This video shows two models of intimal plaque development in murine arteries and emphasizes the differences in myointimal hyperplasia and atherosclerosis.
Various in vivo laboratory rodent models for the induction of artery stenosis have been established to mimic diseases that include arterial plaque formation and stenosis, as observed for example in ischemic heart disease. Two highly reproducible mouse models – both resulting in artery stenosis but each underlying a different pathway of development – are introduced here. The models represent the two most common causes of artery stenosis; namely one mouse model for each myointimal hyperplasia, and atherosclerosis are shown. To induce myointimal hyperplasia, a balloon catheter injury of the abdominal aorta is performed. For the development of atherosclerotic plaque, the ApoE -/- mouse model in combination with western fatty diet is used. Different model-adapted options for the measurement and evaluation of the results are named and described in this manuscript. The introduction and comparison of these two models provides information for scientists to choose the appropriate artery stenosis model in accordance to the scientific question asked.
In industrialized nations ischemic heart disease remains a leading cause of mortality1. The causes for coronary artery stenosis are manifold and include myointimal hyperplasia as well as atherosclerosis, with revascularization remaining the most common treatment strategy2. Research models that clearly distinguish between the mechanistic pathways of intimal hyperplasia and atherosclerosis are essential to investigate the pathobiological and pathophysiological processes in arterial plaque development. In this video two different mouse models used to study either the development of myointimal hyperplasia or atherosclerosis are introduced.
Myointimal hyperplasia is postulated to form via the “response-to-injury” paradigm originally described for atherosclerosis3. The mechanical disruption of the endothelial layer leads to an intense remodeling enhanced by paracrine effects. There are several different animal models commonly used to study myointimal hyperplasia. Some groups use metal devices in the ascending aorta of rats4. The aortic denudation model performed with a balloon catheter is also commonly used in laboratory rats5,6. The intimal hyperplasia model performed in laboratory mice7 implements ligation of the carotid artery and induces myointimal lesions8. In our lab, the abdominal aortic denudation model – to study the development of myointimal hyperplasia – as well as a humanized stent restenosis model9 are commonly used. This video emphasizes that choosing the proper experimental animal model is crucial for mechanistic or pathophysiologic studies of arterial stenosis.
Myointimal hyperplasia models must be distinguished from atherosclerosis models. For the latter, apolipoprotein E-deficient (ApoE -/-) mice in combination with western diet are commonly used to induce atherosclerotic lesions10,11,12,13. Examples for the induction of both of these types of myointimal disease in mice are shown here, along with different model-adapted options to analyze vessel stenosis14.
All animal work should be carried out according to relevant animal care guidelines. Obtain institutional approval for animal work prior to beginning protocol.
1. Myointimal Hyperplasia Model (A)
For the intimal hyperplasia model, purchase C57BL/6J (Stock number 000664, C57BL/6J) mice at the age of 8 weeks weighing approximately 25 g. House mice for these experiments under conventional conditions; feed mice standard mouse chow and provide water ad libitum.
2. Atherosclerosis Model (B)
For the atherosclerosis model, purchase apolipoprotein E-deficient (ApoE -/-) mice (Stock number 002052, B6.129P2-Apoetm1Unc/J) at an age of 4 weeks, and then fed for 4-6 months. House mice for these experiments under conventional conditions; feed mice high lipid western diet upon arrival (Harlan Laboratories TD.88137) and provide water ad libitum for a duration of 4 to 6 months.
3. Analysis
Figure 1 shows different analysis options and the induced disease state for both models. For the intimal hyperplasia model, the analysis of representative cross sections in trichrome staining is shown. From these cross sections, results like I/M ratios, maximum plaque thickness, maximum intimal thickness in the lumen, luminal obliteration in percent, as well as plaque area can be measured and calculated.
To evaluate the outcome of the atherosclerosis model, all methods named above can be used. In addition, the quantitative plaque area in the abdominal aorta, the extent of plaque formation at the aortic valve, the aortic arch, and the descending aorta can be measured via trichrome staining.
