Mitochondrial calcium uniporter-mediated mitochondrial dynamics imbalance contributes to contrast medium-induced renal tubular cell injury

Abstract

Background Contrast-induced acute kidney injury (CI-AKI) is the acute onset of renal failure occurring 24–48 hours after intravascular injection of contrast medium (CM), which is a common cause of hospital-acquired acute kidney injury. Previous researches on CI-AKI have demonstrated that cytoplasmic Ca2+ overload and mitochondrial damage were strongly associated with CI-AKI, but the precise pathogenesis remains elusive. Therefore, we aimed to identify the role of mitochondrial calcium uniporter (MCU), the most important Ca2+ unidirectional channel of mitochondria, in CM-induced tubular epithelial cell injury and explore the molecular conformation of MCU interacting with iohexol. Methods Human renal proximal tubular epithelial (HK-2) cells were incubated with 100 mg I/ml iohexol. Cell injury and apoptosis were detected by Cell Counting Kit-8 and flow cytometry. The mitochondrial Ca2+ level was evaluated by Rhod-2 fluorescence. Mitochondrial damage was assessed by transmission electron microscopy, fluorescence of mitotracker, and JC-1. Protein expression of dynamin-related protein 1 (DRP1) and optic atrophy 1 (OPA1) was assessed by Western Blot. Results Iohexol administration successfully induced HK-2 cell injury and apoptosis. Moreover, there is an interaction between Iohexol and MCU. We also demonstrated that iohexol could lead to increase of mitochondrial Ca2+ concentration, upregulation of MCU expression, mitochondrial injury, and mitochondrial dynamics imbalance (excessive mitochondrial fission and loss of mitochondrial fusion) in HK-2 cells. Of note, inhibiting MCU by Ru360 efficiently maintaining mitochondrial function by reducing mitochondrial Ca2+ influx and improving impaired mitochondrial dynamics, thereby protecting HK-2 cells from CM-induced injury and apoptosis. On the contrary, the activation of MCU by spermine aggravated cell injury under the same mechanisms. Conclusions The present study illustrated a novel molecular mechanism of CI-AKI involving MCU-mediated mitochondrial dynamics imbalance, and suppression of MCU exhibited a cytoprotective effect on CM-treated renal tubular cells.