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Cooperative control of striated muscle mass and metabolism by MuRF1 and MuRF2.

Witt CC, Witt SH, Lerche S, Labeit D, Back W, Labeit S - EMBO J. (2007)

Bottom Line: The muscle-specific RING finger proteins MuRF1 and MuRF2 have been proposed to regulate protein degradation and gene expression in muscle tissues.Muscle hypertrophy in dKO mice was maintained throughout the murine life span and was associated with chronically activated muscle protein synthesis.Other catabolic factors such as MAFbox/atrogin1 were expressed at normal levels and did not respond to or prevent muscle hypertrophy in dKO mice.

View Article: PubMed Central - PubMed

Affiliation: Institute of Anesthesiology and Intensive Care, Universitätsklinikum Mannheim, Mannheim, Germany.

ABSTRACT
The muscle-specific RING finger proteins MuRF1 and MuRF2 have been proposed to regulate protein degradation and gene expression in muscle tissues. We have tested the in vivo roles of MuRF1 and MuRF2 for muscle metabolism by using knockout (KO) mouse models. Single MuRF1 and MuRF2 KO mice are healthy and have normal muscles. Double knockout (dKO) mice obtained by the inactivation of all four MuRF1 and MuRF2 alleles developed extreme cardiac and milder skeletal muscle hypertrophy. Muscle hypertrophy in dKO mice was maintained throughout the murine life span and was associated with chronically activated muscle protein synthesis. During ageing (months 4-18), skeletal muscle mass remained stable, whereas body fat content did not increase in dKO mice as compared with wild-type controls. Other catabolic factors such as MAFbox/atrogin1 were expressed at normal levels and did not respond to or prevent muscle hypertrophy in dKO mice. Thus, combined inhibition of MuRF1/MuRF2 could provide a potent strategy to stimulate striated muscles anabolically and to protect muscles from sarcopenia during ageing.

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Characterization of altered signaling pathways in dKO myocardium by western blot studies. (A) Upregulation of the MuRF1/MuRF2 binding proteins CARP, FHL2, and SQSTM1 in dKO myocardium. Striking upregulation required the deletion of all four MuRF1/2 alleles, suggesting that both MuRF1 and MuRF2 synergistically control the transcriptional regulators CARP, FHL2, and SQSTM1. Below, cTnI and total multi-ubiquitinated protein species were not affected by the inactivation of MuRF1 and MuRF2 alleles. Among SUMO family members, we noticed for SUMO4 differential reactivity in the 8–30 kDa region. (B, C) Hyperactive stretch signaling in dKO as suggested by chronic upregulation of stretch-dependent signaling markers. (B) In myocardium, ANP is barely detectable in WT, MuRF1-KO, and MuRF2-KO hearts. ANP is strikingly upregulated in dKO myocardium (ventricles, 12 months old). Other markers for cardiomyopathy/hypertrophy remain normal or are moderately upregulated: SERCA2a (used as a marker for heart failure/calcium overload), SRF (previously implicated in stretch-dependent MuRF2 signaling), p38 Map kinase (a marker for ERK signaling and heart failure). (C) In dKO quadriceps muscles, hyperactive stretch signaling was suggested by the effect of 72 h immobilization on the stretch marker MLP: abnormally high levels of MLP/Crsp3 are maintained after 72 h immobilization in dKO quadriceps (NT=no treatment, byc=bycast immobilization).
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f5: Characterization of altered signaling pathways in dKO myocardium by western blot studies. (A) Upregulation of the MuRF1/MuRF2 binding proteins CARP, FHL2, and SQSTM1 in dKO myocardium. Striking upregulation required the deletion of all four MuRF1/2 alleles, suggesting that both MuRF1 and MuRF2 synergistically control the transcriptional regulators CARP, FHL2, and SQSTM1. Below, cTnI and total multi-ubiquitinated protein species were not affected by the inactivation of MuRF1 and MuRF2 alleles. Among SUMO family members, we noticed for SUMO4 differential reactivity in the 8–30 kDa region. (B, C) Hyperactive stretch signaling in dKO as suggested by chronic upregulation of stretch-dependent signaling markers. (B) In myocardium, ANP is barely detectable in WT, MuRF1-KO, and MuRF2-KO hearts. ANP is strikingly upregulated in dKO myocardium (ventricles, 12 months old). Other markers for cardiomyopathy/hypertrophy remain normal or are moderately upregulated: SERCA2a (used as a marker for heart failure/calcium overload), SRF (previously implicated in stretch-dependent MuRF2 signaling), p38 Map kinase (a marker for ERK signaling and heart failure). (C) In dKO quadriceps muscles, hyperactive stretch signaling was suggested by the effect of 72 h immobilization on the stretch marker MLP: abnormally high levels of MLP/Crsp3 are maintained after 72 h immobilization in dKO quadriceps (NT=no treatment, byc=bycast immobilization).

