Expression of the sodium-coupled monocarboxylate transporters SMCT1 (SLC5A8) and SMCT2 (SLC5A12) in retina.
OBJECTIVE
Monocarboxylates are primary energy substrates in the retina. Recently, the authors identified two sodium-coupled monocarboxylate transporters (SMCTs), SMCT1 (a high-affinity transporter) and SMCT2 (a low-affinity transporter). Expression of SMCT1 and SMCT2 has been studied in several tissues; however, little is known about their expression in retina. In the present study, the authors asked whether SMCT1 and SMCT2 are also expressed in retina and, if so, in which particular retinal cell types.


METHODS
SMCT1 and SMCT2 expression was analyzed in intact mouse retina and cultured retinal cells (ganglion, Müller, RPE) by RT-PCR, in situ hybridization, and immunofluorescence. Uptake assays were performed to demonstrate SMCT1 (RGC-5 and ARPE-19 cells) and SMCT2 (rMC-1 cells) expression at the functional level.


RESULTS
SMCT1 mRNA and protein were detected in the ganglion cell layer, inner nuclear layer, inner/outer plexiform layers, photoreceptor inner segments, and RPE. In RPE, the expression of SMCT1 was restricted to the basolateral membrane. SMCT2 mRNA and protein were detected only in neural retina, with a pattern of protein localization consistent with labeling of Müller cells. In vitro studies confirmed the cell type-specific expression of SMCT1 and SMCT2. Uptake assays demonstrated Na(+)-coupled monocarboxylate transport in RGC-5, ARPE-19, and rMC-1 cells.


CONCLUSIONS
These data provide the first evidence for the expression of SMCT1 and SMCT2 in the retina and for the cell-type specific distribution of these transporters within the retina. These studies suggest that SMCT1 and SMCT2 play a differential role in monocarboxylate transport in the retina in a cell type-specific manner.
Martin
Pamela M
PM
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, Georgia 30912, USA. pmmartin@mail.mcg.edu
Dun
Ying
Y
Mysona
Barbara
B
Ananth
Sudha
S
Roon
Penny
P
Smith
Sylvia B
SB
Ganapathy
Vadivel
V
D000818:Animals; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D003239:Connective Tissue Cells / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D017403:In Situ Hybridization; D051379:Mice; D008810:Mice, Inbred C57BL; D027501:Monocarboxylic Acid Transporters / Q000235:genetics / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000378:metabolism*; D012165:Retinal Ganglion Cells / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D027682:Cation Transport Proteins; D027501:Monocarboxylic Acid Transporters; D012333:RNA, Messenger; C508556:Slc5a12 protein, mouse; C507459:Slc5a8 protein, mouse