Modeling Ischemic Stroke In Vitro: Status Quo and Future Perspectives

Synergistic amelioration between Ligusticum striatum DC and borneol against cerebral ischemia by promoting astrocytes-mediated neurogenesis

ETHNOPHARMACOLOGICAL RELEVANCE

Ligusticum chuanxiong Hort (LCH), with the accepted name of Ligusticum striatum DC in "The Plant List" database, is a widely used ethnomedicine in treating ischemic stroke, and borneol (BO) is usually prescribed with LCH for better therapy. Our previous study confirmed their synergistic effect on neurogenesis against cerebral ischemia. However, the underlying mechanism is still unclear.

AIM OF THE STUDY

More and more evidence indicated that astrocytes (ACs) might be involved in the modulation of neurogenesis via polarization reaction. The study was designed to explore the synergic mechanism between LCH and BO in promoting astrocyte-mediated neurogenesis.

MATERIALS AND METHODS

After primary cultures and identifications of ACs and neural stem cells (NSCs), the oxygen-glucose deprivation (OGD) model and the concentrations of LCH and BO were optimized. After the OGD-injured ACs were treated by LCH, BO, and their combination, the conditioned mediums were used to culture the OGD-injured NSCs. The proliferation, migration, and differentiation of NSCs were assessed, and the secretions of BDNF, CNTF, and VEGF from ACs were measured. Then the expressions of C3 and PTX3 were detected. Moreover, the mice were performed a global cerebral ischemia/reperfusion model and treated with LCH and (or) BO. After the assessments of Nissl staining, the expressions of Nestin, DCX, GFAP, C3, PTX3, p65 and p-p65 were probed.

RESULTS

The most appropriate duration of OGD for the injury of both NSCs and ACs was 6 h, and the optimized concentrations of LCH and BO were 1.30 μg/mL and 0.03 μg/mL, respectively. The moderate OGD environment induced NSCs proliferation, migration, astrogenesis, and neurogenesis, increased the secretions of CNTF and VEGF from ACs, and upregulated the expressions of C3 and PTX3. For the ACs, LCH further increased the secretions of BDNF and CNTF, enhanced PTX3 expression, and reduced C3 expression. Additionally, the conditioned medium from LCH-treated ACs further enhanced NSC proliferation, migration, and neurogenesis. The in vivo study showed that LCH markedly enhanced the Nissl score and neurogenesis, and decreased astrogenesis which was accompanied by downregulations of C3, p-p65, and p-p65/p65 and upregulation of PTX3. BO not only decreased the expression of C3 in ACs both in vitro and in vivo but also downregulated p-p65 and p-p65/p65 in vivo. Additionally, BO promoted the therapeutic effect of LCH for most indices.

CONCLUSION

A certain degree of OGD might induce ACs to stimulate the proliferation, astrogenesis, and neurogenesis of NSCs. LCH and BO exhibited a marked synergy in promoting ACs-mediated neurogenesis and reducing astrogenesis, in which LCH played a dominant role and BO boosted the effect of LCH. The mechanism of LCH might be involved in switching the polarization of ACs from A1 to A2, while BO preferred to inhibit the formation of A1 phenotype via downregulating NF-κB pathway.

Unraveling brain diseases: The promise of brain-on-a-chip models

Brain disorders, encompassing a wide spectrum of neurological and psychiatric conditions, present a formidable challenge in modern medicine. Despite decades of research, the intricate complexity of the human brain still eludes comprehensive understanding, impeding the development of effective treatments. Recent advancements in microfluidics and tissue engineering have led to the development of innovative platforms known as "Brain-on-a-Chip" (BoC) i.e., advanced in vitro systems that aim to replicate the microenvironment of the brain with the highest possible fidelity. This technology offers a promising test-bed for studying brain disorders at the cellular and network levels, providing insights into disease mechanisms, drug screening, and, in perspective, the development of personalized therapeutic strategies. In this review, we provide an overview of the BoC models developed over the years to model and understand the onset and progression of some of the most severe neurological disorders in terms of incidence and debilitation (stroke, Parkinson's, Alzheimer's, and epilepsy). We also report some of the cutting-edge therapeutic approaches whose effects were evaluated by means of these technologies. Finally, we discuss potential challenges, and future perspectives of the BoC models.

Long-Term Alterations in Motor Skills, Neurogenesis and Astrocyte Numbers following Transient Cerebral Ischemia in Mice

Background and Objectives. Neurogenesis is an integral process in post-stroke recovery, involving the recruitment of proliferating neuroblasts from neurogenic niches of the mammal brain. However, the role of neurogenesis in the long-term restoration following ischemic stroke is fragmented. Post-stroke motor dysfunction includes challenges in the proper, coordinated use of hands and is present in roughly two-thirds of human patients. In this study, we investigated chronic behavioral and biochemical alterations after transient cerebral ischemia in adult male mice. Materials and Methods: Twelve-week-old C57BL/6N male mice were used, and fMCAo lasting 60 min was induced. At multiple timepoints after fMCAo induction, a single pellet reaching task was performed. Six months after the procedure, we immunohistochemically determined the number of proliferating neuroblasts (BrdU and DCX-positive) and the number of differentiated astrocytes (GFAP-positive) in both brain hemispheres. Results: The reaching ability of fMCAo mice was impaired from one month to six months after the induction of ischemia. Neuroblast proliferation was increased in the ipsilateral SVZ, whereas GFAP+ cell count was elevated in the hippocampal DG of both hemispheres of the fMCAo group mice. Conclusions: Our current report demonstrates the long-term effects of transient cerebral ischemia on mice functional parameters and neurogenesis progression. Our data demonstrate that transient cerebral ischemia promotes a long-lasting regenerative response in the ipsilateral brain hemisphere, specifically in the neurogenic SVZ and DG regions.

Kaempferol-3-O-(2″-O-galloyl-β-D-glucopyranoside): a novel neuroprotective agent from Diospryros kaki against cerebral ischemia-induced brain injury

Our previous study demonstrated neuroprotective and therapeutic effects of a standardized flavonoid extract from leaves of Diospyros kaki L.f. (DK) on middle cerebral artery occlusion-and-reperfusion (MCAO/R)-induced brain injury and its underlying mechanisms. This study aimed to clarify flavonoid components responsible for the effects of DK using in vitro and in vivo transient brain ischemic models. Organotypic hippocampal slice cultures (OHSCs) subjected to oxygen- and glucose-deprivation (OGD) were performed to evaluate in vitro neuroprotective activity of DK extract and nine isolated flavonoid components. MCAO/R mice were employed to elucidate in vivo neuroprotective effects of the flavonoid component that exhibited the most potent neuroprotective effect in OHSCs. DK extract and seven flavonoids [quercetin, isoquercetin, hyperoside, quercetin-3-O-(2″-O-galloyl-β-D-galactopyranoside), kaempferol, astragalin, and kaempferol-3-O-(2″-O-galloyl-β-D-glucopyranoside) compound (9)] attenuated OGD-induced neuronal cell damage and compound (9) possessed the most potent neuroprotective activity in OHSCs. The MCAO/R mice showed cerebral infarction, massive weight loss, characteristic neurological symptoms, and deterioration of neuronal cells in the brain. Compound (9) and a reference drugs, edaravone, significantly attenuated these physical and neurological impairments. Compound (9) mitigated the blood-brain barrier dysfunction and the change of glutathione and malondialdehyde content in the MCAO mouse brain. Edaravone suppressed the oxidative stress but did not significantly affect the blood-brain barrier permeability. The present results indicated that compound (9) is a flavonoid constituent of DK with a potent neuroprotective activity against transient ischemia-induced brain damage and this action, at least in part, via preservation of blood-brain barrier integrity and suppression of oxidative stress caused by ischemic insult.

