Collagen (I) homotrimer potentiates the osteogenesis imperfecta (oim) mutant allele and reduces survival in male mice

The osteogenesis imperfecta murine (oim) model with solely homotrimeric (alpha 1)3 type I collagen, owing to a dysfunctional alpha 2(I) collagen chain, has a brittle bone phenotype, implying that the (alpha 1)2(alpha 2)1 heterotrimer is required for physiological bone function. Here, we comprehensively show, for the first time, that mice lacking the alpha 2(I) chain do not have impaired bone biomechanical or structural properties, unlike oim homozygous mice. However, Mendelian inheritance was affected in male mice of both lines, and male mice null for the alpha 2(I) chain exhibited age-related loss of condition. Compound heterozygotes were generated to test whether gene dosage was responsible for the less-severe phenotype of oim heterozygotes, after allelic discrimination showed that the oim mutant allele was not downregulated in heterozygotes. Compound heterozygotes had impaired bone structural properties compared to those of oim heterozygotes, albeit to a lesser extent than those of oim homozygotes. Hence, the presence of heterotrimeric type I collagen in oim heterozygotes alleviates the effect of the oim mutant allele, but a genetic interaction between homotrimeric type I collagen and the oim mutant allele leads to bone fragility.

Automated summary

The study found that mice lacking the alpha 2(I) chain do not exhibit impaired bone biomechanical or structural properties like oim homozygous mice. However, male mice from both lines were affected in terms of Mendelian inheritance, and male mice null for the alpha 2(I) chain showed age-related loss of condition. Compound heterozygotes had impaired bone structural properties compared to oim heterozygotes, but to a lesser extent than oim homozygotes, suggesting a genetic interaction between homotrimeric type I collagen and the oim mutant allele leads to bone fragility.