Long-term survival and regeneration of neuronal and vasculature cells inside the core region after ischemic stroke in adult mice

Acute and chronic excitotoxicity in ischemic stroke and late-onset Alzheimer's disease

Stroke and Alzheimer's disease are common neurological disorders and often occur in the same individuals. The comorbidity of the two neurological disorders represents a grave health threat to older populations. This review presents a brief background of the development of novel concepts and their clinical potentials. The activity of glutamatergic N-methyl-D-aspartate receptors and N-methyl-D-aspartate receptor-mediated Ca 2+ influx is critical for neuronal function. An ischemic insult induces prompt and excessive glutamate release and drastic increases of intracellular Ca 2+ mainly via N-methyl-D-aspartate receptors, particularly of those at the extrasynaptic site. This Ca 2+ -evoked neuronal cell death in the ischemic core is dominated by necrosis within a few hours and days known as acute excitotoxicity. Furthermore, mild but sustained Ca 2+ increases under neurodegenerative conditions such as in the distant penumbra of the ischemic brain and early stages of Alzheimer's disease are not immediately toxic, but gradually set off deteriorating Ca 2+ -dependent signals and neuronal cell loss mostly because of activation of programmed cell death pathways. Based on the Ca 2+ hypothesis of Alzheimer's disease and recent advances, this Ca 2+ -activated "silent" degenerative excitotoxicity evolves from years to decades and is recognized as a unique slow and chronic neuropathogenesis. The N-methyl-D-aspartate receptor subunit GluN3A, primarily at the extrasynaptic site, serves as a gatekeeper for the N-methyl-D-aspartate receptor activity and is neuroprotective against both acute and chronic excitotoxicity. Ischemic stroke and Alzheimer's disease, therefore, share an N-methyl-D-aspartate receptor- and Ca 2+ -mediated mechanism, although with much different time courses. It is thus proposed that early interventions to control Ca 2+ homeostasis at the preclinical stage are pivotal for individuals who are susceptible to sporadic late-onset Alzheimer's disease and Alzheimer's disease-related dementia. This early treatment simultaneously serves as a preconditioning therapy against ischemic stroke that often attacks the same individuals during abnormal aging.

Jun-activated SOCS1 enhances ubiquitination and degradation of CCAAT/enhancer-binding protein β to ameliorate cerebral ischaemia/reperfusion injury

This study investigates the molecular mechanisms behind ischaemia/reperfusion (I/R) injury in the brain, focusing on neuronal apoptosis. It scrutinizes the role of the Jun proto-oncogene in apoptosis, involvement of SOCS1 in neural precursor cell accumulation in ischaemic regions, and the upregulation of C-EBPβ in the hippocampus following I/R. Key to the study is understanding how Jun controls C-EBPβ degradation via SOCS1, potentially offering new clinical treatment avenues for I/R. Techniques such as mRNA sequencing, KEGG enrichment analysis and protein-protein interaction (PPI) in mouse models have indicated involvement of Jun (AP-1) in I/R-induced cerebral damage. The study employs middle cerebral artery occlusion in different mouse models and oxygen-glucose deprivation/reoxygenation in cortical neurons to examine the impacts of Jun and SOCS1 manipulation on cerebral I/R injury and neuronal damage. The findings reveal that I/R reduces Jun expression in the brain, but its restoration lessens cerebral I/R injury and neuron death. Jun activates SOCS1 transcriptionally, leading to C-EBPβ degradation, thereby diminishing cerebral I/R injury through the SOCS1/C-EBPβ pathway. These insights provide a deeper understanding of post-I/R cerebral injury mechanisms and suggest new therapeutic targets for cerebral I/R injury. KEY POINTS: Jun and SOCS1 are poorly expressed, and C-EBPβ is highly expressed in ischaemia/reperfusion mouse brain tissues. Jun transcriptionally activates SOCS1. SOCS1 promotes the ubiquitination-dependent C-EBPβ protein degradation. Jun blunts oxygen-glucose deprivation/reoxygenation-induced neuron apoptosis and alleviates neuronal injury. This study provides a theoretical basis for the management of post-I/R brain injury.

Considering Context-Specific microRNAs in Ischemic Stroke with Three "W": Where, When, and What

MicroRNAs are short non-coding RNA molecules that function as critical regulators of various biological processes through negative regulation of gene expression post-transcriptionally. Recent studies have indicated that microRNAs are potential biomarkers for ischemic stroke. In this review, we first illustrate the pathogenesis of ischemic stroke and demonstrate the biogenesis and transportation of microRNAs from cells. We then discuss several promising microRNA biomarkers in ischemic stroke in a context-specific manner from three dimensions: biofluids selection for microRNA extraction (Where), the timing of sample collection after ischemic stroke onset (When), and the clinical application of the differential-expressed microRNAs during stroke pathophysiology (What). We show that microRNAs have the utilities in ischemic stroke diagnosis, risk stratification, subtype classification, prognosis prediction, and treatment response monitoring. However, there are also obstacles in microRNA biomarker research, and this review will discuss the possible ways to improve microRNA biomarkers. Overall, microRNAs have the potential to assist clinical treatment, and developing microRNA panels for clinical application is worthwhile.

Iron changes within infarct tissue in ischemic stroke patients after successful reperfusion quantified using QSM

PURPOSE

For nearly half of patients who undergo Endovascular Thrombectomy following ischemic stroke, successful recanalisation does not guarantee a good outcome. Understanding the underlying tissue changes in the infarct tissue with the help of biomarkers specific to ischemic stroke could offer valuable insights for better treatment and patient management decisions. Using quantitative susceptibility mapping (QSM) MRI to measure cerebral iron concentration, this study aims to track the progression of iron within the infarct lesion after successful reperfusion.

METHODS

In a prospective study of 87 ischemic stroke patients, successfully reperfused patients underwent MRI scans at 24-to-72 h and 3 months after reperfusion. QSM maps were generated from gradient-echo MRI images. QSM values, measured in parts per billion (ppb), were extracted from ROIs defining the infarct and mirror homolog in the contralateral hemisphere and were compared cross-sectionally and longitudinally.

RESULTS

QSM values in the infarct ROIs matched those of the contralateral ROIs at 24-to-72 h, expressed as median (interquartile range) ppb [0.71(-7.67-10.09) vs. 2.20(-10.50-14.05) ppb, p = 0.55], but were higher at 3 months [10.68(-2.30-21.10) vs. -1.27(-12.98-9.82) ppb, p < 0.001]. The infarct QSM values at 3 months were significantly higher than those at 24-to-72 h [10.41(-2.50-18.27) ppb vs. 1.68(-10.36-12.25) ppb, p < 0.001]. Infarct QSM at 24-to-72 h and patient outcome measured at three months did not demonstrate a significant association.

CONCLUSION

Following successful endovascular reperfusion, iron concentration in infarct tissue, as measured by QSM increases over time compared to that in healthy tissue. However, its significance warrants further investigation.

Hippocampal neurogenesis modulated by Quinic acid: A therapeutic strategy for the neurodegenerative disorders

Neural progenitor cells (NPCs) reside in the brain and participate in the mechanism of neurogenesis that permits the brain to generate the building blocks for enhancement of cognitive abilities and acquisition of new skills. The existence of NPCs in brain has opened a novel dimension of research to explore their potential for treatment of various neurodegenerative disorders. The present study provides novel insights into the intracellular mechanisms in neuronal cells proliferation, maturation and differentiation regulated by Quinic acid (QA). Furthermore, this study might help in discovery and development of lead molecule that can overcome the challenges in the treatment of neurodegenerative diseases. The growth supporting effect of QA was studied using MTT assay. For that purpose, hippocampal cell cultures of neonatal rats were treated with different concentrations of QA and incubated for 24, 48 and 72 h. Gene and protein expressions of the selected molecular markers nestin, neuron-specific class III beta-tubulin (Tuj-1), neuronal nuclear protein (NeuN), neuronal differentiation 1 (NeuroD1), glial fibrillary acidic protein (GFAP), neuroligin (NLGN) and vimentin were analyzed. QA-induced cell proliferation and differentiation of hippocampal progenitor cells was also accompanied by significantly increased expression of progenitor and immature neuronal marker, mature neuronal marker and differentiating factor, that is, nestin, Tuj-1, NeuN and NeuroD1, respectively. On the other hand, vimentin downregulation and constant GFAP expression were observed following QA treatment. Additionally, the effects of QA on the recovery of stressed cells was studied using in vitro model of oxygen glucose deprivation (OGD). It was observed that hippocampal cells were able to recover from OGD following the treatment with QA. These findings suggest that QA treatment promotes hippocampal neurogenesis by proliferating and differentiating of NPCs and recovers neurons from stress caused by OGD. Thus, the neurogenic potential of QA can be explored for the treatment of neurodegenerative disorders.

