PCSK9 regulates expression of scavenger receptors and ox-LDL uptake in macrophages

Aims Proprotein convertase subtilisin/kexin type 9 (PCSK9) has been shown to influence macrophage biology and modulate atherogenesis. We conducted this study to examine the regulation of scavenger receptors (SRs) (LOX-1, SRA, and CD36) and oxidized liporoptein cholesterol (ox-LDL) uptake in macrophages by PCSK9. Methods and results Treatment of mouse peritoneal macrophages with tumour necrosis factor alpha (TNF-alpha) resulted in concentration-dependent modest, but significant, increase in PCSK9 expression. Importantly, treatment of TNF-alpha primed macrophages with recombinant murine PCSK9 increased the expression of LOX-1, SRA, and CD36 2-5 fold, and enhanced ox-LDL uptake by approximate to five-fold. The increase in LOX-1 was much greater than in SRA or CD36. PCSK9 inhibition (by siRNA transfection or use of macrophages from PCSK9(-/-) mice) reduced the expression of SRs (LOX-1 >> SRA or CD36). Ox-LDL uptake in response to PCSK9 was also inhibited in macrophages from LOX-1(-/-) mice (P < 0.05 vs. macrophages from SRA(-/-) and CD36(-/-) mice). Upregulation of PCSK9 by cDNA transfection induced intense ox-LDL uptake which was inhibited by co-transfection of cells with siRNA LOX-1 (P < 0.05 vs. siRNA SRA or siRNA CD36). Further, TNF-alpha-mediated PCSK9 upregulation and subsequent expression of SRs and ox-LDL uptake were reduced in macrophages from gp91phox(-/-), p47phox(-/-) and p22phox(-/-) mice (vs. macrophages from wild-type mice). Conclusions This study shows that in an inflammatory milieu, elevated levels of PCSK9 potently stimulate the expression of SRs (principally LOX-1) and ox-LDL uptake in macrophages, and thus contribute to the process of atherogenesis.