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Re-examination of Dietary Amino Acid Sensing Reveals a GCN2-Independent Mechanism.

Leib DE, Knight ZA - Cell Rep (2015)

Bottom Line: Animals cannot synthesize nine essential amino acids (EAAs) and must therefore obtain them from food.In contrast to previous results, we find that mice cannot rapidly identify threonine- or leucine-deficient food in common feeding paradigms.These behaviors are independent of the proposed amino acid sensor GCN2, pointing to the existence of an undescribed mechanism for rapid sensing of dietary EAAs.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of California, San Francisco, San Francisco, CA 94158, USA.

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Consumption of Threonine-Deficient Food Does Not Activate GCN2 in the Brain(A) Plasma concentrations of threonine, leucine, and lysine of mice fed threonine-, leucine-, and lysine-deficient food, respectively, versus control food (n = 3 mice per data point). In each case, plasma concentrations were not significantly different between control and deficient food at 1 hr but gained significance at 3 hr of feeding (T-def, p = 0.0003; L-def, p = 0.004; K-def, p = 0.009).(B) Plasma concentrations for all amino acids measured in the same experiment as (A), expressed as a percentage of concentration during control feeding.(C) (Left) Wild-type and Gcn2−/− mice were fed control or T-def food for 1 hr or 12 hr. Food intake in grams by each mouse is listed above the top panel. Protein extracts made from APC, MBH, and liver from these mice were analyzed by western blot for p-EIF2A (Ser-51), total EIF2A, and beta-actin loading control. (Right) Quantification of p-EIF2A/EIF2A in the APC, MBH, and liver after 1 or 12 hr consumption of control or T-def food is shown. In the APC, p-EIF2A/EIF2A was significantly lower in Gcn2−/− mice than wild-type controls at 1 hr (p = 0.02) and 12 hr (p = 0.0007). In the MBH, Gcn2−/− mice had significantly higher p-EIF2A/EIF2A ratios than wild-type at 1 hr (p = 0.03) and 12 hr (p = 0.01). There was no significant effect of diet or interaction between diet and genotype in the APC or MBH. There were no significant differences in the liver but a trend toward a higher p-EIF2A/EIF2A ratio in wild-type mice fed T-def food compared to control at 1 hr.See also Figure S3 and Table S1.
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Figure 2: Consumption of Threonine-Deficient Food Does Not Activate GCN2 in the Brain(A) Plasma concentrations of threonine, leucine, and lysine of mice fed threonine-, leucine-, and lysine-deficient food, respectively, versus control food (n = 3 mice per data point). In each case, plasma concentrations were not significantly different between control and deficient food at 1 hr but gained significance at 3 hr of feeding (T-def, p = 0.0003; L-def, p = 0.004; K-def, p = 0.009).(B) Plasma concentrations for all amino acids measured in the same experiment as (A), expressed as a percentage of concentration during control feeding.(C) (Left) Wild-type and Gcn2−/− mice were fed control or T-def food for 1 hr or 12 hr. Food intake in grams by each mouse is listed above the top panel. Protein extracts made from APC, MBH, and liver from these mice were analyzed by western blot for p-EIF2A (Ser-51), total EIF2A, and beta-actin loading control. (Right) Quantification of p-EIF2A/EIF2A in the APC, MBH, and liver after 1 or 12 hr consumption of control or T-def food is shown. In the APC, p-EIF2A/EIF2A was significantly lower in Gcn2−/− mice than wild-type controls at 1 hr (p = 0.02) and 12 hr (p = 0.0007). In the MBH, Gcn2−/− mice had significantly higher p-EIF2A/EIF2A ratios than wild-type at 1 hr (p = 0.03) and 12 hr (p = 0.01). There was no significant effect of diet or interaction between diet and genotype in the APC or MBH. There were no significant differences in the liver but a trend toward a higher p-EIF2A/EIF2A ratio in wild-type mice fed T-def food compared to control at 1 hr.See also Figure S3 and Table S1.

Mentions: GCN2 is proposed to detect the amino acid content of food by sensing rapid, post-ingestive changes in the level of amino acids in the blood. We therefore next determined how the consumption of EAA-deficient food alters the EAA composition of the blood by feeding mice amino-acid-deficient diets and then collecting blood for amino acid analysis. Consumption of T-def, L-def, and K-def food resulted in a progressive decrease in the concentration of the deficient amino acid in the blood (Figure 2A). This decrease was significant compared to control after 3 hr but not after 1 hr of feeding (Figure 2A). By contrast, the concentrations of other amino acids remained near 100% of control values, except that the concentrations of isoleucine and valine increased during L-def consumption (Figure 2B). This rise in isoleucine and valine concentrations has been previously reported, although the mechanism is not fully understood (Clark et al., 1966; Harper et al., 1984). Thus, plasma imbalance of amino acids develops over several hours of eating an imbalanced diet, but the changes in the first hour are small.


