Changes and expressions of Redd1 in neurons and glial cells in the gerbil hippocampus proper following transient global cerebral ischemia

Dysregulation of mTOR Signaling after Brain Ischemia

In this review, we provide recent data on the role of mTOR kinase in the brain under physiological conditions and after damage, with a particular focus on cerebral ischemia. We cover the upstream and downstream pathways that regulate the activation state of mTOR complexes. Furthermore, we summarize recent advances in our understanding of mTORC1 and mTORC2 status in ischemia–hypoxia at tissue and cellular levels and analyze the existing evidence related to two types of neural cells, namely glia and neurons. Finally, we discuss the potential use of mTORC1 and mTORC2 as therapeutic targets after stroke.

CD200 Change Is Involved in Neuronal Death in Gerbil Hippocampal CA1 Field Following Transient Forebrain Ischemia and Postischemic Treatment with Risperidone Displays Neuroprotection without CD200 Change

It has been reported that CD200 (Cluster of Differentiation 200), expressed in neurons, regulates microglial activation in the central nervous system, and a decrease in CD200 expression causes an increase in microglial activation and neuronal loss. The aim of this study was to investigate time-dependent changes in CD200 expression in the hippocampus proper (CA1, 2, and 3 fields) after transient forebrain ischemia for 5 min in gerbils. In this study, 5-min ischemia evoked neuronal death (loss) of pyramidal neurons in the CA1 field, but not in the CA2/3 fields, at 5 days postischemia. In the sham group, CD200 expression was found in pyramidal neurons of the CA1 field, and the immunoreactivity in the group with ischemia was decreased at 6 h postischemia, dramatically increased at 12 h postischemia, decreased (to level found at 6 h postischemia) at 1 and 2 days postischemia, and significantly increased again at 5 days postischemia. At 5 days postischemia, CD200 immunoreactivity was strongly expressed in microglia and GABAergic neurons. However, in the CA3 field, the change in CD200 immunoreactivity in pyramidal neurons was markedly weaker than that in the CA1 field, showing there was no expression of CD 200 in microglia and GABAergic neurons. In addition, treatment of 10 mg/kg risperidone (an atypical antipsychotic drug) after the ischemia hardly changed CD200 immunoreactivity in the CA1 field, showing that CA1 pyramidal neurons were protected from the ischemic injury. These results indicate that the transient ischemia-induced change in CD200 expression may be associated with specific and selective neuronal death in the hippocampal CA1 field following transient forebrain ischemia.

Improved HCN channels in pyramidal neurons and their new expression levels in pericytes and astrocytes in the gerbil hippocampal CA1 subfield following transient ischemia

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels have been known to participate in the regulation of neuronal excitability, synaptic transmission and long-term potentiation in the hippocampus. The present study investigated transient ischemia-induced changes of HCN1 and HCN2 expressions in the Cornu Ammonis 1 (CA1) subfield of the hippocampus in gerbils subjected to 5 min transient global cerebral ischemia (tgCI). Neuronal death was exhibited in pyramidal neurons of the striatum pyramidale in the CA1 subfield 4 days after tgCI. HCN1 and HCN2 immunoreactivities were demonstrated in intact CA1 pyramidal neurons, and were transiently and markedly increased in the CA pyramidal neurons at 6 h after ischemia. Thereafter, they gradually decreased in a time-dependent manner. A total of 4 days after ischemia, HCN1 and HCN2 immunoreactivities were barely detected in the CA1 pyramidal neurons; however, HCN1 and HCN2 were began to be expressed in pericytes and astrocytes at 4 days after ischemia. The results indicated that HCN1 and HCN2 expression levels were apparently changed in the gerbil hippocampal CA1 subfield following tgCI and suggested that ischemia-induced alterations in HCN1 and HCN2 expression levels may be closely associated with the death of CA1 pyramidal neurons following 5 min of tgCI.

