ZKSCAN3 counteracts cellular senescence by stabilizing heterochromatin

Targeting ONECUT2 inhibits tumor angiogenesis via down-regulating ZKSCAN3/VEGFA

OC-2 plays a vital role in tumor growth, metastasis and angiogenesis, but molecular mechanism how OC-2 regulates angiogenic factors is unclear. We found that OC-2 was highly expressed in HepG2, COLO, MCF-7, SKOV3 cells and rectum carcinoma tissues, and angiogenic factors levels were positively related to OC-2. Then OC-2 KD inhibited the tumor growth, metastasis and angiogenesis process in vitro and vivo. ChIP-Seq showed that 228 target genes of OC-2 were identified and they were associated with tumor growth, metastasis, angiogenesis and signal transduction; OC-2 bound to ZKSCAN3 at promoter region. Luciferase assays showed that ZKSCAN3 was identified as target gene of OC-2 and VEGFA was identified as target gene of ZKSCAN3; OC-2 promoted VEGFA expression via activating ZKSCAN3 transcriptional program. Importantly, OC-2 KD down-regulated VEGFA secretion to suppress tumor angiogenesis of HUVECs. Besides VEGFA, OC-2 was positively correlated with other angiogenic factors HIF-1α, FGF2, EGFL6 and HGF. Meanwhile, ERK1/2 and Smad1 signaling pathways might be related to function of OC-2 driving tumor aggressiveness. We revealed that OC-2 might regulate tumor growth, metastasis, angiogenesis via ERK1/2, Smad1 signaling pathways and regulate VEGFA expression for tumor angiogenesis via activating ZKSCAN3 transcriptional program, indicating that OC-2 was a convincing target to develop novel anti-tumor drugs based on angiogenesis.

Expression of ZKSCAN3 protein suppresses proliferation, migration, and invasion of pancreatic cancer through autophagy

Elevated autophagy activity enhances the malignancy of pancreatic cancer (PaCa), and autophagy is recognized as a novel therapeutic target. Zinc finger protein with KRAB and SCAN domains 3 (ZKSCAN3) is a transcription factor that suppresses autophagy, but its association with PaCa is unknown. We analyzed the function of ZKSCAN3 in PaCa and investigated whether autophagy regulation through ZKSCAN3 could become a new therapeutic target for PaCa. Using reverse transcription-quantitative polymerase chain reaction and western blotting, we observed that ZKSCAN3 expression was upregulated in several PaCa cell lines compared with normal pancreatic ductal epithelial cells. Additionally, comparing ZKSCAN3 expression with the prognosis of PaCa patients using web databases, we found that higher ZKSCAN3 expression in PaCa was associated with extended overall survival. Knocking down ZKSCAN3 promoted the proliferation of PaCa cells. Moreover, following ZKSCAN3 knockdown, PaCa cells exhibited significantly enhanced migratory and invasive properties. Conversely, overexpression of ZKSCAN3 significantly suppressed the proliferation, migration and invasion of PaCa cells. Additionally, the knockdown of ZKSCAN3 increased the expression of LC3-II, a marker of autophagy, whereas ZKSCAN3 overexpression decreased LC3-II expression. In a xenograft mouse model, tumors formed by MIA PaCa-2 cells in which ZKSCAN3 was knocked down significantly increased in size compared with the control group. In conclusion, ZKSCAN3 expression was upregulated in several pancreatic cancer cells. Additionally, it was revealed that ZKSCAN3 is negatively correlated with the malignancy of PaCa through autophagy. These results suggest that autophagy regulation via ZKSCAN3 may be a new therapeutic target for PaCa.

The sirtuin-associated human senescence program converges on the activation of placenta-specific gene PAPPA

Sirtuins are pro-longevity genes with chromatin modulation potential, but how these properties are connected is not well understood. Here, we generated a panel of isogeneic human stem cell lines with SIRT1-SIRT7 knockouts and found that any sirtuin deficiency leads to accelerated cellular senescence. Through large-scale epigenomic analyses, we show how sirtuin deficiency alters genome organization and that genomic regions sensitive to sirtuin deficiency are preferentially enriched in active enhancers, thereby promoting interactions within topologically associated domains and the formation of de novo enhancer-promoter loops. In all sirtuin-deficient human stem cell lines, we found that chromatin contacts are rewired to promote aberrant activation of the placenta-specific gene PAPPA, which controls the pro-senescence effects associated with sirtuin deficiency and serves as a potential aging biomarker. Based on our survey of the 3D chromatin architecture, we established connections between sirtuins and potential target genes, thereby informing the development of strategies for aging interventions.

PML-mediated nuclear loosening permits immunomodulation of mesenchymal stem/stromal cells under inflammatory conditions

Nuclear configuration plays a critical role in the compartmentalization of euchromatin and heterochromatin and the epigenetic regulation of gene expression. Under stimulation by inflammatory cytokines IFN-γ and TNF-α, human mesenchymal stromal cells (hMSCs) acquire a potent immunomodulatory function enabled by drastic induction of various effector genes, with some upregulated several magnitudes. However, whether the transcriptional upregulation of the immunomodulatory genes in hMSCs exposed to inflammatory cytokines is associated with genome-wide nuclear reconfiguration has not been explored. Here, we demonstrate that hMSCs undergo remarkable nuclear reconfiguration characterized by an enlargement of the nucleus, downregulation of LMNB1 and LMNA/C, decondensation of heterochromatin, and derepression of repetitive DNA. Interestingly, promyelocytic leukaemia-nuclear bodies (PML-NBs) were found to mediate the nuclear reconfiguration of hMSCs triggered by the inflammatory cytokines. Significantly, when PML was depleted, the immunomodulatory function of hMSCs conferred by cytokines was compromised, as reflected by the attenuated expression of effector molecules in hMSCs and their failure to block infiltration of immune cells to lipopolysaccharide (LPS)-induced acute lung injury. Our results indicate that the immunomodulatory function of hMSCs conferred by inflammatory cytokines requires PML-mediated chromatin loosening.

ALKBH5 suppresses autophagic flux via N6-methyladenosine demethylation of ZKSCAN3 mRNA in acute pancreatitis

BACKGROUND

Increasing evidence has demonstrated that N6-methyladenosine (m6A) RNA modification plays an essential role in a wide range of pathological conditions. Impaired autophagy is a critical hallmark of acute pancreatitis (AP).

