WHI-131 Promotes Osteoblast Differentiation and Prevents Osteoclast Formation and Resorption in Mice

The small molecule WHI-131 is a potent therapeutic agent with anti-inflammatory, antiallergic, and antileukemic potential. However, the regulatory effects of WHI-131 on osteoblast and osteoclast activity are unclear. We examined the effects of WHI-131 on osteoblast and osteoclast differentiation with respect to bone remodeling. The production of receptor activator of nuclear factor kappa-B ligand (RANKL) by osteoblasts in response to interleukin (IL)-1 or IL-6 stimulation decreased by 56.8% or 50.58%, respectively, in the presence of WHI-131. WHI-131 also abrogated the formation of mature osteoclasts induced by IL-1 or IL-6 stimulation. Moreover, WHI-131 treatment decreased RANKL-induced osteoclast differentiation of bone marrow-derived macrophages, and reduced the resorbing activity of mature osteoclasts. WHI-131 further decreased the mRNA and protein expression levels of c-Fos and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) by almost twofold, and significantly downregulated the mRNA expression of the following genes: tartrate-resistant acid phosphatase (TRAP), osteoclast-associated receptor (OSCAR), DC-STAMP, OC-STAMP, ATP6v0d2, and cathepsin K (CtsK) compared with the control group. WHI-131 further suppressed the phosphorylation of protein kinase B (Akt) and degradation of inhibitor of kappa B (IκB); Ca(2+) oscillation was also affected, and phosphorylation of the C-terminal Src kinase (c-Src)-Bruton agammaglobulinemia tyrosine kinase (Btk)-phospholipase C gamma 2 (PLCγ2) (c-Src-Btk-PLCg2 calcium signaling pathway) was inhibited following WHI-131 treatment. The Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway was activated by WHI-131, accompanied by phosphorylation of STAT3 Ser727 and dephosphorylation of STAT6. In osteoblasts, WHI-131 caused an approximately fourfold increase in alkaline phosphatase activity and Alizarin Red staining intensity. Treatment with WHI-131 increased the mRNA expression levels of genes related to osteoblast differentiation, and induced the phosphorylation of Akt, p38, and Smad1/5/8. Furthermore, 5-week-old ICR mice treated with WHI-131 exhibited antiresorbing effects in a lipopolysaccharide-induced calvaria bone loss model in vivo and increased bone-forming activity in a calvarial bone formation model. Therefore, the results of this study show that WHI-131 plays a dual role by inhibiting osteoclast differentiation and promoting osteoblast differentiation. Thus, WHI-131 could be a useful pharmacological agent to treat osteoporosis by promoting bone growth and inhibiting resorption.