Impairment of methylglyoxal detoxification systems causes mitochondrial dysfunction and behavioral deficits

Methylglyoxal (MG) is a reactive alpha-dicarbonyl by-product of glycolysis. Several bio-defense systems to detoxify the highly toxic MG are equipped in our body, including an enzymatic system by glyoxalase (GLO) 1 and GLO2 and a scavenge system by vitamin B6 (VB6). We have reported that some population of patients with schizophrenia shows impairment of the MG detoxification systems. Although we have evidences showing a link between impairment of MG detoxification systems and development of schizophrenia, the molecular mechanism to connect them remains poorly understood. Here, we generated a novel mouse model for MG detoxification deficits by feeding Glo1 knockout mice with VB6-lacking diets (KO/VB6(-)), and evaluate effects of impaired MG detoxification systems on brain function. KO/VB6(-) mice showed the accumulation of MG in the prefrontal cortex (PFC), hippocampus, and striatum, and displayed schizophrenia-like behavioral deficits, such as social deficits, cognitive impairment, a sensorimotor deficit in the prepulse inhibition test. Furthermore, we found aberrant gene expression related to mitochondria function in the PFC of the KO/VB6(-) mice by RNA-seq and weighted gene correlation network analysis (WGCNA). Finally, we actually demonstrated respiratory deficits in mitochondria isolated from the PFC of KO/VB6(-) mice. These findings suggest that MG detoxification deficits might cause schizophrenia-like behavioral deficits via mitochondrial dysfunction in the PFC. Glo1 KO and wild-type mice were fed with a vitamin B6 (VB6)-lacking diet containing 5 micro g/100 g VB6 pellets from 8 to 12 weeks of age, while control mice in normal VB6 condition were fed with a normal diet, with 1.4 mg/100 g VB6 pellets. As the result, we have four groups: WT/VB6(+), WT/VB6(-), KO/VB6(+) and KO/VB6(-). Each group contains 5 mice. RNA-seq were constructed using RNAs extracted from prefrontal cortex, striatum and hippocampus of these mice.甲基乙二醛（Methylglyoxal, MG）是糖酵解过程中产生的活性α-二羰基副产物。人体拥有多种可对高毒性MG进行解毒的生物防御系统，包括由乙二醛酶（glyoxalase, GLO）1与GLO2组成的酶促系统，以及由维生素B6（vitamin B6, VB6）介导的清除系统。本团队此前已有研究报道，部分精神分裂症患者存在MG降解系统功能受损的情况。尽管已有证据表明MG降解系统受损与精神分裂症的发病存在关联，但二者之间的分子调控机制仍未被充分解析。 本研究构建了一种新型的MG降解功能缺陷小鼠模型：将GLO1基因敲除小鼠喂食不含VB6的饲料（KO/VB6(-)），以此评估MG降解系统受损对脑功能的影响。KO/VB6(-)小鼠的前额叶皮层（prefrontal cortex, PFC）、海马体与纹状体中出现MG蓄积，并表现出精神分裂症样的行为缺陷，包括社交障碍、认知损伤以及前脉冲抑制试验（prepulse inhibition test）中出现的感觉运动功能缺损。此外，通过RNA测序（RNA-seq）与加权基因共表达网络分析（weighted gene correlation network analysis, WGCNA），本团队发现KO/VB6(-)小鼠前额叶皮层内存在与线粒体功能相关的异常基因表达。最终，我们还在KO/VB6(-)小鼠前额叶皮层分离的线粒体中证实了呼吸功能缺陷。上述研究结果表明，MG降解功能缺陷可能通过前额叶皮层的线粒体功能异常，引发精神分裂症样行为缺陷。 本研究中，GLO1基因敲除小鼠与野生型小鼠均被分为正常VB6喂养组与VB6缺乏喂养组：VB6缺乏喂养组自8周龄至12周龄喂食VB6含量为5μg/100g的饲料颗粒，正常VB6喂养组则喂食VB6含量为1.4mg/100g的正常饲料颗粒。最终实验共分为四组：WT/VB6(+)、WT/VB6(-)、KO/VB6(+)与KO/VB6(-)，每组包含5只实验小鼠。本研究通过提取上述小鼠前额叶皮层、纹状体与海马体的总RNA，构建了RNA-seq文库。