Amino acid absorption and protein synthesis responses of turbot Scophthalmus maximus to lysine and leucine in free, dipeptide and tripeptide forms
AQUACULTURE NUTRITION
Authors: Wei, Yuliang; Xu, Houguo; Liang, Mengqing
Abstract
The study aimed to investigate the effects of crystalline Lys and Leu, Lys-Leu dipeptide and Lys-Leu-Lys/Leu-Lys-Leu tripeptide, on growth, postprandial Lys and Leu concentrations, gene expression of peptide and amino acid (AA) transporters and related gene expression of protein synthesis pathway in turbot. Three diets (CAA, Di and Tri) contained Lys and Leu as free (Lys and Leu), dipeptide (Lys-Leu) and tripeptide (Lys-Leu-Lys/Leu-Lys-Leu) forms, respectively. Improved growth was observed in the Di group compared with the CAA group. For peptide and AAs transporters, PepT1, B(0)AT1 and y(+)LAT2 mRNA levels were affected in proximal intestine by dietary treatments. Free Lys and Leu concentrations in the CAA group were significantly higher than that of the Di and Tri groups at 6 hr postfeeding in serum and at 2, 6 and 24 hr postfeeding in muscle. For protein synthesis pathway in muscle, Akt2, TOR and S6k1 gene expression were the highest in the Di group and the lowest in the CAA group, whereas MuRF1 relative expression was the highest in the Tri group. In conclusion, dietary Lys-Leu dipeptide was utilized more efficiently than free Lys and Leu or Lys-Leu-Lys/Leu-Lys-Leu tripeptide for turbot by regulating AAs transport, postprandial AAs concentration and the synthesis of muscle proteins.
Downregulation of Akt2 attenuates ER stress-induced cytotoxicity through JNK-Wnt pathway in cardiomyocytes
BIOORGANIC & MEDICINAL CHEMISTRY LETTERS
Authors: Gao, Yan-Xia; He, Wen-Ting; Pan, Long-Fei; Feng, Hui; Sun, Jiang-Li; Zhang, Bin; Yu, Lei; Li, Li-Jun
Abstract
Akt, also known as protein kinase B (PKB), is a serine/threonine kinase that promotes survival and growth in response to extracellular signals. Akt1 has been demonstrated to play vital roles in cardiovascular diseases, but the role of Akt2 in cardiomyocytes is not fully understood. This study investigated the effect of Akt2 knockdown on tunicamycin (TM)-induced cytotoxicity in cardiomyocytes and the underlying mechanisms with a focus on the JNK-Wnt pathway. TM treatment significantly increased the expression of Akt2 at both mRNA and protein levels, which was shown to be mediated by the induction of reactive oxygen species (ROS). Knockdown of Akt2 expression via siRNA transfection markedly increased cell viability, decreased lactate dehydrogenase (LDH) release and reduced cell apoptosis after TM exposure. The results of western blot showed that downregulation of Akt2 also attenuated the TM-induced activation of the unfolded protein response (UPR) factors and ER stress associated pro-apoptotic proteins. In addition, Si-Akt2 transfection partially prevented the TM-induced decrease in nuclear localization of beta-catenin. By using the selective inhibitor SP-600,125 to inhibit JNK phosphorylation, we found that knockdown of Akt2-induced protection and inhibition of ER stress was mediated by reversing TM-induced decrease of Wnt through the JNK pathway. In summary, these data suggested that Akt2 play a pivotal role in regulating cardiomyocyte survival during ER stress by modulating the JNK-Wnt pathway. (C) 2017 Elsevier Ltd. All rights reserved.