Glutathione peroxidase-1 knockout potentiates behavioral sensitization induced by cocaine in mice via σ-1 receptor-mediated ERK signaling: A comparison with the case of glutathione peroxidase-1 overexpressing transgenic mice

EGCG Attenuates CA1 Neuronal Death by Regulating GPx1, NF-κB S536 Phosphorylation and Mitochondrial Dynamics in the Rat Hippocampus following Status Epilepticus

Epigallocatechin-3-gallate (EGCG) is an antioxidant that directly scavenges reactive oxygen species (ROS) and inhibits pro-oxidant enzymes. Although EGCG protects hippocampal neurons from status epilepticus (SE, a prolonged seizure activity), the underlying mechanisms are not fully understood. As the preservation of mitochondrial dynamics is essential for cell viability, it is noteworthy to elucidate the effects of EGCG on impaired mitochondrial dynamics and the related signaling pathways in SE-induced CA1 neuronal degeneration, which are yet unclear. In the present study, we found that EGCG attenuated SE-induced CA1 neuronal death, accompanied by glutathione peroxidase-1 (GPx1) induction. EGCG also abrogated mitochondrial hyperfusion in these neurons by the preservation of extracellular signal-regulated kinase 1/2 (ERK1/2)-dynamin-related protein 1 (DRP1)-mediated mitochondrial fission, independent of c-Jun N-terminal kinase (JNK) activity. Furthermore, EGCG abolished SE-induced nuclear factor-κB (NF-κB) serine (S) 536 phosphorylation in CA1 neurons. ERK1/2 inhibition by U0126 diminished the effect of EGCG on neuroprotection and mitochondrial hyperfusion in response to SE without affecting GPx1 induction and NF-κB S536 phosphorylation, indicating that the restoration of ERK1/2-DRP1-mediated fission may be required for the neuroprotective effects of EGCG against SE. Therefore, our findings suggest that EGCG may protect CA1 neurons from SE insults through GPx1-ERK1/2-DRP1 and GPx1-NF-κB signaling pathways, respectively.

Sigma-1 receptor increases intracellular calcium in cultured astrocytes and contributes to mechanical allodynia in a model of neuropathic pain

Recent studies have revealed that glial sigma-1 receptor (Sig-1R) in the spinal cord may be a critical factor to mediate sensory function. However, the functional role of Sig-1R in astrocyte has not been clearly elucidated. Here, we determined whether Sig-1Rs modulate calcium responses in primary cultured astrocytes and pathological changes in spinal astrocytes, and whether they contribute to pain hypersensitivity in naïve mice and neuropathic pain following chronic constriction injury (CCI) of the sciatic nerve in mice. Sig-1R was expressed in glial fibrillary acidic protein (GFAP)-positive cultured astrocytes. Treatment with the Sig-1R agonist, PRE-084 or neurosteroid dehydroepiandrosterone (DHEA) increased intracellular calcium responses in cultured astrocytes, and this increase was blocked by the pretreatment with the Sig-1R antagonist, BD-1047 or neurosteroid progesterone. Intrathecal administration of PRE-084 or DHEA for 10 days induced mechanical and thermal hypersensitivity and increased the number of Sig-1R-immunostained GFAP-positive cells in the superficial dorsal horn (SDH) region of the spinal cord in naïve mice, and these changes were inhibited by administration with BD-1047 or progesterone. In CCI mice, intrathecal administration of BD-1047 or progesterone at post-operative day 14 suppressed the developed mechanical allodynia and the number of Sig-1R-immunostained GFAP-positive cells that were increased in the SDH region of the spinal cord following CCI of the sciatic nerve. These results demonstrate that Sig-1Rs play an important role in the modulation of intracellular calcium responses in cultured astrocytes and pathological changes in spinal astrocytes and that administration of BD-1047 or progesterone alleviates the Sig-1R-induced pain hypersensitivity and the peripheral nerve injury-induced mechanical allodynia.

GPx-1-encoded adenoviral vector attenuates dopaminergic impairments induced by methamphetamine in GPx-1 knockout mice through modulation of NF-κB transcription factor

We suggested that selenium-dependent glutathione peroxidase (GPx) plays a protective role against methamphetamine (MA)-induced dopaminergic toxicity. We focused on GPx-1, a major selenium-dependent enzyme and constructed a GPx-1 gene-encoded adenoviral vector (Ad-GPx-1) to delineate the role of GPx-1 in MA-induced dopaminergic neurotoxicity. Exposure to Ad-GPx-1 significantly induced GPx activity and GPx-1 protein levels in GPx-1-knockout (GPx-1-KO) mice. MA-induced dopaminergic impairments [i.e., hyperthermia; increased nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) DNA-binding activity; and decreased dopamine levels, TH activity, and behavioral activity] were more pronounced in GPx-1-KO mice than in WT mice. In contrast, exposure to Ad-GPx-1 significantly attenuated MA-induced dopaminergic loss in GPx-1-KO mice. The protective effect exerted by Ad-GPx-1 was comparable to that exerted by pyrrolidine dithiocarbamate (PDTC), an NF-κB inhibitor against MA insult. Consistently, GPx-1 overexpression significantly attenuated MA dopaminergic toxicity in mice. PDTC did not significantly impact the protective effect of GPx-1 overexpression, suggesting that interaction between NF-κB and GPx-1 is critical for dopaminergic protection. Thus, NF-κB is a potential therapeutic target for GPx-1-mediated dopaminergic protective activity. This study for the first time demonstrated that Ad-GPx-1 rescued dopaminergic toxicity in vivo following MA insult. Furthermore, GPx-1-associated therapeutic interventions may be important against dopaminergic toxicity.

Glutathione peroxidase-1 and neuromodulation: Novel potentials of an old enzyme

Glutathione peroxidase (GPx) acts in co-ordination with other signaling molecules to exert its own antioxidant role. We have demonstrated the protective effects of GPx,/GPx-1, a selenium-dependent enzyme, on various neurodegenerative disorders (i.e., Parkinson's disease, Alzheimer's disease, cerebral ischemia, and convulsive disorders). In addition, we summarized the recent findings indicating that GPx-1 might play a role as a neuromodulator in neuropsychiatric conditions, such as, stress, bipolar disorder, schizophrenia, and drug intoxication. In this review, we attempted to highlight the mechanistic scenarios mediated by the GPx/GPx-1 gene in impacting these neurodegenerative and neuropsychiatric disorders, and hope to provide new insights on the therapeutic interventions against these disorders.