Immunohistochemical analysis of nucleotide excision repair factors XPA and XPB in adult rat brain.

To study the regional and cellular distribution of xeroderma pigmentosum group A and B (XPA and XPB) proteins, two nucleotide excision repair (NER) factors, in the mammalian brain we used immunohistochemistry and triple fluorescent immunostaining combined with confocal microscope scanning in brain slices of adult rat brain, including the cerebral cortex, striatum, substantia nigra compacta, ventral tegmental area, red nucleus, hippocampus, and cerebellum. Both XPA and XPB proteins were mainly expressed in neurons, because the XPA- or XPB-immunopositive cells were only costained with NeuN, a specific neuronal marker, but not with glial fibrillary acidic acid, a specific astrocyte marker, in the striatum. Furthermore, XPA- and XPB-positive staining were observed in the neuronal nuclei. Such subcellular distribution was consistent with the location of the NER in the cells. This study provides the first evidence that NER factors XPA and XPB exist in the nuclei of neurons in the brain, suggesting that the NER may play important roles in the process of DNA repair in adult brain neurons.

Bcl-2 enhances neurogenesis and inhibits apoptosis of newborn neurons in adult rat brain following a transient middle cerebral artery occlusion.

To determine whether Bcl-2 could influence adult neurogenesis and prevent apoptosis of newborn neurons, we injected Bcl-2 expressing plasmid into the lateral ventricle of rat brain immediately following a 30-min occlusion of the middle cerebral artery (MCAO). We found that Bcl-2 increased neural progenitor cells (BrdU+-DCX+) in the ipsilateral striatum, newborn immature neurons (BrdU+-Tuj-1+) and newborn mature neurons (BrdU+-MAP-2+) in the ipsilateral striatum and frontal cortex at 1 to 4 weeks following MCAO. Bcl-2 overexpression promoted development of newborn neurons into GABAergic and cholinergic neurons in the ipsilateral striatum. Moreover, Bcl-2 significantly decreased the apoptosis of newborn neurons, determined by double staining of Tuj-1 and activated caspase-3 (Tuj-1+-Casp+). These results indicate that overexpression of Bcl-2 in adult rat brain enhances neurogenesis and survival of newborn neurons. Increasing neurogenesis and preventing the death of newborn neuron may be a strategy to aid in the repair of adult brain after stroke.

Induction of Bcl-2 and Bax was related to hyperphosphorylation of tau and neuronal death induced by okadaic acid in rat brain.

Abnormal hyperphosphorylation of the cytoskeletal protein tau is a characteristic feature of neurodegeneration in Alzheimer's disease (AD) brain. Okadaic acid (OA), a protein phosphatase inhibitor, induces neuronal death and hyperphosphorylation of tau. In the present study using a model of microinjection of OA into rat frontal cortex, we aimed to investigate if OA-induced hyperphosphorylation of tau and neuronal death are related to the expression of Bcl-2, an apoptosis inhibitor, or Bax, an apoptosis inducer. Immunohistochemistry and Western blot analysis showed that OA injection dose- and time-dependently induced the expression of Bcl-2 and Bax protein in the surrounding of OA injection areas, which were similar with that of AT8 immunostaining, a marker of hyperphosphorylated tau. However, the ratios of Bcl-2 over Bax had a negative relationship to the expression of AT8. Furthermore, double fluorescent staining showed that AT8-positive neurons mainly costained with terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick-end labeling, a marker of DNA damage, indicating that tau hyperphosphorylation may be associated with DNA damage in the neurons of rat brain. In the areas more adjacent to the OA injection site, most neurons with AT8-positive staining showed vulnerability to OA toxicity and could be triple-stained with Bcl-2 and Bax or double-stained with Bcl-2. However, in the areas further from the OA injection site, neurons with few AT8-positive staining showed resistance to OA toxicity and only stained with Bcl-2, but not Bax. The results suggest that the ratios of Bcl-2 over Bax expression may have an effect on tau hyperphosphorylation and neuronal death following OA injection.

Induction of CRMP-4 in striatum of adult rat after transient brain ischemia.

AIM: To study the expression of collapsing response mediated protein-4 (CRMP-4) and nestin in the ischemic adult rat brain following transient brain ischemia. METHODS: Brain ischemia was induced by transient left middle cerebral artery occlusion (MCAO) for 60 min in adult rats. The expression of CRMP-4, nestin and bromodeoxyuridine (BrdU) was analyzed by immunohistochemical method. The co-localization of CRMP-4 and nestin or BrdU was analyzed by double staining combined with confocal laser scanning microscopy. RESULTS: CRMP-4, a marker of immature neuron, could be expressed in the ipsilateral striatum and cerebral cortex at 1st and 2nd week after the ischemia-reperfusion; nestin, a marker of neural stem cell, occurred in above regions from several hours to 2 weeks. CRMP-4 costained with nestin and with BrdU incorporation. CONCLUSION: Neural stem cells may present in the striatum and cerebral cortex of adult rat and can be triggered to differentiate into newborn neuron there by ischemic brain trauma.

Distribution of Flk-1 and Flt-1 receptors in neonatal and adult rat brains.

