Urothelium-Specific Deletion of Connexin43 in the Mouse Urinary Bladder Alters Distension-Induced ATP Release and Voiding Behavior

Abstract

Connexin43 (Cx43), the main gap junction and hemichannel forming protein in the urinary bladder, participates in the regulation of bladder motor and sensory functions and has been reported as an important modulator of day–night variations in functional bladder capacity. However, because Cx43 is expressed throughout the bladder, the actual role played by the detrusor and the urothelial Cx43 is still unknown. For this purpose, we generated urothelium-specific Cx43 knockout (uCx43KO) mice using Cre-LoxP system. We evaluated the day–night micturition pattern and the urothelial Cx43 hemichannel function of the uCx43KO mice by measuring luminal ATP release after bladder distention. In wild-type (WT) mice, distention-induced ATP release was elevated, and functional bladder capacity was decreased in the animals’ active phase (nighttime) when Cx43 expression was also high compared to levels measured in the sleep phase (daytime). These day–night differences in urothelial ATP release and functional bladder capacity were attenuated in uCx43KO mice that, in the active phase, displayed lower ATP release and higher functional bladder capacity than WT mice. These findings indicate that urothelial Cx43 mediated ATP signaling and coordination of urothelial activity are essential for proper perception and regulation of responses to bladder distension in the animals’ awake, active phase.

Functional roles for PIEZO1 and PIEZO2 in urothelial mechanotransduction and lower urinary tract interoception

“…Our second insight relates to the PIEZO channel-dependence of serosal mediator release from the native urothelium, and its hypothesized role in communication with subjacent tissues (37). In the case of ATP, there are a plethora of studies that have explored the mechanisms and pathways of urothelial ATP release, including reports that filling-induced ATP release is decreased in P2rx3, Trpv1, Trpv4, Slc17a9 (VNUT), Cnx43 KO mice (53,(55)(56)(57)(58)(59), or increased in urothelial conditional Itgb1 (b1-integrin) KO mice (60). However, none of these studies unambiguously identified the mechanosensor, and in all cases, only mucosal ATP release was measured.…”

“…An additional possibility is that the PIEZO1/2-expressing umbrella cells produce a diffusible signaling molecule that is critical for mechanical responses in adjacent urothelial cells. This hypothesized signaling molecule could function by way of a paracrine signaling pathway, by way of connexin channels that are expressed by the urothelium ( 20 , 53 ). In this model, our results could be explained, for example, if PIEZO1 and PIEZO2 form heteromeric channels, but in the absence of its binding partner, the PIEZO channels form homomeric ones that still retain some degree of functionality.…”

Flavonoid Nobiletin Attenuates Cyclophosphamide-Induced Cystitis in Mice through Mechanisms That Involve Inhibition of IL-1β Induced Connexin 43 Upregulation and Gap Junction Communication in Urothelial Cells

“…To assess the involvement of urothelial Cx43 in mechanisms of CYP-induced cystitis, we conducted studies with the urothelium-specific Cx43 KO mice (uCx43KO mice) [30]. On macroscopic examination, the development of bladder erythema at 24 h after CYP administration was attenuated in the uCx43KO CYP mice when compared to that in the Cx43 fx/fx CYP mice (Figure 5A).…”

“…Eight-week-old female C57BL/6 mice were purchased from CLEA Japan (Tokyo, Japan). The Upk2Cre+ mice and the Cx43 fx/fx mice were obtained from the Jackson Laboratory (Bar Harbor, ME, USA) and the bladder urothelium-specific Cx43 knockout (uCx43KO) female mice were generated by crossing UPK2-Cre+ and Cx43 fx/fx mice, as described previously [30]. Mice were housed at constant room temperature with a cycle of 12 h light (7:00 to 19:00) and 12 h dark (7:00 to 19:00).…”

“…A recent in vivo study, conducted to assess the effects of NOB treatment on bovine oocyte maturation and subsequent embryo development, have also shown that the expression of several genes, including GJA1, which encodes Cx43, are altered in the cumulus cells from oocytes matured in the presence of NOB [29]. In the bladder, Cx43 is expressed not only in the detrusor smooth muscle layer but also in the urothelium and has been shown to be an essential player in mechanisms that regulate functional bladder capacity [28,[30][31][32]. The role that urothelial dysfunction plays in bladder inflammation and in the emergence of urinary and pelvic pain symptoms has been the focus of intense research [33,34], but the involvement of urothelial Cx43 in the underlying mechanisms is still unknown.…”