Two microRNAs, miR-330 and miR-125b-5p, mark the juxtaglomerular cell and balance its smooth muscle phenotype.

We have shown that microRNAs (miRNAs) are necessary for renin cell specification and kidney vascular development. Here, we used a screening strategy involving microarray and in silico analyses, along with in situ hybridization and in vitro functional assays to identify miRNAs important for renin cell identity. Microarray studies using vascular smooth muscle cells (SMCs) of the renin lineage and kidney cortex under normal conditions and after reacquisition of the renin phenotype revealed that of 599 miRNAs, 192 were expressed in SMCs and 234 in kidney cortex. In silico analysis showed that the highly conserved miR-330 and miR-125b-5p have potential binding sites in smoothelin (Smtn), calbindin 1, smooth muscle myosin heavy chain, α-smooth muscle actin, and renin genes important for the myoepithelioid phenotype of the renin cell. RT-PCR studies confirmed miR-330 and miR-125b-5p expression in kidney and SMCs. In situ hybridization revealed that under normal conditions, miR-125b-5p was expressed in arteriolar SMCs and in juxtaglomerular (JG) cells. Under conditions that induce reacquisition of the renin phenotype, miR-125b-5p was downregulated in arteriolar SMCs but remained expressed in JG cells. miR-330, normally absent, was expressed exclusively in JG cells of treated mice. In vitro functional studies showed that overexpression of miR-330 inhibited Smtn expression in SMCs. On the other hand, miR-125b-5p increased Smtn expression, whereas its inhibition reduced Smtn expression. Our results demonstrate that miR-330 and miR-125b-5p are markers of JG cells and have opposite effects on renin lineage cells: one inhibiting and the other favoring their smooth muscle phenotype.