IOVS Arteriosclerosis, Thrombosis, and Vascular Biology
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Originally published In Press as doi:10.1167/iovs.08-2245 on August 8, 2008
 (Investigative Ophthalmology and Visual Science. 2008;49:5151-5160.)
© 2008 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.08-2245
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Expression and Function of System N Glutamine Transporters (SN1/SN2 or SNAT3/SNAT5) in Retinal Ganglion Cells

Nagavedi S. Umapathy,1 Ying Dun,2 Pamela M. Martin,1 Jennifer N. Duplantier,2 Penny Roon,2 Puttur Prasad,1 Sylvia B. Smith,2,3 and Vadivel Ganapathy1

1From the Departments of Biochemistry and Molecular Biology, 2Cellular Biology and Anatomy, and 3Ophthalmology, Medical College of Georgia, Augusta, Georgia.

PURPOSE. Glutamine transport is essential for the glutamate-glutamine cycle, which occurs between neurons and glia. System N, consisting of SN1 (SNAT3) and SN2 (SNAT5), is the principal mediator of glutamine transport in retinal Müller cells. Mediators of glutamine transport in retinal ganglion cells were investigated.

METHODS. The relative contributions of various transport systems for glutamine uptake (systems N, A, L, y+L, ASCT, and ATB0,+) were examined in RGC-5 cells based on differential features of the individual transport systems. mRNA for the genes encoding members of these transport systems were analyzed by RT-PCR. Based on these data, SN1 and SN2 were analyzed in mouse retina, RGC-5 cells, and primary mouse ganglion cells (GCs) by in situ hybridization (ISH), immunofluorescence (IF), and Western blotting.

RESULTS. Three transport systems—N, A, and L—participated in glutamine uptake in RGC-5 cells. System N was the principal contributor; systems A and L contributed considerably less. ISH and IF revealed SN1 and SN2 expression in the ganglion, inner nuclear, and photoreceptor cell layers. SN1 and SN2 colocalized with the ganglion cell marker Thy 1.2 and with the Müller cell marker vimentin, confirming their presence in both retinal cell types. SN1 and SN2 proteins were detected in primary mouse GCs.

CONCLUSIONS. These findings suggest that in addition to its role in glutamine uptake in retinal glial cells, system N contributes significantly to glutamine uptake in ganglion cells and, hence, contributes to the retinal glutamate-glutamine cycle.






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