ATP7B knockout disturbs copper and lipid metabolism in Caco-2 cells

Intestinal cells control delivery of lipids to the body by adsorption, storage and secretion. Copper (Cu) is an important trace element and has been shown to modulate lipid metabolism. Mutation of the liver Cu exporter ATP7B is the cause of Wilson disease and is associated with Cu accumulation in different tissues. To determine the relationship of Cu and lipid homeostasis in intestinal cells, a CRISPR/Cas9 knockout of ATP7B (KO) was introduced in Caco-2 cells. KO cells showed increased sensitivity to Cu, elevated intracellular Cu storage, and induction of genes regulating oxidative stress. Chylomicron structural protein ApoB48 was significantly downregulated in KO cells by Cu. Apolipoproteins ApoA1, ApoC3 and ApoE were constitutively induced by loss of ATP7B. Formation of small sized lipid droplets (LDs) was enhanced by Cu, whereas large sized LDs were reduced. Cu reduced triglyceride (TG) storage and secretion. Exposure of KO cells to oleic acid (OA) resulted in enhanced TG storage. The findings suggest that Cu represses intestinal TG lipogenesis, while loss of ATP7B results in OA-induced TG storage.肠道细胞可通过吸附、储存与分泌过程调控脂质向机体的递送。铜（Copper, Cu）是一种重要的微量元素，现已被证实可调控脂质代谢。肝脏铜输出蛋白ATP7B的突变是威尔逊病的致病诱因，且与多种组织内的铜蓄积相关。为明确肠道细胞内铜与脂质稳态的相互关系，研究人员在Caco-2细胞中构建了ATP7B的CRISPR/Cas9敲除（KO）细胞模型。该敲除细胞对铜的敏感性升高，细胞内铜储存量增加，同时调控氧化应激的基因表达被诱导上调。铜处理可使敲除细胞内的乳糜微粒结构蛋白ApoB48表达显著下调；而ATP7B缺失则会持续诱导载脂蛋白ApoA1、ApoC3及ApoE的表达。铜可促进小型脂滴（lipid droplets, LDs）的形成，却会减少大型脂滴的生成。铜可降低甘油三酯（triglyceride, TG）的储存与分泌量。将敲除细胞暴露于油酸（oleic acid, OA）环境后，其细胞内甘油三酯储存量进一步升高。本研究结果表明，铜可抑制肠道内甘油三酯的脂质合成过程，而ATP7B的缺失则会导致油酸诱导的甘油三酯储存增强。