Name: quantification of atherosclerosis in mice
Uploaded: 2019-06-12T15:00:00
Duration: 6 min 59 s
Description: Watch this Scientific Journal Video about Quantification of Atherosclerosis in Mice at JoVE.com

We thank all past members of G&#246;ran K Hansson&#8217;s experimental cardiovascular research unit that helped develop this protocol over the past quarter-century. We are particularly grateful for the contributions by Antonino Nicoletti, Xinghua Zhou, Anna-Karin Robertson, and Inger Bodin. This work was supported by project grant 06816 and Linnaeus support 349-2007-8703 from the Swedish Research Council, and by grants from the Swedish Heart-Lung Foundation, Stockholm County Council, Professor Nanna Svartz foundation, Loo and Hans Osterman Foundation for Medical Research, Karolinska Institutet&#8217;s Research Foundation and Foundation for Geriatric Diseases at Karolinska Institutet.

<ol>
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F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunostaining+of+Lymphocytes+in+Mouse+Atherosclerotic+Plaque.">Immunostaining of Lymphocytes in Mouse Atherosclerotic Plaque.</a> Methods in Molecular Biology. 1339, 149-159 (2015).</li><li>Gistera, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transforming+growth+factor-beta+signaling+in+T+cells+promotes+stabilization+of+atherosclerotic+plaques+through+an+interleukin-17-dependent+pathway.">Transforming growth factor-beta signaling in T cells promotes stabilization of atherosclerotic plaques through an interleukin-17-dependent pathway.</a> Science Translational Medicine. 5 (196), (2013).</li><li>Gistera, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-Density+Lipoprotein-Reactive+T+Cells+Regulate+Plasma+Cholesterol+Levels+and+Development+of+Atherosclerosis+in+Humanized+Hypercholesterolemic+Mice.">Low-Density Lipoprotein-Reactive T Cells Regulate Plasma Cholesterol Levels and Development of Atherosclerosis in Humanized Hypercholesterolemic Mice.</a> Circulation. 138 (22), 2513-2526 (2018).</li><li>Daugherty, A., Whitman, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+atherosclerosis+in+mice.">Quantification of atherosclerosis in mice.</a> Methods in Molecular Biology. 209, 293-309 (2003).</li><li>Baglione, J., Smith, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+assay+for+mouse+atherosclerosis+in+the+aortic+root.">Quantitative assay for mouse atherosclerosis in the aortic root.</a> Methods in Molecular Biology. 129, 83-95 (2006).</li><li>Schiller, N. K., Kubo, N., Boisvert, W. A., Curtiss, L. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+gamma-irradiation+and+bone+marrow+transplantation+on+atherosclerosis+in+LDL+receptor-deficient+mice.">Effect of gamma-irradiation and bone marrow transplantation on atherosclerosis in LDL receptor-deficient mice.</a> Arteriosclerosis, Thrombosis, and Vascular Biology. 21 (10), 1674-1680 (2001).</li><li>Naghavi, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+vulnerable+plaque+to+vulnerable+patient:+a+call+for+new+definitions+and+risk+assessment+strategies:+Part+I.">From vulnerable plaque to vulnerable patient: a call for new definitions and risk assessment strategies: Part I.</a> Circulation. 108 (14), 1664-1672 (2003).</li><li>Seijkens, T. T. 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The authors have nothing to disclose.