Mentions: To gain insights into the mechanisms causing cardiac hypertrophy in dKO mice, we analyzed their transcriptomes by gene expression profiling. The transcriptional changes we found in dKO ventricles resembled those present in pressure induced aortic constriction (Zhao et al, 2004), including the upregulation of skeletal-type alpha actin 1, myosin light chains, atrial natriuretic peptide (ANP; isoforms A and B), and thrombospondin (see Supplementary Figure 9 and ArrayExpress accession E-MEXP-1321). Consistent with elevated stretch signaling, ANP was strikingly upregulated in dKO ventricles (Figure 5B). Normal to moderately elevated expression of other markers for cardiac hypertrophy suggested that the ANP induction was not a secondary consequence of heart failure and calcium overload (Figure 5A). SERCA2a (a marker for calcium overload during heart failure), serum response factor (SRF, previously suggested to transmit titin kinase/MuRF2-dependent stretch signals; Lange et al, 2005), and p38 MAPK (activated by the ERK/Map kinase pathway) were not affected by the absence of MuRF1 or MuRF2. In dKO myocardium, neither microarrays nor western blots showed an upregulation of SRF (Figure 5B and Supplementary Table 9).


Cooperative control of striated muscle mass and metabolism by MuRF1 and MuRF2.

Witt CC, Witt SH, Lerche S, Labeit D, Back W, Labeit S - EMBO J. (2007)

Characterization of altered signaling pathways in dKO myocardium by western blot studies. (A) Upregulation of the MuRF1/MuRF2 binding proteins CARP, FHL2, and SQSTM1 in dKO myocardium. Striking upregulation required the deletion of all four MuRF1/2 alleles, suggesting that both MuRF1 and MuRF2 synergistically control the transcriptional regulators CARP, FHL2, and SQSTM1. Below, cTnI and total multi-ubiquitinated protein species were not affected by the inactivation of MuRF1 and MuRF2 alleles. Among SUMO family members, we noticed for SUMO4 differential reactivity in the 8–30 kDa region. (B, C) Hyperactive stretch signaling in dKO as suggested by chronic upregulation of stretch-dependent signaling markers. (B) In myocardium, ANP is barely detectable in WT, MuRF1-KO, and MuRF2-KO hearts. ANP is strikingly upregulated in dKO myocardium (ventricles, 12 months old). Other markers for cardiomyopathy/hypertrophy remain normal or are moderately upregulated: SERCA2a (used as a marker for heart failure/calcium overload), SRF (previously implicated in stretch-dependent MuRF2 signaling), p38 Map kinase (a marker for ERK signaling and heart failure). (C) In dKO quadriceps muscles, hyperactive stretch signaling was suggested by the effect of 72 h immobilization on the stretch marker MLP: abnormally high levels of MLP/Crsp3 are maintained after 72 h immobilization in dKO quadriceps (NT=no treatment, byc=bycast immobilization).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2168395&req=5

