INVOLVEMENT OF P38 MAPK IN REACTIVE ASTROGLIOSIS INDUCED BY ISCHEMIC STROKE

Purpose: Reactive astrogliosis is an important response during early phase of cerebral ischemia but as time progresses; these activated astrocytes develop into a glial scar. During acute phase of ischemia, astrocyte activation is beneficial as it limits the spread of infarct however in long term the glial scar developed becomes a barrier to migrating axons and hinder the recovery process. The hallmark of astrogliosis is an increase in the expression of GFAP (Glial fibrillary acidic protein). However the signaling events underlying these phenomenons have not been yet clearly elucidated. p38MAPK, a stress signaling Mitogen activate protein kinase plays an essential role in inflammation and has been widely reported to be activated during ischemic injury. Since inflammation is major determinant of events after ischemic injury in brain, we hypothesize that p38 MAPK plays a critical role in reactive astrogliosis after ischemic injury and its inhibition attenuates glial scar formation Methods: For in vitro studies rodent primary astrocytes were used and were subjected to Oxygen-glucose deprivation (OGD) for 3h. p38MAPK's role in astrocyte activation was determined pharmacologically with a p38 inhibitor (SB 239063) and genetically by an astrocyte specific p38 knockout. 24 hours following insult and the expression of GFAP was determined using Western blots. Wound healing and Transwell assay were used to determine role of P38 in astrocyte migration. For in vivo studies astrocyte specific conditional p38 knockout mice (p38KO) were used. Transient or Permanent middle cerebral artery occlusion (tMCAO or pMCAO) was performed to model ischemic stroke. Walk initiation, Negative geotaxis and Ladder rung walking test were used to determine motor dysfunction after MCAO. Astrogliosis morphometric analysis was to quantify glial scar in GFAP stained brain sections Results: In primary astrocyte cultures, hypoxia and scratch injury-induced astrogliosis was attenuated by both p38 inhibition and knockout of p38 MAPK. In vivo studies showed that p38KO mice after permanent MCAO had a significantly smaller glial scar compared to their wild type (WT) littermates. Results also indicated that p38KO mice performed significantly better in behavioral studies compared to their WT only in tMCAO Conclusions: p38MAPK plays an essential role in evolution of glial scar after ischemia and its inhibition attenuates glial scar formation. P38 inhibition significantly improves motor dysfunction in tMCAO but the protection is lost in pMCAO