Autonomous aldosterone production is emerging as a significant clinical problem. It is not regulated by salt status or the renin-angiotensin system. Autonomy is severe in primary aldosteronism, prevalent in low-renin and resistant hypertension, and subtle but evident in normotension. When inappropriate for salt status, aldosterone promotes cardiovascular disease. The central premise of this application is that the anatomical, rosette-like organization of aldosterone producing cells (zona Glomerulosa, zG) within the adrenal cortex dictates their cellular behavior. Thus, understanding how zG cell behavior is controlled by the rosette structure will reveal ways to control autonomous aldosterone production that at present do not exist. Previously, we discovered that zG cells behave as electrical oscillators when their cellular connectivity is maintained within rosettes. Using genetically encoded Ca2+ indicators, we have built on this discovery and now provide exciting preliminary data identifying one potential new target, the TRPV4 channel, and one potentially new mode for zG cell activation, mechanoactivation. Our overall hypothesis is that TRPV4 activity in rosettes sets the limits of zG cell excitability. We further propose that this TRPV4 activity is controlled by second messengers, mechanical stimuli and cadherin-mediated adhesion, thus providing additional ways of regulating zG cell behavior.
In Aim 1 of this proposal we seek to establish the role of TRPV4 activity in voltage and Ca2+ oscillations in zG cells using high speed imaging tools and all optical electrophysiology.
In Aim 2 of this proposal we seek to determine how adherens junctions (AJ) recruit and control coordinated Ca2+ signals among zG cells within rosettes. We will target the LGR4/5 or ROBO1/3 signaling pathways to dynamically regulate the integrity/composition of the AJ complex (N-cadherin/?-catenin/?-catenin/vinculin/actin) and assess resulting Ca2+ signals.
In Aim 3 of this proposal we seek to determine how adherens junctions facilitate autonomous aldosterone production evoked by mechanoactivation and how these junctions also enhance the steroidogenic sensitivity to Ang II. We measure two steroidogenic indices: aldosterone and NAD(P)H generation. This project will be conducted using advanced, high-resolution, epifluorescence/confocal imaging methods with genetically encoded probes, state-of-the-art image analysis and biochemical, molecular and electrophysiology methods. This research is expected to (1) discover how the rosette organizes cellular activity within the zG layer and, (2) identify new mechanisms and therapeutic targets that can be exploited to control aldosterone autonomy.
One approach to understand how a tissue functions is to isolate and study the activity of its individual cells. However, in some tissues, such as the aldosterone producing layer of the adrenal gland, these cells behave quite differently when they are tightly compacted and discretely organized as they are in the tissue layer. The focus of this project is to understand how aldosterone producing cells communicate and support each other to produce aldosterone, a steroid hormone that is central to the body?s control of salt and water, and which is inappropriately produced in a significant portion of the US population.
