De-regulated expression of the BRG1 chromatin remodeling factor in bone marrow mesenchymal stromal cells induces senescence associated with the silencing of NANOG and changes in the levels of chromatin proteins

Epigenetic regulations of cellular senescence in osteoporosis

Osteoporosis (OP) is a prevalent age-related disease that is characterized by a decrease in bone mineral density (BMD) and systemic bone microarchitectural disorders. With age, senescent cells accumulate and exhibit the senescence-associated secretory phenotype (SASP) in bone tissue, leading to the imbalance of bone homeostasis, osteopenia, changes in trabecular bone structure, and increased bone fragility. Cellular senescence in the bone microenvironment involves osteoblasts, osteoclasts, and bone marrow mesenchymal stem cells (BMSCs), whose effects on bone homeostasis are regulated by epigenetics. Therefore, the epigenetic regulatory mechanisms of cellular senescence have received considerable attention as potential targets for preventing and treating osteoporosis. In this paper, we systematically review the mechanisms of aging-associated epigenetic regulation in osteoporosis, emphasizing the impact of epigenetics on cellular senescence, and summarize three current methods of targeting cellular senescence, which is helpful better to understand the pathogenic mechanisms of cellular senescence in osteoporosis and provides strategies for the development of epigenetic drugs for the treatment of osteoporosis.

Regulation Mechanisms and Maintenance Strategies of Stemness in Mesenchymal Stem Cells

Stemness pertains to the intrinsic ability of mesenchymal stem cells (MSCs) to undergo self-renewal and differentiate into multiple lineages, while simultaneously impeding their differentiation and preserving crucial differentiating genes in a state of quiescence and equilibrium. Owing to their favorable attributes, including uncomplicated isolation protocols, ethical compliance, and ease of procurement, MSCs have become a focal point of inquiry in the domains of regenerative medicine and tissue engineering. As age increases or ex vivo cultivation is prolonged, the functionality of MSCs decreases and their stemness gradually diminishes, thereby limiting their potential therapeutic applications. Despite the existence of several uncertainties surrounding the comprehension of MSC stemness, considerable advancements have been achieved in the clarification of the potential mechanisms that lead to stemness loss, as well as the associated strategies for stemness maintenance. This comprehensive review provides a systematic overview of the factors influencing the preservation of MSC stemness, the molecular mechanisms governing it, the strategies for its maintenance, and the therapeutic potential associated with stemness. Finally, we underscore the obstacles and prospective avenues in present investigations, providing innovative perspectives and opportunities for the preservation and therapeutic utilization of MSC stemness.

Epigenetic regulation of mesenchymal stem cell aging through histone modifications

Stem cell senescence and exhaustion, a hallmark of aging, lead to declines in tissue repair and regeneration in aged individuals. Emerging evidence has revealed that epigenetic regulation plays critical roles in the self-renew, lineage-commitment, survival, and function of stem cells. Moreover, epigenetic alterations are considered important drivers of stem cell dysfunction during aging. In this review, we focused on current knowledge of the histone modifications in the aging of mesenchymal stem cells (MSCs). The aberrant epigenetic modifications on histones, including methylation and acetylation, have been found in aging MSCs. By disturbing the expression of specific genes, these epigenetic modifications affect the self-renew, survival, and differentiation of MSCs. A set of epigenetic enzymes that write or erase these modifications are critical in regulating the aging of MSCs. Furthermore, we discussed the rejuvenation strategies based on epigenetics to prevent stem cell aging and/or rejuvenate senescent MSCs.

Impact of Environmental and Epigenetic Changes on Mesenchymal Stem Cells during Aging

Many crucial epigenetic changes occur during early skeletal development and throughout life due to aging, disease and are heavily influenced by an individual’s lifestyle. Epigenetics is the study of heritable changes in gene expression as the result of changes in the environment without any mutation in the underlying DNA sequence. The epigenetic profiles of cells are dynamic and mediated by different mechanisms, including histone modifications, non-coding RNA-associated gene silencing and DNA methylation. Given the underlining role of dysfunctional mesenchymal tissues in common age-related skeletal diseases such as osteoporosis and osteoarthritis, investigations into skeletal stem cells or mesenchymal stem cells (MSC) and their functional deregulation during aging has been of great interest and how this is mediated by an evolving epigenetic landscape. The present review describes the recent findings in epigenetic changes of MSCs that effect growth and cell fate determination in the context of aging, diet, exercise and bone-related diseases.

