Early treatment with minocycline following stroke in rats improves functional recovery and differentially modifies responses of peri-infarct microglia and astrocytes

Microglia in Ischemic Stroke: Pathogenesis Insights and Therapeutic Challenges

Ischemic stroke is the most common type of stroke, which is the main cause of death and disability on a global scale. As the primary immune cells in the brain that are crucial for preserving homeostasis of the central nervous system microenvironment, microglia have been found to exhibit dual or even multiple effects at different stages of ischemic stroke. The anti-inflammatory polarization of microglia and release of neurotrophic factors may provide benefits by promoting neurological recovery at the lesion in the early phase after ischemic stroke. However, the pro-inflammatory polarization of microglia and secretion of inflammatory factors in the later phase of injury may exacerbate the ischemic lesion, suggesting the therapeutic potential of modulating the balance of microglial polarization to predispose them to anti-inflammatory transformation in ischemic stroke. Microglia-mediated signaling crosstalk with other cells may also be key to improving functional outcomes following ischemic stroke. Thus, this review provides an overview of microglial functions and responses under physiological and ischemic stroke conditions, including microglial activation, polarization, and interactions with other cells. We focus on approaches that promote anti-inflammatory polarization of microglia, inhibit microglial activation, and enhance beneficial cell-to-cell interactions. These targets may hold promise for the creation of innovative therapeutic strategies.

Intranasal Delivery of Mitochondria Attenuates Brain Injury by AMPK and SIRT1/PGC-1α Pathways in a Murine Model of Photothrombotic Stroke

Ischemic stroke is one of the major causes of morbidity and mortality worldwide. Mitochondria play a vital role in the pathological processes of cerebral ischemic injury, but its transplantation and underlying mechanisms remain unclear. In the present study, we examined the effects of mitochondrial therapy on the modulation of AMPK and SIRT1/PGC-1α signaling pathway, oxidative stress, and NLRP3 inflammasome activation after photothrombotic ischemic stroke (pt-MCAO). The adult male mice were subjected to the pt-MCAO in which the proximal-middle cerebral artery was exposed with a 532-nm laser beam for 4 min by retro-orbital injection of a photosensitive dye (Rose Bengal: 15 mg/kg) before the laser light exposure and isolated mitochondria (100 μg protein) were administered intranasally at 30 min, 24 h, and 48 h following post-stroke. After 72 h, mice were tested for neurobehavioral outcomes and euthanized for infarct volume, brain edema, and molecular analysis. First, we found that mitochondria therapy significantly decreased brain infarct volume and brain edema, improved neurological dysfunction, attenuated ischemic stroke-induced oxidative stress, and neuroinflammation. Second, mitochondria treatment inhibited NLRP3 inflammasome activation. Finally, mitochondria therapy accelerated p-AMPKα(Thr172) and PGC-1α expression and resorted SIRT1 protein expression levels in pt-MCAO mice. In conclusion, our results demonstrate that mitochondria therapy exerts neuroprotective effects by inhibiting oxidative damage and inflammation, mainly dependent on the heightening activation of the AMPK and SIRT1/PGC-1α signaling pathway. Thus, intranasal delivery of mitochondria might be considered a new therapeutic strategy for ischemic stroke treatment.

Drivers of Chronic Pathology Following Ischemic Stroke: A Descriptive Review

Stroke is the third leading cause of death and long-term disability in the world. Considered largely a disease of aging, its global economic and healthcare burden is expected to rise as more people survive into advanced age. With recent advances in acute stroke management, including the expansion of time windows for treatment with intravenous thrombolysis and mechanical thrombectomy, we are likely to see an increase in survival rates. It is therefore critically important to understand the complete pathophysiology of ischemic stroke, both in the acute and subacute stages and during the chronic phase in the months and years following an ischemic event. One of the most clinically relevant aspects of the chronic sequelae of stroke is its extended negative effect on cognition. Cognitive impairment may be related to the deterioration and dysfunctional reorganization of white matter seen at later timepoints after stroke, as well as ongoing progressive neurodegeneration. The vasculature of the brain also undergoes significant insult and remodeling following stroke, undergoing changes which may further contribute to chronic stroke pathology. While inflammation and the immune response are well established drivers of acute stroke pathology, the chronicity and functional role of innate and adaptive immune responses in the post-ischemic brain and in the peripheral environment remain largely uncharacterized. In this review, we summarize the current literature on post-stroke injury progression, its chronic pathological features, and the putative secondary injury mechanisms underlying the development of cognitive impairment and dementia. We present findings from clinical and experimental studies and discuss the long-term effects of ischemic stroke on both brain anatomy and functional outcome. Identifying mechanisms that occur months to years after injury could lead to treatment strategies in the chronic phase of stroke to help mitigate stroke-associated cognitive decline in patients.

Inflammation, Anti-inflammatory Interventions, and Post-stroke Cognitive Impairment: a Systematic Review and Meta-analysis of Human and Animal Studies

The pathophysiology and treatment of post-stroke cognitive impairment (PSCI) are not clear. Stroke triggers an inflammatory response, which might affect synapse function and cognitive status. We performed a systematic review and meta-analysis to assess whether patients with PSCI have increased levels of inflammatory markers and whether anti-inflammatory interventions in animals decrease PSCI. We systematically searched PubMed, EMBASE, and PsychInfo for studies on stroke. For human studies, we determined the standardized mean difference (SMD) on the association between PSCI and markers of inflammation. For animal studies, we determined the SMD of post-stroke cognitive outcome after an anti-inflammatory intervention. Interventions were grouped based on proposed mechanism of action. In patients, the SMD of inflammatory markers for those with versus those without PSCI was 0.46 (95% CI 0.18; 0.76; I2 = 92%), and the correlation coefficient between level of inflammation and cognitive scores was - 0.25 (95% CI - 0.34; - 0.16; I2 = 75%). In animals, the SMD of cognition for those treated with versus those without anti-inflammatory interventions was 1.43 (95% CI 1.12; 1.74; I2 = 83%). The largest effect sizes in treated animals were for complement inhibition (SMD = 1.94 (95% CI 1.50; 2.37), I2 = 51%) and fingolimod (SMD = 2.1 (95% CI 0.75; 3.47), I2 = 81%). Inflammation is increased in stroke survivors with cognitive impairment and is negatively correlated with cognitive functioning. Anti-inflammatory interventions seem to improve cognitive functioning in animals. Complement inhibition and fingolimod are promising therapies on reducing PSCI.

Acute minocycline treatment inhibits microglia activation, reduces infarct volume, and has domain-specific effects on post-ischemic stroke cognition in rats

Ischemic stroke affects millions of individuals worldwide and a high prevalence of survivors experience cognitive deficits. At present, the underlying mechanisms that drive post-stroke cognitive decline are not well understood. Microglia play a critical role in the post-stroke inflammatory response, but experimental studies show that an accumulation of chronically activated microglia can be harmful and associates with cognitive impairment. This study assessed the effect of acute post-stroke minocycline treatment on chronic microglia and astrocyte expression within the infarct and remote white matter regions, as well as its effect on various domains of cognitive function post-stroke. Nine-month-old male rats received an injection of endothelin-1 into the right dorsal striatum to induce transient focal ischemia, and then were treated with minocycline or saline for 4 days post-stroke. Rats were tested using a series of lever-pressing tasks and the Morris water maze to assess striatal-based learning, cognitive flexibility, and spatial learning and reference memory. We found that minocycline-treated rats had smaller stroke-induced infarcts and less microglia activation in the infarct area and remote white matter regions compared to saline-treated rats at 28 days post-stroke. The behavioural testing results differed according to the cognitive domain; whereas minocycline-treated rats trended towards improved striatal-based learning in a lever-pressing task, but cognitive flexibility was unaffected during the subsequent set-shifting task. Furthermore, minocycline treatment unexpectedly impaired spatial learning, yet it did not alter reference memory. Collectively, we show that post-stroke minocycline treatment can reduce chronic microglia activation even in remote brain regions, with domain-specific effects on cognitive function.

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.

Neuroinflammation and anti-inflammatory therapy for ischemic stroke

Stroke remains one of the most devastating and challenging neurological diseases worldwide. Inflammation, as well as oxidative stress is one of the main contributors to post-stroke injuries, and oxidative stress can further induce inflammation. Moreover, the inflammatory response is closely related to immune modulation in ischemic stroke progression. Hence, major ischemic stroke treatment strategies include targeting inflammatory responses, immune modulation (especially immune cells), and inflammatory response to suppress stroke progression. To date, several drugs have demonstrated clinical efficacy, such as Etanercept and Fingolimod. However, only edaravone dexborneol has successfully passed the phase III clinical trial and been approved by the National Medical Products Administration (NMPA) to treat ischemic stroke in China, which can restore redox balance and regulate inflammatory immune responses, thus providing neuroprotection in ischemic stroke. In this review, we will comprehensively summarize the current advances in the application of inflammatory biomarkers, neuroinflammation and neuro-immunotherapeutic scenarios for ischemic stroke, thus aiming to provide a theoretical basis and new prospects and frontiers for clinical applications.

