Figure 4.

Probable mechanism of gut microbial population and their metabolites to cause neuroinflammation. Intensification and accumulation of pathogenic gut microbiota due to dysbacteriosis lead to the formation of an inflamed and leaky gut. Microbes and their associated metabolites can enter the peripheral circulatory system, where they further lower the expression of tight junction proteins in brain endothelial cells and lead to the disintegration of the blood–brain barrier that promotes the entrance of pathogenic microbes, some of them carrying prions into the brain. Meanwhile, microbial metabolites stimulate the extravasation of immune cells into the brain, all of which together trigger cytokine storm, the cause of neuroinflammation, one of the important hallmarks of neurological disorders characterized by degenerated and demyelinated neurons.