Fine-tuned rest: unveiling the regulatory landscape of adult quiescent neural stem cells

Cell quiescence is an essential mechanism that allows cells to temporarily halt proliferation while preserving the potential to resume it at a later time. The molecular mechanisms underlying cell quiescence are complex and involve the regulation of various signaling pathways, transcription factors and epigenetic modifications. The importance of unveiling the mechanisms regulating the quiescent state is undeniable, as its long-term maintenance is key to sustain tissue homeostasis throughout life. Neural stem cells (NSCs) are maintained in the subependymal zone (SEZ) niche of adult mammalian brains mostly as long-lasting quiescent cells, owing to multiple intrinsic and extrinsic cues that actively regulate this state. Differently from other non-proliferative states, quiescence is a reversible and tightly regulated condition that can re-activate to support the formation of new neurons throughout adult lifespan. Decoding its regulatory mechanisms in homeostasis and unveiling how it is modulated in the context of the aged brain or during tumorigenesis, could bring us closer to the development of new potential strategies to intervene in adult neurogenesis with therapeutic purposes. Starting with a general conceptualization of the quiescent state in different stem cell niches, we here review what we have learned about NSC quiescence in the SEZ, encompassing the experimental strategies used for its study, to end up discussing the modulation of quiescence in the context of a physiology or pathological NSC dysregulation.

The multifactorial nature of healthy brain ageing: Brain changes, functional decline and protective factors

As the global population faces a progressive shift towards a higher median age, understanding the mechanisms underlying healthy brain ageing has become of paramount importance for the preservation of cognitive abilities. The first part of the present review aims to provide a comprehensive look at the anatomical changes the healthy brain endures with advanced age, while also summarizing up to date findings on modifiable risk factors to support a healthy ageing process. Subsequently, we describe the typical cognitive profile displayed by healthy older adults, conceptualizing the well-established age-related decline as an impairment of four main cognitive factors and relating them to their neural substrate previously described; different cognitive trajectories displayed by typical Alzheimer's Disease patients and successful agers with a high cognitive reserve are discussed. Finally, potential effective interventions and protective strategies to promote cognitive reserve and defer cognitive decline are reviewed and proposed.

The cilium-centrosome axis in coupling cell cycle exit and cell fate

The centrosome is an evolutionarily conserved, ancient organelle whose role in cell division was first described over a century ago. The structure and function of the centrosome as a microtubule-organizing center, and of its extracellular extension - the primary cilium - as a sensory antenna, have since been extensively studied, but the role of the cilium-centrosome axis in cell fate is still emerging. In this Opinion piece, we view cellular quiescence and tissue homeostasis from the vantage point of the cilium-centrosome axis. We focus on a less explored role in the choice between distinct forms of mitotic arrest - reversible quiescence and terminal differentiation, which play distinct roles in tissue homeostasis. We outline evidence implicating the centrosome-basal body switch in stem cell function, including how the cilium-centrosome complex regulates reversible versus irreversible arrest in adult skeletal muscle progenitors. We then highlight exciting new findings in other quiescent cell types that suggest signal-dependent coupling of nuclear and cytoplasmic events to the centrosome-basal body switch. Finally, we propose a framework for involvement of this axis in mitotically inactive cells and identify future avenues for understanding how the cilium-centrosome axis impacts central decisions in tissue homeostasis.

Regulation of adult stem cell quiescence and its functions in the maintenance of tissue integrity

Adult stem cells are important for mammalian tissues, where they act as a cell reserve that supports normal tissue turnover and can mount a regenerative response following acute injuries. Quiescent stem cells are well established in certain tissues, such as skeletal muscle, brain, and bone marrow. The quiescent state is actively controlled and is essential for long-term maintenance of stem cell pools. In this Review, we discuss the importance of maintaining a functional pool of quiescent adult stem cells, including haematopoietic stem cells, skeletal muscle stem cells, neural stem cells, hair follicle stem cells, and mesenchymal stem cells such as fibro-adipogenic progenitors, to ensure tissue maintenance and repair. We discuss the molecular mechanisms that regulate the entry into, maintenance of, and exit from the quiescent state in mice. Recent studies revealed that quiescent stem cells have a discordance between RNA and protein levels, indicating the importance of post-transcriptional mechanisms, such as alternative polyadenylation, alternative splicing, and translation repression, in the control of stem cell quiescence. Understanding how these mechanisms guide stem cell function during homeostasis and regeneration has important implications for regenerative medicine.

Three-dimensional chromatin re-organization during muscle stem cell aging

Age-related skeletal muscle atrophy or sarcopenia is a significant societal problem that is becoming amplified as the world's population continues to increase. The regeneration of damaged skeletal muscle is mediated by muscle stem cells, but in old age muscle stem cells become functionally attenuated. The molecular mechanisms that govern muscle stem cell aging encompass changes across multiple regulatory layers and are integrated by the three-dimensional organization of the genome. To quantitatively understand how hierarchical chromatin architecture changes during muscle stem cell aging, we generated 3D chromatin conformation maps (Hi-C) and integrated these datasets with multi-omic (chromatin accessibility and transcriptome) profiles from bulk populations and single cells. We observed that muscle stem cells display static behavior at global scales of chromatin organization during aging and extensive rewiring of local contacts at finer scales that were associated with variations in transcription factor binding and aberrant gene expression. These data provide insights into genome topology as a regulator of molecular function in stem cell aging.

Aging Hallmarks and the Role of Oxidative Stress

Aging is a complex biological process accompanied by a progressive decline in the physical function of the organism and an increased risk of age-related chronic diseases such as cardiovascular diseases, cancer, and neurodegenerative diseases. Studies have established that there exist nine hallmarks of the aging process, including (i) telomere shortening, (ii) genomic instability, (iii) epigenetic modifications, (iv) mitochondrial dysfunction, (v) loss of proteostasis, (vi) dysregulated nutrient sensing, (vii) stem cell exhaustion, (viii) cellular senescence, and (ix) altered cellular communication. All these alterations have been linked to sustained systemic inflammation, and these mechanisms contribute to the aging process in timing not clearly determined yet. Nevertheless, mitochondrial dysfunction is one of the most important mechanisms contributing to the aging process. Mitochondria is the primary endogenous source of reactive oxygen species (ROS). During the aging process, there is a decline in ATP production and elevated ROS production together with a decline in the antioxidant defense. Elevated ROS levels can cause oxidative stress and severe damage to the cell, organelle membranes, DNA, lipids, and proteins. This damage contributes to the aging phenotype. In this review, we summarize recent advances in the mechanisms of aging with an emphasis on mitochondrial dysfunction and ROS production.