Novel Programmed Death Ligand 1-AKT-engineered Mesenchymal Stem Cells Promote Neuroplasticity to Target Stroke Therapy

Although tissue plasminogen activator (t-PA) and endovascular thrombectomy are well-established treatments for acute ischemic stroke, over half of patients with stroke remain disabled for a long time. Thus, a significant unmet need exists to develop an effective strategy for treating acute stroke. We developed a combination of programmed cell death-ligand 1 (PD-L1) and AKT-modified umbilical cord mesenchymal stem cells (UMSC-PD-L1-AKT) implanted through intravenous (IV) and intracarotid (IA) routes to enhance therapeutic efficacy in a murine stroke model for overcoming the hypoxic environment of the ischemic brain, to prolong stem cell survival, and to attenuate systemic inflammation to protect neuroglial cells from ischemic injury. Higher cellular proliferation and survival upon exposure to toxic agents were observed in UMSC-PD-L1-AKT cells than in UMSCs in vitro. Moreover, increased attenuation of CFSE+ cell proliferation and increased survival of primary cortical cells were verified by the interaction with UMSC-PD-L1-AKT. Consistently, dual-route administration (IV + IA) of UMSC-PD-L1-AKT resulted in a significant reduction in infarction volume and improvement of neurological dysfunction in a stroke model. Furthermore, enhancing CD8+CD122+IL-10+ T-regulatory (Treg) cells and reducing CD11b+CD80+ microglial/macrophages and CD3+CD8+TNF-α+ and CD3+CD8+ IFN-α+ cytotoxic T cells induced an anti-inflammatory microenvironment to protect neuroglial cells in the ischemic brain. Collectively, therapeutic intervention using UMSC-PD-L1-AKT could provide a niche for inducing neuroplastic regeneration in brains after stroke.

Neuroprotective effect of, a flavonoid, sudachitin in mice stroke model

A flavonoid, sudachitin, has been reported to show some beneficial health effects, including as an anti-inflammatory in LPS-stimulated macrophages, as well as improving glucose and lipid metabolism in mice fed a high-fat diet. In this study, we investigated the neuroprotective effect of sudachitin in the transient middle cerebral artery occlusion (tMCAO) mouse model. After daily pre-treatment of vehicle or sudachitin (5 or 50 mg/kg) for 14 days, mice (n = 76) were subjected to a sham operation or tMCAO for 45 min, and on the following days, they were treated daily with vehicle or sudachitin. The administration of sudachitin significantly reduced (p < 0.05) cerebral infarct volume and attenuated apoptosis, 5 days after tMCAO. Neurological impairment improved, the expression of an oxidative stress marker, 4-HNE, decreased, and the Sirt1/PGC-1α pathway was activated 5 days after tMCAO in the sudachitin-treated group. This is the first report to demonstrate the neuroprotective effect of sudachitin in cerebral ischemia/reperfusion injury mice model, probably by activating the Sirt1/PGC-1α axis. Sudachitin may be a promising supplement or therapeutic agent for reducing injury caused by ischemic strokes.

Extrasynaptic NMDA receptors in acute and chronic excitotoxicity: implications for preventive treatments of ischemic stroke and late-onset Alzheimer's disease

Stroke and late-onset Alzheimer's disease (AD) are risk factors for each other; the comorbidity of these brain disorders in aging individuals represents a significant challenge in basic research and clinical practice. The similarities and differences between stroke and AD in terms of pathogenesis and pathophysiology, however, have rarely been comparably reviewed. Here, we discuss the research background and recent progresses that are important and informative for the comorbidity of stroke and late-onset AD and related dementia (ADRD). Glutamatergic NMDA receptor (NMDAR) activity and NMDAR-mediated Ca²⁺ influx are essential for neuronal function and cell survival. An ischemic insult, however, can cause rapid increases in glutamate concentration and excessive activation of NMDARs, leading to swift Ca²⁺ overload in neuronal cells and acute excitotoxicity within hours and days. On the other hand, mild upregulation of NMDAR activity, commonly seen in AD animal models and patients, is not immediately cytotoxic. Sustained NMDAR hyperactivity and Ca²⁺ dysregulation lasting from months to years, nevertheless, can be pathogenic for slowly evolving events, i.e. degenerative excitotoxicity, in the development of AD/ADRD. Specifically, Ca²⁺ influx mediated by extrasynaptic NMDARs (eNMDARs) and a downstream pathway mediated by transient receptor potential cation channel subfamily M member (TRPM) are primarily responsible for excitotoxicity. On the other hand, the NMDAR subunit GluN3A plays a "gatekeeper" role in NMDAR activity and a neuroprotective role against both acute and chronic excitotoxicity. Thus, ischemic stroke and AD share an NMDAR- and Ca²⁺-mediated pathogenic mechanism that provides a common receptor target for preventive and possibly disease-modifying therapies. Memantine (MEM) preferentially blocks eNMDARs and was approved by the Federal Drug Administration (FDA) for symptomatic treatment of moderate-to-severe AD with variable efficacy. According to the pathogenic role of eNMDARs, it is conceivable that MEM and other eNMDAR antagonists should be administered much earlier, preferably during the presymptomatic phases of AD/ADRD. This anti-AD treatment could simultaneously serve as a preconditioning strategy against stroke that attacks ≥ 50% of AD patients. Future research on the regulation of NMDARs, enduring control of eNMDARs, Ca²⁺ homeostasis, and downstream events will provide a promising opportunity to understand and treat the comorbidity of AD/ADRD and stroke.

Neurotoxic and cytoprotective mechanisms in the ischemic neocortex

Neuronal damage in ischemic stroke occurs due to permanent imbalance between the metabolic needs of the brain and the ability of the blood-vascular system to maintain glucose delivery and adequate gas exchange. Oxidative stress and excitotoxicity trigger complex processes of neuroinflammation, necrosis, and apoptosis of both neurons and glial cells. This review summarizes data on the structural and chemical changes in the neocortex and main cytoprotective effects induced by focal ischemic stroke. We focus on the expression of neurotrophins (NT) and molecular and cellular changes in neurovascular units in ischemic brain. We also discuss how these factors affect the apoptosis of cortical cells. Ischemic damage involves close interaction of a wide range of signaling molecules, each acting as an efficient marker of cell state in both the ischemic core and penumbra. NTs play the main regulatory role in brain tissue recovery after ischemic injury. Heterogeneous distribution of the BDNF, NT-3, and GDNF immunoreactivity is concordant with the selective response of different types of cortical neurons and glia to ischemic injury and allows mapping the position of viable neurons. Astrocytes are the central link in neurovascular coupling in ischemic brain by providing other cells with a wide range of vasotropic factors. The NT expression coincides with the distribution of reactive astrocytes, marking the boundaries of the penumbra. The development of ischemic stroke is accompanied by a dramatic change in the distribution of GDNF reactivity. In early ischemic period, it is mainly observed in cortical neurons, while in late one, the bulk of GDNF-positive cells are various types of glia, in particular, astrocytes. The proportion of GDNF-positive astrocytes increases gradually throughout the ischemic period. Some factors that exert cytoprotective effects in early ischemic period may display neurotoxic and pro-apoptotic effects later on. The number of apoptotic cells in the ischemic brain tissue correlates with the BDNF levels, corroborating its protective effects. Cytoprotection and neuroplasticity are two lines of brain protection and recovery after ischemic stroke. NTs can be considered an important link in these processes. To develop efficient pharmacological therapy for ischemic brain injury, we have to deepen our understanding of neurochemical adaptation of brain tissue to acute stroke.

Glycosaminoglycan scaffolding and neural progenitor cell transplantation promotes regenerative immunomodulation in the mouse ischemic brain

Ischemic stroke is a leading cause of morbidity and mortality, with limited treatments that can facilitate brain regeneration. Neural progenitor cells (NPCs) hold promise for replacing tissue lost to stroke, and biomaterial approaches may improve their efficacy to overcome hurdles in clinical translation. The immune response and its role in stroke pathogenesis and regeneration may interplay with critical mechanisms of stem cell and biomaterial therapies. Cellular therapy can modulate the immune response to reduce toxic neuroinflammation early after ischemia. However, few studies have attempted to harness the regenerative effects of neuroinflammation to augment recovery. Our previous studies demonstrated that intracerebrally transplanted NPCs encapsulated in a chondroitin sulfate-A hydrogel (CS-A + NPCs) can improve vascular regeneration after stroke. In this paper, we found that CS-A + NPCs affect the microglia/macrophage response to promote a regenerative phenotype following stroke in mice. Following transplantation, PPARγ-expressing microglia/macrophages, and MCP-1 and IL-10 protein levels are enhanced. Secreted immunomodulatory factor expression of other factors was altered compared to NPC transplantation alone. Post-stroke depression-like behavior was reduced following cellular and material transplantation. Furthermore, we showed in cultures that microglia/macrophages encapsulated in CS-A had increased expression of angiogenic and arteriogenic mediators. Neutralization with anti-IL-10 antibody negated these effects in vitro. Cumulatively, this work provides a framework for understanding the mechanisms by which immunomodulatory biomaterials can enhance the regenerative effects of cellular therapy for ischemic stroke and other brain injuries.

