types of musculoskeletal diseases and pathologies, targeting their root cause, the aging process itself, has the potential to slow or prevent multiple age-related musculoskeletal conditions simultaneously. However, the development of approaches to delay onset of age related diseases, including musculoskeletal pathologies, has been slowed by the relatively long lifespan of rodent models of aging. Thus, to expedite the development of therapeutic approaches for age-related musculoskeletal disease, the implementation of mouse models of accelerated musculoskeletal aging are of great utility. Currently there are multiple genetically diverse mouse models that mirror certain aspects of normal human and mouse aging. Here, we provide a review of some of the most relevant murine models of accelerated aging that mimic many aspects of natural musculoskeletal aging, highlighting their relative strengths and weaknesses. Importantly, these murine models of accelerated aging recapitulate phenotypes of musculoskeletal age-related decline observed in humans.

DNA damage in aging, the stem cell perspective

DNA damage is one of the most consistent cellular process proposed to contribute to aging. The maintenance of genomic and epigenomic integrity is critical for proper function of cells and tissues throughout life, and this homeostasis is under constant strain from both extrinsic and intrinsic insults. Considering the relationship between lifespan and genotoxic burden, it is plausible that the longest-lived cellular populations would face an accumulation of DNA damage over time. Tissue-specific stem cells are multipotent populations residing in localized niches and are responsible for maintaining all lineages of their resident tissue/system throughout life. However, many of these stem cells are impacted by genotoxic stress. Several factors may dictate the specific stem cell population response to DNA damage, including the niche location, life history, and fate decisions after damage accrual. This leads to differential handling of DNA damage in different stem cell compartments. Given the importance of adult stem cells in preserving normal tissue function during an individual's lifetime, DNA damage sensitivity and accumulation in these compartments could have crucial implications for aging. Despite this, more support for direct functional effects driven by accumulated DNA damage in adult stem cell compartments is needed. This review will present current evidence for the accumulation and potential influence of DNA damage in adult tissue-specific stem cells and propose inquiry directions that could benefit individual healthspan.

Extracellular vesicles from human urine-derived stem cells prevent osteoporosis by transferring CTHRC1 and OPG

Osteoporosis is a debilitating bone disease affecting millions of people. Here, we used human urine-derived stem cells (USCs), which were noninvasively harvested from unlimited and easily available urine, as a “factory” to obtain extracellular vesicles (USC-EVs) and demonstrated that the systemic injection of USC-EVs effectively alleviates bone loss and maintains bone strength in osteoporotic mice by enhancing osteoblastic bone formation and suppressing osteoclastic bone resorption. More importantly, the anti-osteoporotic properties of USC-EVs are not notably disrupted by the age, gender, or health condition (with or without osteoporosis) of the USC donor. Mechanistic studies determined that collagen triple-helix repeat containing 1 (CTHRC1) and osteoprotegerin (OPG) proteins are enriched in USC-EVs and required for USC-EV-induced pro-osteogenic and anti-osteoclastic effects. Our results suggest that autologous USC-EVs represent a promising novel therapeutic agent for osteoporosis by promoting osteogenesis and inhibiting osteoclastogenesis by transferring CTHRC1 and OPG.

How Could We Slow or Reverse the Human Aging Process and Extend the Healthy Life Span with Heterochronous Autologous Hematopoietic Stem Cell Transplantation

The senescence of the immune system contributes considerably to the age-related diseases that are the main causes of death after the age of 65. In this study, we present an appealing option for the prevention of immune senescence and slowing or reversing the aging process, which can be achieved by heterochronous autologous hematopoietic stem cell transplantation (haHSCT), where healthy autologous bone marrow stem cells are collected from donors while young, cryopreserved and stored for a long period, and reinfused at a later time when indicated. After reinfusion and homing, these young HSCs could participate in normal hemato- and immunopoiesis and improve several immune functions by expanding the immune- as well as hematopoietic cell repertoire. Several animal studies have already confirmed the feasibility of this procedure, which extended the longevity of the treated animals. If translated to human medicine, haHSCT could prevent or mitigate age-related immune defects and extend the healthy life span. In this review, we describe the concept of haHSCT, recent studies that confirm its feasibility, and discuss the further research needed to translate this heterochronous methodology.

Nuclear Genomic Instability and Aging

The nuclear genome decays as organisms age. Numerous studies demonstrate that the burden of several classes of DNA lesions is greater in older mammals than in young mammals. More challenging is proving this is a cause rather than a consequence of aging. The DNA damage theory of aging, which argues that genomic instability plays a causal role in aging, has recently gained momentum. Support for this theory stems partly from progeroid syndromes in which inherited defects in DNA repair increase the burden of DNA damage leading to accelerated aging of one or more organs. Additionally, growing evidence shows that DNA damage accrual triggers cellular senescence and metabolic changes that promote a decline in tissue function and increased susceptibility to age-related diseases. Here, we examine multiple lines of evidence correlating nuclear DNA damage with aging. We then consider how, mechanistically, nuclear genotoxic stress could promote aging. We conclude that the evidence, in toto, supports a role for DNA damage as a nidus of aging.

Cell therapy to improve regeneration of skeletal muscle injuries

Diseases that jeopardize the musculoskeletal system and cause chronic impairment are prevalent throughout the Western world. In Germany alone, ~1.8 million patients suffer from these diseases annually, and medical expenses have been reported to reach 34.2bn Euros. Although musculoskeletal disorders are seldom fatal, they compromise quality of life and diminish functional capacity. For example, musculoskeletal disorders incur an annual loss of over 0.8 million workforce years to the German economy. Among these diseases, traumatic skeletal muscle injuries are especially problematic because they can occur owing to a variety of causes and are very challenging to treat. In contrast to chronic muscle diseases such as dystrophy, sarcopenia, or cachexia, traumatic muscle injuries inflict damage to localized muscle groups. Although minor muscle trauma heals without severe consequences, no reliable clinical strategy exists to prevent excessive fibrosis or fatty degeneration, both of which occur after severe traumatic injury and contribute to muscle degeneration and dysfunction. Of the many proposed strategies, cell-based approaches have shown the most promising results in numerous pre-clinical studies and have demonstrated success in the handful of clinical trials performed so far. A number of myogenic and non-myogenic cell types benefit muscle healing, either by directly participating in new tissue formation or by stimulating the endogenous processes of muscle repair. These cell types operate via distinct modes of action, and they demonstrate varying levels of feasibility for muscle regeneration depending, to an extent, on the muscle injury model used. While in some models the injury naturally resolves over time, other models have been developed to recapitulate the peculiarities of real-life injuries and therefore mimic the structural and functional impairment observed in humans. Existing limitations of cell therapy approaches include issues related to autologous harvesting, expansion and sorting protocols, optimal dosage, and viability after transplantation. Several clinical trials have been performed to treat skeletal muscle injuries using myogenic progenitor cells or multipotent stromal cells, with promising outcomes. Recent improvements in our understanding of cell behaviour and the mechanistic basis for their modes of action have led to a new paradigm in cell therapies where physical, chemical, and signalling cues presented through biomaterials can instruct cells and enhance their regenerative capacity. Altogether, these studies and experiences provide a positive outlook on future opportunities towards innovative cell-based solutions for treating traumatic muscle injuries-a so far unmet clinical need.

