Mast cell proteases and their significance in physiology, pathology, and therapeutic approaches.

Mast cells (MCs) are versatile, multifunctional immune cells with broad roles in physiological homeostasis and pathogenic processes. MCs are found in most tissues, including skin, lungs, intestines, and peritoneum, and they vary in numbers, types, and biological functions. MCs are implicated in host defense against various pathogens, including bacteria, viruses, and fungi. Additionally, MCs are crucial in protecting against toxins, including those present in venoms from multiple species, such as honeybees, snakes, scorpions, and lizards. Although MCs play an essential role in host defense, they are mostly known for their detrimental actions in allergic reactions, such as asthma, food allergy, anaphylaxis, mastocytosis, and various inflammatory skin conditions. Under such conditions, MCs are activated (via IgE-mediated or other mechanisms) and release a range of potent proinflammatory mediators, including tumor necrosis factor α. In addition to cytokines, they are major producers of histamine and various proteases, including chymase, tryptase, and carboxypeptidase A3. As a result, these mediators contribute to the pathological manifestations associated with inflammatory conditions and other disorders. This review focuses mainly on the biological role of MCs and their proteases, with a focus on chymase and tryptase, as well as their inhibitors as candidate therapies for MC-driven diseases. SIGNIFICANCE STATEMENT: Mast cells (MCs) and their proteases are central regulators of tissue homeostasis, barrier defense, and inflammation across multiple organs, but are also associated with numerous diseases. Ongoing research has shown that the function of MCs is highly dependent on their tissue location, where the local tissue environment shapes their phenotype, protease expression, and, consequently, their biological functions. However, further investigation is required to more precisely understand the physiological conditions governing the transition of MCs from maintaining tissue homeostasis to acquiring pathogenic functions, particularly with respect to their protease-dependent activities. By profiling MC heterogeneity using multiomics approaches to map protease-driven signaling networks, it will be possible to gain deeper insight into their functional roles and establish a conceptual framework to guide the development of next-generation, mechanism-based therapeutics that selectively modulate MC activity in human diseases.