The Role of SASP Factor GDF15 in Vascular Smooth Muscle Cell Senescence and Atherosclerosis

Abstract

Atherosclerosis is an aging-related disease characterized by the buildup of plaque and hardening of the arteries over time. Previous studies have identified senescent cells in mouse and human atherosclerotic plaques. Cellular senescence, a hallmark of cells in aging tissues, is marked by irreversible growth arrest, elevated lysosomal activity, and increased production of p16, p21, p53 and SASP factors such as cytokines (e.g. IL-6, IL-8), chemokines (e.g. CCL2), adhesion molecules (e.g. ICAM-1), and angiogenic factors (e.g. VEGF). VSMCs cultured from atherosclerotic plaques express numerous markers of senescence, suggesting an important role for senescent cells in the development of vascular disease; however, the mechanisms that regulate senescence in vascular cells remain mostly unknown. In order to deepen our understanding of VSMC senescence, we assessed the changes in gene expression following exposure to senescence-inducing hypoxia. We identified a number of transcripts that were differentially expressed in senescent VSMCs using a microarray, and one transcript, GDF15 mRNA, encoding the growth factor GDF15, involved in the regulation of the cell cycle, was strongly and continuously induced with the progression of senescence. GDF15 has previously been found to be a novel SASP factor secreted in response to cellular stress and evidence suggests it can have pro- and anti-apoptotic and pro- and anti-inflammatory roles depending on the context and stage of vascular disease progression. Paracrine signaling to the surrounding cells (endothelial, macrophages, VSMCs, etc.) via SASP is crucial to the development of atherosclerosis in senescent cells, but little is known about the role of GDF15 in this process. We tested VSMCs with the traditional senescence model (Doxorubicin) and confirmed the significant increase in GDF15 mRNA conserved across different senescence systems in VSMCs, including hypoxia-induced senescence. Further, knockdown of GDF15 in pre-senescent VSMCs resulted in increased cell proliferation and decreased levels of senescence markers p21 and IL-6 mRNAs. Overall, our preliminary data suggests that VSMCs induce GDF15 steadily during the progression to senescence and that reducing GDF15 can help slow the progression of senescence in pre-senescent cells. We hypothesize that enhanced GDF15 expression in senescent VSMCs promotes inflammation and atherosclerosis development, and that therapeutically targeting GDF15 could offer new avenues for attenuating vascular disease. To confirm this, we will further investigate the role of GDF15 in senescent VSMCs using immunofluorescence and murine models of atherosclerosis to determine the mechanism by which GDF15 uniquely contributes to vascular cell senescence and increased disease progression.