Astrocyte GGTI-mediated Rac1 prenylation upregulates NF-κB expression and promotes neuronal apoptosis following hypoxia/ischemia

Abstract

Stroke is the fifth leading cause of death for Americans, and about 87% of all strokes are ischemic strokes. Astrogliosis plays a crucial role in the pathophysiology of delayed neuronal death (DND) following ischemic stroke. Here we reported that astrocyte geranylgeranyltransferase I (GGTI)-mediated Rac1 activation up-regulated NF-κB expression and promoted the neuronal apoptosis after oxygen-glucose deprivation followed by oxygen-glucose regeneration (OGD/R). We found that GGTIβ (a specific subunit of GGTI) and NF-κB-p65 levels as determined by Western blot and/or immunofluorescent analysis were significantly up-regulated in the reactive astrocytes both in rat transient middle cerebral artery occlusion (tMCAO) and in cell OGD/R models. The increased expression of GGTIβ and p65 was associated with the DND in the ischemic brain. Inhibiting astrocyte GGTI activity by its specific inhibitor GGTi-2147 treatment reduced the activity of Rac1 (one of substrates for GGTI), down-regulated the expression of p65, and ameliorated the OGD/R-induced neuronal apoptosis. Astrocytes transfected with wild type Rac1, but not the unprenylated Rac1, up-regulated the p65 protein levels and promoted the co-cultured neuronal apoptosis. Furthermore, over-expression of unprenylated Rac1 in astrocytes significantly decreased the neuronal apoptosis. In addition, over-expression of NF-κB-p65 in astrocytes significantly increased the co-cultured neuronal apoptosis under OGD/R condition. Our findings suggest that astrocyte GGTI-mediated Rac1 activation contributed to the DND and that GGTI-Rac1-NF-κB signaling may be a potential target for the therapy of ischemic stroke.

Keywords: Apoptosis; Brain ischemia; Geranylgeranyltransferase I; NF-κB; Rac1; Stroke.