AIM

To explore the role of the m6A modification of ZKSCAN3 in the regulation of autophagy in AP.

METHODS

The AP mouse cell model was established by cerulein-treated mouse pancreatic acinar cells (MPC-83), and the results were confirmed by the levels of amylase and inflammatory factors. Autophagy activity was evaluated by specific identification of the autophagy-related microstructure and the expression of autophagy-related genes. ZKSCAN3 and ALKBH5 were knocked down to study the function in AP. A m6A RNA binding protein immunoprecipitation assay was used to study how the m6A modification of ZKSCAN3 mRNA is regulated by ALKBH.

RESULTS

The increased expression of amylase and inflammatory factors in the supernatant and the accumulation of autophagic vacuoles verified that the AP mouse cell model was established. The downregulation of LAMP2 and upregulation of LC3-II/I and SQSTM1 demonstrated that autophagy was impaired in AP. The expression of ZKSCAN3 was upregulated in AP. Inhibition of ZKSCAN3 increased the expression of LAMP2 and decreased the expression of the inflammatory factors, LC3-II/I and SQSTM1. Furthermore, ALKBH5 was upregulated in AP. Knockdown of ALKBH5 downregulated ZKSCAN3 expression and restored decreased autophagic flux in AP. Notably, the bioinformatic analysis revealed 23 potential m6A modification sites on ZKSCAN3 mRNA. The m6A modification of ZKSCAN3 mRNA was significantly decreased in AP. Knockdown of ALKBH5 increased the modification of ZKSCAN3 mRNA, which confirmed that ALKBH5 upregulated ZKSCAN3 expression in a m6A-dependent manner.

CONCLUSION

ALKBH5 inhibits autophagic flux through m6A demethylation of ZKSCAN3 mRNA in AP, thereby aggravating the severity of the disease.

Mechanotransduction and epigenetic modulations of chromatin: Role of mechanical signals in gene regulation

Mechanical forces may be generated within a cell due to tissue stiffness, cytoskeletal reorganization, and the changes (even subtle) in the cell's physical surroundings. These changes of forces impose a mechanical tension within the intracellular protein network (both cytosolic and nuclear). Mechanical tension could be released by a series of protein-protein interactions often facilitated by membrane lipids, lectins and sugar molecules and thus generate a type of signal to drive cellular processes, including cell differentiation, polarity, growth, adhesion, movement, and survival. Recent experimental data have accentuated the molecular mechanism of this mechanical signal transduction pathway, dubbed mechanotransduction. Mechanosensitive proteins in the cell's plasma membrane discern the physical forces and channel the information to the cell interior. Cells respond to the message by altering their cytoskeletal arrangement and directly transmitting the signal to the nucleus through the connection of the cytoskeleton and nucleoskeleton before the information despatched to the nucleus by biochemical signaling pathways. Nuclear transmission of the force leads to the activation of chromatin modifiers and modulation of the epigenetic landscape, inducing chromatin reorganization and gene expression regulation; by the time chemical messengers (transcription factors) arrive into the nucleus. While significant research has been done on the role of mechanotransduction in tumor development and cancer progression/metastasis, the mechanistic basis of force-activated carcinogenesis is still enigmatic. Here, in this review, we have discussed the various cues and molecular connections to better comprehend the cellular mechanotransduction pathway, and we also explored the detailed role of some of the multiple players (proteins and macromolecular complexes) involved in mechanotransduction. Thus, we have described an avenue: how mechanical stress directs the epigenetic modifiers to modulate the epigenome of the cells and how aberrant stress leads to the cancer phenotype.

Multimodal Omics Approaches to Aging and Age-Related Diseases

Aging is associated with a progressive decline in physiological capacities and an increased risk of aging-associated disorders. An increasing body of experimental evidence shows that aging is a complex biological process coordinately regulated by multiple factors at different molecular layers. Thus, it is difficult to delineate the overall systematic aging changes based on single-layer data. Instead, multimodal omics approaches, in which data are acquired and analyzed using complementary omics technologies, such as genomics, transcriptomics, and epigenomics, are needed for gaining insights into the precise molecular regulatory mechanisms that trigger aging. In recent years, multimodal omics sequencing technologies that can reveal complex regulatory networks and specific phenotypic changes have been developed and widely applied to decode aging and age-related diseases. This review summarizes the classification and progress of multimodal omics approaches, as well as the rapidly growing number of articles reporting on their application in the field of aging research, and outlines new developments in the clinical treatment of age-related diseases based on omics technologies.

Lamins: The backbone of the nucleocytoskeleton interface

The nuclear lamina (NL) is a crucial component of the inner nuclear membrane (INM) and consists of lamin filaments and associated proteins. Lamins are type V intermediate filament proteins essential for maintaining the integrity and mechanical properties of the nucleus. In human cells, 'B-type' lamins (lamin B1 and lamin B2) are ubiquitously expressed, while 'A-type' lamins (lamin A, lamin C, and minor isoforms) are expressed in a tissue- and development-specific manner. Lamins homopolymerize to form filaments that localize primarily near the INM, but A-type lamins also localize to and function in the nucleoplasm. Lamins play central roles in the assembly, structure, positioning, and mechanics of the nucleus, modulating cell signaling and influencing development, differentiation, and other activities. This review highlights recent findings on the structure and regulation of lamin filaments, providing insights into their multifaceted functions, including their role as "mechanosensors", delving into the emerging significance of lamin filaments as vital links between cytoskeletal and nuclear structures, chromatin organization, and the genome.

Human ESC-derived vascular cells promote vascular regeneration in a HIF-1α dependent manner

Hypoxia-inducible factor (HIF-1α), a core transcription factor responding to changes in cellular oxygen levels, is closely associated with a wide range of physiological and pathological conditions. However, its differential impacts on vascular cell types and molecular programs modulating human vascular homeostasis and regeneration remain largely elusive. Here, we applied CRISPR/Cas9-mediated gene editing of human embryonic stem cells and directed differentiation to generate HIF-1α-deficient human vascular cells including vascular endothelial cells, vascular smooth muscle cells, and mesenchymal stem cells (MSCs), as a platform for discovering cell type-specific hypoxia-induced response mechanisms. Through comparative molecular profiling across cell types under normoxic and hypoxic conditions, we provide insight into the indispensable role of HIF-1α in the promotion of ischemic vascular regeneration. We found human MSCs to be the vascular cell type most susceptible to HIF-1α deficiency, and that transcriptional inactivation of ANKZF1, an effector of HIF-1α, impaired pro-angiogenic processes. Altogether, our findings deepen the understanding of HIF-1α in human angiogenesis and support further explorations of novel therapeutic strategies of vascular regeneration against ischemic damage.

