elastic fiber

{{Short description|Type of connective tissue in animals}}

{{Use American English|date=March 2021}}

{{Use mdy dates|date=March 2021}}

{{Infobox anatomy

| Name = Elastic fiber

| Latin =

| Image = Gray377.png

| Caption = Subcutaneous tissue from a young rabbit. Highly magnified. (Elastic fibers labeled at right)

| System =

| Precursor =

}}

Elastic fibers (or yellow fibers) are an essential component of the extracellular matrix composed of bundles of proteins (elastin) which are produced by a number of different cell types including fibroblasts, endothelial, smooth muscle, and airway epithelial cells.{{cite journal | vauthors = Vindin H, Mithieux SM, Weiss AS | title = Elastin architecture | journal = Matrix Biology | volume = 84 | pages = 4–16 | date = November 2019 | pmid = 31301399 | doi = 10.1016/j.matbio.2019.07.005 | s2cid = 196458819 }} 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 include elastin, elaunin and oxytalan.

Elastic fibers are formed via elastogenesis,{{cite journal | vauthors = Mithieux SM, Weiss AS | title = Elastin | journal = Advances in Protein Chemistry | volume = 70 | pages = 437–61 | date = 2005 | pmid = 15837523 | doi = 10.1016/s0065-3233(05)70013-9 | publisher = Elsevier | isbn = 978-0-12-034270-9 }}{{cite journal |vauthors=Thunnissen E, Motoi N, Minami Y, Matsubara D, Timens W, Nakatani Y, Ishikawa Y, Baez-Navarro X, Radonic T, Blaauwgeers H, Borczuk AC, Noguchi M |title=Elastin in pulmonary pathology: relevance in tumours with a lepidic or papillary appearance. A comprehensive understanding from a morphological viewpoint |journal=Histopathology |volume= 80|issue= 3|pages= 457–467|date=August 2021 |pmid=34355407 |doi=10.1111/his.14537 |pmc=9293161 |url=|doi-access=free }} 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.{{cite journal | vauthors = Robertson IB, Horiguchi M, Zilberberg L, Dabovic B, Hadjiolova K, Rifkin DB | title = Latent TGF-β-binding proteins | journal = Matrix Biology | volume = 47 | pages = 44–53 | date = September 2015 | pmid = 25960419 | pmc = 4844006 | doi = 10.1016/j.matbio.2015.05.005 }}{{cite journal | vauthors = Pilecki B, Holm AT, Schlosser A, Moeller JB, Wohl AP, Zuk AV, Heumüller SE, Wallis R, Moestrup SK, Sengle G, Holmskov U, Sorensen GL | display-authors = 6 | title = Characterization of Microfibrillar-associated Protein 4 (MFAP4) as a Tropoelastin- and Fibrillin-binding Protein Involved in Elastic Fiber Formation | journal = The Journal of Biological Chemistry | volume = 291 | issue = 3 | pages = 1103–14 | date = January 2016 | pmid = 26601954 | pmc = 4714194 | doi = 10.1074/jbc.M115.681775 | doi-access = free }}{{cite journal | vauthors = Dabovic B, Chen Y, Choi J, Vassallo M, Dietz HC, Ramirez F, von Melchner H, Davis EC, Rifkin DB | display-authors = 6 | title = Dual functions for LTBP in lung development: LTBP-4 independently modulates elastogenesis and TGF-beta activity | journal = Journal of Cellular Physiology | volume = 219 | issue = 1 | pages = 14–22 | date = April 2009 | pmid = 19016471 | pmc = 2719250 | doi = 10.1002/jcp.21643 }}{{cite journal | vauthors = Nakamura T, Lozano PR, Ikeda Y, Iwanaga Y, Hinek A, Minamisawa S, Cheng CF, Kobuke K, Dalton N, Takada Y, Tashiro K, Ross J, Honjo T, Chien KR | display-authors = 6 | title = Fibulin-5/DANCE is essential for elastogenesis in vivo | journal = Nature | volume = 415 | issue = 6868 | pages = 171–5 | date = January 2002 | pmid = 11805835 | doi = 10.1038/415171a | s2cid = 4343659 }} In this process tropoelastin, 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 by glycosaminoglycans, heparan, and other molecules.{{cite journal | vauthors = Yeo GC, Keeley FW, Weiss AS | title = Coacervation of tropoelastin | journal = Advances in Colloid and Interface Science | volume = 167 | issue = 1–2 | pages = 94–103 | date = September 2011 | pmid = 21081222 | doi = 10.1016/j.cis.2010.10.003 }}{{cite journal | vauthors = Wu WJ, Vrhovski B, Weiss AS | title = Glycosaminoglycans mediate the coacervation of human tropoelastin through dominant charge interactions involving lysine side chains | journal = The Journal of Biological Chemistry | volume = 274 | issue = 31 | pages = 21719–24 | date = July 1999 | pmid = 10419484 | doi = 10.1074/jbc.274.31.21719 | doi-access = free }}{{cite journal | vauthors = Tu Y, Weiss AS | title = Glycosaminoglycan-mediated coacervation of tropoelastin abolishes the critical concentration, accelerates coacervate formation, and facilitates spherule fusion: implications for tropoelastin microassembly | journal = Biomacromolecules | volume = 9 | issue = 7 | pages = 1739–44 | date = July 2008 | pmid = 18547105 | doi = 10.1021/bm7013153 }} 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 onto fibrillin microfibrillar scaffolds.

