Abstract Tu0010: Smooth muscle cell PCSK6 deficiency aggravates mouse abdominal aortic aneurysm progression via increased inflammation and dysfunctional coagulation control

Background and aims: We have previously discovered that Proprotein Convertase Subtilisin/Kexin type 6 (PCSK6) plays a key role in vascular disease by smooth muscle cell (VSMC) migration, proliferation, and extracellular matrix (ECM) remodeling via MMP2/MMP14 axis. Transcriptomic data from the Stockholm abdominal aortic aneurysm (AAA) biobank demonstrated elevated PCSK6, especially in the medial layer, while histology showed its presence in T cells. This study aimed to investigate the role and regulatory mechanisms of Pcsk6 in AAA further. Methods and Results: Bulk RNA-seq AAA data from the Munich aortic biobank confirmed the upregulation of PCSK6 in AAA tissues, in particular in patients with ruptures. Human scRNA-seq data from AAAs showed strong PCSK6 expression in fibroblasts, T cells and macrophages, while mouse scRNA-seq data detected it in multiple cell types, most notably ECs, VSMCs, fibroblasts, T cells and macrophages. Functional in vivo studies were therefore performed using 1) peri-adventitial porcine pancreatic elastase (PPE) and 2) Ang II infusion-induced AAA models in male global Pcsk6 -/- mice, VSMC-ablated Tagln cre/cre Pcsk6 fl/fl mice, as well as these mice on ApoE -/- background and appropriate controls. After 4 weeks of AAA diameter follow-up with ultrasound, abdominal and thoracic aorta tissues were harvested for RNA-seq profiling and histology. Although there was no difference in baseline aortic function between Pcsk6 ablated vs. control mice by ex vivo myograph studies, ultrasound imaging showed that VSMC-ablated mice manifested larger AAAs with increased rupture rates. Mechanistically, AAA tissues from VSMC-ablated Pcsk6 mice revealed a reduction in collagen abundance, but remarkably increased T-cell and macrophage infiltration, as well as higher expression of Mmp2, Mmp14, and Il6. Moreover, RNA-seq data showed significantly elevated levels of platelet glycoprotein V (GP5) in VSMC Pcsk6 deficient aneurysms, indicating platelet and coagulant dysfunction. Conclusion: Aortic Pcsk6 plays an essential role in VSMC activation, ECM production, inflammation inhibition, as well as platelet and coagulant function, which are critical processes to prevent AAA progression and rupture.