Polarized distribution of heme transporters in retinal pigment epithelium and their regulation in the iron-overload disease hemochromatosis

Jaya P. Gnana-Prakasam, Sushma K. Reddy, Rajalakshmi Veeranan-Karmegam, Sylvia B Smith, Pamela Moore Martin, Vadivel Ganapathy

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

Purpose. 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.

Original languageEnglish (US)
Pages (from-to)9279-9286
Number of pages8
JournalInvestigative Ophthalmology and Visual Science
Volume52
Issue number12
DOIs
StatePublished - Nov 1 2011

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Iron Overload
Hemochromatosis
Retinal Pigment Epithelium
Heme
Retina
Membranes
Iron
Poisons
Genetic Models
Cytomegalovirus Infections
Fluorescent Antibody Technique
Down-Regulation
Pathology
Polymerase Chain Reaction

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems
  • Cellular and Molecular Neuroscience
  • Medicine(all)

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Polarized distribution of heme transporters in retinal pigment epithelium and their regulation in the iron-overload disease hemochromatosis. / Gnana-Prakasam, Jaya P.; Reddy, Sushma K.; Veeranan-Karmegam, Rajalakshmi; Smith, Sylvia B; Martin, Pamela Moore; Ganapathy, Vadivel.

In: Investigative Ophthalmology and Visual Science, Vol. 52, No. 12, 01.11.2011, p. 9279-9286.

Research output: Contribution to journalArticle

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abstract = "Purpose. 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.",
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AU - Gnana-Prakasam, Jaya P.

AU - Reddy, Sushma K.

AU - Veeranan-Karmegam, Rajalakshmi

AU - Smith, Sylvia B

AU - Martin, Pamela Moore

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N2 - Purpose. 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.

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