Phenotypic and Expressional Heterogeneity in the Invasive Glioma Cells

BACKGROUND: Tumor cell invasion is a hallmark of glioblastoma (GBM) and a major contributing factor for treatment failure, tumor recurrence, and the poor prognosis of GBM. Despite this, our understanding of the molecular machinery that drives invasion is limited. METHODS: Time-lapse imaging of patient-derived GBM cell invasion in a 3D collagen gel matrix, analysis of both the cellular invasive phenotype and single cell invasion pattern with microarray expression profiling. RESULTS: GBM invasion was maintained in a simplified 3D-milieue. Invasion was promoted by the presence of the tumorsphere graft. In the absence of this, the directed migration of cells subsided. The strength of the pro-invasive repulsive signaling was specific for a given patient-derived culture. In the highly invasive GBM cultures, the majority of cells had a neural progenitor-like phenotype, while the less invasive cultures had a higher diversity in cellular phenotypes. Microarray expression analysis of the non-invasive cells from the tumor core displayed a higher GFAP expression and a signature of genes containing VEGFA, hypoxia and chemo-repulsive signals. Cells of the invasive front expressed higher levels of CTGF, TNFRSF12A and genes involved in cell survival, migration and cell cycle pathways. A mesenchymal gene signature was associated with increased invasion. CONCLUSION: The GBM tumorsphere core promoted invasion, and the invasive front was dominated by a phenotypically defined cell population expressing genes regulating traits found in aggressive cancers. The detected cellular heterogeneity and transcriptional differences between the highly invasive and core cells identifies potential targets for manipulation of GBM invasion.

Early IV-injected human dermis-derived mesenchymal stem cells after transient global cerebral ischemia do not pass through damaged blood-brain barrier

There is lack of researches on effects of intravenously injected mesenchymal stem cells (MSCs) against transient cerebral ischemia (TCI). We investigated the disruption of the neurovascular unit (NVU), which comprises the blood-brain barrier and examined entry of human dermis-derived MSCs (hDMSCs) into the damaged hippocampal CA1 area in a gerbil model of TCI and their subsequent effects on neuroprotection and cognitive function. Impairments of neurons and blood-brain barrier were examined by immunohistochemistry, electron microscopy, and Evans blue and immunoglobulin G leakage. Neuronal death was observed in pyramidal neurons 5-day postischemia. NVU were structurally damaged; in particular, astrocyte end-feet were severely damaged from 2-day post-TCI and immunoglobulin G leaked out of the CA1 area 2 days after 5 min of TCI; however, Evans blue extravasation was not observed. On the basis of the results of NVU damages, ischemic gerbils received PKH2-transfected hDMSCs 3 times at early times (3 hr, 2, and 5 days) after TCI, and fluorescence imaging was used to detect hDMSCs in the tissue. PKH2-transfected hDMSCs were not found in the CA1 from immediate time to 8 days after injection, although they were detected in the liver. Furthermore, hDMSCs transplantation did not protect CA1 pyramidal neurons and did not improve cognitive impairment. Intravenously transplanted hDMSCs did not migrate to the damaged CA1 area induced by TCI. These findings suggest no neuroprotection and cognitive improvement by intravenous hDMSCs transplantation after 5 min of TCI.

Transient cerebral ischemia induces albumin expression in microglia only in the CA1 region of the gerbil hippocampus

Albumin, the most abundant plasma protein, is known to exhibit a neuroprotective effect in animal models of focal and global cerebral ischemia. In the present study, the expression and immunoreactivity of albumin was examined in the hippocampus following 5 min of transient cerebral ischemia in gerbils. Albumin immunoreactivity was observed in microglia of the CA1 hippocampal region 2 days post-ischemic insult, and it was significantly increased at 4 days following ischemia-reperfusion. In addition, at 4 days post-ischemic insult, albumin-immunoreactive microglia were abundant in the stratum pyramidale of the CA1 region. The present results demonstrated that albumin was newly expressed post-injury in microglia in the CA1 region, suggesting ischemia-induced neuronal loss. Albumin expression may therefore be associated with ischemia-induced delayed neuronal death in the CA1 region following transient cerebral ischemia.

