Expression and Chromosomal Mapping of Mouse Gpx2 Gene Encoding the Gastrointestinal Form of Glutathione Peroxidase, GPX-GI

GPX-GI is a cytosolic tetrameric Se-dependent glutathione peroxidase, similar in properties to GPX-1. Unlike the almost ubiquitous GPX-1, GPX-GI is mainly expressed in the epithelium of gastrointestinal tract. GPX-GI contributes to at least fifty percent of GPX activity in rodent small intestmal epithelium. The total GPX activity consists of at least 70% of selenium-dependent GPX activity in this compartment.By analyzing a panel of mouse mterspecies DNA from the Jackson Laboratory's backcross resource,we mapped Gpx2 gene to mouse chromosome 12 between D12Mit4 and D12Mit5, near the Ccs1 locus which contains a colon cancer susceptibility gene. A pseudogene, Gpx2-ps is mapped to mouse chromosome 7.Comparison of Gpx2 gene expression in three pairs of C57BL/6Ha and ICR/Ha mice which are respectively resistant and sensitive to dimethylhydrazine-induced colon cancer, we found a higher Gpx2 mRNA level in C57BL/6Ha colon than ICR/Ha colon. Interestingly, a lower level of GPX activity is found in the resistant strain of mice. Because GPX-1 has three times higher specific activity than GPX GI, our data suggest that the decreased GPX activity may result from a higher level of Gpx2 gene expression in those cells co-express GPx1 gene

Flavonoids from the stems and leaves of Scutellaria baicalensis Georgi attenuate H_2O_2-induced oxidative damage to rat cortical neurons

Primary cultures of rat cortical neurons were treated with H2O2 in an in vitro model of free radical neurotoxicity. Flavonoids extracted from the stems and leaves of Scutellaria baicalensis Georgi, known as SSF, at concentrations of 18.98, 37.36 and 75.92 μg/mL, protected neurons against H2O2 injury in a dose-dependent manner. SSF increased cell survival, reduced lactate dehydrogenase release and inhibited malondialdehyde production. SSF also inhibited reductions in superoxide dismutase, glutathione peroxidase and Na＋-K＋-ATPase activities. These results in-dicate that SSF can protect rat cortical neurons against H2O2-induced oxidative injury.

Single-neuron neurodegeneration as a degenerative model for Parkinson’s disease

The positive effect of levodopa in the treatment of Parkinson’s disease,although it is limited in time and has severe side effects,has encouraged the scientific community to look for new drugs that can stop the neurodegenerative process or even regenerate the neuromelanin-containing dopaminergic nigrostriatal neurons.Successful preclinical studies with coenzyme Q10,mitoquinone,isradipine,nilotinib,TCH346,neurturin,zonisamide,deferiprone,prasinezumab,and cinpanemab prompted clinical trials.However,these failed and after more than 50 years levodopa continues to be the key drug in the treatment of the disease,despite its severe side effects after 4–6 years of chronic treatment.The lack of translated successful results obtained in preclinical investigations based on the use of neurotoxins that do not exist in the human body as new drugs for Parkinson’s disease treatment is a big problem.In our opinion,the cause of these failures lies in the experimental animal models involving neurotoxins that do not exist in the human body,such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and 6-hydroxydopamine,that induce a very fast,massive and expansive neurodegenerative process,which contrasts with the extremely slow one of neuromelanin-containing dopaminergic neurons.The exceedingly slow progress of the neurodegenerative process of the nigrostriatal neurons in idiopathic Parkinson’s patients is due to(i)a degenerative model in which the neurotoxic effect of an endogenous neurotoxin affects a single neuron,(ii)a neurotoxic event that is not expansive and(iii)the fact that the neurotoxin that triggers the neurodegenerative process is produced inside the neuromelanin-containing dopaminergic neurons.The endogenous neurotoxin that fits this degenerative model involving one single neuron at a time is aminochrome,since it(i)is generated within neuromelanin-containing dopaminergic neurons,(ii)does not cause an expansive neurotoxic effect and(iii)triggers all the mechanisms involved in the neurodegenerative process of the nigrostriatal neurons in idiopathic Parkinson’s disease.In conclusion,based on the hypothesis that the neurodegenerative process of idiopathic Parkinson’s disease corresponds to a single-neuron neurodegeneration model,we must search for molecules that increase the expression of the neuroprotective enzymes DT-diaphorase and glutathione transferase M2-2.It has been observed that the activation of the Kelch-like ECH-associated protein 1/nuclear factor(erythroid-derived 2)-like 2 pathway is associated with the transcriptional activation of the DT-diaphorase and glutathione transferase genes.

