Activation of the liver X receptor-β potently inhibits osteoclastogenesis from lipopolysaccharide-exposed bone marrow-derived macrophages

Abstract

Bacterial-induced bone diseases, such as periodontitis and osteomyelitis, are chronic inflammatory diseases characterized by increased bone destruction as a result of enhanced osteoclastogenesis. The LXRα and -β are important modulators of inflammatory signaling and can potently inhibit RANKL-induced osteoclast differentiation. Here, we investigated the effects of the LXR agonist GW3965 on LPS-induced osteoclast differentiation. Mouse BMMs primed with RANKL for 24 h, then exposed to LPS in the presence of GW3965 for 4 days, formed significantly fewer and smaller TRAP(+)-multinucleated osteoclasts with reduced expression of osteoclast markers (Acp5, Ctsk, Mmp-9, Dc-stamp, and Itgβ3), along with inhibition of actin ring development. GW3965 was able to repress proinflammatory cytokine (TNF-α, IL-1β, IL-6, and IL-12p40) expression in BMMs exposed to LPS alone; however, once BMMs entered the osteoclast lineage following RANKL priming, GW3965 no longer inhibited cytokine expression. The inhibitory action of GW3965 involved the Akt pathway but seemed to be independent of MAPKs (p38, ERK, JNK) and NF-κB signaling. GW3965 acted in a LXRβ-dependent mechanism, as osteoclast differentiation was not inhibited in BMMs derived from LXRβ-/- mice. Finally, activation of LXR also inhibited differentiation in LPS-exposed mouse RAW264.7 cells. In conclusion, GW3965 acts through LXRβ to potently inhibit osteoclast differentiation from RANKL-primed BMMs in a LPS environment. In this respect, activation of the LXR could have a beneficial, therapeutic effect in the prevention of bacterial-induced bone erosion.

Hyperglycemia Suppresses RANKL-Induced Osteoclast Differentiation through LXRβ Expression in RAW264.7 Cells

“…Another is antibone resorption agents, including estrogen, calcitonin, bisphosphonate, and raloxifene. Recently, Robertson Remen et al reported that administration of the LXR agonist GW3965 protects lipopolysaccharide and/ or RANKL-induced inflammatory bone loss induced by inhibiting osteoclastogenesis in mice (18,19). Our results also showed suppression of RANKL-induced osteoclastogenesis by GW3965 treatment (data not shown).…”

“…There has also been great interest in these receptors as novel therapeutic targets for inflammatory diseases, as they inhibit inflammatory gene expression downstream of toll-like receptor 4-, interleukin-1␤-, and tumor necrosis factor ␣-mediated signaling (16,17). Robertson Remen et al demonstrated the effect of GW3965 in lipopolysaccharide (LPS) with RANKL-induced differentiation of bone marrow-derived macrophages (BMMs) (18) and RANKL-induced differentiation of RAW264.7 cells, a murine macrophage cell line (19), into OCLs via an LXR␤-dependent (but not an LXR␣-dependent) mechanism.…”

Deletion of Nlrp3 Augments Survival during Polymicrobial Sepsis by Decreasing Autophagy and Enhancing Phagocytosis

“…The phagocytic activity of peritoneal neutrophils was measured by the uptake of red fluorescent pHrodo Escherichia coli bioparticles (35, 36) as described. Briefly, 1× 10 6 neutrophils were suspended in 100 uL of HBSS containing 20 mM HEPES, pH 7.4, and mixed with 5uL of pHrodo E. coli bioparticles.…”

“…To determine whether autophagy regulates phagocytosis, neutrophils (10 5 cells) in Opti-MEM ® medium are pre-treated with 10 μM cytochalasin D (phagocytosis inhibitor) or 10 mM 3-methyladenine (autophagy inhibitor) for one hour, followed by addition of pHrodo ™ BioParticles® (35, 36). The degree of phagocytosis was measured.…”

Minireview: Nuclear Receptor Regulation of Osteoclast and Bone Remodeling

“…Kleyer et al (109) show that LXR agonists can protect female mice from OVX-induced bone loss by decreasing the RANKL to OPG ratio. Similarly, two reports in 2013 show that LXR agonists can attenuate lipopolysaccharide-induced osteoclast differentiation by suppressing the activity of NFB and c-fos to reduce the expression of osteoclast markers Acp5, Ctsk, Mmp-9, dendritic cell-specific transmembrane protein, and Itg␤3 (110,111). In addition to inhibiting osteoclast differentiation, LXR agonists also accelerate apoptosis in mature osteoclasts through the induction of caspase-3 and caspase-9 activity and Bcl-2 interacting mediator of cell death expression (110).…”