EAAC1 gene deletion reduces adult hippocampal neurogenesis after transient cerebral ischemia

Intracerebral hirudin injection alleviates cognitive impairment and oxidative stress and promotes hippocampal neurogenesis in rats subjected to cerebral ischemia

Cerebral ischemia starts with cerebral blood flow interruption that causes severely limited oxygen and glucose supply, eliciting a cascade of pathological events, such as excitotoxicity, oxidative stress, calcium dysregulation, and inflammatory response, which could ultimately result in neuronal death. Hirudin has beneficial effects in ischemic stroke and possesses antioxidant and anti-inflammatory properties. Therefore, we investigated the biological functions of hirudin and its related mechanisms in cerebral ischemia. The ischemia-like conditions were induced by transient middle cerebral artery occlusion (MCAO). To investigate hirudin roles, intracerebroventricular injection of 10 U hirudin was given to the rats. Cognitive and motor functions were examined by beam walking and Morris water maze tests. 2,3,5-triphenyl tetrazolium chloride-stained brain sections were used to measure infarct volume. Oxidative stress was determined by assessment of oxidative stress markers. The proliferated cells were labeled by BrdU and Nestin double staining. Western blotting was performed to measure protein levels. Hirudin administration improved cognitive and motor deficits post-ischemia. Hirudin reduced brain infarction and neurological damage in MCAO-subjected rats. Hirudin alleviated oxidative stress and enhanced neurogenesis in ischemic rats. Hirudin facilitated the promotion of phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 and serine-threonine kinase. In sum, hirudin alleviates cognitive deficits by attenuating oxidative stress and promoting hippocampal neurogenesis through the regulation of ERK1/2 and serine-threonine kinase in MCAO-subjected rats.

The Protective Role of Glutathione on Zinc-Induced Neuron Death after Brain Injuries

Glutathione (GSH) is necessary for maintaining physiological antioxidant function, which is responsible for maintaining free radicals derived from reactive oxygen species at low levels and is associated with improved cognitive performance after brain injury. GSH is produced by the linkage of tripeptides that consist of glutamic acid, cysteine, and glycine. The adequate supplementation of GSH has neuroprotective effects in several brain injuries such as cerebral ischemia, hypoglycemia, and traumatic brain injury. Brain injuries produce an excess of reactive oxygen species through complex biochemical cascades, which exacerbates primary neuronal damage. GSH concentrations are known to be closely correlated with the activities of certain genes such as excitatory amino acid carrier 1 (EAAC1), glutamate transporter-associated protein 3-18 (Gtrap3-18), and zinc transporter 3 (ZnT3). Following brain-injury-induced oxidative stress, EAAC1 function is negatively impacted, which then reduces cysteine absorption and impairs neuronal GSH synthesis. In these circumstances, vesicular zinc is also released into the synaptic cleft and then translocated into postsynaptic neurons. The excessive influx of zinc inhibits glutathione reductase, which inhibits GSH's antioxidant functions in neurons, resulting in neuronal damage and ultimately in the impairment of cognitive function. Therefore, in this review, we explore the overall relationship between zinc and GSH in terms of oxidative stress and neuronal cell death. Furthermore, we seek to understand how the modulation of zinc can rescue brain-insult-induced neuronal death after ischemia, hypoglycemia, and traumatic brain injury.

Prophylactic Zinc Administration Combined with Swimming Exercise Prevents Cognitive-Emotional Disturbances and Tissue Injury following a Transient Hypoxic-Ischemic Insult in the Rat

Exercise performance and zinc administration individually yield a protective effect on various neurodegenerative models, including ischemic brain injury. Therefore, this work was aimed at evaluating the combined effect of subacute prophylactic zinc administration and swimming exercise in a transient cerebral ischemia model. The prophylactic zinc administration (2.5 mg/kg of body weight) was provided every 24 h for four days before a 30 min common carotid artery occlusion (CCAO), and 24 h after reperfusion, the rats were subjected to swimming exercise in the Morris Water Maze (MWM). Learning was evaluated daily for five days, and memory on day 12 postreperfusion; anxiety or depression-like behavior was measured by the elevated plus maze and the motor activity by open-field test. Nitrites, lipid peroxidation, and the activity of superoxide dismutase (SOD) and catalase (CAT) were assessed in the temporoparietal cortex and hippocampus. The three nitric oxide (NO) synthase isoforms, chemokines, and their receptor levels were measured by ELISA. Nissl staining evaluated hippocampus cytoarchitecture and Iba-1 immunohistochemistry activated the microglia. Swimming exercise alone could not prevent ischemic damage but, combined with prophylactic zinc administration, reversed the cognitive deficit, decreased NOS and chemokine levels, prevented tissue damage, and increased Iba-1 (+) cell number. These results suggest that the subacute prophylactic zinc administration combined with swimming exercise, but not the individual treatment, prevents the ischemic damage on day 12 postreperfusion in the transient ischemia model.

