[Regulation of hypoxia inducible factor-1alpha on osteoblast function in osteogenesis]

Abstract

Objective: To explore the regulation of hypoxia inducible factor-1alpha (HIF-1alpha) on osteoblast function in osteogenesis.

Methods: Skull-cap bone of HIF-1alpha Loxp/Loxp and VHL Loxp/Loxp C57/BL6 mice were taken out and cultured so as to obtain osteoblasts which were infected with the recombinant adenovirus Ad-Cre so as to conditionally knock out the HIF-1alpha gene and its up-stream gene for von Hippel-Lindau disease (VHL) using Cre-Loxp recombinase technique. Then the osteoblasts were cultured under 2% O2 for 48 hours. Real-time PCR and Western-blotting were used to detect the mRNA and protein expression of vascular endothelial growth factor (VEGF), core binding factor al (RunX2), alkaline phosphatase (ALP) and osteocalcin (OC). Transgenic FVB mice mated with C57/BL6 mice with both HIF-1alpha and VHL alleles to obtain the mice with the osteoblasts with the HIF-1alpha and VHL genes conditionally knocked-out. At the age of 3 months the distal femurs of HIF-1alpha/VHL conditionally knocked-out mice and wild type mice were obtained to undergo hematoxylin-eosin staining and micro-CT to evaluate the bone histomorphometry and bone mineral density (BMD).

Results: The mRNA and protein expressions of VEGF, RunX2, ALP, and OC of the HIF-1alpha conditionally knocked-out osteoblasts were all decreased and the mRNA and protein expressions of VEGF, RunX2, ALP, and OC of the VHL conditionally knocked-out osteoblasts were all increased. The values of bone histomorphometry and bone mineral density (BMD) of the HIF-1alpha conditionally knocked-out mice were both significantly lower than those of the wild-type mice, whereas the values of bone histomorphometry and BMD of the VHL conditionally knocked-out mice were both significantly higher than those of the wild-type mice (all P < 0.01).

Conclusion: Under both the physiological and pathological hypoxia environment in bone tissues HIF-1alpha can promote the bone formation ability of osteoblast.