Because exosomes have gained attention as a source of biomarkers, we investigated if miRNAs in exosomes (exo-miRs) can report the disease progression of organ injury. Using rat renal ischemia-reperfusion injury (IRI) as a model of acute kidney injury (AKI), University of Miyazaki researchers determined temporally-released exo-miRs in urine during IRI and found that these exo-miRs could reliably mirror the progression of AKI. From the longitudinal measurements of miRNA expression in kidney and urine, they found that release of exo- miRs was a regulated sorting process. In the injury state, miR-16, miR-24, and miR-200c were increased in the urine. Interestingly, expression of target mRNAs of these exo-miRs was significantly altered in renal medulla. Next, in the early recovery state, exo-miRs (miR-9a, miR-141, miR-200a, miR-200c, miR-429), which share Zeb1/2 as a common target mRNA, were upregulated together, indicating that they reflect TGF-β-associated renal fibrosis. Finally, release of exo-miRs (miR-125a, miR-351) was regulated by TGF-β1 and was able to differentiate the sham and IRI even after the injured kidneys were recovered. Altogether, these data indicate that exo-miRs released in renal IRI are associated with TGF-β signaling. Temporal release of exo-miRs which share targets might be a regulatory mechanism to control the progression of AKI.
Injury state-specific and recovery state-specific miRNAs in urinary exosomes after renal IR
(a) Volcano plots of urinary exo-miR expression at the indicated time points following renal IR and combined all time points. The significance values and fold changes of all expressed miRNAs were computed using EdgeR. (b) Heat map with hierarchical clustering of differentially expressed genes with FDR < 0.01 in at least one time point. (c) Venn diagram representing overlap of differentially expressed miRNAs in kidney at 1.5 days, 3 days, 14 days post renal IR with differentially expressed urinary exo-miR at 1 day, 2 days, 3 days, 7 days, and 14 days post renal IR.