Limits...
Effects of endotoxaemia on protein metabolism in rat fast-twitch skeletal muscle and myocardium.

Murton AJ, Alamdari N, Gardiner SM, Constantin-Teodosiu D, Layfield R, Bennett T, Greenhaff PL - PLoS ONE (2009)

Bottom Line: It is unclear if the rat myocardium undergoes the same rapid reductions in protein content that are classically observed in fast-twitch skeletal muscle during endotoxaemia.The protein-to-DNA ratio, a marker of protein content, was significantly reduced in the EDL following 24 h LPS administration (23%; P<0.05), but was no different from controls in the myocardium.In summary, these findings suggest that the myocardium does not undergo the same catabolic response as skeletal muscle during early endotoxaemia, partly due to the absence of transcriptional and signalling events in the myocardium typically associated with increased muscle proteolysis and the suppression of protein synthesis.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, Queen's Medical Centre, University of Nottingham, Nottingham, UK. andrew.murton@nottingham.ac.uk

ABSTRACT

Background: It is unclear if the rat myocardium undergoes the same rapid reductions in protein content that are classically observed in fast-twitch skeletal muscle during endotoxaemia.

Methodology/principal findings: To investigate this further, and to determine if there is any divergence in the response of skeletal muscle and myocardium in the mechanisms that are thought to be largely responsible for eliciting changes in protein content, Sprague Dawley rats were implanted with vascular catheters and administered lipopolysaccharide (LPS; 150 microg kg(-1) h(-1)) intravenously for 2 h, 6 h or 24 h (saline administered control animals were also included), after which the extensor digitorum longus (EDL) and myocardium were removed under terminal anaesthesia. The protein-to-DNA ratio, a marker of protein content, was significantly reduced in the EDL following 24 h LPS administration (23%; P<0.05), but was no different from controls in the myocardium. At the same time point, a significant increase in MAFbx/atrogin-1 and MuRF1 mRNA (3.7+/-0.7- and 19.5+/-1.9-fold increase vs. controls, respectively; P<0.05), in addition to protein levels of alpha1-3, 5-7 subunits of the 20S proteasome, were observed in EDL but not myocardium. In contrast, elevations in phosphorylation of p70 S6K residues Thr(421)/Ser(424), and 4E-BP1 residues Thr(37)/Thr(46) (P<0.05), consistent with an elevation in translation initiation, were seen exclusively in the myocardium of LPS-treated animals.

Conclusions/significance: In summary, these findings suggest that the myocardium does not undergo the same catabolic response as skeletal muscle during early endotoxaemia, partly due to the absence of transcriptional and signalling events in the myocardium typically associated with increased muscle proteolysis and the suppression of protein synthesis.

Show MeSH

Related in: MedlinePlus

Protein to DNA ratio in muscle and myocardium following LPS infusion.A) ASP to DNA ratio following 2 h, 6 h and 24 h LPS infusion expressed as a percentage of treatment group relative to control groups. Values represent mean±SEM. n = 5–8 per group. B) Quantity of alkaline soluble proteins and DNA in a 20 µl aliquot of muscle extract. Solid lines indicate alkaline soluble proteins; dashed lines, DNA; (□) mean of values from EDL of saline treated animals; (Δ) EDL/LPS; (▪) myocardium/saline and (▴) myocardium/LPS. By two-way ANOVA, significant differences were observed for main effects of treatment (P = 0.02) and time (P = 0.03) and treatment-time interaction (P = 0.02). * indicates significantly different from control (P<0.05).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2736646&req=5

pone-0006945-g002: Protein to DNA ratio in muscle and myocardium following LPS infusion.A) ASP to DNA ratio following 2 h, 6 h and 24 h LPS infusion expressed as a percentage of treatment group relative to control groups. Values represent mean±SEM. n = 5–8 per group. B) Quantity of alkaline soluble proteins and DNA in a 20 µl aliquot of muscle extract. Solid lines indicate alkaline soluble proteins; dashed lines, DNA; (□) mean of values from EDL of saline treated animals; (Δ) EDL/LPS; (▪) myocardium/saline and (▴) myocardium/LPS. By two-way ANOVA, significant differences were observed for main effects of treatment (P = 0.02) and time (P = 0.03) and treatment-time interaction (P = 0.02). * indicates significantly different from control (P<0.05).

Mentions: A significant reduction (23%; P<0.05) in the ASP:DNA ratio relative to controls was observed in the EDL after 24 h of LPS infusion (Fig. 2A). This appeared the result of a decline in levels of ASP in muscle extracts as opposed to a change in DNA content (Fig. 2B), indicative of a decline in muscle protein content. In contrast to skeletal muscle, there were no significant changes in ASP levels, DNA content (Fig. 2B), or the ASP:DNA ratio (Fig. 2A) of the myocardium at any time point compared to controls.


