CD34+ synovial fibroblasts exhibit high osteogenic potential in synovial chondromatosis.

Synovial chondromatosis (SC) is a disorder of the synovium characterized by the formation of osteochondral nodules within the synovium. This study aimed to identify the abnormally differentiated progenitor cells and possible pathogenic signaling pathways. Loose bodies and synovium were obtained from patients with SC during knee arthroplasty. Single-cell RNA sequencing was used to identify cell subsets and their gene signatures in SC synovium. Cells derived from osteoarthritis (OA) synovium were used as controls. Multi-differentiation and colony-forming assays were used to identify progenitor cells. The roles of transcription factors and signaling pathways were investigated through computational analysis and experimental verification. We identified an increased proportion of CD34+ sublining fibroblasts in SC synovium. CD34+CD31- cells and CD34-CD31- cells were sorted from SC synovium. Compared with CD34- cells, CD34+ cells had larger alkaline phosphatase (ALP)-stained area and calcified area after osteogenic induction. In addition, CD34+ cells exhibited a stronger tube formation ability than CD34- cells. Our bioinformatic analysis suggested the expression of TWIST1, a negative regulator of osteogenesis, in CD34- sublining fibroblasts and was regulated by the TGF-ß signaling pathway. The experiment showed that CD34+ cells acquired the TWIST1 expression during culture and the combination of TGF-ß1 and harmine, an inhibitor of Twist1, could further stimulate the osteogenesis of CD34+ cells. Overall, CD34+ synovial fibroblasts in SC synovium have multiple differentiation potentials, especially osteogenic differentiation potential, and might be responsible for the pathogenesis of SC.

Fibroblast growth factor 2 involved in the pathogenesis of synovial chondromatosis of temporomandibular joint.

BACKGROUND: Synovial chondromatosis (SC) of temporomandibular joint (TMJ) is a rare proliferative disorder characterized by the formation of cartilaginous or osteocartilaginous nodules in synovium and joint space. Fibroblast growth factor 2 (FGF-2) is frequently applied in chondrogenic differentiation assays. Therefore, we hypothesized that FGF-2 might involved in the pathogenesis of SC. METHODS: SC synovium and loose bodies (LBs) specimens were observed by histological and immunohistochemical methods. Real-time PCR was conducted for comparing genes expressions in SC and normal synovium. SC synoviocytes were stimulated by FGF-2 in the presence or absence of its antagonist long pentraxin-3 (PTX3) for 6 days. Real-time PCR and alkaline phosphatase (ALP) activity were performed to examine the effects exerted by FGF-2 and PTX3. RESULTS: SC synovium, no matter facing the articular cavity or covering LB, was characterized by increased quantity of synoviocytes and blood vessels. FGF-2 was expressed in chondrocytes and fibroblast-like cells of LBs, and the wall of blood vessels. Expressions of chondrogenic genes (Sox9 and Wnt-4), osteogenic genes (Foxc2), FGF-2, and VEGF-A mRNA were significantly higher in SC synovium than that of the control group. The stimulation of FGF-2 on SC synoviocytes increased ALP activity and expressions of chondrogenic genes (Sox9, Col2α1, and Aggrecan), osteogenic genes (Foxc2, osteocalcin, and Col1α1), and VEGF-A, but PTX3 inhibited these effects. CONCLUSION: FGF-2 was responsible for the formation of cartilaginous loose bodies and involved in the pathogenesis of SC.

Bone morphogenetic proteins are involved in the pathobiology of synovial chondromatosis.

Synovial chondromatosis is characterized by the formation of osteocartilaginous nodules (free bodies) under the surface of the synovial membrane in joints. Free bodies and synovium isolated from synovial chondromatosis patients expressed high levels of BMP-2 and BMP-4 mRNAs. BMP-2 stimulated the expression of Sox9, Col2a1, and Aggrecan mRNAs in free-body and synovial cells and that of Runx2, Col1a1, and Osteocalcin mRNAs in the synovial [corrected] cells only. BMP-2 increased the number of alcian blue-positive colonies in the free-body cell culture but not in the synovial cell culture. Noggin suppressed the expression of Sox9, Col2a1, Aggrecan, and Runx2 mRNAs in both the free-body and synovial cells. Further, it inhibited Osteocalcin expression in the synovial cells. These results suggest that BMPs are involved in the pathobiology of cartilaginous and osteogenic metaplasia observed in synovial chondromatosis.

