Endocrine Abstracts

The Mineralocorticoid Receptor (MR, NR3C2) mediates sodium-retaining action of aldosterone. Recently, we have shown that the physiological sodium loss observed in newborns in their first days of life is due to a low renal MR expression. However, the underlying molecular mechanisms remain unknown to date. In the adult renal KC3AC1 cell line, we demonstrated that variations in extracellular tonicity, which exist in the nephron, modulate MR expression by posttranscriptional mechanisms involving recruitment of microRNAs (miRNAs) such as miR-30c-2-3p and miR-324-5p. These posttranscriptional regulators can bind to the 3’-untranslated (3’-UTR) region of target mRNA to modulate their stability and/or translation. Thus, we hypothesize that these same mechanisms may be responsible for the modulation of renal MR expression in the perinatal period, where variations in tonicity are observed due to the transition from intra-amniotic to extra-uterine life. Using primary culture of renal epithelial cells from neonatal mouse kidneys, harvested at day of birth (D0) and at Day 8 postnatal (D8), we showed that only miR-30c-2-3p regulates MR expression at D8. Therefore, we performed a complete transcriptomic analysis (RNA-Seq and miRNA-Seq) of kidneys collected at D0 and D8 to identify all miRNAs specifically involved in the regulation of MR expression in the perinatal period. To identify all the deregulated miRNAs and transcripts and to specify their involvement in biological processes and signaling pathways, we performed a comprehensive bioinformatics analysis. Then, we mainly focused on deregulated miRNAs that could modulate MR expression and affect mineralocorticoid signaling pathway. miR-Sequecing enabled us to identify 221 differentially expressed miRNAs. We first selected 3 underexpressed (miR-30a-5p, miR-30e-5p, and miR-802-5p) and 3 overexpressed (miR-431-5p, miR-409-3p, and miR-92a-1-5p) candidate miRNAs (FDR<0.05 and log2FC>1) having putative binding sites in MR 3’-UTR. Paradoxically, our results showed that overexpression of miR-30a-5p, miR-30e-5p, or miR-802-5p increased MR expression (from 50 to 100%, P<0.05) at D0, suggesting that these miRNAs could either positively modulate MR expression during renal development or involve an intermediate factor. Conversely, overexpression of miR-92a-1-5p, miR-431-5p, and miR-409-3p at D8 induced a decrease (from 30-40%, P<0.05) in MR expression, suggesting that these miRNAs could also modulate MR expression in the postnatal period. Currently, we are evaluating whether these miRNAs could be used as severity or prognostic biomarkers of sodium loss in neonates by quantifying their expression in urinary exosomes of preterm and term infants with the goal to better understand molecular mechanisms regulating MR expression in the perinatal period.