Nox4 expression is not required for OVX-induced osteoblast senescence and bone loss in mice

Authors: CHEN, JIN-RAN - Arkansas Children'S Nutrition Research Center (ACNC); LAZARENKO, OXANA - Arkansas Children'S Nutrition Research Center (ACNC); ZHAO, HAIJUN - Arkansas Children'S Nutrition Research Center (ACNC); WANKHADE, UMESH - Arkansas Children'S Nutrition Research Center (ACNC); PEDERSEN, KIM - Louisiana State University; WATT, JAMES - Louisiana State University; RONIS, MARTIN J.J. - Louisiana State University

Submitted to: JBMR Plus
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2020
Publication Date: 5/26/2020
Citation: Chen, J., Lazarenko, O.P., Zhao, H., Wankhade, U.D., Pedersen, K., Watt, J., Ronis, M. 2020. Nox4 expression is not required for OVX-induced osteoblast senescence and bone loss in mice. JBMR Plus. https://doi.org/10.1002/jbm4.10376.
DOI: https://doi.org/10.1002/jbm4.10376

Interpretive Summary: Estrogen is an important bone-promoting hormone, and so loss of overies (variectomy (OVX)) in female mice is a model for postmenopausal bone loss. Increased oxidative stress might be one of mechanisms for OVX-induced bone loss in both animals and humans, but further testing of this concept is needed. It is known that activation of enzymes called nicotinamide adenine dinucleotide phosphate oxidases (Nox) produce reactive oxygen species (ROS) to increase oxidative stress. By studying OVX effects in a mouse model in which the Nox4 is deleted, we investigated the role of Nox4 in OVX- induced bone loss. Six month old mice were allocated to a control group, OVX, and OVX plus estrogen treatment (8 weeks). Decreased bone mass, including bone mineral density and bone mineral content, were evident in OVX group compared with healthy control mice, and estrogen treatment completely reversed OVX-induced bone loss. Nox4 gene deletion did not prevent OVX-induced bone loss in 8 and 11 month old mice. These data suggest that Nox4-mediated ROS in bone osteoblastic cells is dispensable for sex steroid deficiency-induced bone loss. The results point to the likelihood that other Nox enzymes or mechanisms are involved in generating ROS that associate with bone loss. Future studies can test the bone effects of modifying these other pathways, and how the pathways respond to changes in diet or other interventions such as exercise.

Technical Abstract: Estrogen deficiency and aging play critical roles in the pathophysiology of bone as the result of increased oxidative stress. It has been suggested that prevention of NADPH (nicotinamide adenine dinucleotide phosphate) oxidase (Nox)-dependent accumulation of reactive oxygen species (ROS) may be an approach to potentially minimize bone loss due to these conditions. Using ovariectomized (OVX) and Nox4 gene deletion mouse models, we investigated the role of Nox4 in OVX-induced bone loss and osteoblast senescence signaling. 6 month old wild type C57Bl6 mice were allocated to a Sham control group, OVX, and OVX plus E2 treatment group for eight weeks. Decreased bone mass including bone mineral density and content were found in OVX group compared with Sham control (P<0.05), E2 treatment completely reversed OVX-induced bone loss. Interestingly, prevention of OVX-induced bone loss by E2 was associated with elimination of increased senescence signaling in bone osteoblastic cells from OVX group. E2 blunted OVX-induced p53 and p21 over-expression, but not p16 and Nox4 in bone. In addition, eight and eleven month old Nox4 knockout (KO) female mice were OVX for eight weeks. Significant bone loss and increased bone osteoblastic cell senescence signaling occurred not only in Nox4 KO OVX mice compared with Sham operated animals, but also in eleven-month-old Nox4 KO Sham mice compared to eight-month-old Nox4 KO Sham mice (P<0.05). These data suggest that Nox4-mediated ROS in bone osteoblastic cells may be dispensable for sex steroid deficiency-induced bone loss and senescence.