Regulative Effect Of Glutamate On Intestinal Injuryand Muscle Protein Synthesis And Degradation Of Piglets After Lipopolysaccharide Challenge

These experiments were conducted to evaluate the regulative role of glutamate (Glu) on intestinal injury and muscle protein synthesis and degradation of piglets after lipopolysaccharide (LPS) challenge and its mechanisms.1. This experiment was conducted to investigate whether Glu could alleviate LPS-induced intestinal injury in piglets via modulation of mammalian target of rapamycin (mTOR), toll-like receptor 4 (TLR4) and nucleotide binding oligomerization domain protein (NOD) signaling pathways. Twenty-four pigs (Duroc x Large White x Landrace,7.02+ 0.21 kg initial body weight) were allotted to four treatments including:1) control group; 2) LPS+0% Glu group; 3) LPS+1.0% Glu group; 4) LPS+2.0% Glu group. On d 28, the LPS+0% Glu group, LPS+1.0% Glu group and LPS+2.0% Glu group were injected with LPS at 100 μg/kg BW, and the control group was injected with the same amount of 0.9% NaCl solution. At 4 h post-injection, pigs were slaughtered and intestinal samples were collected. The results showed that:Glu increased villus height/crypt depth ratio, RNA/DNA ratio, protein/DNA ratio and the protein abundance of claudin-1 in jejunum and ileum, increased activities of lactase, maltase and sucrase in ileum, and decreased crypt depth in jejunum. Glu also decreased mRNA abundance of jejunal TLR4, myeloid differentiation factor 88 (MyD88), IL-1 receptor-associated kinase (IRAKI), TNF receptor associated factor 6 (TRAF6), NOD1, NOD2, receptor-interacting serine/threonine-protein kinase 2 (RIPK2), nuclear factor-KB (NF-κB), Erbb2 interacting protein (ERBB2IP), centaurin β1 (ACAP1) and ileal MyD88, NOD1, suppressor of cytokine signaling 1 (SOCS1), and increased mRNA abundance of jejunal toll-interacting protein (Tollip) and ileal Tollip, cluster of differentiation 14 (CD14). In addition, Glu increased phosphorylated mTOR (p-mTOR)/total mTOR (t-mTOR) ratio in jejunum and p-mTOR/t-mTOR ratio, the protein abundance of total eIF4E binding protein 1 (t-4EBP1) and phosphorylated 4EBP1 (p-4EBP1) in ileum. These results indicate that Glu may suppress pro-inflammatory cytokine production via regulation of TLR4 and NOD signaling pathways, and therefore improve protein mass through maintenance of mTOR signaling to alleviate LPS-induced intestinal injury.2. This experiment was conducted to investigate whether Glu could alleviate LPS-induced muscle protein degradation in piglets via modulation of protein kinase b (Akt)/mTOR, Akt/forkhead box o (FOXO), TLR4 and NOD signaling pathways. Twenty-four pigs were allotted to four treatments including:1) control group; 2) LPS+0% Glu group; 3) LPS+1.0% Glu group; 4) LPS+2.0% Glu group. On d 28, the LPS+0% Glu group, LPS+1.0% Glu group and LPS+2.0% Glu group were injected with LPS at 100μg/kg BW, and the control group was injected with the same amount of 0.9% NaCl solution. At 4 h post-injection, pigs were slaughtered and muscle samples were obtained. The results showed that: Glu increased muscle protein mass indicated by higher protein/DNA ratio in gastrocnemius, and higher protein content and protein/DNA ratio in longissimus dorsi. Glu also decreased mRNA abundance of TLR4, IRAK1, RIPK2, NF-κB in gastrocnemius and MyD88, TNF-a in longissimus dorsi. In addition, Glu decreased mRNA abundance of FOXO1 and FOXO4 in longissimus dorsi, and increased p-Akt/t-Akt and p-FOXO1/t-FOXO1 ratios in gastrocnemius. Moreover, Glu increased p-mTOR/t-mTOR and p-4EBP1/t-4EBP1 ratios in gastrocnemius, and increased p-4EBP1/ t-4EBP1 ratio in longissimus dorsi. These results indicate that Glu may suppress muscle pro-inflammatory cytokine production via regulation of TLR4 and NOD signaling pathways, and therefore improve muscle protein mass, possibly through maintenance of Akt/mTOR and Akt/FOXO signalings.