Myocardial expression of Murf-1 and MAFbx after induction of chronic heart failure: Effect on myocardial contractility.
OBJECTIVE
In chronic heart failure (CHF) the myocardial expression of the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha), which is thought to contribute to myocardial remodeling, was found to be increased. However, it is unknown whether the E3-ubiquitin ligases MAFbx and Murf-1 are involved in this remodeling process and whether their expression is regulated by TNF-alpha.


METHODS
Rats underwent ligation of the left coronary artery to induce CHF or were sham-operated. The expression of MAFbx/Murf-1 and troponin I was analyzed by RT-PCR and Western blotting in the non-infarcted area of the left ventricle. In cell culture experiments the potency of TNF-alpha to stimulate Murf-1/MAFbx expression, the intracellular signaling pathway, and the involvement of the E3-ligases for the impairment of contractility were assessed.


RESULTS
In CHF the myocardial expression of TNF-alpha was elevated 3.1-fold as compared to control. This was associated with a 4.5-fold and 2.7-fold increase in MAFbx and Murf-1 expression, respectively. A positive correlation between TNF-alpha and the expression of MAFbx or Murf-1 was evident. In neonatal rat cardiomyocytes, TNF-alpha induced the expression of MAFbx through p38MAPK-dependent pathways, whereas the induction of Murf-1 required the activation of the p42/44 MAPK pathway. Exposure of cardiomyocytes to TNF-alpha resulted in troponin I ubiquitinylation, subsequent degradation, and a decline in contractility. This was completely abrogated by siRNAs against Murf-1/MAFbx.


CONCLUSIONS
TNF-alpha, which is increasingly expressed in CHF, induces troponin I degradation through a MAFbx/Murf-1-dependent pathway. This was associated with an impairment of contractility and might be one mechanism involved in the adverse remodeling process in CHF.
Adams
Volker
V
University Leipzig-Heart Center Leipzig, Department of Cardiology, Leipzig, Germany. adav@medizin.uni-leipzig.de
Linke
Axel
A
Wisloff
Ulrik
U
Döring
Christian
C
Erbs
Sandra
S
Kränkel
Nicolle
N
Witt
Christian C
CC
Labeit
Siegfried
S
Müller-Werdan
Ursula
U
Schuler
Gerhard
G
Hambrecht
Rainer
R
D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western / Q000379:methods; D004452:Echocardiography; D005419:Flavonoids / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006333:Heart Failure / Q000276:immunology / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors; D023421:Models, Animal; D009124:Muscle Proteins / Q000032:analysis* / Q000235:genetics; D009206:Myocardium / Q000737:chemistry*; D011725:Pyridines / Q000494:pharmacology; D034622:RNA Interference; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011921:Rats, Inbred WKY; D044843:SKP Cullin F-Box Protein Ligases / Q000032:analysis* / Q000235:genetics; D000070584:Tripartite Motif Proteins; D019210:Troponin I / Q000032:analysis / Q000235:genetics; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism / Q000494:pharmacology; D044767:Ubiquitin-Protein Ligases / Q000032:analysis* / Q000235:genetics; D018487:Ventricular Dysfunction, Left; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors
D005419:Flavonoids; D007093:Imidazoles; D009124:Muscle Proteins; D011725:Pyridines; D012333:RNA, Messenger; D000070584:Tripartite Motif Proteins; D019210:Troponin I; D014409:Tumor Necrosis Factor-alpha; C486692:Fbxo32 protein, rat; D044843:SKP Cullin F-Box Protein Ligases; C499086:Trim63 protein, rat; D044767:Ubiquitin-Protein Ligases; D019950:Mitogen-Activated Protein Kinase 1; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one