Cartilage Signal Research Articles

Stage-specific Control of Connective Tissue Growth Factor (CTGF/CCN2) Expression in Chondrocytes by Sox9 and β-Catenin

CCN2/connective tissue growth factor is highly expressed in hypertrophic chondrocytes and is required for chondrogenesis. However, the transcriptional mechanisms controlling its expression in cartilage are largely unknown. The activity of the Ccn2 promoter was, therefore, investigated in osteochondro-progenitor cells and hypertrophic chondrocytes to ascertain these mechanisms. Sox9 and T-cell factor (TCF) x lymphoid enhancer factor (LEF) factors contain HMG domains and bind to related consensus sites. TCF x LEF factors are normally repressive but when bound to DNA in a complex with beta-catenin become activators of gene expression. In silico analysis of the Ccn2 proximal promoter identified multiple consensus TCF x LEF elements, one of which was also a consensus binding site for Sox9. Using luciferase reporter constructs, the TCF x LEF x Sox9 site was found to be involved in stage-specific expression of Ccn2. Luciferase, electrophoretic mobility shift assay (EMSA), and ChIP analysis revealed that Sox9 represses Ccn2 expression by binding to the consensus TCF x LEF x Sox9 site. On the other hand, the same assays showed that in hypertrophic chondrocytes, TCF x LEF x beta-catenin complexes occupy the consensus TCF x LEF x Sox9 site and activate Ccn2 expression. Furthermore, transgenic mice in which lacZ expression is driven under the control of the proximal Ccn2 promoter revealed that the proximal Ccn2 promoter responded to Wnt signaling in cartilage. Hence, we propose that differential occupancy of the TCF x LEF x Sox9 site by Sox9 versus beta-catenin restricts high levels of Ccn2 expression to hypertrophic chondrocytes.

The cartilage black line sign: an unexpected MRI appearance of deep cartilage fissuring in three patients

Many patterns of cartilage signal anomalies have been described in the knee since the advent of magnetic resonance imaging (MRI). With the now widespread use of preoperative MRI, some of these anomalies have proven to represent true pathology, while others have been shown to be normal variants or artifacts at arthroscopy. We describe three patients with an MR cartilage abnormality, not previously illustrated in the literature, consisting of a thin dark signal line on T2-weighted imaging, oriented perpendicular to the plane of imaging. This aberration proved to represent a deep cartilage cleft at arthroscopy (two patients) and at CT arthrography (one patient). Such full thickness fissures are generally considered to have the opposite appearance, that of fluid signal intensity on T2-weighted images.

TAK1 regulates cartilage and joint development via the MAPK and BMP signaling pathways

The importance of canonical transforming growth factor β (TGF-β) and bone morphogenetic protein (BMP) signaling during cartilage and joint development is well established, but the necessity for noncanonical (SMAD-independent) signaling during these processes is largely unknown. TGF-β activated kinase 1 (TAK1) is a MAP3K activated by TGF-β, BMP, and other mitogen-activated protein kinase (MAPK) signaling components. We set out to define the potential role for noncanonical, TAK1-mediated signaling in cartilage and joint development via deletion of Tak1 in chondrocytes (Col2Cre;Tak1f/f) and the developing limb mesenchyme (Prx1Cre;Tak1f/f). Deletion of Tak1 in chondrocytes resulted in novel embryonic developmental cartilage defects including decreased chondrocyte proliferation, reduced proliferating chondrocyte survival, delayed onset of hypertrophy, reduced Mmp13 expression, and a failure to maintain interzone cells of the elbow joint, which were not observed previously in another Col2Cre;Tak1f/f model. Deletion of Tak1 in limb mesenchyme resulted in widespread joint fusions likely owing to the differentiation of interzone cells to the chondrocyte lineage. The Prx1Cre;Tak1f/f model also allowed us to identify novel columnar chondrocyte organization and terminal maturation defects owing to the interplay between chondrocytes and the surrounding mesenchyme. Furthermore, both our in vivo models and in vitro cell culture studies demonstrate that loss of Tak1 results in impaired activation of the downstream MAPK target p38, as well as diminished activation of the BMP/SMAD signaling pathway. Taken together, these data demonstrate that TAK1 is a critical regulator of both MAPK and BMP signaling and is necessary for proper cartilage and joint development. © 2010 American Society for Bone and Mineral Research.

