Expression of folate receptor α in the mammalian retinol pigmented epithelium and retina

Sylvia B Smith, Ramesh Kekuda, Xiaolin Gu, Christy Chancy, Simon J. Conway, Vadivel Ganapathy

Research output: Contribution to journalArticle

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Abstract

PURPOSE. Folic acid is essential for DNA, RNA, and protein synthesis, and deficiencies in folate can lead to nutritional amblyopia and optic neuropathy. The transport of folate from the choroidal blood supply to the retina is only now beginning to be understood. The reduced-folate transporter was reported recently to be present in cultured human retinal pigment epithelial (RPE) cells and is thought to be localized to the apical region of these cells. The authors hypothesize that the RPE plays a role in the vectorial transport of folate from the choroidal blood to the neural retina and uses not only the reduced-folate transporter but also the folate receptor α in mediating this transport. The purpose of the present study was to determine whether the folate receptor α was present in the RPE and, if so, whether it was distributed along the basolateral membrane of the RPE, supporting a role for the protein in the initial steps of folate transport into the RPE. METHODS. The expression of the folate receptor α in mouse RPE was analyzed by reverse transcription-polymerase chain reaction (RT-PCR), functional assays, in situ hybridization, immunohistochemistry, and laser scanning confocal microscopy. RESULTS. RT-PCR analysis, cloning of the RT- PCR product, and subsequent sequencing established that folate receptor α mRNA transcripts are expressed in the mouse RPE/choroid and are expressed also in the neural retina. A heterologous functional expression assay using MTX(R)-ZR-75-1 cells showed that the folate receptor α cDNA obtained by RT- PCR from the RPE/choroid complex and the neural retina was functional as assessed by the binding of folic acid and by the uptake of N5- methyltetrahydrofolate. In situ hybridization localized the folate receptor α mRNA to the mouse RPE cells and to cells of the neural retina. The folate receptor α was detected immunohistochemically in the mouse and rat RPE and in several layers of the neural retina. Laser scanning confocal microscopy revealed the distribution of the folate receptor α along the basolateral region of the RPE and not the apical region. CONCLUSIONS. The present work represents the first analysis of the folate receptor α expression in intact mammalian retina. The receptor is present and functional in mouse RPE. It is distributed specifically along the basolateral surface of the RPE and is proposed to work in a coordinated manner with the reduced-folate transporter in the vectorial transport of folate from the choroidal blood to the neural retina.

Original languageEnglish (US)
Pages (from-to)840-848
Number of pages9
JournalInvestigative Ophthalmology and Visual Science
Volume40
Issue number5
StatePublished - Apr 13 1999

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Vitamin A
Folic Acid
Retinal Pigments
Retina
Epithelium
Folic Acid Transporters
Polymerase Chain Reaction
Choroid
Confocal Microscopy
Reverse Transcription
In Situ Hybridization
Epithelial Cells
Protein Deficiency
Optic Nerve Diseases
Messenger RNA
Amblyopia
Organism Cloning

ASJC Scopus subject areas

  • Ophthalmology

Cite this

Expression of folate receptor α in the mammalian retinol pigmented epithelium and retina. / Smith, Sylvia B; Kekuda, Ramesh; Gu, Xiaolin; Chancy, Christy; Conway, Simon J.; Ganapathy, Vadivel.

In: Investigative Ophthalmology and Visual Science, Vol. 40, No. 5, 13.04.1999, p. 840-848.

