Comparison of glial activation in the hippocampal CA1 region between the young and adult gerbils after transient cerebral ischemia

Tat-CCT2 Protects the Neurons from Ischemic Damage by Reducing Oxidative Stress and Activating Autophagic Removal of Damaged Protein in the Gerbil Hippocampus

CCT2 is a eukaryotic chaperonin TCP-1 ring complex subunit that mediates protein folding, autophagosome incorporation, and protein aggregation. In this study, we investigated the effects of CCT on oxidative and ischemic damage using in vitro and in vivo experimental models. The Tat-CCT2 fusion protein was efficiently delivered into HT22 cells in a concentration- and time-dependent manner, and the delivered protein was gradually degraded in HT22 cells. Incubation with Tat-CCT2 significantly ameliorated the 200 µM hydrogen peroxide (H2O2)-induced reduction in cell viability in a concentration-dependent manner, and 8 µM Tat-CCT2 treatment significantly alleviated H2O2-induced DNA fragmentation and reactive oxygen species formation in HT22 cells. In gerbils, CCT2 protein was efficiently delivered into pyramidal cells in CA1 region by intraperitoneally injecting 0.5 mg/kg Tat-CCT2, as opposed to control CCT2. In addition, treatment with 0.2 or 0.5 mg/kg Tat-CCT2 mitigated ischemia-induced hyperlocomotive activity 1 d after ischemia and confirmed the neuroprotective effects by NeuN immunohistochemistry in the hippocampal CA1 region 4 d after ischemia. Tat-CCT2 treatment significantly reduced the ischemia-induced activation of astrocytes and microglia in the hippocampal CA1 region 4 d after ischemia. Furthermore, treatment with 0.2 or 0.5 mg/kg Tat-CCT2 facilitated ischemia-induced autophagic activity and ameliorated ischemia-induced autophagic initiation in the hippocampus 1 d after ischemia based on western blotting for LC3B and Beclin-1, respectively. Levels of p62, an autophagic substrate, significantly increased in the hippocampus following treatment with Tat-CCT2. These results suggested that Tat-CCT2 exerts neuroprotective effects against oxidative stress and ischemic damage by promoting the autophagic removal of damaged proteins or organelles.

Targeting the Erk1/2 and autophagy signaling easily improved the neurobalst differentiation and cognitive function after young transient forebrain ischemia compared to old gerbils

The hippocampal neurogenesis occurs constitutively throughout adulthood in mammalian species, but declines with age. In this study, we overtly found that the neuroblast proliferation and differentiation in the subgranular zone and the maturation into fully functional and integrated neurons in the granule-cell layer in young gerbils following cerebral ischemia/reperfusion was much more than those in old gerbils. The neurological function and cognitive and memory-function rehabilitation in the young gerbils improved faster than those in the old one. These results demonstrated that, during long term after cerebral ischemia/reperfusion, the ability of neurogenesis and recovery of nerve function in young animals were significantly higher than that in the old animals. We found that, after 14- and 28-day cerebral ischemia/reperfusion, the phosphorylation of MEK1/2, ERK1/2, p90RSK, and MSK1/2 protein levels in the hippocampus of young gerbils was significantly much higher than that of old gerbils. The levels of autophagy-related proteins, including Beclin-1, Atg3, Atg5, and LC3 in the hippocampus were effectively maintained and elevated at 28 days after cerebral ischemia/reperfusion in the young gerbils compared with those in the old gerbils. These results indicated that an increase or maintenance of the phosphorylation of ERK1/2 signal pathway and autophagy-related proteins was closely associated with the neuroblast proliferation and differentiation and the process of maturation into neurons. Further, we proved that neuroblast proliferation and differentiation in the dentate gyrus and cognitive function were significantly reversed in young cerebral ischemic gerbils by administering the ERK inhibitor (U0126) and autophagy inhibitor (3MA). In brief, following experimental young ischemic stroke, the long-term promotion of the neurogenesis in the young gerbil’s hippocampal dentate gyrus by upregulating the phosphorylation of ERK signaling pathway and maintaining autophagy-related protein levels, it overtly improved the neurological function and cognitive and memory function.

