Discordant regulation of eIF2 kinase GCN2 and mTORC1 during nutrient stress

Appropriate regulation of the Integrated stress response (ISR) and mTORC1 signaling are central for cell adaptation to starvation for amino acids. Halofuginone (HF) is a potent inhibitor of aminoacylation of tRNAPro with broad biomedical applications. Here, we show that in addition to translational control directed by activation of the ISR by general control nonderepressible 2 (GCN2), HF increased free amino acids and directed translation of genes involved in protein biogenesis via sustained mTORC1 signaling. Deletion of GCN2 reduced cell survival to HF whereas pharmacological inhibition of mTORC1 afforded protection. HF treatment of mice synchronously activated the GCN2-mediated ISR and mTORC1 in liver whereas Gcn2-null mice allowed greater mTORC1 activation to HF, resulting in liver steatosis and cell death. We conclude that HF causes an amino acid imbalance that uniquely activates both GCN2 and mTORC1. Loss of GCN2 during HF creates a disconnect between metabolic state and need, triggering proteostasis collapse

Glutamine and glutamate: Nonessential or essential amino acids?

Glutamine and glutamate are not considered essential amino acids but they play important roles in maintaining growth and health in both neonates and adults. Although glutamine and glutamate are highly abundant in most feedstuffs there is increasing evidence that they may be limiting during pregnancy, lactation and neonatal growth, particularly when relatively low protein diets are fed. Supplementation of diets with glutamine, glutamate or both at 0.5 to 1.0% to both suckling and recently weaned piglets improves intestinal and immune function and results in better growth. In addition such supplementation to the sow prevents some of the loss of lean body mass during lactation, and increases milk glutamine content. However, a number of important questions related to physiological condition, species under study and the form and amount of the supplements need to be addressed before the full benefits of glutamine and glutamate supplementation in domestic animal production can be realized. Keywords: Amino acid, Glutamate, Glutamine, Lactation, Pregnancy, Growt

Changes in renal metabolite profile and ammoniagenesis during acute and chronic metabolic acidosis in dog and rat

Changes in renal metabolite profile and ammoniagenesis during acute and chronic metabolic acidosis in dog and rat. Acute metabolic acidosis was induced by an i.v. administration of hydrochloric acid to dogs and rats to decrease the plasma bicarbonate concentration from 22 to 12mM in dogs and from 26 to 10mM in rats. Chronic metabolic acidosis was also induced in dogs by ammonium chloride feeding for 5 days. Rats also were given ammonium chloride for 24 hours. The renal metabolite profile was determined on the freeze-clamped renal tissue before and after 100min (dogs) or 30 to 240min (rats) of acute acidosis. Measurements on chronically acidotic dogs and rats with 24-hour acidosis were obtained also for comparison with acute acidosis. In both species, kidney glutamine, glutamate, and alpha-ketoglutarate concentrations decreased drastically following induction of acute or chronic acidosis. In the dog, or in the rat during the first 2 hours of acidosis, malate concentration was unchanged. Malate concentration fell significantly in the rat kidney only after 2 hours of acidosis without change in phosphoenolpyruvate (PEP) concentration. In chronically acidotic dogs, malate and oxaloacetate rose fivefold with no change in PEP concentration. Phosphoenolpyruvate carboxykinase (PEPCK) activity was not stimulated by chronic metabolic acidosis in the dog in contrast to the rat. Acute acidosis by hydrochloric acid increased net renal glutamine extraction in the rat but not in the dog. These data suggest that an increased metabolic flux occurs between alpha-ketoglutarate and malate in both rat and dog kidney during acute metabolic acidosis. In the rat, however, after 2 hours, PEPCK activation modifies the kidney metabolite profile. Intrarenal glutamine transport seems to be a rate-limiting factor for adaptation to acute acidosis in the dog but not in the rat kidney.Profil métabolique rénal et ammoniogénèse au cours de l'acidose métabolique aiguë et chronique chez le chien et le rat. Une acidose métabolique aiguë a été produite par l'administration intraveineuse d'acide chlorhydrique à des chiens et des rats de telle sorte que la concentration plasmatique de bicarbonates soit abaissée de 22 à 12mM (chiens) et de 26 à 102mM (rats). Une acidose métabolique chronique a aussi été produite par l'administration orale de chlorure d'ammonium pendant 5 jours (chiens) ou 24 heures (rats). Le profil métabolique rénal a été déterminé sur du tissu cortical prélevé en congélation instantanée avant et après 1002min (chiens) ou 30 à 2402min (rats) d'acidose aiguë. Les données ont été comparées aux valeurs retrouvées dans les reins de chiens et de rats en acidose chronique. Chez les deux espèces, la concentration rénale de glutamine, de glutamate, et d'alphacétoglutarate a considérablement diminué après l'induction de l'acidose aiguë ou chronique. Cependant, chez le chien, ou chez le rat pendant les premières 2 heures d'acidose, la concentration de malate ne s'est pas modifiée. La concentration de malate n'a diminué significativement chez le rat qu'après 2 heures d'acidose. Chez le chien en acidose chronique, la concentration de malate et d'oxaloacétate a quintuplé sans modification de la concentration phosphoenolpyruvate (PEP). L'activité de la PEP-carboxykinase (PEPCK) n'a pas été stimulée par l'acidose métabolique chronique chez le chien. L'acidose aiguë a augmenté l'extraction nette de glutamine par le rein chez le rat mais non chez le chien. Ces résultats suggèrent que la voie métabolique ammoniogénique est stimulée par l'acidose à une étape située entre l'alphacétoglutarate et le malate chez le rat comme chez le chien. Chez le rat, cependant, l'activation de la PEPCK modifie le profil métabolique rénal à partir de la deuxième heure d'acidose. Le transport intrarénal de glutamine semble être un facteur limitant de l'adaptation à l'acidose aiguë chez le chien mais non chez le rat