Expression of thymosin β in the rat brain following transient global ischemia

Thymosin β (Tβ) isoforms play an important role in the organization of the cytoskeleton by sequestering G-actin during development of the mammalian brain. In this study, we examined changes in the expression of Tβ4 and Tβ15 after transient global ischemia. Tβ15 mRNA increased gradually in the dentate gyrus (DG) of the hippocampal formation from 3 h after reperfusion and peaked 9 h later. Similarly, a significant increase in Tβ4 mRNA level was observed in the DG 12 h after reperfusion. Tβ4 and Tβ15 proteins were found in different cell types in control brains; Tβ15 was expressed in a subset of doublecortin (DCX)-positive cells in the DG, whereas Tβ4-IR was observed in DG neurons and nearby microglial cells. After ischemia, Tβ15-IR was found in DG neurons and Tβ4-IR in the reactivated microglial cells. Interestingly, Tβ15-IR accumulated in the nuclei of CA1 neurons, which are vulnerable to ischemic insults. These results suggest that Tβ4 and Tβ15 function in different cellular contexts during ischemia-induced responses.