Topography of neurotrophins in the rat neocortex and their role in neuron apoptosis after experimental ischemic stroke

Neuronal loss due to apoptosis after ischemic injury depends on the trophic support of neurons and cytoprotective effects of neurotrophins (NTs). Different NTs may activate both pro- and antiapoptotic factors. Their distribution in the ischemic core (IC) and penumbra (IP) has been poorly studied. The available data on the localization of NTs in the ischemic brain are contradictory and depend to a certain degree on the pathogenetic model used. The distribution of NTs in different layers of the ischemic cortex is also largely unknown hindering our understanding of their exact effects and targets in different zones of the ischemic brain. We examined the immunolocalization of brain-derived neurotrophic factor (BDNF), neurotrophin-3, and glial cell line-derived neurotrophic factor (GDNF) in the parietal cortex using a rat model of ischemic stroke due to permanent occlusion of the middle cerebral artery. The spatial density of immunoreactive (IR) cells varied across the cortical layers and changed with time after ischemic injury. Their distribution in the IC differed considerably from that in the IP. The immunolocalization of neurotrophins in the contralateral hemisphere was similar to that in IP. We also studied the distribution of pro- and anti-apoptotic factors in IC and IP with and without intravenous BDNF administration. In the model without BDNF administration, the proportions of Bcl-2-, p53-, caspase-3-, and Mdm2-IR cells showed different dynamics during the ischemic period. In the model with BDNF administration, Mdm2 immunoreactivity was mainly observed in pyramidal cells of layers V/VI, and Bcl-2, in interneurons of layers II and III. The dynamics of p53 immunoreactivity was opposite to that of caspase-3 throughout the ischemic period. The present results suggest that after ischemic injury, 1) the number of neurotrophin-positive cells increases in the early ischemic period and decreases afterwards; 2) there is a close metabolic relationship between astrocytes and neurons contributing to their adaptation to ischemic conditions; 3) the IP borders undergo constant changes; 4) in the IP, neuronal loss occurs mainly by apoptotic pathway throughout the ischemic period; 5) BDNF may enhance considerably antiapoptotic mechanisms with a predominance of Mdm-2 activity in pyramidal neurons.

Potential Variables for Improved Reproducibility of Neuronal Cell Grafts at Stroke Sites

Interest is growing in using cell replacements to repair the damage caused by an ischemic stroke. Yet, the usefulness of cell transplants can be limited by the variability observed in their successful engraftment. For example, we recently showed that, although the inclusion of donor-derived vascular cells was necessary for the formation of large grafts (up to 15 mm3) at stroke sites in mice, the size of the grafts overall remained highly variable. Such variability can be due to differences in the cells used for transplantation or the host environment. Here, as possible factors affecting engraftment, we test host sex, host age, the extent of ischemic damage, time of transplant after ischemia, minor differences in donor cell maturity, and cell viability at the time of transplantation. We find that graft size at stroke sites correlates with the size of ischemic damage, host sex (females having graft sizes that correlate with damage), donor cell maturity, and host age, but not with the time of transplant after stroke. A general linear model revealed that graft size is best predicted by stroke severity combined with donor cell maturity. These findings can serve as a guide to improving the reproducibility of cell-based repair therapies.

Classification and Characteristics of Mesenchymal Stem Cells and Its Potential Therapeutic Mechanisms and Applications against Ischemic Stroke

Ischemic stroke is a serious cerebral disease that often induces death and long-term disability. As a currently available therapy for recanalization after ischemic stroke, thrombolysis, including intravenous thrombolysis and endovascular therapy, still cannot be applicable to all patients due to the narrow time window. Mesenchymal stem cell (MSC) transplantation therapy, which can trigger neuronal regeneration and repair, has been considered as a significant advance in treatment of ischemic stroke. MSC transplantation therapy has exhibited its potential to improve the neurological function in ischemic stroke. Our review describes the current progress and future perspective of MSC transplantation therapy in ischemic stroke treatment, including cell types, transplantation approaches, therapeutic mechanisms, and preliminary clinical trials of MSC transplantation, for providing us an update role of MSC transplantation in ischemic stroke treatment.

DL-3-n-butylphthalide Increases Collateriogenesis and Functional Recovery after Focal Ischemic Stroke in Mice

Recent evidence indicates that collateral circulation is critical for the outcome of ischemic stroke. DL-3-n-butylphthalide (NBP), a synthesized compound based on an extract from seeds of celery Apium graveolens Linn, has been used as a therapeutic drug, showing multiple neuroprotective and regenerative activities. A potential effect of NBP on collateral arterial regulation is unknown. We examined the effects of NBP on arteriogenesis of collateral arteries in vitro and a mouse ischemic stroke model. In cultures of mouse iPS cell-derived vascular progenitors, NBP (10 μM) significantly increased α-smooth muscle actin (αSMA)/CD-31 co-labeled cells and the expression of newly formed vasculature marker PDGFRα. A sensorimotor cortex ischemia was induced in transgenic mice expressing αSMA-GFP that allowed direct observation of arterial vasculatures in brain regions. NBP (80 mg/kg) was intranasally delivered 1 hr after stroke and once daily for 14 days. To label proliferating cells, 5-Bromo-2’-deoxyuridine (BrdU, 50 mg/kg, i.p.) was administrated every day from 3 days after stroke. Western blotting of peri-infarct tissue detected increased expressions of VEGF, Ang-1 and reduced nNOS level in NBP-treated mice. The NBP treatment significantly increased αSMA/BrdU co-labeled cells, the diameter of ipsilateral collaterals, and arterial area in ischemic and peri-infarct regions examined 14 days after stroke. Examined 3 days after stroke, NBP prevented functional deficits in the cylinder test and corner test. The NBP treatment of 14 days improved the local cerebral blood flow (LCBF) and functional performance in multiple tests. Thus, NBP promotes collateriogenesis, short and long-term structural and functional improvements after ischemic stroke.

GPR37 modulates progenitor cell dynamics in a mouse model of ischemic stroke

The generation of neural stem and progenitor cells following injury is critical for the function of the central nervous system, but the molecular mechanisms modulating this response remain largely unknown. We have previously identified the G protein-coupled receptor 37 (GPR37) as a modulator of ischemic damage in a mouse model of stroke. Here we demonstrate that GPR37 functions as a critical negative regulator of progenitor cell dynamics and gliosis following ischemic injury. In the central nervous system, GPR37 is enriched in mature oligodendrocytes, but following injury we have found that its expression is dramatically increased within a population of Sox2-positive progenitor cells. Moreover, the genetic deletion of GPR37 did not alter the number of mature oligodendrocytes following injury but did markedly increase the number of both progenitor cells and injury-induced Olig2-expressing glia. Alterations in the glial environment were further evidenced by the decreased activation of oligodendrocyte precursor cells. These data reveal that GPR37 regulates the response of progenitor cells to ischemic injury and provides new perspectives into the potential for manipulating endogenous progenitor cells following stroke.

Changes in Gene Expression and Neuroinflammation in the Hippocampus after Focal Brain Ischemia: Involvement in the Long-Term Cognitive and Mental Disorders

Ischemic brain injuries are accompanied by the long-term changes in gene expression in the hippocampus, the limbic system structure, involved in the regulation of key aspects of the higher nervous activity, such as cognitive functions and emotions. The altered expression of genes and proteins encoded by them may be related to the development of post-ischemic psycho-emotional and cognitive disturbances. Activation of neuroinflammation following stroke in the hippocampus has been suggested to play an essential role in induction of long-lasting consequences. Identification of changes in the gene expression patterns after ischemia and investigation of the dynamics of these changes in the hippocampus are the necessary first steps toward understanding molecular pathways responsible for the development of post-stroke cognitive impairments and mental pathologies.

