High-Mobility Group Box 1 Promotes Metalloproteinase-9 Upregulation Through Toll-Like Receptor 4 After Cerebral Ischemia

Background and Purpose—HMGB1 is a nuclear protein and an alarmin that signals cell damage in response to injury. It is believed that after release from injured cells, HMGB1 binds to its receptors to stimulate cross-talk among cells and to drive components of the inflammatory cascade. This study was intended to investigate the role of extracellular HMGB1 in ischemic stroke by examining the response of the zymogen matrix metalloproteinase-9 (MMP-9) to HMGB1 in vivo and in vitro. Methods—Toll-like receptor 2 (TLR2), TLR4, receptor for advanced glycation endproducts (RAGE), and MMP-9 expression was examined using quantitative RT-PCR in primary cultured neurons, astrocytes, and mouse brain after HMGB1 addition. MMP-9 expression/activity was examined using zymography. Middle cerebral artery occlusion was induced for 60 minutes using a filament model. Results—TLR4 is constitutively expressed in neurons, astrocytes, and mouse brain. HMGB1 addition to neuronal and glial cell cultures caused MMP-9 upregulation in a...