Cardiovascular disease is the main killer in the world and new preventive measurements are needed2. Mouse models of the disease provide a comprehensive platform for investigation of pathophysiology and experimental treatments13. Reliable lesion size quantification is essential for this approach. However, quantification methods differ between laboratories. Standardization and optimization have been an ongoing process since the 1980&#8217;s13,27,33,34. Aortic roots have emerged as the most popular site to quantify experimental atherosclerosis. Cross-sections of plaques enable comparison of plaque volume between groups. En face preparations are favored for lesion quantification in larger segments of the aorta. The en face method visualizes plaque quantity and enables quantification of plaque area coverage, but do not take plaque thickness in account. The biological relevance for observed differences is substantiated by coherent results at different locations in the vascular tree. Evaluating atherosclerosis development at different locations addresses possible site specific effects. The effect of transplanted hematopoietic cells on atherosclerosis development can be assessed in hypercholesterolemic Ldlr-/- chimeras. However, whole-body irradiation affects the atherosclerosis process with site specific effects. More prominent atherosclerotic lesions are developed in the aortic root, while reduced lesion development is observed in aortic arches35.
Importantly, not only lesion size needs to be addressed in studies of experimental atherosclerosis. Lesion composition is also a key parameter. Several plaque features have been associated with manifestations of the disease in humans36. Serial sectioning of the aortic root leaves several sections available for careful analysis of plaque composition. Plaque rupture in humans is characterized by a thin fibrous cap with few smooth muscle cells, sparse collagen content and signs of inflammation in the plaques36. Although plaque rupture is a rare event in mouse models of atherosclerosis, markers for plaque stability are informative to evaluate. Translational approaches could confirm mechanistic findings from mouse models and uncover important features of human disease31. Inflammatory status of atherosclerotic plaques could be determined by immunohistochemistry staining of VCAM-1, MHC class II, macrophages, and lymphocytes30. Some protocols use longitudinal sections in the coronal plane of the aortic arch or the brachiocephalic artery for measuring atherosclerotic lesion size and composition37. However, this alternative method leaves only few sections to be analyzed, which limits its applications.
An initial critical step in this protocol is the ability to harvest aortas efficiently. Hand-eye coordination under the microscope requires practice and is crucial both for the microdissection and the subsequent pinning of the aortic arch. The next critical step in this protocol is the collection of serial sections from the aortic root. Eighty consecutive sections should be collected for each mouse, which requires both focus and patience. Methodological proficiency could speed up the described processes considerably. Nevertheless, atherosclerotic lesion quantification is still a time-consuming task. New technology, automated handling, and small animal imaging might facilitate quantification of experimental atherosclerosis in the future. The progression of atherosclerosis is slow and most experimental protocols in mouse models take more than four months to complete13. Therefore, aortas need to be collected in an optimized way at study endpoints. This protocol provides a comprehensive guide to harvest aortas efficiently and the proposed processing prepares aortas for multi-purpose use including lesion quantification in aortic root, aortic arch, and brachiocephalic artery. Hopefully the protocol can reduce experimental variability, enhance reliability of results, and lead to findings that will pave the way for new treatments against atherosclerosis.

