Abstract
Bladder dysfunctions associated with overactive bladder are highly prevalent in the aging population and impose a huge financial cost, however the underlying mechanisms are poorly understood. The newly recognised sensory role of the urothelium provides a new direction of research into the pathogenesis of overactive bladder. As the activity of this sensory structure is highly important for correct bladder function, it is imperative to identify new regulators of this tissue. A role for transient receptor potential vallinoid 4 (TRPV4) channels in bladder function has been recently evidenced. This work aimed to explore the role of TRPV4 in urothelial ATP release, the key step in urothelial sensory transduction, elucidate the underlying mechanisms and assess changes to TRPV4 expression and function in aging and overactive bladders. Immunohistochemistry and western blotting assessed the expression and localization of TRPV4 throughout the bladder. Bladder strips from animals and humans were challenged with the selective TRPV4 agonist GSK1016790A and ATP release and tissue contractility measured. Various antagonists were employed to uncover the mechanisms. The role of Ca2+ in TRPV4-mediated responses was explored using live-cell Ca2+ imaging. The effect of TRPV4 activation on reactive oxygen species production was also measured. The interaction between TRPV4 and the principal urothelial receptor P2Y was assessed, supplemented with P2Y2 knockout mice. The responses between young and aging guinea pigs and normal and overactive human bladders were compared. This is the first study to establish a role for TRPV4 in mucosal ATP release and the underlying mechanisms. This study demonstrates increased TRPV4 expression with age and a functional link between TRPV4 and P2Y receptors as a result of aging. This work also provides preliminary evidence for an increased TRPV4-mediated ATP release in overactive human bladders. These novel findings identify a fundamental role for TRPV4 in bladder physiology and pathophysiology and present experimental evidence that pharmacological manipulation of this receptor may provide a novel method for treatment of overactive bladder.