Senotherapeutics for mesenchymal stem cell senescence and rejuvenation

Mesenchymal stem cells (MSCs) are susceptible to replicative senescence and senescence-associated functional decline, which hampers their use in regenerative medicine. Senotherapeutics are drugs that target cellular senescence through senolytic and senomorphic functions to induce apoptosis and suppress chronic inflammation caused by the senescence-associated secreted phenotype (SASP), respectively. Therefore, senotherapeutics could delay aging-associated degeneration. They could also be used to eliminate senescent MSCs during in vitro expansion or bioprocessing for transplantation. In this review, we discuss the role of senotherapeutics in MSC senescence, rejuvenation, and transplantation, with examples of some tested compounds in vitro. The prospects, challenges, and the way forward in clinical applications of senotherapeutics in cell-based therapeutics are also discussed.

Molecular Crosstalk between Chromatin Remodeling and Tumor Microenvironment in Multiple Myeloma

Multiple myeloma (MM) is a complex disease driven by numerous genetic and epigenetic alterations that are acquired over time. Despite recent progress in the understanding of MM pathobiology and the availability of innovative drugs, which have pronounced clinical outcome, this malignancy eventually progresses to a drug-resistant lethal stage and, thus, novel therapeutic drugs/models always play an important role in effective management of MM. Modulation of tumor microenvironment is one of the hallmarks of cancer biology, including MM, which affects the myeloma genomic architecture and disease progression subtly through chromatin modifications. The bone marrow niche has a prime role in progression, survival, and drug resistance of multiple myeloma cells. Therefore, it is important to develop means for targeting the ecosystem between multiple myeloma bone marrow microenvironment and chromatin remodeling. Extensive gene expression profile analysis has indeed provided the framework for new risk stratification of MM patients and identifying novel molecular targets and therapeutics. However, key tumor microenvironment factors/immune cells and their interactions with chromatin remodeling complex proteins that drive MM cell growth and progression remain grossly undefined.

The Mechanism of Stem Cell Aging

Stem cells have self-renewal ability and multi-directional differentiation potential. They have tissue repair capabilities and are essential for maintaining the tissue homeostasis. The depletion of stem cells is closely related to the occurrence of body aging and aging-related diseases. Therefore, revealing the molecular mechanisms of stem cell aging will set new directions for the therapeutic application of stem cells, the study of aging mechanisms, and the prevention and treatment of aging-related diseases. This review comprehensively describes the molecular mechanisms related to stem cell aging and provides the basis for further investigations aimed at developing new anti-stem cell aging strategies and promoting the clinical application of stem cells.

Cyclic DNA remethylation following active demethylation at euchromatic regions in mouse embryonic stem cells

DNA methylation is an essential epigenetic mark that regulates normal mammalian embryonic development. DNA methylation profiles are not always static, especially during germline development. In zygotes, DNA is typically highly methylated but, during preimplantation, DNA methylation is erased globally. Then, at the start of post-implantation development in mouse embryos, DNA again becomes dramatically hypermethylated. Chromatin structure regulates the accessibility of DNA-modifying enzymes to target DNA. Beyond that, however, our understanding of the pathway by which chromatin regulation initiates changes in global DNA methylation during mouse embryonic development remains incomplete. To analyse the relationship between global regulation of DNA methylation and chromatin status, we examined 5-methylcytosine (5mC), modified by the DNA methyltransferase DNMT, and the oxidative derivative 5-hydroxymethylation (5hmC), converted from 5mC by TET-family enzymes, by means of immunofluorescence staining of mitotic chromosomes in mouse embryonic stem cells (ESCs). Our comparison of immunostaining patterns for those epigenetic modifications in wild-type, DNMT-deficient, and TET-deficient ESCs allowed us to visualise cell cycle-mediated DNA methylation changes, especially in euchromatic regions. Our findings suggest that DNA methylation patterns in undifferentiated mouse ESCs are stochastically balanced by the opposing effects of two activities: demethylation by TET and subsequent remethylation by DNMT.

