[Degenerative DNA alterations in osteoarthritis]. / Degenerative DNA-Veränderungen in der Arthrose.

Osteoarthritis is a complex disease involving not only the cartilage but also the adjacent bone and the synovial membrane. The etiology of osteoarthritis involves multiple factors. Unlike secondary forms of osteoarthritis, which are the result of other diseases or excessive mechanical stress, the origins of primary forms of osteoarthritis lie within the cartilage. In primary osteoarthritis complex interactions of cytokines leading to a derangement of homeostasis have been discovered, which lead to a slow and progressive degeneration of the cartilage and bone, ultimately resulting in destruction of the joint. Damage to the cartilage matrix is caused by an increased activity of matrix metalloproteases induced by catabolic cytokines. One of the initial events triggering these processes might be degenerative DNA alterations causing local defects in multiple genes leading to an impaired function of chondrocytes and a phenotype similar to senescence.

[Pigmented villonodular synovitis. A rare differential diagnosis of synovial joint swelling]. / Pigmentierte villonoduläre Synovialitis. Eine seltene Differenzialdiagnose der synovialen Gelenkschwellung.

BACKGROUND: Pigmented villonodular synovitis (PVNS) describes a rare disease caused by an abnormal proliferation of the synovial membrane in large and small joints. In order to achieve an optimal result of treatment it is necessary to carry out specific diagnostics and a targeted therapy approach. OBJECTIVE: This article gives a review of the epidemiology, etiopathogenesis and diagnostic management of PVNS as well as presenting the current therapy and treatment recommendations. MATERIAL AND METHODS: A systematic search of the literature was performed in the databank of the National Center for Biotechnology Information ( http://www.ncbi.nlm.nih.gov/pubmed ). The search targeted randomized clinical and experimental studies, systematic and non-systematic review articles, expert opinions and case reports related to PVNS, independent of the level of evidence attained by each study. RESULTS: The differential diagnosis of PVNS should be considered in cases of recurrent hemorrhagic joint effusions. The cause of the disease has not yet been exactly clarified. The final diagnosis can ultimately only be confirmed by histological investigations. In order to obtain representative histological tissue samples for the diagnosis, magnetic resonance imaging (MRI) with the appropriate heme sequences should be carried out prior to taking samples. The management of PVNS is often difficult due to the high risk of recurrence depending on the various forms. In view of the high rate of recurrence, therapy should include a complete synovectomy. CONCLUSION: For the surgical approach arthroscopic and open procedures have been described, which are currently controversially discussed with respect to the complication and recurrence rates. Adjuvant interventional therapy forms, such as radiosynoviorthesis are recommended to reduce the recurrence rate.

Neuroprotection in preterm infants.

Preterm infants born before the 30th week of pregnancy are especially at risk of perinatal brain damage which is usually a result of cerebral ischemia or an ascending intrauterine infection. Prevention of preterm birth and early intervention given signs of imminent intrauterine infection can reduce the incidence of perinatal cerebral injury. It has been shown that administering magnesium intravenously to women at imminent risk of a preterm birth leads to a significant reduction in the likelihood of the infant developing cerebral palsy and motor skill dysfunction. It has also been demonstrated that delayed clamping of the umbilical cord after birth reduces the rate of brain hemorrhage among preterm infants by up to 50%. In addition, mesenchymal stem cells seem to have significant neuroprotective potential in animal experiments, as they increase the rate of regeneration of the damaged cerebral area. Clinical tests of these types of therapeutic intervention measures appear to be imminent. In the last trimester of pregnancy, the serum concentrations of estradiol and progesterone increase significantly. Preterm infants are removed abruptly from this estradiol and progesterone rich environment. It has been demonstrated in animal experiments that estradiol and progesterone protect the immature brain from hypoxic-ischemic lesions. However, this neuroprotective strategy has unfortunately not yet been subject to sufficient clinical investigation.

Revised histopathological consensus classification of joint implant related pathology.