Zinc finger protein 831 promotes apoptosis and enhances chemosensitivity in breast cancer by acting as a novel transcriptional repressor targeting the STAT3/Bcl2 signaling pathway

Emerging evidence suggested that zinc finger protein 831 (ZNF831) was associated with immune activity and stem cell regulation in breast cancer. Whereas, the roles and molecular mechanisms of ZNF831 in oncogenesis remain unclear. ZNF831 expression was significantly diminished in breast cancer which was associated with promoter CpG methylation but not mutation. Ectopic over-expression of ZNF831 suppressed breast cancer cell proliferation and colony formation and promoted apoptosis in vitro, while knockdown of ZNF831 resulted in an opposite phenotype. Anti-proliferation effect of ZNF831 was verified in vivo. Bioinformatic analysis of public databases and transcriptome sequencing both showed that ZNF831 could enhance apoptosis through transcriptional regulation of the JAK/STAT pathway. ChIP and luciferase report assays demonstrated that ZNF831 could directly bind to one specific region of STAT3 promoter and induce the transcriptional inhibition of STAT3. As a result, the attenuation of STAT3 led to a restraint of the transcription of Bcl2 and thus accelerated the apoptotic progression. Augmentation of STAT3 diminished the apoptosis-promoting effect of ZNF831 in breast cancer cell lines. Furthermore, ZNF831 could ameliorate the anti-proliferation effect of capecitabine and gemcitabine in breast cancer cell lines. Our findings demonstrate for the first time that ZNF831 is a novel transcriptional suppressor through inhibiting the expression of STAT3/Bcl2 and promoting the apoptosis process in breast cancer, suggesting ZNF831 as a novel biomarker and potential therapeutic target for breast cancer patients.

Retroelement-Age Clocks: Epigenetic Age Captured by Human Endogenous Retrovirus and LINE-1 DNA methylation states

Human endogenous retroviruses (HERVs), the remnants of ancient viral infections embedded within the human genome, and long interspersed nuclear elements 1 (LINE-1), a class of autonomous retrotransposons, are silenced by host epigenetic mechanisms including DNA methylation. The resurrection of particular retroelements has been linked to biological aging. Whether the DNA methylation states of locus specific HERVs and LINEs can be used as a biomarker of chronological age in humans remains unclear. We show that highly predictive epigenetic clocks of chronological age can be constructed from retroelement DNA methylation states in the immune system, across human tissues, and pan-mammalian species. We found retroelement epigenetic clocks were reversed during transient epigenetic reprogramming, accelerated in people living with HIV-1, responsive to antiretroviral therapy, and accurate in estimating long-term culture ages of human brain organoids. Our findings support the hypothesis of epigenetic dysregulation of retroelements as a potential contributor to the biological hallmarks of aging.

SGF29 nuclear condensates reinforce cellular aging

Phase separation, a biophysical segregation of subcellular milieus referred as condensates, is known to regulate transcription, but its impacts on physiological processes are less clear. Here, we demonstrate the formation of liquid-like nuclear condensates by SGF29, a component of the SAGA transcriptional coactivator complex, during cellular senescence in human mesenchymal progenitor cells (hMPCs) and fibroblasts. The Arg 207 within the intrinsically disordered region is identified as the key amino acid residue for SGF29 to form phase separation. Through epigenomic and transcriptomic analysis, our data indicated that both condensate formation and H3K4me3 binding of SGF29 are essential for establishing its precise chromatin location, recruiting transcriptional factors and co-activators to target specific genomic loci, and initiating the expression of genes associated with senescence, such as CDKN1A. The formation of SGF29 condensates alone, however, may not be sufficient to drive H3K4me3 binding or achieve transactivation functions. Our study establishes a link between phase separation and aging regulation, highlighting nuclear condensates as a functional unit that facilitate shaping transcriptional landscapes in aging.

Telomere Checkpoint in Development and Aging

The maintenance of genome integrity through generations is largely determined by the stability of telomeres. Increasing evidence suggests that telomere dysfunction may trigger changes in cell fate, independently of telomere length. Telomeric multiple tandem repeats are potentially highly recombinogenic. Heterochromatin formation, transcriptional repression, the suppression of homologous recombination and chromosome end protection are all required for telomere stability. Genetic and epigenetic defects affecting telomere homeostasis may cause length-independent internal telomeric DNA damage. Growing evidence, including that based on Drosophila research, points to a telomere checkpoint mechanism that coordinates cell fate with telomere state. According to this scenario, telomeres, irrespective of their length, serve as a primary sensor of genome instability that is capable of triggering cell death or developmental arrest. Telomeric factors released from shortened or dysfunctional telomeres are thought to mediate these processes. Here, we discuss a novel signaling role for telomeric RNAs in cell fate and early development. Telomere checkpoint ensures genome stability in multicellular organisms but aggravates the aging process, promoting the accumulation of damaged and senescent cells.

Choreography of lamina-associated domains: structure meets dynamics

Lamina-associated domains are large regions of heterochromatin positioned at the nuclear periphery. These domains have been implicated in gene repression, especially in the context of development. In mammals, LAD organization is dependent on nuclear lamins, inner nuclear membrane proteins, and chromatin state. In addition, chromatin readers and modifier proteins have been implicated in this organization, potentially serving as molecular tethers that interact with both nuclear envelope proteins and chromatin. More recent studies have focused on teasing apart the rules that govern dynamic LAD organization and how LAD organization, in turn, relates to gene regulation and overall 3D genome organization. This review highlights recent studies in mammalian cells uncovering factors that instruct the choreography of LAD organization, re-organization, and dynamics at the nuclear lamina, including LAD dynamics in interphase and through mitotic exit, when LAD organization is re-established, as well as intra-LAD subdomain variations.

