Saponins From Panax japonicus Ameliorate High‐Fat Diet‐Induced Intestinal Barrier Dysfunction Through the Mfn2‐PERK Signaling Axis

Background The intestinal barrier is crucial for maintaining gastrointestinal homeostasis by preventing pathogen invasion and systemic disorders. A high‐fat diet (HFD) leads to lipid dysregulation, chronic inflammation, and endoplasmic reticulum stress (ERS), which collectively disrupt intestinal barrier integrity. Saponins from Panax japonicus (SPJ), known for their anti‐inflammatory and metabolic regulatory properties, were investigated for their potential protective effects. Methods This study investigated the protective effects of SPJ against HFD‐induced intestinal barrier dysfunction and the role of the Mfn2‐PERK signaling axis. In vivo, HFD‐fed mice were treated with SPJ and assessed for jejunal barrier integrity (claudin‐1, ZO‐1), inflammatory responses, ERS markers, mitochondrial morphology, and Mfn2 expression. In vitro, Caco‐2 cell monolayers were pretreated with the PERK agonist CCT020312 and/or SPJ for 1 h, followed by palmitic acid (PA) exposure for 24 h to induce lipotoxicity. Protein expression of claudin‐1 and Mfn2 was analyzed by Western blot to evaluate epithelial permeability and mitochondrial‐ER regulatory mechanisms. Results SPJ treatment restored intestinal barrier function in HFD‐fed mice, as evidenced by elevated expression of claudin‐1 and ZO‐1, and significantly alleviated HFD‐induced jejunal inflammation and ERS. HFD induced mitochondrial fragmentation accompanied by reduced Mfn2 expression, which were effectively reversed by SPJ treatment. Consistent with in vivo findings, SPJ reduced PA‐induced hyperpermeability, upregulated Mfn2, and inhibited PERK pathway activation in Caco‐2 monolayers. Further mechanistic validation revealed that co‐treatment with the PERK agonist CCT020312 attenuated SPJ‐mediated claudin‐1 upregulation, confirming PERK pathway dependency for barrier protection. Notably, SPJ maintained Mfn2 upregulation even under PERK activation. Conclusions We conclude that SPJ ameliorate HFD‐ and PA‐induced intestinal barrier dysfunction by upregulating Mfn2 to enhance mitochondria–ER interactions and attenuating PERK‐mediated ERS. These findings highlight SPJ as a potential therapeutic agent for metabolic stress–associated intestinal disorders.