Conjugated linoleic acid inhibits osteoclast differentiation of RAW264.7 cells by modulating RANKL signaling

Md Mizanur Rahman,Arunabh Bhattacharya,Gabriel Fernandes

doi:10.1194/jlr.m600151-jlr200

Abstract

Bone destruction is a pathological hallmark of several chronic inflammatory diseases, including rheumatoid arthritis, periodontitis, and osteoporosis. Inflammation-induced bone loss of this sort results from increased numbers of bone-resorbing osteoclasts. Numerous studies have indicated that conjugated linoleic acid (CLA) positively influences calcium and bone metabolism. Gene-deletion studies have shown that receptor activator of nuclear factor-kappaB ligand (RANKL) is one of the critical mediators of osteoclastogenesis. In this report, we examine the ability of CLA to suppress RANKL signaling and osteoclastogenesis in RAW264.7 cells, a murine monocytic cell line. Treatment of these cells with RANKL activated nuclear factor-kappaB (NF-kappaB), and preexposure of the cells to CLA significantly suppressed RANKL-induced NF-kappaB activation, including phosphorylation of I-kappaBalpha, degradation of I-kappaBalpha, and nuclear translocation of p65. RANKL induced osteoclastogenesis in these monocytic cells, and CLA inhibited RANKL-induced tumor necrosis factor-alpha production and osteoclast differentiation, including osteoclast-specific genes such as tartrate-resistant acid phosphatase, cathepsin K, calcitonin receptor, and matrix metalloproteinase-9 expression and osteoclast-specific transcription factors such as c-Fos, nuclear factor of activated T-cells expression, and bone resorption pit formation. CLA also inhibited RANKL-induced activation of mitogen-activated protein kinase p38 but had little effect on c-Jun N-terminal kinase activation. Collectively, these data demonstrate for the first time that CLA inhibits osteoclastogenesis by modulating RANKL signaling. Thus, CLA may have important therapeutic implications for the treatment of bone diseases associated with enhanced bone resorption by excessive osteoclastogenesis.

Highlights

Bone destruction is a pathological hallmark of several chronic inflammatory diseases, including rheumatoid arthritis, periodontitis, and osteoporosis
The binding of receptor activator of nuclear factor-kB ligand (RANKL) to its receptor RANK leads to the recruitment of tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) to the cytoplasmic domain of RANK, thereby resulting in the activation of distinct signaling cascades mediated by mitogen-activated protein kinases (MAPKs), including cJun N-terminal kinase (JNK) and p38 MAPK (p38) [10]
To determine whether in vitro added fatty acids incorporate into cells, we examined the fatty acid profile in linoleic acid (LA)/ conjugated linoleic acid (CLA)-treated RAW264.7 cells using GC

Summary

Introduction

Bone destruction is a pathological hallmark of several chronic inflammatory diseases, including rheumatoid arthritis, periodontitis, and osteoporosis. RANKL induced osteoclastogenesis in these monocytic cells, and CLA inhibited RANKL-induced tumor necrosis factor-a production and osteoclast differentiation, including osteoclast-specific genes such as tartrate-resistant acid phosphatase, cathepsin K, calcitonin receptor, and matrix metalloproteinase-9 expression and osteoclast-specific transcription factors such as c-Fos, nuclear factor of activated T-cells expression, and bone resorption pit formation. Differentiation of osteoclasts is regulated by soluble or membrane-bound molecules expressed by osteoblasts and stromal cells in the bone microenvironment [5] One such factor, receptor activator of nuclear factor-kB ligand (RANKL), a member of the tumor necrosis factor (TNF) family [6,7,8,9], plays an essential role in osteoclastogenesis. It has been shown that JNK1-activated c-Jun signaling in cooperation with nuclear factor of activated T cells (NFAT) is key to RANKL-regulated osteoclast differentiation [11].

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Conclusion