Renin, the key hormone of the renin-angiotensin system, regulates blood pressure and fluid-electrolyte homeostasis. In early embryonic development, renin precursor cells are present in the undifferentiated metanephric mesenchyme. Later in fetal life, renin cells are broadly distributed along intrarenal arteries and inside the glomeruli. With maturation, renin cells are fewer and restricted to the classical adult juxtaglomerular (JG) localization. If blood pressure or fluid-electrolyte homeostasis is threatened, the number of renin cells increases along preglomerular arteries, glomeruli and interstitium resembling the embryonic pattern. The increase in renin cell number (recruitment) is due to de-differentiation of preexisting adult cells and does not involve cell migration or replication. In fact, using a cre-lox system we found that renin cells are precursors that give rise to arteriolar smooth muscle (SM), mesangial, and interstitial cells and it is these cells that re-express renin when homeostasis is threatened. Further, using a dually labeled cell model we found that arteriolar SM cells reacquire the renin phenotype upon cAMP stimulation, an effect mediated by chromatin remodeling and binding of CREB at the cAMP responsive element in the renin promoter. In addition to this epigenetic/ transcriptional control, the acquisition and maintenance of renin cell identity may be regulated by endogenous microRNAs, a group of non-coding small RNAs that regulate gene expression at the post-transcriptional level and are known to regulate cell fate. Conditional deletion of Dicer in renin cells resulted in the disappearance of JG cells in the kidney suggesting that microRNAs may regulate renin cell specification and kidney vascular development. Using stringent exclusion criteria and a screening strategy involving multiple methodologies and functional assays, we identified two exciting and unique renin cell specific microRNAs (miR-330 and miR- 125b-5p) that regulate crucial genes for the maintenance of the myoepithelioid renin cell phenotype. We hypothesize that miR-330 and miR-125b-5p regulate the identity of the renin cell by controlling the expression of renin and vascular smooth muscle genes. Using in vivo and in vitro approaches, we will test the following hypotheses: 1) microRNAs determine the temporal and spatial pattern of renin cell differentiation during development, 2) miR-330 and miR-125b-5p have a characteristic distribution pattern and expression levels that regulate the state of differentiation of the renin cell, and 3) miR-330 and miR-125b-5p regulate the identity and fate of renin cells and nephron morphogenesis.
Understanding the mechanisms that govern the identity and plasticity of the renin cell is of fundamental biological and medical importance. Information gained from the proposed studies may help children and adults affected by kidney diseases and hypertension.
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