Role of Bruton's Tyrosine Kinase in mast cell driven urothelial barrier injury in an LL-37 induced model of interstitial cystitis.

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic urinary disorder with unclear pathogenesis. Previous studies identified BTK as a hub gene potentially involved in IC/BPS. This study investigates BTK's role in mast cell (MC) activation and bladder inflammation. An LL-37-induced IC/BPS rat model and an in vitro MCs Co-culture system were established. BTK expression was modulated via adenoviral vectors and cell transfection. Bladder inflammation, MC degranulation, and urothelial barrier function were assessed using histology, ELISA, RT-qPCR, Western blot, IHC, TEM, and IF. MC function was evaluated via CCK-8, flow cytometry, Transwell, and TEM. LL-37 upregulated BTK in IC/BPS rats, promoting inflammation, cytokine release, collagen deposition, MC degranulation, and urothelial damage. BTK overexpression exacerbated, while knockdown alleviated these effects. In vitro, LL-37 stimulated MC proliferation, invasion, and degranulation, and reduced apoptosis. Co-culture with activated MCs decreased glycosaminoglycan (GAG) and tight junction (TJ) proteins in SV-HUC-1 cells, enhanced by BTK overexpression and reversed by knockdown. BTK promotes LL-37-induced MC activation and urothelial barrier disruption by suppressing GAGs and TJ proteins, contributing to IC/BPS pathophysiology.