Altered expression of apoptosis-related genes in osteocytes exposed to high-dose steroid hormones and hypoxic stress.
OBJECTIVE
High-dose steroid hormones cause necrosis of the femoral head. Since steroid hormones function as blood coagulants, we hypothesized that ischemic hypoxia induced by steroid hormones is critical for apoptosis which occurs before necrosis of osteocytes.


METHODS
We performed an analysis of gene expression in the process of leading osteocytes to apoptosis, using a mouse cell line. Cultured osteocytes were loaded with hypoxic stress with or without exposure to steroid hormones, and the gene expression under these conditions was investigated using a cDNA array and real-time quantitative RT-PCR.


RESULTS
The proapoptotic p53 gene was downregulated under a hypoxic (1% O2) condition without exposure to steroid hormones. On the other hand, the expression of antiapoptotic Bcl-2 gene was increased by exposure to high-dose steroid hormones under a normoxic condition (20% O2). Interestingly, both proapoptotic (p53 and Bax) and antiapoptotic (Bcl-2 and MDM2)genes were downregulated in osteocytes treated with high-dose steroid hormones in the hypoxic environment.


CONCLUSIONS
These findings suggest that osteocytes exposed to high-dose steroid hormones appear to be more sensitive to apoptosis in the hypoxic environment than those without exposure to steroid hormones. This concept helps to understand the pathogenesis of idiopathic necrosis of the bone.
Tsuji
Muneharu
M
Department of Pathology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
Ikeda
Hitoshi
H
Ishizu
Akihiro
A
Miyatake
Yukiko
Y
Hayase
Hiroko
H
Yoshiki
Takashi
T
D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D015687:Cell Hypoxia; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D005271:Femur Head Necrosis / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects*; D020869:Gene Expression Profiling; D005938:Glucocorticoids / Q000494:pharmacology*; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D010011:Osteocytes / Q000187:drug effects* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013312:Stress, Physiological / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C494827:Bax protein, mouse; D005938:Glucocorticoids; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D003907:Dexamethasone; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2