Effects of acute fluctuations of extracellular Zinc on network activity of human iPSC-derived neurons; impact of NMDA Receptor and L-Type Calcium Channel Activation

Zinc is an essential trace element involved in numerous biological processes including in the central nervous system. Strong genetic evidence has implicated dysregulation of free Zn 2+ levels in the pathophysiology of schizophrenia and there is evidence for its involvement in other psychiatric and neurological disorders. This study aimed to investigate the effects of fluctuations in extracellular Zn 2+ levels on human neuronal function to better understand possible pathophysiological mechanisms. Using multi-electrode array (MEA) methods, we examined the effects of manipulating extracellular Zn 2+ on intrinsic neuronal function and coordinated neuronal network activity in human induced pluripotent stem cell-derived neurons. We confirmed effects were related to extracellular free Zn 2+ ions using the specific membrane-impermeable chelator ZX1. We then manipulated NMDA receptors (NMDARs) and L-type calcium channels (LTCCs) with drug compounds and assessed gene expression with qPCR to probe molecular mechanisms of Zn 2+ effects. Extracellular Zn 2+ affected network activity in a dose-dependent manner. Addition of nMolar concentrations of ZnCl 2 within the physiological range had specific effects on neuronal synchrony that were reversible by chelation of free Zn 2+ and by NMDAR or LTCC activation. Following addition of higher, μMolar, concentrations of ZnCl 2 the effects of Zn 2+ were associated with impaired intrinsic neuronal excitability, irreversible network dysfunction that was resistant to NMDAR or LTCC activation and upregulation of the apoptosis cell death marker cleaved caspase-3. Acute fluctuations in extracellular Zn 2+ can impact both phasic neuronal connectivity and at higher levels can lead to neuronal toxicity in human neurons. The data may have relevance for, and explain in part, the known links between Zn 2+ and conditions such as schizophrenia, where the malfunctioning synapse is increasingly the focus of pathology, and neurological conditions associated with neurotoxicity.