Structural and functional bladder changes associated with disrupted voiding cycle in a murine model of cutaneous vesicostomy.

BACKGROUND

The bladder cycle consists of a low-pressure storage phase and a voiding phase marked by detrusor smooth muscle (DSM) contraction and urethral sphincter relaxation. Disruptions to the normal bladder cycle that occur in urinary diversion (UD), severe incontinence, or prolonged dialysis in end-stage renal disease (ESRD) can lead to significant alterations in bladder function, including reduced DSM contractility, increased fibrosis, decreased bladder capacity and compliance, and diminished responsiveness of DSM to cholinergic agents.

OBJECTIVE

To study the effects and underlying mechanisms of voiding dysfunction following disruption of the normal bladder voiding cycle, we developed a mouse model of surgically induced cutaneous vesicostomy (CV).

METHODS

Female CD-1 mice (N = 50, 8 wks old) underwent either surgically induced CV or Sham procedure. The CV group underwent surgery to create a stoma for UD through the skin. Ten days postoperative, bladder function was assessed using in vitro bladder strip contractility recordings, histological analysis with Masson's trichrome staining, and gene expression analysis via quantitative PCR (qPCR) and immunofluorescence microscopy.

RESULTS

Histological analysis revealed a 4.3-fold increase in the lamina propria thickness, accompanied by an increased local inflammatory response, and a 53.5 % decrease in DSM thickness relative to the total bladder wall thickness in the CV group (p < 0.05 vs. Sham). Functionally, CV mice exhibited a 55.1 % reduction in DSM depolarization in response to KCl, and a decrease in nerve-mediated contractions (p < 0.05 vs. Sham). CV mice demonstrated a two-fold increase in peak force response to Substance P, an endogenous Mrgprb2 agonist, indicating enhanced Substance P sensitivity. Real-time PCR detected an upregulated Mrgprb2 mRNA expression in addition to increased Mrgprb2 protein levels in the CV group. A rightward shift in the carbachol dose-response curve suggested reduced cholinergic sensitivity, although no significant changes were observed in the expression of muscarinic acetylcholine receptors Chrm2 and Chrm3.

CONCLUSION

Our findings suggest that CV-induced bladder cycling disruption leads to significant structural and functional bladder changes mediated by upregulation of Mrgprb2 and increased response to its agonist, Substance P, suggesting this receptor plays a key role in mediating bladder changes following UD.

CLINICAL/TRANSLATIONAL APPLICABILITY: Our findings support that bladder structural and functional changes following bladder cycling disruption with temporary UD may be linked to MRGPRX2/Mrgprb2-Substance P signaling. Future studies should explore the underlying pathways and assess bladder recovery upon restoration of normal cycling, aiming to identify potential therapeutic targets for UD-associated bladder pathologies.