title: Cholesterol Depletion Alters Cardiomyocyte Subcellular Signaling and Increases Contractility.
abstract: Membrane cholesterol levels play an important factor in regulating cell function. Sarcolemmal cholesterol is concentrated in lipid rafts and caveolae, which are flask-shaped invaginations of the plasma membrane. The scaffolding protein caveolin permits the enrichment of cholesterol in caveolae, and caveolin interactions with numerous proteins regulate their function. The purpose of this study was to determine whether acute reductions in cardiomyocyte cholesterol levels alter subcellular protein kinase activation, intracellular Ca2+ and contractility.
  
  
  METHODS
  Ventricular myocytes, isolated from adult Sprague Dawley rats, were treated with the cholesterol reducing agent methyl-β-cyclodextrin (MβCD, 5 mM, 1 hr, room temperature). Total cellular cholesterol levels, caveolin-3 localization, subcellular, ERK and p38 mitogen activated protein kinase (MAPK) signaling, contractility, and [Ca2+]i were assessed.
  
  
  RESULTS
  Treatment with MβCD reduced cholesterol levels by ~45 and shifted caveolin-3 from cytoskeleton and triton-insoluble fractions to the triton-soluble fraction, and increased ERK isoform phosphorylation in cytoskeletal, cytosolic, triton-soluble and triton-insoluble membrane fractions without altering their subcellular distributions. In contrast the primary effect of MβCD was on p38 subcellular distribution of p38α with little effect on p38 phosphorylation. Cholesterol depletion increased cardiomyocyte twitch amplitude and the rates of shortening and relaxation in conjunction with increased diastolic and systolic [Ca2+]i.
  
  
  CONCLUSIONS
  These results indicate that acute reductions in membrane cholesterol levels differentially modulate basal cardiomyocyte subcellular MAPK signaling, as well as increasing [Ca2+]i and contractility.
authors.affiliation: Interim Translational Research Institute, Department of Internal Medicine, Academic Health System, Hamad Medical Corporation, Doha, Qatar.|Hypertension and Vascular Research, Department of Internal Medicine, Henry Ford Hospital, 2799 West Grand Blvd., Detroit, MI 48202, United States of America.
authors.forename: Mohammed Z
authors.identifier: http://orcid.org/0000-0002-9280-8677
authors.initials: MZ
authors.lastname: Haque
authors.affiliation: Department of Physiology, Wayne State University School of Medicine, 1104 Elliman Bldg., 421 East Canfield, Detroit, MI 48201, United States of America.
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: McIntosh
authors.affiliation: Interim Translational Research Institute, Department of Internal Medicine, Academic Health System, Hamad Medical Corporation, Doha, Qatar.
authors.forename: Abdul B
authors.initials: AB
authors.lastname: Abou Samra
authors.affiliation: Interim Translational Research Institute, Department of Internal Medicine, Academic Health System, Hamad Medical Corporation, Doha, Qatar.
authors.forename: Ramzi M
authors.initials: RM
authors.lastname: Mohammad
authors.affiliation: Department of Physiology, Wayne State University School of Medicine, 1104 Elliman Bldg., 421 East Canfield, Detroit, MI 48201, United States of America.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Lasley
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D042541:Intracellular Space / Q000378:metabolism; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D013347:Subcellular Fractions / Q000378:metabolism; D047392:beta-Cyclodextrins / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D002118:Calcium