Myeloid-Specific Deletion of Lnx2 Attenuates Estrogen-Deficiency-Induced Bone Loss by Inhibiting Osteoclastogenesis via the NUMB/NOTCH2 Axis

Background: We previously reported that knocking down the ubiquitin E3 ligase LNX2 in bone marrow monocytes by shRNAs attenuated osteoclastogenesis in vitro. However, the role of LNX2 in the regulation of osteoclasts and bone homeostasis in vivo remains unknown. Methods: In this study, we generated myeloid Lnx2 conditional knockout mice by crossing Lnx2-flox mice with LysM-Cre mice. The role of LNX2 was verified through in vitro osteoclast induction experiments using mononuclear macrophages and experiments on estrogen-deficient osteoporosis models. Results: Micro-CT and histological analysis unveiled that loss of Lnx2 in osteoclast precursor cells decreased osteoclast numbers and increased trabecular bone mass in mice. Moreover, Lnx2 deficiency prevented bone loss in an ovariectomized mouse model of postmenopausal osteoporosis. In vitro mechanistic studies identified that the loss of Lnx2 had little effect on cell proliferation but significantly inhibited the formation of osteoclasts and bone resorption. Furthermore, the deletion of Lnx2 decreased the expression of NOTCH2 and its downstream HES1 via enhancing the level of the NOTCH2 inhibitor, NUMB. Conclusions: Our findings elucidate an important role of Lnx2 in the regulation of osteoclasts and bone metabolism and indicate that Lnx2 is a potential therapeutic target for the treatment of osteoporosis.