American journal of respiratory cell and molecular biology
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Am. J. Respir. Cell Mol. Biol. · Jan 2011
Non-muscle myosin light chain kinase isoform is a viable molecular target in acute inflammatory lung injury.
Acute lung injury (ALI) and mechanical ventilator-induced lung injury (VILI), major causes of acute respiratory failure with elevated morbidity and mortality, are characterized by significant pulmonary inflammation and alveolar/vascular barrier dysfunction. Previous studies highlighted the role of the non-muscle myosin light chain kinase isoform (nmMLCK) as an essential element of the inflammatory response, with variants in the MYLK gene that contribute to ALI susceptibility. To define nmMLCK involvement further in acute inflammatory syndromes, we used two murine models of inflammatory lung injury, induced by either an intratracheal administration of lipopolysaccharide (LPS model) or mechanical ventilation with increased tidal volumes (the VILI model). ⋯ Intravenous injections of nmMLCK silencing RNA, either directly or as cargo within angiotensin-converting enzyme (ACE) antibody-conjugated liposomes (to target the pulmonary vasculature selectively), decreased nmMLCK lung expression (∼70% reduction) and significantly attenuated LPS-induced and VILI-induced lung inflammation (∼40% reduction in bronchoalveolar lavage protein). Compared with wild-type mice, nmMLCK knockout mice were significantly protected from VILI, with significant reductions in VILI-induced gene expression in biological pathways such as nrf2-mediated oxidative stress, coagulation, p53-signaling, leukocyte extravasation, and IL-6-signaling. These studies validate nmMLCK as an attractive target for ameliorating the adverse effects of dysregulated lung inflammation.
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The decrease of lung compliance in pulmonary edema underlies ventilator-induced lung injury. However, the cause of the decrease in compliance is unknown. We tested the hypothesis that in pulmonary edema, the mechanical effects of liquid-filled alveoli increase tissue stress in adjacent air-filled alveoli. ⋯ However, at near TLC, the air-filled alveolus was larger than it was in the pre-edematous control tissue. In pulmonary edema, liquid-filled alveoli induce mechanical stress on air-filled alveoli, reducing the compliance of air-filled alveoli, and hence overall lung compliance. Because of increased mechanical stress, air-filled alveoli may be susceptible to overdistension injury during mechanical ventilation of the edematous lung.
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Am. J. Respir. Cell Mol. Biol. · Jan 2011
Involvement of Gax gene in hypoxia-induced pulmonary hypertension, proliferation, and apoptosis of arterial smooth muscle cells.
Hypoxia down-regulates the expression of the growth arrest-specific homeobox (Gax) in pulmonary arterial smooth muscle cells (PASMCs), resulting in increased cell proliferation and decreased apoptosis, but the mechanism for this response remains unclear. The present study investigated the role of Gax in the development of hypoxia-induced pulmonary hypertension (PH). We found that hypoxia suppressed the expression of endogenous Gax in rats, but not in those pretreated intratracheally with a Gax construct (Ad-Gax). ⋯ The PASMCs with Ad-Gax transfection exhibited hyperexpression of the Bcl-2-associated X protein (Bax) and hypoexpression of B-cell lymphoma 2 (Bcl-2), leading to cell apoptosis. Thus, our data indicate that the enhanced expression of Gax inhibits hypoxia-induced PASMC proliferation, probably via the extracellular-signal-regulated kinase (ERK) 1/2 pathway, and induces the apoptosis of hypoxic PASMCs via the Bcl-2/Bax pathway. Gax may be a potential new therapeutic target for pulmonary hypertension.