The Extracellular Zn²⁺ Concentration Surrounding Excited Neurons Is High Enough to Bind Amyloid‐β Revealed by a Nanowire Transistor

Abstract

The Zn2+ stored in the secretory vesicles of glutamatergic neurons is coreleased with glutamate upon stimulation, resulting in the elevation of extracellular Zn2+ concentration (CZn2+ex). This elevation of CZn2+ex regulates the neurotransmission and facilitates the fibrilization of amyloid‐β (Aβ). However, the exact CZn2+ex surrounding neurons under (patho)physiological conditions is not clear and the connection between CZn2+ex and the Aβ fibrilization remains obscure. Here, a silicon nanowire field‐effect transistor (SiNW‐FET) with the Zn2+‐sensitive fluorophore, FluoZin‐3 (FZ‐3), to quantify the CZn2+ex in real time is modified. This FZ‐3/SiNW‐FET device has a dissociation constant of ≈12 × 10−9m against Zn2+. By placing a coverslip seeded with cultured embryonic cortical neurons atop an FZ‐3/SiNW‐FET, the CZn2+ex elevated to ≈110 × 10−9m upon stimulation with α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA). Blockers against the AMPA receptor or exocytosis greatly suppress this elevation, indicating that the Zn2+ stored in the synaptic vesicles is the major source responsible for this elevation of CZn2+ex. In addition, a SiNW‐FET modified with Aβ could bind Zn2+ with a dissociation constant of ≈633 × 10−9m and respond to the Zn2+ released from AMPA‐stimulated neurons. Therefore, the CZn2+ex can reach a level high enough to bind Aβ and the Zn2+ homeostasis can be a therapeutic strategy to prevent neurodegeneration.

Intracellular Zn2+ transients modulate global gene expression in dissociated rat hippocampal neurons

“…These tool limitations do not provide definitive evidence that synaptic Zn 2+ is absent from dissociated cultures. In contrast, using a different detection system, a recent study observed release of Zn 2+ from stimulated cortical neurons and calculated the local synaptic Zn 2+ concentration as approximately 100 nM 25 , which is in accordance with previous estimates 15,16,42 . Although we could not definitively confirm the presence of synaptic Zn 2+ , we were able to rigorously define the resting cytosolic labile Zn 2+ concentration to be approximately 60 pM (using ZapCV2) to 110 pM (using FluoZin3 AM), and we observed a small transient rise in Zn 2+ to roughly 150 pM upon depolarization with KCl.…”

“…The extent of synaptic Zn 2+ mobilization in neuron cultures would inform any analysis of Zn 2+ -dependent global changes. Unfortunately, while dissociated hippocampal neurons have been shown to both release Zn 2+ and exhibit cytosolic Zn 2+ dynamics upon intensive glutamate stimulation 17,25 , no rigorous characterization of synaptic Zn 2+ or synaptic Zn 2+ machinery has been performed in these cultures.…”

Zn 2+ influx activates ERK and Akt signaling pathways

“…structure or facilitate catalysis, and these proteins are thought to constitutively bind Zn 2+ (1,12,46). Recently, we have seen an increase in examples of Zn 2+ dynamics in cells (3,7,8,11,47) and evidence that Zn 2+ can play a regulatory role for a variety of cell processes (7,(48)(49)(50). Although Zn 2+ has long been suggested to serve as a cellular signal, much like calcium, the precise molecular details of how Zn 2+ accomplishes this task remains elusive for most systems.…”

Clinically oriented Alzheimer's biosensors: expanding the horizons towards point-of-care diagnostics and beyond

“…, cultured cortical neurons). 203 This strategy can serve as a highly sensitive device via examining how Zn 2+ homeostasis modulates neuronal activities. Furthermore, it can be a useful strategy in neurodegenerative disease prevention.…”