1. ¹Urological Diseases Research Center, Department of Urology, Children's Hospital Boston, Boston, MA, USA
2. ²Department of Surgery, Harvard Medical School, Boston, MA, USA
3. ³Division of Urology, The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada
4. ⁴Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA

Correspondence: Dr MR Freeman, PhD, Urological Diseases Research Center, Department of Urology, Children's Hospital Boston, 300 Longwood Avenue, John F Enders Research Laboratories, Suite 1161, Boston, MA 02115, USA. E-mail: michael.freeman@childrens.harvard.edu

Received 8 August 2006; Revised 7 September 2006; Accepted 8 September 2006; Published online 16 October 2006.

Abstract

Urinary bladder outlet obstruction results in sustained stretch of the detrusor muscle and can lead to pathological smooth muscle hyperplasia and hypertrophy. The epidermal growth factor receptor (EGFR) is a cognate receptor for mitogens implicated in bladder hyperplasia/hypertrophy. Here, we investigated the potential for modulation of this pathway by pharmacologic targeting with a clinically available EGFR antagonist using an organ culture model of bladder stretch injury as a test system. Urinary bladders from adult female rats were distended in vivo with medium containing the EGFR inhibitor ZD1839 (gefitinib, Iressa). The bladders were excised and incubated in ex vivo organ culture for 4–24 h. EGFR phosphorylation, DNA proliferation, and the extent of apoptosis in the cultured tissues were assessed. To verify that the smooth muscle cells (SMC) are a target of the EGFR inhibitor, primary culture human and rat bladder SMC were subjected to cyclic mechanical stretch in vitro in the presence of ZD1839. Levels of phosphorylated EGFR were significantly increased in the detrusor muscle with 12 h of stretch in the organ cultures. This activation coincided with a subsequent 23-fold increase in DNA synthesis and a 30-fold decrease in apoptosis in the muscle compartment at 24 h. In the presence of ZD1839, DNA synthesis was reduced to basal levels without an increase in the rate of apoptosis under ex vivo conditions. Mechanical stretch of bladder SMC in vitro resulted in a significant increase in DNA synthesis, which was completely abrogated by treatment with ZD1839 but not by AG825, an inhibitor of the related receptor, ErbB2. Our results indicate that the EGFR pathway is a physiologically relevant signaling mechanism in hypertrophic bladder disease resulting from mechanical distension and may be amenable to pharmacologic intervention.