Journal
JOURNAL OF BONE AND MINERAL RESEARCH
Volume 21, Issue 7, Pages 1068-1074Publisher
WILEY
DOI: 10.1359/JBMR.060402
Keywords
mouse; ovariectomy; estrogen depletion; transgenic; knockout; bone histomorphometry
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Introduction: The ovariectomized (OVX) rat is the most widely used preclinical rodent model for postmenopausal osteoporosis. However, the underlying mechanisms of bone disorders, including osteoporosis, have been explored predominantly in the mouse. The purpose of this study was to evaluate mice (129P3 and C5713L/6 inbred strains and their F-2 hybrid offspring, B6129PF2), commonly used for gene knockout and overexpression studies, for their potential as preclinical models of postmenopausal bone loss. Materials and Methods: The mice were OVX or sham-operated at 4 months of age and killed at 1 or 3 months after surgery. Lumbar vertebrae and distal femora were subjected to histomorphometric assessment. Results: Mice in the two strains and the F-2 hybrids (will be referred to as strain for the remainder of the abstract) lost vertebral cancellous bone after OVX; bone volume (BV/TV) was 20% and 27% lower at 1 and 3 months after surgery, respectively. The decreased cancellous BV/TV was associated with an increase in osteoclast surface at I month after OVX in the 129P3 strain only. Osteoblast surface was increased by 20% with OVX at both 1 and 3 months after surgery, irrespective of mouse strain. However, bone formation rate was not altered by OVX in any of the mouse strains. In contrast to the lumbar vertebrae, cancellous bone loss in response to OVX differed in the distal femur among the three mouse strains. OVX had no significant effect on distal femur BV/TV in the B6129PF2 mouse strain. In the C57BL/6 strain, cancellous BV/TV was reduced by OVX at I month after surgery but not at 3 months after surgery, whereas distal femur BV/TV in 129P3 mice was reduced at 3 months after surgery. Osteoclast surface was not affected by OVX at either time-point in the C5713L/6 strain, but was increased by 116% at I month after surgery in the 129P3 strain. Osteoblast surface was increased with OVX at 1 month after surgery, irrespective of strain, whereas bone formation rate was not altered by OVX at either time-point in any of the strains. Conclusions: The magnitude of cancellous bone loss and cellular indices of increased bone turnover in response to OVX varied with mouse strain and skeletal site, but in general, were less pronounced and less consistent than in the Sprague-Dawley rat. Although mouse models will continue to provide insights into genetic influences on bone mass and turnover, caution should be exercised when using 129P3 and C5713L/6 mice, and their F-2 hybrids, as models for postmenopausal bone loss and preclinical testing of potential therapies for osteoporosis.
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