Iron overload induces cerebral endothelial senescence in aged mice and in primary culture in a sex-dependent manner

Iron imbalance in the brain negatively affects brain function. With aging, iron levels increase in the brain and contribute to brain damage and neurological disorders. Changes in the cerebral vasculature with aging may enhance iron entry into the brain parenchyma, leading to iron overload and its deleterious consequences. Endothelial senescence has emerged as an important contributor to age-related changes in the cerebral vasculature. Evidence indicates that iron overload may induce senescence in cultured cell lines. Importantly, cells derived from female human and mice generally show enhanced senescence-associated phenotype, compared with males. Thus, we hypothesize that cerebral endothelial cells (CEC) derived from aged female mice are more susceptible to iron-induced senescence, compared with CEC from aged males. We found that aged female mice, but not males, showed cognitive deficits when chronically treated with ferric citrate (FC), and their brains and the brain vasculature showed senescence-associated phenotype. We also found that primary culture of CEC derived from aged female mice, but not male-derived CEC, exhibited senescence-associated phenotype when treated with FC. We identified that the transmembrane receptor Robo4 was downregulated in the brain vasculature and in cultured primary CEC derived from aged female mice, compared with those from male mice. We discovered that Robo4 downregulation contributed to enhanced vulnerability to FC-induced senescence. Thus, our study identifies Robo4 downregulation as a driver of senescence induced by iron overload in primary culture of CEC and a potential risk factor of brain vasculature impairment and brain dysfunction.

Reducing oxidative protein folding alleviates senescence by minimizing ER-to-nucleus H2 O2 release

Oxidative protein folding occurs in the endoplasmic reticulum (ER) to generate disulfide bonds, and the by-product is hydrogen peroxide (H2 O2 ). However, the relationship between oxidative protein folding and senescence remains uncharacterized. Here, we find that the protein disulfide isomerase (PDI), a key oxidoreductase that catalyzes oxidative protein folding, accumulated in aged human mesenchymal stem cells (hMSCs) and deletion of PDI alleviated hMSCs senescence. Mechanistically, knocking out PDI slows the rate of oxidative protein folding and decreases the leakage of ER-derived H2 O2 into the nucleus, thereby decreasing the expression of SERPINE1, which was identified as a key driver of cell senescence. Furthermore, we show that depletion of PDI alleviated senescence in various cell models of aging. Our findings reveal a previously unrecognized role of oxidative protein folding in promoting cell aging, providing a potential target for aging and aging-related disease intervention.

MAVS Antagonizes Human Stem Cell Senescence as a Mitochondrial Stabilizer

Mitochondrial dysfunction is a hallmark feature of cellular senescence and organ aging. Here, we asked whether the mitochondrial antiviral signaling protein (MAVS), which is essential for driving antiviral response, also regulates human stem cell senescence. To answer this question, we used CRISPR/Cas9-mediated gene editing and directed differentiation techniques to generate various MAVS-knockout human stem cell models. We found that human mesenchymal stem cells (hMSCs) were sensitive to MAVS deficiency, as manifested by accelerated senescence phenotypes. We uncovered that the role of MAVS in maintaining mitochondrial structural integrity and functional homeostasis depends on its interaction with the guanosine triphosphatase optic atrophy type 1 (OPA1). Depletion of MAVS or OPA1 led to the dysfunction of mitochondria and cellular senescence, whereas replenishment of MAVS or OPA1 in MAVS-knockout hMSCs alleviated mitochondrial defects and premature senescence phenotypes. Taken together, our data underscore an uncanonical role of MAVS in safeguarding mitochondrial homeostasis and antagonizing human stem cell senescence.

Nuclear lamina erosion-induced resurrection of endogenous retroviruses underlies neuronal aging

The primate frontal lobe (FL) is sensitive to aging-related neurocognitive decline. However, the aging-associated molecular mechanisms remain unclear. Here, using physiologically aged non-human primates (NHPs), we depicted a comprehensive landscape of FL aging with multidimensional profiling encompassing bulk and single-nucleus transcriptomes, quantitative proteome, and DNA methylome. Conjoint analysis across these molecular and neuropathological layers underscores nuclear lamina and heterochromatin erosion, resurrection of endogenous retroviruses (ERVs), activated pro-inflammatory cyclic GMP-AMP synthase (cGAS) signaling, and cellular senescence in post-mitotic neurons of aged NHP and human FL. Using human embryonic stem-cell-derived neurons recapitulating cellular aging in vitro, we verified the loss of B-type lamins inducing resurrection of ERVs as an initiating event of the aging-bound cascade in post-mitotic neurons. Of significance, these aging-related cellular and molecular changes can be alleviated by abacavir, a nucleoside reverse transcriptase inhibitor, either through direct treatment of senescent human neurons in vitro or oral administration to aged mice.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

Effect of Lacking ZKSCAN3 on Autophagy, Lysosomal Biogenesis and Senescence

Transcription factors can affect autophagy activity by promoting or inhibiting the expression of autophagic and lysosomal genes. As a member of the zinc finger family DNA-binding proteins, ZKSCAN3 has been reported to function as a transcriptional repressor of autophagy, silencing of which can induce autophagy and promote lysosomal biogenesis in cancer cells. However, studies in Zkscan3 knockout mice showed that the deficiency of ZKSCAN3 did not induce autophagy or increase lysosomal biogenesis. In order to further explore the role of ZKSCAN3 in the transcriptional regulation of autophagic genes in human cancer and non-cancer cells, we generated ZKSCAN3 knockout HK-2 (non-cancer) and Hela (cancer) cells via the CRISPR/Cas9 system and analyzed the differences in gene expression between ZKSCAN3 deleted cells and non-deleted cells through fluorescence quantitative PCR, western blot and transcriptome sequencing, with special attention to the differences in expression of autophagic and lysosomal genes. We found that ZKSCAN3 may be a cancer-related gene involved in cancer progression, but not an essential transcriptional repressor of autophagic or lysosomal genes, as the lacking of ZKSCAN3 cannot significantly promote the expression of autophagic and lysosomal genes.

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.

