Cell senescence impedes the self‑renewal and osteogenic capacity of bone marrow mesenchymal stem cells (BMSCs), thus limiting their application in tissue regeneration. The present study aimed to elucidate the role and mechanism of repetitive element (RE) activation in BMSC senescence and osteogenesis, as well as the intervention effect of quercetin. In an H2O2‑induced BMSC senescence model, quercetin treatment alleviated senescence as shown by a decrease in senescence‑associated β‑galactosidase (SA‑β‑gal)‑positive cell ratio, increased colony formation ability and decreased mRNA expression of p21 and senescence‑associated secretory phenotype genes. DNA damage response marker γ‑H2AX increased in senescent BMSCs, while expression of epigenetic markers methylation histone H3 Lys9, heterochromatin protein 1α and heterochromatin‑related nuclear membrane protein lamina‑associated polypeptide 2 decreased. Quercetin rescued these alterations, indicating its ability to ameliorate senescence by stabilizing heterochromatin structure where REs are primarily suppressed. Transcriptional activation of REs accompanied by accumulation of cytoplasmic double‑stranded (ds)RNA, as well as triggering of the RNA sensor retinoic acid‑inducible gene I (RIG‑I) receptor pathway in H2O2‑induced senescent BMSCs were shown. Similarly, quercetin treatment inhibited these responses. Additionally, RIG‑I knockdown led to a decreased number of SA‑β‑gal‑positive cells, confirming its functional impact on senescence. Induction of senescence or administration of dsRNA analogue significantly hindered the osteogenic capacity of BMSCs, while quercetin treatment or RIG‑I knockdown reversed the decline in osteogenic function. The findings of the current study demonstrated that quercetin inhibited the activation of REs and the RIG‑I RNA sensing pathway via epigenetic regulation, thereby alleviating the senescence of BMSCs and promoting osteogenesis.

Summary In most eukaryotic cells, euchromatin is localized in the nuclear interior, whereas heterochromatin is enriched at the nuclear envelope (NE). This conventional chromatin organization is established by heterochromatin tethering to the NE, however its importance for cellular homeostasis is largely unexplored. Peripheral heterochromatin localization relies on redundant NE-tethering systems. One tether is constituted by the lamin B receptor (LBR) in mammals, but the enigmatic nature of the other tethers has hampered functional analyses. Here we demonstrate that the downregulation of abundant, ubiquitous NE proteins can induce the global detachment of heterochromatin from the NE. Among these factors, we identify LBR and LAP2 as major players in bulk heterochromatin attachment to the NE in pluripotent and differentiated mammalian cells. Their loss leads to repositioning of heterochromatin to the nuclear interior, changes in chromatin accessibility, deregulation of gene expression including activation of antiviral innate immunity, and defects in cell fate determination.

The Nuclear envelope (NE) is frequently challenged by mechanical stimuli involving cells passing through a tight space and such stress is known as "NE stress." Various factors that cooperate to repair the NE have been identified, including endosomal sorting complex required for transport-III (ESCRT-III). Recently, vacuolar protein sorting 4 homolog B (VPS4B) has been reported to modulate the recycling of ESCRT-III during NE repair, but the regulatory mechanism remains unclear. Our previous study revealed that U251MG cells, derived from the glioblastoma (GBM), exhibited nuclear deformation followed by DNA damage upon mechanical NE stress while these phenotypes were not observed in U87MG, another GBM-derived cell line. Here, we found that VPS4B expression was lower in U251MG than in U87MG. Our functional analysis demonstrated that insufficient VPS4B triggers an inadequate response to NE stress and that VPS4B regulates the dynamics of ESCRT-III, uncovering the mechanism underlying the NE stress response in GBM.

Dysfunction of the ribosome manifests during cellular senescence and contributes to tissue aging, functional decline, and development of aging-related disorders in ways that have remained enigmatic. Here, we conducted a comprehensive CRISPR-based loss-of-function (LOF) screen of ribosome-associated genes (RAGs) in human mesenchymal progenitor cells (hMPCs). Through this approach, we identified ribosomal protein L22 (RPL22) as the foremost RAG whose deficiency mitigates the effects of cellular senescence. Consequently, absence of RPL22 delays hMPCs from becoming senescent, while an excess of RPL22 accelerates the senescence process. Mechanistically, we found in senescent hMPCs, RPL22 accumulates within the nucleolus. This accumulation triggers a cascade of events, including heterochromatin decompaction with concomitant degradation of key heterochromatin proteins, specifically heterochromatin protein 1γ (HP1γ) and heterochromatin protein KRAB-associated protein 1 (KAP1). Subsequently, RPL22-dependent breakdown of heterochromatin stimulates the transcription of ribosomal RNAs (rRNAs), triggering cellular senescence. In summary, our findings unveil a novel role for nucleolar RPL22 as a destabilizer of heterochromatin and a driver of cellular senescence, shedding new light on the intricate mechanisms underlying the aging process.
© The Author(s) 2024. Published by Oxford University Press on behalf of Nucleic Acids Research.

Aging has a profound impact on the gingiva and significantly increases its susceptibility to periodontitis, a worldwide prevalent inflammatory disease. However, a systematic characterization and comprehensive understanding of the regulatory mechanism underlying gingival aging is still lacking. Here, we systematically dissected the phenotypic characteristics of gingiva during aging in primates and constructed the first single-nucleus transcriptomic landscape of gingival aging, by which a panel of cell type-specific signatures were elucidated. Epithelial cells were identified as the most affected cell types by aging in the gingiva. Further analyses pinpointed the crucial role of YAP in epithelial self-renew and homeostasis, which declined during aging in epithelial cells, especially in basal cells. The decline of YAP activity during aging was confirmed in the human gingival tissues, and downregulation of YAP in human primary gingival keratinocytes recapitulated the major phenotypic defects observed in the aged primate gingiva while overexpression of YAP showed rejuvenation effects. Our work provides an in-depth understanding of gingival aging and serves as a rich resource for developing novel strategies to combat aging-associated gingival diseases, with the ultimate goal of advancing periodontal health and promoting healthy aging.
© The Author(s) 2024. Published by Oxford University Press on behalf of Higher Education Press.