Abstract Tu0053: Senescent cells accumulate by escaping immunosurveillance and temporarily suppressing the activity of macrophages in atherosclerosis

Senescent cells are detrimental to vascular diseases of aging, including atherosclerosis, mainly through the production of the senescence-associated secretory phenotype (SASP) and its downstream effects. An understudied but highly important aspect of senescent cell accumulation in the vasculature is the immune system’s inability to clear these damaging cells. We hypothesize that senescent cells escape immunosurveillance to impair immune function in the atherosclerotic niche. To investigate this, we set out to 1) characterize the effect of senescent VSMCs on macrophage function and 2) map the cell surface of senescent human vascular smooth muscle cells (VSMCs) to determine the proteins interacting with the immune cells. First, we measured the capacity of senescent VSMCs for oxLDL uptake, which was impaired compared to control cells. Next, we obtained monocytes from human peripheral blood and differentiated them into macrophages using granulocyte-macrophage colony-stimulating factor (GM-CSF). We treated the macrophages with conditioned media derived from proliferating, quiescent, and senescent VSMCs and measured oxLDL uptake, phagocytosis, and efferocytosis. The results demonstrated impaired phagocytic activity of both oxLDL and zymosan green, and reduced ability to clear senescent cells compared to controls. Next, to understand the proteins mediating these functional changes, we performed cell surface capture proteomics on senescent and proliferating VSMCs. Mass spectrometry analysis revealed 160 proteins were increased, whereas 20 proteins were decreased on the cell surface of senescent as compared to proliferating VSMCs using |log2 fold change| > 1.5. Notably, proteins involved in immune checkpoint inhibition and complement mediated-cell lysis protection, such as programmed death-ligand 1 (PD-L1, CD274) and CD59, respectively, were increased; DPP4 which has been previously reported to increase in senescent VSMCs was also elevated. We propose that senescent cells may express immune checkpoint and integrin-like proteins that can help them escape immunosurveillance, allowing the SASP to disrupt the phagocytic function of macrophages, and hindering their capacity to clear the senescent cells. Therefore, disrupting the senescent VSMC-macrophage communication through surface or secreted proteins may offer promising avenues of therapeutic development to prevent or improve inflammatory vascular diseases.