Role of M3 mAChR in in vivo and in vitro models of LPS-induced inflammatory response

We tested the potential role of the mAChR in lipopolysaccharide (LPS)‐induced inflammatory response in in vivo and in vitro models and a possible signaling pathway involved in the inflammatory process. Anesthetized mice were challenged with intratracheal LPS to induce acute lung injury. The cytology and histopathology changes, expression of cytokines and pulmonary vascular permeability were used to evaluate the effects of the cholinergic agent. Alveolar macrophage cell line NR8383 was also used to confirm the role of mAChRs and the molecular mechanisms underlying the LPS-induced events. LPS-induced acute lung injury (ALI) was significantly improved by atropine (a non-selective mAChR antagonist) and 4-DAMP (a M3 mAChR antagonist), as indicated by the diminution of neutrophil infiltration, pulmonary vascular permeability and IL-6 and TNF-α production. LPS-induced TNF-α production from the alveolar macrophage was significantly inhibited by atropine and 4-DAMP, but not pirenzepine (a M1 mAChR antagonist) and methoctramine (a M2 mAChR antagonist). Interestingly, LPS-induced TNF-α production was enhanced by the muscarinic receptor agonist pilocarpine, and treatment with pilocarpine alone was able to trigger TNF-α production from the alveolar macrophage, which was effectively attenuated by 4-DAMP. Western blot analysis showed that LPS-induced degradation of IκBα was strongly blocked by atropine/4-DAMP both in vivo and in vitro, indicating that M3 mAChR was involved in LPS-induced lung inflammation by mediating the NF-κB signaling pathway. Our findings bring the evidence that the blockage of mAChR exerts anti-inflammatory properties, in which the M3 mAChR plays an important role in the LPS-induced lung inflammation.