Role of Rac1 GTPase in NADPH oxidase activation and cognitive impairment following cerebral ischemia in the rat

The mechanisms of minocycline in alleviating ischemic stroke damage and cerebral ischemia-reperfusion injury

Stroke is a group of diseases resulting from cerebral vascular rupture or obstruction and subsequent brain blood circulation disorder, leading to rapid neurological deficits. Ischemic stroke accounts for the majority of all stroke cases. The current treatments for ischemic stroke mainly include t-PA thrombolytic therapy and surgical thrombectomy. However, these interventions aimed at recanalizing cerebral vessels can paradoxically lead to ischemia-reperfusion injury, which exacerbates the severity of brain damage. Minocycline, a semi-synthetic tetracycline antibiotic, has been shown to possess a wide range of neuroprotective effects independent of its antibacterial activity. Here we summarize the mechanisms underlying the protective effects of minocycline against cerebral ischemia-reperfusion injury based on the pathogenesis of cerebral ischemia-reperfusion injury, including its modulation of oxidative stress, inflammatory response, excitotoxicity, programmed cell death and blood-brain barrier injury, and also introduce the role of minocycline in alleviating stroke-related complications, in order to provide a theoretical basis for the clinical application of minocycline in cerebral ischemia-reperfusion injury.

AGE-RAGE axis culminates into multiple pathogenic processes: a central road to neurodegeneration

Advanced glycation end-products (AGEs; e.g., glyoxal, methylglyoxal or carboxymethyl-lysine) are heterogenous group of toxic compounds synthesized in the body through both exogenous and endogenous pathways. AGEs are known to covalently modify proteins bringing about loss of functional alteration in the proteins. AGEs also interact with their receptor, receptor for AGE (RAGE) and such interactions influence different biological processes including oxidative stress and apoptosis. Previously, AGE-RAGE axis has long been considered to be the maligning factor for various human diseases including, diabetes, obesity, cardiovascular, aging, etc. Recent developments have revealed the involvement of AGE-RAGE axis in different pathological consequences associated with the onset of neurodegeneration including, disruption of blood brain barrier, neuroinflammation, remodeling of extracellular matrix, dysregulation of polyol pathway and antioxidant enzymes, etc. In the present article, we attempted to describe a new avenue that AGE-RAGE axis culminates to different pathological consequences in brain and therefore, is a central instigating component to several neurodegenerative diseases (NGDs). We also invoke that specific inhibitors of TIR domains of TLR or RAGE receptors are crucial molecules for the therapeutic intervention of NGDs. Clinical perspectives have also been appropriately discussed.

Neuroprotective Effects and Mechanisms of Senegenin, an Effective Compound Originated From the Roots of Polygala Tenuifolia

Senegenin is the main bioactive ingredient isolated from the dried roots of Polygala tenuifolia Willd. In recent years, senegenin has been proved to possess a variety of pharmacological activities, such as anti-oxidation, anti-inflammation, anti-apoptosis, enhancement of cognitive function. Besides, it has a good development prospect for the treatment of neurodegenerative diseases, depression, osteoporosis, cognitive dysfunction, ischemia-reperfusion injury and other diseases. However, there is no systematic literature that fully demonstrates the pharmacological effects of senegenin. In order to meet the needs of new drug research and precise medication, this review summarized the neuroprotective effects, mechanisms and gastrointestinal toxicity of senegenin based on the literatures published from the past 2 decades. In addition, an in-depth analysis of the existing problems in the current research as well as the future research directions have been conducted in order to provide a basis for the clinical application of this important plant extract.

A multiomics and network pharmacological study reveals the neuroprotective efficacy of Fu-Fang-Dan-Zhi tablets against glutamate-induced oxidative cell death

Neuroprotective therapy after ischemic stroke remains a significant need, but current measures are still insufficient. The Fu-Fang-Dan-Zhi tablet (FFDZT) is a proprietary Chinese medicine clinically employed to treat ischemic stroke in the recovery period. This work aims to systematically investigate the neuroprotective mechanism of FFDZT. A systems strategy that integrated metabolomics, transcriptomics, network pharmacology, and in vivo and in vitro experiments was used. First, middle cerebral artery occlusion (MCAO) model rats were treated with FFDZT. FFDZT treatment significantly reduced the infarct volume in the brains of middle cerebral artery occlusion (MCAO) model rats. Then, samples of serum and brain tissue were taken for metabolomics and transcriptomics studies, respectively; gene expression profiles of MCF7 cells treated with FFDZT and its 4 active compounds (senkyunolide I, formononetin, drilodefensin, and tanshinone IIA) were produced for CMAP analysis. Computational analysis of metabolomics and transcriptomics results suggested that FFDZT regulated glutamate and oxidative stress-related metabolites (2-hydroxybutanoic acid and 2-hydroxyglutaric acid), glutamate receptors (NMDAR, KA, and AMPA), glutamate involved pathways (glutamatergic synapse pathway; d-glutamine and d-glutamate metabolism; alanine, aspartate and glutamate metabolism), as well as the reactive oxygen species metabolic process. CMAP analysis indicated that two active ingredients of FFDZT (tanshinone ⅡA and senkyunolide I) could act as glutamate receptor antagonists. Next, putative therapeutic targets of FFDZT's active ingredients identified in the brain were collected from multiple resources and filtered by statistical criteria and tissue expression information. Network pharmacological analysis revealed extensive interactions between FFDZT's putative targets, anti-IS drug targets, and glutamate-related enzymes, while the resulting PPI network exhibited modular topology. The targets in two of the modules were significantly enriched in the glutamatergic synapse pathway. The interactions between FFDZT's ingredients and important targets were verified by molecular docking. Finally, in vitro experiments validated the effects of FFDZT and its ingredients in suppressing glutamate-induced PC12 cell injury and reducing the generation of reactive oxygen species. All of our findings indicated that FFDZT's efficacy for treating ischemic stroke could be due to its neuroprotection against glutamate-induced oxidative cell death.

Intertwined associations between oxidative and nitrosative stress and endocannabinoid system pathways: Relevance for neuropsychiatric disorders

The endocannabinoid system (ECS) appears to regulate metabolic, cardiovascular, immune, gastrointestinal, lung, and reproductive system functions, as well as the central nervous system. There is also evidence that neuropsychiatric disorders are associated with ECS abnormalities as well as oxidative and nitrosative stress pathways. The goal of this mechanistic review is to investigate the mechanisms underlying the ECS's regulation of redox signalling, as well as the mechanisms by which activated oxidative and nitrosative stress pathways may impair ECS-mediated signalling. Cannabinoid receptor (CB)1 activation and upregulation of brain CB2 receptors reduce oxidative stress in the brain, resulting in less tissue damage and less neuroinflammation. Chronically high levels of oxidative stress may impair CB1 and CB2 receptor activity. CB1 activation in peripheral cells increases nitrosative stress and inducible nitric oxide (iNOS) activity, reducing mitochondrial activity. Upregulation of CB2 in the peripheral and central nervous systems may reduce iNOS, nitrosative stress, and neuroinflammation. Nitrosative stress may have an impact on CB1 and CB2-mediated signalling. Peripheral immune activation, which frequently occurs in response to nitro-oxidative stress, may result in increased expression of CB2 receptors on T and B lymphocytes, dendritic cells, and macrophages, reducing the production of inflammatory products and limiting the duration and intensity of the immune and oxidative stress response. In conclusion, high levels of oxidative and nitrosative stress may compromise or even abolish ECS-mediated redox pathway regulation. Future research in neuropsychiatric disorders like mood disorders and deficit schizophrenia should explore abnormalities in these intertwined signalling pathways.

