Name: lung fixation under constant pressure for evaluation of emphysema in mice
Uploaded: 2019-09-26T12:30:00
Description: Watch this Scientific Journal Video about Lung Fixation under Constant Pressure for Evaluation of Emphysema in Mice at JoVE.com

This work was supported in part by JSPS KAKENHI Grant Number 26461199 (T. Sato) and the Institute for Environmental and Gender-Specific Medicine, Juntendo University Graduate School of Medicine, Grant Number E2920 (T. Sato). The funder had no role in the design of the current methods and in writing the manuscript.

The following methods have been approved by the Animal Care and Use Committees of Juntendo University School of Medicine. The Guidelines for Proper Conduct of Animal Experiments, Science Council of Japan, June 1, 2006 were followed. There are three main steps in this method: 1) mouse dissection, 2) lung exsanguination, and 3) fixation of lung tissues assisted by specialized equipment. Typically, lung specimens are processed to embedment after 48 h of fixation12,15</sup...

<ol>
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The fixation procedure for rodent lungs presented here is not novel; however, this system has several advantages. Firstly, it can fix many lungs (maximum of 20) with the same condition at one time. The Society of Toxicologic Pathology states that the pressure for gravity instillation vary from 22&#8211;25 cmH2O22. Notably, several studies have performed lung fixation at a pressure of 25 cmH2O13,19,<sup clas...

COPD is one of the leading worldwide causes of death1. Cigarette smoke is the most important cause of COPD, but the mechanisms of pathogenesis remain incompletely defined. COPD demonstrates two main characteristics, including progressive limitation of airflow and an abnormal inflammatory response of the lung. Emphysematous disorder frequently occurs in the lungs of COPD patients2. The pathological findings of emphysema are characterized by alveolar wall destruction3. Several animal species have been used to generate COPD models in vivo (i.e., dogs, guinea pigs, monkeys, and rodents)4. However, the mouse has become the most commonly used in the construction of COPD models. This has many advantages, including its low cost, ability to be genetically modified, extensive genomic information availability, availability of antibodies, and ability to use a variety of mouse strains5. Presently, there is no mouse model that can mimic the full features of human COPD; thus, individual researchers must choose which model is most suitable for the specific COPD research6. The emphysematous mouse model is one of many COPD mouse models that are currently available. Additional models include the exacerbation mouse model, systemic co-morbidities model, and COPD susceptibility model7.
The emphysematous mouse model can be generated by several types of exogenous agents, including chemical agents and cigarette smoke exposure4. Chemical exposure (e.g., to elastase) produces a severe type of emphysema, while cigarette smoke results in mild emphysema8,9. Cigarette smoke is believed to be the main cause for the pathogenesis of COPD; therefore, the choice of cigarette smoke as a means to create a COPD mouse model is reasonable10. Many studies have used cigarette smoke to create emphysema in the mouse. For example, Nikula et al. successfully created an emphysematous mouse model from B6C3F1 female mice by exposing them to cigarette smoke for 7 or 13 months11. We have also established an emphysematous mouse model via senescence marker protein/SMP-30 KO mice12. It is crucial to perform a lung fixation method that can properly visualize this mild emphysema model by cigarette smoke exposure.
Various methods for lung fixation have been established13. However, there is no gold standard method of lung tissue fixation for evaluating emphysema14. Several studies from this lab have shown that the fixation system presented here is useful by creating a stable condition for evaluating emphysema12,15,16,17,18. The main advantage of the current system is that it can fix many lungs with the same condition at one time without lung collapse or deflation. The current lung fixation system uses some special equipment that allows lung specimens to be inflated at an appropriate constant pressure for a given period. This special equipment consists of three parts, including a lower container, upper container, and pump. Lung specimens are placed in the lower container that is connected to pressurized fixing agents, resulting in a 25 cmH2O pressure difference in the level of agents between the upper and lower containers19.

