title: Increased expression of antioxidant and antiapoptotic genes in islets that may contribute to beta-cell survival during chronic hyperglycemia.
abstract: Hypertrophy is one mechanism of pancreatic beta-cell growth and is seen as an important compensatory response to insulin resistance. We hypothesized that the induction of protective genes contributes to the survival of enlarged (hypertrophied) beta-cells. Here, we evaluated changes in stress gene expression that accompany beta-cell hypertrophy in islets from hyperglycemic rats 4 weeks after partial pancreatectomy (Px). A variety of protective genes were upregulated, with markedly increased expression of the antioxidant genes heme oxygenase-1 and glutathione peroxidase and the antiapoptotic gene A20. Cu/Zn-superoxide dismutase (SOD) and Mn-SOD were modestly induced, and Bcl-2 was modestly reduced; however, several other stress genes (catalase, heat shock protein 70, and p53) were unaltered. The increases in mRNA levels corresponded to the degree of hyperglycemia and were reversed in Px rats by 2-week treatment with phlorizin (treatment that normalized hyperglycemia), strongly suggesting the specificity of hyperglycemia in eliciting the response. Hyperglycemia in Px rats also led to activation of nuclear factor-kappaB in islets. The profound change in beta-cell phenotype of hyperglycemic Px rats resulted in a reduced sensitivity to the beta-cell toxin streptozotocin. Sensitivity to the toxin was restored, along with the beta-cell phenotype, in islets from phlorizin-treated Px rats. Furthermore, beta-cells of Px rats were not vulnerable to apoptosis when further challenged in vivo with dexamethasone, which increases insulin resistance. In conclusion, beta-cell adaptation to chronic hyperglycemia and, hence, increased insulin demand is accompanied by the induction of protective stress genes that may contribute to the survival of hypertrophied beta-cells.
authors.affiliation: Section of Islet Transplantation and Cell Biology, Joslin Diabetes Center, Boston, Massachusetts, USA.
authors.forename: D Ross
authors.initials: DR
authors.lastname: Laybutt
authors.forename: Hideaki
authors.initials: H
authors.lastname: Kaneto
authors.forename: Wendy
authors.initials: W
authors.lastname: Hasenkamp
authors.forename: Shane
authors.initials: S
authors.lastname: Grey
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Jonas
authors.forename: Dennis C
authors.initials: DC
authors.lastname: Sgroi
authors.forename: Adam
authors.initials: A
authors.lastname: Groff
authors.forename: Christiane
authors.initials: C
authors.lastname: Ferran
authors.forename: Susan
authors.initials: S
authors.lastname: Bonner-Weir
authors.forename: Arun
authors.initials: A
authors.lastname: Sharma
authors.forename: Gordon C
authors.initials: GC
authors.lastname: Weir
mesh_terms: D000818:Animals; D002470:Cell Survival / Q000235:genetics; D002908:Chronic Disease; D003907:Dexamethasone / Q000494:pharmacology; D004586:Electrophoresis; D015870:Gene Expression / Q000502:physiology*; D005938:Glucocorticoids / Q000494:pharmacology; D006943:Hyperglycemia / Q000235:genetics* / Q000503:physiopathology*; D007150:Immunohistochemistry; D007515:Islets of Langerhans / Q000187:drug effects / Q000503:physiopathology*; D016328:NF-kappa B / Q000235:genetics; D019001:Nitric Oxide Synthase / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D010088:Oxidoreductases / Q000235:genetics*; D010180:Pancreatectomy / Q000379:methods; D011506:Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013312:Stress, Physiological / Q000235:genetics; D051996:Transcription Factor RelA
chemical_list: D005938:Glucocorticoids; D016328:NF-kappa B; D011506:Proteins; D012333:RNA, Messenger; D051996:Transcription Factor RelA; D003907:Dexamethasone; D010088:Oxidoreductases; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat