The effects of targeted disruption of a gene encoding rate-limiting enzyme of the TCA Cycle on mice

为了探索糖尿病等代谢性疾病的根本解决方案，有必要重新评估三羧酸（tricarboxylic acid， TCA）循环这一最重要的高效代谢途径的意义。为了研究抑制循环的作用，在小鼠中破坏了循环限速酶之一柠檬酸合成酶（CS）的编码基因。纯合子（CS-/-）小鼠表现出早期胚胎致死性，而杂合子（CS+/-）小鼠在mRNA、蛋白和酶活性水平上均表现出CS基因的部分表达。野生型与CS+/-小鼠在体重、基础代谢率、血压、空腹血糖/胰岛素水平、血脂水平等方面均无显著差异，但CS+/-小鼠的呼吸商（呼吸交换比）显著低于野生型，血清乙酰乙酸水平显著高于野生型。对野生型和CS+/-小鼠进行1个月或2个月的高脂高糖饮食后，静脉葡萄糖负荷后的血浆反应明显变钝，CS+/-小鼠的葡萄糖反应与野生型小鼠没有任何差异。我们认为，该小鼠可能是研究能量代谢紊乱背后的胰岛素抵抗机制的有用模型。

In order to explore the fundamental solution over metabolic disorders like diabetes, it is necessary to re-evaluate the significance of tricarboxylic acid (TCA) cycle, the most important metabolic pathway with very high efficiency. To investigate the effects of inhibiting the cycle, the gene encoding citrate synthase (CS), one of rate-limiting enzymes of the cycle, was disrupted in mice. Homozygous (CS-/-) mice showed early embryonic lethality but heterozygous mice (CS+/-) showed partial expression of the CS gene in each of the mRNA, protein, and enzyme activity levels. Whereas there were no differences in weight, basal metabolic rate, blood pressure, fasting plasma glucose/insulin levels, serum lipid levels between wild-type and CS+/-mice, it is clarified that respiratory quotient (respiratory exchange ratio) was significantly lower and serum acetoacetate levels were significantly higher in CS+/-mice. High-fat high-sugar diet of one or two months for both wild-type and CS+/-mice resulted in marked blunted plasma response after intravenous glucose load without any differences in glucose responses in CS+/-mice compared with wild-type mice. It is thought that the mouse could be a useful model to investigate the mechanisms of insulin resistance underlying energy metabolism disorders.