A Signature of Senescence Based on An Analysis of Selected Markers in Primary Vascular Smooth Muscle Cells Cultured In Vitro and Derived from Atherosclerotic Plaque

Cellular senescence is a state of stable growth arrest that is accompanied by a characteristic phenotype. The senescent phenotype is dynamic and heterogeneous, and it depends on both the type of cell and the factors that trigger senescence. There is no single biomarker that is shared by all senescent cell types. Therefore, our studies aimed to define a set of biomarkers that can discriminate among proliferating, senescent and temporally growth-arrested (quiescent) cells. We analysed vascular smooth muscle cells (VSMCs) derived from healthy aortae that underwent senescence in vitro but also VSMCs isolated from human atherosclerotic plaques that underwent senescence in vivo. Our results demonstrate that changes in the levels of nuclear proteins (Lamin B1, HMGB1, PARP1) are the most consistent, stable and widespread in cells senescing in vitro while changes in the levels of signalling proteins implicated in senescence (p53, p21CIP, p16INK4A) appeared to be more variable. VSMCs derived from atherosclerotic plaques reflects pattern of senescence biomarker expression observed in VSMCs undergoing in vitro senescence but some differences were revealed. There was a gradual decrease in p21CIP level and an increase in p16INK4A level as VSMCs cultured in vitro progressed toward late senescence or entered replicative senescence, whereas plaque-derived senescent VSMCs showed increased p21CIP and p16INK4A protein expression compared with proliferating VSMCs from healthy aortas. Overall, we have defined a set of biomarkers that is common for VSMCs undergoing in vitro and in vivo senescence and enable to recognize senescent cells with high confidence, regardless of senescence trigger and senescence phase (early versus late).