Downregulation of reduced-folate transporter by glucose in cultured RPE cells and in RPE of diabetic mice
- PMID: 11818404
- PMCID: PMC4639924
Downregulation of reduced-folate transporter by glucose in cultured RPE cells and in RPE of diabetic mice
Abstract
Purpose: The polarized distribution of reduced-folate transporter (RFT)-1 to the apical retinal pigment epithelial (RPE) membrane was demonstrated recently. Nitric oxide (NO) significantly decreases the activity of RFT-1 in cultured RPE cells. NO is elevated in diabetes, and therefore in the present study the alteration of RFT-1 activity in RPE under conditions of high glucose was investigated.
Methods: Human ARPE-19 cells were incubated in media containing 5 mM glucose plus 40 mM mannitol (control) or 45 mM glucose for varying periods and the activity of RFT-1 was assessed by determining the uptake of [3H]-N(5)-methyltetrahydrofolate (MTF). The levels of mRNA encoding RFT-1 were determined by RT-PCR and protein levels by Western blot analysis. The activity of RFT-1 and expression of mRNA encoding RFT-1 were analyzed also in RPE of streptozotocin-induced diabetic mice.
Results: Exposure of RPE cells to 45 mM glucose for as short an incubation time as 6 hours resulted in a 35% decrease in MTF uptake. Kinetic analysis showed that the hyperglycemia-induced attenuation was associated with a decrease in the maximal velocity of the transporter with no significant change in the substrate affinity. Semiquantitative RT-PCR demonstrated that the mRNA encoding RFT-1 was significantly decreased in cells exposed to high glucose, and Western blot analysis showed a significant decrease in protein levels. The uptake of [3H]-MTF in RPE of diabetic mice was reduced by approximately 20%, compared with that in nondiabetic, age-matched control animals. Semiquantitative RT-PCR demonstrated that the mRNA encoding RFT-1 was decreased significantly in RPE of diabetic mice.
Conclusions: These findings demonstrate for the first time that hyperglycemic conditions reduce the expression and activity of RFT-1 and may have profound implications for the transport of folate by RPE in diabetes.
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References
-
- Wu G. Retina: The Fundamentals. Philadelphia: WB Saunders; 1995. Diabetic retinopathy; pp. 31–48.
-
- Verma D. Pathogenesis of diabetic retinopathy: the missing link (review)? Med Hypotheses. 1993;41:205–210. - PubMed
-
- Shiels IA, Zhang S, Ambler J, Taylor SM. Vascular leakage stimulates phenotype alteration in ocular cells, contributing to the pathology of proliferative vitreoretinopathy. Med Hypotheses. 1998;50:113–117. - PubMed
-
- Hewitt AT, Adler R. The retinal pigment epithelium and interphotoreceptor matrix: structure and specialized functions. In: Ogden TE, Schachat AP, editors. Retina. Vol. 1. St Louis: CB: Mosby; 1997. pp. 58–71.
-
- Hughes BA, Gallemore RP, Miller SS. Transport mechanisms in the retinal pigment epithelium. In: Marmor MF, Wolfensberger TJ, editors. The Retinal Pigment Epithelium: Function and Disease. New York: Oxford University Press; 1998. pp. 103–134.
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