Four Decades of Ischemic Penumbra and Its Implication for Ischemic Stroke

The ischemic penumbra defined four decades ago has been the main battleground of ischemic stroke. The evolving ischemic penumbra concept has been providing insight for the development of vascular and cellular approaches as well as diagnostic tools for the treatment of ischemic stroke. rt-PA thrombolytic therapy to prevent the transition of ischemic penumbra to core has been approved for acute ischemic stroke within 3 h and was later recommended to extend to 4.5 h after symptom onset. Mechanical thrombectomy was introduced for the treatment of acute ischemic stroke with a therapeutic window of up to 24 h after stroke onset. Multiple modalities brain imaging techniques have been developed that provide guidance to define ischemic penumbra for reperfusion therapy in clinical practice. Cellular and molecular dissection of ischemic penumbra has been providing targets for the development of neuroprotective therapy for ischemic stroke. However, the dynamic nature of ischemic penumbra implicates that infarct core eventually expands into penumbra over time without reperfusion, dictating relative short therapeutic windows and limiting the impact of current reperfusion intervention. Entering the 5^th decade since the introduction, ischemic penumbra remains the main focus of ischemic stroke research and clinical practice. In this review, we summarized the evolving ischemic penumbra concept and its implication in the development of vascular and cellular interventions as well as diagnostic tools for acute ischemic stroke. In addition, we discussed future perspectives on expansion of the campaign beyond ischemic penumbra to develop treatment for ischemic stroke.

Conversion of Reactive Astrocytes to Induced Neurons Enhances Neuronal Repair and Functional Recovery After Ischemic Stroke

The master neuronal transcription factor NeuroD1 can directly reprogram astrocytes into induced neurons (iNeurons) after stroke. Using viral vectors to drive ectopic ND1 expression in gliotic astrocytes after brain injury presents an autologous form of cell therapy for neurodegenerative disease. Cultured astrocytes transfected with ND1 exhibited reduced proliferation and adopted neuronal morphology within 2-3 weeks later, expressed neuronal/synaptic markers, and extended processes. Whole-cell recordings detected the firing of evoked action potentials in converted iNeurons. Focal ischemic stroke was induced in adult GFAP-Cre-Rosa-YFP mice that then received ND1 lentivirus injections into the peri-infarct region 7 days after stroke. Reprogrammed cells did not express stemness genes, while 2-6 weeks later converted cells were co-labeled with YFP (constitutively activated in astrocytes), mCherry (ND1 infection marker), and NeuN (mature neuronal marker). Approximately 66% of infected cells became NeuN-positive neurons. The majority (~80%) of converted cells expressed the vascular glutamate transporter (vGLUT) of glutamatergic neurons. ND1 treatment reduced astrogliosis, and some iNeurons located/survived inside of the savaged ischemic core. Western blotting detected higher levels of BDNF, FGF, and PSD-95 in ND1-treated mice. MultiElectrode Array (MEA) recordings in brain slices revealed that the ND1-induced reprogramming restored interrupted cortical circuits and synaptic plasticity. Furthermore, ND1 treatment significantly improved locomotor, sensorimotor, and psychological functions. Thus, conversion of endogenous astrocytes to neurons represents a plausible, on-site regenerative therapy for stroke.

Roles of Microglial Ion Channel in Neurodegenerative Diseases

As the average age and life expectancy increases, the incidence of both acute and chronic central nervous system (CNS) pathologies will increase. Understanding mechanisms underlying neuroinflammation as the common feature of any neurodegenerative pathology, we can exploit the pharmacology of cell specific ion channels to improve the outcome of many CNS diseases. As the main cellular player of neuroinflammation, microglia play a central role in this process. Although microglia are considered non-excitable cells, they express a variety of ion channels under both physiological and pathological conditions that seem to be involved in a plethora of cellular processes. Here, we discuss the impact of modulating microglia voltage-gated, potential transient receptor, chloride and proton channels on microglial proliferation, migration, and phagocytosis in neurodegenerative diseases.

Delayed Exercise-induced Upregulation of Angiogenic Proteins and Recovery of Motor Function after Photothrombotic Stroke in Mice

Treatments promoting post-stroke functional recovery continue to be an unmet therapeutic problem with physical rehabilitation being the most reproduced intervention in preclinical and clinical studies. Unfortunately, physiotherapy is typically effective at high intensity and early after stroke - requirements that are hardly attainable by stroke survivors. The aim of this study was to directly evaluate and compare the dose-dependent effect of delayed physical rehabilitation (daily 5 h or overnight voluntary wheel running; initiated on post-stroke day 7 and continuing through day 21) on recovery of motor function in the mouse photothrombotic model of ischemic stroke and correlate it with angiogenic potential of the brain. Our observations indicate that overnight but not 5 h access to running wheels facilitates recovery of motor function in mice in grid-walking test. Western blotting and immunofluorescence microscopy experiments evaluating the expression of angiogenesis-associated proteins VEGFR2, doppel and PDGFRβ in the peri-infarct and corresponding contralateral motor cortices indicate substantial upregulation of these proteins (≥2-fold) in the infarct core and surrounding cerebral cortex in the overnight running mice on post-stroke day 21. These findings indicate that there is a dose-dependent relationship between the extent of voluntary exercise, motor recovery and expression of angiogenesis-associated proteins in this expert-recommended mouse ischemic stroke model. Notably, our observations also point out to enhanced angiogenesis and presence of pericytes within the infarct core region during the chronic phase of stroke, suggesting a potential contribution of this tissue area in the mechanisms governing post-stroke functional recovery.

Neuroinflammation and microglia/macrophage phenotype modulate the molecular background of post-stroke depression: A literature review

Increasing evidence hints to the central role of neuroinflammation in the development of post-stroke depression. Danger signals released in the acute phase of ischemia trigger microglial activation, along with the infiltration of neutrophils and macrophages. The increased secretion of proinflammatory cytokines interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor α (TNFα) provokes neuronal degeneration and apoptosis, whereas IL-6, interferon γ (IFNγ), and TNFα induce aberrant tryptophane degradation with the accumulation of the end-product quinolinic acid in resident glial cells. This promotes glutamate excitotoxicity via hyperexcitation of N-methyl-D-aspartate receptors and antagonizes 5-hydroxy-tryptamine, reducing synaptic plasticity and neuronal survival, thus favoring depression. In the post-stroke period, CX3CL1 and the CD200-CD200R interaction mediates the activation of glial cells, whereas CCL-2 attracts infiltrating macrophages. CD206 positive cells grant the removal of excessive danger signals; the high number of regulatory T cells, IL-4, IL-10, transforming growth factor β (TGFβ), and intracellular signaling via cAMP response element-binding protein (CREB) support the M2 type differentiation. In favorable conditions, these cells may exert efficient clearance, mediate tissue repair, and might be essential players in the downregulation of molecular pathways that promote post-stroke depression.

Modulation of Stem Cells as Therapeutics for Severe Mental Disorders and Cognitive Impairments

Severe mental illnesses (SMI) such as schizophrenia and bipolar disorder affect 2-4% of the world population. Current medications and diagnostic methods for mental illnesses are not satisfying. In animal studies, stem cell therapy is promising for some neuropsychiatric disorders and cognitive/social deficits, not only treating during development (targeting modulation and balancing) but also following neurodegeneration (cell replacement and regenerating support). We believe that novel interventions such as modulation of particular cell populations to develop cell-based treatment can improve cognitive and social functions in SMI. With pathological synaptic/myelin damage, oligodendrocytes seem to play a role. In this review, we have summarized oligodendrogenesis mechanisms and some related calcium signals in neural cells and stem/progenitor cells. The related benefits from endogenous stem/progenitor cells within the brain and exogenous stem cells, including multipotent mesenchymal-derived stromal cells (MSC), fetal neural stem cells (NSC), pluripotent stem cells (PSC), and differentiated progenitors, are discussed. These also include stimulating mechanisms of oligodendrocyte proliferation, maturation, and myelination, responsive to the regenerative effects by both endogenous stem cells and transplanted cells. Among the mechanisms, calcium signaling regulates the neuronal/glial progenitor cell (NPC/GPC)/oligodendrocyte precursor cell (OPC) proliferation, migration, and differentiation, dendrite development, and synaptic plasticity, which are involved in many neuropsychiatric diseases in human. On the basis of numerous protein annotation and protein-protein interaction databases, a total of 119 calcium-dependent/activated proteins that are related to neuropsychiatry in human are summarized in this investigation. One of the advanced methods, the calcium/cation-channel-optogenetics-based stimulation of stem cells and transplanted cells, can take advantage of calcium signaling regulations. Intranasal-to-brain delivery of drugs and stem cells or local delivery with the guidance of brain imaging techniques may provide a unique new approach for treating psychiatric disorders. It is also expected that preconditioning stem cell therapy following precise brain imaging as pathological confirmation has high potential if translated to cell clinic use. Generally, modulable cell transplantation followed by stimulations should provide paracrine protection, synaptic modulation, and myelin repair for the brain in SMI.

