Ursolic acid attenuates hepatic steatosis, fibrosis, and insulin resistance by modulating the circadian rhythm pathway in diet-induced obese mice

Background/Objectives: The aim of the current study was to elucidate the effects of long-term supplementation with dietary ursolic acid (UR) on obesity and associated comorbidities, such as hepatic fibrosis, by analyzing transcriptional and metabolic responses, focusing on the role of UR in the modulation of the circadian rhythm pathway in particular. Subjects/Methods: C57BL/6J mice were divided into three groups and fed a normal diet, high-fat diet (HFD), or high-fat + 0.05% (w/w) UR diet for 16 weeks. Results: Oligonucleotide microarray profiling revealed that the liver transcriptome was more significantly altered by UR supplementation than that of the skeletal muscle and epididymal white adipose tissue, suggesting that UR is an effective regulator of the liver transcriptome. Furthermore, Kyoto Encyclopedia of Genes and Genomes pathway mapper analyses showed that canonical pathways associated with the “circadian rhythm” and “extracellular matrix (ECM)-receptor interactions” were effectively regulated by UR in the liver. UR altered the expression of various clock and clock-controlled genes (CCGs), which may be linked to the improvement of hepatic steatosis and fibrosis via lipid metabolism control and detoxification enhancement. UR reduced excessive reactive oxygen species production via an increase in plasma paraoxonase activity, adipokine/cytokine dysregulation, and ECM accumulation in the liver, which also contributed to improve hepatic lipotoxicity and fibrosis. In addition, UR treatment improved and normalized pancreatic islet dysfunction, and suppressed hepatic gluconeogenesis, thereby reducing obesity-associated insulin resistance in HFD-fed mice. Conclusions: Therapeutic approaches targeting hepatic circadian clock and CCGs using UR may ameliorate the deleterious effects of diet-induced obesity and associated complications such as hepatic fibrosis. Total RNA of liver, skeletal muscle and adipose tissues was obtained from normal diet, high-fat diet and ursolic acid added high-fat diet-fed mice and mRNA expression-associated with lipid metabolism and inflammation was measured.

背景与研究目标：本研究旨在通过分析转录组与代谢应答，阐明长期膳食补充熊果酸（ursolic acid, UR）对肥胖及相关合并症（如肝纤维化）的影响，重点探究UR在调控昼夜节律（circadian rhythm）通路中的具体作用。

研究对象与方法：将C57BL/6J小鼠分为三组，分别饲喂普通饲料、高脂饮食（high-fat diet, HFD）以及高脂+0.05%（质量分数）UR饲料，持续干预16周。

结果：寡核苷酸微阵列谱分析显示，与骨骼肌和附睾白色脂肪组织相比，UR补充对肝脏转录组的调控效果更为显著，提示UR可有效调节肝脏转录组。进一步采用京都基因与基因组百科全书（Kyoto Encyclopedia of Genes and Genomes, KEGG）通路映射分析发现，肝脏中与“昼夜节律”及“细胞外基质（extracellular matrix, ECM）-受体相互作用”相关的经典通路可被UR有效调控。UR可改变多种生物钟基因及生物钟调控基因（clock-controlled genes, CCGs）的表达，这一效应可能通过调控脂质代谢、增强解毒功能，改善肝脂肪变与肝纤维化。UR可通过提升血浆对氧磷酶活性、改善脂肪因子与细胞因子失调及减少肝脏细胞外基质沉积，减少过量活性氧（reactive oxygen species）生成，该效应同样有助于改善肝脏脂毒性与肝纤维化。此外，UR处理可改善并恢复胰岛功能障碍，抑制肝脏糖异生，从而降低高脂饮食喂养小鼠的肥胖相关胰岛素抵抗。

结论：以UR靶向调控肝脏生物钟及CCGs的治疗策略，或可改善饮食诱导肥胖及其相关并发症（如肝纤维化）带来的有害影响。本研究提取普通饲料、高脂饲料及添加熊果酸的高脂饲料喂养小鼠的肝脏、骨骼肌与脂肪组织总RNA，并检测与脂质代谢及炎症相关的mRNA表达水平。