Objective: To explore the expression pattern and effects of hypoxia inducible factor-1alpha (HIF-1alpha) in the fetal vertebra development.
Methods: Fetuses at different developmental stages were obtained from C57BL6 mice. The vertebrae of the fetuses were isolated and the development of vertebra was observed by stereoscopic and light microscope. The mRNA expression of HIF-1alpha at different time points was detected by using reverse transcription-polymerase chain reaction (RT-PCR) and the protein expression of HIF-1alpha was detected by immunohistochemistry. RT-PCR was used to detect the mRNA expression the gene of vascular endothelia growth factor (VEGF), the Col2a1, gene for the chondroblast marker collagen type 2, and the gene of the osteoblast marker, osteocalcin (OCN).
Results: The cartilaginous spine column began to form at E13.5. The primary ossification center was observed at E15.5, and then the osteogenesis expanded and extended to both sides. HIF-1alpha mRNA began to express at E13.5, and more significantly at E14.5 (P < 0.05), then decreased. The VEGF mRNA was expressed coincidently with HIF-1alpha. while the HIF-1alpha protein expression was observed at E14.5 and lasted a little longer till the time when the fetus was to be born. The Col2a1 mRNA expression was high at E13.3 - E15.5 and decreased at e16.5 - E18.5, however, the OCN mRNA expression was low at E13.5 - E15.5 and became high at E16.5 - 18.5.
Conclusion: The vertebra development pattern appears to be an endochondral osteogenesis process. There exists a hypoxia microenvironment in the vertebra that may increase the mRNA and protein expression of HIF1alpha and the expression of VEGF, its downstream gene. It shows that HIF1alpha activates the downstream genes and initiates the cascade of endochondral osteogenesis.