Cardiovascular disease is the main cause of death in the world with ischemic heart disease and stroke accounting for one in every four deaths1. Most cases are caused by atherosclerosis, a disease characterized by a slow build-up of lipid-laden plaques with signs of chronic inflammation in large- and medium-sized arteries2. The disease usually remains unnoticed over several decades until a rupture or erosion of the plaque elicits an arterial thrombosis that leads to ischemic tissue damage.
A normal artery consists of an intima layer with endothelial cells and sparsely distributed smooth muscle cells, a media layer with smooth muscle cells and elastic lamellae, and a surrounding adventitial layer with loose connective tissue3. An intimal retention of LDL offsets atherosclerosis development4. Accumulation and modification of lipoproteins lead to aggregation and entrapment within the arterial intima5. An inflammatory response is evoked by the trapped and modified lipoproteins6. Endothelial cells start to express adhesion molecules, such as VCAM-1 at sites in the arterial tree with turbulent blood flow, leading to recruitment of circulating monocytes and other leukocytes7. The infiltrating monocytes differentiate into macrophages that engulf lipid with ensuing transformation to macrophage foam cells8.
Atherosclerosis has been studied in mouse models with increasing frequency since the mid-1980s. C57BL/6 is the most commonly used inbred mouse strain for these studies, and it is used as the genetic background for the majority of genetically modified strains9. This strain was established in the 1920&#8217;s10, and its genome was published in 200211. Experiments in mouse models have several benefits: the colonies reproduce fast, housing is space-efficient, and inbreeding reduces experimental variability. The model also allows for genetic manipulations, such as targeted gene deletions and insertion of transgenes. This has led to new pathophysiological understanding of the disease and new therapy targets12.
Wild-type C57BL/6 mice are naturally resistant to atherosclerosis. They have most of the circulating cholesterol in HDL, and complex atherosclerotic lesions are not formed even when fed a high-fat and high-cholesterol diet13. Hypercholesterolemic mice, such as Apoe-/- on the C57BL/6-background, are therefore used as experimental models of atherosclerosis14,15. The lack of ApoE impairs hepatic uptake of remnant lipoproteins and severely perturbs lipid metabolism. In Apoe-/- mice, circulating cholesterol is predominantly in VLDL particles, and the mice develop complex atherosclerotic plaques on a regular chow diet.
Ldlr-/- mice mimic the development of atherosclerosis seen in humans with familial hypercholesterolemia16. The Ldlr-/- mice need a Western type diet to develop atherosclerosis17. Western diet mimics human food intake and usually contains 0.15% cholesterol. The LDL receptor recognizes ApoB100 and ApoE and mediates uptake of LDL particles through endocytosis. LDL receptors are fundamental for liver clearance of LDL from circulation, while LDL receptor expression in hematopoietic cells does not influence this process. This opens the possibility for bone marrow transplantation of Ldlr+/+ cells into hypercholesterolemic Ldlr-/- recipients and assessment of atherosclerosis development. Bone marrow chimeras have commonly been used to study the participation of hematopoietic cells in experimental atherosclerosis. However, bone marrow transplantation could influence the size and composition of atherosclerotic plaques, making interpretation of results ambiguous.
Different variants of Apoe-/- and Ldlr-/- mice with additional genetic alterations have been developed to study specific processes of the disease18. One example is human APOB100-transgenic Ldlr-/- (HuBL) mice that carry the full-length human APOB100 gene19,20. These mice develop hypercholesterolemia and atherosclerosis on a regular chow diet. However, the development of complex atherosclerotic plaques takes at least six months and shorter experimental protocols usually use Western diet21. A large fraction of plasma cholesterol is circulating in LDL particles, which gives HuBL mice a more human-like dyslipidemic lipoprotein profile compared to Apoe-/- and Ldlr-/- mice. HuBL mice also allow studies of human apoB as an autoantigen22.
The mouse models of atherosclerosis develop complex atherosclerotic plaques with shared features of human disease. However, the plaques are fairly resistant to rupture with ensuing myocardial infarction. Atherothrombosis is only sporadically detected and experimentally challenging to assess23,24,25. Special models of plaque rupture have been developed, but the experimental field lacks a reliable and reproducible model for assessment of plaque stabilizing agents.
Quantification of atherosclerosis has been reported in numerous ways in the literature. Recent efforts have tried to standardize experimental design, execution, and reporting of animal studies26. Investigators have different preferences and techniques adapted to their laboratories. Most research projects are also unique in a way that they require some protocol modifications. Due to the multifactorial nature of the disease, optimal controls vary between projects. Local conditions and lack of standardization may cause observed differences in disease development, which hampers advances of the research field. Differences in experimental variability also means that statistical power calculations need to be based on pilot studies under local conditions.
Quantification of atherosclerosis is recommended at several locations in the vascular tree. This protocol describes how to obtain results from the aortic root, the aortic arch, and the brachiocephalic artery in a single mouse, in addition to leaving the rest of the thoracoabdominal aorta for other analyses. En face preparations allow rapid quantification of lipid-laden plaques in the aortic arch. Disease burden in the brachiocephalic artery can also be quantified if the specimens are carefully displayed. The more time consuming cross-sectioning of the aortic root leaves several sections available for detailed evaluation of plaque composition.