Hypobaric Hypoxia Induces Deficits in Adult Neurogenesis and Social Interaction via Cyclooxygenase-1/ EP1 Receptor Pathway Activating NLRP3 Inflammasome

Low oxygen environments, like hypobaric hypoxia (HH), are common nodes in a number of diseases characterized by neuroinflammation, which is detrimental to the structural and functional aspects of hippocampal circuitry. Hypoxic conditions lead to elevation of inflammasome-mediated inflammation that may contribute to cognitive deficits. However, a systematic investigation of the impact of inflammasome-mediated neuroinflammation on the components of neurogenic niche during HH remains to be elusive. Cerebral hypoxia was induced in adult male Sprague Dawley rats via decreasing partial pressure of oxygen. The effect of HH (1, 3, and 7 days at 25,000 ft) on social memory, anxiety, adult neurogenesis, and NLRP3- (NLR family pyrin domain containing 3) mediated neuroinflammation in the dentate gyrus (DG) was explored in detail. Furthermore, we explored the therapeutic efficacy of cyclooxygenase-1 inhibitor (valeryl salicylate, 5 mg/kg/day, i.p.) and EP1 receptor (EP1R) antagonist (SC19220, 1 mg/kg/day, i.p.) on HH-induced deficits. Seven days of HH exposure induced alteration in social and anxiety-like behavior along with perturbation in adult neurogenesis. Elevation in NLRP3, caspase-1, and IL-1β levels was observed during HH from day 1. A notable increase in the COX-1/EP1R pathway in activated glial cells in DG was evident during HH. COX-1 inhibitor and EP1R antagonist mitigated the detrimental effects of HH on social memory, adult neurogenesis via blunting NLRP3-mediated inflammation. Our data showed induction of the COX-1/EP1R pathway in the glial cells, which is detrimental to neurogenesis and social memory, opening up the possibility that the COX-1/EP1R pathway is a plausible target for inflammasome-related neurogenesis impairments.

The novel effectiveness of Tai Chi on cardiopulmonary fitness among stroke patients in the recovery phase: a study protocol for a randomized controlled trial

BACKGROUND

Stroke is the leading cause of death worldwide. China faces a similar risk of stroke as developed countries because of considerable changes in lifestyle, such as overeating and smoking. Tai Chi is a traditional form of mind-body exercise that has been widely practiced in China for thousands of years. However, there are few studies on the effect of Tai Chi on the cardiopulmonary function of stroke patients in the recovery phase. Therefore, it is necessary to observe the effect of Tai Chi on the cardiorespiratory fitness of patients after stroke.

METHODS

This is a parallel-design, two-arm, analyst assessor-blinded, randomized controlled trial. A total of 226 stroke patients in the recovery phase will be recruited and assigned randomly to a control group or Tai Chi group at a 1:1 ratio. The patients in the Tai Chi group will perform the Tai Chi exercise. The patients in the control group will perform walking exercises. Patients in both groups will receive conventional treatments and healthy education. The primary outcomes will be VO2peak and scores on the MOS item short form health survey (SF-36) scale. Secondary outcomes will include vital capacity (VC), ejection fractions (EF), and cardiac output (CO). The assessments of the tests will be performed at three time points (before exercise, at the end of exercise, and 6 weeks after exercise). Adverse events will be recorded faithfully during the study.

DISCUSSION

If the results are positive, this study will contribute to the establishment of further guided Tai Chi rehabilitation programs.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2000034719 . Registered on 16 July 2020.

Protective Role of Glutathione in the Hippocampus after Brain Ischemia

Stroke is a major cause of death worldwide, leading to serious disability. Post-ischemic injury, especially in the cerebral ischemia-prone hippocampus, is a serious problem, as it contributes to vascular dementia. Many studies have shown that in the hippocampus, ischemia/reperfusion induces neuronal death through oxidative stress and neuronal zinc (Zn²⁺) dyshomeostasis. Glutathione (GSH) plays an important role in protecting neurons against oxidative stress as a major intracellular antioxidant. In addition, the thiol group of GSH can function as a principal Zn²⁺ chelator for the maintenance of Zn²⁺ homeostasis in neurons. These lines of evidence suggest that neuronal GSH levels could be a key factor in post-stroke neuronal survival. In neurons, excitatory amino acid carrier 1 (EAAC1) is involved in the influx of cysteine, and intracellular cysteine is the rate-limiting substrate for the synthesis of GSH. Recently, several studies have indicated that cysteine uptake through EAAC1 suppresses ischemia-induced neuronal death via the promotion of hippocampal GSH synthesis in ischemic animal models. In this article, we aimed to review and describe the role of GSH in hippocampal neuroprotection after ischemia/reperfusion, focusing on EAAC1.