Re-examination of Dietary Amino Acid Sensing Reveals a GCN2-Independent Mechanism.

Leib DE, Knight ZA - Cell Rep (2015)

Consumption of Threonine-Deficient Food Does Not Activate GCN2 in the Brain(A) Plasma concentrations of threonine, leucine, and lysine of mice fed threonine-, leucine-, and lysine-deficient food, respectively, versus control food (n = 3 mice per data point). In each case, plasma concentrations were not significantly different between control and deficient food at 1 hr but gained significance at 3 hr of feeding (T-def, p = 0.0003; L-def, p = 0.004; K-def, p = 0.009).(B) Plasma concentrations for all amino acids measured in the same experiment as (A), expressed as a percentage of concentration during control feeding.(C) (Left) Wild-type and Gcn2−/− mice were fed control or T-def food for 1 hr or 12 hr. Food intake in grams by each mouse is listed above the top panel. Protein extracts made from APC, MBH, and liver from these mice were analyzed by western blot for p-EIF2A (Ser-51), total EIF2A, and beta-actin loading control. (Right) Quantification of p-EIF2A/EIF2A in the APC, MBH, and liver after 1 or 12 hr consumption of control or T-def food is shown. In the APC, p-EIF2A/EIF2A was significantly lower in Gcn2−/− mice than wild-type controls at 1 hr (p = 0.02) and 12 hr (p = 0.0007). In the MBH, Gcn2−/− mice had significantly higher p-EIF2A/EIF2A ratios than wild-type at 1 hr (p = 0.03) and 12 hr (p = 0.01). There was no significant effect of diet or interaction between diet and genotype in the APC or MBH. There were no significant differences in the liver but a trend toward a higher p-EIF2A/EIF2A ratio in wild-type mice fed T-def food compared to control at 1 hr.See also Figure S3 and Table S1.
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Figure 2: Consumption of Threonine-Deficient Food Does Not Activate GCN2 in the Brain(A) Plasma concentrations of threonine, leucine, and lysine of mice fed threonine-, leucine-, and lysine-deficient food, respectively, versus control food (n = 3 mice per data point). In each case, plasma concentrations were not significantly different between control and deficient food at 1 hr but gained significance at 3 hr of feeding (T-def, p = 0.0003; L-def, p = 0.004; K-def, p = 0.009).(B) Plasma concentrations for all amino acids measured in the same experiment as (A), expressed as a percentage of concentration during control feeding.(C) (Left) Wild-type and Gcn2−/− mice were fed control or T-def food for 1 hr or 12 hr. Food intake in grams by each mouse is listed above the top panel. Protein extracts made from APC, MBH, and liver from these mice were analyzed by western blot for p-EIF2A (Ser-51), total EIF2A, and beta-actin loading control. (Right) Quantification of p-EIF2A/EIF2A in the APC, MBH, and liver after 1 or 12 hr consumption of control or T-def food is shown. In the APC, p-EIF2A/EIF2A was significantly lower in Gcn2−/− mice than wild-type controls at 1 hr (p = 0.02) and 12 hr (p = 0.0007). In the MBH, Gcn2−/− mice had significantly higher p-EIF2A/EIF2A ratios than wild-type at 1 hr (p = 0.03) and 12 hr (p = 0.01). There was no significant effect of diet or interaction between diet and genotype in the APC or MBH. There were no significant differences in the liver but a trend toward a higher p-EIF2A/EIF2A ratio in wild-type mice fed T-def food compared to control at 1 hr.See also Figure S3 and Table S1.
Mentions: GCN2 is proposed to detect the amino acid content of food by sensing rapid, post-ingestive changes in the level of amino acids in the blood. We therefore next determined how the consumption of EAA-deficient food alters the EAA composition of the blood by feeding mice amino-acid-deficient diets and then collecting blood for amino acid analysis. Consumption of T-def, L-def, and K-def food resulted in a progressive decrease in the concentration of the deficient amino acid in the blood (Figure 2A). This decrease was significant compared to control after 3 hr but not after 1 hr of feeding (Figure 2A). By contrast, the concentrations of other amino acids remained near 100% of control values, except that the concentrations of isoleucine and valine increased during L-def consumption (Figure 2B). This rise in isoleucine and valine concentrations has been previously reported, although the mechanism is not fully understood (Clark et al., 1966; Harper et al., 1984). Thus, plasma imbalance of amino acids develops over several hours of eating an imbalanced diet, but the changes in the first hour are small.

Bottom Line: Animals cannot synthesize nine essential amino acids (EAAs) and must therefore obtain them from food.In contrast to previous results, we find that mice cannot rapidly identify threonine- or leucine-deficient food in common feeding paradigms.These behaviors are independent of the proposed amino acid sensor GCN2, pointing to the existence of an undescribed mechanism for rapid sensing of dietary EAAs.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of California, San Francisco, San Francisco, CA 94158, USA.

Show MeSH
Related in: MedlinePlus