Expression and function of system N glutamine transporters (SN1/SN2 or SNAT3/SNAT5) in retinal ganglion cells.
OBJECTIVE
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 ATB(0,+)) 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.
Umapathy
Nagavedi S
NS
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, Georgia 30912, USA.
Dun
Ying
Y
Martin
Pamela M
PM
Duplantier
Jennifer N
JN
Roon
Penny
P
Prasad
Puttur
P
Smith
Sylvia B
SB
Ganapathy
Vadivel
V
D026921:Amino Acid Transport Systems, Neutral / Q000096:biosynthesis / Q000235:genetics*; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D015870:Gene Expression; D017403:In Situ Hybridization; D051379:Mice; D018377:Neurotransmitter Agents; D012333:RNA, Messenger / Q000235:genetics*; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction
D026921:Amino Acid Transport Systems, Neutral; D018377:Neurotransmitter Agents; D012333:RNA, Messenger; C424137:SLC38A5 protein, human; C403222:system N protein 1