NF449 Is a Novel Inhibitor of Fibroblast Growth Factor Receptor 3 (FGFR3) Signaling Active in Chondrocytes and Multiple Myeloma Cells

The FGFR3 receptor tyrosine kinase represents an attractive target for therapy due to its role in several human disorders, including skeletal dysplasias, multiple myeloma, and cervical and bladder carcinomas. By using molecular library screening, we identified a compound named NF449 with inhibitory activity toward FGFR3 signaling. In cultured chondrocytes and murine limb organ culture, NF449 rescued FGFR3-mediated extracellular matrix loss and growth inhibition, which represent two major cellular phenotypes of aberrant FGFR3 signaling in cartilage. Similarly, NF449 antagonized FGFR3 action in the multiple myeloma cell lines OPM2 and KMS11, as evidenced by NF449-mediated reversal of ERK MAPK activation and transcript accumulation of CCL3 and CCL4 chemokines, both of which are induced by FGFR3 activation. In cell-free kinase assays, NF449 inhibited the kinase activity of both wild type and a disease-associated FGFR3 mutant (K650E) in a fashion that appeared non-competitive with ATP. Our data identify NF449 as a novel antagonist of FGFR3 signaling, useful for FGFR3 inhibition alone or in combination with inhibitors that target the ATP binding site.

Small Field-Of-View Surface Coil MR Imaging of Talar Osteochondral Lesions

Osteochondral lesion (OCL) treatment is based on patient symptoms, lesion size, and lesion stability. MRI of talar OCL identifies the presence and the characteristics of the lesion and attempts to establish lesion stability. We report our experience that the depiction of OCL can be improved by using a small field-of-view (FOV) surface coil. We studied 24 patients (25 lesions) with OCLs of the talar dome. Standard FOV MRI followed by small FOV MRI of the ankle was performed at 1.5-T. Standard FOV MRI was taken using a quadrature knee coil or a 21 cm x 53 cm circularly flexible coil. A 4-cm circular polarized receiver surface coil was used for small FOV imaging. Twelve aspects characteristics of OCLs were assessed, including lesion matrix, margin characteristics, lesion cortical surface, cartilage surface, cartilage depth, cartilage signal, cartilage integrity, and osteochondral gap. Small FOV MRI provided more detailed morphological information of talar OCL. The following differences were noted. Small FOV coil imaging reclassified cortical surface from flush to depressed in seven cases and from unclear in two cases to flush in one case and proud in the other. Small FOV coil imaging reclassified cartilage integrity from unclear to intact in 16 cases and from unclear to fracture in three cases. For assessment of osteochondral gap, small FOV coil MR imaging reclassified from absent to present in two cases and from unclear to absent in one case. For osteochondral fragment, small FOV coil MR imaging reclassified assessment from absent to present in three cases and from unclear to absent in three cases. Small FOV coil improved visualization of the talar OCL.

Extracellular sulfatases support cartilage homeostasis by regulating BMP and FGF signaling pathways