f5: Characterization of altered signaling pathways in dKO myocardium by western blot studies. (A) Upregulation of the MuRF1/MuRF2 binding proteins CARP, FHL2, and SQSTM1 in dKO myocardium. Striking upregulation required the deletion of all four MuRF1/2 alleles, suggesting that both MuRF1 and MuRF2 synergistically control the transcriptional regulators CARP, FHL2, and SQSTM1. Below, cTnI and total multi-ubiquitinated protein species were not affected by the inactivation of MuRF1 and MuRF2 alleles. Among SUMO family members, we noticed for SUMO4 differential reactivity in the 8–30 kDa region. (B, C) Hyperactive stretch signaling in dKO as suggested by chronic upregulation of stretch-dependent signaling markers. (B) In myocardium, ANP is barely detectable in WT, MuRF1-KO, and MuRF2-KO hearts. ANP is strikingly upregulated in dKO myocardium (ventricles, 12 months old). Other markers for cardiomyopathy/hypertrophy remain normal or are moderately upregulated: SERCA2a (used as a marker for heart failure/calcium overload), SRF (previously implicated in stretch-dependent MuRF2 signaling), p38 Map kinase (a marker for ERK signaling and heart failure). (C) In dKO quadriceps muscles, hyperactive stretch signaling was suggested by the effect of 72 h immobilization on the stretch marker MLP: abnormally high levels of MLP/Crsp3 are maintained after 72 h immobilization in dKO quadriceps (NT=no treatment, byc=bycast immobilization).
Mentions: To gain insights into the mechanisms causing cardiac hypertrophy in dKO mice, we analyzed their transcriptomes by gene expression profiling. The transcriptional changes we found in dKO ventricles resembled those present in pressure induced aortic constriction (Zhao et al, 2004), including the upregulation of skeletal-type alpha actin 1, myosin light chains, atrial natriuretic peptide (ANP; isoforms A and B), and thrombospondin (see Supplementary Figure 9 and ArrayExpress accession E-MEXP-1321). Consistent with elevated stretch signaling, ANP was strikingly upregulated in dKO ventricles (Figure 5B). Normal to moderately elevated expression of other markers for cardiac hypertrophy suggested that the ANP induction was not a secondary consequence of heart failure and calcium overload (Figure 5A). SERCA2a (a marker for calcium overload during heart failure), serum response factor (SRF, previously suggested to transmit titin kinase/MuRF2-dependent stretch signals; Lange et al, 2005), and p38 MAPK (activated by the ERK/Map kinase pathway) were not affected by the absence of MuRF1 or MuRF2. In dKO myocardium, neither microarrays nor western blots showed an upregulation of SRF (Figure 5B and Supplementary Table 9).

Bottom Line: The muscle-specific RING finger proteins MuRF1 and MuRF2 have been proposed to regulate protein degradation and gene expression in muscle tissues.Muscle hypertrophy in dKO mice was maintained throughout the murine life span and was associated with chronically activated muscle protein synthesis.Other catabolic factors such as MAFbox/atrogin1 were expressed at normal levels and did not respond to or prevent muscle hypertrophy in dKO mice.

View Article: PubMed Central - PubMed

Affiliation: Institute of Anesthesiology and Intensive Care, Universitätsklinikum Mannheim, Mannheim, Germany.

ABSTRACT
The muscle-specific RING finger proteins MuRF1 and MuRF2 have been proposed to regulate protein degradation and gene expression in muscle tissues. We have tested the in vivo roles of MuRF1 and MuRF2 for muscle metabolism by using knockout (KO) mouse models. Single MuRF1 and MuRF2 KO mice are healthy and have normal muscles. Double knockout (dKO) mice obtained by the inactivation of all four MuRF1 and MuRF2 alleles developed extreme cardiac and milder skeletal muscle hypertrophy. Muscle hypertrophy in dKO mice was maintained throughout the murine life span and was associated with chronically activated muscle protein synthesis. During ageing (months 4-18), skeletal muscle mass remained stable, whereas body fat content did not increase in dKO mice as compared with wild-type controls. Other catabolic factors such as MAFbox/atrogin1 were expressed at normal levels and did not respond to or prevent muscle hypertrophy in dKO mice. Thus, combined inhibition of MuRF1/MuRF2 could provide a potent strategy to stimulate striated muscles anabolically and to protect muscles from sarcopenia during ageing.

Show MeSH
Related in: MedlinePlus