IGF‐I Signaling in Osterix‐Expressing Cells Regulates Secondary Ossification Center Formation, Growth Plate Maturation, and Metaphyseal Formation During Postnatal Bone Development

• Published in: Journal of bone and mineral research Vol. 30; no. 12; pp. 2239 - 2248
• Main Authors: Wang, Yongmei, Menendez, Alicia, Fong, Chak, ElAlieh, Hashem Z, Kubota, Takuo, Long, Roger, Bikle, Daniel D
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.12.2015
• Subjects: Animals; Bone and Bones - metabolism; Bone and Bones - pathology; Bone Development; Bone Marrow Cells - cytology; Cartilage - metabolism; Cartilage - pathology; Cell Differentiation; Cell Proliferation; Chondrocytes - cytology; ENDOCHONDRAL BONE FORMATION; Ephrin-B2 - metabolism; Female; Femur - pathology; Gene Deletion; Genotype; Green Fluorescent Proteins - metabolism; Growth Plate - metabolism; IGF‐I RECEPTOR; Immunohistochemistry; Insulin-Like Growth Factor I - metabolism; Integrases - metabolism; Matrix Metalloproteinases - metabolism; Mice; Mice, Knockout; Osteoblasts - cytology; Osteoblasts - metabolism; OSTERIX‐EXPRESSING CELLS; PERICHONDRIUM; Phenotype; Promoter Regions, Genetic; Real-Time Polymerase Chain Reaction; Receptors, Somatomedin - genetics; Receptors, Somatomedin - metabolism; SECONDARY OSSIFICATION CENTER; Signal Transduction; Tibia - pathology; Vascular Endothelial Growth Factor A - metabolism; IGF-I RECEPTOR; ENDOCHONDRAL BONE FORMATION; SECONDARY OSSIFICATION CENTER; PERICHONDRIUM; OSTERIX-EXPRESSING CELLS
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1002/jbmr.2563

ABSTRACT To investigate the role of IGF‐I signaling in osterix (OSX)‐expressing cells in the skeleton, we generated IGF‐I receptor (IGF‐IR) knockout mice (OSXIGF‐IRKO) (floxed‐IGF‐IR mice × OSX promoter‐driven GFP‐labeled cre‐recombinase [OSXGFPcre]), and monitored postnatal bone development. At day 2 after birth (P2), OSXGFP‐cre was highly expressed in the osteoblasts in the bone surface of the metaphysis and in the prehypertrophic chondrocytes (PHCs) and inner layer of perichondral cells (IPCs). From P7, OSXGFP‐cre was highly expressed in PHCs, IPCs, cartilage canals (CCs), and osteoblasts (OBs) in the epiphyseal secondary ossification center (SOC), but was only slightly expressed in the OBs in the metaphysis. Compared with the control mice, the IPC proliferation was decreased in the OSXIGF‐IRKOs. In these mice, fewer IPCs invaded into the cartilage, resulting in delayed formation of the CC and SOC. Immunohistochemistry indicated a reduction of vessel number and lower expression of VEGF and ephrin B2 in the IPCs and SOC of OSXIGF‐IRKOs. Quantitative real‐time PCR revealed that the mRNA levels of the matrix degradation markers, MMP‐9, 13 and 14, were decreased in the OSXIGF‐IRKOs compared with the controls. The OSXIGF‐IRKO also showed irregular morphology of the growth plate and less trabecular bone in the tibia and femur from P7 to 7 weeks, accompanied by decreased chondrocyte proliferation, altered chondrocyte differentiation, and decreased osteoblast differentiation. Our data indicate that during postnatal bone development, IGF‐I signaling in OSX‐expressing IPCs promotes IPC proliferation and cartilage matrix degradation and increases ephrin B2 production to stimulate vascular endothelial growth factor (VEGF) expression and vascularization. These processes are required for normal CC formation in the establishment of the SOC. Moreover, IGF‐I signaling in the OSX‐expressing PHC is required for growth plate maturation and osteoblast differentiation in the development of the metaphysis. © 2015 American Society for Bone and Mineral Research.