Background: Calcific aortic valve disease (CAVD), the most common valve disease is comprised of a chronic interplay of inflammation, fibrosis, and calcification. In this study, sortilin (SORT1) was identified as a novel key player in the pathophysiology of CAVD, and its role in the transformation of valvular interstitial cells (VICs) into pathological phenotypes is explored.

Methods: An aortic valve (AV) wire injury (AVWI) mouse model with sortilin deficiency was used to determine the effects of sortilin on AV stenosis, fibrosis and calcification. In vitro experiments employed human primary VICs cultured in osteogenic conditions for 7, 14 and 21 days; and processed for imaging, proteomics and transcriptomics including single-cell RNA sequencing (scRNA-seq).

Results: The AVWI mouse model showed reduced AV fibrosis, calcification, and stenosis in sortilin-deficient mice versus littermate controls. Protein studies identified the transition of human VICs into a myofibroblast-like phenotype mediated by sortilin. Sortilin loss-of-function decreased in vitro VIC calcification. ScRNA-seq identified 12 differentially expressed cell clusters in human VIC samples, where a novel combined inflammatory myofibroblastic-osteogenic VIC (IMO-VIC) phenotype was detected with increased expression of SORT1, COL1A1, WNT5A, IL-6 and SAA1. VICs sequenced with sortilin deficiency showed decreased IMO-VIC phenotype.

Conclusions: Sortilin promotes experimental CAVD by mediating valvular fibrosis and calcification, and newly identified phenotype (IMO-VIC). This is the first study to examine the role of sortilin in valvular calcification and it may render it a therapeutic target to inhibit IMO-VIC emergence by simultaneously reducing inflammation, fibrosis, and calcification, the three key pathological processes underlying CAVD.