The Novel P38 Inhibitor,pamapimod,inhibits Osteoclastogenesis And Counteracts Estrogen-Dependent Bone Loss In Mice

Objective:Pamapimod(PAM)is a novel selective p38 mitogen-activated protein(MAP)kinases inhibitor proved to be effective in rheumatoid arthritis in phase ? clinical trial.Here,we explored its effect on osteoclast-associated osteoporosis and the underlying mechanisms.Methods:Tartrate-resistant acid phosphatase(TRAP)staining was used to evaluate the formation of osteoclasts.Resorption pit assay was done to examine osteoclast bone resorption capacity.Immunofluorescence was done to observe the location of associated proteins.Quantitative-PCR and Western blot detected mRNA and protein levels respectively.Small interfering RNA was used for gene-silencing.Chromatin imnunoprecipitation assay was used to detect the interaction between transcription factors and DNA in the cell.An ovariectomy(OVX)induced osteoporosis mouse model was established to investigate the effects of PAM.Results:PAM suppressed receptor activator of nuclear factor-?B ligand(RANKL)-induced osteoclast formation via inhibition of p38 phosphorylation and subsequent c-Fos and nuclear factor of activated T cells cl(NFATcl)expression.The expression of osteoclast-related genes,c-Fos,NFATcl,CTSK and TRAP were also downregulated.In addition,the downregulated NFATcl leads to reduced expression of its targeting gene disintegrin and metalloproteinase domain-containing protein 12(ADAM 12),which was further proved to be critical for osteoclastic bone resorption.OVX mice treated with PAM revealed a protective effect of PAM on osteoporosis in vivo.Conclusion:PAM can prevent OVX induced bone loss through suppression of p38/NFATcl induced osteoclast formation and NFATcl/ADAM12 associated bone resorption.