Activating transcription factor 4-dependent hsa-miR-663a transcription mediates mTORC1/p70S6K1 signaling underleucine deprivation.

The mechanistic target of rapamycin complex 1 (mTORC1) is involved in nutrient-induced signaling and is a master regulator of cell growth and metabolism. Amino acid-deficient conditions affect mTORC1 activity; however, its upstream regulators warrant further investigation. MicroRNAs are key regulators of nutrient-related responses; therefore, the present study aimed to assess the leucine starvation-induced microRNA profile and its impact on mTORC1 activity. Transcriptome analysis of human hepatocellular carcinoma cells (HepG2) under leucine deprivation revealed that hsa-miR-663a and hsa-miR-1469 were altered in a transcription factor 4-dependent manner. Overexpression of these microRNAs induced phosphorylation of the ribosomal protein S6 kinase beta-1, a mTORC1 downstream target. Furthermore, hsa-miR-663a downregulated proline-rich Akt1 substrate of 40 kDa (PRAS40), one of the mTORC1 components. In summary, this study provides new insights into the regulatory role of microRNAs in amino acid metabolism and demonstrates alterations in microRNA profile under leucine deprivation in human hepatocytes.

Dietary Genistein Prevents Denervation-Induced Muscle Atrophy in Male Rodents via Effects on Estrogen Receptor-α.

BACKGROUND: Genistein has high estrogenic activity. Previous studies have shown beneficial effects of estrogen or hormone replacement therapy on muscle mass and muscle atrophy. OBJECTIVE: We investigated the preventive effects and underlying mechanisms of genistein on muscle atrophy. METHODS: In Expt. 1, male Wistar rats were fed a diet containing no genistein [control (CON)] or 0.05% genistein (GEN; wt:wt diet) for 24 d. On day 14, the sciatic nerve in the left hind leg was severed, and the right hind leg was sham-treated. In Expt. 2, male C57BL6J mice were subcutaneously administered a vehicle (Veh group) or the estrogen receptor (ER) antagonist ICI 182,780 (ICI group) via an osmotic pump for 27 d, and each group was subsequently fed CON or GEN diets from day 3 to day 27. Muscle atrophy was induced on day 17 as in Expt. 1. In Expt. 3, male C57BL6J mice were subcutaneously administered vehicle or a selective ER agonist-ER-α [4,4',4'-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT)] or ER-ß [2,3-bis(4-hydroxyphenyl)-propionitrile (DPN)]-or genistein (GEN-sc-i) via an osmotic pump for 13 d, and muscle atrophy was induced on day 3 as in Expt. 1. The ratio of denervated soleus muscle weight to sham-operated soleus muscle weight (d/s ratio) was used as the index of muscle atrophy. RESULTS: Expt. 1: The d/s ratio in the GEN group was 20% higher than that in the CON group (P < 0.05). Expt. 2: The d/s ratio in the Veh-GEN group was 14% higher than that in the Veh-CON group (P < 0.05), although there was no significant difference between ICI-CON and ICI-GEN groups (P = 0.69). Expt. 3: The d/s ratio in the PPT-treated group was 20% greater than that in the Veh group (P < 0.05), but DPN and GEN-sc-i had no effect on the d/s ratio (P ≥ 0.05 compared with vehicle). CONCLUSION: Genistein intake mitigated denervation-induced soleus muscle atrophy. ER-α was related to the preventive effect of genistein on muscle atrophy.

Adverse effects of excessive leucine intake depend on dietary protein intake: a transcriptomic analysis to identify useful biomarkers.

The present study was conducted to identify reliable gene biomarkers for the adverse effects of excessive leucine (Leu) in Sprague-Dawley rats by DNA microarray. It has long been known that the adverse effects of excessive amino acid intake depend on dietary protein levels. Male rats were divided into 12 groups (n=6) and fed for 1 wk a diet containing low (6%), moderate (12%) or high (40%) protein. Different levels of Leu (0, 2, 4, and 8%) were added to the diets. Consumption of diets containing more than 4% Leu in 6% protein resulted in growth retardation and reduced liver weight, whereas the administration of the same dose of Leu with 12% or 40% protein did not affect them. By a process of systematic data extraction, 6 candidate gene markers were identified. The liver gene expression data obtained from another experiment with 0, 2, 3, 4, and 8% Leu in a low-protein diet was used to examine the validity of these biomarker candidates with receiver operating characteristic (ROC) curve analysis. All of AUC values of the biomarker candidates were more than 0.700, suggesting the effectiveness of the marker candidates as the indices of Leu excess. The cut-off value for the ROC curve of the gene-marker panel, which was obtained by multiple regression analysis of gene markers, indicated that Leu levels higher than 3% have adverse effects. In conclusion, the gene-marker panel suggested that for male rats dietary Leu supplementation of 2% is the NOAEL dose in low-protein (6%) diets.