title: Hypoxia activates the notch signaling pathway in cells of the intervertebral disc: implications in degenerative disc disease.
abstract: OBJECTIVE
  To investigate whether hypoxia regulates Notch signaling, and whether Notch plays a role in intervertebral disc cell proliferation.
  
  
  METHODS
  Reverse transcription-polymerase chain reaction and Western blotting were used to measure expression of Notch signaling components in intervertebral disc tissue from mature rats and from human discs. Transfections were performed to determine the effects of hypoxia and Notch on target gene activity.
  
  
  RESULTS
  Cells of the nucleus pulposus and annulus fibrosus of rat disc tissue expressed components of the Notch signaling pathway. Expression of Notch-2 was higher than that of the other Notch receptors in both the nucleus pulposus and annulus fibrosus. In both tissues, hypoxia increased Notch1 and Notch4 messenger RNA (mRNA) expression. In the annulus fibrosus, mRNA expression of the Notch ligand Jagged1 was induced by hypoxia, while Jagged2 mRNA expression was highly sensitive to hypoxia in both tissues. A Notch signaling inhibitor, L685458, blocked hypoxic induction of the activity of the Notch-responsive luciferase reporters 12xCSL and CBF1. Expression of the Notch target gene Hes1 was induced by hypoxia, while coexpression with the Notch-intracellular domain increased Hes1 promoter activity. Moreover, inhibition of Notch signaling blocked disc cell proliferation. Analysis of human disc tissue showed that there was increased expression of Notch signaling proteins in degenerated discs.
  
  
  CONCLUSIONS
  In intervertebral disc cells, hypoxia promotes expression of Notch signaling proteins. Notch signaling is an important process in the maintenance of disc cell proliferation, and thus offers a therapeutic target for the restoration of cell numbers during degenerative disc disease.
authors.affiliation: Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Hiyama
authors.forename: Renata
authors.initials: R
authors.lastname: Skubutyte
authors.forename: Dessislava
authors.initials: D
authors.lastname: Markova
authors.forename: D Greg
authors.initials: DG
authors.lastname: Anderson
authors.forename: Sanjay
authors.initials: S
authors.lastname: Yadla
authors.forename: Daisuke
authors.initials: D
authors.lastname: Sakai
authors.forename: Joji
authors.initials: J
authors.lastname: Mochida
authors.forename: Todd J
authors.initials: TJ
authors.lastname: Albert
authors.forename: Irving M
authors.initials: IM
authors.lastname: Shapiro
authors.forename: Makarand V
authors.initials: MV
authors.lastname: Risbud
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D002453:Cell Cycle / Q000502:physiology; D049109:Cell Proliferation; D002478:Cells, Cultured; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D007150:Immunohistochemistry; D007403:Intervertebral Disc / Q000166:cytology / Q000378:metabolism*; D008875:Middle Aged; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D051880:Receptors, Notch / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D012333:RNA, Messenger; D051880:Receptors, Notch