Abstract
KEY POINTS: Hypoxia-inducible factor-1 α -mediated induction of miR-295 in renal tubular cells in hyperuricemic nephropathy. This study reveals a hypoxia-inducible factor-1 α /miR-295/factor inhibiting hypoxia-inducible factor-1 positive feedback loop that regulates tubular damage and fibrosis in hyperuricemic nephropathy. BACKGROUND: Hyperuricemia is a common metabolic disorder and a risk factor for multiple diseases, including CKD. Hyperuricemic nephropathy (HN) affects many individuals with hyperuricemia, yet its molecular mechanisms are not fully understood, and effective treatments are lacking. METHODS: In vitro , human tubular epithelial cells (HK-2) were exposed to uric acid for 36 hours, followed by transfection with microRNA mimic or factor inhibiting hypoxia-inducible factor-1 (FIH-1) siRNA. In vivo , HN was induced in mice using potassium oxonate and adenine for 2 weeks. miR-295 mimic or anti-miR-295 was administered through tail vein injection, and mice were euthanized for analysis. RESULTS: We demonstrated a significant increase of miR-295 in renal tubular cells in HN mice. Hyperuricemia led to the activation of hypoxia inducible factor-1 α (HIF-1 α ), and inhibition of HIF-1 α by YC-1 (a HIF-1 α inhibitor) prevented the increase of miR-295. Chromatin immunoprecipitation assay further verified HIF-1 α binding to the miR-295 gene promoter directly. Functionally, inhibition of miR-295 led to increased cell death and tubulointerstitial fibrosis in HN mice, whereas supplementation of miR-295 mimic had kidney-protective effects in this model. miR-295 suppressed the expression of FIH-1) in both in vitro and in vivo models of HN. Luciferase microRNA target reporter assay further verified FIH-1 as a direct target of miR-295. In addition, knockdown of FIH-1 inhibits tubular cell apoptosis and profibrotic cytokines production in HK2 cells during uric acid treatment. CONCLUSIONS: This study reveals a HIF-1 α /miR-295/FIH-1 positive feedback loop that regulates tubular damage and fibrosis in HN.