The time course of elastin fiber degeneration in a rat aneurysm model

Ectodermal origin and tissue dedifferentiation in the podocyst production by the polyps of the Asian moon jelly (Aurelia coerulea)

The histological origin of podocysts in scyphozoans has long been undetermined, with uncertainty whether they arise from mesenchymal amoebocytes or stalk and pedal disc ectoderm in polyps. Histological investigation on the pedal disc was difficult due to the settlement of polyps on hard substrates. In this study, we investigated the histological characteristics of polyps during podocyst production in Asian moon jelly (Aurelia coerulea) with utilizing those attached on thin polystyrene substrates. Fine histological features of the pedal disc became possible after the substrates were decomposed during histological processing. Our findings unequivocally demonstrate that the cell mass of podocysts originates from the ectoderm of the pedal disc and the stalk without the involvement of amoebocytes in the mesoglea. Preceding the podocyst formation, the pedal disc undergoes enlargement facilitated by the elongated stalk ectodermal cells, which attach to a substrate. Subsequently, the pedal disc ectoderm give rise to the primary podocyst cells with accumulating nutrient granules in the cytoplasm and forming the cyst capsule cooperatively with the invaginated pedal disc ectoderm. Direct transformation from the ectodermal cells to podocyst cells suggests that podocyst formation involves tissue dedifferentiation. Throughout the period of podocyst production, the gastrodermis of polyps is physically separated from the ectoderm by the mesoglea and shows no histological changes, and no amoebocytes appear in the mesoglea. These histological properties are totally different from those in other modes of asexual reproduction, which incorporate the endoderm of polyps, suggesting the developmental and evolutionary differences between these asexual reproductions and podocyst production in Scyphozoa.

CD73 deficiency does not aggravate angiotensin II-induced aortic inflammation in mice

Vascular inflammation plays a key role in the development of aortic diseases. A potential novel target for treatment might be CD73, an ecto-5'-nucleotidase that generates anti-inflammatory adenosine in the extracellular space. Here, we investigated whether a lack of CD73 results in enhanced aortic inflammation. To this end, angiotensin II was infused into wildtype and CD73-/- mice over 10 days. Before and after infusion, mice were analyzed using magnetic resonance imaging, ultrasound, flow cytometry, and histology. The impact of age and gender was investigated using female and male mice of three and six months of age, respectively. Angiotensin II infusion led to increased immune cell infiltration in both genotypes' aortae, but depletion of CD73 had no impact on immune cell recruitment. These findings were not modified by age or sex. No substantial difference in morphological or functional characteristics could be detected between wildtype and CD73-/- mice. Interestingly, the expression of CD73 on neutrophils decreased significantly in wildtype mice during treatment. In summary, we have found no evidence that CD73 deficiency affects the onset of aortic inflammation. However, as CD73 expression decreased during disease induction, an increase in CD73 by pharmaceutical intervention might result in lower vascular inflammation and less vascular disease.

Degeneration and Regeneration of Smooth Muscle Cells in Two Different Abdominal Aortic Aneurysm Models in Rabbits

BACKGROUND

We aimed to investigate the formation and self-healing process of rabbit abdominal aortic aneurysm (AAA) by focus on the degeneration and regeneration of smooth muscle cells (SMCs) in elastase-induced AAA model and enlarging AAA model in rabbits.

METHODS

Sixty rabbits were equally divided into 2 aneurysm groups (Group A and Group B). Rabbits received a 10-min incubation of elastase in Group A (10 units/µL) and Group B (1 unit/µL). Rabbits underwent aortic stenosis above the incubated segment in Group B. Aortic diameter was measured and rabbits were sacrificed for histopathological and immunohistochemical studies.

RESULTS

The incubated aorta dilated immediately and ran up to maxima by day 21 in Group A. All aneurysms formed by day 21 and enlarged progressively in Group B. SMCs content, elastin content and intima-media thickness decreased significantly by day 0 in Group A. SMCs and elastic fibers were destroyed gradually in Group B, however, SMCs content was significantly lower than Group A by day 70. Intimal thickness increased significantly by day 70 in the Aneurysm groups. MMP2 maintained moderate expression in Group A, which decreased significantly by day 3 in Group B. MMP9 and RAM11 expressions were higher by day 1, but decreased significantly by day 3 in Group B.

