Neuropathology in tauopathies stem from depolarization-induced alterations in the planar distribution of phosphoinositides

Tau缠结是阿尔茨海默病相关痴呆（ADRD）的常见特征，并诱导一系列的神经元凋亡。 神经元的病理扰动，包括过度兴奋和Ca 2+稳态失调。在本申请中， 我们使用果蝇来证明由Tau或六核苷酸重复序列引起的进行性神经毒性， C9 ORF 72的扩增涉及第二信使三磷酸肌醇（IP 3）的产生增加， IP 3受体（IP 3R）介导的ER Ca 2+释放的激活。因此，表达导致的过早死亡 的ADRD引起的转基因几乎完全抑制IP 3生产或敲低IP 3Rs的衰减。 虽然IP 3R以前与神经变性有关，但我们发现了一种新的机制， 潜在的通道过度激活。我们发现引起ADRD的转基因的表达导致神经元的丧失， 膜电位，并且由此产生的去极化是增加IP 3R活性的原因。我们的初步研究结果 与去极化增加负责IP 3的酶的缔合的概念一致 磷脂酶Cb（PLCb）及其磷酸肌醇底物PIP 2。更强的PLCb-PIP 2相互作用 在去极化的细胞中，在PLCb偶联受体的刺激下导致IP 3产生升高。目标1： 将在表达突变tau的果蝇和小鼠神经元中检验上述假设。我们还问ADRD如何 神经元失去维持膜电位的能力。根据电生理记录和分析 根据RNA-seq数据集，我们假设慢性去极化源于神经元的丰度减少， 建立正常静息膜电位所需的K+渗漏通道。目标2： 确定去极化如何增强PLCb-IP 3R信号传导。我们的研究结果表明， PLCb-PIP 2结合和水解的依赖性调节依赖于脂质的酰基侧链。采取 结合我们的发现，去极化促进IP 3的生产，我们假设PLCb的活动， 依赖于PIP 2侧链身份，并且由于PIP 2的优先水解， 具有更长和更不饱和侧链的物种。成功完成拟议的研究将 证明ADRD神经元中的IP 3R过度激活对因果突变是不可知的-这一见解 说明了我们的发现具有广泛的适用性我们还希望制定可以利用的战略， 选择性改变质膜上PIP 2种类的数量，以纠正病理性Ca 2 + 发生在ADRD中的动态平衡障碍。

Tau tangles are common features of Alzheimer’s disease related dementias (ADRDs) and induce a range of pathological perturbations in neurons including hyperexcitability and Ca2+ dyshomeostasis. In this application, we use Drosophila to demonstrate that progressive neurotoxicity elicited by Tau or hexanucleotide repeat expansion of C9ORF72 involves elevated production of the second messenger, inositol trisphosphate (IP3), and activation of IP3 receptor (IP3R)-mediated ER Ca2+ release. Thus, premature lethality stemming from expression of ADRD-causing transgenes was almost fully suppressed by attenuation of IP3 production or knockdown IP3Rs. Although IP3Rs have been previously implicated in neurodegeneration, we have uncovered a novel mechanism underlying channel hyperactivation. We show expression of ADRD-causing transgenes leads to loss of neuronal membrane potential, and that the resulting depolarization is what increases IP3R activity. Our preliminary findings are consistent with the notion that depolarization increases association of an enzyme responsible for IP3 production, phospholipase Cb (PLCb), with its phosphoinositide substrate, PIP2. Greater PLCb–PIP2 interactions in depolarized cells lead to elevated IP3 production upon stimulation of PLCb-coupled receptors. In Aim 1, we will test the aforementioned hypothesis in fly and mouse neurons expressing mutant tau. We also ask how ADRD neurons lose their ability to maintain membrane potential. Based on electrophysiological recordings and analyses of RNA-seq datasets, we hypothesize that chronic depolarization stems from diminished abundance of neuronal K+ leak channels that are needed for establishing normal resting membrane potential. In Aim 2, we seek to determine how depolarization potentiates PLCb–IP3R signaling. Our findings suggest that membrane potential dependent regulation of PLCb—PIP2 association and hydrolysis depend on the lipids’ acyl side chains. Taken in conjunction with our findings that depolarization promotes IP3 production, we hypothesize that PLCb activity depends on PIP2 side chain identity, and increases in depolarized cells due to the preferential hydrolysis of species with longer and more unsaturated side chains. Successful completion of the proposed studies would demonstrate that IP3R hyperactivation in ADRD neurons is agnostic to the causal mutations — an insight that speaks to the wide applicability of our findings. We also hope to develop strategies that can be leveraged to selectively change the population of PIP2 species at the plasma membrane in order to correct pathological Ca2+ dyshomeostasis that occurs in ADRD.