Inhibition of sphingosine 1-phosphate protects mice against chondrocyte catabolism and osteoarthritis.

OBJECTIVE: Cartilage loss observed in osteoarthritis (OA) is prevented when osteoclasts in the subchondral bone are inhibited in mice. Here, we investigated the role of the osteoclast secretome and of the lipid mediator sphingosine 1-phosphate (S1P) in chondrocyte metabolism and OA. MATERIALS AND METHODS: We used SphK1LysMCre and wild type mice to assess the effect of murine osteoclast secretome in chondrocyte metabolism. Gene and protein expressions of matrix metalloproteinase (Mmp) were quantified in chondrocytes and explants by RT-qPCR and Western blots. SphK1LysMCre mice or wild type mice treated with S1P2 receptor inhibitor JTE013 or anti-S1P neutralizing antibody sphingomab are analyzed by OA score and immunohistochemistry. RESULTS: The osteoclast secretome increased the expression of Mmp3 and Mmp13 in murine chondrocytes and cartilage explants and activated the JNK signaling pathway, which led to matrix degradation. JTE013 reversed the osteoclast-mediated chondrocyte catabolism and protected mice against OA, suggesting that osteoclastic S1P contributes to cartilage damage in OA via S1P/S1P2 signaling. The activity of sphingosine kinase 1 (SphK1) increased with osteoclast differentiation, and its expression was enhanced in subchondral bone of mice with OA. The expression of Mmp3 and Mmp13 in chondrocytes was low upon stimulation with the secretome of Sphk1-lacking osteoclasts. Cartilage damage was significantly reduced in SphK1LysMCre mice, but not the synovial inflammation. Finally, intra-articular administration of sphingomab inhibited the cartilage damage and synovial inflammation. CONCLUSIONS: Lack of S1P in myeloid cells and local S1P neutralization alleviates from osteoarthritis in mice. These data identify S1P as a therapeutic target in OA.

Identification of TGFß signatures in six murine models mimicking different osteoarthritis clinical phenotypes.

OBJECTIVE: TGFß is a key player in cartilage homeostasis and OA pathology. However, few data are available on the role of TGFß signalling in the different OA phenotypes. Here, we analysed the TGFß pathway by transcriptomic analysis in six mouse models of OA. METHOD: We have brought together seven expert laboratories in OA pathophysiology and, used inter-laboratories standard operating procedures and quality controls to increase experimental reproducibility and decrease bias. As none of the available OA models covers the complexity and heterogeneity of the human disease, we used six different murine models of knee OA: from post-traumatic/mechanical models (meniscectomy (MNX), MNX and hypergravity (HG-MNX), MNX and high fat diet (HF-MNX), MNX and seipin knock-out (SP-MNX)) to aging-related OA and inflammatory OA (collagenase-induced OA (CIOA)). Four controls (MNX-sham, young, SP-sham, CIOA-sham) were added. OsteoArthritis Research Society International (OARSI)-based scoring of femoral condyles and ribonucleic acid (RNA) extraction from tibial plateau samples were done by single operators as well as the transcriptomic analysis of the TGFß family pathway by Custom TaqMan® Array Microfluidic Cards. RESULTS: The transcriptomic analysis revealed specific gene signatures in each of the six models; however, no gene was deregulated in all six OA models. Of interest, we found that the combinatorial Gdf5-Cd36-Ltbp4 signature might discriminate distinct subgroups of OA: Cd36 upregulation is a hallmark of MNX-related OA while Gdf5 and Ltbp4 upregulation is related to MNX-induced OA and CIOA. CONCLUSION: These findings stress the OA animal model heterogeneity and the need of caution when extrapolating results from one model to another.

Iron overload in a murine model of hereditary hemochromatosis is associated with accelerated progression of osteoarthritis under mechanical stress.

OBJECTIVE: Hereditary hemochromatosis (HH) is a disease caused by mutations in the Hfe gene characterised by systemic iron overload and associated with an increased prevalence of osteoarthritis (OA) but the role of iron overload in the development of OA is still undefined. To further understand the molecular mechanisms involved we have used a murine model of HH and studied the progression of experimental OA under mechanical stress. DESIGN: OA was surgically induced in the knee joints of 10-week-old C57BL6 (wild-type) mice and Hfe-KO mice. OA progression was assessed using histology, micro CT, gene expression and immunohistochemistry at 8 weeks after surgery. RESULTS: Hfe-KO mice showed a systemic iron overload and an increased iron accumulation in the knee synovial membrane following surgery. The histological OA score was significantly higher in the Hfe-KO mice at 8 weeks after surgery. Micro CT study of the proximal tibia revealed increased subchondral bone volume and increased trabecular thickness. Gene expression and immunohistochemical analysis showed a significant increase in the expression of matrix metallopeptidase 3 (MMP-3) in the joints of Hfe-KO mice compared with control mice at 8 weeks after surgery. CONCLUSIONS: HH was associated with an accelerated development of OA in mice. Our findings suggest that synovial iron overload has a definite role in the progression of HH-related OA.

