Vasa vasorum formation is associated with rupture of intracranial aneurysms

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OBJECTIVE

Subarachnoid hemorrhage (SAH) has a poor outcome despite modern advancements in medical care. The development of a novel therapeutic strategy to prevent rupture of intracranial aneurysms (IAs) or a novel diagnostic marker to predict rupture-prone lesions is thus mandatory. Therefore, in the present study, the authors established a rat model in which IAs spontaneously rupture and examined this model to clarify histopathological features associated with rupture of lesions.

METHODS

Female Sprague Dawley rats were subjected to bilateral ovariectomy; the ligation of the left common carotid, the right external carotid, and the right pterygopalatine arteries; induced systemic hypertension; and the administration of a lysyl oxidase inhibitor.

RESULTS

Aneurysmal SAH occurred in one-third of manipulated animals and the locations of ruptured IAs were exclusively at a posterior or anterior communicating artery (PCoA/ACoA). Histopathological examination using ruptured IAs, rupture-prone IAs induced at a PCoA or ACoA, and IAs induced at an anterior cerebral artery–olfactory artery bifurcation that never ruptured revealed the formation of vasa vasorum as an event associated with rupture of IAs.

CONCLUSIONS

The authors propose the contribution of a structural change in an adventitia, i.e., vasa vasorum formation, to the rupture of IAs. Findings from this study provide important insights about the pathogenesis of IAs.

ABBREVIATIONS ACA = anterior cerebral artery; ACoA = anterior communicating artery; BA = basilar artery; CCA = common carotid artery; ECA = external carotid artery; EVG = elastica van Gieson; FOV = field of view; IA = intracranial aneurysm; ICA = internal carotid artery; IEL = internal elastic lamina; MPO = myeloperoxidase; MRA = MR angiography; OA = olfactory artery; OVX = ovariectomy; PCoA = posterior communicating artery; RT-PCR = real-time polymerase chain reaction; SAH = subarachnoid hemorrhage; SD = Sprague Dawley; SMA = smooth muscle actin.

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Article Information

Correspondence Tomohiro Aoki: National Cerebral and Cardiovascular Center, Osaka, Japan. tomoaoki@ncvc.go.jp.

INCLUDE WHEN CITING Published online August 16, 2019; DOI: 10.3171/2019.5.JNS19405.

Disclosures This work was supported in part by special coordination funds from the Ministry of Education, Culture, Sports, Science and Technology of Japan and from Astellas Pharma Inc., in the Creation of Innovation Centers for Advanced Interdisciplinary Research Areas (Dr. Aoki); by CREST on Mechanobiology from the Japan AMED (grant no. JP18gm0810006, Dr. Aoki); and by a grant-in-aid for scientific research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (no. 16K10719, Dr. Aoki).

Dr. Narumiya is supported (as was Dr. Aoki until March 31, 2017) by the coordination fund from the Japanese Ministry for Education, Culture, Sports, Science and Technology of Japan and Astellas Pharma Inc., to Kyoto University, and is a scientific advisor to Astellas Pharma.

© AANS, except where prohibited by US copyright law.

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Figures

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    Incidence of SAH, morphological changes of the vasculature, alteration of blood flow, and formation of aneurysms at an ACoA or PCoA after aneurysm induction. A: Cumulative incidence of SAH in 10-week-old female rats with bilateral OVX subjected to ligation of the left CCA, right ECA, and right pterygopalatine artery, and to systemic hypertension by sodium overload (n = 20). B: Morphological changes of the vasculature after aneurysm induction. MRA images were obtained in 10-week old female rats before (pre) and after (post) they were subjected to the surgical manipulations to induce IAs. Arrows and arrowheads indicate an ACoA or PCoA, respectively. Note the remarkable dilation and meandering of a PCoA after surgical manipulation. C: The sequential changes of mean blood flow volume and the velocity of the right ICA and BA. The mean blood flow volume and the velocity of the right ICA and BA were sequentially measured by a phase-contrast MRI analysis before (pre) and 1, 12, and 29 days after the surgical manipulations. All bars show mean ± SEM (n = 4). Statistical analysis was performed using a Kruskal-Wallis test. * p < 0.05. D and E: Macroscopic view of the brain surface and the circle of Willis from rats with unruptured (rupture-prone, D) and ruptured (E) aneurysms. Arrows and arrowheads indicate the IA lesion induced at an ACoA or PCoA, respectively.

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    Abundance of vasa vasorum formation in ruptured IA lesions. The number (left) and area (right) of vasa vasorum in ruptured IAs (n = 16), rupture-prone IAs (n = 16), or IAs induced at ACA-OA bifurcations (n = 10) are shown. All bars indicate mean ± SEM. Statistical analysis was conducted using a Kruskal-Wallis test followed by a Steel test. * p < 0.05.

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    Images demonstrating the predominance of the presence of vasa vasorum and infiltrating macrophages around a rupture site. A: Macroscopic image of the brain surface from rats with SAH. B: Histological examination of ruptured aneurysms by EVG staining (left) and immunohistochemistry (right). Arrows in B indicate the disruption of arterial walls. Bar = 500 μm. C–F: Predominance of the presence of vasa vasorum with α-SMA–positive media, abundant infiltration of CD68-positive macrophages, and MMP-9 production around a rupture site (1). Representative images of immunostaining for CD68 (green, C and D) or MMP-9 (green, E and F) and SMA (red, B–F), of nuclear staining by DAPI, and merged images using sequential sections are shown. Merged images in C–F correspond to the squares (1 and 2) in panel B, right.

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    Upregulation of Fgf2 in rupture-prone aneurysms. Total RNA was purified from IA lesions induced at a PCoA or ACoA (n = 14) as rupture-prone or at an ACA-OA bifurcation (n = 7) as lesions that never rupture and subjected to RT-PCR analysis (left) or digital PCR analysis (dd-PCR; right) to assess expression of Fgf2. Bars indicate mean ± SEM. Statistical analysis was conducted using a Wilcoxon signed-rank test. 2.5.E-03 = 0.0025. * p < 0.05.

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    Histological similarity of vasa vasorum present in ruptured IAs in a human case (left) and a rat model (right). Histological examination of ruptured IAs by EVG staining (A and B) and immunohistochemistry for α-SMA (C and D) are shown in both a human and rat sample. A magnified image of vasa vasorum in the human IA specimen is also shown in the inset. Representative images of immunostaining corresponding to the squares in A and B for α-SMA (red), nuclear staining by DAPI (blue), and merged images are shown in C and D. Bar = 200 μm.

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