Introduction:
In this study, we validated the changes in microRNA (miRNA) expression in hypoxic human kidney 2 (HK2) cell-derived extracellular vesicles (EVs). Additionally, we investigated the mechanism by which miRNA that are derived from EVs alleviated renal ischemia-reperfusion (I/R) injury.

Material and methods:
HK2 cells were treated in a hypoxic chamber (1% O2) for 12 h.EVs were obtained as supernatant from ultracentrifugation and characterized. After examining 16 differentially expressed EV-miRNAs between normoxic and hypoxic conditions by RT-PCR and bioinformatics analysis, miR-125b-5p was selected for further analysis. Normoxic and hypoxic HK2 cells-derived EVs as well as EVs that were isolated from miR-125b-5p negative control (miR-NC)-transfected or miR-125b-5p mimic (miR-MI)-transfected HK2 cells were injected in mice with renal I/R injury. The degree of renal injury was assessed by periodic acid-Schiff staining, renal tubule injury score, and plasma creatinine levels. Bioinformatics analysis was performed to determine the potential target genes of differentially expressed miRNAs. RT-PCR,western blotting, luciferase reporter assay, and immunohistochemistry were performed to investigate the relationship between miR-125b-5p and the NLR family CARD domain containing 5 (NLRC5).

Results:
RT-PCR revealed that from 16 differentially expressed miRNAs, four EV-miRNAs were upregulated. Animal study showed that miR-125b-5p overexpression in EVs alleviated renal I/R injury. Bioinformatics analysis predicted that NLRC5 was targeted by miR-125b-5p. Moreover, the relationship between miR-125b-5p and NLRC5 was also validated.

Conclusions:
There were several miRNAs that were upregulated (including miR-125b-5p) in hypoxic HK2 cells. Hypoxia induced EVs that alleviate renal IRI, can be attributed to miR-125b-5p for targeting NLRC5.