α4β2 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 κB (NF-κB) activity and thereby proinflammatory cytokine (PIC) production in SHEP1 cells stably transfected with α4β2 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-κB translocation and production of PICs interleukin (IL)-1β and IL-6 but only partially blocked inhibitor of nuclear factor-κBα (IκBα) phosphorylation. These effects were exclusively in cells transfected with α4β2 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-κB translocation and IκBα phosphorylation. However, the effects of nicotine on NF-κB activity were significantly blocked by the highly specific janus kinase 2 (JAK2) inhibitor α-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 α4β2-mediated attenuation of LPS-induced inflammation. Anti-inflammatory effects of nicotine may therefore be mediated through α4β2 receptors, the predominant high-affinity binding sites for nicotine in the central nervous system, in addition to the better-established α7 receptors.