Differences in TNF‑α and TNF‑R1 expression in damaged neurons and activated astrocytes of the hippocampal CA1 region between young and adult gerbils following transient forebrain ischemia

Tumor necrosis factor (TNF)-α and TNF receptor 1 (TNF-R1) play diverse roles in modulating the neuronal damage induced by cerebral ischemia. The present study compared the time-dependent changes of TNF-α and TNF-R1 protein expression levels in the hippocampal subfield cornu ammonis 1 (CA1) between adult and young gerbils following transient forebrain ischemia (tFI), via western blot and immunohistochemistry analyses. In adult gerbils, delayed neuronal death of pyramidal neurons, the principal neurons in CA1, was recorded 4 days after tFI; however, in young gerbils, delayed neuronal death was recorded 7 days after tFI. TNF-α protein expression levels gradually increased in both groups following tFI; however, TNF-α expression was higher in young gerbils compared with adult gerbils. TNF-R1 protein expression levels markedly increased in both groups 1 day after tFI. Subsequently, TNF-R1 expression gradually decreased in young gerbils, whereas TNF-R1 expression levels were irregularly altered in adult gerbils following tFI. Notably, TNF-α immunoreactivity significantly increased in pyramidal neurons in both groups 1 day after tFI; however, the patterns altered between both groups. In adult gerbils, TNF-α immunoreactivity was rarely exhibited in pyramidal neurons 4 days after tFI due to neuronal death, suggesting that TNF-α immunoreactivity was newly expressed in astrocytes. In young gerbils, TNF-α immunoreactivity increased in pyramidal neurons 4 days after tFI, and TNF-α immunoreactivity was newly expressed in astrocytes. In addition, TNF-R1 immunoreactivity was exhibited in pyramidal cells of both sham groups, and significantly increased 1 day after tFI; however, the patterns altered between both groups. In adult gerbils, TNF-R1 immunoreactivity was rarely exhibited 4 days after tFI, and astrocytes newly expressed TNF-R1 immunoreactivity. In young gerbils, TNF-R1 immunoreactivity increased in pyramidal neurons 4 days after tFI; however, TNF-R1 immunoreactivity was not reported in pyramidal neurons and astrocytes thereafter. Taken together, the results of the present study suggest that different expression levels of TNF-α and TNF-R1 in ischemic CA1 between adult and young gerbils may be due to age-dependent differences of tFI-induced neuronal death.

YES-10, A Combination of Extracts from Clematis mandshurica RUPR. and Erigeron annuus (L.) PERS., Prevents Ischemic Brain Injury in A Gerbil Model of Transient Forebrain Ischemia

: Clematis mandshurica RUPR. (CMR) and Erigeron annuus (L.) PERS. (EALP) have pharmacological effects including anti-inflammatory activity and been used in traditional medicines in Asia. However, neuroprotective effects of CMR and/or EALP extracts against brain ischemic insults have never been addressed. Thus, the aim of this study was to examine neuroprotective effects of YES-10, a combination of extracts from CMR and EALP (combination ratio, 1:1), in the hippocampus following ischemia/reperfusion in gerbils. Protection of neurons was investigated by cresyl violet staining, fluoro-jade B histofluorescence staining and immunohistochemistry for neuronal nuclei. In addition, attenuation of gliosis was studied by immunohistochemistry for astrocytic and microglial markers. Treatments with 50 or 100 mg/kg YES-10 failed to protect neurons in the hippocampus after ischemia/reperfusion injury. However, administration of 200 mg/kg YES-10 protected neurons from ischemia/reperfusion injury and attenuated reactive gliosis. These findings strongly suggest that a combination of extracts from CMR and EALP can be used as a prevention approach/drug against brain ischemic damage.

