Objective. To determine the actions of lithium chloride (LiCl) on catabolic events in human articular chondrocytes, and the effects of LiCl on the progression and severity of cartilage degradation in interleukin-1␤ (IL-1␤)-treated mouse knee joints and after surgical induction of osteoarthritis (OA) in a mouse model.Methods. Human articular chondrocytes were treated with LiCl followed by IL-1␤, and the expression levels of catabolic genes were determined by real-time polymerase chain reaction. To understand the mechanism by which LiCl affects catabolic events in articular chondrocytes after IL-1␤ treatment, the activation of NF-B was determined using luciferase reporter assays, and the activities of MAPKs and the STAT-3 signaling pathway were determined by immunoblot analysis of total cell lysates. Cultures of mouse femoral head explants treated with IL-1␤ and a mouse model of surgically induced OA were used to determine the effects of LiCl on proteoglycan loss and cartilage degradation.Results. LiCl treatment resulted in decreased catabolic marker messenger RNA levels and activation of NF-B, p38 MAPK, and STAT-3 signaling in IL-1␤-treated articular chondrocytes. Furthermore, LiCl directly inhibited IL-6-stimulated activation of STAT-3 signaling. Consequently, the loss of proteoglycan and severity of cartilage destruction in LiCl-treated mouse knee joints 8 weeks after OA induction surgery or in LiCl-treated mouse femoral head explants after IL-1␤ treatment were markedly reduced compared to that in vehicle-treated joints or explants. Conclusion.LiCl reduced catabolic events in IL-1␤-treated human articular chondrocytes and attenuated the severity of cartilage destruction in IL-1␤-treated mouse femoral head explants and in the knee joints of mice with surgically induced OA, acting via inhibition of the activities of the NF-B, p38, and STAT-3 signaling pathways.

Objective. ANXA6, the gene for annexin A6, is highly expressed in osteoarthritic (OA) articular chondrocytes but not in healthy articular chondrocytes. This study was undertaken to determine whether annexin A6 affects catabolic events in these cells.Methods. Articular chondrocytes were isolated from Anxa6-knockout mice, wild-type (WT) mice, and human articular cartilage in which ANXA6 was overexpressed. Cells were treated with interleukin-1␤ (IL-1␤) or tumor necrosis factor ␣ (TNF␣), and expression of catabolic genes and activation of NF-B were determined by real-time polymerase chain reaction and luciferase reporter assay. Anxa6؊/؊ and WT mouse knee joints were injected with IL-1␤ or the medial collateral ligament was transected and partial resection of the medial meniscus was performed to determine the role of Anxa6 in IL-1␤-mediated cartilage destruction and OA progression. The mechanism by which Anxa6 stimulates NF-B activity was determined by coimmunoprecipitation and immunoblot analysis of nuclear and cytoplasmic fractions of IL-1␤-treated Anxa6 ؊/؊ and WT mouse chondrocytes for p65 and Anxa6.Results. Loss of Anxa6 resulted in decreased NF-B activation and catabolic marker messenger RNA (mRNA) levels in IL-1␤-or TNF␣-treated articular chondrocytes, whereas overexpression of ANXA6 resulted in increased NF-B activity and catabolic marker mRNA levels. Annexin A6 interacted with p65, and loss of Anxa6 caused decreased nuclear translocation and retention of the active p50/p65 NF-B complex. Cartilage destruction in Anxa6 ؊/؊ mouse knee joints after IL-1␤ injection or partial medial meniscectomy was reduced as compared to that in WT mouse joints.Conclusion. Our data define a role of annexin A6 in the modulation of NF-B activity and in the stimulation of catabolic events in articular chondrocytes.Annexins, cytoplasmic proteins that, in the presence of Ca 2ϩ

The progressive ankylosis protein (ANK) is a transmembrane protein that transports intracellular pyrophosphate (PPi) to the extracellular milieu. In this study we show increased fatty degeneration of the bone marrow of adult ank/ank mice, which lack a functional ANK protein. In addition, isolated bone marrow stromal cells (BMSCs) isolated from ank/ank mice showed a decreased proliferation rate and osteogenic differentiation potential, and an increased adipogenic differentiation potential compared to BMSCs isolated from wild type (WT) littermates. Wnt signaling pathway PCR array analysis revealed that Wnt ligands, Wnt receptors and Wnt signaling proteins that stimulate osteoblast differentiation were expressed at markedly lower levels in ank/ank BMSCs than in WT BMSCs. Lack of ANK function also resulted in impaired bone fracture healing, as indicated by a smaller callus formed and delayed bone formation in the callus site. Whereas 5 weeks after fracture, the fractured bone in WT mice was further remodeled and restored to original shape, the fractured bone in ank/ank mice was not fully restored and remodeled to original shape. In conclusion, our study provides evidence that ANK plays a critical role in the adipogenic/osteogenic fate decision of adult mesenchymal precursor cells. ANK functions in precursor cells are required for osteogenic differentiation of these cells during adult bone homeostasis and repair, whereas lack of ANK functions favors adipogenic differentiation.