The balance between anabolic and catabolic signaling pathways is critical in maintaining cartilage homeostasis and its disturbance contributes to joint diseases such as osteoarthritis (OA). A unique mechanism that modulates the activity of cell signaling pathways is controlled by extracellular heparan endosulfatases Sulf-1 and Sulf-2 (Sulfs) that are overexpressed in OA cartilage. This study addressed the role of Sulfs in cartilage homeostasis and in regulating bone morphogenetic protein (BMP)/Smad and fibroblast growth factor (FGF)/Erk signaling in articular cartilage. Spontaneous cartilage degeneration and surgically induced OA were significantly more severe in Sulf-1(-/-) and Sulf-2(-/-) mice compared with wild-type mice. MMP-13, ADAMTS-5, and the BMP antagonist noggin were elevated whereas col2a1 and aggrecan were reduced in cartilage and chondrocytes from Sulf(-/-) mice. Articular cartilage and cultured chondrocytes from Sulf(-/-) mice showed reduced Smad1 protein expression and Smad1/5 phosphorylation, whereas Erk1/2 phosphorylation was increased. In human chondrocytes, Sulfs siRNA reduced Smad phosphorylation but enhanced FGF-2-induced Erk1/2 signaling. These findings suggest that Sulfs simultaneously enhance BMP but inhibit FGF signaling in chondrocytes and maintain cartilage homeostasis. Approaches to correct abnormal Sulf expression have the potential to protect against cartilage degradation and promote cartilage repair in OA.

Quantitative Proteomics Analysis of Chondrogenic Differentiation of C3H10T1/2 Mesenchymal Stem Cells by iTRAQ Labeling Coupled with On-line Two-dimensional LC/MS/MS

The chondrogenic potential of multipotent mesenchymal stem cells (MSCs) makes them a promising source for cell-based therapy of cartilage defects; however, the exact intracellular molecular mechanisms of chondrogenesis as well as self-renewal of MSCs remain largely unknown. To gain more insight into the underlying molecular mechanisms, we applied isobaric tag for relative and absolute quantitation (iTRAQ) labeling coupled with on-line two-dimensional LC/MS/MS technology to identify proteins differentially expressed in an in vitro model for chondrogenesis: chondrogenic differentiation of C3H10T1/2 cells, a murine embryonic mesenchymal cell line, was induced by micromass culture and 100 ng/ml bone morphogenetic protein 2 treatment for 6 days. A total of 1756 proteins were identified with an average false discovery rate <0.21%. Linear regression analysis of the quantitative data gave strong correlation coefficients: 0.948 and 0.923 for two replicate two-dimensional LC/MS/MS analyses and 0.881, 0.869, and 0.927 for three independent iTRAQ experiments, respectively (p < 0.0001). Among 1753 quantified proteins, 100 were significantly altered (95% confidence interval), and six of them were further validated by Western blotting. Functional categorization revealed that the 17 up-regulated proteins mainly comprised hallmarks of mature chondrocytes and enzymes participating in cartilage extracellular matrix synthesis, whereas the 83 down-regulated were predominantly involved in energy metabolism, chromatin organization, transcription, mRNA processing, signaling transduction, and cytoskeleton; except for a number of well documented proteins, the majority of these altered proteins were novel for chondrogenesis. Finally, the biological roles of BTF3l4 and fibulin-5, two novel chondrogenesis-related proteins identified in the present study, were verified in the context of chondrogenic differentiation. These data will provide valuable clues for our better understanding of the underlying mechanisms that modulate these complex biological processes and assist in the application of MSCs in cell-based therapy for cartilage regeneration.

