Collagen is the most abundant protein in the human body, providing structure to tissues like skin, bones, and muscles. Of the more than 28 different kinds, Collagen Type V is a less plentiful but important type that plays a specialized role in the body’s architecture. It is a fibrillar collagen that helps form the fine, thread-like fibers that give tissues their strength and framework.
The Role of Collagen Type V in the Body
Collagen Type V is a minor component of the collagen matrix, but it initiates collagen fibrillogenesis, the formation of stable collagen fibers. This process is necessary for the assembly of larger fibers. It is present in cell surfaces, placental tissues, the skin, bones, and muscles.
One of the most well-understood locations of Collagen Type V is the cornea of the eye, where it is directly related to transparency. The precise arrangement and uniform diameter of collagen fibrils allow light to pass through without scattering. Collagen Type V helps regulate this uniformity to keep the corneal tissue clear. A deficiency in this collagen can lead to a loss of corneal transparency.
Beyond the eye, this collagen contributes to the elasticity and integrity of the skin. It is found at the dermal-epidermal junction, which anchors the outer layer of skin (epidermis) to the layer beneath it (dermis). In bone tissue, it works alongside more abundant collagens to create a strong scaffold.
Relationship With Other Collagen Types
The function of Collagen Type V is interconnected with other, more abundant collagens, particularly Type I. Over 90% of the body’s collagen is Type I, forming the primary structural component of tissues like skin, tendons, and bones. Collagen Type V does not form large fibers on its own; instead, it co-assembles with Type I collagen to form heterotypic fibrils, which are fibers composed of more than one collagen type.
Within these mixed fibrils, Collagen Type V regulates the diameter of the Type I collagen fibers. By integrating into the fibril structure, it limits how wide the fibrils can become. For instance, in the skin and cornea, having uniformly thin fibrils is necessary for flexibility and transparency. This regulatory function is a primary aspect of its role in tissue formation.
The assembly process begins with the formation of procollagen molecules, which are processed by enzymes into mature collagen. These molecules, including both Type V and Type I, arrange themselves into thin fibrils. These fibrils ultimately form the extracellular matrix, the supportive network surrounding cells.
Associated Medical Conditions
Defects in Collagen Type V are linked to genetic disorders, most notably Classical Ehlers-Danlos Syndrome (cEDS). This condition arises from mutations in the COL5A1 and COL5A2 genes, which provide instructions for making this collagen. These genes code for the alpha chains that form the procollagen molecule. A mutation can disrupt this process, leading to a reduced quantity of functional Collagen Type V protein.
The symptoms of cEDS are a direct consequence of the faulty collagen framework. Individuals with the condition exhibit skin hyperextensibility, where the skin can be stretched more than normal. They also experience atrophic scarring, where wounds heal with thin and widened scars. This occurs because disorganized collagen fibrils cannot provide the support for proper healing.
Another feature of cEDS is generalized joint hypermobility, where joints have an unusually large range of movement. This laxity can lead to frequent dislocations and chronic pain. The underlying cause is that connective tissues, including ligaments and tendons, are weakened due to the defective collagen structure.