Salidroside protects bovine hepatocytes against fatty acid-induced lipid accumulation and inflammation by activating AMPK/SIRT1 pathway

Fat mobilization and elevated circulating levels of nonesterified fatty acids (NEFA) resulting from severe negative energy balance (NEB) are the major causes of hepatic lipid accumulation and inflammation in dairy cows during the transition period. However, there is a lack of promising therapeutic agents to control NEFA-induced lipotoxicity in the liver of dairy cows. Thus, the objective of this study was to investigate the effects of salidroside (Sal), the principal bioactive component of Rhodiola, on NEFA-induced lipotoxicity in bovine hepatocytes, as well as the underlying molecular mechanisms. Bovine hepatocytes were isolated from 5 healthy Holstein female newborn calves (1 d of age, 30-40 kg, fasting) and treated with NEFA (1.2 mM), Sal (0, 5, 25, 50, 100, or 200 μM), or both for 12 h. To elucidate the role of the AMP-activated protein kinase (AMPK)/silent information regulator 1 (SIRT1) signaling axis, hepatocytes were additionally treated with inhibitors against AMPK or SIRT1. The results showed that Sal treatment significantly alleviated NEFA-induced increases in triacylglycerol (TAG) content, protein abundance of sterol regulatory element-binding protein 1c (SREBP-1c) and mRNA levels of SREBP1 and Acetyl-CoA Carboxylase 1 (ACACA). Furthermore, Sal alleviated the downregulation of Peroxisome Proliferator-activated Receptor α (PPARA) protein abundance and mRNA levels of PPARA and carnitine palmitoyltransferase 1A (CPT1A). In addition, Sal treatment markedly decreased NEFA-induced phosphorylation levels of nuclear factor κB (NF-κB) and its inhibitor (IκB)α, as well as mRNA levels of IL1B, IL6, and tumor necrosis factor α (TNFA). These results demonstrate that Sal possesses the capacity to effectively alleviate the lipotoxic effects provoked by NEFA in bovine hepatocytes. Moreover, Sal treatment prevented the inhibition of AMPK/SIRT1 signaling pathway in NEFA-challenged bovine hepatocytes. Importantly, the blockage of AMPK/SIRT1 abrogated the protective effects of Sal against NEFA-induced lipid accumulation and inflammation, as evidenced by increased TAG content, elevated protein abundance of SREBP-1c and phosphorylation levels of NF-κB and IκBα, along with upregulated mRNA levels of SREBP1, ACACA, IL1B, IL6, and TNFA. Concurrently, PPARA protein expression and the gene expression of PPARA and CPT1A were decreased. In conclusion, these findings suggest that Sal ameliorates lipid accumulation and inflammation by activating AMPK/SIRT1 pathway in bovine hepatocytes, which may represent a promising therapeutic strategy to mitigate the hepatic lipotoxicity of elevated NEFA levels during transition periods in dairy cows.

AMPK/SIRT1 pathway; bovine hepatocytes; inflammation; lipid accumulation; salidroside.