Background Lipocalin-2 (LCN2) is a member of the lipocalin superfamily and plays a critical role in the regulation of various physiological processes, such as inflammation and obesity. Although LCN2 is known to influence osteoblast differentiation, its role in osteoclast development remains unclear.
Objectives The aim of this study was to investigate the role of LCN2 in osteoclast development mediated by M-CSF and RANKL.
Methods Osteoclastogenesis was assessed using mouse primary bone marrow-derived macrophages. The mRNA expression was analyzed by Real-time or RT-PCR. RANKL or M-CSF signaling was assessed by immunoblotting and NF-κB transcriptional activity by luciferase reporter assay. Apoptosis assay was performed by cell death ELISA and cell proliferation using BrdU ELISA system.
Results The overexpression of LCN2 in bone marrow-derived macrophages or the addition of recombinant LCN2 protein inhibits the formation of multinuclear osteoclasts. LCN2 suppresses macrophage colony-stimulating factor (M-CSF)-induced proliferation of osteoclast precursor cells without affecting their apoptotic cell death. Interestingly, LCN2 decreases the expression of the M-CSF receptor, c-Fms, and subsequently blocks its downstream signaling cascades. In addition, LCN2 inhibits RANKL-induced osteoclast differentiation and attenuates the expression of c-Fos and nuclear factor of activated T cells c1 (NFATc1), which are important modulators in osteoclastogenesis. Mechanistically, LCN2 inhibits NF-κB signaling pathways, as demonstrated by the suppression of IκBa phosphorylation, nuclear translocation of p65, and NF-κB transcriptional activity.
Conclusions Our study demonstrates that LCN2 plays an important role in osteoclast development. LCN2 negatively regulates osteoclast formation by arresting the proliferation of osteoclast precursors and retarding their differentiation. Thus, our study establishes LCN2 as an anti-osteoclastogenic molecule of osteoclast development.
Teitelbaum SL, Ross FP. Genetic regulation of osteoclast development and function. Nat Rev Genet 2003:4:638-649.
Flo TH, et al. Lipocalin 2 mediates an innate immune response to bacterial infection by sequestrating iron. Nature 2004;432:917-921.
Shashidharamurthy R, et al. Differential role of lipocalin 2 during immune complex-mediated acute and chronic inflammation in mice. Arthritis and rheumatism 2013;65:1064-1073.
Acknowledgements This research was supported by the Basic Science Research Program (NRF-2013R1A1A2A10005515) and a grant (NRF-2014R1A5A2009242) of the National Research Foundation (NRF) of Korea funded by the Ministry of Education, Science, and Technology; the BK21 Plus funded by the Ministry of Education, Korea (21A20132212094); and the Bio & Medical Technology Development Program of the NRF funded by the Ministry of Science, ICT & Future Planning, Korea (NRF-2013M3A9B6046416).
Disclosure of Interest None declared