Complement Component C4B Prioritization Through Drug‒Target Mendelian Randomization and Proteomic Analysis Reveals a Novel Therapeutic Target for Calcific Aortic Valve Stenosis

No pharmacotherapies effectively halt the progression of calcific aortic valve stenosis (CAVS). We leveraged multi-omic analyses to identify potential drug targets of CAVS. We integrated druggable genome with cis-expression quantitative trait locus (eQTLs) data from the eQTLGen Consortium to identify instrumentable genes. Two independent genome-wide association study (GWAS) datasets for CAVS were used for Mendelian randomization (MR) analysis (Finngen dataset for discovery, a genome-wide meta-analysis cohort for replication). Genes showing significant associations in both cohorts underwent Bayesian colocalization, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes enrichment analyses. Candidates were verified by proteomic analysis (liquid chromatography-tandem mass spectrometry, LC-MS/MS) and immunohistochemical (IHC) analysis of human aortic valves. Additionally, a phenome-wide association study (PheWAS) was conducted to assess the horizontal pleiotropy. A reverse MR analysis was performed to assess potential reverse causality. Seven druggable genes were significantly associated with CAVS in both cohorts. Among these, C4A and C4B exhibited robust colocalization evidence (both posterior probabilities PP.H4 > 80%). While LC-MS/MS confirmed the significant upregulation of C4A and C4B at the protein level (fold changes of 1.58 and 1.51, respectively; p < 0.05), only C4B was established as a risk factor for CAVS (odds ratio: 1.04, 95% confidence interval: 1.03–1.06, p = 3.49 × 10 − 9 in the replication phase). The reverse MR analysis validated the causal effect, and the PheWAS analysis revealed no significant association with broad phenotypes. IHC localized C4B expression predominantly in aortic valve interstitial cells, with significantly higher integrated density in calcific valves (1916.95 ± 1118.89 vs. 502.34 ± 474.27; p = 0.025). Our study offers a genetically anchored therapeutic hypothesis involving the immune-complement system and identifies C4B as a prioritized candidate with therapeutic potential for CAVS.