ATP-Dependent Chromatin Remodeling Complex in the Lineage Specification of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) present in multiple tissues can self-renew and differentiate into multiple lineages including the bone, cartilage, muscle, cardiac tissue, and connective tissue. Key events, including cell proliferation, lineage commitment, and MSC differentiation, are ensured by precise gene expression regulation. ATP-dependent chromatin alteration is one form of epigenetic modifications that can regulate the transcriptional level of specific genes by utilizing the energy from ATP hydrolysis to reorganize chromatin structure. ATP-dependent chromatin remodeling complexes consist of a variety of subunits that together perform multiple functions in self-renewal and lineage specification. This review highlights the important role of ATP-dependent chromatin remodeling complexes and their different subunits in modulating MSC fate determination and discusses the proposed mechanisms by which ATP-dependent chromatin remodelers function.

ATP-dependent chromatin remodelers in ageing and age-related disorders

Ageing is characterized by the perturbation in cellular homeostasis associated with genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion and altered intracellular communication. Changes in the epigenome represent one of the crucial mechanisms during ageing and in age-related disorders. The ATP-dependent chromatin remodelers are an evolutionarily conserved family of nucleosome remodelling factors and generally regulate DNA repair, replication, recombination, transcription and cell cycle. Here, we review the chromatin based epigenetic changes that occur in ageing and age-related disorders with a specific reference to chromatin remodelers. We also discuss the link between dietary restriction and chromatin remodelers in regulating age-related processes with a view for consideration in future intervention studies.

Heat Shock Alters Mesenchymal Stem Cell Identity and Induces Premature Senescence

Heat stress can have a serious impact on the health of both humans and animals. A major question is how heat stress affects normal development and differentiation at both the cellular and the organism levels. Here we use an in vitro experimental system to address how heat shock treatment influences the properties of bovine mesenchymal stem cells (MSCs)—multipotent progenitor cells—which are found in most tissues. Because cattle are sensitive to harsh external temperatures, studying the effects of heat shock on MSCs provides a unique platform to address cellular stress in a physiologically relevant model organism. Following isolation and characterization of MSCs from the cow’s umbilical cord, heat shock was induced either as a pulse (1 h) or continuously (3 days), and consequent effects on MSCs were characterized. Heat shock induced extensive phenotypic changes in MSCs and dramatically curtailed their capacity to proliferate and differentiate. These changes were associated with a partial arrest in the G1/S or G2/M checkpoints. Furthermore, MSCs lost their ability to resolve the inflammatory response of RAW macrophages in coculture. A possible explanation for this loss of function is the accumulation of reactive oxygen species and malfunction of the mitochondria in the treated cells. Heat shock treatments resulted in stress-induced premature senescence, affecting the MSCs’ ability to proliferate properly for many cell passages to follow. Exposure to elevated external temperatures leads to mitochondrial damage and oxidative stress, which in turn conveys critical changes in the proliferation, differentiation, and immunomodulatory phenotype of heat-stressed MSCs. A better understanding of the effect of heat shock on humans and animals may result in important health and economic benefits.

Epigenetic Regulation in Mesenchymal Stem Cell Aging and Differentiation and Osteoporosis

Mesenchymal stem cells (MSCs) are a reliable source for cell-based regenerative medicine owing to their multipotency and biological functions. However, aging-induced systemic homeostasis disorders in vivo and cell culture passaging in vitro induce a functional decline of MSCs, switching MSCs to a senescent status with impaired self-renewal capacity and biased differentiation tendency. MSC functional decline accounts for the pathogenesis of many diseases and, more importantly, limits the large-scale applications of MSCs in regenerative medicine. Growing evidence implies that epigenetic mechanisms are a critical regulator of the differentiation programs for cell fate and are subject to changes during aging. Thus, we here review epigenetic dysregulations that contribute to MSC aging and osteoporosis. Comprehending detailed epigenetic mechanisms could provide us with a novel horizon for dissecting MSC-related pathogenesis and further optimizing MSC-mediated regenerative therapies.