Compression of morbidity in a progeroid mouse model through the attenuation of myostatin/activin signalling

BACKGROUND

One of the principles underpinning our understanding of ageing is that DNA damage induces a stress response that shifts cellular resources from growth towards maintenance. A contrasting and seemingly irreconcilable view is that prompting growth of, for example, skeletal muscle confers systemic benefit.

METHODS

To investigate the robustness of these axioms, we induced muscle growth in a murine progeroid model through the use of activin receptor IIB ligand trap that dampens myostatin/activin signalling. Progeric mice were then investigated for neurological and muscle function as well as cellular profiling of the muscle, kidney, liver, and bone.

RESULTS

We show that muscle of Ercc1^Δ/- progeroid mice undergoes severe wasting (decreases in hind limb muscle mass of 40-60% compared with normal mass), which is largely protected by attenuating myostatin/activin signalling using soluble activin receptor type IIB (sActRIIB) (increase of 30-62% compared with untreated progeric). sActRIIB-treated progeroid mice maintained muscle activity (distance travel per hour: 5.6 m in untreated mice vs. 13.7 m in treated) and increased specific force (19.3 mN/mg in untreated vs. 24.0 mN/mg in treated). sActRIIb treatment of progeroid mice also improved satellite cell function especially their ability to proliferate on their native substrate (2.5 cells per fibre in untreated progeroids vs. 5.4 in sActRIIB-treated progeroids after 72 h in culture). Besides direct protective effects on muscle, we show systemic improvements to other organs including the structure and function of the kidneys; there was a major decrease in the protein content in urine (albumin/creatinine of 4.9 sActRIIB treated vs. 15.7 in untreated), which is likely to be a result in the normalization of podocyte foot processes, which constitute the filtration apparatus (glomerular basement membrane thickness reduced from 224 to 177 nm following sActRIIB treatment). Treatment of the progeric mice with the activin ligand trap protected against the development of liver abnormalities including polyploidy (18.3% untreated vs. 8.1% treated) and osteoporosis (trabecular bone volume; 0.30 mm³ in treated progeroid mice vs. 0.14 mm³ in untreated mice, cortical bone volume; 0.30 mm³ in treated progeroid mice vs. 0.22 mm³ in untreated mice). The onset of neurological abnormalities was delayed (by ~5 weeks) and their severity reduced, overall sustaining health without affecting lifespan.

CONCLUSIONS

This study questions the notion that tissue growth and maintaining tissue function during ageing are incompatible mechanisms. It highlights the need for future investigations to assess the potential of therapies based on myostatin/activin blockade to compress morbidity and promote healthy ageing.

Rapamycin Rescues Age-Related Changes in Muscle-Derived Stem/Progenitor Cells from Progeroid Mice

Aging-related loss of adult stem cell function contributes to impaired tissue regeneration. Mice deficient in zinc metalloproteinase STE24 (Zmpste24^−/−) exhibit premature age-related musculoskeletal pathologies similar to those observed in children with Hutchinson-Gilford progeria syndrome (HGPS). We have reported that muscle-derived stem/progenitor cells (MDSPCs) isolated from Zmpste24^−/− mice are defective in their proliferation and differentiation capabilities in culture and during tissue regeneration. The mechanistic target of rapamycin complex 1 (mTORC1) regulates cell growth, and inhibition of the mTORC1 pathway extends the lifespan of several animal species. We therefore hypothesized that inhibition of mTORC1 signaling would rescue the differentiation defects observed in progeroid MDSPCs. MDSPCs were isolated from Zmpste24^−/− mice, and the effects of mTORC1 on MDSPC differentiation and function were examined. We found that mTORC1 signaling was increased in senescent Zmpste24^−/− MDSPCs, along with impaired chondrogenic, osteogenic, and myogenic differentiation capacity versus wild-type MDSPCs. Interestingly, we observed that mTORC1 inhibition with rapamycin improved myogenic and chondrogenic differentiation and reduced levels of apoptosis and senescence in Zmpste24^−/− MDSPCs. Our results demonstrate that age-related adult stem/progenitor cell dysfunction contributes to impaired regenerative capacities and that mTORC1 inhibition may represent a potential therapeutic strategy for improving differentiation capacities of senescent stem and muscle progenitor cells.

Muscle-derived stem cells: important players in peripheral nerve repair

INTRODUCTION

Stem cell therapy for peripheral nerve repair is a rapidly evolving field in regenerative medicine. Although most studies to date have investigated stem cells originating from bone marrow or adipose, skeletal muscle has recently been recognized as an abundant and easily accessible source of stem cells. Muscle-derived stem cells (MDSCs) are a diverse population of multipotent cells with pronounced antioxidant and regenerative capacity. Areas covered: The current literature on the various roles MDSCs serve within the micro- and macro-environment of nerve injury. Furthermore, the exciting new research that is establishing MDSC-cellular therapy as an important therapeutic modality to improve peripheral nerve regeneration. Expert opinion: MDSCs are a promising therapeutic agent for the repair of peripheral nerves; MDSCs not only undergo gliogenesis and angiogenesis, but they also orchestrate larger pro-regenerative host responses. However, the isolation, transformation, and in-vivo behavior of MDSCs require further evaluation prior to clinical application.

Clinical efficiency of bone marrow mesenchymal stem cell implantation for osteonecrosis of the femoral head: a matched pair control study with simple core decompression

Background

To date, several trials have reported the use of mesenchymal stem cell (MSC) implantation for osteonecrosis of the femoral head (ONFH). However, the clinical outcomes have not been conclusive. This study compared the clinical and radiological results of bone marrow mesenchymal stem cell (BMMSC) implantation with traditional simple core decompression (CD) using a matched pair case–control design.

Methods

We retrospectively reviewed 100 patients with ONFH (106 hips) who had been treated by CD alone (50 patients, 53 hips) and CD + BMMSC implantation (50 patients, 53 hips) between February 2004 and October 2014. We assessed the total hip replacement arthroplasty (THA) conversion rate and ARCO (Association Research Circulation Osseous) stage progression. Survivor rate analysis was performed using the Kaplan–Meier method, and an additional THA was defined as the primary endpoints.

