Elastic fibres

The elastic fibres are an important part of the connective tissue framework of the skin and other organs. They are important for the contouring of the body and the mechanical properties of the skin. Together with the collagen fibres of the skin, elastic fibres ensure tension, elasticity and tear resistance of the skin. These are decisive parameters for the extent of the skin and its ability to return the skin to its original state after mechanical changes in shape. There are fundamental individual differences in these properties. Furthermore, these biomechanical properties decrease with increasing age (intrinsic aging process). Furthermore, UV rays have been proven to damage the elastic fibres. They are transformed into a homogeneously cloggy material (elastosis). The (irreversible) UV-induced elastotic degeneration of elastin in the skin is called actinic elastosis. It causes loss of elasticity and wrinkling of the skin.

Elastic fibers consist of a central matrix of elastin and surrounding microfibrils, which have a linear or striped arrangement. The ratio of the two components microfibrils and elastin is subject to changes in the ageing process. In adults, the proportion of microfibrils in the elastic fibres is about 15%, whereas in children it is 50% (Lewis KG et al. 2004). The elastic fibres of the papillary dermis - oxytalan and elaunin fibres, are significantly finer than the mature elastic fibres located in the reticular dermis, which have a length of 1-3um (Tronnier M 2017).

Elastin itself is a fibrillar, elastic structural protein that is close to collagen and is found in most vertebrates. Elastin consists of elongated, coiled polypeptide chains cross-linked by desmosin (condensation product of the amino acid lysine) (Uitto J 1979). This network structure determines the elasticity of the structural protein. The building blocks are glycine, alanine, valine, proline, leucine and isoleucine. They are present in the repeating partial sequence Gly-Gly-Val-Pro and Gly-Val-Pro-Gly.

Elastin is secreted by fibroblasts in soluble, non-cross-linked form (tropoelastin) and then cross-linked by the copper-dependent enzyme lysyl oxidase (LOX). The amino acid lysine is responsible for this cross-linking. Copper deficiency and mutations in the LOX gene can lead to a reduction in the enzyme activity of lysyl oxidase and to cutis laxa. Deletion of chromosome 7q11.23 causes disorders of elastin(Williams-Beuren syndrome).

The physical property "elasticity" distinguishes the structural protein elastin from the related structural protein collagen. The close bond between collagen and elastin in tissues (e.g. in large vessels) provides both elastic and tear-resistant properties. In vertebrate organisms, elastin is mainly found in organs in which elastic properties are of great functional importance, such as the lungs, skin and blood vessels. In particular, elastin in elastic fibres is responsible for the stretchability of large blood vessels (e.g. the aorta). Histologically, elastin can be represented by the Elastica van Gieson staining (EvG staining). Elastin is a very durable protein with a half-life of > 70 years. The formation of elastin begins before birth and is only continued in the first years of life.

Elastin has a high resistance to most proteases. The proteases that can split elastin are called elastases. They can break down elastin and other scleroproteins, e.g. collagen type I, II, III, IV, VIII, IX, X and XI, as well as structural glycoproteins. Physiological counterparts are alpha1-antitrypsin and alpha2-macroglobulin. If the amount of alpha1-antitrypsin is insufficient, the elastase has a destructive effect (e.g. in pulmonary emphysema). Other diseases in which neutrophil elastase appears to play a significant role are cystic fibrosis, adult respiratory distress syndrome (ARDS), rheumatoid arthritis and infectious diseases. The elastic fibrous skeleton presents itself in every phase of life as a balance between the formation and degradation of new fibres. It is thus a result of intrinsic aging processes, various extrinsic influences and pathological inflammatory or congenital processes (El-Khoury J et al. (2014).

clinical pictures:

• Cutis laxa
• Cutis laxa acquisita
• Cutis laxa hereditaria
• Mid-dermal elastolysis/mediodermal elastolysis
• Anetodermia
• Pseudoxanthoma elasticum-like papillary dermal elastolysis (PXE-like PDE)
• Anular elastolytic giant cell granuloma
• Acrokeratoelastoidosis
• Granulomatous slack skin (GSS)
• Williams-Beuren syndrome (WPS)

1. El-Khoury J et al (2014) Elastophagocytosis: underlying mechanisms and associated cutaneous entities. J Am Acad Dermatol 70:934-944.
2. Lewis KG et al (2004) Acquired disorders of elastic tissue: part I. Increased elastic tissue and solar elastotic syndromes. J Am Acad Dermatol 51:1-21
3. Tronnier M (2018) Elastolysis and skin diseases with loss of elastic fibers. J Dtsch Dermatol Ges 16:183-191.
4. Uitto J (1979) Biochemistry of the elastic fibers in normal connective tissues and is alterations in diseases.J Invest Dermatol 72:1-10.