棕榈酸是循环中最丰富的饱和脂肪酸，会引起肝细胞毒性和炎症。由于饱和脂肪酸也会扰乱昼夜节律，因此目前的工作评估了时钟基因和 NAD 依赖性 Sirtuins 在保护肝细胞免受脂质诱导损伤方面的联系。用较高剂量的棕榈酸（400-600μM）处理的肝细胞（永生细胞PH5CH8、肝癌细胞HepG2）表现出典型的脂肪变性特征，伴有生长抑制和炎症标志物（IL-6、IL-8、IL-1α和IL）水平升高。 -1β) 以及 NAD 水平下降。棕榈酸处理的肝细胞不仅显示 SIRT2 的蛋白质水平显着下降，而且其下游靶标（微管蛋白和 NF-ƙB）的乙酰化状态也显示其活性显着下降。此外，只有非癌性肝细胞 PH5CH8 细胞中存在棕榈酸时，SIRT2 和 BMAL1 的昼夜节律表达均受到抑制。从患有 NASH 相关纤维化（从无纤维化（F0）到肝硬化（F4））受试者中获得的临床标本显示 SIRT2 和 BMAL1 水平显着下降，尤其是在肝硬化肝脏中。与 HepG2 细胞相比，在 PH5CH8 细胞中，BMAL1 的异位表达或通过补充烟酰胺核苷（NAD 前体）激活 SIRT2 更有效地抑制棕榈酸诱导的脂肪炎症和脂毒性。从机制上讲，棕榈酸通过破坏 BMAL1 在其启动子位点的染色质占据来引起 SIRT2 的转录抑制。总体而言，这项工作表明 SIRT2 是一个受 BMAL1 转录调控的时钟控制基因。总之，BMAL1-NAD -SIRT2 轴的激活通过预防脂毒性和抑制炎症显示出保肝作用。© 2024。作者获得纳瓦拉大学的独家许可。

Palmitic acid is the most abundant saturated fatty acid in circulation and causes hepatocyte toxicity and inflammation. As saturated fatty acid can also disrupt the circadian rhythm, the present work evaluated the connection between clock genes and NAD+ dependent Sirtuins in protecting hepatocytes from lipid-induced damage. Hepatocytes (immortal cells PH5CH8, hepatoma cells HepG2) treated with higher doses of palmitic acid (400-600μM) showed typical features of steatosis accompanied with growth inhibition and increased level of inflammatory markers (IL-6 IL-8, IL-1α and IL-1β) together with decline in NAD+ levels. Palmitic acid treated hepatocytes showed significant decline in not only the protein levels of SIRT2 but also its activity as revealed by the acetylation status of its downstream targets (Tubulin and NF-ƙB). Additionally, the circadian expression of both SIRT2 and BMAL1 was inhibited in presence of palmitic acid in only the non-cancerous hepatocytes, PH5CH8 cells. Clinical specimens obtained from subjects with NASH-associated fibrosis, ranging from absent (F0) to cirrhosis (F4), showed a significant decline in levels of SIRT2 and BMAL1, especially in the cirrhotic liver. Ectopic expression of BMAL1 or activating SIRT2 by supplementation with nicotinamide riboside (precursor of NAD+) dampened the palmitic acid induced lipoinflammation and lipotoxicity more effectively in PH5CH8 cells as compared to HepG2 cells. Mechanistically, palmitic acid caused transcriptional suppression of SIRT2 by disrupting the chromatin occupancy of BMAL1 at its promoter site. Overall, the work suggested that SIRT2 is a clock-controlled gene that is transcriptionally regulated by BMAL1. In conclusion the activation of the BMAL1-NAD+-SIRT2 axis shows hepatoprotective effects by preventing lipotoxicity and dampening inflammation.© 2024. The Author(s) under exclusive licence to University of Navarra.