Dietary fluoride restriction does not alter femoral biomechanical strength in col1a2-deficient (oim) mice with type I collagen glomerulopathy

Osteogenesis imperfecta (OI) is a clinically and genetically heterogeneous disease due primarily to mutations in the type I procollagen genes, COL1A1 and COL1A2, causing bone deformity and numerous lifetime fractures. OI murine (oim) model mice carry a mutation in the col1a2 gene causing aberrant production of homotrimeric type I collagen [α1(I)₃], leading to bone fragility and glomerular accumulation of type I collagen. Previous studies demonstrated that heterozygous (+/oim) and homozygous (oim/oim) mice have elevated tibiae fluoride concentrations but reduced femoral biomechanics. However, it is unclear whether these 2 variables are causally related, because impaired renal function could reduce urinary fluoride excretion, thus elevating bone fluoride concentrations regardless of disease status. Our goal in this study was to determine whether dietary fluoride restriction would improve femoral biomechanics in oim mice. Wild-type, +/oim, and oim/oim mice were fed a control (5 mg/kg fluoride) or fluoride-restricted diet (0 mg/kg fluoride) for ∼13 wk, at which time plasma and femora were analyzed for fluoride concentrations and bone biomechanical properties. In wild-type, +/oim, and oim/oim mice, dietary fluoride restriction reduced femoral fluoride burden by 54-74%, respectively (P < 0.05), without affecting glomerular collagen deposition. Oim/oim mice fed the fluoride-restricted diet had reduced material tensile strength (P < 0.05) compared with oim/oim mice fed the control diet. However, dietary fluoride restriction did not affect stiffness or whole bone femoral breaking strength, regardless of genotype. These data suggest that oim mice have reduced bone strength due to homotrimeric type I collagen, independent of bone fluoride content.