Non-alcoholic fatty liver disease (NAFLD) is a metabolic disorder characterized by excess lipid accumulation in the liver without significant consumption of alcohol. The transmembrane 6 superfamily member 2 (TM6SF2) E167K missense variant strongly associates with NAFLD in humans. The E167K mutation destabilizes TM6SF2, resulting in hepatic lipid accumulation and low serum lipid levels. However, the molecular mechanism by which TM6SF2 regulates lipid metabolism remains unclear. By using tandem affinity purification in combination with mass spectrometry, we found that apolipoprotein B (APOB), ER lipid raft protein (ERLIN) 1 and 2 were TM6SF2-interacting proteins. ERLINs and TM6SF2 mutually bound and stabilized each other. TM6SF2 bound and stabilized APOB via two luminal loops. ERLINs did not interact with APOB directly but still increased APOB stability through stabilizing TM6SF2. This APOB stabilization was hampered by the E167K mutation that reduced the protein expression of TM6SF2. In mice, knockout of Tm6sf2 and knockdown of Tm6sf2 or Erlins decreased hepatic APOB protein level, causing lipid accumulation in the liver and lowering lipid levels in the serum. We conclude that defective APOB stabilization, as a result of ERLINs or TM6SF2 deficiency or E167K mutation, is a key factor contributing to NAFLD.

非酒精性脂肪肝疾病（NAFLD）是一种代谢性疾病，其特征是肝脏中脂质过多积聚，而没有大量饮酒。跨膜6超家族成员2（TM6SF2）E167K错义变体与人类的NAFLD密切相关。E167K突变破坏了TM6SF2的稳定性，导致肝脂质积聚和低血清脂质水平。然而，TM6SF2调节脂质代谢的分子机制仍不清楚。通过串联亲和纯化与质谱联用，我们发现载脂蛋白B（APOB），ER脂筏蛋白（ERLIN）1和2是与TM6SF2相互作用的蛋白。ERLIN和TM6SF2相互绑定并彼此稳定。TM6SF2通过两个腔环绑定并稳定了APOB。ERLIN并不直接与APOB相互作用，而是通过稳定TM6SF2来提高APOB的稳定性。E167K突变降低了TM6SF2的蛋白表达，从而阻碍了APOB的稳定。在小鼠中，敲除Tm6sf2Tm6sf2或Erlins的敲低会降低肝脏APOB的蛋白水平，从而引起肝脏中脂质的蓄积并降低血清中的脂质水平。我们得出的结论是，由于ERLIN或TM6SF2缺乏或E167K突变而导致的APOB稳定缺陷是导致NAFLD的关键因素。