Abstract Body: Senescent vascular smooth muscle cells (VSMCs) accumulate during atherosclerosis and produce the senescence-associated secretory phenotype (SASP), which disrupts the extracellular matrix and increases the necrotic core. Growth differentiation factor-15 (GDF15), a conserved SASP factor, is a known prognostic marker for cardiovascular disease and aging, suggesting that GDF15 plays a key role in the intersection of senescence and vascular disease. In human VSMCs, GDF15 levels are elevated early in senescence and remain high as senescence progresses. Additionally, GDF15 protein levels are increased in atherosclerotic mice and young and old monkeys fed a high-fat diet. In humans with high Framingham risk scores, circulating GDF15 levels are also elevated compared to those with low risk. To investigate the role of GDF15 in early senescence, we silenced GDF15 (GDF KO) using CRISPRi and performed RNA sequencing. Pathway analysis revealed enrichment in interferon signaling upon GDF15 loss, which was validated, and coincided with an increased phosphorylation of STAT1 and CREB, as determined by a phosphoarray. Overexpression of GDF15 via CRISPRa suppressed the same interferon-related transcripts. Given the role of interferons in activating and regulating macrophage function in atherosclerosis, we hypothesize that GDF15 is crucial for the suppression of interferon signaling, which may influence immune cell activity within the atherosclerotic microenvironment. To test this hypothesis, we examined the effects of conditioned media from senescent VSMCs, with or without GDF15 KO, on macrophages differentiated from the peripheral blood of six individuals (both male and female). Macrophages exposed to GDF15 KO media exhibited significantly increased ox-LDL uptake and enhanced general phagocytosis compared to those treated with control media. Furthermore, macrophages treated with GDF15 KO media demonstrated enhanced clearance of senescent cells via efferocytosis. RNA sequencing of these macrophages revealed increased expression of phagocytosis-related transcripts and downstream effectors, suggesting that senescent VSMCs produce GDF15 to suppress macrophage phagocytic function. This repression may prevent the clearance of senescent cells, allowing their accumulation and promoting arterial remodeling and disease progression.