Department of Biology, The Catholic University of America, Washington D. C.
Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska.
Am J Physiol Gastrointest Liver Physiol. 2019 Oct 1;317(4):G373-G386. doi: 10.1152/ajpgi.00026.2019. Epub 2019 Aug 2.
Although steatosis (fatty liver) is a clinically well-described early stage of alcoholic liver disease, surprisingly little is known about how it promotes hepatotoxicity. We have shown that ethanol consumption leads to microtubule hyperacetylation that can explain ethanol-induced defects in protein trafficking. Because almost all steps of the lipid droplet life cycle are microtubule dependent and because microtubule acetylation promotes adipogenesis, we examined droplet dynamics in ethanol-treated cells. In WIF-B cells treated with ethanol and/or oleic acid (a fatty acid associated with the "Western" diet), we found that ethanol dramatically increased lipid droplet numbers and led to the formation of large, peripherally located droplets. Enhanced droplet formation required alcohol dehydrogenase-mediated ethanol metabolism, and peripheral droplet distributions required intact microtubules. We also determined that ethanol-induced microtubule acetylation led to impaired droplet degradation. Live-cell imaging revealed that droplet motility was microtubule dependent and that droplets were virtually stationary in ethanol-treated cells. To determine more directly whether microtubule hyperacetylation could explain impaired droplet motility, we overexpressed the tubulin-specific acetyltransferase αTAT1 to promote microtubule acetylation in the absence of alcohol. Droplet motility was impaired in αTAT1-expressing cells but to a lesser extent than in ethanol-treated cells. However, in both cases, the large immotile droplets (but not small motile ones) colocalized with dynein and dynactin (but not kinesin), implying that altered droplet-motor microtubule interactions may explain altered dynamics. These studies further suggest that modulating cellular acetylation is a potential strategy for treating alcoholic liver disease. Chronic alcohol consumption with the "Western diet" enhances the development of fatty liver and leads to impaired droplet motility, which may have serious deletrious effects on hepatocyte function.
尽管脂肪变性（脂肪肝）是一种临床上描述得很好的酒精性肝病的早期阶段，但人们对它如何促进肝毒性知之甚少。我们已经表明，乙醇消耗导致微管过度乙酰化，这可以解释乙醇诱导的蛋白质运输缺陷。由于几乎所有的脂滴生命周期步骤都依赖于微管，并且微管乙酰化促进脂肪生成，因此我们检查了乙醇处理细胞中的液滴动力学。在用乙醇和/或油酸（与“西方”饮食相关的脂肪酸）处理的 WIF-B 细胞中，我们发现乙醇显着增加了脂质滴的数量，并导致了大的、位于外围的液滴的形成。增强的液滴形成需要醇脱氢酶介导的乙醇代谢，而外围液滴分布需要完整的微管。我们还确定，乙醇诱导的微管乙酰化导致液滴降解受损。活细胞成像显示，液滴运动依赖于微管，并且在乙醇处理的细胞中液滴几乎处于静止状态。为了更直接地确定微管过度乙酰化是否可以解释液滴运动受损，我们过表达了微管特异性乙酰转移酶αTAT1，以在没有酒精的情况下促进微管乙酰化。在过表达αTAT1 的细胞中，液滴运动受损，但程度低于乙醇处理的细胞。然而，在这两种情况下，大的无动力液滴（而不是小的动力液滴）与动力蛋白和动力蛋白激活蛋白（但不是驱动蛋白）共定位，这表明改变的液滴-马达微管相互作用可能解释了改变的动力学。这些研究进一步表明，调节细胞内乙酰化可能是治疗酒精性肝病的一种潜在策略。慢性酒精摄入与“西方饮食”相结合会增强脂肪肝的发展，并导致液滴运动受损，这可能对肝细胞功能产生严重的有害影响。