Repurposed anti-cancer epidermal growth factor receptor inhibitors: mechanisms of neuroprotective effects in Alzheimer's disease

Numerous molecular mechanisms are being examined in an attempt to discover disease-modifying drugs to slow down the underlying neurodegeneration in Alzheimer’s disease. Recent studies have shown the beneficial effects of epidermal growth factor receptor inhibitors on the enhancement of behavioral and pathological sequelae in Alzheimer’s disease. Despite the promising effects of epidermal growth factor receptor inhibitors in Alzheimer’s disease, there is no irrefutable neuroprotective evidence in well-established animal models using epidermal growth factor receptor inhibitors due to many un-explored downstream signaling pathways. This caused controversy about the potential involvement of epidermal growth factor receptor inhibitors in any prospective clinical trial. In this review, the mystery beyond the under-investigation of epidermal growth factor receptor in Alzheimer’s disease will be discussed. Furthermore, their molecular mechanisms in neurodegeneration will be explained. Also, we will shed light on SARS-COVID-19 induced neurological manifestations mediated by epidermal growth factor modulation. Finally, we will discuss future perspectives and under-examined epidermal growth factor receptor downstream signaling pathways that warrant more exploration. We conclude that epidermal growth factor receptor inhibitors are novel effective therapeutic approaches that require further research in attempts to be repositioned in the delay of Alzheimer’s disease progression.

LncRNA MEG3 Alleviates Diabetic Cognitive Impairments by Reducing Mitochondrial-Derived Apoptosis through Promotion of FUNDC1-Related Mitophagy via Rac1-ROS Axis

Mitochondrial dysfunction and elevated ROS generation are predominant contributors of neuronal death that is responsible for the diabetes-related cognitive impairments. Emerging evidence has demonstrated that long noncoding RNA-MEG3 can serve as an important regulator in the pathogenesis of diabetes. However, the underlying mechanisms remain to be further clarified. Here, it was observed that MEG3 was significantly down-regulated in STZ (streptozotocin)-induced diabetic rats. MEG3 overexpression noticeably improved diabetes-induced cognitive dysfunctions, accompanied by the abatement of Rac1 activation and ROS production, as well as the inhibition of mitochondria-associated apoptosis. Furthermore, either MEG3 overexpression or Rac1 inhibition promoted FUNDC1 dephosphorylation and suppressed oxidative stress and neuro-inflammation. Similarly, in vitro studies confirmed that hyperglycemia also down-regulated MEG3 expression in PC12 cells. MEG3 reintroduction protected PC12 cells against hyperglycemia-triggered neurotoxicity by improving mitochondrial fitness and repressing mitochondria-mediated apoptosis. Moreover, these neuroprotective effects of MEG3 relied on FUNDC1-related mitophagy, since silencing of FUNDC1 abolished these beneficial outcomes. Additionally, MEG3 rescued HG-induced neurotoxicity was involved in inhibiting Rac1 expression via interaction with Rac1 3'UTR. Conversely, knockdown of MEG3 showed opposite effects. NSC23766, a specific inhibitor of Rac1, fully abolished harmful effects of MEG3 depletion. Consistently, knockdown of Rac1 potentiated FUNDC1-associated mitophagy. Meanwhile, colocalization of Rac1 and FUNDC1 was found in mitochondria under hyperglycemia, which was interrupted by MEG3 overexpression. Furthermore, silencing of Rac1 promoted PGAM5 expression, and FUNDC1 strongly interacted with LC3 in Rac1-deleted cells. Altogether, our findings suggested that the Rac1/ROS axis may be a downstream signaling pathway for MEG3-induced neuroprotection, which was involved in FUNDC1-associated mitophagy.

PPARγ in Ischemia-Reperfusion Injury: Overview of the Biology and Therapy

Ischemia-reperfusion injury (IRI) is a complex pathophysiological process that is often characterized as a blood circulation disorder caused due to various factors (such as traumatic shock, surgery, organ transplantation, burn, and thrombus). Severe metabolic dysregulation and tissue structure destruction are observed upon restoration of blood flow to the ischemic tissue. Theoretically, IRI can occur in various tissues and organs, including the kidney, liver, myocardium, and brain, among others. The advances made in research regarding restoring tissue perfusion in ischemic areas have been inadequate with regard to decreasing the mortality and infarct size associated with IRI. Hence, the clinical treatment of patients with severe IRI remains a thorny issue. Peroxisome proliferator-activated receptor γ (PPARγ) is a member of a superfamily of nuclear transcription factors activated by agonists and is a promising therapeutic target for ameliorating IRI. Therefore, this review focuses on the role of PPARγ in IRI. The protective effects of PPARγ, such as attenuating oxidative stress, inhibiting inflammatory responses, and antagonizing apoptosis, are described, envisaging certain therapeutic perspectives.

Lapatinib ditosylate rescues memory impairment in D-galactose/ovariectomized rats: Potential repositioning of an anti-cancer drug for the treatment of Alzheimer's disease

Epidermal growth factor receptor (EGFR) signaling plays a substantial role in learning and memory. The upregulation of EGFR has been embroiled in the pathophysiology of Alzheimer's disease (AD). Nevertheless, most of EGFR-tyrosine kinase inhibitors (EGFR-TKIs) have been extensively studied for non-CNS diseases such as cancer and rheumatoid arthritis. TKIs targeting-based research in neurodegenerative disorders sounds to be lagging behind those of other diseases. Hence, this study aims to explore the molecular signaling pathways and the efficacy of treatment with lapatinib ditosylate (LAP), as one of EGFR-TKIs that has not yet been investigated in AD, on cognitive decline induced by ovariectomy (OVX) with chronic administration of D-galactose (D-gal) in female Wistar albino rats. OVX rats were injected with 150 mg/kg/day D-gal ip for 8 weeks to induce AD. Administration of 100 mg/kg/day LAP p.o. for 3 weeks starting after the 8^th week of D-gal administration improved memory and debilitated histopathological alterations. LAP decreased the expression of GFAP, p-tau, and Aβ 1-42. Besides, it reduced EGFR, HER-2, TNF-α, NOX-1, GluR-II, p38 MAPK, and p-mTOR. LAP increased nitrite, and neuronal pro-survival transduction proteins; p-PI3K, p-AKT, and p-GSK-3β levels. Taken together, these findings suggest the role of LAP in ameliorating D-gal-induced AD in OVX rats via activating the pro-survival pathway; PI3K-Akt-GSK-3β, while inhibiting p-mTOR, NOX-1, and p38 MAPK pathways. Moreover, this research offered a significant opportunity to advance awareness of the repositioning of TKI anti-cancer drugs for the treatment of AD.

Pathophysiology and Therapeutic Potential of NADPH Oxidases in Ischemic Stroke-Induced Oxidative Stress

Stroke is a leading cause of death and disability in humans. The excessive production of reactive oxygen species (ROS) is an important contributor to oxidative stress and secondary brain damage after stroke. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, an enzyme complex consisting of membrane subunits and cytoplasmic subunits, regulates neuronal maturation and cerebrovascular homeostasis. However, NADPH oxidase overproduction contributes to neurotoxicity and cerebrovascular disease. NADPH oxidase has been implicated as the principal source of ROS in the brain, and numerous studies have shown that the knockout of NADPH exerts a protective effect in the model of ischemic stroke. In this review, we summarize the mechanism of activation of the NADPH oxidase family members, the pathophysiological effects of NADPH oxidase isoforms in ischemic stroke, and the studies of NADPH oxidase inhibitors to explore potential clinical applications.

The Protective Effects of Peroxisome Proliferator-Activated Receptor Gamma in Cerebral Ischemia-Reperfusion Injury

Cerebral ischemia-reperfusion injury (CI/RI) is a complex pathological process that often occurs secondary to trauma, surgery, and shock. Peroxisome proliferator activated receptor gamma (PPARγ) is a subunit of the PPAR and is a ligand-activated nuclear transcription factor. After being activated by its ligand, PPARγ can combine with specific DNA response elements to regulate the transcription and expression of genes. It has a wide range of biological functions, such as regulating lipid metabolism, improving insulin sensitivity, modulating anti-tumor mechanisms, and inhibiting inflammation. In recent years, some studies have shown that PPARγ exerts a protective effect during CI/RI. This article aims to summarize the research progress of studies that have investigated the protective effects of PPARγ in CI/RI and the cellular and molecular mechanisms through which these effects are modulated, including inhibition of excitatory amino acid toxicity, reduced Ca2+ overload, anti-oxidative stress, anti-inflammation, inhibition of microglial activation, maintain the BBB, promotion of angiogenesis, and neurogenesis and anti-apoptotic processes.

