Melatonin Reduces NLRP3 Inflammasome Activation by Increasing α7 nAChR-Mediated Autophagic Flux.

Víctor Farré-Alins,Alicia Muñoz-Montero,Alejandra Palomino-Antolín,Eva Ramos,Luis Gandía,Paloma Narros-Fernández,Francisco López-Muñoz,Esther Parada,Javier Egea,Ana Belen Lopez-Rodriguez,Alejandro Romero,Águeda González-Rodríguez,Vanessa Gómez-Rangel,Céline Decouty-Pérez

doi:10.3390/antiox9121299

Abstract

Microglia controls the immune system response in the brain. Specifically, the activation and dysregulation of the NLRP3 inflammasome is responsible for the initiation of the inflammatory process through IL-1β and IL-18 release. In this work, we have focused on studying the effect of melatonin on the regulation of the NLRP3 inflammasome through α7 nicotinic receptor (nAChR) and its relationship with autophagy. For this purpose, we have used pharmacological and genetic approaches in lipopolysaccharide (LPS)-induced inflammation models in both in vitro and in vivo models. In the BV2 cell line, LPS inhibited autophagy, which increased NLRP3 protein levels. However, melatonin promoted an increase in the autophagic flux. Treatment of glial cultures from wild-type (WT) mice with LPS followed by extracellular adenosine triphosphate (ATP) produced the release of IL-1β, which was reversed by melatonin pretreatment. In cultures from α7 nAChR knock-out (KO) mice, melatonin did not reduce IL-1β release. Furthermore, melatonin decreased the expression of inflammasome components and reactive oxygen species (ROS) induced by LPS; co-incubation of melatonin with α-bungarotoxin (α-bgt) or luzindole abolished the anti-inflammatory and antioxidant effects. In vivo, melatonin reverted LPS-induced cognitive decline, reduced NLRP3 levels and promoted autophagic flux in the hippocampi of WT mice, whereas in α7 nAChR KO mice melatonin effect was not observed. These results suggest that melatonin may modulate the complex interplay between α7 nAChR and autophagy signaling.

Highlights

Inflammation is a crucial signal response to initiate protective immunity
Chloroquine (50 nM), an autophagy inhibitor, produced the same effect than LPS, the rise was slightly higher (Figure 1A,B). These results suggest that LPS blocks autophagic flux in a similar way to chloroquine, confirming that acute inflammation induces the blockage of autophagy
It has been reported that a lack of basal autophagy in the brain is common in different neurodegenerative diseases

Summary

Introduction

Inflammation is a crucial signal response to initiate protective immunity. uncontrolled inflammation can be harmful, leading to tissue damage and the development of inflammatory and/or autoimmune diseases [1]. Inflammasomes are multi-protein molecular platforms involved in the activation of caspase-1, followed by a downstream cleavage and the release of pro-inflammatory cytokines, such as IL-1β and IL-18, from innate immune cells [5,6]. In this regard, hyperinflammation caused by uncontrolled inflammasome activation is linked with many inflammatory, metabolic, degenerative and aging-related diseases [7]. Accumulating evidence indicates that NLRP3 and autophagy pathways are linked by reciprocal regulation, and recent studies have shown autophagy-dependent degradation of NLRP3 [8,9,10,11,12], pointing to autophagy as a main regulatory mechanism of inflammasomes [13]

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