title: Absence of phosphoglucose isomerase-1 in retinal photoreceptor, pigment epithelium and Muller cells.
abstract: Macroarray analysis was used to compare equal amounts of cDNA from wild-type and rd/rd (retinal degeneration) mice, collected at P90 when photoreceptor degeneration is virtually complete. A stronger signal for the glycolytic enzyme phosphoglucose isomerase (Gpi1) was observed in the rd/rd sample. Extracellularly, Gpi1 may act as a cytokine, independently described as neuroleukin and autocrine motility factor. Retinal Gpi1 expression was investigated by Northern and Western blot analysis and immunohistochemistry. Double-labelling was performed with antibodies against Gpi1 and calbindin-D, glutamine synthetase, RPE65, calretinin and ultraviolet opsin in order to provide positive cell type identification. Northern and Western blots showed double expression levels per microgram of RNA and protein, respectively, in the rd/rd retina compared with wild-type. However, the total amount of Gpi1 protein per retina was indistinguishable. Gpi1 immunoreactivity was found in ganglion, amacrine, horizontal and bipolar cells, but not in rods, cones, pigment epithelium and Muller cells. This distribution explains why the absolute amounts of Gpi1 protein were not appreciably different between wild-type and the rd/rd phenotype, where rods and cones are absent, whilst the relative contribution of Gpi1 to the total protein and RNA pools differed. Some extracellular immunoreactivity was observed in the photoreceptor matrix around cones in freshly fixed tissue only, which could possibly reflect a role as a cytokine. We propose that glycolysis in Gpi1-negative cells proceeds entirely through the pentose phosphate pathway, creating NADPH at the cost of organic carbon. We hypothesize that the unique metabolic needs of photoreceptors justify this trade-off.
authors.affiliation: School of Biomedical and Molecular Sciences, University of Surrey, Guildford GU2 7XH, UK.
authors.forename: Simon N
authors.initials: SN
authors.lastname: Archer
authors.forename: Poonam
authors.initials: P
authors.lastname: Ahuja
authors.forename: Romeo
authors.initials: R
authors.lastname: Caffé
authors.forename: Catherine
authors.initials: C
authors.lastname: Mikol
authors.forename: Russell G
authors.initials: RG
authors.lastname: Foster
authors.forename: Theo
authors.initials: T
authors.lastname: van Veen
authors.forename: Malcolm
authors.initials: M
authors.lastname: von Schantz
mesh_terms: D000818:Animals; D015152:Blotting, Northern / Q000379:methods; D015153:Blotting, Western / Q000379:methods; D064032:Calbindin 2; D064026:Calbindins; D002352:Carrier Proteins; D005136:Eye Proteins; D005956:Glucose-6-Phosphate Isomerase / Q000378:metabolism*; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D051379:Mice; D008815:Mice, Inbred Strains; D008817:Mice, Mutant Strains; D009457:Neuroglia / Q000201:enzymology*; D009474:Neurons / Q000201:enzymology; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods; D010786:Photoreceptor Cells / Q000201:enzymology*; D010857:Pigment Epithelium of Eye / Q000201:enzymology*; D011506:Proteins / Q000378:metabolism; D012313:RNA / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012162:Retinal Degeneration / Q000201:enzymology* / Q000235:genetics* / Q000473:pathology; D017299:Rod Opsins / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase
chemical_list: D064032:Calbindin 2; D064026:Calbindins; D002352:Carrier Proteins; D005136:Eye Proteins; D005956:Glucose-6-Phosphate Isomerase; D005974:Glutamate-Ammonia Ligase; D011506:Proteins; D012313:RNA; D017299:Rod Opsins; D064030:S100 Calcium Binding Protein G; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase; C576764:CALB2 protein, human; C576511:Calb2 protein, mouse; C576512:Calb2 protein, rat