Anti‐inflammatory cholinergic system modulates LPS‐induced acute lung injury

Abstract

Lung cholinergic system suing acetylcholine (ACh) as a neurotransmitter regulates lung inflammation and is believed to play an anti-inflammatory role via activation of nicotinic (nAChR) and/or muscarinic (mAChR) acetylcholine receptors expressed in lung tissue. Therefore, studies that evaluate the effects of lung cholinergic deficiency are relevant to understand the multiple actions of ACh in acute lung injury (ALI). Aim To evaluate whether VAChT deficiency and treatment with agonist α-7 nAChR affects lung alterations observed in an experimental model of ALI. Methods Wild-Type (WT) mice and mice with decreased expression of VAChT KDHOM, which is correlated with 70% less of ACh release, received PNU-282987 (specific α7nAChR agonist,10 mg/kg) 6 hours after LPS (1mg/kg) intratracheal instillation. We evaluated lung inflammation focusing on inflammation in bronchioalveolar lavage fluid (BALF). We also compared the expression levels of α-7 and α-4 nAChRs in lung tissue using radioligand binding assays. Results LPS treatment induced higher increase in inflammatory cells in BALF in VAChT KDHOM compared to WT mice. The activation α-7 nAChR by treatment with PNU-282987 reduced the total cells, macrophages, and neutrophils recovered in BALF (p<0.001 for all comparisons) in both VAChT-KDHOM and WT that received LPS. The LPS induced upregulate α-7 nAChR levels in WT mice but not in the VAChT KDHOM mice. However, treatment with PNU-282987 induced increase in α-7 nAChR levels in LPS-treated VAChT-KDHOM mice. Unlike α-7 nAChR, α-4 nAChR expression was not changed by VAChT reduction, LPS-induce, and PNU-282987 treatment. Conclusion Our preliminary results suggest that α-7 nAChR upregulation contributes to the anti-inflammatory effect of lung cholinergic system. Unlike WT mice, VAChT-KDHOM mice did not upregulate α-7 nAChR in response to inflammatory insult (LPS treatment) resulting in higher inflammation in VAChT-KDHOM mice than WT mice. Furthermore, treatment of VAChT-KDHOM mice with PNU-282987 resulted in increase in α-7 nAChR expression in lung tissue and reduction of LPS-induced lung inflammation. Experiments to determine mAChRs expression in WT vs. VAChT-KDHOM mice are ongoing.