TRP Channels Regulation of Rho GTPases in Brain Context and Diseases

Neurological and neuropsychiatric disorders are mediated by several pathophysiological mechanisms, including developmental and degenerative abnormalities caused primarily by disturbances in cell migration, structural plasticity of the synapse, and blood-vessel barrier function. In this context, critical pathways involved in the pathogenesis of these diseases are related to structural, scaffolding, and enzymatic activity-bearing proteins, which participate in Ca²⁺- and Ras Homologs (Rho) GTPases-mediated signaling. Rho GTPases are GDP/GTP binding proteins that regulate the cytoskeletal structure, cellular protrusion, and migration. These proteins cycle between GTP-bound (active) and GDP-bound (inactive) states due to their intrinsic GTPase activity and their dynamic regulation by GEFs, GAPs, and GDIs. One of the most important upstream inputs that modulate Rho GTPases activity is Ca²⁺ signaling, positioning ion channels as pivotal molecular entities for Rho GTPases regulation. Multiple non-selective cationic channels belonging to the Transient Receptor Potential (TRP) family participate in cytoskeletal-dependent processes through Ca²⁺-mediated modulation of Rho GTPases. Moreover, these ion channels have a role in several neuropathological events such as neuronal cell death, brain tumor progression and strokes. Although Rho GTPases-dependent pathways have been extensively studied, how they converge with TRP channels in the development or progression of neuropathologies is poorly understood. Herein, we review recent evidence and insights that link TRP channels activity to downstream Rho GTPase signaling or modulation. Moreover, using the TRIP database, we establish associations between possible mediators of Rho GTPase signaling with TRP ion channels. As such, we propose mechanisms that might explain the TRP-dependent modulation of Rho GTPases as possible pathways participating in the emergence or maintenance of neuropathological conditions.

Targeting Transcription Factor Nrf2 (Nuclear Factor Erythroid 2-Related Factor 2) for the Intervention of Vascular Cognitive Impairment and Dementia

Vascular cognitive impairment and dementia (VCID) is an age-related, mild to severe mental disability due to a broad panel of cerebrovascular disorders. Its pathobiology involves neurovascular dysfunction, blood-brain barrier disruption, white matter damage, microRNAs, oxidative stress, neuroinflammation, and gut microbiota alterations, etc. Nrf2 (Nuclear factor erythroid 2-related factor 2) is the master regulator of redox status and controls the transcription of a panel of antioxidative and anti-inflammatory genes. By interacting with NF-κB (nuclear factor-κB), Nrf2 also fine-tunes the cellular oxidative and inflammatory balance. Aging is associated with Nrf2 dysfunction, and increasing evidence has proved the role of Nrf2 in mitigating the VCID process. Based on VCID pathobiologies and Nrf2 studies from VCID and other brain diseases, we point out several hypothetical Nrf2 targets for VCID management, including restoration of endothelial function and neurovascular coupling, preservation of blood-brain barrier integrity, reduction of amyloidopathy, promoting white matter integrity, and mitigating oxidative stress and neuroinflammation. Collectively, the Nrf2 pathway could be a promising direction for future VCID research. Targeting Nrf2 would shed light on VCID managing strategies.

Superoxide and Non-ionotropic Signaling in Neuronal Excitotoxicity

Excitotoxicity is classically attributed to Ca²⁺ influx through NMDA receptors (NMDAr), leading to production of nitric oxide by neuronal nitric oxide synthase and superoxide by mitochondria, which react to form highly cytotoxic peroxynitrite. More recent observations warrant revision of the classic view and help to explain some otherwise puzzling aspects of excitotoxic cell injury. Studies using pharmacological and genetic approaches show that superoxide produced by NMDAr activation originates primarily from NADPH oxidase rather than from mitochondria. As NADPH oxidase is localized to the plasma membrane, this also provides an explanation for the extracellular release of superoxide and cell-to-cell “spread” of excitotoxic injury observed in vitro and in vivo. The signaling pathway linking NMDAr to NADPH oxidase involves Ca²⁺ influx, phosphoinositol-3-kinase, and protein kinase Cζ, and interventions at any of these steps can prevent superoxide production and excitotoxic injury. Ca²⁺ influx specifically through NMDAr is normally required to induce excitotoxicity, through a mechanism presumed to involve privileged Ca²⁺ access to local signaling domains. However, experiments using selective blockade of the NMDAr ion channel and artificial reconstitution of Ca²⁺ by other routes indicate that the special effects of NMDAr activation are attributable instead to concurrent non-ionotropic NMDAr signaling by agonist binding to NMDAr. The non-ionotropic signaling driving NADPH oxidase activation is mediated in part by phosphoinositol-3-kinase binding to the C-terminal domain of GluN2B receptor subunits. These more recently identified aspects of excitotoxicity expand our appreciation of the complexity of excitotoxic processes and suggest novel approaches for limiting neuronal injury.

Angelica sinensis extract protects against ischemia-reperfusion injury in the hippocampus by activating p38 MAPK-mediated p90RSK/p-Bad and p90RSK/CREB/BDNF signaling after transient global cerebral ischemia in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Angelica sinensis (Oliv.) Diels, commonly known as Dang Gui (DG), is one of the most popular traditional Chinese herbal medicines for the treatment of stroke. However, the effects of DG on transient global cerebral ischemia (GCI) and its precise mechanisms remain unclear.

AIM OF THE STUDY

This study aimed to investigate the effects of the DG extract on ischemia-reperfusion (I/R) injury in the hippocampus 7 d after transient GCI and to identify the potential mitogen-activated protein kinase (MAPK)-related signaling pathway in the hippocampus involved in the effects.

MATERIALS AND METHODS

Rats were intragastrically administered DG at doses of 0.25 g/kg (DG-0.25g), 0.5 g/kg (DG-0.5g), or 1 g/kg (DG-1g) 1, 3, and 5 d after GCI.

RESULTS

DG-0.5g and DG-1g treatments effectively promoted hippocampal cornu ammonis 1 (CA1) neuronal survival. DG-0.5g and DG-1g treatments markedly increased phospho-p38 MAPK (p-p38 MAPK), phospho-90-kDa ribosomal S6 kinase (p-p90RSK), cytosolic and mitochondrial phospho-Bad (p-Bad), phospho-cAMP response element-binding protein (p-CREB), brain-derived neurotrophic factor (BDNF), and p-CREB/BDNF expression; decreased 4-hydroxy-2-nonenal, cytochrome c (Cytc), and cleaved caspase-3 expression, and inhibited apoptosis in the hippocampal CA1 region. Pretreatment with a specific inhibitor of p38 MAPK, SB203580, completely blocked the effects of DG-1g on the expression of the aforementioned proteins.

CONCLUSIONS

DG-0.5g and DG-1g treatments exerted neuroprotective effects on I/R injury by activating p38 MAPK-mediated p90RSK/p-Bad-induced anti-apoptotic-Cytc/caspase-3-related and p90RSK/CREB/BDNF survival signaling in the hippocampus 7 d after transient GCI.

Dysregulation of Rac or Rho elicits death of motor neurons and activation of these GTPases is altered in the G93A mutant hSOD1 mouse model of amyotrophic lateral sclerosis

Rho GTPases play a central role in neuronal survival; however, the antagonistic relationship between Rac and Rho in the regulation of motor neuron survival remains poorly defined. In the current study, we demonstrate that treatment with NSC23766, a selective inhibitor of the Rac-specific guanine nucleotide exchange factors, Tiam1 and Trio, is sufficient to induce the death of embryonic stem cell (ESC)-derived motor neurons. The mode of cell death is primarily apoptotic and is characterized by caspase-3 activation, de-phosphorylation of ERK5 and AKT, and nuclear translocation of the BH3-only protein Bad. As opposed to the inhibition of Rac, motor neuron cell death is also induced by constitutive activation of Rho, via a mechanism that depends on Rho kinase (ROCK) activity. Investigation of Rac and Rho in the G93A mutant, human Cu, Zn-superoxide dismutase (hSOD1) mouse model of amyotrophic lateral sclerosis (ALS), revealed that active Rac1-GTP is markedly decreased in spinal cord motor neurons of transgenic mice at disease onset and end-stage, when compared to age-matched wild type (WT) littermates. Furthermore, although there is no significant change in active RhoA-GTP, total RhoB displays a striking redistribution from motor neuron nuclei in WT mouse spinal cord to motor neuron axons in end-stage G93A mutant hSOD1 mice. Collectively, these data suggest that the intricate balance between pro-survival Rac signaling and pro-apoptotic Rho/ROCK signaling is critical for motor neuron survival and therefore, disruption in the balance of their activities and/or localization may contribute to the death of motor neurons in ALS.

