alpha 4 beta 2 Nicotinic Receptors Partially Mediate Anti-Inflammatory Effects through Janus Kinase 2-Signal Transducer and Activator of Transcription 3 but Not Calcium or cAMP Signaling

Despite evidence that smoking confers protection against neurological disorders, how and whether specific nicotinic receptor subtypes are involved is unknown. We reported previously that nicotine suppresses constitutive nuclear factor kappa B (NF-kappa B) activity and thereby proinflammatory cytokine (PIC) production in SHEP1 cells stably transfected with alpha 4 beta 2 nicotinic receptors. Here, we report the anti-inflammatory effects of nicotine pretreatment in lipopolysaccharide (LPS)-stimulated SHEP1 cells. Nicotine (100-300 nM, concentrations found in smoker's blood) blocked LPS-induced NF-kappa B translocation and production of PICs interleukin (IL)-1 beta and IL-6 but only partially blocked inhibitor of nuclear factor-kappa B alpha (I kappa B alpha) phosphorylation. These effects were exclusively in cells transfected with alpha 4 beta 2 receptors but not in wild types. The cell-permeable calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester, the adenylate cyclase stimulant forskolin, and a specific protein kinase A (PKA) inhibitor PKI 14-22-amide failed to block the effect of nicotine on LPS-induced NF-kappa B translocation and I kappa B alpha phosphorylation. However, the effects of nicotine on NF-kappa B activity were significantly blocked by the highly specific janus kinase 2 (JAK2) inhibitor alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide (AG-490) and the signal transducer and activator of transcription 3 (STAT3) inhibitor 2-hydroxy-4-[[[[(4-methylphenyl)sulfonyl]oxy]acetyl]amino]benzoic acid (NSC74859). These findings reveal a calcium-and cAMP-PKA-independent signaling cascade and suggest a role for JAK2-STAT3 transduction in alpha 4 beta 2-mediated attenuation of LPS-induced inflammation. Anti-inflammatory effects of nicotine may therefore be mediated through alpha 4 beta 2 receptors, the predominant high-affinity binding sites for nicotine in the central nervous system, in addition to the better-established alpha 7 receptors.