Research output: Contribution to journalArticle

Smith, SB, Kekuda, R, Gu, X, Chancy, C, Conway, SJ & Ganapathy, V 1999, 'Expression of folate receptor α in the mammalian retinol pigmented epithelium and retina', Investigative Ophthalmology and Visual Science, vol. 40, no. 5, pp. 840-848.
Smith, Sylvia B ; Kekuda, Ramesh ; Gu, Xiaolin ; Chancy, Christy ; Conway, Simon J. ; Ganapathy, Vadivel. / Expression of folate receptor α in the mammalian retinol pigmented epithelium and retina. In: Investigative Ophthalmology and Visual Science. 1999 ; Vol. 40, No. 5. pp. 840-848.
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abstract = "PURPOSE. Folic acid is essential for DNA, RNA, and protein synthesis, and deficiencies in folate can lead to nutritional amblyopia and optic neuropathy. The transport of folate from the choroidal blood supply to the retina is only now beginning to be understood. The reduced-folate transporter was reported recently to be present in cultured human retinal pigment epithelial (RPE) cells and is thought to be localized to the apical region of these cells. The authors hypothesize that the RPE plays a role in the vectorial transport of folate from the choroidal blood to the neural retina and uses not only the reduced-folate transporter but also the folate receptor α in mediating this transport. The purpose of the present study was to determine whether the folate receptor α was present in the RPE and, if so, whether it was distributed along the basolateral membrane of the RPE, supporting a role for the protein in the initial steps of folate transport into the RPE. METHODS. The expression of the folate receptor α in mouse RPE was analyzed by reverse transcription-polymerase chain reaction (RT-PCR), functional assays, in situ hybridization, immunohistochemistry, and laser scanning confocal microscopy. RESULTS. RT-PCR analysis, cloning of the RT- PCR product, and subsequent sequencing established that folate receptor α mRNA transcripts are expressed in the mouse RPE/choroid and are expressed also in the neural retina. A heterologous functional expression assay using MTX(R)-ZR-75-1 cells showed that the folate receptor α cDNA obtained by RT- PCR from the RPE/choroid complex and the neural retina was functional as assessed by the binding of folic acid and by the uptake of N5- methyltetrahydrofolate. In situ hybridization localized the folate receptor α mRNA to the mouse RPE cells and to cells of the neural retina. The folate receptor α was detected immunohistochemically in the mouse and rat RPE and in several layers of the neural retina. Laser scanning confocal microscopy revealed the distribution of the folate receptor α along the basolateral region of the RPE and not the apical region. CONCLUSIONS. The present work represents the first analysis of the folate receptor α expression in intact mammalian retina. The receptor is present and functional in mouse RPE. It is distributed specifically along the basolateral surface of the RPE and is proposed to work in a coordinated manner with the reduced-folate transporter in the vectorial transport of folate from the choroidal blood to the neural retina.",
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AU - Conway, Simon J.

AU - Ganapathy, Vadivel

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N2 - PURPOSE. Folic acid is essential for DNA, RNA, and protein synthesis, and deficiencies in folate can lead to nutritional amblyopia and optic neuropathy. The transport of folate from the choroidal blood supply to the retina is only now beginning to be understood. The reduced-folate transporter was reported recently to be present in cultured human retinal pigment epithelial (RPE) cells and is thought to be localized to the apical region of these cells. The authors hypothesize that the RPE plays a role in the vectorial transport of folate from the choroidal blood to the neural retina and uses not only the reduced-folate transporter but also the folate receptor α in mediating this transport. The purpose of the present study was to determine whether the folate receptor α was present in the RPE and, if so, whether it was distributed along the basolateral membrane of the RPE, supporting a role for the protein in the initial steps of folate transport into the RPE. METHODS. The expression of the folate receptor α in mouse RPE was analyzed by reverse transcription-polymerase chain reaction (RT-PCR), functional assays, in situ hybridization, immunohistochemistry, and laser scanning confocal microscopy. RESULTS. RT-PCR analysis, cloning of the RT- PCR product, and subsequent sequencing established that folate receptor α mRNA transcripts are expressed in the mouse RPE/choroid and are expressed also in the neural retina. A heterologous functional expression assay using MTX(R)-ZR-75-1 cells showed that the folate receptor α cDNA obtained by RT- PCR from the RPE/choroid complex and the neural retina was functional as assessed by the binding of folic acid and by the uptake of N5- methyltetrahydrofolate. In situ hybridization localized the folate receptor α mRNA to the mouse RPE cells and to cells of the neural retina. The folate receptor α was detected immunohistochemically in the mouse and rat RPE and in several layers of the neural retina. Laser scanning confocal microscopy revealed the distribution of the folate receptor α along the basolateral region of the RPE and not the apical region. CONCLUSIONS. The present work represents the first analysis of the folate receptor α expression in intact mammalian retina. The receptor is present and functional in mouse RPE. It is distributed specifically along the basolateral surface of the RPE and is proposed to work in a coordinated manner with the reduced-folate transporter in the vectorial transport of folate from the choroidal blood to the neural retina.

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