MicroRNA-668 represses MTP18 to preserve mitochondrial dynamics in ischemic acute kidney injury.

The pathogenesis of ischemic diseases remains unclear. Here we demonstrate the induction of microRNA-668 (miR-668) in ischemic acute kidney injury (AKI) in human patients, mice, and renal tubular cells. The induction was HIF-1 dependent, as HIF-1 deficiency in cells and kidney proximal tubules attenuated miR-668 expression. We further identified a functional HIF-1 binding site in the miR-668 gene promoter. Anti-miR-668 increased apoptosis in renal tubular cells and enhanced ischemic AKI in mice, whereas miR-668 mimic was protective. Mechanistically, anti-miR-668 induced mitochondrial fragmentation, whereas miR-668 blocked mitochondrial fragmentation during hypoxia. We analyzed miR-668 target genes through immunoprecipitation of microRNA-induced silencing complexes followed by RNA deep sequencing and identified 124 protein-coding genes as likely targets of miR-668. Among these genes, only mitochondrial protein 18 kDa (MTP18) has been implicated in mitochondrial dynamics. In renal cells and mouse kidneys, miR-668 mimic suppressed MTP18, whereas anti-miR-668 increased MTP18 expression. Luciferase microRNA target reporter assay further verified MTP18 as a direct target of miR-668. In renal tubular cells, knockdown of MTP18 suppressed mitochondrial fragmentation and apoptosis. Together, the results suggest that miR-668 is induced via HIF-1 in ischemic AKI and that, upon induction, miR-668 represses MTP18 to preserve mitochondrial dynamics for renal tubular cell survival and kidney protection.