Characterization of astrocytes and microglial cells in the hippocampal CA1 region after transient focal cerebral ischemia in rats treated with Ilexonin A

Ilexonin A is a compound isolated from the root of Ilex pubescens, a traditional Chinese medicine. Ilexonin A has been shown to play a neuroprotective role by regulating the activation of astrocytes and microglia in the peri-infarct area after ischemia. However, the effects of ilexonin A on astrocytes and microglia in the infarct-free region of the hippocampal CA1 region remain unclear. Focal cerebral ischemia models were established by 2-hour occlusion of the middle cerebral artery in rats. Ilexonin A (20, 40 or 80 mg/kg) was administered immediately after ischemia/reperfusion. The astrocyte marker glial fibrillary acidic protein, microglia marker Iba-1, neural stem cell marker nestin and inflammation markers were detected by immunohistochemistry and western blot assay. Expression levels of tumor necrosis factor-α and interleukin 1β were determined by enzyme linked immunosorbent assay in the hippocampal CA1 tissue. Astrocytes were activated immediately in progressively increasing numbers from 1, 3, to 7 days post-ischemia/reperfusion. The number of activated astrocytes further increased in the hippocampal CA1 region after treatment with ilexonin A. Microglial cells remained quiescent after ischemia/reperfusion, but became activated after treatment with ilexonin A. Ilexonin A enhanced nestin expression and reduced the expression of tumor necrosis factor-α and interleukin 1β in the hippocampus post-ischemia/reperfusion. The results of the present study suggest that ilexonin A has a neuroprotective effect in the hippocampus after ischemia/reperfusion, probably through regulating astrocytes and microglia activation, promoting neuronal stem cell proliferation and reducing the levels of pro-inflammatory factors. This study was approved by the Animal Ethics Committee of the Fujian Medical University Union Hospital, China.

Time-course pattern of neuronal loss and gliosis in gerbil hippocampi following mild, severe, or lethal transient global cerebral ischemia

Transient ischemia in the whole brain leads to neuronal loss/death in vulnerable brain regions. The striatum, neocortex and hippocampus selectively loose specific neurons after transient ischemia. Just 5 minutes of transient ischemia can cause pyramidal neuronal death in the hippocampal cornu ammonis (CA) 1 field at 4 days after transient ischemia. In this study, we investigated the effects of 5-minute (mild), 15-minute (severe), and 20-minute (lethal) transient ischemia by bilateral common carotid artery occlusion (BCCAO) on behavioral change and neuronal death and gliosis (astrocytosis and microgliosis) in gerbil hippocampal subregions (CA1–3 region and dentate gyrus). We performed spontaneous motor activity test to evaluate gerbil locomotor activity, cresyl violet staining to detect cellular distribution, neuronal nuclei immunohistochemistry to detect neuronal distribution, and Fluoro-Jade B histofluorescence to evaluate neuronal death. We also conducted immunohistochemical staining for glial fibrillary acidic protein and ionized calcium-binding adapter molecule 1 (Iba1) to evaluate astrocytosis and microgliosis, respectively. Animals subjected to 20-minute BCCAO died in at least 2 days. BCCAO for 15 minutes led to pyramidal cell death in hippocampal CA1–3 region 2 days later and granule cell death in hippocampal dentate gyrus 5 days later. Similar results were not found in animals subjected to 5-minute BCCAO. Gliosis was much more rapidly and severely progressed in animals subjected to 15-minute BCCAO than in those subjected to 5-minute BCCAO. Our results indicate that neuronal loss in the hippocampal formation following transient ischemia is significantly different according to regions and severity of transient ischemia. The experimental protocol was approved by Institutional Animal Care and Use Committee (AICUC) of Kangwon National University (approval No. KW-180124-1) on May 22, 2018.

Intermittent fasting increases SOD2 and catalase immunoreactivities in the hippocampus but does not protect from neuronal death following transient ischemia in gerbils

