The mTORC1-Signaling Pathway and Hepatic Polyribosome Profile Are Enhanced after the Recovery of a Protein Restricted Diet by a Combination of Soy or Black Bean with Corn Protein

Abstract

Between 6% and 11% of the world's population suffers from malnutrition or undernutrition associated with poverty, aging or long-term hospitalization. The present work examined the effect of different types of proteins on the mechanistic target of rapamycin (mTORC1)-signaling pathway in: (1) healthy; and (2) protein restricted rats. (1) In total, 200 rats were divided into eight groups and fed one of the following diets: 20% casein (C), soy (S), black bean (B), B + Corn (BCr), Pea (P), spirulina (Sp), sesame (Se) or Corn (Cr). Rats fed C or BCr had the highest body weight gain; rats fed BCr had the highest pS6K1/S6K1 ratio; rats fed B, BCr or P had the highest eIF4G expression; (2) In total, 84 rats were fed 0.5% C for 21 day and protein rehabilitated with different proteins. The S, soy + Corn (SCr) and BCr groups had the highest body weight gain. Rats fed SCr and BCr had the highest eIF4G expression and liver polysome formation. These findings suggest that the quality of the dietary proteins modulate the mTORC1-signaling pathway. In conclusion, the combination of BCr or SCr are the best proteins for dietary protein rehabilitation due to the significant increase in body weight, activation of the mTORC1-signaling pathway in liver and muscle, and liver polysome formation.

Keywords: SNAT2; black bean protein; mTORC1-signaling pathway; polysome profiling; protein rehabilitation; soy protein.

Figure 1

Serum Homocysteine (Hcy) concentration in healthy rats fed different types of dietary protein: (A) Fasting serum Hcy concentration and after 30, 60, 90 and 120 min of feeding casein (C), soy protein (S), black bean (B), black bean + corn (BCr), pea (P), spirulina (SP), sesame (Se) or corn (Cr); and (B) values are means ± SEM, n = 5. Different letter superscript indicates significant differences among rows, p < 0.05, a > b > c.

Figure 2

Western blot analysis and quantification of the: (A) phosphorylation of mTORC1; (B) phosphorylation of S6K1; (C) protein abundance of eIF4G in livers of healthy rats fed different types of dietary proteins and (D) representative immunoblot. Values are means ± SEM, n = 3. Different letter superscript indicates significant differences among groups, p < 0.05, a > b > c.

Figure 3

mRNA gene expression and Western blot analysis of SNAT2 in liver of healthy rats fed different types of dietary protein: (A) Snat2 mRNA abundance; (B) protein abundance of Snat2; and (C) representative immunoblot of SNAT2. Values are means ± SEM, n = 3. Different letter superscript indicates significant differences among different times of feeding, p < 0.05, a > b > c.

Figure 4

mRNA gene expression and Western blot analysis of SREBP1C and FASN in healthy rats: (A) Srebp1c and (B) Fasn mRNA abundance; (C) protein abundance of SREBP1c; and (D) FASN. Values are means ± SEM, n = 3. Different letter superscript in the bars indicates significant differences among groups, p < 0.05, a > b > c.

Figure 5

Western blot analysis and quantification of the: (A) phosphorylation of mTORC1; (B) phosphorylation of S6K1; and (C) protein abundance of eIF4G in the livers of rats fed different types of proteins after a protein restricted period; and (D) representative Western blot analysis. Values are means ± SEM, n = 3. Different letter superscript indicates significant differences among groups, p < 0.05, a > b > c.

Figure 6

mRNA gene expression and Western blot analysis of SNAT2 in liver of rats fed different types of proteins after a protein restricted period: (A) Snat2 mRNA abundance; (B) protein abundance of Snat2; and (C) representative Western blot analysis. Values are means ± SEM, n = 3. Different letter superscript indicates significant differences among time, p < 0.05, a > b > c.

Figure 7

Western blot analysis and quantification of GCN2 and eIF2α in liver of rats fed different types of proteins after a protein restricted period: (A) representative Western blot analysis of GCN2 and (B) eIF2α; (C) protein abundance of GCN2; and (D) protein abundance of eIF2α. Values are means ± SEM, n = 3, p < 0.05, a > b > c.

Figure 8

mRNA gene expression and Western blot analysis of SREBP1C and FASN in rats fed different types of proteins after a protein restricted period: (A) Srebp1c mRNA abundance; (B) Fasn mRNA abundance; (C) abundance of SREBP1c; and (D) abundance of FASN. Values are means ± SEM, n = 3. Different letter superscript indicates significant differences among groups, p < 0.05, a > b > c.

Figure 9

Hepatic polysome profile of rats fed different types of dietary proteins after a protein restricted period: (A) 0.5% casein; (B) casein; (C) soy; (D) black bean; (E) black bean + corn; (F) soy + corn; (G) corn; and (H) area under the curve analysis. The values are mean ± SEM, n = 3 per group. Different letter superscript indicates significant differences among groups, p < 0.05, a > b > c.

Figure 10

Western blot analysis and quantification of the: (A) phosphorylation of mTORC1; (B) phosphorylation of S6K1; (C) protein abundance of muscle eIF4G; and (D) representative Western blot of rats fed different types of protein for seven days after a protein restricted period. Values are means ± SEM, n = 3. Different letter superscript indicates significant differences among groups, p < 0.05, a> b > c.