Beclin 1 positively regulates osteoprotegerin-induced inhibition of osteoclastogenesis by increasing autophagy in vitro.

Osteoclastogenesis is induced by receptor activator of nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF), and can be suppressed by osteoprotegerin (OPG). Beclin1 has a dual role in osteoclastogenesis. However, the role of Beclin1-mediated autophagy during OPG-induced inhibition of osteoclastogenesis remains unclear. Here, we found that Beclin1 and matrix metalloproteinase 9 (MMP-9) expression were increased during osteoclastogenesis. OPG (20, 40, and 80 ng/mL) decreased Src and MMP-9 expression, but augmented Beclin1 expression and fluorescence intensity. Similarly, treatment with the autophagy activator rapamycin increased Beclin1 expression during OPG-induced inhibition of osteoclastogenesis. Further, Beclin1 knockdown restored osteoclast numbers by reducing autophagy during OPG-induced inhibition of osteoclastogenesis. These results indicate that Beclin1 has a positive role during OPG-induced inhibition of osteoclastogenesis by regulating autophagy, which might provide a potential basis for osteoclastogenesis.

Cadmium Toxicity on Chondrocytes and the Palliative Effects of 1α, 25-Dihydroxy Vitamin D3 in White Leghorns Chicken's Embryo.

Cadmium (Cd) can causes osteoporosis and joint swelling. However, the mechanism of Cd toxicity in chondrocytes and how to alleviate Cd poisoning to chondrocytes are still unclear. Herein, we evaluated the toxicity of Cd to chicken chondrocytes, and whether vitamin D can relieve the toxicity of Cd to chondrocytes. Primary chondrocytes were collected from knee-joint cartilage of 15-day-old chicken embryos. They were treated with (0, 1, 2, and 4) µM Cd alone, 10-8 M 1α,25-(OH)2D3 alone, or 2 µM Cd combined with 10-8 M 1α,25-(OH)2D3. We found that Cd significantly inhibited Sox9 and ACAN mRNA expression, which are markers for chondrocyte differentiation, downregulated the mitochondrial membrane potential, upregulated the Bax/B-cell lymphoma 2 ratio. Furthermore, Cd significantly promoted matrix metalloproteinase (MMP)-9 expression, thus accelerating the degradation of extracellular matrix. And Cd also inhibited the expression of main macromolecular protein of extracellular matrix, Collagen type IIα1 (COL2A1) and acid mucopolysaccharide. However, 1α,25-(OH)2D3 pretreatment significantly alleviated the toxicity effects of Cd on the differentiation, apoptosis and extracellular matrix gene expression in primary chondrocytes. Conclusively, Cd exposure could inhibited chicken embryo chondrocytes differentiation, extracellular matrix gene expression, and induced chondrocyte apoptosis. However, these toxic effects of Cd are alleviated by the pretreatment of chondrocytes with 1α,25-(OH)2D3.

Vitamin D Inhibition of TRPV5 Expression During Osteoclast Differentiation.

BACKGROUND: Vitamin D is an important steroid that can regulate bone metabolism including osteoclast (OC) differentiation. Transient receptor potential cation channel subfamily V member 5 (TRPV5), is a calcium channel protein involved in OC differentiation. However, the impact of vitamin D on TRPV5 expression during OC differentiation is not clear. OBJECTIVES: To determine if 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) regulates the expression of TRPV5 during OC differentiation. METHODS: Bone marrow mononuclear macrophage (BMMs) were induced to differentiate into OC with or without treatment with 10 nM 1,25(OH)2D3. The expression levels of vitamin D receptor (VDR) and TRPV5 were examined. The expression of several OC markers, including tartrate resistant acid phosphatase (TRAP), carbonic anhydrase II (Ca II), cathepsin K (CTSK), and vacuolar-type H+-ATPase (V-ATPase) were also detected. RESULTS: We found that the VDR was expressed in murine bone marrow-derived macrophages at the early stage of OC differentiation. TRPV5 expression was increased during OC differentiation, which was down-regulated by 1,25(OH)2D3 after a prolonged exposure. The 1,25(OH)2D3 and TRPV5 inhibitors inhibited OC differentiation. CONCLUSIONS: 1,25(OH)2D3 can inhibit TRPV5 expression as well as TRPV5 inhibitors during OC differentiation. This suggests that 1,25(OH)2D3 may suppress OC differentiation by inhibiting TRPV5 expression.