New Insights into the Genetics and Epigenetics of Aging Plasticity

Biological aging is characterized by irreversible cell cycle blockade, a decreased capacity for tissue regeneration, and an increased risk of age-related diseases and mortality. A variety of genetic and epigenetic factors regulate aging, including the abnormal expression of aging-related genes, increased DNA methylation levels, altered histone modifications, and unbalanced protein translation homeostasis. The epitranscriptome is also closely associated with aging. Aging is regulated by both genetic and epigenetic factors, with significant variability, heterogeneity, and plasticity. Understanding the complex genetic and epigenetic mechanisms of aging will aid the identification of aging-related markers, which may in turn aid the development of effective interventions against this process. This review summarizes the latest research in the field of aging from a genetic and epigenetic perspective. We analyze the relationships between aging-related genes, examine the possibility of reversing the aging process by altering epigenetic age.

Resurrection of endogenous retroviruses during aging reinforces senescence

Whether and how certain transposable elements with viral origins, such as endogenous retroviruses (ERVs) dormant in our genomes, can become awakened and contribute to the aging process is largely unknown. In human senescent cells, we found that HERVK (HML-2), the most recently integrated human ERVs, are unlocked to transcribe viral genes and produce retrovirus-like particles (RVLPs). These HERVK RVLPs constitute a transmissible message to elicit senescence phenotypes in young cells, which can be blocked by neutralizing antibodies. The activation of ERVs was also observed in organs of aged primates and mice as well as in human tissues and serum from the elderly. Their repression alleviates cellular senescence and tissue degeneration and, to some extent, organismal aging. These findings indicate that the resurrection of ERVs is a hallmark and driving force of cellular senescence and tissue aging.

Structural insights into the recognition of telomeric variant repeat TTGGGG by broad-complex, tramtrack and bric-à-brac - zinc finger protein ZBTB10

Multiple proteins bind to telomeric DNA and are important for the role of telomeres in genome stability. A recent study established a broad-complex, tramtrack and bric-à-brac - zinc finger (BTB-ZF) protein, ZBTB10 (zinc finger and BTB domain-containing protein 10), as a telomeric variant repeat-binding protein at telomeres that use an alternative method for lengthening telomeres). ZBTB10 specifically interacts with the double-stranded telomeric variant repeat sequence TTGGGG by employing its tandem C2H2 zinc fingers (ZF1-2). Here, we solved the crystal structure of human ZBTB10 ZF1-2 in complex with a double-stranded DNA duplex containing the sequence TTGGGG to assess the molecular details of this interaction. Combined with calorimetric analysis, we identified the vital residues in TTGGGG recognition and determined the specific recognition mechanisms that are different from those of TZAP (telomere zinc finger-associated protein), a recently defined telomeric DNA-binding protein. Following these studies, we further identified a single amino-acid mutant (Arg767Gln) of ZBTB10 ZF1-2 that shows a preference for the telomeric DNA repeat TTAGGG sequence. We solved the cocrystal structure, providing a structural basis for telomeric DNA recognition by C2H2 ZF proteins.

Epigenetic regulation of aging: implications for interventions of aging and diseases

Aging is accompanied by the decline of organismal functions and a series of prominent hallmarks, including genetic and epigenetic alterations. These aging-associated epigenetic changes include DNA methylation, histone modification, chromatin remodeling, non-coding RNA (ncRNA) regulation, and RNA modification, all of which participate in the regulation of the aging process, and hence contribute to aging-related diseases. Therefore, understanding the epigenetic mechanisms in aging will provide new avenues to develop strategies to delay aging. Indeed, aging interventions based on manipulating epigenetic mechanisms have led to the alleviation of aging or the extension of the lifespan in animal models. Small molecule-based therapies and reprogramming strategies that enable epigenetic rejuvenation have been developed for ameliorating or reversing aging-related conditions. In addition, adopting health-promoting activities, such as caloric restriction, exercise, and calibrating circadian rhythm, has been demonstrated to delay aging. Furthermore, various clinical trials for aging intervention are ongoing, providing more evidence of the safety and efficacy of these therapies. Here, we review recent work on the epigenetic regulation of aging and outline the advances in intervention strategies for aging and age-associated diseases. A better understanding of the critical roles of epigenetics in the aging process will lead to more clinical advances in the prevention of human aging and therapy of aging-related diseases.

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on “healthy aging” raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

Selective pericentromeric heterochromatin dismantling caused by TP53 activation during senescence

Cellular senescence triggers various types of heterochromatin remodeling that contribute to aging. However, the age-related mechanisms that lead to these epigenetic alterations remain elusive. Here, we asked how two key aging hallmarks, telomere shortening and constitutive heterochromatin loss, are mechanistically connected during senescence. We show that, at the onset of senescence, pericentromeric heterochromatin is specifically dismantled consisting of chromatin decondensation, accumulation of DNA breakages, illegitimate recombination and loss of DNA. This process is caused by telomere shortening or genotoxic stress by a sequence of events starting from TP53-dependent downregulation of the telomere protective protein TRF2. The resulting loss of TRF2 at pericentromeres triggers DNA breaks activating ATM, which in turn leads to heterochromatin decondensation by releasing KAP1 and Lamin B1, recombination and satellite DNA excision found in the cytosol associated with cGAS. This TP53–TRF2 axis activates the interferon response and the formation of chromosome rearrangements when the cells escape the senescent growth arrest. Overall, these results reveal the role of TP53 as pericentromeric disassembler and define the basic principles of how a TP53-dependent senescence inducer hierarchically leads to selective pericentromeric dismantling through the downregulation of TRF2.

The kidney-expressed transcription factor ZKSCAN3 is dispensable for autophagy transcriptional regulation and AKI progression in mouse

Acute kidney injury (AKI) is a common clinical disease that can cause serious harm to the kidneys, but it has no effective treatment till now. The modulation of autophagy pathway regulation is considered a potentially effective therapeutic approach in AKI prevention and treatment. ZKSCAN3 has been shown to be an important transcription factor that negatively regulates autophagy activity in cancer tissues. In order to determine whether autophagy could be activated by knocking out ZKSCAN3 to exert the renal protective effect of autophagy, we constructed AKI models with Zkscan3 knockout (KO) mice and detected renal pathological changes and renal function changes as well as autophagy-related indicators. We found that Zkscan3 KO had no significant effect on kidney development. Besides, no significant changes in autophagy activity were observed under normal physiological or AKI conditions. In non-tumor tissues, ZKSCAN3 did not mediate transcriptional regulation of autophagy-related genes. These findings suggest that because ZKSCAN3 may not function in the transcriptional regulation of autophagy-related genes in non-tumor tissues, it may not be used as a therapeutic target for AKI.

