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Insulin regulation of amino acid transport in mesenchymal cells from avian and mammalian tissues.

ABSTRACT: Insulin regulation of amino acid transport across the cell membrane was studied in a variety of mesenchymal cell directly isolated from avian and mammalian tissues or collected from confluent cultures. Transport activity of the principal systems of mediation in the presence and absence of insulin was evaluated by measuring the uptake of representative amino acids under conditions approaching initial entry rates. Insulin enhanced the transport rate of substrate amino acids from the A system(alpha-aminoisobutyric acid, L-proline, glycine, L-alanine and L-serine) in fibroblasts and osteoblasts from chick-embryo tissues, in mesenchymal cells (fibroblasts and smooth muscle cells) from immature rat uterus, in thymic lymphocytes from young rats and in chick-embryo fibroblasts from confluent secondary cultures. In these tissues, the uptake of amino acid substrates of transport systems L and Ly+ (L-leucine, L-phenylalanine, L-lysine) was not affected by the presence of the hormone. No insulin control of amino acid transport was detected in chick-embryo chondroblasts and rat peritoneal macrophages. These observations identify the occurrence of hormonal regulatory patterns of amino acid transport for different mesenchymal cells types and indicate that these properties emerge early during cell differentiation.

SUBMITTER: Guidotti GG

PROVIDER: S-EPMC1164234 | biostudies-other | 1976 Nov

REPOSITORIES: biostudies-other

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Project description:BackgroundAmino acid availability stimulates protein synthesis via the mTORC1 (mechanistic target of rapamycin complex 1) signaling pathway. In response to an increase in cellular amino acid availability, translocation of cytosolic mTORC1 to the lysosomal surface is required to stimulate mTORC1 kinase activity. However, research elucidating the amino acid responsive mechanisms have thus far only been conducted in in vitro models. Our primary objective was to determine whether an increase in amino acid availability within human skeletal muscle in vivo would alter the expression of genes associated with amino acid sensing, transport and mTORC1 regulation. Our secondary objective was to determine whether an acute perturbation in lysosomal function would disrupt the normal pattern of muscle amino acid responsive gene expression.MethodsWe recruited 13 young adults into one of two groups: The first group ingested 10 g of essential amino acids (EAA). The second group ingested 10 g of EAA in the presence of chloroquine (CQ), a lysosomotropic agent. The subjects from each group had biopsies of the vastus lateralis taken before and after EAA ingestion. We determined the relative mRNA expression of 51 potential amino acid responsive genes using RT-qPCR.ResultsThere was a differential mRNA expression for 22 genes, with 15 mRNAs significantly changing (P < 0.05) in response to EAA ingestion (e.g., REDD1: +209 ± 35%; SLC38A9: +31 ± 9%; SLC38A10: +57 ± 15%). In the CQ group, EAA ingestion resulted in a differential expression as compared to EAA alone (i.e., 11 out of the 22 genes were different (P < 0.05) between the two groups.).ConclusionsExpression of several amino acid sensing, transport, and mTORC1 regulatory genes in human skeletal muscle are responsive to an increase in amino acid availability. Furthermore, potential acute disruption of lysosomal function by ingestion of chloroquine interferes with the normal pattern of gene expression following feeding. Our in vivo data in humans provide preliminary support for the in vitro work linking amino acid sensing pathways to mTORC1 translocation to the lysosome.Trial registrationNCT00891696. Registered 29 April 2009.

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Insulin regulation of amino acid transport in mesenchymal cells from avian and mammalian tissues.

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