Cenicriviroc prevents dysregulation of astrocyte/endothelial cross talk induced by ischemia and HIV-1 via inhibiting the NLRP3 inflammasome and pyroptosis

Blood-brain barrier (BBB) breakdown is one of the pathophysiological characteristics of ischemic stroke, which may contribute to the progression of brain tissue damage and subsequent neurological impairment. Human immunodeficiency virus (HIV)-infected individuals are at greater risk for ischemic stroke due to diminished immune function and HIV-associated vasculopathy. Studies have shown that astrocytes are involved in maintaining BBB integrity and facilitating HIV-1 infection in the brain. The present study investigated whether targeting astrocyte-endothelial cell signaling with cenicriviroc (CVC), a dual chemokine receptor (CCR)2 and CCR5 antagonist, may protect against dysregulation of cross talk between these cells after oxygen-glucose deprivation/reoxygenation (OGD/R) combined with HIV-1 infection. Permeability assay with 10 kDa fluorescein isothiocyanate (FITC)-dextran demonstrated that CVC alleviated endothelial barrier disruption in noncontact coculture of human brain microvascular endothelial cells (HBMECs) with HIV-1-infected human astrocytes, and reversed downregulation of tight junction protein claudin-5 induced by OGD/R- and HIV-1. Moreover, CVC attenuated OGD/R- and HIV-1-triggered upregulation of the NOD-like receptor protein-3 (NLRP3) inflammasome and IL-1β secretion. Treatment with CVC also suppressed astrocyte pyroptosis by attenuating cleaved caspase-1 levels and the formation of cleaved N-terminal GSDMD (N-GSDMD). Secretome profiling revealed that CVC ameliorated secretion levels of chemokine CC chemokine ligand 17 (CCL17), adhesion molecule intercellular adhesion molecule-1 (ICAM-1), and T cell activation modulator T cell immunoglobulin and mucin domain 3 (TIM-3) by astrocytes synergistically induced by OGD/R and HIV-1. Overall, these results suggest that CVC contributes to restoring astrocyte-endothelial cross interactions in an astrocyte-dependent manner via protection against NLRP3 activation and pyroptosis.NEW & NOTEWORTHY The present study reveals the role of astrocytic NOD-like receptor protein-3 (NLRP3) inflammasome in dysfunctional astrocyte-endothelial cross interactions triggered in response to oxygen/glucose deprivation injury associated with human immunodeficiency virus type 1 (HIV-1) infection. Our results suggest that blocking NLRP3 inflammasome activation and pyroptosis-mediated inflammation with cenicriviroc (CVC) may constitute a potentially effective therapeutic strategy for blood-brain barrier (BBB) protection during HIV-1-associated ischemic stroke.

Focal Cerebral Ischemia Induces Global Subacute Changes in the Number of Neuroblasts and Neurons and the Angiogenic Factor Density in Mice

Background and Objectives: Dissecting the complex pathological cascade of an ischemic stroke in preclinical models is highly warranted to understand the course of this disease in humans. Neurogenesis and angiogenesis are integral for post-stroke recovery, yet it is not clear how these processes are altered months after an ischemic stroke. In this study, we investigated the changes that take place subacutely after focal cerebral ischemia in experimental adult male mice. Materials and Methods: Male 12-week-old C57BL/6 mice underwent a 60 min long fMCAo or sham surgery. Two months after the procedure, we examined the immunohistochemistry to assess the changes in neuroblast (DCX) and differentiated neuron (NeuN) numbers, as well as the density of the pro-angiogenic factor VEGF. Results: We found decreased neuroblast numbers in both brain hemispheres of the fMCAo mice: by more than 85% in the dentate gyrus and by more than 70% in the subventricular zone. No neuroblasts were found in the contralateral hemisphere of the fMCAO mice or the sham controls, but a small population was detected in the ipsilateral ischemic core of the fMCAo mice. Intriguingly, the number of differentiated neurons in the ipsilateral ischemic core was lower by 20% compared to the contralateral hemisphere. VEGF expression was diminished in both brain hemispheres of the fMCAo mice. Conclusions: Our current report shows that focal cerebral ischemia induces changes in neuroblast numbers and the pro-angiogenic factor VEGF in both cerebral hemispheres 2 months after an fMCAo in mice. Our data show that focal cerebral ischemia induces a long-term regenerative response in both brain hemispheres.

Mesenchymal stromal cells secretome restores bioenergetic and redox homeostasis in human proximal tubule cells after ischemic injury

BACKGROUND

Ischemia/reperfusion injury is the leading cause of acute kidney injury (AKI). The current standard of care focuses on supporting kidney function, stating the need for more efficient and targeted therapies to enhance repair. Mesenchymal stromal cells (MSCs) and their secretome, either as conditioned medium (CM) or extracellular vesicles (EVs), have emerged as promising options for regenerative therapy; however, their full potential in treating AKI remains unknown.

METHODS

In this study, we employed an in vitro model of chemically induced ischemia using antimycin A combined with 2-deoxy-D-glucose to induce ischemic injury in proximal tubule epithelial cells. Afterwards we evaluated the effects of MSC secretome, CM or EVs obtained from adipose tissue, bone marrow, and umbilical cord, on ameliorating the detrimental effects of ischemia. To assess the damage and treatment outcomes, we analyzed cell morphology, mitochondrial health parameters (mitochondrial activity, ATP production, mass and membrane potential), and overall cell metabolism by metabolomics.

RESULTS

Our findings show that ischemic injury caused cytoskeletal changes confirmed by disruption of the F-actin network, energetic imbalance as revealed by a 50% decrease in the oxygen consumption rate, increased oxidative stress, mitochondrial dysfunction, and reduced cell metabolism. Upon treatment with MSC secretome, the morphological derangements were partly restored and ATP production increased by 40-50%, with umbilical cord-derived EVs being most effective. Furthermore, MSC treatment led to phenotype restoration as indicated by an increase in cell bioenergetics, including increased levels of glycolysis intermediates, as well as an accumulation of antioxidant metabolites.

CONCLUSION

Our in vitro model effectively replicated the in vivo-like morphological and molecular changes observed during ischemic injury. Additionally, treatment with MSC secretome ameliorated proximal tubule damage, highlighting its potential as a viable therapeutic option for targeting AKI.

Advanced rehabilitation in ischaemic stroke research

At present, due to the rapid progress of treatment technology in the acute phase of ischaemic stroke, the mortality of patients has been greatly reduced but the number of disabled survivors is increasing, and most of them are elderly patients. Physicians and rehabilitation therapists pay attention to develop all kinds of therapist techniques including physical therapy techniques, robot-assisted technology and artificial intelligence technology, and study the molecular, cellular or synergistic mechanisms of rehabilitation therapies to promote the effect of rehabilitation therapy. Here, we discussed different animal and in vitro models of ischaemic stroke for rehabilitation studies; the compound concept and technology of neurological rehabilitation; all kinds of biological mechanisms of physical therapy; the significance, assessment and efficacy of neurological rehabilitation; the application of brain-computer interface, rehabilitation robotic and non-invasive brain stimulation technology in stroke rehabilitation.

Bedside to bench: the outlook for psychedelic research

There has recently been a resurgence of interest in psychedelic compounds based on studies demonstrating their potential therapeutic applications in treating post-traumatic stress disorder, substance abuse disorders, and treatment-resistant depression. Despite promising efficacy observed in some clinical trials, the full range of biological effects and mechanism(s) of action of these compounds have yet to be fully established. Indeed, most studies to date have focused on assessing the psychological mechanisms of psychedelics, often neglecting the non-psychological modes of action. However, it is important to understand that psychedelics may mediate their therapeutic effects through multi-faceted mechanisms, such as the modulation of brain network activity, neuronal plasticity, neuroendocrine function, glial cell regulation, epigenetic processes, and the gut-brain axis. This review provides a framework supporting the implementation of a multi-faceted approach, incorporating in silico, in vitro and in vivo modeling, to aid in the comprehensive understanding of the physiological effects of psychedelics and their potential for clinical application beyond the treatment of psychiatric disorders. We also provide an overview of the literature supporting the potential utility of psychedelics for the treatment of brain injury (e.g., stroke and traumatic brain injury), neurodegenerative diseases (e.g., Parkinson's and Alzheimer's diseases), and gut-brain axis dysfunction associated with psychiatric disorders (e.g., generalized anxiety disorder and major depressive disorder). To move the field forward, we outline advantageous experimental frameworks to explore these and other novel applications for psychedelics.

The atypical antidepressant tianeptine confers neuroprotection against oxygen-glucose deprivation

Proregenerative and neuroprotective effects of antidepressants are an important topic of inquiry in neuropsychiatric research. Oxygen-glucose deprivation (OGD) mimics key aspects of ischemic injury in vitro. Here, we studied the effects of 24-h pretreatment with serotonin (5-HT), citalopram (CIT), fluoxetine (FLU), and tianeptine (TIA) on primary mouse cortical neurons subjected to transient OGD. 5-HT (50 μM) significantly enhanced neuron viability as measured by MTT assay and reduced cell death and LDH release. CIT (10 μM) and FLU (1 μM) did not increase the effects of 5-HT and neither antidepressant conferred neuroprotection in the absence of supplemental 5-HT in serum-free cell culture medium. By contrast, pre-treatment with TIA (10 μM) resulted in robust neuroprotection, even in the absence of 5-HT. Furthermore, TIA inhibited mRNA transcription of candidate genes related to cell death and hypoxia and attenuated lipid peroxidation, a hallmark of neuronal injury. Finally, deep RNA sequencing of primary neurons subjected to OGD demonstrated that OGD induces many pathways relating to cell survival, the inflammation-immune response, synaptic dysregulation and apoptosis, and that TIA pretreatment counteracted these effects of OGD. In conclusion, this study highlights the comparative strength of the 5-HT independent neuroprotective effects of TIA and identifies the molecular pathways involved.

