Abstract 3789: Induction of Murf-1 is Required for Tnf-alpha Induced Loss of Skeletal Muscle Function

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Background: Inflammatory cytokines like tumor necrosis factor alpha (TNF-α) are known to impair skeletal muscle (SM) function. Furthermore, TNF-α induces the expression of atrogin-like muscle specific ubiquitin E3-ligases, presumed to mediate muscle atrophy. The relative contributions of respective ubiquitin ligases, like MuRF1 for the TNF-α induced reduction in muscle function are not known. Methods: TNF-α or saline was injected either into C57Bl6 or MuRF1 −/− mice. After 16 –24h the expression of MuRF1 in the SM was quantified by qRT-PCR and western blot. Muscle function was measured in an organ bath. To obtain a broader overview on potential alterations, 2D-gel electrophoresis was performed. Results: WT animals injected with TNF-α had higher MuRF1 mRNA (saline: 56.6±12.1 vs. TNF-α: 133.6±30.3 arb. Units; p<0.05) and protein expression (saline: 0.38±0.11 vs. TNF-α: 1.07±0.25 arb. Units; p<0.05) as compared to saline injected littermates. However, TNF- α was unable to induce MurRF1 expression in MuRF1 −/− mice. Furthermore, TNF- α reduced force development at 150Hz by 25% in C57Bl6 animals (saline: 2412±120 vs. TNF-α: 1799±114 g/cm2; p<0.05), but not in MuRF1 −/− mice (saline: 2424±198 vs. TNF-α: 2431±180 g/cm2; p=NS). The proteome analysis revealed a significant down-regulation of fast skeletal muscle troponin T (TNNT3) in WT animals treated with TNF- α as compared to MuRF1 −/− mice receiving TNF-α . In addition, TNF-α injection into C57Bl6 animals resulted in a down-regulation of eEF1γ ( WT: 0.60±0.02 vs. WT+TNF-α: 0.39±0.05 arb. Units; p<0.05). This reduction was not seen in MuRF1 −/− mice receiving TNF- α (KO: 0.59±0.03 vs. KO+TNF-α: 0.68±0.01 arb. Units; p<0.05) Conclusion: The results of this study demonstrate for the first time, that the TNF- α induced reduction in SM 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-α-MuRF1-mediated down-regulation of TNNT3 and the elongation factor eEF1γ.

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