Airborne Particles Alter the Alveolar Epithelial Barrier via a Decrease in the Tight Junction Protein Occludin

Abstract

PURPOSE:To determine whether exposure of the alveolar epithelium to airborne particles alters alveolar barrier function and decreases tight junction proteins. METHODS:Rat alveolar type II cells (ATII) were cultured on transwells inserts, and lung adenocarcinoma A549 on 100 mm culture dishes. These cells were exposed to particulate matter < 10 microns in diameter (PM10) (1,5 ,10 and 20 μg/cm 2 ) or vehicle for up to 24 hours, after which the plasma membranes were isolated and examined using immunofluorescence and immunoblotting to measure changes in occludin. Measurement of paracellular permeability to 4 kDa FITC-dextran and transepithelial electrical resistance (TER) were performed to assess barrier function. Mice were anesthetized and a 20-gauge angiocath was placed transorally into the trachea under direct visualization. We instilled either PM (200 μg) suspended in 50 μl of sterile PBS or 50 μl of sterile PBS in two equal aliquots, 3 min apart. Lungs were taken 24 hours later.RESULTS: PM10 at 10 and 20 μg/cm 2 caused a significant TER drop after 24 hours, changes occurring first at 3 hours with 20 μg/cm 2 (p<0.001). ATII paracellular permeability was increased (70%) after 24 hours of exposure to PM10 (20 μg/cm 2 ). The total abundance at the plasma membrane of occludin was decreased in alveolar epithelial cells after exposure to PM10 for 3 hours and in whole lungs of mice exposed PM10 for 24 hours. Also, there was a loss of interaction between the tight junction protein ZO-1 and occludin after exposure to PM10 for 3 hours. CONCLUSION:Particulate matter alters the alveolar epithelial barrier, possibly via a decrease in the tight junction protein occludin.CLINICAL IMPLICATIONS: Higher morbidity and mortality from pulmonary and cardiovascular events due to air pollution may be explained by an alveolar epithelial barrier dysfunction causing airborne particles to directly traverse the lung epithelium or indirectly induce pulmonary inflammation.

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“…TJ proteins are very dynamic and change their location when the permeability of the epithelial monolayer is changing [ 37 , 38 ]. Yshii and colleagues [ 39 ] exposed mice as well as in vitro cultured alveolar epithelial cells to PM10 and demonstrated a decrease in the total abundance of occludin. They also observed that connections of occludin with the protein zonula occludens-1 were altered.…”