Endothelial nitric oxide synthase deficiency in mice results in reduced chondrocyte proliferation and endochondral bone growth.
OBJECTIVE
Nitric oxide (NO) and aberrant chondrocyte differentiation have both been implicated in the pathogenesis of osteoarthritis, but whether these processes are connected is unknown, and the role of specific NO synthase (NOS) enzymes in chondrocyte physiology is unclear. This study was undertaken to examine the effects of inactivation of endothelial cell NOS (eNOS) on cartilage development in mice.


METHODS
Skeletal growth and development of mice carrying a null mutation in the eNOS gene was compared with that of their control littermates. In situ analyses were complemented by experiments with primary chondrocytes and tibial explants from these mice.


RESULTS
Mice that were deficient in eNOS showed increased fatality and reduced bone growth, with hypocellular growth plates and a marked reduction in the number of proliferating chondrocytes. In vitro studies demonstrated lower chondrocyte numbers and reduced endochondral bone growth in mutant mice, suggesting that the role of eNOS signaling in chondrocyte proliferation is cell autonomous. Reduced chondrocyte numbers appear to be caused by decreased cyclin D1 and increased p57 expression in mutant mice, resulting in slower cell cycle progression and earlier cell cycle exit. In addition, expression of early chondrocyte markers such as SOX9 was reduced, and prehypertrophic markers were expressed prematurely in mutant mice.


CONCLUSIONS
Our findings identify a novel and important role of eNOS in chondrocyte proliferation and endochondral bone growth and demonstrate that loss of eNOS results in premature cell cycle exit and prehypertrophic chondrocyte differentiation during cartilage development.
Yan
Qian
Q
University of Western Ontario, London, Ontario, Canada.
Feng
Qingping
Q
Beier
Frank
F
D000818:Animals; D049628:Body Size / Q000235:genetics; D001846:Bone Development / Q000235:genetics*; D001842:Bone and Bones / Q000473:pathology / Q000502:physiology; D001947:Breeding; D002452:Cell Count; D002453:Cell Cycle / Q000502:physiology; D002454:Cell Differentiation / Q000235:genetics; D049109:Cell Proliferation; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000201:enzymology*; D019938:Cyclin D1 / Q000378:metabolism; D005260:Female; D006801:Humans; D008136:Longevity / Q000235:genetics; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D052250:Nitric Oxide Synthase Type III / Q000172:deficiency* / Q000235:genetics; D055758:SOX9 Transcription Factor / Q000378:metabolism
C530105:Ccnd1 protein, mouse; D055758:SOX9 Transcription Factor; C527933:Sox9 protein, mouse; D019938:Cyclin D1; D052250:Nitric Oxide Synthase Type III