Glutamine alleviates feed restriction-induced barrier function injury in yak rumen epithelium

The yak (<i>Bos grunniens</i>) is a crucial species for herders on the Qinghai-Tibet Plateau. Cold-season forage scarcity often leads to starvation, impairing the rumen epithelial barrier function and growth performance. Glutamine (Gln) has been shown to mitigate injury to the gastrointestinal tract barrier function, but its efficacy and mechanism against feed restriction (FR)-induced barrier injury in yaks remains unclear. This study combined in vivo and in vitro experiments to investigate this. Twenty-four healthy yaks (31 months, 265.35 ± 25.81 kg) were randomly divided into three groups (<i>n</i> = 8 per group) and fed for 60 d : the control (Con, ad libitum access to the basal diet), FR (50% of the basal diet), and FR + Gln (50% of the basal diet in the first month, with 1% Gln added to the 50% basal diet in the second month). Yak rumen epithelial cells (YRECs) were treated under four conditions: Control (normal medium), Gln (normal medium + 10 mmol/L Gln), Gln deficiency (Gln-D, Gln-free medium), and Gln-D + Gln (Gln-free medium + 10 mmol/L Gln). Results showed that FR significantly decreased the average daily gain (ADG) and the Gln concentration in ruminal epithelial tissue and serum (<i>P</i> < 0.05) and increased serum levels of permeability parameters (diamine oxidase, D-lactate, lipopolysaccharide, and histamine) compared to the Con group (<i>P</i> < 0.05). In addition, FR in vivo or Gln-D in vitro significantly down-regulated the protein expression of tight junction (TJ) proteins (ZO-1, occludin, and claudin-1) (<i>P</i> < 0.05) and enhanced the phosphorylation of nuclear factor-κB p65 (NF-κB p65), p38 mitogen-activated protein kinase (p38 MAPK), and c-junN-terminal kinase (JNK) (<i>P</i> < 0.05). Gln supplementation effectively reversed these changes, significantly reducing serum permeability (<i>P</i> < 0.001), restoring TJ protein expression, and suppressing the phosphorylation of NF-κB p65, p38 MAPK, and JNK compared to the FR or Gln-D groups (<i>P</i> < 0.01). Crucially, the ability of Gln to restore TJ integrity was abolished by p38 MAPK and JNK activators in YRECs (<i>P</i> < 0.001). Overall, this suggests that dietary Gln supplementation alleviates FR-induced rumen epithelial barrier damage in yaks through the MAPK/NF-κB pathway.