A Post-stroke Therapeutic Regimen with Omega-3 Polyunsaturated Fatty Acids that Promotes White Matter Integrity and Beneficial Microglial Responses after Cerebral Ischemia

Dual action of sphingosine 1-phosphate pathway in in vitro models of global cerebral ischemia

It is well accepted that sphingolipids play an important role in the pathological process of cerebral ischemia. In the present study we have investigated the involvement of sphingosine 1-phosphate (S1P) pathway in two different in vitro models of global ischemia. In organotypic hippocampal slices exposed to oxygen and glucose deprivation (OGD) we evaluated the mRNA expression of S1P metabolic enzymes and receptors (S1P1-5) by Real Time-PCR. In the same model we investigated the effect of the inhibitor of S1P lyase (SPL), LX2931, the selective antagonists of S1P2, JTE-013, and S1P3, CAY10444, quantifying the cell death in the CA1 region by propidium iodide fluorescence, and morphological and tissue organization alterations by immunohistochemistry and confocal microscopy. Moreover, we performed extracellular recordings of field excitatory postsynaptic potentials in acute slices exposed to OGD. In organotypic slices OGD induced a significant increase of SPL at mRNA level and of S1P2 and S1P3 at both mRNA and protein level. The incubation with LX2931, JTE-013 or CAY10444 was able to reduce CA1 damage induced by OGD in organotypic slices and provoked a significant delay of the onset of anoxic depolarization on acute slices. Moreover, S1P2 and S1P3 antagonists prevented the increase of TREM2 induced by OGD. Our results reveal a dual role of S1P pathway in brain ischemia: intracellular S1P, degraded via SPL, appears to be beneficial whereas signaling via S1P2 and S1P3 is detrimental to the disease. These findings support the notion that SPL, S1P2 and S1P3 are promising therapeutic targets in brain ischemia.

Sulforaphane: An emerging star in neuroprotection and neurological disease prevention

Neurological diseases, including both acute injuries and chronic neurodegenerative disorders, represent major contributors to morbidity and mortality worldwide. Chronic neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), which require long-term management, present significant challenges in the search for neuroprotective agents with reduced adverse effects and enhanced therapeutic efficacy. Sulforaphane (SFN), a bioactive compound found in cruciferous vegetables like broccoli and cauliflower, has garnered considerable attention for its potent neuroprotective properties and overall health benefits. Marketed primarily as a dietary supplement, SFN has shown a variety of biological activities and therapeutic potential in neurological diseases. Recent surging studies including ours have highlighted its ability to impede the progression of AD, PD, and cerebral ischemia by fostering neurogenesis and inhibiting apoptosis, oxidative stress, and neuroinflammation. This review aims to summarize the latest research on SFN, exploring its advanced therapeutic potential and underlying mechanisms in various neurological diseases, offering a comprehensive overview for researchers focused on neurological pathogenesis and drug development in neuroprotection.

Veterinary medical care in rodent models of stroke: Pitfalls and refinements to balance quality of science and animal welfare

Rodent models of cerebral ischemia provide a valuable contribution to a better understanding of stroke pathophysiology, to validate diagnostic methods, and to enable testing of new treatments for ischemia-reperfusion damage and comorbidities. However, ethical concerns have led to increased attention to the welfare aspects of such models. Supportive therapies are an essential part of the overall animal care and use program and should be tailored to the experimental model being studied, the regulatory requirements, and research objectives to achieve high-quality preclinical studies and ethical research practices. On the other hand, the use of veterinary medical treatments in preclinical models of stroke must balance the needs of animal care and potential sources of bias in experimental results. This report provides a systematic review of the scientific literature covering the relevant period from years 1988 to September 2024, with the aim to investigating veterinary medical interventions useful to minimize suffering in rodent models of stroke without producing experimental bias. The research findings, consolidated from 181 selected studies, published from 1991 to 2023, indicate the feasibility of implementing personalized protocols of anesthesia, analgesics, antibiotics, and other supportive therapies in rodent models of stroke, while avoiding scientific interferences. These data fill a gap in current knowledge and could be of interest for an interdisciplinary audience working with rodent models of stroke, stimulating further refinements to safeguard both animal welfare and the validity of experimental findings, and may promote the culture of ethical conduct in various research fields and disciplines.

Dietary omega-3 polyunsaturated fatty acids reduce cytochrome c oxidase in brain white matter and sensorimotor regions while increasing functional interactions between neural systems related to escape behavior in postpartum rats

Introduction

Previously, we showed that omega-3 polyunsaturated fatty acid n-3 (PUFA) supplementation improved the performance of postpartum rats in the shuttle box escape test (SBET).

Methods

The brains of these rats were used in the current study which examined brain cytochrome c oxidase (CCO) activity in white matter bundles and 39 regions spanning sensorimotor, limbic, and cognitive areas to determine the effects of n-3 PUFAs on neural metabolic capacity and network interactions.

Results

We found that n-3 PUFA supplementation decreased CCO activity in white matter bundles, deep and superficial areas within the inferior colliculus, the anterior and barrel field regions of the primary somatic sensorimotor cortex, the secondary somatic sensorimotor cortex, the lateral, anterior regions of the secondary visual cortex and the ventral posterior nucleus of the thalamus, and the medial nucleus of the amygdala. Structural equation modeling revealed that animals consuming diets without n-3 PUFAs exhibited fewer inter-regional interactions when compared to those fed diets with n-3 PUFAs. Without n-3 PUFAs, inter-regional interactions were observed between the posterior cingulate cortex and amygdala as well as among amygdala subregions. With n-3 PUFAs, more inter-regional interactions were observed, particularly between regions associated with fear memory processing and escape. Correlations between regional CCO activity and SBET behavior were observed in rats lacking dietary n-3 PUFAs but not in those supplemented with these nutrients.

Discussion

In conclusion, consumption of n-3 PUFAs results in reduced CCO activity in white matter bundles and sensorimotor regions, reflecting more efficient neurotransmission, and an increase in inter-regional interactions, facilitating escape from footshock.

A dietary intervention with conjugated linoleic acid enhances microstructural white matter reorganization in experimental stroke

Background

A dietary supplementation with conjugated linoleic acid (CLA) was shown to attenuate inflammation and increase the proportions of circulating regulatory T cells (Tregs) and M2-type macrophages in disease models such as autoimmune encephalitis and arteriosclerosis. Since Tregs and anti-inflammatory (M2-type) macrophages were found to enhance stroke recovery, we hypothesized that CLA-supplementation might improve stroke recovery via immune modulatory effects.

Methods

Functional assessment was performed over 90 days after induction of experimental photothrombotic stroke in wild type mice (n = 37, sham n = 10). Subsequently, immunological characterization of different immunological compartments (n = 16), ex vivo magnetic resonance (MR, n = 12) imaging and immunohistochemical staining (n = 8) was performed. Additionally, we tested the effect of CLA in vitro on peripheral blood mononuclear cells from human stroke patients and healthy controls (n = 12).

Results

MR diffusion tensor imaging (DTI) demonstrated enhanced microstructural reorganization of interhemispheric white matter tracts, dependent on lesion size. Functional recovery over 90 days remained unaffected. Detailed immunological analyses across various compartments revealed no significant long-term immunological alterations due to CLA. However, analyses of human blood samples post-stroke showed reduced levels of pro-inflammatory interferon-γ (IFN-γ) and tumor necrosis factor alpha (TNF-α) release by T-lymphocytes following in vitro treatment with CLA.

Conclusion

We aimed to explore the efficacy of a dietary intervention with minimal known side effects that could be accessible to human stroke patients, regardless of the degree of disability, and without the risks associated with aggressive immunomodulatory therapies. Our main findings include improved microstructural reorganization in small infarcts and a reduced inflammatory response of human T cells in vitro.

Unraveling the impact of Omega-3 polyunsaturated fatty acids on blood-brain barrier (BBB) integrity and glymphatic function

Alzheimer's disease (AD) and other forms of dementia represent major public health challenges but effective therapeutic options are limited. Pathological brain aging is associated with microvascular changes and impaired clearance systems. The application of omega-3 polyunsaturated fatty acids (n-3 or omega-3 PUFAs) is one of the most promising nutritional interventions in neurodegenerative disorders from epidemiological data, clinical and pre-clinical studies. As essential components of neuronal membranes, n-3 PUFAs have shown neuroprotection and anti-inflammatory effects, as well as modulatory effects through microvascular pathophysiology, amyloid-beta (Aβ) clearance and glymphatic pathways. This review meticulously explores these underlying mechanisms that contribute to the beneficial effects of n-3 PUFAs against AD and dementia, synthesizing evidence from both animal and interventional studies.

