Abstract 19083: Macrophage Expression of Pcsk9 Influences Atherosclerosis Development
Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secretory protein that regulates low-density lipoprotein (LDL) cholesterol levels by binding and degrading hepatic LDL receptor (LDLR), thus contributing to atherosclerosis. Little is known of PCSK9 effect in macrophages and whether this contributes to the development of the atheroma.
First, we demonstrated that murine peritoneal macrophages (MPM) express endogenous (m) PCSK9 both at the mRNA and protein level. Then, to test the effect of human (h) PCSK9 on atherosclerosis we developed transgenic mice expressing hPCSK9 from multiple tissues and cells, including macrophages. As it occurs in hepatocytes, hPCSK9 reduced LDLR levels in MPM. The effect on LDLR was more evident in resident than in elicited MPM, and was completely abolished after culturing MPM in medium containing FBS or LPDS, that cause LDLR upregulation. Co-immunoprecipitation experiments showed a direct interaction of hPCSK9 with LDL-R. In addition, we found that PCSK9 also interacts with LRP-1, a member of the LDL-R gene family involved in modulation of inflammatory responses and cell survival. It has been recently reported that PCSK9 reduces LRP1 levels in transduced renal HEK293T cells. However, we found that the interaction of hPCSK9 with LRP1 did not affect either total or membrane levels of the receptor. Surprisingly, analyses of spleen lysates from hPCSK9 transgenics revealed an increase in the percentage of Ly6Chi and CD11b positive cells compared with WT. To study the effect of macrophage PCSK9 in the atheroma, bone marrow from hPCSK9/apoE-/- or apoE-/- mice was transplanted into apoE-/- recipients. Low levels of hPCSK9 were detected in serum of hPCSK9/apoE-/- marrow recipients, but no effects on cholesterol were noted. Although lesion size was not different, lesion composition analyses showed a higher percentage of Ly6Chi positive cells in recipients of hPCSK9/apoE-/- marrow compared to controls (7.4±1.5% vs. 5.6±1.1%, respectively, p<0.05).
Our results show for first time that PCSK9 expression by macrophages directly influences atherosclerotic plaque composition in the absence of changes in serum cholesterol levels, suggesting a direct effect of macrophage PCSK9 in inflammation and plaque development.
- © 2013 by American Heart Association, Inc.