title: Epiphyseal chondrocyte secondary ossification centers require thyroid hormone activation of Indian hedgehog and osterix signaling.
abstract: Thyroid hormones (THs) are known to regulate endochondral ossification during skeletal development via acting directly in chondrocytes and osteoblasts. In this study, we focused on TH effects on the secondary ossification center (SOC) because the time of appearance of SOCs in several species coincides with the time when peak levels of TH are attained. Accordingly, micro-computed tomography (µCT) evaluation of femurs and tibias at day 21 in TH-deficient and control mice revealed that endochondral ossification of SOCs is severely compromised owing to TH deficiency and that TH treatment for 10 days completely rescued this phenotype. Staining of cartilage and bone in the epiphysis revealed that whereas all of the cartilage is converted into bone in the prepubertal control mice, this conversion failed to occur in the TH-deficient mice. Immunohistochemistry studies revealed that TH treatment of thyroid stimulating hormone receptor mutant (Tshr(-/-) ) mice induced expression of Indian hedgehog (Ihh) and Osx in type 2 collagen (Col2)-expressing chondrocytes in the SOC at day 7, which subsequently differentiate into type 10 collagen (Col10)/osteocalcin-expressing chondro/osteoblasts at day 10. Consistent with these data, treatment of tibia cultures from 3-day-old mice with 10 ng/mL TH increased expression of Osx, Col10, alkaline phosphatase (ALP), and osteocalcin in the epiphysis by sixfold to 60-fold. Furthermore, knockdown of the TH-induced increase in Osx expression using lentiviral small hairpin RNA (shRNA) significantly blocked TH-induced ALP and osteocalcin expression in chondrocytes. Treatment of chondrogenic cells with an Ihh inhibitor abolished chondro/osteoblast differentiation and SOC formation. Our findings indicate that TH regulates the SOC initiation and progression via differentiating chondrocytes into bone matrix-producing osteoblasts by stimulating Ihh and Osx expression in chondrocytes.
authors.affiliation: Musculoskeletal Disease Center, Jerry L. Pettis Memorial VA Medical Center, Loma Linda, CA, USA; Department of Medicine, Loma Linda University, Loma Linda, CA, USA.
authors.forename: Weirong
authors.initials: W
authors.lastname: Xing
authors.forename: Shaohong
authors.initials: S
authors.lastname: Cheng
authors.forename: Jon
authors.initials: J
authors.lastname: Wergedal
authors.forename: Subburaman
authors.initials: S
authors.lastname: Mohan
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism*; D024043:Collagen Type II / Q000235:genetics; D004838:Epiphyses / Q000166:cytology*; D005269:Femur / Q000000981:diagnostic imaging / Q000187:drug effects; D053823:Hedgehog Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D008954:Models, Biological; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism; D015675:Osteocalcin / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects* / Q000235:genetics; D011859:Radiography; D011989:Receptors, Thyrotropin / Q000172:deficiency / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics*; D000076182:Sp7 Transcription Factor; D013963:Thyroid Hormones / Q000172:deficiency / Q000494:pharmacology*; D013977:Tibia / Q000000981:diagnostic imaging / Q000187:drug effects; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D015415:Biomarkers; D024043:Collagen Type II; D053823:Hedgehog Proteins; D011989:Receptors, Thyrotropin; D000076182:Sp7 Transcription Factor; C479466:Sp7 protein, mouse; D013963:Thyroid Hormones; D014157:Transcription Factors; C514061:ihh protein, mouse; D015675:Osteocalcin
keywords: BONE FORMATION; CHONDROCYTES; DIFFERENTIATION; HYPOTHYROIDISM; OSSIFICATION; OSTEOBLASTS; THYROID HORMONE
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