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Absence of Cpla2 in Lrp1 Smooth Muscle Cell-Deficient Mice Promotes Severe Aortic Atherosclerotic Disease

      Smooth muscle cell targeted deficiency of low-density lipoprotein (LDL) receptor-related protein 1 (LRP1) in a mouse model (smLRP1–/–) results in accelerated aortic atherosclerosis through activation of cytoplasmic phospholipase A2 (cPLA2), leading to reduced ABCA1 expression in vascular smooth muscle cells, and increased intracellular cholesterol accumulation. We therefore hypothesized that deficiency of cPLA2 would impede atherogenesis in the smLRP1–/– mouse model.

      Methods

      Adult male smLRP1–/–;cPLA2–/–;LDLR–/– (triple knockout) mice were placed on a high cholesterol diet for 16 weeks and compared with age- and diet-matched sibling control smLRP1+/+;cPLA2–/–;LDLR–/– mice. Histologic analysis was performed using en face whole aorta Oil red O (ORO) staining, as well as a cross-sectional analysis of the aortic root with ORO, Picro Sirius red, Alizarin red, and immunofluorescence. Immunoblot protein analysis was performed using lysed whole aortas. Data are presented as mean ± standard error of the mean. Statistical analysis was performed using one- and two-way analysis of variance with Tukey’s correction.

      Results

      En face ORO analysis revealed increased lipid accumulation in triple knockout mice as compared with controls (60 ± 3% vs 13 ± 2%; P < .001) (Fig). Uniquely, triple knockout mice develop extensive necrotic cores and thin fibrous caps in atherosclerotic lesions in the aortic root (Fig). ABCA1 is paradoxically increased both in whole aorta lysate as well as in immunofluorescence staining of the aortic root.

      Conclusions

      Deficiency of cPLA2 in the smLRP1–/– mouse model rescued ABCA1 expression, but unexpectedly increased lipid accumulation within the plaque and generated more vulnerable plaque. Future studies will underpin the mechanisms that guide severe disease development in our triple knockout mice via regulation of ABCA1.

      Funding

      NHLBI R37 HL063762 and NINDS/NIA R01NS108115.
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      FigHistologic analysis using en face whole aorta and aortic root cryosection Oil red O (ORO) staining for atherosclerotic lesions.