Apoptotic signaling in methylglyoxal-treated human osteoblasts involves oxidative stress, c-Jun N-terminal kinase, caspase-3, and p21-activated kinase 2.
Methylglyoxal (MG) is a reactive dicarbonyl compound endogenously produced mainly from glycolytic intermediates. MG is cytotoxic through induction of cell death, and elevated MG levels in diabetes patients are believed to contribute to diabetic complications. In this report, we show for the first time that MG treatment triggers apoptosis in human osteoblasts. We further show that MG-induced apoptosis of osteoblasts involves specific apoptotic biochemical changes, including oxidative stress, c-Jun N-terminal kinase (JNK) activation, mitochondrial membrane potential changes, cytochrome C release, increased Bax/Bcl-2 protein ratios, and activation of caspases (caspase-9, caspase-3) and p21-activated protein kinase 2 (PAK2). Treatment of osteoblasts with SP600125, a JNK-specific inhibitor, led to a reduction in MG-induced apoptosis and decreased activation of caspase-3 and PAK2, indicating that JNK activity is upstream of these events. Experiments using anti-sense oligonucleotides against PAK2 further showed that PAK2 activation is required for MG-induced apoptosis in osteoblasts. Interestingly, we also found that MG treatment triggered nuclear translocation of NF-kappaB, although the precise regulatory role of NF-kappaB activation in MG-induced apoptosis remains unclear. Lastly, we examined the effect of MG on osteoblasts in vivo, and found that exposure of rats to dietary water containing 100-200 microM MG caused bone mineral density (BMD) loss. Collectively, these results reveal for the first time that MG treatment triggers apoptosis in osteoblasts via specific apoptotic signaling, and causes BMD loss in vivo.
Chan
Wen-Hsiung
WH
Department of Bioscience Technology and Center for Nanotechnology, Chung Yuan Christian University, Chung Li, Taiwan. whchan@cycu.edu.tw
Wu
Hsin-Jung
HJ
Shiao
Nion-Heng
NH
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015519:Bone Density / Q000187:drug effects; D053148:Caspase 3 / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006801:Humans; D015151:Immunoblotting; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000235:genetics; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011765:Pyruvaldehyde / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection; D054462:p21-Activated Kinases
D016328:NF-kappa B; D016376:Oligonucleotides, Antisense; D017382:Reactive Oxygen Species; D011765:Pyruvaldehyde; C515907:PAK2 protein, human; C515910:Pak2 protein, rat; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D053148:Caspase 3; D053453:Caspase 9