RESUMEN
Exposure to maternal malnutrition impairs postnatal health. Acute nutritional stress is less clearly implicated in intrauterine programming. We studied the effects of stressing pregnant mothers on perinatal growth and adult glucose homeostasis. We compared one group ("stressed", mothers fasted for 16 hours) with controls ("unstressed"). We found that fasting stress had adverse effects on the weight of the fetuses conceived (p<0.005) and the placental efficiency (p<0.001) in stressed compared to unstressed offspring. Placental weight was increased (p<0.001) presumably in compensation. Stress affected the glucose homeostasis of the offspring when they became adults (p<0.005) when analysed as individuals. We previously linked nutritional stress throughout pregnancy with a mitochondrial stress response. We modelled placenta with cultured human trophoblast cells (BeWos) and fetal tissues with mouse embryonic fibroblasts (MEFs). High throughput imaging showed that the mitochondria of both cell types underwent a similar sequence of changes in morphology, induced by nutritional stresses. The contrasting stress responses on fetal and placental weight were not captured by the cellular models. The stress of maternal fasting may be an important determinant of perinatal outcome in the mouse and might be relevant to nutritional stress in human pregnancy.
RESUMEN
IDO is the rate-limiting enzyme in the kynurenine pathway, catabolizing tryptophan to kynurenine. Tryptophan depletion by IDO-expressing tumors is a common mechanism of immune evasion inducing regulatory T cells and inhibiting effector T cells. Because mammalian cells cannot synthesize tryptophan, it remains unclear how IDO(+) tumor cells overcome the detrimental effects of local tryptophan depletion. We demonstrate that IDO(+) tumor cells express a novel amino acid transporter, which accounts for â¼50% of the tryptophan uptake. The induced transporter is biochemically distinguished from the constitutively expressed tryptophan transporter System L by increased resistance to inhibitors of System L, resistance to inhibition by high concentrations of most amino acids tested, and high substrate specificity for tryptophan. Under conditions of low extracellular tryptophan, expression of this novel transporter significantly increases tryptophan entry into IDO(+) tumors relative to tryptophan uptake through the low-affinity System L alone, and further decreases tryptophan levels in the microenvironment. Targeting this additional tryptophan transporter could be a way of pharmacological inhibition of IDO-mediated tumor escape. These findings highlight the ability of IDO-expressing tumor cells to thrive in a tryptophan-depleted microenvironment by expressing a novel, highly tryptophan-specific transporter, which is resistant to inhibition by most other amino acids. The additional transporter allows tumor cells to strike the ideal balance between supply of tryptophan essential for their own proliferation and survival, and depleting the extracellular milieu of tryptophan to inhibit T cell proliferation.
Asunto(s)
Sistema de Transporte de Aminoácidos L/inmunología , Indolamina-Pirrol 2,3,-Dioxigenasa/inmunología , Neoplasias/inmunología , Triptófano/inmunología , Sistema de Transporte de Aminoácidos L/metabolismo , Animales , Transporte Biológico/inmunología , Proliferación Celular , Supervivencia Celular/inmunología , Células HeLa , Humanos , Indolamina-Pirrol 2,3,-Dioxigenasa/metabolismo , Ratones , Neoplasias/enzimología , Linfocitos T/inmunología , Linfocitos T/metabolismo , Triptófano/metabolismoRESUMEN
The nature of Cambridge (UK) placental and fetal research in the middle third of the twentieth century is reviewed on the basis of published literature and personal recollection. Joseph Barcroft is a central figure who came to fetal research late in an extremely productive career which is briefly sketched. Contemporaneous Cambridge academics in the field included J.D. Boyd (the authors father), J. Hammond, F.H.A. Marshall, R.A. McCance, J. Needham, A.S. Parkes and Elsie Widdowson. The then current Cambridge academic geography is explained and features of its scientific life such as funding, institutional structure and ethos, teaching and clinical duties, domestic and gender roles, and political context, including war and empire, are briefly considered. The testing of research findings against general principles and use of quantitative thinking are identified as important features. Intergenerational connections, often within individual families, are identified as a striking feature. The long-term impact of Cambridge work of this period; locally, in current trophoblast and feto-placental genetic research, in Oxford in probably influencing G.S. Dawes research leadership, and internationally, especially through D.H. Barron, and through him to the Denver School, is considered. That human placental and embryological specimens collected by J.D. Boyd have received a new lease of life as the "Boyd Collection", including use by Allen Enders is noted. Mechanisms for the maintenance of scientific quality and productivity during the period, mainly through the scientist himself relying on an internalised sense of "obligation", are contrasted with those current in the UK and more widely; formal peer-review at frequent intervals, with subsequent allocation of short-term funding. The strengths and weaknesses of each are considered.
