Expression And Regulation Of Proprotein Convertase Subtilisin/Kexin Type 9 In Vascular Smooth Muscle Cells

PCSK9 is a key regulator of cholesterol homeostasis, acting via degradation of the LDL-receptor (LDL-R). Loss-of-function PCSK9 mutations result in very low LDL serum levels and protection from cardiovascular disease (CVD), supporting its important function as drug-target. Originating mainly from the liver and being absent in mononuclear inflammatory cells (MNCs), PCSK9 has been identified recently in vascular smooth muscle cells (VSMCs). Thus, the aim of this study was to investigate the regulation of PCSK9 in VSMCs by atherogenic/inflammatory growth factors and to determine the impact of VSMC-released PCSK9 on LDL-R expression in MNCs. Methods and results: PCSK9 mRNA and protein levels were selectively upregulated by the toll-like receptor-4 (TLR4) ligand lipopolysaccharide (LPS; 100 ng/ml), whereas TGFβ1 or angiotensin II stimulation had no effect. LPS facilitated PCSK9 mRNA and protein expression in a time- and concentration dependent manner. PCSK9 increases were selectively inhibited by TLR4 inhibition with the receptor-blocker CLI-059 and the JNK-inhibitor SP600125, whereas pharmacological inhibitors of ERK1/2, p38 or PI3-kinase pathways had no effect. ELISA-based analyses demonstrated that LPS significantly increased PCSK9 releases from VSMCs, which was further augmented by atorvastatin (10 μM) and ablated by gemfibrozil (250 μM). Furthermore, incubation of human monocytic THP-1 cells in conditioned media from LPS-stimulated VSMCs resulted in a significant reduction of LDL-R levels in MNCs, comparable to the effects of recombinant PCSK9. In contrast, LPS stimulation of MNCs did not affect LDL-R expression. Conclusion: TLR4 signaling, upregulates PCSK9 in VSMCs thereby integrating metabolism and inflammation,. Inflammation-induced PCSK9 is diversely affected by cholesterol-lowering drug: whereas statin-treatment augments PCSK9, fibrates inhibit it. Furthermore, we demonstrate that PCSK9 secretion from VSMCs facilitates LDL-R degradation in MNCs, suggesting tide interplay of VSMCs and MNCs in cholesterol homeostasis crucial to CVD.