Comparison of Trophic Factors Changes in the Hippocampal CA1 Region Between the Young and Adult Gerbil Induced by Transient Cerebral Ischemia

Brain-Derived Neurotrophic Factor in Pediatric Acquired Brain Injury and Recovery

We review emerging preclinical and clinical evidence regarding brain-derived neurotrophic factor (BDNF) protein, genotype, and DNA methylation (DNAm) as biomarkers of outcomes in three important etiologies of pediatric acquired brain injury (ABI), traumatic brain injury, global cerebral ischemia, and stroke. We also summarize evidence suggesting that BDNF is (1) involved in the biological embedding of the psychosocial environment, (2) responsive to rehabilitative therapies, and (3) potentially modifiable. BDNF's unique potential as a biomarker of neuroplasticity and neural repair that is reflective of and responsive to both pre- and post-injury environmental influences separates it from traditional protein biomarkers of structural brain injury with exciting potential to advance pediatric ABI management by increasing the accuracy of prognostic tools and informing clinical decision making through the monitoring of therapeutic effects.

Enhanced autophagy interacting proteins negatively correlated with the activation of apoptosis-related caspase family proteins after focal ischemic stroke of young rats

Background

Neuronal injury induced in young rats by cerebral ischemia reperfusion (CIR) is known to differ substantially from that in adult rats. In the present study, we investigated the specific differences in neuronal injury induced by focal CIR between young and adult rats.

Results

2, 3, 5-triphenyl tetrazolium chloride (TTC) staining revealed a gradual increase in the infarct volume of both young and adult rats in accordance with I/R times and was significantly lower in young rats than in adult rats under the same conditions. The number of cells in the cortex showing immunoreactivity for neuronal nuclei (NeuN) gradually decreased in both young and adult rats in accordance with I/R times; these numbers were significantly higher in young rats than in adult rats under the same conditions. Similarly, as the duration of I/R increased, the degree of glial activation in the cortex penumbra region became more severe in both young and adult groups; however, glial activation was significantly lower in the cortex penumbra region of young rats when compared with that in adult rats. In addition, the expression of Beclin-1 was significantly higher in the infarct penumbra of young rats than adult rats and was more frequently co-expressed with neurons. The levels of autophagy-related proteins increased significantly in the penumbra region after I/R in both young and adult groups, this increase was more pronounced in young rats than in adult rats. Following CIR, analysis revealed significantly lower levels of pro-apoptosis-related factors and significantly higher levels of anti-apoptosis-related proteins in the young rats than in adult rats.

Conclusions

Collectively, the present results suggest that the the reduced levels of neuronal death after CIR in young rats were closely related to enhanced levels of autophagy and reduced levels of pro-apoptosis in neurons.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-022-00740-w.

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.

Treatment of ischemic neuronal death by introducing brain-derived neurotrophic factor mRNA using polyplex nanomicelle

Ischemic neuronal death causes serious lifelong neurological deficits; however, there is no proven effective treatment that can prevent neuronal death after the ischemia. We investigated the feasibility of mRNA therapeutics for preventing the neuronal death in a rat model of transient global ischemia (TGI). By intraventricular administration of mRNA encoding brain-derived neurotrophic factor (BDNF) using a polymer-based carrier, polyplex nanomicelle, the mRNA significantly increased the survival rate of hippocampal neurons after TGI, with a rapid rise of BDNF in the hippocampus. Interestingly, mRNA administration on Day 2 after TGI provided significantly better survival rate than the administration immediately after TGI. Eventually, dosing twice on Day 2 and 5 exerted long-term therapeutic effects, which were confirmed by a Y-maze behavioral test demonstrating improved spatial memory compared with untreated rats on Day 20. Immunohistochemical analysis showed that astrocytes were chief targets of the BDNF mRNA-loaded nanomicelles, suggesting that the augmented BDNF secretion from astrocytes creates a supportive microenvironment for the neurons to tolerate changes caused by ischemic stresses, and terminate the process of progressive neuronal death after the ischemic attack. Overall, the unique mechanism of action of mRNA therapeutics provide a promising approach for preventing ischemic neuronal death.