Rac1 relieves neuronal injury induced by oxygenglucose deprivation and re-oxygenation via regulation of mitochondrial biogenesis and function

Certain microRNAs (miRNAs) can function as neuroprotective factors after reperfusion/ischemia brain injury. miRNA-142-3p can participate in the occurrence and development of tumors and myocardial ischemic injury by negatively regulating the activity of Rac1, but it remains unclear whether miRNA-142-3p also participates in cerebral ischemia/reperfusion injury. In this study, a model of oxygen-glucose deprivation/re-oxygenation in primary cortical neurons was established and the neurons were transfected with miR-142-3p agomirs or miR-142-3p antagomirs. miR-142-3p expression was down-regulated in neurons when exposed to oxygen-glucose deprivation/re-oxygenation. Over-expression of miR-142-3p using its agomir remarkably promoted cell death and apoptosis induced by oxygen-glucose deprivation/re-oxygenation and improved mitochondrial biogenesis and function, including the expression of peroxisome proliferator-activated receptor-γ coactivator-1α, mitochondrial transcription factor A, and nuclear respiratory factor 1. However, the opposite effects were produced if miR-142-3p was inhibited. Luciferase reporter assays verified that Rac Family Small GTPase 1 (Rac1) was a target gene of miR-142-3p. Over-expressed miR-142-3p inhibited NOX2 activity and expression of Rac1 and Rac1-GTPase (its activated form). miR-142-3p antagomirs had opposite effects after oxygen-glucose deprivation/re-oxygenation. Our results indicate that miR-142-3p down-regulates the expression and activation of Rac1, regulates mitochondrial biogenesis and function, and inhibits oxygen-glucose deprivation damage, thus exerting a neuroprotective effect. The experiments were approved by the Committee of Experimental Animal Use and Care of Central South University, China (approval No. 201703346) on March 7, 2017.

Effects of CXCR7-neutralizing antibody on neurogenesis in the hippocampal dentate gyrus and cognitive function in the chronic phase of cerebral ischemia

Stromal cell-derived factor-1 and its receptor CXCR4 are essential regulators of the neurogenesis that occurs in the adult hippocampal dentate gyrus. However, the effects of CXCR7, a new atypical receptor of stromal cell-derived factor-1, on hippocampal neurogenesis after a stroke remain largely unknown. Our study is the first to investigate the effect of a CXCR7-neutralizing antibody on neurogenesis in the dentate gyrus and the associated recovery of cognitive function of rats in the chronic stage of cerebral ischemia. The rats were randomly divided into sham, sham + anti-CXCR7, ischemia and ischemia + anti-CXCR7 groups. Endothelin-1 was injected in the ipsilateral motor cortex and striatum to induce focal cerebral ischemia. Sham group rats were injected with saline instead of endothelin-1 via intracranial injection. Both sham and ischemic rats were treated with intraventricular infusions of CXCR7-neutralizing antibodies for 6 days 1 week after surgery. Immunofluorescence staining with doublecortin, a marker for neuronal precursors, was performed to assess the neurogenesis in the dentate gyrus. We found that anti-CXCR7 antibody infusion enhanced the proliferation and dendritic development of doublecortin-labeled cells in the dentate gyrus in both ischemic and sham-operated rats. Spatial learning and memory functions were assessed by Morris water maze tests 30–32 days after ischemia. CXCR7-neutralizing antibody treatment significantly reduced the escape latency of the spatial navigation trial and increased the time spent in the target quadrant of spatial probe trial in animals that received ischemic insult, but not in sham operated rats. These results suggest that CXCR7-neutralizing antibody enhances the neurogenesis in the dentate gyrus and improves the cognitive function after cerebral ischemia in rats. All animal experimental protocols and procedures were approved by the Institutional Animal Care and Use Committee of China Medical University (CMU16089R) on December 8, 2016.

Effects of resveratrol on learning and memory in rats with vascular dementia

The purpose of the present study was to study the effects of resveratrol on cognitive function in rats with vascular dementia and to investigate the molecular mechanisms of its neuroprotective effects. Forty-five SD rats were randomly divided into 3 groups: The control group (Con group, n=15), the model group (VD group, n=15) and the resveratrol-treated VD group (Res group, n=15). The VD rats (the VD group and the Res group) were generated by bilateral common carotid artery occlusion. The rats in the Res group received daily resveratrol treatment intraperitoneally for 4 weeks. Cognitive function was tested using the Morris water maze test. The levels of SOD and MDA (oxidative stress indicators) were detected by ELISA kits. The protein expression of Bax, Bcl-2 and caspase-3 was detected by western blotting. Compared with the rats in the Con group, the rats in the VD group exhibited decreased cognitive function, significantly increased hippocampal content of MDA, Bax and caspase-3 (P<0.05), and significantly reduced hippocampal expression of SOD and Bcl-2 (P<0.05). Compared with the rats in the VD group, the rats in the Res group exhibited increased cognitive ability, reduced hippocampal content of MDA, Bax and caspase-3 (P<0.05), and increased hippocampal expression of SOD and Bcl-2 (P<0.05). Resveratrol treatment significantly improved the spatial learning and memory of the VD rats. The mechanism associated with the neuroprotective effects of resveratrol may be closely related to the inhibition of the apoptosis pathway and oxidative stress injury.

Suppression of Cerebral Ischemia/Reperfusion Injury by Efficient Release of Encapsulated Ifenprodil From Liposomes Under Weakly Acidic pH Conditions

Although N-methyl-d-aspartate receptor antagonists are hopeful therapeutic agents against cerebral ischemia/reperfusion (I/R) injury, effective approaches are needed to allow such agents to pass through the blood-brain barrier, thus increasing bioavailability of the antagonists to realize secure treatment. We previously demonstrated the usefulness of liposomal delivery of neuroprotectants via spaces between the disrupted blood-brain barrier induced after cerebral I/R. In the present study, a liposomal formulation of an N-methyl-d-aspartate receptor antagonist, ifenprodil, was newly designed; and the potential of liposomal ifenprodil was evaluated in transient middle cerebral artery occlusion rats. Ifenprodil was encapsulated into liposomes by a remote loading method using pH gradient between internal and external water phases of liposomes, focusing on differences of its solubility in water depending on pH. The encapsulated ifenprodil could be quickly released from the liposomes in vitro under a weakly acidic pH condition, which is a distinctive condition after cerebral I/R. Liposomal ifenprodil treatment significantly alleviated I/R-induced increase in permeability of the BBB by inhibiting superoxide anion production, resulting in ameliorating ischemic brain damage. Taken together, these results suggest that Ifen-Lip could become a hopeful neuroprotectant for cerebral I/R injury via efficient release of the encapsulated ifenprodil under weakly acidic pH conditions.

Beneficial Effects of Theta-Burst Transcranial Magnetic Stimulation on Stroke Injury via Improving Neuronal Microenvironment and Mitochondrial Integrity

Recent work suggests that repetitive transcranial magnetic stimulation (rTMS) may beneficially alter the pathological status of several neurological disorders, although the mechanism remains unclear. The current study was designed to investigate the effects of rTMS on behavioral deficits and potential underlying mechanisms in a rat photothrombotic (PT) stroke model. From day 0 (3 h) to day 5 after the establishment of PT stroke, 5-min daily continuous theta-burst rTMS (3 pulses of 50 Hz repeated every 200 ms, intensity at 200 G) was applied on the infarct hemisphere. We report that rTMS significantly attenuated behavioral deficits and infarct volume after PT stroke. Further investigation demonstrated that rTMS remarkably reduced synaptic loss and neuronal degeneration in the peri-infarct cortical region. Mechanistic studies displayed that beneficial effects of rTMS were associated with robust suppression of reactive micro/astrogliosis and the overproduction of pro-inflammatory cytokines, as well as oxidative stress and oxidative neuronal damage especially at the late stage following PT stroke. Intriguingly, rTMS could effectively induce a shift in microglial M1/M2 phenotype activation and an A1 to A2 switch in astrocytic phenotypes. In addition, the release of anti-inflammatory cytokines and mitochondrial MnSOD in peri-infarct regions were elevated following rTMS treatment. Finally, rTMS treatment efficaciously preserved mitochondrial membrane integrity and suppressed the intrinsic mitochondrial caspase-9/3 apoptotic pathway within the peri-infarct cortex. Our novel findings indicate that rTMS treatment exerted robust neuroprotection when applied at least 3 h after ischemic stroke. The underlying mechanisms are partially associated with improvement of the local neuronal microenvironment by altering inflammatory and oxidative status and preserving mitochondrial integrity in the peri-infarct zone. These findings provide strong support for the promising therapeutic effect of rTMS against ischemic neuronal injury and functional deficits following stroke.