<table>
	<tbody>
		<tr>
			<td>10% formalin (formalin neutral buffer solution)</td>
			<td>Wako</td>
			<td>060-01667</td>
			<td></td>
		</tr>
		<tr>
			<td>Bent forceps</td>
			<td>Hammacher</td>
			<td>HSC187-11</td>
			<td></td>
		</tr>
		<tr>
			<td>Cannula, size 20G</td>
			<td>Terumo</td>
			<td>SR-FS2032</td>
			<td></td>
		</tr>
		<tr>
			<td>Cannula, size 22G</td>
			<td>Terumo</td>
			<td>SR-OT2225C</td>
			<td>Cannula to exsanguinate lung</td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>Hammacher</td>
			<td>HSC184-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Kimtowel</td>
			<td>Nippon Paper Crecia (Kimberly Clark)</td>
			<td>61000</td>
			<td></td>
		</tr>
		<tr>
			<td>Kimwipe</td>
			<td>Nippon Paper Crecia (Kimberly Clark)</td>
			<td>62011</td>
			<td></td>
		</tr>
		<tr>
			<td>Lower container (acrylic glass material)</td>
			<td>Tokyo Science</td>
			<td>Custom-made</td>
			<td>Pressure equipment component</td>
		</tr>
		<tr>
			<td>Roller pump</td>
			<td>Nissin Scientific Corp</td>
			<td>NRP-75</td>
			<td>Pump machine to exsanguinate lung</td>
		</tr>
		<tr>
			<td>Roller pump RP-2000</td>
			<td>Eyela (Tokyo Rikakikai Co. Ltd)</td>
			<td>160200</td>
			<td>Pressure equipment pump</td>
		</tr>
		<tr>
			<td>Silicone tube &#216; 9 mm</td>
			<td>Sansyo</td>
			<td>94-0479</td>
			<td>Pressure equipment component</td>
		</tr>
		<tr>
			<td>Somnopentyl (64.8 mg/mL)</td>
			<td>Kyoritsu Seiyaku</td>
			<td>SOM02-YA1312</td>
			<td>Pentobarbital Sodium</td>
		</tr>
		<tr>
			<td>Surgical scissor</td>
			<td>Hammacher</td>
			<td>HSB014-11</td>
			<td></td>
		</tr>
		<tr>
			<td>Suture thread, size 0</td>
			<td>Nescosuture</td>
			<td>GA01SW</td>
			<td></td>
		</tr>
		<tr>
			<td>Syringe, 1 mL</td>
			<td>Terumo</td>
			<td>SS-01T</td>
			<td></td>
		</tr>
		<tr>
			<td>Syringe, 1 ml with needle</td>
			<td>Terumo</td>
			<td>SS-01T2613S</td>
			<td></td>
		</tr>
		<tr>
			<td>Syringe, 10 mL</td>
			<td>Terumo</td>
			<td>SS-10ESZ</td>
			<td></td>
		</tr>
		<tr>
			<td>Three-way stopcock</td>
			<td>Terumo</td>
			<td>TS-TR1K01</td>
			<td></td>
		</tr>
		<tr>
			<td>Upper container (acrylic glass material)</td>
			<td>Tokyo Science</td>
			<td>Custom-made</td>
			<td>Pressure equipment component</td>
		</tr>
	</tbody>
</table>

lung fixation under constant pressure for evaluation of emphysema in mice

Emphysema is a significant feature of chronic obstructive pulmonary disease (COPD). Studies involving an emphysematous mouse model require optimal lung fixation to produce reliable histological specimens of the lung. Due to the nature of the lung&rsquo;s structural composition, which consists largely of air and tissue, there is a risk that it collapses or deflates during the fixation process. Various lung fixation methods exist, each of which has its own advantages and disadvantages. The lung fixation method presented here utilizes constant pressure to enable optimal tissue evaluation for studies using an emphysematous mouse lung model. The main advantage is that it can fix many lungs with the same condition at one time. Lung specimens are obtained from chronic cigarette smoke-exposed mice. Lung fixation is performed using specialized equipment that enables the production of constant pressure. This constant pressure maintains the lung in a reasonably inflated state. Thus, this method generates a histological specimen of the lung that is suitable to evaluate cigarette smoke-induced mild emphysema.

