ABSTRACT
Human monocyte chemoattractant protein-1 (MCP-1) in mice has two orthologs, MCP-1 and MCP-5. MCP-1, which is highly expressed in osteoclasts rather than in osteoclast precursor cells, is an important factor in osteoclast differentiation. However, the roles of MCP-5 in osteoclasts are completely unknown. In this study, contrary to MCP-1, MCP-5 was downregulated during receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast differentiation and was considered an inhibitory factor in osteoclast differentiation. The inhibitory role of MCP-5 in osteoclast differentiation was closely related to the increase in Ccr5 expression and the inhibition of IκB degradation by RANKL. Transgenic mice expressing MCP-5 controlled by Mx-1 promoter exhibited an increased bone mass because of a decrease in osteoclasts. This result strongly supported that MCP-5 negatively regulated osteoclast differentiation. MCP-5 also prevented severe bone loss caused by RANKL.
Subject(s)
Cell Differentiation , Membrane Glycoproteins , Monocyte Chemoattractant Proteins , Osteoclasts , Animals , Humans , Male , Mice , Cells, Cultured , Membrane Glycoproteins/metabolism , Mice, Inbred ICR , Monocyte Chemoattractant Proteins/genetics , Monocyte Chemoattractant Proteins/metabolism , Monocyte Chemoattractant Proteins/pharmacology , NF-kappa B/metabolism , Osteoclasts/cytology , Osteoclasts/metabolism , RANK Ligand/pharmacology , RANK Ligand/metabolism , Receptor Activator of Nuclear Factor-kappa B/metabolism , Up-RegulationABSTRACT
Several members of the transforming growth factor beta (TGF-ß) superfamily regulate the proliferation, differentiation, and function of bone-forming osteoblasts and bone-resorbing osteoclasts. However, it is still unknown whether Nodal, a member of the TGF-ß superfamily, serves a function in bone cells. In this study, we found that Nodal did not have any function in osteoblasts but instead negatively regulated osteoclast differentiation. Nodal inhibited RANKL-induced osteoclast differentiation by downregulating the expression of pro-osteoclastogenic genes, including c-fos, Nfatc1, and Blimp1, and upregulating the expression of antiosteoclastogenic genes, including Bcl6 and Irf8. Nodal activated STAT1 in osteoclast precursor cells, and STAT1 downregulation significantly reduced the inhibitory effect of Nodal on osteoclast differentiation. These findings indicate that Nodal activates STAT1 to downregulate or upregulate the expression of pro-osteoclastogenic or antiosteoclastogenic genes, respectively, leading to the inhibition of osteoclast differentiation. Moreover, the inhibitory effect of Nodal on osteoclast differentiation contributed to the reduction of RANKL-induced bone loss in vivo.
Subject(s)
Cell Differentiation , Nodal Protein , Osteoclasts , STAT1 Transcription Factor , Animals , Mice , Bone Resorption/metabolism , Bone Resorption/genetics , Bone Resorption/pathology , Interferon Regulatory Factors/metabolism , Interferon Regulatory Factors/genetics , NFATC Transcription Factors/metabolism , NFATC Transcription Factors/genetics , Osteoblasts/metabolism , Osteoclasts/metabolism , Osteogenesis/genetics , Phosphorylation , Positive Regulatory Domain I-Binding Factor 1/metabolism , Positive Regulatory Domain I-Binding Factor 1/genetics , Proto-Oncogene Proteins c-bcl-6/metabolism , Proto-Oncogene Proteins c-bcl-6/genetics , Proto-Oncogene Proteins c-fos/metabolism , Proto-Oncogene Proteins c-fos/genetics , RANK Ligand/metabolism , Signal Transduction , STAT1 Transcription Factor/metabolism , STAT1 Transcription Factor/genetics , Male , Mice, Inbred ICR , Nodal Protein/genetics , Nodal Protein/metabolism , Nodal Protein/pharmacologyABSTRACT
Sestrins are stress-responsive proteins with antioxidant properties. They participate in cellular redox balance and protect against oxidative damage. This study investigated the effects of Sestrin2 (Sesn2) on osteoclast differentiation and function. Overexpressing Sesn2 in osteoclast precursor cells significantly inhibited receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclastogenesis. This was assessed as reduced expression of various osteoclast markers, including c-Fos, nuclear factor of activated T cells 1 (NFATc1), osteoclast-associated receptor, tartrate-resistant acid phosphatase, and cathepsin K. Conversely, downregulation of Sesn2 produced the opposite effect. Mechanistically, Sesn2 overexpression enhanced AMPK activation and the nuclear translocation of nuclear factor erythroid-derived factor 2-related factor 2 (Nrf2), promoting antioxidant enzymes. Moreover, azithromycin (Azm) induced Sesn2 expression, which suppressed RANKL-induced osteoclast differentiation. Specifically, Azm treatment reduced RANKL-induced production of reactive oxygen species in osteoclasts. Furthermore, intraperitoneal administration of Azm ameliorated RANKL-induced bone loss by reducing osteoclast activity in mice. Taken together, our results suggested that Azm-induced Sesn2 act as a negative regulator of RANKL-induced osteoclast differentiation through the AMPK/NFATc1 signaling pathway. Concisely, targeting Sesn2 can be a potential pharmacological intervention in osteoporosis.