Flammier S, Peyruchaud O, Bourguillault F, et al. - Autotaxin (ATX, a secreted enzyme produced by several tissues, such as the brain, liver, and adipose tissue) was targeted by inhibitory treatment with pharmacologic drugs and also by conditional inactivation of the ATX gene Ennp2 in murine osteoclast (OC) in order to explicate that OCs produce functionally active ATX in murine arthritis, illustrate that blocking ATX inhibits systemic bone loss and bone erosion under inflammatory conditions accompanying murine RA, without conflicting with physiologic noninflammatory bone remodeling and give evidence that OC- derived ATX is a principal regulator whose inhibition uncouples inflammation from bone resorption. ATX was overexpressed by OCs seen at sites of inflammation. In human tumor necrosis factor–transgenic (hTNF^+/−) mice, pharmacologic inhibition of ATX, as contrasted to vehicle-treated controls, markedly decreased focal bone erosion and systemic bone loss, without affecting synovial inflammation. In OC bone resorptive activity, OC-derived ATX was shown to be instrumental and was up-regulated by the inflammation evoked in the presence of TNF or lipopolysaccharide (LPS). In OCs from mice subjected to ovariectomy, specific loss of ATX considerably guarded against the systemic bone loss and erosion that had been provoked with LPS and K/BxN serum treatments, without conferring bone-protective properties. In conclusion, these outcomes recognize ATX as a novel OC factor that precisely controls inflammation-induced bone erosions and systemic bone loss. Moreover, for potentially inhibiting bone erosion in individuals with RA, ATX inhibition proposes a novel therapeutic strategy.