FIBROBLAST GROWTH FACTOR 10-MEDIATED DELAY IN BLADDER WOUND HEALING IN INDUCIBLE TRANSGENIC MICE

Abstract

and identified by N-terminal sequencing. MAL cDNAs were cloned and sequenced, antibodies to MAL were used to localize it in bladder urothelium by LM and EM techniques. Mice lacking the MAL gene, and those over-expressing the MAL gene, were generated by transgenic techniques. RESULTS: N-terminal sequencing of the bovine p18 identified it as the ‘myelin-and-lymphocyte-protein’ (MAL). This protein has four transmembrane domains interconnected by short hydrophilic domains. It is expressed in bladder urothelium in a differentiation-dependent manner. EM localization studies showed that it is associated with the uroplakin-delivering vesicles of all stages in urothelial umbrella cells, including the small discoidal vesicles, the mature fusiform vesicles, and the apical urothelial surface. In the latter two cases, the MAL is selectively associated with the ‘hinge areas’ that interconnect the urothelial plaques. Genetic ablation of the mouse MAL gene results in the accumulation of fusiform vesicles. Conversely, over-expression of MAL in transgenic mouse urothelium results in a reduction of the fusiform vesicles and, concurrently, the accumulation of multivesicular bodies that are involved in the endocytic degradation of uroplakins. CONCLUSIONS: Our results indicate that (i) MAL is highly expressed in bladder urothelium as a major urothelial differentiation marker, (ii) MAL knockout blocks the fusion of the fusiform vesicles with the urothelial apical surface, and (iii) MAL over-expression increases the delivery of uroplakins to apical surface and their endocytic degradation. Therefore, MAL is a key component in regulating the targeting and degradation of the uroplakin complexes, which serve as the receptor for the uropathogenic E. coli, and contribute to the bladder permeability barrier function.