CARD9 S12N Mutation Is Associated with an Increased Risk of IgAN in Han Chinese

Background: Caspase recruitment domain family member 9 (CARD9) gene has been identified as susceptibility gene for IgA nephropathy (IgAN) in previous genome-wide association studies, which encodes an adaptor protein that plays a pivotal role in pathogen defense and innate immunity. This study aimed to explore whether CARD9 polymorphisms correlate with IgAN susceptibility, clinical phenotypes and disease progression, and to elucidate their potential roles in inflammatory and immune responses. Methods: A total of 3,319 IgAN patients and 6,785 healthy controls were enrolled across three independent cohorts, and 10 candidate single-nucleotide polymorphisms were selected for genotyping. The serum levels of cytokines and galactose-deficient IgA1 were measured by a multiplex immunoassay kit and ELISA, respectively. Molecular docking and molecular dynamics simulation were applied to characterize the mutation of residues in the protein structure and the dynamic properties of CARD9 protein. Expression profiling data from the GEO database were used to investigate CARD9 expression and relevant pathways in renal tissues of IgAN patients. Results: We found that rs4077515-T (S12N mutation) conferred an increased risk of IgAN (OR = 1.26, 95% CI = 1.07–1.49, P = 0.006), and was also associated with a higher incidence of microscopic hematuria and mesangial hypercellularity. Furthermore, the S12N mutation was independently associated with renal survival after adjustments for multiple confounders. The S12N mutation was significantly correlated with elevated serum levels of proinflammatory cytokines (IL-5, IL-6, IL-17, and IL-8) and galactose-deficient IgA1. MD simulations demonstrated that the S12N mutation reduced the structural stability of the CARD9 protein and decreased its binding affinity to BCL10. Gene expression profiling data suggested significant upregulation of CARD9 expression in renal interstitial tissues of IgAN patients, which was correlated with the expression of Dectin-1, NF-κB, and the activation of B cell-mediated immune responses. Conclusion: Our results suggest that CARD9 S12N mutation confers susceptibility to IgAN, probably by modulating the inflammatory and immune responses.