The role of the Non-neuronal Cholinergic System in immune regulation

Abstract

Activation of nicotinic acetylcholine receptors (nAChRs) by agonists like acetylcholine (ACh) can have anti-inflammatory properties via the regulation of cytokines. A recent novel class of nAChR specific molecules termed silent agonists are also thought to induce nAChRdependent metabotropic signaling cascades, while causing very little channel opening. These molecules may therefore be potent immune regulators. This study assessed the expression of cholinergic genes in human macrophages and gained insights on the anti-inflammatory properties of nAChR agonists, silent agonists and cholinergic inhibitors in human macrophages. For both aims, two human monocytic cell lines (THP-1 and U937) were cultured and differentiated into macrophages using phorbol 12-myristate 13-acetate (PMA) to obtain Mo macrophages and in some cases, further polarized into M1 (INF-γ) or M2 (IL-13 and IL-4). Expression of cholinergic genes were first determined via Western Blot and PCR. Secondly, experiments assessing expression of cell markers, cytokine expression, and viability were carried out following treatment with various conditions in the presence of LPS. It was hypothesized that macrophages would express cholinergic proteins and that nAChR agonists/silent agonists would result in anti-inflammatory responses whereas cholinergic inhibitors would result in proinflammatory responses. Overall, we found that differentiated macrophages expressed most cholinergic proteins and that the inhibition of cholinergic proteins and nAChR agonism modulated LPS-induced cytokine release. These experiments gave pertinent information regarding the presence of cholinergic genes and the anti-inflammatory properties of agonists/silent agonists in human macrophages.