Abstract 640: Genetic Inactivation of Col15a1 in Smooth Muscle Cells Decreases Plaque Size and Decreases Indices of Plaque Stability

Abstract

In the development of atherosclerosis, it is widely believed that contractile smooth muscle cells (SMC) increase their migratory and proliferative capacity and invade the neointima where they secrete extracellular matrix (ECM) to form a plaque stabilizing fibrous cap. We previously identified that collagen, type XV, alpha 1 (COL15A1) expression is increased in human atherosclerotic plaques and associated with lesion burden. COL15A1 has been shown to link large fibrillar collagens to confer ECM stability. Of interest, siRNA knockdown of Col15a1 in cultured human aortic SMC results in a decrease in proliferation and an increase in migration of SMC. Taken together, we hypothesize that SMC-derived COL15A1 plays a critical role in atherosclerosis by promoting matrix organization needed for lesion and fibrous cap stability. Due to ambiguity in identifying dedifferentiated SMC without lineage tracing, the contribution of SMC in producing COL15A1 and how loss of SMC-derived COL15A1 alters plaque morphology and cellular composition is unknown. As such, we generated inducible SMC specific lineage tracing ( Myh11 -CreER T2 ROSA floxed STOP eYFP ApoE -/- ) Col15a1 knockout (SMC- Col15a1 KO ) and wild-type (SMC- Col15a1 WT ) mice and placed them on Western diet for 18 weeks. SMC- Col15a1 KO exhibited a drastic decrease in overall plaque (~4 fold) and vessel (~1.5 fold) size. In addition, SMC- Col15a1 KO have a decrease in overall plaque collagen content (~3 fold) and collagen fiber maturation. With respect to cell type, SMC- Col15a1 KO demonstrated a decrease in overall plaque cell number (DAPI+, ~2 fold) and an increase in the proportion of macrophage (LGALS3+) cells and decrease in the proportion of SMC (YFP+) within plaques. SMC- Col15a1 KO showed a decrease in lesion SMC proliferative capacity in vivo (~2 fold) that was recapitulated in vitro in population doubling proliferation experiments using isolated primary aortic SMC from SMC- Col15a1 WT and SMC- Col15a1 KO . Interestingly, mixing 1:1 of WT and KO SMC lines was able to rescue the proliferation deficit. These studies provide the first evidence that a SMC derived collagen, COL15A1, is a significant and novel player in advanced atherosclerotic plaque progression, stability, and cellular content.