As described previously, the specialized equipment, which generates extended constant pressure, can be divided into three parts (Figure 3A). The lower part is the point at which to insert the lung sample (Figure 4A). The lung is connected via a cannula (20 G) to the tip of formalin flow using a three-way stop cock (Figure 4B). Pressure is generated from the different surface levels ...

Watch this Scientific Journal Video about Lung Fixation under Constant Pressure for Evaluation of Emphysema in Mice at JoVE.com

Lung Fixation under Constant Pressure for Evaluation of Emphysema in Mice

Presented here is a useful protocol for lung fixation that creates a stable condition for histological evaluate of lung specimens from a mouse model of emphysema. The main advantage of this model is that it can fix many lungs with the same constant pressure without lung collapse or deflation.

Emphysema is a significant feature of chronic obstructive pulmonary disease (COPD). Studies involving an emphysematous mouse model require optimal lung ...

The constant pressure within the fixation device maintains the lungs in a reasonably inflated state generating a histological lung specimen suitable for evaluating mild cigarette smoke induced emphysema. The main advantage of this model is that it can fix many lungs at the same time using the same constant pressure without lung collapse or deflation. Demonstrating the procedure will be Naoko Arano a graduate student from my laboratory.After confirming a lack of response to reflex motion make an incision in the skin and muscle tissue along the medial line of the mouse, aiming for the cephalic region, and cut laterally to create a wider working space. After exposing the diaphragm layer puncture the tissue with forceps and open the thoracic space. Cut the sternal area allowing the lungs and heart to be visualized.And cut the left atrium and right ventricle. Insert a 24 gauge cannula connected to a perfusion pump into the right ventricle area and direct the cannula to the cephalic area until it reaches the pulmonary artery. Then, turn on the pump and perfuse the tissue with approximately 200 milliliters of PBS for one hour until all of the lung tissue has changed to a white color.At the end of the perfusion cut the connective tissue surrounding the trachea, lungs and heart, and use a suture to tie off the right main bronchus. Next, harvest all of the individual lobes of the right lung and place the heart and lobes of the left lung into individual 10 milliliter syringes containing an appropriate fixative. Retract the plunger creating a vacuum in the syringe to inflate the lungs and remove the lung from the syringe.Insert a 20 gauge cannula into the trachea and use a suture to secure the cannula in place. Connect a one milliliter syringe filled with fixative to the cannula and fill the lung with additional fixative to check for leaks. Be sure that the insertion site was secured to prevent the lung specimen from detaching from the pulmonary board during the fixation.Then transfer the tissue to the lung fixation pressure equipment, removing the sample and tying off the trachea with a knot at the end of the fixation period. The lower component of the lung fixation pressure equipment into which the lung sample is inserted is connected via 20 gauge cannula to the tip of the formalin flow with a three-way stopcock. Pressure is generated from the different surface levels of the fixative between the lower and upper compartments.The pressure difference is 25 centimeters of water but the height adjustment knob can be used to adjust the pressure to between 25 and 30 centimeters of water. A pump connects the lower and upper containers, preserving a 25 centimeter difference in the fixative surface height, and directs the flow of the agent. After 48 hours of fixation the lungs from SMP30 knockout mice exposed to ambient air do not exhibit a marked airspace enlargement.Significant airspace enlargement and alveolar wall destruction, however, are observed in SMP30 knockout mice exposed to chronic cigarette smoke. In addition, the mean linear intercept and destructive index of the lung specimens are significantly greater in the smoke exposed SMP30 knockout mice than in the air exposed animals. Our lab uses 10%formalin but researchers can use other fixation agents according to their experimental needs.As we have reported using the demonstrated fixation system lung samples can be harvested from various mouse emphysema models for their morphometric evaluation. As fixing agents can be hazardous always wear the appropriate personnel protective equipment and work in a well-ventilated room.

Research

JoVE Journal

Medicine

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