This extended classification of joint implant related pathology is a practical histopathologic classification based on defined morphological criteria covering the complete spectrum of pathohistologic changes in periprosthetic tissues. These changes may occur as a consequence of endoprosthetic replacement of large joints and may lead to a reduction in the prosthesis survival rate. We describe the established consensus classification of the periprosthetic membrane, in which aseptic and septic prosthetic loosening can be subdivided into four histological types, as well as histopathological criteria for additional significant pathologies including endoprosthetic-associated arthrofibrosis, particle-induced immunological, inflammatory and toxic mechanisms (adverse reactions), and bone tissue pathologies. These characteristic tissue alterations and their relationships are summarized in the extended classification. Since particle heterogeneity in periprosthetic tissue is high and particle identification is a necessary part of diagnosis, the identification of different types of particles is described in the histopathological particle algorithm. The morphological qualities of prosthetic material particles and the demarcation between abrasion and non-abrasion endogenous particles are also summarized. This feasible classification which is based on low cost standard tissue processing and examination and on well-defined diagnostic criteria is a solid platform for the histological diagnosis of implant associated pathologies providing a stable and reproducible tool for the surgical pathologist. Since this classification is suitable for standardized histopathological diagnostics, it might also provide a useful data set for joint arthroplasty registers, particularly for registers based on so-called routine data.

DNA damage, discoordinated gene expression and cellular senescence in osteoarthritic chondrocytes.

OBJECTIVE: The initiation/progression factors of osteoarthritic (OA) cartilage degeneration and the involved biological mechanisms remain rather enigmatic. One core reason for this might be a cellular senescence-like phenotype of OA chondrocytes, which might show a fundamentally different behavior pattern unexpected from the biological mechanism established in young cells. DESIGN: This study was designed to investigate one core property of senescent cells, the heterogeneity of gene expression, in OA chondrocytes by double-labeling immunolocalization using two genes (vimentin, S-100 protein) as surrogates, which are constitutively expressed by (normal) chondrocytes. The level of genomic DNA damage in OA chondrocytes was compared to normal chondrocytes and in vitro experiments designed to demonstrate that stochastic genomic DNA damage is able to induce heterogeneity of gene expression in chondrocytes. RESULTS: We show a significantly increased heterogeneity of gene expression for vimentin and S-100 protein as well as a significantly increased genomic DNA damage in the OA compared to normal chondrocytes, whereas no evidence of critical telomere shortening was found. In vitro experiments demonstrated that stochastic genomic DNA damage induced by increased oxidative or genotoxic stress is able to induce the heterogeneity in gene expression found in the OA cells in situ. CONCLUSIONS: Our results suggest that OA chondrocytes show a special form of age-related cell degeneration, "progressive/stress-induced senescence", progressing over time due to accumulated DNA damage and subsequent chaotic gene activation pattern. This promotes increased malfunctioning of the cells and finally the loss of their capacity to keep up cell and tissue homeostasis, i.e., prevent OA.

[Osteoarthritis. Etiology, typing, staging and histological grading]. / Arthrose. Ätiologie, Typisierung, Stadieneinteilung und histologische Graduierung.

Degenerative disorders of the musculoskeletal system, in particular osteoarthritis, are among the most common diseases of the elderly and their importance in an aging society is continuously increasing. Correspondingly, many surgical interventions are undertaken and pathological specimens submitted for histopathologic workup. The pathophysiology of osteoarthritis, which ultimately leads to joint destruction, is still poorly understood. The question remains as to whether the cause lies (mainly) within the chondrocytes themselves (e.g. cellular aging/senescence) or whether the synovial membrane or the subchondral bone are equally or even more important factors. The process of joint destruction can be evaluated in terms of pathogenesis (typing), extent (staging) and degree of the most extensive focal damage (grading). Because of the heterogeneity of the disease and substantial individual differences in progression, classification and grading of cartilage degeneration represents a complex task. Any pathology report should be concise and delineate only the essential features. Differentiating between primary osteoarthritis and secondary degenerative changes, e.g., due to previously unknown rheumatoid disease, bone necrosis or an infection of the joint, is of particular clinical interest.

DNA methylation is not responsible for p21WAF1/CIP1 down-regulation in osteoarthritic chondrocytes.