Effects of endotoxaemia on protein metabolism in rat fast-twitch skeletal muscle and myocardium.

Murton AJ, Alamdari N, Gardiner SM, Constantin-Teodosiu D, Layfield R, Bennett T, Greenhaff PL - PLoS ONE (2009)

Protein to DNA ratio in muscle and myocardium following LPS infusion.A) ASP to DNA ratio following 2 h, 6 h and 24 h LPS infusion expressed as a percentage of treatment group relative to control groups. Values represent mean±SEM. n = 5–8 per group. B) Quantity of alkaline soluble proteins and DNA in a 20 µl aliquot of muscle extract. Solid lines indicate alkaline soluble proteins; dashed lines, DNA; (□) mean of values from EDL of saline treated animals; (Δ) EDL/LPS; (▪) myocardium/saline and (▴) myocardium/LPS. By two-way ANOVA, significant differences were observed for main effects of treatment (P = 0.02) and time (P = 0.03) and treatment-time interaction (P = 0.02). * indicates significantly different from control (P<0.05).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2736646&req=5

pone-0006945-g002: Protein to DNA ratio in muscle and myocardium following LPS infusion.A) ASP to DNA ratio following 2 h, 6 h and 24 h LPS infusion expressed as a percentage of treatment group relative to control groups. Values represent mean±SEM. n = 5–8 per group. B) Quantity of alkaline soluble proteins and DNA in a 20 µl aliquot of muscle extract. Solid lines indicate alkaline soluble proteins; dashed lines, DNA; (□) mean of values from EDL of saline treated animals; (Δ) EDL/LPS; (▪) myocardium/saline and (▴) myocardium/LPS. By two-way ANOVA, significant differences were observed for main effects of treatment (P = 0.02) and time (P = 0.03) and treatment-time interaction (P = 0.02). * indicates significantly different from control (P<0.05).
Mentions: A significant reduction (23%; P<0.05) in the ASP:DNA ratio relative to controls was observed in the EDL after 24 h of LPS infusion (Fig. 2A). This appeared the result of a decline in levels of ASP in muscle extracts as opposed to a change in DNA content (Fig. 2B), indicative of a decline in muscle protein content. In contrast to skeletal muscle, there were no significant changes in ASP levels, DNA content (Fig. 2B), or the ASP:DNA ratio (Fig. 2A) of the myocardium at any time point compared to controls.

Bottom Line: It is unclear if the rat myocardium undergoes the same rapid reductions in protein content that are classically observed in fast-twitch skeletal muscle during endotoxaemia.The protein-to-DNA ratio, a marker of protein content, was significantly reduced in the EDL following 24 h LPS administration (23%; P<0.05), but was no different from controls in the myocardium.In summary, these findings suggest that the myocardium does not undergo the same catabolic response as skeletal muscle during early endotoxaemia, partly due to the absence of transcriptional and signalling events in the myocardium typically associated with increased muscle proteolysis and the suppression of protein synthesis.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, Queen's Medical Centre, University of Nottingham, Nottingham, UK. andrew.murton@nottingham.ac.uk

ABSTRACT

Background: It is unclear if the rat myocardium undergoes the same rapid reductions in protein content that are classically observed in fast-twitch skeletal muscle during endotoxaemia.

Methodology/principal findings: To investigate this further, and to determine if there is any divergence in the response of skeletal muscle and myocardium in the mechanisms that are thought to be largely responsible for eliciting changes in protein content, Sprague Dawley rats were implanted with vascular catheters and administered lipopolysaccharide (LPS; 150 microg kg(-1) h(-1)) intravenously for 2 h, 6 h or 24 h (saline administered control animals were also included), after which the extensor digitorum longus (EDL) and myocardium were removed under terminal anaesthesia. The protein-to-DNA ratio, a marker of protein content, was significantly reduced in the EDL following 24 h LPS administration (23%; P<0.05), but was no different from controls in the myocardium. At the same time point, a significant increase in MAFbx/atrogin-1 and MuRF1 mRNA (3.7+/-0.7- and 19.5+/-1.9-fold increase vs. controls, respectively; P<0.05), in addition to protein levels of alpha1-3, 5-7 subunits of the 20S proteasome, were observed in EDL but not myocardium. In contrast, elevations in phosphorylation of p70 S6K residues Thr(421)/Ser(424), and 4E-BP1 residues Thr(37)/Thr(46) (P<0.05), consistent with an elevation in translation initiation, were seen exclusively in the myocardium of LPS-treated animals.

Conclusions/significance: In summary, these findings suggest that the myocardium does not undergo the same catabolic response as skeletal muscle during early endotoxaemia, partly due to the absence of transcriptional and signalling events in the myocardium typically associated with increased muscle proteolysis and the suppression of protein synthesis.

Show MeSH
Related in: MedlinePlus