<table>
	<tbody>
		<tr>
			<td>Acetone</td>
			<td>VWR Chemicals</td>
			<td>20066.296</td>
			<td>For fixation of sections for immunohistochemistry.</td>
		</tr>
		<tr>
			<td>Black electrical insulation tape (50 mm wide)</td>
			<td>Any specialized retailer</td>
			<td>-</td>
			<td>To create pinning beds for aortic arches.</td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Eppendorf</td>
			<td>5417C</td>
			<td>Benchtop microcentrifuge.</td>
		</tr>
		<tr>
			<td>Cork board</td>
			<td>Any specialized retailer</td>
			<td>-</td>
			<td>For cutting hearts in the preparation to cryomount aortic roots.</td>
		</tr>
		<tr>
			<td>Cryostat</td>
			<td>Thermo Scientific</td>
			<td>Microm HM 560</td>
			<td>For serial cryosectioning of aortic roots.</td>
		</tr>
		<tr>
			<td>Deionized water</td>
			<td>-</td>
			<td>-</td>
			<td>For rinsing and preparation of solutions.</td>
		</tr>
		<tr>
			<td>Digital camera</td>
			<td>Leica Microsystems</td>
			<td>DC480</td>
			<td>5.1 megapixel CCD for high-resolution images of aortic arches and aortic root sections.</td>
		</tr>
		<tr>
			<td>Dissecting scissors (10 cm, straight)</td>
			<td>World Precision Instruments</td>
			<td>14393</td>
			<td>For general dissection of organs.</td>
		</tr>
		<tr>
			<td>Dumont forceps #5 (11 cm, straight)</td>
			<td>World Precision Instruments</td>
			<td>500341</td>
			<td>For microdissection of aorta.</td>
		</tr>
		<tr>
			<td>Ethanol 70% (v/v)</td>
			<td>VWR Chemicals</td>
			<td>83801.290</td>
			<td>Highly flammable liquid and vapour, store in a well-ventilated place, and keep cool.</td>
		</tr>
		<tr>
			<td>Ethanol absolute &#8805;99.8%</td>
			<td>VWR Chemicals</td>
			<td>20821.310</td>
			<td>Highly flammable liquid and vapour, store in a well-ventilated place, and keep cool.</td>
		</tr>
		<tr>
			<td>Formaldehyde 4% stabilised, buffered (pH 7.0)</td>
			<td>VWR Chemicals</td>
			<td>9713.1000</td>
			<td>Harmful by inhalation, in contact with skin and if swallowed.</td>
		</tr>
		<tr>
			<td>ImageJ</td>
			<td>NIH</td>
			<td>-</td>
			<td>Image analysis software.</td>
		</tr>
		<tr>
			<td>Iris forceps (10 cm, curved, serrated)</td>
			<td>World Precision Instruments</td>
			<td>15915-G</td>
			<td>Used as anatomical forceps.</td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Merck</td>
			<td>1096341011</td>
			<td>Flammable liquid, causes serious eye irritation, and may cause drowsiness or dizziness.</td>
		</tr>
		<tr>
			<td>Kaiser&#39;s glycerol gelatine</td>
			<td>Merck</td>
			<td>1092420100</td>
			<td>Aqueous mounting medium containing phenol. Suspected of causing genetic defects.</td>
		</tr>
		<tr>
			<td>Light microscope</td>
			<td>Leica Microsystems</td>
			<td>DM LB2</td>
			<td>For analysis during sectioning and documentation of Oil Red O stained micrographs.</td>
		</tr>
		<tr>
			<td>Mayer&#39;s hematoxylin</td>
			<td>Histolab</td>
			<td>1820</td>
			<td>Non-toxic staining solution without chloral hydrate, but causes serious eye irritation.</td>
		</tr>
		<tr>
			<td>Mayo scissors (17 cm, straight)</td>
			<td>World Precision Instruments</td>
			<td>501751-G</td>
			<td>For general dissection.</td>
		</tr>
		<tr>
			<td>Micro Castroviejo needle holder (9 cm, straight)</td>
			<td>World Precision Instruments</td>
			<td>503376</td>
			<td>For pinning of aortic arches.</td>
		</tr>
		<tr>
			<td>Microcentrifuge tubes</td>
