Exogenous hydrogen sulfide and miR-21 antagonism attenuates macrophage-mediated inflammation in ischemia reperfusion injury of the aged kidney

Ischemia reperfusion injury (IRI) is a common cause of acute kidney injury (AKI) in the aging population. A reduction of hydrogen sulfide (H₂S) production in the old kidney and renal IRI contribute to renal pathology and injury. Recent studies suggest that microRNAs (miRs) play an important role in the pathophysiology of AKI and a significant crosstalk exists between H₂S and miRs. Among the miRs, miR-21 is highly expressed in AKI and is reported to have both pathological and protective role. In the present study, we sought to determine the effects of age-induced reduction in H₂S and mir-21 antagonism in AKI. Wild type (WT, C57BL/6J) mice aged 12-14 weeks and 75-78 weeks underwent bilateral renal ischemia (27 min) and reperfusion for 7 days and were treated with H₂S donor, GYY4137 (GYY, 0.25 mg/kg/day, ip) or locked nucleic acid anti-miR-21 (20 mg/kg b.w., ip) for 7 days. Following IRI, old kidney showed increased macrophage polarization toward M1 inflammatory phenotype, cytokine upregulation, endothelial-mesenchymal transition, and fibrosis compared to young kidney. Treatment with GYY or anti-miR-21 reversed the changes and improved renal vascular density, blood flow, and renal function in the old kidney. Anti-miR-21 treatment in mouse glomerular endothelial cells showed upregulation of H₂S-producing enzymes, cystathionine β-synthase (CBS), and cystathionineγ-lyase (CSE), and reduction of matrix metalloproteinase-9 and collagen IV expression. In conclusion, exogenous H₂S and inhibition of miR-21 rescued the old kidney dysfunction due to IRI by increasing H₂S levels, reduction of macrophage-mediated injury, and promoting reparative process suggesting a viable approach for aged patients sustaining AKI.