Delayed PARP-1 Inhibition Alleviates Post-stroke Inflammation in Male Versus Female Mice: Differences and Similarities

Post-stroke inflammation is almost involved in the whole process of stroke pathogenesis, which serves as a prime target for developing new stroke therapies. Despite known sex differences in the incidence and outcome of stroke, few preclinical or clinical studies take into account sex bias in treatment. Recent evidence suggests that poly (ADP-ribose) polymerase (PARP)-1 inhibitor exerts sex-specific neuroprotection in the ischemic stroke. This study was aimed to investigate the effects of delayed PARP-1 inhibition on post-stroke inflammation and possible sexual dimorphism, and explore the possible relevant mediators. In male and female C57BL/6 mice subjected to transit middle cerebral artery occlusion (MCAO), we found that delayed treatment of PARP-1 inhibitor at 48 h following reperfusion could comparably alleviate neuro-inflammation at 72 h after stroke. Whereas, more remarkable reduction of iNOS and MMP9 induced by PARP-1 inhibition were found in male MCAO mice, and the improvement of behavioral outcomes was more prominent in male MCAO mice. In addition, we further identified that PARP-1 inhibitor might equivalently suppress microglial activation in males and females in vivo and in vitro. With proteomic analysis and western blotting assay, it was found that stroke-induced peroxiredoxin-1 (Prx1) expression was significantly affected by PARP-1 inhibition. Interestingly, injection of recombinant Prx1 into the ischemic core could block the anti-inflammatory effects of PARP-1 inhibitor in the experimental stroke. These findings suggest that PARP-1 inhibitor has effects on regulating microglial activation and post-stroke inflammation in males and females, and holds promise as a novel therapeutic agent for stroke with extended therapeutic time window. Efforts need to be made to delineate the actions of PARP-1 inhibition in stroke, and here we propose that Prx1 might be a critical mediator.

Neuropsychological Deficits Chronically Developed after Focal Ischemic Stroke and Beneficial Effects of Pharmacological Hypothermia in the Mouse

Stroke is a leading cause of human death and disability, with around 30% of stroke patients develop neuropsychological/neuropsychiatric symptoms, such as post-stroke depression (PSD). Basic and translational research on post-stroke psychological disorders is limited. In a focal ischemic stroke mouse model with selective damage to the sensorimotor cortex, sensorimotor deficits develop soon after stroke and spontaneous recovery is observed in 2-4 weeks. We identified that mice subjected to a focal ischemic insult gradually developed depression/anxiety like behaviors 4 to 8 weeks after stroke. Psychological/psychiatric disorders were revealed in multiple behavioral examinations, including the forced swim, tail suspension, sucrose preference, and open field tests. Altered neuronal plasticity such as suppressed long-term potentiation (LTP), reduced BDNF and oxytocin signaling, and disturbed dopamine synthesis/uptake were detected in the prefrontal cortex (PFC) during the chronic phase after stroke. Pharmacological hypothermia induced by the neurotensin receptor 1 (NTR1) agonist HPI-363 was applied as an acute treatment after stroke. A six-hr hypothermia treatment applied 45 min after stroke prevented depression and anxiety like behaviors examined at 6 weeks after stroke, as well as restored BDNF expression and oxytocin signaling. Additionally, hypothermia induced by physical cooling also showed an anti-depression and anti-anxiety effect. The data suggested a delayed beneficial effect of acute hypothermia treatment on chronically developed post-stroke neuropsychological disorders, associated with regulation of synaptic plasticity, neurotrophic factors, dopaminergic activity, and oxytocin signaling in the PFC.

Angiogenesis and neuronal remodeling after ischemic stroke

Increased microvessel density in the peri-infarct region has been reported and has been correlated with longer survival times in ischemic stroke patients and has improved outcomes in ischemic animal models. This raises the possibility that enhancement of angiogenesis is one of the strategies to facilitate functional recovery after ischemic stroke. Blood vessels and neuronal cells communicate with each other using various mediators and contribute to the pathophysiology of cerebral ischemia as a unit. In this mini-review, we discuss how angiogenesis might couple with axonal outgrowth/neurogenesis and work for functional recovery after cerebral ischemia. Angiogenesis occurs within 4 to 7 days after cerebral ischemia in the border of the ischemic core and periphery. Post-ischemic angiogenesis may contribute to neuronal remodeling in at least two ways and is thought to contribute to functional recovery. First, new blood vessels that are formed after ischemia are thought to have a role in the guidance of sprouting axons by vascular endothelial growth factor and laminin/β1-integrin signaling. Second, blood vessels are thought to enhance neurogenesis in three stages: 1) Blood vessels enhance proliferation of neural stem/progenitor cells by expression of several extracellular signals, 2) microvessels support the migration of neural stem/progenitor cells toward the peri-infarct region by supplying oxygen, nutrients, and soluble factors as well as serving as a scaffold for migration, and 3) oxygenation induced by angiogenesis in the ischemic core is thought to facilitate the differentiation of migrated neural stem/progenitor cells into mature neurons. Thus, the regions of angiogenesis and surrounding tissue may be coupled, representing novel treatment targets.

Pharmacological hypothermia induced neurovascular protection after severe stroke of transient middle cerebral artery occlusion in mice

Therapeutic hypothermia is a potential protective strategy after stroke. The present study evaluated the neurovascular protective potential of pharmacological hypothermia induced by the neurotensin receptor 1 agonist HPI-201 after severe ischemic stroke. Adult C57BL/6 mice were subjected to filament insertion-induced occlusion of the middle cerebral artery (60 min MCAO). HPI-201 was i.p. injected 120 min after the onset of MCAO to initiate and maintain the body temperature at 32-33°C for 6 hrs. The infarct volume, cell death, integrity of the blood brain barrier (BBB) and neurovascular unit (NVU), inflammation, and functional outcomes were evaluated. The hypothermic treatment significantly suppressed the infarct volume and neuronal cell death, accompanied with reduced caspase-3 activation and BAX expression while Bcl-2 increased in the peri-infarct region. The cellular integrity of the BBB and NVU was significantly improved and brain edema was attenuated in HPI-201-treated mice compared to stroke controls. The hypothermic treatment decreased the expression of inflammatory factors including tumor necrosis factor-α (TNF-α), MMP-9, interleukin-1β (IL-1β), the M1 microglia markers IL-12 and inducible nitric oxide synthase (iNOS), while increased the M2 marker arginase-1 (Arg-1). Stroke mice received the hypothermic treatment showed lower neurological severity score (NSS), performed significantly better in functional tests, the mortality rate in the hypothermic group was noticeably lower compared with stroke controls. Taken together, HPI-201 induced pharmacological hypothermia is protective for different neurovascular cells after a severely injured brain, mediated by multiple mechanisms.

Long-lasting neurobehavioral alterations in burn-injured mice resembling post-traumatic stress disorder in humans

OBJECTIVE

To establish an animal model for posttraumatic stress disorder in burn-injured patients.

METHODS

Thermal-injured mice with 15% total body surface area were subjected to a series of neurobehavioral tests at 1 and 3 months postburn. Brains were collected for analysis of key molecules expression, spleens for T cell function analysis, and blood for biochemistry and hormones detection.

RESULTS

Comparison with sham mice, burn mice showed extremely high locomotion in homecage, open field, and forced swimming tests, indicating a hyper-arousal state. Burn mice exhibited improved spatial memory in Morris Water Maze test and heightened context fear memory in context fear conditioning, suggesting re-experiencing behavior. Although burn mice showed pronounced passive avoidance in the step-through test, their active avoidance capability in response to the conditional stimulus in the shuttle box test was relatively deteriorated. Likewise, the retention of cue-feared memory was impaired in fear conditioning test. The above negative alterations in mood were recapitulated in open-field test, in which the burn mice displayed an anxiety-like behavior with less time spent in the center. However, no sign of depression was found in the forced swimming and sucrose preference tests. The negative mood of burn mice was reinforced by a deficit in sociality and preference for social novelty in social interaction test. These neurobehavioral alterations were associated with an increased expression of brain-derived neurotrophic factor along with a remarkable microgliosis and a moderate astrocytosis in the brain of burn vs. sham mice. Moreover, a prominent Th2 switch and consequent increased nuclear NF-κB translocation were seen in the splenic T cells from burn relative to sham mice.

CONCLUSIONS

We conclude that even mild burn injury could lead to long-lasting cognitive and effective alterations in mice. These findings shed light on the interactions among neuropsychology, neurobiology, and immunology throughout the recovery period of burn injury.