Metabolic Reprogramming in Gliocyte Post-cerebral Ischemia/ Reperfusion: From Pathophysiology to Therapeutic Potential

Ischemic stroke is a leading cause of disability and death worldwide. However, the clinical efficacy of recanalization therapy as a preferred option is significantly hindered by reperfusion injury. The transformation between different phenotypes of gliocytes is closely associated with cerebral ischemia/ reperfusion injury (CI/RI). Moreover, gliocyte polarization induces metabolic reprogramming, which refers to the shift in gliocyte phenotype and the overall transformation of the metabolic network to compensate for energy demand and building block requirements during CI/RI caused by hypoxia, energy deficiency, and oxidative stress. Within microglia, the pro-inflammatory phenotype exhibits upregulated glycolysis, pentose phosphate pathway, fatty acid synthesis, and glutamine synthesis, whereas the anti-inflammatory phenotype demonstrates enhanced mitochondrial oxidative phosphorylation and fatty acid oxidation. Reactive astrocytes display increased glycolysis but impaired glycogenolysis and reduced glutamate uptake after CI/RI. There is mounting evidence suggesting that manipulation of energy metabolism homeostasis can induce microglial cells and astrocytes to switch from neurotoxic to neuroprotective phenotypes. A comprehensive understanding of underlying mechanisms and manipulation strategies targeting metabolic pathways could potentially enable gliocytes to be reprogrammed toward beneficial functions while opening new therapeutic avenues for CI/RI treatment. This review provides an overview of current insights into metabolic reprogramming mechanisms in microglia and astrocytes within the pathophysiological context of CI/RI, along with potential pharmacological targets. Herein, we emphasize the potential of metabolic reprogramming of gliocytes as a therapeutic target for CI/RI and aim to offer a novel perspective in the treatment of CI/RI.

Arachidonic and docosahexaenoic acid supplementation and brain maturation in preterm infants; a double blind RCT

BACKGROUND

Arachidonic acid (ARA) and docosahexaenoic acid (DHA) are important structural components of neural cellular membranes and possess anti-inflammatory properties. Very preterm infants are deprived of the enhanced placental supply of these fatty acids, but the benefit of postnatal supplementation on brain development is uncertain. The aim of this study was to test the hypothesis that early enteral supplementation with ARA and DHA in preterm infants improves white matter (WM) microstructure assessed by diffusion-weighted MRI at term equivalent age.

METHODS

In this double-blind, randomized controlled trial, infants born before 29 weeks gestational age were allocated to either 100 mg/kg ARA and 50 mg/kg DHA (ARA:DHA group) or medium chain triglycerides (control). Supplements were started on the second day of life and provided until 36 weeks postmenstrual age. The primary outcome was brain maturation assessed by diffusion tensor imaging (DTI) using Tract-Based Spatial Statistics (TBSS) analysis.

RESULTS

We included 120 infants (60 per group) in the trial; mean (range) gestational age was 26+3 (22+6 - 28+6) weeks and postmenstrual age at scan was 41+3 (39+1 - 47+0) weeks. Ninety-two infants underwent MRI imaging, and of these, 90 had successful T1/T2 weighted MR images and 74 had DTI data of acceptable quality. TBSS did not show significant differences in mean or axial diffusivity between the groups, but demonstrated significantly higher fractional anisotropy in several large WM tracts in the ARA:DHA group, including corpus callosum, the anterior and posterior limb of the internal capsula, inferior occipitofrontal fasciculus, uncinate fasciculus, and the inferior longitudinal fasciculus. Radial diffusivity was also significantly lower in several of the same WM tracts in the ARA:DHA group.

CONCLUSION

This study suggests that supplementation with ARA and DHA at doses matching estimated fetal accretion rates improves WM maturation compared to control treatment, but further studies are needed to ascertain any functional benefit.

CLINICAL TRIAL REGISTRATION

www.

CLINICALTRIALS

gov; ID:NCT03555019.

Phenomic Microglia Diversity as a Druggable Target in the Hippocampus in Neurodegenerative Diseases

Phenomics, the complexity of microglia phenotypes and their related functions compels the continuous study of microglia in disease animal models to find druggable targets for neurodegenerative disorders. Activation of microglia was long considered detrimental for neuron survival, but more recently it has become apparent that the real scenario of microglia morphofunctional diversity is far more complex. In this review, we discuss the recent literature on the alterations in microglia phenomics in the hippocampus of animal models of normal brain aging, acute neuroinflammation, ischemia, and neurodegenerative disorders, such as AD. Microglia undergo phenomic changes consisting of transcriptional, functional, and morphological changes that transform them into cells with different properties and functions. The classical subdivision of microglia into M1 and M2, two different, all-or-nothing states is too simplistic, and does not correspond to the variety of phenotypes recently discovered in the brain. We will discuss the phenomic modifications of microglia focusing not only on the differences in microglia reactivity in the diverse models of neurodegenerative disorders, but also among different areas of the brain. For instance, in contiguous and highly interconnected regions of the rat hippocampus, microglia show a differential, finely regulated, and region-specific reactivity, demonstrating that microglia responses are not uniform, but vary significantly from area to area in response to insults. It is of great interest to verify whether the differences in microglia reactivity may explain the differential susceptibility of different brain areas to insults, and particularly the higher sensitivity of CA1 pyramidal neurons to inflammatory stimuli. Understanding the spatiotemporal heterogeneity of microglia phenomics in health and disease is of paramount importance to find new druggable targets for the development of novel microglia-targeted therapies in different CNS disorders. This will allow interventions in three different ways: (i) by suppressing the pro-inflammatory properties of microglia to limit the deleterious effect of their activation; (ii) by modulating microglia phenotypic change to favor anti-inflammatory properties; (iii) by influencing microglia priming early in the disease process.

Else_BRB_110660Docosahexaenoic acid promotes M2 microglia phenotype via activating PPARγ-mediated ERK/AKT pathway against cerebral ischemia-reperfusion injury

In ischemia-reperfusion stroke, microglia play a dual role in brain injury as well as brain repair, and promoting their switch from a pro-inflammatory M1 phenotype to an anti-inflammatory M2 phenotype is considered to be a potential therapeutic strategy. Docosahexaenoic acid (DHA) is an essential long-chain omega-3 polyunsaturated fatty acid that exhibits potent anti-inflammatory properties in the acute phase of ischemic stroke, but its effect on microglia polarization is unknown. Thus, the objective of this study was to investigate the neuroprotective effects of DHA on rat brain following ischemia-reperfusion injury, and to investigate the mechanism by which DHA regulates microglia polarization. We administered DHA 5mg/kg intraperitoneally daily for 3 d following a transient middle cerebral artery occlusion reperfusion model in rats. The protective effects of DHA on cerebral ischemia-reperfusion injury were detected by TTC staining, HE staining, Nissler staining, and TUNEL staining. Quantitative real-time PCR, immunofluorescence, western blot, and enzyme-linked immunosorbent assay were used to detect the expression of M1 and M2 microglia-associated markers and PPARγ-mediated ERK/AKT signaling pathway proteins. We found that DHA significantly improved brain injury by decreasing the expression of the M1 phenotypic marker (iNOS, CD16) and increasing the expression of the M2 phenotypic marker (Arg-1, CD206). DHA also increased the expression of peroxisome proliferator-activated receptor gamma (PPARγ) mRNA and protein, increased the expression of the pathway protein AKT, and decreased the expression of ERK1/2. In addition, DHA promoted the expression of anti-inflammatory factor IL-10 and decreased the expression of pro-inflammatory factors TNF-α and IL-1β. However, the PPARγ antagonist GW9662 greatly blocked these beneficial effects. These results suggest that DHA may activate PPARγ to inhibit ERK and activate AKT signaling pathways to regulate microglia polarization, thereby reducing neuroinflammation and promoting neurological recovery to alleviate cerebral ischemia-reperfusion injury.

Systematic Analysis of RNA Expression Profiles in Different Ischemic Cortices in MCAO Mice

The prognosis of ischemic stroke patients is highly associated with the collateral circulation. And the competing endogenous RNAs (ceRNAs) generated from different compensatory supply regions may also involve in the regulation of ischemic tissues prognosis. In this study, we found the apoptosis progress of ischemic neurons in posterior circulation-supplied regions (close to PCA, cortex2) was much slower than that in anterior circulation-supplied territory (close to ACA, cortex1) in MCAO-3-h mice. Using the RNA sequencing and functional enrichment analysis, we analyzed the difference between RNA expression profile in cortex1 and cortex2 and the related biological processes. The results indicated that the differential expressed ceRNAs in cortex1 were involved in cell process under acute injury, while the differential expressed ceRNAs in cortex2 was more likely to participate in long-term injury and repair process. Besides, by establishing the miRNA-ceRNA interaction network we further sorted out two specifically distributed miRNAs, namely mmu-miR446i-3p (in cortex1) and mmu-miR3473d (in cortex2). And the specifically increased mmu-miR3473d in cortex2 mainly involved the angiogenesis and cell proliferation after ischemic stroke, which may be the critical reason for the longer therapeutic time window in cortex2. In conclusion, the present study reported the specific changes of ceRNAs in distinct compensatory regions potentially involved in the evolution of cerebral ischemic tissues and the unbalance prognosis after stroke. It provided more evidence for the collateral compensatory effects on patients' prognosis and carried out the new targets for the ischemic stroke therapy.

Intracerebral Hemorrhage Models and Behavioral Tests in Rodents

Intracerebral hemorrhage (ICH) is one of the common types of stroke, which can cause neurological dysfunction. In preclinical ICH studies, researchers often established rodent models by donor/autologous whole blood or a collagenase injection. White matter injury (WMI) can result from primary and secondary injuries after ICH. WMI can lead to short- and long-term neurological impairment, and functional recovery can assess the effect of drug therapy after ICH. Therefore, researchers have devised various behavioral tests to assess dysfunction. This review compares the two ICH modeling methods in rodents and summarizes the pathological mechanisms underlying dysfunction after ICH. We also summarize the functions and characteristics of various behavioral methods, including sensation, motion, emotion, and cognition, to assist researchers in selecting the appropriate tests for preclinical ICH research.

