Objective: The study was performed to investigate bone deteriorations and the molecular responses of bone to early estrogen deficiency induced by ovariectomy (OVX) in rats.
Methods: The female rats were subjected to OVX (4 or 8 week) and sham (4 or 8 week) operation. All rats were killed 4 week or 8 week after the surgical operation. The biomarkers in serum and urine were measured. Hematoxylin & Eosin and tartate-resistant acid phosphatase staining were performed on paraffin-embedded bone sections. Expression of genes and proteins were analyzed by reverse transcription polymerase chain reaction and western blotting respectively.
Results: The OVX rats showed the decreased level of serum Ca and the increased level of urinary Ca excretion at 8 week post-OVX. The level of PTH and TRACP-5b increased at 4 and 8 week post-OVX. At both 4 and 8 week, FGF-23 was significantly lower in OVX rats than sham rats. The H&E staining showed remarkable bone abnormalities, including increased disconnections and separation of trabecular bone network in proximal metaphysis of tibia at OVX (4 and 8 week) group. In addition, the mRNA expression ratio of OPG/RANKL was reduced in the proximal tibia. The mRNA expression of MMP-9, CAII, EphA2 and ephrinA2, and the protein expression of EphA2 and ephrinA2 were markedly up-regulated in the proximal tibia. Moreover, the mRNA expression of TGF-β, EphB4 and ephrinB2, and the protein expression of EphB4 and ephrinB2 were down-regulated in proximal metaphysis of tibia at OVX group.
Conclusions: The endogenous estrogen deficiency was detrimental to bone, and the underlying mechanism was mediated, at least partially, through the local bone Eph/ephrin signaling pathway.
Keywords: Eph/ephrin; OVX; bone.