Effect of mast cell granules on urinary tract epithelial cells in culture

Elevated levels of mast cells in the bladder as well as increased mast cell metabolites in the urine of interstitial cystitis (IC) patients have been reported by several investigators, but as yet a mechanism relating these observations and the pathologic changes in the bladder urothelium has not been established. Because heparin is known to inhibit cell proliferation, we considered the possibility that mast cell granules with their high content of heparin proteoglycan could contribute to the epithelial defects seen in IC by interfering with epithelial repair. With MDCK cells (dog kidney–derived epithelial cells) and RT4 cells (human bladder transitional-cell papilloma cells), we have observed that granules inhibit the ability of preconfluent cell cultures to achieve confluency. We further noted that RT4 cell cultures treated with granules stratified into several more layers than control cultures, suggesting a possible failure of the treated cells to migrate over the gelatin substrate. To study the effect of granules on primary isolates of normal urothelial cells, cultures were initiated from surgical and autopsy samples. Epithelial origin of the isolates was confirmed by the presence of the expected cytokeratins, desmosomes, E-cadherin, and characteristic morphologic changes in response to calcium concentration. In these cultures, we have seen a similar failure to achieve confluence in granule-treated cultures compared with controls. The effect was assessed quantitatively by measuring cell-free area. Measurement of the number of cells by the CyQUANT (Molecular Probes, Eugene, Ore) cell proliferation assay technique showed fewer cells in cultures treated with granules (20 μg/mL of the heparin proteoglycan) compared with controls. The effect may result from increased cell loss or decreased cell replication. We are pursuing studies to distinguish between these possibilities and to evaluate the contribution of interference with cell spreading and cell migration to the effect.