Post-stroke Neurogenesis Research Articles

Single-Cell Mapping of Brain Myeloid Cell Subsets Reveals Key Transcriptomic Changes Favoring Neuroplasticity after Ischemic Stroke.

Interactions between brain-resident and peripheral infiltrated immune cells are thought to contribute to neuroplasticity after cerebral ischemia. However, conventional bulk sequencing makes it challenging to depict this complex immune network. Using single-cell RNA sequencing, we mapped compositional and transcriptional features of peri-infarct immune cells. Microglia were the predominant cell type in the peri-infarct region, displaying a more diverse activation pattern than the typical pro- and anti-inflammatory state, with axon tract-associated microglia (ATMs) being associated with neuronal regeneration. Trajectory inference suggested that infiltrated monocyte-derived macrophages (MDMs) exhibited a gradual fate trajectory transition to activated MDMs. Inter-cellular crosstalk between MDMs and microglia orchestrated anti-inflammatory and repair-promoting microglia phenotypes and promoted post-stroke neurogenesis, with SOX2 and related Akt/CREB signaling as the underlying mechanisms. This description of the brain's immune landscape and its relationship with neurogenesis provides new insight into promoting neural repair by regulating neuroinflammatory responses.

The Role of Progranulin (PGRN) in the Pathogenesis of Ischemic Stroke.

Stroke is a life-threatening medical condition and is a leading cause of disability. Cerebral ischemia is characterized by a distinct inflammatory response starting with the production of various cytokines and other inflammation-related agents. Progranulin (PGRN), a multifunctional protein, is critical in diverse physiological reactions, such as cell proliferation, inflammation, wound healing, and nervous system development. A mature PGRN is anti-inflammatory, while granulin, its derivative, conversely induces pro-inflammatory cytokine expression. PGRN is significantly involved in the brain tissue and its damage, for example, improving mood and cognitive disorders caused by cerebral ischemia. It may also have protective effects against nerve and spinal cord injuries by inhibiting neuroinflammatory response and apoptosis or it may be related to the proliferation, accumulation, differentiation, and activation of microglia. PGRN is a neurotrophic factor in the central nervous system. It may increase post-stroke neurogenesis of the subventricular zone (SVZ), which is particularly important in improving long-term brain function following cerebral ischemia. The neurogenesis enhanced via PGRN in the ischemic brain SVZ may be attributed to the induction of PI3K/AKT and MAPK/ERK signaling routes. PGRN can also promote the proliferation of neural stem/progenitor cells through PI3K/AKT signaling pathway. PGRN increases hippocampal neurogenesis, reducing anxiety and impaired spatial learning post-cerebral ischemia. PGRN alleviates cerebral ischemia/reperfusion injury by reducing endoplasmic reticulum stress and suppressing the NF-κB signaling pathway. PGRN can be introduced as a potent neuroprotective agent capable of improving post-ischemia neuronal actions, mainly by reducing and elevating the inflammatory and anti-inflammatory cytokines. Expression, storage, cleavage, and function of progranulin (PGRN) in the pathogenesis of ischemic stroke.

Nattokinase Promotes Post-stroke Neurogenesis and Cognition Recovery via Increasing Circulating Irisin.

The therapeutic potential of treatments for post-stroke cognitive impairment (PSCI) is severely limited by the autonomic regeneration capacity of the adult brain. Nattokinase (NK), a serine protease from the traditional food natto, has many beneficial effects on the cardiovascular system by modulating the blood system. While the role of blood factors in neurogenesis and cognition is well-established, it remains unclear whether NK can serve as an anti-PSCI agent through these factors. Our study demonstrates that NK protects against acute ischemic stroke and impressively promotes neurogenesis in rat models by increasing peripheral blood irisin, leading to improved cognitive functions. Our findings demonstrate NK to be a promising candidate for treating PSCI, and we also highlight irisin as a novel target of NK, suggesting its potential role in the peripheral blood-to-brain axis.

Stroke and Neurogenesis: Bridging Clinical Observations to New Mechanistic Insights from Animal Models.

Stroke was the 2nd leading cause of death and a major cause of morbidity. Unfortunately, there are limited means to promote neurological recovery post-stroke, but research has unearthed potential targets for therapies to encourage post-stroke neurogenesis and neuroplasticity. The occurrence of neurogenesis in adult mammalian brains, including humans, was not widely accepted until the 1990s. Now, adult neurogenesis has been extensively studied in human and mouse neurogenic brain niches, of which the subventricular zone of the lateral ventricles and subgranular zone of the dentate gyrus are best studied. Numerous other niches are under investigation for neurogenic potential. This review offers a basic overview to stroke in the clinical setting, a focused summary of recent and foundational research literature on cortical neurogenesis and post-stroke brain plasticity, and insights regarding how the meninges and choroid plexus have emerged as key players in neurogenesis and neuroplasticity in the context of focal cerebral ischemia disrupting the anterior circulation. The choroid plexus and meninges are vital as they are integral sites for neuroimmune interactions, glymphatic perfusion, and niche signaling pertinent to neural stem cells and neurogenesis. Modulating neuroimmune interactions with a focus on astrocyte activity, potentially through manipulation of the choroid plexus and meningeal niches, may reduce the exacerbation of stroke by inflammatory mediators and create an environment conducive to neurorecovery. Furthermore, addressing impaired glymphatic perfusion after ischemic stroke likely supports a neurogenic environment by clearing out inflammatory mediators, neurotoxic metabolites, and other accumulated waste. The meninges and choroid plexus also contribute more directly to promoting neurogenesis: the meninges are thought to harbor neural stem cells and are a niche amenable to neural stem/progenitor cell migration. Additionally, the choroid plexus has secretory functions that directly influences stem cells through signaling mechanisms and growth factor actions. More research to better understand the functions of the meninges and choroid plexus may lead to novel approaches for stimulating neuronal recovery after ischemic stroke.

