Deregulation of miR‐21 Contributes to Differential Macrophage Activation in Acute Kidney Injury in Aged Mice

Abstract

Age-dependent renal changes increase the risk for acute kidney injury (AKI). The recruitment and activation of macrophages (M) is a prominent feature in this pathology wherein, distinct subsets of macrophages contribute to inflammation (M1) and tissue remodeling (M2). Recent studies suggest that microRNAs (miRs) play a significant role in AKI and functional recovery. The miRs are small non-coding RNA's which inhibit mRNA transcripts or block protein translation thus affecting the microenvironment a vital factor in the differentiation of macrophages to M1 and M2 phenotype. In this study, we determined whether deregulation of miR-21 contributes to macrophage polarization in renal ischemia reperfusion injury in aged mice. Young (12-14 wks) and aged (72-75 wks) wild type mice underwent bilateral renal ischemia for 25 minutes followed by 7 days reperfusion. Plasma creatinine and kidney injury molecule-1 measurement revealed severe renal dysfunction in aged mice vs. young. The level of miR-21 was increased in aged mice. Renal mononuclear cell preparation and staining with F4/80 and CD40/CD206 (M1, M2 respectively) revealed increased expression of CD40 in aged kidney. In addition, cytokine profiling showed increased mRNA and protein expression for TNFα, IL-6 and decreased IL-10 and Arg1 compared to young mice. Transfection of RAW264.7 cells (early vs. late passage) with miR-21 mimic and lipopolysaccharide increased the levels of iNOS and TNFα suggesting pro-inflammatory M1 response in late passage cells, whereas miR-21 inhibitor diminished their expression. Our data suggests that following acute kidney injury in aged mice, dynamic changes in miR-21 contributes to macrophage polarization leading to severe renal injury.