Protective Effect of Mesenchymal Stem Cells Against the Development of Intracranial Aneurysm Rupture in Mice

Abstract

Background: Mesenchymal stem cells (MSCs) are multipotent stem or stromal cells found in multiple tissues. Intravenous MSC injections have been used to treat various diseases with an inflammatory component in animals and humans. Inflammation is emerging as a key component of pathophysiology of intracranial aneurysms. Modulation of inflammation by MSCs may affect sustained inflammatory processes that lead to aneurysmal rupture.

Objective: To assess the effect of MSCs on the development of aneurysm rupture using a mouse model.

Methods: Intracranial aneurysms were induced with a combination of a single elastase injection into the cerebrospinal fluid and deoxycorticosterone acetate salt-induced hypertension in mice. We administered allogeneic bone marrow-derived MSCs or vehicle, 6 and 9 d after aneurysm induction.

Results: MSC administration significantly reduced rupture rate (vehicle control vs MSCs, 90% vs 36%; P < .05). In cell culture experiments with an MSC and mast cell coculture, MSCs stabilized mast cells through cyclooxygenase-2 (COX-2)-dependent production of prostaglandin E2, thereby reducing the release of proinflammatory cytokines from mast cells. Pretreatment of MSCs with COX-2 inhibitor, NS-398, abolished the protective effect of MSCs against the development of aneurysm rupture.

Conclusion: Intravenous administration of MSCs after aneurysm formation prevented aneurysmal rupture in mice. The protective effect of MSCs against the development of aneurysm rupture appears to be mediated in part by the stabilization of mast cells by MSCs.

Keywords: Intracranial aneurysm; Mesenchymal stem cells; Stroke; Subarachnoid hemorrhage.

FIGURE 1.

A, Experimental protocol. Our previous studies showed that the ability of an experimental agent to reduce aneurysm rupture can be tested by treating mice with the agent from day 6 postaneurysm induction.^,, Therefore, in this study, mesenchymal stem cells (MSCs; 1 × 10⁶ cells in 150 μL PBS) were injected intravenously, 6 and 9 d after aneurysm induction through the jugular vein. B, Incidence of aneurysms and symptom-free survival curve. MSCs: mice received MSCs. NS398: cyclooxygenase-2 (COX-2) inhibitor. C, Symptom-free survival curve. As an exploratory analysis, survival analysis was performed using log-rank test. Mice that did not develop aneurysms were excluded from the survival analysis.

FIGURE 2.

Intracranial aneurysms in the mouse model. Mouse cerebral arteries were visualized by bromophenol blue perfusion. A, No aneurysm. B, Unruptured aneurysm. C, Ruptured aneurysms and subarachnoid hemorrhage.

FIGURE 3.

Mast cell in intracranial aneurysm tissues from the mouse model. A, Representative toluidine staining of mast cells in the aneurysms and adjacent tissues in a mice after aneurysmal induction. B, Mast cell counting. Control: mice that did not receive aneurysm induction surgery or MSC treatment. Vehicle: mice that received aneurysm induction surgery and vehicle treatment. MSC: mice that received aneurysm induction surgery and MSC treatment.

FIGURE 4.

Effect of MSCs on mast cells in coculture. A, Activation of mast cells assessed by TNF-α release. MSCs and prostaglandin E2 (PGE2) suppressed activation of mast cells. Ca: ionophore (calcimycin). *: P < .05 compared to “Mast cell + Ca.” #: P < .05 compared to “Mast cell + DMSO.” B, COX-2 inhibitor (NS398) suppressed the production of the COX-2 inhibitor (NS398) in a dose-dependent manner. *: P < .05 compared to “MSC + vehicle.” C, Effect of the COX-2 inhibitor treatment on the MSCs-induced stabilization of mast cells. MSCs stabilized mast cells and reduced TNF-α release. Treatment with COX-2 inhibitor (NS398) suppressed the stabilizing effect of MSCs. *: P < .05 compared to “Mast cell + Ca.” #: P < .05 compared to “Mast cell + Ca + MSC.”