Lipopolysaccharide activates calcineurin in ventricular myocytes

J Am Coll Cardiol. 2007 Jan 30;49(4):491-9. doi: 10.1016/j.jacc.2006.10.043. Epub 2007 Jan 12.

Abstract

Objectives: We investigated whether lipopolysaccharide (LPS), a proximate cause of inflammation, activates calcineurin in cardiac myocytes and if calcineurin regulates apoptosis in this setting.

Background: Calcineurin regulates myocardial growth and hypertrophy, but its role in inflammation is unknown. Calcineurin has proapoptotic or antiapoptotic effects depending on the stimuli.

Methods: Calcineurin activity was measured in left ventricular myocytes from adult Sprague Dawley rats. Cardiac apoptosis was measured by terminal deoxy-nucleotidyl transferase-mediated dUTP nick end-labeling staining and caspase-3 activity after in vitro and in vivo exposure to LPS.

Results: Lipopolysaccharide increased calcineurin activity in myocytes over 1 to 24 h (t 1/2 = 4.8 h) with an EC(50) of 0.80 ng/ml LPS (p < 0.05, n = 4). The LPS (10 ng/ml) effects were mimicked by angiotensin II (Ang II) (100 nmol/l); both increased calcineurin activity and induced apoptosis without additive effects (p < 0.05, n = 5 to 9). Lipopolysaccharide and/or Ang II effects were prevented by 1 h pre-treatment with an Ang II type 1 receptor blocker (losartan, 1 micromol/l), calcineurin inhibitor (cyclosporin A, 0.5 micromol/l), calcium chelator (1,2-Bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl) ester, 0.1 micromol/l), or by inhibiting sarcoplasmic reticulum (SR) calcium (Ca)-ATPase (thapsigargin, 1 micromol/l) or SR calcium release channel (ryanodine, 1 micromol/l). Left ventricular apoptosis increased from 4 to 24 h after LPS (1 mg/kg intravenously) in vivo, but not in rats pre-treated with cyclosporin A (20 mg/kg/day subcutaneously) for 3 days (p < 0.05, n = 5).

Conclusions: In cardiac myocytes, LPS activates calcineurin in association with apoptosis by Ang II and SR calcium-dependent mechanisms. This expands the paradigm for cardiac calcineurin to be activated by low levels of LPS in inflammation and chronic conditions (e.g., infections, smoking, and heart failure).

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Analysis of Variance
  • Animals
  • Apoptosis / drug effects
  • Apoptosis / physiology
  • Calcineurin / drug effects
  • Calcineurin / physiology*
  • Heart Ventricles / cytology*
  • Lipopolysaccharides / pharmacology*
  • Myocytes, Cardiac / drug effects
  • Myocytes, Cardiac / physiology*
  • Rats
  • Rats, Sprague-Dawley

Substances

  • Lipopolysaccharides
  • Calcineurin