F-spondin regulates chondrocyte terminal differentiation and endochondral bone formation.
This study examines the role of F-spondin, an extracellular matrix protein of osteoarthritic cartilage, during chondrocyte maturation in embryonic growth plate cartilage. In chick tibia, F-spondin expression localized to the hypertrophic and calcified zones of the growth plate. Functional studies using tibial organ cultures indicated that F-spondin inhibited (∼35%, p = 0.02), and antibodies to F-spondin increased (∼30%, p < 0.1) longitudinal limb growth relative to untreated controls. In cell cultures, induction of chondrocyte maturation, by retinoic acid (RA) or transforming growth factor (TGF)-β treatment led to a significant upregulation of F-spondin (p < 0.05). F-spondin transfection increased mineral deposition, alkaline phosphatase (AP) and matrix metalloproteinase (MMP)-13 mRNA levels (p < 0.05), and AP activity following RA stimulation, compared to mock transfected controls. Using AP as a differentiation marker we then investigated the mechanism of F-spondin promaturation effects. Blocking endogenous F-spondin via its thrombospondin (TSR) domain inhibited RA induced AP activity 40% compared to controls (p < 0.05). The stimulatory effect of F-spondin on AP expression was also inhibited following depletion of TGF-β from culture supernatants. Our findings indicate that F-spondin is expressed in embryonic cartilage, where it has the capacity to enhance chondrocyte terminal differentiation and mineralization via interactions in its TSR domain and TGF-β dependent pathways.
Palmer
Glyn D
GD
Division of Rheumatology, New York University School of Medicine, Hospital for Joint Diseases, New York, New York, USA.
Piton
Alejandro H
AH
Thant
Lwin Mon
LM
Oliveira
Serafim M
SM
D'Angelo
Marina
M
Attur
Mukundan G
MG
Abramson
Steven B
SB
Teixeira
Cristina C
CC
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002642:Chick Embryo; D019902:Chondrocytes / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D016326:Extracellular Matrix Proteins / Q000502:physiology*; D005260:Female; D006132:Growth Plate / Q000166:cytology / Q000502:physiology; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D023421:Models, Animal; D010012:Osteogenesis / Q000502:physiology*; D011247:Pregnancy; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014212:Tretinoin / Q000494:pharmacology
D016326:Extracellular Matrix Proteins; C552523:F-spondin protein, mouse; D016212:Transforming Growth Factor beta; D014212:Tretinoin; D000469:Alkaline Phosphatase; D053509:Matrix Metalloproteinase 13