CONCLUSIONS

Irreversible degeneration of SMCs is critical to a rapid formation of elastase-induced rabbit AAA model, and SMCs excessive regeneration accounts for the selfhealing process. SMCs degradation and regeneration remain relatively stable in an enlarging AAA model. SMCs should be the key target for studying the mechanism of AAA and intervention therapy.

Translating mouse models of abdominal aortic aneurysm to the translational needs of vascular surgery

Introduction

Abdominal aortic aneurysm (AAA) is a condition that has considerable socioeconomic impact and an eventual rupture is associated with high mortality and morbidity. Despite decades of research, surgical repair remains the treatment of choice and no medical therapy is currently available. Animal models and, in particular, murine models, of AAA are a vital tool for experimental in vivo research. However, each of the different models has individual limitations and provide only partial mimicry of human disease. This narrative review addresses the translational potential of the available mouse models, highlighting unanswered questions from a clinical perspective. It is based on a thorough presentation of the available literature and more than a decade of personal experience, with most of the available models in experimental and translational AAA research.

Results

From all the models published, only the four inducible models, namely the angiotensin II model (AngII), the porcine pancreatic elastase perfusion model (PPE), the external periadventitial elastase application (ePPE), and the CaCl₂ model have been widely used by different independent research groups. Although the angiotensin II model provides features of dissection and aneurysm formation, the PPE model shows reliable features of human AAA, especially beyond day 7 after induction, but remains technically challenging. The translational value of ePPE as a model and the combination with β-aminopropionitrile to induce rupture and intraluminal thrombus formation is promising, but warrants further mechanistic insights. Finally, the external CaCl₂ application is known to produce inflammatory vascular wall thickening. Unmet translational research questions include the origin of AAA development, monitoring aneurysm growth, gender issues, and novel surgical therapies as well as novel nonsurgical therapies.

Conclusion

New imaging techniques, experimental therapeutic alternatives, and endovascular treatment options provide a plethora of research topics to strengthen the individual features of currently available mouse models, creating the possibility of shedding new light on translational research questions.

Animal models in the research of abdominal aortic aneurysms development

Abdominal aortic aneurysm (AAA) is a prevalent and potentially life threatening disease. Many animal models have been developed to simulate the natural history of the disease or test preclinical endovascular devices and surgical procedures. The aim of this review is to describe different methods of AAA induction in animal models and report on the effectiveness of the methods described in inducing an analogue of a human AAA. The PubMed database was searched for publications with titles containing the following terms "animal" or "animal model(s)" and keywords "research", "aneurysm(s)", "aorta", "pancreatic elastase", "Angiotensin", "AngII" "calcium chloride" or "CaCl(2)". Starting date for this search was set to 2004, since previously bibliography was already covered by the review of Daugherty and Cassis (2004). We focused on animal studies that reported a model of aneurysm development and progression. A number of different approaches of AAA induction in animal models has been developed, used and combined since the first report in the 1960's. Although specific methods are successful in AAA induction in animal models, it is necessary that these methods and their respective results are in line with the pathophysiology and the mechanisms involved in human AAA development. A researcher should know the advantages/disadvantages of each animal model and choose the appropriate model.

Degradation of elastic fiber and elevated elastase expression in long head of biceps tendinopathy

Tendinopathy of the long head of the biceps (TLHB) involves various types of extracellular matrix degeneration, but previous studies have not evaluated elastic fibers. The purpose of this study was to investigate elastic fiber distribution in long head of the biceps (LHB). The TLHB tendons of 16 consecutive patients (eight men and eight women; average age of 55.75 years; age range of 40-71 years) were transected and harvested. Three cadaveric LHB tendons were used as the control group. The expression of collagen type I was decreased, but type III was increased in TLHB. Disruption of elastic fibers was particularly observed in grade II specimens where the level of elastase-positive staining was significantly higher than in grade I specimens. Elastic fibers were not observed in the grade III area, implying a higher expression of elastase than in the grade I area. Results of Western blotting showed that the expression of elastin was higher in the control group and the levels of elastin significantly decreased in grades II and III of TLHB. Levels of osteopontin and elastase were increased in primary culture of human tenocytes after experiencing elastic derived peptide treatment. These results suggested that elastase may be caused by the disruption of elastic fibers in the development of chronic tendinopathy and that elastic derived peptide may enhance elastase and osteopontin expression. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1919-1926, 2017.