Regenerative Effect of Umbilical Cord-Derived Mesenchymal Stromal Cells in a Rat Model of Established Limb Ischemia

BACKGROUND

Although regenerative cell therapy is expected to be an alternative treatment for peripheral artery disease (PAD), many regenerative cell therapies have failed to show sufficient efficacy in clinical trials. Most preclinical studies have used acute ischemia models, despite PAD being a chronic disease. In addition, aging and atherosclerosis decrease the quality of a patient's stem cells. Therefore, using a non-acute ischemic preclinical model and stem cells with high regenerative potency are important for the development of effective regenerative therapy. In this study, we assessed the tissue regenerative potential of umbilical cord-derived mesenchymal stromal cells (UCMSCs), which could potentially be an ideal cell source, in a rat model of established ischemia.

METHODS AND RESULTS

The regenerative capacity of UCMSCs was analyzed in terms of angiogenesis and muscle regeneration. In vitro analysis showed that UCMSCs secrete high amounts of cytokines associated with angiogenesis and muscle regeneration. In vivo experiments in a rat non-acute ischemia model showed significant improvement in blood perfusion after intravenous injection of UCMSCs compared with injection of culture medium or saline. Histological analysis revealed UCMSCs injection enhanced angiogenesis, with an increased number of von Willebrand factor-positive microcapillaries, and improved muscle regeneration.

CONCLUSIONS

These results suggest that intravenous administration of UCMSCs may be useful for treating patients with PAD.

Reduced Range of Gait Speed: A Parkinson's Disease-Specific Symptom?

Reduced range of gait speed (RGS) may lead to decreased environmental adaptability in persons with Parkinson's disease (PwPD). Therefore, lab-measured gait speed, step time, and step length during slow, preferred, and fast walking were assessed in 24 PwPD, 19 stroke patients, and 19 older adults and compared with 31 young adults. Only PwPD, but not the other groups, showed significantly reduced RGS compared to young adults, driven by step time in the low and step length in the high gait speed range. These results suggest that reduced RGS may occur as a PD-specific symptom, and different gait components seem to contribute.

Ageing and rejuvenation of tissue stem cells and their niches

Most adult organs contain regenerative stem cells, often organized in specific niches. Stem cell function is critical for tissue homeostasis and repair upon injury, and it is dependent on interactions with the niche. During ageing, stem cells decline in their regenerative potential and ability to give rise to differentiated cells in the tissue, which is associated with a deterioration of tissue integrity and health. Ageing-associated changes in regenerative tissue regions include defects in maintenance of stem cell quiescence, differentiation ability and bias, clonal expansion and infiltration of immune cells in the niche. In this Review, we discuss cellular and molecular mechanisms underlying ageing in the regenerative regions of different tissues as well as potential rejuvenation strategies. We focus primarily on brain, muscle and blood tissues, but also provide examples from other tissues, such as skin and intestine. We describe the complex interactions between different cell types, non-cell-autonomous mechanisms between ageing niches and stem cells, and the influence of systemic factors. We also compare different interventions for the rejuvenation of old regenerative regions. Future outlooks in the field of stem cell ageing are discussed, including strategies to counter ageing and age-dependent disease.

Sequential events during the quiescence to proliferation transition establish patterns of follicle cell differentiation in the Drosophila ovary

Stem cells cycle between periods of quiescence and proliferation to promote tissue health. In Drosophila ovaries, quiescence to proliferation transitions of follicle stem cells (FSCs) are exquisitely feeding-dependent. Here, we demonstrate feeding-dependent induction of follicle cell differentiation markers, eyes absent (Eya) and castor (Cas) in FSCs, a patterning process that does not depend on proliferation induction. Instead, FSCs extend micron-scale cytoplasmic projections that dictate Eya-Cas patterning. We identify still life and sickie as necessary and sufficient for FSC projection growth and Eya-Cas induction. Our results suggest that sequential, interdependent events establish long-term differentiation patterns in follicle cell precursors, independently of FSC proliferation induction.

Current Trends and Approaches to the Search for Genetic Determinants of Aging and Longevity

Aging is a natural process of extinction of the body and the main aspect that determines the life expectancy for individuals who have survived to the post-reproductive period. The process of aging is accompanied by certain physiological, immune, and metabolic changes in the body, as well as the development of age-related diseases. The contribution of genetic factors to human life expectancy is estimated at about 25-30%. Despite the success in identifying genes and metabolic pathways that may be involved in the life extension process in model organisms, the key question remains to what extent these data can be extrapolated to humans, for example, because of the complexity of its biological and sociocultural systems, as well as possible species differences in life expectancy and causes of mortality. New molecular genetic methods have significantly expanded the possibilities for searching for genetic factors of human life expectancy and identifying metabolic pathways of aging, the interaction of genes and transcription factors, the regulation of gene expression at the level of transcription, and epigenetic modifications. The review presents the latest research and current strategies for studying the genetic basis of human aging and longevity: the study of individual candidate genes in genetic population studies, variations identified by the GWAS method, immunogenetic differences in aging, and genomic studies to identify factors of "healthy aging." Understanding the mechanisms of the interaction between factors affecting the life expectancy and the possibility of their regulation can become the basis for developing comprehensive measures to achieve healthy longevity.

Supplementary Information

The online version contains supplementary material available at 10.1134/S1022795422120067.

Quercetin Prevents Intestinal Stem Cell Aging via Scavenging ROS and Inhibiting Insulin Signaling in Drosophila

Adult stem cells, a class of cells that possess self-renewal and differentiation capabilities, modulate tissue regeneration, repair, and homeostasis maintenance. These cells undergo functional degeneration during aging, resulting in decreased tissue regeneration ability and increased disease incidence. Thus, it is essential to provide effective therapeutic solutions to preventing the aging-related functional decline of stem cells. Quercetin (Que) is a popular natural polyphenolic flavonoid found in various plant species. It exhibits many beneficial effects against aging and aging-related diseases; however, its efficacy against adult stem cell aging remains largely unclear. Drosophila possesses a mammalian-like intestinal system with a well-studied intestinal stem cell (ISC) lineage, making it an attractive model for adult stem cell research. Here, we show that Que supplementation could effectively prevent the hyperproliferation of ISCs, maintain intestinal homeostasis, and prolong the lifespan in aged Drosophila. In addition, we found that Que could accelerate recovery of the damaged gut and improve the tolerance of Drosophila to stressful stimuli. Furthermore, results demonstrated that Que prevents the age-associated functional decline of ISCs via scavenging reactive oxygen species (ROS) and inhibiting the insulin signaling pathway. Overall, our findings suggest that Que plays a significant role in delaying adult stem cell aging.

The universal stem cell

Current dogma is that there exists a hematopoietic pluripotent stem cell, resident in the marrow, which is quiescent, but with tremendous proliferative and differentiative potential. Furthermore, the hematopoietic system is essentially hierarchical with progressive differentiation from the pluripotent stem cells to different classes of hematopoietic cells. However, results summarized here indicate that the marrow pluripotent hematopoietic stem cell is actively cycling and thus continually changing phenotype. As it progresses through cell cycle differentiation potential changes as illustrated by sequential changes in surface expression of B220 and GR-1 epitopes. Further data indicated that the potential of purified hematopoietic stem cells extends to multiple other non-hematopoietic cells. It appears that marrow stem cells will give rise to epithelial pulmonary cells at certain points in cell cycle. Thus, it appears that the marrow "hematopoietic" stem cell is also a stem cell for other non-hematopoietic tissues. These observations give rise to the concept of a universal stem cell. The marrow stem cell is not limited to hematopoiesis and its differentiation potential continually changes as it transits cell cycle. Thus, there is a universal stem cell in the marrow which alters its differentiation potential as it progresses through cell cycle. This potential is expressed when it resides in tissues compatible with its differentiation potential, at a particular point in cell cycle transit, or when it interacts with vesicles from that tissue.

