Regulation of Nrf2 pathway to protect ventilator induce lung injury in vivo via inhibition of caveolin phosphorylation

Objective To investigate whether the inhibition of caveolin-1 (Cav-1) phosphorylation will regulate effectively nuclear factor-erythroid 2-related factor (Nrf2) signal pathway and downstream effector molecules and protest against ventilation induced lung injury (VILI) in an animal model in vivo. Methods Ninety male Sprague-Dawley (SD) rats were randomly divided into nine groups (each n = 10): sham group in which rats did not receive ventilation but received tracheotomy; lung protective ventilation (PV) for 1 hour or 2 hours group; mechanical ventilation (MV) at high volume tidal (VT, 40 mL/kg) for 1 hour or 2 hours group; protein tyrosine kinase inhibitor PP2 or rosiglitazone (Rsg) pretreatment + high VT ventilation for 1 hour or 2 hours groups. The two pretreatment groups were given intraperitoneal injection PP2 15 mg/kg or intragastric administration of Rsg 5 mg/kg 1 hour before ventilation respectively. The rats were sacrificed after model reproduction, and bronchoalveolar lavage fluid (BALF) was collected. Pulmonary vascular permeability was measured by Evans blue (EB). The levels of tumor necrosis factor-α (TNF-α), activator protein-1 (AP-1), nuclear factor-κB (NF-κB), and interleukin-8 (IL-8) in BALF were determined by enzyme linked immunosorbent assay (ELISA). Then the lung tissues were collected, the lung wet/dry ratio (W/D) was calculated, the changes in pathology was observed with light microscope, and myeloperoxidase (MPO) activity was determined by colorimetric analysis. Nrf2 mRNA was determined by reverse transcription-polymerase chain reaction (RT-PCR). The expressions of Cav-1 tyrosine residues 14 phosphorylation (pCav-1-Y14), Cav-1, peroxisome proliferators-activated receptor γ (PPARγ) and claudin-5 as well as Nrf2 in cytoplasm and nucleus were determined by Western Blot. The positive expressions of PPARγ and claudin-5 in lung tissues were assayed with immunohistochemistry staining. Results There were no obvious pathological changes in the lung tissue in sham group and PV groups, and there were no significant differences in all the parameters between the two groups either. However, the injury in lung tissue was severe in the high VT groups in which W/D ratio, EB contents, MPO activity, and TNF-α, AP-1, IL-8, NF-κB levels in BALF as well as the protein expressions of Cav-1 and pCav-1-Y14 were significantly higher than those of sham group and PV groups, and the protein expressions of PPARγ and claudin-5 were significant lower than those of sham group and PV groups with a dose-dependent manner; but Nrf2 expressions in cytoplasm and nucleus did not show a statistical increase. After pretreatment of PP2 or Rsg, W/D ratio, MPO activity, EB contents, TNF-α, AP-1, IL-8, and NF-κB in BALF were significantly decreased as compared with those of high VT group, and RT-PCR showed significant up-regulation of Nrf2 mRNA in lung tissues too. Moreover, there was a statistically significant increase in expressed Nrf2 proteins in nucleus in PP2 or Rsg groups as compared with those of high VT groups [Nrf2 in nucleus (gray value): 0.61±0.06, 0.56±0.06 vs. 0.31±0.02 at 1 hour, 0.38±0.06, 0.43±0.07 vs. 0.22±0.03 at 2 hours; all P < 0.05], but no significant difference was found in the expression of Nrf2 protein in the cytoplasm among all groups. The protein expressions of pCav-1-Y14 in PP2 pretreatment groups were significantly lower than those of high VT groups (gray value: 0.89±0.04 vs. 1.48±0.02 at 1 hour, 0.86±0.02 vs. 1.31±0.01 at 2 hours; both P < 0.05); but expressed PPARγ proteins and expressed claudin-5 proteins in PP2 or Rsg pretreatment groups were significantly higher than those of high VT groups [PPARγ (gray value): 0.34±0.07, 0.42±0.13 vs. 0.17±0.07 at 1 hour, 0.38±0.09, 0.33±0.07 vs. 0.16±0.03 at 2 hours; claudin-5 (gray value): 0.33±0.05, 0.38±0.07 vs. 0.14±0.03 at 1 hour; 0.30±0.06, 0.31±0.04 vs. 0.17±0.04 at 2 hours; all P < 0.05]. Conclusions The inhibition of Cav-1-Y14 phosphorylation can increase the expression of Nrf2 in the nucleus, then result in an increase in the protein expressions of PPARγ and claudin-5 of its effector molecules. This effect can reduce the inflammation and capillary permeability of lung tissue in the model of VILI. Key words: Phosphorylation of caveolin-1; Nrf2; Peroxisome proliferators-activated receptor γ; Claudin-5; Ventilator-induced lung injury