The Role of NADPH Oxidase in Neuronal Death and Neurogenesis after Acute Neurological Disorders

Oxidative stress is a well-known common pathological process involved in mediating acute neurological injuries, such as stroke, traumatic brain injury, epilepsy, and hypoglycemia-related neuronal injury. However, effective therapeutic measures aimed at scavenging free reactive oxygen species have shown little success in clinical trials. Recent studies have revealed that NADPH oxidase, a membrane-bound enzyme complex that catalyzes the production of a superoxide free radical, is one of the major sources of cellular reactive oxygen species in acute neurological disorders. Furthermore, several studies, including our previous ones, have shown that the inhibition of NADPH oxidase can reduce subsequent neuronal injury in neurological disease. Moreover, maintaining appropriate levels of NADPH oxidase has also been shown to be associated with proper neurogenesis after neuronal injury. This review aims to present a comprehensive overview of the role of NADPH oxidase in neuronal death and neurogenesis in multiple acute neurological disorders and to explore potential pharmacological strategies targeting the NADPH-related oxidative stress pathways.

Role of Excitatory Amino Acid Carrier 1 (EAAC1) in Neuronal Death and Neurogenesis After Ischemic Stroke

Although there have been substantial advances in knowledge regarding the mechanisms of neuron death after stroke, effective therapeutic measures for stroke are still insufficient. Excitatory amino acid carrier 1 (EAAC1) is a type of neuronal glutamate transporter and considered to have an additional action involving the neuronal uptake of cysteine, which acts as a crucial substrate for glutathione synthesis. Previously, our lab demonstrated that genetic deletion of EAAC1 leads to decreased neuronal glutathione synthesis, increased oxidative stress, and subsequent cognitive impairment. Therefore, we hypothesized that reduced neuronal transport of cysteine due to deletion of the EAAC1 gene might exacerbate neuronal injury and impair adult neurogenesis in the hippocampus after transient cerebral ischemia. EAAC1 gene deletion profoundly increased ischemia-induced neuronal death by decreasing the antioxidant capacity. In addition, genetic deletion of EAAC1 also decreased the overall neurogenesis processes, such as cell proliferation, differentiation, and survival, after cerebral ischemia. These studies strongly support our hypothesis that EAAC1 is crucial for the survival of newly generated neurons, as well as mature neurons, in both physiological and pathological conditions. Here, we present a comprehensive review of the role of EAAC1 in neuronal death and neurogenesis induced by ischemic stroke, focusing on its potential cellular and molecular mechanisms.

Zinc transporter 3 modulates cell proliferation and neuronal differentiation in the adult hippocampus

The subgranular zone of the dentate gyrus is a subregion of the hippocampus that has two uniquely defining features; it is one of the most active sites of adult neurogenesis as well as the location where the highest concentrations of synaptic zinc are found, the mossy fiber terminals. Therefore, we sought to investigate the idea that vesicular zinc plays a role as a modulator of hippocampal adult neurogenesis. Here, we used ZnT3^−/− mice, which are depleted of synaptic‐vesicle zinc, to test the effect of targeted deletion of this transporter on adult neurogenesis. We found that this manipulation reduced progenitor cell turnover as well as led to a marked defect in the maturation of newborn cells that survive in the DG toward a neuronal phenotype. We also investigated the effects of zinc (ZnCl₂), n‐acetyl cysteine (NAC), and ZnCl₂ plus 2NAC (ZN) supplement on adult hippocampal neurogenesis. Compared with ZnCl₂ or NAC, administration of ZN resulted in an increase in proliferation of progenitor cells and neuroblast. ZN also rescued the ZnT3 loss‐associated reduction of neurogenesis via elevation of insulin‐like growth factor‐1 and ERK/CREB activation. Together, these findings reveal that ZnT3 plays a highly important role in maintaining adult hippocampal neurogenesis and supplementation by ZN has a beneficial effect on hippocampal neurogenesis, as well as providing a therapeutic target for enhanced neuroprotection and repair after injury as demonstrated by its ability to prevent aging‐dependent cognitive decline in ZnT3^−/− mice. Therefore, the present study suggests that ZnT3 and vesicular zinc are essential for adult hippocampal neurogenesis.

Excitatory Amino Acid Transporters in Physiology and Disorders of the Central Nervous System

Excitatory amino acid transporters (EAATs) encompass a class of five transporters with distinct expression in neurons and glia of the central nervous system (CNS). EAATs are mainly recognized for their role in uptake of the amino acid glutamate, the major excitatory neurotransmitter. EAATs-mediated clearance of glutamate released by neurons is vital to maintain proper glutamatergic signalling and to prevent toxic accumulation of this amino acid in the extracellular space. In addition, some EAATs also act as chloride channels or mediate the uptake of cysteine, required to produce the reactive oxygen speciesscavenger glutathione. Given their central role in glutamate homeostasis in the brain, as well as their additional activities, it comes as no surprise that EAAT dysfunctions have been implicated in numerous acute or chronic diseases of the CNS, including ischemic stroke and epilepsy, cerebellar ataxias, amyotrophic lateral sclerosis, Alzheimer’s disease and Huntington’s disease. Here we review the studies in cellular and animal models, as well as in humans that highlight the roles of EAATs in the pathogenesis of these devastating disorders. We also discuss the mechanisms regulating EAATs expression and intracellular trafficking and new exciting possibilities to modulate EAATs and to provide neuroprotection in course of pathologies affecting the CNS.