Insulin-like growth factor binding proteins 7 prevents dental pulp-derived mesenchymal stem cell senescence via metabolic downregulation of p21

Cellular senescence affects the efficacy of mesenchymal stem cells (MSCs)-mediated tissue regeneration. Insulin-like growth factor binding proteins-7 (IGFBP7), as a member of the IGF family, is associated with osteogenic differentiation and the senescence of MSCs, but its exact function and mechanism remain unclear. We found IGFBP7 promoted the osteogenic differentiation and prevented the senescence of dental pulp-derived MSCs (DPSCs), as observed in the gain-of-function and loss-of-function analyses, the senescence-associated marker p21 showed the most pronounced expression changes. We demonstrated that IGFBP7 activated the biological activity of SIRT1 deacetylase via metabolism, resulting in a deacetylation of H3K36ac and a decrease of the binding affinity of H3K36ac to p21 promoter, thereby reducing the transcription of p21, which ultimately prevents DPSCs senescence and promotes tissue regeneration. The activation of the mitochondrial electron transport chain (ETC) by Coenzyme Q10 could rescue the promotion of DPSC senescence induced by the knockdown of IGFBP7, whereas the inhibition of ETC by rotenone attenuated the prevention of DPSC senescence induced by IGFBP7 overexpression. In conclusion, our present results reveal a novel function of IGFBP7 in preventing DPSC senescence via the metabolism-induced deacetylation of H3K36ac and reduction of p21 transcription, suggesting that IGFBP7 is a potential target for promoting tissue regeneration in an aging environment.

Therapeutic Antiaging Strategies

Aging constitutes progressive physiological changes in an organism. These changes alter the normal biological functions, such as the ability to manage metabolic stress, and eventually lead to cellular senescence. The process itself is characterized by nine hallmarks: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. These hallmarks are risk factors for pathologies, such as cardiovascular diseases, neurodegenerative diseases, and cancer. Emerging evidence has been focused on examining the genetic pathways and biological processes in organisms surrounding these nine hallmarks. From here, the therapeutic approaches can be addressed in hopes of slowing the progression of aging. In this review, data have been collected on the hallmarks and their relative contributions to aging and supplemented with in vitro and in vivo antiaging research experiments. It is the intention of this article to highlight the most important antiaging strategies that researchers have proposed, including preventive measures, systemic therapeutic agents, and invasive procedures, that will promote healthy aging and increase human life expectancy with decreased side effects.

Oxidative stress, aging, antioxidant supplementation and their impact on human health: An overview

Aging is characterized by a progressive loss of tissue and organ function due to genetic and environmental factors, nutrition, and lifestyle. Oxidative stress is one the most important mechanisms of cellular senescence and increased frailty, resulting in several age-linked, noncommunicable diseases. Contributing events include genomic instability, telomere shortening, epigenetic mechanisms, reduced proteome homeostasis, altered stem-cell function, defective intercellular communication, progressive deregulation of nutrient sensing, mitochondrial dysfunction, and metabolic unbalance. These complex events and their interplay can be modulated by dietary habits and the ageing process, acting as potential measures of primary and secondary prevention. Promising nutritional approaches include the Mediterranean diet, the intake of dietary antioxidants, and the restriction of caloric intake. A comprehensive understanding of the ageing processes should promote new biomarkers of risk or diagnosis, but also beneficial treatments oriented to increase lifespan.

Non-neutral clonal selection and its potential role in mammalian germline stem cell dysfunction with advancing age

The concept of natural selection, or "survival of the fittest", refers to an evolutionary process in nature whereby traits emerge in individuals of a population through random gene alterations that enable those individuals to better adapt to changing environmental conditions. This genetic variance allows certain members of the population to gain an advantage over others in the same population to survive and reproduce in greater numbers under new environmental pressures, with the perpetuation of those advantageous traits in future progeny. Here we present that the behavior of adult stem cells in a tissue over time can, in many respects, be viewed in the same manner as evolution, with each stem cell clone being representative of an individual within a population. As stem cells divide or are subjected to cumulative oxidative damage over the lifespan of the organism, random genetic alterations are introduced into each clone that create variance in the population. These changes may occur in parallel to, or in response to, aging-associated changes in microenvironmental cues perceived by the stem cell population. While many of these alterations will be neutral or silent in terms of affecting cell function, a small fraction of these changes will enable certain clones to respond differently to shifts in microenvironmental conditions that arise with advancing age. In some cases, the same advantageous genetic changes that support survival and expansion of certain clones over others in the population (viz. non-neutral competition) could be detrimental to the downstream function of the differentiated stem cell descendants. In the context of the germline, such a situation would be devastating to successful propagation of the species across generations. However, even within a single generation, the “evolution” of stem cell lineages in the body over time can manifest into aging-related organ dysfunction and failure, as well as lead to chronic inflammation, hyperplasia, and cancer. Increased research efforts to evaluate stem cells within a population as individual entities will improve our understanding of how organisms age and how certain diseases develop, which in turn may open new opportunities for clinical detection and management of diverse pathologies.

Overview of the Main Species of Ticks and Animal and Human Tick-Related Diseases in the Caribbean, Particularly in Haiti

The Caribbean region faces a wide diversity of ticks and tick-borne diseases (TBDs) in animals and humans. But to date, these have been the subject of few studies, resulting in a relative lack of knowledge of their epidemiology, pathogenicity, and the best prevention and control methods. Ticks are hematophagous mites, which feed on the blood of mammals, birds, and reptiles. They are subdivided into two large families: the Ixodidae or hard ticks and the Argasidae or soft ticks. Each collection of blood by ticks from infected hosts can lead to their infection, which will contaminate other previously unharmed animals and contribute to the spread of tick-borne diseases caused mainly by bacteria, viruses, and parasites. It seems important to us to draw up a state of knowledge on ticks. Some long-known tick species like Rhipicephalus, Dermacentor, and Amblyomma and diseases like Anaplasmosis and Babesiosis deserve to be better studied, and others are yet to be identified for further research. The study consists of a review of the various documents published on this theme by Haitian and foreign researchers. The data are analyzed to assess the spatiotemporal distribution of ticks and identify the pathogenic germs they harbor and the various pathologies they induce in the Caribbean and Haiti.

