title: Leptin regulates chondrocyte differentiation and matrix maturation during endochondral ossification.
abstract: Leptin has been suggested to mediate a variety of actions, including bone development, via its ubiquitously expressed receptor (Ob-Rb). In this study, we investigated the role of leptin in endochondral ossification at the growth plate. The growth plates of wild-type and ob/ob mice were analyzed. Effects of leptin on chondrocyte gene expression, cell cycle, apoptosis and matrix mineralization were assessed using primary chondrocyte culture and the ATDC5 cell differentiation culture system. Immunohistochemistry and in situ hybridization showed that leptin was localized in prehypertrophic chondrocytes in normal mice and that Ob-Rb was localized in hypertrophic chondrocytes in normal and ob/ob mice. Growth plates of ob/ob mice were more fragile than those of wild-type mice in a mechanical test and were broken easily at the chondro-osseous junction. The growth plates of ob/ob mice showed disturbed columnar structure, decreased type X collagen expression, less organized collagen fibril arrangement, increased apoptosis and premature mineralization. Leptin administration in ob/ob mice led to an increase in femoral and humeral lengths and decrease in the proportional length of the calcified hypertrophic zone to the whole hypertrophic zone. In primary chondrocyte culture, the matrix mineralization in ob/ob chondrocytes was stronger than that of wild-type mice; this mineralization in both types of mice was abolished by the addition of exogenous leptin (10 ng/ml). During ATDC5 cell differentiation culture, exogenous leptin at a concentration of 1-10 ng/ml (equivalent to the normal serum concentration of leptin) altered type X collagen mRNA expression and suppressed apoptosis, cell growth and matrix calcification. In conclusion, we demonstrated that leptin modulates several events associated with terminal differentiation of chondrocytes. Our finding that the growth plates of ob/ob mice were fragile implies a disturbance in the differentiation/maturation process of growth plates due to depletion of leptin signaling in ob/ob mice. These findings suggest that peripheral leptin signaling plays an essential role in endochondral ossification at the growth plate.
authors.affiliation: Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kishida
authors.forename: Makoto
authors.initials: M
authors.lastname: Hirao
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Tamai
authors.forename: Akihide
authors.initials: A
authors.lastname: Nampei
authors.forename: Tetsuho
authors.initials: T
authors.lastname: Fujimoto
authors.forename: Takanobu
authors.initials: T
authors.lastname: Nakase
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Shimizu
authors.forename: Hideki
authors.initials: H
authors.lastname: Yoshikawa
authors.forename: Akira
authors.initials: A
authors.lastname: Myoui
mesh_terms: D000818:Animals; D017209:Apoptosis; D001857:Bone Matrix / Q000502:physiology*; D002113:Calcification, Physiologic / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000032:analysis; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002478:Cells, Cultured; D019902:Chondrocytes / Q000737:chemistry / Q000166:cytology* / Q000502:physiology; D024121:Collagen Type X / Q000096:biosynthesis / Q000235:genetics; D005269:Femur / Q000033:anatomy & histology / Q000502:physiology; D015870:Gene Expression; D006132:Growth Plate / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D006811:Humerus / Q000033:anatomy & histology / Q000502:physiology; D020738:Leptin / Q000096:biosynthesis / Q000494:pharmacology / Q000502:physiology*; D051379:Mice; D008820:Mice, Obese; D010012:Osteogenesis / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000502:physiology; D054411:Receptors, Leptin; D015398:Signal Transduction / Q000502:physiology
chemical_list: D024121:Collagen Type X; D020738:Leptin; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; C515447:leptin receptor, mouse; D002118:Calcium