The present study aimed to investigate the effects of eccentric treadmill exercise on adaptive hypertrophy of skeletal muscle in rats. Thirty-two 3-month-old Sprague Dawley (SD) rats were selected and randomly assigned to one of the four groups based on their body weights: 2-week quiet control group (2C), 2-week downhill running exercise group (2E), 4-week quiet control group (4C), and 4-week downhill running exercise group (4E). The downhill running protocol for rats in the exercise groups involved slope of -16°, running speed of 16 m/min, training duration of 90 min, and 5 training sessions per week. Twenty-four hours after the final session of training, all the four groups of rats underwent an exhaustion treadmill exercise. After resting for 48 h, all the rats were euthanized and their gastrocnemius muscles were harvested for analysis. HE staining was used to measure the cross-sectional area (CSA) and diameter of muscle fibers. Transmission electron microscope was used to observe the ultrastructural changes in muscle fibers. Purithromycin surface labeling translation method was used to measure protein synthesis rate. Immunofluorescence double labeling was used to detect the colocalization levels of lysosomal-associated membrane protein 2 (Lamp2)-leucyl-tRNA synthetase (LARS) and Lamp2-mammalian target of rapamycin (mTOR). Western blot was used to measure the protein expression levels of myosin heavy chain (MHC) IIb and LARS, as well as the phosphorylation levels of mTOR, p70 ribosomal protein S6 kinase (p70S6K), and eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1). The results showed that, compared with the 2C group rats, the 2E group rats showed significant increases in wet weight of gastrocnemius muscle, wet weight/body weight ratio, running distance, running time, pre- and post-exercise blood lactate levels, myofibrillar protein content, colocalization levels of Lamp2-LARS and Lamp2-mTOR, and LARS protein expression. Besides these above changes, compared with the 4C group, the 4E group further exhibited significantly increased fiber CSA, fiber diameter, protein synthesis rate, and phosphorylation levels of mTOR, p70S6K, and 4E-BP1. Compared with the quiet control groups, the exercise groups exhibited ultrastructural damage of rat gastrocnemius muscle, which was more pronounced in the 4E group. These findings suggest that eccentric treadmill exercise may promote mTOR translocation to lysosomal membrane, activating mTOR signaling via up-regulating LARS expression. This, in turn, increases protein synthesis rate through the mTOR-p70S6K-4E-BP1 signaling pathway, promoting protein deposition and inducing adaptive skeletal muscle hypertrophy. Although the ultrastructural changes of skeletal muscle are more pronounced, the relatively long training cycles during short-term exercise periods have a more significant effect on promoting gastrocnemius muscle protein synthesis and adaptive hypertrophy.
Animals ; Rats, Sprague-Dawley ; Physical Conditioning, Animal/physiology* ; Rats ; Muscle, Skeletal/metabolism* ; TOR Serine-Threonine Kinases/metabolism* ; Male ; Hypertrophy ; Adaptation, Physiological/physiology* ; Adaptor Proteins, Signal Transducing/metabolism* ; Ribosomal Protein S6 Kinases, 70-kDa/metabolism* ; Intracellular Signaling Peptides and Proteins

OBJECTIVETo illustrate the molecular mechanism of skeletal muscle growth by examining the effect of swimming training on skeletal muscle growth and p70s6k, rpS6 protein expression.

METHODSTwenty four male SD rats were used to establish swimming training models with a 15% body mass load. The training protocol adopted interval swimming training (every other day with 8 weeks). The gastrocnemius and soleus muscle were collected and weighed after training, and the protein expression of p70s6k, rpS6 and their phosphorylated forms were examined.

RESULTSAfter 8 weeks treatment, no significant change was observed in skeletal muscle mass between training group (T) and control group (C) (P > 0.05), but muscle mass in training rapamycin (TR) group has a significantly decrease compared with that in T and C groups (P < 0.05). Soleus and gastrocnemius muscle mass index in T group increased significantly compared with C group (P < 0.05). Compared with the C group, the ratio of P-p70s6k/p70s6k in T group increased with significant difference (P < 0.05), but the ratio in TR group was significantly reduced (P < 0.05). The ratio of P-rpS6/rpS6 had a significant difference between TR and T group (P < 0.05).

CONCLUSIONThese results suggest that the interval training protocol is helpful to increase the relative muscle hypertrophy, and has a role in promoting the expression of p70s6k and rpS6.

