LAUSR

Background: Aging is an independent risk factor for the rupture of intracranial aneurysm. One of the hallmarks of aging is chronic tissue inflammation. Sirtuin-1 keeps inflammation in check through the deacetylation of various proteins. It is well known that the levels of Sirtuin-1 in vascular tissues decrease with aging, resulting in chronic vascular inflammation. Age-dependent decrease in Sirtuin-1 may explain the link between aging and increased risk for aneurysmal rupture. Hypothesis: Reduction of Sirtuin-1 promotes aneurysmal rupture by inducing sustained aneurysmal wall inflammation. Methods: First, we assessed the levels of Sirtuin-1 expression in intracranial aneurysm tissues from patients older than 70 y.o. and compared with those from the younger patients (40 to 50 y.o.). Second, using a mouse model, we tested effects of Sirtuin-1 specific activator SRT1720 (15mg/kg/day) and specific inhibitor EX-527 (2.5mg/kg/day) on the development of aneurysmal rupture. In addition, we assessed the mRNA expression of inflammatory cytokines (IL-6, IL-1beta, MCP-1, and MMP-9) in cerebral arteries and aneurysms in mice treated with vehicle, SRT1720, or EX-527. Results: Sirtuin-1 expression levels in intracranial aneurysm tissues from the older patients were lower than those from the younger patients. The pharmacological inhibition of Sirtuin-1 increased rupture rate in mice (vehicle vs. EX-527: 58% vs. 88%, P <0.05). Moreover, the pharmacological activation of Sirtuin-1 reduced rupture rate in mice (vehicle vs. SRT1720: 80% vs. 50%, P <0.05). Levels of IL-6, MMP-9 mRNAs in cerebral arteries were significantly higher in the inhibitor group than in the vehicle group. On the other hand, both mRNA levels were lower in the activator group than in the vehicle group. Conclusions: Our findings suggest that the reduction of Sirtuin-1 promotes aneurysmal rupture via the induction of inflammation. This may explain the increased risk for aneurysmal subarachnoid hemorrhage in the older population. Our findings may become a basis for future studies to develop new therapies that target Sirtuin-1 for the prevention of aneurysmal rupture, especially in older patients.