Growth hormone and Insulin-like growth factor-I (IGF-I) modulate the expression of L-type amino acid transporters in the muscles of spontaneous dwarf rats and L6 and C2C12 myocytes
Growth hormone and Insulin-like growth factor-I (IGF-I) modulate the expression of L-type amino acid transporters in the muscles of spontaneous dwarf rats and L6 and C2C12 myocytes
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DOI：
10.1016/j.ghir.2018.09.002
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发表时间：
2018-10-01
影响因子：
1.4
通讯作者：
Okimura, Yasuhiko
中科院分区：
文献类型：
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作者：
Sawa, Ran;Nishida, Hikaru;Okimura, Yasuhiko
目的：支链氨基酸（BCAA）已被报道通过激活雷帕霉素复合物1（mTORC 1）的机制靶点来抑制几种类型的肌肉萎缩。然而，我们以前发现，支链氨基酸没有激活mTORC 1生长激素（GH）缺乏自发性侏儒大鼠（SDR），和GH恢复刺激作用的支链氨基酸对mTORC 1。本研究的目的是确定GH或胰岛素样生长因子-I（IGF-I）是否刺激递送BCAA的L型氨基酸转运蛋白（LAT）的表达，以及LAT是否参与mTORC 1激活。设计：连续给予GH后，将SDR的骨骼肌中的肌纤维横截面积（CSA）和LAT mRNA水平与接受生理盐水的SDR的那些进行比较。在L 6和C2 C12心肌细胞中测定GH和IGF-I对LAT mRNA水平的影响。结果：生长激素可上调SDRs肌纤维中LAT 1和LAT 4 mRNA的表达，并与肌纤维CSA表达的增加相一致。IGF-I，而不是生长激素，在培养的L 6肌细胞中增加LAT 1 mRNA水平。IGF-I还增加了另一种肌细胞系C2 C12中的LAT 1 mRNA水平。此外，IGF-I降低了两种细胞系中的LAT 3和LAT 4 mRNA水平。GH降低L 6细胞中LAT 3和LAT 4 mRNA水平。BCH降低了基础C2 C12细胞的增殖，并降低了IGF-I诱导的4 E-BP 1和S6 K的磷酸化，这两者都是mTORC 1的靶点，但LAT 1 siRNA并不影响磷酸化。结论：IGF-I可增加心肌细胞LAT 1 mRNA的表达。然而，LAT 1在IGF-I诱导的mTORC 1活化和细胞功能中的作用仍不清楚。
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.