Proliferative remodeling of the spatial organization of human superficial chondrocytes distant from focal early osteoarthritis

Objective Human superficial chondrocytes show distinct spatial organizations, and they commonly aggregate near osteoarthritic (OA) fissures. The aim of this study was to determine whether remodeling or destruction of the spatial chondrocyte organization might occur at a distance from focal (early) lesions in patients with OA. Methods Samples of intact cartilage (condyles, patellofemoral groove, and proximal tibia) lying distant from focal lesions of OA in grade 2 joints were compared with location-matched nondegenerative (grade 0–1) cartilage samples. Chondrocyte nuclei were stained with propidium iodide, examined by fluorescence microscopy, and the findings were recorded in a top-down view. Chondrocyte arrangements were tested for randomness or significant grouping via point pattern analyses (Clark and Evans Aggregation Index) and were correlated with the OA grade and the surface cell densities. Results In grade 2 cartilage samples, superficial chondrocytes were situated in horizontal patterns, such as strings, clusters, pairs, and singles, comparable to the patterns in nondegenerative cartilage. In intact cartilage samples from grade 2 joints, the spatial organization included a novel pattern, consisting of chondrocytes that were aligned in 2 parallel lines, building double strings. These double strings correlated significantly with an increased number of chondrocytes per group and an increased corresponding superficial zone cell density. They were observed in all grade 2 condyles and some grade 2 tibiae, but never in grade 0–1 cartilage. Conclusion This study is the first to identify a distinct spatial reorganization of human superficial chondrocytes in response to distant early OA lesions, suggesting that proliferation had occurred distant from focal early OA lesions. This spatial reorganization may serve to recruit metabolically active units as an attempt to repair focal damage.National Institutes of Health (U.S.) (grant P5O-AR39239)National Institutes of Health (U.S.) (grant R01-AR33236)Deutsche Forschungsgemeinschaft (DFG) (grant RO 2511/1-1)Deutsche Forschungsgemeinschaft (DFG) (grant RO 2511/2-1

X-ray detection of structural orientation in human articular cartilage

AbstractObjective: To determine the feasibility of detecting the structural orientation in cartilage with Diffraction Enhanced X-Ray Imaging.Design: Human tali and femoral head specimens were Diffraction Enhanced X-Ray Imaged (DEI) at the SYRMEP beamline at Elettra at various energy levels to detect the architectural arrangement of collagen within cartilage. DEI utilizes a monochromatic and highly collimated beam, with an analyzer crystal that selectively weights out photons according to the angle they have been deviated with respect to the original direction. This provides images of very high contrast, and with the rejection of X-ray scatter.Results: DEI allowed the visualization of articular cartilage and a structural orientation, resembling arcades, within.Conclusion: Our diffraction enhanced images represent the first radiographic detection of the structural orientation in cartilage. Our data are in line with previous studies on the structural organization of joint cartilage. They confirm the model of a vaulting system of collagen fiber bundles interrupted by proteoglycan aggregates

Post-translational events in proteoglycan synthesis : Kinetics of synthesis of chondroitin sulfate and oligosaccharides on the core protein

Chondrocytes isolated from the Swarm rat chondrosarcoma were incubated in culture with [1-3H]glucose for 30 min to 8 h. Labeled proteoglycans were isolated, treated with borohydride under alkaline conditions, and the three complex sugar structures purified: N- and O-linked oligosaccharides and chondroitin sulfate chains. The amount of incorporated radioactivity into each component sugar was analyzed by HPLC after enzyme digestion and hydrolysis. The kinetic data for labeling of each sugar over the time course of the experiment were fit to first-order rate equations and the half times (t 1 2) to linear labeling were calculated. The t 1 2 values were essentially the same, 5-8 min, for galactose in all three complex sugar structures and for chain glucuronic acid in chondroitin sulfate, while that for xylitol in chondroitin sulfate, 15.8 min, was significantly longer. Thus, oligosaccharide synthesis is concomitant with chondroitin sulfate chain synthesis; the addition of the chondroitin sulfate linkage galactose occurs at or nearly at the same time as chain elongation while the addition of linkage xylose residues to the core protein may precede chain synthesis by up to 8 min. Since the intracellular t 1 2 of the core protein precursor for these cells is 45 to 90 min, the data strongly suggest that the addition of xylose is not completed to any significant extent while the polypeptide is still nascent or shortly after its release into the rough endoplasmic reticulum. It is proposed that the addition of xylose to the core protein precursor is a late endoplasmic reticulum or early Golgi event. The analytical data were consistent with the presence of ester phosphate on about 80% of the xylose residues of the newly synthesized proteoglycan