OBJECTIVE: In this study, we were interested in the overall methylation level in aged and degenerated cartilage. Also, we looked at one gene which might be involved in the re-initiation of replicative activity in osteoarthritis (OA) chondrocytes, p21(WAF1/CIP1). p21(WAF1/CIP1) was previously suggested to be down-regulated in OA chondrocytes and is known to be regulated by epigenetic modulation. METHODS: Total methylation levels were analyzed by high pressure liquid chromatography (HPLC), mRNA expression of p21(WAF1/CIP1) and DNMT enzymes by real-time polymerase chain reaction. The methylation status of the p21(WAF1/CIP1)- promotor using bisulfite genomic sequencing was evaluated. RESULTS: General methylation analysis of genomic DNA showed no difference in between normal and aged/OA chondrocytes. Also no difference in methylation of the promotor of the p21(WAF1/CIP1) gene was detectable, which was significantly down-regulated in OA chondrocytes. DNMT1 and DNMT3a were expressed with no significant changes of expression levels found in OA chondrocytes. CONCLUSION: Cell cycle progression inhibitor p21(WAF1/CIP1) is expressed in normal and significantly down-regulated in OA articular chondrocytes, which may mediate the re-initiation of cell proliferation in OA cartilage. However, the suppression of p21(WAF1/CIP1) mRNA expression is not due to hypermethylation of its promotor. No overall changes in genome methylation levels were found in aged or OA cartilage. Interestingly, significant expression of DNA methyltransferases was found in articular chondrocytes, which supports that DNA methylation could still be a relevant mechanism of gene regulation in (osteoarthritic) chondrocytes, though not on an overall genomic level nor specifically for the regulation of the p21(WAF1/CIP1) gene.

[Typing, grading and staging of osteoarthritis: histopathological assessment of joint degeneration]. / Typisierung, Graduierung und Stadieneinteilung der Osteoarthrose: Histopathologische Begutachtung der Gelenkdegeneration.

Osteoarthritis (degenerative arthropathy) is one of the most common diseases particular in the elderly. Osteoarthritis can principally affect all joints, although the knee, hip and phalangeal joints are most commonly involved in a clinically relevant manner. The grading and classification of changes during cartilage degeneration is complex and only partly informative for clinical management. Overall, the process of joint destruction can always be evaluated for the pathogenesis ("typing"), extent ("staging") and the degree of focal damage ("grading"). However, particularly in the final stages of the disease (e. g. in connection with prosthetic surgery) a description and report should be limited to only the most essential features, because no specific clinical relevance exists for further evaluation. Only the identification of secondary types of degenerative changes, due to as yet unknown rheumatoid diseases, gout or extensive osteonecrosis is of particular interest to clinical colleagues (i.e. typing of the joint lesion).

Pathobiology of osteoarthritis: pathomechanisms and potential therapeutic targets.

Osteoarthritis, a degenerative joint disease, is the most disabling condition of the Western world. It affects first and foremost the articular cartilages and leads to a molecular and supramolecular destruction of the extracellular cartilage matrix. In addition, the cells, the chondrocytes, show severe alterations of their phenotype: they get anabolically and catabolically activated, change accordingly their gene expression pattern, lose their differentiated phenotype, and undergo focally cell death and cell degeneration. All these processes represent potential targets for therapeutic intervention and drug development. Apart from the cartilage itself, however, other joint tissues are also involved in the disease: thus, the synovial capsule and membrane as well as the subchondral bone account not only for most of the symptoms of the disease, but are also presumably involved in the progression of the degenerative process. Both, inflammation and stiffening within the joint capsule accelerate joint destruction. Stiffening of the subchondral bone increases the mechanical stress over the overlying cartilage during physiological movement. Altogether, there is a plethora of tissues, disease processes and targets for treating osteoarthritic joint degeneration, which will need to be followed up systematically in the future.

CDRAP is expressed in adult articular cartilage, but its expression is not significantly regulated in osteoarthritic chondrocytes.

OBJECTIVE: In this study we assessed the differential in vivo mRNA expression levels of CDRAP, a potential marker of cartilage degeneration. METHODS: Conventional and real time PCR in a large series of normal (n = 18) and late stage osteoarthritic (n = 24) cartilage specimens were performed. RESULTS: Conventional PCR analysis could demonstrate the presence of CDRAP mRNA in normal and osteoarthritic chondrocytes. Real time quantitative PCR confirmed the presence of CDRAP mRNA expression in normal articular chondrocytes in vivo (and in vitro). No significant up-regulation of CDRAP was observed in osteoarthritic chondrocytes in vivo. CONCLUSION: The presented results confirm expression of CDRAP by normal and osteoarthritic articular chondrocytes, but indicate that increased expression levels by chondrocytes are not the cause of the increased levels of CDRAP in the synovial fluid of patients with osteoarthritis.