Senescence in Mesenchymal Stem Cells: Functional Alterations, Molecular Mechanisms, and Rejuvenation Strategies

Mesenchymal stem cells (MSCs) are multipotent cells capable of self-renewal and differentiation. There is increasing evidence of the therapeutic value of MSCs in various clinical situations, however, these cells gradually lose their regenerative potential with age, with a concomitant increase in cellular dysfunction. Stem cell aging and replicative exhaustion are considered as hallmarks of aging and functional attrition in organisms. MSCs do not proliferate infinitely but undergo only a limited number of population doublings before becoming senescent. This greatly hinders their clinical application, given that cultures must be expanded to obtain a sufficient number of cells for cell-based therapy. Here, we review the current knowledge of the phenotypic and functional characteristics of senescent MSCs, molecular mechanisms underlying MSCs aging, and strategies to rejuvenate senescent MSCs, which can broaden their range of therapeutic applications.

Molecular Mechanisms Contributing to Mesenchymal Stromal Cell Aging

Mesenchymal stem/stromal cells (MSCs) are a reservoir for tissue homeostasis and repair that age during organismal aging. Beside the fundamental in vivo role of MSCs, they have also emerged in the last years as extremely promising therapeutic agents for a wide variety of clinical conditions. MSC use frequently requires in vitro expansion, thus exposing cells to replicative senescence. Aging of MSCs (both in vivo and in vitro) can affect not only their replicative potential, but also their properties, like immunomodulation and secretory profile, thus possibly compromising their therapeutic effect. It is therefore of critical importance to unveil the underlying mechanisms of MSC senescence and to define shared methods to assess MSC aging status. The present review will focus on current scientific knowledge about MSC aging mechanisms, control and effects, including possible anti-aging treatments.

Rapid Detection of Senescent Mesenchymal Stromal Cells by a Fluorescent Probe

Despite intense interest in human mesenchymal stromal cells (MSCs), monitoring of the progressive occurrence of senescence has been hindered by the lack of efficient detection tools. Here, the discovery of a novel MSC senescence-specific fluorescent probe (CyBC9) identified by a high-throughput screen is reported. Compared with the prototypical senescence-associated β-galactosidase (SA-β-gal) staining, the CyBC9 assay is rapid (2 h) and nontoxic and can thus be applied to live cells. It is shown that CyBC9 is able to stain early and late senescent populations both in monolayer- and in microcarrier-based cultures. Finally, to investigate the mechanism of CyBC9, colocalization assays are performed and it is found that CyBC9 is accumulated in the mitochondria of senescent MSCs presumably due to the loss of membrane potential. Taken together, it is expected that CyBC9 will be a useful tool to ameliorate cell therapy through rapid and early screening of senescent phenotypes in clinically relevant MSCs.

Senescence Phenomena and Metabolic Alteration in Mesenchymal Stromal Cells from a Mouse Model of Rett Syndrome

Chromatin modifiers play a crucial role in maintaining cell identity through modulation of gene expression patterns. Their deregulation can have profound effects on cell fate and functions. Among epigenetic regulators, the MECP2 protein is particularly attractive. Mutations in the Mecp2 gene are responsible for more than 90% of cases of Rett syndrome (RTT), a progressive neurodevelopmental disorder. As a chromatin modulator, MECP2 can have a key role in the government of stem cell biology. Previously, we showed that deregulated MECP2 expression triggers senescence in mesenchymal stromal cells (MSCs) from (RTT) patients. Over the last few decades, it has emerged that senescent cells show alterations in the metabolic state. Metabolic changes related to stem cell senescence are particularly detrimental, since they contribute to the exhaustion of stem cell compartments, which in turn determine the falling in tissue renewal and functionality. Herein, we dissect the role of impaired MECP2 function in triggering senescence along with other senescence-related aspects, such as metabolism, in MSCs from a mouse model of RTT. We found that MECP2 deficiencies lead to senescence and impaired mitochondrial energy production. Our results support the idea that an alteration in mitochondria metabolic functions could play an important role in the pathogenesis of RTT.

