TABLE Proteoglycans 6.4 kDa, kilodaltons. Molecular Molecular Name Weight (kDa) Composition Localization Function Aggrecan 250 Linear molecule; binds via a Cartilage, Responsible for hydration of link protein to hyaluronan; Chondrocytes extracellular matrix of contains 100 to 150 molecules cartilage of keratan sulfate and chondroitin sulfate chains Decorin 38 Small protein that contains Connective tissue, Functions in collagen only one chondroitin sulfate fibroblasts, cartilage, fibrillogenesis; by attaching or dermatan sulfate chain and bone to neighboring collagen molecules, helps to orient fibers. Regulates the thickness of the fibril and interacts with transforming growth factor (TGF-) Versican 260 Associated with a link protein; Fibroblasts, skin, Possesses EGF-like domains contains main and 12–15 smooth muscle, on the core protein; chains of chondroitin sulfate brain, and mesangial participates in cell-to-cell and attached to core protein cells of the kidney cell-to-extracellular matrix interactions; binds to fibulin-1 Syndecan 33 Family of at least four different Embryonic epithelia, The extracellular domain types of transmembrane mesenchymal cells, binds collagens, heparin, proteoglycans, containing developing lymphatic tenascin, and fibronectin, varying amounts of both tissue cells, intracellular domain binds heparan sulfate and lymphocytes, and to cytoskeleton via actin chondroitin sulfate molecules plasma cells
The myofibroblast displays properties of both fibrmyosinoblasts and smooth muscle cells.
The myofbroblast is an elongated, spindly connective tissue cell not readily identifiable in routine H&E preparations. It is characterized by the presence of bundles of actin filament with associated actin motor proteins such as nonmuscle myosin (page 61). Expression of the -smooth muscle actin ( -SMA; actin isoform found in the vascular smooth muscles) in myo fibroblasts is regulated by TGF-1. The actin bundles transverse the cell cytoplasm originating and terminating on the opposite sites of the plasma membrane. The site of actin fibers attachment to the plasma membrane also serves as a cell-to-ECM anchoring junction and is called fbronexus. It resembles focal adhesion found in the epithelial cells (page 144). This arrangement is of the basis of a mechanotransduction system in which force that is generated by the contraction of intracellular actin bundles is transmitted to the ECM. With the TEM, the myofibroblast displays typical characteristics of the fibroblast along with characteristics of smooth muscle cells. In addition to rER and Golgi profiles, the myofibroblast  contains bundles of longitudinally disposed actin filaments and dense bodies similar to those observed in smooth muscle cells (Fig. 6.21). As in the smooth muscle cell, the nucleus often shows an undulating surface profile, a phenomenon  associated with cell contraction. The myofibroblast differs from the smooth muscle cell in that it lacks a surrounding basal lamina (smooth muscle cells are surrounded by a basal or external lamina). Also, it usually exists as an isolated cell, although its processes may contact the processes of other  myofibroblasts. Such points of contact exhibit gap junctions, indicating intercellular communication.
FIGURE 6.18 • Common multiadhesive glycoproteins. These proteins reside in the extracellular matrix and are important in stabilizing the matrix and linking it to the cell surface. They are multifunctional molecules of different shapes and possess multiple binding sites for a variety of extracellular matrix proteins such as collagens, proteoglycans, and GAGs. Note that multiadhesive proteins interact with basal membrane receptors such as integrin and laminin receptors.