ИСТИНА

Recent studies have uncovered profound alterations in the protein secretion from senescent cells, which is collectively called the senescence-associated secretory phenotype (SASP). The SASP factors secreted by senescent cells may contribute to the proliferative arrest of surrounding cells through autocrine/paracrine pathways, thus promoting their senescence. The secretome profiling of human endometrium-derived mesenchymal stem cells (MSCs) remains yet unknown. Here, we for the first time provide insights into MSCs secretome. Initially, we tested the hypothesis that the conditioned media from senescent (H2O2-treated) MSCs (CM-sen) are capable of triggering the premature senescence in young MSCs. Exposure to CM-sen induced phosphorylation of ATM, H2A.X, 53BP1 and their co-localization within discrete foci, leading to activation of both DNA damage response and p53/p21/Rb pathway. In young MSCs, CM-sen contributed to a reduction in the proliferation rate, the significant changes in the cell phenotype as well as an increase in SA-ß-Gal staining. Further, by applying high resolution LC-MS analysis we carried out a comprehensive study of MSCs secretome. The quantitative analysis performed by spectral counting revealed that 92 and 141 proteins were uniquely identified in secretome of senescent and control cells respectively while a set of proteins was significantly up- and down-regulated in CM-sen versus CM-ctr. A bioinformatic analysis revealed that a significant number of proteins up-regulated in senescent cells was involved in cell-matrix interactions, cytoskeleton organization, cell-adhesion complexes, cell growth regulation. Among proteins strongly up-regulated in senescent cell secretome, insulin-like growth factor binding protein 3 (IGFBP3) was found. To evaluate its role in senescence promoting of young cells, the CM-sen immunodepletion assays were performed. Treatment with anti-IGFBP3 antibody evidenced a blocking effect on the pro-senescence activity of CM-sen. Together, the results obtained suggest a crucial role for the extracellular secreted IGFBP3 in the regulation of cellular senescence.