TAK1 And Akt Serve As Potential Therapeutic Targets For Early Brain Injury After Subarachnoid Hemorrhage

Background and aims:Subarachnoid hemorrhage(SAH)is associated with high rates of morbidity and mortality around the world.Accumulating evidence suggests that early brain injury(EBI),which occurs within the first 72 h after SAH,plays a pivotal role in poor prognosis of patients after SAH.Unfortunately,treatment options are limited as no effective therapeutic intervention has been identified thus far.In order to design new effective treatment strategies for SAH and improve outcome in subarachnoid hemorrhage,the pathophysiology of the development and progression of SAH brain injury should be studied extensively.Multiple signaling pathways which activated within minutes after the initial bleeding are identified to contribute to early brain injury(EBI).Among them,the activation of mitogen-activated protein kinases(MAPKs)and nuclear factor NF-?B(NF-?B)exacerbate SAH injury by provoking proapoptotic and proinflammatory cellular signaling.TGF?-activated kinase 1(TAK1)which can simultaneously activate the NF-?B and MAPK signaling pathways,is supposed to be involved in EBI.However,the role of TAK1 in EBI following SAH is still to be elucidated.Thus,the first part of our studies is aimed to evaluate the role of TAK1 in EBI after SAH.Furthermore,a number of experimental studies have demonstrated that Akt also plays an important role in EBI.More specifically,the acute activation of Akt in the brain confers protection against EBI and deactivation of Akt contributes to pathogenesis of EBI.These results indicate that Akt selective activator SC79 might be a valid target in chilinical treatment in paitenst after SAH.Thus,in the second part of our studies,we evaluated the possible neuroprotective effect of Akt specific activator SC79 in an experimental rat model of SAH.Methods:SAH was induced by injecting 300 ?l of blood into the prechiasmatic cistern.In the first experiment,the cellular location and expression level of TAK1 in the basal temporal lobe following SAH were evaluated,we also evaluated the expression of phosphorylated TAK1.Then,TAK1 selective inhibitor 5Z-7-oxozeaenol(OZ)was injected through intracerebroventricular(ICV)to evulate the role of TAK1 in EBI after SAH.In the second experiment,Akt specific activator SC79 was injected through ICV or intraperitoneal injection(IP)to evulate its neuroprotective roles and mechanisms in EBI after SAH.Results:In the first part of the experiment,the results showed that the expression levels of TAK1 and phosphorylated TAK1(Ser 439)did not present significant alternation in the basal temporal lobe after SAH,however,the expression of phosphorylated TAK1(Thr187)increased at 12 h after SAH,reaching its peak at 24 h post SAH.As compared with vehicle-treated group,ICV(10 min post-SAH)injection of a selective TAK1 inhibitor OZ,significantly reduced the levels of TAK1 and p-TAK1(Thr187)at 24 h post SAH.Involvement of MAPKs and NF-?B signaling pathways was revealed that OZ inhibited SAH-induced phosphorylation of p38 and JNK,the degradation of the NF-?B inhibitor I?Ba and nuclear translocation of NF-?Bp65.Further,OZ administration diminished the SAH-induced apoptosis and EBI.As a result,neurological deficits caused by SAH were reversed.In the second part of the experiment,ICV injection of SC79(30 min post-SAH)induced the p-Akt(Ser 473)expression in a dose-dependent manner,with the maximum effective dose at 100 ?g per rat.As compared with vehicle-treated group,a single ICV dose treatment of SC79(100 ?g/rat)significantly increased the expression of Bcl-2 and p-GSK-3?(Ser 9),decreased the protein levels of Bax,cytoplasm cytochrome c,and cleaved caspase 3,and reduced the number of apoptotic cells.Moreover,SC79 treatment significantly alleviated SAH-induced oxidative stress and improved neurological deficits.Strikingly,treatment of SC79 provided a beneficial outcome against neurologic deficit with a therapeutic window of at least 4 h post SAH by ICV injection.Lastly,SC79 exerted its neuro-protective at 30 min post SAH by IP injectionConclusion Modulation of TAK1 and Akt activity alleviate EBI via reducing cell apoptosis following SAH.Thus,TAK1 might be a promising new molecular target for the treatment of EBI after SAH.Furthermore,these data provide a basic platform to consider OZ and SC79 as novel therapeutic agents for EBI following SAH.