Results

The mean follow-up period was 4.28 years. There was a difference in the THA conversion rate between the CD (49%) and CD + BMMSC groups (28.3%) (p = 0.028). ARCO stage progression was noted in 20 of 53 hips (37.7%) in the CD group and 19 of 53 hips (35.8%) in the CD + BMMSC group. Among collapsed cases (ARCO stages III and IV), there was no difference in clinical failure rate between the two groups. Conversely, in the pre-collapse cases (ARCO stages I and II), only 6 of 30 hips (20%) progressed to clinical failure in the CD + BMMSC group, whereas 15 of 30 hips (50%) progressed to clinical failure in the CD group (p = 0.014). Kaplan–Meier survival analysis showed a significant difference in the time to failure between the two groups up to 10-year follow-up (log-rank test p = 0.031). There was no significant difference in terms of age (p = 0.87) and gender (p = 0.51) when comparing THA conversion rates between groups. No complication was noted.

Conclusions

These results suggest that implantation of MSCs into the femoral head at an early stage of ONFH lowers the THA conversion rate. However, ARCO stage progression is not affected by this treatment.

Trial registration

Retrospectively registered

Modeling Alzheimer's disease in progeria mice. An age-related concept

The prevalence of Alzheimer’s disease (AD) is expected to dramatically increase in older people worldwide. Efforts to find disease-modifying treatments have been largely unsuccessful because of the focus on disease-specific pathogenesis, and lack of animal models to study AD in the context of aging and age-related co-morbidities. The geroscience approach to studying AD would suggest that modulation of aging per se would be a useful strategy, but a mammalian model system that combines both aging and AD is not available. One approach to study old age and AD is to utilize murine models of progeroid syndrome, which can provide a number of advantages not only for basic aging biology but also for preclinical drug testing. A progeria background, such as the Ercc1 mutant mouse (Ercc1^−/Δ), provides an aging component not seen in current murine models of AD that lack age-related co-morbidities typical of AD patients.

Ercc1^−/Δ mice experience the same types of stochastic endogenous DNA damage as WT mice, but accumulate lesions faster due to impaired DNA repair, which accelerates the normal aging process by 6-fold. These mice do not show frank AD pathology but represent a predisposed or hypersensitive environment for AD pathology, where pathogenic elements of AD can be introduced, either by crossing with well-established AD transgenic mouse lines, or transcranial stereotaxic delivery directly into the brain. Since Ercc1^−/Δ mice age five to six times faster than WT mice, very rapid characterization and testing of therapeutic interventions is possible. Studies are urgently needed to capitalize on the highly informative potential of this novel AD mouse model.

Fisetin is a senotherapeutic that extends health and lifespan

BACKGROUND

Senescence is a tumor suppressor mechanism activated in stressed cells to prevent replication of damaged DNA. Senescent cells have been demonstrated to play a causal role in driving aging and age-related diseases using genetic and pharmacologic approaches. We previously demonstrated that the combination of dasatinib and the flavonoid quercetin is a potent senolytic improving numerous age-related conditions including frailty, osteoporosis and cardiovascular disease. The goal of this study was to identify flavonoids with more potent senolytic activity.

METHODS

A panel of flavonoid polyphenols was screened for senolytic activity using senescent murine and human fibroblasts, driven by oxidative and genotoxic stress, respectively. The top senotherapeutic flavonoid was tested in mice modeling a progeroid syndrome carrying a p16INK4a-luciferase reporter and aged wild-type mice to determine the effects of fisetin on senescence markers, age-related histopathology, disease markers, health span and lifespan. Human adipose tissue explants were used to determine if results translated.

FINDINGS

Of the 10 flavonoids tested, fisetin was the most potent senolytic. Acute or intermittent treatment of progeroid and old mice with fisetin reduced senescence markers in multiple tissues, consistent with a hit-and-run senolytic mechanism. Fisetin reduced senescence in a subset of cells in murine and human adipose tissue, demonstrating cell-type specificity. Administration of fisetin to wild-type mice late in life restored tissue homeostasis, reduced age-related pathology, and extended median and maximum lifespan.

INTERPRETATION

The natural product fisetin has senotherapeutic activity in mice and in human tissues. Late life intervention was sufficient to yield a potent health benefit. These characteristics suggest the feasibility to translation to human clinical studies. FUND: NIH grants P01 AG043376 (PDR, LJN), U19 AG056278 (PDR, LJN, WLL), R24 AG047115 (WLL), R37 AG013925 (JLK), R21 AG047984 (JLK), P30 DK050456 (Adipocyte Subcore, JLK), a Glenn Foundation/American Federation for Aging Research (AFAR) BIG Award (JLK), Glenn/AFAR (LJN, CEB), the Ted Nash Long Life and Noaber Foundations (JLK), the Connor Group (JLK), Robert J. and Theresa W. Ryan (JLK), and a Minnesota Partnership Grant (AMAY-UMN#99)-P004610401-1 (JLK, EAA).

Oxidative Stress in Mesenchymal Stem Cell Senescence: Regulation by Coding and Noncoding RNAs

SIGNIFICANCE

Mesenchymal stem cells (MSCs), adult stem cells with the potential of differentiation into mesodermal lineages, play an important role in tissue homeostasis and regeneration. In different organs, a subpopulation of MSCs is located near the vasculature and possibly represents the original source of lineage-committed mesenchymal progenitors. Recent Advances: The plasticity and immune characteristics of MSCs render them a preferential tool for regenerative cell therapy.

CRITICAL ISSUES

The culture expansion needed before MSC transplantation is associated with cellular senescence. Moreover, accelerated senescence of the total and perivascular MSC pool has been observed in humans and mouse models of premature aging disorders. MSC dysfunction is acknowledged as a culprit for the aging-associated degeneration of mesodermal tissues, but the underlying epigenetic pathways remain elusive. This article reviews current understanding of mechanisms impinging on MSC health, including oxidative stress, Nrf2-antioxidant responsive element activity, sirtuins, noncoding RNAs, and PKCs.

FUTURE DIRECTIONS

We provide evidence that epigenetic profiling of MSCs is utilitarian to the prediction of therapeutic outcomes. In addition, strategies that target oxidative stress-associated mechanisms represent promising approaches to counteract the detrimental effect of age and senescence in MSCs.-Antioxid. Redox Signal. 29, 864-879.

