Extracellular matrix gene responses in a novel ex vivo model of bladder stretch injury

Congenital bladder outlet obstruction from either mechanical or functional causes often results in clinical bladder fibrosis. We tested the hypothesis that early molecular changes relevant to fibrosis occur in response to stretch injury of the bladder wall and that specific extracellular matrix receptors mediate some of these responses. Furthermore, we introduce a novel ex vivo model of bladder injury which has advantages over previously described in vivo bladder outlet obstruction models by uniquely interrogating molecular responses to bladder distention.

The bladders of Sprague Dawley rats were hydrodistended transurethrally, the ureters and bladder neck were ligated, and the whole bladder was excised and incubated in culture medium in the distended state. At fixed time-points control and stretch bladders were snap frozen, RNA was extracted, and semiquantitative reverse transcription polymerase chain reaction for collagens I, III and XII, and RHAMM (receptor for hyaluronic acid) messenger (m) RNA was performed to establish trends in stretch related gene expression. Bladder specimens were also subjected to routine histological evaluation.

An average 3-fold reduction in collagen I mRNA expression was seen with 8 hours of static stretch (p <0.05). Bladder stretch increased collagen III mRNA levels approximately 2.5-fold (p <0.05). Whole bladder collagen XII and RHAMM mRNA were elevated as much as 5-fold (p <0.05) with stretch. Blocking RHAMM function significantly attenuated these matrix gene responses (p = 0.01 to 0.005).

The ex vivo model of whole bladder stretch is viable and easily reproducible for the study of molecular pathophysiological mechanisms contributing to maladaptive bladder disease. Furthermore, collagen gene transcription is revealed to be rapidly responsive to stretch injury of the bladder. Intact RHAMM receptor function is involved in these responses. Elucidation of the intermediate steps in this response to injury may allow for the development of novel therapeutic strategies which may prevent pathological matrix remodeling seen in clinical bladder disease.