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

Purpose: Congenital bladder outlet obstruction from either mechanical or fu nctional causes often results in clinical bladder fibrosis. We tested the h ypothesis that early molecular changes relevant to fibrosis occur in respon se to stretch injury of the bladder wall and that specific extracellular ma trix 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 interrogat ing molecular responses to bladder distention. Materials and Methods: The bladders of Sprague Dawley rats were hydrodisten ded transurethrally, the ureters and bladder neck were ligated, and the who le bladder was excised and incubated in culture medium in the distended sta te. 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 relate d gene expression. Bladder specimens were also subjected to routine histolo gical evaluation. Results: An average 3-fold reduction in collagen I mRNA expression was seen with 8 hours of static stretch (p <0.05). Bladder stretch increased collag en III mRNA levels approximately 2.5-fold (p <0.05). Whole bladder collagen XII and RHAMM mRNA were elevated as much as Ei-fold (p <0.05) with stretch . Blocking RHAMM function significantly attenuated these matrix gene respon ses (p = 0.01 to 0.005). Conclusions: The ex vivo model of whole bladder stretch is viable and easil y reproducible for the study of molecular pathophysiological mechanisms con tributing to maladaptive bladder disease. Furthermore, collagen gene transc ription is revealed to be rapidly responsive to stretch injury of the bladd er. Intact RHAMM receptor function is involved in these responses. Elucidat ion 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.