PURPOSE - Pathological alterations in the relationship between cells and the extracellular matrix have a profound effect on tissue morphology and function. Transforming growth factor-beta1 is thought to have a role in bladder pathology by modulating the bladder smooth muscle cell phenotype and, thus, interactions with the extracellular matrix. We investigated the effects of transforming growth factor-beta1 on the organization of an in vitro extracellular matrix by bladder smooth muscle cells.
MATERIALS AND METHODS - Rat bladder smooth muscle cells were seeded at different densities (5 x 10(4), 1 x 10(5) and 2.5 x 10(5) cells) on anchored collagen gels and allowed to contract for 18 or 24 hours. Transforming growth factor-beta1 effects on collagen organization were assessed by analyzing collagen fibril orientation using small angle light scattering. Phase contrast microscopy was used to correlate changes in bladder smooth muscle cell morphology to areas of high fibril orientation. Bladder smooth muscle cells were trypsinized from the gels to confirm altered collagen architecture.
RESULTS - Transforming growth factor-beta1 altered collagen fibril organization locally but this was only significant in the highest cell population. Transforming growth factor-beta1 induced a population dependent effect, in which bladder smooth muscle cells formed bundles or aggregates. These aggregates corresponded with local areas of high collagen fibril alignment. These changes in collagen architecture were maintained macroscopically after removing the bladder smooth muscle cells.
CONCLUSIONS - Changes in collagen architecture organization in response to transforming growth factor-beta1 indicate changes in the bladder smooth muscle cell phenotype, resulting in altered cell/extracellular matrix interactions. Changes in this relationship at the microscopic level could be an important component of tissue remodeling and subsequent dysfunction, and indicate a possible role for transforming growth factor-beta1 in bladder pathology cases.