Functional Studies of Variants of the Bipolar Risk Gene CACNA1C in Human Neurons

描述（由申请人提供）：这是一项新的R21申请，用于研究活的人类神经元中编码神经元钙通道的双相情感障碍易感基因的功能。钙离子通道在所有可兴奋细胞和许多不可兴奋细胞中表达，将细胞膜上的电信号转化为钙内流的化学电位。钙是第二信使，其细胞内浓度控制着许多细胞功能，包括肌肉收缩、神经递质释放、细胞存活和生长。钙离子通道是治疗高血压和神经性疼痛的重要药物靶点。CACNA1C钙离子通道基因的编码突变导致一种罕见的遗传性疾病，称为蒂莫西综合征，影响心脏、大脑和其他器官。双相情感障碍是一种慢性和严重的精神疾病，在美国人口中终生患病率为1-2%。双相情感障碍患者患有反复发作的躁狂和抑郁，目前的双相情感障碍治疗，如锂，对许多患者往往无效。在更好地了解致病风险的潜在分子过程之前，双相情感障碍的治疗选择不太可能取得实质性进展。双相情感障碍有明显的遗传风险，但很难确定任何特定基因与双相情感障碍的明确风险关联。三个独立队列的大规模全基因组关联研究和一项大型荟萃分析显示，双相情感障碍易感性与CACNA1C基因12号染色体上的基因组位点之间存在强烈而一致的关联。有趣的是，同样的基因组区域在去年被发现与精神分裂症和重度抑郁症的易感性相关，使其成为精神病学遗传学中最具可重复性和一致性的关联之一。这些令人兴奋的遗传发现为研究CACNA1C基因的基因组变异如何影响神经元钙通道活性提供了独特的机会。最近，小鼠和人成纤维细胞通过异位表达三种转录因子（ASCL1, MYT1L, BRN2）直接转化为功能性神经细胞。这一技术突破使人类特异性体外神经元模型成为可能。转录激活因子样效应核酸酶（TALEN）技术是一种分子工程工具，可识别基因组位点中的独特序列，在原生基因组中引入位点特异性变化，并有助于阐明等基因背景下的基因型-表型关系。我们将利用基因组编辑，结合基因表达、生化和电生理分析，揭示CACNA1C内含子单核苷酸多态性（SNP）变异在控制人类诱导神经元中l型钙通道活性中的功能作用。我们的工作有可能为精神疾病遗传风险位点的分子机制提供新的见解，并验证一种系统的方法来研究复杂大脑疾病中遗传变异的功能后果。

DESCRIPTION (provided by applicant): This is a new R21 application to study in live human neurons the function of a bipolar disorder susceptibility gene encoding a neuronal calcium channel. Calcium ion channels are expressed in all excitable and many non-excitable cells to transduce electric signals at the cell membrane into chemical potentials of calcium influx. Calcium is a second messenger whose intracellular concentration controls many cellular functions including muscle contraction, neurotransmitter release, cell survival and growth. Calcium ion channels are important drug targets for hypertension and neuropathic pain. Coding mutations in the CACNA1C calcium ion channel gene cause a rare hereditary disorder called Timothy Syndrome, affecting the heart, the brain, and other organs. Bipolar disorder is a chronic and severe mental illness with 1-2% lifetime prevalence in population of the United States. Individuals with bipolar disorder suffer from recurrent episodes of mania and depression, and current bipolar treatments, such as lithium, are often ineffective in many patients. Treatment options for bipolar disorder are unlikely to advance substantially until the underlying molecular processes in pathogenic risk are better understood. There is a clear heritable risk in bipolar disorder, but it has been difficult to establish clear risk associations in any particular gene wit bipolar disorder. Large-scale genome-wide association studies in three independent cohorts and a large meta-analysis have revealed a strong and consistent association between bipolar disorder susceptibility and a genomic locus on chromosome 12 in the CACNA1C gene. Interestingly, the same genomic region was found to be associated with schizophrenia and major depression susceptibility last year, making it one of the most replicable and consistent associations in psychiatric genetics. These exciting genetic discoveries present unique opportunities to study how genomic variations in the CACNA1C gene may influence neuronal calcium channel activity. Recently, mouse and human fibroblasts have been directly converted to functional neuronal cells through ectopic expression of three transcription factors (ASCL1, MYT1L, BRN2). This technological breakthrough makes human-specific in vitro neuronal models possible. Transcription activator-like effector nuclease (TALEN) technology is a molecular engineering tool that recognizes unique sequences in a genomic locus, introduces site-specific changes in the native genome, and helps elucidate genotype-phenotype relationships in an isogenic background. We will use genome editing, together with a combination of gene expression, biochemical, and electrophysiological analyses, to reveal the functional role of intronic single nucleotide polymorphism (SNP) variations of CACNA1C in controlling L-type calcium channel activity in human induced neurons. Our work has the potential to provide novel insights into the molecular mechanism of a genetic risk locus for psychiatric illness and to validate a systematic approach to study the functional consequences of genetic variations in complex brain disorders.