Neuroprotection of Tat-GluR6-9c against Neuronal Death Induced by Kainate in Rat Hippocampus via Nuclear and Non-nuclear Pathways

Abstract

Nature 392, 601-605). In this study, we show that kainate can enhance the assembly of the GluR6-PSD95-MLK3 module and facilitate the phosphorylation of JNK in rat hippocampal CA1 and CA3/dentate gyrus (DG) subfields. More important, a peptide containing the Tat protein transduction sequence (Tat-GluR6-9c) perturbed the assembly of the GluR6-PSD95-MLK3 signaling module and suppressed the activation of MLK3, MKK7, and JNK. As a result, the inhibition of JNK activation by Tat-GluR6-9c diminished the phosphorylation of the transcription factor c-Jun and downregulated Fas ligand expression in hippocampal CA1 and CA3/DG regions. The inhibition of JNK activation by Tat-Glur6 -9c attenuated Bax translocation, the release of cytochrome c, and the activation of caspase-3 in CA1 and CA3/DG subfields. Furthermore, kainate-induced neuronal loss in hippocampal CA1 and CA3 subregions was prevented by intracerebroventricular injection of Tat-Glur6 -9c. Taken together, our findings strongly suggest that the GluR6-PSD95-MLK3 signaling module mediates activation of the nuclear and non-nuclear pathways of JNK, which is involved in brain injury induced by kainate. Tat-GluR6-9c, the peptide we constructed, gives new insight into seizure therapy.As the major excitatory neurotransmitter in the central nervous system, glutamate gates three types of ionotropic receptors: N-methyl-Daspartate, ␣-amino-3-hydroxy-5-methyl-4-isoxazole propionate, and kainate receptors. Kainate receptors are composed of five subunits, glutamate receptor (GluR) 2 5, GluR6, GluR7, KA1, and KA2 (1). Kainic acid (KA) is a potent exogenous agonist of kainate receptors and ␣-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors, and systemic administration of KA produces epilepsy in rats and mice accompanied by neuronal damage mainly in limbic structures. In particular, hippocampal pyramidal neurons are highly vulnerable to the excitotoxicity of kainate (2). Kainate-induced seizures in rodents have been widely used as a model of human temporal lobe epilepsy on the basis of both behavioral and pathological similarities (3).Although the expression of a number of cell death regulatory genes and receptors has been investigated in the seizure model, the exact molecular regulation mechanisms of this process remain poorly understood. Recent studies have indicated that GluR6 subunit-deficient and Jnk3 gene knock-out mice share similar phenotypes, including resistance to KA-induced seizures and neuronal toxicity (4, 5). Additional studies have indicated that the RLPGKETMA motif of the C terminus of GluR6 can bind to the PDZ1 domain of the postsynaptic density protein PSD95/SAP90 through specific interaction (6, 7). Previous studies have also shown that MLK3, an upstream kinase of JNK (8), can interact with the SH3 (Src homology) domain of PSD95 (9). Thus, the triple complex GluR6-PSD95-MLK3 may exist, which can facilitate JNK activation. However, whether signaling module-mediated JNK activation exists in epileptic rat hippocampal CA1and CA3 regions is still unknown.Our p...

Differential contribution of kainate receptors to excitatory postsynaptic currents in superficial layer neurons of the rat medial entorhinal cortex

“…In support of this, a considerable amount of work has clearly demonstrated the presence of postsynaptic KARs at the mossy fiber-CA3 synapse, and GluR6-deficient mice are less susceptible to KA-induced seizures and excitotoxic neuronal death in the CA3 region of the hippocampus (Mulle et al, 1998, Fisahn et al, 2004. Furthermore, the intracerebroventricular injection of a peptide that disrupts GluR6-PSD95-MLK3 signaling can prevent kainate-induced neuronal loss in CA3 neurons (Liu et al, 2006). In contrast, enhanced expression of GluR6 leads to a excitotoxic degeneration in cultured fibroblasts as well as CA3 and CA1 neurons from hippocampal slice cultures (Bergold et al, 1993).…”

Activation of GluR6-containing Kainate Receptors Induces Ubiquitin-dependent Bcl-2 Degradation via Denitrosylation in the Rat Hippocampus after Kainate Treatment

“…We have reported previously that the Bcl-2 (B-cell lymphoma gene 2) levels are down-regulated in a KA-induced rat epileptic seizure model (3). The Bcl-2 family proteins are mainly located in the mitochondrial outer membrane and are divided into pro-apoptotic and the anti-apoptotic groups (4 -7).…”

“…However, KA1 and KA2 can only form functional receptors by combining with one of the GluR5-7 subunits (2). Kainic acid (KA) is a potent exogenous agonist of the KA receptors, and the systemic administration of KA produces epilepsy in rats or mice accompanied by neuronal damage, mainly in limbic structures such as the hippocampal pyramidal neurons in particular (3). KA-induced seizures in rodents have been widely used as a model of human temporal lobe epilepsy.…”

“…Glutamate receptors are classified into metabolic glutamate receptors (GluRs) 3 and ionic GluRs. Glutamate itself gates three types of ionotropic receptors: NMDA, AMPA, and kainate (KA) receptors.…”

Docosahexaenoic acid provides protective mechanism in bilaterally MPTP-lesioned rat model of Parkinson's disease

“…Bcl-2 is a 26-kDa protein preferentially located at contact sites between the inner and outer mitochondrial membranes [61]. Phosphorylation inactivates Bcl-2, thus promoting apoptosis, possibly by releasing Bax from Bcl-2/Bax dimers [62][63][64]. The Bcl-2/Bax heterodimer is the active component for death protection [65,66].…”