Atrogin-1, MuRF1, and FoXO, as well as phosphorylated GSK-3beta and 4E-BP1 are reduced in skeletal muscle of chronic spinal cord-injured patients.
Chronic complete spinal cord injury (SCI) is associated with severe skeletal muscle atrophy as well several atrophy and physical-inactivity-related comorbidity factors such as diabetes, obesity, lipid disorders, and cardiovascular diseases. Intracellular mechanisms associated with chronic complete SCI-related muscle atrophy are not well understood, and thus their characterization may assist with developing strategies to reduce the risk of comorbidity factors. Therefore, the aim of this study was to determine whether there was an increase in catabolic signaling targets, such as atrogin-1, muscle ring finger-1 (MuRF1), forkhead transcription factor (FoXO), and myostatin, and decreases in anabolic signaling targets, such as insulin-like growth factor (IGF), v-akt murine thymoma viral oncogene (Akt), glycogen synthase kinase-beta (GSK-3beta), mammalian target of rapamycin (mTOR), eukaryotic initiation factor 4E binding protein 1 (4E-BP1), and p70(s6kinase) in chronic complete SCI patients. In SCI patients, when compared with controls, there was a significant reduction in mRNA levels of atrogin-1 (59%; P < 0.05), MuRF1 (55%; P < 0.05), and myostatin (46%; P < 0.01), and in protein levels of FoXO1 (72%; P < 0.05), FoXO3a (60%; P < 0.05), and atrogin-1 (36%; P < 0.05). Decreases in the protein levels of IGF-1 (48%; P < 0.001) and phosphorylated GSK-3beta (54%; P < 0.05), 4E-BP1 (48%; P < 0.05), and p70(s6kinase) (60%; P = 0.1) were also observed, the latter three in an Akt- and mTOR-independent manner. Reductions in atrogin-1, MuRF1, FoXO, and myostatin suggest the existence of an internal mechanism aimed at reducing further loss of muscle proteins during chronic SCI. The downregulation of signaling proteins that regulate anabolism, such as IGF, GSK-3beta, and 4E-BP1, would reduce the ability to increase protein synthesis rates.
Léger
Bertrand
B
Institut de Recherche en Réadaptation-Réinsertion, Sion, Switzerland.
Senese
Rosalba
R
Al-Khodairy
Abdul W
AW
Dériaz
Olivier
O
Gobelet
Charles
C
Giacobino
Jean-Paul
JP
Russell
Aaron P
AP
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000328:Adult; D016022:Case-Control Studies; D018797:Cell Cycle Proteins; D002908:Chronic Disease; D015536:Down-Regulation / Q000502:physiology*; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D008875:Middle Aged; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism; D055435:Myostatin / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013119:Spinal Cord Injuries / Q000000981:diagnostic imaging / Q000473:pathology*; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D051858:Forkhead Transcription Factors; D009124:Muscle Proteins; D055435:Myostatin; D010750:Phosphoproteins; D012333:RNA, Messenger; D000070584:Tripartite Motif Proteins; C440907:FBXO32 protein, human; D044843:SKP Cullin F-Box Protein Ligases; C440908:TRIM63 protein, human; D044767:Ubiquitin-Protein Ligases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; D018995:Myosin Heavy Chains