FAT-SUPPRESSED SPOILED GRADIENT-RECALLED IMAGING OF EQUINE METACARPOPHALANGEAL ARTICULAR CARTILAGE

The purpose was to evaluate the capacity of 1.5 T magnetic resonance (MR) imaging to assess articular cartilage in racehorses with naturally occurring metacarpophalangeal joint osteoarthritis. A sagittal, three-dimensional spoiled gradient-recalled echo (SPGR) with fat saturation (FS) sequence was acquired ex vivo on 20 joints. Following joint dissection, specific areas on the third metacarpal condyle were designated for subsequent sampling for histologic cartilage thickness measurement and modified Mankin scoring. Cartilage thickness was measured and cartilage signal intensity was also graded (0-3) on MR images at these selected metacarpal sites. Cartilage structure was graded (0-3) macroscopically and on MR images by two examiners in defined subregions of the proximal phalanx, third metacarpal, and proximal sesamoid bones. There was good precision (mean error 0.11 mm) and moderate correlation (r = 0.44; P < 0.0001) of cartilage thickness measurements between MR images (0.90 +/- 0.17mm) and histology (0.79 +/- 0.16 mm). There was moderate correlation between modified Mankin histologic score and signal intensity of cartilage (r = 0.36; P < 0.01) or MR cartilage structure assessment (r = 0.49, P > 0.001) on SPGR-FS. The sensitivity to detect full-thickness cartilage erosion on MR was only moderate (0.56), and these lesions were often underestimated, particularly when linear in nature. However, the specificity to detect such lesions on MR was high (0.92). While few limitations were identified, the use of a clinically applicable SPGR-FS sequence allows a reasonably accurate method to assess structural changes affecting the articular cartilage of the equine metacarpophalangeal joint.

IGFBP-5 Metabolism Is Disrupted in the Rat Medial Meniscal Tear Model of Osteoarthritis.

Insulin-like growth factor binding protein 5 (IGFBP-5) has been proposed to promote cartilage anabolism through insulin-like growth factor (IGF-1) signaling. A proteolytic activity towards IGFBP-5 has been detected in synovial fluids from human osteoarthritic (OA) joints. The purpose of this study was to determine if protease activity towards IGFBP-5 is present in the rat medial meniscal tear (MMT) model of OA and whether inhibition of this activity would alter disease progression. Sprague-Dawley rats were subject to MMT surgery. Synovial fluid lavages were assessed for the presence of IGFBP-5 proteolytic activity. Treatment animals received intra-articular injections of vehicle or protease inhibitor peptide PB-145. Cartilage lesions were monitored by India ink staining followed by macroscopic measurement of lesion width and depth. The MMT surgery induced a proteolytic activity towards IGFPB-5 that was detectable in joint fluid. This activity was stimulated by calcium and was sensitive to serine protease inhibitors as well as peptide PB-145. Significantly, intra-articular administration of PB-145 after surgery protected cartilage from lesion development. PB-145 treatment also resulted in an increase in cartilage turnover as evidenced by increases in serum levels of procollagen type II C-propeptide (CPII) as well as synovial fluid lavage levels of collagen type II neoepitope (TIINE). IGFBP-5 metabolism is disrupted in the rat MMT model of OA, potentially contributing to cartilage degradation. Inhibition of IGFBP-5 proteolysis protected cartilage from lesion development and enhanced cartilage turnover. These data are consistent with IGFBP-5 playing a positive role in anabolic IGF signaling in cartilage.

Mechanical signals control SOX-9, VEGF, and c-Mycexpression and cell proliferation during inflammation via integrin-linked kinase, B-Raf, and ERK1/2-dependent signaling in articular chondrocytes

IntroductionThe importance of mechanical signals in normal and inflamed cartilage is well established. Chondrocytes respond to changes in the levels of proinflammatory cytokines and mechanical signals during inflammation. Cytokines like interleukin (IL)-1β suppress homeostatic mechanisms and inhibit cartilage repair and cell proliferation. However, matrix synthesis and chondrocyte (AC) proliferation are upregulated by the physiological levels of mechanical forces. In this study, we investigated intracellular mechanisms underlying reparative actions of mechanical signals during inflammation.MethodsACs isolated from articular cartilage were exposed to low/physiologic levels of dynamic strain in the presence of IL-1β. The cell extracts were probed for differential activation/inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling cascade. The regulation of gene transcription was examined by real-time polymerase chain reaction.ResultsMechanoactivation, but not IL-1β treatment, of ACs initiated integrin-linked kinase activation. Mechanical signals induced activation and subsequent C-Raf-mediated activation of MAP kinases (MEK1/2). However, IL-1β activated B-Raf kinase activity. Dynamic strain did not induce B-Raf activation but instead inhibited IL-1β-induced B-Raf activation. Both mechanical signals and IL-1β induced ERK1/2 phosphorylation but discrete gene expression. ERK1/2 activation by mechanical forces induced SRY-related protein-9 (SOX-9), vascular endothelial cell growth factor (VEGF), and c-Myc mRNA expression and AC proliferation. However, IL-1β did not induce SOX-9, VEGF, and c-Myc gene expression and inhibited AC cell proliferation. More importantly, SOX-9, VEGF, and Myc gene transcription and AC proliferation induced by mechanical signals were sustained in the presence of IL-1β.ConclusionsThe findings suggest that mechanical signals may sustain their effects in proinflammatory environments by regulating key molecules in the MAP kinase signaling cascade. Furthermore, the findings point to the potential of mechanosignaling in cartilage repair during inflammation.