Chromatin remodeling gene ARID2 targets cyclin D1 and cyclin E1 to suppress hepatoma cell progression

Exome and whole-genome sequencing studies have drawn attention to the role of somatic mutations in SWI/SNF chromatin remodeling complexes in the carcinogenesis of hepatocellular carcinoma (HCC). Here, we explored the molecular mechanisms underlying the biological roles of AT-rich interactive domain 2 (ARID2) in the pathogenesis of HCC. We found that ARID2 expression was significantly downregulated in HCC tissues compared with non-tumorous tissues. Restoration of ARID2 expression in hepatoma cells was sufficient to suppress cell proliferation and tumor growth in mice, whereas ARID2 knockdown contributed to the enhancement of cellular proliferation and tumorigenicity. Suppression of ARID2 expression accelerated G1/S transition associated with upregulation of cyclin D1, cyclin E1, CDK4, and phosphorylation of the retinoblastoma protein (Rb). Furthermore, we demonstrated that ARID2 physically interacts with E2F1 and decreases binding of E2F1/RNA Pol II to the promoters of CCND1 and CCNE1. Taken together, these results demonstrate that ARID2 suppresses tumor cell growth through repression of cyclin D1 and cyclin E1 expression, thereby retarding cell cycle progression and cell proliferation in hepatoma cells. These findings highlight the potential role of ARID2 as a tumor growth suppressor in HCC.

SATB2-Nanog axis links age-related intrinsic changes of mesenchymal stem cells from craniofacial bone

Bone mesenchymal stem cells (BMSCs) senescence contributes to age-related bone loss. The alveolar bone in jaws originates from neural crest cells and possesses significant site- and age-related properties. However, such intrinsic characteristics of BMSCs from alveolar bone (AB-BMSCs) and the underlying regulatory mechanisms still remain unknown. Here, we found that the expression of special AT-rich binding protein 2 (SATB2) in human AB-BMSCs significantly decreased with aging. SATB2 knockdown on AB-BMSCs from young donors displayed these aging-related phenotypes in vitro. Meanwhile, enforced SATB2 overexpression could rejuvenate AB-BMSCs from older donors. Importantly, satb2 gene- modified BMSCs therapy could prevent the alveolar bone loss during the aging of rats. Mechanistically, the stemness regulator Nanog was identified as the direct transcriptional target of SATB2 in BMSCs and functioned as a downstream mediator of SATB2. Collectively, our data reveal that SATB2 in AB-BMSCs associates with their age-related properties, and prevents AB-BMSCs senescence via maintaining Nanog expression. These findings highlight the translational potential of transcriptional factor-based cellular reprogramming for anti-aging therapy.

SMARCD1 regulates senescence-associated lipid accumulation in hepatocytes

Previously, we have identified 16 senescence-associated genes by a subtractive proteomic analysis using presenescent and senescent human fibroblast cells, TIG-1. The aim of this study was to clarify the role of SMARCD1, one of the identified genes, also known as BAF60a, in hepatic senescence. SMARCD1 is a member of the SWI/SNF chromatin remodeling complex family, and regulates the transcription of target genes through the alterations of chromatin structure. We demonstrated that the reduced expression of SMARCD1 triggers cellular senescence and induces the accumulation of lipids, suggesting that SMARCD1 acts as a mediator in these processes. Furthermore, palmitic acid treatment and high-fat diet led to a significant reduction of SMARCD1 expression, and consequently induced cellular senescence and lipid accumulation in HepG2 cells and mouse liver, respectively. The results obtained here suggest that dietary nutrient-associated impaired expression of SMARCD1 triggers cellular senescence and lipid accumulation, indicating a potential application of SMARCD1 in the prevention of lifestyle-related diseases.

