Collagen alpha-1(VII) chain is a protein that in humans is encoded by the COL7A1 gene. [5] It is composed of a triple helical, collagenous domain flanked by two non-collagenous domains, and functions as an anchoring fibril between the dermal-epidermal junction in the basement membrane. [6] Mutations in COL7A1 cause all types of dystrophic epidermolysis bullosa, and the exact mutations vary based on the specific type or subtype. [7] It has been shown that interactions between the NC-1 domain of collagen VII and several other proteins, including laminin-5 and collagen IV, contribute greatly to the overall stability of the basement membrane. [6] [8]
Type VII collagen is composed of three main domains in the following order: a non-collagenous domain, abbreviated NC-1; a collagenous domain; and a second non-collagenous domain, NC-2. [6] The NC-1 domain has a cartilage matrix protein (CMP), nine fibronectin III (FNIII)-like subdomains, and a von Willebrand Factor A-like subdomain (VWFA1); a notable segment in the NC-2 domain is analogous to a Kunitz protease inhibitor molecule. [9]
This gene encodes the alpha chain of type VII collagen. The type VII collagen fibril, composed of three identical alpha collagen chains, is restricted to the basement zone beneath stratified squamous epithelia. It functions as an anchoring fibril between the external epithelia and the underlying stroma. Mutations in this gene are associated with all forms of dystrophic epidermolysis bullosa. [10] In the absence of mutations, however, an autoimmune response against type VII collagen can result in an acquired form of this disease called epidermolysis bullosa acquisita. [11]
Type VII collagen is also found in the retina; its function in this organ is unknown. [12]
COL7A1 is located on the short arm of human chromosome 3, in the chromosomal region denoted 3p21.31. The gene is approximately 31,000 base pairs in size and is remarkable for the extreme fragmentation of its coding sequence into 118 exons. [13] [14] COL7A1 is transcribed into an mRNA of 9,287 bases. [15] In the skin, the type VII collagen protein is synthesized by keratinocytes and dermal fibroblasts. [16]
The symbol for the orthologous gene in the mouse is Col7a1.
The inherited disease, dystrophic epidermolysis bullosa, is caused by recessive or dominant mutations in COL7A1. [17] Recessive dystrophic epidermolysis bullosa, the most severe type of epidermolysis bullosa, has two subtypes, generalized intermediate and generalized severe, which have been linked to different mutations in the COL7A1 gene. [7] [9] Recessive dystrophic epidermolysis bullosa, generalized intermediate, is caused primarily by missense, in-frame, and splice-site mutations on one allele. The generalized severe subtype may be caused by premature termination codons in both alleles. These mutations cause little to no expression of collagen VII, which manifests primarily as generalized blistering in the skin and mucosal membranes. [7] This blistering may also lead to several other complications, such as eye abrasions, esophageal stricture, deformity of the hands and feet, and squamous cell carcinoma, among others. [7] [9]
Dominant dystrophic epidermolysis bullosa is most often caused by missense mutations, especially glycine substitutions in the collagenous domain. [7] [9] The symptoms of dominant dystrophic epidermolysis bullosa are less severe than those of the recessive types, with mild blistering and loss of nails. [7] [9]
Epidermolysis bullosa acquisita involves an autoimmune reaction to this form of collagen. [18]
Beremagene geperpavec (Vyjuvek), is a gene therapy indicated for the treatment of wounds for people with dystrophic epidermolysis bullosa with mutation(s) in the collagen type VII alpha 1 chain (COL7A1) gene. [19] [20]
Collagen, type VII, alpha 1 forms a complex network with several other proteins in the basement membrane. [6] It has been shown to interact with laminin 5 [21] and fibronectin, as well as collagen IV, by binding these proteins in the NC-1 domain. [22] [23] [8] The stability of the basement membrane and dermal-epidermal junction is thought to be due to these interactions. [6] [24]
Epidermolysis bullosa (EB) is a group of rare medical conditions that result in easy blistering of the skin and mucous membranes. Blisters occur with minor trauma or friction and are painful. Its severity can range from mild to fatal. Inherited EB is a rare disease with a prevalence in the United States of 8.2 per million live births. Those with mild cases may not develop symptoms until they start to crawl or walk. Complications may include esophageal narrowing, squamous cell skin cancer, and the need for amputations.