Epigenetic modifier SMCHD1 maintains a normal pool of long-term hematopoietic stem cells

SMCHD1 (structural maintenance of chromosomes hinge domain containing 1) is a noncanonical SMC protein that mediates long-range repressive chromatin structures. SMCHD1 is required for X chromosome inactivation in female cells and repression of imprinted and clustered autosomal genes, with SMCHD1 mutations linked to human diseases facioscapulohumeral muscular dystrophy (FSHD) and bosma arhinia and micropthalmia syndrome (BAMS). We used a conditional mouse model to investigate SMCHD1 in hematopoiesis. Smchd1-deleted mice maintained steady-state hematopoiesis despite showing an impaired reconstitution capacity in competitive bone marrow transplantations and age-related hematopoietic stem cell (HSC) loss. This phenotype was more pronounced in Smchd1-deleted females, which showed a loss of quiescent HSCs and fewer B cells. Gene expression profiling of Smchd1-deficient HSCs and B cells revealed known and cell-type-specific SMCHD1-sensitive genes and significant disruption to X-linked gene expression in female cells. These data show SMCHD1 is a regulator of HSCs whose effects are more profound in females.

•

SMCHD1 is not required to maintain steady-state hematopoiesis

•

Smchd1-deletion leads to loss of adult hematopoietic stem cells

•

Smchd1-deleted female mice are more severely affected than males

•

SMCHD1 maintains cellular quiescence in female hematopoietic stem cells

Antiaging Mechanism of Natural Compounds: Effects on Autophagy and Oxidative Stress

Aging is a natural biological process that manifests as the progressive loss of function in cells, tissues, and organs. Because mechanisms that are meant to promote cellular longevity tend to decrease in effectiveness with age, it is no surprise that aging presents as a major risk factor for many diseases such as cardiovascular disease, neurodegenerative disorders, cancer, and diabetes. Oxidative stress, an imbalance between the intracellular antioxidant and overproduction of reactive oxygen species, is known to promote the aging process. Autophagy, a major pathway for protein turnover, is considered as one of the hallmarks of aging. Given the progressive physiologic degeneration and increased risk for disease that accompanies aging, many studies have attempted to discover new compounds that may aid in the reversal of the aging process. Here, we summarize the antiaging mechanism of natural or naturally derived synthetic compounds involving oxidative stress and autophagy. These compounds include: 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO) derivatives (synthetic triterpenoids derived from naturally occurring oleanolic acid), caffeic acid phenethyl ester (CAPE, the active ingredient in honey bee propolis), xanthohumol (a prenylated flavonoid identified in the hops plant), guggulsterone (a plant steroid found in the resin of the guggul plant), resveratrol (a natural phenol abundantly found in grape), and sulforaphane (a sulfur-containing compound found in cruciferous vegetables).

TLR4 downregulation by the RNA-binding protein PUM1 alleviates cellular aging and osteoarthritis

Dysfunction of mRNA or RNA-binding proteins (RBPs) causes cellular aging and age-related degenerative diseases; however, information regarding the mechanism through which RBP-mediated posttranscriptional regulation affects cellular aging and related disease processes is limited. In this study, PUM1 was found to be associated with the self-renewal capacity and aging process of human mesenchymal stem cells (MSC). PUM1 interacted with the 3'-untranslated region of Toll-like receptor 4 (TLR4) to suppress TLR4 mRNA translation and regulate the activity of nuclear factor-κB (NF-κB), a master regulator of the aging process in MSCs. PUM1 overexpression protected MSCs against H₂O₂-induced cellular senescence by suppressing TLR4-mediated NF-κB activity. TLR4-mediated NF-κB activation is a key regulator in osteoarthritis (OA) pathogenesis. PUM1 overexpression enhanced the chondrogenic potential of MSCs even under the influence of inflammation-inducing factors, such as lipopolysaccharide (LPS) or interleukin-1β (IL-1β), whereas the chondrogenic potential was reduced following the PUM1 knockdown-mediated TLR4 activation. PUM1 levels decreased under inflammatory conditions in vitro and during OA progression in human and mouse disease models. PUM1 knockdown in human chondrocytes promoted chondrogenic phenotype loss, whereas PUM1 overexpression protected the cells from inflammation-mediated disruption of the chondrogenic phenotype. Gene therapy using a lentiviral vector encoding mouse PUM1 showed promise in preserving articular cartilage integrity in OA mouse models. In conclusion, PUM1 is a novel suppressor of MSC aging, and the PUM1-TLR4 regulatory axis represents a potential therapeutic target for OA.

Time makes histone H3 modifications drift in mouse liver

To detect the epigenetic drift of time passing, we determined the genome-wide distributions of mono- and tri-methylated lysine 4 and acetylated and tri-methylated lysine 27 of histone H3 in the livers of healthy 3, 6 and 12 months old C57BL/6 mice. The comparison of different age profiles of histone H3 marks revealed global redistribution of histone H3 modifications with time, in particular in intergenic regions and near transcription start sites, as well as altered correlation between the profiles of different histone modifications. Moreover, feeding mice with caloric restriction diet, a treatment known to retard aging, reduced the extent of changes occurring during the first year of life in these genomic regions.

Age-Related Changes in the Fibroblastic Differon of the Dermis: Role in Skin Aging

Skin aging is a multi-factorial process that affects nearly every aspect of skin biology and function. The processes developing in the skin during aging are based on fundamental molecular mechanisms associated with fibroblasts, the main cellular population of the dermis. It has been revealed that the amount of fibroblasts decreases markedly with age and their functional activity is also reduced. This inevitably leads to a decrease in the regenerative abilities of the skin and the progression of its aging. In this review we consider the mechanisms underlying these processes, mainly the changes observed with age in the stem/progenitor cells that constitute the fibroblastic differon of the dermis and form their microenvironment (niches). These changes lead to the depletion of stem cells, which, in turn, leads to a decrease in the number of differentiated (mature) dermal fibroblasts responsible for the production of the dermal extracellular matrix and its remodeling. We also describe in detail DNA damages, their cellular and systemic consequences, molecular mechanisms of DNA damage response, and also the role of fibroblast senescence in skin aging.

Extending the Lifespan of Multicellular Organisms via Periodic and Stochastic Intercellular Competition

Resolution of the intrinsic conflict between the reproduction of single cells and the homeostasis of a multicellular organism is central to animal biology and has direct impact on aging and cancer. Intercellular competition is indispensable in multicellular organisms because it weeds out senescent cells, thereby increasing the organism's fitness and delaying aging. In this Letter, we describe the growth dynamics of multicellular organisms in the presence of intercellular competition and show that the lifespan of organisms can be extended and the onset of cancer can be delayed if cells alternate between competition (a fair strategy) and noncompetitive growth, or cooperation (a losing strategy). This effect recapitulates the weak form of the game-theoretic Parrondo's paradox, whereby strategies that are individually fair or losing achieve a winning outcome when alternated. We show in a population model that periodic and stochastic switching between competitive and cooperative cellular strategies substantially extends the organism lifespan and reduces cancer incidence, which cannot be achieved simply by optimizing the competitive ability of the cells. These results indicate that cells could have evolved to optimally mix competitive and cooperative strategies, and that periodic intercellular competition could potentially be exploited and tuned to delay aging.

