Abstract

Background: Hyperuricemia is a common metabolic disorder and a risk factor for multiple diseases, including chronic kidney disease (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 FIH-1 siRNA. In vivo, HN was induced in mice using potassium oxonate (PO) and adenine (Ad) for two weeks. miR-295 mimic or anti-miR-295 was administered via tail vein injection, and mice were sacrificed 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-1a (HIF-1a), and inhibition of HIF-1a by YC-1 (a HIF-1a inhibitor) prevented the increase of miR-295. ChIP assay further verified HIF-1a 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 factor inhibiting hypoxia-inducible factor-1 (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.

Conclusion: This study reveals a HIF-1α/miR-295/FIH-1 positive feedback loop that regulates tubular damage and fibrosis in HN.