TRPV4 channels augment macrophage activation and ventilator-induced lung injury

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Abstract
We have previously implicated transient receptor potential vanilloid 4 (TRPV4) channels and alveolar macrophages in initiating the permeability increase in response to high peak inflation pressure (PIP) ventilation. Alveolar macrophages were harvested from TRPV4−/−and TRPV4+/+mice and instilled in the lungs of mice of the opposite genotype. Filtration coefficients ( Kf) measured in isolated perfused lungs after ventilation with successive 30-min periods of 9, 25, and 35 cmH2O PIP did not significantly increase in lungs from TRPV4−/−mice but increased >2.2-fold in TRPV4+/+lungs, TRPV4+/+lungs instilled with TRPV4−/−macrophages, and TRPV4−/−lungs instilled with TRPV4+/+macrophages after ventilation with 35 cmH2O PIP. Activation of TRPV4 with 4-α-phorbol didecanoate (4αPDD) significantly increased intracellular calcium, superoxide, and nitric oxide production in TRPV4+/+macrophages but not TRPV4−/−macrophages. Cross-sectional areas increased nearly 3-fold in TRPV4+/+macrophages compared with TRPV4−/−macrophages after 4αPDD. Immunohistochemistry staining of lung tissue for nitrotyrosine revealed increased amounts in high PIP ventilated TRPV4+/+lungs compared with low PIP ventilated TRPV4+/+or high PIP ventilated TRPV4−/−lungs. Thus TRPV4+/+macrophages restored susceptibility of TRPV4−/−lungs to mechanical injury. A TRPV4 agonist increased intracellular calcium and reactive oxygen and nitrogen species in harvested TRPV4+/+macrophages but not TRPV4−/−macrophages. Kfincreases correlated with tissue nitrotyrosine, a marker of peroxynitrite production.

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