New pathways driving sodium dysregulation under acute metabolic stress

脑细胞内Na+的稳态严格依赖于完整的能量代谢。因此，细胞内Na+浓度的增加是能量缺乏的直接和主要后果。尽管能量供应受限对神经元和星形胶质细胞Na+浓度的影响、Na+超载的细胞机制、其病理意义以及星形胶质细胞在此过程中的具体作用，人们对它的了解还只有一部分。在本项目中，我们在小鼠大脑的谷氨酸能突触的原位、活体和人类细胞中解决了这些问题。为此，我们将使用基于荧光的Na+动态成像结合电生理学来确定急性代谢应激下神经元和星形胶质细胞中Na+的变化。我们的目的是识别不同的途径导致Na+调节异常，分析它们的相互作用，并研究它们在限制能量供应时突触功能障碍和细胞损伤的发病机制中的相关性。根据第一个资助期的结果，我们将重点研究TRPV4通道作为新发现的钠离子负荷途径(目标1)。此外，我们将补充我们在Na+依赖的酸碱转运体的相关性方面的工作，并旨在建立以细胞外酸化为导向的向缺血区的靶向药物输送(目标2)。最后，我们将研究能量耗竭对脑有机体和来源于人IPSCs的有机体切片培养的影响(目标3)。因此，我们的项目将提供有关早期Na+调节失调的机制以及代谢失败时触发突触功能障碍的第一步和事件的高度相关信息。

Intracellular Na+ homeostasis in the brain is strictly dependent on an intact energy metabolism. An increase in the intracellular Na+ concentration is thus an immediate and prime consequence of energy deprivation. Notwithstanding its pivotal role, the consequences of restricted energy supply on the Na+ concentration of neurons and astrocytes, the cellular mechanisms of Na+ overloading, its pathological relevance, as well as the specific role of astrocytes herein, are only partly understood. In the present project, we address these questions at glutamatergic synapses of the mouse brain in situ and in vivo and in human cells. To this end, we will employ fluorescence-based dynamic imaging of Na+ combined with electrophysiology to determine changes in Na+ in neurons and astrocytes under acute metabolic stress. Our aim is to identify the different pathways driving Na+ dysregulation, to analyse their interplay and to study their relevance in the pathogenesis of synaptic malfunction and cellular damage during restricted energy supply. Based on results obtained in the first funding period, we will focus on TRPV4 channels as newly identified pathways for Na+ loading (objective 1). Moreover, we will complement our work on the relevance of Na+-dependent acid-base transporters and aim to establish targeted delivery of drugs to ischemic areas guided by extracellular acidification (objective 2). Finally, we will study effects of energy depletion on brain organoids and organoid slice cultures derived from human iPSCs (objective 3). Our project will thus provide highly relevant information about the mechanisms of early Na+ dysregulation and the first steps and events triggering synaptic malfunction upon metabolic failure.