title: Chronic insulin treatment of diabetes does not fully normalize alterations in the retinal transcriptome.
abstract: BACKGROUND
  Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. Approximately 95% of patients with Type 1 diabetes develop some degree of retinopathy within 25 years of diagnosis despite normalization of blood glucose by insulin therapy. The goal of this study was to identify molecular changes in the rodent retina induced by diabetes that are not normalized by insulin replacement and restoration of euglycemia.
  
  
  METHODS
  The retina transcriptome (22,523 genes and transcript variants) was examined after three months of streptozotocin-induced diabetes in male Sprague Dawley rats with and without insulin replacement for the later one and a half months of diabetes. Selected gene expression changes were confirmed by qPCR, and also examined in independent control and diabetic rats at a one month time-point.
  
  
  RESULTS
  Transcriptomic alterations in response to diabetes (1376 probes) were clustered according to insulin responsiveness. More than half (57%) of diabetes-induced mRNA changes (789 probes) observed at three months were fully normalized to control levels with insulin therapy, while 37% of probes (514) were only partially normalized. A small set of genes (5%, 65 probes) was significantly dysregulated in the insulin-treated diabetic rats. qPCR confirmation of findings and examination of a one month time point allowed genes to be further categorized as prevented or rescued with insulin therapy. A subset of genes (Ccr5, Jak3, Litaf) was confirmed at the level of protein expression, with protein levels recapitulating changes in mRNA expression.
  
  
  CONCLUSIONS
  These results provide the first genome-wide examination of the effects of insulin therapy on retinal gene expression changes with diabetes. While insulin clearly normalizes the majority of genes dysregulated in response to diabetes, a number of genes related to inflammatory processes, microvascular integrity, and neuronal function are still altered in expression in euglycemic diabetic rats. Gene expression changes not rescued or prevented by insulin treatment may be critical to the pathogenesis of diabetic retinopathy, as it occurs in diabetic patients receiving insulin replacement, and are prototypical of metabolic memory.
authors.affiliation: Department of Pharmacology, Penn State College of Medicine, Hershey, PA, USA.
authors.forename: Georgina V
authors.initials: GV
authors.lastname: Bixler
authors.forename: Heather D
authors.initials: HD
authors.lastname: Vanguilder
authors.forename: Robert M
authors.initials: RM
authors.lastname: Brucklacher
authors.forename: Scot R
authors.initials: SR
authors.lastname: Kimball
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Bronson
authors.forename: Willard M
authors.initials: WM
authors.lastname: Freeman
mesh_terms: D000818:Animals; D001699:Biometry; D015342:DNA Probes / Q000378:metabolism; D003920:Diabetes Mellitus / Q000188:drug therapy* / Q000235:genetics; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects; D053263:Gene Regulatory Networks / Q000235:genetics; D007328:Insulin / Q000494:pharmacology* / Q000627:therapeutic use*; D008297:Male; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012160:Retina / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D015342:DNA Probes; D007328:Insulin; D012333:RNA, Messenger