Context-dependent pro- and anti-resection roles of ZKSCAN3 in the regulation of fork processing during replication stress

Uncontrolled resection of replication forks under stress can cause genomic instability and influence cancer formation. Extensive fork resection has also been implicated in the chemosensitivity of “BReast CAncer gene” BRCA-deficient cancers. However, how fork resection is controlled in different genetic contexts and how it affects chromosomal stability and cell survival remains incompletely understood. Here, we report a novel function of the transcription repressor ZKSCAN3 in fork protection and chromosomal stability maintenance under replication stress. We show disruption of ZKSCAN3 function causes excessive resection of replication forks by the exonuclease Exo1 and homologous DNA recombination/repair protein Mre11 following fork reversal. Interestingly, in BRCA1-deficient cells, we found ZKSCAN3 actually promotes fork resection upon replication stress. We demonstrate these anti- and pro-resection roles of ZKSCAN3, consisting of a SCAN box, Kruppel-associated box, and zinc finger domain, are mediated by its SCAN box domain and do not require the Kruppel-associated box or zinc finger domains, suggesting that the transcriptional function of ZKSCAN3 is not involved. Furthermore, despite the severe impact on fork structure and chromosomal stability, depletion of ZKSCAN3 did not affect the short-term survival of BRCA1-proficient or BRCA1-deficient cells after treatment with cancer drugs hydroxyurea, PARPi, or cisplatin. Our findings reveal a unique relationship between ZKSCAN3 and BRCA1 in fork protection and add to our understanding of the relationships between replication fork protection, chromosomal instability, and chemosensitivity.

The Role of Antioxidants in the Interplay between Oxidative Stress and Senescence

Cellular senescence is an irreversible state of cell cycle arrest occurring in response to stressful stimuli, such as telomere attrition, DNA damage, reactive oxygen species, and oncogenic proteins. Although beneficial and protective in several physiological processes, an excessive senescent cell burden has been involved in various pathological conditions including aging, tissue dysfunction and chronic diseases. Oxidative stress (OS) can drive senescence due to a loss of balance between pro-oxidant stimuli and antioxidant defences. Therefore, the identification and characterization of antioxidant compounds capable of preventing or counteracting the senescent phenotype is of major interest. However, despite the considerable number of studies, a comprehensive overview of the main antioxidant molecules capable of counteracting OS-induced senescence is still lacking. Here, besides a brief description of the molecular mechanisms implicated in OS-mediated aging, we review and discuss the role of enzymes, mitochondria-targeting compounds, vitamins, carotenoids, organosulfur compounds, nitrogen non-protein molecules, minerals, flavonoids, and non-flavonoids as antioxidant compounds with an anti-aging potential, therefore offering insights into innovative lifespan-extending approaches.

Deciphering aging at three-dimensional genomic resolution

Aging is characterized by progressive functional declines at the organismal, organic, and cellular levels and increased susceptibility to aging-related diseases. Epigenetic alteration is a hallmark of aging, senescent cells show epigenomic changes at multiple scales, such as 3D genome reorganization, alterations of histone modifications and chromatin accessibility, and DNA hypomethylation. Chromosome conformation capture (3C)-based technologies have enabled the generation of key information on genomic reorganizations during senescence. A comprehensive understanding of epigenomic alterations during aging will yield important insights into the underlying epigenetic mechanism for aging regulation, the identification of aging-related biomarkers, and the development of potential aging intervention targets.

Epigenetic therapy targeting bone marrow mesenchymal stem cells for age-related bone diseases

As global aging accelerates, the prevention and treatment of age-related bone diseases are becoming a critical issue. In the process of senescence, bone marrow mesenchymal stem cells (BMSCs) gradually lose the capability of self-renewal and functional differentiation, resulting in impairment of bone tissue regeneration and disorder of bone tissue homeostasis. Alteration in epigenetic modification is an essential factor of BMSC dysfunction during aging. Its transferability and reversibility provide the possibility to combat BMSC aging by reversing age-related modifications. Emerging evidence demonstrates that epigenetic therapy based on aberrant epigenetic modifications could alleviate the senescence and dysfunction of stem cells. This review summarizes potential therapeutic targets for BMSC aging, introduces some potential approaches to alleviating BMSC aging, and analyzes its prospect in the clinical application of age-related bone diseases.

Destabilizing heterochromatin by APOE mediates senescence

Apolipoprotein E (APOE) is a component of lipoprotein particles that function in the homeostasis of cholesterol and other lipids. Although APOE is genetically associated with human longevity and Alzheimer's disease, its mechanistic role in aging is largely unknown. Here, we used human genetic, stress-induced and physiological cellular aging models to explore APOE-driven processes in stem cell homeostasis and aging. We report that in aged human mesenchymal progenitor cells (MPCs), APOE accumulation is a driver for cellular senescence. By contrast, CRISPR-Cas9-mediated deletion of APOE endows human MPCs with resistance to cellular senescence. Mechanistically, we discovered that APOE functions as a destabilizer for heterochromatin. Specifically, increased APOE leads to the degradation of nuclear lamina proteins and a heterochromatin-associated protein KRAB-associated protein 1 via the autophagy-lysosomal pathway, thereby disrupting heterochromatin and causing senescence. Altogether, our findings uncover a role of APOE as an epigenetic mediator of senescence and provide potential targets to ameliorate aging-related diseases.

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.

Zinc Finger Proteins in Neuro-Related Diseases Progression

Zinc finger proteins (ZNF) are among the most abundant proteins in eukaryotic genomes. It contains several zinc finger domains that can selectively bind to certain DNA or RNA and associate with proteins, therefore, ZNF can regulate gene expression at the transcriptional and translational levels. In terms of neurological diseases, numerous studies have shown that many ZNF are associated with neurological diseases. The purpose of this review is to summarize the types and roles of ZNF in neuropsychiatric disorders. We will describe the structure and classification of ZNF, then focus on the pathophysiological role of ZNF in neuro-related diseases and summarize the mechanism of action of ZNF in neuro-related diseases.

