TGF-beta1 mediates glucose-evoked up-regulation of connexin-43 cell-to-cell communication in HCD-cells.

BACKGROUND/AIMS In the current study we examined if the multifunctional cytokine TGF-beta1 mediated glucose-evoked increases in connexin-43(Cx43)-mediated intercellular communication in cells of the human collecting duct (HCD). METHODS RT-PCR and western blot analysis were used to confirm mRNA and protein expression of TGF-beta1 and Cx43 in HCD-cells. The effect of TGF-beta1 and high glucose (25 mM) on Cx43 protein expression, cytoskeletal organisation and cell-cell communication was determined in the presence/absence of TGF-beta1 specific immuno-neutralising antibodies. Functional cell-cell communication was determined using Ca2+-microfluorimetry. RESULTS At 24 hrs, high glucose (25 mM) significantly increased Cx43 mRNA and protein expression. Changes were mimicked by TGF-beta1 (2 ng/ml) at low glucose (5 mM). Both high glucose and TGF-beta1 mediated changes were completely reversed by a pan-specific immuno-neutralising antibody to TGF-beta. Furthermore, high glucose-evoked changes were inhibited by a TGF-beta1-specific monoclonal antibody. Mannitol (25 mM), an osmotic control for high glucose, failed to alter Cx43 expression. TGF-beta1 evoked changes in Cx43 expression were biphasic. An early (4-8 hr) transient decrease in expression was followed by an increase in protein expression (12-24 hr). The decrease in Cx43 expression was paralleled by a transient reorganisation of the actin cytoskeleton, whilst increased Cx43 expression at 24 hrs coincided with a TGF-beta1 specific increase in touch-evoked transmission of Ca2+-signals between coupled cells. CONCLUSIONS High glucose evoked a TGF-beta1 mediated increase in Cx43 expression and gap-junction mediated cell-cell communication in HCD-cells. These changes may maintain epithelial integrity of the collecting duct following hyperglycaemic assault as observed in diabetes.