HIF-1-mediated expression of Foxo1 serves an important role in the proliferation and apoptosis of osteoblasts derived from children's iliac cancellous bone

摘要

Activation of the transcription factor hypoxia inducible factor-1 alpha (HIF-1 alpha) is considered critical for the stimulation of osteogenic markers including runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP) and osteocalcin, which are closely associated with forkhead boxclass O1 (Foxo1) levels in osteoblasts. The present study explored the associations between HIF-1 alpha and Foxo1 in the regulation of cell viability, proliferation and apoptosis of osteoblasts. Osteoblasts obtained from children's iliac cancellous bone were used in the present study, which were confirmed by immunofluorescence staining for the osteoblast marker osteocalcin. The results revealed that the levels of reactive oxygen species and apoptosis were markedly increased in cells with knockdown of HIF-1 alpha. By contrast, these were reduced in response to overexpressed HIF-1 alpha. In addition, HIF-1 alpha overexpression significantly stimulated cell viability, which was suppressed by silencing HIF-1 alpha. HIF-1 alpha overexpression also significantly increased the transcriptional and translational levels of Foxo1. Conversely, silencing HIF-1 markedly suppressed the expression levels of Foxo1. Furthermore, silencing HIF-1 alpha reduced the expression of osteogenic markers, including Runx2, ALP and osteocalcin. Runx2 and ALP expression induced by HIF1 alpha were markedly reversed by Foxo1 small interfering (si)RNA, whereas osteocalcin was not significantly affected by Foxo1 siRNA. Therefore, the cooperation of and interactions between HIF-1 alpha and Foxo1 may be involved in the regulation of osteoblast markers, and serve a pivotal role in the proliferation and apoptosis of osteoblast. The HIF1 alpha-induced expression of Runx2 and ALP may be completely dependent on the expression levels of Foxo1, and in turn, osteocalcin may be partially dependent on Foxo1 expression.