Abstract

BackgroundIntracranial aneurysm (IA) is a socially important disease due to its high incidence in the general public and the severity of resultant subarachnoid hemorrhage that follows rupture. Despite the social importance of IA as a cause of subarachnoid hemorrhage, there is no medical treatment to prevent rupture, except for surgical procedures, because the mechanisms regulating IA formation are poorly understood. Therefore, these mechanisms should be elucidated to identify a therapeutic target for IA treatment. In human IAs, the presence of inflammatory responses, such as an increase of tumor necrosis factor (TNF)-alpha, have been observed, suggesting a role for inflammation in IA formation. Recent investigations using rodent models of IAs have revealed the crucial role of inflammatory responses in IA formation, supporting the results of human studies. Thus, we identified nuclear factor (NF)-kappaB as a critical mediator of inflammation regulating IA formation, by inducing downstream pro-inflammatory genes such as MCP-1, a chemoattractant for macrophages, and COX-2. In this study, we focused on TNF-alpha signaling as a potential cascade that regulates NF-kappaB-mediated IA formation.ResultsWe first confirmed an increase in TNF-alpha content in IA walls during IA formation, as expected based on human studies. Consistently, the activity of TNF-alpha converting enzyme (TACE), an enzyme responsible for TNF-alpha release, was induced in the arterial walls after aneurysm induction in a rat model. Next, we subjected tumor necrosis factor receptor superfamily member 1a (TNFR1)-deficient mice to the IA model to clarify the contribution of TNF-alpha-TNFR1 signaling to pathogenesis, and confirmed significant suppression of IA formation in TNFR1-deficient mice. Furthermore, in the IA walls of TNFR1-deficient mice, inflammatory responses, including NF-kappaB activation, subsequent expression of MCP-1 and COX-2, and infiltration of macrophages into the IA lesion, were greatly suppressed compared with those in wild-type mice.ConclusionsIn this study, using rodent models of IAs, we clarified the crucial role of TNF-alpha-TNFR1 signaling in the pathogenesis of IAs by inducing inflammatory responses, and propose this signaling as a potential therapeutic target for IA treatment.

Highlights

  • Intracranial aneurysm (IA) is a lesion with a regional bulging of intracranial arteries, usually located at bifurcation sites

  • Increased tumor necrosis factor (TNF)-alpha content in IA lesion in a rat model In this study, we used the rodent model of IAs to examine the contribution of TNF-alpha signaling to IA formation

  • Consistent with these results, the content of TNF-alpha in the intracranial artery, examined by multi-suspension array, was significantly increased in rats with advanced stage IAs three months after aneurysm induction (0 months, 39.4 ± 7.2 pg/mg total protein; 0.5 months, 37.0 ± 4.8 pg/mg total protein; 1 month, 27.3 ± 3.0 pg/mg total protein; 3 months, 75.2 ± 6.1 pg/mg total protein; n = 6 in each group, 0 months compared to 3 months, p = 0.0497; 0.5 months compared to 3 months, p = 0.0497; 1 month compared to 3 months, p = 0.020) (Figure 1B)

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Summary

Introduction

Intracranial aneurysm (IA) is a lesion with a regional bulging of intracranial arteries, usually located at bifurcation sites. Recent experiments using animal models of IAs support the interpretation of human studies that inflammatory responses in intracranial arterial walls regulate IA formation and progression. Despite the social importance of IA as a cause of subarachnoid hemorrhage, there is no medical treatment to prevent rupture, except for surgical procedures, because the mechanisms regulating IA formation are poorly understood. These mechanisms should be elucidated to identify a therapeutic target for IA treatment. Recent investigations using rodent models of IAs have revealed the crucial role of inflammatory responses in IA formation, supporting the results of human studies. We focused on TNF-alpha signaling as a potential cascade that regulates NF-kappaB-mediated IA formation

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