Double-fluorescence staining was combined with confocal laser scanning microscopy to localize fetal liver kinase-1 (Flk-1) and fms-like tyrosine kinase-1 (Flt-1) in the neonatal rat brain. The results showed that Flk-1 and Flt-1 immunostaining was observed in the cells with neuron-specific enolase, a neuronal marker, and with factor VIII (F VIII), an endothelium marker, but not in cells with glial fibrillary acidic protein (GFAP), a glial marker, of brain sections from rats on postnatal day 7 (P7). This indicates that both vascular endothelial growth factor (VEGF) receptors were distributed in the neurons and the vascular endothelium. A regional analysis showed that Flt-1 was distributed most densely in the hippocampus, followed by the retrosplenial agranular cortex and the striatum, and Flk-1 was evenly distributed throughout the brain. In a comparison of the density of immunopositive staining neurons, Flt-1 was much higher than Flk-1 in most of the brain regions. A time-course analysis showed that both Flt-1 and Flk-1 were highly expressed in the cerebral vessel of rats on P1, P7, and P14, and then declined in adults, consistent with the development of angiogenesis in neonates. In the neurons, Flt-1 was highest in the cerebral cortex and hippocampus of P1-P14 rats, and then gradually decreased, whereas Flk-1 abruptly increased and reached its highest level in adults. The results suggest that Flt-1 and Flk-1 are expressed in the neurons with their individual time-dependent manners and regional distribution in the brain. However, the significance of the neuronal distribution of Flt-1 and Flk-1 remains to be determined.

Role of vascular endothelial growth factor in neuronal DNA damage and repair in rat brain following a transient cerebral ischemia.

The antisense knockdown technique and confocal laser scanning microscopic analysis were used to elucidate vascular endothelial growth factor (VEGF) induction and its effect on DNA damage and repair in rat brain following a transient middle cerebral artery occlusion. Immunohistochemical study and in situ hybridization showed that the expression of VEGF and its mRNA was enhanced in the ischemic core and penumbra of ischemic brain. Western blot analysis further illustrated that VEGF induction was time-dependently changed in these areas. Double-staining analysis indicated that VEGF-positive staining existed in the neuron, but not in the glia, and it colocalized with excision repair cross-complementing group 6 (ERCC6) mRNA, a DNA repair factor. VEGF antisense oligodeoxynucleotide infusion reduced VEGF induction and resulted in an enlargement of infarct volume of the brain caused by ischemia. Moreover, it also increased the number of DNA damaged cells and lessened the induction of ERCC6 mRNA in ischemic brains. These results suggest that the induction of endogenous VEGF in ischemic neurons plays a neuroprotective role probably associated with the expression of ERCC6 mRNA.

[Okadaic acid induces the expression of glutamate transporter EAAT1 in the neurons of rat brain].

To study the relationship between tau hyperphosphorylation and the function of glutamate transporter okadaic acid (OA), a protein phosphatase inhibitor, 20 ng in a 0.5 microl volume, was injected into the frontal cortex of rat brain and immunostaining was used to observe the phosphorylation of tau protein and the expression of excitatory amino acid transporter 1 (EAAT1) in the brain following the injection. The results showed that (1) the neurons in the center of the injection region displayed cytoplasmic shrinkage, swelling, nuclear pyknosis, and dislocation at the early stage, and necrosis appeared 3 d after the injection. However, most neurons in the peri-injected areas showed normal morphological characters with immuno positive reaction for AT8, a tau phosphorylated marker; (2) morphological analysis showed that tau hyperphosphorylation caused by OA treatment was mainly observed in the axons and dendrites of neuronal cells at 6 h in the cell body at 1 d, which brought about dystrophic neurites and neurofibrillary tangle (NFT)-like pathological changes; (3) the induction of glutamate transporter EAAT1 was observed in the involved areas corresponding to that with AT8 immunopositive staining, and the number of EAAT1-positive staining cells markedly increased at 12 h (P<0.01), peaked at 1 d (P<0.001), then decreased at 3 d following the injection. Combined with a confocal laser scanning microscopic analysis, double fluorescent immunostaining showed that EAAT1 positive staining appeared in neurons as well as astrocytes in the peri-injected areas of the frontal cortex. These results demonstrate that OA increases glutamate transporter EAAT1 expression in neurons while it induces tau hyperphosphorylation. However, the mechanism and significance of the induction of glutamate transporter EAAT1 expression remain to be further elucidated.

Neuroprotection by melatonin against ischemic neuronal injury associated with modulation of DNA damage and repair in the rat following a transient cerebral ischemia.

In the present study, double fluorescence staining combined with confocal laser scanning microscopy analysis were used to examine the effects of melatonin on ischemia-induced neuronal DNA strand breaks and its possible mechanisms in a transient middle cerebral artery (MCA) occlusion model. Results showed that melatonin dose-dependently reduced infarct areas and decreased both DNA double and single strand breaks (DSB and SSB) and enhanced cell viability in the peri-ischemic brain regions. Furthermore, Bcl-2 induction in the ischemic brain was further enhanced by melatonin treatment. Double staining analysis indicated that the cells costained for Bcl-2 and TdT-mediated-deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL), a DSB marker, displayed a relative regular morphology compared with the cells only stained with TUNEL. Transient ischemia induced an expression of excision repair cross-complementing factor 6 (ERCC6) mRNA, a gene essential for the preferential repair of nuclear excision repair, in the injured neurons. Double labeling showed that ERCC6 only co-localized with proliferating cell nuclear antigen (PCNA), a member of the nuclear excision repair complex, but not with TUNEL. Melatonin further and statistical significantly up-regulated ERCC6 mRNA expression in the peri-ischemic region of rat brains. The results suggest that neuroprotection by melatonin against ischemic injury may be related to modulation of apoptosis and DNA repair capacity.