PCSK9 with a gain of function D374Y mutation aggravates atherosclerosis by inhibiting PPARα expression

The preprotein convertase, Bacillus subtilis protease/kexin type 9 serine protease (PCSK9), has garnered significant attention as a potential lipid lowering and therapeutic drug target for atherosclerosis (AS). Peroxisome proliferator-activated receptor alpha (PPARα) is expressed in various tissues and has crucial roles in lipid metabolism and the inflammatory response; however, the precise impact of PCSK9 on AS progression through its regulation of PPARα remains uncertain. The present study aimed to examine the impact of introducing stable liver transduction of human derived PCSK9 with a gain of function D374Y mutation (PCSK9^DY) into systemic PPARα knockout mice (PPARα^-/-) on plasma lipid levels and AS. Enzymatic assays were employed to evaluate plasma lipid concentrations at various time points, and aortic plaque formation and the degree of inflammatory infiltration quantified. Subsequently, we validated our in vivo results using mouse primary peritoneal macrophages (MPMs). Furthermore, AAV8.2-PPARα virus vector was transduced into transgenic mice of human PCSK9(hPCSK9^DY-Tg) by tail vein, and the changes of plasma lipid level and AS were detected. PCSK9^DY expression exacerbated symptoms of hypercholesterolemia in PPARα^-/- mice. En face analysis and quantification of aortic root sections demonstrated a significant increase in aortic plaque area and inflammatory infiltration in PCSK9^DY transduced PPARα^-/- mice. Secretion of inflammatory cytokines was elevated in PCSK9^DY transduced PPARα^-/- mice. In vitro, recombinant hPCSK9 protein promotes the foam cell formation and inflammatory cytokines secretion of PPARα^-/- MPMs by increasing the expression of SR-A and TLR4/NF-κB pathway proteins. AAV8.2-PPARα virus vector can reduce the plasma lipid level and AS formation in hPCSK9^DY-Tg mice. These finding demonstrate that PCSK9^DY expression notably facilitated AS progression in PPARα^-/- mice by increasing plasma lipid concentrations and inflammation. However, overexpression of PPARα can reduce AS formation in hPCSK9^DY-Tg mice.