RvD1binding with FPR2 attenuates inflammation via Rac1/NOX2 pathway after neonatal hypoxic-ischemic injury in rats

Neuroinflammation plays a crucial role in the pathological development after neonatal hypoxia-ischemia (HI). Resolvin D1 (RvD1), an agonist of formyl peptide receptor 2 (FPR2), has been shown to exert anti-inflammatory effects in many diseases. The objective of this study was to explore the protective role of RvD1 through reducing inflammation after HI and to study the contribution of Ras-related C3 botulinum toxin substrate 1 (Rac1)/nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) pathways in RvD1-mediated protection. Rat pups (10-day old) were subjected to HI or sham surgery. RvD1 was administrated by intraperitoneal injection 1 h after HI. FPR2 small interfering ribonucleic acid (siRNA) and Rac1 activation CRISPR were administered prior to RvD1 treatment to elucidate the possible mechanisms. Time course expression of FPR2 by Western blot and RvD1 by ELISA were conducted at 6 h, 12 h, 24 h, 48 h and 72 h post HI. Infarction area, short-term neurological deficits, immunofluorescent staining and Western blot were conducted at 24 h post HI. Long-term neurological behaviors were evaluated at 4 weeks post HI. Endogenous expression levels of RvD1 decreased in time dependent manner while the expression of FPR2 increased after HI, peaking at 24 h post HI. Activation of FPR2, with RvD1, reduced percent infarction area, and alleviated short- and long-term neurological deficits. Administration of RvD1 attenuated inflammation after HI, while, either inhibition of FPR2 with siRNA or activation of Rac1 with CRISPR reversed those effects. Our results showed that RvD1 attenuated neuroinflammation through FPR2, which then interacted with Rac1/NOX2 signaling pathway, thereby reducing infarction area and alleviating neurological deficits after HI in neonatal rat pups. RvD1 may be a potential therapeutic approach to reduce inflammation after HI.

Arterial stiffness induced by carotid calcification leads to cerebral gliosis mediated by oxidative stress

BACKGROUND

Arterial stiffness is a risk factor for cognitive decline and dementia. However, its precise effects on the brain remain unexplored. Using a mouse model of carotid stiffness, we investigated its effect on glial activation and oxidative stress.

METHODS

Arterial stiffness was induced by the application of calcium chloride to the adventitial region of the right carotid. Superoxide anion production, NADPH activity and levels, as well as glial activation were examined with immunohistochemical and biochemical approaches, 2-week postcalcification. Antioxidant treatment was done with Tempol (1 mmol/l) administered in the drinking water during 2 weeks.

RESULTS

The current study revealed that arterial stiffness increases the levels of the microglial markers ionized calcium-binding adapter molecule 1 and cluster of differentiation 68 in hippocampus, and of the astrocyte marker, s100 calcium binding protein β in hippocampus and frontal cortex. The cerebral inflammatory effects of arterial stiffness were specific to the brain and not due to systemic inflammation. Treatment with Tempol prevented the increase in superoxide anion in mice with carotid stiffness and attenuated the activation of microglia and astrocytes in the hippocampus. To determine whether the increased oxidative stress derives from NADPH oxidase, superoxide anion production was assessed by incubating brain tissue in the presence of gp91ds-tat, a selective NADPH oxidase 2 inhibitor. This peptide inhibited superoxide anion production to a greater extent in the brains of mice with carotid calcification compared with controls.

CONCLUSION

Carotid calcification leads to cerebral gliosis mediated by oxidative stress. Correcting arterial stiffness could offer a novel paradigm to protect the brain in populations where stiffness is prominent.

Proinsulin C-Peptide Enhances Cell Survival and Protects against Simvastatin-Induced Myotoxicity in L6 Rat Myoblasts

The repair capacity of progenitor skeletal muscle satellite cells (SC) in Type 1 diabetes mellitus (T1DM) is decreased. This is associated with the loss of skeletal muscle function. In T1DM, the deficiency of C-peptide along with insulin is associated with an impairment of skeletal muscle functions such as growth, and repair, and is thought to be an important contributor to increased morbidity and mortality. Recently, cholesterol-lowering drugs (statins) have also been reported to increase the risk of skeletal muscle dysfunction. We hypothesised that C-peptide activates key signaling pathways in myoblasts, thus promoting cell survival and protecting against simvastatin-induced myotoxicity. This was tested by investigating the effects of C-peptide on the L6 rat myoblast cell line under serum-starved conditions. Results: C-peptide at concentrations as low as 0.03 nM exerted stimulatory effects on intracellular signaling pathways—MAP kinase (ERK1/2) and Akt. When apoptosis was induced by simvastatin, 3 nM C-peptide potently suppressed the apoptotic effect through a pertussis toxin-sensitive pathway. Simvastatin strongly impaired Akt signaling and stimulated the reactive oxygen species (ROS) production; suggesting that Akt signaling and oxidative stress are important factors in statin-induced apoptosis in L6 myoblasts. The findings indicate that C-peptide exerts an important protective effect against death signaling in myoblasts. Therefore, in T1DM, the deficiency of C-peptide may contribute to myopathy by rendering myoblast-like progenitor cells (involved in muscle regeneration) more susceptible to the toxic effects of insults such as simvastatin.

The Role of NADPH Oxidases and Oxidative Stress in Neurodegenerative Disorders

For a number of years, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) was synonymous with NOX2/gp91^phox and was considered to be a peculiarity of professional phagocytic cells. Over the last decade, several more homologs have been identified and based on current research, the NOX family consists of NOX1, NOX2, NOX3, NOX4, NOX5, DUOX1 and DUOX2 enzymes. NOXs are electron transporting membrane proteins that are responsible for reactive oxygen species (ROS) generation-primarily superoxide anion (O₂^●-), although hydrogen peroxide (H₂O₂) can also be generated. Elevated ROS leads to oxidative stress (OS), which has been associated with a myriad of inflammatory and degenerative pathologies. Interestingly, OS is also the commonality in the pathophysiology of neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). NOX enzymes are expressed in neurons, glial cells and cerebrovascular endothelial cells. NOX-mediated OS is identified as one of the main causes of cerebrovascular damage in neurodegenerative diseases. In this review, we will discuss recent developments in our understanding of the mechanisms linking NOX activity, OS and neurodegenerative diseases, with particular focus on the neurovascular component of these conditions. We conclude highlighting current challenges and future opportunities to combat age-related neurodegenerative disorders by targeting NOXs.

Identification of novel regulatory partners of the glutamate transporter GLT-1

We used proximity-dependent biotin identification (BioID) to find proteins that potentially interact with the major glial glutamate transporter, GLT-1, and we studied how these interactions might affect its activity. GTPase Rac1 was one protein identified, and interfering with its GTP/GDP cycle in mixed primary rat brain cultures affected both the clustering of GLT-1 at the astrocytic processes and the transport kinetics, increasing its uptake activity at low micromolar glutamate concentrations in a manner that was dependent on the effector kinase PAK1 and the actin cytoskeleton. Interestingly, the same manipulations had a different effect on another glial glutamate transporter, GLAST, inhibiting its activity. Importantly, glutamate acts through metabotropic receptors to stimulate the activity of Rac1 in astrocytes, supporting the existence of cross-talk between extracellular glutamate and the astrocytic form of the GLT-1 regulated by Rac1. CDC42EP4/BORG4 (a CDC42 effector) was also identified in the BioID screen, and it is a protein that regulates the assembly of septins and actin fibers, influencing the organization of the cytoskeleton. We found that GLT-1 interacts with septins, which reduces its lateral mobility at the cell surface. Finally, the G-protein subunit GNB4 dampens the activity of GLT-1, as revealed by its response to the activator peptide mSIRK, both in heterologous systems and in primary brain cultures. This effect occurs rapidly and thus, it is unlikely to depend on cytoskeletal dynamics. These novel interactions shed new light on the events controlling GLT-1 activity, thereby helping us to better understand how glutamate homeostasis is maintained in the brain.