Decreased glutathione reductase2 leads to early leaf senescence in Arabidopsis

Glutathione reductase（GR） catalyzes the reduction of glutathione disulfide（GSSG） to reduced glutathione（GSH）and participates in the ascorbate-glutathione cycle, which scavenges H_2O_2. Here, we report that chloroplastic/mitochondrial GR2 is an important regulator of leaf senescence. Seed development of the homozygous gr2 knockout mutant was blocked at the globular stage. Therefore, to investigate the function of GR2 in leaf senescence, we generated transgenic Arabidopsis plants with decreased GR2 using RNAi. The GR2 RNAi plants displayed early onset of age-dependent and darkand H2O2-induced leaf senescence, which was accompanied by the induction of the senescence-related marker genes SAG12 and SAG13. Furthermore, transcriptome analysis revealed that genes related to leaf senescence, oxidative stress, and phytohormone pathways were upregulated directly before senescence in RNAi plants. In addition, H2O2 accumulated to higher levels in RNAi plants than in wild-type plants and the levels of H_2O_2 peaked in RNAi plants directly before the early onset of leaf senescence. RNAi plants showed a greater decrease in GSH/GSSG levels than wild-type plants during leaf development. Our results suggest that GR2 plays an important role in leaf senescence by modulating H_2O_2 and glutathione signaling in Arabidopsis.

Astrocytes protect dopaminergic neurons against aminochrome neurotoxicity

Astrocytes protect neurons by modulating neuronal function and survival.Astrocytes support neurons in several ways.They provide energy through the astrocyte-neuron lactate shuttle,protect neurons from excitotoxicity,and internalize neuronal lipid droplets to degrade fatty acids for neuronal metabolic and synaptic support,as well as by their high capacity for glutamate uptake and the conversion of glutamate to glutamine.A recent reported astrocyte system for protection of dopamine neurons against the neurotoxic products of dopamine,such as aminochrome and other o-quinones,were generated under neuromelanin synthesis by oxidizing dopamine catechol structure.Astrocytes secrete glutathione transferase M2-2 through exosomes that transport this enzyme into dopaminergic neurons to protect these neurons against aminochrome neurotoxicity.The role of this new astrocyte protective mechanism in Parkinson´s disease is discussed.

Pigment epithelium-derived factor protects retinal ganglion cells from hypoxia-induced apoptosis by preventing mitochondrial dysfunction

AIM： To investigate the potential of pigment epitheliumderived factor（PEDF） to protect the immortalized rat retinal ganglion cells-5（RGC-5） exposed to Co Cl2-induced chemical hypoxia. METHODS： After being differentiated with staurosporine（SS）, RGC-5 cells were cultured in four conditions： control group cells cultured in Dulbecco ＇s modified eagle medium（DMEM） supplemented with 10% fetal bovine serum, 100 μmol/m L streptomycin and penicillin（named as normal conditions）; hypoxia group cells cultured in DMEM containing 300 μmol/m L Co Cl2; cells in the group protected by PEDF were first pretreated with 100 ng/m L PEDF for 2h and then cultured in the same condition as hypoxia group cells; and PEDF group cells that were cultured in the presence of 100 ng/m L PEDF under normal conditions. The cell viability was assessed by MTT assay, the percentage of apoptotic cells was quantified using Annexin V-FITC apoptosis kit, and intra-cellar reactive oxygen species（ROS） was measured by dichloro-dihydro-fluorescein diacetate（DCFH-DA） probe. The mitochondria-mediated apoptosis was also examined to further study the underlying mechanism of the protective effect of PEDF. The opening of mitochondrial permeability transition pores（m PTPs） and membrane potential（Δψm） were tested as cellular adenosine triphosphate（ATP） level and glutathione（GSH）. Also, the expression and distribution of Cyt C and apoptosis inducing factor（AIF） were observed.RESULTS： SS induced differentiation of RGC-5 cells resulting in elongation of their neurites and establishing contacts between outgrowths. Exposure to 300 μmol/m L Co Cl2 triggered death of 30% of the total cells in cultures within 24 h. At the same time, pretreatment with 100 ng/m L PEDF significantly suppressed the cell death induced by hypoxia（P〈0.05）. The apoptosis induced by treatment of Co Cl2 was that induced cell death accompanied with increasing intracellar ROS and decreasing GSH and ATP level. PEDF pretreatment suppressed these effects（P〈0.05）. Additionally, PEDF treatment inhibited the opening of m PTPs and suppressed decreasing of Δψm in RGC-5 cells, resulting in blocking of the mitochondrial apoptotic pathway.CONCLUSION： Pretreatment of RGC-5 cells with 100 ng/m L PEDF significantly decreases the extent of apoptosis. PEDF inhibits the opening of m PTPs and suppresses decreasing of Δψm. Moreover, PEDF also reduces ROS production and inhibits cellular ATP level＇s reduction. Cyt C and AIF activation in PEDF-pretreated cultures are also reduced. These results demonstrate the potential for PEDF to protect RGCs against hypoxic damage in vitro by preventing mitochondrial dysfunction.