Claudin-12 sustains urothelial barrier defense against uropathogenic E. coli via calcium-dependent immunomodulation.

Urothelial barrier compromise defines inflammatory cystitis, though molecular regulators remain elusive. We identify claudin-12-a bladder-enriched tight junction protein-as an essential barrier component against uropathogenic E. coli (UPEC) invasion. At 72 h post-infection in the murine model of UPEC-induced cystitis, infection triggered dysregulation of canonical tight junction components (claudin-12, ZO-1, occludin), with claudin-12 exhibiting maximal depletion. Immunofluorescence confirmed profound tight junction disassembly in infected bladders. Consistent with this structural defect, claudin-12-knockout mice developed exacerbated acute cystitis, manifesting elevated bacterial colonization, neutrophil/monocyte infiltration, pro-inflammatory gene upregulation, and epithelial denudation. Mechanistically, claudin-12 loss increased calcium permeability in urothelial cells during UPEC infection, driving intracellular calcium accumulation and subsequent activation of apoptosis-related pathways. Notably, pharmacological inhibition of calcium accumulation by TMB-8 reversed both UPEC-induced apoptosis and claudin-12 depletion. Thus, claudin-12 emerges as a pivotal orchestrator of urothelial defense, wherein its regulation of calcium flux restrains UPEC-driven inflammation-revealing therapeutic potential for barrier-repair strategies.