Collagen is a family of structural proteins that are abundant in the extracellular matrix (ECM) of various animal tissues. It is the most abundant protein in mammals, accounting for about 25-35% of the total protein content. Collagen provides strength, structure, and support to various tissues and plays a crucial role in maintaining the integrity and function of organs, bones, tendons, ligaments, blood vessels, and skin.
There are at least 28 different types of collagen, each with its specific function and tissue distribution. However, the majority of collagen in the body falls into three main types:
- Type I collagen: This is the most abundant type, found in skin, tendon, ligaments, bone, teeth, and blood vessels. Type I collagen provides tensile strength to tissues and is responsible for their resistance to deformation and stretching.
- Type II collagen: This type is predominantly found in cartilage, the smooth, elastic tissue that covers and protects the ends of bones at joints. Type II collagen forms a network of fibers that give cartilage its strength and flexibility.
- Type III collagen: Often found alongside type I collagen, type III collagen is present in skin, blood vessels, and various organs such as the lungs, liver, and spleen. It contributes to the structural integrity of these tissues and plays a role in tissue repair and remodeling.
The synthesis of collagen occurs within cells called fibroblasts, which secrete procollagen molecules into the ECM. Procollagen is then converted into mature collagen by specific enzymes that remove its terminal regions. The mature collagen molecules assemble into fibrils, which further aggregate to form collagen fibers, providing the structural framework for tissues.
Collagen has a unique triple-helical structure, which gives it remarkable tensile strength and stability. However, collagen can be degraded by various enzymes, called matrix metalloproteinases (MMPs), in processes such as tissue remodeling, wound healing, and inflammation. Dysregulation of collagen synthesis or degradation can lead to various diseases and disorders, including osteoarthritis, Ehlers-Danlos syndrome, and scleroderma.