A Case-Control Study of the Genetic Variability in Reactive Oxygen Species-Metabolizing Enzymes in Melanoma Risk

Recent studies have shown that ultraviolet (UV)-induced chemiexcitation of melanin fragments leads to DNA damage; and chemiexcitation of melanin fragments requires reactive oxygen species (ROS), as ROS excite an electron in the melanin fragments. In addition, ROS also cause DNA damages on their own. We hypothesized that ROS producing and metabolizing enzymes were major contributors in UV-driven melanomas. In this case-control study of 349 participants, we genotyped 23 prioritized single nucleotide polymorphisms (SNPs) in nicotinamide adenine dinucleotide phosphate (NADPH) oxidases 1 and 4 (NOX1 and NOX4, respectively), CYBA, RAC1, superoxide dismutases (SOD1, SOD2, and SOD3) and catalase (CAT), and analyzed their associated melanoma risk. Five SNPs, namely rs1049255 (CYBA), rs4673 (CYBA), rs10951982 (RAC1), rs8031 (SOD2), and rs2536512 (SOD3), exhibited significant genotypic frequency differences between melanoma cases and healthy controls. In simple logistic regression, RAC1 rs10951982 (odds ratio (OR) 8.98, 95% confidence interval (CI): 5.08 to 16.44; p < 0.001) reached universal significance (p = 0.002) and the minor alleles were associated with increased risk of melanoma. In contrast, minor alleles in SOD2 rs8031 (OR 0.16, 95% CI: 0.06 to 0.39; p < 0.001) and SOD3 rs2536512 (OR 0.08, 95% CI: 0.01 to 0.31; p = 0.001) were associated with reduced risk of melanoma. In multivariate logistic regression, RAC1 rs10951982 (OR 6.15, 95% CI: 2.98 to 13.41; p < 0.001) remained significantly associated with increased risk of melanoma. Our results highlighted the importance of RAC1, SOD2, and SOD3 variants in the risk of melanoma.

A Mini-Review of the NADPH oxidases in Vascular Dementia: Correlation with NOXs and Risk Factors for VaD

Oxidative stress (OS) is one of the factors that cause dementia conditions such as Alzheimer’s disease and vascular dementia (VaD). In the pathogenesis of VaD, OS is associated with risk factors that include increased age, hypertension, and stroke. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) are a molecular source of reactive oxygen species (ROS). According to recent studies, inhibition of NOX activity can reduce cognitive impairment in animal models of VaD. In this article, we review the evidence linking cognitive impairment with NOX-dependent OS, including the vascular NOX and non-vascular NOX systems, in VaD.

The Ubiquitin E3 Ligase TRAF6 Exacerbates Ischemic Stroke by Ubiquitinating and Activating Rac1

Stroke is one of the leading causes of morbidity and mortality worldwide. Inflammation, oxidative stress, apoptosis, and excitotoxicity contribute to neuronal death during ischemic stroke; however, the mechanisms underlying these complicated pathophysiological processes remain to be fully elucidated. Here, we found that the expression of tumor necrosis factor receptor-associated factor 6 (TRAF6) was markedly increased after cerebral ischemia/reperfusion (I/R) in mice. TRAF6 ablation in male mice decreased the infarct volume and neurological deficit scores and decreased proinflammatory signaling, oxidative stress, and neuronal death after cerebral I/R, whereas transgenic overexpression of TRAF6 in male mice exhibited the opposite effects. Mechanistically, we demonstrated that TRAF6 induced Rac1 activation and consequently promoted I/R injury by directly binding and ubiquitinating Rac1. Either functionally mutating the TRAF6 ubiquitination site on Rac1 or inactivating Rac1 with a specific inhibitor reversed the deleterious effects of TRAF6 overexpression during I/R injury. In conclusion, our study demonstrated that TRAF6 is a key promoter of ischemic signaling cascades and neuronal death after cerebral I/R injury. Therefore, the TRAF6/Rac1 pathway might be a promising target to attenuate cerebral I/R injury.SIGNIFICANCE STATEMENT Stroke is one of the most severe and devastating neurological diseases globally. The complicated pathophysiological processes restrict the translation of potential therapeutic targets into medicine. Further elucidating the molecular mechanisms underlying cerebral ischemia/reperfusion injury may open a new window for pharmacological interventions to promote recovery from stroke. Our study revealed that ischemia-induced tumor necrosis factor receptor-associated factor 6 (TRAF6) upregulation binds and ubiquitinates Rac1 directly, which promotes neuron death through neuroinflammation and neuro-oxidative signals. Therefore, precisely targeting the TRAF6-Rac1 axis may provide a novel therapeutic strategy for stroke recovery.

Neuronal Rho GTPase Rac1 elimination confers neuroprotection in a mouse model of permanent ischemic stroke

The Rho GTPase Rac1 is a multifunctional protein involved in distinct pathways ranging from development to pathology. The aim of the present study was to unravel the contribution of neuronal Rac1 in regulating the response to brain injury induced by permanent focal cerebral ischemia (pMCAO). Our results show that pMCAO significantly increased total Rac1 levels in wild type mice, mainly through rising nuclear Rac1, while a reduction in Rac1 activation was observed. Such changes preceded cell death induced by excitotoxic stress. Pharmacological inhibition of Rac1 in primary neuronal cortical cells prevented the increase in oxidative stress induced after overactivation of glutamate receptors. However, this was not sufficient to prevent the associated neuronal cell death. In contrast, RNAi-mediated knock down of Rac1 in primary cortical neurons prevented cell death elicited by glutamate excitotoxicity and decreased the activity of NADPH oxidase. To test whether in vivo down regulation of neuronal Rac1 was neuroprotective after pMCAO, we used tamoxifen-inducible neuron-specific conditional Rac1-knockout mice. We observed a significant 50% decrease in brain infarct volume of knockout mice and a concomitant increase in HIF-1α expression compared to littermate control mice, demonstrating that ablation of Rac1 in neurons is neuroprotective. Transmission electron microscopy performed in the ischemic brain showed that lysosomes in the infarct of Rac1- knockout mice were preserved at similar levels to those of non-infarcted tissue, while littermate mice displayed a decrease in the number of lysosomes, further corroborating the notion that Rac1 ablation in neurons is neuroprotective. Our results demonstrate that Rac1 plays important roles in the ischemic pathological cascade and that modulation of its levels is of therapeutic interest.

Differential regulation of the Rac1 GTPase-activating protein (GAP) BCR during oxygen/glucose deprivation in hippocampal and cortical neurons

Brain ischemia causes oxygen and glucose deprivation (OGD) in neurons, triggering a cascade of events leading to synaptic accumulation of glutamate. Excessive activation of glutamate receptors causes excitotoxicity and delayed cell death in vulnerable neurons. Following global cerebral ischemia, hippocampal CA1 pyramidal neurons are more vulnerable to injury than their cortical counterparts, but the mechanisms that underlie this difference are unclear. Signaling via Rho-family small GTPases, their upstream guanine nucleotide exchange factors, and GTPase-activating proteins (GAPs) is differentially dysregulated in response to OGD/ischemia in hippocampal and cortical neurons. Increased Rac1 activity caused by OGD/ischemia contributes to neuronal death in hippocampal neurons via diverse effects on NADPH oxidase activity and dendritic spine morphology. The Rac1 guanine nucleotide exchange factor Tiam1 mediates an OGD-induced increase in Rac1 activity in hippocampal neurons; however, the identity of an antagonistic GAP remains elusive. Here we show that the Rac1 GAP breakpoint cluster region (BCR) associates with NMDA receptors (NMDARs) along with Tiam1 and that this protein complex is more abundant in hippocampal compared with cortical neurons. Although total BCR is similar in the two neuronal types, BCR is more active in hippocampal compared with cortical neurons. OGD causes an NMDAR- and Ca²⁺-permeable AMPAR-dependent deactivation of BCR in hippocampal but not cortical neurons. BCR knockdown occludes OGD-induced Rac1 activation in hippocampal neurons. Furthermore, disrupting the Tiam1–NMDAR interaction with a fragment of Tiam1 blocks OGD-induced Tiam1 activation but has no effect on the deactivation of BCR. This work identifies BCR as a critical player in Rac1 regulation during OGD in hippocampal neurons.

