Roles of Cdk5 in neurodevelopment and neurodegeneration

在过去的一年里，我们在对衰老和神经变性的理解上取得了两大进展。在前一年，我们已经表明，在我们的神经退行性疾病模型中，无菌炎症--一种在没有感染的情况下发生的炎症反应--是神经细胞死亡的主要原因。然而，在这个过程中，我们意识到，当我们在没有正常细菌微生物群的情况下饲养动物时，衰老过程的整个架构似乎发生了变化。在今年，我们对此进行了详细的研究，发现我们通常认为是正常衰老一部分的过程中，有70%实际上与衰老完全没有必要的联系。相反，它们是发生在动物身上的变化，因为它对生活在动物身上和动物体内的细菌属性的变化做出反应。这从根本上改变了我们对衰老的看法，因为我们长期以来认为对这个过程至关重要的许多过程后来被证明是免疫学的方面，而不是衰老。我们的实验还确定了30%的与年龄相关的过程，这些过程不依赖于动物的细菌数量；这些更有可能是衰老计划的内在因素。我们取得的另一个重大进展是令人惊讶的发现，亨廷顿病中突变的HTT基因和阿尔茨海默病中编码β-淀粉样蛋白的基因APP实际上是单个分子机器的两个部分。两者都编码Abl酪氨酸激酶的调节基因，该基因是慢性粒细胞白血病和急性淋巴细胞白血病的主要致病基因，也是神经连接发展和维持的核心。值得注意的是，HTT和APP之间存在拉锯关系，HTT抑制ABL，APP激活ABL。在它们之间，它们的作用是将Abl保持在对产生和维持神经结构至关重要的中等活动水平。我们现在知道HTT和APP突变体的发育缺陷实际上是由于Abl活性的改变；HD和AD的退变是否也部分是由于Abl的改变是一个关键的问题，有待进一步研究。

In the past year we have made two major advances in our understanding of aging and neurodegeneration. In the preceding year, we had shown that sterile inflammation - an inflammatory response that occurs in the absence of infection - was a major cause of neuronal cell death in our model of neurodegenerative disease. In the process, however, we realized that the whole architecture of the aging process seemed to be altered when we grew animals in the absence of their normal bacterial microbiome. In the current year we have examined this in detail, and discovered that 70% of the processes that we normally think of as being part of normal aging, actually have no necessary connection to aging at all. Rather, they are changes that occur in the animal as it responds to the changing properties of the bacteria that live on and in the animal. This fundamentally changes our view of aging, since many of the processes that we have long thought are central to the process turn out to be aspects of immunology, not aging. Our experiments also identify the 30% of age-related processes that are NOT dependent on the bacterial population of the animal; these are more likely to be intrinsic to the aging program. The other major advance we made was the surprising discovery that the HTT gene, which is mutated in Huntingtons Disease, and APP, the gene that encodes beta-amyloid in Alzheimers Disease, are actually two parts of a single molecular machine. Both encode regulators of the Abl tyrosine kinase, the causative gene in Chronic Myelogenous Leukemia and in a substantial fraction of acute Lymphocytic Leukemia that is also central to the development and maintenance of neural wiring. Remarkably, HTT and APP have a see-saw relationship where HTT suppresses Abl and APP activates it. Between them their role is to keep Abl at an intermediate level of activity that is essential to producing and maintaining neural structure. We now know that developmental defects in HTT and APP mutants are actually due to altered activity of Abl; whether degeneration in HD and AD are also due in part to altered Abl is a crucial question for further study.