Abstract 053: Urinary Extracellular Messenger RNA Transcripts as Biomarkers of Mineralocorticoid Receptor Activity

Abstract

Objectives: Mineralocorticoid receptor (MR) activation regulates sodium homeostasis & blood pressure. Our objective was to identify a non-invasive biomarker of MR activation in humans. Background: MR is a ligand-activated transcription factor that alters expression of target genes in the distal renal tubule, as shown in cell & animal models. Renal tubular cells secrete extracellular vesicles which carry RNA into urine. Whether human urinary extracellular mRNA reflects changes in gene expression in the renal tubule & thus might provide insight into MR activation is unknown. Methods: Pre-hypertensive participants consumed a low-sodium diet followed by sodium loading. We designed qPCR assays for MR gene targets & control genes not expected to respond to MR activation. Using samples collected during low-sodium diet & after sodium infusion, we assayed plasma renin activity (PRA), serum aldosterone, urinary sodium & urinary MR-responsive & control extracellular mRNA. Results: Eighteen participants’ low-sodium & 17 participants’ sodium-loaded urine samples were available. PRA & serum aldosterone were higher ( P <0.001) & urinary sodium excretion was lower ( P <0.001) during low-sodium diet. Four of 14 target gene qPCR assays (29%) changed after sodium loading, including assays for SCNN1A , SCNN1G & TSC22D3 ( P =0.006 to 0.01), whereas an assay for SGK1 approached significance ( P =0.07). In contrast, only 1 out of 10 control gene assays (for NR3C2 , encoding MR itself) was significantly different after sodium loading ( P =0.003). Log serum aldosterone inversely associated with C t values for 7 of 14 target gene assays (including assays for SCNN1A , SCNN1G , SGK1 & TSC22D3 [r= -0.46 to -0.52, P =0.003 to 0.048]) & for control gene assays for NR3C2 & UMOD . C t values for 6 of 14 target gene qPCR assays associated with log urinary sodium/creatinine ratio including assays for SCNN1A , SCNN1G , SGK1 & TSC22D3 associated with log urinary sodium/creatinine ratio ([r= 0.36 to 0.52, P =0.003 to 0.048]) but not with control gene assays. Conclusions: Perturbations in human endocrine physiology can be detected as changes in urinary extracellular mRNA. Our findings suggest a new strategy to screen for mineralocorticoid excess & to assess pharmacologic or dietary changes in MR activity.