Inositol-metabolizing enzyme gene-manipulated mice towards molecular dissection of pathophysiology of mental disorders.

在这项研究中，我们成功地培育了携带操纵基因的IMPase（肌醇单磷酸酶）小鼠：Impa1-Tg、Impa2-Tg、Impa1-ENU和Impa2-KO小鼠。其中，脑特异性IMPA2过表达转基因小鼠在升高加迷宫（EPM）和明暗箱（LD）试验中表现出中度焦虑表型。我们的分析表明，在Impal基因编码区不同位置引入诱变原ENU（乙基-亚硝基-尿素）错义突变的三个Impa1-ENU系中，至少有一个完全丧失了Impal蛋白所赋予的酶活性。我们的研究还表明，IMPA2的启动子单倍型可能通过增强转录而增加日本人群双相情感障碍的风险。结合IMPA2 - tg小鼠的表型，这些数据强烈提示IMPA2在情绪障碍，特别是双相情感障碍的发病机制中的作用。此外，我们首次在体外证明了IMPA2蛋白具有IMPase活性。IMPA1和IMPA2表现出明显不同的组织分布，对锂的敏感性也不同。为了进一步了解IMPA2基因产物，我们首先揭示了该蛋白的晶体结构。虽然IMPA2蛋白的整体结构与IMPA1相似，具有锂抑制的强IMPase活性，但IMPA2具有比IMPA1更宽的开腔。这些观察结果表明，IMPA2在细胞的生化过程中具有特定的功能，可能具有特定的体内底物，这与IMPA1不同。

In this study, we successfully developed mice with manipulated genes for IMPase (inositol monophosphatase) : Impa1-Tg, Impa2-Tg, Impa1-ENU and Impa2-KO mice. Among them, transgenic mice with brain-specific IMPA2 overexpression exhibited moderate anxiety phenotype when evaluated in elevated plus maze (EPM) and light and dark (LD) box tests. Our analysis showed that at least one of three Impa1-ENU lines, where a missense mutation is introduced by a mutagen ENU (ethyl-nitroso-urea) at different position in the coding region of Impal gene, completely losses the enzymatic activity given by the Impal protein.Our study also showed that a promoter haplotype of IMPA2 confers a possible risk for bipolar disorder in Japanese population possibly by enhancing transcription. Taken together with phenotype of Impa2-Tg mice, these data strongly suggest the function of IMPA2 in the pathogenesis of mood disorders, in particular, bipolar disorder.Moreover, we first proved that the IMPA2 protein exhibits IMPase activity in vitro. IMPA1 and IMPA2 show clearly different tissue distributions, and have different sensitivities to lithium. To obtain further insight for the IMPA2 gene product, we first revealed the crystal structure of this protein. While the overall structure of the IMPA2 protein is similar to that of IMPA1, which exhibits lithium-inhibitable strong IMPase activity, IMPA2 possesses more widely opened cavity than that of IMPA1. These observations imply a specific function of IMPA2 in the biochemical process(es) in the cell, possibly having specific in vivo substrate(s), which is different from that for IMPA1.