title: HIF-1-PHD2 axis controls expression of syndecan 4 in nucleus pulposus cells.
abstract: Intervertebral disc degeneration is the leading cause of chronic back pain. Recent studies show that raised level of SDC4, a cell-surface heparan sulfate (HS) proteoglycan, plays a role in pathogenesis of disc degeneration. However, in nucleus pulposus (NP) cells of the healthy intervertebral disc, the mechanisms that control expression of SDC4 and its physiological function are unknown. Hypoxia induced SDC4 mRNA and protein expression by ~2.4- and 4.4-fold (P<0.05), respectively, in NP cells. While the activity of the SDC4 promoter containing hypoxia response element (HRE) was induced 2-fold (P<0.05), the HRE mutation decreased the activity by 40% in hypoxia. Transfections with plasmids coding prolyl-4-hydroxylase domain protein 2 (PHD2) and ShPHD2 show that hypoxic expression of SDC4 mRNA and protein is regulated by PHD2 through controlling hypoxia-inducible factor 1α (HIF-1α) levels. Although overexpression of HIF-1α significantly increased SDC4 protein levels, stable suppression of HIF-1α and HIF-1β decreased SDC4 expression by 50% in human NP cells. Finally, suppression of SDC4 expression, as well as HS function, resulted in an ~2-fold increase in sex-determining region Y (SRY)-box 9 (Sox9) mRNA, and protein (P<0.05) and simultaneous increase in Sox9 transcriptional activity and target gene expression. Taken together, our findings suggest that in healthy discs, SDC4, through its HS side chains, contributes to maintenance of the hypoxic tissue niche by controlling baseline expression of Sox9.
authors.affiliation: Department of Orthopaedic Surgery and Graduate Program in Cell and Developmental Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA; Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan; and.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Fujita
authors.affiliation: Department of Orthopaedic Surgery and Graduate Program in Cell and Developmental Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA; Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan; and.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Hirose
authors.affiliation: Department of Orthopaedic Surgery and Graduate Program in Cell and Developmental Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA;
authors.forename: Cassie M
authors.initials: CM
authors.lastname: Tran
authors.affiliation: Department of Orthopaedic Surgery, Kitasato University, Kitasato Institute Hospital, Tokyo, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Chiba
authors.affiliation: Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan; and.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Miyamoto
authors.affiliation: Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan; and.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Toyama
authors.affiliation: Department of Orthopaedic Surgery and Graduate Program in Cell and Developmental Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA;
authors.forename: Irving M
authors.initials: IM
authors.lastname: Shapiro
authors.affiliation: Department of Orthopaedic Surgery and Graduate Program in Cell and Developmental Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA; makarand.risbud@jefferson.edu.
authors.forename: Makarand V
authors.initials: MV
authors.lastname: Risbud
mesh_terms: D000818:Animals; D006801:Humans; D000860:Hypoxia / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases / Q000502:physiology*; D007403:Intervertebral Disc / Q000378:metabolism*; D016328:NF-kappa B / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D055758:SOX9 Transcription Factor / Q000096:biosynthesis; D053671:Syndecan-4 / Q000096:biosynthesis*
chemical_list: C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016328:NF-kappa B; D012333:RNA, Messenger; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; D053671:Syndecan-4; C490190:EGLN1 protein, human; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases
keywords: cartilage; hypoxia; intervertebral disc