Effects of HF-rTMS on microglial polarization and white matter integrity in rats with poststroke cognitive impairment

Poststroke cognitive impairment (PSCI) occurs frequently after stroke, but effective treatments are lacking. Previous studies have revealed that high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) has a beneficial effect on PSCI, but the mechanism is unclear. This study aimed to evaluate the effect of 10 and 20 Hz HF-rTMS on PSCI and the possible mechanisms. An ischemic stroke rat model was established by transient middle cerebral artery occlusion (tMCAO). The modified neurological deficit score (mNSS) and Morris water maze tests were conducted to assess neurological function and cognitive function. Luxol Fast Blue (LFB) staining was performed to evaluate white matter damage. Proinflammatory and anti-inflammatory cytokines were measured using enzyme-linked immunosorbent assays (ELISA). Immunofluorescence was used to assess microglial activation and polarization. Western blotting was performed to measure JAK2-STAT3 pathway-related protein expression. We found that HF-rTMS decreased the neurological deficit score. Compared with 10 Hz HF-rTMS, 20 Hz HF-rTMS more markedly improved the cognitive function of tMCAO rats at day 28 after operation. Furthermore, 20 Hz HF-rTMS attenuates white matter lesion, decreased proinflammatory cytokine levels, and increased anti-inflammatory cytokine levels. It also decreased the number of CD68- and CD16/32-positive microglia and increased the number of CD206-positive microglia. In addition, p-JAK2, JAK2, p-STAT3 and STAT3 expression was increased. These findings suggest that HF-rTMS improves cognitive function and attenuates white matter lesion in tMCAO rats by shifting microglia toward the M2 phenotype. Mechanisms may be related to regulation JAK2-STAT3 pathways.

Relationship between Hypoxic and Immune Pathways Activation in the Progression of Neuroinflammation: Role of HIF-1α and Th17 Cells

Neuroinflammation is a common event in degenerative diseases of the central and peripheral nervous system, triggered by alterations in the immune system or inflammatory cascade. The pathophysiology of these disorders is multifactorial, whereby the therapy available has low clinical efficacy. This review propounds the relationship between the deregulation of T helper cells and hypoxia, mainly Th17 and HIF-1α molecular pathways, events that are involved in the occurrence of the neuroinflammation. The clinical expression of neuroinflammation is included in prevalent pathologies such as multiple sclerosis, Guillain-Barré syndrome, and Alzheimer's disease, among others. In addition, therapeutic targets are analyzed in relation to the pathways that induced neuroinflammation.

Amelioration of central neurodegeneration by docosahexaenoic acid in trigeminal neuralgia rats through the regulation of central neuroinflammation

Trigeminal neuralgia (TN) is a stubborn head and face neuropathic pain with complex pathogenesis. Patients with TN have a significantly increased risk of central neurodegeneration, which manifests as cognitive impairment and memory loss, but the specific mechanism underlying central nervous degeneration is still unclear. This study aimed to explore central neurodegeneration and its possible mechanism of action in TN rats based on changes in the brain fatty acid content and microglia-related neuroinflammation. Using a TN neuropathic pain model established by us, we found that TN rats have obvious cognitive impairment. Furthermore, changes in the brain fatty acid content were analyzed using gas chromatography-mass spectrometry (GC-MS). It was found that the docosahexaenoic acid (DHA) content in the central nervous system (CNS) of TN rats was significantly decreased compared to that in the CNS of Sham rats. An important component in maintaining brain cognition, DHA also plays a key role in regulating central neuroinflammation. Here, by continuous supplementation of DHA, the CNS DHA content was increased to a certain extent in TN rats. The cognitive impairment of TN rats was improved after restoring the central DHA level; this may be related to the improvement of neuroinflammation through the DHA-mediated regulation of microglial polarization. Overall, this study provides a theoretical basis for explaining the pathogenesis of central neurodegeneration in TN. It also suggests DHA as a target for protecting the CNS of patients with TN from damage.

High-resolution micro-CT for 3D infarct characterization and segmentation in mice stroke models

Characterization of brain infarct lesions in rodent models of stroke is crucial to assess stroke pathophysiology and therapy outcome. Until recently, the analysis of brain lesions was performed using two techniques: (1) histological methods, such as TTC (Triphenyltetrazolium chloride), a time-consuming and inaccurate process; or (2) MRI imaging, a faster, 3D imaging method, that comes at a high cost. In the last decade, high-resolution micro-CT for 3D sample analysis turned into a simple, fast, and cheaper solution. Here, we successfully describe the application of brain contrasting agents (Osmium tetroxide and inorganic iodine) for high-resolution micro-CT imaging for fine location and quantification of ischemic lesion and edema in mouse preclinical stroke models. We used the intraluminal transient MCAO (Middle Cerebral Artery Occlusion) mouse stroke model to identify and quantify ischemic lesion and edema, and segment core and penumbra regions at different time points after ischemia, by manual and automatic methods. In the transient-ischemic-attack (TIA) mouse model, we can quantify striatal myelinated fibers degeneration. Of note, whole brain 3D reconstructions allow brain atlas co-registration, to identify the affected brain areas, and correlate them with functional impairment. This methodology proves to be a breakthrough in the field, by providing a precise and detailed assessment of stroke outcomes in preclinical animal studies.

Role of Glial Cell-Derived Oxidative Stress in Blood-Brain Barrier Damage after Acute Ischemic Stroke

The integrity of the blood-brain barrier (BBB) is mainly maintained by endothelial cells and basement membrane and could be regulated by pericytes, neurons, and glial cells including astrocytes, microglia, oligodendrocytes (OLs), and oligodendrocyte progenitor cells (OPCs). BBB damage is the main pathological basis of hemorrhage transformation (HT) and vasogenic edema after stroke. In addition, BBB damage-induced HT and vasogenic edema will aggravate the secondary brain tissue damage. Of note, after reperfusion, oxidative stress-initiated cascade plays a critical role in the BBB damage after acute ischemic stroke (AIS). Although endothelial cells are the target of oxidative stress, the role of glial cell-derived oxidative stress in BBB damage after AIS also should receive more attention. In the current review, we first introduce the physiology and pathophysiology of the BBB, then we summarize the possible mechanisms related to BBB damage after AIS. We aim to characterize the role of glial cell-derived oxidative stress in BBB damage after AIS and discuss the role of oxidative stress in astrocytes, microglia cells and oligodendrocytes in after AIS, respectively.

Roles of Fatty Acids in Microglial Polarization: Evidence from In Vitro and In Vivo Studies on Neurodegenerative Diseases

Microglial polarization to the M1 phenotype (classically activated) or the M2 phenotype (alternatively activated) is critical in determining the fate of immune responses in neurodegenerative diseases (NDs). M1 macrophages contribute to neurotoxicity, neuronal and synaptic damage, and oxidative stress and are the first line of defense, and M2 macrophages elicit an anti-inflammatory response to regulate neuroinflammation, clear cell debris, and promote neuroregeneration. Various studies have focused on the ability of natural compounds to promote microglial polarization from the M1 phenotype to the M2 phenotype in several diseases, including NDs. However, studies on the roles of fatty acids in microglial polarization and their implications in NDs are a rare find. Most of the studies support the role of polyunsaturated fatty acids (PUFAs) in microglial polarization using cell and animal models. Thus, we aimed to collect data and provide a narrative account of microglial types, markers, and studies pertaining to fatty acids, particularly PUFAs, on microglial polarization and their neuroprotective effects. The involvement of only PUFAs in the chosen topic necessitates more in-depth research into the role of unexplored fatty acids in microglial polarization and their mechanistic implications. The review also highlights limitations and future challenges.

Pathways Involved in Remyelination after Cerebral Ischemia

Brain ischemia, also known as ischemic stroke, occurs when there is a lack of blood supply into the brain. When an ischemic insult appears, both neurons and glial cells can react in several ways that will determine the severity and prognosis. This high heterogeneity of responses has been a major obstacle in developing effective treatments or preventive methods for stroke. Although white matter pathophysiology has not been deeply assessed in stroke, its remodelling can greatly influence the clinical outcome and the disability degree. Oligodendrocytes, the unique cell type implied in CNS myelination, are sensible to ischemic damage. Loss of myelin sheaths can compromise axon survival, so new Oligodendrocyte Precursor Cells are required to restore brain function. Stroke can, therefore, enhance oligodendrogenesis to regenerate those new oligodendrocytes that will ensheath the damaged axons. Given that myelination is a highly complex process that requires coordination of multiple pathways such as Sonic Hedgehog, RTKs or Wnt/β-catenin, we will analyse new research highlighting their importance after brain ischemia. In addition, oligodendrocytes are not isolated cells inside the brain, but rather form part of a dynamic environment of interactions between neurons and glial cells. For this reason, we will put some context into how microglia and astrocytes react against stroke and influence oligodendrogenesis to highlight the relevance of remyelination in the ischemic brain. This will help to guide future studies to develop treatments focused on potentiating the ability of the brain to repair the damage.

Effects of enriched environment on microglia and functional white matter recovery in rats with post stroke cognitive impairment

BACKGROUND

White matter damage is an important contributor to cognitive impairment after stroke. This study was designed to explore the beneficial effects of enriched environment (EE) on white matter recovery and cognitive dysfunction after stroke, and further explore the potential mechanism of EE on white matter recovery from the perspective of microglia and microglia-mediated neuroinflammation.

