title: Insulin suppresses ischemic preconditioning-mediated cardioprotection through Akt-dependent mechanisms.
abstract: It is believed that the diabetic myocardium is refractory to cardioprotection by ischemic preconditioning (IPC) mainly because of impaired insulin signaling to phosphatidylinositol 3-kinase (PI3K) and protein kinase B (PKB or Akt). However, human as well as animal studies have clearly showed that the hearts of type 2 diabetic humans and animals may exhibit increased signaling through PI3K-Akt but yet are resistant to cardioprotection by IPC or ischemic post-conditioning. Therefore, this study was designed to determine whether activation of insulin signaling prior to IPC is detrimental for cardioprotection and to assess the role of insulin receptors (IRs) and Akt in mediating this effect. Wild-type (WT) hearts, hearts lacking IRs or hearts expressing an active form of Akt (myrAkt1) were perfused ex vivo using a Langendorff preparation and were subjected to IPC (3cycles of 5min ischemia followed by 5min reflow before 30min no flow ischemia and then by 45min reperfusion) in the presence or absence of 1nmol/L insulin. Interestingly, whereas insulin was protective against I/R (30min no flow ischemia and 45min reperfusion), it completely abolished cardioprotection by IPC in WT hearts but not in mice lacking insulin receptors (IRs) in cardiomyocytes (CIRKO) or in all cardiac cells (TIRKO). The suppression of IPC-mediated cardioprotection was mediated through downstream signaling to Akt and Gsk3β. In addition, transgenic induction of Akt in the heart was sufficient to abrogate IPC even when insulin was absent, further confirming the involvement of Akt in insulin's suppression of cardioprotection by IPC. These data provide evidence that excessive insulin signaling to Akt is detrimental for cardioprotection by IPC and could explain the failure of the diabetic myocardium to precondition.
authors.affiliation: Division of Endocrinology, Metabolism and Diabetes, Program in Molecular Medicine, University of Utah School of Medicine, Salt Lake City, UT 84112, USA.
authors.forename: Tanner M
authors.initials: TM
authors.lastname: Fullmer
authors.forename: Shaobo
authors.initials: S
authors.lastname: Pei
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhu
authors.forename: Crystal
authors.initials: C
authors.lastname: Sloan
authors.forename: Robert
authors.initials: R
authors.lastname: Manzanares
authors.forename: Brandon
authors.initials: B
authors.lastname: Henrie
authors.forename: Karla M
authors.initials: KM
authors.lastname: Pires
authors.forename: James E
authors.initials: JE
authors.lastname: Cox
authors.forename: E Dale
authors.initials: ED
authors.lastname: Abel
authors.forename: Sihem
authors.initials: S
authors.lastname: Boudina
mesh_terms: D000818:Animals; D002316:Cardiotonic Agents / Q000378:metabolism / Q000494:pharmacology; D006003:Glycogen / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D019157:Ischemic Preconditioning, Myocardial; D019344:Lactic Acid / Q000096:biosynthesis; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D020928:Mitogen-Activated Protein Kinases; D015428:Myocardial Reperfusion Injury / Q000235:genetics / Q000378:metabolism / Q000517:prevention & control; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D002316:Cardiotonic Agents; D007328:Insulin; D019344:Lactic Acid; D006003:Glycogen; D011972:Receptor, Insulin; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3
keywords: Cardioprotection; Insulin; Insulin signaling; Ischemia; Reperfusion