Deciphering STAT3 signaling in cholinergic inhibition of inflammation

We previously reported that stimulation of the vagus nerve attenuates macrophage responses by activating the intracellular Jak2-STAT3 signaling pathway. Here, we further analyzed the potential of STAT3 to modulate TNF responses using STAT silencing strategies, pharmacological blockade, and dominant negative STAT3 constructs. We reveal that deletion of STAT3 using siRNA strategies augments the TNF production by endotoxin, confirming that STAT3 is a negative regulator of the immune response. On the other hand, pharmacological blockade of JAK2STAT3 phosphorylation attenuates LPS-induced TNF production and NF-kB activation in macrophages. Expression of a mutant form that allows STAT3 tyrosine phosphorylation, but not STAT3 DNA binding, prevents the anti-inflammatory potential of nicotine. STAT3 inhibition specifically prevents the activation of the p65RelA/p50NF-kB1 pathway without affecting alternative other NF-kB signaling routes. These data suggest that nicotinic inhibition of inflammation in macrophages is dependent on STAT3 DNA binding and STAT3 protein, rather than STAT3 phosphorylation. Hypothetically, unphosphorylated STAT3 (U-STAT) can be important in mediating the anti-inflammatory effect of nAChR activation, via binding to NF-kB20 and inhibition of NF-kB-activation of TNF transcription. van de Zanden.indb 64 23-5-2011 11:43:50 65 Deciphering STAT3 signaling in cholinergic immune-modulation