Non-muscle Mlck is required for β-catenin- and FoxO1-dependent downregulation of Cldn5 in IL-1β-mediated barrier dysfunction in brain endothelial cells

Abstract

Aberrant elevation in the levels of the pro-inflammatory cytokine interleukin-1b (IL-1b) contributes to neuroinflammatory diseases. Blood-brain barrier (BBB) dysfunction is a hallmark phenotype of neuroinflammation. It is known that IL-1b directly induces BBB hyperpermeability but the mechanisms remain unclear. Claudin-5 (Cldn5) is a tight junction protein found at endothelial cell-cell contacts that are crucial for maintaining brain microvascular endothelial cell (BMVEC) integrity. Transcriptional regulation of Cldn5 has been attributed to the transcription factors b-catenin and forkhead box protein O1 (FoxO1), and the signaling molecules regulating their nuclear translocation. Non-muscle myosin light chain kinase (nmMlck, encoded by the Mylk gene) is a key regulator involved in endothelial hyperpermeability, and IL-1b has been shown to mediate nmMlck-dependent barrier dysfunction in epithelia. Considering these factors, we tested the hypothesis that nmMlck modulates IL-1b-mediated downregulation of Cldn5 in BMVECs in a manner that depends on transcriptional repression mediated by b-catenin and FoxO1. We found that treating BMVECs with IL-1b induced barrier dysfunction concomitantly with the nuclear translocation of b-catenin and FoxO1 and the repression of Cldn5. Most importantly, using primary BMVECs isolated from mice null for nmMlck, we identified that Cldn5 repression caused by b-catenin and FoxO1 in IL-1b-mediated barrier dysfunction was dependent on nmMlck.

Brain endothelial TAK1 and NEMO safeguard the neurovascular unit

“…At present, we cannot exclude that under inflammatory conditions the situation might be different and high levels of endothelial NF-B activity could damage the BBB, in the sense of a bell-shaped relationship between NF-B activity and BBB integrity. However, this assumption is not necessarily required, because NF-B-independent mechanisms that are instead mediated by ARNO, ARF6, -catenin, and FoxO1 increase endothelial permeability in response to inflammatory factors (Zhu et al, 2012;Beard et al, 2014). In addition, activation of NF-B in neighboring astrocytes and pericytes leads to the release of inflammatory mediators that subsequently break down the BBB (Zhang et al, 2007;Bell et al, 2012).…”

Protein tyrosine kinase 6 mediates TNFα-induced endothelial barrier dysfunction

“…These mediators trigger intracellular signaling events of the microvascular endothelium leading to changes of endothelial structure proteins which give rise to endothelial hyperpermeability. [6,7] TNFα is a cytokine released from activated leukocytes involved in mediating systemic inflammatory response syndrome (SIRS). [8] In fact, intravenous injection of TNFα induces SIRS in rats.…”

Melatonin Protects the Esophageal Epithelial Barrier by Suppressing the Transcription, Expression and Activity of Myosin Light Chain Kinase Through ERK1/2 Signal Transduction

“…Prior studies have demonstrated that ERK phosphorylation contributes to the activation of the MLCK signaling pathway, which leads to barrier dysfunction in the vascular endothelium or intestinal epithelium [6]. Although MLCK is implicated in endothelial and epithelial barrier dysfunction [25,26], its specific role in the impairment of the esophageal epithelial barrier has not been reported. Our study provides direct evidence that ERK-mediated activation of MLCK plays a critical role in esophageal epithelial barrier dysfunction.…”