[Histopathological examination of joint degeneration: typing, grading and staging of osteoarthritis]. / Histopathologische Begutachtung der Gelenkdegeneration. Typing, Grading und Staging der Osteoarthrose.

Degenerative arthropathy (osteoarthritis) is one of the most common diseases in modern western societies, in particular in the elderly. The classification and grading of changes during cartilage degeneration represent complex endeavors which are only of limited value in daily pathological practice. In general, the process of joint destruction can always be evaluated for the determining pathogenesis ("typing"), extent ("staging") and degree of the most extensive focal damage ("grading"). However, for routine use one might best restrict description and reporting to the most essential features. This is in particular true for specimens obtained from endoprosthetic surgery (hips and knees), because there is currently no specific clinical relevance for further evaluation. Only the identification of secondary types of degenerative changes, such as those due to unknown rheumatoid disease, gout or extensive osteonecrosis, is of particular interest to the clinical colleague (i.e. typing of the joint lesion).

MMP-9/gelatinase B is a gene product of human adult articular chondrocytes and increased in osteoarthritic cartilage.

OBJECTIVE: Collagen fibril degeneration involves initially the cleavage within the triple helix by the collagenases 1 (MMP-1) and 3 (MMP-13), but then mainly involves also the gelatinases A (MMP-2) and B (MMP-9). The objective of this study was to determine the quantitative expression levels as well as the distribution in normal and osteoarthritic cartilage of gelatinase B and in cultured articular chondrocytes with and without stimulation by Il-1Beta. METHODS: Conventional and real-time quantitative PCR technology and immunohistochemistry were used to determine gelatinase B expression on the mRNA and protein level. RESULTS: Conventional PCR analysis could demonstrate the presence of gelatinase B mRNA only in osteoarthritic chondrocytes. Real-time quantitative PCR confirmed the increased expression of gelatinase B mRNA expression in osteoarthritic chondrocytes. No significant up-regulation of gelatinase B was observed by Il-1Beta. Immunostaining for gelatinase B showed the presence of gelatinase B in a subset of normal and in a large portion of osteoarthritic chondrocytes with a more extended distribution in the latter. CONCLUSION: In osteoarthritic cartilage destruction, gelatinase B is involved in collagen destruction though still at a very much lower level than gelatinase A. Only a very small subset of normal adult articular chondrocytes express gelatinase B in vivo suggesting that gelatinase B unlike gelatinase A is hardly or only very focally involved in physiological collagen turnover.

Immunolocalization of matrix proteins in different human cartilage subtypes.

Cartilage exerts many functions in different tissues and parts of the body. Specific requirements presumably also account for a specific biochemical composition. In this study, we investigated the presence and distribution pattern of matrix components, in particular collagen types in the major human cartilages (hyaline, fibrous, and elastic cartilage) by histochemical and immunohistochemical means. Macroscopically normal articular cartilages, menisci, disci (lumbar spine), epiglottal, and tracheal tissues were obtained from donors at autopsy. Aurical and nasal cartilages were part of routine biopsy samples from tumor resection specimens. Conventional histology and immunohistochemical stainings with collagen types I, II, III, IV, V, VI, and X and S-100 protein antibodies were performed on paraformaldehyde-fixed and paraffin-embedded specimens. The extracellular matrix is the functional component of all cartilages as indicated by the low cell densities. In particular major scaffold forming collagen types I (in fibrous cartilage) and II (in hyaline and elastic cartilages) as well as collagen type X (in the calcified layer of articular cartilages, the inner part of tracheal clips, and epiglottis cartilage) showed a specific distribution. In contrast, the "minor" collagen types III, V, and VI were found in all, collagen type IV in none of the cartilage subtypes. In this study, we present a biochemical profile of the major cartilage types of the human body which is important for understanding the physiology and the pathophysiology of cartilages.

Type II collagen, but not aggrecan expression, distinguishes clear cell chondrosarcoma and chondroblastoma.