Gpi-anchored proteins regulate cell signaling and cell intercalation in growth plate cartilage

Gpi-anchored proteins regulate cell signaling and cell intercalation in growth plate cartilage

Posteromedial Elbow Impingement: MRI Findings in Overhead Throwing Athletes and Results of Arthroscopic Treatment (SS-26)

Posteromedial elbow pain as a result of impingement has a reproducible pattern of pathology on MRI in throwing athletes. Arthroscopic debridement, olecranon spur excision, and loose body excision if present allows return to throwing sports, and excellent subjective and objective results. Posteromedial elbow pain in throwing athletes may be the result of valgus extension overlead and UCL insufficiency or due to posteromedial impingement due synovitis or olecranon spurring. An MRI with or without intra-articular contrast is the gold standard imaging modality. To date, no pattern of MRI findings has been reported in the setting of clinical posteromedial elbow impingement. The purpose of this study was to define the MRI pattern and assess the results of arthroscopic treatment. Over an 8 year period, a total of 10 throwing athletes were identified retrospectively, who were diagnosed with posteromedial elbow impingement who had an MRI, and who failed non-operative treatment and ultimately required arthroscopy. Any patients with UCL insufficiency were excluded from the study. Those with a clinical diagnosis of posteromedial elbow impingement underwent an MRI examination using either a standard noncontrast protocol, or a direct MR arthrographic protocol. All MRIs were acquired at 1.5 tesla using a dedicated extremity receiver coil with the patient's affected arm extended while prone on the scanner in a ‘superman' position. All studies included edema sensitive T2 weighted fast spin echo fat suppressed sequences in 3 planes, while the direct MR arthrographic studies included high resolution T1 weighted spin echo fat suppressed images in at least two planes. MRIs were reviewed by a fellowship trained musculoskeletal radiologist blinded to clinical history other than age and gender. Arthroscopic treatment included debridement of posteromedial synovitis, loose body (if present) excision, and excision of any olecranon spur. All patients underwent a physical examination and completion of the Andrews-Carson scale with a minimum follow-up of 12 months (range: 12 - 73). All patients were male with an average age of 21.2 (range: 15 - 34). The dominant arm (right = 9) was affected in all patients. The average length of symptoms prior to surgery was 9 months (range: 5 - 24). At MRI, a reproducible pattern of pathology was noted. All patients had pathology recorded at the articular surfaces of the posterior trochlea and the anterior, medial olecranon, ranging from abnormal edema like signal in the hyaline cartilage (grade 1 chondrosis) to partial thickness cartilage defects and subjacent, subchondral bone marrow edema (grade 2 or 3 chondrosis). Additional MRI findings included joint effusion, synovitis within the posteromedial recess, marginal osteophytes at the trochlea and olecranon, soft tissue edema about the distal, medial triceps insertion, ulnar collateral ligament hypertrophy, and flexor/pronator tendon origin strain. Findings at surgery included posteromedial synovitis and olecranon spurring in all patients, and loose bodies in 3 patients. Based on the Andrews-Carson scale, the subjective and objective outcome was considered excellent in 8 patients and good in 2. Posteromedial elbow pain as a result of impingement has a reproducible pattern of pathology on MRI in throwing athletes. Arthroscopic debridement, olecranon spur excision, and loose body excision if present allows return to throwing sports, and excellent subjective and objective results.

