Co-induction of αB-crystallin and MAPKAPK-2 in astrocytes in the penumbra after transient focal cerebral ischemia

αB-crystallin (α-BC), a member of the small heat-shock proteins (sHSP), is constitutively expressed in the vertebrate lens and in non-ocular tissues including the central nervous system (CNS). In this study we investigated the expression of α-BC in the rat brain after middle cerebral artery occlusion (MCAO). α-BC transcript and protein were transiently expressed 4 h after MCAO/reperfusion in the pyramidal neurons in the peri-infarct region of the ischemic hemisphere. Beginning 2 days after MCAO, significant α-BC induction appeared in reactive astrocytes in the penumbra, and this induction was sustained for several days. In addition, levels of MAPKAPK-2, one of the α-BC upstream kinases, and its phosphorylated form were upregulated gradually and peaked 4 days after ischemia/reperfusion injury. The immunohistochemical study indicated that α-BC was co-localized with MAPKAPK-2 and p-MAPKAPK-2. Furthermore, p38β MAPK, an upstream kinase of MAPKAPK-2, which has been known to be involved in compensatory responses to stress, was also co-localized with α-BC in the penumbra. Our results suggest that the p38β-dependent α-BC induction in neurons and astrocytes in the penumbra may play an important role in the postischemic brain.