MicroRNAs in Kidney Injury & Repair: Characterizing the Role of miR-132

Abstract

Acute kidney injury (AKI) is a serious public health problem and there are no specific treatments that promote the recovery of the damaged kidney. In recent years, microRNAs (miRNAs) have been shown to mediate various aspects of AKI and are increasingly recognized as pharmacological targets. To better understand how miRNAs respond to kidney damage, we conducted small RNA sequencing on kidneys from mice at various stages after the induction of folic acid (FA) nephropathy. We identified miR-132 as being among the top-five upregulated miRNAs in the kidney at five different time points after FA injury and confirmed that miR-132 correlated with kidney injury in two additional mouse models. We found that miR-132 was upregulated in injured tubular epithelial cells (TECs) of mice subjected to FA injury and in human biopsies with chronic kidney disease (CKD), as well as in primary human proximal TECs (HPTECs) treated with diverse nephrotoxicants. To test the role of miR-132 in vivo, we subjected miR-132 global knockout (miR-132-/-) mice and wild-type (WT) littermate controls to FA injury. As a result, both groups incurred initial kidney damage at day 1, but on day 2 miR-132-/- mice had less tubular injury, lower serum creatinine, and less inflammation, and had attenuated fibrosis on day 14. Isobaric tag-based proteomics on HPTECs revealed that miR-132 inhibited negative regulators of the cell cycle and suppressed detoxification pathways. In addition, miR-132 overexpression in HPTECs resulted in the inhibition of p21, increased cell cycle progression, and more TEC death following genotoxic injury. Tissue-based cyclic immunofluorescence (CyCIF) was adapted to analyze mouse kidney tissue and revealed that miR-132 upregulation caused early cell cycle activation in TECs at day 1 and increased TEC injury and DNA damage by day 2 after FA injury. In addition, injured TECs had more p21 expression in the absence of miR-132. Taken together, these data suggest the miR-132 increases the sensitivity of TECs to DNA damage by promoting cell cycle progression of injured TECs. Given the robust expression of miR-132 in mice and in human TECs, miR-132 inhibition may improve outcomes for patients with AKI and prevent the development of CKD.