METHODS

Male SD rats underwent middle cerebral artery occlusion(MCAO) or sham surgery. During the MCAO operation, a laser Doppler blood flow meter was used to monitor the blood flow to ensure the success of the model. At 72 hours after the operation, 3 rats were selected for TTC staining to identify the infarct size. One week after surgery, the rats were randomly assigned into four different groups-MCAO+standard environment (SE), MCAO+enriched environment(EE), Sham+SE and Sham+EE for 4 weeks. At four weeks after MCAO surgery, neurological function deficiency condition and cognitive function were assessed using Longa score and Morris Water Maze prior to euthanasia. The loss or regeneration of myelin was stained with LFB, the expression of myelin regeneration-related protein and microglia protein was quantified by western blot and immunofluorescence, and the level of inflammatory factors was measured by ELISA.

RESULTS

EE treatment remarkably decreased the neurological deficit score, ameliorated the cognitive functional deficit in MCAO rats. Furthermore, EE alleviated white matter lesions and demyelination, increased myelin basic protein expression and decreased the number of activated microglia in the hippocampus of MCAO rats. In addition, ELISA analysis indicated that EE decreased the level of IL-1β, IL-6, which further suggests that EE may reduce the level of pro-inflammatory factors by affecting the expression of microglia marker, IBA1, provide a benefit physiological environment for myelin recovery, and improve post stroke cognitive impairment.

CONCLUSIONS

Our results suggest that exposure to EE substantially reduced the damage to brain tissue caused by activation of microglia activation, decreased the level of pro-inflammatory cytokins, which may induced by microglia, protected and promote white matter recovery to improve cognitive function after stroke. Our findings also indicate exposure to EE is beneficial for patients with white matter impairment characterised by white matter disease-related inflammation.

Hypoxia/Ischemia-Induced Rod Microglia Phenotype in CA1 Hippocampal Slices

The complexity of microglia phenotypes and their related functions compels the continuous study of microglia in diseases animal models. We demonstrated that oxygen-glucose deprivation (OGD) induced rapid, time- and space-dependent phenotypic microglia modifications in CA1 stratum pyramidalis (SP) and stratum radiatum (SR) of rat organotypic hippocampal slices as well as the degeneration of pyramidal neurons, especially in the outer layer of SP. Twenty-four h following OGD, many rod microglia formed trains of elongated cells spanning from the SR throughout the CA1, reaching the SP outer layer where they acquired a round-shaped amoeboid phagocytic head and phagocytosed most of the pyknotic, damaged neurons. NIR-laser treatment, known to preserve neuronal viability after OGD, prevented rod microglia formation. In CA3 SP, pyramidal neurons were less damaged, no rod microglia were found. Thirty-six h after OGD, neuronal damage was more pronounced in SP outer and inner layers of CA1, rod microglia cells were no longer detectable, and most microglia were amoeboid/phagocytic. Damaged neurons, more numerous 36 h after OGD, were phagocytosed by amoeboid microglia in both inner and outer layers of CA1. In response to OGD, microglia can acquire different morphofunctional phenotypes which depend on the time after the insult and on the subregion where microglia are located.

The mechanism of microglia-mediated immune inflammation in ischemic stroke and the role of natural botanical components in regulating microglia: A review

Ischemic stroke (IS) is one of the most fatal diseases. Neuroimmunity, inflammation, and oxidative stress play important roles in various complex mechanisms of IS. In particular, the early proinflammatory response resulting from the overactivation of resident microglia and the infiltration of circulating monocytes and macrophages in the brain after cerebral ischemia leads to secondary brain injury. Microglia are innate immune cells in the brain that constantly monitor the brain microenvironment under normal conditions. Once ischemia occurs, microglia are activated to produce dual effects of neurotoxicity and neuroprotection, and the balance of the two effects determines the fate of damaged neurons. The activation of microglia is defined as the classical activation (M1 type) or alternative activation (M2 type). M1 type microglia secrete pro-inflammatory cytokines and neurotoxic mediators to exacerbate neuronal damage, while M2 type microglia promote a repairing anti-inflammatory response. Fine regulation of M1/M2 microglial activation to minimize damage and maximize protection has important therapeutic value. This review focuses on the interaction between M1/M2 microglia and other immune cells involved in the regulation of IS phenotypic characteristics, and the mechanism of natural plant components regulating microglia after IS, providing novel candidate drugs for regulating microglial balance and IS drug development.

Maternal n-3 Polyunsaturated Fatty Acid Enriched Diet Commands Fatty Acid Composition in Postnatal Brain and Protects from Neonatal Arterial Focal Stroke

The fetus is strongly dependent on nutrients from the mother, including polyunsaturated fatty acids (PUFA). In adult animals, n-3 PUFA ameliorates stroke-mediated brain injury, but the modulatory effects of different PUFA content in maternal diet on focal arterial stroke in neonates are unknown. This study explored effects of maternal n-3 or n-6 enriched PUFA diets on neonatal stroke outcomes. Pregnant mice were assigned three isocaloric diets until offspring reached postnatal day (P) 10–13: standard, long-chain n-3 PUFA (n-3) or n-6 PUFA (n-6) enriched. Fatty acid profiles in plasma and brain of mothers and pups were determined by gas chromatography–mass spectrometry and cytokines/chemokines by multiplex protein analysis. Transient middle cerebral artery occlusion (tMCAO) was induced in P9-10 pups and cytokine and chemokine accumulation, caspase-3 and calpain-dependent spectrin cleavage and brain infarct volume were analyzed. The n-3 diet uniquely altered brain lipid profile in naïve pups. In contrast, cytokine and chemokine levels did not differ between n-3 and n-6 diet in naïve pups. tMCAO triggered accumulation of inflammatory cytokines and caspase-3-dependent and -independent cell death in ischemic-reperfused regions in pups regardless of diet, but magnitude of neuroinflammation and caspase-3 activation were attenuated in pups on n-3 diet, leading to protection against neonatal stroke. In conclusion, maternal/postnatal n-3 enriched diet markedly rearranges neonatal brain lipid composition and modulates the response to ischemia. While standard diet is sufficient to maintain low levels of inflammatory cytokines and chemokines under physiological conditions, n-3 PUFA enriched diet, but not standard diet, attenuates increases of inflammatory cytokines and chemokines in ischemic-reperfused regions and protects from neonatal stroke.

Identification of miRNAs That Mediate Protective Functions of Anti-Cancer Drugs During White Matter Ischemic Injury

We have previously shown that two anti-cancer drugs, CX-4945 and MS-275, protect and preserve white matter (WM) architecture and improve functional recovery in a model of WM ischemic injury. While both compounds promote recovery, CX-4945 is a selective Casein kinase 2 (CK2) inhibitor and MS-275 is a selective Class I histone deacetylase (HDAC) inhibitor. Alterations in microRNAs (miRNAs) mediate some of the protective actions of these drugs. In this study, we aimed to (1) identify miRNAs expressed in mouse optic nerves (MONs); (2) determine which miRNAs are regulated by oxygen glucose deprivation (OGD); and (3) determine the effects of CX-4945 and MS-275 treatment on miRNA expression. RNA isolated from MONs from control and OGD-treated animals with and without CX-4945 or MS-275 treatment were quantified using NanoString nCounter^® miRNA expression profiling. Comparative analysis of experimental groups revealed that 12 miRNAs were expressed at high levels in MONs. OGD upregulated five miRNAs (miR-1959, miR-501-3p, miR-146b, miR-201, and miR-335-3p) and downregulated two miRNAs (miR-1937a and miR-1937b) compared to controls. OGD with CX-4945 upregulated miR-1937a and miR-1937b, and downregulated miR-501-3p, miR-200a, miR-1959, and miR-654-3p compared to OGD alone. OGD with MS-275 upregulated miR-2134, miR-2141, miR-2133, miR-34b-5p, miR-153, miR-487b, miR-376b, and downregulated miR-717, miR-190, miR-27a, miR-1959, miR-200a, miR-501-3p, and miR-200c compared to OGD alone. Interestingly, miR-501-3p and miR-1959 were the only miRNAs upregulated by OGD, and downregulated by OGD plus CX-4945 and MS-275. Therefore, we suggest that protective functions of CX-4945 or MS-275 against WM injury maybe mediated, in part, through miRNA expression.

Microglia-leucocyte axis in cerebral ischaemia and inflammation in the developing brain

Development of the Central Nervous System (CNS) is reliant on the proper function of numerous intricately orchestrated mechanisms that mature independently, including constant communication between the CNS and the peripheral immune system. This review summarizes experimental knowledge of how cerebral ischaemia in infants and children alters physiological communication between leucocytes, brain immune cells, microglia and the neurovascular unit (NVU)-the "microglia-leucocyte axis"-and contributes to acute and long-term brain injury. We outline physiological development of CNS barriers in relation to microglial and leucocyte maturation and the plethora of mechanisms by which microglia and peripheral leucocytes communicate during postnatal period, including receptor-mediated and intracellular inflammatory signalling, lipids, soluble factors and extracellular vesicles. We focus on the "microglia-leucocyte axis" in rodent models of most common ischaemic brain diseases in the at-term infants, hypoxic-ischaemic encephalopathy (HIE) and focal arterial stroke and discuss commonalities and distinctions of immune-neurovascular mechanisms in neonatal and childhood stroke compared to stroke in adults. Given that hypoxic and ischaemic brain damage involve Toll-like receptor (TLR) activation, we discuss the modulatory role of viral and bacterial TLR2/3/4-mediated infection in HIE, perinatal and childhood stroke. Furthermore, we provide perspective of the dynamics and contribution of the axis in cerebral ischaemia depending on the CNS maturational stage at the time of insult, and modulation independently and in consort by individual axis components and in a sex dependent ways. Improved understanding on how to modify crosstalk between microglia and leucocytes will aid in developing age-appropriate therapies for infants and children who suffered cerebral ischaemia.

