title: Conditional Deletion of Prolyl Hydroxylase Domain-Containing Protein 2 (Phd2) Gene Reveals Its Essential Role in Chondrocyte Function and Endochondral Bone Formation.
abstract: The hypoxic growth plate cartilage requires hypoxia-inducible factor (HIF)-mediated pathways to maintain chondrocyte survival and differentiation. HIF proteins are tightly regulated by prolyl hydroxylase domain-containing protein 2 (Phd2)-mediated proteosomal degradation. We conditionally disrupted the Phd2 gene in chondrocytes by crossing Phd2 floxed mice with type 2 collagen-α1-Cre transgenic mice and found massive increases (>50%) in the trabecular bone mass of long bones and lumbar vertebra of the Phd2 conditional knockout (cKO) mice caused by significant increases in trabecular number and thickness and reductions in trabecular separation. Cortical thickness and tissue mineral density at the femoral middiaphysis of the cKO mice were also significantly increased. Dynamic histomorphometric analyses revealed increased longitudinal length and osteoid surface per bone surface in the primary spongiosa of the cKO mice, suggesting elevated conversion rate from hypertrophic chondrocytes to mineralized bone matrix as well as increased bone formation in the primary spongiosa. In the secondary spongiosa, bone formation measured by mineralizing surface per bone surface and mineral apposition rate were not changed, but resorption was slightly reduced. Increases in the mRNA levels of SRY (sex determining region Y)-box 9, osterix (Osx), type 2 collagen, aggrecan, alkaline phosphatase, bone sialoprotein, vascular endothelial growth factor, erythropoietin, and glycolytic enzymes in the growth plate of cKO mice were detected by quantitative RT-PCR. Immunohistochemistry revealed an increased HIF-1α protein level in the hypertrophic chondrocytes of cKO mice. Infection of chondrocytes isolated from Phd2 floxed mice with adenoviral Cre resulted in similar gene expression patterns as observed in the cKO growth plate chondrocytes. Our findings indicate that Phd2 suppresses endochondral bone formation, in part, via HIF-dependent mechanisms in mice.
authors.affiliation: Musculoskeletal Disease Center (S.C., W.X., S.P., J.S., S.M.), Jerry L. Pettis Veterans Affairs Medical Center, Loma Linda, California 92357; and Department of Medicine (W.X., S.M.), Loma Linda University, Loma Linda, California 92354.
authors.forename: Shaohong
authors.initials: S
authors.lastname: Cheng
authors.affiliation: Musculoskeletal Disease Center (S.C., W.X., S.P., J.S., S.M.), Jerry L. Pettis Veterans Affairs Medical Center, Loma Linda, California 92357; and Department of Medicine (W.X., S.M.), Loma Linda University, Loma Linda, California 92354.
authors.forename: Weirong
authors.initials: W
authors.lastname: Xing
authors.affiliation: Musculoskeletal Disease Center (S.C., W.X., S.P., J.S., S.M.), Jerry L. Pettis Veterans Affairs Medical Center, Loma Linda, California 92357; and Department of Medicine (W.X., S.M.), Loma Linda University, Loma Linda, California 92354.
authors.forename: Sheila
authors.initials: S
authors.lastname: Pourteymoor
authors.affiliation: Musculoskeletal Disease Center (S.C., W.X., S.P., J.S., S.M.), Jerry L. Pettis Veterans Affairs Medical Center, Loma Linda, California 92357; and Department of Medicine (W.X., S.M.), Loma Linda University, Loma Linda, California 92354.
authors.forename: Jan
authors.initials: J
authors.lastname: Schulte
authors.affiliation: Musculoskeletal Disease Center (S.C., W.X., S.P., J.S., S.M.), Jerry L. Pettis Veterans Affairs Medical Center, Loma Linda, California 92357; and Department of Medicine (W.X., S.M.), Loma Linda University, Loma Linda, California 92354.
authors.forename: Subburaman
authors.initials: S
authors.lastname: Mohan
mesh_terms: D015502:Absorptiometry, Photon; D000818:Animals; D015519:Bone Density; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism*; D020219:Chondrogenesis; D003433:Crosses, Genetic; D005260:Female; D005269:Femur / Q000166:cytology / Q000000981:diagnostic imaging / Q000254:growth & development / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006132:Growth Plate / Q000166:cytology / Q000000981:diagnostic imaging / Q000254:growth & development / Q000378:metabolism*; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases / Q000235:genetics / Q000378:metabolism*; D008159:Lumbar Vertebrae / Q000166:cytology / Q000000981:diagnostic imaging / Q000254:growth & development / Q000378:metabolism; D008297:Male; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009928:Organ Specificity; D010012:Osteogenesis; D013977:Tibia / Q000166:cytology / Q000000981:diagnostic imaging / Q000254:growth & development / Q000378:metabolism; D055114:X-Ray Microtomography
chemical_list: C490189:Egln1 protein, mouse; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases