TRPV4 Mediates Acute Bladder Responses to Bacterial Lipopolysaccharides

Abstract

Urinary tract infections (UTI) affect a large proportion of the population, causing among other symptoms, more frequent and urgent micturition. Previous studies reported that the gram-negative bacterial wall component lipopolysaccharides (LPS) trigger acute epithelial and bladder voiding responses, but the underlying mechanisms remain unknown. The cation channel TRPV4 is implicated in the regulation of the bladder voiding. Since TRPV4 is activated by LPS in airway epithelial cells, we sought to determine whether this channel plays a role in LPS-induced responses in urothelial cells (UCs). We found that human-derived UCs display a fast increase in intracellular Ca 2+ concentration upon acute application of Escherichia coli LPS. Such responses were detected also in freshly isolated mouse UCs, and found to be dependent on TRPV4, but not to require the canonical TLR4 signaling pathway of LPS detection. Confocal microscopy experiments revealed that TRPV4 is dispensable for LPS-induced nuclear translocation of NF-κB in mouse UCs. On the other hand, quantitative RT PCR determinations showed an enhanced LPS-induced production of proinflammatory cytokines in TRPV4-deficient UCs. Cystometry experiments in anesthetized wild type mice revealed that acute intravesical instillation of LPS rapidly increases voiding frequency. This effect was not observed in TRPV4-deficient animals, but was largely preserved in Tlr4 KO and Trpa1 KO mice. Our results suggest that activation of TRPV4 by LPS in UCs regulates the proinflammatory response and contributes to LPS-induced increase in voiding frequency. These findings further support the concept that TRP channels are sensors of LPS, mediating fast innate immunity mechanisms against gram-negative bacteria.

TRP Channels as Cellular Targets of Particulate Matter

“…LPS molecules on the surface of bacterial particles increase activity of TRPV4 in a matrix stiffness-dependent manner [ 57 ]. Of note, multiple TRP channels, including TRPV1 [ 58 , 59 , 60 ], TRPV4 [ 23 , 61 ], TRPA1 [ 60 , 62 , 63 , 64 , 65 ], TRPM3 [ 60 ] and TRPM8 [ 60 ] have been described as targets of LPS, probably via the induction of modifications in the plasma membrane [ 66 , 67 ]. Therefore, these TRP channels may mediate the action of PM contaminated with this bacterial component.…”

Transient Receptor Potential Channels in the Epithelial-to-Mesenchymal Transition

“…TRPV4 —TRPV4 expression is well described for various epithelial tissues and is activated by warm temperatures, mechanical forces and lipid mediators such as arachidonic acid and its metabolites [ 9 , 10 , 87 , 88 ]. A recent review focused on the potential role of TRPV4 in tumorigenesis and its therapeutic potential [ 89 ].…”

“…As such, TRPV5 and TRPV6 are very well described as epithelial channels involved in the regulation of calcium (re)absorption across epithelial membranes [ 8 ]. TRPV4 channels are expressed in airway epithelial and urothelial cells and potentially regulate immune responses [ 9 , 10 ]. TRPM members observed in epithelial cells include TRPM6 [ 11 ], TRPM4 and TRPM7 [ 12 , 13 , 14 ].…”

Emerging roles of the TRPV4 channel in bladder physiology and dysfunction

“…However, there has also been evidence that uroepithelial TRPV4 may be an effector of LPS independently of the canonical TLR4 signalling. Accordingly, in primary cultured human and mouse uroepithelial cells, LPS was found to evoke TRPV4-dependent but TLR4-independent fast increases in intracellular Ca 2+ concentration (Alpizar et al 2020). In the mouse in vivo, intravesical infusion of LPS was found to increase voiding frequency within a few minutes (Gonzalez et al 2005) and this effect was found to be dependent on TRPV4 (Alpizar et al 2020).…”

“…Accordingly, in primary cultured human and mouse uroepithelial cells, LPS was found to evoke TRPV4‐dependent but TLR4‐independent fast increases in intracellular Ca 2+ concentration (Alpizar et al . 2020). In the mouse in vivo , intravesical infusion of LPS was found to increase voiding frequency within a few minutes (Gonzalez et al .…”