Protein phosphatase 2A contributes to the cardiac dysfunction induced by endotoxemia.
OBJECTIVE
Sepsis-associated cardiac dysfunction represents an intrinsic impairment of cardiomyocyte function due in part to a decrease in myofilament Ca(2+) sensitivity associated with a sustained increase in cardiac troponin I (cTnI) phosphorylation at Ser23/24. Dephosphorylation of cTnI is under regulatory control. Thus, muscarinic and adenosine A(1)-receptor agonists antagonize beta-adrenergic stimulation via activation of protein phosphatase 2A (PP2A). The aim of this study was to determine whether modulation of PP2A and thus cTnI phosphorylation could improve sepsis-induced contractile dysfunction.


RESULTS
Cardiomyocytes were isolated from control or septic mice 16-18 h after an injection of vehicle or lipopolysaccharide (LPS; 9 mg/kg ip) respectively. Protein expression and phosphatase activity were determined in homogenates of control and septic hearts. Our data showed that LPS significantly increased cTnI phosphorylation at Ser23/24 in cardiomyocytes and reduced contraction amplitude without affecting Ca(2+)-transients. Treatment of cardiomyocytes with the A(1) agonist cyclopentyladenosine (CPA) or the protein kinase A inhibitor H89 significantly attenuated the LPS-induced contractile dysfunction without effect on Ca(2+)-transients. Co-treatment with CPA and H89 completely reversed the contractile dysfunction. Increased cTnI phosphorylation in septic hearts was associated with a significant reduction in the protein expression of both the catalytic and regulatory subunits (B56 alpha) of PP2A and a decrease in PP2A activity. CPA treatment of septic hearts increased PP2A activity. An increase in the protein expression of demethylated PP2A and a decrease in the PP2A-methyltransferase (PPMT; the methyltransferase that catalyses this reaction) were also observed.


CONCLUSIONS
These data support the hypothesis that sustained cTnI phosphorylation underlies the contractile dysfunction seen in sepsis.
Marshall
Melanie
M
Cardiovascular Division, Department of Cardiology, King's College London, James Black Centre, London SE5 9NU, UK. melanie.marshall@kcl.ac.uk
Anilkumar
Narayana
N
Layland
Joanne
J
Walker
Simon J
SJ
Kentish
Jonathan C
JC
Shah
Ajay M
AM
Cave
Alison C
AC
D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D058907:Adenosine A1 Receptor Agonists; D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004195:Disease Models, Animal; D019446:Endotoxemia / Q000139:chemically induced / Q000201:enzymology* / Q000503:physiopathology; D007546:Isoquinolines / Q000494:pharmacology; D008070:Lipopolysaccharides; D008745:Methylation; D051379:Mice; D008810:Mice, Inbred C57BL; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology*; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011496:Protein Methyltransferases / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000071636:Protein Phosphatase 2C; D011499:Protein Processing, Post-Translational; D043682:Receptor, Adenosine A1 / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D013997:Time Factors; D019210:Troponin I / Q000378:metabolism
D058907:Adenosine A1 Receptor Agonists; D007546:Isoquinolines; D008070:Lipopolysaccharides; D047428:Protein Kinase Inhibitors; D043682:Receptor, Adenosine A1; D013449:Sulfonamides; D019210:Troponin I; C440499:lipopolysaccharide, Escherichia coli O111 B4; D019319:Okadaic Acid; D011496:Protein Methyltransferases; D017868:Cyclic AMP-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D000071636:Protein Phosphatase 2C; D000241:Adenosine; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide