title: High-fat diet-induced obesity leads to resistance to leptin-induced cardiomyocyte contractile response.
abstract: Levels of the obese gene product leptin are often elevated in obesity and may contribute to obesity-induced cardiovascular complications. However, the role of leptin in obesity-associated cardiac abnormalities has not been clearly defined. This study was designed to determine the influence of high-fat diet-induced obesity on cardiac contractile response of leptin. Mechanical and intracellular Ca(2+) properties were evaluated using an IonOptix system in cardiomyocytes from adult rats fed low- and high-fat diets for 12 weeks. Cardiomyocyte contractile and intracellular Ca(2+) properties were examined including peak shortening, duration and maximal velocity of shortening/relengthening (TPS/TR(90), +/-dl/dt), Fura-2-fluorescence intensity change (DeltaFFI), and intracellular Ca(2+) decay rate (tau). Expression of the leptin receptor (Ob-R) was evaluated by western blot analysis. High-fat diet increased systolic blood pressure and plasma leptin levels. PS and +/-dl/dt were depressed whereas TPS and TR(90) were prolonged after high-fat diet feeding. Leptin elicited a concentration-dependent (0-1,000 nmol/l) inhibition of PS, +/-dl/dt, and DeltaFFI in low-fat but not high-fat diet-fed rat cardiomyocytes without affecting TPS and TR(90). The Janus kinase 2 (JAK2) inhibitor AG490, the mitogen-activated protein kinase (MAPK) inhibitor SB203580, and the nitric oxide synthase (NOS) inhibitor L-NAME abrogated leptin-induced cardiomyocyte contractile response in low-fat diet group without affecting the high-fat diet group. High-fat diet significantly downregulated cardiac expression of Ob-R. Elevation of extracellular Ca(2+) concentration nullified obesity-induced cardiomyocyte mechanical dysfunction and leptin-induced depression in PS. These data indicate presence of cardiac leptin resistance in diet-induced obesity possibly associated with impaired leptin receptor signaling.
authors: Division of Pharmaceutical Sciences, University of Wyoming College of Health Sciences, Laramie, Wyoming, USA. jren@uwyo.edu
authors: Jun
authors: J
authors: Ren
authors: Bang-Hao
authors: BH
authors: Zhu
authors: David P
authors: DP
authors: Relling
authors: Lucy B
authors: LB
authors: Esberg
authors: Asli F
authors: AF
authors: Ceylan-Isik
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D018752:Diet, Fat-Restricted; D004041:Dietary Fats / Q000009:adverse effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D020738:Leptin / Q000378:metabolism / Q000502:physiology*; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000502:physiology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009765:Obesity / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology*; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D054411:Receptors, Leptin / Q000378:metabolism; D020032:Tyrphostins / Q000494:pharmacology
chemical_list: D004041:Dietary Fats; D004791:Enzyme Inhibitors; D007093:Imidazoles; D020738:Leptin; D011725:Pyridines; D054411:Receptors, Leptin; D020032:Tyrphostins; C095512:alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide; C093642:SB 203580; D002118:Calcium; D019331:NG-Nitroarginine Methyl Ester