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The less intense tissue reaction around metal on metal total hip replacements (THRs) compared to metal on polyethylene (PE) THRs may be explained by the differences in the characteristics of metal wear particles. In this study, transmission electron microscopy was used to study metal wear particles that were either in situ in cells or had been extracted from the cells by a new technique based on enzymatic tissue digestion. The tissues were obtained from 13 patients undergoing revision of metal on metal THRs with cobalt-chromium-molybdenum (CoCrMo) bearing couples. Most of the CoCrMo wear particles were smaller than 50 nm (range 6-834 nm) and round to oval in shape with irregular boundaries. This size range is considerably smaller than that reported for PE particles. While even a small volume of metal wear will produce high numbers of particles, the apparently less severe local tissue reaction to metal particles may be due to the possibility that corrosion, dissolution, and dissemination of metal particles may result in fewer local biological effects than the long-term retention of PE particles in the periprosthetic tissues.

Abstract:The less intense tissue reaction around metal on metal total hip replacements (THRs) compared to metal on polyethylene (PE) THRs may be explained by the differences in the characteristics of metal wear particles. In this study, transmission electron microscopy was used to study metal wear particles that were either in situ in cells or had been extracted from the cells by a new technique based on enzymatic tissue digestion. The tissues were obtained from 13 patients undergoing revision of metal on metal THRs with cobalt-chromium-molybdenum (CoCrMo) bearing couples. Most of the CoCrMo wear particles were smaller than 50 nm (range 6-834 nm) and round to oval in shape with irregular boundaries. This size range is considerably smaller than that reported for PE particles. While even a small volume of metal wear will produce high numbers of particles, the apparently less severe local tissue reaction to metal particles may be due to the possibility that corrosion, dissolution, and dissemination of metal particles may result in fewer local biological effects than the long-term retention of PE particles in the periprosthetic tissues.

CCN2/Connective Tissue Growth Factor (CTGF) is a matricellular protein that regulates cell adhesion, migration, and survival. CCN2 is best known for its ability to promote fibrosis by mediating the ability of transforming growth factor β (TGFβ) to induce excess extracellular matrix production. In addition to its role in pathological processes, CCN2 is required for chondrogenesis. CCN2 is also highly expressed during development in endothelial cells, suggesting a role in angiogenesis. The potential role of CCN2 in angiogenesis is unclear, however, as both pro- and anti-angiogenic effects have been reported. Here, through analysis of Ccn2-deficient mice, we show that CCN2 is required for stable association and retention of pericytes by endothelial cells. PDGF signaling and the establishment of the endothelial basement membrane are required for pericytes recruitment and retention. CCN2 induced PDGF-B expression in endothelial cells, and potentiated PDGF-B-mediated Akt signaling in mural (vascular smooth muscle/pericyte) cells. In addition, CCN2 induced the production of endothelial basement membrane components in vitro, and was required for their expression in vivo. Overall, these results highlight CCN2 as an essential mediator of vascular remodeling by regulating endothelial-pericyte interactions. Although most studies of CCN2 function have focused on effects of CCN2 overexpression on the interstitial extracellular matrix, the results presented here show that CCN2 is required for the normal production of vascular basement membranes.

Abstract. Primary monolayers of rabbit articular chondrocytes synthesize high levels of type II collagen and proteoglycan. This capacity was used as a marker for the expression of the differentiated phenotype. Such cells were treated with 1 Bg/ml retinoic acid (RA) for 10 d to produce a modulated collagen phenotype devoid of type II and consisting of predominantly type I trimer and type III collagen. After transfer to secondary culture in the presence of RA, the stability of the RA-modulated phenotype was investigated by culture in the absence of RA. Little reexpression of type II collagen synthesis occurred in this period unless cultures were treated with 3 x 10 -6 M dihydrocytochalasin B to modify microfilament structures.Reexpression of the differentiated phenotype began between days 6-8 and was essentially complete by day 14. Substantial reexpression occurred by day 8 without a detectable increase in cell rounding. Colony formation, characteristic of primary chondrocytes, was infrequent even after reexpression was complete. These data suggest that the integrity of microfilament cytoskeletal structures can be a source of regulatory signals that mechanistically appear to be more proximal to phenotypic change than the overt changes in cell shape that accompany reexpression of subculturemodulated chondrocytes in agarose culture (Benya, P. D., and J. D. Shaffer, 1982. Cell. 30:215-224).

