High-fat diets adversely affect bone strength in mice while simultaneously increasing systemic glucocorticoid levels. We hypothesise that a mechanistic link exists between high-fat intake, increased glucocorticoid signalling in osteoblasts and poor bone health. We tested this hypothesis in a transgenic (tg) mouse model in which glucocorticoid signalling has been selectively disrupted in osteoblasts/osteocytes via targeted overexpression of the glucocorticoid-inactivating enzyme, 11β-hydroxysteroid dehydrogenase type 2. Seven-week-old male tg mice and their wild type (WT) littermates (n=6-9/group) were fed ad libitum a control diet (14.3% energy from fat, 25.5% from protein) or an isoenergetic high-fat diet (HFD; 43.0% energy from fat, 25.5% from protein) for 18 weeks. Body weight and food intake were measured weekly. Serum corticosterone levels were quantified after 10 weeks of feeding, and body composition and bone parameters were assessed at endpoint.
As animals were fed an isoenergetic diet, changes in body weight and body composition did not differ between the four groups. Both WT and tg mice fed the HFD had higher serum corticosterone levels than WT or tg control mice (pooled measures: 386±35nM for HFD vs. 285±36nM for control diet; p=0.054). Corticosterone levels in WT and tg mice fed the same diets (either HFD or control) were similar. At endpoint, WT mice fed a HFD had significantly lower BMD than both WT mice receiving the control diet (0.058±0.001g/cm2 vs. 0.064± 0.0007g/cm2; p<0.005) and tg animals fed the HFD (0.058±0.001g/cm2 vs. 0.063±0.001g/cm2; p<0.005). Similarly, WT mice on HFD exhibited lower BMC than WT control mice (0.64±0.02g vs. 0.74±0.02g; p<0.005) and tg mice receiving the HFD (0.64±0.02g vs. 0.72±0.02g; p<0.005). Neither BMD nor BMC differed significantly between tg control and tg HFD mice.
We conclude that high dietary fat intake negatively affects bone mass via glucocorticoid signalling in osteoblasts and osteocytes.