Ovariectomy in mice primes hippocampal microglia to exacerbate behavioral sickness responses

Estrogens are a group of steroid hormones that promote the development and maintenance of the female reproductive system and secondary sex characteristics. Estrogens also modulate immune responses; estrogen loss at menopause increases the risk of inflammatory disorders. Elevated inflammatory responses in the brain can lead to affective behavioral changes, which are characteristic of menopause. Thus, here we examined whether loss of estrogens sensitizes microglia, the primary innate immune cell of the brain, leading to changes in affective behaviors. To test this question, adult C57BL/6 mice underwent an ovariectomy to remove endogenous estrogens and then received estradiol hormone replacement or vehicle. After a one-month recovery, mice received an immune challenge with lipopolysaccharide (LPS) or vehicle control treatment and underwent behavioral testing. Ovariectomized, saline-treated mice exhibited reduced social investigation compared to sham-operated mice. Furthermore, ovariectomized mice that received LPS exhibited an exacerbated decrease in sucrose preference, which was ameliorated by estradiol replacement. These results indicate that ovariectomy modulates affective behaviors at baseline and in response to an inflammatory challenge. Ovariectomy-related behavioral changes were associated with downregulation of Cx3cr1, a microglial receptor that limits activation, suggesting that estrogen loss can disinhibit microglia to immune stimuli. Indeed, estradiol treatment reduced ovariectomy-induced increases in Il1b and Il6 expression after an immune challenge. Changes in microglial reactivity following ovariectomy are likely subtle, as overt changes in microglial morphology (e.g., soma size and branching) were limited. Collectively, these results suggest that a lack of estrogens may allow microglia to confer exaggerated neuroimmune responses, thereby raising vulnerability to adverse affective- and sickness-related behavioral changes.

After Ischemic Stroke, Minocycline Promotes a Protective Response in Neurons via the RNA-Binding Protein HuR, with a Positive Impact on Motor Performance

Ischemic stroke is the most common cause of adult disability and one of the leading causes of death worldwide, with a serious socio-economic impact. In the present work, we used a new thromboembolic model, recently developed in our lab, to induce focal cerebral ischemic (FCI) stroke in rats without reperfusion. We analyzed selected proteins implicated in the inflammatory response (such as the RNA-binding protein HuR, TNFα, and HSP70) via immunohistochemistry and western blotting techniques. The main goal of the study was to evaluate the beneficial effects of a single administration of minocycline at a low dose (1 mg/kg intravenously administered 10 min after FCI) on the neurons localized in the penumbra area after an ischemic stroke. Furthermore, given the importance of understanding the crosstalk between molecular parameters and motor functions following FCI, motor tests were also performed, such as the Horizontal Runway Elevated test, CatWalk™ XT, and Grip Strength test. Our results indicate that a single administration of a low dose of minocycline increased the viability of neurons and reduced the neurodegeneration caused by ischemia, resulting in a significant reduction in the infarct volume. At the molecular level, minocycline resulted in a reduction in TNFα content coupled with an increase in the levels of both HSP70 and HuR proteins in the penumbra area. Considering that both HSP70 and TNF-α transcripts are targeted by HuR, the obtained results suggest that, following FCI, this RNA-binding protein promotes a protective response by shifting its binding towards HSP70 instead of TNF-α. Most importantly, motor tests showed that reduced inflammation in the brain damaged area after minocycline treatment directly translated into a better motor performance, which is a fundamental outcome when searching for new therapeutic options for clinical practice.

Pathophysiological basis and promise of experimental therapies for Gulf War Illness, a chronic neuropsychiatric syndrome in veterans

This article describes the pathophysiology and potential treatments for Gulf War Illness (GWI), which is a chronic neuropsychiatric illness linked to a combination of chemical exposures experienced by service personnel during the first Gulf War in 1991. However, there is currently no effective treatment for veterans with GWI. The article focuses on the current status and efficacy of existing therapeutic interventions in preclinical models of GWI, as well as potential perspectives of promising therapies. GWI stems from changes in brain and peripheral systems in veterans, leading to neurocognitive deficits, as well as physiological and psychological effects resulting from multifaceted changes such as neuroinflammation, oxidative stress, and neuronal damage. Aging not only renders veterans more susceptible to GWI symptoms, but also attenuates their immune capabilities and response to therapies. A variety of experimental models are being used to investigate the pathophysiology and develop therapies that have the ability to alleviate devastating symptoms. Over two dozen therapeutic interventions targeting neuroinflammation, mitochondrial dysfunction, neuronal injury, and neurogenesis are being tested, including agents such as curcumin, curcumin nanoparticles, monosodium luminol, melatonin, resveratrol, fluoxetine, rolipram, oleoylethanolamide, ketamine, levetiracetam, nicotinamide riboside, minocycline, pyridazine derivatives, and neurosteroids. Preclinical outcomes show that some agents have promise, including curcumin, resveratrol, and ketamine, which are being tested in clinical trials in GWI veterans. Neuroprotectants and other compounds such as monosodium luminol, melatonin, levetiracetam, oleoylethanolamide, and nicotinamide riboside appear promising for future clinical trials. Neurosteroids have been shown to have neuroprotective and disease-modifying properties, which makes them a promising medicine for GWI. Therefore, accelerated clinical studies are urgently needed to evaluate and launch an effective therapy for veterans displaying GWI.

Neuroinflammation and brain-peripheral interaction in ischemic stroke: A narrative review

Excessive immune activation within the lesion site can be observed after stroke onset. Such neuroinflammation within the brain parenchyma represents the innate immune response, as well as the result of the additional interactions between peripheral and resident immune cells. Accumulative studies have illustrated that the pathological process of ischemic stroke is associated with resident and peripheral immunity. The infiltration of peripheral immune cells within the brain parenchyma implicitly contributes to secondary brain injuries. Therefore, better understanding of the roles of resident and peripheral immune reactions toward ischemic insult is necessary. In this review, we summarized the interaction between peripheral and resident immunity on systemic immunity and the clinical outcomes after stroke onset and also discussed various potential immunotherapeutic strategies.

Intrathecal minocycline does not block the adverse effects of repeated, intravenous morphine administration on recovery of function after SCI

Opioids are among the most effective analgesics for the management of pain in the acute phase of a spinal cord injury (SCI), and approximately 80% of patients are treated with morphine in the first 24 h following SCI. We have found that morphine treatment in the first 7 days after SCI increases symptoms of pain at 42 days post-injury and undermines the recovery of locomotor function in a rodent model. Prior research has implicated microglia/macrophages in opioid-induced hyperalgesia and the development of neuropathic pain. We hypothesized that glial activation may also underlie the development of morphine-induced pain and cell death after SCI. Supporting this hypothesis, our previous studies found that intrathecal and intravenous morphine increase the number of activated microglia and macrophages present at the spinal lesion site, and that the adverse effects of intrathecal morphine can be blocked with intrathecal minocycline. Recognizing that the cellular expression of opioid receptors, and the intracellular signaling pathways engaged, can change with repeated administration of opioids, the current study tested whether minocycline was also protective with repeated intravenous morphine administration, more closely simulating clinical treatment. Using a rat model of SCI, we co-administered intravenous morphine and intrathecal minocycline for the first 7 days post injury and monitored sensory and locomotor recovery. Contrary to our hypothesis and previous findings with intrathecal morphine, we found that minocycline did not prevent the negative effects of morphine. Surprisingly, we also found that intrathecal minocycline alone is detrimental for locomotor recovery after SCI. Using ex vivo cell cultures, we investigated how minocycline and morphine altered microglia/macrophage function. Commensurate with published studies, we found that minocycline blocked the effects of morphine on the release of pro-inflammatory cytokines but, like morphine, it increased glial phagocytosis. While phagocytosis is critical for the removal of cellular and extracellular debris at the spinal injury site, increased phagocytosis after injury has been linked to the clearance of stressed but viable neurons and protracted inflammation. In sum, our data suggest that both morphine and minocycline alter the acute immune response, and reduce locomotor recovery after SCI.

Enriched environment promotes post-stroke angiogenesis through astrocytic interleukin-17A

Objective

Our previous studies have revealed that the protective effect of an enriched environment (EE) may be linked with astrocyte proliferation and angiogenesis. However, the relationship between astrocytes and angiogenesis under EE conditions still requires further study. The current research examined the neuroprotective effects of EE on angiogenesis in an astrocytic interleukin-17A (IL-17A)-dependent manner following cerebral ischemia/reperfusion (I/R) injury.

