Matrix compartments in the growth plate of the proximal tibia of rats

Abstract

The cartilaginous matrix in the growth plate of the proximal tibia of rats is subdivided into various compartments according to criteria established by electron microscopic examination. In conventionally fixed specimens, the arrangement of collagen fibrils was analyzed by transmission and scanning electron microscopy. Distribution of proteoglycans and relations between matrix and cells were studied after fixation in media containing cationic dyes. Matrix compartments are best characterized by the density and arrangement of their collagen fibrils. On the other hand, proteoglycans are distributed almost homogenously all over the matrix. Each chondrocyte is surrounded by a thin envelope of proteoglycans, the pericellular matrix. Adjacent to this is a layer dominated by the content and order of its collagen fibrils, the territorial matrix. Its inner part covers the pericellular matrix with a thin net of intersecting fibrils. The outer part unites the cells of each column by a sheath of tightly packed longitudinal fibrils. This distinction is only possible in the longitudinal parts of the territorial matrix, whereas in the transverse septa both layers fuse into a common network. The interterritorial matrix is interposed between the columnar units and thus represents the central part of the longitudinal septa. Mineralization is restricted to the interterritorial matrix and matrix vesicles are coincidentally found in the same compartment. During growth, this structural organization undergoes a permanent and relatively fast remodeling, a process that is discussed in view of possible cell matrix interactions.

Endochondral calcification by hypertrophic chondrocytes in the Meckel's cartilage grafted into the isogenic mouse spleen.

“…Therefore, the middle area of normal Meckel's cartilage bar does not form calcified cartilage. Essentially, since endochondral ossification including mandibular condyle (SILBERMANN andFROMMER, 1972, 1974) or the growth plate (EGGLI et al,1985; JEE,1988) usually occurs in the hypertrophic chondrocyte-associated areas of the chondro-osseous junction, the calcification throughout hypertrophic zone or, occasionally, maturating zone cells-such as observed in the present study-was a unique phenomenon. When Meckel's cartilage of the same stage was cultivated in vivo in the subcutaneous, muscle, or peritoneal cavity, hypertrophic chondrocytes degenerated rapidly and no calcified cartilage matrix was formed (ISHIZEKI, unpublished data).…”

Three‐dimensional in situ zonal morphology of viable growth plate chondrocytes: A confocal microscopy study

“…At least two major reasons could explain this difference. First, chemical fixation technique, which would result in proteoglycan loss in the matrix and could cause changes in the aspect of chondrocytes and their surrounding matrix, 31 was used in the earlier study while chondrocytes were maintained intact in their extracellular matrix in our study. Furthermore, the absence of intracellular signaling in fixation techniques may inhibit regulatory mechanisms such as volume change 21 through the cytoskeleton, and could eventually affect the evaluated morphological parameters.…”

“…Chondrocytes in the reserve zone were round and randomly scattered in the extracellular matrix of the growth plate with no special alignment, while flattened proliferative and spherical hypertrophied chondrocytes were aligned along the direction of bone growth. In a study by Eggli et al, 31 pericellular matrix (PCM) of chondrocytes in rat tibial growth plates has been shown to consist exclusively of proteoglycans. Presence of PCM around a cell is fully dependent on the preservation of these proteoglycans in situ as extraction of the proteoglycans by standard chemical fixation was found to result in profound changes in chondrocytes shape and size.…”

“…Presence of PCM around a cell is fully dependent on the preservation of these proteoglycans in situ as extraction of the proteoglycans by standard chemical fixation was found to result in profound changes in chondrocytes shape and size. 31 Considering the dense proteoglycan coat in proliferative PCM as compared to the hypertrophic and reserve PCM 31 in which proteoglycan coats are less compact, the specific proliferative chondrocyte shape could be dictated by proteoglycan distribution in their PCM. In a study by Fujii et al 33 collagen fibrils were shown to be randomly oriented in the reserve zone as compared to their longitudinal orientation in the two other zones.…”

The Biology of Small Leucine-rich Proteoglycans in Bone Pathophysiology

“…further removed from the cell or inter-territorial), whereas others are localized both to the ECM and pericellular matrix (territorial, immediately surrounding cells) (7,14,15). In addition, the localization of SLRPs to specific compartments is dependent on the tissue of origin (16,17). ECM-proper SLRPs bind to various types of collagens, thereby regulating the kinetics, assembly, and special organization of fibrils in skin, tendons, bone, and cornea ( Fig.…”