Caspase-11 mediates ischemia-induced astrocyte death: involvement of endoplasmic reticulum stress and C/EBP homologous protein.

Astrocytes are essential cells for maintaining brain integrity. We have recently shown that the transcription factor C/EBP homologous protein (CHOP), associated with endoplasmic reticulum (ER) stress, plays a key role in the astrocyte death induced by ischemia. Meanwhile, mediators of apoptosis downstream of CHOP in the ER stress-dependent pathway remain to be elucidated. Our aim in this work was to determine whether caspase-11, able to activate apoptotic and proinflammatory pathways, is implicated in ER stress-dependent astrocyte death in ischemic conditions. According to our results, caspase-11 is up-regulated in primary astrocyte cultures following either oxygen and glucose deprivation (OGD) or treatment with the ER-stress inducers thapsigargin and tunicamycin. Moreover, these same stimuli increased caspase-11 mRNA levels and luciferase activity driven by a caspase-11 promoter, indicating that caspase-11 is regulated at the transcriptional level. Our data also illustrate the involvement of ER stress-associated CHOP in caspase-11 regulation, insofar as CHOP overexpression by means of an adenoviral vector caused a significant raise in caspase-11. In turn, caspase-11 suppression with siRNA rescued astrocytes from OGD- and ER stress-induced death, supporting the idea that caspase-11 is responsible for the deleterious effects of ischemia on astrocytes. Finally, inhibition of caspase-1 and caspase-3 significantly reduced astrocyte death, which indicates that these proteases act as death effectors of caspase-11. In conclusion, our work contributes to clarifying the pathways leading to astrocyte death in response to ischemia by defining caspase-11 as a key mediator of the ER stress response acting downstream of CHOP. (c) 2009 Wiley-Liss, Inc.