Methods

A rat model of ischemic stroke based on middle cerebral artery occlusion (MCAO) for 120 min followed by reperfusion was established, after which rats were housed in either EE or standard conditions. A set of behavior tests were conducted, including the modified neurological severity scores (mNSS) and the rotarod test. The infarct volume was evaluated by means of 2,3,5-Triphenyl tetrazolium chloride (TTC) staining. To evaluate the levels of angiogenesis, the protein levels of CD34 were examined by means of immunofluorescence and western blotting, while the protein and mRNA levels of IL-17A, vascular endothelial growth factor (VEGF), and the angiogenesis-associated factors interleukin-6 (IL-6), JAK2, and STAT3 were detected by western blotting and real-time quantitative PCR (RT-qPCR).

Results

We found that EE promoted functional recovery, reduced infarct volume, and enhanced angiogenesis compared to rats in standard conditions. IL-17A expression in astrocytes was also increased in EE rats. EE treatment increased the levels of microvascular density (MVD) and promoted the expression of CD34, VEGF, IL-6, JAK2, and STAT3 in the penumbra, while the intracerebroventricular injection of the IL-17A-neutralizing antibody in EE rats attenuated EE-mediated functional recovery and angiogenesis.

Conclusion

Our findings revealed a possible neuroprotective mechanism of astrocytic IL-17A in EE-mediated angiogenesis and functional recovery after I/R injury, which might provide the theoretical basis for EE in clinical practise for stroke patients and open up new ideas for the research on the neural repair mechanism mediated by IL-17A in the recovery phase of stroke.

A Novel Improved Thromboembolism-Based Rat Stroke Model That Meets the Latest Standards in Preclinical Studies

The animal thromboembolic model of ischemia perfectly mimics human ischemic stroke which remains the leading cause of disability and mortality in humans. The development of new treatment strategies was therefore imperative. The purpose of this study is to improve the thromboembolic stroke model in rats in order to design experiments that use motor tests, and are in accordance with the 3R principles to prevent complications and maintain the same size of the infarct repeatedly. Tail vein dye application, a protective skull mask and a stress minimization protocol were used as additional modifications to the animal stroke model. These modifications significantly minimized the pain and stress severity of the procedures in this model. In our experimental group of Long-Evans rats, a photo-induced stroke was caused by the application of a photosensitive dye (Rose Bengal) activated with white-light irradiation, thus eliminating the need to perform a craniotomy. The animals' neurological status was evaluated using a runway elevated test. Histological examination of the brain tissue was performed at 12, 24 and 48 h, and seven days post-stroke. Tissue examination revealed necrotic foci in the cortex and the subcortical regions of the ipsilateral hemisphere in all experimental groups. Changes in the area, width and depth of the necrotic focus were observed over time. All the experimental groups showed motor disturbances after stroke survival. In the proposed model, photochemically-induced stroke caused long-term motor deficits, showed high reproducibility and low mortality rates. Consequently, the animals could participate in motor tests which are particularly suitable for assessing the efficacy of neuro-regenerative therapies, while remaining in line with the latest trends in animal experimental design.

Zebrafish as a potential model for stroke: A comparative study with standardized models

Animal models of cerebral ischemia have improved our understanding of the pathophysiology and mechanisms involved in stroke, as well as the investigation of potential therapies. The potential of zebrafish to model human diseases has become increasingly evident. The availability of these models allows for an increased understanding of the role of chemical exposure in human conditions and provides essential tools for mechanistic studies of disease. To evaluate the potential neuroprotective properties of minocycline against ischemia and reperfusion injury in zebrafish and compare them with other standardized models. In vitro studies with BV-2 cells were performed, and mammalian transient middle cerebral artery occlusion (tMCAO) was used as a comparative standard with the zebrafish stroke model. Animals were subjected to ischemia and reperfusion injury protocols and treated with minocycline. Infarction size, cytokine levels, oxidative stress, glutamate toxicity, and immunofluorescence for microglial activation, and behavioral test results were determined and compared. Administration of minocycline provided significant protection in the three stroke models in different parameters analyzed. Both experimental models complement each other in their particularities. The proposal also strengthens the findings in the literature in rodent models and allows the validation of alternative models so that they can be used in further research involving diseases with ischemia and reperfusion injury.

Structural plasticity of motor cortices assessed by voxel-based morphometry and immunohistochemical analysis following internal capsular infarcts in macaque monkeys

Compensatory plastic changes in the remaining intact brain regions are supposedly involved in functional recovery following stroke. Previously, a compensatory increase in cortical activation occurred in the ventral premotor cortex (PMv), which contributed to the recovery of dexterous hand movement in a macaque model of unilateral internal capsular infarcts. Herein, we investigated the structural plastic changes underlying functional changes together with voxel-based morphometry (VBM) analysis of magnetic resonance imaging data and immunohistochemical analysis using SMI-32 antibody in a macaque model. Unilateral internal capsular infarcts were pharmacologically induced in 5 macaques, and another 5 macaques were used as intact controls for immunohistochemical analysis. Three months post infarcts, we observed significant increases in the gray matter volume (GMV) and the dendritic arborization of layer V pyramidal neurons in the contralesional rostral PMv (F5) as well as the primary motor cortex (M1). The histological analysis revealed shrinkage of neuronal soma and dendrites in the ipsilesional M1 and several premotor cortices, despite not always detecting GMV reduction by VBM analysis. In conclusion, compensatory structural changes occur in the contralesional F5 and M1 during motor recovery following internal capsular infarcts, and the dendritic growth of pyramidal neurons is partially correlated with GMV increase.

Microglial phagocytosis and regulatory mechanisms after stroke

Stroke, including ischemic stroke and hemorrhagic stroke can cause massive neuronal death and disruption of brain structure, which is followed by secondary inflammatory injury initiated by pro-inflammatory molecules and cellular debris. Phagocytic clearance of cellular debris by microglia, the brain's scavenger cells, is pivotal for neuroinflammation resolution and neurorestoration. However, microglia can also exacerbate neuronal loss by phagocytosing stressed-but-viable neurons in the penumbra, thereby expanding the injury area and hindering neurofunctional recovery. Microglia constantly patrol the central nervous system using their processes to scour the cellular environment and start or cease the phagocytosis progress depending on the "eat me" or "don't eat me'' signals on cellular surface. An optimal immune response requires a delicate balance between different phenotypic states to regulate neuro-inflammation and facilitate reconstruction after stroke. Here, we examine the literature and discuss the molecular mechanisms and cellular pathways regulating microglial phagocytosis, their resulting effects in brain injury and neural regeneration, as well as the potential therapeutic targets that might modulate microglial phagocytic activity to improve neurological function after stroke.

Motor Cortex Plasticity During Functional Recovery Following Brain Damage

Although brain damage causes functional impairment, it is often followed by partial or total recovery of function. Recovery is believed to occur primarily because of brain plasticity. Both human and animal studies have significantly contributed to uncovering the neuronal basis of plasticity. Recent advances in brain imaging technology have enabled the investigation of plastic changes in living human brains. In addition, animal experiments have revealed detailed changes at the neural and genetic levels. In this review, plasticity in motor-related areas of the cerebral cortex, which is one of the most well-studied areas of the neocortex in terms of plasticity, is reviewed. In addition, the potential of technological interventions to enhance plasticity and promote functional recovery following brain damage is discussed. Novel neurorehabilitation technologies are expected to be established based on the emerging research on plasticity from the last several decades.

Microglia-mediated neuroinflammation and neuroplasticity after stroke

Stroke remains a major cause of long-term disability and mortality worldwide. The immune system plays an important role in determining the condition of the brain following stroke. As the resident innate immune cells of the central nervous system, microglia are the primary responders in a defense network covering the entire brain parenchyma, and exert various functions depending on dynamic communications with neurons, astrocytes, and other neighboring cells under both physiological or pathological conditions. Microglia activation and polarization is crucial for brain damage and repair following ischemic stroke, and is considered a double-edged sword for neurological recovery. Microglia can exist in pro-inflammatory states and promote secondary brain damage, but they can also secrete anti-inflammatory cytokines and neurotrophic factors and facilitate recovery following stroke. In this review, we focus on the role and mechanisms of microglia-mediated neuroinflammation and neuroplasticity after ischemia and relevant potential microglia-based interventions for stroke therapy.

Characterization of Astrocytes in the Minocycline-Administered Mouse Photothrombotic Ischemic Stroke Model

Astrocytes, together with microglia, play important roles in the non-infectious inflammation and scar formation at the brain infarct during ischemic stroke. After ischemia occurs, these become highly reactive, accumulate at the infarction, and release various inflammatory signaling molecules. The regulation of astrocyte reactivity and function surrounding the infarction largely depends on intercellular communication with microglia. However, the mechanisms involved remain unclear. Furthermore, recent molecular biological studies have revealed that astrocytes are highly divergent under both resting and reactive states, whereas it has not been well reported how the communication between microglia and astrocytes affects astrocyte divergency during ischemic stroke. Minocycline, an antibiotic that reduces microglial activity, has been used to examine the functional roles of microglia in mice. In this study, we used a mouse photothrombotic ischemic stroke model to examine the characteristics of astrocytes after the administration of minocycline during ischemic stroke. Minocycline increased astrocyte reactivity and affected the localization of astrocytes in the penumbra region. Molecular characterization revealed that the induced expression of mRNA encoding the fatty acid binding protein 7 (FABP7) by photothrombosis was enhanced by the minocycline administration. Meanwhile, minocycline did not significantly affect the phenotype or class of astrocytes. The expression of Fabp7 mRNA was well correlated with that of tumor-necrosis factor α (TNFα)-encoding Tnf mRNA, indicating that a correlated expression of FABP7 from astrocytes and TNFα is suppressed by microglial activity.

