What is elastin, and where is it located?
Elastic fibers are connective tissue that can stretch when hydrated and return to their original length after being stretched. Elastic fiber is a mixture of elastin and fibrous fibrillin. Elastin is encoded by the ELN gene on chromosome 7. Elastin is synthesized by smooth muscle cells and less so by fibroblasts. Elastin comprises a significant portion of the dry weight of ligaments (up to 70%–80%), lungs, larger blood vessels such as aorta (30%–60%), and skin (2%–5%). Elastin is a polymer of tropoelastin monomers, which contain 850 amino acids, predominantly valine, proline, glycine, and alanine. When tropoelastin molecules associate to form a fiber, lysine residues crosslink by forming desmosine and isodesmosine, which are unique to elastin. Mutations in the elastin gene (ELN) can cause cutis laxa and supravalvular aortic stenosis among others. Elastases, which are serine proteases, are capable of degrading elastase. Elastases are located in tissues, macrophages, leukocytes, and platelets. Such elastases may contribute to blood vessel wall damage and aneurysm formation in the vasculitides. Urinary desmosine levels are used as a measure of elastin degradation.