title: Mechanical strain differentially regulates endothelial nitric-oxide synthase and receptor activator of nuclear kappa B ligand expression via ERK1/2 MAPK.
abstract: Exercise promotes positive bone remodeling through controlling cellular processes in bone. Nitric oxide (NO), generated from endothelial nitric-oxide synthase (eNOS), prevents resorption, whereas receptor activator of nuclear kappa B ligand (RANKL) promotes resorption through regulating osteoclast activity. Here we show that mechanical strain differentially regulates eNOS and RANKL expression from osteoprogenitor stromal cells in a magnitude-dependent fashion. Strain (0.25-2%) induction of eNOS expression was magnitude-dependent, reaching a plateau at 218 +/- 36% of control eNOS. This was accompanied by increases in eNOS protein and a doubling of NO production. Concurrently, 0.25% strain inhibited RANKL expression with increasing response up to 1% strain (44 +/- 3% of control RANKL). These differential responses to mechanical input were blocked when an ERK1/2 inhibitor was present during strain application. Inhibition of NO generation did not prevent strain-activated ERK1/2. To confirm the role of ERK1/2, cells were treated with an adenovirus encoding a constitutively activated MEK; Ad.caMEK significantly increased eNOS expression and NO production by more than 4-fold and decreased RANKL expression by half. In contrast, inhibition of strain-activated c-Jun kinase failed to prevent strain effects on either eNOS or RANKL. Our data suggest that physiologic levels of mechanical strain utilize ERK1/2 kinase to coordinately regulate eNOS and RANKL in a manner leading to positive bone remodeling.
authors.affiliation: Department of Medicine, Veterans Affairs Medical Center and Emory University School of Medicine, Atlanta, Georgia 30033, USA. jrubi02@emory.edu
authors.forename: Janet
authors.initials: J
authors.lastname: Rubin
authors.forename: Tamara C
authors.initials: TC
authors.lastname: Murphy
authors.forename: Liping
authors.initials: L
authors.lastname: Zhu
authors.forename: Eileen
authors.initials: E
authors.lastname: Roy
authors.forename: Mark S
authors.initials: MS
authors.lastname: Nanes
authors.forename: Xian
authors.initials: X
authors.lastname: Fan
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D004727:Endothelium / Q000201:enzymology*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D008024:Ligands; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000737:chemistry* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D053245:RANK Ligand; D012333:RNA, Messenger / Q000378:metabolism; D053246:Receptor Activator of Nuclear Factor-kappa B; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013314:Stress, Mechanical
chemical_list: D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D008024:Ligands; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; C505686:TNFRSF11A protein, human; C505688:TNFSF11 protein, human; C505687:Tnfrsf11a protein, mouse; C505689:Tnfsf11 protein, mouse; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019331:NG-Nitroarginine Methyl Ester