Influence of estrogen deficiency on guided bone augmentation: investigation of rat calvarial model and osteoblast-like MC3T3-E1 cells

The effect of estrogen deficiency in bone augmentation, and the mechanisms by which estrogen deficiency impedes osteoblast differentiation and collagen matrix production, were examined. Twenty female Jcl: Wistar rats were divided into two groups: ovariectomized rats; and control rats. Guided bone augmentation was performed by positioning plastic caps in the calvarium of all animals at 8 wk after ovariectomy or sham surgery. Micro-computed tomography and histological sections were used to determine the amount of bone augmentation within the plastic caps. At 8 wk, there was statistically significantly less newly formed bone volume in ovariectomized rats. Immunohistological staining revealed the rare alignment of runt-related transcription factor 2-positive osteoblast-like cells and collagen I-positive bundle fibers in ovariectomized rats. In cell culture experiments, pre-osteoblastlike cells, MC3T3-E1, were treated with the estrogen receptor antagonist, fulvestrant. In treated cells, alkaline phosphatase activity remained high, whereas Alizarin Red staining was completely inhibited. Extracellular staining intensity of collagen I was decreased after fulvestrant treatment. Consistent with these observations, gene-expression analysis confirmed that fulvestrant treatment led to weaker expression of mRNA for osteogenic transcription factors and bone matrix protein-related genes. The results demonstrate that estrogen deficiency suppresses osteoblast differentiation and collagen matrix production in bone augmentation.