miRNA profiling of urinary exosomes to assess the progression of acute kidney injury

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 renal ischemia-reperfusion injury (IRI) as a model of acute kidney injury (AKI), we 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, we found that release of exo-miRs was regulated sorting process, rather than simply representing their intracellular biosynthesis. 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, urinary exo-miRs (miR-9a, miR-141, miR-200a, miR-200c, miR-429), which shares Zeb1/2 as a common target mRNA, were upregulated, indicating that they reflect TGF--associated renal fibrosis. Finally, release of exo-miRs (miR-125a, miR-351) was regulated by TGF-1 and was able to differentiate the sham and IRI even after the injured kidneys were functionally recovered. Altogether, these data indicate that exo-miRs released in renal IRI are largely associated with TGF- signaling. Temporal release of exo-miRs which share targets might be a regulatory mechanism to control the disease progression of AKI. The exosomal miRNA dataset was compared at the indicated times with the miRNAs differentially expressed in(side) kidneys at day 1.5, day 3, and day 14 post IRI surgery. miRNAs in kidney were analyzed using Affymetrix Transciptome Analysis Console 4.0 and the miRNAs in the IR group were selected by using a fold change threshold of at least 2 and a nominal P value cutoff of 0.05 in comparison with the sham group (n = 3 for each group at each time point).