Uromodulin and Progression of IgA Nephropathy

Abstract

Background This study investigates the link between genetic variants associated with kidney function and IgA nephropathy (IgAN) progression. Methods We recruited 961 biopsy-proven IgAN patients and 651 non-IgAN end-stage renal disease (ESRD) patients from Ruijin Hospital. The clinical and renal pathological data were collected. The primary outcome was the time for ESRD. A healthy population was defined as eGFR > 60 ml/min/1.73m2 without albuminuria or hematuria. Fifteen single-nucleotide polymorphisms (SNPs) were selected from a genome-wide association study of kidney function and genotyped by the SNaPshot. Immunohistochemistry in renal tissue and ELISA in urine samples were performed to explore the potential functions of genetic variations. Results The rs77924615-G was independently associated with an increased risk for ESRD in IgAN patients after adjustments for clinical, pathologic indices, and treatment (adjusted Hazard Ratio, 2.10; 95% CI, 1.14 to 3.88). No significant differences in ESRD-free survival time among different genotypes in non-IgAN ESRD patients (log-rank, p = 0.480). Moreover, rs77924615 exhibited allele-specific enhancer activity by dual-luciferase reporter assay. Accordingly, the urinary uromodulin-creatinine ratio (uUCR) was significantly higher in healthy individuals with rs77924615 AG or GG than in individuals with AA. Furthermore, uromodulin expression in tubular epithelial cells was higher in patients with rs77924615 AG or GG. Finally, we confirmed that an increased uUCR (p = 0.009) was associated with faster IgAN progression. Conclusion The SNP rs77924615, which modulates the enhancer activity of the UMOD gene, is associated with renal function deterioration in IgAN patients by increasing uromodulin levels in both the renal tubular epithelium and urine.