| Elastic fiber | |
|---|---|
 Subcutaneous tissue from a young rabbit. Highly magnified. (Elastic fibers labeled at right) | |
| Identifiers | |
| FMA | 63868 |
| Anatomical terminology | |
Elastic fibers (oryellow fibers) are an essential component of theextracellular matrix composed of bundles ofproteins (elastin) which are produced by a number of different cell types including fibroblasts, endothelial, smooth muscle, and airway epithelial cells.[1] These fibers are able to stretch many times their length, and snap back to their original length when relaxed without loss of energy. Elastic fibers includeelastin,elaunin andoxytalan.
Elastic fibers are formed viaelastogenesis,[2][3] a highly complex process involving several key proteins including fibulin-4, fibulin-5, latent transforming growth factor β binding protein 4, and microfibril associated protein 4.[4][5][6][7] In this processtropoelastin, the soluble monomeric precursor to elastic fibers is produced by elastogenic cells and chaperoned to the cell surface. Following excretion from the cell, tropoelastin self associates into ~200 nm particles by coacervation, an entropically driven process involving interactions between tropoelastin's hydrophobic domains, which is mediated byglycosaminoglycans, heparan, and other molecules.[8][9][10] These particles then fuse to give rise to 1-2 micron spherules which continue to grow as they move down from the cells surface before being deposited ontofibrillin microfibrillar scaffolds.[1]
Following deposition onto microfibrils tropoelastin is insolubilized via extensive crosslinking by members of thelysyl oxidase and lysyl oxidase like family of copper-dependent amine oxidases into amorphouselastin, a highly resilient, insoluble polymer that is metabolically stable over a human lifespan.[1] These two families of enzymes react with the manylysine residues present in tropoelastin to form reactivealdehydes andallysine viaoxidative deamination.[11]
These reactive aldehydes and allysines can react with other lysine and allysine residues to formdesmosine,isodesmosine, and a number of other polyfunctional crosslinks that join surrounding molecules of tropoelastin into an extensively crosslinked elastin matrix. This process creates a diverse array of intramolecular and intermolecularcrosslinks[12] These unique crosslinks are responsible for elastin's durability and persistence. Maintenance of crosslinked elastin is carried out by a number of proteins including lysyl oxidase-like 1 protein.[13]
Mature elastic fibers consist of an amorphouselastin core surrounded by a glycosaminoglycans, heparan sulphate,[14] and number of other proteins such as microfibrillar-associatedglycoproteins,fibrillin,fibullin, and theelastin receptor.
Elastic fibers are found in theskin,lungs,arteries,veins,connective tissue proper,elastic cartilage,periodontal ligament,fetaltissue and other tissues which must undergo mechanical stretching.[1] In the lung there are thick and thin elastic fibers.[3]
Elastic fibers are absent fromscarring,keloids anddermatofibromas and they are decreased greatly, or are absent inanetodermas.[15]
Elastic fibers stain well withaldehyde fuchsin,orcein,[16] andWeigert's elastic stain inhistological sections.
Thepermanganate-bisulfite-toluidine blue reaction is a highly selective and sensitive method for demonstrating elastic fibers under polarizing optics. The inducedbirefringence demonstrates the highly ordered molecular structure of the elastin molecules in the elastic fiber. This is not readily apparent under normal optics.
There is evidence to believe that certain defects of any components of the elastic matrix may impair and alter the structural appearance of elastic andcollagen fibers.
Cutis laxa andWilliams syndrome have elastic matrix defects that have been directly associated with alterations in the elastin gene.
Alpha-1 antitrypsin deficiency is a genetic disorder where elastin is excessively degraded byelastase, a degrading protein released byneutrophils during the inflammatory response. This leads most often toemphysema and liver disease in affected individuals.
Buschke–Ollendorff syndrome,Menkes disease,pseudoxanthoma elasticum, andMarfan's syndrome have been associated with defects in copper metabolism and lysyl oxidase or defects in the microfibril (defects infibrillin, orfibullin for example).
Hurler disease, alysosomal storage disease, is associated with an altered elastic matrix.
Hypertension and somecongenital heart defects are associated with alterations in thegreat arteries,arteries, andarterioles with alterations in the elastic matrix.
Elastosis is the buildup of elastic fibers in tissues, and is a form ofdegenerative disease.[17] There are a multitude of causes, but the most commons cause isactinic elastosis of the skin, also known assolar elastosis, which is caused by prolonged and excessive sun exposure, a process known asphotoaging. Uncommon causes of skin elastosis includeelastosis perforans serpiginosa,perforating calcific elastosis andlinear focal elastosis.[17]
| Condition | Distinctive features | Histopathology |
|---|---|---|
| Actinic elastosis (most common, also called solar elastosis) | Elastin replacing collagen fibers of thepapillary dermis andreticular dermis |  |
| Elastosis perforans serpiginosa | Degenerated elastic fibers and transepidermal perforating canals (arrow in image points at one of them)[18] |  |
| Perforating calcific elastosis | Clumping of short elastic fibers in the dermis.[18] |  |
| Linear focal elastosis | Accumulation of fragmented elastotic material within the papillary dermis and transcutaneous elimination of elastotic fibers.[18] |  |
Elastic fibers are absent from scarring processes such as scars, keloids, and dermatofibromas