Archiv - Juli 2009

TGF-ß1 Inhibits Cx43 Expression and Formation of Functional Syncytia in Cultured Smooth Muscle Cells from Human Detrusor

Neuhaus J, Heinrich M, Schwalenberg T, Stolzenburg JU

Department of Urology, University of Leipzig, Leipzig, Germany

Eur Urol 2009; 55(2): 491-498

Abstract

Background
Human 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-ß1 upregulates Cx43 expression in human aortic smooth muscle cells.

Objective
In this study, we examined the TGF-ß1 effects on Cx43 expression in cultured hBSMCs.

Design, Setting, and Participants
hBSMC cultures, established from patients undergoing cystectomy, were treated with recombinant human TGF-ß1.

Measurements
Cx43 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 Limitations
Dye-coupling experiments revealed stable formation of functional syncytia in passaged cell cultures (P1–P4). Stimulation with TGF-ß1 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.

Conclusions
Our experiments demonstrated a significant down regulation of connexin 43 by TGF-ß1 in cultured hBSMCs. These findings support the view that TGF-ß1 is involved in the pathophysiology of urinary bladder dysfunction.

Take Home Message
Connexin 43 is upregulated in the detrusor muscle of urge-incontinent patients. Increased TGF-ß1 levels might be involved in protein regulation. We demonstrate for the first time that TGF-ß1 affects connexin 43 expression in cultured smooth muscle cells of human bladder.

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