Effect of severe short-term malnutrition on diaphragm muscle signal transduction pathways influencing protein turnover.
The aim of this study was to evaluate the effect of nutritional deprivation (ND) on signal transduction pathways influencing the translational apparatus in the diaphragm muscle. Male rats were divided into two groups: 1) 20% of usual food intake for 4 days (ND) with water provided at libitum and 2) free-eating control (Ctl). Total protein and RNA were extracted from the diaphragm. Insulin-like growth factor I mRNA was analyzed by RT-PCR. Protein analyses of key cytoplasmic proteins for three signaling pathways deemed important in influencing protein turnover [phosphatidylinositol 3-kinase- Akt-mammalian target of rapamycin, P13K/Akt/glycogen synthase kinase (GSK)-3, and MAPK-ERK] were performed by Western blot. Body weight decreased 30% in ND and increased 17% in Ctl animals. Diaphragm mass decreased 29% in ND animals. Muscle insulin-like growth factor I mRNA abundance was reduced 63% in ND animals. ND resulted in a 55% reduction in phosphorylated (Ser473) Akt. Phosphorylation of mammalian target of rapamycin at Ser2448 was reduced by 85% in ND animals. Downstream effectors important in translation initiation were also affected by ND. Phosphorylated (Thr389) 70-kDa ribosomal protein S6 kinase was significantly reduced (35%) by ND. ND also resulted in significant dephosphorylation of the translational repressor initiation factor 4E-binding protein 1. Phosphorylation of GSK-3alpha (Ser21) and GSK-3beta (Ser9) was increased 55 and 45%, respectively, with ND. Phosphorylation of ERK1 (Thr202) and ERK2 (Tyr204), p44 and p42, respectively, was reduced 64 and 55%, respectively, with ND. Total protein concentration for all signaling intermediates of the three pathways was preserved. We conclude that short-term ND altered the phosphorylation states of key proteins of several pathways involved in protein turnover. This forms the framework for future studies aimed at identifying therapeutic targets in the management of short-term nutritionally induced cachectic states.
Division of Pulmonary/Critical Care Medicine, Burns and Allen Research Institute, Cedars-Sinai Medical Center, 8700 Beverly Blvd., Rm. 6732, Los Angeles, CA 90048, USA. michael.lewis@cshs.org
Michael I
MI
Lewis
Sue C
SC
Bodine
Nader
N
Kamangar
Xuan
X
Xu
Xiaoyu
X
Da
Mario
M
Fournier
D000818:Animals; D003964:Diaphragm / Q000737:chemistry / Q000502:physiology*; D038362:Glycogen Synthase Kinase 3 / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D008297:Male; D044342:Malnutrition / Q000503:physiopathology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D009124:Muscle Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D019893:Ribosomal Protein S6 Kinases / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D020123:Sirolimus / Q000494:pharmacology
D009124:Muscle Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D038362:Glycogen Synthase Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases; D020123:Sirolimus