Cartilage is a resilient and smooth type of connective tissue. It is a semi-transparent and non-porous type of tissue. It is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and the bronchial tubes, and the intervertebral discs. In other taxa, such as chondrichthyans, but also in cyclostomes, it may constitute a much greater proportion of the skeleton. It is not as hard and rigid as bone, but it is much stiffer and much less flexible than muscle. The matrix of cartilage is made up of glycosaminoglycans, proteoglycans, collagen fibers and, sometimes, elastin. It usually grows quicker than bone.
Chondroitin sulfate is a sulfated glycosaminoglycan (GAG) composed of a chain of alternating sugars. It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities. Chondroitin sulfate is an important structural component of cartilage, and provides much of its resistance to compression. Along with glucosamine, chondroitin sulfate has become a widely used dietary supplement for treatment of osteoarthritis, although large clinical trials failed to demonstrate any symptomatic benefit of chondroitin.
Chondrocytes are the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans. Although the word chondroblast is commonly used to describe an immature chondrocyte, the term is imprecise, since the progenitor of chondrocytes can differentiate into various cell types, including osteoblasts.
Versican is a large extracellular matrix proteoglycan that is present in a variety of human tissues. It is encoded by the VCAN gene.
Keratan sulfate (KS), also called keratosulfate, is any of several sulfated glycosaminoglycans that have been found especially in the cornea, cartilage, and bone. It is also synthesized in the central nervous system where it participates both in development and in the glial scar formation following an injury. Keratan sulfates are large, highly hydrated molecules which in joints can act as a cushion to absorb mechanical shock.
Perlecan (PLC) also known as basement membrane-specific heparan sulfate proteoglycan core protein (HSPG) or heparan sulfate proteoglycan 2 (HSPG2), is a protein that in humans is encoded by the HSPG2 gene. The HSPG2 gene codes for a 4,391 amino acid protein with a molecular weight of 468,829. It is one of the largest known proteins. The name perlecan comes from its appearance as a "string of pearls" in rotary shadowed images.
Decorin is a protein that in humans is encoded by the DCN gene.
Biglycan is a small leucine-rich repeat proteoglycan (SLRP) which is found in a variety of extracellular matrix tissues, including bone, cartilage and tendon. In humans, biglycan is encoded by the BGN gene which is located on the X chromosome.
Syndecan 1 is a protein which in humans is encoded by the SDC1 gene. The protein is a transmembrane heparan sulfate proteoglycan and is a member of the syndecan proteoglycan family. The syndecan-1 protein functions as an integral membrane protein and participates in cell proliferation, cell migration and cell-matrix interactions via its receptor for extracellular matrix proteins. Syndecan-1 is a sponge for growth factors and chemokines, with binding largely via heparan sulfate chains. The syndecans mediate cell binding, cell signaling, and cytoskeletal organization and syndecan receptors are required for internalization of the HIV-1 tat protein.
Syndecan-2 is a protein that in humans is encoded by the SDC2 gene.
A disintegrin and metalloproteinase with thrombospondin motifs 4 is an enzyme that in humans is encoded by the ADAMTS4 gene.
Stromelysin-2 also known as matrix metalloproteinase-10 (MMP-10) or transin-2 is an enzyme that in humans is encoded by the MMP10 gene.
Laminin subunit alpha-1 is a protein that in humans is encoded by the LAMA1 gene.
Syndecan-3 is a protein that in humans is encoded by the SDC3 gene.
Matrix metalloproteinase-19 (MMP-19) also known as matrix metalloproteinase RASI is an enzyme that in humans is encoded by the MMP19 gene.
Hyaluronan and proteoglycan link protein 1 is a protein that in humans is encoded by the HAPLN1 gene.
Tumor necrosis factor-inducible gene 6 protein also known as TNF-stimulated gene 6 protein or TSG-6 is a protein that in humans is encoded by the TNFAIP6 gene.
Neutrophil collagenase, also known as matrix metalloproteinase-8 (MMP-8) or PMNL collagenase (MNL-CL), is a collagen cleaving enzyme which is present in the connective tissue of most mammals. In humans, the MMP-8 protein is encoded by the MMP8 gene. The gene is part of a cluster of MMP genes which localize to chromosome 11q22.3. Most MMP's are secreted as inactive proproteins which are activated when cleaved by extracellular proteinases. However, the enzyme encoded by this gene is stored in secondary granules within neutrophils and is activated by autolytic cleavage.
Chondroitin sulfate proteoglycan 5 is a protein that in humans is encoded by the CSPG5 gene.
A Link domain or Link module, also known as Xlink domain, is a protein domain that binds to hyaluronic acid. It is important in blood cell migration and apoptosis. The link domain is found in some extracellular proteins in vertebrates such as the hyalectans. It appears to be involved in extracellular matrix assembly and stability, cell adhesion, and migration.
