DEVELOPMENT AND ANALYSIS OF A MODEL MOUSE FOR NONKETOTIC HYPERGLYCINEMIA

非酮症高血糖(NKH)是一种遗传性代谢性疾病，其特征是体液中甘氨酸水平显著升高和严重的神经异常。NKH是由线粒体甘氨酸裂解系统(GCS)缺陷引起的。GCS由四种蛋白质组成，称为P-、T-、H-和L蛋白质。在中枢神经系统中，GCS在前脑和小脑的总活性较高，而在脊髓和脑干中几乎检测不到GCS。与此一致，甘氨酸在脊髓和大脑中含量较高，而在大脑皮层和小脑中含量较低。为了阐明NKH的分子发病机制，我们利用转基因技术检测了小鼠脑内的GCS。我们将小鼠P-蛋白基因定位在19C染色体上，并分离到一个基因内CA重复标记。我们获得了一只在CAG启动子控制下过量表达人P蛋白基因的转基因(TG)小鼠。转基因小鼠在小鼠脑内不同区域表达大量的人P蛋白mRNA和总的GCS活性。与野生型小鼠相比，转基因小鼠脊髓甘氨酸含量明显降低。这些结果表明，GCS在中枢各区域的总活性与P-蛋白的表达水平密切相关，GCS在调节中枢各区域的甘氨酸含量中起着关键作用。

Nonketotic hyperglycinemia (NKH) is an inherited metabolic disease, characterized by marked elevation of the glycine level in body fluid and severe neurological abnormalities. NKH is caused by defect in the mitochondrial glycine cleavage system (GCS). The GCS consists of the four protein components referred to as P-, T-, H-, and L-proteins. In the central nervus system (CNS) the overall activity of the GCS was high in forebrain and cerebellum, whereas it was hardly detected in spinal cord and brain stem. In line with this observation the glycine content was high in spinal cord and cerebrum, but low in cerebral cortex and cerebellum. To elucidate the molecular pathogenesis of NKH we examines the GCS in mouse brain by using a transgenic technique. We mapped mouse P-protein gene was on chromosome 19C and isolated a intragenic CA repeat marker. We generated a transgenic (Tg) mouse overxpressing the human P-protein cDNA which was under control of potent CAG promoter. The Tg mouse expressed a large amount of human P-protein mRNA and the overall GCS activities in various regions of mouse brain. The glycine content in the spinal cord of the Tg mouse was markedly reduced compared with wild type mouse. These data suggested that the overall activities of the GCS in each region of CNS was closely correlated with the expression level of the P-protein, and the GCS plays a pivotal role in regulation of the glycine content in various regions of CNS.