Juvenile mice exhibit inverse catch‐up growth but retain disorganized growth plates following a high‐fat to low‐fat diet intervention
Authors: Machnicki Allison L. , White Cassaundra A. , Serrat Maria A. 
Published: May 2022

Obesity can negatively impact the skeleton. We previously reported that a high‐fat diet causes rapid and dysregulated bone elongation. Our goal was to determine whether a diet intervention could mitigate or even reverse some of these effects on skeletal growth plates. We tested theHYPOTHESISthat rapid and dysregulated growth caused by a high‐fat diet will be mitigated by a low‐fat diet intervention. We expected to see a reduction in growth rate and changes in growth plate morphology that matched controls after switching to a low‐fat diet.METHODS3‐week old C57BL/6 mice (N=96 mixed sex) were fed control (10% kcal fat) or high‐fat (60% kcal fat) diets for one week. Some high‐fat diet mice were switched to control diet and examined at 5‐, 6‐, and 8‐weeks age (at least N=5/diet/age). Sex by diet interactions were tested at 5‐weeks. Body mass was recorded. Tibial elongation rate was measured from oxytetracycline labeled (7.5 mg/kg IP) slab sections. Growth plate height and columnar orientation (angle of proliferative column relative to long axis) were quantified in ImageJ. Statistical significance (p<0.05) was determined in SPSS by ANOVA with post‐hoc tests.RESULTSThere were no sex by diet interactions, so females were analyzed separately to discriminate diet effects. High‐fat and intervention groups were both heavier than controls at 4‐weeks before the intervention (F=7.7, p<.001). Body mass declined sharply after the diet switch and intervention mice were similar to controls at 5‐, 6‐, and 8‐weeks, while high‐fat diet mice remained heavier (p<0.001). Tibial elongation rate was faster in high‐fat diet mice (F=12.2, p<0.001), but slower in the intervention group compared to controls at both 5‐ (p<.001) and 6‐weeks age (p<0.01). Relative to controls, the most significant changes in growth plate height (F=10.7, p<0.001) were enlarged growth plates in high‐fat diet mice at 5‐weeks (p<0.001) and smaller growth plates in intervention mice at 6‐weeks (p=0.003). Chondrocyte columns in controls aligned within 2 degrees of the long axis at 5 weeks, while columns in both high‐fat and intervention mice deviated over 10 degrees (F=17.3, p<0.001). Columns remained disorganized in high‐fat and intervention groups at 6‐ and 8‐weeks (p<0.01).DISCUSSIONAfter switching from high‐ to low‐fat diet, intervention mice exhibited a rapid decrease in body mass, tibial elongation rate, and growth plate height. While we hypothesized that diet intervention would attenuate these to control levels, we surprisingly found that tibial elongation rate in the intervention group was actually slower than that of controls, resembling “inverse catch‐up growth” to achieve a potential target growth rate. However, chondrocyte columns remained disorganized, suggesting a possible lasting consequence of high‐fat diet.SIGNIFICANCEThese results demonstrate that the skeleton is exquisitely sensitive to diet in the earliest stages of postnatal bone elongation and are relevant for establishing interventions to prevent childhood obesity and its negative effects on bone structure.