Expression of CD90 decreases with progression of synovial chondromatosis in the temporomandibular joint.

OBJECTIVES: The aim of the present study was to investigate the factors that contribute to the progression of synovial chondromatosis in the temporomandibular joint (TMJ). METHODS: The authors investigated the expression of CD105 and CD90 in specimens from 17 patients with synovial chondromatosis in the TMJ, using immunohistochemical staining, and expression of CD105 and CD90 in cartilaginous nodules was scored semiquantitatively. RESULTS: The expression of CD105 and CD90 was found in almost all the cases. In particular, the expression of CD90 in cartilaginous nodules significantly decreased with the progression of synovial chondromatosis. DISCUSSION: The factors that determine progression of synovial chondromatosis are not fully understood. The results of this study suggest that CD90 may play an important role in the progression of synovial chondromatosis in the TMJ.

Transforming growth factor beta 3 involved in the pathogenesis of synovial chondromatosis of temporomandibular joint.

Synovial chondromatosis (SC) of temporomandibular joint is rare proliferative disorder featured by the formation of cartilaginous nodules in synovium and joint space. Transforming growth factor beta 3 (TGF-ß3) is closely related to chondrogenic differentiation, and might participate in pathogenesis of SC. We discovered that increased quantity of synoviocytes and blood vessels were observed in SC synovium. The vessel wall and sublining fibroblasts were stained positively by the antibodies against TGF-ß3, fibroblast growth factor 2 (FGF-2), and CD34. In loose bodies (LBs), TGF-ß3 was mainly expressed in chondrocytes and FGF-2 was expressed in chondrocytes, fibroblasts, and vessel walls. Expressions of TGF-ß1, TGF-ß3, FGF-2, Sox9, Wnt-4, Foxc2, and VEGF-A mRNA were significantly higher in SC synovium. Stimulation of TGF-ß3 on synoviocytes increased alkaline phosphatase (ALP) activity and expressions of chondrogenic genes (Sox9, Col2α1, Aggrecan, Wnt-4, and Wnt-11), osteogenic genes (Runx2, Foxc2, osteocalcin, and Col1α1), and VEGF-A, but failed to influence FGF-2 expression. However, the addition of FGF-2 increased TGF-ß3 expression. In conclusion, TGF-ß3 existed in synovium and LBs of SC, and was responsible for the pathogenesis of SC.

Growth potential of loose bodies: an immunohistochemical examination of primary and secondary synovial osteochondromatosis.

Histologic and immunohistochemical studies of growth potential were performed on 53 surgically removed loose bodies representing 10 cases of primary synovial osteochondromatosis, 37 bodies representing 12 cases of secondary synovial osteochondromatosis, and five bodies representing five cases of osteochondral fracture. Loose bodies in primary synovial osteochondromatosis were nodular, showing plump chondrocytes and irregular calcification, and all contained proliferative cell nuclear antigen-positive chondrocytes (labeling index: 42.5%; range: 36.0-52.0%). Other markers stained less frequently. Loose bodies in secondary synovial osteochondromatosis showed uniform chondrocytes and annular calcification surrounding core tissue. Eighteen of 37 loose bodies showed proliferative cell nuclear antigen-positive chondrocytes, mostly peripherally. Chondrocyte labeling indices were less than 5% for proliferative cell nuclear antigen and other markers, although some connective tissue cells in the outer layer were stained. Loose bodies from osteochondral fractures were composed of articular cartilage, subchondral bone, and connective tissue; cartilage was negative for markers, whereas connective tissue contained positive cells. One specimen showed cartilaginous metaplasia of connective tissue. These results suggest that loose bodies have the potential for slow growth by proliferation of chondrocytes in primary synovial osteochondromatosis and by metaplasia following proliferation of surrounding connective tissue in secondary synovial osteochondromatosis.

