Growth factors in bladder wound healing

Surgical and traumatic injuries to the bladder initiate a complex series of biological processes that result in wound healing. This process involves cellular proliferation, migration and differentiation; removal of damaged tissue; and production of extracellular matrix all of which may be controlled by growth factors. In skin, keratinocyte growth factor (KGF) is induced following incisional injury. We hypothesize that in bladder wound healing KGF and other growth factors are induced to modulate tissue repair.

We have created a model of surgical bladder injury in the rodent. At 12, 24 and 48 hrs and 5 and 7 days after injury, the bladder was bisected and total RNA extracted from the anterior or wounded half and posterior or non-wounded half. Histological analysis of the bladder wound was performed with Mason's Trichrome and immunohistochemistry against smooth muscle alpha actin. RNase protection assays were performed to examine the expression of KGF, transforming growth factor (TGF)alpha and TGF beta 2 and 3 as well as the receptors for KGF and epidermal growth factor (EGF). Lastly, the effects of the exogenous administration of KGF on the bladder was tested on neonatal mice by daily injections of 5 micrograms KGF per gram body weight for 5 days.

At 12 hours after injury KGF mRNA expression in the anterior wounded bladder half and posterior non-wounded bladder half was 8 and 6 times higher respectively, compared to unoperated control bladders. A similar response was seen for TGF alpha, where the 12 hour mRNA expression was 4.5 times higher in the anterior wounded bladder half and 3.5 times higher in the posterior non-wounded bladder half compared to unoperated control bladders. The nadir mRNA expression for both KGF and TGF alpha occurred at 7 days after bladder injury and was the same as in unoperated control bladders. EGFR mRNA expression was approximately 2 times higher in both the anterior wounded and posterior non-wounded bladder halves compared to the nadir levels which occurred at 24 hours after injury. TGF beta 2 and beta 3 mRNA levels did not significantly change in either the anterior wounded or posterior non-wounded bladder halves. Exogenous KGF stimulation resulted in a marked urothelial proliferation when compared to age matched control animals.

During the early phases of bladder wound healing (12-24 hours post injury), mRNA for KGF and TGF alpha increased, whereas TGF beta 2 and beta 3 and the KGFR and EGFR remain unchanged. Additionally, exogenous KGF has a direct effect on urothelial proliferation. KGF and TGF alpha warrant further study as potential mediators of bladder wound healing.