Supplemental N-3 Polyunsaturated Fatty Acids Limit A1-Specific Astrocyte Polarization via Attenuating Mitochondrial Dysfunction in Ischemic Stroke in Mice

Ischemic stroke is one of the leading causes of death and disability for adults, which lacks effective treatments. Dietary intake of n-3 polyunsaturated fatty acids (n-3 PUFAs) exerts beneficial effects on ischemic stroke by attenuating neuron death and inflammation induced by microglial activation. However, the impact and mechanism of n-3 PUFAs on astrocyte function during stroke have not yet been well investigated. Our current study found that dietary n-3 PUFAs decreased the infarction volume and improved the neurofunction in the mice model of transient middle cerebral artery occlusion (tMCAO). Notably, n-3 PUFAs reduced the stroke-induced A1 astrocyte polarization both in vivo and in vitro. We have demonstrated that exogenous n-3 PUFAs attenuated mitochondrial oxidative stress and increased the mitophagy of astrocytes in the condition of hypoxia. Furthermore, we provided evidence that treatment with the mitochondrial-derived antioxidant, mito-TEMPO, abrogated the n-3 PUFA-mediated regulation of A1 astrocyte polarization upon hypoxia treatment. Together, this study highlighted that n-3 PUFAs prevent mitochondrial dysfunction, thereby limiting A1-specific astrocyte polarization and subsequently improving the neurological outcomes of mice with ischemic stroke.

Carbonyl Reductase 1 Attenuates Ischemic Brain Injury by Reducing Oxidative Stress and Neuroinflammation

Oxidative stress and neuroinflammatory response after the ischemic injury are important pathophysiologic mechanisms that cause brain tissue loss and neurological deficit. This study aims to observe the expression and role of carbonyl reductase 1 (CBR1), an NADPH-dependent oxidoreductase with specificity for carbonyl compounds such as 4-hydroxynonenal (4-HNE), in the brain after ischemic injury and to investigate the influence of CBR1 on ischemia-induced neuroinflammation. CBR1 expresses in the neurons, astrocyte, and microglia in the normal brain. The expression of CBR1 decreased in the ischemic regions following cerebral ischemia, and also reduced in primary neurons after OGD (oxygen-glucose deprivation); however, the expression of CBR1 significantly increased in microglia in the ischemic penumbra. Furthermore, TAT-CBR1 fusion protein played neuroprotective effects in reducing the infarct volume and improving neurological outcomes after ischemic injury. Mechanistically, CBR1 decreased the levels of 4-HNE in the brain after stroke; it also modulated microglial polarization toward the M2 phenotype, which was well-known to confer neuroprotection after ischemic injury. Our results demonstrate that CBR1 provides neuroprotection against ischemic injury by reducing oxidative stress and neuroinflammation, making a promising agent for cerebral ischemia treatment.

DHA attenuated Japanese Encephalitis virus infection-induced neuroinflammation and neuronal cell death in cultured rat Neuron/glia

Japanese Encephalitis Virus (JEV) is a neurotropic virus and its Central Nervous System (CNS) infection causes fatal encephalitis with high mortality and morbidity. Microglial activation and consequences of bystander damage appear to be the dominant mechanisms for Japanese Encephalitis and complications. Docosahexaenoic acid (DHA), an essential fatty acid and a major component of brain cell membranes, possesses additional biological activities, including anti-apoptosis, anti-inflammation, and neuroprotection. Through this study, we have provided experimental evidence showing the anti-inflammatory, neuroprotective, and anti-viral effects of DHA against JEV infection in rat Neuron/glia cultures. By Neuron/glia and Neuron cultures, DHA protected against neuronal cell death upon JEV infection and reduced JEV amplification. In Neuron/glia and Microglia cultures, the effects of DHA were accompanied by the downregulation of pro-inflammatory M1 microglia, upregulation of anti-inflammatory M2 microglia, and reduction of neurotoxic cytokine expression, which could be attributed to its interference in the Toll-Like Receptor (TLR), Mitogen-Activated Protein Kinase (MAPK), and Interferon/Janus Kinase/Signal Transducers and Activators of Transcription (Stat), along with the NF-κB, AP-1, and c-AMP Response Element Binding Protein (CREB) controlled transcriptional programs. Parallel anti-inflammatory effects against JEV infection were duplicated by G Protein-Coupled Receptor (GPR120) and GPR40 agonists and a reversal of DHA-mediated anti-inflammation was seen in the presence of GPR120 antagonist, while the GPR40 was less effectiveness. Since increasing evidence indicates its neuroprotection against neurodegenerative diseases, DHA is a proposed anti-inflammatory and neuroprotective candidate for the treatment of neuroinflammation-accompanied viral pathogenesis such as Japanese Encephalitis.

Acute Injection of Omega-3 Triglyceride Emulsion Provides Very Similar Protection as Hypothermia in a Neonatal Mouse Model of Hypoxic-Ischemic Brain Injury

Therapeutic hypothermia (HT) is a currently accepted treatment for neonatal asphyxia and is a promising strategy in adult stroke therapy. We previously reported that acute administration of docosahexaenoic acid (DHA) triglyceride emulsion (tri-DHA) protects against hypoxic-ischemic (HI) injury in neonatal mice. We questioned if co-treatment with HT and tri-DHA would achieve synergic effects in protecting the brain from HI injury. Neonatal mice (10-day old) subjected to HI injury were placed in temperature-controlled chambers for 4 h of either HT (rectal temperature 31–32°C) or normothermia (NT, rectal temperature 37°C). Mice were treated with tri-DHA (0.375 g tri-DHA/kg bw, two injections) before and 1 h after initiation of HT. We observed that HT, beginning immediately after HI injury, reduced brain infarct volume similarly to tri-DHA treatment (~50%). Further, HT delayed 2 h post-HI injury provided neuroprotection (% infarct volume: 31.4 ± 4.1 vs. 18.8 ± 4.6 HT), while 4 h delayed HT did not protect against HI insult (% infarct volume: 30.7 ± 5.0 vs. 31.3 ± 5.6 HT). HT plus tri-DHA combination treatment beginning at 0 or 2 h after HI injury did not further reduce infarct volumes compared to HT alone. Our results indicate that HT offers similar degrees of neuroprotection against HI injury compared to tri-DHA treatment. HT can only be provided in tertiary care centers, requires intense monitoring and can have adverse effects. In contrast, tri-DHA treatment may be advantageous in providing a feasible and effective strategy in patients after HI injury.

Role of polyunsaturated fatty acids in ischemic stroke - A perspective of specialized pro-resolving mediators

Polyunsaturated fatty acids (PUFAs) have been proposed as beneficial for cardiovascular health. However, results from both epidemiological studies and clinical trials have been inconsistent, whereas most of the animal studies showed promising benefits of PUFAs in the prevention and treatment of ischemic stroke. In recent years, it has become clear that PUFAs are metabolized into various types of bioactive derivatives, including the specialized pro-resolving mediators (SPMs). SPMs exert multiple biofunctions, such as to limit excessive inflammatory responses, regulate lipid metabolism and immune cell functions, decrease production of pro-inflammatory factors, increase anti-inflammatory mediators, as well as to promote tissue repair and homeostasis. Inflammation has been recognised as a key contributor to the pathophysiology of acute ischemic stroke. Owing to their potent pro-resolving actions, SPMs are potential for development of novel anti-stroke therapy. In this review, we will summarize current knowledge of epidemiological studies, basic research and clinical trials concerning PUFAs in stroke prevention and treatment, with special attention to SPMs as the unsung heroes behind PUFAs.

Transcriptomic characterization of microglia activation in a rat model of ischemic stroke

Microglia are key regulators of inflammatory response after stroke and brain injury. To better understand activation of microglia as well as their phenotypic diversity after ischemic stroke, we profiled the transcriptome of microglia after 75 min transient focal cerebral ischemia in 3-month- and 12-month-old male spontaneously hypertensive rats. Microglia were isolated from the brains by FACS sorting on days 3 and 14 after cerebral ischemia. GeneChip Rat 1.0ST microarray was used to profile the whole transcriptome of sorted microglia. We identified an evolving and complex pattern of activation from 3 to 14 days after stroke onset. M2-like patterns were extensively and persistently upregulated over time. M1-like patterns were only mildly upregulated, mostly at day 14. Younger 3-month-old brains showed a larger microglial response in both pro- and anti-inflammatory pathways, compared to older 12-month-old brains. Importantly, our data revealed that after stroke, most microglia are activated towards a wide spectrum of novel polarization states beyond the standard M1/M2 dichotomy, especially in pathways related to TLR2 and dietary fatty acid signaling. Finally, classes of transcription factors that might potentially regulate microglial activation were identified. These findings should provide a comprehensive database for dissecting microglial mechanisms and pursuing neuroinflammation targets for acute ischemic stroke.

Effect of vitamin D and/or omega-3 fatty acid supplementation on stroke outcomes: A randomized trial

BACKGROUND AND PURPOSE

Among stroke patients, low serum 25-hydroxyvitamin D predicts poor outcomes. In mice, higher omega-3 (n-3) fatty acid intake diminishes brain damage after stroke. In this study, we tested whether vitamin D or n-3 fatty acids supplementation prior to stroke reduces the risk of functional limitations and physical disability after stroke.

