Gut–Brain Axis: Focus on Neurodegeneration and Mast Cells

Abstract

Many studies highlighted that a bidirectional communication between the gut and the central nervous system (CNS) exists. A vigorous immune response to antigens must be avoided, and pathogenic organisms crossing the gut barrier must be detected and killed. For this reason, the immune system developed fine mechanisms able to maintain this delicate balance. The microbiota is beneficial to its host, providing protection against pathogenic bacteria. It is intimately involved in numerous aspects of host physiology, from nutritional status to behavior and stress response. In the last few years, the implication of the gut microbiota and its bioactive microbiota-derived molecules in the progression of multiple diseases, as well as in the development of neurodegenerative disorders, gained increasing attention. The purpose of this review is to provide an overview of the gut microbiota with particular attention toward neurological disorders and mast cells. Relevant roles are played by the mast cells in neuroimmune communication, such as sensors and effectors of cytokines and neurotransmitters. In this context, the intake of beneficial bacterial strains as probiotics could represent a valuable therapeutic approach to adopt in combination with classical therapies. Further studies need to be performed to understand if the gut bacteria are responsible for neurological disorders or if neurological disorders influence the bacterial profile.

Crosstalk between Gut and Brain in Alzheimer’s Disease: The Role of Gut Microbiota Modulation Strategies

“…This makes it possible to carry out joint analyses of the host phenotypes, metabolome, and microbiome to identify mechanistic links [ 31 ]. The GM metabolizes a plethora of neurotransmitters and neuromodulators (such as short-chain fatty acids (SCFA), gamma-aminobutyric acid, acetylcholine, dopamine, glutamate, and serotonin) [ 32 , 33 , 34 ]. Microbial species such as Saccharomyces , Bacillus , Lactobacillus , Escherichia , and Bifidobacterium are known to produce these types of neurotransmitters [ 33 ].…”

“…The GM metabolizes a plethora of neurotransmitters and neuromodulators (such as short-chain fatty acids (SCFA), gamma-aminobutyric acid, acetylcholine, dopamine, glutamate, and serotonin) [ 32 , 33 , 34 ]. Microbial species such as Saccharomyces , Bacillus , Lactobacillus , Escherichia , and Bifidobacterium are known to produce these types of neurotransmitters [ 33 ]. Preliminary human studies have revealed that bacterial-based interventions can also change neurotransmitter levels involved in synaptic plasticity (including brain-derived neurotrophic factor), and regulate the activity of N -methyl-d-aspartate and serotonin receptors [ 34 ].…”

“…Preliminary human studies have revealed that bacterial-based interventions can also change neurotransmitter levels involved in synaptic plasticity (including brain-derived neurotrophic factor), and regulate the activity of N -methyl-d-aspartate and serotonin receptors [ 34 ]. Impairment of the GM composition or their metabolites modulates the gut–brain axis [ 33 ] and regulates cognition, memory, mood, and social behavior [ 35 , 36 ]. Moreover, dysbiosis may result in the formation of toxic misfolded proteins with a β-sheet conformation that promotes loss of synaptic connections, cellular cell dysfunction, and neurodegeneration [ 37 ].…”

“…Probiotics compete with pathogenic bacteria for nutrients and binding sites [ 132 ]. Additionally, they increase the integrity of the barrier and mucus production by exerting a trophic effect on intestinal mucosa and effects on epithelial cell cytokine secretion [ 33 , 133 ]. Oral bacteriotherapy with probiotics has been recently identified to treat and prevent many pathologies [ 134 , 135 ].…”

“…GM metabolites may affect the host cellular pathways involved in differentiation, maturation, and proliferation functions [ 33 ]. Well-defined methodological standards are needed to compare the studies, and other variables such as drugs, concomitant pathologies, and diet must be carefully considered in analyses [ 158 ].…”