Elastic fibers are a component of the extracellular matrix (ECM) in connective tissues and provide elasticity, resilience, and support to various structures in the body. They enable tissues to return to their original shape after being stretched or compressed, which is essential for the normal function of organs and structures such as blood vessels, skin, lungs, and ligaments.
Elastic fibers are primarily composed of two main proteins:
- Elastin: Elastin is a highly flexible and stretchable protein that forms the core of elastic fibers. It is rich in the amino acids glycine, proline, and hydroxyproline, which allow for the formation of cross-linked structures that provide elasticity. Elastin can stretch up to 150% of its original length and return to its initial shape without damage or deformation.
- Fibrillin: Fibrillin is a glycoprotein that forms microfibrils, which are thin, thread-like structures that surround and support the elastin core within elastic fibers. Fibrillin plays a crucial role in the formation and organization of elastic fibers, as well as in the regulation of elastin synthesis and deposition.
These are synthesized by cells called fibroblasts (in the skin and other connective tissues) and smooth muscle cells (in blood vessels). The synthesis of elastin and fibrillin proteins occurs in the endoplasmic reticulum and Golgi apparatus of these cells. Once secreted into the extracellular space, the proteins are assembled into E.F. through a complex process that involves cross-linking of elastin molecules and the formation of microfibrils by fibrillin.
The amount and distribution of this fibers vary depending on the tissue type and its specific functional requirements. For example, elastic fibers are abundant in tissues that experience frequent and reversible stretching or compression, such as the walls of large arteries, the lungs, and the skin.
Dysfunction or abnormalities in the synthesis, assembly, or maintenance of E.F. can lead to various connective tissue disorders. For instance, Marfan syndrome is a genetic disorder caused by mutations in the fibrillin-1 gene, resulting in the defective formation of microfibrils and weakened elastic fibers in the ECM. This can lead to a range of symptoms, including cardiovascular, skeletal, and ocular abnormalities. Similarly, the loss of elastin and the degradation of elastic fibers with age contribute to the development of wrinkles, sagging skin, and decreased lung function.