The Spectrum of Fundamental Basic Science Discoveries Contributing to Organismal Aging

Aging research has undergone unprecedented advances at an accelerating rate in recent years, leading to excitement in the field as well as opportunities for imagination and innovation. Novel insights indicate that, rather than resulting from a preprogrammed series of events, the aging process is predominantly driven by fundamental non-adaptive mechanisms that are interconnected, linked, and overlap. To varying degrees, these mechanisms also manifest with aging in bone where they cause skeletal fragility. Because these mechanisms of aging can be manipulated, it might be possible to slow, delay, or alleviate multiple age-related diseases and their complications by targeting conserved genetic signaling pathways, controlled functional networks, and basic biochemical processes. Indeed, findings in various mammalian species suggest that targeting fundamental aging mechanisms (eg, via either loss-of-function or gain-of-function mutations or administration of pharmacological therapies) can extend healthspan; ie, the healthy period of life free of chronic diseases. In this review, we summarize the evidence supporting the role of the spectrum of fundamental basic science discoveries contributing to organismal aging, with emphasis on mammalian studies and in particular aging mechanisms in bone that drive skeletal fragility. These mechanisms or aging hallmarks include: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. Because these mechanisms are linked, interventions that ameliorate one hallmark can in theory ameliorate others. In the field of bone and mineral research, current challenges include defining the relative contributions of each aging hallmark to the natural skeletal aging process, better understanding the complex interconnections among the hallmarks, and identifying the most effective therapeutic strategies to safely target multiple hallmarks. Based on their interconnections, it may be feasible to simultaneously interfere with several fundamental aging mechanisms to alleviate a wide spectrum of age-related chronic diseases, including osteoporosis. © 2018 American Society for Bone and Mineral Research.

The potential of non-myeloablative heterochronous autologous hematopoietic stem cell transplantation for extending a healthy life span

Aging is a complex multifactorial process, a prominent component being the senescence of the immune system. Consequently, immune-related diseases develop, including atherosclerosis, cancer, and life-threatening infections, which impact on health and longevity. Rejuvenating the aged immune system could mitigate these diseases, thereby contributing to longevity and health. Currently, an appealing option for rejuvenating the immune system is heterochronous autologous hematopoietic stem cell transplantation (haHSCT), where healthy autologous bone marrow/peripheral blood stem cells are collected during the youth of an individual, cryopreserved, and re-infused when he or she has reached an older age. After infusion, young hematopoietic stem cells can reconstitute the compromised immune system and improve immune function. Several studies using animal models have achieved substantial extension of the life span of animals treated with haHSCT. Therefore, haHSCT could be regarded as a potential procedure for preventing age-related immune defects and extending healthy longevity. In this review, the pros, cons, and future feasibility of this approach are discussed.

Somatic mutagenesis in satellite cells associates with human skeletal muscle aging

Human aging is associated with a decline in skeletal muscle (SkM) function and a reduction in the number and activity of satellite cells (SCs), the resident stem cells. To study the connection between SC aging and muscle impairment, we analyze the whole genome of single SC clones of the leg muscle vastus lateralis from healthy individuals of different ages (21–78 years). We find an accumulation rate of 13 somatic mutations per genome per year, consistent with proliferation of SCs in the healthy adult muscle. SkM-expressed genes are protected from mutations, but aging results in an increase in mutations in exons and promoters, targeting genes involved in SC activity and muscle function. In agreement with SC mutations affecting the whole tissue, we detect a missense mutation in a SC propagating to the muscle. Our results suggest somatic mutagenesis in SCs as a driving force in the age-related decline of SkM function.

Aging skeletal muscle shows declining numbers and activity of satellite cells. Here, Franco et al. show that in satellite cells of the human leg muscle vastus lateralis, somatic mutations accumulate with age and that these mutations become enriched in exons and promoters of genes involved in muscle function.

Current perspectives on biological approaches for osteoarthritis

Musculoskeletal injuries that disrupt the structure and function of diarthrodial joints can cause permanent biomechanical alterations and lead to a more severe, chronic condition. Despite advancements that have been made to restore tissue function and delay the need for joint replacement, there are currently no disease-modifying therapies for osteoarthritis (OA). To reduce the risk of OA, innovative preventive medicine approaches have been developed over the last decade to treat the underlying pathology. Several biological approaches are promising treatment modalities for various stages of OA owing to their minimally invasive nature and actively dynamic physiological mechanisms that attenuate tissue degradation and inflammatory responses. Individualized growth factor and cytokine therapies, tissue-engineered biomaterials, and cell-based therapies have revolutionary potential for orthopedic applications; however, the paucity of standardization and categorization of biological components and their counterparts has made it difficult to determine their clinical and biological efficacy. Cell-based therapies and tissue-engineered biologics have become lucrative in sports medicine and orthopedics; nonetheless, there is a continued effort to produce a biological treatment modality tailored to target intra-articular structures that recapitulates tissue function. Advanced development of these biological treatment modalities will potentially optimize tissue healing, regeneration, and joint preservation strategies. Therefore, the purpose of this paper is to review current concepts on several biological treatment approaches for OA.

RhoA/ROCK inhibition improves the beneficial effects of glucocorticoid treatment in dystrophic muscle: implications for stem cell depletion

Glucocorticoid treatment represents a standard palliative treatment for Duchenne muscular dystrophy (DMD) patients, but various adverse effects have limited this treatment. In an effort to understand the mechanism(s) by which glucocorticoids impart their effects on the dystrophic muscle, and potentially reduce the adverse effects, we have studied the effect of prednisolone treatment in dystrophin/utrophin double knockout (dKO) mice, which exhibit a severe dystrophic phenotype due to rapid muscle stem cell depletion. Our results indicate that muscle stem cell depletion in dKO muscle is related to upregulation of mTOR, and that prednisolone treatment reduces the expression of mTOR and other pro-inflammatory mediators, consequently slowing down muscle stem cell depletion. However, prednisolone treatment was unable to improve the myogenesis of stem cells and reduce fibrosis in dKO muscle. We then studied whether glucocorticoid treatment can be improved by co-administration of an inhibitor of RhoA/ROCK signaling, which can be activated by glucocorticoids and was found in our previous work to be over-activated in dystrophic muscle. Our results indicate that the combination of RhoA/ROCK inhibition and glucocorticoid treatment in dystrophic muscle have a synergistic effect in alleviating the dystrophic phenotype. Taken together, our study not only shed light on the mechanism by which glucocorticoid imparts its beneficial effect on dystrophic muscle, but also revealed the synergistic effect of RhoA/ROCK inhibition and glucocorticoid treatment, which could lead to the development of more efficient therapeutic approaches for treating DMD patients.

