title: Post-translational processing of synaptophysin in the rat retina is disrupted by diabetes.
abstract: Synaptophysin, is an abundant presynaptic protein involved in synaptic vesicle recycling and neurotransmitter release. Previous work shows that its content is significantly reduced in the rat retina by streptozotocin (STZ)-diabetes. This study tested the hypothesis that STZ-diabetes alters synaptophysin protein turnover and glycosylation in the rat retina. Whole explant retinas from male Sprague-Dawley rats were used in this study. Rats were made diabetic by a single intraperitoneal STZ injection (65 mg/kg body weight in 10 mM sodium citrate, pH 4.5). mRNA translation was measured using a (35)S-methionine labeling assay followed by synaptophysin immunoprecipitation and autoradiography. A pulse-chase study was used to determine the depletion of newly synthesized synaptophysin. Depletion of total synaptophysin was determined after treatment with cycloheximide. Mannose rich N-glycosylated synaptophysin was detected by treating retinal lysates with endoglycosidase H followed by immunoblot analysis. Synaptophysin mRNA translation was significantly increased after 1 month (p<0.001) and 2 months (p<0.05) of STZ-diabetes, compared to age-matched controls. Newly synthesized synaptophysin degradation was significantly accelerated in the retina after 1 and 2 months of diabetes compared to controls (p<0.05). Mannose rich glycosylated synaptophysin was significantly increased after 1 month of STZ-diabetes compared to controls (p<0.05).These data suggest that diabetes increases mRNA translation of synaptophysin in the retina, resulting in an accumulation of mannose rich glycosylated synaptophysin, a transient post-translational state of the protein. This diabetes-induced irregularity in post-translational processing could explain the accelerated degradation of retinal synaptophysin in diabetes.
authors.affiliation: Department of Ophthalmology, The Penn State Hershey Eye Center, Penn State Hershey College of Medicine, Milton S. Hershey Medical Center, Hershey, Pennsylvania, United States of America.
authors.forename: Travis S
authors.initials: TS
authors.lastname: D'Cruz
authors.forename: Brittany N
authors.initials: BN
authors.lastname: Weibley
authors.forename: Scot R
authors.initials: SR
authors.lastname: Kimball
authors.forename: Alistair J
authors.initials: AJ
authors.lastname: Barber
mesh_terms: D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D008297:Male; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000378:metabolism*; D013311:Streptozocin; D016708:Synaptophysin / Q000235:genetics / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D016708:Synaptophysin; D013311:Streptozocin