Gadolinium-enhanced magnetic resonance imaging of the knee: an experimental approach

The purpose of this study was to examine gadolinium-enhanced magnetic resonance imaging (MRI) for monitoring cartilage degeneration. This is a proof-of-concept study in an animal model. Adult New Zealand rabbits were randomly stratified into five groups. Papain was injected intra-articularly in the right knee in four groups to establish the stages of cartilage degeneration. The left knee and group 5 served as controls. Bilateral MRI was performed 24 h after the initial injection of papain, and 1 week, 1 month, and 3 months following three papain injections. Injection of the contrast agent was followed by bilateral MRI examination immediately upon injection, and at 2 and 4 h post-injection. Signal intensities of articular cartilage and peripheral soft tissues were obtained before animals were sacrificed. Post-mortem bilateral cartilage specimens were studied histologically. Histopathology results verified the staged degeneration of papain-treated articular cartilage. Differences in cartilage signal intensity were significant for the staged model using a special three-dimensional MRI method (P < 0.05) but not using ordinary MRI. No differences were observed within or between the control groups (P > 0.05). Contrast-enhanced MRI examination may be a viable tool for early diagnosis of osteoarticular disease. Prospective studies are warranted to evaluate the potential for clinical application.

Optical imaging of mouse articular cartilage using the glycosaminoglycans binding property of fluorescent-labeled octaarginine

The aim of the current study was to examine the cartilage-specific binding property of polyarginine peptides (R4, 8, 12, and 16) and specifically to test octaarginine peptides for the optical imaging of articular cartilage in experimentally induced arthritis in mice. Four rhodamine-labeled polyarginine peptides each with a different-length arginine chain (R4, 8, 12, or 16) were injected into the knee joints of C57BL/6J mice (n=20). The joints were excised 1h later and the fluorescent signal intensity in cartilage cryosections was compared for the four peptides. To examine the substrate of R8 in cartilage, femoral condyles obtained from another set of mice were treated with chondroitinase ABC (Ch'ase ABC), keratanase or heparitinase then immersed in R8-rhodamine. Fluorescent signals were examined by fluorescent microscopy. Next, R8-rhodamine was injected into the right knee joints of three control and three collagen antibody-induced arthritis (CAIA) mice, and fluorescent intensity in normal and degenerative cartilage was semi-quantitatively analysed on the histological sections using image software. Finally, femoral condyles from normal mice (n=2) and CAIA mice (n=2) were immersed in R8-rhodamine and calcein, then imaged using optical projection tomography (OPT). Fluorescent signals were specifically detected in the cartilage pericellular matrix from the surface to the tide mark but were completely absent in the calcified layer or bone marrow. The number of arginine residues significantly influenced peptide accumulation in articular cartilage, with R8 accumulating the most. The fluorescent signal in the femoral condylar cartilage diminished when it was treated with Ch'ase ABC. R8 accumulation was significantly decreased in the degenerative cartilage of CAIA mice, and this was demonstrated both histologically and in three-dimensional (3D)-reconstruction image by OPT. R8 may be a useful new experimental probe for optical imaging of normal and arthritic articular cartilage.

Global analysis of nuclear receptor expression and dysregulation in human osteoarthritic articular cartilage: Reduced LXR signaling contributes to catabolic metabolism typical of osteoarthritis

