Abstract Body: Aims: Our previous results from single-cell RNA sequencing of human aortic tissue revealed that proprotein convertase subtilisin/kexin type 6 (Pcsk6) expression is reduced in aortic fibroblasts from abdominal aortic aneurysms (AAAs) compared to non-dilated aortas, but increased in inflammatory T cells and macrophages. In mice, Tagln-Cre-mediated deletion of Pcsk6 in mesenchymal cells heightened susceptibility to AAA enlargement and rupture in models induced by topical porcine pancreatic elastase (PPE) or angiotensin II infusion, suggesting a protective role of mesenchymal Pcsk6 in maintaining aortic integrity. This study aimed to define the Pcsk6-dependent pathways and identify upstream regulators of Pcsk6 expression, focusing on fibroblasts, to elucidate its role in AAA development.
Methods: RNA sequencing was performed on aneurysmal aortas from Tagln-Cre+/Pcsk6fl/fl and Tagln-Cre-/Pcsk6fl/fl mice. Differential gene expression analysis was followed by pathway enrichment using Reactome and Hallmark databases. In vitro, cultured human aortic fibroblasts (HAoAFs) were treated with medium, IL-1β, TGF-β1, or IFN-γ to assess Pcsk6 regulation.
Results: Pcsk6 deletion in mesenchymal cells disrupted pathways related to epithelial-to-mesenchymal transition, vascular contractility, and extracellular matrix (ECM) organization. In HAoAFs, IFN-γ markedly downregulated Pcsk6, Acta2, Myh11, and Col1a1, while upregulating Il6, Stat1, Icam1, and Vcam1. Conversely, TGF-β1 increased Pcsk6, Acta2, Myh11, and Col1a1, and reduced Mmp14, Icam1, and Vcam1. IL-1β strongly induced Ccl8, Icam1, and Vcam1, but did not affect Pcsk6 or contractile markers.
Conclusion: Pcsk6 expression in mesenchymal cells, modulated by cytokine signaling, orchestrates immune responses, ECM remodeling and vascular function under aneurysmal conditions.