Collagen fibers give the skin resistance to strain and traction. Collagen constitutes about 70% of skin mass, but total collagen decreases about 1% per year. It may look like a small decline, but as such a major component of the skin it will affect skin volume and its physical properties. Also, aging changes collagen structure. What was an organized pattern in young skin, becomes an assembly of disorganized bundles of thick fibrils in older skin. It is not only quantity, it is also quality.
We know that aging decreases skin thickness and elasticity, and it is likely that collagen is a good part of the solution. If we care about slowing down and reversing skin aging, we should care about collagen too. Because collagen is such a major constituent of the skin, the objective should be to stimulate its synthesis, and preserve the collagen protein in an active, organized structure.
Chemically, we want to prevent glycation, the attachment of sugar moieties to the protein amino acids, a modification that affects protein function. The fibroblasts are the main cells in the dermis. They specialize in producing two types of proteins, collagen and elastin, which are a major part of the extra-cellular matrix.
Collagen is synthesized by fibroblasts, initially as procollagen alpha chains on membrane-bound ribosomes. The alpha chains then interact to form a triple-helical molecule after hydroxylation of proline and lysine amino acids. Stability is further enhanced by disulfide cross-linking. The procollagen is then packaged into secretory vesicles that move to the cell surface. At the cell membrane, procollagen peptidases cleave the procollagen into collagen.
Collagen is a structural, long-lived protein. Even if synthesis decreases, the total content may not decrease, it will depend on how much collagen was hydrolyzed by protease action. Proteolysis is not bad in itself, it is good for the skin to eliminate proteins whose structure and properties have been modified beyond usefulness.
Skin aging means, mostly, photoaging. To see the net effect of UV on skin aging, compare the outside of your arm with the underside, a skin area you don’t usually expose to the sun. UV radiation increases the synthesis of proteases, including collagenase, and this is likely to be a reason why collagen decreases after UV irradiation. Natural aging decreases collagen synthesis and increases the expression of matrix metalloproteinases, whereas photoaging results in an increase of collagen synthesis and greater matrix metalloproteinase expression in human skin in vivo. Thus, the balance between collagen synthesis and degradation leading to collagen deficiency is different in photoaged and naturally aged skin. A good part of the changes in collagen related to aging seem to be associated with decreased levels of estrogen.
-Dr. Hannah Sivak