J Bone Metab.  2016 Feb;23(1):8-15. 10.11005/jbm.2016.23.1.8.

Deficiency of Lipocalin-2 Promotes Proliferation and Differentiation of Osteoclast Precursors via Regulation of c-Fms Expression and Nuclear Factor-kappa B Activation

Affiliations
  • 1Department 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. biohjk@knu.ac.kr, yry@knu.ac.kr
  • 2Skeletal Diseases Genome Research Center, School of Medicine, Kyungpook National University, Daegu, Korea.
  • 3Department of Pharmacology, School of Medicine, Kyungpook National University, Daegu, Korea.
  • 4College of Pharmacy, Yeungnam University, Gyeongsan, Korea.

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 (IkappaBalpha) 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.

Keyword

c-Fms; LCN2; NF-kappaB; Osteoclast

MeSH Terms

Acid Phosphatase
Animals
Apoptosis
Biological Processes
Bone Marrow
Bromodeoxyuridine
Cell Death
Cell Proliferation
Enzyme-Linked Immunosorbent Assay
Glycoproteins
Immunoblotting
Macrophage Colony-Stimulating Factor
Macrophages
Mice
Mice, Knockout
NF-kappa B
Osteoclasts*
Phosphorylation
RANK Ligand
T-Lymphocytes
Transcription Factors
Acid Phosphatase
Bromodeoxyuridine
Glycoproteins
Macrophage Colony-Stimulating Factor
NF-kappa B
RANK Ligand
Transcription Factors
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