The Microbiota–Gut–Brain Axis and Alzheimer Disease. From Dysbiosis to Neurodegeneration: Focus on the Central Nervous System Glial Cells

Abstract

The microbiota–gut system can be thought of as a single unit that interacts with the brain via the “two-way” microbiota–gut–brain axis. Through this axis, a constant interplay mediated by the several products originating from the microbiota guarantees the physiological development and shaping of the gut and the brain. In the present review will be described the modalities through which the microbiota and gut control each other, and the main microbiota products conditioning both local and brain homeostasis. Much evidence has accumulated over the past decade in favor of a significant association between dysbiosis, neuroinflammation and neurodegeneration. Presently, the pathogenetic mechanisms triggered by molecules produced by the altered microbiota, also responsible for the onset and evolution of Alzheimer disease, will be described. Our attention will be focused on the role of astrocytes and microglia. Numerous studies have progressively demonstrated how these glial cells are important to ensure an adequate environment for neuronal activity in healthy conditions. Furthermore, it is becoming evident how both cell types can mediate the onset of neuroinflammation and lead to neurodegeneration when subjected to pathological stimuli. Based on this information, the role of the major microbiota products in shifting the activation profiles of astrocytes and microglia from a healthy to a diseased state will be discussed, focusing on Alzheimer disease pathogenesis.

Danggui-Shaoyao-San Attenuates Cognitive Impairment via the Microbiota–Gut–Brain Axis With Regulation of Lipid Metabolism in Scopolamine-Induced Amnesia

“…A growing body of evidence suggests the hypothesis that the microbiota–gut system can be thought of as a single unit that interacts with the brain via the microbiota–gut–brain axis. Through this axis, a constant interplay mediated by several products originating from the microbiota guarantees the physiological development and shaping of the gut and the brain ( 43 , 44 ). We evaluated gut microbiome diversity and calculated the relative abundances of each group at all kinds of classification level, especially at the level of phylum and genus, to find the changes in the intestinal microbiota structure of different groups.…”

Ginkgo biloba in the Aging Process: A Narrative Review

“…The imbalance in the functions of microglia and astrocytes is also related to the augmentation of extracellular glutamate, which is related to the neuron excitotoxicity resulting from the overactivation of the N-methyl-D-aspartate receptors (NMDA). Besides that, in the neuroinflammation scenario, astrocytes and microglia lose their capacity to release cytokines related to neuron survival and functioning [112,[117][118][119].…”

Gut Microbiota as a Potential Player in Mn-Induced Neurotoxicity

“…Several neurodegenerative diseases, such as Alzheimer’s disease (AD), have been posited to be related to gut microbiota composition. For example, it has been suggested that gut microbiota may modulate amyloid-β accumulation, alter blood–brain barrier permeability, and induce neuroinflammation via its metabolites [ 51 , 52 ]. In fact, several microbiota species, such as enterobacteria, can secrete amyloid protein curli, which accelerate amyloid polymerization and create potent immunogenic complexes that activate immune cells [ 49 ].…”