Abstract 367: Pcsk6 Is a Key Protease Modulating Smooth Muscle Cell Activation in Vascular Remodeling and Plaque Vulnerability

Proprotein convertases (PCSKs) are conserved among species and involved in processing of MMPs and growth factors, but poorly characterised in atherosclerosis. Previously we demonstrated upregulation of PCSK6 in a large cohort of plaques from symptomatic vs. asymptomatic patients. This protease localized to smooth muscle cells (SMCs) and showed a positive correlation to markers of inflammation, extracellular matrix remodeling and cytokines in plaques. Here we aimed at elucidating its role in vascular development and disease. In zebrafish embryos PCSK6 localized to heart and vasculature and its ablation caused defective peripheral vascular patterning with cerebral and myocardial hemorrhage. Increased expression of PCSK6 in vascular pathologies was validated by microarrays from carotid plaques vs. undiseased arteries (n=32 patients, p<0.0001), abdominal (AAA, n=14, p<0.0001) and thoracic aortic aneurysms (TAA, n=244, p=0.012). By immunohistochemistry, PCSK6 localized mainly to SMCs in the fibrous cap and neo-vessels in plaques, AAA and TAA tissues. Investigation of mouse carotid ligation, rat artery balloon injury and human restenosis tissues with pronounced intimal hyperplasia confirmed induction of PCSK6 in proliferating SMCs. By microarrays following progression of rat carotid injury, PCSK6 was downregulated in early phases defined by inflammatory pathways, while upregulated in later phases with SMCs activation and localized in SMCs. Expression of PCSK6 in this model was positively correlated to PDGFB and IGF1 (Spearman r>0.7, p<0.0001). PCSK6 overexpression in SMCs in vitro increased their migration in a wound-healing assay, especially upon PDGFBB stimulation. By eQTL analyses several polymorphisms in the PCSK6 gene were found to influence its expression in plaques and aneurysm tissue. Among these, rs6598465 showed association with maximum progression of arterial intima-media thickness in high-risk coronary artery disease subjects (n=3400, p=0.037). We identified a functional link between elevated expression of PCSK6 and vascular remodeling characterized by SMC activation. The present study establishes PCSK6 as one of the key modulators of pathological processes in relation to plaque vulnerability.