AIM: Chondroblastoma and clear cell chondrosarcoma are uncommon skeletal neoplasms that have a strong tendency to involve the epiphysis of long bones. They also share some overlapping histological features. Thus, it can be difficult both radiographically and histologically to distinguish these neoplasms. So far there are no immunohistochemical markers available that have been shown to be helpful in differentiating these neoplasms. METHODS: In our study of a series of clear cell chondrosarcomas (n = 15) and chondroblastomas (n = 35), S100, vimentin, aggrecan and collagen type II were detected by immunohistochemistry. RESULTS: We detected immunohistochemical evidence of type II collagen within both the extracellular matrix-rich (chondroid) and matrix-poor areas in all 15 cases of clear cell chondrosarcoma. In contrast, immunohistochemical analysis failed to show staining of collagen type II in any of the 35 chondroblastomas. Other markers, including S100 protein, vimentin and aggrecan proteoglycan were tested in parallel and found to be focally positive in both neoplasms. CONCLUSION: Therefore, our data show that in cases when clear cell chondrosarcoma and chondroblastoma pose a diagnostic challenge, the presence of type II collagen in the extracellular tumour matrix significantly supports the diagnosis of clear cell chondrosarcoma and aids in distinguishing it from chondroblastoma.

Comparison of the chondrosarcoma cell line SW1353 with primary human adult articular chondrocytes with regard to their gene expression profile and reactivity to IL-1beta.

OBJECTIVE: In this study, the human chondrosarcoma cell line SW1353 was investigated by gene expression analysis in order to validate it as an in vitro model for primary human (adult articular) chondrocytes (PHCs). METHODS: PHCs and SW1353 cells were cultured as high density monolayer cultures with and without 1ng/ml interleukin-1beta (IL-1beta). RNA was isolated and assayed using a custom-made oligonucleotide microarray representing 312 chondrocyte-relevant genes. The expression levels of selected genes were confirmed by real-time polymerase chain reaction and the gene expression profiles of the two cell types, both with and without IL-1beta treatment, were compared. RESULTS: Overall, gene expression profiling showed only very limited similarities between SW1353 cells and PHCs at the transcriptional level. Similarities were predominantly seen with respect to catabolic effects after IL-1beta treatment. In both cell systems matrix metalloproteinase-1 (MMP-1), MMP-3 and MMP-13 were strongly induced by IL-1beta, without significant induction of MMP-2. IL-6 was also found to be up-regulated by IL-1beta in both cellular models. On the other hand, intercellular mediators such as leukemia inhibitory factor (LIF) and bone morphogenetic protein-2 (BMP-2) were not induced by IL-1beta in SW1353 cells, but significantly up-regulated in PHCs. Bioinformatical analysis identified nuclear factor kappa-B (NFkappaB) as a common transcriptional regulator of IL-1beta induced genes in both SW1353 cells and PHCs, whereas other transcription factors were only found to be relevant for individual cell systems. CONCLUSION: Our data characterize SW1353 cells as a cell line with only a very limited potential to mimic PHCs, though SW1353 cells can be of value to study the induction of protease expression within cells, a phenomenon also seen in chondrocytes.

Mesenchymal chondrosarcoma: an immunohistochemical study of 10 cases examining prognostic significance of proliferative activity and cellular differentiation.

AIMS: Mesenchymal chondrosarcoma is a rare malignant chondrogenic neoplasm that tends to affect young adults and teenagers. The prognosis is unpredictable, and the identification of prognostic markers that could aid in determining the behaviour of this tumour would be helpful. There are few studies in the literature that have attempted to address this issue. METHODS AND RESULTS: In this study, we explored the prognostic significance of three different parameters: (1) tissue morphology of small cell areas, (2) the expression of tumour differentiation marker genes, and (3) the proliferation rate. Our results did not show a correlation of prognosis with the histological features of the neoplastic small cell areas or the expression of tumour differentiation genes. However, the proliferative activity of the tumour cells appeared to have some prognostic significance as related to patient survival. CONCLUSION: Mesenchymal chondrosarcoma is a rare tumour with a wide clinical range of behaviour. Therefore, it is difficult to obtain reliable prognostic parameters. Nevertheless, our study suggests that proliferative activity may be a useful prognostic parameter for mesenchymal chondrosarcomas.

Osteophyte development--molecular characterization of differentiation stages.