Keratin 14 is a member of the type I keratin family of intermediate filament proteins. Keratin 14 was the first type I keratin sequence determined. Keratin 14 is also known as cytokeratin-14 (CK-14) or keratin-14 (KRT14). In humans it is encoded by the KRT14 gene.
Hemidesmosomes are very small stud-like structures found in keratinocytes of the epidermis of skin that attach to the extracellular matrix. They are similar in form to desmosomes when visualized by electron microscopy; however, desmosomes attach to adjacent cells. Hemidesmosomes are also comparable to focal adhesions, as they both attach cells to the extracellular matrix. Instead of desmogleins and desmocollins in the extracellular space, hemidesmosomes utilize integrins. Hemidesmosomes are found in epithelial cells connecting the basal epithelial cells to the lamina lucida, which is part of the basal lamina. Hemidesmosomes are also involved in signaling pathways, such as keratinocyte migration or carcinoma cell intrusion.
The basement membrane, also known as base membrane, is a thin, pliable sheet-like type of extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between epithelial tissues including mesothelium and endothelium, and the underlying connective tissue.
Plectin is a giant protein found in nearly all mammalian cells which acts as a link between the three main components of the cytoskeleton: actin microfilaments, microtubules and intermediate filaments. In addition, plectin links the cytoskeleton to junctions found in the plasma membrane that structurally connect different cells. By holding these different networks together, plectin plays an important role in maintaining the mechanical integrity and viscoelastic properties of tissues.
Epidermolysis bullosa simplex (EBS) is a disorder resulting from mutations in the genes encoding keratin 5 or keratin 14. It is one of the major forms of epidermolysis bullosa, a group of genetic conditions that cause the skin to be very fragile and to blister easily.
Kindler syndrome is a rare congenital disease of the skin caused by a mutation in the KIND1 gene.
Keratin 5, also known as KRT5, K5, or CK5, is a protein that is encoded in humans by the KRT5 gene. It dimerizes with keratin 14 and forms the intermediate filaments (IF) that make up the cytoskeleton of basal epithelial cells. This protein is involved in several diseases including epidermolysis bullosa simplex and breast and lung cancers.
Collagen XVII, previously called BP180, is a transmembrane protein which plays a critical role in maintaining the linkage between the intracellular and the extracellular structural elements involved in epidermal adhesion, identified by Diaz and colleagues in 1990.
Epidermolysis bullosa dystrophica or dystrophic EB (DEB) is an inherited disease affecting the skin and other organs.
Integrin, beta 4 (ITGB4) also known as CD104, is a human gene.
Laminin subunit gamma-2 is a protein that in humans is encoded by the LAMC2 gene.
Laminin subunit alpha-3 is a protein that in humans is encoded by the LAMA3 gene.
Laminin subunit beta-3 is a protein that in humans is encoded by the LAMB3 gene.
Anchoring fibrils extend from the basal lamina of epithelial cells and attach to the lamina reticularis by wrapping around the reticular fiber bundles. The basal lamina and lamina reticularis together make up the basement membrane. Anchoring fibrils are essential to the functional integrity of the dermoepidermal junction.
Bart syndrome, also known as aplasia cutis congenita type VI, is a rare genetic disorder characterized by the association of congenital localized absence of skin, mucocutaneous blistering and absent and dystrophic nails.
Junctional epidermolysis bullosa is a skin condition characterized by blister formation within the lamina lucida of the basement membrane zone.
Transient bullous dermolysis of the newborn (TBDN) is a skin condition that presents in newborns. It is characterized by blister formation secondary to even mild trauma.
Daniel S. Greenspan is an American biomedical scientist, academic and researcher. He is Kellett professor of Cell and Regenerative Biology at the University of Wisconsin-Madison School of Medicine and Public Health. He has authored over 120 publications. His research has mainly focused on genes encoding proteins of the extracellular space and possible links between defects in such genes and human development and disease.
Beremagene geperpavec, sold under the brand name Vyjuvek, is a gene therapy for the treatment of wounds. Beremagene geperpavec is the first approved gene therapy to use herpes-simplex virus type 1 as a vector. Beremagene geperpavec is a genetically modified herpes-simplex virus used to deliver normal copies of the COL7A1 gene to the wounds.