Effect of hyperthermia on calbindin-D 28k immunoreactivity in the hippocampal formation following transient global cerebral ischemia in gerbils

Calbindin D-28K (CB), a Ca²⁺-binding protein, maintains Ca²⁺ homeostasis and protects neurons against various insults. Hyperthermia can exacerbate brain damage produced by ischemic insults. However, little is reported about the role of CB in the brain under hyperthermic condition during ischemic insults. We investigated the effects of transient global cerebral ischemia on CB immunoreactivity as well as neuronal damage in the hippocampal formation under hyperthermic condition using immunohistochemistry for neuronal nuclei (NeuN) and CB, and Fluoro-Jade B histofluorescence staining in gerbils. Hyperthermia (39.5 ± 0.2°C) was induced for 30 minutes before and during transient ischemia. Hyperthermic ischemia resulted in neuronal damage/death in the pyramidal layer of CA1–3 area and in the polymorphic layer of the dentate gyrus at 1, 2, 5 days after ischemia. In addition, hyperthermic ischemia significantly decreaced CB immunoreactivity in damaged or dying neurons at 1, 2, 5 days after ischemia. In brief, hyperthermic condition produced more extensive and severer neuronal damage/death, and reduced CB immunoreactivity in the hippocampus following transient global cerebral ischemia. Present findings indicate that the degree of reduced CB immunoreactivity might be related with various neuronal damage/death overtime and corresponding areas after ischemic insults.

Effects of ischemic preconditioning on VEGF and pFlk-1 immunoreactivities in the gerbil ischemic hippocampus after transient cerebral ischemia

Ischemia preconditioning (IPC) displays an important adaptation of the CNS to sub-lethal ischemia. In the present study, we examined the effect of IPC on immunoreactivities of VEGF-, and phospho-Flk-1 (pFlk-1) following transient cerebral ischemia in gerbils. The animals were randomly assigned to four groups (sham-operated-group, ischemia-operated-group, IPC plus (+) sham-operated-group, and IPC+ischemia-operated-group). IPC was induced by subjecting gerbils to 2 min of ischemia followed by 1 day of recovery. In the ischemia-operated-group, a significant loss of neurons was observed in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) alone 5 days after ischemia-reperfusion, however, in all the IPC+ischemia-operated-groups, pyramidal neurons in the SP were well protected. In immunohistochemical study, VEGF immunoreactivity in the ischemia-operated-group was increased in the SP at 1 day post-ischemia and decreased with time. Five days after ischemia-reperfusion, strong VEGF immunoreactivity was found in non-pyramidal cells, which were identified as pericytes, in the stratum oriens (SO) and radiatum (SR). In the IPC+sham-operated- and IPC+ischemia-operated-groups, VEGF immunoreactivity was significantly increased in the SP. pFlk-1 immunoreactivity in the sham-operated- and ischemia-operated-groups was hardly found in the SP, and, from 2 days post-ischemia, pFlk-1 immunoreactivity was strongly increased in non-pyramidal cells, which were identified as pericytes. In the IPC+sham-operated-group, pFlk-1 immunoreactivity was significantly increased in both pyramidal and non-pyramidal cells; in the IPC+ischemia-operated-groups, the similar pattern of VEGF immunoreactivity was found in the ischemic CA1, although the VEGF immunoreactivity was strong in non-pyramidal cells at 5 days post-ischemia. In brief, our findings show that IPC dramatically augmented the induction of VEGF and pFlk-1 immunoreactivity in the pyramidal cells of the CA1 after ischemia-reperfusion, and these findings suggest that the increases of VEGF and Flk-1 expressions may be necessary for neurons to survive from transient ischemic damage.