Research

Juxtaglomerular (JG) cells are sensors, perfected throughout evolution to interpret and respond to changes in blood pressure and the composition and volume of the extracellular fluid. Normally, renin release from JG cells suffice to maintain homeostasis. However, under intense and prolonged physiological challenges (dehydration, sodium depletion, hypotension) smooth muscle cells (SMCs) along the kidney arterioles reacquire the renin phenotype and restore homeostasis. Once homeostasis is reestablished, the transformed cells stop making renin and become SMCs again. Conversely, if the inciting threat is not removed or overcome [as in spontaneous or experimental mutations of the renin-angiotensin system (RAS) genes or chronic inhibition of the RAS in mice, rats, and humans] the relentless chronic stimulation of renin cells leads to the concentric hypertrophy of intrarenal arteries and arterioles. Numerous hypertrophic renin cells surround -and insert chaotically within- the arteriolar walls. SMCs accumulate concentrically and inwardly, narrowing the vessel lumens and restricting blood flow, resulting in ischemia, fibrosis, and renal failure. In spite of its medical importance, and the prevalent use of RAS inhibitors in children and adolescents, the mechanisms underlying the development of this severe, albeit silent, disease are not known. Our renin cell ablation studies indicated that renin cells are responsible for vascular disease not only by physically participating in the thickening of the vessel wall but also by their direct cell-to-cell interaction with SMCs. Abundant preliminary data from our laboratory suggest that the cAMP and Notch pathways are responsible for the transformation of renin cells and arterial disease. We hypothesize that under chronic unrestrained stimulation, p300 remodels the chromatin of renin cells leading them to a dual embryonic-senescent phenotype. Further, the transformed renin cells, via Notch activation induce the concentric vascular hypertrophy of the adjacent SMCs. Aim 1 will test the hypothesis that specific imprinted chromatin domains determine the progressive changes in cell fate responsible for concentric arterial hypertrophy. Aim 1A will define the identity and fate of the cells that compose the diseased arterioles. Aim 1B will test whether cells derived from the diseased arterioles are retained in (or reverted to) an embryonic/progenitor state. Aim 2 will test the hypothesis that Histone acetyltransferase p300 is responsible for the generation of those chromatin domains that determine the pathological transformation of renin cells and the concentric arterial hypertrophy. Aim 3 will test the hypothesis that the concentric accumulation of adjacent SMCs is mediated by Notch signaling via the engagement of the Jagged1 ligand in renin cells with the Notch2 receptor in SMCs. Using novel conceptual and technical approaches, the proposed work will uncover the fundamental mechanisms, chromatin domains, and transcriptional drivers responsible for the changes in cell fate leading to this severe arterial disease. The work has the potential to open new translational opportunities for the rational identification of targets for the design of specific therapies that protect the kidneys of children and adults with kidney diseases and hypertension.

Young children with salt wasting renal diseases are at high risk of developing chronic and severe extracellular fluid (ECF) volume contraction, leading to growth retardation and poor renal perfusion. Chronic conditions that threaten homeostasis such as hypotension, hypokalemia, salt depletion, and/or the prolonged used of angiotensin-converting enzyme inhibitors (ACEi) or angiotensin receptor blockers (ARBs) in young children induce the recruitment of renin-producing cells with the resulting hypertrophy of the renal arterioles. This response however, cannot be sustained for too long without affecting renal perfusion. However, it is unclear what are the major vascular growth factors involved in this process, and how they affect the growth of renin producing cells. Previous studies, including our own preliminary work, suggest that Transforming Growth Factor-b (TGF-b) and Fibroblast Growth Factor-2 (FGF-2) interacting with Angiotensin II, play a key role modulating vascular tone, hypertrophy, and proliferation of juxtaglomerular (JG) and renal vascular smooth muscle cells (RVSMC). However, very little is known about the role that TGF-b and FGF-2 play in the regulation of renin release and the phenotype of renin producing cells in young infants. Here, we will test the hypothesis that under conditions that represent a physiological threat to maintain the ECF volume and/or renal perfusion in infancy, the Ang II-TGF-b and FGF-2 axis plays a critical role maintaining the normal fate and function of renin-producing cells and RVSMC.  In addition, we hypothesize that when the balance between the RAS, TGF-b and FGF-2 pathways is disrupted, cells programed for the renin phenotype integrate in a disorderly manner inside the renal arterioles, precipitating the development of vascular concentric hypertrophic lesions leading to poor renal perfusion and kidney fibrosis. Using time and cell specific conditional deletion approaches, and single cell transcriptomic analysis, we will test this hypothesis in three aims.  In aim 1 we will test hypothesis that a functional TGF-b receptor 1 signaling pathway in Ren1 + cells is necessary to sustain the hypertrophy of JG and RVSMC in response to chronic changes in dietary Na+ / K+ intake or RAS inhibition during early postnatal life, and determine how renin and the cAMP pathway interact with TGF-b and/or FGF-2 in JG and RVSMC to modulate their endocrine and contractile phenotypes. In aim 2, we will test the hypothesis that FGF signaling contributes to maintain the proper balance between the RAS and TGF-b  in JG and RVSMCs under conditions of chronic RAS stimulation and suppression in young mice.  In aim 3 we will  define the transcriptome profile and protein changes that occur in renal arterioles and cells shed in the urine of young rats with poor renal perfusion induced by Na+ depletion and RAS inhibition, and validate these findings in cells and tissues derived from young infants undergoing similar conditions. These studies will elucidate new mechanisms whereby the RAS interacts with the TGF-b and FGF-2 pathways during infancy to modulate the growth of JG and RVSMCs, and maintain the ECF homeostasis and renal perfusion under conditions of chronic RAS stimulation or suppression in infancy.