METHODS

We used data from VITAL (the VITamin D and OmegA-3 TriaL) which randomized middle-aged and older men and women without cardiovascular disease to vitamin D₃ (2000 IU/day) and/or marine n-3 fatty acids (1 g/day) and followed them for incident stroke events. Individuals experiencing a non-fatal stroke were mailed questionnaires assessing functional limitations (the physical performance scale adapted from Nagi) and physical disability (the modified Katz Activities of Daily Living and Rosow-Breslau Functional Health scales). We used logistic regression to analyze associations between randomized treatment and limitations on each scale.

RESULTS

A total of 290 individuals experienced their first stroke during the trial, of whom 197 stroke survivors completed the stroke outcomes questionnaire a median of 1.4 years after diagnosis. We observed no associations between randomized treatment to vitamin D and functional limitations (odds ratio [OR] 1.01, 95% confidence interval [CI] 0.52, 1.97) or physical disability (Rosow-Breslau scale: OR 0.92, 95% CI 0.50, 1.67; Katz scale: OR 1.03, 95% CI 0.31, 3.42). Those randomized to n-3 fatty acids had a non-significantly lower risk of functional limitations (OR 0.55, 95% CI 0.28, 1.09) and physical disability (Rosow-Breslau scale: OR 0.56, 95% CI 0.31, 1.02; Katz sclae: OR 0.32, 95% CI 0.50, 1.67).

CONCLUSION

Vitamin D or omega-3 fatty acid supplementation prior to stroke did not result in significantly improved post-stroke outcomes.

Demyelinating processes in aging and stroke in the central nervous system and the prospect of treatment strategy

Demyelination occurs in response to brain injury and is observed in many neurodegenerative diseases. Myelin is synthesized from oligodendrocytes in the central nervous system, and oligodendrocyte death‐induced demyelination is one of the mechanisms involved in white matter damage after stroke and neurodegeneration. Oligodendrocyte precursor cells (OPCs) exist in the brain of normal adults, and their differentiation into mature oligodendrocytes play a central role in remyelination. Although the differentiation and maturity of OPCs drive endogenous efforts for remyelination, the failure of axons to remyelinate is still the biggest obstacle to brain repair after injury or diseases. In recent years, studies have made attempts to promote remyelination after brain injury and disease, but its cellular or molecular mechanism is not yet fully understood. In this review, we discuss recent studies examining the demyelination process and potential therapeutic strategies for remyelination in aging and stroke. Based on our current understanding of the cellular and molecular mechanisms underlying remyelination, we hypothesize that myelin and oligodendrocytes are viable therapeutic targets to mitigate brain injury and to treat demyelinating‐related neurodegeneration diseases.

An Overview on the Differential Interplay Among Neurons-Astrocytes-Microglia in CA1 and CA3 Hippocampus in Hypoxia/Ischemia

Neurons have been long regarded as the basic functional cells of the brain, whereas astrocytes and microglia have been regarded only as elements of support. However, proper intercommunication among neurons-astrocytes-microglia is of fundamental importance for the functional organization of the brain. Perturbation in the regulation of brain energy metabolism not only in neurons but also in astrocytes and microglia may be one of the pathophysiological mechanisms of neurodegeneration, especially in hypoxia/ischemia. Glial activation has long been considered detrimental for survival of neurons, but recently it appears that glial responses to an insult are not equal but vary in different brain areas. In this review, we first take into consideration the modifications of the vascular unit of the glymphatic system and glial metabolism in hypoxic conditions. Using the method of triple-labeling fluorescent immunohistochemistry coupled with confocal microscopy (TIC), we recently studied the interplay among neurons, astrocytes, and microglia in chronic brain hypoperfusion. We evaluated the quantitative and morpho-functional alterations of the neuron-astrocyte-microglia triads comparing the hippocampal CA1 area, more vulnerable to ischemia, to the CA3 area, less vulnerable. In these contiguous and interconnected areas, in the same experimental hypoxic conditions, astrocytes and microglia show differential, finely regulated, region-specific reactivities. In both areas, astrocytes and microglia form triad clusters with apoptotic, degenerating neurons. In the neuron-astrocyte-microglia triads, the cell body of a damaged neuron is infiltrated and bisected by branches of astrocyte that create a microscar around it while a microglial cell phagocytoses the damaged neuron. These coordinated actions are consistent with the scavenging and protective activities of microglia. In hypoxia, the neuron-astrocyte-microglia triads are more numerous in CA3 than in CA1, further indicating their protective effects. These data, taken from contiguous and interconnected hippocampal areas, demonstrate that glial response to the same hypoxic insult is not equal but varies significantly. Understanding the differences of glial reactivity is of great interest to explain the differential susceptibility of hippocampal areas to hypoxia/ischemia. Further studies may evidence the differential reactivity of glia in different brain areas, explaining the higher or lower sensitivity of these areas to different insults and whether glia may represent a target for future therapeutic interventions.

Acute injection of a DHA triglyceride emulsion after hypoxic-ischemic brain injury in mice increases both DHA and EPA levels in blood and brain✰

We recently reported that acute injection of docosahexaenoic acid (DHA) triglyceride emulsions (tri-DHA) conferred neuroprotection after hypoxic-ischemic (HI) injury in a neonatal mouse stroke model. We showed that exogenous DHA increased concentrations of DHA in brain mitochondria as well as DHA-derived specialized pro-resolving mediator (SPM) levels in the brain. The objective of the present study was to investigate the distribution of emulsion particles and changes in plasma lipid profiles after tri-DHA injection in naïve mice and in animals subjected to HI injury. We also examined whether tri-DHA injection would change DHA- and eicosapentaenoic acid (EPA)-derived SPM levels in the brain. To address this, neonatal (10-day-old) naïve and HI mice were injected with radiolabeled tri-DHA emulsion (0.375 g tri-DHA/kg bw), and blood clearance and tissue distribution were analyzed. Among all the organs assayed, the lowest uptake of emulsion particles was in the brain (<0.4% recovered dose) in both naïve and HI mice, while the liver had the highest uptake. Tri-DHA administration increased DHA concentrations in plasma lysophosphatidylcholine and non-esterified fatty acids. Additionally, treatment with tri-DHA after HI injury significantly elevated the levels of DHA-derived SPMs and monohydroxy-containing DHA-derived products in the brain. Further, tri-DHA administration increased resolvin E2 (RvE2, 5S,18R-dihydroxy-eicosa-6E,8Z,11Z,14Z,16E-pentaenoic acid) and monohydroxy-containing EPA-derived products in the brain. These results suggest that the transfer of DHA through plasma lipid pools plays an important role in DHA brain transport in neonatal mice subjected to HI injury. Furthermore, increases in EPA and EPA-derived SPMs following tri-DHA injection demonstrate interlinked metabolism of these two fatty acids. Hence, changes in both EPA and DHA profile patterns need to be considered when studying the protective effects of DHA after HI brain injury. Our results highlight the need for further investigation to differentiate the effects of DHA from EPA on neuroprotective pathways following HI damage. Such information could contribute to the development of specific DHA-EPA formulations to improve clinical endpoints and modulate potential biomarkers in ischemic brain injury.

Microglial Responses to Brain Injury and Disease: Functional Diversity and New Opportunities

As an integral part of the innate immune system of the brain, resident microglia must react rapidly to the onset of brain injury and neurological disease. These dynamic cells then continue to shift their phenotype along a multidimensional continuum with overlapping pro- and anti-inflammatory states, allowing them to adapt to microenvironmental changes during the progression of brain disorders. However, the ability of microglia to shift phenotype through nimble molecular, structural, and functional changes comes at a cost, as the extreme pro-inflammatory states may prevent these professional phagocytes from clearing toxic debris and secreting tissue-repairing neurotrophic factors. Evolution has strongly favored heterogeneity in microglia in both the spatial and temporal dimensions-they can assume diverse roles in different brain regions, throughout the course of brain development and aging, and during the spatiotemporal progression of brain injuries and neurological diseases. Age and sex differences add further diversity to microglia functional status under physiological and pathological conditions. This article reviews recent advances in our knowledge of microglia with emphases on molecular mediators of phenotype shifts and functional diversity. We describe microglia-targeted therapeutic opportunities, including pharmacologic modulation of phenotype and repopulation of the brain with fresh microglia. With the advent of powerful new tools, research on microglia has recently accelerated in pace and may translate into potential therapeutics against brain injury and neurological disease.

Novel Approaches for Omega-3 Fatty Acid Therapeutics: Chronic Versus Acute Administration to Protect Heart, Brain, and Spinal Cord

This article reviews novel approaches for omega-3 fatty acid (FA) therapeutics and the linked molecular mechanisms in cardiovascular and central nervous system (CNS) diseases. In vitro and in vivo research studies indicate that omega-3 FAs affect synergic mechanisms that include modulation of cell membrane fluidity, regulation of intracellular signaling pathways, and production of bioactive mediators. We compare how chronic and acute treatments with omega-3 FAs differentially trigger pathways of protection in heart, brain, and spinal cord injuries. We also summarize recent omega-3 FA randomized clinical trials and meta-analyses and discuss possible reasons for controversial results, with suggestions on improving the study design for future clinical trials. Acute treatment with omega-3 FAs offers a novel approach for preserving cardiac and neurological functions, and the combinations of acute treatment with chronic administration of omega-3 FAs might represent an additional therapeutic strategy for ameliorating adverse cardiovascular and CNS outcomes.