A team led by Yoshinori Katakura at Kyushu University tried to clarify the molecular mechanisms of pathogenesis of fatty liver, focused on SMARCD1, one of the identified senescence-associated genes, and revealed its pivotal roles in cellular senescence induction and lipid accumulation in hepatocytes. SMARCD1 is a member of the SWI/SNF chromatin remodeling complex family and known to regulate the transcription of target genes through the alteration of chromatin structure. The results obtained here suggest that dietary imbalance such as high-fat diet impaires expression of SMARCD1, which triggers cellular senescence and lipid accumulation in hepatocytes, indicating a potential role of SMARCD1 in the prevention of lifestyle-related diseases.

NANOG Reverses the Myogenic Differentiation Potential of Senescent Stem Cells by Restoring ACTIN Filamentous Organization and SRF-Dependent Gene Expression

Cellular senescence as a result of organismal aging or progeroid diseases leads to stem cell pool exhaustion hindering tissue regeneration and contributing to the progression of age related disorders. Here we discovered that ectopic expression of the pluripotent factor NANOG in senescent or progeroid myogenic progenitors reversed cellular aging and restored completely the ability to generate contractile force. To elicit its effects, NANOG enabled reactivation of the ROCK and Transforming Growth Factor (TGF)-β pathways-both of which were impaired in senescent cells-leading to ACTIN polymerization, MRTF-A translocation into the nucleus and serum response factor (SRF)-dependent myogenic gene expression. Collectively our data reveal that cellular senescence can be reversed and provide a novel strategy to regain the lost function of aged stem cells without reprogramming to the pluripotent state. Stem Cells 2017;35:207-221.

Differential Expression of SWI/SNF Chromatin Remodeler Subunits Brahma and Brahma-Related Gene During Drug-Induced Liver Injury and Regeneration in Mouse Model

The chromatin remodeling activity of mammalian SWI/SNF complex is carried out by either Brahma (BRM) or Brahma-related gene (BRG-1). The BRG-1 regulates genes involved in cell proliferation, whereas BRM is associated with cell differentiation, and arrest of cell growth. Global modifications of histones and expression of genes of chromatin-remodeling subunits have not been studied in in vivo model systems. In the present study, we investigate epigenetic modifications of histones and the expression of genes in thioacetamide (TAA)-induced liver injury and regeneration in a mouse model. In the present study, we report that hepatocyte proliferation and H3S10 phosphorylation occur during 60 to 72 h post TAA treatment in mice. Furthermore, there was change in the H3K9 acetylation and H3K9 trimethylation pattern with respect to liver injury and regeneration phase. Looking into the expression pattern of Brg-1 and Brm, it is evident that they contribute substantially to the process of liver regeneration. The SWI/SNF remodeler might contain BRG-1 as its ATPase subunit during injury phase. Whereas, BRM-associated SWI/SNF remodeler might probably be predominant during decline of injury phase and initiation of regeneration phase. Furthermore, during the regeneration phase, BRG-1-containing remodeler again predominates. Considering all these observations, the present study depicts an interplay between chromatin interacting machineries in different phases of thioacetamide-induced liver injury and regeneration.

The Impact of Epigenetics on Mesenchymal Stem Cell Biology

Changes in epigenetic marks are known to be important regulatory factors in stem cell fate determination and differentiation. In the past years, the investigation of the epigenetic regulation of stem cell biology has largely focused on embryonic stem cells (ESCs). Contrarily, less is known about the epigenetic control of gene expression during differentiation of adult stem cells (AdSCs). Among AdSCs, mesenchymal stem cells (MSCs) are the most investigated stem cell population because of their enormous potential for therapeutic applications in regenerative medicine and tissue engineering. In this review, we analyze the main studies addressing the epigenetic changes in MSC landscape during in vitro cultivation and replicative senescence, as well as follow osteocyte, chondrocyte, and adipocyte differentiation. In these studies, histone acetylation, DNA methylation, and miRNA expression are among the most investigated phenomena. We describe also epigenetic changes that are associated with in vitro MSC trans-differentiation. Although at the at initial stage, the epigenetics of MSCs promise to have profound implications for stem cell basic and applied research. J. Cell. Physiol. 231: 2393-2401, 2016. © 2016 Wiley Periodicals, Inc.