Altered expression of microRNA miR-146a correlates with the development of chronic renal inflammation.

MicroRNAs (miRNAs) are highly conserved small non-coding RNAs that act as post-transcriptional regulators of target mRNA. In this study, we sought to identify the microRNA underlying local inflammation in a murine model of chronic kidney disease (CKD). In microarray analysis of kidneys, the expression of miR-146a/b was elevated in B6.MRLc1 CKD mice that spontaneously develop renal inflammation with age. Primary-microRNA analysis found that elevated miR-146a/b expression in the kidneys of B6.MRLc1 mice was mainly derived from miR-146a rather than miR-146b, and this expression increased with the development of CKD. Histopathological scores for glomerular and interstitial lesions, mRNA expression of inflammatory mediators, and macrophage infiltration were significantly higher in B6.MRLc1 than C57BL/6 mice and were positively correlated with miR-146a expression. In situ hybridization and laser microdissection-RT-PCR showed that miR-146a expression in interstitial lesions containing inflammatory cells was higher than in the glomerulus. The increased expression of the inflammatory-associated genes RELA, IRAK1, IL1B, IL10, and CXCLs was noted in miR-146a/b-silenced human monocytes. The amount of miR-146a was higher in urine sediments of B6.MRLc1 than of C57BL/6 mice. Thus, miR-146a expression in the kidneys and its urinary excretion was specifically associated with the development of interstitial lesions and correlated with inflammatory cell infiltration.