The microbiota-inflammasome-brain axis as a pathogenic mediator of neurodegenerative disorders

In various neurodegenerative disorders, inflammation and associated inflammasome activation play an important role. The most prevalent and extensively researched inflammasomes are NLRP3 inflammasomes, which are triggered by pathogens or danger signals mediating inflammatory reaction. Extracellular ATP also activates NLRP3 by stimulating the purinergic receptor P2X7 (P2X7R). Central and peripheral cells, including those in the gut, have been shown to have activated inflammasomes during pathological changes co-occurring with inflammation in various neurodegenerative disorders. Gut injury or dysfunction is increasingly recognised as one of the peripheral pathogenic characteristics of many neurodegenerative disorders, and has been found to associate with changes in gut microbes. In this article, we review data from preclinical and clinical studies regarding the involvement of the NLRP3 inflammasome and the purinergic receptor P2X7R in the pathophysiology of major CNS disorders involving neurodegeneration, including Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), Huntington's disease (HD), and the most common form of motor neuron disease, amyotrophic lateral sclerosis (ALS). We also scrutinise the relationship of the NLRP3 inflammasome to intestinal microbiota alterations in these diseases. Both the NLRP3 inflammasome and P2X7R have been shown to play important roles in the pathogenesis and progression of these neurodegenerative diseases. However, most studies have focused on central nervous system (CNS) pathology, particularly within the brain, with comparatively less attention given to their contribution to gut pathology. Additionally, changes in the microbial ecosystems of the intestine have also been implicated in these disorders. However, the association between gut microbiota alterations and inflammasome activity in the pathology of these neurodegenerative disorders remains poorly understood. Therefore, further investigation is urgently needed to explore the microbiota-inflammasome-brain axis in these neurodegenerative conditions, in order to better understand their contribution to disease pathogenesis and progression, and identify novel therapeutic targets and new approaches to prevention and treatment.