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ARS Home » Plains Area » Grand Forks, North Dakota » Grand Forks Human Nutrition Research Center » Healthy Body Weight Research » Research » Publications at this Location » Publication #232901
Title: High-fat Diet Decreases Cancellous Bone Mass But Has No Effect on Cortical Bone Mass in the Tibia in Mice

Author
item Cao, Jay
item Gregoire, Brian
item GAO, HONGWEI - UNIV OF NORTH DAKOTA

Submitted to: Bone
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2009
Publication Date: 6/1/2009
Citation: Cao, J.J., Gregoire, B.R., Gao, H. 2009. High-fat Diet Decreases Cancellous Bone Mass But Has No Effect on Cortical Bone Mass in the Tibia in Mice. Bone. 44:1097-1104.

Interpretive Summary: Obesity has been thought advantageous to bone and a protective factor for osteoporosis in humans despite being a risk factor for many chronic health disorders. While body mass has positive effect on bone mineral density and the strength, whether obesity or fat mass, in particular, is beneficial to bone and the mechanism by which obesity affects bone metabolism have not been established. To examine the effects of obesity on bone structure and osteoblast function, we measured bone structure with micro-computed tomography in mice fed either a control diet (10 kcal% energy as fat) or high-fat diet (HFD, 45 kcal% energy as fat) for 14 weeks. We also cultured bone marrow stromal/osteoblastic cells (BMSCs) for up to 28 days and measured osteoprogenitor activity and mineralization as well as the expression of key osteoblast factors. Our data showed that mice fed HFD were 31% heavier than those fed control diet. There were more alkaline phosphatase positive colony forming units at d 14 and calcium nodules at d 28 of culture by BMSCs from HFD mice than from control mice. The ratio of RANKL to OPG expression in HFD animals was higher than in control diet animals. Compared with control mice, tibial trabecular bone volume/total volume was reduced, and trabecular separation was increased in HFD mice. Trabecular number was lower and connectivity density tended to be less (P = 0.07) in HFD mice than in control mice. In summary, our results suggest that obesity induced by high-fat diet reduces bone mass. The changes are accompanied by altered expression of RANKL in osteoblasts. High-fat diet may alter the balance of bone modeling/remodeling process in favor of bone resorption.

Technical Abstract: Introduction: Body mass has a positive effect on bone mineral density and the strength. Whether mass derived from an obesity condition is beneficial to bone has not been established; neither have the mechanism by which obesity affects bone metabolism. The aim of this study was to examine the effects of obesity on bone structure and osteoblastic expression of key markers involved in bone formation and resorption in a diet-induced obesity mouse model. Materials and Methods: Six-week-old male C57BL/6 mice (n = 21) were randomly assigned to two groups and fed either a control (10 kcal% energy as fat) or high-fat diet (HFD, 45 kcal% energy as fat) for 14 weeks. Bone marrow stromal/osteoblastic cells (BMSC) were cultured for up to 28 days. Osteoprogenitor activity [alkaline phosphatase (ALP) positive colonies] and mineralization (calcium nodule formation) were determined. Expression of key osteoblast factors [ALP, alpha collagen (COLL), osteocalcin (OC), RANKL, OPG, M-CSF)] were measured using quantitative real-time PCR (qPCR). Bone structure of proximal and mid-shaft of tibia was evaluated by micro-computed tomography. Results: Mice fed HFD were 31% heavier (P < 0.01) than those fed control diet, 41 ± 2 vs. 31 ± 1 g, respectively. There were more alkaline phosphatase (ALP) positive colony forming units (CFU-ALP+) at d 14 and calcium nodules at d 28 of culture by BMSC from HFD mice than from control mice (P < 0.01). ALP and RANKL mRNA levels in BMSC from HFD were higher (P < 0.05) than from control mice. The ratio of RANKL to OPG expression in HFD animals was higher (P < 0.01) than in control diet animals. There were no significant differences in tibial fat-free weight, length, and mid-shaft diameter between the two groups. Furthermore, measurements of tibial mid-shaft of HFD mice (total bone area, cortical thickness, bone area, and medullary area) did not show difference from those of control mice. Compared with control mice, tibial trabecular bone volume/total volume was reduced, and trabecular separation was increased in HFD mice. Trabecular number was lower (P < 0.05) and connectivity density tended to be less (P = 0.07) in HFD mice than in control mice. Conclusions: Our data suggest that obesity induced by high-fat diet reduces bone mass by decreasing trabecular number and increasing trabecular separation. The changes are accompanied by altered expression of RANKL in osteoblasts. High-fat diet may alter the balance of bone modeling/remodeling process in favor of resorptive processes that mitigate the positive effect that increased body weight has on bone formation.