Proprotein Convertase Subtilisin/Kexin Type 6 Is A Key Protease In The Control Of Smooth Muscle Cell Function In Vascular Disease

Proprotein convertases (PCSKs) process matrix metalloproteases (MMPs) and cytokines. Apart from PCSK9, the role of these enzymes in vascular disease is largely unknown. Previously, we demonstrated upregulation of PCSK6 in carotid atherosclerosis, primarily localized to smooth muscle cells (SMCs) and positively correlated to inflammation, extracellular matrix remodeling and cytokines. Here, we extended these findings to determine the role of PCSK6 in vascular development and disease. Increased expression of PCSK6 in vascular disease was validated by microarrays from two non-overlapping cohorts of carotid plaques vs. non-atherosclerotic arteries (n=50 patients and n=32 patients, p<0.0001), as well as abdominal (AAA, n=14, p<0.0001) and thoracic aortic aneurysms (TAA, n=244, p=0.012). By eQTL, variants in the PCSK6 gene were found to influence it’s expression in both plaques and aneurysms. Among these, rs6598465 also showed association with maximum progression of carotid intima-media thickness in high-risk coronary artery disease subjects (n=3388, p=0.037). By IHC, PCSK6 localized mainly to SMCs in the fibrous cap and neovessels in atherosclerotic, AAA and TAA tissues. In mouse-, rat-, and human intimal hyperplasia, PCSK6 was expressed in proliferating SMCs. By microarrays, after rat carotid balloon injury there was an early downregulation of PCSK6 followed by an upregulation in later phases during SMC activation, as well as positive correlation to PDGFB and IGF1 (Spearman r>0.7, p<0.0001) and to MMP2 and MMP14 (r>0.5, p<0.0001). In zebrafish embryos, PCSK6 localized to heart and vasculature and its ablation caused defective peripheral vascular patterning with cerebral and myocardial hemorrhage. PCSK6 -/- mice did not present an obvious vascular phenotype but showed reduced intimal hyperplasia compared to wild-type mice after carotid artery ligation (p=0.015). In vitro, PCSK6 overexpression markedly increased SMC migration upon PDGFBB stimulation (p<0.0001). The present study establishes PCSK6 as a key modulator of SMC function in vascular disease and demonstrates a functional link between PCSK6 expression and SMC migration in vascular remodeling.