The role of TxnRd2 in cortical circuit formation

描述(申请人提供)：线粒体氧化还原失衡和抗氧化剂防御能力下降-细胞维持细胞呼吸产生的自由基和酶自由基解毒之间的动态平衡的能力下降-可能伴随着神经精神障碍患者皮质回路组织和功能的改变。然而，目前尚不清楚皮层回路发育过程中抗氧化剂防御和活性氧物种积累(ROS)的减少是否会导致异常回路的形成及其后果。22q11缺失综合征(22q11DS)患者比其他人群更容易发生精神障碍，因此22q11DS被建议作为研究神经精神障碍神经发育起源的模型。位于22q11DS常见缺失区域的基因中，约有四分之一编码定位于线粒体的蛋白质。我建议在22q11DS小鼠模型中描述由于线粒体功能改变而发育的皮质神经元发育能力的变化，并确定这些变化如何影响电路形成。在22q11线粒体基因中，硫氧还蛋白还原酶(TxnRd2)在大脑皮层环路分化过程中表达最高，编码线粒体主要的过氧化氢清除剂。因此，我将研究TxnRd2的清除活性中断如何影响线粒体的抗氧化防御和改变皮质神经元的发育。我将验证一个假设，即由于TxnRd2剂量的减少，在神经元发育的后期阶段线粒体抗氧化防御能力减弱，扰乱了皮质神经元建立最佳连接的能力。为了验证这一假设，将使用可诱导的Cre-重组酶系统(Cux2GFP-Cre)在发育中的皮质投射神经元中产生一系列TxnRd2突变的等位基因。将分析神经元生长、分化和细胞器分布的完整性，以评估皮质神经元参与正常电路发育的能力的变化。ROS代谢将在TxnRd2耗尽的神经元中进一步操纵，将抗氧化防御与单个神经元建立电路的能力联系起来。我的研究将确定由于抗氧化剂防御减弱而导致的线粒体ROS积累对神经元完整性的影响，并将确定锥体神经元分化改变在22q11DS回路形成中的作用。具有基因控制的酶类抗氧化防御的同质神经元群体允许比较具有相同代谢需求的细胞中氧化还原平衡的调节，并分析改变的神经元能力以实现最佳皮质回路发育。我的数据将确立抗氧化防御在单个神经元建立电路的能力中的作用，并将为深入了解氧化还原失衡在广泛的行为障碍中异常电路连接中的作用提供依据。

DESCRIPTION (provided by applicant): Mitochondrial redox imbalance and decreased antioxidant defense-a decline in a cell's ability to maintain homeostasis between free radicals generated from cellular respiration and enzymatic free radical detoxification-may accompany altered cortical circuit organization and function in patients with neuropsychiatric disorders. However, it is unknown if decreased antioxidant defense and reactive oxygen species accumulation (ROS) during development of cortical circuits contributes to aberrant circuit formation and its consequences. Patients with 22q11 deletion syndrome (22q11DS) are more susceptible to psychiatric disorders than the rest of the population; therefore, 22q11DS has been suggested as a model for studying the neurodevelopmental origins of neuropsychiatric disorders. About one quarter of the genes located in the commonly deleted region in the 22q11DS encode proteins that localize to mitochondria. I propose to characterize changes in the developmental capacity of cortical neurons that develop due to altered mitochondrial function in mouse models of 22q11DS and determine how these changes could compromise circuit formation. Among 22q11 mitochondrial genes, thioredoxin reductase (TxnRd2), maximally expressed during cortical circuit differentiation, encodes a primary mitochondrial H2O2 scavenger. Thus, I will investigate how disrupted scavenging activity of TxnRd2 impacts mitochondrial antioxidant defense and alters cortical neuron development. I will test the hypothesis that diminished mitochondrial antioxidant defense during late stages of neuronal development, due to diminished dosage of TxnRd2, disrupts the capacity of cortical neurons to establish optimal connections. To test this hypothesis, an allelic series of TxnRd2 mutations will be generated specifically in developing cortical projection neurons, using an inducible Cre-recombinase system (Cux2GFP-Cre). Integrity of neuronal growth, differentiation and organelle distribution will be analyzed to evaluate changes in the capacity of cortical neurons to engage in normal circuit development. ROS metabolism will be further manipulated in TxnRd2-depleted neurons to link antioxidant defense to the capacity of individual neurons to build circuits. My studies will define the effects of mitochondrial accumulation of ROS due to diminished antioxidant defense on neuronal integrity, and will establish the role of altered pyramidal neuron differentiation in the formation of circuits in 22q11DS. A homogenous population of neurons with genetically controlled enzymatic antioxidant defense permit comparison of regulation of redox balance in cells with equal metabolic demand, and analysis of altered neuronal capacity for optimal cortical circuit development. My data will establish a role for antioxidant defense in the capacity of individual neurons to build circuits and will provide insight into the role of redox imbalance in aberrant circuit connectivity in a wide range of behavioral disorders.