title: Reduced chondrocyte proliferation, earlier cell cycle exit and increased apoptosis in neuronal nitric oxide synthase-deficient mice.
abstract: OBJECTIVE
  Nitric oxide (NO) has been implicated in the local regulation of bone metabolism. However, the contribution made by specific nitric oxide synthase (NOS) enzymes to skeletal development is unclear. The objective of this study was to examine the effects of inactivation of neuronal nitric oxide synthase (nNOS) on cartilage development in mice.
  
  
  METHODS
  Mice carrying a null mutation in the nNOS gene were used to address our objectives. Histological staining, immunohistochemistry and in situ analyses were employed along with real-time reverse transcriptase - polymerase chain reaction (RT-PCR).
  
  
  RESULTS
  nNOS-null mice show transient growth retardation and shorter long bones. nNOS-deficient growth plates show a reduction in replicating cells. Reduced chondrocyte numbers may in part be due to slower cell cycle progression and premature cell cycle exit caused by decreased cyclin D1 and increased p57 expression in mutants. In addition, apoptosis was increased as shown by increased cleaved-caspase 3 staining in hypertrophic chondrocytes in mutants. Real-time PCR demonstrated that expression of early chondrocyte markers such as Sox genes was reduced in mutant mice, while expression of prehypertrophic markers such as RORα was increased. Histological sections also demonstrated thinner cortical bone, fewer trabeculae and reduced mineralization in mutant mice.
  
  
  CONCLUSIONS
  These data identify an important role of nNOS in chondrocyte proliferation and endochondral bone growth and demonstrate that nNOS coordinates cell cycle exit and chondrocyte differentiation in cartilage development.
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada.
authors.forename: Q
authors.initials: Q
authors.lastname: Yan
authors.forename: Q
authors.initials: Q
authors.lastname: Feng
authors.forename: F
authors.initials: F
authors.lastname: Beier
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology; D002454:Cell Differentiation / Q000235:genetics; D049109:Cell Proliferation; D019902:Chondrocytes / Q000473:pathology*; D020219:Chondrogenesis / Q000235:genetics / Q000502:physiology; D005260:Female; D015870:Gene Expression; D006130:Growth Disorders / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology; D006132:Growth Plate / Q000473:pathology; D006811:Humerus / Q000254:growth & development; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D052248:Nitric Oxide Synthase Type I / Q000172:deficiency* / Q000235:genetics / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013977:Tibia / Q000254:growth & development; D015430:Weight Gain / Q000235:genetics / Q000502:physiology
chemical_list: D052248:Nitric Oxide Synthase Type I; D002118:Calcium