title: Cardiac contractile dysfunction in Lep/Lep obesity is accompanied by NADPH oxidase activation, oxidative modification of sarco(endo)plasmic reticulum Ca2+-ATPase and myosin heavy chain isozyme switch.
abstract: OBJECTIVE
  Obesity is an independent risk factor for heart diseases but the underlying mechanism is not clear. This study examined cardiac contraction, oxidative stress, oxidative modification of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) and the myosin heavy chain (MHC) isoform switch in obese mice.
  
  
  METHODS
  Mechanical properties were evaluated in ventricular myocytes from C57BL/6J lean and Lep/Lep obese mice (formerly known as ob/ob mice), including peak shortening (PS), time to 50 or 90% PS, time to 50 or 90% relengthening (TR50, TR90), maximal velocity of shortening/relengthening (+/-dL/dt), intracellular Ca2+ and its decay (tau). Oxidative stress, lipid peroxidation, protein damage and SERCA activity were assessed by glutathione/glutathione disulfide, malondialdehyde, protein carbonyl and 45Ca2+ uptake, respectively. NADPH oxidase was determined by immunoblotting.
  
  
  RESULTS
  Myocytes from Lep/Lep mice displayed depressed PS and +/- dL/dt, prolonged TR50, TR90, elevated resting [Ca2+]i, prolonged tau, reduced contractile capacity at high stimulus frequencies and diminished responsiveness to extracellular Ca2+ compared with lean controls. Cardiac glutathione/glutathione disulfide was decreased whereas malondialdehyde, protein carbonyl, membrane p47(phox) and membrane gp91(phox) were increased in the Lep/Lep group. SERCA isoenzyme 2a was markedly modified by oxidation in Lep/Lep hearts and associated with decreased 45Ca2+ uptake. The MHC isozyme displayed a shift from the alpha to the beta isoform in Lep/Lep hearts. Short-term incubation of angiotensin II with myocytes mimicked the mechanical defects, SERCA oxidation and 45Ca2+ uptake seen in Lep/Lep myocytes. Incubation of the NADPH oxidase inhibitor apocynin with Lep/Lep myocytes alleviated contractile defects without reversing SERCA oxidation or activity.
  
  
  CONCLUSIONS
  These data indicate that obesity-related cardiac defects may be related to NADPH oxidase activation, oxidative damage to SERCA and the MHC isozyme switch.
authors.affiliation: Division of Pharmaceutical Sciences and Center for Cardiovascular Research and Alternative Medicine, University of Wyoming, 1000 E. University Avenue, Laramie, WY 82071, USA.
authors.forename: S-Y
authors.initials: SY
authors.lastname: Li
authors.forename: X
authors.initials: X
authors.lastname: Yang
authors.forename: A F
authors.initials: AF
authors.lastname: Ceylan-Isik
authors.forename: M
authors.initials: M
authors.lastname: Du
authors.forename: N
authors.initials: N
authors.lastname: Sreejayan
authors.forename: J
authors.initials: J
authors.lastname: Ren
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D018929:Cell Culture Techniques; D004721:Endoplasmic Reticulum / Q000502:physiology*; D004789:Enzyme Activation; D005978:Glutathione / Q000378:metabolism; D019803:Glutathione Disulfide / Q000378:metabolism; D006720:Homozygote; D020738:Leptin / Q000235:genetics*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008820:Mice, Obese; D032342:Muscle Cells / Q000166:cytology / Q000502:physiology; D009200:Myocardial Contraction / Q000502:physiology*; D019255:NADPH Oxidases / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000502:physiology*
chemical_list: D020738:Leptin; D019255:NADPH Oxidases; D000252:Calcium-Transporting ATPases; D005978:Glutathione; D019803:Glutathione Disulfide