Is synovial osteo-chondromatosis a proliferative disease?

In a case of synovial osteo-chondromatosis of the knee joint, foci of hyaline and calcified cartilage in the synovial membrane exhibited neither MIB-1-positive cells nor mitotic figures. Loose bodies of the synovial fluid showed a different proliferation behavior. In addition to cartilaginous nodules without MIB-1-positive cells, some of the bodies contained nearly 17% cells with MIB-1 activity. Besides the huge number of cells expressing the proliferation-associated antigen, no mitoses, except for a rare, possibly pycnotic mitosis, could be detected. It is assumed that owing to delayed fixation of the chondrocytes surrounded by a broad hyaline cartilaginous matrix, mitoses of these cells can be completed even in the absence of physiological nutrition. The observation described may explain the occurrence of multiple loose bodies in osteo-chondromatosis. According to Milgram's theory, pedunculated nodules of the synovial membrane can become detached, and thereafter appear in the synovial fluid. In this nourishing environment, they can grow to a certain degree; larger ones perhaps become fragmented because of the force of movement, resulting in smaller particles that grow again. This indicates a vicious circle that leads to a myriad of loose bodies.

The expression of fibroblast growth factor receptor-3 in synovial osteochondromatosis of the temporomandibular joint.

Primary synovial osteochondromatosis (PSC) is a disease of unknown aetiology. It was reported recently that expression of fibroblast growth factor receptor-3 (FGFR-3) was observed specifically in PSC. We classified six cases of synovial osteochondromatosis (SC) of the temporomandibular joint (TMJ) into two types of SC, PSC (five cases) and secondary synovial osteochondromatosis (SSC) (one case), by means of clinical findings and haematoxylin and eosin stain. The five PSC cases were classified into three different phases according to Milgram's classification. Immunohistochemical staining of FGFR-3 was carried out for each SC case, along with specimens of internal derangement (ID) of the TMJ, and normal articular disc and synovial membrane. FGFR-3 was found in all three phases of PSC, but not in SSC, ID or normal TMJ. Moreover, in a comparison between cultured synovial cells of PSC (Phase III) and ID, reverse transcription-polymerase chain reaction revealed a stronger positive reaction in PSC. These results indicate that the synovial membrane in Phase III PSC can produce cartilage nodules, as in Phases I and II.

Osteochondromatosis with high concentration of procollagen II C peptide in joint fluid.

Procollagen II C peptide is used as a joint fluid marker of collagen synthesis by chondrocytes in patients with osteoarthritis. Since osteochondromatosis activates ectopic chondrogenesis in the synovial membrane, procollagen II C peptide is expected to be a good marker of the disease. Procollagen II C peptide can be used to evaluate the condition of the disease metabolically by simply aspirating the joint fluid. We have experienced a case of osteochondromatosis (Miligram's stage 2) with a high concentration of procollagen II C peptide. This case suggests that the concentration of procollagen II C peptide is a good marker of chondrogenesis by osteochondromatosis.

Fatty lesions in intra-articular loose bodies: a histopathological study of non-primary synovial chondromatosis cases.

Intra-articular loose bodies (ILBs) are not uncommon conditions in patients with various joint diseases. Their morphological alterations have been investigated in detail, but little attention has been paid to their fatty lesions. In this study, we examined fatty bone marrow, fat cells without bone marrow structures (extramedullary fat cells), and their necrotic changes in 55 ILBs surgically removed from 42 patients, excluding primary synovial chondromatosis cases. The presence of viable re-vascularized vessels with or without enchondral ossification could discriminate 19 re-attached ILBs from 36 true free ILBs. Fatty bone marrow was found in 25 ILBs, and its necrosis was recognized in 11 (44.0%) of them. Extramedullary fat cells, characterized by single or clustered fat cells focally or multifocally distributed in fibrous or cartilaginous stroma, were identified in seven true free ILBs (7of 55, 12.7%), and all of them were focally necrotic. Unique lipomembranous changes were detected in 7 (12.7%) of 55 ILBs; they were found in 4 (36.4%) of 11 ILBs of necrotic bone marrow and were associated with 3 (42.9%) of 7 necrotic extramedullary fatty lesions. These changes were highlighted by periodic-acid Schiff and Masson's trichrome stain more clearly. We concluded that extramedullary fat cells represent lipometaplasia in ILBs with no blood supply. We considered that lipomembranous changes in ILBs can be a useful hallmark for necrotic bone marrow or necrosis of extramedullary lipometaplastic lesions.