Guhong injection promotes post-stroke functional recovery via attenuating cortical inflammation and apoptosis in subacute stage of ischemic stroke

BACKGROUND

As a leading cause of death and disability, alternative therapies for stroke are still limited by its complicated pathophysiological manifestations. Guhong injection (GHI), consisting of safflower aqueous extract and aceglutamide, has been widely applied for the clinical treatment of cerebrovascular diseases, especially ischemic stroke and post-stroke recovery, in China. Recently, a series of studies have reported the positive effect of GHI against cerebral ischemia/reperfusion injury via targeting various molecular mechanisms. However, questions remain on whether treatment with GHI contributes to better functional recovery after stroke and if so, the potential mechanisms and active substances.

PURPOSE

The aim of this work was to explore the potential therapeutic possibilities of GHI for the neurological and behavioral recovery after stroke and to investigate the underlying molecular mechanisms as well as active substances.

METHODS

The neural and motor deficits as well as cortical lesions after GHI treatment were investigated in a mouse model of transient ischemic stroke. Based on the substance identification of GHI, network pharmacology combined with an experimental verification method was used to systematically decipher the biological processes and signaling pathways closely related to GHI intervention in response to post-stroke functional outcomes. Subsequently, ingenuity pathway analysis (IPA) analysis was performed to determine the anti-stroke active substances targeting to the hub targets involved in the significant molecular pathways regulated by GHI treatment.

RESULTS

Therapeutically, administration of GHI observably ameliorated the post-stroke recovery of neural and locomotor function as well as reduced infarct volume and histopathological damage to the cerebral cortex in subacute stroke mice. According to 26 identified or tentatively characterized substances in GHI, the compound-target-pathway network was built. Bioinformatics analysis suggested that inflammatory and apoptotic pathways were tightly associated with the anti-stroke effect of GHI. Based on protein-protein interaction network analysis, the hub targets (such as NF-κB p65, TNF-α, IL-6, IL-1β, Bax, Bcl-2, and Caspase-3) involved in inflammation and apoptosis were selected. On the one hand, immunofluorescence and ELISA results showed that GHI (10 ml/kg) treatment obviously reduced NF-κB p65 nuclear translocation as well as decreased the abnormally elevated concentrations of proinflammatory cytokines (TNF-α, IL-6, and IL-1β) in damaged cortex tissues. On the other hand, GHI (10 ml/kg) treatment significantly downregulated the number of TUNEL-positive apoptotic cells in ischemic cortex and effectively restored the abnormal expression of Bax, Bcl-2, and Caspase-3. Based on the results of IPA, hydroxysafflor yellow A, baicalin, scutellarin, gallic acid, syringin, chlorogenic acid, kaempferol, kaempferol-3-O-β-rutinoside, and rutin acted synergistically on core targets, which could be considered as the active substances of GHI.

CONCLUSION

Overall, the current findings showed that the beneficial action of GHI on improving post-stroke functional recovery of subacute stroke mice partly via the modulation of cortical inflammation and apoptosis. These findings not only provide a reliable reference for the clinical application of GHI, but also shed light on a promising alternative therapeutic strategy for ischemic stroke patients.

Adolescent Binge Alcohol Enhances Early Alzheimer's Disease Pathology in Adulthood Through Proinflammatory Neuroimmune Activation

Epidemiological studies suggest that heavy alcohol use early in life is associated with increased risk for Alzheimer's disease (AD). However, mechanisms connecting AD with alcohol use have not been identified. Both heavy alcohol use and AD feature increased proinflammatory signaling. Therefore, we hypothesized that adolescent binge ethanol would increase AD molecular and behavioral pathology in adulthood through proinflammatory signaling. The 3xTg-AD mouse model (APPSwe, tauP301, Psen1^tm1Mpm) which features amyloid (Aβ) and tau pathology beginning at 6-12 months underwent adolescent intermittent ethanol (AIE, 5 g/kg/d, i.g., P25-55) with assessment of AD pathologic mediators at P200. A second group of mice received AIE +/- minocycline (30 mg/kg/d, IP) followed by behavioral testing in adulthood. Behavioral testing and age of testing included: locomotor activity and exploration (27-28 weeks), novel object recognition (NORT, 28-30 weeks), 3-chamber sociability and social memory (29-31 weeks), prepulse inhibition (PPI, 30-32 weeks), Morris Water Maze with reversal (MWM, 31-35 weeks), and Piezo sleep monitoring (35-37 weeks). We found that AIE increased levels of neurotoxic Aβ_1-42 in adult female hippocampus as well as intraneuronal Aβ_1-42 in amygdala and entorhinal cortex. Phosphorylated tau at residue Thr181 (p-tau-181) was also increased in female hippocampus by AIE. Several proinflammatory genes were persistently increased by AIE in the female hippocampus, including IL-1β, MCP-1, IL-6, and IFNα. Expression of these genes was strongly correlated with the levels of Aβ_1-42 and p-tau-181 in hippocampus. AIE caused persistent decreases in locomotor activity (open-field and NORT habituation) and increased anxiety-like behavior (thigmotaxis) while reducing memory retention. Treatment with the anti-inflammatory compound minocycline during AIE blocked persistent increases in Aβ_1-42 in amygdala and p-tau-181 in hippocampus, and prevented AIE-induced thigmotaxis and memory loss. Together, these data find that adolescent binge ethanol enhances AD molecular and behavioral pathology in adulthood through proinflammatory signaling. Blockade of proinflammatory signaling during ethanol exposure prevents ethanol-induced effects on pathologic accumulation of AD-associated proteins and persistent behavior changes relevant to human AD.

Wild Bitter Melon Extract Abrogates Hypoxia-Induced Cell Death via the Regulation of Ferroptosis, ER Stress, and Apoptosis in Microglial BV2 Cells

Microglial cells are well-known phagocytic cells that are resistant to the central nervous system (CNS) and play an important role in the maintenance of CNS homeostasis. Activated microglial cells induce neuroinflammation under hypoxia and typically cause neuronal damage in CNS diseases. In this study, we propose that wild bitter melon extract (WBM) has a protective effect on hypoxia-induced cell death via regulation of ferroptosis, ER stress, and apoptosis. The results demonstrated that hypoxia caused microglial BV-2 the accumulation of lipid ROS, ferroptosis, ER stress, and apoptosis. In this study, we investigated the pharmacological effects of WBM on BV-2 cells following hypoxia-induced cell death. The results indicated that WBM reversed hypoxia-downregulated antiferroptotic molecules Gpx4 and SLC7A11, as well as upregulated the ER stress markers CHOP and Bip. Moreover, WBM alleviated hypoxia-induced apoptosis via the regulation of cleaved-caspase 3, Bax, and Bcl-2. Our results suggest that WBM may be a good candidate for preventing CNS disorders in the future.

Minocycline Pretreatment Prevents Blood-Brain Barrier Disruption in Septic Rats

INTRODUCTION

The aim of the study was to explore the mechanism by which minocycline protects the blood-brain barrier (BBB) in septic rats.

METHODS

A sepsis rat model was generated in healthy, male Sprague-Dawley rats by cecal ligation and puncture (CLP). The rats were randomly divided into four groups and treated as follows: sham-operated plus normal saline (Sham + S group), CLP plus normal saline (CLP + S group), CLP plus minocycline pretreatment (CLP + M1 group), and CLP plus minocycline treatment (CLP + M2 group). Rats in the CLP + M1 group received 45 mg/kg minocycline by intraperitoneal injection every 12 h for 72 h. Rats in the Sham + S and CLP + S groups were injected with the same volume of normal saline every 12 h for 72 h. Rats in the CLP + M2 group were intraperitoneally injected with 45 mg/kg minocycline immediately after CLP and once every 12 h for 72 h. All rats were sacrificed at 72 h after operation. Tumor necrosis factor α and interleukin 6 levels, the expression of ionized calcium-binding adaptor molecule-1 (Iba-1), and the permeability of the BBB were measured. The expression of matrix metalloproteinases-9 (MMP-9) and the tight junction proteins zonula occludens-1 (ZO-1) and occludin was detected by Western blot. In addition, Evans blue (EB) staining, immunohistochemistry, and ELISA analysis were carried out.

