The overall goal of this procedure is to accurately measure the internal surface area of a mouse lung after pneumonectomy and prosthesis implantation. This method helps to analyze the morphological and the physiological functions of the lung in mechanical force-induced adult lung regeneration. The main advantage of this technique is to accurately quantify internal lung surface area, which promise to increase the reliability and the reproducibility of lung function status.
Prepare the mouse for surgery on an intubation platform with its ventral side accessible. Then pull out the tongue and inspect the vocal chords with a small animal laryngoscope that is compatible with guiding catheters. Then gently insert a 20 gauge intravenous intubation canula into the trachea at an interior angle.
Next, put the mouse in a right lateral recumbent position and connect the canula to a mechanical ventilator. Observe the chest to judge the insertion of the canula into the trachea. Set the inspiratory pressure to 12 centimeters of water and set the respiratory rate to 120 breaths per minute.
Now, clean the exposed skin with at least three alternating scrubs of Betadine and 70%ethanol. Then begin the surgery with a two to three centimeter posterolateral thoracotomy incision into the fifth intercostal space. Penetrate the musculature using Noyes spring scissors.
Next, make a 1.5 centimeter incision to expose the left lung. As needed throughout the surgery, use a high temperature cauterizer to stop bleeding. Then, lift 1/3 of the left lung lobe from the chest with blunt tip forceps, and use a cotton swab to pull out the entire left lung.
Now, identify the pulmonary artery and bronchi of the left lung lobe, and tightly ligate the bronchi and vessels at the hilum with a soaked surgical suture. Next, cut out the left lung lobe three to four millimeters from the ligation, being careful not to cut off the suture, which could result in pneumothorax. Next, close the chest wall with one suture.
Then, stitch the muscle layer and the skin layer sequentially, using five to six interrupted sutures with three to four millimeter gaps. Be sure to keep the surgical suture needle away from the heart. Cardiac puncture is lethal.
Lastly, disinfect the surgical area with povidone-iodine. Then, place the mouse on a 38 degrees Celsius thermal pad. Keep using the ventilator until spontaneous breathing returns.
Perform the previously described operation, but just after removing the lung, prepare to insert the prosthesis. Using blunted forceps, grip the center of the ellipsoid silicone prothesis. Next, while holding the rib with forceps to expose the thoracic cavity, very gently insert the prothesis.
Enter at a 45 degree angle between the frontal plane of the prosthesis and the thoracic surface. Using blunt forceps, ensure that the prosthesis is fully within the left empty thoracic cavity. Now, close the chest and monitor the mouse as previously described.
For this procedure, assemble a custom inflation tube that consists of a plunger removed from a 10 milliliter serological pipette, a 40 centimeter long flexible tube with a needle adapter, a flow rate control valve, and an 18 gauge needle. Once assembled, secure the pipette to a sideboard with tape. The distance between the top of the pipette and the bench must be at least 30 centimeters.
After euthanizing the mouse by anesthetic injection, secure it to a sterilized board and carefully open the chest to cut out the sternum and expose the lung lobes. Then, expose the trachea. Next, fill the inflation tube with freshly made 4%PFA and remove all the bubbles from the tube.
Then, insert the needle into the trachea. To avoid leakage, clip the trachea with vessel clips. Now, inflate the lung with fixative at a constant transpulmonary pressure of 25 centimeters of water.
Incubate the lungs at room temperature for two hours for full expansion. After the inflation, take note of the volume displacement of fixative. Now, ligate the trachea and gently dissect out the lungs intact from the surrounding connective tissues.
Use scissors and be very gentle. Next, incubate the lungs in a 50 milliliter conical tube filled with 4%PFA for 12 hours at four degrees Celsius with gentle shaking on a shaker. Then proceed with processing and staining as described in the text protocol.
To quantify the MLI, use images of the agent used in sections collected under bright-field at 20x magnification. From three different lung sections, randomly select a total of 15 non-overlapping views, each about one square millimeter, and then vent them. Only use areas without arteries and veins, major airways, or alveolar ducts.
For the analysis, draw a 10 by 10 grid over each selected area using a ruler tool. The grid lines are thus about 100 microns apart. Then, to find an intercept along the line as the length between two adjacent alveolar epithelia.
For example, the double-headed arrows illustrate the lengths. Count all these lengths along each grid line, and the MLI is the average value of the intercept lengths. Using the described protocols, PNX-treated mice were compared with prosthetic implanted mice.
The mice used were eight-week-old CD-1 males, and their left lung lobes were resected. The prosthesis mimics the size and shape of the left lung lobe and was inserted into the chest after the left lung lobe was removed. 14 days after the surgery, a custom made inflation tube was used to determine the internal volume of the remaining right lung.
The average volume of the right lung in the five PNX-treated mice was approximately 1.4 milliliters, which was significantly greater, 1.05 milliliters for the five prosthesis-implanted mice. The MLI values in the remaining right lungs were significantly greater as well. Using these parameters, the internal lung surface area was calculated and was found to be significantly smaller in the prosthesis-implanted mice.
After watching this video, you should have a good understanding of how to calculate the internal lung surface area for the mechanical force-induced alveolar regeneration mouse model.