Bone status and fractures in 85 adults with Wilson's disease.

UNLABELLED: Wilson's disease is characterized by copper deposition, especially in the liver and central nervous system. We assessed the prevalent fractures and bone mineral density (BMD) and related risk factors in 85 patients. BMD was normal, but patients with severe neurological involvement, low BMI, and/or amenorrhea are at risk for fractures. INTRODUCTION: Wilson's disease (WD) is characterized by copper deposition, especially in the liver and central nervous system. Two studies showed a high prevalence of osteoporosis in WD patients. We wanted to assess the prevalent fractures and bone mineral density (BMD) and to identify risk factors for bone loss and fractures in a large group of WD patients. METHODS: In this prospective cross-sectional survey at National center of reference for WD, we included 85 patients, 47 women, and 38 men, with a mean age of 35 ± 10 years, and mean time from diagnosis to study of 21 ± 9 years; 57 (67%) patients had neurological signs. Peripheral fractures, prevalent radiological vertebral fractures (VFx), and dual-energy X-ray absorptiometry BMD measurements at the femoral neck (FN) and lumbar spine (LS) were studied. RESULTS: Mean LS and FN Z-score was normal (-0.37 ± 1.20 at LS and -0.06 ± 1.20 at FN). BMI <19 kg/m(2) and amenorrhea were associated with low BMD. Prevalent peripheral fractures were noted in 43 (51%) and VF in 7 (8%) patients. Severity of neurological involvement and male sex was associated with peripheral fractures, whereas older age, severe neurological involvement, and low BMD and Z-score values were associated with VF. CONCLUSION: Our data showing normal BMD overall do not support routine bone status evaluation in adults with WD. However, patients with severe neurological involvement, low BMI, and/or amenorrhea are at risk factors for fractures and may require specific monitoring.

Intracellular calcium oscillations in articular chondrocytes induced by basic calcium phosphate crystals lead to cartilage degradation.

OBJECTIVE: Basic calcium phosphate (BCP) crystals, including octacalcium phosphate (OCP), carbonated-apatite (CA) and hydroxyapatite (HA) crystals are associated with destructive forms of osteoarthritis. Mechanisms of BCP-induced cartilage breakdown remain incompletely understood. We assessed the ability of BCP to induce changes in intracellular calcium (iCa(2+)) content and oscillations and the role of iCa(2+) in BCP-induced cartilage degradation. METHODS: Bovine articular chondrocytes (BACs) and bovine cartilage explants (BCEs) were stimulated with BCP or monosodium urate (MSU) crystals. iCa(2+) levels were determined by spectrofluorimetry and oscillations by confocal microscopy. mRNA expression of matrix metalloproteinase 3 (MMP-3), a disintegrin and metalloprotease with thrombospondin-like motifs 4 (ADAMTS-4) and ADAMTS-5 was assessed by quantitative real-time PCR. Glycosaminoglycan (GAG) release was measured in the supernatants of BCE cultures. RESULTS: All three BCP crystals significantly increased iCa(2+) content. OCP also induced iCa(2+) oscillations. Rate of BACs displaying iCa(2+) oscillations increased over time, with a peak after 20 min of stimulation. OCP-induced iCa(2+) oscillations involved both extracellular Ca(2+) (eCa(2+)) influx and iCa(2+) stores. Indeed, OCP-induced iCa(2+) oscillations decreased rapidly in Ca(2+)-free medium. Both voltage- and non-voltage-dependent Ca(2+) channels were involved in eCa(2+) influx. BCP crystal-induced variation in iCa(2+) content was associated with BCP crystal-induced cartilage matrix degradation. However, iCa²(+) was not associated with OCP crystal-induced mRNA expression of MMP-3, ADAMTS-4 or ADAMTS-5. CONCLUSION: BCP crystals can induce variation in iCa(2+) content and oscillations in articular chondrocytes. Furthermore, BCP crystal-induced changes in iCa(2+) content play a pivotal role in BCP catabolic effects on articular cartilage.

The mechanisms of inflammation in gout and pseudogout (CPP-induced arthritis).

