Workers exposed to aerosolized dust present in concentrated animal feeding operations (CAFOs) are susceptible to inflammatory
lung diseases, such as
chronic obstructive pulmonary disease. Extracts of dust collected from hog CAFOs [hog dust extract (HDE)] are potent stimulators of lung inflammatory responses in several model systems. The observation that HDE contains active
proteases prompted the present study, which evaluated the role of CAFO dust
proteases in lung inflammatory processes and tested whether
protease-activated receptors (PARs) are involved in the signaling pathway for these events. We hypothesized that the damaging proinflammatory effect of HDE is due, in part, to the proteolytic activation of PARs, and inhibiting the
proteases in HDE or disrupting PAR activation would attenuate HDE-mediated inflammatory indexes in bronchial epithelial cells (BECs), in mouse lung slices in vitro, and in a murine in vivo exposure model. Human BECs and mouse lung slice cultures stimulated with 5% HDE released significantly more of each of the
cytokines measured (IL-6, IL-8, TNF-α, keratinocyte-derived
chemokine/CXC chemokine ligand 1, and
macrophage inflammatory protein-2/
CXC chemokine ligand 2) than controls, and these effects were markedly diminished by
protease inhibition. Inhibition of PARs also blunted the HDE-induced
cytokine release from BECs. In addition,
protease depletion inhibited HDE-induced BEC intracellular PKCα and PKCε activation. C57BL/6J mice administered 12.5% HDE intranasally, either once or daily for 3 wk, exhibited increased total cellular and neutrophil influx, bronchial alveolar fluid inflammatory
cytokines, lung histopathology, and inflammatory scores compared with mice receiving
protease-depleted HDE. These data suggest that
proteases in dust from CAFOs are important mediators of
lung inflammation, and these
proteases and their receptors may provide novel targets for therapeutic intervention in CAFO dust-induced airways disease.