A potential role for Akt/FOXO signalling in both protein loss and the impairment of muscle carbohydrate oxidation during sepsis in rodent skeletal muscle.
Sepsis causes muscle atrophy and insulin resistance, but the underlying mechanisms are unclear. Therefore, the present study examined the effects of lipopolysaccharide (LPS)-induced endotoxaemia on the expression of Akt, Forkhead Box O (FOXO) and its downstream targets, to identify any associations between changes in FOXO-dependent processes influencing muscle atrophy and insulin resistance during sepsis. Chronically instrumented male Sprague-Dawley rats received a continuous intravenous infusion of LPS (15 microg kg(-1) h(-1)) or saline for 24 h at 0.4 ml h(-1). Animals were terminally anaesthetized and the extensor digitorum longus muscles from both hindlimbs were removed and snap-frozen. Measurements were made of mRNA and protein expression of selected signalling molecules associated with pathways regulating protein synthesis and degradation and carbohydrate metabolism. LPS infusion induced increases in muscle tumour necrosis factor-alpha (8.9-fold, P < 0.001) and interleukin-6 (8.4-fold, P < 0.01), paralleled by reduced insulin receptor substrate-1 mRNA expression (-0.7-fold, P < 0.01), and decreased Akt1 protein and cytosolic FOXO1 and FOXO3 phosphorylation. These changes were accompanied by significant increases in muscle atrophy F-box mRNA (5.5-fold, P < 0.001) and protein (2-fold, P < 0.05) expression, and pyruvate dehydrogenase kinase 4 mRNA (15-fold, P < 0.001) and protein (1.6-fold, P < 0.05) expression. There was a 29% reduction in the muscle protein: DNA ratio, a 56% reduction in pyruvate dehydrogenase complex (PDC) activity (P < 0.05), and increased glycogen degradation and lactate accumulation. The findings of this study suggest a potential role for Akt/FOXO in the simultaneous impairment of carbohydrate oxidation, at the level of PDC, and up-regulation of muscle protein degradation, in LPS-induced endotoxaemia.
Crossland
Hannah
H
Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, Queen's Medical Centre, University of Nottingham, Nottingham NG7 2UH, UK. mbxhc@nottingham.ac.uk
Constantin-Teodosiu
Dumitru
D
Gardiner
Sheila M
SM
Constantin
Despina
D
Greenhaff
Paul L
PL
D000818:Animals; D050260:Carbohydrate Metabolism; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D007333:Insulin Resistance / Q000235:genetics / Q000502:physiology; D008297:Male; D008954:Models, Biological; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D009133:Muscular Atrophy / Q000209:etiology / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism; D018805:Sepsis / Q000150:complications / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D000071161:Forkhead Box Protein O1
D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D012333:RNA, Messenger; D044843:SKP Cullin F-Box Protein Ligases; C499515:FOXO3 protein, rat; C074639:Foxo1 protein, rat; D000071161:Forkhead Box Protein O1; C486692:Fbxo32 protein, rat; C494920:Akt1 protein, rat