Gene expression profiling of intracranial aneurysms

The rupture of intracranial aneurysm (IA) causes subarachnoid hemorrhage associated with high morbidity and mortality. We compared gene expression profiles in aneurysmal domes between unruptured IAs (UIAs) and ruptured IAs (RIAs) to elucidate biological mechanisms predisposing to the rupture of IA. We determined gene expression levels of eight RIAs, five UIAs, and 10 superficial temporal arteries (STAs) with the Agilent microarrays. To explore biological heterogeneity of IAs, we classified the samples into subgroups showing similar gene expression patterns by using clustering methods. The clustering analysis identified four groups: STAs and UIAs were aggregated their own clusters, whereas RIAs segregated into two distinct subgroups (early and late RIAs). By comparing gene expression levels between early RIAs and UIAs, we identified 430 up-regulated and 617 down-regulated genes in early RIAs. The up-regulated genes were associated with inflammatory and immune responses and phagocytosis including S100/calgranulin genes (S100A8, S100A9, and S100A12). The down-regulated genes suggest mechanical weakness of aneurysm walls. The expressions of Krüppel-like family of transcription factors (KLF2, KLF12, and KLF15), which were anti-inflammatory regulators, and CDKN2A, which was located on chromosome 9p21 that was the most consistently replicated locus in genome-wide association studies of IA, were also down-regulated. We demonstrate that gene expression patterns of RIAs were different according to age of the patients. The results suggest that macrophage-mediated inflammation is a key biological pathway for IA rupture. The identified genes can be good candidates for molecular markers of rupture-prone IAs and therapeutic targets. We determined gene expression levels of 8 ruptured intracranial aneurysms (RIAs) (5 early and 3 late RIAs), 5 unruptured intracranial aneurysms (UIAs), and 10 superficial temporal arteries (STAs).