Compare the expression and regulation of nuclear receptors (NRs) in osteoarthritic and normal human articular cartilage. The transcriptional levels of 48 NRs and additional related proteins were measured in mRNA from human articular cartilage from subjects with osteoarthritis (OA) and compared to samples from subjects without OA, using microarrays, individual quantitative reverse transcriptase polymerase chain reaction assays, and a custom human NR TaqMan Low Density Array (TLDA). The functional effect of liver X receptor (LXR) activity in cartilage was studied by measuring proteoglycan (PG) synthesis and degradation in articular cartilage explant cultures following treatment with the synthetic LXR agonist T0901317. Thirty-one of 48 NRs analyzed by TLDA were found to be measurably expressed in human articular cartilage; 23 of these 31 NRs showed significantly altered expression in OA vs unaffected cartilage. Among these, LXRalpha and LXRbeta, and their heterodimeric partners retinoid X receptor (RXR)alpha and RXRbeta were all expressed at significantly lower levels in OA cartilage, as were LXR target genes ABCG1 and apolipoproteins D and E. Addition of LXR agonist to human OA articular chondrocytes and to cartilage explant cultures resulted in activation of LXR-mediated transcription and significant reduction of both basal and interleukin (IL)-1-mediated PG degradation. Articular cartilage expresses a substantial number of NRs, and a large proportion of the expressed NRs are dysregulated in OA. In particular, LXR signaling in OA articular cartilage is impaired, and stimulation of LXR transcriptional activity can counteract the catabolic effects of IL-1. We conclude that LXR agonism may be a possible therapeutic option for OA.

Analysis of STAT1 Activation by Six FGFR3 Mutants Associated with Skeletal Dysplasia Undermines Dominant Role of STAT1 in FGFR3 Signaling in Cartilage

Activating mutations in FGFR3 tyrosine kinase cause several forms of human skeletal dysplasia. Although the mechanisms of FGFR3 action in cartilage are not completely understood, it is believed that the STAT1 transcription factor plays a central role in pathogenic FGFR3 signaling. Here, we analyzed STAT1 activation by the N540K, G380R, R248C, Y373C, K650M and K650E-FGFR3 mutants associated with skeletal dysplasias. In a cell-free kinase assay, only K650M and K650E-FGFR3 caused activatory STAT1(Y701) phosphorylation. Similarly, in RCS chondrocytes, HeLa, and 293T cellular environments, only K650M and K650E-FGFR3 caused strong STAT1 activation. Other FGFR3 mutants caused weak (HeLa) or no activation (293T and RCS). This contrasted with ERK MAP kinase activation, which was strongly induced by all six mutants and correlated with the inhibition of proliferation in RCS chondrocytes. Thus the ability to activate STAT1 appears restricted to the K650M and K650E-FGFR3 mutants, which however account for only a small minority of the FGFR3-related skeletal dysplasia cases. Other pathways such as ERK should therefore be considered as central to pathological FGFR3 signaling in cartilage.

Neoplastic Invasion of Laryngeal Cartilage: Reassessment of Criteria for Diagnosis at MR Imaging

To evaluate whether proposed diagnostic criteria applied to magnetic resonance (MR) images of patients with laryngeal and hypopharyngeal carcinoma may be used to distinguish neoplastic from inflammatory involvement of the laryngeal cartilages. The radiologic and histopathologic data in 121 consecutive patients with primary squamous cell carcinoma of the larynx (n = 63) or hypopharynx (n = 58) who underwent MR imaging before laryngectomy formed the basis of this retrospective study. Patient consent for retrospective chart review was waived by the institutional review board. All laryngectomy specimens were processed with a dedicated histopathologic whole-organ slice technique. MR images were evaluated by two readers according to established ("old") and proposed ("new") diagnostic criteria on the basis of the signal intensity behavior of cartilage on T2-weighted images and contrast material-enhanced T1-weighted images compared with that of the adjacent tumor. Specifically, with the new criteria, T2-weighted or postcontrast T1-weighted cartilage signal intensity greater than that of the adjacent tumor was considered to indicate inflammation, and signal intensity similar to that of the adjacent tumor was considered to indicate neoplastic invasion. The results of the MR image interpretation were compared with the histologic reference standard. The area under the receiver operating characteristic curve for the new criteria (0.94) was nominally but significantly larger than that for the old criteria (0.92) (P = .01). Overall specificity was significantly improved (82% for new vs 74% for old criteria, P < .001) and was greatest for the thyroid cartilage (75% for new vs 54% for old criteria, P < .001) with the new criteria. The sensitivities of the established and the proposed criteria were identical. The proposed MR imaging criteria enable improved differentiation of neoplastic cartilage invasion from peritumoral inflammation.

