Zinc ions regulate opening of tight junction favouring efflux of macromolecules via the GSK3β/snail-mediated pathway

• Published in: Metallomics 2018-01, Vol.1 (1), p.169-179
• Main Authors: Xiao, Ruyue, Yuan, Lan, He, Weijiang, Yang, Xiaoda
• Format: Article
• Language: English
• Subjects: Actin; Amygdala; Animals; Blood-brain barrier; Blood-Brain Barrier - drug effects; Brain; Breakage; Calcineurin; Cell Membrane Permeability - drug effects; Cell Proliferation - drug effects; Coordination Complexes - metabolism; Dogs; Efflux; Europium - metabolism; Extracellular signal-regulated kinase; Gene Expression Regulation - drug effects; Glycogen; Glycogen synthase kinase 3; Glycogen Synthase Kinase 3 beta - metabolism; Hippocampus; JNK protein; Kinases; Macromolecules; Madin Darby Canine Kidney Cells; Matrix metalloproteinase; Membrane permeability; Metabolites; Metalloproteinase; Pentetic Acid - metabolism; Permeability; Phosphorylation; Repressors; Signal Transduction; Snail Family Transcription Factors - metabolism; Snail protein; Subiculum; Tight Junctions - drug effects; Tight Junctions - physiology; Trace elements; Transcription factors; Zinc; Zinc - pharmacology; Zonula occludens-1 protein
• ISSN: 1756-5901; 1756-591X
• DOI: 10.1039/c7mt00288b

Zinc is an essential trace element presenting in particularly high concentration in the brain. In some regions, e.g. lateral amygdala, subiculum and hippocampus, rapidly-exchangeable zinc may transiently reach even up to 600 μM. To explore the possible roles of high-concentration Zn 2+ in regulating the blood-brain barrier (BBB), we investigated the effects of Zn 2+ on the functions and structures of the tight junction (TJ) with an in vitro model of a Madin-Darby canine kidney (MDCK) cell monolayer. The experimental results indicated that high concentrations (>200 μM) of Zn 2+ can affect the TJ integrity in a polarized manner. Basolateral addition of Zn 2+ led to reversible TJ opening with pore paths of r ∼ 2 nm or more depending on Zn 2+ concentration. The efflux/influx ratios of different sized probes were found to be ∼4.6 for FD4 ( M W 4000) and ∼1.8 for Eu-DTPA ( M W 560), suggesting that the Zn 2+ -induced paracelluar channels favour efflux especially for macromolecules. Further mechanistic studies revealed that the elevated intracellular Zn 2+ taken from the basolateral side can increase phosphorylation of glycogen synthase kinase (GSK) 3β, primarily due to the inhibition of calcineurin (CaN), thus resulting in the elevation of the snail transcriptional repressors. Subsequently, Zn 2+ can cause the down-regulation of claudin-1, breakage of occludin and ZO-1 rings, and collapse of basolateral F-actin structures. These overall factors result in the formation of a trumpet-like paracellular channel, which allows asymmetric solute permeation. The ERK1/2 and JNK1/2 pathways may also be involved in the Zn 2+ -induced TJ opening process, while the activation of matrix metalloproteinase was not observed. Our results may suggest a potential role of zinc in regulation of BBB permeability associated with brain clearance of metabolites through the glymphatic system. Zn 2+ -Induced asymmetric paracellular pore paths in MDCK cell monolayer favour efflux of macromolecules via the GSK3β/snail-mediated pathway.