Hypoxia-mediated mitochondrial stress in RAW264.7 cells induces osteoclast-like TRAP-positive cells.
Previously we showed that mitochondrial dysfunction induced by mitochondrial DNA depletion or treatment with electron transport chain inhibitors triggers a stress signaling involving activation of calcineurin and Ca2+-responsive factors. In this study we show that exposure of RAW 264.7 cells to hypoxia, causing increased reactive oxygen species (ROS) production and disruption of mitochondrial transmembrane potential, also induced a similar stress signaling. Hypoxia caused increased [Ca2+]c, activation of cytosolic calcineurin and induced expression of Ryanodine Receptor 2 (RyR2) gene. Prolonged hypoxia (5% O2 for 5-6 days) also induced the expression of calcitonin receptor at high levels, and those of cathepsin K, and tartarate-resistant alkaline phosphatase (TRAP) at low-moderate levels in macrophage cells. Addition of RANKL had an additive effect suggesting different mechanisms of activation. Consistent with this possibility, prolonged hypoxia induced the formation of TRAP-positive osteoclast-like cells suggesting the occurrence of an autocrine mechanism for osteoclastogenesis.
Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA.
Satish
S
Srinivasan
Narayan G
NG
Avadhani
D000135:Acid Phosphatase / Q000378:metabolism; D000818:Animals; D019703:Calcineurin / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D056657:Cathepsin K; D002403:Cathepsins / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D005786:Gene Expression Regulation; D000860:Hypoxia; D007527:Isoenzymes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008564:Membrane Potentials; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D010010:Osteoclasts / Q000378:metabolism*; D015398:Signal Transduction; D000071681:Tartrate-Resistant Acid Phosphatase
D007527:Isoenzymes; D019703:Calcineurin; D000135:Acid Phosphatase; C000605511:Acp5 protein, mouse; D000071681:Tartrate-Resistant Acid Phosphatase; D002403:Cathepsins; D056657:Cathepsin K; C534132:Ctsk protein, mouse; D002118:Calcium