From the Department of Medicine, McMaster University, The Research Institute of St. Joe's Hamilton, Hamilton, Ontario L8N 4A6 and.
the Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute, University of Montreal, Montreal, Quebec H2W 1R7, Canada.
J Biol Chem. 2019 Jun 7;294(23):9037-9047. doi: 10.1074/jbc.RA119.008094. Epub 2019 Apr 19.
The worldwide prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing rapidly. Although this condition is generally benign, accumulating evidence now suggests that patients with NAFLD are also at increased risk of cardiovascular disease (CVD); the leading cause of death in developed nations. Despite the well-established role of the liver as a central regulator of circulating low-density lipoprotein (LDL) cholesterol levels, a known driver of CVD, the mechanism(s) by which hepatic steatosis contributes to CVD remains elusive. Interestingly, a recent study has shown that circulating proprotein convertase subtilisin/kexin type 9 (PCSK9) levels correlate positively with liver steatosis grade. Given that PCSK9 degrades the LDL receptor (LDLR) and prevents the removal of LDL from the blood into the liver, in the present study we examined the effect of hepatic steatosis on LDLR expression and circulating LDL cholesterol levels. We now report that in a manner consistent with findings in patients, diet-induced steatosis increases circulating PCSK9 levels as a result of expression in mice. We also report the finding that steatosis abrogates hepatic LDLR expression and increases circulating LDL levels in a PCSK9-dependent manner. These findings provide important mechanistic insights as to how hepatic steatosis modulates lipid regulatory genes, including and the , and also highlights a novel mechanism by which liver disease may contribute to CVD.
全球范围内非酒精性脂肪性肝病 (NAFLD) 的患病率正在迅速上升。尽管这种情况通常是良性的,但越来越多的证据表明,NAFLD 患者患心血管疾病 (CVD) 的风险也增加;CVD 是发达国家的主要死亡原因。尽管肝脏作为循环低密度脂蛋白 (LDL) 胆固醇水平的中枢调节剂的作用已得到充分确立,而 LDL 胆固醇是 CVD 的已知驱动因素,但肝脂肪变性导致 CVD 的机制仍不清楚。有趣的是,最近的一项研究表明,循环前蛋白转化酶枯草溶菌素/柯萨奇蛋白酶 9 (PCSK9) 水平与肝脂肪变性程度呈正相关。鉴于 PCSK9 降解 LDL 受体 (LDLR) 并阻止 LDL 从血液中清除到肝脏中,在本研究中,我们检查了肝脂肪变性对 LDLR 表达和循环 LDL 胆固醇水平的影响。我们现在报告说,与患者中的发现一致,饮食诱导的脂肪变性会导致小鼠中 PCSK9 的表达增加,从而导致循环 PCSK9 水平升高。我们还报告了这样一个发现,即脂肪变性以 PCSK9 依赖的方式破坏肝脏 LDLR 表达并增加循环 LDL 水平。这些发现为肝脂肪变性如何调节脂质调节基因(包括 LDLR 和 PCSK9)提供了重要的机制见解,并强调了肝脏疾病可能导致 CVD 的一种新机制。
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