Intermittent fasting has been shown to have neuroprotective effects against transient focal cerebral ischemic insults. However, the effects of intermittent fasting on transient global ischemic insult has not been studied much yet. The present study examined effects of intermittent fasting on endogenous antioxidant enzyme expression levels in the hippocampus and investigated whether the fasting protects neurons 5 days after 5 min of transient global cerebral ischemia. Gerbils were randomly subjected to either ad libitum or alternate-day intermittent fasting for two months and assigned to sham surgery or transient ischemia. Changes of antioxidant enzymes were examined using immunohistochemistry for cytoplasmic superoxide dismutase 1 (SOD1), mitochondrial (SOD2), catalase (CAT), and glutathione peroxidase (GPX). The effects of intermittent fasting on ischemia-induced antioxidant changes, neuronal damage/degeneration and glial activation were examined. The weight of fasting gerbils was not different from that of control gerbils. In controls, SOD1 and GPX immunoreactivities were strong in pyramidal neurons of filed cornu ammonis 1 (CA1). Transient ischemia in controls significantly decreased expressions of SOD1 and GPX in CA1 pyramidal neurons. Intermittent fasting resulted in increased expressions of SOD2 and CAT, not of SOD1 and GPX, in CA1 pyramidal neurons. Nevertheless, CA1 pyramidal neurons were not protected in gerbils subjected to fasting after transient ischemia, and inhibition of glial-cell activation was not observed in the gerbils. In summary, intermittent fasting for two months increased SOD2 and CAT immunoreactivities in hippocampal CA1 pyramidal neurons. However, fasting did not protect the CA1 pyramidal neurons from transient cerebral ischemia. The results of the present study indicate that intermittent fasting may increase certain antioxidants, but not protect neurons from transient global ischemic insult.

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.

Accelerated and exacerbated effects of high dietary fat on neuronal damage induced by transient cerebral ischemia in the gerbil septum

BACKGROUND

Obesity induced by high-fat diet (HFD) is one of the most widespread metabolic disorders in current society. However, there has been little research regarding the effects of HFD-induced obesity in the septa of animal models of cerebral ischemia. Therefore, in the present study, we investigated septal effects of HFD on neuronal damage and gliosis induced by transient cerebral ischemia.

METHODS

Body weight, blood glucose levels and serum lipid profiles levels were measured both in the normal diet (ND) and HFD-group. We also investigated the effects of ND and HFD on neuronal damage and gliosis in the septum after transient cerebral ischemia using immunohistochemistry.

RESULTS

The levels of blood glucose, serum triglyceride, and total cholesterol were significantly increased in the HFD-fed gerbils compared with the ND-fed gerbils, although body weight was not significantly changed after HFD feeding. In the ND-fed gerbils, ischemia-induced neuronal damage was found in the septohippocampal nucleus (SHN) of the septum 7 days after ischemia. In the HFD-fed gerbils, ischemia-induced neuronal damage in the SHN was much more severe compared with that of the ND-fed gerbils 4 and 7 days after ischemia. In addition, we found that ischemia-induced glial activation including astrocytes and microglia was accelerated and exacerbated in the HFD-fed gerbils compared with that in the ND-fed gerbils.

CONCLUSION

These results indicate that HFD can lead to much more severe effects in ischemia-induced neuronal damage/death in the septum after ischemia-reperfusion, and that it may be associated with accelerated change in glial activation.

Differences in neuronal damage and gliosis in the hippocampus between young and adult gerbils induced by long duration of transient cerebral ischemia

Response to cerebral ischemia in young animals was very different from that in the adult. The aim of this study was to investigate differences in neuronal death and gliosis in the hippocampal CA1 region (CA1) between adult and young gerbils following 5 and 15 min of transient cerebral ischemia. Delayed neuronal death (DND) of pyramidal cells occurred in the CA1 was similar in all the adult gerbils after 5 and 15 min of ischemia: the DND occurred 4 days after ischemia. In the young groups, DND of pyramidal cells in the CA1 region occurred 7 and 3 days after 5 and 15 min of ischemia, respectively. On the other hand, the activation of GFAP-immunoreactive ((+)) astrocytes and Iba-1(+) microglia was different in the young groups from the adult groups after ischemia. The change pattern of GFAP immunoreactivity in the adult groups was similar in both the adult groups after ischemia; in the young groups, the activation of GFAP(+) astrocytes after 5 min of ischemia was much delayed than that after 15 min of ischemia. Activated Iba-1(+) microglia were aggregated in the stratum pyramidale 4 days after ischemia in all the adult ischemia-operated groups; in the young groups, activated Iba-1(+) microglia were aggregated in the stratum pyramidale 7 days after 5 min of ischemia and 3 days after 15 min of ischemia. These observations indicate that DND in young animals is very different from the adult according to different duration of transient cerebral ischemia and glial activation is very different in young animals after different duration of transient ischemia.