CD74-immunoreactive activated M1 microglia are shown late in the gerbil hippocampal CA1 region following transient cerebral ischemia

Activated M1 microglia secrete proinflammatory cytokines into damaged brain areas. The present study examined activated M1 microglial morphology and expression in the hippocampal Cornu Ammonis (CA) 1 region, which is vulnerable to transient ischemia. Transient cerebral ischemia was performed for 5 min in gerbils, and neuronal death in the CA1 region following transient cerebral ischemia was confirmed using cresyl violet staining, neuronal nuclear antigen immunohistochemistry and Fluoro-Jade B histofluorescent staining. In addition, CA1 regions were stained for cluster of differentiation (CD) 74, a marker for activated M1 microglia and a ligand for macrophage migration inhibitory factor In sham-operated animals, no CD74 immunoreactivity was observed in the hippocampal CA1 region. CD74 immunoreactivity was not observed in the hippocampal CA1 region until 3 days post-ischemic insult; however, elevated CD74 immunoreactivity was detected in the CA1 region from 5 days post-ischemia. Double immunofluorescence staining for CD74 and ionized calcium-binding adapter molecule 1, a marker for M1 microglial cells, confirmed the expression of CD74 on this microglial subtype. These results indicated that M1 microglia are activated late in the hippocampal CA1 region following ischemic stroke. Therefore, optimizing the timing of therapeutic intervention may reduce activated M1 microglial-induced neuronal damage.

Transient Cerebral Ischemia Alters GSK-3β and p-GSK-3β Immunoreactivity in Pyramidal Neurons and Induces p-GSK-3β Expression in Astrocytes in the Gerbil Hippocampal CA1 Area

Glycogen synthase kinase 3β (GSK-3β) is a key downstream protein in the PI3K/Akt pathway. Phosphorylation of serine 9 of GSK-3β (GSK-3β activity inhibition) promotes cell survival. In this study, we examined changes in expressions of GSK-3β and phosphorylation of GSK-3β (p-GSK-3β) in the gerbil hippocampal CA1 area after 5 min of transient cerebral ischemia. GSK-3β immunoreactivity in the CA1 area was increased in pyramidal cells at 6 h after ischemia-reperfusion. It was decreased in CA1 pyramidal cells from 12 h after ischemia-reperfusion, and hardly detected in the CA1 pyramidal cells at 5 days after ischemia-reperfusion. p-GSK-3β immunoreactivity was slightly decreased in CA1 pyramidal cells at 6 and 12 h after ischemia-reperfusion. It was significantly increased in these cells at 1 and 2 days after ischemia-reperfusion. Five days after ischemia-reperfusion, p-GSK-3β immunoreactivity was hardly found in CA1 pyramidal cells. However, p-GSK-3β immunoreactivity was strongly expressed in astrocytes primarily distributed in strata oriens and radiatum. In conclusion, GSK-3β and p-GSK-3β were significantly changed in pyramidal cells and/or astrocytes in the gerbil hippocampal CA1 area following 5 min of transient cerebral ischemia. This finding indicates that GSK-3β and p-GSK-3β are closely related to delayed neuronal death.

Differential activation of c‑Fos in the paraventricular nuclei of the hypothalamus and thalamus following myocardial infarction in rats

Proto-oncogene c-Fos (c-Fos) is frequently used to detect a pathogenesis in central nervous system disorders. The present study examined changes in the immunoreactivity of c-Fos in the paraventricular nucleus of the hypothalamus (PVNH) and paraventricular nucleus of the thalamus (PVNT) following myocardial infarction (MI) in rats. Infarction in the left ventricle was examined by Masson's trichrome staining. Neuronal degeneration was monitored for 56 days after MI using crystal violet and Fluoro-Jade B histofluorescence staining. Changes in the immunoreactivity of c-Fos were determined using immunohistochemistry for c-Fos. The average infarct size of the left ventricle circumference was ~44% subsequent to MI. Neuronal degeneration was not detected in PVNH and PVNT following MI. c-Fos immunoreactive (⁺) cells were infrequently observed in the nuclei of the sham-group. However, the number of c-Fos⁺ cells was increased in the nuclei following MI and peaked in the PVNH and PVNT at 3 and 14 days, respectively. The number of c-Fos⁺ cells were comparable with the sham group at 56 days after MI. Therefore, MI may induce c-Fos immunoreactivity in PVNH and PVNT, this increase of c-Fos expression levels may be associated with the stress that occurs in the brain following MI.