A Novel Modification of the Murine Elastase Infusion Model of Abdominal Aortic Aneurysm Formation

BACKGROUND

To create a novel procedure that will decrease the mortality of experimental animals in the intraarterial infusion of elastase abdominal aortic aneurysm (AAA) model.

METHODS

Novel models were created by means of direct puncture in the infrarenal abdominal aortic aorta, intraluminal elastase in the 1-cm segment of abdominal aorta. Femoral artery cannula approach and infusing with elastase was considered as the traditional group and that infusing with saline solution as the control group. Survival rate, morphology and histology of aneurysms, and inflammation mediators were calculated.

RESULTS

Among the 36 rats, the average length from testicular arteries to left iliolumbar artery was 1.18 ± 0.22 cm, and 77.8% of them were longer than 1 cm. Procedure time was significantly shorter in novel group than that in 2 other groups (P = 0.006; P < 0.0001). During 24 hr postoperation, no death was observed in the novel group. Within 4 wk, survival rate in the control group was 60.6% and 80.8% in the novel group whereas 41.0% in the traditional group. Till the second week, all rats in the traditional and novel group had formed AAAs. And then, the survival rates and rupture rates of AAA between the 2 groups were similar within the following 2 wk (P = 0.487; P = 0.539). Inflammation degree and elastase content in intima media of aneurysms were similar (P = 0.720). However, Tumor necrosis factor alpha and Interleukin-1 beta levels were significantly lower in the novel group than those in the traditional group (P < 0.0001; P < 0.0001).

CONCLUSIONS

A novel rat AAA model was created by intraluminal elastase infusion through direct puncture the infrarenal aorta. This model is efficient and reliable, with a high survival rate and with similar morphology and histology of aortic aneurysms.

Peritendinous elastase treatment induces tendon degeneration in rats: A potential model of tendinopathy in vivo

The purpose of this study was to investigate the role of elastase on tendinopathy, as well as to evaluate the potential for peritendinous injections of elastase into rats to cause tendinopathy. We first investigated the expression of elastase in the tendons of patients with tendinopathy, and then established the effects of elastase injection on the Achilles tendons of rats. Ultrasonographic and incapacitance testing was used to conduct tests for 8 weeks. Tendon tissues were collected for histological observation and protein levels of collagen type I and type III were detected using Western blotting. The percentage of elastase-positive cells increased in human specimens with grades II and III tendinopathy. The rat model demonstrated that the thickness of the tendon increased after elastase injection during Week 2-8. Hypercellularity and focal lesions were detected after Week 2. The expression of elastase was increased and elastin was decreased in Week 8. Collagen type I expression was decreased, but type III was increased in Week 4. These results suggested that elastase may be involved in the development of chronic tendinopathy, and that peritendinous injection of elastase may result in tendinopathy in rats.

Recent Advances in the Development of Experimental Animal Models Mimicking Human Aortic Aneurysms

Aortic aneurysm is a common and life-threatening disease that can cause death from rupture. Current therapeutic options are limited to surgical or endovascular procedures because no pharmacological approaches have been proven to decrease the chance of expansion or rupture. The best approach to the management of aortic aneurysm would be the understanding and prevention of the processes involved in disease occurrence, progression, and rupture. There is a need for animal models that can reproduce the pathophysiological features of human aortic aneurysm, and several such models have been studied. This review will emphasize recent advances in animal models used in the determination of mechanisms and treatments of aortic aneurysms.

Three-dimensional microstructural changes in murine abdominal aortic aneurysms quantified using immunofluorescent array tomography

This study investigated the spatial and temporal remodeling of blood vessel wall microarchitecture and cellular morphology during abdominal aortic aneurysm (AAA) development using immunofluorescent array tomography (IAT), a high-resolution three-dimensional (3D) microscopy technology, in the murine model. Infrarenal aortas of C57BL6 mice (N=20) were evaluated at 0, 7, and 28 days after elastase or heat-inactivated elastase perfusion. Custom algorithms quantified volume fractions (VF) of elastin, smooth muscle cell (SMC) actin, and adventitial collagen type I, as well as elastin thickness, elastin fragmentation, non-adventitial wall thickness, and nuclei amount. The 3D renderings depicted elastin and collagen type I degradation and SMC morphological changes. Elastin VF decreased 37.5% (p<0.01), thickness decreased 48.9%, and fragmentation increased 449.7% (p<0.001) over 28 days. SMC actin VF decreased 78.3% (p<0.001) from days 0 to 7 and increased 139.7% (p<0.05) from days 7 to 28. Non-adventitial wall thickness increased 61.1%, medial nuclei amount increased 159.1% (p<0.01), and adventitial collagen type I VF decreased 64.1% (p<0.001) over 28 days. IAT and custom image analysis algorithms have enabled robust quantification of vessel wall content, microstructure, and organization to help elucidate the dynamics of vascular remodeling during AAA development.

