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，并导致一系列 神经元的病理扰动，包括过度兴奋和钙离子动态平衡失调。在此应用程序中， 我们用果蝇来证明Tau或六核苷酸重复引起的进行性神经毒性 C9ORF72的扩展涉及第二信使三磷酸肌醇(IP3)的产生增加，以及 激活IP3受体(IP3R)介导的内质网钙释放。因此，由表情引起的过早死亡 通过抑制IP3的产生或敲除IP3Rs，几乎完全抑制了导致ADRD的转基因。 尽管IP3Rs以前被认为与神经退行性变有关，但我们已经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的转基因的表达会导致神经元的丧失 膜电位，以及由此产生的去极化是增加IP3R活性的原因。我们的初步调查结果 与去极化增加负责IP3的酶的关联的概念是一致的 生产磷脂酶CB(PLCB)及其磷脂酰肌醇底物PIP2。更大的PLCB-PIP2相互作用 在去极化的细胞中，在PLCB偶联受体的刺激下，IP3的产生增加。在目标1中，我们 将在苍蝇和表达突变tau的小鼠神经元中检验上述假设。我们还询问ADRD如何 神经元失去了维持膜电位的能力。基于电生理记录和分析 在rna-seq数据集中，我们假设慢性去极化源于神经元丰度的减少。 K+泄漏通道是建立正常静息膜电位所必需的。在目标2中，我们寻求 确定去极化如何增强PLCB-IP3R信号。我们的发现表明，膜电位 PLCB-PIP2结合和水解的依赖调节依赖于脂类的酰基侧链。被骗了 结合我们关于去极化促进IP3产生的发现，我们假设PLCB的活性 依赖于PIP2侧链的同一性，并由于优先水解PIP2而在去极化细胞中增加 具有更长和更多不饱和侧链的物种。成功完成拟议的研究将 证明ADRD神经元中IP3R的过度激活与原因突变无关-这一见解 说明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 选择性地改变质膜上PIP2物种的数量以纠正病理性钙离子 在ADRD中发生的代谢紊乱。

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.