Crosstalk between miRNAs and their regulated genes network in stroke

In recent years, more and more studies focus on the roles of genes or miRNAs in stroke. However, the molecular mechanism connecting miRNAs and their targetgenes remains unclear. The aim of this study was to determine the differential regulation and correlations between miRNAs and their targetgenes in human stroke. Stroke-related miRNAs were obtained from the Human MicroRNA Disease Database (HMDD) and their targetgenes were generated from three independent sources. Kappa score was used to create the network and the functional modules. A total of 11 stroke-related miRNAs were identified from the HMDD and 441 overlapping targetgenes were extracted from the three databases. By network construction and GO analysis, 13 functional modules, 186 biological processes, and 21 pathways were found in the network, of which functional module 8 was the largest module, cellular-related process and phosphate-related process were the most important biological processes, and MAPK signaling pathway was the most significant pathway. In our study, all miRNAs regulate the stroke modular network by their targetgenes. After the validation of miRNAs, we found that miR-605 and miR-181d were highly expressed in the blood of stroke patients which never reported before may supply novel target for treatment.

Age-dependent changes in the protein expression levels of Redd1 and mTOR in the gerbil hippocampus during normal aging

Redd1, also known as RTP801/Dig2/DDIT4, is a stress-induced protein and a negative regulator of mammalian target of rapamycin (mTOR). Redd1 is also closely associated with oxidative stress and DNA damage. In the present study, age-related changes in the protein expression levels of mTOR and Redd1 were investigated using immunohistochemistry and western blot in the gerbil hippocampus at postnatal month (PM) 3, 6, 12 and 24. No significant differences were identified in the levels of mTOR among the experimental groups, whereas, the levels of phosphorylated mTOR decreased with age. The protein expression levels of Redd1 were observed to gradually increase with age; in the PM 24 group, the level was significantly increased (~189.2%), compared with the PM 3 group. In addition, Redd1 immunoreactivity was significantly increased in the hippocampal principal neurons of the PM 24 group, including the pyramidal cells in the hippocampus proper and granule cells in the dentate gyrus, compared with the other experimental groups. These results demonstrated that the protein expression of Redd1 in the hippocampus was markedly increased during normal aging, indicating that the age-related increase in the expression of Redd1 may be closely associated with age-related hippocampal change.

Ischemia-Induced Changes of PRAS40 and p-PRAS40 Immunoreactivities in the Gerbil Hippocampal CA1 Region After Transient Cerebral Ischemia

Proline-rich Akt substrate of 40-kDa (PRAS40) is one of the important interactive linkers between Akt and mTOR signaling pathways. The increase of PRAS40 is related with the reduction of brain damage induced by cerebral ischemia. In the present study, we investigated time-dependent changes in PRAS40 and phospho-PRAS40 (p-PRAS40) immunoreactivities in the hippocampal CA1 region of the gerbil after 5 min of transient cerebral ischemia. PRAS40 immunoreactivity in the CA1 region was decreased in pyramidal neurons from 12 h after ischemic insult in a time-dependent manner, and, at 5 days post-ischemia, PRAS40 immunoreactivity was newly expressed in astrocytes. p-PRAS40 immunoreactivity in the CA1 pyramidal neurons was hardly found 12 h and apparently detected again 1 and 2 days after ischemic insult. At 5 days post-ischemia, p-PRAS40 immunoreactivity in the CA1 pyramidal neurons was not found. These results indicate that ischemia-induced changes in PRAS40 and p-PRAS40 immunoreactivities in CA1 pyramidal neurons and astrocytes may be closely associated with delayed neuronal death in the hippocampal CA1 region following transient cerebral ischemia.