Neuroprotective and Antioxidant Properties of CholesteroNitrone ChN2 and QuinolylNitrone QN23 in an Experimental Model of Cerebral Ischemia: Involvement of Necrotic and Apoptotic Cell Death

Ischemic stroke is the leading cause of disability and the second leading cause of death worldwide. However, current therapeutic strategies are scarce and of limited efficacy. The abundance of information available on the molecular pathophysiology of ischemic stroke has sparked considerable interest in developing new neuroprotective agents that can target different events of the ischemic cascade and may be used in combination with existing treatments. In this regard, nitrones represent a very promising alternative due to their renowned antioxidant and anti-inflammatory effects. In this study, we aimed to further investigate the neuroprotective effects of two nitrones, cholesteronitrone 2 (ChN2) and quinolylnitrone 23 (QN23), which have previously shown great potential for the treatment of stroke. Using an experimental in vitro model of cerebral ischemia, we compared their anti-necrotic, anti-apoptotic, and antioxidant properties with those of three reference compounds. Both ChN2 and QN23 demonstrated significant neuroprotective effects (EC₅₀ = 0.66 ± 0.23 μM and EC₅₀ = 2.13 ± 0.47 μM, respectively) comparable to those of homo-bis-nitrone 6 (HBN6) and N-acetylcysteine (NAC) and superior to those of α-phenyl-N-tert-butylnitrone (PBN). While primarily derived from the nitrones' anti-necrotic capacities, their anti-apoptotic effects at high concentrations and antioxidant powers-especially in the case of QN23-also contribute to their neuroprotective effects.

Neural lineage differentiation of human pluripotent stem cells: Advances in disease modeling

Brain diseases affect 1 in 6 people worldwide. These diseases range from acute neurological conditions such as stroke to chronic neurodegenerative disorders such as Alzheimer’s disease. Recent advancements in tissue-engineered brain disease models have overcome many of the different shortcomings associated with the various animal models, tissue culture models, and epidemiologic patient data that are commonly used to study brain disease. One innovative method by which to model human neurological disease is via the directed differentiation of human pluripotent stem cells (hPSCs) to neural lineages including neurons, astrocytes, and oligodendrocytes. Three-dimensional models such as brain organoids have also been derived from hPSCs, offering more physiological relevance due to their incorporation of various cell types. As such, brain organoids can better model the pathophysiology of neural diseases observed in patients. In this review, we will emphasize recent developments in hPSC-based tissue culture models of neurological disorders and how they are being used to create neural disease models.

A balanced formula of essential amino acids promotes brain mitochondrial biogenesis and protects neurons from ischemic insult

Mitochondrial dysfunction plays a key role in the aging process, and aging is a strong risk factor for neurodegenerative diseases or brain injury characterized by impairment of mitochondrial function. Among these, ischemic stroke is one of the leading causes of death and permanent disability worldwide. Pharmacological approaches for its prevention and therapy are limited. Although non-pharmacological interventions such as physical exercise, which promotes brain mitochondrial biogenesis, have been shown to exert preventive effects against ischemic stroke, regular feasibility is complex in older people, and nutraceutical strategies could be valuable alternatives. We show here that dietary supplementation with a balanced essential amino acid mixture (BCAAem) increased mitochondrial biogenesis and the endogenous antioxidant response in the hippocampus of middle-aged mice to an extent comparable to those elicited by treadmill exercise training, suggesting BCAAem as an effective exercise mimetic on brain mitochondrial health and disease prevention. In vitro BCAAem treatment directly exerted mitochondrial biogenic effects and induced antioxidant enzyme expression in primary mouse cortical neurons. Further, exposure to BCAAem protected cortical neurons from the ischemic damage induced by an in vitro model of cerebral ischemia (oxygen-glucose deprivation, OGD). BCAAem-mediated protection against OGD was abolished in the presence of rapamycin, Torin-1, or L-NAME, indicating the requirement of both mTOR and eNOS signaling pathways in the BCAAem effects. We propose BCAAem supplementation as an alternative to physical exercise to prevent brain mitochondrial derangements leading to neurodegeneration and as a nutraceutical intervention aiding recovery after cerebral ischemia in conjunction with conventional drugs.

Suppression of Microglial ERO1a Alleviates Inflammation and Enhances the Efficacy of Rehabilitative Training After Ischemic Stroke

Microglia mediated inflammation plays a crucial role in cellular events and functional recovery post ischemic stroke. In the current study, we profiled the proteome changes of microglia treated with oxygen and glucose deprivation (OGD). Bioinformatics analysis identified that differentially expressed proteins (DEPs) were enriched in pathways associated with oxidate phosphorylation and mitochondrial respiratory chain at both 6h and 24h post OGD. We next focused on one validated target named endoplasmic reticulum oxidoreductase 1 alpha (ERO1a) to study its role in stroke pathophysiology. We showed that over-expression of microglial ERO1a exacerbated inflammation, cell apoptosis and behavioral outcomes post middle cerebral artery occlusion (MCAO). In contrast, suppression of microglial ERO1a significantly reduced activation of both microglia and astrocyte, along with cell apoptosis. Furthermore, knocking down microglial ERO1a improved the efficacy of rehabilitative training and enhanced the mTOR activity in spared corticospinal neurons. Our study provided novel insights into the identification of therapeutic targets and the design of rehabilitative protocols to treat ischemic stroke and other traumatic CNS injuries.

Neuronal and Astrocyte Insulin-like Growth Factor-1 Signaling Differentially Modulates Ischemic Stroke Damage

Ischemic stroke is a leading cause of death and disability, as therapeutic options for mitigating the long-term deficits precipitated by the event remain limited. Acute administration of the neuroendocrine modulator insulin-like growth factor-1 (IGF-1) attenuates ischemic stroke damage in preclinical models, and clinical studies suggest IGF-1 can reduce the risk of stroke and improve overall outcomes. The cellular mechanism by which IGF-1 exerts this protection is poorly defined, as all cells within the neurovascular unit express the IGF-1 receptor. We hypothesize that the functional regulation of both neurons and astrocytes by IGF-1 is critical in minimizing damage in ischemic stroke. To test this, we utilized inducible astrocyte-specific or neuron-specific transgenic mouse models to selectively reduce IGF-1R in the adult mouse brain prior to photothrombotic stroke. Acute changes in blood brain barrier permeability, microglial activation, systemic inflammation, and biochemical composition of the brain were assessed 3 hours following photothrombosis, and significant protection was observed in mice deficient in neuronal and astrocytic IGF-1R. When the extent of tissue damage and sensorimotor dysfunction was assessed for 3 days following stroke, only the neurological deficit score continued to show improvements, and the extent of improvement was enhanced with additional IGF-1 supplementation. Overall, results indicate that neuronal and astrocytic IGF-1 signaling influences stroke damage but IGF-1 signaling within these individual cell types is not required for minimizing tissue damage or behavioral outcome.

An Updated Review of Mitochondrial Transplantation as a Potential Therapeutic Strategy Against Cerebral Ischemia and Cerebral Ischemia/Reperfusion Injury

Regardless of the progress made in the pathogenesis of ischemic stroke, it remains a leading cause of adult disability and death. To date, the most effective treatment for ischemic stroke is the timely recanalization of the occluded artery. However, the short time window and reperfusion injury have greatly limited its application and efficacy. Mitochondrial dysfunction and ATP depletion have become regarded as being hallmarks of neuropathophysiology following ischemic stroke. Mitochondrial transplantation is a novel potential therapeutic intervention for ischemic stroke that has sparked widespread concern during the past few years. This review summarizes and discusses the effects of mitochondrial transplantation in in vitro and in vivo ischemic stroke models. In addition, pharmacological interventions promoting mitochondrial transplantation are reviewed and discussed. We also discuss the potential challenges to the clinical application of mitochondrial transplantation in the treatment of ischemic stroke.

Oxygen gradient generator to improve in vitro modeling of ischemic stroke

Introduction

In the core of a brain infarct, perfusion is severely impeded, and neuronal death occurs within minutes. In the penumbra, an area near the core with more remaining perfusion, cells initially remain viable, but activity is significantly reduced. In principle, the penumbra can be saved if reperfusion is established on time, making it a promising target for treatment. In vitro models with cultured neurons on microelectrode arrays (MEAs) provide a useful tool to investigate how ischemic stroke affects neuronal functioning. These models tend to be uniform, focusing on the isolated penumbra, and typically lack adjacent regions such as a core and unaffected regions (normal perfusion). However, processes in these regions may affect neuronal functioning and survival in the penumbra.

Materials and methods

Here, we designed, fabricated, and characterized a cytocompatible device that generates an oxygen gradient across in vitro neuronal cultures to expose cells to hypoxia of various depths from near anoxia to near normoxia. This marks a step in the path to mimic core, penumbra, and healthy tissue, and will facilitate better in vitro modeling of ischemic stroke.

