Centre for Lipid Research and Chongqing Key Laboratory of Metabolism on Lipid and Glucose, Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China.
Centre for Health Medicine, The Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China.
Am J Physiol Gastrointest Liver Physiol. 2024 Jun 1;326(6):G697-G711. doi: 10.1152/ajpgi.00273.2023. Epub 2024 Apr 9.
Sterol regulatory element binding protein (SREBP) cleavage-activating protein (SCAP) is a widely expressed membrane glycoprotein that acts as an important modulator of lipid metabolism and inflammatory stress. -glycosylation of SCAP has been suggested to modulate cancer development, but its role in nonalcoholic steatohepatitis (NASH) is poorly understood. In this study, the -glycosylation of SCAP was analyzed by using sequential trypsin proteolysis and glycosidase treatment. The liver cell lines expressing wild-type and glycosylation sites mutated SCAP were constructed to investigate the glycosylation role of SCAP in regulating inflammation and lipid accumulation as well as the underlying mechanisms. The hepatic SCAP protein levels were significantly increased in C57BL/6J mice fed with Western diet and sugar water (WD + SW) and diabetic db/db mice, which exhibited typical liver steatosis and inflammation accompanied with hyperglycemia. In vitro, the enhanced glycosylation by high glucose increased the protein stability of SCAP and hence increased its total protein levels, whereas the ablation of glycosylation significantly decreased SCAP protein stability and alleviated lipid accumulation and inflammation in hepatic cell lines. Mechanistically, SCAP glycosylation increased not only the SREBP-1-mediated acetyl-CoA synthetase 2 (ACSS2) transcription but also the AMPK-mediated S659 phosphorylation of ACCS2 protein, causing the enhanced ACSS2 levels in nucleus and hence increasing the histone H3K27 acetylation (H3K27ac), which is a key epigenetic modification associated with NASH. Modulating ACSS2 expression or its location in the nuclear abolished the effects of SCAP glycosylation on H3K27ac and lipid accumulation and inflammation. In conclusion, SCAP glycosylation aggravates inflammation and lipid accumulation through enhancing ACSS2-mediated H3K27ac in hepatocytes. glycosylation of SCAP exacerbates inflammation and lipid accumulation in hepatocytes through ACSS2-mediated H3K27ac. Our data suggest that SCAP glycosylation plays a key role in regulating histone H3K27 acetylation and targeting SCAP glycosylation may be a new strategy for treating nonalcoholic steatohepatitis (NASH).
固醇调节元件结合蛋白（SREBP）裂解激活蛋白（SCAP）是一种广泛表达的膜糖蛋白，作为脂质代谢和炎症应激的重要调节剂。SCAP 的-O-糖基化被认为可以调节癌症的发展，但它在非酒精性脂肪性肝炎（NASH）中的作用知之甚少。在这项研究中，通过连续胰蛋白酶酶解和糖苷酶处理分析了 SCAP 的-O-糖基化。构建了表达野生型和糖基化位点突变 SCAP 的肝细胞系，以研究 SCAP 的糖基化在调节炎症和脂质积累中的作用及其潜在机制。在喂食西方饮食和糖水（WD+SW）的 C57BL/6J 小鼠和糖尿病 db/db 小鼠中，肝组织中 SCAP 蛋白水平显著升高，表现为典型的肝脂肪变性和炎症，伴有高血糖。在体外，高葡萄糖增强的糖基化增加了 SCAP 的蛋白稳定性，从而增加了其总蛋白水平，而糖基化缺失则显著降低了 SCAP 蛋白稳定性，并减轻了肝细胞系中的脂质积累和炎症。在机制上，SCAP 的糖基化不仅增加了 SREBP-1 介导的乙酰辅酶 A 合成酶 2（ACSS2）转录，还增加了 AMPK 介导的 ACCS2 蛋白 S659 磷酸化，导致核内 ACSS2 水平增加，从而增加组蛋白 H3K27 乙酰化（H3K27ac），这是与 NASH 相关的关键表观遗传修饰。调节 ACSS2 的表达或其在核内的位置可消除 SCAP 糖基化对 H3K27ac 和脂质积累及炎症的影响。总之，SCAP 的糖基化通过增强肝细胞中 ACSS2 介导的 H3K27ac 加重炎症和脂质积累。糖基化通过 ACSS2 介导的 H3K27ac 加重了肝细胞中的炎症和脂质积累。我们的数据表明，SCAP 的糖基化在调节组蛋白 H3K27 乙酰化中起关键作用，靶向 SCAP 的糖基化可能是治疗非酒精性脂肪性肝炎（NASH）的一种新策略。
