title: Hypoxic conditions stimulate the release of B-type natriuretic peptide from human retinal pigment epithelium cell culture.
abstract: OBJECTIVE
  A-type peptide, a natriuretic peptide belonging to the natriuretic peptide family, has been shown to be increased in the vitreous of patients suffering from diabetic retinopathy and that human retina has a well-developed natriuretic peptide system. The stimulus to which the synthesis of natriuretic peptides responded in these patients has, however, remained unknown. As the natriuretic peptides have recently been shown to respond to hypoxic conditions, the genes of both A-type and B-type have a hypoxia-response element (HRE) in their promoter sequence, we therefore hypothesized that hypoxia in the human retinal pigment epithelium will increase the secretion of NT-proBNP, the most common natriuretic peptide monitored in clinical medicine.
  
  
  METHODS
  We used cultured human retinal pigment epithelium cell line (ARPE-19) which was exposed either to normoxia or to hypoxia for 2 hr, 4 hr, 6 hr and 24 hr. NT-proBNP was measured with enzyme immunoassay, VEGF with ELISA and HIF-1α with Western blotting.
  
  
  RESULTS
  Hypoxia induced VEGF 165 release in culture medium and HIF-1α expression in cultured ARPE-19 cells. Time-dependent NT-proBNP release was detected when the ARPE-19 cells were cultured under normoxia. When hypoxia was induced, a statistically significant increase in NT-proBNP release was demonstrated in the culture medium.
  
  
  CONCLUSIONS
  Hypoxic conditions increase the release of a natriuretic peptide from retinal pigment epithelium (RPE) cells. The secretion of VEGF was also enhanced. The responses were associated with the up-regulation of the HIF-1α transcription factor. These results explain the previous findings from patients with diabetes, which also suggest that hypoxia is a ubiquitous stimulus for the secretion of natriuretic peptides in human body.
authors.affiliation: Department of Ophthalmology, University Central Hospital, University of Turku, Turku, Finland; Department of Cell Biology and Anatomy, University of Turku, Turku, Finland.
authors.forename: Vesa
authors.initials: V
authors.lastname: Aaltonen
authors.forename: Kati
authors.initials: K
authors.lastname: Kinnunen
authors.forename: Eeva-Mari
authors.initials: EM
authors.lastname: Jouhilahti
authors.forename: Juha
authors.initials: J
authors.lastname: Peltonen
authors.forename: Mikko
authors.initials: M
authors.lastname: Nikinmaa
authors.forename: Kai
authors.initials: K
authors.lastname: Kaarniranta
authors.forename: Olli
authors.initials: O
authors.lastname: Arjamaa
mesh_terms: D015153:Blotting, Western; D002478:Cells, Cultured; D003470:Culture Media; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D007124:Immunoenzyme Techniques; D020097:Natriuretic Peptide, Brain / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D055213:Retinal Pigment Epithelium / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D003470:Culture Media; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D010446:Peptide Fragments; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; C109794:pro-brain natriuretic peptide (1-76); D020097:Natriuretic Peptide, Brain
keywords: HIF-1α; VEGF; hypoxia; natriuretic peptide; retinal pigment epithelium