IL-23 activates the synthesis and production of
leukotriene B4 (
LTB4) in myeloid cells, which modulate inflammatory
arthritis. In this study we investigated the role of
LTB4 and its receptor LTB4R1 (BLT1) in synovial
inflammation and osteoclast differentiation. Specifically, we used
IL-23 in vivo gene transfer to induce
arthritis in mice and showed that elevated serum
LTB4 and synovial expression of
5-lipoxygenase correlated with increased disease severity by histological evaluation and paw swelling compared with GFP gene transfer controls. To further investigate the effect of the
LTB4 pathway in bone loss, we performed osteoclast differentiation assays by stimulating with
M-CSF and receptor activator of NF-κB
ligand bone marrow cells derived from BLT1+/+ and/or BLT1-/- mice and used quantitative PCR for gene expression analysis in terminally differentiated osteoclasts. Deficiency in BLT1 resulted in the upregulation of osteoclast-related genes and an increase in the formation of giant, multinucleated TRAP+ cells capable of
F-actin ring formation. Additionally, BLT1 deficiency showed an increase of phosphorylated NF-κB and phosphorylated IκB levels in osteoclasts. We also performed real-time
calcium imaging to study the effect of BLT1 deficiency in receptor activator of NF-κ-B
ligand-induced activation of intracellular
calcium flux in vitro. Our data show that
LTB4 and its receptor BLT1 exacerbate synovial
inflammation in vivo and
bone resorption in vitro, suggesting that
LTB4 and BLT1 could be effectively targeted for the treatment of
musculoskeletal diseases.