Phase Separation of MRG15 delays cellular senescence [CUT&Tag]

Phase separation, a biophysical process that segregates subcellular environments into condensates, is recognized for its role in regulating transcription. However, the extent of its influence on cellular senescence processes remains to be fully elucidated. Here, we have established that the depletion of MRG15, a conserved chromodomainprotein, leads to cellular senescence in human mesenchymal stem cells (hMSCs). MRG15 is capable of forming phase-separated liquid condensates via its intrinsically disordered region (IDR). Through the utilization of IDR deletion and replacement assays, we have shed light on the pivotal role that MRG15 condensation plays in the senescence of hMSCs. Through epigenomic and transcriptomic analysis, the depletion of MRG15 impacts pathways that are integral to the cell cycle and the senescence process, as evidenced by the diminished binding and the modified expression of key genes, including CDKN1A, LMNB1, CCNB1, NPM1, MYC, and HMGB2. Within a bleomycin-induced model of idiopathic pulmonary fibrosis in mice, hMSCs of the wild-type variety were able to ameliorate inflammation and fibrosis, a stark contrast to the outcomes observed in MSCs where MRG15 was knocked down or its IDR was deleted. Our findings establishes a link between phase separation and senescence regulation and could present a promising new therapeutic target for the alleviation of age-related diseases and the potential extension of lifespan. Overall design: To investigate the genomic binding sites of MRG15 and its role in cellular senescence, we performed Cleavage Under Targets & Tagmentation (CUT&Tag) of MRG15 in HEK293T cells.