The GARP complex is required for cellular sphingolipid homeostasis.
The GARP complex is required for cellular sphingolipid homeostasis.
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DOI：
10.7554/elife.08712
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发表时间：
2015-09-10
期刊：
影响因子：
7.7
通讯作者：
Walther TC
中科院分区：
文献类型：
--
作者：
Fröhlich F;Petit C;Kory N;Christiano R;Hannibal-Bach HK;Graham M;Liu X;Ejsing CS;Farese RV;Walther TC
鞘脂是真核细胞中丰富的膜组分和重要的信号分子。它们的水平和位置受到严格的管制。然而，这种调节的机制在很大程度上仍然未知。在这项研究中，我们确定了高尔基体相关逆行蛋白（GARP）复合物，它的功能内体到高尔基体逆行囊泡运输，作为一个关键的球员在鞘脂稳态。GARP缺乏导致鞘脂合成中间体的积累、固醇分布的变化和溶酶体功能障碍。类似于VPS53等位基因的GARP复合突变导致人类进行性小脑-脑萎缩2型（PCCA 2），在酵母中表现出相似的，尽管较弱的表型，提供了对疾病发病机制的机制见解。对鞘脂从头合成的第一步的抑制足以减轻GARP缺陷型酵母或哺乳动物细胞的许多表型。总之，这些数据表明GARP对于细胞鞘脂稳态是必不可少的，并提出了治疗PCCA 2的治疗策略。DOI：www.example.com每个细胞都被一层膜包裹着，这层膜在细胞和环境之间形成了一道屏障。这种膜含有称为“鞘脂”的脂肪分子，有助于维持膜的结构，使其能够正常工作。这些分子也被用作在细胞内部发送信息的信号，并且是细胞正常生长和分裂所必需的。必须严格控制膜中鞘脂的水平，因为任何不平衡都会对细胞造成压力，并可能导致严重的疾病。鞘脂在细胞内产生，然后被送到一个叫做高尔基体的隔间，然后被送到细胞膜上。为了调节膜中鞘脂的量，这些分子通常以称为内体的小结构返回到细胞内部。从这里，它们可以被分解或通过高尔基体回收回膜。一组被称为高尔基体相关逆行蛋白复合物（或GARP）的蛋白质参与了内体从膜到高尔基体的运动。编码GARP的基因发生突变的人患有严重的神经退行性疾病，称为“进行性小脑-大脑萎缩2型”（PCCA 2），其中脑细胞过早死亡。研究人员认为GARP最重要的作用是对蛋白质进行分类，而蛋白质的错误分类导致PCCA 2。在这里，Frohlich等人使用遗传分析和生物化学技术的组合来研究酵母细胞中的GARP。实验表明，GARP对于鞘脂回收至关重要，缺乏GARP会导致更多的鞘脂被降解，从而导致有毒分子的积累。Frohlich等人产生的酵母细胞在编码GARP的基因中具有与患有PCCA 2的人类患者相同的突变。这些细胞比正常酵母生长得慢得多，并且不太能够将鞘脂从内体运输到高尔基体。像酵母细胞一样，编码GARP的基因活性较低的人类细胞也会积累有毒分子。总之，这些发现表明，有毒脂肪分子的积累可能是PCCA 2患者中观察到的症状的原因。未来的挑战是找出这是否也适用于阿尔茨海默病和其他也影响内体的疾病患者。DOI：www.example.com网站
Sphingolipids are abundant membrane components and important signaling molecules in eukaryotic cells. Their levels and localization are tightly regulated. However, the mechanisms underlying this regulation remain largely unknown. In this study, we identify the Golgi-associated retrograde protein (GARP) complex, which functions in endosome-to-Golgi retrograde vesicular transport, as a critical player in sphingolipid homeostasis. GARP deficiency leads to accumulation of sphingolipid synthesis intermediates, changes in sterol distribution, and lysosomal dysfunction. A GARP complex mutation analogous to a VPS53 allele causing progressive cerebello-cerebral atrophy type 2 (PCCA2) in humans exhibits similar, albeit weaker, phenotypes in yeast, providing mechanistic insights into disease pathogenesis. Inhibition of the first step of de novo sphingolipid synthesis is sufficient to mitigate many of the phenotypes of GARP-deficient yeast or mammalian cells. Together, these data show that GARP is essential for cellular sphingolipid homeostasis and suggest a therapeutic strategy for the treatment of PCCA2. DOI: http://dx.doi.org/10.7554/eLife.08712.001 Every cell is enveloped by a membrane that forms a barrier between the cell and its environment. This membrane contains fat molecules called ‘sphingolipids’, which help to maintain the structure of the membrane and enable it to work correctly. These molecules are also used as signals to send information around the interior of the cell and are required for the cell to grow and divide normally. The levels of sphingolipids in the membrane have to be tightly controlled because any imbalance can cause stress to the cell and can lead to serious diseases. Sphingolipids are made inside the cell and are then sent to a compartment called the Golgi before being delivered to the membrane. To regulate the amount of sphingolipids in the membrane, these molecules are routinely returned to the interior of the cell in small structures called endosomes. From here, they can either be broken down or recycled back to the membrane via the Golgi. A group of proteins known as the Golgi-associated retrograde protein complex (or GARP) is involved in the movement of endosomes from the membrane to the Golgi. People that have a mutation in the gene that encodes GARP suffer from a severe neurodegenerative disease known as ‘progressive cerebello-cerebral atrophy type 2’ (PCCA2) in which brain cells die prematurely. Researchers have assumed that the most important role of GARP is to sort proteins, and that the missorting of proteins leads to PCCA2. Here, Frohlich et al. used a combination of genetic analysis and biochemical techniques to study GARP in yeast cells. The experiments show that GARP is critical for sphingolipid recycling, and that a lack of GARP leads to more sphingolipids being degraded, which results in a build-up of toxic molecules. Frohlich et al. generated yeast cells that have the same mutations in the gene that encodes GARP as those in human patients with PCCA2. These cells grew much slower than normal yeast and were less able to transport sphingolipids from the endosome to the Golgi. Like the yeast cells, human cells in which the gene that encodes GARP was less active also accumulated toxic molecules. Together, these findings suggest that a build-up of toxic fat molecules may be responsible for the symptoms observed in PCCA2 patients. A future challenge is to find out whether this also applies to patients with Alzheimer's disease and other conditions that also affect endosomes. DOI: http://dx.doi.org/10.7554/eLife.08712.002