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in response to acute disuse and oxygen
deprivation
Departments of 1 Orthopaedics and 2 Medicine, University of Cincinnati, Cincinnati, Ohio 45267
Loss of mechanical loading,
or disuse, rapidly precipitates locally mediated bone resorption.
However, the pathway by which this process is initiated and mediated is
poorly understood. In this study, we used a complementary in vivo and
in vitro approach to determine whether disuse-induced osteocyte hypoxia
resulted in upregulation of the hypoxia-dependent transcription factor HIF-1
. We found that acute disuse (1-5 days) resulted in a
significant increase in the percentage of osteocytes staining positive
for HIF-1
vs. normal bone (30.9 ± 6.1 vs. 14.1 ± 3.8%)
and that this response was uniform around the cortex. In addition, we
found that acute oxygen deprivation (4-12 h of 2% O2)
resulted in a 2.1- to 3.7-fold upregulation of HIF-1
protein
expression in MLO-Y4 osteocyte-like cells compared with cells cultured
in parallel under normal oxygen conditions. Given known HIF-1
targets genes, we suggest that osteocyte hypoxia and subsequent
upregulation of hypoxia-dependent pathways may serve to initiate and
mediate disuse-induced bone resorption.
hypoxia; bone resorption; vascular endothelial growth factor
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