Induction and Activation of Protein Kinase Cδ in Hippocampus and Cortex after Kainic Acid Treatment

Abstract

Various isoforms of protein kinase C (PKC), especially the novel PKC subtypes δ, ε, and the atypical subtype PKCζ, are involved in delayed cell death. We studied the expression and late activation of the latter PKC isoforms in comparison with classic PKCα, β, and γ in the brains of rats exposed to systemic kainate injection. The expression of PKCδ mRNA was strikingly upregulated (13-fold) in the cortex and the CA1 and CA3 hippocampal regions on 1 day after kainate administration, whereas PKCζ mRNA was only moderately increased (about 100%) in these three brain regions on day 2 following the drug. PKCε mRNA was slightly increased only in the cortex on days 2 and 6, while the mRNA levels of the classic PKC subtypes (α, β, and γ) remained unchanged or decreased after the treatment. Immunoblotting analyses revealed that the level of PKCδ protein started to increase on day 1 after kainate and was significantly elevated on day 2 in both the membrane and cytosol fractions of cortex and hippocampus. PKCε protein only showed a marginal increase and the level of PKCζ protein remained unaltered in response to the treatment. Cortical and CA1-3 pyramidal neurons displayed strong immunoreactivity for PKCδ on days 1 and 2, and microglia on days 1, 2, and 4 after the drug. The results indicate that the expression of apoptosis-associated isoforms of PKC, most notably that of δ, but to lesser extent also that of ε and ζ, is increased during kainate-induced neuronal death. The predominant induction of PKCδ in neurons and microglia suggests that PKCδ could be the major mediator or modulator of apoptotic and inflammatory responses to excitotoxic insults.