Drosophila renal stem cells enhance fitness by delayed remodeling of adult Malpighian tubules

Drosophila renal stem cells (RSCs) contradict the common expectation that stem cells maintain tissue homeostasis. RSCs are abundant, quiescent, and confined to the peri-ureter region of the kidney-like Malpighian tubules (MTs). Although derived during pupation-like intestinal stem cells, RSCs initially remodel the larval MTs only near the intestinal junction. However, following adult injury to the ureter by xanthine stones, RSCs remodel the damaged region in a similar manner. Thus, RSCs represent stem cells encoding a developmental redesign. The remodeled tubules have a larger luminal diameter and shorter brush border, changes linked to enhanced stone resistance. However, RSC-mediated modifications also raise salt sensitivity and reduce fecundity. Our results suggest that RSCs arose by arresting developmental progenitors to preserve larval physiology until a time in adulthood when it becomes advantageous to complete the development by RSC activation.

Single-cell transcriptomics identifies premature aging features of TERC-deficient mouse brain and bone marrow

Aging is a progressive loss of physiological function and increased susceptibility to major pathologies. Degenerative diseases in both brain and bone including Alzheimer disease (AD) and osteoporosis are common in aging groups. TERC is RNA component of telomerase, and its deficiency accelerates aging-related phenotypes including impaired life span, organ failure, bone loss, and brain dysfunction. In this study, we investigated the traits of bone marrow-brain cross-tissue communications in young mice, natural aging mice, and premature aging (TERC deficient, TERC-KO) mice by single-cell transcriptome sequencing. Differentially expressed gene analysis of brain as well as bone marrow between premature aging mouse and young mouse demonstrated aging-related inflammatory response and suppression of neuron development. Further analysis of senescence-associated secretory phenotype (SASP) landscape indicated that TERC-KO perturbation was enriched in oligodendrocyte progenitor cells (OPCs) and hematopoietic stem and progenitor cells (HSPC). Series of inflammatory associated myeloid cells was activated in premature aging mice brain and bone marrow. Cross-tissue comparison of TERC-KO mice brain and bone marrow illustrated obvious ligand-receptor communications between brain glia cells, macrophages, and bone marrow myeloid cells in premature aging-induced inflammation. Enrichment of co-regulation modules between brain and bone marrow identified premature aging response genes such as Dusp1 and Ifitm3. Our study provides a rich resource for understanding premature aging-associated perturbation in brain and bone marrow and supporting myeloid cells and endothelial cells as promising therapy targeting for age-related brain-bone diseases.

Single-cell transcriptomics reveals age-resistant maintenance of cell identities, stem cell compartments and differentiation trajectories in long-lived naked mole-rats skin

Naked mole-rats (NMR) are subterranean rodents characterized by an unusual longevity coupled with an unexplained resistance to aging. In the present study, we performed extensive in situ analysis and single-cell RNA-sequencing comparing young and older animals. At variance with other species, NMR exhibited a striking stability of skin compartments and cell types, which remained stable over time without aging-associated changes. Remarkably, the number of stem cells was constant throughout aging. We found three classical cellular states defining a unique keratinocyte differentiation trajectory that were not altered after pseudo-temporal reconstruction. Epidermal gene expression did not change with aging either. Langerhans cell clusters were conserved, and only a higher basal stem cell expression of Igfbp3 was found in aged animals. In accordance, NMR skin healing closure was similar in young and older animals. Altogether, these results indicate that NMR skin is characterized by peculiar genetic and cellular features, different from those previously demonstrated for mice and humans. The remarkable stability of the aging NMR skin transcriptome likely reflects unaltered homeostasis and resilience.

Oxysterols are potential physiological regulators of ageing

Delaying and even reversing ageing is a major public health challenge with a tremendous potential to postpone a plethora of diseases including cancer, metabolic syndromes and neurodegenerative disorders. A better understanding of ageing as well as the development of innovative anti-ageing strategies are therefore an increasingly important field of research. Several biological processes including inflammation, proteostasis, epigenetic, oxidative stress, stem cell exhaustion, senescence and stress adaptive response have been reported for their key role in ageing. In this review, we describe the relationships that have been established between cholesterol homeostasis, in particular at the level of oxysterols, and ageing. Initially considered as harmful pro-inflammatory and cytotoxic metabolites, oxysterols are currently emerging as an expanding family of fine regulators of various biological processes involved in ageing. Indeed, depending of their chemical structure and their concentration, oxysterols exhibit deleterious or beneficial effects on inflammation, oxidative stress and cell survival. In addition, stem cell differentiation, epigenetics, cellular senescence and proteostasis are also modulated by oxysterols. Altogether, these data support the fact that ageing is influenced by an oxysterol profile. Further studies are thus required to explore more deeply the impact of the "oxysterome" on ageing and therefore this cholesterol metabolic pathway constitutes a promising target for future anti-ageing interventions.

Biology of aging: Oxidative stress and RNA oxidation

The prevalence of aged people has increased rapidly in recent years and brings profound demographic changes worldwide. The multi-level progression of aging occurs at diverse stages of complexity, from cell to organ systems and eventually to the human as a whole. The cellular and molecular damages are usually regulated by the cells; repair or degrade mechanisms. However, these mechanisms are not entirely functional; their effectiveness decreases with age due to influence from endogenous sources like oxidative stress, which all contribute to the aging process. The hunt for novel strategies to increase the man's longevity since ancient times needs better understandings of the biology of aging, oxidative stress, and their roles in RNA oxidation. The critical goal in developing new strategies to increase the man's longevity is to compile the novel developed knowledge on human aging into a single picture, preferably able to understand the biology of aging and the contributing factors. This review discusses the biology of aging, oxidative stress, and their roles in RNA oxidation, leading to aging in humans.

Combined use of chitosan-PGLA nerve grafts and bone marrow mononuclear cells to repair a 50-mm-long median nerve defect combined with an 80-mm-long ulnar nerve defect in the human upper arm

BACKGROUND

Severe peripheral nerve injury, especially the long-distance peripheral nerve defect caused severe functional disability to patients. And there is always a lack of effective and less side effects of repair methods for clinics. A case study was performed to observe the regenerative outcomes of the surgical repair of long-distance peripheral nerve defects in the upper arm with chitosan-poly(glycolide-co-lactide) (PGLA) nerve grafts combined with bone marrow mononuclear cells (BMMCs).

METHODS

The right upper arm of a 29-year-old woman was injured, leaving a 50-mm-long median nerve defect, an 80-mm-long ulnar nerve defect, and muscle and blood vessel disruptions. The nerve defects were repaired by implanting BMMC-containing chitosan-PGA nerve grafts on the 40th day after injury. A series of functional assessments were carried out from 2 weeks to 66 months after surgical repair. Sensory function was assessed by the pinprick test, two-point discrimination test and Semmes-Weinstein monofilament test. Motor function was evaluated by the range of motion of the wrist joint and muscle power. Autonomic function was monitored by laser-Doppler perfusion imaging (LDPI). Tissue morphology was observed through ultrasonic investigations.