Following deposition onto microfibrils tropoelastin is insolubilized via extensive crosslinking by members of the lysyl oxidase and lysyl oxidase like family of copper-dependent amine oxidases into amorphous elastin, a highly resilient, insoluble polymer that is metabolically stable over a human lifespan. These two families of enzymes react with the many lysine residues present in tropoelastin to form reactive aldehydes and allysine via oxidative deamination.{{cite journal | vauthors = Lucero HA, Kagan HM | title = Lysyl oxidase: an oxidative enzyme and effector of cell function | journal = Cellular and Molecular Life Sciences | volume = 63 | issue = 19–20 | pages = 2304–16 | date = October 2006 | pmid = 16909208 | doi = 10.1007/s00018-006-6149-9 | s2cid = 31863161 | pmc = 11136443 }}

These reactive aldehydes and allysines can react with other lysine and allysine residues to form desmosine, 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 intermolecular crosslinks{{cite journal | vauthors = Schräder CU, Heinz A, Majovsky P, Karaman Mayack B, Brinckmann J, Sippl W, Schmelzer CE | title = Elastin is heterogeneously cross-linked | journal = The Journal of Biological Chemistry | volume = 293 | issue = 39 | pages = 15107–15119 | date = September 2018 | pmid = 30108173 | pmc = 6166741 | doi = 10.1074/jbc.RA118.004322 | doi-access = free }} 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.{{cite journal | vauthors = Liu X, Zhao Y, Gao J, Pawlyk B, Starcher B, Spencer JA, Yanagisawa H, Zuo J, Li T | display-authors = 6 | title = Elastic fiber homeostasis requires lysyl oxidase-like 1 protein | journal = Nature Genetics | volume = 36 | issue = 2 | pages = 178–82 | date = February 2004 | pmid = 14745449 | doi = 10.1038/ng1297 | doi-access = free }}

Mature elastic fibers consist of an amorphous elastin core surrounded by a glycosaminoglycans, heparan sulphate,{{cite journal | vauthors = Gheduzzi D, Guerra D, Bochicchio B, Pepe A, Tamburro AM, Quaglino D, Mithieux S, Weiss AS, Pasquali Ronchetti I | display-authors = 6 | title = Heparan sulphate interacts with tropoelastin, with some tropoelastin peptides and is present in human dermis elastic fibers | journal = Matrix Biology | volume = 24 | issue = 1 | pages = 15–25 | date = February 2005 | pmid = 15748998 | doi = 10.1016/j.matbio.2004.12.001 }} and number of other proteins such as microfibrillar-associated glycoproteins, fibrillin, fibullin, and the elastin receptor.