Abstract：
BACKGROUND: The mitochondria-associated endoplasmic reticulum membrane (MAM) is the central hub for endoplasmic reticulum and mitochondria functional communication. It plays a crucial role in hepatic lipid homeostasis. However, even though MAM has been acknowledged to be rich in enzymes that contribute to lipid biosynthesis, no study has yet investigated the exact role of MAM on hepatic neutral lipid synthesis.
OBJECTIVE: To address these gaps, this study investigated the systemic control mechanisms of MAM on neutral lipids synthesis by recruiting seipin, focusing on the role of the inositol trisphosphate receptor-1,4,5(Ip3r)-75 kDa glucose-regulated protein (Grp75)-voltage-dependent anion channel (Vdac) complex and their relevant Ca2+ signaling in this process.
METHODS: To this end, a model animal for lipid metabolism, yellow catfish (Pelteobagrus fulvidraco), were fed 6 different diets containing a range of palmitic acid (PA) concentrations from 0-150 g/kg in vivo for 10 wk. In vitro, experiments were also conducted to intercept the MAM-mediated Ca2+ signaling in isolated hepatocytes by transfecting them with si-mitochondrial calcium uniporter (mcu). Because mcu was placed in the inner mitochondrial membrane (IMM), si-mcu cannot disrupt MAM\'s structural integrity.
RESULTS: 1. Hepatocellular MAM subproteome analysis indicated excessive dietary PA intake enhanced hepatic MAM structure joined by activating Ip3r-Grp75-Vdac complexes. 2. Dietary PA intake induced hepatic neutral lipid accumulation through MAM recruiting Seipin, which activated lipid droplet biogenesis. Our findings also revealed a previously unidentified mechanism whereby MAM-recruited seipin and controlled hepatic lipid homeostasis, depending on Ip3r-Grp75-Vdac-controlled Ca2+ signaling and not only MAM\'s structural integrity.
CONCLUSIONS: These results offer a novel insight into the MAM-recruited seipin in controlling hepatic lipid synthesis in a MAM structural integrity-dependent and Ca2+ signaling-dependent manner, highlighting the critical contribution of MAM in maintaining hepatic neutral lipid homeostasis.
OBJECTIVE: To address these gaps, this study investigated the systemic control mechanisms of MAM on neutral lipids synthesis by recruiting seipin, focusing on the role of the inositol trisphosphate receptor-1,4,5(Ip3r)-75 kDa glucose-regulated protein (Grp75)-voltage-dependent anion channel (Vdac) complex and their relevant Ca2+ signaling in this process.
METHODS: To this end, a model animal for lipid metabolism, yellow catfish (Pelteobagrus fulvidraco), were fed 6 different diets containing a range of palmitic acid (PA) concentrations from 0-150 g/kg in vivo for 10 wk. In vitro, experiments were also conducted to intercept the MAM-mediated Ca2+ signaling in isolated hepatocytes by transfecting them with si-mitochondrial calcium uniporter (mcu). Because mcu was placed in the inner mitochondrial membrane (IMM), si-mcu cannot disrupt MAM\'s structural integrity.
RESULTS: 1. Hepatocellular MAM subproteome analysis indicated excessive dietary PA intake enhanced hepatic MAM structure joined by activating Ip3r-Grp75-Vdac complexes. 2. Dietary PA intake induced hepatic neutral lipid accumulation through MAM recruiting Seipin, which activated lipid droplet biogenesis. Our findings also revealed a previously unidentified mechanism whereby MAM-recruited seipin and controlled hepatic lipid homeostasis, depending on Ip3r-Grp75-Vdac-controlled Ca2+ signaling and not only MAM\'s structural integrity.
CONCLUSIONS: These results offer a novel insight into the MAM-recruited seipin in controlling hepatic lipid synthesis in a MAM structural integrity-dependent and Ca2+ signaling-dependent manner, highlighting the critical contribution of MAM in maintaining hepatic neutral lipid homeostasis.
摘要：
背景：线粒体相关的内质网膜（MAM），是内质网和线粒体功能交流的中心枢纽。它在肝脏脂质稳态中起着至关重要的作用。然而,尽管已经承认MAM富含有助于脂质生物合成的酶，尚未有研究调查MAM对肝脏中性脂质合成的确切作用。
目标：为了解决这些差距，本研究通过招募Seipin研究了MAM在中性脂质合成中的系统控制机制，重点介绍Ip3r-Grp75-Vdac复合物及其相关Ca2+信号在此过程中的作用。
方法：为此，脂质代谢的模型动物，黄鲶鱼（黄鲈鱼），在体内饲喂六种不同的饮食，其中包含0g/kg至150g/kg的棕榈酸（PA）浓度范围，持续10周。还进行了体外实验，通过用线粒体钙单向转运蛋白（mcu）转染分离的肝细胞来拦截MAM介导的Ca2信号传导。由于mcu位于线粒体内膜(IMM)，si-mcu不能破坏MAM的结构完整性。
结果：1.肝细胞MAM亚蛋白质组分析表明，过量的饮食PA摄入通过激活Ip3r-Grp75电压依赖性阴离子通道（Vdac）复合物来增强肝MAM结构连接。2.膳食PA摄入通过MAM招募Seipin诱导肝中性脂质积累，激活了脂滴生物合成。我们的发现还揭示了以前未知的机制，即MAM招募了Seipin并控制了肝脏脂质稳态，取决于Ip3r-Grp75-Vdac控制的Ca2+信号，而不仅仅是MAM的结构完整性。
结论：这些结果为MAM招募的Seipin以MAM结构完整性依赖性和Ca2信号依赖性方式控制肝脂质合成提供了新的见解，强调MAM在维持肝脏中性脂质稳态方面的关键贡献。
目标：为了解决这些差距，本研究通过招募Seipin研究了MAM在中性脂质合成中的系统控制机制，重点介绍Ip3r-Grp75-Vdac复合物及其相关Ca2+信号在此过程中的作用。
方法：为此，脂质代谢的模型动物，黄鲶鱼（黄鲈鱼），在体内饲喂六种不同的饮食，其中包含0g/kg至150g/kg的棕榈酸（PA）浓度范围，持续10周。还进行了体外实验，通过用线粒体钙单向转运蛋白（mcu）转染分离的肝细胞来拦截MAM介导的Ca2信号传导。由于mcu位于线粒体内膜(IMM)，si-mcu不能破坏MAM的结构完整性。
结果：1.肝细胞MAM亚蛋白质组分析表明，过量的饮食PA摄入通过激活Ip3r-Grp75电压依赖性阴离子通道（Vdac）复合物来增强肝MAM结构连接。2.膳食PA摄入通过MAM招募Seipin诱导肝中性脂质积累，激活了脂滴生物合成。我们的发现还揭示了以前未知的机制，即MAM招募了Seipin并控制了肝脏脂质稳态，取决于Ip3r-Grp75-Vdac控制的Ca2+信号，而不仅仅是MAM的结构完整性。
结论：这些结果为MAM招募的Seipin以MAM结构完整性依赖性和Ca2信号依赖性方式控制肝脂质合成提供了新的见解，强调MAM在维持肝脏中性脂质稳态方面的关键贡献。
