title: Deficiency of Lipocalin-2 Promotes Proliferation and Differentiation of Osteoclast Precursors via Regulation of c-Fms Expression and Nuclear Factor-kappa B Activation.
abstract: BACKGROUND
  Lipocalin-2 (LCN2), a small glycoprotein, has a pivotal role in diverse biological processes such as cellular proliferation and differentiation. We previously reported that LCN2 is implicated in osteoclast formation induced by receptor activator of nuclear factor-kappa B ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). In the present study, we used a knockout mouse model to further investigate the role of LCN2 in osteoclast development.
  
  
  METHODS
  Osteoclastogenesis was assessed using primary bone marrow-derived macrophages. RANKL and M-CSF signaling was determined by immunoblotting, cell proliferation by bromodeoxyuridine (BrdU) enzyme-linked immunosorbent assay (ELISA), and apoptosis by cell death detection ELISA. Bone morphometric parameters were determined using a micro-computed tomography system.
  
  
  RESULTS
  Our results showed that LCN2 deficiency increases tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclast formation in vitro, a finding that reflects enhanced proliferation and differentiation of osteoclast lineage cells. LCN2 deficiency promotes M-CSF-induced proliferation of bone marrow macrophages (BMMs), osteoclast precursors, without altering their survival. The accelerated proliferation of LCN2-deficient precursors is associated with enhanced expression and activation of the M-CSF receptor, c-Fms. Furthermore, LCN2 deficiency stimulates the induction of c-Fos and nuclear factor of activated T cells c1 (NFATc1), key transcription factors for osteoclastogenesis, and promotes RANKL-induced inhibitor of kappa B (IκBα) phosphorylation. Interestingly, LCN2 deficiency does not affect basal osteoclast formation in vivo, suggesting that LCN2 might play a role in the enhanced osteoclast development that occurs under some pathological conditions.
  
  
  CONCLUSIONS
  Our study establishes LCN2 as a negative modulator of osteoclast formation, results that are in accordance with our previous findings.
authors.affiliation: Department of Biomedical Science, Cell and Matrix Research Institute, BK21 Plus KNU Biomedical Convergence Program, Clinical Trial Center, School of Medicine, Kyungpook National University and Hospital, Daegu, Korea.; Skeletal Diseases Genome Research Center, School of Medicine, Kyungpook National University, Daegu, Korea.
authors.forename: Hyun-Ju
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Department of Biomedical Science, Cell and Matrix Research Institute, BK21 Plus KNU Biomedical Convergence Program, Clinical Trial Center, School of Medicine, Kyungpook National University and Hospital, Daegu, Korea.
authors.forename: Boram
authors.initials: B
authors.lastname: Ohk
authors.affiliation: Department of Biomedical Science, Cell and Matrix Research Institute, BK21 Plus KNU Biomedical Convergence Program, Clinical Trial Center, School of Medicine, Kyungpook National University and Hospital, Daegu, Korea.
authors.forename: Woo Youl
authors.initials: WY
authors.lastname: Kang
authors.affiliation: Department of Biomedical Science, Cell and Matrix Research Institute, BK21 Plus KNU Biomedical Convergence Program, Clinical Trial Center, School of Medicine, Kyungpook National University and Hospital, Daegu, Korea.
authors.forename: Sook Jin
authors.initials: SJ
authors.lastname: Seong
authors.affiliation: Department of Pharmacology, School of Medicine, Kyungpook National University, Daegu, Korea.
authors.forename: Kyoungho
authors.initials: K
authors.lastname: Suk
authors.affiliation: College of Pharmacy, Yeungnam University, Gyeongsan, Korea.
authors.forename: Mi-Sun
authors.initials: MS
authors.lastname: Lim
authors.affiliation: Skeletal Diseases Genome Research Center, School of Medicine, Kyungpook National University, Daegu, Korea.
authors.forename: Shin-Yoon
authors.initials: SY
authors.lastname: Kim
authors.affiliation: Department of Biomedical Science, Cell and Matrix Research Institute, BK21 Plus KNU Biomedical Convergence Program, Clinical Trial Center, School of Medicine, Kyungpook National University and Hospital, Daegu, Korea.
authors.forename: Young-Ran
authors.initials: YR
authors.lastname: Yoon
keywords: LCN2; NF-κB; Osteoclast; c-Fms