Indole‐3‐Acetic Acid Protects Bovine Hepatocytes Against Palmitic Acid‐Induced Lipid Accumulation and ER Stress Through SIRT3

Ketotic cows undergo severe negative energy balance, in which increased circulating non‐esterified fatty acids, specifically palmitic acid (PA), serve as primary drivers of liver injury. Yet, effective strategies for alleviating this lipotoxic injury remain limited. Although tryptophan metabolite indole‐3‐acetic acid (3‐IAA) has been documented to exert hepatoprotective effects in non‐ruminants, its role in alleviating lipotoxicity‐induced injury in bovine hepatocytes remains unclear. In the present study, ketotic cows exhibited increased serum β‐hydroxybutyrate and non‐esterified fatty acid concentrations and hepatic triacylglycerol accumulation and decreased serum glucose and 3‐IAA concentrations. Notably, serum 3‐IAA concentration negatively correlated with the hepatic triacylglycerol content. In primary bovine hepatocytes, treatment with 200 μmol/L 3‐IAA improved viability and reduced cytotoxicity under PA challenge. Transcriptomic analysis further indicated that 3‐IAA mainly regulated pathways related to lipid metabolism and endoplasmic reticulum (ER) stress. Further analysis showed that 3‐IAA attenuated PA‐induced lipid accumulation and downregulated sterol regulatory element‐binding protein 1c protein abundance and its downstream target gene expression, while upregulating the expression of fatty acid oxidation‐related molecules, indicating reduced lipogenesis and enhanced fatty acid oxidation. In addition, 3‐IAA markedly alleviated PA‐induced ER stress, as evidenced by reduced expression of ER stress‐related markers. Notably, 3‐IAA increased sirtuin 3 (SIRT3) protein and mRNA expression in PA‐treated hepatocytes, whereas SIRT3 knockdown partially abrogated the protective effects of 3‐IAA. Collectively, these findings demonstrate that 3‐IAA mitigates PA‐induced lipid accumulation and ER stress in bovine hepatocytes, at least in part through a SIRT3‐dependent mechanism, highlighting its potential as an endogenous regulator of hepatic homeostasis in ketotic cows.