Characterization of insulin signaling in rat retina in vivo and ex vivo.
Insulin receptor (IR) signaling cascades have been studied in many tissues, but retinal insulin action has received little attention. Retinal IR signaling and activity were investigated in vivo in rats that were freely fed, fasted, or injected with insulin by phosphotyrosine immunoblotting and by measuring kinase activity. A retina explant system was utilized to investigate the IR signaling cascade, and immunohistochemistry was used to determine which retinal cell layers respond to insulin. Basal IR activity in the retina was equivalent to that in brain and significantly greater than that of liver, and it remained constant between freely fed and fasted rats. Furthermore, IR signaling increased in the retina after portal vein administration of supraphysiological doses of insulin. Ex vivo retinas responded to 10 nM insulin with IR beta-subunit (IRbeta) and IR substrate-2 (IRS-2) tyrosine phosphorylation and AktSer473 phosphorylation. The retina expresses mRNA for all three Akt isoforms as determined by in situ hybridization, and insulin specifically increases Akt-1 kinase activity. Phospho-AktSer473 immunoreactivity increases in retinal nuclear cell layers with insulin treatment. These results demonstrate that the retinal IR signaling cascade to Akt-1 possesses constitutive activity, and that exogenous insulin further stimulates this prosurvival pathway. These findings may have implications in understanding normal and dysfunctional retinal physiology.
Reiter
Chad E N
CE
Department of Cellular and Molecular Physiology, Penn State University College of Medicine, 500 University Drive H166, Hershey, PA 17033, USA.
Sandirasegarane
Lakshman
L
Wolpert
Ellen B
EB
Klinger
Marianne
M
Simpson
Ian A
IA
Barber
Alistair J
AJ
Antonetti
David A
DA
Kester
Mark
M
Gardner
Thomas W
TW
D000818:Animals; D004789:Enzyme Activation; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000378:metabolism*; D012160:Retina / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
D007328:Insulin; D011518:Proto-Oncogene Proteins; D011972:Receptor, Insulin; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt