PDF(Pubmed)
Abstract：
Background: ApoA5 mainly synthesized and secreted by liver is a key modulator of lipoprotein lipase (LPL) activity and triglyceride-rich lipoproteins (TRLs). Although the role of ApoA5 in extrahepatic triglyceride (TG) metabolism in circulation has been well documented, the relationship between ApoA5 and nonalcoholic fatty liver disease (NAFLD) remains incompletely understood and the underlying molecular mechanism still needs to be elucidated. Methods: We used CRISPR/Cas9 gene editing to delete Apoa5 gene from Syrian golden hamster, a small rodent model replicating human metabolic features. Then, the ApoA5-deficient (ApoA5-/-) hamsters were used to investigate NAFLD with or without challenging a high fat diet (HFD). Results: ApoA5-/- hamsters exhibited hypertriglyceridemia (HTG) with markedly elevated TG levels at 2300 mg/dL and hepatic steatosis on a regular chow diet, accompanied with an increase in the expression levels of genes regulating lipolysis and small adipocytes in the adipose tissue. An HFD challenge predisposed ApoA5-/- hamsters to severe HTG (sHTG) and nonalcoholic steatohepatitis (NASH). Mechanistic studies in vitro and in vivo revealed that targeting ApoA5 disrupted NR1D1 mRNA stability in the HepG2 cells and the liver to reduce both mRNA and protein levels of NR1D1, respectively. Overexpression of human NR1D1 by adeno-associated virus 8 (AAV8) in the livers of ApoA5-/- hamsters significantly ameliorated fatty liver without affecting plasma lipid levels. Moreover, restoration of hepatic ApoA5 or activation of UCP1 in brown adipose tissue (BAT) by cold exposure or CL316243 administration could significantly correct sHTG and hepatic steatosis in ApoA5-/- hamsters. Conclusions: Our data demonstrate that HTG caused by ApoA5 deficiency in hamsters is sufficient to elicit hepatic steatosis and HFD aggravates NAFLD by reducing hepatic NR1D1 mRNA and protein levels, which provides a mechanistic link between ApoA5 and NAFLD and suggests the new insights into the potential therapeutic approaches for the treatment of HTG and the related disorders due to ApoA5 deficiency in the clinical trials in future.
摘要：
背景：ApoA5主要由肝脏合成和分泌，是脂蛋白脂肪酶（LPL）活性和富含甘油三酯的脂蛋白（TRLs）的关键调节剂。尽管ApoA5在循环中的肝外甘油三酯（TG）代谢中的作用已得到充分证明，ApoA5与非酒精性脂肪性肝病(NAFLD)之间的关系尚不完全清楚,潜在的分子机制仍有待阐明.方法：我们使用CRISPR/Cas9基因编辑从叙利亚金仓鼠中删除Apoa5基因，复制人类代谢特征的小型啮齿动物模型。然后，ApoA5缺陷型(ApoA5-/-)仓鼠用于研究有或没有挑战高脂肪饮食(HFD)的NAFLD。结果：ApoA5-/-仓鼠表现出高甘油三酯血症（HTG），在2300mg/dL时TG水平显着升高，在常规饮食下肝脏脂肪变性，伴随着脂肪组织中调节脂肪分解和小脂肪细胞的基因表达水平的增加。HFD攻击使ApoA5-/-仓鼠易患重度HTG（sHTG）和非酒精性脂肪性肝炎（NASH）。体外和体内机制研究表明，靶向ApoA5会破坏HepG2细胞和肝脏中NR1D1mRNA的稳定性，从而分别降低NR1D1的mRNA和蛋白质水平。腺相关病毒8（AAV8）在ApoA5-/-仓鼠肝脏中过表达人NR1D1可显着改善脂肪肝，而不影响血浆脂质水平。此外，通过冷暴露或CL316243给药恢复肝脏ApoA5或激活棕色脂肪组织（BAT）中的UCP1可以显着纠正ApoA5-/-仓鼠的sHTG和肝脏脂肪变性。结论：我们的数据表明，仓鼠ApoA5缺乏引起的HTG足以引起肝脏脂肪变性，HFD通过降低肝脏NR1D1mRNA和蛋白水平加重NAFLD，这提供了ApoA5和NAFLD之间的机械联系，并提出了在未来的临床试验中治疗HTG和由于ApoA5缺乏引起的相关疾病的潜在治疗方法的新见解。