Extracellular vesicles and aging

Aging and the chronic diseases associated with aging place a tremendous burden on our healthcare system. As our world population ages dramatically over the next decades, this will only increase. Hence, there is a great need to discover fundamental mechanisms of aging to enable development of strategies for minimizing the impact of aging on our health and economy. There is general agreement that cell autonomous mechanisms contribute to aging. As cells accrue damage over time, they respond to it by triggering individual cell fate decisions that ultimately disrupt tissue homeostasis and thus increase risk of morbidity. However, there are numerous lines of evidence, including heterochronic parabiosis and plasma transfer, indicating that cell non-autonomous mechanisms are critically important for aging as well. In addition, senescent cells, which accumulate in tissues with age, can display a senescence-associated secretory phenotype (SASP) that contributes to driving aging and loss of tissue homeostasis through a non-cell autonomous mechanism(s). Given the diverse roles of blood-borne extracellular vesicles (EVs) in modulating not only the immune response, but also angiogenesis and tissue regeneration, they likely play a key role in modulating the aging process through cell non-autonomous mechanisms. The fact that senescent cells release more EVs and with a different composition suggests they contribute to the adverse effects of senescence on aging. In addition, the ability of EVs from functional progenitor cells to promote tissue regeneration suggests that stem cell-derived EVs could be used therapeutically to extend healthspan. This review focuses on the potential roles of EVs in aging, the potential of EV-based therapeutic applications for extending healthspan and the potential for use of circulating EVs as biomarkers of unhealthy aging.

Hallmarks of progeroid syndromes: lessons from mice and reprogrammed cells

Ageing is a process that inevitably affects most living organisms and involves the accumulation of macromolecular damage, genomic instability and loss of heterochromatin. Together, these alterations lead to a decline in stem cell function and to a reduced capability to regenerate tissue. In recent years, several genetic pathways and biochemical mechanisms that contribute to physiological ageing have been described, but further research is needed to better characterize this complex biological process. Because premature ageing (progeroid) syndromes, including progeria, mimic many of the characteristics of human ageing, research into these conditions has proven to be very useful not only to identify the underlying causal mechanisms and identify treatments for these pathologies, but also for the study of physiological ageing. In this Review, we summarize the main cellular and animal models used in progeria research, with an emphasis on patient-derived induced pluripotent stem cell models, and define a series of molecular and cellular hallmarks that characterize progeroid syndromes and parallel physiological ageing. Finally, we describe the therapeutic strategies being investigated for the treatment of progeroid syndromes, and their main limitations.

Summary: This Review defines the molecular and cellular hallmarks of progeroid syndromes according to the main cellular and animal models, and discusses the therapeutic strategies developed to date.

The role of hydrogen sulfide in aging and age-related pathologies

When humans grow older, they experience inevitable and progressive loss of physiological function, ultimately leading to death. Research on aging largely focuses on the identification of mechanisms involved in the aging process. Several proposed aging theories were recently combined as the 'hallmarks of aging'. These hallmarks describe (patho-)physiological processes that together, when disrupted, determine the aging phenotype. Sustaining evidence shows a potential role for hydrogen sulfide (H₂S) in the regulation of aging. Nowadays, H₂S is acknowledged as an endogenously produced signaling molecule with various (patho-) physiological effects. H₂S is involved in several diseases including pathologies related to aging. In this review, the known, assumed and hypothetical effects of hydrogen sulfide on the aging process will be discussed by reviewing its actions on the hallmarks of aging and on several age-related pathologies.

Emerging candidate treatment strategies for Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS, progeria) is an extremely rare premature aging disorder affecting children, with a disease incidence of ∼1 in 18 million individuals. HGPS is usually caused by a de novo point mutation in exon 11 of the LMNA gene (c.1824C>T, p.G608G), resulting in the increased usage of a cryptic splice site and production of a truncated unprocessed lamin A protein named progerin. Since the genetic cause for HGPS was published in 2003, numerous potential treatment options have rapidly emerged. Strategies to interfere with the post-translational processing of lamin A, to enhance progerin clearance, or directly target the HGPS mutation to reduce the progerin-producing alternative splicing of the LMNA gene have been developed. Here, we give an up-to-date resume of the contributions made by our and other research groups to the growing list of different candidate treatment strategies that have been tested, both in vitro, in vivo in mouse models for HGPS and in clinical trials in HGPS patients.

Senescence and aging: Causes, consequences, and therapeutic avenues

Aging is the major risk factor for cancer, cardiovascular disease, diabetes, and neurodegenerative disorders. Although we are far from understanding the biological basis of aging, research suggests that targeting the aging process itself could ameliorate many age-related pathologies. Senescence is a cellular response characterized by a stable growth arrest and other phenotypic alterations that include a proinflammatory secretome. Senescence plays roles in normal development, maintains tissue homeostasis, and limits tumor progression. However, senescence has also been implicated as a major cause of age-related disease. In this regard, recent experimental evidence has shown that the genetic or pharmacological ablation of senescent cells extends life span and improves health span. Here, we review the cellular and molecular links between cellular senescence and aging and discuss the novel therapeutic avenues that this connection opens.

Regulation of Stem Cell Aging by Metabolism and Epigenetics

Stem cell aging and exhaustion are considered important drivers of organismal aging. Age-associated declines in stem cell function are characterized by metabolic and epigenetic changes. Understanding the mechanisms underlying these changes will likely reveal novel therapeutic targets for ameliorating age-associated phenotypes and for prolonging human healthspan. Recent studies have shown that metabolism plays an important role in regulating epigenetic modifications and that this regulation dramatically affects the aging process. This review focuses on current knowledge regarding the mechanisms of stem cell aging, and the links between cellular metabolism and epigenetic regulation. In addition, we discuss how these interactions sense and respond to environmental stress in order to maintain stem cell homeostasis, and how environmental stimuli regulate stem cell function. Additionally, we highlight recent advances in the development of therapeutic strategies to rejuvenate dysfunctional aged stem cells.

The Clinical Potential of Senolytic Drugs

Senolytic drugs are agents that selectively induce apoptosis of senescent cells. These cells accumulate in many tissues with aging and at sites of pathology in multiple chronic diseases. In studies in animals, targeting senescent cells using genetic or pharmacological approaches delays, prevents, or alleviates multiple age-related phenotypes, chronic diseases, geriatric syndromes, and loss of physiological resilience. Among the chronic conditions successfully treated by depleting senescent cells in preclinical studies are frailty, cardiac dysfunction, vascular hyporeactivity and calcification, diabetes mellitus, liver steatosis, osteoporosis, vertebral disk degeneration, pulmonary fibrosis, and radiation-induced damage. Senolytic agents are being tested in proof-of-concept clinical trials. To do so, new clinical trial paradigms for testing senolytics and other agents that target fundamental aging mechanisms are being developed, because use of long-term endpoints such as lifespan or healthspan is not feasible. These strategies include testing effects on multimorbidity, accelerated aging-like conditions, diseases with localized accumulation of senescent cells, potentially fatal diseases associated with senescent cell accumulation, age-related loss of physiological resilience, and frailty. If senolytics or other interventions that target fundamental aging processes prove to be effective and safe in clinical trials, they could transform geriatric medicine by enabling prevention or treatment of multiple diseases and functional deficits in parallel, instead of one at a time.