Pterostilbene Attenuates Astrocytic Inflammation and Neuronal Oxidative Injury After Ischemia-Reperfusion by Inhibiting NF-κB Phosphorylation

Astrocyte-mediated inflammation and oxidative stress elicit cerebral ischemia-reperfusion (IR) injury after stroke. Nuclear factor (NF)-κB activates astrocytes and generates pro-inflammatory factors. The purpose of the present study is to elucidate the effect of pterostilbene (PTE, a natural stilbene) on astrocytic inflammation and neuronal oxidative injury following cerebral ischemia-reperfusion injury. A middle cerebral artery occlusion-reperfusion (MCAO/R) mouse model and HT22/U251 co-culture model subjected to oxygen-glucose deprivation and re-introduction (OGD/R) were employed, with or without PTE treatment. The data showed that PTE delivery immediately after reperfusion, at 1 h after occlusion, decreased infarct volume, brain edema, and neuronal apoptosis and improved long-term neurological function. PTE decreased oxidation (i.e., production of reactive oxygen species, malondialdehyde) and inflammatory mediators (tumor necrosis factor-α, interleukin-1β, and interleukin-6) and increased anti-oxidative enzyme activities (i.e., of superoxide dismutase, glutathione peroxidase), by inhibiting phosphorylation and nuclear translocation of NF-κB. In conclusion, PTE attenuated astrocyte-mediated inflammation and oxidative injury following IR via NF-κB inhibition. Overall, PTE is a promising neuroprotective agent.

Protective effects of GPR37 via regulation of inflammation and multiple cell death pathways after ischemic stroke in mice

GPCR 37 (GPR37) is a GPCR expressed in the CNS; its physiological and pathophysiological functions are largely unknown. We tested the role of GPR37 in the ischemic brain of GPR37 knockout (KO) mice, exploring the idea that GPR37 might be protective against ischemic damage. In an ischemic stroke model, GPR37 KO mice exhibited increased infarction and cell death compared with wild-type (WT) mice, measured by 2,3,5-triphenyl-2H-tetrazolium chloride and TUNEL staining 24 h after stroke. Moreover, more severe functional deficits were detected in GPR37 KO mice in the adhesive-removal and corner tests. In the peri-infarct region of GPR37 KO mice, there was significantly more apoptotic and autophagic cell death accompanied by caspase-3 activation and attenuated mechanistic target of rapamycin signaling. GPR37 deletion attenuated astrocyte activation and astrogliosis compared with WT stroke controls 24-72 h after stroke. Immunohistochemical staining showed more ionized calcium-binding adapter molecule 1-positive cells in the ischemic cortex of GPR37 KO mice, and RT-PCR identified an enrichment of M1-type microglia or macrophage markers in the GPR37 KO ischemic cortex. Western blotting demonstrated higher levels of inflammatory factors IL-1β, IL-6, monocyte chemoattractant protein, and macrophage inflammatory protein-1α in GPR37-KO mice after ischemia. Thus, GPR37 plays a multifaceted role after stroke, suggesting a novel target for stroke therapy.-McCrary, M. R., Jiang, M. Q., Giddens, M. M., Zhang, J. Y., Owino, S., Wei, Z. Z., Zhong, W., Gu, X., Xin, H., Hall, R. A., Wei, L., Yu, S. P. Protective effects of GPR37 via regulation of inflammation and multiple cell death pathways after ischemic stroke in mice.

The impact of endothelial cell death in the brain and its role after stroke: A systematic review

The supply of oxygen and nutrients to the brain is vital for its function and requires a complex vascular network that, when disturbed, results in profound neurological dysfunction. As part of the pathology in stroke, endothelial cells die. As endothelial cell death affects the surrounding cellular environment and is a potential target for the treatment and prevention of neurological disorders, we have systematically reviewed important aspects of endothelial cell death with a particular focus on stroke. After screening 2876 publications published between January 1, 2010 and August 7, 2019, we identified 154 records to be included. We found that endothelial cell death occurs rapidly as well as later after the onset of stroke conditions. Among the different cell death mechanisms, apoptosis was the most widely investigated (92 records), followed by autophagy (20 records), while other, more recently defined mechanisms received less attention, such as lysosome-dependent cell death (2 records) and necroptosis (2 records). We also discuss the differential vulnerability of brain cells to injury after stroke and the role of endothelial cell death in the no-reflow phenomenon with a special focus on the microvasculature. Further investigation of the different cell death mechanisms using novel tools and biomarkers will greatly enhance our understanding of endothelial cell death. For this task, at least two markers/criteria are desirable to determine cell death subroutines according to the recommendations of the Nomenclature Committee on Cell Death.

Echinocystic acid, a natural plant extract, alleviates cerebral ischemia/reperfusion injury via inhibiting the JNK signaling pathway

Echinocystic acid (EA) was found to possess antiviral, anti-inflammatory and antioxidation activities. A recent study showed the antiapoptotic effects of EA on acute myocardial infarction. In this study, we demonstrated the potential neuroprotective effects of EA on cerebral ischemia/reperfusion (I/R) injury in mice. Intraperitoneal injection of EA 1 h before ischemia significantly reduced the cerebral infarct volume and neurological deficit after 60 min of ischemia and 24 h of reperfusion. The neuroprotective effects of EA occurred in a dose-dependent manner. Then, we explored the mechanisms of neuroprotection by EA. This compound exerted antiapoptotic activity by upregulating the level of Bcl-2 and simultaneously downregulating the levels of cleaved caspase-3 and Bax. Furthermore, EA also possessed anti-inflammatory activity and prevented the excessive phosphorylation of NF-κB (p-P65) and the increase in IL-1β and IL-6 levels. Finally, our data indicated that EA treatment decreased the level of phosphorylated JNK in vivo, and the JNK activator anisomycin (AN) reversed the neuroprotective effects of EA, indicating that the JNK pathway is involved in the antiapoptotic and anti-inflammatory mechanisms of EA. In summary, our findings suggest that EA provides neuroprotective effects through its antiapoptotic and anti-inflammatory activities by inhibiting the JNK signaling pathway in cerebral I/R injury. Due to its safety and lack of toxicity, EA is a potential candidate for the treatment of ischemic stroke in future clinical trials.

Enhanced Neurogenesis and Collaterogenesis by Sodium Danshensu Treatment After Focal Cerebral Ischemia in Mice

Ischemic stroke remains a serious threat to human life. There are limited effective therapies for the treatment of stroke. We have previously demonstrated that angiogenesis and neurogenesis in the brain play an important role in functional recovery following ischemic stroke. Recent studies indicate that increased arteriogenesis and collateral circulation are determining factors for restoring reperfusion and outcomes of stroke patients. Danshensu, the Salvia miltiorrhiza root extract, is used in treatments of various human ischemic events in traditional Chinese medicine. Its therapeutic mechanism, however, is not well clarified. Due to its proposed effect on angiogenesis and arteriogenesis, we hypothesized that danshensu could benefit stroke recovery through stimulating neurogenesis and collaterogenesis in the post-ischemia brain. Focal ischemic stroke targeting the right sensorimotor cortex was induced in wild-type C57BL6 mice and transgenic mice expressing green fluorescent protein (GFP) to label smooth muscle cells of brain arteries. Sodium danshensu (SDS, 700 mg/kg) was administered intraperitoneally (i.p.) 10 min after stroke and once daily until animals were sacrificed. To label proliferating cells, 5-bromo-2′-deoxyuridine (BrdU; 50 mg/kg, i.p.) was administered, starting on day 3 after ischemia and continued once daily until sacrifice. At 14 days after stroke, SDS significantly increased the expression of vascular endothelial growth factor (VEGF), stromal-derived factor-1 (SDF-1), brain-derived neurotrophic factor (BDNF), and endothelial nitric oxide synthase (eNOS) in the peri-infarct region. SDS-treated animals showed increased number of doublecortin (DCX)-positive cells. Greater numbers of proliferating endothelial cells and smooth muscle cells were detected in SDS-treated mice 21 days after stroke in comparison with vehicle controls. The number of newly formed neurons labeled by NeuN and BrdU antibodies increased in SDS-treated mice 28 days after stroke. SDS significantly increased the newly formed arteries and the diameter of collateral arteries, leading to enhanced local cerebral blood flow recovery after stroke. These results suggest that systemic sodium danshensu treatment shows significant regenerative effects in the post-ischemic brain, which may benefit long-term functional recovery from ischemic stroke.