			<td>Corning</td>
			<td>MCT-175-C</td>
			<td>Polypropylene microtubes with snaplock cap.</td>
		</tr>
		<tr>
			<td>Microlance 3 needles, 23 gauge</td>
			<td>BD</td>
			<td>300800</td>
			<td>For blood collection.</td>
		</tr>
		<tr>
			<td>Microlance 3 needles, 27 gauge</td>
			<td>BD</td>
			<td>302200</td>
			<td>For perfusion of mice.</td>
		</tr>
		<tr>
			<td>Microvette 500 &#181;L, K3 EDTA</td>
			<td>Sarstedt</td>
			<td>20.1341.100</td>
			<td>For blood collection.</td>
		</tr>
		<tr>
			<td>Microvette 500 &#181;L, Lithium Heparin</td>
			<td>Sarstedt</td>
			<td>20.1345.100</td>
			<td>For blood collection.</td>
		</tr>
		<tr>
			<td>Minutien insect pins, 0.10 mm</td>
			<td>Fine Science Tools</td>
			<td>26002-10</td>
			<td>For pinning of aortic arches.</td>
		</tr>
		<tr>
			<td>Oil Red O</td>
			<td>Sigma-Aldrich</td>
			<td>O0625</td>
			<td>Not classified as a hazardous substance or mixture.</td>
		</tr>
		<tr>
			<td>Optimum cutting temperature (OCT) cryomount</td>
			<td>Histolab</td>
			<td>45830</td>
			<td>For embedding tissue.</td>
		</tr>
		<tr>
			<td>Parafilm M</td>
			<td>Bemis</td>
			<td>PM992</td>
			<td>Paraffin wax film used to create pinning beds for aortic arches.</td>
		</tr>
		<tr>
			<td>Petri dishes (100x20 mm)</td>
			<td>Any cell culture supplier</td>
			<td>-</td>
			<td>Proposed as a storage container for pinned aortas.</td>
		</tr>
		<tr>
			<td>Phosphate buffered saline (PBS)</td>
			<td>-</td>
			<td>-</td>
			<td>Sterile and RNase-free solution is required for perfusion of mice.</td>
		</tr>
		<tr>
			<td>Qualitative filter paper (grade 1001)</td>
			<td>Munktell</td>
			<td>120006</td>
			<td>For filtering Oil Red O working solution (typical retention 2-3 &#181;m).</td>
		</tr>
		<tr>
			<td>RNAlater RNA stabilization reagent</td>
			<td>Qiagen</td>
			<td>76106</td>
			<td>For stabilization of RNA in tissue samples</td>
		</tr>
		<tr>
			<td>RNaseZap RNase Decontamination Solution</td>
			<td>Invitrogen</td>
			<td>AM9780</td>
			<td>A surface decontamination solution that destroys RNases on contact.</td>
		</tr>
		<tr>
			<td>Scalpel handle #3 (13 cm)</td>
			<td>World Precision Instruments</td>
			<td>500236</td>
			<td>For cutting hearts in the preparation to cryomount aortic roots.</td>
		</tr>
		<tr>
			<td>Standard scalpel blade #10</td>
			<td>World Precision Instruments</td>
			<td>500239</td>
			<td>For cutting hearts in the preparation to cryomount aortic roots.</td>
		</tr>
		<tr>
			<td>Stereomicroscope</td>
			<td>Leica Microsystems</td>
			<td>MZ6</td>
			<td>For dissection and en face documentation</td>
		</tr>
		<tr>
			<td>Sudan IV</td>
			<td>Sigma-Aldrich</td>
			<td>S4261</td>
			<td>Not classified as a hazardous substance or mixture.</td>
		</tr>
		<tr>
			<td>Superfrost Plus microscope slides</td>
			<td>Thermo Scientific</td>
			<td>J1800AMNZ</td>
			<td>To collect aortic root sections.</td>
		</tr>
		<tr>
			<td>Tissue forceps (15 cm)</td>
			<td>World Precision Instruments</td>
			<td>501741-G</td>
			<td>For general dissection.</td>
		</tr>
		<tr>
			<td>Tissue-Tek cryomolds (10x10x5 mm)</td>
			<td>Sakura</td>
			<td>4565</td>
			<td>For embedding aortic roots in OCT.</td>
		</tr>
		<tr>
			<td>Vannas scissors (8 cm, straight)</td>
			<td>World Precision Instruments</td>
			<td>503378</td>
			<td>For microdissection of aorta.</td>
		</tr>
	</tbody>
</table>

