Renin cell identity and blood pressure homeostasis

The Renin-Angiotensin System (RAS) is crucial in the regulation of the blood pressure (BP). Synthesis and secretion of Renin is the key regulated event in the operation of the RAS. One of the main mechanisms that control Renin synthesis and release is the baroreceptor mechanism whereby a decrease in BP results in increased release of Renin by juxtaglomerular (JG) Cells. Under normal circumstances, secretion of Renin by JG cells is sufficient to balance transient changes in BP. However, if the drop in renal perfusion pressure is protracted, additional Cells along the renal arterioles are transformed to the Renin phenotype to meet the perceived demands for Renin and regain homeostasis. In spite of its enormous importance, the nature and location of the renal baroreceptor, and whether mechanical signals are transmitted directly to the Renin cell nucleus to activate Renin gene expression is still unknown. It has been assumed that this pressure sensing mechanism is located at the afferent arterioles either in the JG Cells or the vascular smooth muscle Cells (SMCs) upstream from them. Recent studies from our laboratory identified a unique set of super-enhancers (SEs) that determine the identity of Renin Cells, in which the Renin SE ranked the highest. External mechanical forces may trigger changes in nuclear envelope structure, chromatin organization and gene expression. We hypothesize that JG Cells and/or their descendants sense variations in perfusion pressure and respond to them with marked and unique changes in chromatin configuration resulting in changes in Renin gene expression and in the case of SMCs the adoption of the Renin phenotype via the assembly of a Renin SE. We further hypothesize that this pressure sensing mechanism is a nuclear mechanotransduction process whereby extracellular physical forces are transmitted directly to the chromatin to regulate Renin gene expression, Renin bioavailability and cell identity. Whether the same set of SEs or a different set is activated in response to changes in perfusion pressure is unknown. Using multiple approaches, well established in our laboratories, including genetically modified mice, cell lineage tracing, in vivo high and low perfusion pressure models, epigenomic analysis and editing, and in vitro imaging of chromatin dynamics, we will test the following hypotheses: Aim 1: Changes in perfusion pressure sensed by Renin Cells and/or their descendants result in unique and specific changes in chromatin architecture which in turn control the expression of Renin and the identity of Renin Cells, Aim 2: Integrin β1 controls Renin cell identity via chromatin architectural changes and SE formation, and Aim 3: Lamin A/C regulates chromatin remodeling and the formation of SEs in Renin Cells in response to changes in arterial pressure in vivo and mechanical deformation in vitro. This research is crucial to understand how BP homeostasis is maintained in health and disease. Knowledge gained from the proposed work may open new research avenues and be of help in the prevention and treatment of adults and children suffering from cardiovascular diseases and Hypertension.