The Wnt-independent role of TCF7l2 in CNS myelin formation and repair

少突胶质细胞是中枢神经系统中的髓鞘形成细胞。中枢神经系统髓鞘 形成/修复由两个密切相关的连续事件组成：从少突胶质细胞分化为OL 祖细胞和已经分化的OL的轴突(再)髓鞘形成。这两个事件的缺陷导致 中枢神经系统髓鞘形成异常，如脑室周围白质软化和髓鞘修复能力低下 比如多发性硬化症。我们的长期目标是研究调节中枢神经系统髓鞘的潜在机制 编队/修理。Wnt效应转录因子7-like 2(TCF7L2，又名)的表达。TCF4)在 多发性硬化症病变就是这样一种很有希望的机制。 TCF7L2在转录水平上介导Wnt/β-catenin信号在Wnt激活中的作用已被充分研究 细胞，如结直肠癌细胞。其他人和我们自己的实验室之前的研究表明 规范的Wnt/β-Catenin信号通路的遗传激活抑制OL分化(综述郭美美等， 因此，有人提出TCF7L2通过Wnt/β-连接蛋白抑制OL分化 发信号。然而，我们最近报道了Cre-loxP基因途径条件性干扰TCF7L2 在不干扰Wnt/β-Catenin信号通路的情况下抑制新生儿和出生后早期OL分化 (Hammond等人，2015年)。基于我们的基因数据，我们提出了另一种假设，即TCF7L2，作用于 通过非Wnt通路(目标2)是中枢神经系统髓鞘形成的多模式正向调节因子(目标1)，它 可被操纵以促进髓鞘损伤后的中枢神经系统髓鞘修复(目标3)。 在目标1中，我们将专门消融已经分化的OL中的TCF7L2，以确定其在 随后的轴突髓鞘形成和髓鞘脂类合成。这个目标的实验将揭示一个以前的 未知的TCF7L2在中枢神经系统髓鞘形成中独立于上游OL分化的新作用。在目标2中， 我们将使用体内和体外遗传学方法来检验TCF7L2‘S作为基因功能的假设 抑制因子在中枢神经系统髓鞘形成中起着重要作用。该项目将揭示TCF7L2与TCF7L2 以及抑制OL分化和髓鞘形成的少突胶质细胞自分泌途径。我们的范例- 不断变化的数据使得重新审视和评估TCF7L2的治疗潜力变得必要和重要 在中枢神经系统髓鞘修复过程中，髓鞘被认为是人类多发性硬化症的抑制因子。在AIM 3，我们将使用慢病毒载体介导的基因转移来测试强制TCF7L2的替代假设 在脱髓鞘动物模型中，表达促进OL分化和CNS髓鞘形成。预期中的 这一创新建议的总体影响是，它将从根本上推进我们对机械的理解 和TCF7L2的新作用，并将改变我们传统的抑制观点 TCF7L2促进中枢神经系统髓鞘修复。

Oligodendrocytes (OLs) are myelin-forming cells in the central nervous system (CNS). CNS myelin formation/repair consists of two closely-related sequential events: OL differentiation from oligodendrocyte progenitor cells and axonal (re)myelination by already differentiated OLs. Defects of these two events result in abnormalities of CNS myelin formation such as in periventricular leukomalacia and inability of myelin repair such as in multiple sclerosis. Our long term goal is to study the underlying mechanisms regulating CNS myelin formation/repair. The expression of the Wnt effector transcription factor 7-like 2 (TCF7l2, a.k.a. TCF4) in multiple sclerosis lesions is one such promising mechanism. A well-studied role of TCF7l2 is transcriptionally mediating Wnt/β-catenin signaling in Wnt activated cells such as colorectal cancer cells. Previous studies from others and our own laboratory have shown that genetic activation of canonical Wnt/β-catenin signaling pathway inhibits OL differentiation (review Guo et al., 2015).Therefore, it has been proposed that TCF7l2 inhibits OL differentiation acting through Wnt/β-catenin signaling. However, we recently reported that conditionally disrupting TCF7l2 by Cre-loxP genetic approach inhibits neonatal and early postnatal OL differentiation without perturbing Wnt/β-catenin signaling pathway (Hammond et al., 2015). Based on our genetic data, we propose an alternative hypothesis that TCF7l2, acting through non-Wnt pathways (Aim 2), is a multimodal positive regulator of CNS myelin formation (Aim 1) that can be manipulated to promote CNS myelin repair after myelin damage (Aim 3). In Aim 1, we will specifically ablate TCF7l2 in already differentiated OLs to determine its role in subsequent axonal myelination and myelin lipid synthesis. The experiments in this Aim will reveal a previously unrecognized novel role of TCF7l2 in CNS myelination independent of upstream OL differentiation. In Aim 2, we will use in vivo and in vitro genetic approaches to test the hypothesis that TCF7l2's function as a gene repressor plays an essential role in CNS myelin formation. This project will unveil a novel link between TCF7l2 and an oligodendroglial autocrine pathway that inhibits OL differentiation and myelination. Our paradigm- shifting data make it necessary and important to revisit and reevaluate the therapeutic potential of TCF7l2 during CNS myelin repair which has been proposed as an inhibitory factor in human multiple sclerosis. In Aim 3, we will use lentiviral vector-mediated gene transfer to test the alternative hypothesis that enforced TCF7l2 expression promotes OL differentiation and CNS myelination in demyelination animal models. The expected overall impact of this innovative proposal is that it will fundamentally advance our mechanistic understanding of CNS myelin formation and of novel role of TCF7l2, and will change our conventional view of inhibiting TCF7l2 to enhance CNS myelin repair.