Results

The generator forms a stable and reproducible gradient within 30 min. Oxygen concentrations at the extremes are adjustable in a physiologically relevant range. Application of the generator did not negatively affect electrophysiological recordings or the viability of cultures, thus confirming the cytocompatibility of the device.

Discussion

The developed device is able to impose an oxygen gradient on neuronal cultures and may enrich in vitro stroke models.

Anti-Inflammatory Effects of Flavonoids in Common Neurological Disorders Associated with Aging

Aging reduces homeostasis and contributes to increasing the risk of brain diseases and death. Some of the principal characteristics are chronic and low-grade inflammation, a general increase in the secretion of proinflammatory cytokines, and inflammatory markers. Aging-related diseases include focal ischemic stroke and neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Flavonoids are the most common class of polyphenols and are abundantly found in plant-based foods and beverages. A small group of individual flavonoid molecules (e.g., quercetin, epigallocatechin-3-gallate, and myricetin) has been used to explore the anti-inflammatory effect in vitro studies and in animal models of focal ischemic stroke and AD and PD, and the results show that these molecules reduce the activated neuroglia and several proinflammatory cytokines, and also, inactivate inflammation and inflammasome-related transcription factors. However, the evidence from human studies has been limited. In this review article, we highlight the evidence that individual natural molecules can modulate neuroinflammation in diverse studies from in vitro to animal models to clinical studies of focal ischemic stroke and AD and PD, and we discuss future areas of research that can help researchers to develop new therapeutic agents.

Neural cortical organoids from self-assembling human iPSC as a model to investigate neurotoxicity in brain ischemia

Brain ischemia is a common acute injury resulting from impaired blood flow to the brain. Translation of effective drug candidates from experimental models to patients has systematically failed. The use of human induced pluripotent stem cells (iPSC) offers new opportunities to gain translational insights into diseases including brain ischemia. We used a human 3D self-assembling iPSC-derived model (human cortical organoids, hCO) to characterize the effects of ischemia caused by oxygen-glucose deprivation (OGD). hCO exposed to 2 h or 8 h of OGD had neuronal death and impaired neuronal network complexity, measured in whole-mounting microtubule-associated protein 2 (MAP-2) immunostaining. Neuronal vulnerability was reflected by a reduction in MAP-2 mRNA levels, and increased release of neurofilament light chain (NfL) in culture media, proportional to OGD severity. Glial fibrillary acidic protein (GFAP) gene or protein levels did not change in hCO, but their release in medium increased after prolonged OGD. In conclusion, this human 3D iPSC-based in vitro model of brain ischemic injury is characterized by marked neuronal injury reflected by the release of the translational biomarker NfL which is relevant for testing neuroprotective strategies.

Synthesis and Pharmacological Evaluation of Novel Triazole-Pyrimidine Hybrids as Potential Neuroprotective and Anti-neuroinflammatory Agents

OBJECTIVE

Neuroprotection is a precise target for the treatment of neurodegenerative diseases, ischemic stroke, and traumatic brain injury. Pyrimidine and its derivatives have been proven to use antiviral, anticancer, antioxidant, and antimicrobial activity prompting us to study the neuroprotection and anti-inflammatory activity of the triazole-pyrimidine hybrid on human microglia and neuronal cell model.

METHODS

A series of novel triazole-pyrimidine-based compounds were designed, synthesized and characterized by mass spectra, 1HNMR, 13CNMR, and a single X-Ray diffraction analysis. Further, the neuroprotective, anti-neuroinflammatory activity was evaluated by cell viability assay (MTT), Elisa, qRT-PCR, western blotting, and molecular docking.

RESULTS

The molecular results revealed that triazole-pyrimidine hybrid compounds have promising neuroprotective and anti-inflammatory properties. Among the 14 synthesized compounds, ZA3-ZA5, ZB2-ZB6, and intermediate S5 showed significant anti-neuroinflammatory properties through inhibition of nitric oxide (NO) and tumor necrosis factor-α (TNF-α) production in LPS-stimulated human microglia cells. From 14 compounds, six (ZA2 to ZA6 and intermediate S5) exhibited promising neuroprotective activity by reduced expression of the endoplasmic reticulum (ER) chaperone, BIP, and apoptosis marker cleaved caspase-3 in human neuronal cells. Also, a molecular docking study showed that lead compounds have favorable interaction with active residues of ATF4 and NF-kB proteins.

CONCLUSION

The possible mechanism of action was observed through the inhibition of ER stress, apoptosis, and the NF-kB inflammatory pathway. Thus, our study strongly indicates that the novel scaffolds of triazole-pyrimidine-based compounds can potentially be developed as neuroprotective and anti-neuroinflammatory agents.

Modeling Central Nervous System Injury In Vitro: Current Status and Promising Future Strategies

The central nervous system (CNS) injury, which occurs because of mechanical trauma or ischemia/hypoxia, is one of the main causes of mortality and morbidity in the modern society. Until know, despite the fact that numerous preclinical and clinical studies have been undertaken, no significant neuroprotective strategies have been discovered that could be used in the brain trauma or ischemia treatment. Although there are many potential explanations for the failure of those studies, it is clear that there are questions regarding the use of experimental models, both in vivo and in vitro, when studying CNS injury and searching new therapeutics. Due to some ethical issues with the use of live animals in biomedical research, implementation of experimental strategies that prioritize the use of cells and tissues in the in vitro environment has been encouraged. In this review, we examined some of the most commonly used in vitro models and the most frequently utilized cellular platforms in the research of traumatic brain injury and cerebral ischemia. We also proposed some future strategies that could improve the usefulness of these studies for better bench-to-bedside translational outcomes.

The absence of AQP4/TRPV4 complex substantially reduces acute cytotoxic edema following ischemic injury

Introduction

Astrocytic Aquaporin 4 (AQP4) and Transient receptor potential vanilloid 4 (TRPV4) channels form a functional complex that likely influences cell volume regulation, the development of brain edema, and the severity of the ischemic injury. However, it remains to be fully elucidated whether blocking these channels can serve as a therapeutic approach to alleviate the consequences of having a stroke.

Methods and results

In this study, we used in vivo magnetic resonance imaging (MRI) to quantify the extent of brain lesions one day (D1) and seven days (D7) after permanent middle cerebral artery occlusion (pMCAO) in AQP4 or TRPV4 knockouts and mice with simultaneous deletion of both channels. Our results showed that deletion of AQP4 or TRPV4 channels alone leads to a significant worsening of ischemic brain injury at both time points, whereas their simultaneous deletion results in a smaller brain lesion at D1 but equal tissue damage at D7 when compared with controls. Immunohistochemical analysis 7 days after pMCAO confirmed the MRI data, as the brain lesion was significantly greater in AQP4 or TRPV4 knockouts than in controls and double knockouts. For a closer inspection of the TRPV4 and AQP4 channel complex in the development of brain edema, we applied a real-time iontophoretic method in situ to determine ECS diffusion parameters, namely volume fraction (α) and tortuosity (λ). Changes in these parameters reflect alterations in cell volume, and tissue structure during exposure of acute brain slices to models of ischemic conditions in situ, such as oxygen-glucose deprivation (OGD), hypoosmotic stress, or hyperkalemia. The decrease in α was comparable in double knockouts and controls when exposed to hypoosmotic stress or hyperkalemia. However, during OGD, there was no decrease in α in the double knockouts as observed in the controls, which suggests less swelling of the cellular components of the brain.

Conclusion

Although simultaneous deletion of AQP4 and TRPV4 did not improve the overall outcome of ischemic brain injury, our data indicate that the interplay between AQP4 and TRPV4 channels plays a critical role during neuronal and non-neuronal swelling in the acute phase of ischemic injury.

JAK2/STAT3 pathway mediates neuroprotective and pro-angiogenic treatment effects of adult human neural stem cells in middle cerebral artery occlusion stroke animal models

Mismatches between pre-clinical and clinical results of stem cell therapeutics for ischemic stroke limit their clinical applicability. To overcome these discrepancies, precise planning of pre-clinical experiments that can be translated to clinical trials and the scientific elucidation of treatment mechanisms is important. In this study, adult human neural stem cells (ahNSCs) derived from temporal lobe surgical samples were used (to avoid ethical and safety issues), and their therapeutic effects on ischemic stroke were examined using middle cerebral artery occlusion animal models. 5 × 10⁵ ahNSCs was directly injected into the lateral ventricle of contralateral brain hemispheres of immune suppressed rat stroke models at the subacute phase of stroke. Compared with the mock-treated group, ahNSCs reduced brain tissue atrophy and neurological sensorimotor and memory functional loss. Tissue analysis demonstrated that the significant therapeutic effects were mediated by the neuroprotective and pro-angiogenic activities of ahNSCs, which preserved neurons in ischemic brain areas and decreased reactive astrogliosis and microglial activation. The neuroprotective and pro-angiogenic effects of ahNSCs were validated in in vitro stroke models and were induced by paracrine factors excreted by ahNSCs. When the JAK2/STAT3 signaling pathway was inhibited by a specific inhibitor, AG490, the paracrine neuroprotective and pro-angiogenic effects of ahNSCs were reversed. This pre-clinical study that closely simulated clinical settings and provided treatment mechanisms of ahNSCs for ischemic stroke may aid the development of protocols for subsequent clinical trials of ahNSCs and the realization of clinically available stem cell therapeutics for ischemic stroke.