Dysregulation of hedgehog signalling predisposes to synovial chondromatosis.

Synovial chondromatosis is a condition affecting joints in which metaplastic cartilage nodules arise from the synovium, causing pain, joint dysfunction, and ultimately joint destruction. Because dysregulation of hedgehog signalling is a feature of several benign cartilaginous tumours, expression of the hedgehog target genes PTC1 and GLI1 was examined in this study in samples from human synovial chondromatosis. Significantly higher expression levels were found in synovial chondromatosis than in the synovium, from which it arises. To determine if hedgehog-mediated transcription predisposes to synovial chondromatosis, the extra-toes mutant mouse, which harbours a heterozygous mutation in the hedgehog transcriptional repressor, Gli3, resulting in decreased expression of Gli3 protein, was studied. The extra-toes mutant mouse has a phenotype consistent with overactive hedgehog signalling, suggesting that Gli3 acts as a transcriptional repressor of limb development. Eighty-five per cent of Gli3 mutant mice developed synovial chondromatosis at 18 months of age, compared with 30% of wild-type littermates (p < 0.05). Three of the ten Gli3 mutant mice treated with triparanol, which blocks hedgehog signalling upstream of the Gli transcription factors, developed synovial chondromatosis, compared with eight of ten control mice. These data demonstrate that hedgehog signalling plays an important role in the development of synovial chondromatosis and suggest that blockade of hedgehog signalling may be a potential treatment for this disorder.

C-erb B-2 staining in primary synovial chondromatosis: a comparison with other cartilaginous tumours.

In this study C-erb B-2 immunostaining has been used to highlight distinct differences between the cartilage found in primary synovial chondromatosis (n = 20), normal articular cartilage (n = 10), benign enchondromas (n = 10), and chondrosarcomas (n = 10). There was no positive staining in either the normal cartilage or the chondromas, but 15 cases of synovial chondromatosis showed at least some staining, although in the majority of cases fewer than 50 per cent of cells stained positive. There was no correlation between cellularity/pleomorphism and the extent or intensity of staining. Five of the chondrosarcomas were positive, with more than 50 per cent of cells showing positive staining in three of these cases. All positive cases in this series showed a diffuse cytoplasmic staining pattern. Despite these results, there was no Ki-67 positive staining in synovial chondromatosis, which tends to suggest that the demonstrated expression of C-erb B-2 is not related to proliferative activity. The significance of this staining remains undetermined.

Synovial chondromatosis: the possible role of FGF 9 and FGF receptor 3 in its pathology.

Primary synovial chondromatosis (PSC) is a rare disorder of the synovium typified by cartilaginous nodule formation within the synovial membrane. Fibroblast growth factor receptor 3 (FGFR3) is a recently described specific marker of mesenchymal precartilaginous stem cells. Expression patterns of FGFR3 and its specific ligand, fibroblast growth factor 9 (FGF 9), were evaluated both in situ and in cell cultures. Histologically, cells at the periphery of the cartilage nodules express FGFR3 and PCNA (proliferating cell nuclear antigen). Elevated levels of FGF 9, its specific ligand, have been found in synovial fluids of patients with synovial chondromatosis. Synoviocytes but not chondrocytes from affected patients express FGF9 in culture. This pattern is absent in normal synovium and cartilage. Downregulation of FGF9 may provide a possible nonoperative therapy for PSC.