Abstract 12444: Smooth Muscle-Specific Deletion of Perk Prevents Atherosclerotic Plaque Formation in Mice

Introduction: Lineage tracing and single cell RNA sequencing (scRNA-Seq) studies have identified a subset of phenotypically modulated vascular smooth muscle cells (SMCs) that appear with atherosclerotic plaque formation in hyperlipidemic mice. These modulated SMCs (mSMCs) are de-differentiated, and increase expression of macrophage, fibroblast and stem cell markers. We previously showed that SMCs exposed to free cholesterol in vitro activate an endoplasmic reticulum unfolded protein response (UPR) and assume an mSMC phenotype, and blocking Perk specifically abolishes this SMC modulation. Methods: Here, we sought to define the role of Perk in atherosclerotic plaque formation using SMC-specific Perk knockout in C57BL6 mice ( Perk SMC-KO ) and inducing hyperlipidemia by PSCK9 DY overexpression and a high fat diet for 12 weeks. Results: Aortic Oil Red O staining and en face aortic analysis revealed no plaque formation in the Perk SMC-KO aorta, with the exception of some small plaques in the root, whereas the wild-type (WT) aortas had extensive plaque, especially in the aortic arch (N = 10, p<0.0001, Fig. 1A ). scRNA-Seq analysis of aortic tissue from the root to the arch from these mice showed no major differences in cell clusters between Perk SMC-KO and WT mice at baseline ( Fig. 1B ). In hyperlipidemic WT mice, SMC-derived cluster 8 expands and a new cluster 7 appears (circled in red, Fig. 1B ). In Perk SMC-KO mice, cluster 8 is similarly expanded with hyperlipidemia, while cluster 7 is completely absent ( Fig. 1B , bottom right). Cluster 7 in the WT atherosclerotic aortas is the only cluster with Perk expression and has significantly increased expression of macrophage markers and a subset of fibroblast-specific markers when compared to cluster 8. Conclusions: These data indicate that SMC phenotypic modulation plays a major role in atherosclerotic plaque formation and Perk is a key regulator of the SMC modulation that specifically contributes to atherosclerotic plaque burden.