Modulation of oxidative neurometabolism in ischemia/reperfusion by nitrite

Nitrite has been viewed essentially as an inert metabolic endpoint of nitric oxide (^•NO). However, under certain conditions, nitrite can be a source of ^•NO. In the brain, this alternative source of ^•NO production independent of nitric oxide synthase activity may be particularly relevant in ischemia/reperfusion (I/R), where low oxygen availability limits enzymatic production of ^•NO. Notably, in vivo concentration of nitrite can be easily increased with diet, through the ingestion of nitrate-rich foods, opening the window for a therapeutic intervention based on diet. Considering the modulation of mitochondrial respiration by ^•NO, we have hypothesized that the protective action of nitrite in I/R may also result from modulation of mitochondrial function. We used high-resolution respirometry to evaluate the effects of nitrite in two in vitro models of I/R. In both cases, an increase in oxygen flux was observed following reoxygenation, a phenomenon that has been coined "oxidative burst". The amplitude of this "oxidative burst" was decreased by nitrite in a concentration-dependent manner. Additionally, a pilot in vivo study in which animals received a nitrate-rich diet as a strategy to increase circulating and tissue levels of nitrite also revealed that the "oxidative burst" was decreased in the nitrate-treated animals. These results may provide mechanistic support to the observation of a protective effect of nitrite in situations of brain ischemia.

INF2-mediated actin filament reorganization confers intrinsic resilience to neuronal ischemic injury

During early ischemic brain injury, glutamate receptor hyperactivation mediates neuronal death via osmotic cell swelling. Here we show that ischemia and excess NMDA receptor activation cause actin to rapidly and extensively reorganize within the somatodendritic compartment. Normally, F-actin is concentrated within dendritic spines. However, <5 min after bath-applied NMDA, F-actin depolymerizes within spines and polymerizes into stable filaments within the dendrite shaft and soma. A similar actinification occurs after experimental ischemia in culture, and photothrombotic stroke in mouse. Following transient NMDA incubation, actinification spontaneously reverses. Na+, Cl-, water, and Ca2+ influx, and spine F-actin depolymerization are all necessary, but not individually sufficient, for actinification, but combined they induce activation of the F-actin polymerization factor inverted formin-2 (INF2). Silencing of INF2 renders neurons vulnerable to cell death and INF2 overexpression is protective. Ischemia-induced dendritic actin reorganization is therefore an intrinsic pro-survival response that protects neurons from death induced by cell edema.

Ischemic Stroke, Lessons from the Past towards Effective Preclinical Models

Ischemic stroke is a leading cause of death worldwide, mainly in western countries. So far, approved therapies rely on reperfusion of the affected brain area, by intravenous thrombolysis or mechanical thrombectomy. The last approach constitutes a breakthrough in the field, by extending the therapeutic window to 16-24 h after stroke onset and reducing stroke mortality. The combination of pharmacological brain-protective strategies with reperfusion is the future of stroke therapy, aiming to reduce brain cell death and decrease patients' disabilities. Recently, a brain-protective drug-nerinetide-reduced brain infarct and stroke mortality, and improved patients' functional outcomes in clinical trials. The success of new therapies relies on bringing preclinical studies and clinical practice close together, by including a functional outcome assessment similar to clinical reality. In this review, we focused on recent upgrades of in vitro and in vivo stroke models for more accurate and effective evaluation of therapeutic strategies: from spheroids to organoids, in vitro models that include all brain cell types and allow high throughput drug screening, to advancements in in vivo preclinical mouse stroke models to mimic the clinical reality in surgical procedures, postsurgical care, and functional assessment.

Biphasic effects of statins on neuron cell functions under oxygen-glucose deprivation and normal culturing conditions via different mechanisms

While there is a growing interest in the use of statins, HMG‐CoA reductase inhibitors, to treat neurodegenerative diseases, statins are associated with conflicting effects within the central nervous system (CNS) without clear evidence of the underlying mechanisms. This study systematically investigated effects of four statins (atorvastatin, pitavastatin, cerivastatin, and lovastatin) on neuronal cells under pathological condition using an in vitro model depicting ischemic injury, as well as tested under physiological condition. All four statins at micromolar concentrations display toxic effects on neuron cells under physiological condition. Atorvastatin and cerivastatin but not pitavastatin or lovastatin at nanomolar concentrations display protective effects on neuron cells under ischemic injury condition, via decreased ischemic injury‐induced oxidative stress, oxidative damage, and inflammation. Mechanistically, atorvastatin, pitavastatin, and lovastatin induces neuron cell apoptosis via prenylation‐independent manner. Other mechanisms are involved in the pro‐apoptotic effect of cerivastatin. Prenylation is not involved in the protective effects of statins under ischemic injury condition. Our work provides better understanding on the multiple differential effects of statins on neuron cells under physiological condition and ischemic injury, and elucidate their underlying mechanisms, which may be of relevance to the influence of statins in CNS.

Promising Strategies for the Development of Advanced In Vitro Models with High Predictive Power in Ischaemic Stroke Research

Although stroke is one of the world’s leading causes of death and disability, and more than a thousand candidate neuroprotective drugs have been proposed based on extensive in vitro and animal-based research, an effective neuroprotective/restorative therapy for ischaemic stroke patients is still missing. In particular, the high attrition rate of neuroprotective compounds in clinical studies should make us question the ability of in vitro models currently used for ischaemic stroke research to recapitulate human ischaemic responses with sufficient fidelity. The ischaemic stroke field would greatly benefit from the implementation of more complex in vitro models with improved physiological relevance, next to traditional in vitro and in vivo models in preclinical studies, to more accurately predict clinical outcomes. In this review, we discuss current in vitro models used in ischaemic stroke research and describe the main factors determining the predictive value of in vitro models for modelling human ischaemic stroke. In light of this, human-based 3D models consisting of multiple cell types, either with or without the use of microfluidics technology, may better recapitulate human ischaemic responses and possess the potential to bridge the translational gap between animal-based in vitro and in vivo models, and human patients in clinical trials.

Luminescent Human iPSC-Derived Neurospheroids Enable Modeling of Neurotoxicity After Oxygen-glucose Deprivation

Despite the considerable impact of stroke on both the individual and on society, a neuroprotective therapy for stroke patients is missing. This is partially due to the current lack of a physiologically relevant human in vitro stroke model. To address this problem, we have developed a luminescent human iPSC-derived neurospheroid model that enables real-time read-out of neural viability after ischemia-like conditions. We subjected 1- and 4-week-old neurospheroids, generated from iPSC-derived neural stem cells, to 6 h of oxygen-glucose deprivation (OGD) and measured neurospheroid luminescence. For both, we detected a decrease in luminescent signal due to ensuing neurotoxicity, as confirmed by conventional LDH assay and flow cytometric viability analysis. Remarkably, 1-week-old, but not 4-week-old neurospheroids recovered from OGD-induced injury, as evidenced by their reduced but overall increasing luminescence over time. This underscores the need for more mature neurospheroids, more faithfully recapitulating the in vivo situation. Furthermore, treatment of oxygen- and glucose-deprived neurospheroids with the pan-caspase inhibitor Z-VAD-FMK did not increase overall neural survival, despite its successful attenuation of apoptosis, in a human-based 3D environment. Nevertheless, owing to its three-dimensional organization and real-time viability reporting potential, the luminescent neurospheroids may become readily adopted in high-throughput screens aimed at identification of new therapeutic agents to treat acute ischemic stroke patients.

In Vitro Oxygen Glucose Deprivation Model of Ischemic Stroke: A Proteomics-Driven Systems Biological Perspective

Oxygen glucose deprivation (OGD) of brain cells is the commonest in vitro model of ischemic stroke that is used extensively for basic and preclinical stroke research. Protein mass spectrometry is one of the most promising and rapidly evolving technologies in biomedical research. A systems-level understanding of cell-type-specific responses to oxygen and glucose deprivation without systemic influence is a prerequisite to delineate the response of the neurovascular unit following ischemic stroke. In this systematic review, we summarize the proteomics studies done on different OGD models. These studies have followed an expression or interaction proteomics approach. They have been primarily used to understand the cellular pathophysiology of ischemia-reperfusion injury or to assess the efficacy of interventions as potential treatment options. We compile the limitations of OGD model and downstream proteomics experiment. We further show that despite having limitations, several proteins shortlisted as altered in in vitro OGD-proteomics studies showed comparable regulation in ischemic stroke patients. This showcases the translational potential of this approach for therapeutic target and biomarker discovery. We next discuss the approaches that can be adopted for cell-type-specific validation of OGD-proteomics results in the future. Finally, we briefly present the research questions that can be addressed by OGD-proteomics studies using emerging techniques of protein mass spectrometry. We have also created a web resource compiling information from OGD-proteomics studies to facilitate data sharing for community usage. This review intends to encourage preclinical stroke community to adopt a hypothesis-free proteomics approach to understand cell-type-specific responses following ischemic stroke.