Immunosenescence Induced by Plasma from Individuals with Obesity Caused Cell Signaling Dysfunction and Inflammation

OBJECTIVE

To evaluate the consequences of plasma from individuals with obesity on parameters associated with immunosenescence in unrelated healthy peripheral blood mononuclear cells (PBMC).

METHODS

Freshly isolated PBMC were incubated in media supplemented with 10% of plasma from individuals with obesity or control subjects for the first 4 hours of 24 to 120 hours of culture.

RESULTS

Plasma from individuals with obesity modulated the phenotype of healthy PBMC, leading to a higher rate of apoptosis, lower amounts of phospho-γH2AX and -p53, and mitochondrial dysfunction. After 120 hours, there was a higher secretion of inflammatory cytokines IL-1β and IL-8. CD8⁺ T lymphocytes presented decreased expression of CD28, which is associated with the immunosenescent phenotype. CD14⁺ macrophages showed increased expression of CD80 and CD206, suggesting a modulation in the activation of macrophages.

CONCLUSIONS

These results demonstrate that chronic systemic inflammation observed in obesity induces dysfunctional features in PBMC that are consistent with premature immunosenescence.

Clinical-grade human umbilical cord-derived mesenchymal stem cells reverse cognitive aging via improving synaptic plasticity and endogenous neurogenesis

Cognitive aging is a leading public health concern with the increasing aging population, but there is still lack of specific interventions directed against it. Recent studies have shown that cognitive function is intimately affected by systemic milieu in aging brain, and improvement of systemic environment in aging brain may be a promising approach for rejuvenating cognitive aging. Here, we sought to study the intervention effects of clinical-grade human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) on cognitive aging in a murine model of aging. The conventional aging model in mice induced by d-galactose (d-gal) was employed here. Mice received once every two weeks intraperitoneal administration of hUC-MSCs. After 3 months of systematical regulation of hUC-MSCs, the hippocampal-dependent learning and memory ability was effectively improved in aged mice, and the synaptic plasticity was remarkably enhanced in CA1 area of the aged hippocampus; moreover, the neurobiological substrates that could impact on the function of hippocampal circuits were recovered in the aged hippocampus reflecting in: dendritic spine density enhanced, neural sheath and cytoskeleton restored, and postsynaptic density area increased. In addition, the activation of the endogenic neurogenesis which is beneficial to stabilize the neural network in hippocampus was observed after hUC-MSCs transplantation. Furthermore, we demonstrated that beneficial effects of systematical regulation of hUC-MSCs could be mediated by activation of mitogen-activated protein kinase (MAPK)-ERK-CREB signaling pathway in the aged hippocampus. Our study provides the first evidence that hUC-MSCs, which have the capacity of systematically regulating the aging brain, may be a potential intervention for cognitive aging.

Molecular and physiological manifestations and measurement of aging in humans

Biological aging is associated with a reduction in the reparative and regenerative potential in tissues and organs. This reduction manifests as a decreased physiological reserve in response to stress (termed homeostenosis) and a time-dependent failure of complex molecular mechanisms that cumulatively create disorder. Aging inevitably occurs with time in all organisms and emerges on a molecular, cellular, organ, and organismal level with genetic, epigenetic, and environmental modulators. Individuals with the same chronological age exhibit differential trajectories of age-related decline, and it follows that we should assess biological age distinctly from chronological age. In this review, we outline mechanisms of aging with attention to well-described molecular and cellular hallmarks and discuss physiological changes of aging at the organ-system level. We suggest methods to measure aging with attention to both molecular biology (e.g., telomere length and epigenetic marks) and physiological function (e.g., lung function and echocardiographic measurements). Finally, we propose a framework to integrate these molecular and physiological data into a composite score that measures biological aging in humans. Understanding the molecular and physiological phenomena that drive the complex and multifactorial processes underlying the variable pace of biological aging in humans will inform how researchers assess and investigate health and disease over the life course. This composite biological age score could be of use to researchers seeking to characterize normal, accelerated, and exceptionally successful aging as well as to assess the effect of interventions aimed at modulating human aging.

Advances in Therapeutic Approaches to Extend Healthspan: a perspective from the 2nd Scripps Symposium on the Biology of Aging

The 2^nd Scripps Florida Symposium on The Biology of Aging entitled ‘Advances in Therapeutic Approaches to Extend Healthspan’ was held on January 22^nd–25^th, 2017 at The Scripps Research Institute in Jupiter, Florida. The meeting highlighted a variety of therapeutic approaches in animal models of aging that either are or soon will be in clinic trials. For example, drugs targeting senescent cells, metformin, rapalogs, NAD precursors, young plasma, mitochondrial‐targeted free radical scavengers, stem cells, and stem cell factors all have shown significant preclinical efficacy. This perspective, based on presentations and discussions at the symposium, outlines the current and future state of development of therapeutic approaches to extend human healthspan.

Identification, isolation, quantification and systems approach towards CD34, a biomarker present in the progenitor/stem cells from diverse lineages

Mesenchymal stem cells (MSCs) constitute the diverse progenitor populations in almost every tissue and are of immense importance in the field of regenerative medicine. CD34 is a cell surface glycoprotein identified first as a marker for the MSCs of hematopoietic origin. CD34 is now known to be expressed in cells of diverse lineages (tissues of non-hematopoietic origin) such as ectoderm, mesoderm and endoderm and is considered as a general marker for progenitor cells. Here, we present detailed protocols to obtain pure populations of MSCs from three diverse lineages such as skeletal muscle, skin, and liver from mouse tissues. We also present here the protocol for systems biology approach (proteomic analysis) of these purified cells. This proteomic approach can elucidate key signalling pathways and proteins utilized by these CD34 positive cells in undifferentiated and differentiated conditions. Furthermore in-depth proteomic analysis can also identify the altered proteome which is responsible for their function during non-clinical and clinical conditions.

mTOR signaling plays a critical role in the defects observed in muscle-derived stem/progenitor cells isolated from a murine model of accelerated aging

Mice expressing reduced levels of ERCC1-XPF (Ercc1^-/Δ mice) demonstrate premature onset of age-related changes due to decreased repair of DNA damage. Muscle-derived stem/progenitor cells (MDSPCs) isolated from Ercc1^-/Δ mice have an impaired capacity for cell differentiation. The mammalian target of rapamycin (mTOR) is a critical regulator of cell growth in response to nutrient, hormone, and oxygen levels. Inhibition of the mTOR pathway extends the lifespan of several species. Here, we examined the role of mTOR in regulating the MDSPC dysfunction that occurs with accelerated aging. We show that mTOR signaling pathways are activated in Ercc1^-/Δ MDSPCs compared with wild-type (WT) MDSPCs. Additionally, inhibiting mTOR with rapamycin promoted autophagy and improved the myogenic differentiation capacity of the Ercc1^-/Δ MDSPCs. The percent of apoptotic and senescent cells in Ercc1^-/Δ MDSPC cultures was decreased upon mTOR inhibition. These results establish that mTOR signaling contributes to stem cell dysfunction and cell fate decisions in response to endogenous DNA damage. Therefore, mTOR represents a potential therapeutic target for improving defective, aged stem cells. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1375-1382, 2017.