RESULTS

No adverse events, such as infection, allergy, or rejection, caused by the treatment were detected during the follow-up period. Sensory and pinprick nociception in the affected thumb, index, and middle fingers were restored gradually from the 6th month after surgery. The monofilament tactile sensation was 0.4 g in the terminal finger pulp of the thumb and index finger, 2.0 g in the middle finger, and greater than 300 g in the ring finger and little finger at the 66th month. Motor function recovery was detected at the 5th month after surgery, when the muscle strength of the affected forearm flexors began to recover. At the 66th month after surgery, the patient's forearm flexor strength was grade 4, with 80° of palmar flexion, 85° of dorsal extension, 8° of radial deviation, 40° of ulnar deviation, 40° of anterior rotation, and 85° of posterior rotation of the affected wrist. The patient could perform holding, picking up, and some other daily activities with the affected hand. The patient's sweating function of the affected hand was close to the level of the healthy hand. LDPI showed that the skin blood flow perfusion was significantly increased, with perfusion similar to on the normal side in some areas. Neuromusculoskeletal ultrasonography showed the presence of nerve structures.

CONCLUSIONS

These results suggest that chitosan-PGLA nerve grafts combined with BMMCs could effectively repair long-distance nerve defects and achieve good clinical results.

Cellular senescence, rejuvenation and potential immortality

Ageing, death, and potential immortality lie at the heart of biology, but two seemingly incompatible paradigms coexist in different research communities and have done since the nineteenth century. The universal senescence paradigm sees senescence as inevitable in all cells. Damage accumulates. The potential immortality paradigm sees some cells as potentially immortal, especially unicellular organisms, germ cells and cancerous cells. Recent research with animal cells, yeasts and bacteria show that damaged cell constituents do in fact build up, but can be diluted by growth and cell division, especially by asymmetric cell division. By contrast, mammalian embryonic stem cells and many cancerous and 'immortalized' cell lines divide symmetrically, and yet replicate indefinitely. How do they acquire their potential immortality? I suggest they are rejuvenated by excreting damaged cell constituents in extracellular vesicles. If so, our understanding of cellular senescence, rejuvenation and potential immortality could be brought together in a new synthesis, which I call the cellular rejuvenation hypothesis: damaged cell constituents build up in all cells, but cells can be rejuvenated either by growth and cell division or, in 'immortal' cell lines, by excreting damaged cell constituents. In electronic supplementary material, appendix, I outline nine ways in which this hypothesis could be tested.

Clonal Hematopoiesis Analyses in Clinical, Epidemiologic, and Genetic Aging Studies to Unravel Underlying Mechanisms of Age-Related Dysfunction in Humans

Aging is characterized by increased mortality, functional decline, and exponential increases in the incidence of diseases such as cancer, stroke, cardiovascular disease, neurological disease, respiratory disease, etc. Though the role of aging in these diseases is widely accepted and considered to be a common denominator, the underlying mechanisms are largely unknown. A significant age-related feature observed in many population cohorts is somatic mosaicism, the detectable accumulation of somatic mutations in multiple cell types and tissues, particularly those with high rates of cell turnover (e.g., skin, liver, and hematopoietic cells). Somatic mosaicism can lead to the development of cellular clones that expand with age in otherwise normal tissues. In the hematopoietic system, this phenomenon has generally been referred to as "clonal hematopoiesis of indeterminate potential" (CHIP) when it applies to a subset of clones in which mutations in driver genes of hematologic malignancies are found. Other mechanisms of clonal hematopoiesis, including large chromosomal alterations, can also give rise to clonal expansion in the absence of conventional CHIP driver gene mutations. Both types of clonal hematopoiesis (CH) have been observed in studies of animal models and humans in association with altered immune responses, increased mortality, and disease risk. Studies in murine models have found that some of these clonal events are involved in abnormal inflammatory and metabolic changes, altered DNA damage repair and epigenetic changes. Studies in long-lived individuals also show the accumulation of somatic mutations, yet at this advanced age, carriership of somatic mutations is no longer associated with an increased risk of mortality. While it remains to be elucidated what factors modify this genotype-phenotype association, i.e., compensatory germline genetics, cellular context of the mutations, protective effects to diseases at exceptional age, it points out that the exceptionally long-lived are key to understand the phenotypic consequences of CHIP mutations. Assessment of the clinical significance of somatic mutations occurring in blood cell types for age-related outcomes in human populations of varied life and health span, environmental exposures, and germline genetic risk factors will be valuable in the development of personalized strategies tailored to specific somatic mutations for healthy aging.

Epigenetic alterations in stem cell ageing-a promising target for age-reversing interventions?

Ageing is accompanied by loss of tissue integrity and organismal homeostasis partly due to decline in stem cell function. The age-associated decrease in stem cell abundance and activity is often referred to as stem cell exhaustion and is considered one major hallmark of ageing. Importantly, stem cell proliferation and differentiation potential are tightly coupled to the cellular epigenetic state. Thus, research during the last years has started to investigate how the epigenome regulates stem cell function upon ageing. Here, we summarize the role of epigenetic regulation in stem cell fate decisions and we review the impact of age-related changes of the epigenome on stem cell activity. Finally, we discuss how targeted interventions on the epigenetic landscape might delay ageing and extend health-span.

Aging conundrum: A perspective for ovarian aging

Progressive loss of physiological integrity and accumulation of degenerative changes leading to functional impairment and increased susceptibility to diseases are the main features of aging. The ovary, the key organ that maintains female reproductive and endocrine function, enters aging earlier and faster than other organs and has attracted extensive attention from society. Ovarian aging is mainly characterized by the progressive decline in the number and quality of oocytes, the regulatory mechanisms of which have yet to be systematically elucidated. This review discusses the hallmarks of aging to further highlight the main characteristics of ovarian aging and attempt to explore its clinical symptoms and underlying mechanisms. Finally, the intervention strategies related to aging are elaborated, especially the potential role of stem cells and cryopreservation of embryos, oocytes, or ovarian tissue in the delay of ovarian aging.

OUP accepted manuscript

Stem cell therapies, including stem cell transplantation and rejuvenation of stem cells in situ, are promising avenues for tackling a broad range of diseases. Stem cells can both self-renew and differentiate into other cell types, and play a significant role in the regulation of tissue homeostasis and regeneration after cell degeneration or injury. However, stem cell exhaustion or dysfunction increases with age and impedes the normal function of multiple tissues and systems. Thus, stem cell therapies could provide a solution to aging and age-associated diseases. Here, we discuss recent advances in understanding the mechanisms that regulate stem cell regeneration. We also summarize potential strategies for rejuvenating stem cells that leverage intrinsic and extrinsic factors. These approaches may pave the way toward therapeutic interventions aiming at extending both health and life span.