Increased cyclooxygenase-2 and nuclear factor-κB/p65 expression in mouse hippocampi after systemic administration of tetanus toxin

Brain inflammation has a crucial role in various diseases of the central nervous system. The hippocampus in the mammalian brain exerts an important memory function, which is sensitive to various insults, including inflammation induced by exo/endotoxin stimuli. Tetanus toxin (TeT) is an exotoxin with the capacity for neuronal binding and internalization. The present study investigated changes in inflammatory mediators in the mouse hippocampus proper (CA1‑3 regions) and dentate gyrus (DG) after TeT treatment. The experimental mice were intraperitoneally injected with TeT at a low dosage (100 ng/kg), while the control mice were injected with the same volume of saline. At 6, 12 and 24 h after TeT treatment, changes in the hippocampal levels of inflammatory mediators cyclooxygenase‑2 (COX‑2) and nuclear factor kappa‑B (NF‑κB/p65) were assessed using immunohistochemical and western blot analysis. In the control group, moderate COX‑2 immunoreactivity was observed in the stratum pyramidal (SP) of the CA2‑3 region, while almost no expression was identified in the CA1 region and the DG. COX‑2 immunoreactivity was increased by TeT in the SP and granule cell layer (GCL) of the DG in a time‑dependent manner. At 24 h post‑treatment, COX‑2 immunoreactivity in the SP of the CA1 region and in the GCL of the DG was high, and COX‑2 immunoreactivity in the SP of the CA2/3 region was highest. Furthermore, the present study observed that NF‑κB/p65 immunoreactivity was obviously increased in the SP and GCL at 6, 12 and 24 h after TeT treatment. In conclusion, the present study demonstrated that systemic treatment with TeT significantly increased the expression of COX-2 and NF-κB/p65 in the mouse hippocampus, suggesting that increased COX‑2 and NF-κB/65 expression may be associated with inflammation in the brain induced by exotoxins.

Lipopolysaccharide induction of REDD1 is mediated by two distinct CREB-dependent mechanisms in macrophages

REDD1 is induced by various cellular stresses; however, its expression in response to lipopolysaccharide (LPS) has not been clearly elucidated in immune cells. LPS stimulated CREB-dependent and NF-κB-independent REDD1 expression in macrophages. Early increases in CREB phosphorylation and REDD1 expression at 8h following LPS treatment were blocked by inhibition of p38MAPK and mitogen- and stress-activated protein kinase 1 (MSK1), but not PKA. However, delayed CREB-mediated REDD1 expression at 16h was suppressed by inhibition of cyclooxygenase-2 (COX-2) and PKA. It indicates that LPS induces REDD1 expression by two distinct CREB-mediated mechanisms, the early p38MAPK/MSK1 and the delayed COX-2/PGE2/PKA pathways.

Delayed hippocampal neuronal death in young gerbil following transient global cerebral ischemia is related to higher and longer-term expression of p63 in the ischemic hippocampus

The tumor suppressor p63 is one of p53 family members and plays a vital role as a regulator of neuronal apoptosis in the development of the nervous system. However, the role of p63 in mature neuronal death has not been addressed yet. In this study, we first compared ischemia-induced effects on p63 expression in the hippocampal regions (CA1–3) between the young and adult gerbils subjected to 5 minutes of transient global cerebral ischemia. Neuronal death in the hippocampal CA1 region of young gerbils was significantly slow compared with that in the adult gerbils after transient global cerebral ischemia. p63 immunoreactivity in the hippocampal CA1 pyramidal neurons in the sham-operated young group was significantly low compared with that in the sham-operated adult group. p63 immunoreactivity was apparently changed in ischemic hippocampal CA1 pyramidal neurons in both ischemia-operated young and adult groups. In the ischemia-operated adult groups, p63 immunoreactivity in the hippocampal CA1 pyramidal neurons was significantly decreased at 4 days post-ischemia; however, p63 immunoreactivity in the ischemia-operated young group was significantly higher than that in the ischemia-operated adult group. At 7 days post-ischemia, p63 immunoreactivity was decreased in the hippocampal CA1 pyramidal neurons in both ischemia-operated young and adult groups. Change patterns of p63 level in the hippocampal CA1 region of adult and young gerbils after ischemic damage were similar to those observed in the immunohistochemical results. These findings indicate that higher and longer-term expression of p63 in the hippocampal CA1 region of the young gerbils after ischemia/reperfusion may be related to more delayed neuronal death compared to that in the adults.