Inhibition of NF-κB improves the stress resistance and myogenic differentiation of MDSPCs isolated from naturally aged mice

A decline in the regenerative capacity of adult stem cells with aging is well documented. As a result of this decline, the efficacy of autologous stem cell therapies is likely to decline with increasing donor age. In these cases, strategies to restore the function of aged stem cells would have clinical utility. Globally, the transcription factor NF-κB is up-regulated in aged tissues. Given the negative role that NF-κB plays in myogenesis, we investigated whether the age-related decline in the function of muscle-derived stem/progenitor cells (MDSPCs) could be improved by inhibition of NF-κB. Herein, we demonstrate that pharmacologic or genetic inhibition of NF-κB activation increases myogenic differentiation and improves resistance to oxidative stress. Our results suggest that MDSPC “aging” may be reversible, and that pharmacologic targeting of pathways such as NF-κB may enhance the efficacy of cell-based therapies.

Muscle-derived stem cells in peripheral nerve regeneration: reality or illusion?

Owing to the complicated and time-consuming regenerative process, the repair of injured peripheral nerves depends largely on ongoing stem-cell therapy. Decades ago, researchers successfully isolated and identified muscle-derived stem cells (MDSCs) and discovered their potential for multidifferentiation. MDSCs play an important role in trauma repair associated with neuromuscular and vascular injury by simultaneously promoting tissue regrowth via direct differentiation and systematic secretion under physiological conditions. However, the isolation, culture, induction and application of MDSCs require further methodological analysis before clinical application. In this review, we comprehensively discuss the challenges associated with neural regeneration and reviewed the progress of stem cell based regenerative medicine, in an effort to realize the potential of MDSCs in nerve regeneration.

Bone Marrow Aspirate Concentrate Harvesting and Processing Technique

Bone marrow obtained by iliac crest aspiration is a common source for harvesting mesenchymal stem cells, other progenitor cells, and associated cytokine/growth factors. Recent studies have reported good to excellent outcomes with the use of bone marrow aspirate concentrate (BMAC) for pain relief in the treatment of focal chondral lesions and osteoarthritis of the knee. However, the harvesting and processing technique are crucial to achieve satisfactory results. Several studies have examined outcomes after BMAC injection, with encouraging results, but there is a lack of consensus in terms of the frequency of injection, the amount of BMAC that is injected, and the timing of BMAC injections. The purpose of this Technical Note was to describe a standardized bone marrow aspiration harvesting technique and processing method.

Collection of Serum- and Feeder-free Mouse Embryonic Stem Cell-conditioned Medium for a Cell-free Approach

The capacity of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) to generate various cell types has opened new avenues in the field of regenerative medicine. However, despite their benefits, the tumorigenic potential of ESCs and iPSCs has long been a barrier for clinical applications. Interestingly, it has been shown that ESCs produce several soluble factors that can promote tissue regeneration and delay cellular aging, suggesting that ESCs and iPSCs can also be utilized as a cell-free intervention method. Therefore, the method for harvesting mouse embryonic stem cell (mESC)-conditioned medium (mESC-CM) with minimal contamination of serum components (fetal bovine serum, FBS) and feeder cells (mouse embryonic fibroblasts, MEFs) has been highly demanded. Here, the present study demonstrates an optimized method for the collection of mESC-CM under serum- and feeder-free conditions and for the characterization of mESC-CM using senescence-associated multiple readouts. This protocol will provide a method to collect pure mESC-specific secretory factors without serum and feeder contamination.

Human Induced Pluripotent Stem Cells Differentiate Into Functional Mesenchymal Stem Cells and Repair Bone Defects

Using short-term exposure of embryoid bodies to transforming growth factor-β, the authors directed induced pluripotent stem cells (iPSCs) toward mesenchymal stem cell (MSC) differentiation. Two types of iPSC-derived MSCs were identified: early (aiMSCs) and late (tiMSCs) outgrowing cells. Both types differentiated in vitro in response to osteogenic or adipogenic supplements; aiMSCs demonstrated higher osteogenic potential than tiMSCs. Upon orthotopic injection into radial defects, both types regenerated bone and contributed to defect repair.

Mesenchymal stem cells (MSCs) are currently the most established cells for skeletal tissue engineering and regeneration; however, their availability and capability of self-renewal are limited. Recent discoveries of somatic cell reprogramming may be used to overcome these challenges. We hypothesized that induced pluripotent stem cells (iPSCs) that were differentiated into MSCs could be used for bone regeneration. Short-term exposure of embryoid bodies to transforming growth factor-β was used to direct iPSCs toward MSC differentiation. During this process, two types of iPSC-derived MSCs (iMSCs) were identified: early (aiMSCs) and late (tiMSCs) outgrowing cells. The transition of iPSCs toward MSCs was documented using MSC marker flow cytometry. Both types of iMSCs differentiated in vitro in response to osteogenic or adipogenic supplements. The results of quantitative assays showed that both cell types retained their multidifferentiation potential, although aiMSCs demonstrated higher osteogenic potential than tiMSCs and bone marrow-derived MSCs (BM-MSCs). Ectopic injections of BMP6-overexpressing tiMSCs produced no or limited bone formation, whereas similar injections of BMP6-overexpressing aiMSCs resulted in substantial bone formation. Upon orthotopic injection into radial defects, all three cell types regenerated bone and contributed to defect repair. In conclusion, MSCs can be derived from iPSCs and exhibit self-renewal without tumorigenic ability. Compared with BM-MSCs, aiMSCs acquire more of a stem cell phenotype, whereas tiMSCs acquire more of a differentiated osteoblast phenotype, which aids bone regeneration but does not allow the cells to induce ectopic bone formation (even when triggered by bone morphogenetic proteins), unless in an orthotopic site of bone fracture.

Significance

Mesenchymal stem cells (MSCs) are currently the most established cells for skeletal tissue engineering and regeneration of various skeletal conditions; however, availability of autologous MSCs is very limited. This study demonstrates a new method to differentiate human fibroblast-derived induced pluripotent stem cells (iPSCs) to cells with MSC properties, which we comprehensively characterized including differentiation potential and transcriptomic analysis. We showed that these iPS-derived MSCs are able to regenerate nonunion bone defects in mice more efficiently than bone marrow-derived human MSCs when overexpressing BMP6 using a nonviral transfection method.

