Spinal astrocytes stimulated by tumor necrosis factor-α and/or interferon-γ attenuate connexin 43-gap junction via c-jun terminal kinase activity.

Spinal astrocytes have important mechanistic contributions to the initiation and maintenance of neurodegenerative diseases and chronic pain. Under inflammatory conditions, spinal astrocytes are exposed to cytokines such as tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), and these cytokines could alter astrocytic function by modulating connexin (Cx43), subunits that form channels that modulate intercellular communication in astrocytes. The current study investigated the alteration of Cx43-gap junction in rat primary cultured spinal astrocytes stimulated with cytokines by real-time PCR and Western blotting. The transcriptional and translational levels of Cx43 were significantly but partially reduced 24 and 48 hr treatment with either TNF-α (10 ng/ml) or IFN-γ (5 ng/ml). A mixture of TNF-α and IFN-γ led to a robust decrease of Cx43 expression and, moreover, a moderate reduction of gap junction intercellular communication (GJIC), which was evaluated by a scrap loading/dye transfer assay. Both the decrease of Cx43 expression and the reduction in GJIC induced by the mixture of TNF-α and IFN-γ were prevented by blocking c-jun terminal kinase (JNK) but not by blocking extracellular signaling molecules ERK and p38 kinase, indicating a specific role of astrocytic JNK in the response to cytokines. In addition, treatment with cytokines potently induced the phosphorylation of JNK and c-jun in a time-dependent manner. These results indicate that intercellular communication of astrocytes is significantly disrupted in the inflammatory state and that stimulation of spinal astrocytes with inflammatory cytokines leads to significant inhibition of Cx43-GJIC through activation of the JNK signaling pathway.