Regulation of tight junction proteins and bladder epithelial paracellular permeability by an antiproliferative factor...

Previous reports have suggested that the bladder epithelial barrier may be compromised in interstitial cystitis (IC). Antiproliferative factor (APF) is a small glycoprotein made specifically by bladder epithelial cells in patients with IC that induces changes in expression of certain epithelial cell proteins and profoundly inhibits cell growth. Therefore, we confirmed the increased permeability and decreased tight junction formation of bladder epithelial cell monolayers grown from biopsies in patients with IC compared to cells from normal controls. We then determined the effect of APF on the permeability of normal bladder epithelial cell monolayers and the expression of tight junction proteins.

Permeability was determined by measuring the C-mannitol and H-inulin flux between cells in confluent monolayers on Transwell culture plates (Corning, Corning, New York). Tight junction formation was assessed by immunofluorescence microscopy and the expression of specific proteins was determined by Western blot.

APF treatment caused significant increases in the paracellular permeability of normal bladder epithelial cell monolayers and the attenuation of tight junctions compared to mock APF, similar to changes seen in IC cells. APF treatment also decreased expression of the tight junction proteins zonula occludens-1 and occludin.

Because of its apparent effects on bladder epithelial cell tight junctions and paracellular permeability in vitro, APF may contribute to the leakiness of the bladder epithelial barrier seen in IC.