Molecular insights into the premature aging disease progeria

Hutchinson-Gilford progeria syndrome (HGPS) is an extremely rare premature aging disease presenting many features resembling the normal aging process. HGPS patients die before the age of 20 years due to cardiovascular problems and heart failure. HGPS is linked to mutations in the LMNA gene encoding the intermediate filament protein lamin A. Lamin A is a major component of the nuclear lamina, a scaffold structure at the nuclear envelope that defines mechanochemical properties of the nucleus and is involved in chromatin organization and epigenetic regulation. Lamin A is also present in the nuclear interior where it fulfills lamina-independent functions in cell signaling and gene regulation. The most common LMNA mutation linked to HGPS leads to mis-splicing of the LMNA mRNA and produces a mutant lamin A protein called progerin that tightly associates with the inner nuclear membrane and affects the dynamic properties of lamins. Progerin expression impairs many important cellular processes providing insight into potential disease mechanisms. These include changes in mechanosignaling, altered chromatin organization and impaired genome stability, and changes in signaling pathways, leading to impaired regulation of adult stem cells, defective extracellular matrix production and premature cell senescence. In this review, we discuss these pathways and their potential contribution to the disease pathologies as well as therapeutic approaches used in preclinical and clinical tests.

Translating the Science of Aging into Therapeutic Interventions

Life and health span have been extended in experimental animals using drugs that are potentially translatable into humans. Considerable effort is needed beyond the usual steps in drug development to devise the models, and realistic preclinical and clinical trial strategies are required to advance these agents into clinical application. It will be important to focus on subjects who already have symptoms or are at imminent risk of developing disorders related to fundamental aging processes, to use short-term, clinically relevant outcomes, as opposed to long-term outcomes, such as health span or life span, and to validate endpoint measures so they are acceptable to regulatory agencies. Funding is a roadblock, as is shortage of investigators with combined expertise in the basic biology of aging, clinical geriatrics, and investigational new drug clinical trials. Strategies for developing a path from the bench to the bedside are reviewed for interventions that target fundamental aging mechanisms.

Stem cell death and survival in heart regeneration and repair

Cardiovascular diseases are major causes of mortality and morbidity. Cardiomyocyte apoptosis disrupts cardiac function and leads to cardiac decompensation and terminal heart failure. Delineating the regulatory signaling pathways that orchestrate cell survival in the heart has significant therapeutic implications. Cardiac tissue has limited capacity to regenerate and repair. Stem cell therapy is a successful approach for repairing and regenerating ischemic cardiac tissue; however, transplanted cells display very high death percentage, a problem that affects success of tissue regeneration. Stem cells display multipotency or pluripotency and undergo self-renewal, however these events are negatively influenced by upregulation of cell death machinery that induces the significant decrease in survival and differentiation signals upon cardiovascular injury. While efforts to identify cell types and molecular pathways that promote cardiac tissue regeneration have been productive, studies that focus on blocking the extensive cell death after transplantation are limited. The control of cell death includes multiple networks rather than one crucial pathway, which underlies the challenge of identifying the interaction between various cellular and biochemical components. This review is aimed at exploiting the molecular mechanisms by which stem cells resist death signals to develop into mature and healthy cardiac cells. Specifically, we focus on a number of factors that control death and survival of stem cells upon transplantation and ultimately affect cardiac regeneration. We also discuss potential survival enhancing strategies and how they could be meaningful in the design of targeted therapies that improve cardiac function.

SIRT6 safeguards human mesenchymal stem cells from oxidative stress by coactivating NRF2

SIRT6 belongs to the mammalian homologs of Sir2 histone NAD⁺-dependent deacylase family. In rodents, SIRT6 deficiency leads to aging-associated degeneration of mesodermal tissues. It remains unknown whether human SIRT6 has a direct role in maintaining the homeostasis of mesodermal tissues. To this end, we generated SIRT6 knockout human mesenchymal stem cells (hMSCs) by targeted gene editing. SIRT6-deficient hMSCs exhibited accelerated functional decay, a feature distinct from typical premature cellular senescence. Rather than compromised chromosomal stability, SIRT6-null hMSCs were predominately characterized by dysregulated redox metabolism and increased sensitivity to the oxidative stress. In addition, we found SIRT6 in a protein complex with both nuclear factor erythroid 2-related factor 2 (NRF2) and RNA polymerase II, which was required for the transactivation of NRF2-regulated antioxidant genes, including heme oxygenase 1 (HO-1). Overexpression of HO-1 in SIRT6-null hMSCs rescued premature cellular attrition. Our study uncovers a novel function of SIRT6 in maintaining hMSC homeostasis by serving as a NRF2 coactivator, which represents a new layer of regulation of oxidative stress-associated stem cell decay.

Concentrated Bone Marrow Aspirate for the Treatment of Chondral Injuries and Osteoarthritis of the Knee: A Systematic Review of Outcomes

Background:

Bone marrow aspirate concentrate (BMAC) has emerged as a novel treatment for pathology of the knee. Despite containing a limited number of stem cells, BMAC serves as a source of growth factors that are thought to play an important role as a result of their anabolic and anti-inflammatory effects. To our knowledge, there is no systematic review regarding the outcomes of bone marrow aspirate concentrate used for the treatment of chondral defects and osteoarthritis of the knee.

Purpose:

To perform a systematic review on the outcomes of bone marrow aspirate concentrate for the treatment of chondral defects and osteoarthritis of the knee.

Study Design:

Systematic review; Level of evidence, 4.

Methods:

A systematic review of the literature was performed using the Cochrane Database of Systematic Reviews, the Cochrane Central Register of Controlled Trials, PubMed, and MEDLINE from 1980 to present. Inclusion criteria were as follows: use of BMAC for treatment of chondral defects and osteoarthritis of the knee, English language, and human studies. We excluded cadaveric studies, animal studies, basic science articles, editorial articles, surveys, and studies that did not include the knee. After applying inclusion and exclusion criteria, studies were evaluated for efficacy and safety of BMAC for treatment of articular cartilage knee pathologies.

Results:

Eleven studies were considered. Of these, 5 were prospective studies, 1 was a retrospective study, 2 were case series, and 3 were case reports. Three comparative studies (2 with level 2 evidence, 1 with level 3 evidence) were found in our search; none of them were randomized. Three studies investigated the clinical efficacy of BMAC in the treatment of osteoarthritis, and 8 studies evaluated the efficacy of BMAC on focal cartilage injuries. All 3 studies regarding osteoarthritis and all 8 studies regarding focal chondral defects reported good to excellent overall outcomes with the use of BMAC.

Conclusion:

Although a growing interest for biological alternatives of treating knee pathology has been observed in the past few years, there still remains a paucity of high-quality studies. The studies included in this systematic review reported varying degrees of beneficial results with the use of BMAC with and without an additional procedure for the treatment of chondral defects and early stages of osteoarthritis. Most articles present the use of BMAC as a safe procedure and report good results.