RESULTS

Minocycline pretreatment significantly inhibited microglial activation, decreased the sepsis-induced expression of MMP-9, increased the expression of ZO-1 and occludin, and improved the permeability of the BBB. Minocycline treatment failed to inhibit microglial activation, decrease the sepsis-induced expression of MMP-9, increase the expression of ZO-1 or occluding, or improve the permeability of the BBB.

CONCLUSIONS

Minocycline pretreatment can effectively improve the altered permeability of the BBB caused by sepsis. The mechanism may be related to the inhibition of microglial activation and MMP-9 expression and increased expression of ZO-1 and occludin.

Mycobacterium vaccae immunization in rats ameliorates features of age-associated microglia activation in the amygdala and hippocampus

Aging and reduced exposure to environmental microbes can both potentiate neuroinflammatory responses. Prior studies indicate that immunization with the immunoregulatory and anti-inflammatory bacterium, Mycobacterium vaccae (M. vaccae), in aged rats limits neuroimmune activation and cognitive impairments. However, the mechanisms by which M. vaccae immunization ameliorates age-associated neuroinflammatory “priming” and whether microglia are a primary target remain unclear. Here, we investigated whether M. vaccae immunization protects against microglia morphological changes in response to aging. Adult (3 mos) and aged (24 mos) Fisher 344 × Brown Norway rats were immunized with either M. vaccae or vehicle once every week for 3 weeks. Aging led to elevated Iba1 immunoreactivity, microglial density, and deramification of microglia processes in the hippocampus and amygdala but not other brain regions. Additionally, aged rats exhibited larger microglial somas in the dorsal hippocampus, suggestive of a more activated phenotype. Notably, M. vaccae treatment ameliorated indicators of microglia activation in both the amygdala and hippocampus. While changes in morphology appeared to be region-specific, gene markers indicative of microglia activation were upregulated by age and lowered in response to M. vaccae in all brain regions evaluated. Taken together, these data suggest that peripheral immunization with M. vaccae quells markers of age-associated microglia activation.

Minocycline improves the functional recovery after traumatic brain injury via inhibition of aquaporin-4

Traumatic brain injury (TBI) is one of the main concerns worldwide as there is still no comprehensive therapeutic intervention. Astrocytic water channel aquaporin-4 (AQP-4) system is closely related to the brain edema, water transport at blood-brain barrier (BBB) and astrocyte function in the central nervous system (CNS). Minocycline, a broad-spectrum semisynthetic tetracycline antibiotic, has shown anti-inflammation, anti-apoptotic, vascular protection and neuroprotective effects on TBI models. Here, we tried to further explore the underlying mechanism of minocycline treatment for TBI, especially the relationship of minocycline and AQP4 during TBI treatment. In present study, we observed that minocycline efficaciously reduces the elevation of AQP4 in TBI mice. Furthermore, minocycline significantly reduced neuronal apoptosis, ameliorated brain edema and BBB disruption after TBI. In addition, the expressions of tight junction protein and astrocyte morphology alteration were optimized by minocycline administration. Similar results were found after treating with TGN-020 (an inhibitor of AQP4) in TBI mice. Moreover, these effects were reversed by cyanamide (CYA) treatment, which notably upregulated AQP4 expression level in vivo. In primary cultured astrocytes, small-interfering RNA (siRNA) AQP4 treatment prevented glutamate-induced astrocyte swelling. To sum up, our study suggests that minocycline improves the functional recovery of TBI through reducing AQP4 level to optimize BBB integrity and astrocyte function, and highlights that the AQP4 may be an important therapeutic target during minocycline treating for TBI.

SerpinA3N attenuates ischemic stroke injury by reducing apoptosis and neuroinflammation

Objective

To assess the effect of serine protein inhibitor A3N (serpinA3N) in ischemic stroke and to explore its mechanism of action.

Methods

Mouse ischemic stroke model was induced by transient middle cerebral artery occlusion followed by reperfusion. The expression pattern of serpinA3N was assessed using immunofluorescence, Western blot analysis, and real‐time quantitative PCR. An adeno‐associated virus (AAV) and recombinant serpinA3N were administered. Additionally, co‐immunoprecipitation‐mass spectrometry and immunofluorescence co‐staining were used to identify protein interactions.

Results

SerpinA3N was upregulated in astrocytes and neurons within the ischemic penumbra after stroke in the acute phase. The expression of serpinA3N gradually increased 6 h after reperfusion, peaked on the day 2–3, and then decreased by day 7. Overexpression of serpinA3N by AAV significantly reduced the infarct size and improved motor function, associated with alleviated inflammation and oxidative stress. SerpinA3N treatment also reduced apoptosis both in vivo and in vitro. Co‐immunoprecipitation‐mass spectrometry and Western blotting revealed that clusterin interacts with serpinA3N, and Akt‐mTOR pathway members were upregulated by serpinA3N both in vivo and in vitro.

Conclusions

SerpinA3N is expressed in astrocytes and penumbra neurons after stroke in mice. It reduces brain damage possibly via interacting with clusterin and inhibiting neuronal apoptosis and neuroinflammation.

Non-human Primate Models to Explore the Adaptive Mechanisms After Stroke

The brain has the ability to reconstruct neural structures and functions to compensate for the brain lesions caused by stroke, although it is highly limited in primates including humans. Animal studies in which experimental lesions were induced in the brain have contributed to the current understanding of the neural mechanisms underlying functional recovery. Here, I have highlighted recent advances in non-human primate models using primate species such as macaques and marmosets, most of which have been developed to study the mechanisms underlying the recovery of motor functions after stroke. Cortical lesion models have been used to investigate motor recovery after lesions to the cortical areas involved in movements of specific body parts. Models of a focal stroke at the posterior internal capsule have also been developed to bridge the gap between the knowledge obtained by cortical lesion models and the development of intervention strategies because the severity and outcome of motor deficits depend on the degree of lesions to the region. This review will also introduce other stroke models designed to study the plastic changes associated with development and recovery from cognitive and sensory impairments. Although further validation and careful interpretation are required, considering the differences between non-human primate brains and human brains, studies using brain-lesioned non-human primates offer promise for improving translational outcomes.

Inflammatory resolution and vascular barrier restoration after retinal ischemia reperfusion injury

Background

Several retinal pathologies exhibit both inflammation and breakdown of the inner blood-retinal barrier (iBRB) resulting in vascular permeability, suggesting that treatments that trigger resolution of inflammation may also promote iBRB restoration.

Methods

Using the mouse retinal ischemia-reperfusion (IR) injury model, we followed the time course of neurodegeneration, inflammation, and iBRB disruption and repair to examine the relationship between resolution of inflammation and iBRB restoration and to determine if minocycline, a tetracycline derivative shown to reverse microglial activation, can hasten these processes.

Results

A 90-min ischemic insult followed by reperfusion in the retina induced cell apoptosis and inner retina thinning that progressed for approximately 2 weeks. IR increased vascular permeability within hours, which resolved between 3 and 4 weeks after injury. Increased vascular permeability coincided with alteration and loss of endothelial cell tight junction (TJ) protein content and disorganization of TJ protein complexes. Shunting of blood flow away from leaky vessels and dropout of leaky capillaries were eliminated as possible mechanisms for restoring the iBRB. Repletion of TJ protein contents occurred within 2 days after injury, long before restoration of the iBRB. In contrast, the eventual re-organization of TJ complexes at the cell border coincided with restoration of the barrier. A robust inflammatory response was evident a 1 day after IR and progressed to resolution over the 4-week time course. The inflammatory response included a rapid and transient infiltration of granulocytes and Ly6C⁺ classical inflammatory monocytes, a slow accumulation of Ly6C^neg monocyte/macrophages, and activation, proliferation, and mobilization of resident microglia. Extravasation of the majority of CD45⁺ leukocytes occurred from the superficial plexus. The presence of monocyte/macrophages and increased numbers of microglia were sustained until the iBRB was eventually restored. Intervention with minocycline to reverse microglial activation at 1 week after injury promoted early restoration of the iBRB coinciding with decreased expression of mRNAs for the microglial M1 markers TNF-α, IL-1β, and Ptgs2 (Cox-2) and increased expression of secreted serine protease inhibitor Serpina3n mRNA.

Conclusions

These results suggest that iBRB restoration occurs as TJ complexes are reorganized and that resolution of inflammation and restoration of the iBRB following retinal IR injury are functionally linked.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02237-5.

Differential effects of the cell cycle inhibitor, olomoucine, on functional recovery and on responses of peri-infarct microglia and astrocytes following photothrombotic stroke in rats

Background

Following stroke, changes in neuronal connectivity in tissue surrounding the infarct play an important role in both spontaneous recovery of neurological function and in treatment-induced improvements in function. Microglia and astrocytes influence this process through direct interactions with the neurons and as major determinants of the local tissue environment. Subpopulations of peri-infarct glia proliferate early after stroke providing a possible target to modify recovery. Treatment with cell cycle inhibitors can reduce infarct volume and improve functional recovery. However, it is not known whether these inhibitors can influence neurological function or alter the responses of peri-infarct glia without reducing infarction. The present study aimed to address these issues by testing the effects of the cell cycle inhibitor, olomoucine, on recovery and peri-infarct changes following photothrombotic stroke.