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Biología Evolutiva/historia , Inglaterra , Historia del Siglo XXRESUMEN
Mammalian CD98 heterodimeric amino acid transporters consist of a promiscuous single-pass transmembrane glycoprotein, CD98hc (CD98 heavy chain), and one of six multipass transmembrane proteins or 'light chains'. The heterodimeric complexes of CD98hc and the light chains LAT1 (L-type amino acid transporter 1) or LAT2 specifically promote sodium-independent System L exchange of neutral amino acids, including leucine. CD98hc is also implicated in other processes, including cell fusion, cell adhesion and activation of TOR (target of rapamycin) signalling. Surprisingly, recent reports suggested that insects lack a membrane-bound CD98hc, but in the present study we show that Drosophila CG2791 encodes a functional CD98hc orthologue with conservation in intracellular, transmembrane and extracellular domains. We demonstrate by RNA-interference knockdown in Drosophila Schneider cells that CG2791 and two Drosophila homologues of the mammalian CD98 light chains, Mnd (Minidiscs) and JhI-21, are required for normal levels of System L transport. Furthermore, we show that System L activity is increased by methoprene, an analogue of the developmentally regulated endocrine hormone juvenile hormone, an effect that is potentially mediated by elevated Mnd expression. Co-expression of CG2791 and JhI-21, but not CG2791 and Mnd, in Xenopus oocytes mediates System L transport. Finally, mapping of conserved sequences on to the recently determined crystal structure of the human CD98hc extracellular domain highlights two conserved exposed hydrophobic patches at either end of the domain that are potential protein-protein-interaction surfaces. Therefore our results not only show that there is functional conservation of CD98hc System L transporters in flies, but also provide new insights into the structure, functions and regulation of heterodimeric amino acid transporters.
Asunto(s)
Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Cadena Pesada de la Proteína-1 Reguladora de Fusión/genética , Expresión Génica , Secuencia de Aminoácidos , Sistemas de Transporte de Aminoácidos/genética , Sistemas de Transporte de Aminoácidos/fisiología , Animales , Transporte Biológico , Línea Celular , Secuencia Conservada , Proteínas de Drosophila/fisiología , Drosophila melanogaster/citología , Drosophila melanogaster/metabolismo , Evolución Molecular , Femenino , Cadena Pesada de la Proteína-1 Reguladora de Fusión/fisiología , Cadenas Ligeras de la Proteína-1 Reguladora de Fusión/genética , Cadenas Ligeras de la Proteína-1 Reguladora de Fusión/fisiología , Humanos , Leucina/metabolismo , Datos de Secuencia Molecular , Oocitos/metabolismo , Interferencia de ARN , ARN Mensajero/genética , ARN Mensajero/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homología de Secuencia de Aminoácido , Especificidad de la Especie , XenopusRESUMEN
mTOR (mammalian target of rapamycin) is a highly conserved serine/threonine protein kinase that has roles in cell metabolism, cell growth and cell survival. Although it has been known for some years that mTOR acts as a hub for inputs from growth factors (in particular insulin and insulin-like growth factors), nutrients and cellular stresses, some of the mechanisms involved are still poorly understood. Recent work has implicated mTOR in a variety of important human pathologies, including cancer, Type 2 diabetes and neurodegenerative disorders, heightening interest and accelerating progress in dissecting out the control and functions of mTOR.
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Enfermedad , Proteínas Quinasas/metabolismo , Aminoácidos/metabolismo , Humanos , Especificidad de Órganos , Transducción de Señal , Serina-Treonina Quinasas TOR , Factores de Transcripción/metabolismoRESUMEN
mTOR (mammalian target of rapamycin) plays a key role in determining how growth factor, nutrient and oxygen levels modulate intracellular events critical for the viability and growth of the cell. This is reflected in the impact of aberrant mTOR signalling on a number of major human diseases and has helped to drive research to understand how TOR (target of rapamycin) is itself regulated. While it is clear that amino acids can affect TOR signalling, how these molecules are sensed by TOR remains controversial, perhaps because cells use different mechanisms as environmental conditions change. Even the question of whether they have an effect inside the cell or at its surface remains unresolved. The present review summarizes current ideas and suggests ways in which some of the models proposed might be unified to produce an amino acid detection system that can adapt to environmental change.
