Quantitative real-time RT-PCR determining extracellular matrix protein expression in osteogenesis imperfecta murine (oim) thoracic aortas [abstract]
Abstract
Primary components of the thoracic aorta critical for tissue integrity are collagen and elastin.
Collagen, a rod-like protein contributes to aortic strength and stiffness, while elastin, a highly
extensible protein contributes to aortic compliance. Type I collagen, the predominate collagen in
aortic tissue, is normally a heterotrimeric molecule composed of two proalpha 1(I) chains and one
proalpha 2(I) chain. The osteogenesis imperfecta murine (oim) model is an exceptional system to study
type I collagen's affect on aortic integrity because it is a functional null for the proalpha 2(I) collagen
gene, synthesizing only homotrimeric type I collagen molecules composed of three proalpha 1(I) chains.
Our biomechanical studies of oim mice demonstrate that the absence of proalpha 2(I) collagen chains
significantly reduces thoracic aortic breaking strength and stiffness. Histological analysis suggested
reduced collagen staining in oim/oim and heterozygote aortas. To further investigate the mechanism
of reduced collagen staining, HPLC analysis was done to determine total collagen and crosslinking
content. Results demonstrated a significant reduction of collagen content per tissue content and an
increase of collagen crosslinks in oim/oim and heterozygote aortas compared to wildtype. The reduced
collagen content and increased collagen crosslinks of oim/oim and heterozygote aortas prompted us to
examine the pre-translational amounts of aortic extracellular matrix protein mRNAs. We determined
the COL1A1, COL1A2, COL3A1, ELASTIN, LYSYL OXIDASE, and TUBULIN mRNA levels in thoracic aortas of
oim/oim, heterozygote, and wildtype mice at 3, 8, and 18 months of age using quantitative real-time
RT-PCR.