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Collagen IV (ColIV or Col4) is a type of
collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whol ...
found primarily in the
basal lamina The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits. It is often incorrectly referred to as the basement membrane, though it does constitute a portion of the basement membrane. The bas ...
. The collagen IV C4 domain at the C-terminus is not removed in post-translational processing, and the fibers link head-to-head, rather than in parallel. Also, collagen IV lacks the regular
glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid ( carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinog ...
in every third residue necessary for the tight,
collagen helix In molecular biology, the collagen triple helix or type-2 helix is the main secondary structure of various types of fibrous collagen, including type I collagen. In 1954, Ramachandran & Kartha (13, 14) advanced a structure for the collagen tripl ...
. This makes the overall arrangement more sloppy with kinks. These two features cause the collagen to form in a sheet, the form of the basal lamina. Collagen IV is the more common usage, as opposed to the older terminology of "type-IV collagen". Collagen IV exists in all
metazoa Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...
n phyla, to whom they served as an evolutionary stepping stone to multicellularity. There are six human genes associated with it: *
COL4A1 Collagen alpha-1(IV) chain (COL4A1) is a protein that in humans is encoded by the ''COL4A1'' gene on chromosome 13. It is ubiquitously expressed in many tissues and cell types. COL4A1 is a subunit of the type IV collagen and plays a role in angiog ...
, COL4A2,
COL4A3 Collagen alpha-3(IV) chain is a protein that in humans is encoded by the ''COL4A3'' gene. Type IV collagen, the major structural component of basement membranes, is a multimeric protein composed of 3 alpha subunits; this gene encodes the alpha 3 ...
, COL4A4, COL4A5, COL4A6


Clinical significance

The alpha-3 subunit (COL4A3) of collagen IV is thought to be the antigen implicated in Goodpasture syndrome, wherein the immune system attacks the
basement membrane The basement 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 an ...
s of the glomeruli and the
alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...
upon the antigenic site on the alpha-3 subunit becomes unsequestered due to environmental exposures. Goodpasture syndrome presents with
nephritic syndrome Nephritic syndrome is a syndrome comprising signs of nephritis, which is kidney disease involving inflammation. It often occurs in the glomerulus, where it is called glomerulonephritis. Glomerulonephritis is characterized by inflammation an ...
and
hemoptysis Hemoptysis is the coughing up of blood or blood-stained mucus from the bronchi, larynx, trachea, or lungs. In other words, it is the airway bleeding. This can occur with lung cancer, infections such as tuberculosis, bronchitis, or pneumonia, a ...
. Microscopic evaluation of biopsied renal tissue will reveal linear deposits of
Immunoglobulin G Immunoglobulin G (Ig G) is a type of antibody. Representing approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in blood circulation. IgG molecules are created and released by plasma B cells. Each IgG a ...
by
immunofluorescence Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on microbiological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to spe ...
. This is classically in young adult males. Mutations to the genes coding for collagen IV lead to
Alport syndrome Alport syndrome is a genetic disorder affecting around 1 in 5,000-10,000 children, characterized by glomerulonephritis, end-stage kidney disease, and hearing loss. Alport syndrome can also affect the eyes, though the changes do not usually affect ...
. This will cause thinning and splitting of the
glomerular basement membrane The glomerular basement membrane of the kidney is the basal lamina layer of the glomerulus. The glomerular endothelial cells, the glomerular basement membrane, and the filtration slits between the podocytes perform the filtration function of ...
. It will present as isolated
hematuria Hematuria or haematuria is defined as the presence of blood or red blood cells in the urine. “Gross hematuria” occurs when urine appears red, brown, or tea-colored due to the presence of blood. Hematuria may also be subtle and only detectable w ...
,
sensorineural hearing loss Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve (cranial nerve VIII). SNHL accounts for about 90% of re ...
, and ocular disturbances and is passed on genetically, usually in an
X-linked Sex linked describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome (autosome). In humans, these are termed X-linked recessive, ...
manner, although there are rarer autosomal forms. Liver fibrosis and
cirrhosis Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue rep ...
are associated with the deposition of collagen IV in the liver. Serum Collagen IV concentrations correlate with hepatic tissue levels of collagen IV in subjects with
alcoholic liver disease Alcoholic liver disease (ALD), also called alcohol-related liver disease (ARLD), is a term that encompasses the liver manifestations of alcohol overconsumption, including fatty liver, alcoholic hepatitis, and chronic hepatitis with liver fibros ...
and
hepatitis C Hepatitis C is an infectious disease caused by the hepatitis C virus (HCV) that primarily affects the liver; it is a type of viral hepatitis. During the initial infection people often have mild or no symptoms. Occasionally a fever, dark urine, ...
and fall following successful therapy. Mutations in ''COL4A1'' exons 24 and 25 are associated with HANAC (
autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
hereditary
angiopathy Angiopathy is the generic term for a disease of the blood vessels (arteries, veins, and capillaries). The best known and most prevalent angiopathy is diabetic angiopathy, a common complication of chronic diabetes. Classification By caliber Ther ...
with nephropathy,
aneurysms An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus ( ...
, and muscle cramps). It has also been confirmed that mutations in the ''COL4A1'' gene occur in some patients with porencephaly and
schizencephaly Schizencephaly () is a rare birth defect characterized by abnormal clefts lined with grey matter that form the ependyma of the cerebral ventricles to the pia mater. These clefts can occur bilaterally or unilaterally. Common clinical features of ...
. In humans, a novel mutation of the COL4A1 gene coding for collagen type IV was found to be associated with autosomal dominant congenital cataract in a Chinese family. This mutation was not found in unaffected family members or in 200 unrelated controls. In this study, sequence analysis confirmed that the Gly782 amino acid residue was highly conserved. This report of a new mutation in the COL4A1 gene is the first report of a non-syndromic autosomal dominant congenital cataract that highlights an important role for collagen type IV in the physiological and optical properties of the lens. Additionally, in the cardiovascular field, the COL4A1 and COL4A2 regions on chromosome 13q34 are a highly replicated locus for coronary artery disease. In a normal wall of arteries, collagen type IV acts to inhibit smooth muscle cell proliferation. Accordingly, it was demonstrated that protein expression of collagen type IV in human vascular smooth muscle cells is regulated by both SMAD3 protein and TGFβ mediated stimulation of mRNA. Altogether, it was concluded that the pathogenesis of coronary artery disease may be regulated by COL4A1 and COL4A2 genes. An autosomal recessive encephalopathy associated with mutations in this gene has also been reported.Yaramis A, Lochmüller H, Töpf A, Sonmezler E, Yilmaz E, Hiz S, Yis U, Gungor S, Ipek Polat A, Edem P, Beltran S, Laurie S, Yaramis A, Horvath R, Oktay Y (2020) COL4A1-related autosomal recessive encephalopathy in 2 Turkish children. Neurol Genet 6(1):e392 Increased glomerular and mesangial deposition of collagen IV occurs in
diabetic nephropathy Diabetic nephropathy, also known as diabetic kidney disease, is the chronic loss of kidney function occurring in those with diabetes mellitus. Diabetic nephropathy is the leading causes of chronic kidney disease (CKD) and end-stage renal disease ...
and increased urinary levels are associated with the extent of renal injury.


See also

*
Spongin Spongin, a modified type of collagen protein, forms the fibrous skeleton of most organisms among the phylum Porifera, the sponges. It is secreted by sponge cells known as spongocytes. Spongin gives a sponge its flexibility. True spongin is found ...
, a variant of this collagen type found in some animals


References


External links

* Collagens {{protein-stub