Investigation of the effect of dietary intake of omega-3 polyunsaturated fatty acids on trauma-induced white matter injury with quantitative diffusion MRI in mice

Previous studies suggest that long-term supplementation and dietary intake of omega-3 polyunsaturated fatty acids (PUFAs) may have neuroprotective effects following brain injury. The objective of this study was to investigate potential neuroprotective effects of omega-3 PUFAs on white matter following closed-head trauma. The closed-head injury model of engineered rotational acceleration (CHIMERA) produces a reproducible injury in the optic tract and brachium of the superior colliculus in mice. Damage is detectable using diffusion tensor imaging (DTI) metrics, particularly fractional anisotropy (FA), with sensitivity comparable to histology. We acquired in vivo (n = 38) and ex vivo (n = 41) DTI data in mice divided into sham and CHIMERA groups with two dietary groups: one deficient in omega-3 PUFAs and one adequate in omega-3 PUFAs. We examined injury effects (reduction in FA) and neuroprotection (FA reduction modulated by diet) in the optic tract and brachium. We verified that diet did not affect FA in sham animals. In injured animals, we found significantly reduced FA in the optic tract and brachium (~10% reduction, p < 0.001), and Bayes factor analysis showed strong evidence to reject the null hypothesis. However, Bayes factor analysis showed substantial evidence to accept the null hypothesis of no diet-related FA differences in injured animals in the in vivo and ex vivo samples. Our results indicate no neuroprotective effect from adequate dietary omega-3 PUFA intake on white matter damage following traumatic brain injury. Since damage from CHIMERA mainly affects white matter, our results do not necessarily contradict previous findings showing omega-3 PUFA-mediated neuroprotection in gray matter.

Xuesaitong May Protect Against Ischemic Stroke by Modulating Microglial Phenotypes and Inhibiting Neuronal Cell Apoptosis via the STAT3 Signaling Pathway

BACKGROUND

Xuesaitong mainly comprises Panax notoginseng saponins and has shown a promising feature in an acute ischemic stroke model; however, its effect on long-term recovery following stroke, and the related mechanisms, are unknown.

METHODS

The objective of this study was to investigate the long-term protective effects of xuesaitong against ischemic stroke and its effect on microglial polarization. Experimental cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) for 45 min, and C57BL/6 mice were immediately injected with xuesaitong or vehicle through the caudal vein at the onset of cerebral reperfusion consecutively for 14 days. The animals were randomly divided into three groups: a sham-operated group, vehicle-treated group and xuesaitong-treated group at a dose of 15μg/g. Subsequently, 2,3,5-triphenyltetrazolium chloride staining was used to assess infarct volume, and adhesive removal tests and balance beam tests were used to evaluate neurological deficits at days 1, 3, 7 and 14 following ischemia. Reverse-transcriptase polymerase chain reaction and immunofluorescence staining for M1 markers (CD16, iNOS) and M2 markers (CD206, arginase-1) were performed to characterize phenotypic changes in microglia. Elisa was used to determine the release of pro-inflammatory and anti-inflammatory cytokines. TUNEL staining was conducted to detect neuronal cell apoptosis, and western blots were used to determine the activation of signal transducer and activator of transcription 3 (STAT3).

RESULTS

Our results revealed that xuesaitong treatment, compared with vehicle treatment, significantly reduced cerebral infarct volume 1 and 3 days after MCAO and resulted in significant improvements in long-term neurological outcomes. Furthermore, xuesaitong treatment, compared with vehicle treatment, significantly reduced M1 markers and elevated M2 markers 7 and 14 days after MCAO at both the mRNA and protein level in ipsilateral brain tissue. This finding was also accompanied by a reduction in neuronal cell apoptosis and p-STAT3 transcription factor levels in the xuesaitong-treated group compared with the vehicle-treated group.

CONCLUSION

We demonstrated that xuesaitong has long-term neuroprotective effects against ischemic stroke, possibly by promoting the polarization of microglia to an M2 phenotype and by inhibiting neuronal cell death via down-regulation of the STAT3 signaling pathway, providing new evidence that xuesaitong might be a promising therapeutic strategy for ischemic stroke.

Growth differentiation factor-11 supplementation improves survival and promotes recovery after ischemic stroke in aged mice

Growth differentiation factor (GDF) 11 levels decline with aging. The age-related loss of GDF 11 has been implicated in the pathogenesis of a variety of age-related diseases. GDF11 supplementation reversed cardiac hypertrophy, bone loss, and pulmonary dysfunction in old mice, suggesting that GDF11 has a rejuvenating effect. Less is known about the potential of GDF11 to improve recovery after an acute injury, such as stroke, in aged mice. GDF11/8 levels were assessed in young and aged male mice and in postmortem human brain samples. Aged mice were subjected to a transient middle cerebral artery occlusion (MCAo). Five days after MCAo, mice received and bromodeoxyuridine / 5-Bromo-2'-deoxyuridine (BrdU) and either recombinant GDF11 or vehicle for five days and were assessed for recovery for one month following stroke. MRI was used to determine cerebrospinal fluid (CSF) volume, corpus callosum (CC) area, and brain atrophy at 30 days post-stroke. Immunohistochemistry was used to assess gliosis, neurogenesis, angiogenesis and synaptic density. Lower GDF11/8 levels were found with age in both mice and humans (p<0.05). GDF11 supplementation reduced mortality and improved sensorimotor deficits after stroke. Treatment also reduced brain atrophy and gliosis, increased angiogenesis, improved white matter integrity, and reduced inflammation after stroke. GDF11 may have a role in brain repair after ischemic injury.

Non-Mitogenic Fibroblast Growth Factor 1 Enhanced Angiogenesis Following Ischemic Stroke by Regulating the Sphingosine-1-Phosphate 1 Pathway

Ischemic strokes account for about 80% of all strokes and are associated with a high risk of mortality. Angiogenesis of brain microvascular endothelial cells may contribute to functional restoration following ischemia. Fibroblast growth factor 1 (FGF1), a member of FGF superfamily, involved in embryonic development, angiogenesis, wound healing, and neuron survival. However, the mitogenic activity of FGF1 is known to contribute to several human pathologies, thereby questioning the safety of its clinical applications. Here, we explored the effects and mechanism of action of non-mitogenic FGF1 (nmFGF1) on angiogenesis in mice after ischemia stroke and an oxygen-glucose deprivation (OGD)-induced human brain microvascular endothelial cells (HBMECs) injury model. We found that intranasal administration nmFGF1 significantly promoted angiogenesis in mice after stroke, and significantly increased the formation of matrigel tube and promoted scratch migration in a dose-dependent manner in OGD-induced HBMECs in vitro. However, the co-administration of an FGF receptor 1 (FGFR1)-specific inhibitor PD173074 significantly reversed the effects of nmFGF1 in vitro, suggesting that nmFGF1 functions via FGFR1 activation. Moreover, nmFGF1 activated sphingosine-1-phosphate receptor 1 (S1PR1, S1P1) in mice after stroke in vivo. S1P1 protein antagonist VPC23019 and agonist FTY720 were used to confirm that nmFGF1 promotes angiogenesis in vitro partially through the S1P1 pathway. OGD induced downregulation of S1P1 expression. The S1P1 antagonist VPC23019 blocked the stimulatory effects of nmFGF1, whereas the S1P1 agonist FTY720 exerted effects comparable with those of nmFGF1. Furthermore, PD173074 reversed the effect of nmFGF1 on upregulating S1P1 signaling. In conclusion, nmFGF1 enhanced angiogenesis in mice following stroke and OGD-induced HBMECs through S1P1 pathway regulation mediated via FGFR1 activation. This new discovery suggests the potential therapeutic role of nmFGF1 for the treatment of ischemic strokes.

Omega-3 Polyunsaturated Fatty Acids and Stroke Burden

Stroke is a major leading cause of death and disability worldwide. N-3 polyunsaturated fatty acids (PUFAs) including eicosapentaenoic acid and docosahexaenoic acid have potent anti-inflammatory effects, reduce platelet aggregation, and regress atherosclerotic plaques. Since the discovery that the Greenland Eskimo population, whose diet is high in marine n-3 PUFAs, have a lower incidence of coronary heart disease than Western populations, numerous epidemiological studies to explore the associations of dietary intakes of fish and n-3 PUFAs with cardiovascular diseases, and large-scale clinical trials to identify the benefits of treatment with n-3 PUFAs have been conducted. In most of these studies the incidence and mortality of stroke were also evaluated mainly as secondary endpoints. Thus, a systematic literature review regarding the association of dietary intake of n-3 PUFAs with stroke in the epidemiological studies and the treatment effects of n-3 PUFAs in the clinical trials was conducted. Moreover, recent experimental studies were also reviewed to explore the molecular mechanisms of the neuroprotective effects of n-3 PUFAs after stroke.

