Analysis of mechanism of the bone complication in diabetes mellitus by reactivation of the gene expression through oxidative stress

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To elucidate the mechanism of diabetic bone complication, we focused on the oxidative stress and performed in vitro studies by using mouse bone marrow stromal cell line. Oxidative stress induced by methylglyoxal (MG) treatment upregulated secreted Frizzled-related protein 4 (sFRP-4) gene expression as well that of osteoclast differentiating factor (RANKL) gene while MG treatment suppressed the expression of Osteoprotegerin (OPG, a RANKL antagonist) gene in reciprocal manner. Furthermore we observed oxidative stress suppressed Wnt/ β -catenin signal transduction pathway. In the analysis of sFRP-4 gene promoter region, we found highly methylated two-tandem cytosine-guanine sequences (CpGs) at 5 bases upstream of TATA-box following to downregulation of sFRP-4 gene transcription through methylcytosine binding protein 2 (MeCP2) recruitment. We observed enhanced adhesion of TATA-box binding protein (TBP) to TATA-box under the condition of oxidative stress. These findings elucidated a part of the mechanisms of restoration in sFRP-4 gene expression induced by oxidative stress. We next designed in vivo studies, in which we histomorphologically compared long bones obtained from drug-induced diabetic mice and healthy mice, and we observed reduction of trabecular bones in diabetic mouse femur. Moreover, we originally established sFRP-4 knock-out mice and observed that this animal was resistant to osteopenia due to senescence in natural course. These studies suggest that acute oxidative stress promotes bone resorption through RANKL signaling whereas, in mild and persistent oxidative stress as senescence, sFPR-4 represses turnover of bone metabolism through Wnt/ β-catenin signaling prior to the onset of osteopenia and ultimately osteoporosis