Methods

Stroke was induced by photothrombosis in the forelimb sensorimotor cortex in Sprague-Dawley rats. Olomoucine was administered at 1 h and 24 h after stroke induction. Forelimb function was monitored up to 29 days. The effects of olomoucine on glial cell responses in peri-infarct tissue were evaluated using immunohistochemistry and Western blotting.

Results

Olomoucine treatment did not significantly affect maximal infarct volume. Recovery of the affected forelimb on a placing test was impaired in olomoucine-treated rats, whereas recovery in a skilled reaching test was substantially improved. Olomoucine treatment produced small changes in aspects of Iba1 immunolabelling and in the number of CD68-positive cells in cerebral cortex but did not selectively modify responses in peri-infarct tissue. The content of the astrocytic protein, vimentin, was reduced by 30% in the region of the lesion in olomoucine-treated rats.

Conclusions

Olomoucine treatment modified functional recovery in the absence of significant changes in infarct volume. The effects on recovery were markedly test dependent, adding to evidence that skilled tasks requiring specific training and general measures of motor function can be differentially modified by some interventions. The altered recovery was not associated with specific changes in key responses of peri-infarct microglia, even though these cells were considered a likely target for early olomoucine treatment. Changes detected in peri-infarct reactive astrogliosis could contribute to the altered patterns of functional recovery.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02208-w.

BK Channel-Mediated Microglial Phagocytosis Alleviates Neurological Deficit After Ischemic Stroke

Microglial phagocytosis benefits neurological recovery after stroke. Large-conductance Ca2⁺-activated K⁺ currents are expressed in activated microglia, and BK channel knockout aggravates cerebral ischemic injury. However, the effect of BK channels on microglial phagocytosis after ischemic stroke remains unknown. Here, we explored whether BK channel activation is beneficial for neurological outcomes through microglial phagocytosis after ischemic stroke. ICR mice after transient middle cerebral artery occlusion (tMCAO) were treated with dimethyl sulfoxide (DMSO), BK channel activator NS19504, and inhibitor Paxilline. The results showed a decrease in BK channel expression after tMCAO. BK channel activator NS19504 alleviates neurological deficit after experimental modeling of tMCAO in mice compared to the control. Furthermore, we treated primary microglia with DMSO, NS19504, and Paxilline after oxygen glucose deprivation (OGD). NS19504 promoted primary microglial phagocytosing fluorescent beads and neuronal debris, which reduced neuronal apoptosis after stroke. These effects could be reversed by BK channel inhibitor Paxilline. Finally, NS19504 increased relative phosphorylated extracellular signal-regulated kinase 1/2 expression compared to the Paxilline group at the third day after stroke. Our findings indicate that microglial BK channels are a potential target for acute stage of ischemic stroke therapy.

Immune Cells in the BBB Disruption After Acute Ischemic Stroke: Targets for Immune Therapy?

Blood-Brain Barrier (BBB) disruption is an important pathophysiological process of acute ischemic stroke (AIS), resulting in devastating malignant brain edema and hemorrhagic transformation. The rapid activation of immune cells plays a critical role in BBB disruption after ischemic stroke. Infiltrating blood-borne immune cells (neutrophils, monocytes, and T lymphocytes) increase BBB permeability, as they cause microvascular disorder and secrete inflammation-associated molecules. In contrast, they promote BBB repair and angiogenesis in the latter phase of ischemic stroke. The profound immunological effects of cerebral immune cells (microglia, astrocytes, and pericytes) on BBB disruption have been underestimated in ischemic stroke. Post-stroke microglia and astrocytes can adopt both an M1/A1 or M2/A2 phenotype, which influence BBB integrity differently. However, whether pericytes acquire microglia phenotype and exert immunological effects on the BBB remains controversial. Thus, better understanding the inflammatory mechanism underlying BBB disruption can lead to the identification of more promising biological targets to develop treatments that minimize the onset of life-threatening complications and to improve existing treatments in patients. However, early attempts to inhibit the infiltration of circulating immune cells into the brain by blocking adhesion molecules, that were successful in experimental stroke failed in clinical trials. Therefore, new immunoregulatory therapeutic strategies for acute ischemic stroke are desperately warranted. Herein, we highlight the role of circulating and cerebral immune cells in BBB disruption and the crosstalk between them following acute ischemic stroke. Using a robust theoretical background, we discuss potential and effective immunotherapeutic targets to regulate BBB permeability after acute ischemic stroke.

Administration of 4-Hydroxy-3,5-Di-Tertbutyl Cinnamic Acid Restores Mitochondrial Function in Rabbits with Cerebral Ischemia

The aim of the study is to evaluate the effect of 4-hydroxy-3,5- di-tertbutyl cinnamic acid on the change in mitochondrial function under conditions of experimental cerebral ischemia in rabbits. The study was performed on 48 male rabbits, which were used for modeling permanent cerebral ischemia by occlusion of the common carotid arteries. The test compound was administered before modeling ischemia for 14 days and after the occurrence of reproducing ischemia, in a similar time interval. After that, neurological deficit and the parameters of mitochondrial respiration, the intensity of anaerobic processes, the latent opening time of the mitochondrial permeability transition pore, the value of the mitochondrial membrane potential and the concentration of caspase – 3 were determined. The administration of 100 mg/kg of 4-hydroxy-3,5-di-tertbutyl cinnamic acid into the animals reduced neurological deficit and restored the mitochondrial membrane potential. Prophylactic administration of 4-hydroxy- 3,5-di-tertbutyl cinnamic acid, contributed to an increase in ATPgenerating ability, the maximum level of respiration and respiratory capacity by 4.1 times (p<0.01), 4.8 times (p<0.01) and 4.3 times (p<0.01), respectively. With therapeutic administration, these indicators increased by 11 times (p<0.01), 12.2 times (p<0.01) and 8.6 times (p<0.01), respectively. Also, both the prophylactic and therapeutic use of 4-hydroxy-3,5-di-tret-butyl cinnamic acid normalized aerobic/anaerobic metabolism, as well as reduced the concentration of caspase-3. Based on the obtained data, significant cerebroprotective properties of 4-hydroxy-3,5- di-tertbutyl cinnamic acid can be assumed. Moreover, the potential mechanism of action of this compound may be mediated by the normalization of mitochondrial function.

Minocycline alleviates Gulf War Illness rats via altering gut microbiome, attenuating neuroinflammation and enhancing hippocampal neurogenesis

Accumulating evidences suggest that deficits in neurogenesis, chronic inflammation and gut microbiome dysregulation contribute to the pathophysiology of Gulf War Illness (GWI). Minocycline has been demonstrated to be a potent neuroprotective agent and could regulate neuroinflammation. The present study intends to investigate whether the treatment of minocycline maintains better cognition and mood function in a rat model of GWI and the potential mechanism. Rats received 28 days of GWI-related chemical exposure and restraint stress, along with daily minocycline or vehicle treatment. Cognitive and mood function, neuroinflammation, neurogenesis and gut microbiota were detected. We found that minocycline treatment induces better cognitive and mood function in the GWI rat model, as indicated by open-field test, elevated plus maze test, novel object recognition test and forced swim test. Moreover, minocycline treatment reversed the altered gut microbiome, neuroinflammation and the decreased hippocampal neurogenesis of rats with GWI. Taken together, our study indicated that minocycline treatment exerts better cognitive and mood function in GWI rat model, which is possibly related to gut microbiota remodeling, restrained inflammation and enhanced hippocampal neurogenesis. These results may establish minocycline as a potential prophylactic or therapeutic agent for the treatment of GWI.

A novel prognosis prediction model, including cytotoxic T lymphocyte-associated antigen-4, ischemia-modified albumin, lipoprotein-associated phospholipase A2, glial fibrillary acidic protein, and homocysteine, for ischemic stroke in the Chinese hypertensive population

Background

There is still a lack of tools to assess the prognosis of ischemic stroke patients induced by hypertension. In this study, we built a novel prognostic assessment model for ischemic stroke in the Chinese hypertensive population.

Methods

Mass spectrometry technique was used to analyze the changes in serum protein profiles of hypertensive patients with ischemic stroke. A total of 314 hypertensive patients were divided into the testing group (206 patients) and the validation group (108 patients).

