The Role of Signal Transducer and Activator of Transcription 3 (Stat3) in Stretch Injury to Bladder Smooth Muscle Cells

PurposeExcessive stretch of the bladder can lead to wall thickening including the growth of bladder smooth muscle cells (BSMC) and bladder dysfunction. We uncovered a factor previously unexamined for its role in bladder stretch injury: signal transducer and activator of transcription 3 (STAT3). STAT3 was assessed for its role in mitogen- and stretch-induced BSMC proliferation.Material and methodsIn vivo stretch model: Eight mice underwent bladder hyper-distention (40 cm H2O for 5 min). Controls were catheterized only (n=3). Bladders were harvested and total protein extracts were screened for activated signaling proteins using a bank of phospho-specific antibodies (Kinexus, AB, Canada). Screen results demonstrated novel induction of STAT3, which was assessed further for its requirement in supporting growth factor (GF) and stretch-induced bSMC proliferation. In vitro proliferation and stretch model: Bladder smooth muscle cell were grown on stretch and culture plates. Smooth muscle cell proliferation was induced by growth factors such as EGF, PDGF, 10% serum and mechanical stretch. To half of the plates STAT3 inhibitor was added and bladder smooth muscle proliferation was assessed using 3H-Thymidine incorporation and visual cell counting.ResultsIn vivo stretch model: In vivo bladder stretch confirmed activation of MAPK pathway, as well as a previously unrecognized STAT3. In vitro proliferation and stretch model: Using an upstream STAT3 specific inhibitor, (AG-490) the proliferative responses to mitogenic and mechanical stimuli was blunted. Cell counting confirmed 3H-thymidine incorporation results.ConclusionsSTAT3 signaling is activated by in vivo bladder stretch, a condition associated with FP. In vitro, STAT3 inhibition blocks mitogenic and stretch-induced bSMC proliferation.