During filling and voiding, the degree of tension in the bladder wall must be sensed and then relayed to the central nervous system, otherwise bladder dysfunction ensues. While there is a general understanding of the role of sensory neurons (i.e., wall mechanoceptors) in these events, we have fewer insights into how non-neuronal tissues contribute to tension sensation and transduction in the bladder. Our studies focus on the urothelium, which forms the direct interface between the bladder wall and the urinary space. This tissue responds to changes in tension by modulating its ion transport, membrane traffic, and release of mediators, which are hypothesized to alter bladder function, in part via a local urothelial:afferent reflex. However, we still have limited insights into how tension in the plasma membrane of urothelial cells is sensed, what is the nature of the downstream pathways that are activated in response to stretch, or how do these events contribute to bladder function and dysfunction. We hypothesize that urothelial-expressed PIEZO channels act as mechanosensors that in response to bladder filling promote Ca2+ entry, mediator release, and signaling to afferent nerve processes, promoting normal bladder function. We further hypothesize that dysregulation of PIEZO-dependent mechanotransduction in the urothelium will lead to bladder dysfunction.
In Specific Aim 1, we will determine if PIEZO channels act as bona fide mechanosensors by demonstrating the following: (i) that functional PIEZO channels are expressed at the surface of urothelial cells; (ii) that urothelial expressed PIEZO channels respond to physiologically relevant stimuli (i.e., bladder filling); (iii) that PIEZO channels are required for mechanically regulated events including membrane traffic and mediator release; (iv) and that expression of loss-of-function or gain-of-function PIEZO mutants will lead to altered urothelial responses.
In Specific Aim 2, we seek to understand how PIEZO channels promote urothelial:afferent signaling. Using novel tools, including ex vivo bladder imaging, we will explore the mechanisms by which PIEZO channels stimulate increases in intracellular Ca2+ ([Ca2+]i). Because PIEZO channels rapidly inactivate, there is likely to be a mechanism to amplify the original signal. Thus, we will define whether Ca2+-induced Ca2+ release or membrane depolarization act downstream of PIEZO channels to increase [Ca2+]i. We will also determine if the PIEZO-triggered rise in [Ca2+]i is critical for stimulating exocytosis and mediator release in the urothelium, and if urothelial PIEZO channels modulate urothelial:afferent signaling.
In Specific Aim 3, we will begin to explore whether urothelial PIEZO channels contribute to bladder function and/or dysfunction. Specifically, we will determine whether loss of PIEZO expression or function results in bladder underactivity and if PIEZO channels with gain-of-function mutations lead to bladder overactivity. Finally, we will determine whether urothelial-expressed PIEZO channels contribute to the bladder hyperreflexia and pelvic allodynia associated with cyclophosphamide-induced cystitis.
Our studies seek to understand how PIEZO stretch channels expressed in the epithelial tissue that lines the inner surface of bladder convey information about bladder fullness to the central nervous system. In addition, we seek to understand if altering PIEZO channel activity affects bladder function, and whether PIEZO channels contribute to cyclophosphamide-induced cystitis.