Blockage of NOX2/MAPK/NF-κB Pathway Protects Photoreceptors against Glucose Deprivation-Induced Cell Death

Acute energy failure is one of the critical factors contributing to the pathogenic mechanisms of retinal ischemia. Our previous study demonstrated that glucose deprivation can lead to a caspase-dependent cell death of photoreceptors. The aim of this study was to decipher the upstream signal pathway in glucose deprivation- (GD-) induced cell death. We mimicked acute energy failure by using glucose deprivation in photoreceptor cells (661W cells). GD-induced oxidative stress was evaluated by measuring ROS with the DCFH-DA assay and HO-1 expression by Western blot analysis. The activation of NOX2/MAPK/NF-κB signal was assessed by Western blot and immunohistochemical assays. The roles of these signals in GD-induced cell death were measured by using their specific inhibitors. Inhibition of Rac-1 and NOX2 suppressed GD-induced oxidative stress and protected photoreceptors against GD-induced cell death. NOX2 was an upstream signal in the caspase-dependent cell death cascade, yet the downstream MAPK pathways were activated and blocking MAPK signals rescued 661W cells from GD-induced death. In addition, GD caused the activation of NF-κB signal and inhibiting NF-κB significantly protected 661W cells. These observations may provide insights for treating retinal ischemic diseases and protecting retinal neurons from ischemia-induced cell death.

Upregulation of Cdh1 signaling in the hippocampus attenuates brain damage after transient global cerebral ischemia in rats

Cerebral ischemia is a major cause of brain dysfunction. The E3 ubiquitin ligase anaphase-promoting complex and its coactivator Cdh1 have been reported to be involved in the regulation of neuronal survival, differentiation, axonal growth and synaptic development in the central nervous system. However, its role in the ischemic brain and the underlying mechanisms remain poorly understood. The present study aimed to investigate the effects of Cdh1 overexpression on the ischemic rat brain by direct intra-hippocampal injection of lentivirus-delivered Cdh1 before transient global cerebral ischemia reperfusion. Spatial memory acquisition and retention were assessed using a Morris water maze task. Neuronal damage, glial activation, oxidative stress and the synaptic ultrastructure were also examined. The results indicated that a recombinant Cdh1-encoding lentiviral vector can upregulate the expression of Cdh1 in the rat hippocampus. Cdh1 overexpression increased the survival rates of rats, reversed the abnormal accumulation of cyclin B1, alleviated neuronal death, inhibited glial activation, mitigated oxidative stress, modulated synaptic plasticity and improved neurological deficits caused by ischemia. Our study indicates that targeting the Cdh1 signaling pathway in the hippocampus may provide a promising therapeutic strategy for the clinical treatment of transient global cerebral ischemia.

A non-ionotropic activity of NMDA receptors contributes to glycine-induced neuroprotection in cerebral ischemia-reperfusion injury

NMDA receptor (NMDAR) is known for its ionotropic function. But recent evidence suggests that NMDAR also has a non-ionotropic property. To determine the role of non-ionotropic activity of NMDARs in clinical relevant conditions, we tested the effect of glycine, a co-agonist of NMDARs, in rat middle cerebral artery occlusion (MCAO), an animal model of cerebral ischemia-reperfusion injury after the animals were injected with the NMDAR channel blocker MK-801 and the glycine receptor antagonist strychnine. We show that glycine reduces the infarct volume in the brain of ischemic stroke animals pre-injected with MK-801 and strychnine. The effect of glycine is sensitive to the antagonist of glycine-GluN1 binding site and blocked by Akt inhibition. In the neurobehavioral tests, glycine improves the functional recovery of stroke animals pre-injected with MK-801 and strychnine. This study suggests that glycine-induced neuroprotection is mediated in part by the non-ionotropic activity of NMDARs via Akt activation in cerebral ischemia-reperfusion injury.

Diabetic aggravation of stroke and animal models

Cerebral ischemia in diabetics results in severe brain damage. Different animal models of cerebral ischemia have been used to study the aggravation of ischemic brain damage in the diabetic condition. Since different disease conditions such as diabetes differently affect outcome following cerebral ischemia, the Stroke Therapy Academic Industry Roundtable (STAIR) guidelines recommends use of diseased animals for evaluating neuroprotective therapies targeted to reduce cerebral ischemic damage. The goal of this review is to discuss the technicalities and pros/cons of various animal models of cerebral ischemia currently being employed to study diabetes-related ischemic brain damage. The rational use of such animal systems in studying the disease condition may better help evaluate novel therapeutic approaches for diabetes related exacerbation of ischemic brain damage.

Recombinant Slit2 Reduces Surgical Brain Injury Induced Blood Brain Barrier Disruption via Robo4 Dependent Rac1 Activation in a Rodent Model

Brain tissue surrounding surgical resection site can be injured inadvertently due to procedures such as incision, retractor stretch, and electrocauterization when performing neurosurgical procedures, which is termed as surgical brain injury (SBI). Blood brain barrier (BBB) disruption due to SBI can exacerbate brain edema in the post-operative period. Previous studies showed that Slit2 exhibited vascular anti-permeability effects outside the brain. However, BBB protective effects of Slit2 following SBI has not been evaluated. The objective of this study was to evaluate whether recombinant Slit2 via its receptor roundabout4 (Robo4) and the adaptor protein, Paxillin were involved in reducing BBB permeability in SBI rat model. Our results showed that endogenous Slit2 increased in the surrounding peri-resection brain tissue post-SBI, Robo4 remained unchanged and Paxillin showed a decreasing trend. Recombinant Slit2 administered 1 h before injury increased BBB junction proteins, reduced BBB permeability, and decreased neurodeficits 24 h post-SBI. Furthermore, recombinant Slit2 administration increased Rac1 activity which was reversed by Robo4 and Paxillin siRNA. Our findings suggest that recombinant Slit2 reduced SBI-induced BBB permeability, possibly by stabilizing BBB tight junction via Robo4 mediated Rac1 activation. Slit2 may be beneficial for BBB protection during elective neurosurgeries.

Protective Effect of 17β-Estradiol Upon Hippocampal Spine Density and Cognitive Function in an Animal Model of Vascular Dementia

The current study examined whether the steroid hormone, 17β-estradiol (E2) can exert long-lasting beneficial effects upon axonal health, synaptic plasticity, dementia-related amyloid-beta (Aβ) protein expression, and hippocampal-dependent cognitive function in an animal model of chronic cerebral hypoperfusion and vascular dementia (VaD). Chronic cerebral hypoperfusion and VaD was induced by bilateral common carotid artery occlusion (BCCAO) in adult male Sprague Dawley rats. Low dose E2 administered for the first 3-months after BCCAO exerted long-lasting beneficial effects, including significant neuroprotection of hippocampal CA1 neurons and preservation of hippocampal-dependent cognitive function when examined at 6-months after BCCAO. E2 treatment also prevented BCCAO-induced damage to hippocampal myelin sheaths and oligodendrocytes, enhanced expression of the synaptic proteins synaptophysin and PSD95 in the hippocampus, and prevented BCCAO-induced loss of total and mushroom dendritic spines in the hippocampal CA1 region. Furthermore, E2-treatment also reduced BCCAO induction of dementia-related proteins expression such as p-tau (PHF1), total ubiquitin, and Aβ1-42, when examined at 6 m after BCCAO. Taken as a whole, the results suggest that low-dose E2 replacement might be a potentially promising therapeutic modality to attenuate or block negative neurological consequences of chronic cerebral hypoperfusion and VaD.

