Proteoglycans are large macromolecules found in the extracellular matrix (ECM) and on the cell surface. They consist of a core protein and one or more long chains of carbohydrates called glycosaminoglycans (GAGs) covalently attached to the protein. Proteoglycans play a vital role in maintaining the structure and function of tissues by contributing to the hydration, viscosity, and resistance to compression of the ECM. They also participate in various biological processes, such as cell adhesion, growth factor signaling, and tissue repair.
Some of the main types of proteoglycans include:
- Aggrecan: Aggrecan is the most abundant proteoglycan in cartilage, where it provides resistance to compression and maintains the tissue’s mechanical properties. It consists of a core protein with attached chondroitin sulfate and keratan sulfate GAG chains.
- Decorin: Decorin is a small leucine-rich proteoglycan found in various connective tissues, such as skin, tendon, and bone. It contains a single chondroitin sulfate or dermatan sulfate GAG chain. Decorin interacts with collagen fibers, regulating their assembly and organization, and also modulates growth factor signaling.
- Perlecan: Perlecan is a large proteoglycan found in basement membranes, where it contributes to the structural organization and filtration properties of the membrane. It consists of a core protein with attached heparan sulfate and chondroitin sulfate GAG chains. Perlecan participates in cell adhesion, growth factor signaling, and tissue repair.
- Syndecans: Syndecans are a family of transmembrane proteoglycans that are expressed on the cell surface. They contain heparan sulfate and, in some cases, chondroitin sulfate GAG chains. Syndecans play a role in cell adhesion, migration, and growth factor signaling.
- Versican: Versican is a large chondroitin sulfate proteoglycan found in various connective tissues, such as the dermis, blood vessels, and brain. It contributes to the hydration, viscosity, and resistance to compression of the ECM and is involved in cell adhesion, migration, and tissue repair.
Alterations in the expression or function of proteoglycans can contribute to various pathological conditions, such as osteoarthritis, fibrosis, and cancer. Understanding the role and regulation of proteoglycans is essential for developing therapeutic strategies targeting tissue repair, regeneration, and disease progression.