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Increased iNOS activity is essential for pulmonary epithelial tight junction dysfunction in endotoxemic mice
Xiaonan Han1, Mitchell P Fink, Takashi Uchiyama
1Department of Critical Care Medicine, 616 Scaife Hall, 3550 Terrace St., Pittsburgh, PA 15261, USA.
Summary
Excessive nitric oxide (NO) from inducible NO synthase (iNOS) impairs pulmonary epithelial barrier function by altering tight junction proteins. An iNOS inhibitor protected against this inflammation-induced lung injury.
Area of Science:
- Pulmonary Medicine
- Cell Biology
- Inflammation Research
Background:
- Systemic inflammation can compromise the integrity of the pulmonary epithelial barrier.
- Nitric oxide (NO) production, particularly via inducible NO synthase (iNOS), is implicated in inflammatory responses.
- Tight junctions (TJs) are crucial for maintaining epithelial barrier function.
Purpose of the Study:
- To investigate the role of excessive nitric oxide (NO) production in altering tight junction (TJ) protein expression and function in the pulmonary epithelium during endotoxemia.
- To determine if inhibiting inducible NO synthase (iNOS) can protect the pulmonary epithelial barrier.
Main Methods:
- A murine model of endotoxemia induced by lipopolysaccharide (LPS) injection.
- Assessment of bronchoalveolar barrier function using FITC-dextran leakage.
- Evaluation of iNOS expression, NF-kappaB activation, and TJ protein (ZO-1, ZO-2, ZO-3, occludin) levels via immunoblotting and immunofluorescence.
- In vitro studies using Calu-3 epithelial monolayers treated with cytomix and an iNOS inhibitor (l-NIL).
Main Results:
- Endotoxemia significantly increased bronchoalveolar lavage fluid leakage, indicating impaired barrier function.
- LPS injection upregulated iNOS protein and activated NF-kappaB in lung tissue.
- Expression of key TJ proteins (ZO-1, ZO-2, ZO-3, occludin) was decreased in the lungs of endotoxemic mice.
- Treatment with the iNOS inhibitor l-NIL ameliorated TJ protein changes and preserved barrier function.
- In vitro, cytomix increased Calu-3 monolayer permeability, an effect prevented by l-NIL.
Conclusions:
- Excessive NO production, mediated by iNOS, plays a critical role in the disruption of pulmonary epithelial tight junctions during systemic inflammation.
- Inhibition of iNOS can preserve TJ protein expression and restore pulmonary epithelial barrier function in endotoxemia.
- NO-dependent mechanisms contribute to altered TJ protein expression and function in the lung following inflammatory insults.