Integrative Analysis of the Blood Proteome by Mendelian Randomization Reveals Regulatory Networks in Calcific Aortic Valve Disease

BackgroundCalcific aortic valve disease (CAVD) is a disorder characterized by fibrocalcific remodeling of the aortic valve (AV). The blood molecular phenome involved in CAVD is presently unknown. MethodsWe carried out a proteome-wide two-sample Mendelian randomization (MR) study to identify circulating molecules causally associated with CAVD. We queried as the exposition a large cohort of 35,559 subjects in whom 4,719 blood proteins were measured. For the outcome, we leveraged a recent GWAS for CAVD including 13,765 cases and 640,102 controls. Single-cell RNA-seq was analyzed to highlight potential pathways affected by the blood proteome. ResultsIn MR, we identified 49 blood proteins robustly associated with the risk of CAVD. The blood proteins formed a network enriched in the immune response and ligand-receptor interactions. PCSK9, APOC3, ACE and IL6 were identified as actionable targets suitable for drug repurposing. Modulators of innate (IL6R, CNTFR, KIR2DL3-4) and adaptive (IL15RA, IGLL1, LILRA6) immune responses were associated with CAVD. Different regulators of platelets activity such as soluble GP1BA, COMP and VTN were also related to the risk of CAVD. Circulating modulators of the transforming growth factor-beta (TGF-beta) family such as ASPN, LEFTY2 and FSTL3 were associated with the risk of CAVD and their directional effects were consistent with the role of this pathway in the pathogenesis. Analysis of ligand-receptor interactions in the AV, which was inferred from single cell RNA-seq, provided further evidence that the IL6 and TGF-beta pathways are activated in CAVD. ConclusionsWe identified 49 blood proteins robustly and causally associated with CAVD, which were involved in the metabolism of lipids, immunity, regulation of blood pressure, platelet activation and modulation of growth factors activity. The present MR scan of the blood proteome provides a roadmap for follow-up studies and drug repurposing in CAVD. Clinical PerspectiveO_ST_ABSWhat is new?C_ST_ABSO_LIThe causal blood molecular phenome is presently unknown in CAVD; herein we investigated by Mendelian randomization the causal associations between the blood proteome and the risk of CAVD. C_LIO_LIIn total, 49 blood proteins were found causally associated with the risk of CAVD and were involved in the metabolism of lipids, control of the immune response, regulation of blood pressure, platelet activity and the modulation of growth factors activity. C_LIO_LISingle cell RNA-seq analysis of calcific aortic valves revealed several ligand-receptor interactions potentially affected by the blood phenome. C_LI What are the clinical implications?O_LIThere is no drug therapy available to treat CAVD. C_LIO_LIAnalysis of the blood proteome by Mendelian randomisation showed that in-development, approved drugs or biologics targeting PCSK9, APOC3 and ACE could be repositioned and investigated in order to treat CAVD. C_LI