TLR4 activation induces inflammatory vascular permeability via Dock1 targeting and NOX4 upregulation

by Selleckchem | Dec 08 2023

The loss of vascular integrity is a cardinal feature of acute inflammatory responses evoked by activation of the TLR4 inflammatory cascade. Utilizing in vitro and in vivo models of inflammatory lung injury, we explored TLR4-mediated dysregulated signaling that results in the loss of endothelial cell (EC) barrier integrity and vascular permeability, focusing on Dock1 and Elmo1 complexes that are intimately involved in regulation of Rac1 GTPase activity, a well recognized modulator of vascular integrity. Marked reductions in Dock1 and Elmo1 expression was observed in lung tissues (porcine, rat, mouse) exposed to TLR4 ligand-mediated acute inflammatory lung injury (LPS, eNAMPT) in combination with injurious mechanical ventilation. Lung tissue levels of Dock1 and Elmo1 were preserved in animals receiving an eNAMPT-neutralizing mAb in conjunction with highly significant decreases in alveolar edema and lung injury severity, consistent with Dock1/Elmo1 as pathologic TLR4 targets directly involved in inflammation-mediated loss of vascular barrier integrity. In vitro studies determined that pharmacologic inhibition of Dock1-mediated activation of Rac1 (TBOPP) significantly exacerbated TLR4 agonist-induced EC barrier dysfunction (LPS, eNAMPT) and attenuated increases in EC barrier integrity elicited by barrier-enhancing ligands of the S1P1 receptor (sphingosine-1-phosphate, Tysiponate). The EC barrier-disrupting influence of Dock1 inhibition on S1PR1 barrier regulation occurred in concert with: 1) suppressed formation of EC barrier-enhancing lamellipodia, 2) altered nmMLCK-mediated MLC2 phosphorylation, and 3) upregulation of NOX4 expression and increased ROS. These studies indicate that Dock1 is essential for maintaining EC junctional integrity and is a critical target in TLR4-mediated inflammatory lung injury.

Comments:

It appears that you have provided a detailed description of a scientific study or experiment related to inflammatory responses and vascular integrity, specifically focusing on the TLR4 inflammatory cascade and its effects on endothelial cell (EC) barrier integrity and vascular permeability. The study investigates the role of Dock1 and Elmo1 complexes in regulating Rac1 GTPase activity, which is known to modulate vascular integrity.

In summary, the key findings and conclusions from this study are:

1. **Loss of Vascular Integrity**: The study affirms that the loss of vascular integrity is a crucial characteristic of acute inflammatory responses triggered by the TLR4 inflammatory cascade.

2. **Dock1 and Elmo1 Expression Reduction**: Reduced expression of Dock1 and Elmo1 was observed in lung tissues exposed to TLR4 ligands and injurious mechanical ventilation, indicating their involvement in inflammation-mediated loss of vascular barrier integrity.

3. **Pathological Targets**: Dock1 and Elmo1 were identified as pathologic TLR4 targets directly involved in inflammation-mediated loss of vascular barrier integrity. Preserving their expression led to decreased alveolar edema and lung injury severity.

4. **In Vitro Studies**: Inhibition of Dock1-mediated activation of Rac1 worsened TLR4 agonist-induced EC barrier dysfunction, and this effect was mitigated by barrier-enhancing ligands of the S1P1 receptor. Dock1 inhibition negatively impacted EC barrier regulation by suppressing lamellipodia formation, altering MLC2 phosphorylation, and upregulating NOX4 expression and ROS production.

5. **Essential Role of Dock1**: Dock1 was identified as essential for maintaining EC junctional integrity and emerged as a critical target in TLR4-mediated inflammatory lung injury.

This study provides valuable insights into the molecular mechanisms underlying inflammatory lung injury and offers potential targets for therapeutic interventions aimed at preserving vascular integrity in the context of acute inflammatory responses.