Peptidoglycan derived from S. epidermidis induces Connexin43 hemichannel activity with consequences on the innate immune response in endothelial cells.
Résumé
Gram-positive bacterial cell wall components including peptidoglycan (PGN) elicit a potent pro-inflammatory response in diverse cell types including endothelial cells by activating TLR2 signalling. The functional integrity of the endothelium is under the influence of a network of gap junction intercellular communication channels composed of connexins (Cxs) that also form hemichannels, signalling conduits implicated in ATP release and purinergic signalling. PGN modulates connexin expression in a variety of cell types yet effects in endothelial cells remain unresolved. Using the endothelial cell line b.End5, a 6 h challenge with PGN induced IL-6, TLR2 and Cx43 mRNA expression that was associated with enhanced Cx43 protein expression and GJ coupling. Cx43 hemichannel activity, measured by ATP release from the cells, was induced following 15 min exposure to PGN. Inhibition of hemichannel activity with carbenoxolone or apyrase prevented induction of IL-6 and TLR2 mRNA expression by PGN but had no effect on Cx43 mRNA expression levels. By contrast knockdown of TLR2 expression had no effect on PGN induced hemichannel activity but reduced the level of TLR2 and Cx43 mRNA expression following 6 h PGN challenge. PGN also acutely induced hemichannel activity in HeLa cells transfected to express Cx43 but had no effect in Cx43 deficient HeLa OHIO cells. All ATP responses were blocked with Cx-specific channel blockers. We conclude that acute Cx43 hemichannel signalling plays a role in initiation of early innate immune responses in the endothelium.
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