quantification of atherosclerosis in mice

Cardiovascular disease is the main cause of death in the world. The underlying cause in most cases is atherosclerosis, which is in part a chronic inflammatory disease. Experimental atherosclerosis studies have elucidated the role of cholesterol and inflammation in the disease process. This has led to successful clinical trials with pharmaceutical agents that reduce clinical manifestations of atherosclerosis. Careful and well-controlled experiments in mouse models of the disease could further elucidate the pathogenesis of the disease, which is not fully understood. Standardized lesion analysis is important to reduce experimental variability and increase reproducibility. Determining lesion size in aortic root, aortic arch, and brachiocephalic artery are common endpoints in experimental atherosclerosis. This protocol provides a technical description for evaluation of atherosclerosis at all these sites in a single mouse. The protocol is particularly useful when material is limited, as is frequently the case when genetically modified animals are being characterized.

In mouse models of atherosclerosis the most prominent lesions tend to develop in the aortic root and aortic arch. This protocol describes quantification of atherosclerosis in the aortic root, the aortic arch, and the brachiocephalic artery in a single mouse. Measurable lesions in thoracic descending aorta and abdominal aorta are only present in animals with advance disease. In this protocol, these parts are not analyzed for atherosclerotic burden, but saved for subsequent analysis of mRNA levels or other analyses. Serial sections of atherosclerotic lesions in the aortic root are usually displayed in a graph with lesion size on the y-axis and distance to the aortic sinus on the x-axis28. True cross-sections are crucial for lesion size quantification. Oblique sections can overestimate lesion sizes and a tilting of only 20&#176; could overestimate the absolute lesion surface by 15%29. However, calculating the lesion fraction of total vessel area makes the result less sensitive to possible angle differences during sectioning (Figure 4A). An appropriate statistical method to detect differences between groups is usually a regular 2-way analysis of variance (ANOVA). Bonferroni post-tests are then carried out to detect differences at certain levels. Fisher&#39;s least significant difference could also be used as a follow-up test to ANOVA. It reduces the likelihood of type II statistical errors, but do not account for multiple comparisons. In addition, it could be illustrative to calculate area under the curve or the average lesion size per mouse and present the data in a dot plot to further visualize individual variation within the groups (Figure 4B).
Oil Red O is a fat-soluble bright red diazo dye, which stains neutral lipids. Polar lipids in cell membranes are not stained. Oil Red O staining can be performed on fresh, frozen, or formalin-fixed samples, but not on paraffin-embedded samples due to the removal of lipids in the required deparaffinization process. A quantification of lesional lipid accumulation could be performed by color thresholding the Oil Red O positive area of total lesion area (Figure 4C). Hematoxylin produces a blue staining of cell nuclei, which is helpful to visualize plaque morphology. The right and left coronary arteries usually diverge from the aorta around 250 &#181;m from the aortic sinus27, which often coincide with the most prominent lesion sizes. Cross-sections from this region is often displayed as representative results (Figure 4D).
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/59828/59828fig4.jpg" /> 