Establishment of an In Vitro Model of Human Blood-Brain Barrier to Study the Impact of Ischemic Injury

The blood-brain barrier (BBB), mainly composed of brain microvascular endothelial cells, astrocyte end-feet, and pericytes, serves as a physical and biochemical barrier that selectively limits the passage of circulating molecules into the brain parenchyma. The disruption of its integrity and function is a major cause of increased mortality and disability among ischemic stroke patients. Hence, scrutiny of the cellular and molecular mechanisms that alter BBB permeability following an ischemic injury remains of paramount importance. In this context, establishment of an in vitro model of BBB that closely simulates human cerebral barrier may offer an easy, inexpensive, and straightforward approach to identify signaling pathways involved in BBB breakdown and may help to discover new therapeutic targets to restore its damage. This chapter describes a sequential method pertaining to establishment of a triple culture model of human BBB consisting of the three main cellular components of the cerebral barrier. It also documents how the integrity and function of this barrier are evaluated through measurements of transendothelial electrical resistance (TEER) and paracellular flux of permeability marker and sodium fluorescein (NaF, 376 Da), respectively, both in normal and experimental conditions mimicking ischemic injury.

Modeling ischemic stroke in a triculture neurovascular unit on-a-chip

BACKGROUND

In ischemic stroke, the function of the cerebral vasculature is impaired. This vascular structure is formed by the so-called neurovascular unit (NVU). A better understanding of the mechanisms involved in NVU dysfunction and recovery may lead to new insights for the development of highly sought therapeutic approaches. To date, there remains an unmet need for complex human in vitro models of the NVU to study ischemic events seen in the human brain.

METHODS

We here describe the development of a human NVU on-a-chip model using a platform that allows culture of 40 chips in parallel. The model comprises a perfused vessel of primary human brain endothelial cells in co-culture with induced pluripotent stem cell derived astrocytes and neurons. Ischemic stroke was mimicked using a threefold approach that combines chemical hypoxia, hypoglycemia, and halted perfusion.

RESULTS

Immunofluorescent staining confirmed expression of endothelial adherens and tight junction proteins, as well as astrocytic and neuronal markers. In addition, the model expresses relevant brain endothelial transporters and shows spontaneous neuronal firing. The NVU on-a-chip model demonstrates tight barrier function, evidenced by retention of small molecule sodium fluorescein in its lumen. Exposure to the toxic compound staurosporine disrupted the endothelial barrier, causing reduced transepithelial electrical resistance and increased permeability to sodium fluorescein. Under stroke mimicking conditions, brain endothelial cells showed strongly reduced barrier function (35-fold higher apparent permeability) and 7.3-fold decreased mitochondrial potential. Furthermore, levels of adenosine triphosphate were significantly reduced on both the blood- and the brain side of the model (4.8-fold and 11.7-fold reduction, respectively).

CONCLUSIONS

The NVU on-a-chip model presented here can be used for fundamental studies of NVU function in stroke and other neurological diseases and for investigation of potential restorative therapies to fight neurological disorders. Due to the platform's relatively high throughput and compatibility with automation, the model holds potential for drug compound screening.

Senolytic Therapy for Cerebral Ischemia-Reperfusion Injury

Ischemic stroke is one of the leading causes of death, and even timely treatment can result in severe disabilities. Reperfusion of the ischemic stroke region and restoration of the blood supply often lead to a series of cellular and biochemical consequences, including generation of reactive oxygen species (ROS), expression of inflammatory cytokines, inflammation, and cerebral cell damage, which is collectively called cerebral ischemia-reperfusion (IR) injury. Since ROS and inflammatory cytokines are involved in cerebral IR injury, injury could involve cellular senescence. Thus, we investigated whether senolytic therapy that eliminates senescent cells could be an effective treatment for cerebral IR injury. To determine whether IR induces neural cell senescence in vitro, astrocytes were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R). OGD/R induced astrocyte senescence and senescent cells in OGD/R-injured astrocytes were effectively eliminated in vitro by ABT263, a senolytic agent. IR in rats with intraluminal middle cerebral artery occlusion induced cellular senescence in the ischemic region. The senescent cells in IR-injured rats were effectively eliminated by intravenous injections of ABT263. Importantly, ABT263 treatment significantly reduced the infarct volume and improved neurological function in behavioral tests. This study demonstrated, for the first time, that senolytic therapy has therapeutic potential for cerebral IR injury.

In vivo dynamics of acidosis and oxidative stress in the acute phase of an ischemic stroke in a rodent model

Ischemic cerebral stroke is one of the leading causes of death and disability in humans. However, molecular processes underlying the development of this pathology remain poorly understood. There are major gaps in our understanding of metabolic changes that occur in the brain tissue during the early stages of ischemia and reperfusion. In particular, it is generally accepted that both ischemia (I) and reperfusion (R) generate reactive oxygen species (ROS) that cause oxidative stress which is one of the main drivers of the pathology, although ROS generation during I/R was never demonstrated in vivo due to the lack of suitable methods. In the present study, we record for the first time the dynamics of intracellular pH and H2O2 during I/R in cultured neurons and during experimental stroke in rats using the latest generation of genetically encoded biosensors SypHer3s and HyPer7. We detect a buildup of powerful acidosis in the brain tissue that overlaps with the ischemic core from the first seconds of pathogenesis. At the same time, no significant H2O2 generation was found in the acute phase of ischemia/reperfusion. HyPer7 oxidation in the brain was detected only 24 h later. Comparison of in vivo experiments with studies on cultured neurons under I/R demonstrates that the dynamics of metabolic processes in these models significantly differ, suggesting that a cell culture is a poor predictor of metabolic events in vivo.

Engineering 3D Cortical Spheroids for an In Vitro Ischemic Stroke Model

Three-dimensional (3D) spheroids composed of brain cells have shown great potential to mimic the pathophysiology of the brain. However, a 3D spheroidal brain-disease model for cerebral ischemia has not been reported. This study investigated an ultralow attachment (ULA) surface-mediated formation of 3D cortical spheroids using primary rat cortical cells to recapitulate the cerebral ischemic responses in stroke by oxygen-glucose deprivation-reoxygenation (OGD-R) treatment. Comparison between two-dimensional (2D) and 3D cell culture models confirmed the better performance of the 3D cortical spheroids as normal brain models. The cortical cells cultured in 3D maintained their healthy physiological morphology of a less activated state and suppressed mRNA expressions of pathological stroke markers, S100B, IL-1β, and MBP, selected based on in vivo stroke model. Interestingly, the spheroids formed on the ULA surface exhibited striking aggregation dynamics involving active cell-substrate interactions, whereas those formed on the agarose surface aggregated passively by the convective flow of the media. Accordingly, ULA spheroids manifested a layered arrangement of neurons and astrocytes with higher expressions of integrin β1, integrin α5, N-cadherin, and fibronectin than the agarose spheroids. OGD-R-induced stroke model of the ULA spheroids successfully mimicked the ischemic response as evidenced by the upregulated mRNA expressions of the key markers for stroke, S100B, IL-1β, and MBP. Our study suggested that structurally and functionally distinct cortical spheroids could be generated by simply tuning the cell-substrate binding activities during dynamic spheroidal formation, which should be an essential factor to consider in establishing a brain-disease model.

Effective silencing of miR-126 after ischemic stroke by means of intravenous α-tocopherol-conjugated heteroduplex oligonucleotide in mice

Brain endothelial cells (BECs) are involved in the pathogenesis of ischemic stroke. Recently, several microRNAs (miRNAs) in BECs were reported to regulate the endothelial function in ischemic brain. Therefore, modulation of miRNAs in BECs by a therapeutic oligonucleotide to inhibit miRNA (antimiR) could be a useful strategy for treating ischemic stroke. However, few attempts have been made to achieve this strategy via systemic route due to lack of efficient delivery-method toward BECs. Here, we have developed a new technology for delivering an antimiR into BECs and silencing miRNAs in BECs, using a mouse ischemic stroke model. We designed a heteroduplex oligonucleotide, comprising an antimiR against miRNA-126 (miR-126) known as the endothelial-specific miRNA and its complementary RNA, conjugated to α-tocopherol as a delivery ligand (Toc-HDO targeting miR-126). Intravenous administration of Toc-HDO targeting miR-126 remarkably suppressed miR-126 expression in ischemic brain of the model mice. In addition, we showed that Toc-HDO targeting miR-126 was delivered into BECs more efficiently than the parent antimiR in ischemic brain, and that it was delivered more effectively in ischemic brain than non-ischemic brain of this model mice. Our study highlights the potential of this technology as a new clinical therapeutic option for ischemic stroke.