New insights of epigenetics in vascular and cellular senescence

Vascular senescence plays a vital role in cardiovascular diseases and it is closely related to cellular senescence. At the molecular level, aging begins with a single cell, and it is characterized by telomere shortening, mitochondrial dysfunction, stem cell exhaustion, epigenetic changes, and so on. Epigenetics is an independent discipline that modifies DNA activity without altering the DNA sequence. The application of epigenetics helps to alleviate the occurrence of human diseases, inhibit senescence, and even inhibit tumor occurrence. Epigenetics mainly includes the modification of DNA, histone, and noncoding RNA. Herein, the application of epigenetics in vascular senescence and aging has been reviewed to provide the prospects and innovative inspirations for future research.

Association between Circulating Osteoprogenitor Cells and Sarcopenia

BACKGROUND

Circulating osteoprogenitor (COP) cells are a surrogate of the bone marrow mesenchymal stem cells with high levels observed in osteoporosis and the initial stages of fracture healing. Conversely, a low percentage of COP cells (%COP) is strongly associated with frailty and disability. However, it is unknown whether %COP is associated with sarcopenia, a musculoskeletal disease closely related to frailty.

OBJECTIVES

This study sought to determine the associations between %COP and sarcopenia defined using the Sarcopenia Definitions and Outcomes Consortium (SDOC) criteria.

METHODS

Data from a random sample of 73 community-dwelling older persons enrolled in the Nepean Osteoporosis and Frailty study (median age 74 years; 60% female) were analyzed. %COP was quantified by flow cytometry using selective gating of CD45/osteocalcin (OCN) + cells. Sarcopenia was defined using handgrip strength and gait speed with cut points as per the SDOC criteria. Linear regression was used for analysis.

RESULTS

Sarcopenia was identified in 19% of participants, all of whom were frail. After adjusting for age, sex, and interleukin 6, sarcopenic participants had 36% lower %COP (95% confidence interval [CI] -56%, -6%, p = 0.024). Both grip strength and gait speed showed associations with %COP (p = 0.065 and 0.002, respectively); however, after adjusting for age and frailty, only gait speed remained associated with %COP (0.1 m/s increase in gait velocity was associated with a 5% increase in %COP cells (95% CI 0%, 10%, p = 0.052).

CONCLUSIONS

High levels of %COP are associated with better muscle function. Future longitudinal studies are required to elucidate the clinical utility of %COP as a potential biomarker or disease stratifier for sarcopenia.

Why stem/progenitor cells lose their regenerative potential

Nowadays, it is clear that adult stem cells, also called as tissue stem cells, play a central role to repair and maintain the tissue in which they reside by their self-renewal ability and capacity of differentiating into distinct and specialized cells. As stem cells age, their renewal ability declines and their capacity to maintain organ homeostasis and regeneration is impaired. From a molecular perspective, these changes in stem cells properties can be due to several types of cell intrinsic injury and DNA aberrant alteration (i.e epigenomic profile) as well as changes in the tissue microenviroment, both into the niche and by systemic circulating factors. Strikingly, it has been suggested that aging-induced deterioration of stem cell functions may play a key role in the pathophysiology of the various aging-associated disorders. Therefore, understanding how resident stem cell age and affects near and distant tissues is fundamental. Here, we examine the current knowledge about aging mechanisms in several kinds of adult stem cells under physiological and pathological conditions and the principal aging-related changes in number, function and phenotype that determine the loss of tissue renewal properties. Furthermore, we examine the possible cell rejuvenation strategies. Stem cell rejuvenation may reverse the aging phenotype and the discovery of effective methods for inducing and differentiating pluripotent stem cells for cell replacement therapies could open up new possibilities for treating age-related diseases.

Altered Chromatin States Drive Cryptic Transcription in Aging Mammalian Stem Cells

A repressive chromatin state featuring trimethylated lysine 36 on histone H3 (H3K36me3) and DNA methylation suppresses cryptic transcription in embryonic stem cells. Cryptic transcription is elevated with age in yeast and nematodes, and reducing it extends yeast lifespan, though whether this occurs in mammals is unknown. We show that cryptic transcription is elevated in aged mammalian stem cells, including murine hematopoietic stem cells (mHSCs) and neural stem cells (NSCs) and human mesenchymal stem cells (hMSCs). Precise mapping allowed quantification of age-associated cryptic transcription in hMSCs aged in vitro. Regions with significant age-associated cryptic transcription have a unique chromatin signature: decreased H3K36me3 and increased H3K4me1, H3K4me3, and H3K27ac with age. Genomic regions undergoing such changes resemble known promoter sequences and are bound by TBP even in young cells. Hence, the more permissive chromatin state at intragenic cryptic promoters likely underlies increased cryptic transcription in aged mammalian stem cells.

A stress-induced miR-31-CLOCK-ERK pathway is a key driver and therapeutic target for skin aging

Regressive changes in epithelial stem cells underlie mammalian skin aging, but the driving mechanisms are not well understood. Here, we report that mouse skin hair follicle stem cell (HFSC) aging is initiated by their intrinsic upregulation of miR-31, a microRNA that can be induced by physical injury or genotoxic stress and is also strongly upregulated in aged human skin epithelium. Using transgenic and conditional knockout mouse models plus a lineage-tracing technique, we show that miR-31 acts as a key driver of HFSC aging by directly targeting Clock, a core circadian clock gene whose deregulation activates a MAPK/ERK cascade to induce HFSC depletion via transepidermal elimination. Notably, blocking this pathway by either conditional miR-31 ablation or clinically approved MAPK/ERK inhibitors provides safe and effective protection against skin aging, enlightening a promising therapeutic avenue for treating skin aging and other genotoxic stress-induced skin conditions such as radiodermatitis.

Rejuvenation of Senescent Bone Marrow Mesenchymal Stromal Cells by Pulsed Triboelectric Stimulation

Stem cell senescence contributes to stem cell exhaustion and drives various aging-associated disorders. However, strategies to rejuvenate senescent stem cells are limited. The present study proposes an approach based on triboelectric stimulation to rejuvenate senescent bone marrow mesenchymal stromal cells (BMSCs) by fabricating a pulsed triboelectric nanogenerator (P-TENG) that can produce stable pulsed current output unaffected by the triggered frequency. The senescence phenotypes of aged BMSCs are reversed by triboelectric stimulation at 30 µA at 1.5 Hz. Triboelectric stimulation enhances the proliferation of aged BMSCs and increases their pluripotency and differentiation capacity. Additionally, mechanistic investigations reveal that pulsed triboelectric stimulation by P-TENG rejuvenates senescent BMSCs by enhancing MDM2-dependent p53 degradation, which is demonstrated by loss-of-function studies of MDM2 and p53. Overall, this study identifies a new approach for the rejuvenation of senescent BMSCs and describes a promising therapeutic intervention for many diseases associated with aged BMSCs.

