The extracellular matrix (ECM) is a complex network of proteins and carbohydrates that provides structural support and stability to the cells within tissues and organs. The ECM is a critical component of the cellular microenvironment, as it not only maintains the structural integrity of tissues but also plays an essential role in regulating various cellular processes, such as cell adhesion, migration, proliferation, differentiation, and apoptosis.
The extracellular matrix is composed of various molecules, including:
- Fibrous proteins: These proteins provide the main structural framework of the ECM. The most abundant and well-known fibrous protein is collagen, which forms strong, flexible fibers that offer tensile strength to tissues. Other fibrous proteins include elastin, which imparts elasticity to tissues, and fibronectin, which facilitates cell adhesion and migration.
- Proteoglycans: Proteoglycans are large, complex molecules composed of a core protein linked to long chains of carbohydrates called glycosaminoglycans (GAGs). Proteoglycans can form gel-like structures within the ECM, which help to resist compression and provide hydration to the tissue. Examples of proteoglycans include aggrecan, versican, and decorin.
- Glycoproteins: Glycoproteins are proteins with attached carbohydrate chains. They play a role in cell adhesion, signaling, and other cellular processes. Examples of glycoproteins in the ECM include laminin, which is essential for the formation of basement membranes, and tenascin, which modulates cell adhesion and migration.
- Growth factors and cytokines: These signaling molecules are often associated with the ECM and can regulate various cellular processes, such as cell growth, differentiation, and migration.
The composition and organization of the ECM can vary depending on the specific tissue or organ, as well as in response to various physiological and pathological conditions. Dysregulation of the ECM can contribute to the development of numerous diseases, including fibrosis, arthritis, and cancer.