Upregulation of HMGB1 in wall of ruptured and unruptured human cerebral aneurysms: preliminary results

A growing body of evidence suggests that inflammation plays a crucial role in cerebral aneurysm initiation, progression, and rupture. High-mobility group box 1 (HMGB1) is a non-histone nuclear protein that can serve as an alarmin to drive the pathogenesis of inflammatory disease. The purpose of this study was to investigate the expression of HMGB1 in the wall of ruptured and unruptured human cerebral aneurysms. Human cerebral aneurysms (25 ruptured and 16 unruptured) were immunohistochemically stained for HMGB1. As controls, four specimens of the middle cerebral arteries obtained at autopsy were also immunostained. Immunofluorescence double staining was used to determine HMGB1 cellular distribution. HMGB1 was nearly undetectable in the controls. All aneurysm tissues stained positive for HMGB1 monoclonal antibody, and expression of HMGB1 was more abundant in ruptured aneurysm tissue than unruptured aneurysms (p < 0.05). Furthermore, the expression of HMGB1 had no correlation with aneurysm size and time resected after the rupture. HMGB1 nuclear immunoreactivity was colocalized with immunoreactivity of CD3 in T lymphocytes, CD20 in B lymphocytes, CD68 in macrophages, alpha-SMA in smooth muscle cells, and CD31 in endothelial cells. Cytoplasmic HMGB1 localization was also detected in macrophages and T lymphocytes. Taken together, HMGB1 is expressed in the wall of human cerebral aneurysms and is more abundant in ruptured aneurysms than in unruptured ones. These data indicate a possible role of HMGB1 in the pathophysiology of human cerebral aneurysms.