Influence of dietary availability of protein and carbohydrate on ERK1/2 and Akt signaling in rat liver

Abstract

The dietary reference intakes (DRIs) established an acceptable macronutrient distribution range (AMDR). However, the ideal ratio of dietary protein to carbohydrate for adult health and its nutritional regulation remains unknown. The present study examined the regulation of p44/42 mitogen activated protein kinases (MAPK) pathway and AKT pathway in rats fed with different levels of dietary proteins. Male rats (n=36,~200 g) were trained to meal feed on a Baseline diet (20% of energy as protein, 50% carbohydrates, 30% fat) for 6 days and sacrificed (day 0) at fasted or 90 minutes postprandial (pp), to a 4g breakfast meal. The remaining rats were randomly assigned to either a low‐protein diet (LP group: 15% protein, 55% carbohydrates, 30% fat) or a high‐protein diet (HP group: 30% protein, 40% carbohydrates, 30% fat) for 21 days and sacrificed at fasted or 90 min pp. Protein and RNA samples were extracted from rat liver tissue and western blot were used to detect the protein expression. Phosphorylation of ERK1/2 was significantly highest in LP diet group, followed by HP group and Baseline diet group. In contrast, phospho‐AKT(Ser 473) was lowest in LP group, followed by Baseline diet group and HP diet group. No significant postprandial changes in p‐ERK1/2 and p‐AKT were observed. For phospho‐ERK1/2, three bands were seen in 30% HP diet 90min pp group, indicating high protein diet may induce additional modification in phospho‐ERK1/2. This study demonstrates that changes in protein and carbohydrate intakes within the AMDR results in different nutritional regulation of MAPK pathway and AKT pathway, which may play an important role in adult health.