ABSTRACT
Adipokines derived from adipocytes are important factors that act as circulating regulators of bone metabolism. C1q/tumor necrosis factor (TNF)-related Protein-3 (CTRP3) is a novel adipokine with multiple effects such as lowering glucose levels, inhibiting gluconeogenesis in the liver, and increasing angiogenesis and anti-inflammation. However, the effects and the mechanisms of CTRP3 on bone metabolism, which is regulated by osteoblasts and osteoclasts, have not been investigated. Here, we found that CTRP3 inhibited osteoclast differentiation induced by osteoclastogenic factors in bone marrow cell-osteoblast co-cultures, but did not affect the ratio of receptor activator of nuclear factor κB (NF-κB) ligand (RANKL) to osteoprotegerin (OPG) induced by osteoclastogenic factors in osteoblasts. We also found that CTRP3 inhibited osteoclast differentiation from mouse bone marrow macrophages (BMMs) induced by RANKL in a dose-dependent manner without cytotoxicity. Functionally, CTRP3 inhibited the F-actin formation and bone resorbing activity of mature osteoclasts. Pretreatment with CTRP3 significantly inhibited RANKL-induced expression of c-Fos and nuclear factor of activated T-cells (NFATc1), essential transcription factors for osteoclast development. Surprisingly, the activation of AMP-activated protein kinase (AMPK) was considerably increased by pretreatment with CTRP3 for 1h. The CTRP3-stimulated AMPK activation was also maintained during RANKL-induced osteoclastogenesis. CTRP3 did not affect RANKL-induced p38, ERK, JNK, Akt, IκB, CREB, and calcium signaling (Btk and PLCγ2). These results suggest that CTRP3 plays an important role as a negative regulator of RANKL-mediated osteoclast differentiation by acting as an inhibitor of NFATc1 activation through the AMPK signaling pathway. Furthermore, CTRP3 treatment reduced RANKL-induced osteoclast formation and bone destruction in mouse calvarial bone in vivo based on micro-CT and histologic analysis. In conclusion, these findings strongly suggest that CTRP3 deserves new evaluation as a potential treatment target in various bone diseases associated with excessive osteoclast differentiation and bone destruction.
Subject(s)
Adipokines/metabolism , Osteoclasts/metabolism , Signal Transduction/physiology , AMP-Activated Protein Kinases/metabolism , Animals , Blotting, Western , Bone Marrow Cells/cytology , Bone Marrow Cells/metabolism , Cell Differentiation/physiology , Cells, Cultured , Coculture Techniques , Disease Models, Animal , Enzyme-Linked Immunosorbent Assay , Male , Mice , Mice, Inbred ICR , NFATC Transcription Factors/metabolism , Osteoblasts/cytology , Osteoblasts/metabolism , Osteoclasts/cytology , Proto-Oncogene Proteins c-fos/metabolism , RANK Ligand/metabolism , RNA, Small Interfering , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain Reaction , Transfection , X-Ray MicrotomographyABSTRACT
The IL-4 receptor (IL-4R) and IL-13 genes are candidate genes in atopic diseases. The IL-4Ralpha chain and IL-13 promoter polymorphisms are gain-of-function mutations associated with atopy. We tested whether polymorphisms in the IL-4Ralpha chain and the coding region of the IL-13 gene are associated with allergic rhinitis in a Korean population. Polymerase chain reaction-based assays for IL-4Ralpha Gln551Arg and IL-13 exon 4 G2044A were used for genotyping. There were no differences in the frequencies of the genotypes and alleles of IL-4Ralpha between the controls and patients. The frequency of the IL-13 exon 4 2044A allele was statistically different between the controls and patients. Our results suggest that the IL-13 exon 4 G2044A polymorphism confers susceptibility to the development of allergic rhinitis in Koreans, whereas the IL-4Ralpha Gln551Arg polymorphism is not related to allergic rhinitis.
