Central role of neuronal IkappaBalpha kinase (IKK) in cerebral ischemia

The transcription factor NF-kappaB is activated in cerebral ischemia and promotes ischemic neurodegeneration with inflammatory and apoptotic effects. Activation of NF-kappaB is triggered by IkappaB-kinase (IKK) but may also occur independent of IKK. To find out if IKK is critical for damage in cerebral ischemia, we used both genetic and pharmacological aproaches to reduce IKK activity. Mice with floxed IKK-2 allels were crossed with a nestin-Cre line resulting in selective deficiency of IKK-2 in neural cells or with a CaMKII-Cre line resulting in selective deficiency in neurons. Western-blot-analysis of brain tissue was performed to prove the deficiency of IKK-2 protein. Furthermore, we expressed a dominant-negative mutant of IKK-2 in neurons, which inhibits both subunits of IKK. As a pharmacological approach, we injected BMS-345541, a selective inhibitor of IKK, or NaCl 0.9% as control icv at different time points. All mice underwent an occlusion of the distal branches of the middle cerebral artery (MCAO) by coagulation as a model of permanent cerebral ischemia. IKK was rapidly activated after MCAO followed by decrease of total IkappaBα protein. These processes were reduced in mice with genetic inhibition of IKK. We found a significant reduction of infarct size 48 hours after MCAO in all genetically altered mouse lines. Equally, BMS-345541 in different doses reduced the infarct size up to 60% when injected as late as 4.5 hours after MCAO. The neuroprotective effect of BMS-345541 was confirmed when infarct size was measured 2 weeks after MCAO. TUNEL staining evaluated by laser scanning cytometry showed a reduction of apoptotic signs after treatment with BMS-345541. In summary these data clarify the central role of IKK in ischemic brain damage as shown consistently by different genetic and pharmacological approaches. Above all our experiments suggest that IKK is a worthwile drug target in stroke therapy with a promising therapeutic time frame.