Regeneration, Rejuvenation, and Replacement: Turning Back the Clock on Tissue Aging

While some animals, such as planaria and hydra, appear to be capable of seemingly endless cycles of regeneration, most animals experience a gradual decline in fitness and ultimately die. The progressive loss of cell and tissue function, leading to senescence and death, is generally referred to as aging. Adult ("tissue") stem cells maintain tissue homeostasis and facilitate repair; however, age-related changes in stem cell function over time are major contributors to loss of organ function or disease in older individuals. Therefore, considerable effort is being invested in restoring stem cell function to counter degenerative diseases and age-related tissue dysfunction. Here, we will review strategies that could be used to restore stem cell function, including the use of environmental interventions, such as diet and exercise, heterochronic approaches, and cellular reprogramming. Maintaining optimal stem cell function and tissue homeostasis into late life will likely extend the amount of time older adults are able to be independent and lead healthy lives.

The Use of Stem Cell-Derived Organoids in Disease Modeling: An Update

Organoids represent one of the most important advancements in the field of stem cells during the past decade. They are three-dimensional in vitro culturing models that originate from self-organizing stem cells and can mimic the in vivo structural and functional specificities of body organs. Organoids have been established from multiple adult tissues as well as pluripotent stem cells and have recently become a powerful tool for studying development and diseases in vitro, drug screening, and host-microbe interaction. The use of stem cells-that have self-renewal capacity to proliferate and differentiate into specialized cell types-for organoids culturing represents a major advancement in biomedical research. Indeed, this new technology has a great potential to be used in a multitude of fields, including cancer research, hereditary and infectious diseases. Nevertheless, organoid culturing is still rife with many challenges, not limited to being costly and time consuming, having variable rates of efficiency in generation and maintenance, genetic stability, and clinical applications. In this review, we aim to provide a synopsis of pluripotent stem cell-derived organoids and their use for disease modeling and other clinical applications.

UTX maintains the functional integrity of the murine hematopoietic system by globally regulating aging-associated genes

Epigenetic regulation is essential for the maintenance of the hematopoietic system, and its deregulation is implicated in hematopoietic disorders. In this study, UTX, a demethylase for lysine 27 on histone H3 (H3K27) and a component of COMPASS-like and SWI/SNF complexes, played an essential role in the hematopoietic system by globally regulating aging-associated genes. Utx-deficient (UtxΔ/Δ) mice exhibited myeloid skewing with dysplasia, extramedullary hematopoiesis, impaired hematopoietic reconstituting ability, and increased susceptibility to leukemia, which are the hallmarks of hematopoietic aging. RNA-sequencing (RNA-seq) analysis revealed that Utx deficiency converted the gene expression profiles of young hematopoietic stem-progenitor cells (HSPCs) to those of aged HSPCs. Utx expression in hematopoietic stem cells declined with age, and UtxΔ/Δ HSPCs exhibited increased expression of an aging-associated marker, accumulation of reactive oxygen species, and impaired repair of DNA double-strand breaks. Pathway and chromatin immunoprecipitation analyses coupled with RNA-seq data indicated that UTX contributed to hematopoietic homeostasis mainly by maintaining the expression of genes downregulated with aging via demethylase-dependent and -independent epigenetic programming. Of note, comparison of pathway changes in UtxΔ/Δ HSPCs, aged muscle stem cells, aged fibroblasts, and aged induced neurons showed substantial overlap, strongly suggesting common aging mechanisms among different tissue stem cells.

Beneficial Effects of Exogenous Ketogenic Supplements on Aging Processes and Age-Related Neurodegenerative Diseases

Life expectancy of humans has increased continuously up to the present days, but their health status (healthspan) was not enhanced by similar extent. To decrease enormous medical, economical and psychological burden that arise from this discrepancy, improvement of healthspan is needed that leads to delaying both aging processes and development of age-related diseases, thereby extending lifespan. Thus, development of new therapeutic tools to alleviate aging processes and related diseases and to increase life expectancy is a topic of increasing interest. It is widely accepted that ketosis (increased blood ketone body levels, e.g., β-hydroxybutyrate) can generate neuroprotective effects. Ketosis-evoked neuroprotective effects may lead to improvement in health status and delay both aging and the development of related diseases through improving mitochondrial function, antioxidant and anti-inflammatory effects, histone and non-histone acetylation, β-hydroxybutyrylation of histones, modulation of neurotransmitter systems and RNA functions. Administration of exogenous ketogenic supplements was proven to be an effective method to induce and maintain a healthy state of nutritional ketosis. Consequently, exogenous ketogenic supplements, such as ketone salts and ketone esters, may mitigate aging processes, delay the onset of age-associated diseases and extend lifespan through ketosis. The aim of this review is to summarize the main hallmarks of aging processes and certain signaling pathways in association with (putative) beneficial influences of exogenous ketogenic supplements-evoked ketosis on lifespan, aging processes, the most common age-related neurodegenerative diseases (Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis), as well as impaired learning and memory functions.

SIRT3 consolidates heterochromatin and counteracts senescence

Sirtuin 3 (SIRT3) is an NAD⁺-dependent deacetylase linked to a broad range of physiological and pathological processes, including aging and aging-related diseases. However, the role of SIRT3 in regulating human stem cell homeostasis remains unclear. Here we found that SIRT3 expression was downregulated in senescent human mesenchymal stem cells (hMSCs). CRISPR/Cas9-mediated depletion of SIRT3 led to compromised nuclear integrity, loss of heterochromatin and accelerated senescence in hMSCs. Further analysis indicated that SIRT3 interacted with nuclear envelope proteins and heterochromatin-associated proteins. SIRT3 deficiency resulted in the detachment of genomic lamina-associated domains (LADs) from the nuclear lamina, increased chromatin accessibility and aberrant repetitive sequence transcription. The re-introduction of SIRT3 rescued the disorganized heterochromatin and the senescence phenotypes. Taken together, our study reveals a novel role for SIRT3 in stabilizing heterochromatin and counteracting hMSC senescence, providing new potential therapeutic targets to ameliorate aging-related diseases.

Loosening chromatin and dysregulated transcription: a perspective on cryptic transcription during mammalian aging

Cryptic transcription, the initiation of transcription from non-promoter regions within a gene body, is a type of transcriptional dysregulation that occurs throughout eukaryotes. In mammals, cryptic transcription is normally repressed at the level of chromatin, and this process is increased upon perturbation of complexes that increase intragenic histone H3 lysine 4 methylation or decrease intragenic H3 lysine 36 methylation, DNA methylation, or nucleosome occupancy. Significantly, similar changes to chromatin structure occur during aging, and, indeed, recent work indicates that cryptic transcription is elevated during aging in mammalian stem cells. Although increased cryptic transcription is known to promote aging in yeast, whether elevated cryptic transcription also contributes to mammalian aging is unclear. There is ample evidence that perturbations known to increase cryptic transcription are deleterious in embryonic and adult stem cells, and in some cases phenocopy certain aging phenotypes. Furthermore, an increase in cryptic transcription requires or impedes pathways that are known to have reduced function during aging, potentially exacerbating other aging phenotypes. Thus, we propose that increased cryptic transcription contributes to mammalian stem cell aging.