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Nan Ma, Huang Jie, Ying Liu, Belinda Dana, Carla J Siegfried, David C Beebe, Ying-Bo Shui; Ascorbic acid related transporters SVCT2 and GLUT1 in human and mouse eyes. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4671.
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© ARVO (1962-2015); The Authors (2016-present)
Ascorbic acid (AsA) is believed to play a crucial role of antioxidant protection in the eye. In most tissues, ascorbic acid is transported by the sodium-dependent AsA transporter 2 (SVCT2) and the oxidized form of AsA (dehydroascorbic acid) by facilitated diffusion via glucose transporter 1 (GLUT1), then be reduced back to AsA in cells. This study is to investigate SVCT2 and GLUT1 expression in human eyes compared to mouse.
Five human donor eyes (4 adult and 1 infant) from the local eye bank and 15 adult mouse (C57BL/6) eyes were collected to prepare paraffin sections. Immunofluorescence and in situ hybridization were performed to detect SVCT2 and GLUT1 in the ciliary epithelium. The non-pigmented (NPE) and pigmented epithelia (PE) were separately isolated with a laser micro-dissection system and total RNA was extracted. PCR was performed to detect SVCT2 and GLUT1 in the NPE and PE. Student T Test is applied for the PCR data analysis.
Immunofluorescence and in situ hybridization found that SVCT2 and GLUT1 are expressed in the human ciliary epithelium. However their distributions are different. SVCT2 is only expressed in the PE layer while GLUT1 is expressed in the NPE. Laser micro-dissection could separate both PE and NPE well and PCR confirmed location difference of SVCT2 and GLUT1 (see figure). However, SVCT2 expression was not identified in either PE or NPE in the mouse ciliary body by in situ hybridization and PCR. Interestingly, as in humans, GLUT1 was observed in mouse ciliary body NPE layer only.
These novel findings indicate how AsA is transported into the eye and may explain why humans have more than 10-fold higher AsA levels in aqueous humor as well as vitreous, compared to animals that are able to self-synthesize AsA.
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