What is collagen?
Collagen is the most abundant protein in mammals and is the main structural component of the extracellular matrix. Present in large quantities in connective tissue, it is responsible for providing skin with mechanical properties such as tautness and rigidity. There are 28 types of collagen encoded by 42 different collagen genes identified to date. Collagen is predominantly produced by fibroblast cells. The proteins contain at least 1 triple-helical domain that is secreted and deposited into the extracellular matrix. Collagen is able to aggregate into supramolecular forms, which are complexes made up of multiple molecules bound by noncovalent bonds and can be roughly categorised into major families based on the type of supramolecular structures they assume. Collagen type 1 and collagen type 2 are both included in a family of collagen types called fibril-forming collagens. Fibril-forming collagens exist in tissues as very long fibrils that are then arranged in different combinations and configurations, so as to provide the tissue with its particular physical properties.
Difference between type 1 and type 2 collagen
The most common form of collagen is known as collagen type 1. It makes up over 90% of the collagen in the human body. Collagen Type 1 is formed into large, eosinophilic fibres, which serves as the basic building blocks of all collagen-based tissues, such as tendons and ligaments. In bone, collagen type 1 fibrils are arranged in a parallel, staggered manner with gaps between fibril ends where long, hard hydroxylapatite crystals are deposited. This structure is what gives bone its tensile strength. In skin, it accounts for 75% of its total dry weight, and is responsible for providing the tissue with elasticity and other physical properties. In fact, the increase in skin laxity and formation of wrinkles that is so often observed with aging is partially caused by a decrease in type I collagen.
Collagen type 2 is mainly found in cartilage, which is the elastic tissue that covers and protects the ends of long bones at the joint. Collagen type 2 is a biomarker of osteoarthritis, a painful disease that occurs due to inflammation of the joint. Osteoarthritis can occur due to degenerative changes observed in cartilage, leading to its eventual destruction. Degradation of collagen type 2 plays a role in these degenerative changes, as evidenced by the positive correlation seen between progression of cartilage damage and increasing levels of collagen degradation products in urine. In these cases, oral administration of collagen type 2 has been shown to be effective in the treatment of osteoarthritis.
What happens to collagen with age?
Age plays a key factor in collagen turnover. To illustrate this point, it is known that type 1 and type 1 collagen are present in 1-month-old animals in amounts that are 100-fold higher than that of animals that are 6 months old. In humans, specifically in skin tissue, the same age-dependency of collagens is also seen where ageing results in a decrease in skin elasticity, due to the loss of collagen.
Collagen is an integral part of our body, playing major roles in wound healing, tissue structure and cell signaling. Hence, collagen has many clinical applications, including as biomaterial in bone grafts and tissue regeneration, to aid healing in wound care, and as a supplement for the enhancement of skin, joint, and bone health.