Mechanical ventilation modulates TLR4 and IRAK-3 in a non-infectious, ventilator-induced lung injury model.

BACKGROUND: Previous experimental studies have shown that injurious mechanical ventilation has a direct effect on pulmonary and systemic immune responses. How these responses are propagated or attenuated is a matter of speculation. The goal of this study was to determine the contribution of mechanical ventilation in the regulation of Toll-like receptor (TLR) signaling and interleukin-1 receptor associated kinase-3 (IRAK-3) during experimental ventilator-induced lung injury. METHODS: Prospective, randomized, controlled animal study using male, healthy adults Sprague-Dawley rats weighing 300-350 g. Animals were anesthetized and randomized to spontaneous breathing and to two different mechanical ventilation strategies for 4 hours: high tidal volume (VT) (20 ml/kg) and low VT (6 ml/kg). Histological evaluation, TLR2, TLR4, IRAK3 gene expression, IRAK-3 protein levels, inhibitory kappa B alpha (IkappaBalpha), tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL6) gene expression in the lungs and TNF-alpha and IL-6 protein serum concentrations were analyzed. RESULTS: High VT mechanical ventilation for 4 hours was associated with a significant increase of TLR4 but not TLR2, a significant decrease of IRAK3 lung gene expression and protein levels, a significant decrease of IkappaBalpha, and a higher lung expression and serum concentrations of pro-inflammatory cytokines. CONCLUSIONS: The current study supports an interaction between TLR4 and IRAK-3 signaling pathway for the over-expression and release of pro-inflammatory cytokines during ventilator-induced lung injury. Our study also suggests that injurious mechanical ventilation may elicit an immune response that is similar to that observed during infections.

Activation of the Wnt/ß-catenin signaling pathway by mechanical ventilation is associated with ventilator-induced pulmonary fibrosis in healthy lungs.

BACKGROUND: Mechanical ventilation (MV) with high tidal volumes (V(T)) can cause or aggravate lung damage, so-called ventilator induced lung injury (VILI). The relationship between specific mechanical events in the lung and the cellular responses that result in VILI remains incomplete. Since activation of Wnt/ß-catenin signaling has been suggested to be central to mechanisms of lung healing and fibrosis, we hypothesized that the Wnt/ß-catenin signaling plays a role during VILI. METHODOLOGY/PRINCIPAL FINDINGS: Prospective, randomized, controlled animal study using adult, healthy, male Sprague-Dawley rats. Animals (n = 6/group) were randomized to spontaneous breathing or two strategies of MV for 4 hours: low tidal volume (V(T)) (6 mL/kg) or high V(T) (20 mL/kg). Histological evaluation of lung tissue, measurements of WNT5A, total ß-catenin, non-phospho (Ser33/37/Thr41) ß-catenin, matrix metalloproteinase-7 (MMP-7), cyclin D1, vascular endothelial growth factor (VEGF), and axis inhibition protein 2 (AXIN2) protein levels by Western blot, and WNT5A, non-phospho (Ser33/37/Thr41) ß-catenin, MMP-7, and AXIN2 immunohistochemical localization in the lungs were analyzed. High-V(T) MV caused lung inflammation and perivascular edema with cellular infiltrates and collagen deposition. Protein levels of WNT5A, non-phospho (Ser33/37/Thr41) ß-catenin, MMP-7, cyclin D1, VEGF, and AXIN2 in the lungs were increased in all ventilated animals although high-V(T) MV was associated with significantly higher levels of WNT5A, non-phospho (Ser33/37/Thr41) ß-catenin, MMP-7, cyclin D1, VEGF, and AXIN2 levels. CONCLUSIONS/SIGNIFICANCE: Our findings demonstrate that the Wnt/ß-catenin signaling pathway is modulated very early by MV in lungs without preexistent lung disease, suggesting that activation of this pathway could play an important role in both VILI and lung repair. Modulation of this pathway might represent a therapeutic option for prevention and/or management of VILI.

WNT/ß-catenin signaling is modulated by mechanical ventilation in an experimental model of acute lung injury.

PURPOSE: The mechanisms involved in lung injury progression during acute lung injury (ALI) are still poorly understood. Because WNT/ß-catenin signaling has been shown to be involved in epithelial cell injury and hyperplasia during inflammation and sepsis, we hypothesized that it would be modulated by mechanical ventilation (MV) in an experimental model of sepsis-induced ALI. METHODS: This study was a prospective, randomized, controlled animal study performed using adult male Sprague-Dawley rats. Sepsis was induced by cecal ligation and perforation. At 18 h, surviving animals were randomized to spontaneous breathing or two strategies of MV for 4 h: low tidal volume (V (T)) (6 ml/kg) plus 10 cmH2O of positive end-expiratory pressure (PEEP) versus high (20 ml/kg) tidal volume (V (T)) with zero PEEP. Histological evaluation, measurements of WNT5A, total ß-catenin, and matrix metalloproteinase-7 (MMP7) protein levels by Western blot, and their immunohistochemical localization in the lungs were analyzed. RESULTS: Sepsis and high-V (T) MV caused lung inflammation and perivascular edema with cellular infiltrates and collagen deposition. Protein levels of WNT5A, ß-catenin, and MMP7 in the lungs were increased in animals with sepsis-induced ALI. High-V (T) MV was associated with higher levels of WNT5A, ß-catenin, and MMP7 protein levels (p < 0.001), compared to healthy control animals. By contrast, low-V (T) MV markedly reduced WNT5A, ß-catenin, and MMP7 protein levels (p < 0.001). CONCLUSIONS: Our findings demonstrate that the WNT/ß-catenin signaling pathway is modulated early during sepsis and ventilator-induced lung injury, suggesting that activation of this pathway could play an important role in both lung injury progression and repair.