Connective tissue extracellular matrix fibronectin

These serine proteases are used to remove pathogens by their hydrolytic activity. They degrade cell membrane proteins and connective tissue matrices by hydrolysis of extracellular matrix proteins such as fibronectin, type IV collagen and laminin, or solubilizing fibrous elastins [55, 56]. Immune cell proteases also are capable of cleaving cytokines, growth hormone, neuropeptides, and procoagulant proteins such as Factors X and V. 

Proteoglycan aggregates are typically found in the extracellular matrix of connective tissue. The noncovalent attachment of each proteoglycan to hyaluronic acid via the core protein is mediated by two linker proteins (not shown). Proteoglycans interact with numerous fibrous proteins in the extracellular matrix such as collagen, elastin, and fibronectin (a glycoprotein involved in cell adhesion). 

Connective tissue, such as tendon and cartilage, differs from other solid tissues In that most of Its volume Is made up of extracellular matrix rather than cells. This matrix Is packed with Insoluble protein fibers and contains proteoglycans, various multladhesive proteins, and hyaluronan, a very large, nonsulfated GAG. The most abundant fibrous protein In connective tissue Is collagen. Rubberlike elastin fibers, which can be stretched and relaxed, also are present In deformable sites (e.g., skin, tendons, heart). As discussed later, the fibronectins, a family of multladhesive matrix proteins, form their own distinct fibrils In the matrix of some connective tissues. Although several types of cells are found In connective tissues, the various ECM components are produced largely by cells called fibroblasts. 

Connective tissue, which consists primarily of fibroblasts, produces extracellular matrix materials that surround cells and tissues, determining their appropriate position within the organ (see Chapter 49). These materials include structural proteins (collagen and elastin), adhesive proteins (fibronectin), and glycosaminoglycans (heparan sulfate, chondroitin sulfate). The unique structures of the proteins and carbohydrates found within the extracellular matrix allow tissues and organs to carry out their many functions. A loss of these supportive and barrier functions of connective tissue sometimes leads to significant clinical consequences, such as those that result from the microvascular alterations that lead to blindness or renal failure, or peripheral neuropathies in patients with diabetes mellitus. 

The role of fibronectin, an adhesion glycoprotein present on the surface of cells in connective tissue matrices and in extracellular fluids, has been reviewed with reference to malignant transformation, embryonic diflerentiation, and the function of the reticuloendothelial system. Chemical and physical characteristics of fibronectin and the role of fibronectin and other matrix components in malignant transformation have been surveyed. ... 

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