NADPH oxidase in brain injury and neurodegenerative disorders

Oxidative stress is a common denominator in the pathology of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and multiple sclerosis, as well as in ischemic and traumatic brain injury. The brain is highly vulnerable to oxidative damage due to its high metabolic demand. However, therapies attempting to scavenge free radicals have shown little success. By shifting the focus to inhibit the generation of damaging free radicals, recent studies have identified NADPH oxidase as a major contributor to disease pathology. NADPH oxidase has the primary function to generate free radicals. In particular, there is growing evidence that the isoforms NOX1, NOX2, and NOX4 can be upregulated by a variety of neurodegenerative factors. The majority of recent studies have shown that genetic and pharmacological inhibition of NADPH oxidase enzymes are neuroprotective and able to reduce detrimental aspects of pathology following ischemic and traumatic brain injury, as well as in chronic neurodegenerative disorders. This review aims to summarize evidence supporting the role of NADPH oxidase in the pathology of these neurological disorders, explores pharmacological strategies of targeting this major oxidative stress pathway, and outlines obstacles that need to be overcome for successful translation of these therapies to the clinic.

Inhibiting NADPH oxidase protects against long-term memory impairment induced by neonatal sevoflurane exposure in mice

BACKGROUND

Neonatal exposure to anaesthetics such as sevoflurane has been reported to result in behavioural deficits in rodents. However, while oxidative injury is thought to play an underlying pathological role, the mechanisms of neurotoxicity remain unclear. In the present study, we investigated whether the NADPH oxidase inhibitor apocynin protects against long-term memory impairment produced by neonatal sevoflurane exposure in mice.

METHODS

Postnatal day six mice were divided into four groups; (1) non-anaesthesia, (2) intraperitoneal apocynin (50 mg kg(-1)) treatment, (3) 3% sevoflurane exposure for 6 h, and (4) apocynin treatment combined with sevoflurane exposure. Superoxide concentrations and NADPH oxidase expression in the brain were determined using dihydroethidium fluorescence and immunoblotting, respectively. Cleaved caspase-3 immunoblotting was used for the detection of apoptosis, and cytochrome c immunoblotting was performed to evaluate mitochondrial function. Long-term cognitive impairment was evaluated using the fear conditioning test in adulthood.

RESULTS

Sevoflurane exposure increased concentrations of superoxide (109%) and the NADPH oxidase subunit p22phox (39%) in the brain, and apocynin abolished these increases. Neonatal sevoflurane exposure caused learning deficits in adulthood. Apocynin also maintained long-term memory function in mice given neonatal sevoflurane exposure, and it reduced apoptosis and decreased cytochrome c concentrations in the brains of these mice.

CONCLUSIONS

Apocynin reduces neuronal apoptosis and protects against long-term memory impairment in mice, neonatally exposed to sevoflurane by reducing superoxide concentrations. These findings suggest that NADPH oxidase inhibitors may protect against cognitive dysfunction resulting from neonatal anaesthesia.

Cerebral Small Vessel Disease: Targeting Oxidative Stress as a Novel Therapeutic Strategy?

Cerebral small vessel disease (SVD) is a major contributor to stroke, and a leading cause of cognitive impairment and dementia. Despite the devastating effects of cerebral SVD, the pathogenesis of cerebral SVD is still not completely understood. Moreover, there are no specific pharmacological strategies for its prevention or treatment. Cerebral SVD is characterized by marked functional and structural abnormalities of the cerebral microcirculation. The clinical manifestations of these pathological changes include lacunar infarcts, white matter hyperintensities, and cerebral microbleeds. The main purpose of this review is to discuss evidence implicating oxidative stress in the arteriopathy of both non-amyloid and amyloid (cerebral amyloid angiopathy) forms of cerebral SVD and its most important risk factors (hypertension and aging), as well as its contribution to cerebral SVD-related brain injury and cognitive impairment. We also highlight current evidence of the involvement of the NADPH oxidases in the development of oxidative stress, enzymes that are a major source of reactive oxygen species in the cerebral vasculature. Lastly, we discuss potential pharmacological strategies for oxidative stress in cerebral SVD, including some of the historical and emerging NADPH oxidase inhibitors.

Robust and enduring atorvastatin-mediated memory recovery following the 4-vessel occlusion/internal carotid artery model of chronic cerebral hypoperfusion in middle-aged rats

Chronic cerebral hypoperfusion (CCH) is a common condition associated with the development and/or worsening of age-related dementia.We previously reported persistent memory loss and neurodegeneration after CCH in middle-aged rats. Statin-mediated neuroprotection has been reported after acute cerebral ischemia. Unknown, however, is whether statins can alleviate the outcome of CCH. The present study investigated whether atorvastatin attenuates the cognitive and neurohistological outcome of CCH. Rats (12–15 months old) were trained in a non-food-rewarded radial maze, and then subjected to CCH. Atorvastatin (10 mg/kg, p.o.) was administered for 42 days or 15 days, beginning 5 h after the first occlusion stage. Retrograde memory performance was assessed at 7, 14, 21, 28, and 35 days of CCH, and expressed by “latency,” “number of reference memory errors” and “number of working memory errors.” Neurodegeneration was then examined at the hippocampus and cerebral cortex. Compared to sham, CCH caused profound and persistent memory loss in the vehicle-treated groups, as indicated by increased latency (91.2% to 107.3%) and number of errors (123.5% to 2508.2%), effects from which the animals did not spontaneously recover across time. This CCH-induced retrograde amnesia was completely prevented by atorvastatin (latency: −4.3% to 3.3%; reference/working errors: −2.5% to 45.7%), regardless of the treatment duration. This effect was sustained during the entire behavioral testing period (5 weeks), even after discontinuing treatment. This robust and sustained memory-protective effect of atorvastatin occurred in the absence of neuronal rescue (39.58% to 56.45% cell loss). We suggest that atorvastatin may be promising for the treatment of cognitive sequelae associated with CCH.

Detrimental or beneficial: the role of TRPM2 in ischemia/reperfusion injury

Ischemia/reperfusion (I/R) injury is the main cause of tissue damage and dysfunction. I/R injury is characterized by Ca(2+) overload and production of reactive oxygen species (ROS), which play critical roles in the process of I/R injury to the brain, heart and kidney, but the underlying mechanisms are largely elusive. Recent evidence demonstrates that TRPM2, a Ca(2+)-permeable cationic channel and ROS sensor, is involved in I/R injury, but whether TRPM2 plays a protective or detrimental role in this process remains controversial. In this review, we discuss the recent progress in understanding the role of TRPM2 in reperfusion process after brain, heart and kidney ischemia and the potential of targeting TRPM2 for the development of therapeutic drugs to treat I/R injury.

Senegenin Inhibits Hypoxia/Reoxygenation-Induced Neuronal Apoptosis by Upregulating RhoGDIα

Neuronal apoptosis is an important event in hypoxia/reoxygenation (H/R)-induced neuronal injury. Senegenin (Sen), the predominant and most active component in Radix Polygalae root extracts, displays anti-apoptotic and anti-oxidative properties. Sen protects against H/R-induced neuronal apoptosis of highly differentiated PC12 cells and primary cortical neurons. Sen has also been investigated as a source of potential therapeutic targets. In this study, a proteomic approach was used to identify Sen-regulated proteins in PC12 cells. We found that Sen protected against H/R-induced neuronal apoptosis by upregulating RhoGDIα protein expression. The regulatory functions of RhoGDIα were investigated by knocking down RhoGDIα expression in PC12 cells using small interfering RNA (siRNA), followed by quantification of apoptosis and then altering the expression levels of apoptosis-related proteins. Our data show that after silencing RhoGDIα, the neuroprotective effects of Sen on H/R-induced PC12 cell apoptosis were absent. Furthermore, RhoGDIα silencing alleviated the Sen-mediated inhibition of the JNK pathway. Therefore, these findings indicated that Sen attenuates H/R-induced neuronal apoptosis by upregulating RhoGDIα expression and inhibiting the JNK pathway. In addition to the mechanism underlying neuroprotective effects of Sen, RhoGDIα was identified as a putative target of Sen based on a primary rat cortical neuron model of H/R-induced injury.