Results

Compared with hypertensive patients without ischemic stroke, serum cytotoxic T lymphocyte‐associated antigen‐4 (CTLA‐4), ischemia‐modified albumin (IMA), lipoprotein‐associated phospholipase A2 (Lp‐PLA2), glial fibrillary acidic protein (GFAP), and homocysteine (HCY) levels were significantly increased among hypertensive patients with ischemic stroke (p < 0.05). Then, we built a novel prognostic assessment model for hypertensive patients with ischemic stroke [Logit(P) = 29.172–1.088*CTLA‐4–0.952*IMA‐0.537*Lp‐PLA2 −0.066*GFAP −0.149*HCY]. It showed higher efficiency (AUC = 0.981, sensitivity = 95.5%, specificity = 93.8%) than any single marker. The estimated probability was 0.739, which means if higher than 0.739, it was classified into poor prognosis. Compared with the estimated probability ≤0.739 group, the survival rate of hypertensive patients with ischemic stroke in the estimated probability >0.739 group was significantly decreased (χ² = 40.001, p < 0.001). In the validation group, our novel prognostic assessment model still showed good efficiency (AUC = 0.969, sensitivity = 89.4%, specificity = 92.5%; χ² = 47.551, p < 0.001).

Conclusion

Current novel prognostic assessment model we have built is of great value in the prognostic evaluation for ischemic stroke in the Chinese hypertensive population.

Different Roles of Mitochondria in Cell Death and Inflammation: Focusing on Mitochondrial Quality Control in Ischemic Stroke and Reperfusion

Mitochondrial dysfunctions are among the main hallmarks of several brain diseases, including ischemic stroke. An insufficient supply of oxygen and glucose in brain cells, primarily neurons, triggers a cascade of events in which mitochondria are the leading characters. Mitochondrial calcium overload, reactive oxygen species (ROS) overproduction, mitochondrial permeability transition pore (mPTP) opening, and damage-associated molecular pattern (DAMP) release place mitochondria in the center of an intricate series of chance interactions. Depending on the degree to which mitochondria are affected, they promote different pathways, ranging from inflammatory response pathways to cell death pathways. In this review, we will explore the principal mitochondrial molecular mechanisms compromised during ischemic and reperfusion injury, and we will delineate potential neuroprotective strategies targeting mitochondrial dysfunction and mitochondrial homeostasis.

Neurogenesis After Stroke: A Therapeutic Perspective

Stroke is a major cause of death and disability worldwide. Yet therapeutic strategies available to treat stroke are very limited. There is an urgent need to develop novel therapeutics that can effectively facilitate functional recovery. The injury that results from stroke is known to induce neurogenesis in penumbra of the infarct region. There is considerable interest in harnessing this response for therapeutic purposes. This review summarizes what is currently known about stroke-induced neurogenesis and the factors that have been identified to regulate it. Additionally, some key studies in this field have been highlighted and their implications on future of stroke therapy have been discussed. There is a complex interplay between neuroinflammation and neurogenesis that dictates stroke outcome and possibly recovery. This highlights the need for a better understanding of the neuroinflammatory process and how it affects neurogenesis, as well as the need to identify new mechanisms and potential modulators. Neuroinflammatory processes and their impact on post-stroke repair have therefore also been discussed.

Microglia and bradykinin cross talk in poststroke cognitive impairment in diabetes

Stroke is one of the leading causes of mortality and the leading cause of long-term disability worldwide. Although cognitive impairment is a common consequence of stroke, the underlying pathophysiological processes that lead to it are still poorly understood. Recently, more studies have shown evidence of the involvement of diabetes in producing a chronic neuroinflammatory state, which ultimately alters the recovery of function and cognition after stroke. To better understand the impact of diabetes on poststroke recovery, here we highlight the recent insights on the role of diabetes in neuroinflammation, especially regarding its effect on microglial function, and the emerging data on the involvement of kinins in both diabetes and neuroinflammation.

Emerging Role of Microglia-Mediated Neuroinflammation in Epilepsy after Subarachnoid Hemorrhage

Epilepsy is a common and serious complication of subarachnoid hemorrhage (SAH), giving rise to increased morbidity and mortality. It's difficult to identify patients at high risk of epilepsy and the application of anti-epileptic drugs (AEDs) following SAH is a controversial topic. Therefore, it's pressingly needed to gain a better understanding of the risk factors, underlying mechanisms and the optimization of therapeutic strategies for epilepsy after SAH. Neuroinflammation, characterized by microglial activation and the release of inflammatory cytokines, has drawn growing attention due to its influence on patients with epilepsy after SAH. In this review, we discuss the risk factors for epilepsy after SAH and emphasize the critical role of microglia. Then we discuss how various molecules arising from pathophysiological changes after SAH activate specific receptors such as TLR4, NLRP3, RAGE, P2X7R and initiate the downstream inflammatory pathways. Additionally, we focus on the significant responses implicated in epilepsy including neuronal excitotoxicity, the disruption of blood-brain barrier (BBB) and the change of immune responses. As the application of AEDs for seizure prophylaxis after SAH remains controversial, the regulation of neuroinflammation targeting the key pathological molecules could be a promising therapeutic method. While neuroinflammation appears to contribute to epilepsy after SAH, more comprehensive experiments on their relationships are needed.

Delayed Treatment with Human Dental Pulp Stem Cells Accelerates Functional Recovery and Modifies Responses of Peri-Infarct Astrocytes Following Photothrombotic Stroke in Rats

Dental pulp contains multipotent mesenchymal stem cells that improve outcomes when administered early after temporary middle cerebral artery occlusion in rats. To further assess the therapeutic potential of these cells, we tested whether functional recovery following stroke induced by photothrombosis could be modified by a delayed treatment that was initiated after the infarct attained maximal volume. Photothrombosis induces permanent focal ischemia resulting in tissue changes that better reflect key aspects of the many human strokes in which early restoration of blood flow does not occur. Human dental pulp stem cells (approximately 400 × 10³ viable cells) or vehicle were injected into the infarct and adjacent brain tissue of Sprague-Dawley rats at 3 days after the induction of unilateral photothrombotic stroke in the sensorimotor cortex. Forepaw function was tested up to 28 days after stroke. Cellular changes in peri-infarct tissue at 28 days were assessed using immunohistochemistry. Rats treated with the stem cells showed faster recovery compared with vehicle-treated animals in a test of forelimb placing in response to vibrissae stimulation and in first attempt success in a skilled forelimb reaching test. Total success in the skilled reaching test and forepaw use during exploration in a Perspex cylinder were not significantly different between the 2 groups. At 28 days after stroke, rats treated with the stem cells showed decreased immunolabeling for glial fibrillary acidic protein in tissue up to 1 mm from the infarct, suggesting decreased reactive astrogliosis. Synaptophysin, a marker of synapses, and collagen IV, a marker of capillaries, were not significantly altered at this time by the stem-cell treatment. These results indicate that dental pulp stem cells can accelerate recovery without modifying initial infarct formation. Decreases in reactive astrogliosis in peri-infarct tissue could have contributed to the change by promoting adaptive responses in neighboring neurons.

Covert strokes prior to Alzheimer's disease onset accelerate peri-lesional pathology but not cognitive deficits in an inducible APP mouse model

It is estimated that up to 1 in 3 healthy middle-aged adults will have had a covert stroke during their lifetime. Furthermore, post-stroke, survivors are more than twice as likely to develop dementia. In the present study, we aimed to model the impact of focal subclinical ischemia prior to the onset of AD pathogenesis in a preclinical model. We utilized endothelin-1 to induce ischemia in an iducible transgenic mouse model of Alzheimer's disease, APPsi:tTA, allowing for temporal control of APP gene expression. We induced the focal subclinical ischemic events in the absence of APP expression, thus prior to AD onset. T2 structural magnetic resonance imaging confirmed the volume and location of focal subclinical ischemic lesions to the medial prefrontal cortex. Following recovery from surgery and 7 weeks of APP expression, we found that two subclinical ischemic lesions resulted in a significant localized increase in amyloid load and in microglial activation proximal to the lesion. However, no differences were found in astrogliosis. A battery of behaviour tests was conducted, in which no significant differences were detected in activities of daily living and cognitive function between stroked and sham cohorts. Overall, our results demonstrated that APP expression was the sole driving force behind behavioural deficits. In conclusion, our results suggest that a history of two subclinical strokes prior to AD onset does not worsen early disease trajectory in a mouse model.

Neuroregeneration and functional recovery after stroke: advancing neural stem cell therapy toward clinical application

Stroke is a main cause of death and disability worldwide. The ability of the brain to self-repair in the acute and chronic phases after stroke is minimal; however, promising stem cell-based interventions are emerging that may give substantial and possibly complete recovery of brain function after stroke. Many animal models and clinical trials have demonstrated that neural stem cells (NSCs) in the central nervous system can orchestrate neurological repair through nerve regeneration, neuron polarization, axon pruning, neurite outgrowth, repair of myelin, and remodeling of the microenvironment and brain networks. Compared with other types of stem cells, NSCs have unique advantages in cell replacement, paracrine action, inflammatory regulation and neuroprotection. Our review summarizes NSC origins, characteristics, therapeutic mechanisms and repair processes, then highlights current research findings and clinical evidence for NSC therapy. These results may be helpful to inform the direction of future stroke research and to guide clinical decision-making.

