Smooth Muscle PPARγ Plays a Critical Role in Formation and Rupture of Cerebral Aneurysms in Mice In Vivo

Vascular inflammation plays a critical role in the pathogenesis of cerebral aneurysms. PPARγ protects against vascular inflammation and atherosclerosis, whereas dominant-negative mutations in PPARγ promote atherosclerosis and vascular dysfunction. We tested the role of PPARγ in aneurysm formation and rupture. Aneurysms were induced with a combination of systemic infusion of angiotensin-II and local injection of elastase, in: 1) mice that received the PPARγ antagonist GW9662 or the PPARγ agonist pioglitazone, 2) mice carrying dominant-negative PPARγ mutations in endothelial or smooth muscle cells, and 3) mice that received the Cullin inhibitor MLN4924. Incidence of aneurysm formation, rupture, and mortality were quantified. Cerebral arteries were analyzed for expression of Cullin3, Keap1, Nrf2, NQO-1 and inflammatory marker mRNAs. Neither pioglitazone nor GW9662 altered the incidence of aneurysm formation. GW9662 significantly increased the incidence of aneurysm rupture, whereas pioglitazone tended to decrease the incidence of rupture. Dominant-negative endothelial-specific PPARγ did not alter the incidence of aneurysm formation or rupture. In contrast, dominant-negative smooth muscle-specific PPARγ resulted in an increase in aneurysm formation (p<0.05) and rupture (P=0.05). Dominant-negative smooth muscle-specific PPARγ, but not dominant-negative endothelial-specific PPARγ, resulted in significant decreases in expression of genes encoding Cullin3, Keap1, and Nrf2, along with significant increases in TNF-α, MCP-1, Cxcl1, CD68, MMP-3, -9, and -13. MLN4924 did not alter incidence of aneurysm formation, but increased the incidence of rupture (p<0.05). In summary, endogenous PPARγ, specifically smooth muscle PPARγ, plays an important role in protecting from formation and rupture of experimental cerebral aneurysms in mice.