Role of the Transcriptional Repressor Zinc Finger with KRAB and SCAN Domains 3 (ZKSCAN3) in Retinal Pigment Epithelial Cells

Lysosomes are important for proper functioning of the retinal pigment epithelial (RPE) cells. RPE cells have a daily burden of phagocytosis of photoreceptor outer segments (POS) and also degrade cellular waste by autophagy. Here, we identified the role of Zinc-finger protein with KRAB and SCAN domains 3 (ZKSCAN3) in co-ordinate regulation of lysosomal function and autophagy in the RPE. Our studies show that in the RPE, ZKSCAN3 is predominantly nuclear in healthy cells and its nuclear expression is reduced upon nutrient deprivation. siRNA-mediated knockdown of ZKSCAN3 results in de-repression of some of the ZKSCAN3 target genes. Knockdown of ZKSCAN3 also resulted in an induction in autophagy flux, increase in the number of functional lysosomes and accompanied activation of lysosomal cathepsin B activity in ARPE-19 cells. We also demonstrated that inhibition of P38 mitogen-activated protein kinase (MAPK) retains ZKSCAN3 in the nucleus in nutrient-deprived cells. In summary, our studies elucidated the role of ZKSCAN3 as a transcriptional repressor of autophagy and lysosomal function in the RPE.

Single-nucleus transcriptomic landscape of primate hippocampal aging

The hippocampus plays a crucial role in learning and memory, and its progressive deterioration with age is functionally linked to a variety of human neurodegenerative diseases. Yet a systematic profiling of the aging effects on various hippocampal cell types in primates is still missing. Here, we reported a variety of new aging-associated phenotypic changes of the primate hippocampus. These include, in particular, increased DNA damage and heterochromatin erosion with time, alongside loss of proteostasis and elevated inflammation. To understand their cellular and molecular causes, we established the first single-nucleus transcriptomic atlas of primate hippocampal aging. Among the 12 identified cell types, neural transiently amplifying progenitor cell (TAPC) and microglia were most affected by aging. In-depth dissection of gene-expression dynamics revealed impaired TAPC division and compromised neuronal function along the neurogenesis trajectory; additionally elevated pro-inflammatory responses in the aged microglia and oligodendrocyte, as well as dysregulated coagulation pathways in the aged endothelial cells may contribute to a hostile microenvironment for neurogenesis. This rich resource for understanding primate hippocampal aging may provide potential diagnostic biomarkers and therapeutic interventions against age-related neurodegenerative diseases.

Reduction of lamin B receptor levels by miR-340-5p disrupts chromatin, promotes cell senescence and enhances senolysis

A major stress response influenced by microRNAs (miRNAs) is senescence, a state of indefinite growth arrest triggered by sublethal cell damage. Here, through bioinformatic analysis and experimental validation, we identified miR-340-5p as a novel miRNA that foments cellular senescence. miR-340-5p was highly abundant in diverse senescence models, and miR-340-5p overexpression in proliferating cells rendered them senescent. Among the target mRNAs, miR-340-5p prominently reduced the levels of LBR mRNA, encoding lamin B receptor (LBR). Loss of LBR by ectopic overexpression of miR-340-5p derepressed heterochromatin in lamina-associated domains, promoting the expression of DNA repetitive elements characteristic of senescence. Importantly, overexpressing miR-340-5p enhanced cellular sensitivity to senolytic compounds, while antagonization of miR-340-5p reduced senescent cell markers and engendered resistance to senolytic-induced cell death. We propose that miR-340-5p can be exploited for removing senescent cells to restore tissue homeostasis and mitigate damage by senescent cells in pathologies of human aging.

Mesenchymal stem cells: ideal seeds for treating diseases

Mesenchymal stem cells (MSCs), a kind of multipotent stem cells with self-renewal ability and multi-differentiation ability, have become the “practical stem cells” for the treatment of diseases. MSCs have immunomodulatory properties and can be used to treat autoimmune diseases, such as systemic lupus erythematosus (SLE) and Crohn’s disease. MSCs also can be used in cancer and aging. At present, many clinical experiments are using MSCs. MSCs can reduce the occurrence of inflammation and apoptosis of tissue cells, and promote the proliferation of endogenous tissue and organ cells, so as to achieve the effect of repairing tissue and organs. MSCs presumably also play an important role in Corona Virus Disease 2019 (COVID-19) infection.

The loss of heterochromatin is associated with multiscale three-dimensional genome reorganization and aberrant transcription during cellular senescence

Heterochromatin remodeling is critical for various cell processes. In particular, the "loss of heterochromatin" phenotype in cellular senescence is associated with the process of aging and age-related disorders. Although biological processes of senescent cells, including senescence-associated heterochromatin foci (SAHF) formation, chromosome compaction, and redistribution of key proteins, have been closely associated with high-order chromatin structure, the relationship between the high-order chromatin reorganization and the loss of heterochromatin phenotype during senescence has not been fully understood. By using senescent and deep senescent fibroblasts induced by DNA damage harboring the "loss of heterochromatin" phenotype, we observed progressive 3D reorganization of heterochromatin during senescence. Facultative and constitutive heterochromatin marked by H3K27me3 and H3K9me3, respectively, show different alterations. Facultative heterochromatin tends to switch from the repressive B-compartment to the active A-compartment, whereas constitutive heterochromatin shows no significant changes at the compartment level but enhanced interactions between themselves. Both types of heterochromatin show increased chromatin accessibility and gene expression leakage during senescence. Furthermore, increased chromatin accessibility in potential CTCF binding sites accompanies the establishment of novel loops in constitutive heterochromatin. Finally, we also observed aberrant expression of repetitive elements, including LTR (long terminal repeat) and satellite classes. Overall, facultative and constitutive heterochromatin show both similar and distinct multiscale alterations in the 3D map, chromatin accessibility, and gene expression leakage. This study provides an epigenomic map of heterochromatin reorganization during senescence.

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.

