Hypercholesterolemia and proprotein convertase subtilisin/kexin type 9 potentiate inflammation and fibro-calcific remodeling in bioprosthetic aortic valve

Introduction

Calcific aortic valve stenosis is the more frequent valvular disease, affecting more than 10% of patients > 75 years old. Surgical or transcatheter aortic valve replacement is the only treatment available. There is an increased use of bioprosthetic valves (BP), even if the progressive development of structural BP deterioration (SVD) limits their durability. Recent clinical studies highlighted an association between circulating lipid factors, such as proprotein convertase subtilisin/kexin type 9 (PCSK9), Lipoprotein (a) and low-density-lipoprotein (LDL), and SVD. However, the underlying mechanisms remain unknown.

Objective

We aim at deciphering the role of hypercholesterolemia and/or PCSK9 on the early processes leading to SVD.

Method

Subcutaneous implantation of BP tissue was performed on 10-week-old wild type (WT), PCSK9 knock-out (KO) and PCSK9 overexpressing (PCSK9 OV) mice for 28 days. A qualitative anatomopathological score evaluating cell density, infiltration, and tissue degradation was developed. Infiltrated cells were characterized by IHC and modulated signaling pathways were identified by bulk RNA-sequencing. Mice peritoneal macrophages were stimulated for 6 hours with PCSK9 and/or oxidized-LDL (ox-LDL).

Results

The anatomopathological score was significantly higher in the explanted punches from PCSK9 OV mice as compared to WT and KO (7.0 [4.1–8.4] vs 4.0 [3.0–4.5] and 2.8 [2.0–3.9], respectively; P = 0.008). Macrophages and granulocytes were the more abundant infiltrated cell types with a significant increase of granulocytes in PCSK9 OV mice as compared to WT and KO (P = 0.01 and P = 0.002, respectively). RNA-seq analysis revealed an enrichment of fibro-calcific remodeling signaling pathways in PCSK9 OV mice compared to KO. Macrophages stimulation highlighted differential responses: ox-LDL activated pro-inflammatory signaling pathways whereas PCSK9 promoted pro-calcifying cytokines release.

Conclusion

Hypercholesterolemia and/or high PCSK9 levels potentiate the inflammatory response against the BP tissue, with an infiltration of granuloytes and macrophages, and an activation of fibro-calcific signaling pathways. PCSK9 promotes the activation of pro-calcifying cytokines whereas ox-LDL increases pro-inflammatory pathways. This study points out for a specific role of hypercholesterolemia and PCSK9 in the early phases post implantation of BP tissue, with potential implication in the development of SVD.