Ischemic preconditioning protects neurons from damage and maintains the immunoreactivity of kynurenic acid in the gerbil hippocampal CA1 region following transient cerebral ischemia

Pyramidal neurons in region I of hippocampus proper (CA1) are particularly vulnerable to excitotoxic processes following transient forebrain ischemia. Kynurenic acid (KYNA) is a small molecule derived from tryptophan when this amino acid is metabolized through the kynurenine pathway. In the present study, we examined the effects of ischemic preconditioning (IPC) on the immunoreactivity and protein levels of KYNA following 5 min of transient forebrain ischemia in gerbils. The animals were randomly assigned to 4 groups (sham-operated group, ischemia-operated group, IPC + sham-operated group and IPC + ischemia-operated group). IPC was induced by subjecting the gerbils to 2 min of ischemia followed by 1 day of recovery. In the ischemia-operated group, we observed a significant loss of pyramidal neurons in the CA1 stratum pyramidale (SP) at 5 days post-ischemia; however, in the IPC + ischemia-operated group, the pyramidal neurons were well protected. KYNA immunoreactivity in the SP of the ischemia-operated group was significantly altered following ischemia-reperfusion and was very low 5 days following ischemia-reperfusion. In the IPC + ischemia-operated group, however, KYNA immunoreactivity was constitutively detected in the SP of the CA1 region after the ischemic insult. We also found that the alteration pattern of the KYNA protein level in the CA1 region following ischemia was generally similar to the immunohistochemical changes observed. In brief, our findings demonstrated that IPC maintained and even increased KYNA immunoreactivity in the SP of the CA1 region following ischemia-reperfusion. The data from the present study thus indicate that the enhancement of KYNA expression by IPC may be necessary for neuronal survival following transient ischemic injury.

p63 Expression in the Gerbil Hippocampus Following Transient Ischemia and Effect of Ischemic Preconditioning on p63 Expression in the Ischemic Hippocampus

p63 is a transcription factor of p53 gene family, which are involved in development, differentiation and cell response to stress; however, its roles in ischemic preconditioning (IPC) in the brain are not clear. In the present study, we investigated the effect of IPC on p63 immunoreactivity caused by 5 min of transient cerebral ischemia in gerbils. IPC was induced by subjecting the gerbils to 2 min of transie ischemia 1 day prior to 5 min of transient ischemia. The animals were randomly assigned to four groups (sham-operated-group, ischemia-operated-group, IPC plus (+)-sham-operated-group and IPC + ischemia-operated-group). The number of viable neurons in the stratum pyramidale of the hippocampal CA1 region (CA1) was significantly increased by IPC + ischemia-operated-group compared with that in the ischemia-operated-group 5 days after ischemic insult. We found that strong p63 immunoreactivity was detected in the CA1 pyramidal neurons in the sham-operated-group, and the immunoreactivity was decreased with time after ischemia-reperfusion. In addition, strong p63 immunoreactivity was newly expressed in microglial cells of the CA1 region from 2 days after ischemia-reperfusion. In all the IPC + sham-operated-groups, p63 immunoreactivity in the CA1 pyramidal neurons was similar to that in the sham-operated-group, and the immunoreactivity was well maintained in the IPC + ischemia-operated-groups after cerebral ischemia. In brief, our present findings show that IPC dramatically protected the reduction of p63 immunoreactivity in the pyramidal neurons of the CA1 region after ischemia-reperfusion, and this result suggests that the expression of p63 may be necessary for neurons to survive after transient cerebral ischemia.