TRPV4 channels augment macrophage activation and ventilator-induced lung injury

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. Kf increases correlated with tissue nitrotyrosine, a marker of peroxynitrite production.