The Application of Brain Organoid Technology in Stroke Research: Challenges and Prospects

Stroke is a neurological disease responsible for significant morbidity and disability worldwide. However, there remains a dearth of effective therapies. The failure of many therapies for stroke in clinical trials has promoted the development of human cell-based models, such as brain organoids. Brain organoids differ from pluripotent stem cells in that they recapitulate various key features of the human central nervous system (CNS) in three-dimensional (3D) space. Recent studies have demonstrated that brain organoids could serve as a new platform to study various neurological diseases. However, there are several limitations, such as the scarcity of glia and vasculature in organoids, which are important for studying stroke. Herein, we have summarized the application of brain organoid technology in stroke research, such as for modeling and transplantation purposes. We also discuss methods to overcome the limitations of brain organoid technology, as well as future prospects for its application in stroke research. Although there are many difficulties and challenges associated with brain organoid technology, it is clear that this approach will play a critical role in the future exploration of stroke treatment.

PTD4 Peptide Increases Neural Viability in an In Vitro Model of Acute Ischemic Stroke

Ischemic stroke is a disturbance in cerebral blood flow caused by brain tissue ischemia and hypoxia. We optimized a multifactorial in vitro model of acute ischemic stroke using rat primary neural cultures. This model was exploited to investigate the pro-viable activity of cell-penetrating peptides: arginine-rich Tat(49–57)-NH₂ (R⁴⁹KKRRQRRR⁵⁷-amide) and its less basic analogue, PTD4 (Y⁴⁷ARAAARQARA⁵⁷-amide). Our model included glucose deprivation, oxidative stress, lactic acidosis, and excitotoxicity. Neurotoxicity of these peptides was excluded below a concentration of 50 μm, and PTD4-induced pro-survival was more pronounced. Circular dichroism spectroscopy and molecular dynamics (MD) calculations proved potential contribution of the peptide conformational properties to neuroprotection: in MD, Tat(49–57)-NH₂ adopted a random coil and polyproline type II helical structure, whereas PTD4 adopted a helical structure. In an aqueous environment, the peptides mostly adopted a random coil conformation (PTD4) or a polyproline type II helical (Tat(49–57)-NH₂) structure. In 30% TFE, PTD4 showed a tendency to adopt a helical structure. Overall, the pro-viable activity of PTD4 was not correlated with the arginine content but rather with the peptide’s ability to adopt a helical structure in the membrane-mimicking environment, which enhances its cell membrane permeability. PTD4 may act as a leader sequence in novel drugs for the treatment of acute ischemic stroke.

Microphysiological models of the central nervous system with fluid flow

There are over 1,000 described neurological and neurodegenerative disorders affecting nearly 100 million Americans - roughly one third of the U.S. population. Collectively, treatment of neurological conditions is estimated to cost $800 billion every year. Lowering this societal burden will require developing better model systems in which to study these diverse disorders. Microphysiological systems are promising tools for modeling healthy and diseased neural tissues to study mechanisms and treatment of neuropathology. One major benefit of microphysiological systems is the ability to incorporate biophysical forces, namely the forces derived from biological fluid flow. Fluid flow in the central nervous system (CNS) is a complex but important element of physiology, and pathologies as diverse as traumatic or ischemic injury, cancer, neurodegenerative disease, and natural aging have all been found to alter flow pathways. In this review, we summarize recent advances in three-dimensional microphysiological systems for studying the biology and therapy of CNS disorders and highlight the ability and growing need to incorporate biological fluid flow in these miniaturized model systems.

Telmisartan Inhibits the NLRP3 Inflammasome by Activating the PI3K Pathway in Neural Stem Cells Injured by Oxygen-Glucose Deprivation

Angiotensin II receptor blockers (ARBs) have been shown to exert neuroprotective effects by suppressing inflammatory and apoptotic responses. In the present study, the effects of the ARB telmisartan on the NLRP3 inflammasome induced by oxygen-glucose deprivation (OGD) in neural stem cells (NSCs) were investigated, as well as their possible association with the activation of the PI3K pathway. Cultured NSCs were treated with different concentrations of telmisartan and subjected to various durations of OGD. Cell counting, lactate dehydrogenase, bromodeoxyuridine, and colony-forming unit assays were performed to measure cell viability and proliferation. In addition, the activity of intracellular signaling pathways associated with the PI3K pathway and NLRP3 inflammasome was evaluated. Telmisartan alone did not affect NSCs up to a concentration of 10 μM under normal conditions but showed toxicity at a concentration of 100 μM. Moreover, OGD reduced the viability of NSCs in a time-dependent manner. Nevertheless, treatment with telmisartan increased the viability and proliferation of OGD-injured NSCs. Furthermore, telmisartan promoted the expression of survival-related proteins and mRNA while inhibiting the expression of death-related proteins induced by OGD. In particular, telmisartan attenuated OGD-dependent expression of the NLRP3 inflammasome and its related signaling proteins. These beneficial effects of telmisartan were blocked by a PI3K inhibitor. Together, these results indicate that telmisartan attenuated the activation of the NLRP3 inflammasome by triggering the PI3K pathway, thereby contributing to neuroprotection.

A review of experimental models of focal cerebral ischemia focusing on the middle cerebral artery occlusion model

Cerebral ischemic stroke is a leading cause of death and disability, but current pharmacological therapies are limited in their utility and effectiveness. In vitro and in vivo models of ischemic stroke have been developed which allow us to further elucidate the pathophysiological mechanisms of injury and investigate potential drug targets. In vitro models permit mechanistic investigation of the biochemical and molecular mechanisms of injury but are reductionist and do not mimic the complexity of clinical stroke. In vivo models of ischemic stroke directly replicate the reduction in blood flow and the resulting impact on nervous tissue. The most frequently used in vivo model of ischemic stroke is the intraluminal suture middle cerebral artery occlusion (iMCAO) model, which has been fundamental in revealing various aspects of stroke pathology. However, the iMCAO model produces lesion volumes with large standard deviations even though rigid surgical and data collection protocols are followed. There is a need to refine the MCAO model to reduce variability in the standard outcome measure of lesion volume. The typical approach to produce vessel occlusion is to induce an obstruction at the origin of the middle cerebral artery and reperfusion is reliant on the Circle of Willis (CoW). However, in rodents the CoW is anatomically highly variable which could account for variations in lesion volume. Thus, we developed a refined approach whereby reliance on the CoW for reperfusion was removed. This approach improved reperfusion to the ischemic hemisphere, reduced variability in lesion volume by 30%, and reduced group sizes required to determine an effective treatment response by almost 40%. This refinement involves a methodological adaptation of the original surgical approach which we have shared with the scientific community via publication of a visualised methods article and providing hands-on training to other experimental stroke researchers.

Auraptene Enhances Junction Assembly in Cerebrovascular Endothelial Cells by Promoting Resilience to Mitochondrial Stress through Activation of Antioxidant Enzymes and mtUPR

Junctional proteins in cerebrovascular endothelial cells are essential for maintaining the barrier function of the blood-brain barrier (BBB), thus protecting the brain from the infiltration of pathogens. The present study showed that the potential therapeutic natural compound auraptene (AUR) enhances junction assembly in cerebrovascular endothelial cells by inducing antioxidant enzymes and the mitochondrial unfolded protein response (mtUPR). Treatment of mouse cerebrovascular endothelial cells with AUR enhanced the expression of junctional proteins, such as occludin, zonula occludens-1 (ZO-1) and vascular endothelial cadherin (VE-cadherin), by increasing the levels of mRNA encoding antioxidant enzymes. AUR treatment also resulted in the depolarization of mitochondrial membrane potential and activation of mtUPR. The ability of AUR to protect against ischemic conditions was further assessed using cells deprived of oxygen and glucose. Pretreatment of these cells with AUR protected against damage to junctional proteins, including occludin, claudin-5, ZO-1 and VE-cadherin, accompanied by a stress resilience response regulated by levels of ATF5, LONP1 and HSP60 mRNAs. Collectively, these results indicate that AUR promotes resilience against oxidative stress and improves junction assembly, suggesting that AUR may help maintain intact barriers in cerebrovascular endothelial cells.

