Complex genetic regulation of bone mineral density and insulin-like growth factor-I in C57BL/6J-Chr #A/J/NaJ chromosome substitution strains.

Low bone mineral density (BMD) is a phenotype associated with osteoporosis and increased risk of fracture. Since 60-80% of variation in BMD is associated with genetic factors, we used the novel approach of chromosome substitution strains (CSS) to identify chromosomes that harbor genes that regulate BMD. Specifically, we evaluated 24 wk old C57BL/6J-Chr #(A/J)/NaJ CSS (n = 7 to 18) in which each chromosome in the host C57BL/6J strain is replaced by a corresponding chromosome from the donor A/J strain (19 autosomes, X, Y). We determined several A/J chromosomes contribute to body weight (BW), percent body fat (BF), whole body areal BMD (aBMD), and serum insulin-like growth factor (IGF)-I in both a positive and negative manner when compared with C57BL/6J. Specifically, C57BL/6J-Chr 5(A/J)/NaJ (B.A-5) (males) and B.A-13 (females) contributed to increased BW, whereas B.A-3, 4, 8, 9, 12, and 18 (males) and B.A-3, 4, and 11 (females) contributed to reduced BW. B.A-5 (males) and B.A-13 (females) contributed to increased BF, whereas B.A-12 (males) and B.A-3, 4, 10, and 11 (females) contributed to reduced BF. B.A-14 (females) contributed to increased aBMD and B.A-1, 2, 6, 9, 10, and 18 (males) and B.A-8, 9, and 10 (females) contributed to reduced aBMD. To determine if similar chromosomes regulate aBMD and IGF-I, we determined serum concentrations of IGF-I. B.A-14 and Y (males) and B.A-6 (females) contributed to increased IGF-I and male B.A-3 and female B.A-8 contributed to reduced IGF-I. Overall, we identified several sex-dependent and -independent chromosomes that regulate aBMD and IGF-I in adult mice.