TGF-β1 Inhibits Cx43 Expression and Formation of Functional Syncytia in Cultured Smooth Muscle Cells from Human Detrusor

BackgroundHuman detrusor smooth muscle cells (hBSMCs) are coupled by connexin 43 (Cx43)–positive gap junctions to form functional syncytia. Gap junctional communication likely is necessary for synchronised detrusor contractions and is supposed to be altered in voiding disturbances. Other authors have shown that the pleiotropic cytokine TGF-β1 upregulates Cx43 expression in human aortic smooth muscle cells.ObjectiveIn this study, we examined the TGF-β1 effects on Cx43 expression in cultured hBSMCs.Design, Setting, and ParticipantshBSMC cultures, established from patients undergoing cystectomy, were treated with recombinant human TGF-β1.MeasurementsCx43 expression was then examined by Western blotting, real-time PCR, and immunocytochemistry. Dye-injection experiments were used to study the size of functional syncytia.Results and LimitationsDye-coupling experiments revealed stable formation of functional syncytia in passaged cell cultures (P1–P4). Stimulation with TGF-β1 led to significant reduction of Cx43 immunoreactivity and coupling. Cx43 protein expression was significantly downregulated and Cx43 mRNA was only 30% of the control level. Interestingly, low phosphorylation species of Cx43 were particularly affected.ConclusionsOur experiments demonstrated a significant down regulation of connexin 43 by TGF-β1 in cultured hBSMCs. These findings support the view that TGF-β1 is involved in the pathophysiology of urinary bladder dysfunction.