Animal models of abdominal aortic aneurysm and their role in furthering management of human disease

Abdominal aortic aneurysm is a common degenerative disorder associated with sudden death due to aortic rupture. Current therapy is limited to open surgical repair of the aorta or endovascular placement of covered stents to exclude the abdominal aortic aneurysm from the circulation. A number of different animal models have been developed in order to study abdominal aortic aneurysm in an effort to advance current management deficiencies. Large animal models have been mostly used to assist in developing novel methods to surgically treat abdominal aortic aneurysms. Small animal models, particularly those developed in rodents, have been employed to further the understanding of the mechanisms involved in abdominal aortic aneurysm in order to identify potential new medical treatments. It is expected that findings from these animal models will contribute importantly to new treatments for human abdominal aortic aneurysm. This review explores the animal models which are used in abdominal aortic aneurysm research and highlights their advantages and disadvantages.

Expression of annexin II in experimental abdominal aortic aneurysms

Annexin II is a receptor of tissue-type plasminogen activator (t-PA). We have previously identified annexin II by immunolocalization in human atherosclerotic abdominal aortic aneurysms (AAAs). To investigate possible interactions between annexin II and AAA development, we examined annexin II mRNA and protein expression in a rat model of experimental AAA. AAAs were induced in rats by transient aortic infusion of elastase. The rats were divided into three groups: a saline-treated control group, a group with 15-min elastase infusion, and a group with 30-min elastase infusion. The 15-min elastase-infused group had smaller aneurysms and more preserved media than the 30-min elastase-infused group. Immunohistochemistry showed that annexin II expression was increased in the thickened intima and media of AAA rats as compared with the media of control rats. Furthermore, annexin II was colocalized with macrophages and smooth muscle cells. Quantitative real-time polymerase chain reaction showed that annexin II mRNA levels were up-regulated only in the smaller aneurysm group compared with the control group. In contrast, t-PA mRNA levels were increased in both the 15- and 30-min elastase-infused groups as compared with the control group. These results demonstrate various levels of annexin II expression within the aortic wall of rats with experimental AAAs. It has been suggested that alteration of fibrinolytic activity regulated by annexin II within the aortic wall may be associated with aneurysm formation.

Aneurysm Growth, Elastinolysis, and Attempted Doxycycline Inhibition of Elastase-induced Aneurysms in Rabbits

PURPOSE

To establish the relationship between elastin degradation and aneurysm growth in New Zealand white rabbit model aneurysms, and to explore the potential for pharmacologic inhibition of elastinolysis and aneurysm growth with use of the matrix metalloproteinase (MMP) inhibitor doxycycline.

MATERIALS AND METHODS

Elastase-induced, saccular aneurysms created in the right common carotid artery in 30 animals randomly divided into controls (n = 16) and doxycycline treated (n = 14) were studied. Aneurysm growth was determined by angiography and aneurysm specimens were collected at 7 and 14 days for histologic and immunohistochemical analysis.

RESULTS

Aneurysms were characterized by marked elastin degradation and thickening of the arterial wall media in the absence of inflammatory cell markers. There was no evidence for expression of MMPs in the aneurysm wall at any time point. Aneurysm formation and growth were not prevented by the systemic administration of doxycycline. Mean aneurysm width increased from 3.1 +/- 0.7 mm at 3 days to 3.7 +/- 0.8 mm at 7 days and 4.2 +/- 0.8 mm at 14 days (P =.012 and P =.017, respectively). There was no statistically significant difference in aneurysm size and elastin content at any time point between doxycycline treated and control animals.

CONCLUSION

Elastase-induced rabbit aneurysm formation is accompanied by total elastin destruction that was not inhibited by the administration of doxycycline. Aneurysms in this model may be caused by the initial infusion of elastase, rather than by ongoing degradation from endogenous proteases released by inflammatory cells.