Bronchoalveolar Lavage Exosomes in Lipopolysaccharide-induced Septic Lung Injury

The overall goal of this experiment is to delineate the role of exosomes in the inflammatory responses in an LPS induced, acute septic lung injury mouse model. So this method can help answer key questions related to cell cross talk in acute lung injury and acute respiratory distress syndrome. Especially intercellular communication within the alveolar-micro environment via exosome shuttling.

The main advantage of this technique is that it allows the isolation and characterization of highly purified bronchoalveolar lavage exosomes derived from endotoxin treated septic mice with acute lung injury. Demonstrating the procedure is Dr.Zhihong Yuan and Dr.Chetna Bedi. To begin, load a one milliliter syringe equipped with a 27 gauge needle with 0.1 milliliters of LPS and PBS per mouse and manually restrain the first six to eight week old male C57 black 6J mouse.

Deliver the LPS intra-peritoneally and return the animal to its cage. 24 hours later, make a five millimeter incision in the center of the neck of the first animal and use blunt forceps to gently separate the muscles to expose the trachea. Next, gently insert a 27 gauge needle attached to a sterile 10 milliliter syringe into the trachea and inject one milliliter of sterile PBS.

Then immediately replace the 10 milliliter syringe with a three milliliter syringe equipped with a new 27 gauge needle. Aspirate the bronchoalveolar lavage fluid or BOLF and add the BOLF to an appropriately labeled 15 milliliter conical tube on ice. To isolate the exosomes, centrifuge the BOLF samples and transfer the supernatants to new 15 milliliter tubes.

Centrifuge the samples again and transfer the supernatants to ultra-centrifuge tubes to remove the larger, cellular particles. Transfer the supernatants to new conical tubes and load the samples into 0.2 micron syringe filters to remove any remaining larger particles. Add the filtered samples to new ultra-centrifuge tubes to pellet the exosomes.

Carefully discard the supernatants and re-suspend the pellets in 100 microliters of PBS per tube. Then transfer the exosome samples into individual 1.5 milliliter tubes for their minus 80 degree Celsius storage. To purify the exosomes, add 0.4 microliters of the appropriate exosome dye to one tube containing 100 microliters of suspension solution per sample and quickly add one thawed exosome sample to each tube of dye.

Thoroughly mix the exosomes with the dye and incubate the samples at room temperature for five minutes, protected from light. At the end of the incubation, place one exosome spin column per sample into a 1.5 milliliter illusion tube and transfer the exosome solutions to the center of each spin column. Then centrifuge the samples, discard the columns, and store the alluded samples at minus 20 degrees Celsius.

To measure exosome uptake by recipient cells, first seed one times 10 to the fourth mouse lung epithelial 12 cells in 0.5 milliliters of medium into each well of an eight well chamber slide for a 16 hour culture at 37 degrees Celsius in 5%carbon dioxide. After thawing, add 10 microliters of the purified fluorescent labeled exosomes to each well and return the cell cultures to the incubator for one hour. At the end of the incubation, wash the cells with PBS and fix each co-culture with 1%paraformaldehyde for 10 minutes at room temperature.

Remove the medium and then mount the slide with medium supplemented with DAPI and image the samples by fluorescence microscopy at a 40 times magnification. To verify exosome interaction with recipient cells, seed two times 10 to the fifth mouse lung epithelial 12 cells in two milliliters of medium per well in a 12 well culture plate containing the appropriate culture medium for a two hour incubation at 37 degrees Celsius and 5%carbon dioxide. At the end of the incubation, add 20 micrograms of exosomes to three wells of epithelial cells per experimental group and return the cells to the incubator.

After 24 hours, remove the medium, wash the cells with PBS, and add 600 microliters of lysis buffer to each well with gentle shaking. Then transfer the entire contents of each well into individual 1.5 milliliter tubes and analyze the samples according to the standard real time PCR protocols. Within 24 hours of LPS administration, neutrophilic influx is observed in the lungs of LPS treated animals.

After their isolation and purification as just demonstrated, the presence of exosomes in the BOLF from septic lung injury animals can be confirmed by transmission electron microscopy. The expression of select pro-inflammatory micro RNA is significantly increased in bronchoalveolar fluid exosomes from LPS treated animals compared to controlled PBS treated mice. LPS treated exosomes are taken up by mouse bronchiole epithelial cells as evidenced by the co-localization of fluorescent dye labeled exosomes with DAPI labeled cells after one hour of co-culture.

Pro-inflammatory mediator expression is significantly increased in epithelial cells co-cultured with exosomes from LPS treated animals compared to co-culture with exosomes from control PBS treated mice. Further, cells treated with exosomes from LPS treated mice demonstrate a significantly attenuated expression of zonula occludens one compared to controls indicating a less intact cell integrity after LPS treated exosome co-culture. The intra-peritoneal injection of LPS, the bronchoalveolar lavage extraction, and exosome delegation from the bronchoalveolar lavage all the steps can be completed in a relatively short amount of time.

Following this procedure, other methods like exosome and epithelial cell co-culture can be performed to answer additional questions about the cross talk between innate and structural cells in the lung alveolar micro-environment. Cross talk between innate immune and structural cells via exosome shuttling contributes to the inflammatory response and to structural barrier disruption suggesting exosomal micro-RNA targeting may provide a normal platform for treating acute lung injury and acute respiratory distress syndrome. After watching this video you should have a good understanding of how to induce septic lung injury in mice, isolate bronchoalveolar lavage fluid from mice, isolate exosomes from the lavage fluid, and use a co-culture model for interrogating intracellular cross talk.

Don't forget that working with LPS can be hazardous and that precautions such as wearing the appropriate personal protective equipment should always be taken while performing this procedure.