Animals ; Male ; Muscle, Skeletal ; growth & development ; metabolism ; physiology ; Physical Conditioning, Animal ; Rats ; Rats, Sprague-Dawley ; Ribosomal Protein S6 Kinases, 70-kDa ; metabolism ; Swimming

As glucose is known to induce insulin secretion in pancreatic beta cells, this study investigated the role of a phospholipase D (PLD)-related signaling pathway in insulin secretion caused by high glucose in the pancreatic beta-cell line MIN6N8. It was found that the PLD activity and PLD1 expression were both increased by high glucose (33.3 mM) treatment. The dominant negative PLD1 inhibited glucose-induced Beta2 expression, and glucose-induced insulin secretion was blocked by treatment with 1-butanol or PLD1-siRNA. These results suggest that high glucose increased insulin secretion through a PLD1-related pathway. High glucose induced the binding of Arf6 to PLD1. Pretreatment with brefeldin A (BFA), an Arf inhibitor, decreased the PLD activity as well as the insulin secretion. Furthermore, BFA blocked the glucose-induced mTOR and p70S6K activation, while mTOR inhibition with rapamycin attenuated the glucose induced Beta2 expression and insulin secretion. Thus, when taken together, PLD1 would appear to be an important regulator of glucose-induced insulin secretion through an Arf6/PLD1/mTOR/p70S6K/Beta2 pathway in MIN6N8 cells.
ADP-Ribosylation Factors/metabolism/physiology ; Animals ; Basic Helix-Loop-Helix Transcription Factors/metabolism/physiology ; Cells, Cultured ; Gene Expression Regulation, Enzymologic/drug effects ; Glucose/*pharmacology ; Insulin/*secretion ; Insulin-Secreting Cells/*drug effects/enzymology/metabolism/secretion ; Intracellular Signaling Peptides and Proteins/metabolism/physiology ; Mice ; Models, Biological ; Oligodeoxyribonucleotides, Antisense/pharmacology ; Phospholipase D/antagonists & inhibitors/genetics/metabolism/*physiology ; Protein-Serine-Threonine Kinases/metabolism/physiology ; Ribosomal Protein S6 Kinases, 70-kDa/metabolism/physiology ; Signal Transduction/drug effects/genetics

OBJECTIVETo evaluate the relationship between mammalian target of rapamycin (mTOR) signaling pathway and histone acetylation in cell survival, cell cycle, gene expression and protein level on human gastric cancer cells.

METHODSHuman gastric cancer cell lines, MKN45 and SGC7901 were treated with trichostatin A, rapamycin and/or LY294002, a PI3K inhibitor. Cell viability was analyzed by methylthiazolyl tetrazolium. Cell cycle distribution was evaluated by flow cytometry. The transcription level of p21(WAF1) gene was detected by using real-time polymerase chain reaction. Proteins were detected by Western blotting.

RESULTSCell viability remarkably reduced after treatment by more than two drugs (P< 0.01). Through flow cytometry assessment, MKN45 cells were arrested in G2 phase (P< 0.05), while SGC7901 cells were in G2 or G1 phase (P< 0.05) whether treated with single or more than two drugs. The expression of p21(WAF1) mRNA was remarkably increased in the gastric cancer cells treated with conjoined drugs (P< 0.01). Phosphorylation of Akt, p70S6K and 4E-BP1 was significantly reduced in cells treated with conjoined drugs (P< 0.01). And histone acetylation of H4/H3 was also increased in cells treated with conjoined drugs (P< 0.01).

CONCLUSIONmTOR singnaling pathway has an important relationship with histone acetylation in gastric cancer cell lines. There is a co-effect of mTOR inhibitor and histone deacetylase inhibitor on gastric cancer cells.

Acetylation ; drug effects ; Adaptor Proteins, Signal Transducing ; metabolism ; Blotting, Western ; Cell Cycle ; drug effects ; Cell Line, Tumor ; Cell Survival ; drug effects ; Chromones ; pharmacology ; Cyclin-Dependent Kinase Inhibitor p21 ; genetics ; Flow Cytometry ; Histones ; metabolism ; Humans ; Hydroxamic Acids ; pharmacology ; Morpholines ; pharmacology ; Phosphoproteins ; metabolism ; Phosphorylation ; drug effects ; Polymerase Chain Reaction ; Protein Kinases ; metabolism ; Proto-Oncogene Proteins c-akt ; metabolism ; RNA, Messenger ; genetics ; metabolism ; Reverse Transcriptase Polymerase Chain Reaction ; Ribosomal Protein S6 Kinases, 70-kDa ; metabolism ; Signal Transduction ; drug effects ; physiology ; Sirolimus ; pharmacology ; Stomach Neoplasms ; metabolism ; pathology ; physiopathology ; TOR Serine-Threonine Kinases