A Systems Genetics Approach to Fracture Healing

Phosphate is essential for healthy bone growth and plays an essential role in fracture repair. Although phosphate deficiency has been shown to impair fracture healing, the mechanisms involved in impaired healing are unknown. More recently, studies have shown that the effect of phosphate deficiency on the repair process varied based on the genetic strain of mice, which is not characterized. We used data from microarrays to (1) determine the effects of phosphate restriction on the biologic functions identified from the gene expression in fracture calluses; and (2) examine whether there are genetic differences within the primary biologic functions. Closed stabilized fractures were generated in the femora of three strains of male mice: A/J (AJ), C57BL/6J (B6), and C3H/HeJ (C3) (age: 8- to 12-weeks) (Gerstenfeld LC et al. J Histochem Cytochem, 2006;54(11):1215-28). Phosphate deficiency (Pi) was initiated 2 days prior to fracture and was maintained for 15 days by supplying the mice with a low phosphate diet (Harlan Laboratories, Madison, WI). Phosphate was then replenished and bone healing was allowed to continue until 35 days. For the three strains of mice, control groups were included where the mice were given normal diet throughout the study. The fracture calluses were harvested at various time-points: 3, 5, 7, 10, 14, 18, 21, 28, and 35 post-operative days (n=6 per time-point for each mouse strain and diet condition).