Recent advances have stimulated new interest in the area of crystal arthritis, as microcrystals can be considered to be endogenous "danger signals" and are potent stimulators of immune as well as non-immune cells. The best known microcrystals include urate (MSU), and calcium pyrophosphate (CPP) crystals, associated with gout and pseudogout, respectively. Acute inflammation is the hallmark of the acute tissue reaction to crystals in both gout and pseudogout. The mechanisms leading to joint inflammation in these diseases involve first crystal formation and subsequent coating with serum proteins. Crystals can then interact with plasma cell membrane, either directly or via membrane receptors, leading to NLRP3 activation, proteolytic cleavage and maturation of pro-interleukin-1ß (pro-IL1ß) and secretion of mature IL1ß. Once released, this cytokine orchestrates a series of events leading to endothelial cell activation and neutrophil recruitment. Ultimately, gout resolution involves several mechanisms including monocyte differentiation into macrophage, clearance of apoptotic neutrophils by macrophages, production of Transforming Growth Factor (TGF-ß) and modification of protein coating on the crystal surface. This review will examine these different steps.

Tophaceous gout: an unusual cause of multiple fractures.

OBJECTIVE: Fractures occurring at the site of a tophus have rarely been described in gout. In this paper we review the occurrence, clinical features, and outcome of fractures in tophaceous gout. METHOD: A PubMed search was conducted to identify the relevant literature, following our experience with two patients who developed tophaceous fractures after minor or no trauma. RESULTS: A total of 13 patients were analysed. Eleven cases of tophaceous fracture have been reported since 1950. Common features are: known and long-standing gout with tophi; minor or absence of trauma; specific locations include seven patients with patella bone fractures. Other sites include the cervical spine in two patients, the first and fifth metatarsal, and a phalanx in one patient each, the ilium and pubic bones in one, the medial malleola, and the femoral neck in the latter case. CONCLUSIONS: Monosodium urate (MSU) crystals can contribute to bone lesions by reducing osteoblastic activity and are associated with enhanced osteoclast activity in the vicinity of tophi. Mild trauma triggers MSU crystal release from tophi, resulting in cell activation and production of cytokines and proteases. This could enhance bone erosion leading ultimately to bone fragility and fracture. Our cases exemplify a rare cause of spontaneous fracture. Gouty tophus should be considered when facing a lytic lesion with fracture.

Postoperative spondylodiscitis due to Kytococcus schroeteri in a diabetic woman.

Kytococcus schroeteri, a Gram-positive coccus, is usually regarded as part of the human skin flora. It has been described in prosthetic valve endocarditis but never as being involved in osteoarticular infections. We report here the first case of a spondylodiscitis due to K. schroeteri identified by 16S rRNA gene sequencing.

Osteoprotegerin inhibits cartilage degradation through an effect on trabecular bone in murine experimental osteoarthritis.

OBJECTIVE: To characterize bone microarchitectural changes and to test the hypothesis that disrupting local cytokine equilibrium could modify cartilage degradation in a murine model of experimental osteoarthritis (OA). METHODS: Ten-week-old male C57BL/6 mice underwent medial meniscectomy of their right knees and a sham operation of their left knees. The mice received intraperitoneal injections of osteoprotegerin (OPG) (10 mg/kg), interleukin-1 receptor antagonist (IL-1Ra) (100 mg/kg), or phosphate buffered saline for 6 weeks. The microarchitecture of the trabecular bone, the OA score, and expression of ADAMTS-4 and ADAMTS-5 were assessed. Proteoglycan release was measured in cartilage explant cultures in the presence of IL-1Ra and OPG. RESULTS: In the meniscectomized knees, bone volume/tissue volume (BV/TV) was lower, whereas trabecular separation, the OA score, and aggrecanase expression were higher than in the sham-operated knees. After treatment with OPG, BV/TV was significantly increased and trabecular separation was reduced in the knees that underwent meniscectomy. The OA score and the number of ADAMTS-positive cells were significantly decreased by treatment with OPG but were not affected by IL-1Ra. Moreover, OPG did not directly reduce the release of proteoglycans from cartilage explant cultures. CONCLUSION: In an experimental model of OA, meniscectomy induced bone loss and cartilage degradation at 6 weeks. Systemic administration of OPG prevented bone and cartilage degradation in vivo but had no effect on cartilage in vitro. These data collectively indicate that bone could be a contributor in the early stages of OA pathogenesis. They further suggest that disruption of RANKL/OPG balance might result in the degradation of cartilage subjected to mechanical loading. Specific targeting of the bone cytokine network might help to prevent OA.

Annexin 5 overexpression increased articular chondrocyte apoptosis induced by basic calcium phosphate crystals.

