Ran Sawa1, Hikaru Nishida1, Yu Yamamoto1, Ikumi Wake1, Noriko Kai1, Ushio Kikkawa2, Yasuhiko Okimura3. 1. Department of Nutrition and Food Science, Kobe Women's University Graduate School of Life Sciences, 2-1 Higashisuma-aoyama, Suma-ku, Kobe 654-8585, Japan. 2. Division of Signal Functions, Biosignal Research Center, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan. 3. Department of Nutrition and Food Science, Kobe Women's University Graduate School of Life Sciences, 2-1 Higashisuma-aoyama, Suma-ku, Kobe 654-8585, Japan. Electronic address: y-okimura@suma.kobe-wu.ac.jp.
Abstract
OBJECTIVE: Branched-chain amino acids (BCAAs) have been reported to inhibit several types of muscle atrophy via the activation of the mechanistic target of rapamycin complex 1 (mTORC1). However, we previously found that BCAA did not activate mTORC1 in growth hormone (GH)-deficient spontaneous dwarf rats (SDRs), and that GH restored the stimulatory effect of BCAAs toward the mTORC1. The objective of this study was to determine whether GH or Insulin-like growth factor-I (IGF-I) stimulated the expression of L-type amino acid transporters (LATs) that delivered BCAAs, and whether LATs were involved in the mTORC1 activation. DESIGN: After the continuous administration of GH, cross-sectional areas (CSAs) of muscle fibers and LAT mRNA levels in the skeletal muscles of SDRs were compared to those from the SDRs that received normal saline. The effect of GH and IGF-I on LAT mRNA levels were determined in L6 and C2C12 myocytes. The effects of 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid (BCH), a blocker for LATs, and LAT1 siRNA on mTORC1 activation and cell functions were examined in C2C12 cells. RESULTS: GH increased LAT1 and LAT4 mRNA levels in accordance with the increase in CSAs of muscle fibers in SDRs. IGF-I, and not GH, increased LAT1 mRNA levels in cultured L6 myocytes. IGF-I also increased LAT1 mRNA level in another myocyte line, C2C12. Furthermore, IGF-I reduced LAT3 and LAT4 mRNA levels in both cell lines. GH reduced LAT3 and LAT4 mRNA levels in L6 cells. BCH decreased basal C2C12 cell proliferation and reduced IGF-I-induced phosphorylation of 4E-BP1 and S6K, both of which are mTORC1 targets, but LAT1 siRNA did not affect the phosphorylation. This suggests that BCH may exert its effect via other pathway than LAT1. CONCLUSIONS: IGF-I increased LAT1 mRNA level in myocytes. However, the role of LAT1 in IGF-I-induced mTORC1 activation and cell functions remains unclear.
OBJECTIVE:Branched-chain amino acids (BCAAs) have been reported to inhibit several types of muscle atrophy via the activation of the mechanistic target of rapamycin complex 1 (mTORC1). However, we previously found that BCAA did not activate mTORC1 in growth hormone (GH)-deficient spontaneous dwarf rats (SDRs), and that GH restored the stimulatory effect of BCAAs toward the mTORC1. The objective of this study was to determine whether GH or Insulin-like growth factor-I (IGF-I) stimulated the expression of L-type amino acid transporters (LATs) that delivered BCAAs, and whether LATs were involved in the mTORC1 activation. DESIGN: After the continuous administration of GH, cross-sectional areas (CSAs) of muscle fibers and LAT mRNA levels in the skeletal muscles of SDRs were compared to those from the SDRs that received normal saline. The effect of GH and IGF-I on LAT mRNA levels were determined in L6 and C2C12 myocytes. The effects of 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid (BCH), a blocker for LATs, and LAT1 siRNA on mTORC1 activation and cell functions were examined in C2C12 cells. RESULTS:GH increased LAT1 and LAT4 mRNA levels in accordance with the increase in CSAs of muscle fibers in SDRs. IGF-I, and not GH, increased LAT1 mRNA levels in cultured L6 myocytes. IGF-I also increased LAT1 mRNA level in another myocyte line, C2C12. Furthermore, IGF-I reduced LAT3 and LAT4 mRNA levels in both cell lines. GH reduced LAT3 and LAT4 mRNA levels in L6 cells. BCH decreased basal C2C12 cell proliferation and reduced IGF-I-induced phosphorylation of 4E-BP1 and S6K, both of which are mTORC1 targets, but LAT1 siRNA did not affect the phosphorylation. This suggests that BCH may exert its effect via other pathway than LAT1. CONCLUSIONS:IGF-I increased LAT1 mRNA level in myocytes. However, the role of LAT1 in IGF-I-induced mTORC1 activation and cell functions remains unclear.
Authors: Silvana Duran-Ortiz; Jonathan A Young; Adam Jara; Elizabeth A Jensen; Reetobrata Basu; Edward O List; Yanrong Qian; John J Kopchick; Darlene E Berryman Journal: J Neuroendocrinol Date: 2020-10-12 Impact factor: 3.627
Authors: Betina Biagetti; J R Herance; Roser Ferrer; Anna Aulinas; Martina Palomino-Schätzlein; Jordi Mesa; J P Castaño; Raul M Luque; Rafael Simó Journal: J Clin Med Date: 2019-09-26 Impact factor: 4.241