Figure 1. Denuded mouse aortas are harvested, paraffin embedded, and a representative cross section is shown in trichrome staining (A). I/M ratios are calculated on trichrome stained sections by measuring intima and media thickness using computer analysis followed by calculation of the ratio (B). Maximum plaque thickness is measured as the maximum intimal thickness in the lumen by computer morphometry (B). Luminal obliteration (in percent) is determined by subtracting the new inner lumen from the former lumen, divided by the former lumen, multiplied by 100% (C). The plaque area is assessed by subtracting the new inner lumen from the former lumen (C). The descending aorta, opened longitudinally with lipophilic structures and stained with Sudan red is shown (D). To determine the quantitative plaque area, Sudan red stained lesions as well as the total aortic area, are measured and analyzed using image analysis software. Cross sections of paraffin embedded samples of the aortic valve, the aortic arch, and the descending aorta in trichrome are depicted (E). Luminal obliteration, plaque area, and maximum plaque thickness are calculated as described above. Please click here to view a larger version of this figure.
Although both diseases result in similar symptoms in the patient, the underlying mechanisms of plaque development and therefore the treatment approaches are very different2. In different forms of arterial stenosis the clinical findings in the patients as well as the timeframe of plaque development depend on the underlying mechanism.
Depending on the clinical findings in the patient, different methods of sample analysis must be performed5,15. It is necessary to adapt the analysis to the characteristic findings in the disease that is being mimicked by the chosen model14. Vice versa, depending on the disease being studied, the most feasible and appropriate animal model should be chosen. Moreover, it is crucial that new drugs should mechanistically match the model.
Both models introduced in this publication are quick and easy to perform and highly reproducible. There are some major differences between the models. For example, the observation time in the myointimal hyperplasia model is 28 days16, while atherosclerotic plaque development needs four to six months17.
Another major difference is the applicability to different mouse strains. The atherosclerosis model relies on the ApoE -/- or LDL -/- in mice and can therefore only be performed in mice carrying this specific knockout. To create mice carrying both the ApoE -/- and another desired knockout is very time consuming. The myointimal hyperplasia inducing balloon injury surgery can be performed in any mouse. The myointimal hyperplasia model yields more potential to modify the mouse strain of interest, while the atherosclerotic model faces a strict limitation to mice carrying the ApoE -/-.
The intensity of balloon denudation is crucial for the outcome of the myointimal hyperplasia lesions. If the catheter injury is performed too aggressively, aneurysm formation might occur; if the denudation is performed too gently, plaque development might be too weak to see differences between groups. In this procedure it is helpful if all surgeries within one study are performed by the same person. The advantage of the balloon injury towards other techniques that require the introduction of stiff or sharp obstacles like wires, is the flexibility as well as the option to adjust the size and pressure of the balloon via the inflation of the balloon-tipped catheter. Furthermore the uninflated balloon-tipped catheter is thin and can be inserted into the aorta via a relatively small incision compared to thicker, more rigid denudation tools. For the atherosclerotic plaque formation model it can be crucial to start feeding the western diet at a young age of the mice because that can have a large impact on the severity of the lesions. Since lesions in both introduced models develop in both female and male mice, the gender can be adapted to the requirements of the experiment.
The authors have nothing to disclose.
The authors thank Christiane Pahrmann for technical assistance. S.S. received funding from the Deutsche Forschungsgemeinschaft (DFG) (SCHR992/3-2 and SCHR992/4-2).
Name | Company | Catalog number | Comments |
Thyoglycollate Broth 3% | Fluka | 70157 | powder |
PFA 4% | Electron Microscopy Sciences | #157135S | 20% |
Sudan III staining solution | Sigma Aldrich | S4131 | powder |
mouse C57BL/6J | Jackson Laboratories | Stock # 0006664 | |
mouse ApoE-/- | Jackson Laboratories | Stock #002052 | |
Western Diet | Harlan Laboratories | TD.88137 | |
hair clipper | WAHL | 8786-451A ARCO SE | |
Forene | Abbott | Isoflurane | |
microsurgical clamp | Fine Science Tools | 18055-04 | Micro-Serrefine – 4mm |
clamp applicator | Fine Science Tools | 18056-14 | |
catheter | |||
10-0 prolene suture | Ethicon | 788G | |
6-0 prolene suture | Ethicon | 8709H | |
5-0 prolene suture | Ethicon | EH7229H | |
Rimadyl | Pfizer | Carprofen | |
Metacam 1.5mg/ml | Boehringer Ingelheim | Metamizol |