OBJECTIVES: Basic calcium phosphate (BCP) crystals (octacalcium phosphate (OCP), carbapatite (CA) and hydroxyapatite (HA)) are associated with severe forms of osteoarthritis. In advanced osteoarthritis, cartilage shows chondrocyte apoptosis, overexpression of annexin 5 (A5) and BCP crystal deposition within matrix vesicles. We assessed in vitro whether BCP crystals and overexpression of A5 increased chondrocyte apoptosis. METHODS: Apoptosis was induced by BCP crystals, tumour necrosis factor (TNF)-alpha (20 ng/ml) and Fas ligand (20 ng/ml) in normal articular chondrocytes (control) and in A5 overexpressed chondrocytes, performed by adenovirus infection. Apoptosis was assessed by caspase 3 (Cas3) activity, and DNA fragmentation. RESULTS: All BCP crystals, TNF-alpha and Fas ligand induced chondrocyte apoptosis as demonstrated by decreased cell viability and increased Cas3 activity and DNA fragmentation. TUNEL (terminal deoxyribonucleotide transferase-mediated dUTP nick end-labelling)-positive staining chondrocytes were increased by OCP (12.4 (5.2)%), CA (9.6 (2.6)%) and HA (9.2 (3.0)%) crystals and TNF-alpha (9.6 (2.4)%) stimulation compared with control (3.1 (1.9)%). BCP crystals increased Cas3 activity in a dose-dependent fashion. BCP-crystal-induced chondrocyte apoptosis was independent from TNF-alpha and interleukin-1beta pathways but required cell-crystal contact and intralysosomal crystal dissolution. Indeed, preincubation with ammonium chloride, a lysosomal inhibitor of BCP crystal dissolution, significantly decreased BCP-crystal-induced Cas3 activity. Finally, overexpression of A5 enhanced BCP crystal- and TNF-alpha-induced chondrocyte apoptosis. CONCLUSIONS: Overexpression of A5 and the presence of BCP crystals observed in advanced osteoarthritis contributed to chondrocyte apoptosis. Our results suggest a new pathophysiological mechanism for calcium-containing crystal arthropathies.

Lack of linkage and association of adrenomedullin and its receptor genes in French Caucasian rheumatoid arthritis trio families.

OBJECTIVE: Rheumatoid arthritis (RA) is characterized by hyperplasia of fibro-blast-like synoviocytes (FLSs), in part due to apoptosis resistance. Adrenomedullin, an anti-apoptotic peptide, is secreted more by RA than osteoarthritis FLSs. Adrenomedullin binds to a heterodimeric functional receptor, of calcitonin receptor-like receptor (CRLR) coupled with a receptor activity-modifying protein-2 (RAMP-2), which is also overexpressed by rheumatoid synoviocytes. Since adrenomedullin decreases RA FLS apoptosis, possibly contributing to the development of pannus, study of adrenomedullin and its receptor genes might reveal a linkage and association in French Caucasian RA trio families. METHODS: Within each of 100 families, one RA-affected patient and both parents underwent genotyping for polymorphisms of adrenomedullin, CRLR and RAMP-2, by PCR-restricted fragment-length polymorphism (RFLP) or Taqman 5' allelic discrimination assay. Statistical analysis relied on the transmission disequilibrium test, the affected family-based controls and the genotype relative risk. Haplotypes of CRLR were inferred, and linkage and association studies were performed. RESULTS: No significant transmission disequilibrium or association between the three genes and RA was observed. CRLR haplotypes revealed two major haplotypes, but no significant linkage with RA. CONCLUSION: Our findings provided no significant linkage or association of adrenomedullin and CRLR-RAMP-2 genes with RA in the studied trio families. The two CRLR polymorphisms rs3771076 and rs3771084 should be investigated in larger samples.

Estradiol inhibits adhesion and promotes apoptosis in murine osteoclasts in vitro.

Osteoporosis caused by estrogen deficiency is characterized by enhanced bone resorption mediated by osteoclasts. Adhesion to bone matrix and survival of differentiated osteoclasts is necessary to resorb bone. The aim of our study was to investigate the in vitro effects of estradiol on murine osteoclasts. RAW 264.7 cells treated with 30 ng/ml RANK-L were used as a model for osteoclastogenesis. Estradiol (10(-8)M) for 5 days induced an inhibition of osteoclast differentiation and beta3 expression. Estradiol inhibited significantly the adhesion of mature osteoclasts by 30%. Furthermore estradiol-induced apoptosis shown by with nuclear condensation and Bax/Bcl2 ratio. In addition, estradiol enhanced caspase-3, -8 and -9 activities. This effect completely disappeared using specific caspase-8 inhibitor. However, increased caspase-3 activity by estradiol was observed in the presence of caspase-9 inhibitor, indicating the preferential involvement of caspase-8 pathway. Fas and FasL mRNA expression was not regulated by estradiol. However, estradiol enhanced caspase-3 activity in Fas-induced apoptosis on mature osteoclasts, suggesting that this might interact with the Fas-signaling pathway. These data suggest that estradiol decreases bone resorption by several mechanisms including adhesion and apoptosis of osteoclasts.