Location: Arkansas Children's Nutrition CenterTitle: Impairment of osteoclastic bone resorption in rapidly growing female p47phox knockout mice Author
Submitted to: Journal of Bone and Mineral Research
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/2012
Publication Date: 1/10/2013
Citation: Chen, J., Mercer, K., Lazarendo, O.P., Badger, T.M., Ronis, M.J. 2013. Impairment of osteoclastic bone resorption in rapidly growing female p47phox knockout mice [abstract]. Journal of Bone and Mineral Research. 27(Issue Supplement 1):http://www.asbmr.org/Meetings/PastAnnualMeetings.aspx. Interpretive Summary: There are two types of cells in the bone, one is called osteoblasts which are responsible to build new bone, and the other one is called osteoclasts which are responsible for removing old bones. This bone building and removing process needs to be well balanced to keep the wealth of bone. Osteoblast cell activity is controlled by variety of genes. One such gene we have previously thought is nicotinamide adenine dinucleotide phosphate-oxidase (Nox). This gene also controls synthesizing reactive oxygen species (ROS), and ROS has been suggested to inhibit bone building. In this report, we have utilized a mouse model in which the majority of Nox genes were removed. We found that, in female Nox gene removed mice at 6 weeks of age, bone mineral density and bone mineral content were higher in comparison to wild type controls (P< 0.05). Consistent with this, bone strength (resistant to bone fracture) was found to be higher in femur from Nox gene removed mice, compared with those from wild type controls (P<0.05). Osteoclast cell number was lower in Nox gene removed mice compared with their wild type controls (P<0.05). These data indicate that the high bone mass in 6 week old female Nox removed mice is due to lower ROS generation leading to decreased osteoclast formation.
Technical Abstract: Bone formation is dependent on the activity and differentiation of osteoblasts; whereas resorption of preexisting mineralized bone matrix by osteoclasts is necessary not only for bone development but also for regeneration and remodeling. Bone remodeling is a process in which osteoblasts and osteoclasts are coupled. It changes dramatically during the course of development as it undergoes age-dependent regulation. Accumulation of reactive oxygen species (ROS) has been suggested to inhibit bone remodeling at each life stage. Tightly controlled and cell-specific NADPH-oxidase (Nox) activities represent one of the major sources of ROS in many cell types. Here, we have utilized a p47phox knockout mouse model in which the majority of Nox activity is lost as the result of loss of an essential cytosolic co-activator, and characterized bone phenotype in these mice compared to their wild type controls. We found that, in female p47phox -/- mice at 6 weeks of age, bone mineral density and bone mineral content were higher in comparison to wild type controls (P< 0.05). Consistent with this, bone strength was found to be higher in femur from p47phox - /- mice, compared with those from wild type controls, in three point bending tests (P<0.05). Flow cytometric analysis showed that osteoblastic calvarial cells isolated from female p47phox - /- mice had significantly lower levels of ROS. Furthermore, bone histomorphometric analysis revealed that osteoclast number was lower in p47phox - /- mice compared with their wild type controls (P<0.05). This is in agreement with reduced gene expression of bone resorption markers RANKL and TRAP in RNA isolated from both femur and bone marrow cells from female p47phox - /- mice compared to their wild type controls (P<0.05). Moreover, in ex vivo primary osteoblast and osteoclast precursor co-culture, TRAPase staining revealed lower numbers of mature osteoclasts (containing 3 or more nuclei) in wild type primary osteoblasts plus p47phox - /- pre-osteoclast cultures compared with wild type primary osteoblasts plus wild type pre-osteoclast cultures. These data indicate that the high bone mass in 6-week-old female p47phox - /- mice is due to lower ROS generation leading to decreased osteoclastogenesis.