Retinoic acid attenuates nuclear factor kappaB mediated induction of NLRP3 inflammasome

Acetylcholine (ACh), a neurotransmitter and a part of the cholinergic system, can modify immune responses. Expression of acetylcholine receptors (AChR) in immune cells, including macrophages, leads to modulation of their function. Inflammasomes are part of the innate immune system and have been linked to a variety of inflammatory diseases. The NLRP3/ASC/caspase-1/IL-1 axis has emerged as a critical signaling pathway in inflammation process initiation. The role of ACh in modulating inflammasomes in macrophages remains relatively under-explored.

The effect of AChR agonist carbachol on inflammasome expression was investigated using murine and human macrophages. Cell lysates were assessed by western blot for protein analysis. Immunofluorescence studies were used to study the translocation of p65. The experiments were conducted in the presence of NF-ĸB inhibitor, AChR antagonists, and retinoic acid (RA) to study the role of NF-ĸB, ACh receptors, and RA, respectively.

We found that carbachol increased the expression of NLRP3 inflammasome (NLRP3, ASC, cleaved caspase-1, IL-1β, and IL-18). The treated cells also showed an increase in NF-ĸB activation. The effect of carbachol was diminished by NF-ĸB inhibitor and atropine, a mAChR antagonist. The addition of RA also significantly reduced the effect of carbachol on NLRP3 inflammasomes.

Our current study suggests that carbachol induces NLRP3 inflammasome activation through mAChR and NF-ĸB, and that RA abolishes the inflammatory response. It reveals the potentials of co-administration of RA with cholinergic drugs to prevent inflammatory responses during cholinergic medications.