title: Aquaporin 1 and 5 expression decreases during human intervertebral disc degeneration: Novel HIF-1-mediated regulation of aquaporins in NP cells.
abstract: Objectives of this study were to investigate whether AQP1 and AQP5 expression is altered during intervertebral disc degeneration and if hypoxia and HIF-1 regulate their expression in NP cells. AQP expression was measured in human tissues from different degenerative grades; regulation by hypoxia and HIF-1 was studied using promoter analysis and gain- and loss-of-function experiments. We show that both AQPs are expressed in the disc and that mRNA and protein levels decline with human disease severity. Bioinformatic analyses of AQP promoters showed multiple evolutionarily conserved HREs. Surprisingly, hypoxia failed to induce promoter activity or expression of either AQP. While genomic chromatin immunoprecipitation showed limited binding of HIF-1α to conserved HREs, their mutation did not suppress promoter activities. Stable HIF-1α suppression significantly decreased mRNA and protein levels of both AQPs, but HIF-1α failed to induce AQP levels following accumulation. Together, our results demonstrate that AQP1 and AQP5 expression is sensitive to human disc degeneration and that HIF-1α uniquely maintains basal expression of both AQPs in NP cells, independent of oxemic tension and HIF-1 binding to promoter HREs. Diminished HIF-1 activity during degeneration may suppress AQP levels in NP cells, compromising their ability to respond to extracellular osmolarity changes.
authors.affiliation: Department of Orthopaedic Surgery and Graduate Program in Cell and Developmental Biology, Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Zariel I
authors.initials: ZI
authors.lastname: Johnson
authors.affiliation: Department of Orthopaedic Surgery and Graduate Program in Cell and Developmental Biology, Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Shilpa S
authors.initials: SS
authors.lastname: Gogate
authors.affiliation: Biomedical Research Centre, Sheffield Hallam University, Sheffield, UK.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Day
authors.affiliation: Biomedical Research Centre, Sheffield Hallam University, Sheffield, UK.
authors.forename: Abbie
authors.initials: A
authors.lastname: Binch
authors.affiliation: Department of Orthopaedic Surgery and Graduate Program in Cell and Developmental Biology, Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Dessislava Z
authors.initials: DZ
authors.lastname: Markova
authors.affiliation: Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, UK.
authors.forename: Neil
authors.initials: N
authors.lastname: Chiverton
authors.affiliation: Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, UK.
authors.forename: Ashley
authors.initials: A
authors.lastname: Cole
authors.affiliation: Biomedical Research Centre, Sheffield Hallam University, Sheffield, UK.
authors.forename: Matt
authors.initials: M
authors.lastname: Conner
authors.affiliation: Department of Orthopaedic Surgery and Graduate Program in Cell and Developmental Biology, Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Irving M
authors.initials: IM
authors.lastname: Shapiro
authors.affiliation: Biomedical Research Centre, Sheffield Hallam University, Sheffield, UK.
authors.forename: Christine L
authors.initials: CL
authors.lastname: Le Maitre
authors.affiliation: Department of Orthopaedic Surgery and Graduate Program in Cell and Developmental Biology, Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Makarand V
authors.initials: MV
authors.lastname: Risbud
mesh_terms: D000818:Animals; D051398:Aquaporin 1 / Q000096:biosynthesis*; D051402:Aquaporin 5 / Q000096:biosynthesis*; D015153:Blotting, Western; D015687:Cell Hypoxia / Q000502:physiology; D047369:Chromatin Immunoprecipitation; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007150:Immunohistochemistry; D055959:Intervertebral Disc Degeneration / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D051381:Rats; D060888:Real-Time Polymerase Chain Reaction; D020218:Response Elements / Q000502:physiology; D014162:Transfection
chemical_list: C496036:AQP5 protein, human; D051402:Aquaporin 5; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051398:Aquaporin 1
keywords: HIF-1; Pathology Section; aquaporin 1; aquaporin 5; intervertebral disc; nucleus pulposus
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