N-3 polyunsaturated fatty acids stimulate osteoclastogenesis through PPARγ-mediated enhancement of c-Fos expression, and suppress osteoclastogenesis through PPARγ-dependent inhibition of NFkB activation

Abstract

n-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been reported to suppress osteoclastogenesis in vivo. In this study, the effect of PUFAs on receptor for activation of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis was examined using bone marrow-derived monocytes/macrophage precursor cells (BMMs) or bone marrow cells (BMCs) in vitro. EPA and DHA stimulated the osteoclastic differentiation of BMMs, but n-6 PUFAs, linoleic acid and arachidonic acid had no effect. The stimulation of osteoclastogenesis of BMMs by EPA and DHA was associated with enhancement of the gene expressions of c-Fos, tartrate-resistant acid phosphatase, cathepsin K and peroxisome proliferator-activated receptor-γ (PPARγ) and the protein levels of c-Fos, PPARγ and nuclear factor of activated T cells, cytoplasmic, calcineurin-dependent-1 (NFATc1). The PPARγ agonists, rosiglitazone and GW1929, also stimulated the osteoclastogenesis of BMMs. The PPARγ antagonists, T0070907 and GW9662, inhibited the stimulations of osteoclastogenesis and c-Fos expression by EPA or DHA. However, EPA and DHA inhibited the osteoclastogenesis in BMCs including BMMs and mesenchymal stem cells (MSCs). This inhibition was associated with suppression of the expression of RANKL and nuclear factor-κB (NFκB)-regulating genes, cyclooxygenase 2, TNFα and IL-6 in BMCs and MSCs. The agonists and antagonists of PPARγ showed that the inhibitions of NFκB transcriptional activity and osteoclastogenesis by EPA and DHA were PPARγ-dependent. These results suggest that EPA and DHA directly act on BMMs and stimulate osteoclastogenesis through enhancing c-Fos expression mediated by PPARγ but suppress osteoclastogenesis through the PPARγ-dependent inhibition of NFκB activation of MSCs in BMCs.