title: The role of nitric oxide in the mechanical repression of RANKL in bone stromal cells.
abstract: Both mechanical loading and nitric oxide (NO) have positive influences on bone mass. NO production is induced by mechanical strain via upregulation of eNOS mRNA and protein, the predominant NOS in adult bone. At the same time, strain causes decreased expression of RANKL, a factor critical for osteoclastogenesis. In this study, we harvested primary stromal cells from wild-type (WT) and eNOS(-/-) mice to test whether induction of NO by mechanical strain was necessary for transducing mechanical inhibition of RANKL. We found that strain inhibition of RANKL expression was prevented by NOS inhibitors (L-NAME and L-NMMA) in WT stromal cells. Surprisingly, stromal cells from eNOS(-/-) mice showed significant mechanical repression of RANKL expression (p<0.05). Mechanical strain still increased NO production in the absence of eNOS, and was abolished by SMTC, a specific nNOS inhibitor. nNOS mRNA and protein expression were increased by strain in eNOS(-/-) but not in WT cells, revealing that nNOS was mechanically sensitive. When NO synthesis was blocked with either SMTC or siRNA targeting nNOS in eNOS(-/-) cells however, strain still was able to suppress RANKL expression by 34%. This indicated that strain suppression of RANKL can also occur through non-NO dependent pathways. While our results confirm the importance of NO in the mechanical control of skeletal remodeling, they also suggest alternative signaling pathways by which mechanical force can produce anti-catabolic effects on the skeleton.
authors.affiliation: Applied Physiology, Georgia Institute of Technology College of Sciences, Atlanta GA 30332, USA.
authors.forename: Jill
authors.initials: J
authors.lastname: Rahnert
authors.affiliation: Veterans Affairs Medical Center, Atlanta GA 30033, USA. Electronic address: xfan@emory.edu.
authors.forename: Xian
authors.initials: X
authors.lastname: Fan
authors.affiliation: Department of Medicine, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA.
authors.forename: Natasha
authors.initials: N
authors.lastname: Case
authors.affiliation: Department of Pediatrics, Emory University School of Medicine, Atlanta GA 30322, USA.
authors.forename: Tamara C
authors.initials: TC
authors.lastname: Murphy
authors.affiliation: Laboratory of Immunology and Genetics, Istituti Ortopedici Rizzoli, Bologna, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Grassi
authors.affiliation: Department of Medicine, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA.
authors.forename: Buer
authors.initials: B
authors.lastname: Sen
authors.affiliation: Department of Medicine, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA.
authors.forename: Janet
authors.initials: J
authors.lastname: Rubin
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000378:metabolism*; D016723:Bone Remodeling; D002478:Cells, Cultured; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009569:Nitric Oxide / Q000502:physiology*; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism; D053245:RANK Ligand / Q000037:antagonists & inhibitors* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013314:Stress, Mechanical; D017154:Stromal Cells / Q000378:metabolism
chemical_list: D053245:RANK Ligand; C505689:Tnfsf11 protein, mouse; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III