Abstract Body: Vascular diseases, including atherosclerotic disease, are the leading cause of mortality worldwide. Epidemiological data points to sex-based differences in vascular disease risk, but the pathophysiological mechanisms remain poorly understood. Clinical observations suggest these differences originate within the vessel wall, but the mechanism that governs these sex-specific difference is not known. We hypothesized that sex-specific vascular disease susceptibility arises from interactions between sex chromosome–encoded epigenetic regulators and environmental exposures such as cigarette smoke. To study this, male and female ApoE knockout mice were exposed to cigarette smoke for 7 weeks and fed high-fat diet (HFD) for 8 weeks (Exposed cohort). As a control cohort, the other set were only fed HFD for 8 weeks. Throughout the exposure period, weekly weights and blood pressures were obtained. The aortic roots and descending aortae were harvested and processed for single-cell transcriptomic analysis (scRNA-seq). The data was integrated with human genetic data to identify the biological processes and regulatory regions driving sex-specific responses. A set of the aortic root and descending aorta were also used for immunohistology. At the end of the exposure period, there was gross evidence of early plaque development in the aortic root and descending aorta. Differential gene expression analysis of each segmental cell population reveals increased sex differences in smooth muscle cells (SMCs) and fibroblasts, compared to other cell types present. Increased transcriptomic differences show up in both male and female SMCs and fibroblasts for smoking and high-fat diet exposure relative to HFD alone. Further, GSEA reveals over-enrichment of pathways related to epigenetic modifications in female cells, compared to male cells. Notably, the X-linked histone demethylase Kdm6a and Kdm5c emerged as a top differentially expressed gene in descending SMCs with strong sex-specific significance, while showing modest regulation in root-derived cells. Smoking exposure downregulated Kdm6a and Kdm5c for both the sex, females more than males, as compared to HFD only which further affected matrix remodeling pathway. This study reveals significant sex-specific, vascular cell-type specific transcriptional and epigenetic mechanisms in vascular disease and shows sex chromosome-encoded epigenetic modifiers, particularly Kdm6a and Kdm5c, as pivotal in vascular cell plasticity in atherosclerosis.