title: Pigment epithelium-derived factor is a substrate for matrix metalloproteinase type 2 and type 9: implications for downregulation in hypoxia.
abstract: OBJECTIVE
  Pigment epithelium-derived factor (PEDF), a protein secreted by the retinal pigment epithelium (RPE), acts on retinal survival and angiogenesis. Because hypoxia and VEGF regulate matrix metalloproteinases (MMPs), their effects on PEDF proteolysis were explored.
  
  
  METHODS
  Mouse models for retinopathy of prematurity (ROP) were used. Cultured monkey RPE cells were exposed to low oxygen and chemical hypoxia mimetics. PEDF and VEGF mRNA levels in RPE were determined by RT-PCR. MMPs were assessed by zymography, DQ-gelatin degradation solution assays, and MMP immunostaining. PEDF proteolysis was assayed in solution and followed by SDS-PAGE and immunostaining. MMP induction by VEGF was performed in baby hamster kidney (BHK) cells. Retinal R28 cell survival, ex vivo chick embryonic aortic vessel sprouting, and directed in vivo angiogenesis assays were performed.
  
  
  RESULTS
  Levels of PEDF in RPE/choroid significantly decreased in the ROP model. Hypoxia decreased PEDF levels in the media conditioned by RPE cells, with no significant change in PEDF mRNA. Conversely, PEDF proteolysis, gelatinolytic activities of approximately 57-kDa and approximately 86-kDa zymogens, and MMP-2 immunoreactivities increased with hypoxia. Addition of VEGF to BHK cells caused a time and dose-related upregulation of approximately 57-kDa zymogens and of DQ-gelatinolytic and PEDF-degrading activity. The PEDF-degrading activity and approximately 57-kDa zymogens in the BHK media shared MMP protease inhibition patterns and MMP-2 immunoreactivities with those in the vitreous. Limited proteolysis with MMP-2 and -9 degraded PEDF in a Ca(+2)-dependent fashion. MMP-mediated proteolysis of PEDF abolished the retinal survival and antiangiogenic activities of the PEDF protein.
  
  
  CONCLUSIONS
  Hypoxia and VEGF can downregulate PEDF through proteolytic degradation. PEDF is a novel substrate for MMP-2 and -9. These results reveal a novel posttranslational mechanism for downregulating PEDF, and provide an explanation for hypoxia-provoked increases in VEGF/PEDF ratios, in angiogenesis and/or in neuronal death.
authors.affiliation: Laboratory of Retinal Cell and Molecular Biology, National Eye Institute, National Institutes of Health, Bethesda, MD 20892-0607, USA.
authors.forename: Luigi
authors.initials: L
authors.lastname: Notari
authors.forename: Amanda
authors.initials: A
authors.lastname: Miller
authors.forename: Alfredo
authors.initials: A
authors.lastname: Martínez
authors.forename: Juan
authors.initials: J
authors.lastname: Amaral
authors.forename: Meihua
authors.initials: M
authors.lastname: Ju
authors.forename: Gregory
authors.initials: G
authors.lastname: Robinson
authors.forename: Lois E H
authors.initials: LE
authors.lastname: Smith
authors.forename: S Patricia
authors.initials: SP
authors.lastname: Becerra
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D002478:Cells, Cultured; D002642:Chick Embryo; D006224:Cricetinae; D004195:Disease Models, Animal; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D000860:Hypoxia / Q000201:enzymology*; D007231:Infant, Newborn; D008251:Macaca; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009389:Neovascularization, Pathologic / Q000378:metabolism; D009414:Nerve Growth Factors / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000633:toxicity; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012178:Retinopathy of Prematurity / Q000201:enzymology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015843:Serpins / Q000235:genetics / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D000099174:Pigment Epithelium-Derived Factor
chemical_list: D005136:Eye Proteins; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9; D009414:Nerve Growth Factors; D010100:Oxygen; D012333:RNA, Messenger; D015843:Serpins; D042461:Vascular Endothelial Growth Factor A; D000099174:Pigment Epithelium-Derived Factor