Little is known about the pathology and pathogenesis of the rupture of intracranial aneurysms. For a better understanding of the molecular processes involved in intracranial aneurysm (IA) formation we performed a gene expression analysis comparing ruptured and unruptured aneurysm tissue to a control artery. Tissue samples of six ruptured and four unruptured aneurysms, and four cerebral arteries serving as controls, were profiled using oligonucleotide microarrays. Gene ontology classification of the differentially expressed genes was analyzed and regulatory functional networks and canonical pathways were identified with a network-based computational pathway analysis tool. Real time reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemical staining were performed as confirmation. Analysis of aneurysmal and control tissue revealed 521 differentially expressed genes. The most significantly associated gene ontology term was antigen processing (P=1.64E-16). Further network-based analysis showed the top scoring regulatory functional network to be built around overexpressed major histocompatibility class (MHC) I and II complex related genes and confirmed the canonical pathway "Antigen Presentation" to have the highest upregulation in IA tissue (P=7.3E-10). Real time RT-PCR showed significant overexpression of MHC class II genes. Immunohistochemical staining showed strong positivity for MHC II molecule specific antibody (HLA II), for CD68 (macrophages, monocytes), for CD45RO (T-cells) and HLA I antibody. Our results offer strong evidence for MHC class II gene overexpression in human IA tissue and that antigen presenting cells (macrophages, monocytes) play a key role in IA formation.

We sought to clarify the involvement of caspase-12, a representative molecule related to endoplasmic reticulum (ER) stress-induced cell-death signaling pathways, in neuronal death resulting from ischemia/reperfusion in mice. Transient focal cerebral ischemia (1 h) was produced by intraluminal occlusion of the middle cerebral artery (MCA). We assessed the expression patterns of caspase-12, Bip/GRP78, an ER-resident molecular chaperone whose expression serves as a good marker of ER stress, and caspase-7 by Western blotting and/or immunohistochemistry. Double-fluorescent staining of caspase-12 immunohistochemistry and the terminal deoxynucleotidyl transferase-mediated DNA nick-end labeling (TUNEL) method was performed to clarify the involvement of caspase-12 in cell death. We confirmed that ER stress was induced during reperfusion in our model, as witnessed by up-regulated Bip/GRP78 expression in the MCA territory. Western blot analysis revealed that caspase-12 activation occurred at 5-23 h of reperfusion, and immunoreactivity for caspase-12 was enhanced mainly in striatal neurons on the ischemic side at the same time points. We found the co-localization of caspase-12 immunoreactivity and DNA fragmentation detectable by the TUNEL method. We did not detect the presence of caspase-7 in the ER fraction at the period of caspase-12 cleavage. Our results imply that cerebral ischemia/reperfusion induces ER stress and that caspase-12 activation concurred with ER stress. Caspase-12 seems to be involved in neuronal death induced by ischemia/reperfusion. Caspase-7 is not likely to contribute to the cleavage of caspase-12 in our experimental model.