Bidirectional modulation of TNF-α transcription via α- and β-adrenoceptors in cultured astrocytes from rat spinal cord.

Noradrenaline (NA) suppresses TNF-α production via β-adrenoceptors (ARs) in brain astrocytes. However, the downstream pathways from β-ARs, and the involvement of α-ARs, remains unknown. In this study, we investigated the AR-mediated regulation of TNF-α mRNA levels in cultured astrocytes from rat spinal cord. NA, the α₁-agonist phenylephrine, and the β-agonist isoproterenol decreased the TNF-α mRNA level, while the α₂-agonist dexmedetomidine increased it. The isoproterenol-induced TNF-α mRNA decrease was accompanied by a decrease in ERK phosphorylation. An adenylyl cyclase activator and an ERK inhibitor mimicked these effects. These results indicate that the transcriptional regulation of TNF-α by β-ARs is mediated via cAMP pathways followed by the ERK pathway inhibition. The dexmedetomidine-induced TNF-α mRNA increase was accompanied by phosphorylation of JNK and ERK, which was blocked by a JNK inhibitor. Furthermore, the LPS-induced increase in the TNF-α mRNA level was accompanied by NF-κB nuclear translocation, and both these effects were blocked by phenylephrine. An NF-κB inhibitor suppressed the LPS-induced increase in the TNF-α mRNA level. These results suggest that α₁-ARs suppress the LPS-induced increase in the TNF-α mRNA level via inhibition of NF-κB nuclear translocation. Taken together, our study reveals that both α- and β-ARs are involved in the transcriptional regulation of TNF-α in astrocytes.

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