Induction of MuRF1 is essential for TNF-alpha-induced loss of muscle function in mice.
BACKGROUND
Humoral circulating inflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha) can impair skeletal muscle contractility. Furthermore, TNF-alpha expression correlates with elevated levels of atrogin-like muscle-specific ubiquitin E3 ligases, which are presumed to mediate muscle protein breakdown and atrophy. However, the casual relationships between MuRF1 and TNF-alpha and their relative contributions to muscle function impairment are not known.


METHODS
TNF-alpha or saline was injected into either C57Bl6 or MuRF1(-/-) mice. After 16-24 h, the expression of MuRF1 in skeletal muscle was quantified by quantitative reverse transcription-PCR and Western blot analysis. Muscle function was measured in an organ bath. To obtain a broader overview on potential alterations, two-dimensional gel electrophoresis was performed.


RESULTS
Wild-type animals injected with TNF-alpha had higher MuRF1 mRNA expression (saline versus TNF-alpha: 56.6+/-12.1 versus 133.6+/-30.3 arbitrary units; p<0.05) and protein expression (saline versus TNF-alpha: 0.38+/-0.11 versus 1.07+/-0.25 arbitrary units; p<0.05) as compared to saline-injected littermates. Furthermore, TNF-alpha reduced force development at 150 Hz by 25% in C57Bl6 animals (saline versus TNF-alpha: 2412+/-120 versus 1799+/-114 g/cm(2); p<0.05), but not in MuRF1(-/-) mice (saline versus TNF-alpha: 2424+/-198 versus 2431+/-180 g/cm(2); p=NS). Proteome analysis revealed a significant down-regulation of fast skeletal muscle troponin T in wild-type animals treated with TNF-alpha as compared to MuRF1(-/-) mice that received TNF-alpha.


CONCLUSIONS
The results of this study demonstrate for the first time that TNF-alpha-induced reduction in skeletal muscle force development depends on the induction of the atrophy-related E3 ubiquitin ligase MuRF1. A link for the reduction in muscle force may be the TNF-alpha/MuRF1-mediated down-regulation of fast skeletal muscle troponin T.
Adams
Volker
V
Heart Center Leipzig, University Leipzig, Strümpellstrasse 39, D-04289 Leipzig, Germany. adav@medizin.uni-leipzig.de
Mangner
Norman
N
Gasch
Alexander
A
Krohne
Christian
C
Gielen
Stephan
S
Hirner
Stephanie
S
Thierse
Hermann-Josef
HJ
Witt
Christian C
CC
Linke
Axel
A
Schuler
Gerhard
G
Labeit
Siegfried
S
D000818:Animals; D002460:Cell Line; D015536:Down-Regulation / Q000187:drug effects; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D047468:Immunoprecipitation; D066298:In Vitro Techniques; D051379:Mice; D008954:Models, Biological; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D020648:Peptide Elongation Factor 1 / Q000378:metabolism; D000070584:Tripartite Motif Proteins; D020107:Troponin T / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism*
D039561:Eukaryotic Initiation Factor-4E; D009124:Muscle Proteins; D020648:Peptide Elongation Factor 1; D000070584:Tripartite Motif Proteins; D020107:Troponin T; D014409:Tumor Necrosis Factor-alpha; D025801:Ubiquitin; C499084:Trim63 protein, mouse; D044767:Ubiquitin-Protein Ligases