title: Exendin-4 ameliorates cardiac ischemia/reperfusion injury via caveolae and caveolins-3.
abstract: BACKGROUND
  Exendin-4, an exogenous glucagon-like peptide-1 receptor (GLP-1R) agonist, protects the heart from ischemia/reperfusion injury. However, the mechanisms for this protection are poorly understood. Caveolae, sarcolemmal invaginations, and caveolins, scaffolding proteins in caveolae, localize molecules involved in cardiac protection. We tested the hypothesis that caveolae and caveolins are essential for exendin-4 induced cardiac protection using in vitro and in vivo studies in control and caveolin-3 (Cav-3) knockout mice (Cav-3 KO).
  
  
  METHODS
  Myocytes were treated with exendin-4 and then incubated with methyl-β-cyclodextrin (MβCD) to disrupt caveolae formation. This was then followed by simulated ischemia/reperfusion (SI/R). In addition, cardiac protection in vivo was assessed by measuring infarct size and cardiac troponin levels.
  
  
  RESULTS
  Exendin-4 protected cardiac myocytes (CM) from SI/R [35.6 ± 12.6% vs. 64.4 ± 18.0% cell death, P = 0.034] and apoptosis but this protection was abolished by MβCD (71.8 ± 10.8% cell death, P = 0.004). Furthermore, Cav-3/GLP-1R co-localization was observed and membrane fractionation by sucrose density gradient centrifugation of CM treated with MβCD + exendin-4 revealed that buoyant (caveolae enriched) fractions decreased Cav-3 compared to CM treated with exendin-4 exclusively. Furthermore, exendin-4 induced a reduction in infarct size and cardiac troponin relative to control (infarct size: 25.1 ± 8.2% vs. 41.4 ± 4.1%, P < 0.001; troponin: 36.9 ± 14.2 vs. 101.1 ± 22.3 ng/ml, P < 0.001). However, exendin-4 induced cardiac protection was abolished in Cav-3 KO mice (infarct size: 43.0 ± 6.4%, P < 0.001; troponin: 96.8 ± 26.6 ng/ml, P = 0.001).
  
  
  CONCLUSIONS
  We conclude that caveolae and caveolin-3 are critical for exendin-4 induced protection of the heart from ischemia/reperfusion injury.
authors.forename: Yasuo M
authors.initials: YM
authors.lastname: Tsutsumi
authors.forename: Rie
authors.initials: R
authors.lastname: Tsutsumi
authors.forename: Eisuke
authors.initials: E
authors.lastname: Hamaguchi
authors.forename: Yoko
authors.initials: Y
authors.lastname: Sakai
authors.forename: Asuka
authors.initials: A
authors.lastname: Kasai
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ishikawa
authors.forename: Utako
authors.initials: U
authors.lastname: Yokoyama
authors.forename: Katsuya
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D021941:Caveolae / Q000378:metabolism*; D051244:Caveolin 3 / Q000378:metabolism*; D000077270:Exenatide; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007511:Ischemia / Q000378:metabolism* / Q000517:prevention & control; D008297:Male; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D015428:Myocardial Reperfusion Injury / Q000378:metabolism* / Q000517:prevention & control; D009206:Myocardium / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology*; D017208:Rats, Wistar; D014688:Venoms / Q000494:pharmacology*
chemical_list: D051244:Caveolin 3; D007004:Hypoglycemic Agents; D010455:Peptides; D014688:Venoms; D000077270:Exenatide