Developmental underpinnings of substantia nigra vulnerability

摘要：DA神经元变性，导致DA信号不足，是衰弱运动的基础 帕金森病(PD)的症状。在DA神经元中，位于黑质腹侧层的神经元 致密部(SNC)与位于SNC背层或腹侧的致密部相比尤其脆弱 被盖区(VTA)。选择性DA神经元脆弱性的机制解释仍然是一个重要的 由于对DA神经元之间的内在差异缺乏了解，这一目标在一定程度上受到了阻碍。 我们假设，即使在像SNC这样的单个神经解剖学簇中，也存在DA 具有不同发展历史和可能影响其脆弱性的内在特性的亚型。 我们实验室基于单细胞表达谱的DA神经元分类揭示了关键基因的存在 由Sox6和Aldh1a1定义的SNC群体-该亚型位于SNC的腹层，并且 在帕金森氏病的毒素模型中更容易受到攻击。我们的初步数据表明，这个种群存在于 人类SNC，并且在死后PD样本中也选择性地易受攻击。审问…的基础 在SNC中选择性脆弱性的深入，我们接下来开发了一套交叉式遗传策略，其中 在Sox6表达式定义的SNC中明显地定义了一条断层线，Sox6+细胞位于腹侧 形成背层的SOX6-细胞。在这些研究的基础上，几个关键问题仍然没有得到回答。 背侧和腹侧SNC亚型在发育上是不同的吗？这些神经元有不同的解剖结构吗？ 功能和DA版本特征？是这些神经元分支的大小，这一属性与 脆弱，不同？钙离子通量和线粒体生物能特性有区别吗？ 为了回答这些问题，在目标1中，我们将确定SNC神经元亚型的起源。我们将使用 交叉、减法和可诱导的遗传方法，以及一种新的锚定命运的祖先 标测方法(PRISM)检验背侧和腹侧DA层神经元是 在发展上由Sox6区别对待。然后我们将测试Sox6+内侧地板与Sox6-横向地板的潜力 当移植到帕金森病模型中时，板祖细胞可以产生SNC神经元。在目标2中，我们将研究 遗传定义的SNC神经元的树状化，因为这一特征已与其脆弱性联系在一起。vbl.使用 一种新的稀疏标记工具，我们将绘制遗传定义的SNC DA神经元亚型的投影，以及 确定它们乔木的大小，并探索广泛分枝的分子决定因素。我们会 也研究轴突和树突的DA释放，以确定背侧和腹侧层神经元是否 可通过这些标准区分的，也与脆弱性有关。在目标3中，我们将测试SNC的假设 DA神经元亚型具有独特的生理特性，这些差异转化为 躯体树突间和轴突间线粒体氧化应激的差异。总体而言，我们的研究 根据血统重新定义SNC将为选择性漏洞提供重要的见解。

Abstract: DA neuron degeneration, resulting in deficient DA signaling, underpins the debilitating motor symptoms of Parkinson’s disease (PD). Among DA neurons, those located in ventral tier of the substantia nigra pars compacta (SNc), are particularly vulnerable, compared to those in the dorsal tier of the SNc or ventral tegmental area (VTA). A mechanistic explanation of selective DA neuron vulnerability remains an important goal, that has been hampered in part by a lack of understanding of the intrinsic differences between DA neurons. We hypothesize that even within a single neuroanatomical cluster like the SNc, there exist DA subtypes with distinct developmental histories and intrinsic properties that may influence their vulnerability. Single cell expression profiling based DA neuron classification from our lab revealed the presence of a key SNc population defined by Sox6 and Aldh1a1 - this subtype was located in the ventral tier of the SNc, and was preferentially vulnerable in a toxin model of PD. Our preliminary data indicate that this population exists in human SNc, and is also selectively vulnerable in post-mortem PD samples. To interrogate the basis for selectively vulnerability in the SNc in depth, we next developed a set of intersectional genetic strategies, which strikingly defined a fault-line in the SNc defined by Sox6 expression, with Sox6+ cells being located ventrally and Sox6- cells forming the dorsal tier. Building on these studies, several key questions remain unanswered. Are dorsal and ventral SNc subtypes developmentally distinct? Do these neurons have different anatomical features and DA release characteristics? Is the size of arborizations of these neurons, a property linked to vulnerability, different? Are calcium fluxes and mitochondrial bioenergetic properties distinct? To answer these questions, in Aim 1, we will determine the origin of SNc neuron subtypes. We will use intersectional, subtractive, and inducible genetic approaches, as well as a novel progenitor anchored fate mapping approach (PRISM) to test the hypothesis that the dorsal and ventral tier DA neurons are developmentally distinguished by Sox6. We will then test the potential of Sox6+ medial vs Sox6- lateral floor plate progenitors to give rise to SNc neurons when transplanted into a PD model. In Aim 2, we will examine the arborization of genetically defined SNc neurons, since this feature has been linked to their vulnerability. Using a new sparse labeling tool, we will plot the projections of genetically defined SNc DA neuron subtypes, and determine the size of their arbors, and explore the molecular determinants of extensive arborization. We will also study DA release from axons and dendrites to determine if dorsal and ventral tier neurons are distinguishable by these criteria, also linked to vulnerability. In Aim 3, we will test the hypothesis that the SNc DA neuron subtypes have distinctive physiological properties and that these differences translate into differences in mitochondrial oxidant stress in somatodendritic and axonal compartments. Overall, our studies redefining the SNc based on lineage will provide important insights into selective vulnerability.