Background: Our lab has identified a role for proprotein convertase subtilisin/kexin type9 (Pcsk9) in murine abdominal aortic aneurysm (AAA). Beyond its pathological effects on degradation of LDL-receptors, and enhancement of tissue inflammation via the NF-kB pathway, reports suggest that it alters vascular smooth muscle cell (VSMC) senescence and metabolism. However, the specific cellular mechanisms connecting Pcsk9 to AAA disease (particularly SMC-derived Pcsk9) are still unclear. Hypothesis: Intercellular communication between VSMCs and macrophages via enhanced local Pcsk9 expression drives macrophages towards pro-inflammatory polarization and promotes AAA growth by upregulated aortic wall inflammation. Pcsk9 also enhances mitochondrial metabolism in VSMCs, contributing to cell senescence. Pcsk9 knockdown inhibits these effects. Aims: We explored the impacts of SMC-derived Pcsk9 on aortic inflammation and VSMC behavior, seeking to further understand AAA pathophysiology and provide a basis for re-purposing Pcsk9 inhibitors as a treatment for non-surgical AAA. Methods: Single-cell RNASeq of murine AAA tissue (porcine pancreatic elastase model) utilizing control and Pcsk9-knockout mice (systemic) was performed to examine local changes in aortic wall cell-subtype gene expression. Pcsk9 silenced VSMCs (with siRNA) were co-cultured with macrophages to assess polarization towards pro-inflammatory phenotype and pro-inflammatory gene/protein expression was identified. VSMCs were also treated either with exogenous Pcsk9 or Pcsk9 siRNA in vitro to assess mitochondrial metabolism via Seahorse assay. Results: Pcsk9 knock-out AAA tissue exhibited reductions in pro-inflammatory gene expression profiles in vascular cell sub-populations (compared to wildtype). In vitro, Pcsk9-silenced VSMC-cocultured macrophages presented decreased inflammatory profile assessed by flow cytometry. Further, exogenous Pcsk9-treated-VSMCs displayed metabolic changes compared to control (Mann-Whitney Test). Conclusions: Our data suggest significant mechanistic involvement of Pcsk9 in AAA disease at the cellular level. Absence of Pcsk9 appears to mitigate vascular inflammation and alter VSMC metabolism in ways that may decelerate AAA.
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