View from the Biological Property: Insight into the Functional Diversity and Complexity of the Gut Mucus

HIGHLIGHTS: What are the main findings? Mucus, as the most widely distributed biofilm and vital protective barrier on the surface of mucous membranes throughout the body, fulfills a number of critical activities in the maintenance of cellular and organismal homeostasis. Morphologic and biochemical evidence corroborate that the mucin family is composed of the transmembrane and gel-forming mucins, which have diverse functional modules. What is the implication of the main findings? Goblet cells are responsible for synthesis, storage, and secreting, which are implicated in either beneficial or detrimental factors. Excessive or insufficient mucus secretion as well as phenotypic alternation may be associated with gastrointestinal disorders, offering potential therapeutic targets for prevention in clinical practice. ABSTRACT: Due to mucin’s important protective effect on epithelial tissue, it has garnered extensive attention. The role played by mucus in the digestive tract is undeniable. On the one hand, mucus forms “biofilm” structures that insulate harmful substances from direct contact with epithelial cells. On the other hand, a variety of immune molecules in mucus play a crucial role in the immune regulation of the digestive tract. Due to the enormous number of microorganisms in the gut, the biological properties of mucus and its protective actions are more complicated. Numerous pieces of research have hinted that the aberrant expression of intestinal mucus is closely related to impaired intestinal function. Therefore, this purposeful review aims to provide the highlights of the biological characteristics and functional categorization of mucus synthesis and secretion. In addition, we highlight a variety of the regulatory factors for mucus. Most importantly, we also summarize some of the changes and possible molecular mechanisms of mucus during certain disease processes. All these are beneficial to clinical practice, diagnosis, and treatment and can provide some potential theoretical bases. Admittedly, there are still some deficiencies or contradictory results in the current research on mucus, but none of this diminishes the importance of mucus in protective impacts.