Spreading depolarization and neuronal damage or survival in mouse neocortical brain slices immediately and 12 hours following middle cerebral artery occlusion

Whereas many studies have examined the properties of the compromised neocortex in the first several days following ischemia, there is less information regarding the initial 12 h poststroke. In this study we examined live mouse neocortical slices harvested immediately and 12 h after a 30-min middle cerebral artery occlusion (MCAo). We compared nonischemic and ischemic hemispheres with regard to the propensity for tissue swelling and for generating spreading depolarization (SD), as well as evoked synaptic responses and single pyramidal neuron electrophysiological properties. We observed spontaneous SD in 7% of slices on the nonstroked side and 25% in the stroked side following the 30-min MCAo. Spontaneous SD was rare in 12-h recovery slices. The region of the ischemic core and surround in slices was not susceptible to SD induced by oxygen and glucose deprivation. At the neuronal level, neocortical gray matter is surprisingly unaltered in brain slices harvested immediately poststroke. However, by 12 h, the fields of pyramidal and striatal neurons that comprise the infarcted core are electrophysiologically silent because the majority are morphologically devastated. Yet, there remains a subset of diffusely distributed "healthy" pyramidal neurons in the core at 12 h post-MCAo that persist for days poststroke. Their intact electrophysiology and dendritic morphology indicate a surprisingly selective resilience to stroke at the neuronal level. NEW & NOTEWORTHY It is generally accepted that the injured core region of the brain resulting from a focal stroke contains no functioning neurons. Our study shows that some neurons, although surrounded by devastated neighbors, can maintain their structure and electrical activity. This surprising finding raises the possibility of discovering how these neurons are protected to pinpoint new strategies for reducing stroke injury.

Angiogenesis in the ischemic core: A potential treatment target?

The ischemic penumbra is both a concept in understanding the evolution of cerebral tissue injury outcome of focal ischemia and a potential therapeutic target for ischemic stroke. In this review, we examine the evidence that angiogenesis can contribute to beneficial outcomes following focal ischemia in model systems. Several studies have shown that, following cerebral ischemia, endothelial proliferation and subsequent angiogenesis can be detected beginning four days after cerebral ischemia in the border of the ischemic core, or in the ischemic periphery, in rodent and non-human primate models, although initial signals appear within hours of ischemia onset. Components of the neurovascular unit, its participation in new vessel formation, and the nature of the core and penumbra responses to experimental focal cerebral ischemia, are considered here. The potential co-localization of vascular remodeling and axonal outgrowth following focal cerebral ischemia based on the definition of tissue remodeling and the processes that follow ischemic stroke are also considered. The region of angiogenesis in the ischemic core and its surrounding tissue (ischemic periphery) may be a novel target for treatment. We summarize issues that are relevant to model studies of focal cerebral ischemia looking ahead to potential treatments.

Selective Brain Hypothermia Augmenting Neuroprotective Effects of Decompressive Craniectomy for Permanent Middle Cerebral Artery Infarction in a Rat Model

OBJECTIVE

To evaluate the combined effects of a decompressive craniectomy and prolonged selective brain hypothermia on large hemispheric infarction in a rat model.

METHODS

Permanent middle cerebral artery infarction using an endovascular occlusion technique was created in rats assigned to 4 groups. Normothermia was maintained without a craniectomy in group A (n = 20) as the control, prolonged (>44 hours), selective brain hypothermic treatment was performed on group B (n = 20), a craniectomy was performed on group C (n = 18), and prolonged, selective brain hypothermic treatment using a cooling coil implanted in the craniectomy site was combined with a craniectomy for group D (n = 18).

RESULTS

Group B and C exhibited a significantly reduced infarct volume when compared with the control. Furthermore, group D showed a significantly reduced infarct volume when compared with group C, plus a significantly improved neurologic score. These results for group D were associated with an increased neuronal cell count and reduced hyperactive microglia and hypertrophic astrocytes in the cortical penumbra (P < 0.01). Moreover, a greater preservation of normal-appearing axonal bundles and the blood-brain barrier was observed in the core infarct region at the caudoputamen.

CONCLUSIONS

A decompressive craniectomy reduced the infarct volume and improved the neurologic outcomes in a rat model of middle cerebral artery infarction. Furthermore, when combined with prolonged selective brain hypothermia, significant additional benefits were observed for the neurologic outcomes, infarct volume, and degree of neuroinflammation.

Growth Differentiation Factor 11 Promotes Neurovascular Recovery After Stroke in Mice

Background: Growth differentiation factor 11 (GDF11), a member of transforming growth factor-β (TGF-β) superfamily, was shown to rejuvenate cardiac and skeletal muscle function and to improve cerebral vasculature and neurogenesis in old mice. However, recent experimental data reported that raising GDF11 levels inhibited skeletal muscle regeneration and had no effect on cardiac hypertrophy. Our aim was to investigate the effects of GDF11 on brain repair during the recovery phase after stroke.

Methods: Mice were subjected to distal middle cerebral artery occlusion, and recombinant GDF11 (rGDF11) was injected intraperitoneally once a day during days 7–13 after stroke. Neuronal precursor cells (NPCs) proliferation and angiogenesis were assayed at 14 days. Neuronal regeneration was assayed at 42 days. The beam-walking test and CatWalk were used to evaluate behavioral functions. Downstream pathways of GDF11 were also investigated.

Results: GDF11 was upregulated in the ipsilateral peri-infarct cortex and subventricular zone (SVZ) at 14 days after stroke. Treatment with rGDF11 enhanced the number of newborn NPCs and endothelial cells, microvascular length and area, and brain capillary perfusion. Western blots showed that rGDF11 upregulated brain-derived neurotrophic factor (BDNF) and increased the levels of proangiogenic factor angiopoietin-2 (Ang-2) and phosphorylation of vascular endothelial growth factor receptor-2 (VEGFR-2). We also found that rGDF11 upregulated the transcription factors Smad2 and Smad3 phosphorylation, but these activations were blocked by a TGF-β receptor inhibitor SB431542. Moreover, rGDF11-induced angiogenic remodeling and NPCs proliferation were reversed by injection of SB431542, suggesting that GDF11 may exert its effect via the TGF-β/Smad2/3 signaling pathway. Finally, treating mice with rGDF11 resulted in a significant increase in neuronal regeneration and functional recovery.

Conclusion: GDF11 promoted neurogenesis and angiogenesis and contributed to functional recovery after stroke in mice.

Priming of the Cells: Hypoxic Preconditioning for Stem Cell Therapy

Objective:

Stem cell-based therapies are promising in regenerative medicine for protecting and repairing damaged brain tissues after injury or in the context of chronic diseases. Hypoxia can induce physiological and pathological responses. A hypoxic insult might act as a double-edged sword, it induces cell death and brain damage, but on the other hand, sublethal hypoxia can trigger an adaptation response called hypoxic preconditioning or hypoxic tolerance that is of immense importance for the survival of cells and tissues.

Data Sources:

This review was based on articles published in PubMed databases up to August 16, 2017, with the following keywords: “stem cells,” “hypoxic preconditioning,” “ischemic preconditioning,” and “cell transplantation.”

Study Selection:

Original articles and critical reviews on the topics were selected.

Results:

Hypoxic preconditioning has been investigated as a primary endogenous protective mechanism and possible treatment against ischemic injuries. Many cellular and molecular mechanisms underlying the protective effects of hypoxic preconditioning have been identified.

Conclusions:

In cell transplantation therapy, hypoxic pretreatment of stem cells and neural progenitors markedly increases the survival and regenerative capabilities of these cells in the host environment, leading to enhanced therapeutic effects in various disease models. Regenerative treatments can mobilize endogenous stem cells for neurogenesis and angiogenesis in the adult brain. Furthermore, transplantation of stem cells/neural progenitors achieves therapeutic benefits via cell replacement and/or increased trophic support. Combinatorial approaches of cell-based therapy with additional strategies such as neuroprotective protocols, anti-inflammatory treatment, and rehabilitation therapy can significantly improve therapeutic benefits. In this review, we will discuss the recent progress regarding cell types and applications in regenerative medicine as well as future applications.

Delayed and repeated intranasal delivery of bone marrow stromal cells increases regeneration and functional recovery after ischemic stroke in mice

BACKGROUND

Stroke is a leading cause of death and disability worldwide, yet there are limited treatments available. Intranasal administration is a novel non-invasive strategy to deliver cell therapy into the brain. Cells delivered via the intranasal route can migrate from the nasal mucosa to the ischemic infarct and show acute neuroprotection as well as functional benefits. However, there is little information about the regenerative effects of this transplantation method in the delayed phase of stroke. We hypothesized that repeated intranasal deliveries of bone marrow stromal cells (BMSCs) would be feasible and could enhance delayed neurovascular repair and functional recovery after ischemic stroke.

