Synaptic Pruning and Complement Gene in Schizophrenia: Imaging & Cellular Studies

摘要：多种证据表明，突触修剪的增加具有病理生理学意义。 用于精神分裂症（SZ）。新的证据表明遗传因素与突触增加有关 在 SZ 进行修剪。最近的全基因组关联研究令人信服地证明补体 (C4) 基因 重复次数与 SZ 风险显着相关，特别是 C4A 长形式 (C4AL)。 C4蛋白表达 精神分裂症患者的大脑与 C4AL 重复次数成比例地增加。一只老鼠 在啮齿动物模型中，C4 类似物与突触修剪的增加有关。我们建议开发两个 关于遗传因素与突触修剪之间关系的独立证据。我们的体内方法 将纵向检查使用超高场结构 MRI 获得的突触修剪措施，并 基线、6 个月和 1 年时 7 特斯拉的磷磁共振波谱 (31P MRS) 患有早发性精神分裂症 (EOS) 和健康对照 (HC) 的青少年及其与认知表现的关系 （目标 1），C4 重复和通过多基因风险评分 (PGRS) 测量的全局遗传责任（目标 2）。的 对青少年 EOS 和 HC 进行纵向检查的基本原理得到了更突出的突触的支持 青春期修剪。 7 特斯拉的超高场结构 MRI 和 31P MRS 可提供卓越的分辨率 以及代谢物定量的更高灵敏度。 31P MRS 测量膜磷脂的代谢物 （MPL）遍布整个大脑。 MPL前体指数降低会减少神经纤维形成，而 MPL 分解产物的增加反映了神经纤维收缩。由于突触嵌入神经纤维中 膜扩张的主要部分是由突触、树突分支和树突棘贡献的， 与相比，MPL 代谢水平可提供更特异和更灵敏的神经纤维测量 灰质指标。衡量神经纤维收缩的另一个指标是通过皮质厚度 测量。 PGRS 是对全基因组变异带来的整体遗传风险的更准确测量。 我们的体外方法将检查树突棘密度和形态与 C4 蛋白表达的关系 - 在分化人类过程中自然地和诱导 C4 蛋白的过度表达和表达不足 诱导多能干细胞 (hiPSC) 衍生的神经元类器官（目标 3）。类器官是 3 维的 神经元培养物显示出更精细的微观解剖特征，能够重现某些特定的特征 与二维文化相比的大脑功能。除了提供独立证据外 突触密度与C4蛋白表达相关，hiPSC模型为 31P MRS 和皮质厚度结果可能代表突触修剪。只提出一条证据 关于遗传因素与神经纤维修剪之间的关系留下了悬而未决的问题。检查一个重要的 与遗传风险相关的病理生理过程，即突触修剪，可能有助于识别关键的 最终开发 SZ 新疗法的途径和具体分子靶点。

Abstract: Multiple lines of evidence suggest that increased synaptic pruning is pathophysiologically significant for schizophrenia (SZ). Emerging evidence suggests that genetic factors are associated with increased synaptic pruning in SZ. Recent genome-wide association studies convincingly demonstrated that Complement (C4) gene repeats were significantly associated with SZ risk, specifically C4A long form (C4AL). C4 protein expression in the brains of schizophrenia patients was increased proportionate to the number of C4AL repeats. A mouse analog of C4 was associated with increased synaptic pruning in a rodent model. We propose to develop two independent lines of evidence on the association of genetic factors with synaptic pruning. Our in vivo approach will longitudinally examine measures of synaptic pruning obtained using ultra-high field structural MRI and phosphorus magnetic resonance spectroscopy (31P MRS) at 7 Tesla at baseline, 6-months and 1-year among adolescents with early onset SZ (EOS) and healthy controls (HC), and its association with cognitive performance (Aim 1), C4 repeats and global genetic liability measured through polygenic risk score (PGRS) (Aim 2). The rationale for longitudinal examination of adolescent EOS and HC is supported by more prominent synaptic pruning during adolescence. Ultra-high field structural MRI and 31P MRS at 7 Tesla provides superior resolution and greater sensitivity for metabolite quantification. 31P MRS measures metabolites of membrane phospholipids (MPL) across the entire brain. Decreased MPL precursors index decreased neuropil formation whereas increased MPL breakdown products reflect neuropil contraction. Since synapses are embedded in the neuropil and major part of membrane expansion is contributed by synapses, dendritic branches and dendritic spines, MPL metabolite levels are proposed to provide more specific and sensitive measure of neuropil compared to gray matter metrics. An additional measure to index neuropil contraction is through cortical thickness measurements. PGRS is a more accurate measure of overall genetic risk conferred by genomewide variations. Our in vitro approach will examine dendritic spine density and morphology in relation to expression of C4 proteins - both naturalistically and with induction of over- and under- expression of C4 proteins in differentiating human induced pluripotent stem cell (hiPSC)-derived neuronal organoids (Aim 3). Organoids are 3-dimensional neuronal cultures that show more refined microanatomic feature capable of recapitulating some specific functions of the brain compared to 2-dimensional cultures. In addition to providing independent evidence of synaptic density related to C4 protein expression, hiPSC model provides some corroborative evidence for the 31P MRS and cortical thickness findings that may represent synaptic pruning. Proposing only one line of evidence leaves open questions about the association of genetic factors with neuropil pruning. Examining an important pathophysiological process, namely synaptic pruning, in relation to genetic risk may help identify critical pathways and specific molecular targets for eventual development of novel treatments for SZ.