OBJECTIVE: Osteophytes are non-neoplastic osteo-cartilaginous protrusions growing at the margins of osteoarthritic joints. They can not only be considered as in situ repair tissue, but also represent an excellent in vivo model for induced cartilage repair processes. Our focus was to identify different steps of osteophyte development via analysis of expression patterns of marker genes of chondrocytic differentiation. DESIGN: We performed an extensive analysis of the presence and expression of matrix components using histochemical, immunohistochemical and in situ hybridization technology. RESULTS: Four different stages of osteophyte formation could be identified based on histomorphological and cell biological parameters: starting from mesenchymal condensates, chondrogenic differentiation is indicated by the onset of Col2A and aggrecan expression (stage I). Stage II shows fibrocartilage with an admixture of cartilaginous and fibrous matrix components such as Col2 and aggrecan on the one hand and Col1 on the other hand. The proliferating osteophyte (stage III) shows a zonal organization similar to the fetal growth plate cartilage with extensive chondrocyte hypertrophy in the zones next to ongoing endochondral bone formation. 'Mature' osteophytes (stage IV) resembled largely articular hyaline cartilage with a predominance of Col2 and aggrecan and Col6 found mainly pericellularily. CONCLUSIONS: The development of osteophytes is a good in vivo model to pursue chondrocyte differentiation from pluripotent mesenchymal cells to mature or hypertrophic chondrocytes in situ in the adult. The analysis of marker molecules of mesenchymal differentiation allows to identify different stages of repair tissue development and the transformation from fibrous tissue to neo-cartilage. Tissue architecture and matrix composition in mature osteophytes suggests that metaplastic neo-cartilagenous tissue might be one potential source of cartilage repair tissue in the adult joint.

Ultrastructural localization of type VI collagen in normal adult and osteoarthritic human articular cartilage.

OBJECTIVE: Type VI collagen is a major component of the pericellular matrix compartment in articular cartilage and shows severe alterations in osteoarthritic cartilage degeneration. In this study, we analysed the exact localization of type VI collagen in its relationship to the chondrocyte and the (inter)territorial cartilage matrix. Additionally, we were interested in its ultrastructural appearance in normal and osteoarthritic cartilage. DESIGN: Distribution and molecular appearance was investigated by conventional immunostaining, by multilabeling confocal scanning microscopy, conventional transmission, and immunoelectron microscopy. RESULTS: Our analysis confirmed the pericellular concentration of type VI collagen in normal and degenerated cartilage. Type VI collagen formed an interface in between the cell surface and the type II collagen network. The type VI collagen and the type II collagen networks appeared to have a slight physical overlap in both normal and diseased cartilage. Additionally, some epitope staining was observed in the cell-associated interterritorial cartilage matrix, which did not appear to have an immediate relation to the type II collagen fibrillar network as evaluated by immunoelectron microscopy. In osteoarthritic cartilage, significant differences were found compared with normal articular cartilage: the overall dimension of the lacunar volume increased, and a significantly increased type VI collagen epitope staining was observed in the interterritorial cartilage matrix. Also, the banded isoform of type VI collagen was found around many chondrocytes. CONCLUSIONS: Our study confirms the close association of type VI collagen with both, the chondrocyte cell surface and the territorial cartilage matrix. They show severe alterations in type VI collagen distribution and appearance in osteoarthritic cartilage. Our immunohistochemical and ultrastructural data are compatible with two ways of degradation of type VI collagen in osteoarthritic cartilage: (1) the pathologically increased physiological molecular degradation leading to the complete loss of type VI collagen filaments from the pericellular chondrocyte matrix and (2) the transformation of the fine filaments to the band-like form of type VI collagen. Both might implicate a significant loss of function of the pericellular microenvironment in osteoarthritic cartilage.

The C5 domain of Col6A3 is cleaved off from the Col6 fibrils immediately after secretion.

In articular cartilage, type VI collagen is concentrated in the pericellular matrix compartment. During protein synthesis and processing at least the alpha3(VI) chain undergoes significant posttranslational modification and cleavage. In this study, we investigated the processing of type VI collagen in articular cartilage. Immunostaining with a specific polyclonal antiserum against the C5 domain of alpha3(VI) showed strong cellular staining seen in nearly all chondrocytes of articular cartilage. Confocal laser-scanning microscopy and immunoelectron microscopy allowed localization of this staining mainly to the cytoplasm and the immediate pericellular matrix. Double-labeling experiments showed a narrow overlap of the C5 domain and the pericellular mature type VI collagen. Our results suggest that at least in human adult articular cartilage the C5 domain of alpha3(VI) collagen is synthesized and initially incorporated into the newly formed type VI collagen fibrils, but immediately after secretion is cut off and is not present in the mature pericellular type VI matrix of articular cartilage.