Abstract Body: Introduction: Foam cell formation is the key driver of plaque build-up in atherosclerosis. Recent lineage tracing and single-cell analyses have shown that, in addition to macrophages, smooth muscle cell (SMC)-derived cells represent major contributors to plaque foam cells in mice and human atherosclerosis. Compared to macrophages, SMCs have a lower expression of lysosomal acid lipase (LIPA), the only known acidic lipase responsible for lipid hydrolysis within the lysosome. In vitro cell culture studies suggest that supplementing LIPA in SMCs reduces foam cell formation by enhancing lysosomal lipid breakdown, implying that LIPA overexpression in SMCs may have atheroprotective effects. This study aims to assess how SMC-specific overexpression of Lipa will affect atherogenesis in vivo using mouse models.
Methods: Myh11-CreER^T2-mediated SMC-Lipa overexpression mice (SMC-Lipa^KI) and the respective control mice (Ctrl), both on an Ldlr^-/- background, were crossed with a floxed tdTomato reporter mice to enable SMC lineage tracing during experimental atherosclerosis.
Results: LIPA protein levels in SMCs were 1.59-fold higher in advanced plaques (16 weeks) than in early plaques (8 weeks) of Western diet (WD) feeding. In human carotid plaques, LIPA protein levels were also higher in αSMC⁺ intimal SMCs than medial SMCs (1.31-fold). OxLDL loading significantly increased both mRNA and protein levels of LIPA in primary human coronary artery SMCs (hCASMC). Myh11-CreER^T2-mediated SMC-Lipa^KI mice showed a significant increase in thoracic lesion area compared to Ctrl mice after 12 and 20 weeks of WD feeding. Additionally, SMC-Lipa^KI mice fed a WD for 20 weeks exhibited increased lesion area and necrotic core area, along with reduced fibrous cap thickness in the aortic sinus, compared to Ctrl mice, without changes in plasma cholesterol levels. Mechanistically, SMC-Lipa^KI significantly increased the percentage of SMC-derived foam cells relative to total SMCs in aortic lesions. siRNA-mediated knockdown of LIPA in hCASMCs resulted in the neutral lipids sequestration within the lysosomes and reduced cholesterol efflux, while oxLDL uptake remained unaffected. Conversely, In primary mouse SMCs, Lipa^KI increased oxLDL uptake and promoted neutral lipid accumulation.
Conclusion: Our results suggest that SMC-Lipa^KI significantly increased atherosclerosis by increasing SMC-derived foam cell formation.