Asunto(s)
Aminoácidos/metabolismo , Proteínas Quinasas/metabolismo , Sistemas de Transporte de Aminoácidos/metabolismo , Animales , Alimentos , Humanos , Péptidos y Proteínas de Señalización Intercelular/metabolismo , Modelos Biológicos , Serina-Treonina Quinasas TORRESUMEN
A quantitative method has been developed for determining the affinity of substrates for the peptide transporter PepT1, allowing oral availability of drugs via PepT1 to be estimated.
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Algoritmos , Péptidos/química , Simportadores/química , Sitios de Unión , Transporte Biológico , Estructura Molecular , Transportador de Péptidos 1 , Péptidos/metabolismo , Especificidad por Sustrato , Simportadores/metabolismoRESUMEN
The stereochemistry of thiodipeptides of proline [e.g. Ala-Psi[CS-N]-Pro] can be controlled using pH, allowing the trans-preference for substrates of the peptide transporter PepT1 to be confirmed.
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Proteínas de Transporte de Membrana/química , Péptidos/química , Compuestos de Sulfhidrilo/química , Concentración de Iones de Hidrógeno , Espectroscopía de Resonancia Magnética , Proteínas de Transporte de Membrana/metabolismo , Estructura Molecular , Péptidos/metabolismo , EstereoisomerismoRESUMEN
The conformation at the first residue of dipeptide substrates for the peptide transporter PepT1 has been probed using constrained peptide analogues, and the active conformation has been identified.
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Dipéptidos/química , Simportadores/química , Modelos Moleculares , Transportador de Péptidos 1 , Conformación Proteica , Especificidad por SustratoRESUMEN
The placenta is essential to nutrition before birth. Recent work has shown that a range of clearly defined alterations can be found in the placentas of infants with intrauterine growth restriction (IUGR). In the mouse, a placental specific knockout of a single imprinted gene, encoding IGF-2, results in one pattern of alterations in placenta structure and function which leads to IUGR. We speculate that the alterations in the human placenta can also be grouped into patterns, or phenotypes, that are associated with specific patterns of fetal growth. Identifying the placental phenotypes of different fetal growth patterns will improve the ability of clinicians to recognize high-risk patients, of laboratory scientists to disentangle the complexities of IUGR, and of public health teams to target interventions aimed at ameliorating the long-term adverse effects of inadequate intrauterine growth.
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Desarrollo Fetal , Retardo del Crecimiento Fetal , Placenta/fisiología , Animales , Femenino , Humanos , Intercambio Materno-Fetal , Ratones , Fenotipo , Placenta/anatomía & histología , Placenta/irrigación sanguínea , EmbarazoRESUMEN
Growth in normal and tumour cells is regulated by evolutionarily conserved extracellular inputs from the endocrine insulin receptor (InR) signalling pathway and by local nutrients. Both signals modulate activity of the intracellular TOR kinase, with nutrients at least partly acting through changes in intracellular amino acid levels mediated by amino acid transporters. We show that in Drosophila, two molecules related to mammalian proton-assisted SLC36 amino acid transporters (PATs), CG3424 and CG1139, are potent mediators of growth. These transporters genetically interact with TOR and other InR signalling components, indicating that they control growth by directly or indirectly modulating the effects of TOR signalling. A mutation in the CG3424 gene, which we have named pathetic (path), reduces growth in the fly. In a heterologous Xenopus oocyte system, PATH also activates the TOR target S6 kinase in an amino acid-dependent way. However, functional analysis reveals that PATH has an extremely low capacity and an exceptionally high affinity compared with characterised human PATs and the CG1139 transporter. PATH and potentially other PAT-related transporters must therefore control growth via a mechanism that does not require bulk transport of amino acids into the cell. As PATH is likely to be saturated in vivo, we propose that one specialised function of high-affinity PAT-related molecules is to maintain growth as local nutrient levels fluctuate during development.