Figure 4: Atherosclerotic lesions in the aortic root. (A) Twenty-eight weeks old male bone marrow chimeras fed Western diet for eight weeks were evaluated to determine the effect of Smad7-deficient T cells on atherosclerosis development. Experimental Ldlr-/- chimeras received Cd4-Cre+Smad7fl/fl bone marrow and controls received Cd4-Cre+Smad7fl/+ bone marrow. The graph shows quantification of atherosclerotic lesion area from eight consecutive sections, 100 - 800 &#181;m from the aortic sinus displayed as lesion fraction of total vessel surface (Cd4-Cre+Smad7fl/+/Ldlr-/- n=6, Cd4-Cre+Smad7fl/fl/Ldlr-/- n = 9, 2-way ANOVA with Bonferroni&#8217;s post test, graph shows mean &#177;SEM, braces indicate significance level for strain comparison). (B) The combined dot plot and bar graph shows the mean atherosclerotic lesion area from the aortic root sections (Cd4-Cre+Smad7fl/+/Ldlr-/- n=6, Cd4-Cre+Smad7fl/fl/Ldlr-/- n = 9, Student&#8217;s t-test) (C) Fraction of Oil Red O-stained area in the lesions (Cd4-Cre+Smad7fl/+/Ldlr-/- n = 4, Cd4-Cre+Smad7fl/fl/Ldlr-/- n = 6, Student&#8217;s t-test, ns=non-significant) (B-C) Dots represent individual mice and bars show mean &#177;SEM. (D) Representative micrographs showing Oil Red O staining (in red color) of neutral lipids in the aortic root 300 &#181;m from aortic sinus (50x magnification), Scale bar =&#160;500 &#181;m. *p&#160;&#8804; 0.05, ***p&#160;&#8804; 0.001. This figure has been modified from Gister&#229; et al.31. <a href="https://www.jove.com/files/ftp_upload/59828/59828fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Oil Red O could be used for staining of en face prepared aortas, but this protocol uses Sudan IV, another convenient fat-soluble diazo dye. Sudan IV clearly visualizes atherosclerotic plaques in an orange-red color by staining lipids, triglycerides, and lipoproteins. Removing the dark background in representative images of the en face aortic arches could enhance the visual display (Figure 5A). Usually lesion size is normally distributed within groups, allowing statistical testing with Student&#8217;s t-test between groups. A dot plot that shows both individual mice and the mean, which is compared between groups, is an informative way to display the results (Figure 5B-C). Since the variation within groups typically is different between locations in the vascular tree, separate power calculations are usually needed. Unnecessary variation can be avoided by method proficiency and protocol standardization. Obtaining statistically significant results is important, but the biological relevance for an observed difference always needs to be considered as well.
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/59828/59828fig5.jpg" /> 
Figure 5: Atherosclerotic lesions in aortic arch and brachiocephalic artery. (A) Representative en face micrographs of aortic arches with lipid-laden plaques stained with Sudan IV (in orange color) from 20 weeks old mice fed Western diet for ten weeks, visualized together. Scale bar = 2 mm. Human APOB100-transgenic Ldlr-/- (HuBL) mice were used as controls and the experimental group consisted of TCR-transgenic mice with LDL-reactive T cells (BT1) crossbred to HuBL mice. (B) Atherosclerotic lesions in the aortic arch (HuBL n = 10, BT1xHuBL n = 12; Student&#8217;s t-test). (C) Atherosclerotic lesions in the brachiocephalic artery (HuBL n = 8, BT1xHuBL n = 9, Student&#8217;s t-test). (B-C) Dots represent individual mice, bars show mean &#177;SEM. *p&#160;&#8804; 0.05. This figure has been modified from Gister&#229; et al.32. <a href="https://www.jove.com/files/ftp_upload/59828/59828fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Supplemental Figure 1: Alternative organization of slides for serial sections of the aortic root. A simplified systematic slide organization for collection of sections from the aortic root. The collection enables Oil Red O staining for lipids and immunohistochemistry or immunofluorescence staining. Dedicated slides for Picrosirius red staining of collagen are omitted. <a href="https://www.jove.com/files/ftp_upload/59828/2019-JoVE-Figure-S1.eps">Please click here to download this file.</a>

Watch this Scientific Journal Video about Quantification of Atherosclerosis in Mice at JoVE.com

Quantification of Atherosclerosis in Mice

Murine models of atherosclerosis are useful tools to investigate pathogenic pathways on a molecular level, but require standardized quantification of lesion development. This protocol describes an optimized method to determine lesion size in the major arterial vessels including the aortic root, aortic arch, and brachiocephalic artery.

Cardiovascular disease is the main cause of death in the world. The underlying cause in most cases is atherosclerosis, which is in part a chronic ...

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