title: Polarized distribution of heme transporters in retinal pigment epithelium and their regulation in the iron-overload disease hemochromatosis.
abstract: OBJECTIVE
  FLVCR, BCRP, and PCFT/HCP-1 represent the three heme transporters identified thus far in mammalian cells, but there is very little known about their expression and regulation in the retina. In this study, the expression of these transporters in mouse retina and retinal pigment epithelium (RPE) and their regulation in the iron-overload disease hemochromatosis were examined.
  
  
  METHODS
  The expression of FLVCR, BCRP, and PCFT in mouse retina and primary mouse RPE cells was studied by RT-PCR and immunofluorescence. Polarized localization of the transporters in RPE was studied by co-localization using a specific marker of the RPE apical membrane. Uptake of heme in primary RPE cells was determined using zinc-mesoporphyrin, a fluorescent heme analogue. The regulation of heme transporters by iron overload was studied in two genetic models of hemochromatosis (HFE-null mouse and HJV-null mouse) and in two nongenetic models of iron overload (cytomegalovirus infection and treatment with ferric ammonium citrate).
  
  
  RESULTS
  All three heme transporters were expressed in the retina and RPE. In the RPE, the expression of FLVCR was restricted to the apical membrane, and the expression of BCRP and PCFT was restricted to the basolateral membrane. In all cases of iron overload, the expression of FLVCR and PCFT was upregulated and that of BCRP was downregulated.
  
  
  CONCLUSIONS
  Hemochromatosis is associated not only with excessive accumulation of free iron in the retina and RPE but also with excessive accumulation of heme. Since heme is toxic at high levels, as is free iron, heme-induced oxidative damage may also play a role in hemochromatosis-associated retinal pathology.
authors: Department of Biochemistry and Molecular Biology, Medical College of Georgia, Georgia Health Sciences University, Augusta, Georgia 30912, USA.
authors: Jaya P
authors: JP
authors: Gnana-Prakasam
authors: Sushma K
authors: SK
authors: Reddy
authors: Rajalakshmi
authors: R
authors: Veeranan-Karmegam
authors: Sylvia B
authors: SB
authors: Smith
authors: Pamela M
authors: PM
authors: Martin
authors: Vadivel
authors: V
authors: Ganapathy
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D005786:Gene Expression Regulation / Q000502:physiology*; D006418:Heme / Q000378:metabolism; D006432:Hemochromatosis / Q000235:genetics* / Q000378:metabolism; D006566:Herpesviridae Infections / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D019190:Iron Overload / Q000378:metabolism; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008665:Metalloporphyrins / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018146:Muromegalovirus / Q000502:physiology; D058979:Proton-Coupled Folate Transporter / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D011991:Receptors, Virus / Q000235:genetics* / Q000378:metabolism; D012160:Retina / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000378:metabolism*
chemical_list: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; C501412:Abcg2 protein, mouse; C526650:Flvcr1 protein, mouse; D026901:Membrane Transport Proteins; D008665:Metalloporphyrins; D058979:Proton-Coupled Folate Transporter; D012333:RNA, Messenger; D011991:Receptors, Virus; C516877:Slc46a1 protein, mouse; D006418:Heme; C058069:zinc mesoporphyrin; D007501:Iron