Replacing fishmeal with composite plant protein meal affects nutrient metabolism via mTOR signaling pathway of Pacific white shrimp (Litopenaeus vannamei)

This study evaluated the effects of a fishmeal-reduced diet containing a composite plant protein meal (soybean meal:peanut meal:gluten meal ratio = 20:10:3) on growth performance, metabolic homeostasis, and nutrient-sensing signaling pathway activation in Pacific white shrimp (<i>Litopenaeus vannamei</i>). In an 8-week feeding trial, 720 shrimp (initial weight = 0.85 ± 0.01 g) were randomly divided into 12 tanks (3 tanks per group) and fed four isonitrogenous and isolipidic diets with different plant protein levels (30%, 36%, 43%, and 50 %) named as PP30, PP36, PP43, and PP50, respectively. Results showed that increasing dietary plant protein levels significantly reduced the growth performance, feed utilization, survival rate (<i>P</i> < 0.05), and the muscle free amino acid concentrations (from 22.50 to 18.73 mg/g; <i>P</i> = 0.001), and significantly increased the hepatopancreas lipid droplet area (from 11.52% to 23.70%; <i>P</i> = 0.002), while enhancing the lipogenesis pathway, as evidenced by the significant upregulation of lipogenesis-related genes-sterol-regulatory element binding protein (<i>srebp</i>), fatty acid synthase (<i>fas</i>), acetyl-CoA carboxylase (<i>acc</i>), and 6-phosphogluconate dehydrogenase (<i>6pgd</i>) (<i>P</i> < 0.05). It also suppressed the protein synthesis pathway, the mechanistic target of rapamycin (mTOR) pathway, and activated the general control non-derepressible 2 (GCN2) pathway, which detects uncharged tRNA and inhibits protein synthesis. The AMP-activated protein kinase (AMPK) pathway was activated indicating energy deprivation in response to dietary plant protein. In summary, high levels of dietary plant protein inhibited the mTOR signaling pathway, activated the GCN2 and AMPK signaling pathways, and promoted lipid deposition in the hepatopancreas. These findings provide insights into the molecular mechanisms underlying phenotypic changes in shrimp fed different protein sources.