Modeling of Hypoxic Brain Injury through 3D Human Neural Organoids

Brain organoids have emerged as a novel model system for neural development, neurodegenerative diseases, and human-based drug screening. However, the heterogeneous nature and immature neuronal development of brain organoids generated from pluripotent stem cells pose challenges. Moreover, there are no previous reports of a three-dimensional (3D) hypoxic brain injury model generated from neural stem cells. Here, we generated self-organized 3D human neural organoids from adult dermal fibroblast-derived neural stem cells. Radial glial cells in these human neural organoids exhibited characteristics of the human cerebral cortex trend, including an inner (ventricular zone) and an outer layer (early and late cortical plate zones). These data suggest that neural organoids reflect the distinctive radial organization of the human cerebral cortex and allow for the study of neuronal proliferation and maturation. To utilize this 3D model, we subjected our neural organoids to hypoxic injury. We investigated neuronal damage and regeneration after hypoxic injury and reoxygenation. Interestingly, after hypoxic injury, reoxygenation restored neuronal cell proliferation but not neuronal maturation. This study suggests that human neural organoids generated from neural stem cells provide new opportunities for the development of drug screening platforms and personalized modeling of neurodegenerative diseases, including hypoxic brain injury.

Physiopathology of ischemic stroke and its modulation using memantine: evidence from preclinical stroke

Ischemic stroke is the most common type of cerebrovascular disease and is caused by an interruption of blood flow in the brain. In this disease, two different damage areas are identifying: the lesion core, in which cells quickly die; and the penumbra (surrounding the lesion core), in which cells are functionally weakened but may recover and restore their functions. The currently approved treatments for ischemic stroke are the recombinant tissue plasminogen activator and endovascular thrombectomy, but they have a short therapeutic window (4.5 and 6 hours after stroke onset, respectively) and a low percentage of stroke patients actually receive these treatments. Memantine is an approved drug for the treatment of Alzheimer’s disease. Memantine is a noncompetitive, low affinity and use-dependent antagonist of N-methyl-D-aspartate glutamate receptor. Memantine has several advantages over developing a new drug to treat focal ischemic stroke, but the most important is that it has sufficient safe probes in preclinical models and humans, and if the preclinical studies provide more evidence about pharmacological actions in tissue protection and repair, this could help to increase the number of clinical trials. The present review summarizes the physiopathology of isquemic stroke and the pharmacological actions in neuroprotection and neuroplasticity of memantine in the post stroke stage of preclinical stroke models, to illustrate their potential to improve functional recovery in human patients.

In Vitro Oxygen-Glucose Deprivation-Induced Stroke Models with Human Neuroblastoma Cell- and Induced Pluripotent Stem Cell-Derived Neurons

Stroke is a devastating neurological disorder and one of the leading causes of mortality and disability. To understand the cellular and molecular mechanisms of stroke and to develop novel therapeutic approaches, two different in vitro human cell-based stroke models were established using oxygen-glucose deprivation (OGD) conditions. In addition, the effect of adipose stem cells (ASCs) on OGD-induced injury was studied. In the present study, SH-SY5Y human neuroblastoma cells and human induced pluripotent stem cells (hiPSCs) were differentiated into neurons, cultured under OGD conditions (1% O₂) for 24 h, and subjected to a reperfusion period for 24 or 72 h. After OGD, ASCs were cocultured with neurons on inserts for 24 or 72 h to study the neuroprotective potential of ASCs. The effect of OGD and ASC coculture on the viability, apoptosis, and proliferation of and axonal damage to neuronal cells was studied. The results showed that OGD conditions induced cytotoxicity and apoptosis of SH-SY5Y- and hiPSC-derived neurons, although more severe damage was detected in SH-SY5Y-derived neurons than in hiPSC-derived neurons. Coculture with ASCs was protective for neurons, as the number of dead ASC-cocultured neurons was lower than that of control cells, and coculture increased the proliferation of both cell types. To conclude, we developed in vitro human cell-based stroke models in SH-SY5Y- and hiPSC-derived neurons. This was the first time hiPSCs were used to model stroke in vitro. Since OGD had different effects on the studied cell types, this study highlights the importance of using several cell types in in vitro studies to confirm the outcomes of the study. Here, ASCs exerted a neuroprotective effect by increasing the proliferation and decreasing the death of SH-SY5Y- and hiPSC-derived neurons after OGD.

Hypoxia and extracellular vesicles: A review on methods, vesicular cargo and functions

Hypoxia is an essential hallmark of several serious diseases such as cardiovascular and metabolic disorders and cancer. A decline in the tissue oxygen level induces hypoxic responses in cells which strive to adapt to the changed conditions. A failure to adapt to prolonged or severe hypoxia can trigger cell death. While some cell types, such as neurons, are highly vulnerable to hypoxia, cancer cells take advantage of a hypoxic environment to undergo tumour growth, angiogenesis and metastasis. Hypoxia-induced processes trigger complex intercellular communication and there are now indications that extracellular vesicles (EVs) play a fundamental role in these processes. Recent developments in EV isolation and characterization methodology have increased the awareness of the importance of EV purity in functional and cargo studies. Cell death, a hallmark of severe hypoxia, is a known source of intracellular contaminants in isolated EVs. In this review, methodological aspects of studies investigating hypoxia-induced EVs are critically evaluated. Key concerns and gaps in the current knowledge are highlighted and future directions for studies are set. To accelerate and advance research, an in-depth analysis of the functions and cargo of hypoxic EVs, compared to normoxic EVs, is provided with the focus on the altered microRNA contents of the EVs.

Nanoparticle-microglial interaction in the ischemic brain is modulated by injury duration and treatment

Cerebral ischemia is a major cause of death in both neonates and adults, and currently has no cure. Nanotechnology represents one promising area of therapeutic development for cerebral ischemia due to the ability of nanoparticles to overcome biological barriers in the brain. ex vivo injury models have emerged as a high-throughput alternative that can recapitulate disease processes and enable nanoscale probing of the brain microenvironment. In this study, we used oxygen-glucose deprivation (OGD) to model ischemic injury and studied nanoparticle interaction with microglia, resident immune cells in the brain that are of increasing interest for therapeutic delivery. By measuring cell death and glutathione production, we evaluated the effect of OGD exposure time and treatment with azithromycin (AZ) on slice health. We found a robust injury response with 0.5 hr of OGD exposure and effective treatment after immediate application of AZ. We observed an OGD-induced shift in microglial morphology toward increased heterogeneity and circularity, and a decrease in microglial number, which was reversed after treatment. OGD enhanced diffusion of polystyrene-poly(ethylene glycol) (PS-PEG) nanoparticles, improving transport and ability to reach target cells. While microglial uptake of dendrimers or quantum dots (QDs) was not enhanced after injury, internalization of PS-PEG was significantly increased. For PS-PEG, AZ treatment restored microglial uptake to normal control levels. Our results suggest that different nanoparticle platforms should be carefully screened before application and upon doing so; disease-mediated changes in the brain microenvironment can be leveraged by nanoscale drug delivery devices for enhanced cell interaction.

Murine induced pluripotent stem cell-derived neuroimmune cell culture models emphasize opposite immune-effector functions of interleukin 13-primed microglia and macrophages in terms of neuroimmune toxicity

Cellular models of induced pluripotent stem cell (iPSC)-derived microglia and macrophages are an emerging toolbox to investigate neuroinflammation in vitro. We previously demonstrated that murine iPSC-microglia and iPSC-macrophages display phenotypical activation properties highly comparable to microglia and macrophages in vivo. Here we extended the characterization of iPSC-microglia and iPSC-macrophages with the analysis of their transcriptome profile. Next, these cellular models were employed to evaluate neuroimmune toxicity in vitro and to investigate the immune-modulatory properties of interleukin 13 (IL13), a cytokine known for its ability to protect against neuroinflammation-induced pathology by modulating microglia and macrophage activation. iPSC-microglia and iPSC-macrophages, in co-culture with astrocyte-committed neural stem cells (NSC), were (pre)treated with IL13 and stimulated with lipopolysaccharide (LPS) and interferon γ (IFNγ), to assess how IL13 modulates their inflammatory response. Additionally, the use of luciferase-expressing NSC (Luc-NSC) allowed real-time monitoring of immune-mediated neurotoxicity. Despite the known anti-inflammatory properties of IL13, iPSC-microglia primed with IL13 before LPS + IFNγ stimulation significantly increased NO secretion. This was associated with a marked reduction of the luminescence signal produced by Luc-NSC. Interestingly, we observed that IL13 signaling has a divergent functional outcome in microglia as compared to macrophages, as for the latter no major alterations in NO release and Luc-NSC viability were observed upon IL13 (pre)treatment. Finally, the striking IL13-induced upregulation of NO secretion by microglia under pro-inflammatory conditions was confirmed in vivo, where intracerebral delivery of IL13 increased inducible nitric oxide synthase mRNA expression. Concluding, we applied iPSC-derived neuroimmune cell culture models to identify distinct neuroimmune (toxicity) responses of microglia and macrophages to IL13-based immune modulation.