εPKC Is Required for the Induction of Tolerance by Ischemic and NMDA-Mediated Preconditioning in the Organotypic Hippocampal Slice

Abstract

Glutamate receptors and calcium have been implicated as triggering factors in the induction of tolerance by ischemic preconditioning (IPC) in the brain. However, little is known about the signal transduction pathway that ensues after the IPC induction pathway. The main goals of the present study were to determine whether NMDA induces preconditioning via a calcium pathway and promotes translocation of the protein kinase C ⑀ (⑀PKC) isozyme and whether this PKC isozyme is key in the IPC signal transduction pathway. We corroborate here that IPC and a sublethal dose of NMDA were neuroprotective, whereas blockade of NMDA receptors during IPC diminished IPC-induced neuroprotection. Calcium chelation blocked the protection afforded by both NMDA and ischemic preconditioning significantly, suggesting a significant role of calcium. Pharmacological preconditioning with the nonselective PKC isozyme activator phorbol myristate acetate could not emulate IPC, but blockade of PKC activation with chelerythrine during IPC blocked its neuroprotection. These results suggested that there might be a dual involvement of PKC isozymes during IPC. This was corroborated when neuroprotection was blocked when we inhibited ⑀PKC during IPC and NMDA preconditioning, and IPC neuroprotection was emulated with the activator of ⑀PKC. The possible correlation between NMDA, Ca 2ϩ , and ⑀PKC was found when we emulated IPC with the diacylglycerol analog oleoylacetyl glycerol, suggesting an indirect pathway by which Ca 2ϩ could activate the calcium-insensitive ⑀PKC isozyme. These results demonstrated that the ⑀PKC isozyme played a key role in both IPC-and NMDA-induced tolerance.

Poststroke neuronal rescue and synaptogenesis mediated in vivo by protein kinase C in adult brains

“…Instead of intervening in the pathological process that already has occurred in the ischemic brain (25,26), we used bryostatin-1 (21,27), a potent PKC activator with an antitumorigenic pharmacologic profile, in an attempt to boost neurorepair activity and synaptogenesis pharmacologically. Bryostatin-1, which crosses the blood-brain barrier when administered peripherally (28), produces a relatively selective activation of the PKC isozyme, which is neuroprotective (29)(30)(31) and has a lower median effective dose than PKC␦ for bryostatin-1 in its translocation (thus activation), whereas PKC␦ is most likely involved in ischemic injury during ischemia-reperfusion (32)(33)(34). We recently showed that PKC activation with bryostatin-1 enhanced exactly those synaptogenesis, presynaptic/postsynaptic ultrastructural specialization, and protein synthesis functions involved in rat maze learning and memory (20,35).…”

The neuroprotective mechanism of brain ischemic preconditioning

“…Activation of PKCε increased synaptosomal mitochondrial respiration and phosphorylation of mitochondrial respiratory chain proteins [40] . Delivery of a PKCε inhibitory peptide abated NMDA-induced preconditioning in cell culture and isolated hippocampal slice models [41] . Correspondingly, delivery of a PKCε-specific activator peptide reduced damage, as measured with lactate dehydrogenase (LDH) release, when administered before OGD in pure neuronal and mixed neuronal/astrocyte cultures [42] .…”

Cortical δ-Opioid Receptors Potentiate K+ Homeostasis During Anoxia and Oxygen–Glucose Deprivation

“…Protein kinase A and PKC are important signaling molecules in a variety of cellular functions, including modulation of neurotransmitter release, regulation of ion channels and enzymes, control of growth and differentiation, and modification of neuronal plasticity (Majewski and Iannazzo, 1998;Leenders and Sheng, 2005). In addition to involvement in normal physiologic events, these two kinases have also been shown to play an important role in d-opioid receptor and extracellular K + D Chao et al pathophysiologic events such as response to hypoxia/ischemia (Tanaka, 2001;Selvatici et al, 2002;Raval et al, 2003;Libien et al, 2005). Our previous studies and those of others have shown that DOR regulates PKA and PKC activities under certain conditions (Lou and Pei, 1997;Yao et al, 2003;Ma et al, 2005), suggesting an involvement of these protein kinases in DOR signaling.…”