Kruppel-like factor-6 signaling in myelin formation and repair

描述（由申请人提供）：在多发性硬化症（MS）中，轴突脱髓鞘产生传导阻滞和包括瘫痪和失明在内的症状，而髓鞘修复（髓鞘再生）带来功能恢复。MS研究的一个关键目标是增强髓鞘再生，髓鞘再生自发发生，但效率低下，特别是在MS的后期阶段。 疾病少突胶质细胞祖细胞（Oligodendrocyte progenitors，OLP）是髓鞘再生细胞的主要储存库。它们的分化通过内在的转录程序发生，该程序由外在途径促进，包括Stat 3，Smad 3，Akt-PI 3激酶，Erk 1/2和Tralpha 1/RXR信号传导。阐明这些途径如何促进分化可能会发现新的策略，以提高髓鞘再生。 最近，我们确定了Krppel样转录激活因子Klf 6作为中枢神经系统髓鞘形成的重要协调者。重要的是，我们的数据还表明Klf 6信号转导将外在途径与内在分化程序联系起来。值得注意的是，关键的外源性前髓鞘形成途径（Stat 3和Smad 3信号传导）在分化细胞中强烈诱导Klf 6，并且Klf 6过表达加速分化。相反，体外或体内Klf 6缺失 阻断分化的重要步骤，并导致髓鞘形成的完全失败。这种病理 部分模拟由Stat 3或Smad 3失活引起的缺陷。Klf 6的作用仅限于分化程序-增殖或成熟细胞中的失活产生病理学。我们的数据进一步表明，在成人中的重要作用，在正常的髓鞘营业额，关键是，在髓鞘再生。Klf 6在髓鞘再生损伤中被强烈诱导，与外源性前髓鞘形成途径的激活平行。 为了理解Klf 6的作用机制，我们现在使用了染色质占用的全基因组分析和转录谱分析。这项工作已经确定了一个新的和预期的Klf 6调控基因的程序。重要的是，它们的作用表明Klf 6对分化中的顺序步骤有贡献。此外，我们的数据进一步表明Klf 6结合还招募表观遗传共激活因子到靶位点，并且这些增强其转录靶点的反式激活。总之，我们的研究结果表明Klf 6可能与转录和表观遗传共激活因子形成复合物，以促进分化和髓鞘形成。 在这个建议中，我们将测试中心的假设，Klf 6连接的外在监管机构与内在的分化程序是必不可少的中枢神经系统髓鞘再生。 我们提出三个具体目标。在目标1中，我们将测试外源性前髓鞘形成因子通过Klf 6信号传导促进分化的程度。在目标2中，我们将定义Klf 6控制分化的作用机制。在目标3中，我们将测试 Klf 6在成人白色物质、正常髓鞘更新和关键的髓鞘再生中的信号传导。 这项工作将定义髓鞘形成所需的新机制，这可能对修复至关重要。阐明外在途径如何促进成熟可能会发现新的策略，以提高髓鞘再生。

DESCRIPTION (provided by applicant): In multiple sclerosis (MS), demyelination of axons produces conduction block and symptoms including paralysis and blindness, while myelin repair (remyelination) brings functional recovery. A key goal in MS research is to enhance remyelination, which occurs spontaneously but is inefficient, especially in the later stages of the disease. Oligodendrocyte progenitors (OLP) are the major reservoir of remyelinating cells. Their differentiation occurs via an intrinsic transcriptional program, which is promoted by extrinsic pathways, including Stat3, Smad3, Akt-PI3kinase, Erk1/2 and Tralpha1/RXR signaling. Elucidating how these pathways promote differentiation may identify new strategies to enhance remyelination. Recently, we identified the Kr�ppel-like transcriptional activator Klf6 as an essential coordinator of CNS myelination. Importantly, our data also indicate that Klf6 signaling links extrinsic pathways to the intrinsic differentiation program. Notably, key extrinsic pro-myelinating pathways (Stat3 and Smad3 signaling) strongly induce Klf6 in differentiating cells, and Klf6 over-expression accelerates differentiation. Conversely, Klf6 deletion in vitro or in vivo blocks vital steps in differentiation, and leads to complete failure of myelination. This pathology partly mimics deficits resulting from Stat3 or Smad3 inactivation. The effects of Klf6 are restricted to the differentiation program - inactivation in proliferating or mature cells produces o pathology. Our data further suggest important roles in adults, in normal myelin turnover and, critically, in remyelination. Klf6 is strongly induced in remyelinating lesions, paralleling activaion of extrinsic pro-myelinating pathways. To understand Klf6 mechanism of action, we have now used genome-wide analysis of chromatin occupancy, and transcriptional profiling. This work has identified a program of both novel and anticipated Klf6- regulated genes. Importantly, their roles propose Klf6 contributions to sequential steps in differentiation. Moreover, our data further indicate that Klf6 binding also recruits epigenetic coactivators to target loci, and that these enhance transactivation of its transcriptional targets. Together, our findings suggest that Klf6 may form complexes with transcriptional and epigenetic coactivators, to promote differentiation and myelin formation. In this proposal, we will test the central hypothesis that Klf6 linkage of extrinsic regulators with the intrinsic differentiation program is essential for CNS remyelination. We propose three Specific Aims. In Aim 1, we will test the extent to which extrinsic pro-myelinating factors promote differentiation via Klf6 signaling. In Aim 2, we will define the mechanism of action by which Klf6 controls differentiation. In Aim 3, we will then test the role of Klf6 signaling in adult white matter, in normal myelin turnover and, critically, in remyelination. This work will define a new mechanism required for myelin formation, and which may be vital for repair. Elucidating how extrinsic pathways promote maturation may identify new strategies to enhance remyelination.