Abstract. The differentiated phenotype of rabbit articular chondrocytes was modulated in primary culture by treatment with 1 pg/ml retinoic acid (RA) and reexpressed in secondary culture by treatment with the microfilament-disruptive drug dihydrocytochalasin B (DHCB) in the absence of RA. Because the effective dose of DHCB (3 ~tM) did not elicit detectable cell rounding or retraction, the nature and extent of microfilament modification responsible for induction of reexpression was evaluated. The network of microfilament stress fibers detected with rhodamine-labeled phalloidin in primary control chondrocytes was altered by RA to a "cobblestone" pattern of circularly oriented fibers at the cell periphery. Subsequent treatment with DHCB resulted in rapid changes in this pattern before overt reexpression. Stress fibers decreased in number and were reoriented. Parallel arrays of long fibers that traversed the cell were evident, in addition to fiber fragments and focal condensations of staining. Immunofluorescent staining of intermediate filaments revealed a marked decrease in complexity and intensity during RA treatment but no change during reexpression. An extended microtubular architecture was present throughout the study. These results clearly identify microfilaments as the principal affected cytoskeletal element and demonstrate that their modification, rather than complete disruption, is sufficient for reexpression. The specificity of DHCB and the reorientation of these filaments before reexpression of the differentiated phenotype suggests a causative role in the mechanism of reexpression. CHONDROCYTES exhibit high levels of synthesis of cartilage-specific proteoglycan and type II collagen as a major part of their differentiated phenotype. The expression of this phenotype has been shown to be responsive to changes in cell shape, the maintenance (13) or resumption (5) of spherical conformation promoting the expression of the differentiated phenotype. In contrast modulating agents such as fibronectin (17, 26) and retinoic acid (RA) t (4), which appear to enhance both adhesion and spreading of cultured chondrocytes, also enhance the rate at which the differentiated phenotype is lost. These observations, together with the results of more recent studies on the effects of microfilament-modifying drugs on chondrogenesis (18, 27), suggest the involvement of some element of the cytoskeleton in modulation of the chondrocyte phenotype.To study this involvement, the cytoskeletal architecture of rabbit articular chondrocytes has been examined by immunofluorescent techniques during both RA modulation of the differentiated phenotype and its subsequent reexpression as induced by the microfilament-modifying drug dihydrocytochalasin B (DHCB). Transitions in the synthesis of genetically distinct collagen types were used as markers for defined phenotypic change, and are reported separately (4, 6). Briefly, RA modulation of the phenotype was marked by a cessation of type II collagen synthesis and a transient stimulation of type III a...

The radioactive collagens synthesized by the fourth subculture progeny of rabbit articular chondrocytes were extracted and purified after limited pepsin digestion by neutral and acid salt precipitation. In order to identify the different types of collagen present, denatured collagen chains were fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis on 5% gels, electrophoretically eluted, and cleaved with cyanogen bromide, and the resultant peptides were fractionated by a new sodium dodecyl sulfate electrophoresis system (tris(hydroxymethyl)aminomethane-borate buffer, 15% gels). Comparison of these separate peptide profiles with those from alpha1(I) and alpha1(III) collagen chains permitted the unambiguous identification of these chains in the radioactive collagen synthesized by chondrocytes. Although cartilage slices predominantly synthesized alpha1(II) chains, only alpha1(I) chains were made by cells in fourth subculture. A large fraction of these alpha1(I) chains could not be accounted for by the presence of type I collagen. While in a native, triple-helical conformation, some of these extra alpha1(I) chains were completely separated from type I collagen by their solubility at pH 8.0 in 2.6 M NaCl and therefore identified as [alpha1(I)]3, type I trimer. In addition to type I collagen and type I trimer, these chondrocyte progeny also synthesized type III collagen and two new collagen chains, X and Y. Each collagen type was further characterized by carboxymethylcellulose chromatography and its distribution between the medium and the cell layer. These findings support the idea that cultured chondrocytes assume a collagen phenotype similar to that of their undifferentiated mesenchymal cell precursors.