Fibroblast growth factor inhibits interferon γ-STAT1 and interleukin 6-STAT3 signaling in chondrocytes

Activation of fibroblast growth factor receptor 3 (FGFR3) leads to attenuation of cartilage growth. The members of the STAT family of transcription factors are believed to participate in FGFR3 signaling in cartilage, however the molecular mechanism of this action is poorly understood. Here, we demonstrate that a chronic FGF stimulus leads to accumulation of STAT1, 3, 5 and 6, evident in both in vitro chondrocyte model and murine limb explant cultures. Despite the accumulation, both endogenous and cytokine-induced activation of STAT1 and STAT3 is impaired by FGF, as demonstrated by imaging of active STAT nuclear translocation and analyses of STAT activatory phosphorylation and transcriptional activation. Further, we demonstrate that FGF induces expression of CIS, SOCS1 and SOCS3 inhibitors of gp130, a common receptor for the IL6-family of cytokines. Since cytokine-gp130 signaling represents an important positive regulator of cartilage, its inhibition may contribute to the growth-inhibitory effect of FGFR3 in cartilage.

Wnt signaling in cartilage development and degeneration

The Wnt signaling network, which is composed of Wnt ligands, receptors, antagonists, and intracellular signaling molecules, has emerged as a powerful regulator of cell fate, proliferation, and function in multicellular organisms. Over the past two decades, the critical role of Wnt signaling in embryonic cartilage and bone development has been well established, and much has been learnt regarding the role of Wnt signaling in chondrogenesis and cartilage development. However, relatively little is known about the role of Wnt signaling in adult articular cartilage and degenerative cartilage tissue. This review will briefly summarize recent advances in Wnt regulation of chondrogenesis and hypertrophic maturation of chondrocytes, and review data concerning the role of Wnt signaling in the maintenance and degeneration of articular chondrocytes and cartilage.

Large Osteochondral Fractures of the Lateral Femoral Condyle in the Adolescent: Outcome of Bioabsorbable Pin Fixation

Large osteochondral fractures of the lateral femoral condyle of the knee in adolescent patients can be diagnostically and therapeutically challenging. Historically, management has involved removal of the fragment, leaving a large area of bone devoid of articular cartilage on the weight-bearing surface of the lateral femoral condyle. This study assessed open reduction and internal fixation of the osteochondral fragments with use of multiple polyglycolic acid rods. Eight patients, between twelve and fifteen years old, with a large (>4 cm(2)) osteochondral fracture of the lateral femoral condyle were treated with open reduction and internal fixation with use of multiple polyglycolic acid rods. Each patient was evaluated at more than five years (a mean of nine years) after the index procedure with a clinical assessment, during which the knee was scored according to the International Knee Documentation Committee and Cincinnati knee rating systems, plain radiographs were made, and magnetic resonance imaging scans were acquired. The majority of patients scored well on both knee rating systems, with no poor results. Five of the eight patients had normal findings on knee radiographs, and three had radiographs that showed minor changes. Magnetic resonance imaging scans of all patients demonstrated intact articular cartilage in the lateral compartment with no area of full-thickness articular cartilage loss. No evidence of articular cartilage thinning was seen in two knees; a small area of <2 cm(2) of cartilage thinning, in four; a moderate area of 2.7 cm(2) of cartilage thinning, in one; and a large area of 11.2 cm(2) of abnormal cartilage signal, in one knee. Osteochondral fracture of the lateral femoral condyle is an injury to which adolescents with ligamentous laxity of the knee are prone. Our results show that internal fixation of these osteochondral fragments with bioabsorbable implants is possible and is a worthwhile option.