Contributions in astrocytes of SMIT1/2 and HMIT to myo-inositol uptake at different concentrations and pH
Contributions in astrocytes of SMIT1/2 and HMIT to myo-inositol uptake at different concentrations and pH
复制标题
星形胶质细胞中 SMIT1/2 和 HMIT 在不同浓度和 pH 值下对肌醇摄取的贡献
DOI：
10.1016/j.neuint.2012.04.010
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发表时间：
2012-07-01
影响因子：
4.2
通讯作者：
Peng, Liang
中科院分区：
文献类型：
--
作者：
Fu, Hui;Li, Baoman;Peng, Liang
肌醇对细胞质和胞内细胞器中的细胞信号传导都很重要。它存在于质膜和细胞质中，用于维持磷脂酰肌醇二磷酸（PIP2）合成第二信使肌醇三磷酸（IP3）和二酰基甘油（DAG），也存在于细胞器中，作为IP3和PIP2合成复杂信号磷脂和肌醇磷酸的前体。肌醇必须被吸收到使用它的细胞中，因为神经元和星形胶质细胞都不能合成它。它也是一种渗透物，在对周围高渗透压的反应中被吸收，在低渗透压时被释放。肌醇转运蛋白有三种，分别是依赖ne的SMIT1和SMIT2，以及与h共同转运肌醇的HMIT。它们在星形细胞和神经元中的相对表达尚不清楚。肌醇在星形胶质细胞中的摄取动力学已经多次被确定，但总是假设只有一种成分，而对单个转运蛋白的动力学未知。本文证明直接从大脑中获得的星形胶质细胞表达SMIT1和HMIT，但很少表达SMIT2，并且这三种转运蛋白都在神经元中表达。培养的小鼠星形胶质细胞表现出高亲和力/低容量肌醇摄取（V-max: 60.0 +/- 3.0 pmol/min / mg蛋白；K-m: 16.7 +/- 2.6 μ M），由SMIT1介导，可能部分由SMIT2介导。在用HMIT-siRNA预处理的细胞中测定，并通过特异性抑制SMIT来证实。然而，在生理相关的肌醇浓度下，大多数摄取是由HMIT介导的低亲和力/高容量摄取（V-max: 358 +/- 60 pmol/min / mg蛋白质；K-m: 143 +/- 36 μ M），并通过smit介导的总摄取减去smit决定。在高肌醇浓度下，在pH升高的培养基中孵育会抑制肌醇的摄取，而在细胞内NH4Cl酸化过程中则会增加肌醇的摄取。这与HMIT单独的文献数据一致。在低浓度下，SMIT1/2活性变得重要，氨诱导的细胞内酸化减少了肌醇摄取，这与文献中报道的转运体的pH敏感性一致。(c) 2012 Elsevier Ltd.版权所有。
myo-Inositol is important for cell signaling both in cytoplasm and in intracellular organelles. It is required in the plasma membrane and cytoplasm for maintained synthesis of the second messengers, inositoltrisphosphate (IP3) and diacylglycerol (DAG) from phosphatidylinositol bisphosphate (PIP2), and in organelles as precursor for synthesis of complex signaling phospholipids and inositolphosphates from IP3 and PIP2. myo-Inositol must be taken up into the cell where its is used, because neither neurons nor astrocytes synthesize it. It is also an osmolyte, taken up in response to surrounding hyperosmolarity and released during hypo-osmolarity. There are three myo-inositol transporters, the Ne-dependent SMIT1 and SMIT2, and HMIT, which co-transports myo-inositol with H. Their relative expressions in astrocytes and neurons are unknown. Uptake kinetics for myo-inositol in astrocytes has repeatedly been determined, but always on the assumption of only one component, leaving kinetics for the individual transporters unknown. This paper demonstrates that astrocytes obtained directly from the brain express SMIT1 and HMIT, but little SMIT2, and that all three transporters are expressed in neurons. Cultured mouse astrocytes show a high-affinity/low-capacity myo-inositol uptake (V-max: 60.0 +/- 3.0 pmol/min per mg protein; K-m: 16.7 +/- 2.6 mu M), mediated by SMIT1 and perhaps partly by SMIT2. It was determined in cells pre-treated with HMIT-siRNA and confirmed by specific inhibition of SMIT. However at physiologically relevant myo-inositol concentrations most uptake is by a lower-affinity/higher-capacity uptake, mediated by HMIT (V-max: 358 +/- 60 pmol/min per mg protein; K-m: 143 +/- 36 mu M) and determined by subtraction of SMIT-mediated from total uptake. At high myo-inositol concentrations, its uptake is inhibited by incubation in medium with increased pH, and increased during intracellular acidification with NH4Cl. This is in agreement with literature data for HMIT alone. At low concentration, where SMIT1/2 activity gains importance, myo-inositol uptake is reduced by ammonia-induced intracellular acidification, consistent with the transporter's pH sensitivity reported in the literature. (c) 2012 Elsevier Ltd. All rights reserved.