RESULTS

Reverse transcription polymerase chain reaction and immunocytochemistry were performed to analyze the expression of regenerative factors including SDF-1α, CXCR4, VEGF and FAK in BMSCs. Ischemic stroke targeting the somatosensory cortex was induced in adult C57BL/6 mice by permanently occluding the right middle cerebral artery and temporarily occluding both common carotid arteries. Hypoxic preconditioned (HP) BMSCs (HP-BMSCs) with increased expression of surviving factors HIF-1α and Bcl-xl (1 × 106 cells/100 μl per mouse) or cell media were administered intranasally at 3, 4, 5, and 6 days after stroke. Mice received daily BrdU (50 mg/kg) injections until sacrifice. BMSCs were prelabeled with Hoechst 33342 and detected within the peri-infarct area 6 and 24 h after transplantation. In immunohistochemical staining, significant increases in NeuN/BrdU and Glut-1/BrdU double positive cells were seen in stroke mice received HP-BMSCs compared to those received regular BMSCs. HP-BMSC transplantation significantly increased local cerebral blood flow and improved performance in the adhesive removal test.

CONCLUSIONS

This study suggests that delayed and repeated intranasal deliveries of HP-treated BMSCs is an effective treatment to encourage regeneration after stroke.

Cognitive Deficits after Cerebral Ischemia and Underlying Dysfunctional Plasticity: Potential Targets for Recovery of Cognition

Cerebral ischemia affects millions of people worldwide and survivors suffer from long-term functional and cognitive deficits. While stroke and cardiac arrest are typically considered when discussing ischemic brain injuries, there is much evidence that smaller ischemic insults underlie neurodegenerative diseases, including Alzheimer's disease. The "regenerative" capacity of the brain relies on several aspects of plasticity that are crucial for normal functioning; less affected brain areas may take over function previously performed by irreversibly damaged tissue. To harness the endogenous plasticity mechanisms of the brain to provide recovery of cognitive function, we must first understand how these mechanisms are altered after damage, such as cerebral ischemia. In this review, we discuss the long-term cognitive changes that result after cerebral ischemia and how ischemia alters several plasticity processes. We conclude with a discussion of how current and prospective therapies may restore brain plasticity and allow for recovery of cognitive function, which may be applicable to several disorders that have a disruption of cognitive processing, including traumatic brain injury and Alzheimer's disease.

Cerebral ischemia and neuroregeneration

Cerebral ischemia is one of the leading causes of morbidity and mortality worldwide. Although stroke (a form of cerebral ischemia)-related costs are expected to reach 240.67 billion dollars by 2030, options for treatment against cerebral ischemia/stroke are limited. All therapies except anti-thrombolytics (i.e., tissue plasminogen activator) and hypothermia have failed to reduce neuronal injury, neurological deficits, and mortality rates following cerebral ischemia, which suggests that development of novel therapies against stroke/cerebral ischemia are urgently needed. Here, we discuss the possible mechanism(s) underlying cerebral ischemia-induced brain injury, as well as current and future novel therapies (i.e., growth factors, nicotinamide adenine dinucleotide, melatonin, resveratrol, protein kinase C isozymes, pifithrin, hypothermia, fatty acids, sympathoplegic drugs, and stem cells) as it relates to cerebral ischemia.

Stem cell transplantation therapy for multifaceted therapeutic benefits after stroke

One of the exciting advances in modern medicine and life science is cell-based neurovascular regeneration of damaged brain tissues and repair of neuronal structures. The progress in stem cell biology and creation of adult induced pluripotent stem (iPS) cells has significantly improved basic and pre-clinical research in disease mechanisms and generated enthusiasm for potential applications in the treatment of central nervous system (CNS) diseases including stroke. Endogenous neural stem cells and cultured stem cells are capable of self-renewal and give rise to virtually all types of cells essential for the makeup of neuronal structures. Meanwhile, stem cells and neural progenitor cells are well-known for their potential for trophic support after transplantation into the ischemic brain. Thus, stem cell-based therapies provide an attractive future for protecting and repairing damaged brain tissues after injury and in various disease states. Moreover, basic research on naïve and differentiated stem cells including iPS cells has markedly improved our understanding of cellular and molecular mechanisms of neurological disorders, and provides a platform for the discovery of novel drug targets. The latest advances indicate that combinatorial approaches using cell based therapy with additional treatments such as protective reagents, preconditioning strategies and rehabilitation therapy can significantly improve therapeutic benefits. In this review, we will discuss the characteristics of cell therapy in different ischemic models and the application of stem cells and progenitor cells as regenerative medicine for the treatment of stroke.

Longitudinal MRI evaluation of neuroprotective effects of pharmacologically induced hypothermia in experimental ischemic stroke

Pharmacologically induced hypothermia (PIH) shows promising neuroprotective effects after stroke insult. However, the dynamic evolution of stroke infarct during the hypothermic therapy has not been understood very well. In the present study, MRI was utilized to longitudinally characterize the infarct evolution in a mouse model of ischemic stroke treated by PIH using the neurotensin agonist HPI201. Adult male C57BL/6 mice underwent permanent occlusion of the right middle cerebra artery (MCA). Each animal received a vehicle or HPI201 intraperitoneal injection. The temporal changes of stroke lesion were examined using T2-weighted imaging and diffusion-weighted imaging (DWI) in the acute phase (1-3h) and 24h post stroke. Significantly reduced infarct and edema volumes were observed in PIH treated stroke mice, in agreement with TTC staining findings. Also, the TUNEL staining results indicated apoptotic cells were widely distributed among the ischemic cortex in control group but limited in PIH treated mice. Dramatically reduced growth rate of infarction was seen in PIH treated stroke mice. These results demonstrate HPI201 has strong neuroprotection effects during acute stroke. In particular, MRI with the numerical modelling of temporal infarct evolution could provide a unique means to examine and predict the dynamic response of the PIH treatment on infarct evolution.

Neuroprotective mechanisms and translational potential of therapeutic hypothermia in the treatment of ischemic stroke

Stroke is a leading cause of disability and death, yet effective treatments for acute stroke has been very limited. Thus far, tissue plasminogen activator has been the only FDA-approved drug for thrombolytic treatment of ischemic stroke patients, yet its application is only applicable to less than 4–5% of stroke patients due to the narrow therapeutic window (< 4.5 hours after the onset of stroke) and the high risk of hemorrhagic transformation. Emerging evidence from basic and clinical studies has shown that therapeutic hypothermia, also known as targeted temperature management, can be a promising therapy for patients with different types of stroke. Moreover, the success in animal models using pharmacologically induced hypothermia (PIH) has gained increasing momentum for clinical translation of hypothermic therapy. This review provides an updated overview of the mechanisms and protective effects of therapeutic hypothermia, as well as the recent development and findings behind PIH treatment. It is expected that a safe and effective hypothermic therapy has a high translational potential for clinical treatment of patients with stroke and other CNS injuries.

Regulation of therapeutic hypothermia on inflammatory cytokines, microglia polarization, migration and functional recovery after ischemic stroke in mice

Stroke is a leading threat to human life and health in the US and around the globe, while very few effective treatments are available for stroke patients. Preclinical and clinical studies have shown that therapeutic hypothermia (TH) is a potential treatment for stroke. Using novel neurotensin receptor 1 (NTR1) agonists, we have demonstrated pharmacologically induced hypothermia and protective effects against brain damages after ischemic stroke, hemorrhage stroke, and traumatic brain injury (TBI) in rodent models. To further characterize the mechanism of TH-induced brain protection, we examined the effect of TH (at ±33°C for 6h) induced by the NTR1 agonist HPI-201 or physical (ice/cold air) cooling on inflammatory responses after ischemic stroke in mice and oxygen glucose deprivation (OGD) in cortical neuronal cultures. Seven days after focal cortical ischemia, microglia activation in the penumbra reached a peak level, which was significantly attenuated by TH treatments commenced 30min after stroke. The TH treatment decreased the expression of M1 type reactive factors including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-12, IL-23, and inducible nitric oxide synthase (iNOS) measured by RT-PCR and Western blot analyses. Meanwhile, TH treatments increased the expression of M2 type reactive factors including IL-10, Fizz1, Ym1, and arginase-1. In the ischemic brain and in cortical neuronal/BV2 microglia cultures subjected to OGD, TH attenuated the expression of monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1α (MIP-1α), two key chemokines in the regulation of microglia activation and infiltration. Consistently, physical cooling during OGD significantly decreased microglia migration 16h after OGD. Finally, TH improved functional recovery at 1, 3, and 7days after stroke. This study reveals the first evidence for hypothermia mediated regulation on inflammatory factor expression, microglia polarization, migration and indicates that the anti-inflammatory effect is an important mechanism underlying the brain protective effects of a TH therapy.