Differential connexin expression, gap junction intercellular coupling, and hemichannel formation in NT2/D1 human neural progenitors and terminally differentiated hNT neurons

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Abstract
Connexin‐mediated gap junctions and open hemichannels in nonjunctional membranes represent two biologically relevant mechanisms by which neural progenitors can coordinate their response to changes in the extracellular environment. NT2/D1 cells are a teratocarcinoma progenitor line that can be induced to differentiate terminally into functional hNT neurons and NT‐G nonneuronal cells. Clinical transplants of hNT neurons and experimental grafts of NT2/D1 progenitors or hNT neurons have been used in cell‐replacement therapy in vivo. Previous studies have shown that NT2/D1 cells express connexin 43 (Cx43) and that NT2/D1 progenitors are capable of dye transfer. To determine whether NT2/D1 progenitors and differentiated hNT cultures express other connexins, Cx26, Cx30, Cx32, Cx36, Cx37, Cx43, and Cx46.6 mRNA and protein were analyzed. NT2/D1 progenitors express Cx30, Cx36, Cx37, and Cx43. hNT/NT‐G cultures express Cx36, Cx37, and de novo Cx46.6. Cx26 and Cx32 were not expressed in NT2/D1 or hNT/NT‐G cells. NT2/D1 progenitors formed functional gap junctions as assessed by dye coupling as well as open hemichannels in nonjunctional membranes as assessed by dye‐uptake studies. Dye coupling was inhibited by the gap junction blocker 18α‐glycyrrhetinic acid. Hemichannel activity was inhibited by the dual‐specificity chloride channel/connexin hemichannel inhibitor flufenamic acid but not by the chloride channel inhibitor 4,4′‐diisothiocyanatostilbene‐2,2′‐disulfonic acid. Both dye coupling and dye uptake were substantially reduced following differentiation of NT2/D1 progenitors. We conclude that the pattern of connexin expression in NT2/D1 cells changes over the course of differentiation corresponding with a reduction in biochemical coupling and hemichannel activity in differentiated cells.

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