Intestinal Barrier Function and Neurodegenerative Disease.

Neurodegenerative diseases are caused by the loss of neurons and/or their myelin sheaths, which deteriorate over time and become dysfunctional. Alzheimer's disease, Parkinson's disease, and multiple sclerosis are among the most prominent neurodegenerative diseases that affect millions of older adults worldwide. Despite extensive research over several decades, controversies still surround the etiology of neurodegenerative diseases, and many of them remain incurable. Meanwhile, an increasing number of new mechanistic studies related to the microbiota-gut-brain axis have emerged, among which the relationship between the function of the intestinal barrier and neurodegenerative diseases has received widespread attention. As one of the first lines of defense between the body and the external environment, the impaired function of the intestinal barrier is closely related to the development of neurodegenerative pathologies. Among them, the microbiota-gut-brain axis disorder characterized by intestinal barrier disruption mainly includes impaired function of the intestinal microbial barrier, chemical barrier, mechanical barrier, and immune barrier. This review focuses on the structure and molecular mechanisms of the various layers of the intestinal barrier as well as their relationship with neurodegenerative lesions. In recent years, intestinal barrier repair therapies have provided new ideas for the studied disease treatment modalities. We believe that a better understanding of the role of the intestinal barrier in neurodegenerative diseases would provide new insights for the development of viable therapeutic strategies for patients.