Early Thalamic Injury After Resuscitation From Severe Asphyxial Cardiac Arrest in Developing Rats

Children who survive cardiac arrest often develop debilitating sensorimotor and cognitive deficits. In animal models of cardiac arrest, delayed neuronal death in the hippocampal CA1 region has served as a fruitful paradigm for investigating mechanisms of injury and neuroprotection. Cardiac arrest in humans, however, is more prolonged than in most experimental models. Consequently, neurologic deficits in cardiac arrest survivors arise from injury not solely to CA1 but to multiple vulnerable brain structures. Here, we develop a rat model of prolonged pediatric asphyxial cardiac arrest and resuscitation, which better approximates arrest characteristics and injury severity in children. Using this model, we characterize features of microglial activation and neuronal degeneration in the thalamus 24 h after resuscitation from 11 and 12 min long cardiac arrest. In addition, we test the effect of mild hypothermia to 34°C for 8 h after 12.5 min of arrest. Microglial activation and neuronal degeneration are most prominent in the thalamic Reticular Nucleus (nRT). The severity of injury increases with increasing arrest duration, leading to frank loss of nRT neurons at longer arrest times. Hypothermia does not prevent nRT injury. Interestingly, injury occurs selectively in intermediate and posterior nRT segments while sparing the anterior segment. Since all nRT segments consist exclusively of GABA-ergic neurons, we asked if GABA-ergic neurons in general are more susceptible to hypoxic-ischemic injury. Surprisingly, cortical GABA-ergic neurons, like their counterparts in the anterior nRT segment, do not degenerate in this model. Hence, we propose that GABA-ergic identity alone is not sufficient to explain selective vulnerability of intermediate and posterior nRT neurons to hypoxic-ischemic injury after cardiac arrest and resuscitation. Our current findings align the animal model of pediatric cardiac arrest with human data and suggest novel mechanisms of selective vulnerability to hypoxic-ischemic injury among thalamic GABA-ergic neurons.

Filling the gaps on stroke research: Focus on inflammation and immunity

For the last two decades, researchers have placed hopes in a new era in which a combination of reperfusion and neuroprotection would revolutionize the treatment of stroke. Nevertheless, despite the thousands of papers available in the literature showing positive results in preclinical stroke models, randomized clinical trials have failed to show efficacy. It seems clear now that the existing data obtained in preclinical research have depicted an incomplete picture of stroke pathophysiology. In order to ameliorate bench-to-bed translation, in this review we first describe the main actors on stroke inflammatory and immune responses based on the available preclinical data, highlighting the fact that the link between leukocyte infiltration, lesion volume and neurological outcome remains unclear. We then describe what is known on neuroinflammation and immune responses in stroke patients, and summarize the results of the clinical trials on immunomodulatory drugs. In order to understand the gap between clinical trials and preclinical results on stroke, we discuss in detail the experimental results that served as the basis for the summarized clinical trials on immunomodulatory drugs, focusing on (i) experimental stroke models, (ii) the timing and selection of outcome measuring, (iii) alternative entry routes for leukocytes into the ischemic region, and (iv) factors affecting stroke outcome such as gender differences, ageing, comorbidities like hypertension and diabetes, obesity, tobacco, alcohol consumption and previous infections like Covid-19. We can do better for stroke treatment, especially when targeting inflammation following stroke. We need to re-think the design of stroke experimental setups, notably by (i) using clinically relevant models of stroke, (ii) including both radiological and neurological outcomes, (iii) performing long-term follow-up studies, (iv) conducting large-scale preclinical stroke trials, and (v) including stroke comorbidities in preclinical research.

Time- and area-dependent macrophage/microglial responses after focal infarction of the macaque internal capsule

We quantitatively investigated temporal changes of macrophages and microglia (MΦ/MG) after focal infarction of the internal capsule using a macaque model we recently established. Immunoreactivity for Iba1, a general marker for MΦ/MG, in the periinfarct core gradually increased from 0 days to 2-3 weeks after infarction, and the increased immunoreactivity continued at least until 6 months; no study in rodents has reported increased Iba1-immunoreactive cells for so long. Retrograde atrophy or degeneration of neurons in layer V of the primary motor cortex, where the descending motor tract originates, was seen as secondary damage. Here we found that Iba1-positive MΦ/MG transiently increased in layer V during several weeks after the infarction. Therefore, the time course of MΦ/MG activation differs between the perilesional area and the remote brain area where secondary damage occurs to tissue initially preserved after the infarct. Detailed analyses using the functional phenotype markers CD68, CD86, and CD206, as well as cytokines released by cells with each phenotype, suggest an anti-inflammatory role for activated MΦ/MG both in the periinfarct core during the chronic phase and in the primary motor cortex.

Monocyte Transmodulation: The Next Novel Therapeutic Approach in Overcoming Ischemic Stroke?

The immune response following neuroinflammation is a vital element of ischemic stroke pathophysiology. After the onset of ischemic stroke, a specialized vasculature system that effectively protects central nervous system tissues from the invasion of blood cells and other macromolecules is broken down within minutes, thereby triggering the inflammation cascade, including the infiltration of peripheral blood leukocytes. In this series of processes, blood-derived monocytes have a significant effect on the outcome of ischemic stroke through neuroinflammatory responses. As neuroinflammation is a necessary and pivotal component of the reparative process after ischemic stroke, understanding the role of infiltrating monocytes in the modulation of inflammatory responses may offer a great opportunity to explore new therapies for ischemic stroke. In this review, we discuss and highlight the function and involvement of monocytes in the brain after ischemic injury, as well as their impact on tissue damage and repair.

Tracking elemental changes in an ischemic stroke model with X-ray fluorescence imaging

Stroke is a leading cause of long-term disability in adults and a leading cause of death in developed nations. The cascade of cellular events and signalling that occur after cerebral ischemia are complex, however, analyzing global element markers of metabolic state affords the means to monitor stroke severity, status of injury, and recovery. These markers provide a multi-parameter method for assessing changes through the post-stroke time course. We employ synchrotron-based elemental mapping to follow elemental changes in the brain at 1 h, 1-, 2-, and 3-days, and at 1-, 2-, 3-, and 4-weeks post-stroke in a photothrombotic stroke model in mice. Our analysis reveals a highly consistent metabolic penumbra that can be readily identified based on the level of dysregulated potassium and other key elements. Maps of elemental distributions are also useful to demarcate events in the cellular response to the inflammatory cascade, including ion dysregulation, recruitment of cells to the lesion, and glial scar formation.

Suppression of microglial activation and monocyte infiltration ameliorates cerebellar hemorrhage induced-brain injury and ataxia

Ataxia, characterized by uncoordinated movement, is often found in patients with cerebellar hemorrhage (CH), leading to long-term disability without effective management. Microglia are among the first responders to CNS insult. Yet the role and mechanism of microglia in cerebellar injury and ataxia after CH are still unknown. Using Ki20227, an inhibitor for colony-stimulating factor 1 receptor which mediates the signaling responsible for the survival of microglia, we determined the impact of microglial depletion on cerebellar injury and ataxia in a murine model of CH. Microglial depletion reduced cerebellar lesion volume and alleviated gait abnormality, motor incoordination, and locomotor dysfunction after CH. Suppression of CH-initiated microglial activation with minocycline ameliorated cerebellum infiltration of monocytes/macrophages, as well as production of proinflammatory cytokines and chemokine C-C motif ligand-2 (CCL-2) that recruits monocytes/macrophages. Furthermore, both minocycline and bindarit, a CCL-2 inhibitor, prevented apoptosis and electrophysiological dysfunction of Purkinje cells, the principal neurons and sole outputs of the cerebellar cortex, and consequently improved ataxia-like motor abnormalities. Our findings suggest a detrimental role of microglia in neuroinflammation and ataxic motor symptoms after CH, and pave a new path to understand the neuroimmune mechanism underlying CH-induced cerebellar ataxia.

Urolithin A Prevents Focal Cerebral Ischemic Injury via Attenuating Apoptosis and Neuroinflammation in Mice

Neuroinflammation contributes to neuronal death in cerebral ischemia. Urolithin A (UA), a gut microbial metabolite of ellagic acid, has emerged as a potential anti-inflammatory agent. However, its roles and precise mechanisms in stroke remain unknown. Here we found that UA treatment ameliorated infarction, neurological deficit scores, and spatial memory deficits after cerebral ischemia. Furthermore, UA significantly reduced neuron loss and promoted neurogenesis after ischemic stroke. We also found that UA attenuated apoptosis by regulating apoptotic-related proteins. Meanwhile, UA treatment inhibited glial activation via affecting inflammatory signaling pathways, specifically by enhancing cerebral AMPK and IκBa activation while decreasing the activation of Akt, P65NFκB, ERK, JNK, and P38MAPK. Our findings reveal a key role of UA against ischemic stroke through modulating apoptosis and neuroinflammation in mice.