Cell based therapy reduces secondary damage and increases extent of microglial activation following cortical injury

Cortical injury elicits long-term cytotoxic and cytoprotective mechanisms within the brain and the balance of these pathways can determine the functional outcome for the individual. Cytotoxicity is exacerbated by production of reactive oxygen species, accumulation of iron, and peroxidation of cell membranes and myelin. There are currently no neurorestorative treatments to aid in balancing the cytotoxic and cytoprotective mechanisms following cortical injury. Cell based therapies are an emerging treatment that may function in immunomodulation, reduction of secondary damage, and reorganization of surviving structures. We previously evaluated human umbilical tissue-derived cells (hUTC) in our non-human primate model of cortical injury restricted to the hand area of primary motor cortex. Systemic hUTC treatment resulted in significantly greater recovery of fine motor function compared to vehicle controls. Here we investigate the hypothesis that hUTC treatment reduces oxidative damage and iron accumulation and increases the extent of the microglial response to cortical injury. To test this, brain sections from these monkeys were processed using immunohistochemistry to quantify oxidative damage (4-HNE) and activated microglia (LN3), and Prussian Blue to quantify iron. hUTC treated subjects exhibited significantly reduced oxidative damage in the sublesional white matter and iron accumulation in the perilesional area as well as a significant increase in the extent of activated microglia along white matter pathways. Increased perilesional iron accumulation was associated with greater perilesional oxidative damage and larger reconstructed lesion volume. These findings support the hypothesis that systemic hUTC administered 24 h after cortical damage decreases the cytotoxic response while increasing the extent of microglial activation.

Distinctive functional deficiencies in axonal conduction associated with two forms of cerebral white matter injury

Aims

This study determines whether assessment with compound action potentials (CAPs) can distinguish two different forms of cerebral white matter injury at the functional levels.

Methods

A pure demyelination model was induced in C57/BL6 adult mice by dietary supplementation of cuprizone (0.2%) for 6 weeks. Callosal L‐N5‐(1‐Iminoethyl) ornithine (L‐NIO) hydrochloride (27 mg/mL) was injected into the corpus callosum (CC) to induce a focal white matter stroke (WMS), resulting in both demyelination and axonal injury. White matter integrity was assessed by performing CAP recording, electron microscopy, and immunohistological and luxol fast blue (LFB) staining.

Results

Immunohistological and electron microscopic analyses confirmed the induction of robust demyelination in CC with cuprizone, and mixed demyelination and axonal damage with L‐NIO. Electrophysiologically, cuprizone‐induced demyelination significantly reduced the amplitude of negative peak 1 (N1), but increased the amplitude of negative peak 2 (N2), of the CAPs compared to the sham controls. However, cuprizone did not affect the axonal conduction velocity. In contrast, the amplitude and area of both N1 and N2 along with N1 axonal conduction velocity were dramatically decreased in L‐NIO‐induced WMS.

Conclusions

Concertedly, parameters of the CAPs offer a novel functional assessment strategy for cerebral white matter injury in rodent models.

L-Cysteine-Derived H2S Promotes Microglia M2 Polarization via Activation of the AMPK Pathway in Hypoxia-Ischemic Neonatal Mice

We have reported previously that L-cysteine-derived hydrogen sulfide (H₂S) demonstrates a remarkable neuroprotective effect against hypoxia-ischemic (HI) insult in neonatal animals. Here, we assessed some of the mechanisms of this protection as exerted by L-cysteine. Specifically, we examined the capacity for L-cysteine to stimulate microglial polarization of the M2 phenotype and its modulation of complement expression in response to HI in neonatal mice. L-cysteine treatment suppressed the production of inflammatory cytokines, while dramatically up-regulating levels of anti-inflammatory cytokines in the damaged cortex. This L-cysteine administration promoted the conversion of microglia from an inflammatory M1 to an anti-inflammatory M2 phenotype, an effect which was associated with inhibiting the p38 and/or JNK pro-inflammatory pathways, nuclear factor-κB activation and a decrease in HI-derived levels of the C1q, C3a and C3a complement receptor proteins. Notably, blockade of H₂S-production clearly prevented L-cysteine-mediated M2 polarization and complement expression. L-cysteine also inhibited neuronal apoptosis as induced by conditioned media from activated M1 microglia in vitro. We also show that L-cysteine promoted AMP-activated protein kinase (AMPK) activation and the AMPK inhibitor abolished these anti-apoptotic and anti-inflammatory effects of L-cysteine. Taken together, our findings demonstrate that L-cysteine-derived H₂S attenuated neuronal apoptosis after HI and suggest that these effects, in part, result from enhancing microglia M2 polarization and modulating complement expression via AMPK activation.

Role of UCHL1 in axonal injury and functional recovery after cerebral ischemia

Many neuroprotective strategies have failed to translate to clinical trials, perhaps because of a failure to preserve white matter function. Ubiquitin C-terminal hydrolase L1 (UCHL1), a neuron-specific protein essential for axonal function, is deactivated by reactive lipids produced after cerebral ischemia. Mutation of the cysteine residue 152-reactive lipid-binding site of UCHL1 decreased axonal injury after hypoxia and ischemia in vitro and in vivo, preserved axonal conductance and synaptic function, and improved motor behavior after ischemia in mice. These results suggest that UCHL1 may play an important role in maintaining axonal function after cerebral ischemia. Restoration of UCHL1 activity or prevention of degradation of UCHL1 activity by preventing binding of substrates to cysteine residue 152 could be useful approaches for treatment of stroke.

Ubiquitin C-terminal hydrolase L1 (UCHL1) is a unique brain-specific deubiquitinating enzyme. Mutations in and aberrant function of UCHL1 have been linked to many neurological disorders. UCHL1 activity protects neurons from hypoxic injury, and binding of stroke-induced reactive lipid species to the cysteine 152 (C152) of UCHL1 unfolds the protein and disrupts its function. To investigate the role of UCHL1 and its adduction by reactive lipids in inhibiting repair and recovery of function following ischemic injury, a knock-in (KI) mouse expressing the UCHL1 C152A mutation was generated. Neurons derived from KI mice had less cell death and neurite injury after hypoxia. UCHL1 C152A KI and WT mice underwent middle cerebral artery occlusion (MCAO) or sham surgery. White matter injury was significantly decreased in KI compared with WT mice 7 d after MCAO. Histological analysis revealed decreased tissue loss at 21 d after injury in KI mice. There was also significantly improved sensorimotor recovery in postischemic KI mice. K63- and K48-linked polyubiquitinated proteins were increased in penumbra of WT mouse brains but not in KI mouse brains at 24 h post MCAO. The UCHL1 C152A mutation preserved excitatory synaptic drive to pyramidal neurons and their excitability in the periinfarct zone; axonal conduction velocity recovered by 21 d post MCAO in KI mice in corpus callosum. These results demonstrate that UCHL1 activity is an important determinant of function after ischemia and further demonstrate that the C152 site of UCHL1 plays a significant role in functional recovery after stroke.

Hypoxic preconditioning improves long-term functional outcomes after neonatal hypoxia-ischemic injury by restoring white matter integrity and brain development

Aims

Neonatal hypoxia–ischemia (H/I) results in gray and white matter injury, characterized by neuronal loss, failure of neural network formation, retarded myelin formation, and abnormal accumulation of oligodendrocyte progenitor cells (OPCs). These changes lead to severe neurological deficits and mortality. Sublethal hypoxic preconditioning (HPC) can protect the developing brain against H/I. However, limited evidence is available concerning its effect on white matter injury.

Methods

In this study, P6 neonatal Sprague‐Dawley rats were subjected to normoxic (21% O₂) or HPC (7.8% O₂) for 3 hours followed 24 hours later by H/I brain injury. Neurological deficits were assessed by gait, righting reflex, foot fault, and Morris water maze tests. Compound action potential of the corpus callosum was recorded 35 days after surgery, and the correlation between axon myelination and neurological function was determined.

Results

Hypoxic preconditioning significantly attenuated H/I brain injury at 7 days and remarkably improved both sensorimotor and cognitive functional performances up to 35 days after H/I. HPC‐afforded improvement in long‐term neurological outcomes was attributable, at least in part, to restoration of the differentiation and maturation capacity in oligodendrocyte progenitor cells, amelioration of microglia/macrophage activation and neuroinflammation, and continuation of brain development after H/I.

Conclusions

Hypoxic preconditioning restores white matter repair, development, and functional integrity in developing brain after H/I brain injury.

Negative regulation of glial Tim-3 inhibits the secretion of inflammatory factors and modulates microglia to antiinflammatory phenotype after experimental intracerebral hemorrhage in rats

AIMS

To investigate the critical role of Tim-3 in the polarization of microglia in intracerebral hemorrhage (ICH)-induced secondary brain injury (SBI).

METHODS

An in vivo ICH model was established by autologous whole blood injection into the right basal ganglia in rats. The primary cultured microglia were treated with oxygen-hemoglobin (OxyHb) to mimic ICH in vitro. In this experiment, specific siRNA for Tim-3 and recombinant human TIM-3 were exploited both in vivo and in vitro.

RESULTS

Tim-3 was increased in the brain after ICH, which mainly distributed in microglia, but not neurons and astrocytes. However, the blockade of Tim-3 by siRNA markedly reduced secretion of inflammatory factors, neuronal degeneration, neuronal cell death, and brain edema. Meanwhile, downregulation of Tim-3 promoted the transformation of microglia phenotype from M1 to M2 after ICH. Furthermore, upregulation of Tim-3 can increase the interaction between Tim-3 and Galectin-9 (Gal-9) and activate Toll-like receptor 4 (TLR-4) pathway after ICH. Increasing the expression of Tim-3 may be related to the activation of HIF-1α.

CONCLUSION

Tim-3 may be an important link between neuroinflammation and microglia polarization through Tim-3/Gal-9 and TLR-4 signaling pathways which induced SBI after ICH.