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. © 2026 The Author(s). Animal Research and One Health published by John Wiley & Sons Australia, Ltd on behalf of Institute of Animal Science, Chinese Academy of Agricultural Sciences.