Therapeutic Effects of Kidney Stem Cell-Derived Exosomes via Hypoxia-Inducible Factor Pathway Activation in AKI

Background: During acute kidney injury (AKI), damaged renal tubules possess the ability to regenerate. We previously established adult kidney stem/progenitor cells (KS cells), derived from adult rat kidneys, which exhibit both proliferative and differentiation capacities. Our findings suggest that KS cells promote kidney regeneration by secreting protective factors, as well as by directly proliferating and differentiating to replace damaged tubular cells. In this study, we explored the therapeutic effects of exosomes derived from KS cells (KS-Exo), mediated by hypoxia-inducible factor (HIF). Methods: KS cells were cultured under normal culture condition, hypoxic (3% O2) and HIF-PH inhibitor (DMOG)-supplemented conditions. KS-Exo were isolated from the culture supernatant using the T-cell immunoglobulin and mucin domain 4 (TIM-4) affinity method. Each KS-Exo type was intravenously administered to 8-week-old male C57BL/6N mice with AKI induced by unilateral ischemia-reperfusion (I/R) and contralateral nephrectomy. The efficacy of the treatment was assessed based on renal function and histological analyses. In vitro, the protective effects of KS-Exo against cisplatin-induced injury in renal tubular epithelial cells (HK-2 cells) were assessed. Results: KS-Exo from hypoxic and DMOG-supplemented conditions significantly improved kidney function (BUN, serum Cr) and reduced tubular damage by Day 3 [BUN (mg/dL): I/R control: 41.7±5.5; hypoxic: 32.1±3.5; DMOG: 33.0±5.6; p < 0.05 vs I/R control], while no significant improvement was observed with KS-Exo from normal conditions. These groups also showed increased p-Histone H3-positive cells and Nestin-positive areas, and reduced F4/80-positive areas, suggesting that the therapeutic effects of KS-Exo are mediated via the HIF pathway, through the promotion of tubular epithelial cell proliferation and dedifferentiation, and the suppression of inflammation. In vitro, TUNEL analysis demonstrated that KS-Exo suppressed cisplatin-induced apoptosis in renal tubular cells. Furthermore, real-time cell analysis using ECIS revealed that KS-Exo promoted cell proliferation and adhesion, further supporting their therapeutic potential. Conclusion: Exosomes derived from kidney stem cells exert therapeutic effects during AKI, in part via HIF pathway activation involving multiple downstream mechanisms. Funding: Private Foundation Support