Genome-wide R-loop Landscapes during Cell Differentiation and Reprogramming

DNA:RNA hybrids play key roles in both physiological and disease states by regulating chromatin and genome organization. Their homeostasis during cell differentiation and cell plasticity remains elusive. Using an isogenic human stem cell platform, we systematically characterize R-loops, DNA methylation, histone modifications, and chromatin accessibility in pluripotent cells and their lineage-differentiated derivatives. We confirm that a portion of R-loops formed co-transcriptionally at pluripotency genes in pluripotent stem cells and at lineage-controlling genes in differentiated lineages. Notably, a subset of R-loops maintained after differentiation are associated with repressive chromatin marks on silent pluripotency genes and undesired lineage genes. Moreover, in reprogrammed pluripotent cells, cell-of-origin-specific R-loops are initially present but are resolved with serial passaging. Our analysis suggests a multifaceted role of R-loops in cell fate determination that may serve as an additional layer of modulation on cell fate memory and cell plasticity.

The functional impact of nuclear reorganization in cellular senescence

Cellular senescence is the irreversible cell cycle arrest in response to DNA damage. Because senescent cells accumulate with age and contribute to chronic inflammation, they are promising therapeutic targets for healthspan extension. The senescent phenotype can vary depending on cell type and on the specific insults that induce senescence. This variability is also reflected in the extensive remodeling of the genome organization within the nucleus of senescent cells. Here, we give an overview of the nuclear changes that occur in different forms of senescence, including changes to chromatin state and composition and to the three-dimensional organization of the genome, as well as alterations to the nuclear envelope and to the accessibility of repetitive genomic regions. Many of these changes are shared across all forms of senescence, implicating nuclear organization as a fundamental driver of the senescent state and of how senescent cells interact with the surrounding tissue.

Control of the Autophagy Pathway in Osteoarthritis: Key Regulators, Therapeutic Targets and Therapeutic Strategies

Autophagy is involved in different degenerative diseases and it may control epigenetic modifications, metabolic processes, stem cells differentiation as well as apoptosis. Autophagy plays a key role in maintaining the homeostasis of cartilage, the tissue produced by chondrocytes; its impairment has been associated to cartilage dysfunctions such as osteoarthritis (OA). Due to their location in a reduced oxygen context, both differentiating and mature chondrocytes are at risk of premature apoptosis, which can be prevented by autophagy. AutophagomiRNAs, which regulate the autophagic process, have been found differentially expressed in OA. AutophagomiRNAs, as well as other regulatory molecules, may also be useful as therapeutic targets. In this review, we describe and discuss the role of autophagy in OA, focusing mainly on the control of autophagomiRNAs in OA pathogenesis and their potential therapeutic applications.

Apelin Rejuvenates Aged Human Mesenchymal Stem Cells by Regulating Autophagy and Improves Cardiac Protection After Infarction

The protective effects of mesenchymal stem cell (MSC)-based therapy for myocardial infarction (MI) are largely hampered as they age. Apelin is an endogenous ligand of its receptor APJ and plays an essential role in regulating multiple biological activities including MSC proliferation and survival. In this study, we investigated whether Apelin regulates MSC senescence and whether its overexpression could rejuvenate aged MSCs (AMSCs) to improve cardiac protection following infarction in mice. MSC senescence was evaluated by senescence-associated β-galactosidase assays. Apelin level was examined by western blotting. Autophagy was determined by transmission electron microscopy. The cardioprotective effect of AMSCs with Apelin overexpression (Apelin-AMSCs) was assessed in a mouse MI model. Apelin expression was dramatically reduced in AMSCs. Interestingly, knockdown of Apelin induced young MSCs (YMSC) senescence, whereas overexpression rescued AMSC senescence. Apelin overexpression also increased AMSC angiogenic capacity. Mechanistically, Apelin overexpression upregulated the autophagy level of AMSCs by activating AMP-activated protein kinase (AMPK) signaling, thereby rejuvenating AMSCs. Compared with AMSCs, transplantation of Apelin-AMSCs achieved better therapeutic efficacy for MI by enhancing cell survival and angiogenesis. In conclusion, our results reveal that Apelin activates AMPK to rejuvenate AMSCs by increasing autophagy and promotes cardioprotection following infarction in mice. This study identified a novel target to rejuvenate AMSCs and enhance their therapeutic efficacy.

Stabilization of heterochromatin by CLOCK promotes stem cell rejuvenation and cartilage regeneration

Accumulating evidence indicates an association between the circadian clock and the aging process. However, it remains elusive whether the deregulation of circadian clock proteins underlies stem cell aging and whether they are targetable for the alleviation of aging-associated syndromes. Here, we identified a transcription factor-independent role of CLOCK, a core component of the molecular circadian clock machinery, in counteracting human mesenchymal stem cell (hMSC) decay. CLOCK expression was decreased during hMSC aging. In addition, CLOCK deficiency accelerated hMSC senescence, whereas the overexpression of CLOCK, even as a transcriptionally inactive form, rejuvenated physiologically and pathologically aged hMSCs. Mechanistic studies revealed that CLOCK formed complexes with nuclear lamina proteins and KAP1, thus maintaining heterochromatin architecture and stabilizing repetitive genomic sequences. Finally, gene therapy with lentiviral vectors encoding CLOCK promoted cartilage regeneration and attenuated age-related articular degeneration in mice. These findings demonstrate a noncanonical role of CLOCK in stabilizing heterochromatin, promoting tissue regeneration, and mitigating aging-associated chronic diseases.

METTL3 counteracts premature aging via m6A-dependent stabilization of MIS12 mRNA

N6-Methyladenosine (m6A) messenger RNA methylation is a well-known epitranscriptional regulatory mechanism affecting central biological processes, but its function in human cellular senescence remains uninvestigated. Here, we found that levels of both m6A RNA methylation and the methyltransferase METTL3 were reduced in prematurely senescent human mesenchymal stem cell (hMSC) models of progeroid syndromes. Transcriptional profiling of m6A modifications further identified MIS12, for which m6A modifications were reduced in both prematurely senescent hMSCs and METTL3-deficient hMSCs. Knockout of METTL3 accelerated hMSC senescence whereas overexpression of METTL3 rescued the senescent phenotypes. Mechanistically, loss of m6A modifications accelerated the turnover and decreased the expression of MIS12 mRNA while knockout of MIS12 accelerated cellular senescence. Furthermore, m6A reader IGF2BP2 was identified as a key player in recognizing and stabilizing m6A-modified MIS12 mRNA. Taken together, we discovered that METTL3 alleviates hMSC senescence through m6A modification-dependent stabilization of the MIS12 transcript, representing a novel epitranscriptional mechanism in premature stem cell senescence.