Sphingosine-1-phosphate receptor modulation improves neurogenesis and functional recovery after stroke.

Cerebral ischemia activates neural progenitors that participate in brain remodeling following acute injury. Sphingosine-1-phosphate receptor (S1PR) signaling governs cell proliferation and mobilization, yet its potential impact on neural progenitors and stroke recovery remains poorly understood. The goal of this study was to investigate the impact of S1PR modulation on post-stroke neurogenesis and functional recovery, using a S1PR modulator BAF312. Mice were subjected to 60 min middle cerebral artery occlusion (MCAO) and received BAF312 starting from day 3 after MCAO until the end of experiment. BAF312 facilitated motor function recovery in MCAO mice until day 14 after surgery. Flow cytometry analysis revealed that BAF312 treatment led to an increase of type A cells in subventricular zone (SVZ), but not other progenitor cell subsets in MCAO mice. We found an increase of BrdU incorporation in SVZ DCX+ cells from MCAO mice receiving BAF312 and augmented proliferation of DCX+ cells in cultured neurospheres isolated from SVZ tissues. Notably, a S1PR1 antagonist W146 abolished BAF312-induced increase of SVZ type A cells from MCAO mice and proliferation of DCX+ cells in cultured neurospheres. Additionally, the benefit of BAF312 to improve neurogenesis and stroke recovery remains in Rag2-/- mice lacking of T and B cells. Our results demonstrate that S1PR modulation improves neurogenesis and functional recovery following brain ischemia.

Long-Term Intranasal Nerve Growth Factor Treatment Favors Neuron Formation in de novo Brain Tissue.

ObjectiveTo date, no safe and effective pharmacological treatment has been clinically validated for improving post-stroke neurogenesis. Growth factors are good candidates but low safety has limited their application in the clinic. An additional restraint is the delivery route. Intranasal delivery presents many advantages.Materials and MethodsA brain lesion was induced in twenty-four rats. Nerve growth factor (NGF) 5 μg/kg/day or vehicle was given intranasally from day 10 post-lesion for two periods of five weeks, separated by a two-week wash out period with no treatment. Lesion volume and atrophy were identified by magnetic resonance imaging (MRI). Anxiety and sensorimotor recovery were measured by behavior tests. Neurogenesis, angiogenesis and inflammation were evaluated by histology at 12 weeks.ResultsRemarkable neurogenesis occurred and was visible at the second and third months after the insult. Tissue reconstruction was clearly detected by T2 weighted MRI at 8 and 12 weeks post-lesion and confirmed by histology. In the new tissue (8.1% of the lesion in the NGF group vs. 2.4%, in the control group at 12 weeks), NGF significantly increased the percentage of mature neurons (19% vs. 7%). Angiogenesis and inflammation were not different in the two groups. Sensorimotor recovery was neither improved nor hampered by NGF during the first period of treatment, but NGF treatment limited motor recovery in the second period.InterpretationThe first five-week period of treatment was very well tolerated. This study is the first presenting the effects of a long treatment with NGF and has shown an important tissue regeneration rate at 8 and 12 weeks post-injury. NGF may have increased neuronal differentiation and survival and favored neurogenesis and neuron survival through subventricular zone (SVZ) neurogenesis or reprogramming of reactive astrocytes. For the first time, we evidenced a MRI biomarker of neurogenesis and tissue reconstruction with T2 and diffusion weighted imaging.

The Role of Stem Cells in the Therapy of Stroke.

Stroke is a major challenge in neurology due to its multifactorial genesis and irreversible consequences. Processes of endogenous post-stroke neurogenesis, although insufficient, may indicate possible direction of future therapy. Multiple research considers stem-cell-based approaches in order to maximize neuroregeneration and minimize post-stroke deficits. Aim of this study is to review current literature considering post-stroke stem-cell- based therapy and possibilities of inducing neuroregeneration after brain vascular damage. Papers included in this article were obtained from PubMed and MEDLINE databases. The following medical subject headings (MeSH) were used: "stem cell therapy", "post-stroke neurogenesis", "stem-cells stroke", "stroke neurogenesis", "stroke stem cells", "stroke", "cell therapy", "neuroregeneration", "neurogenesis", "stem-cell human", "cell therapy in human". Ultimate inclusion was made after manual review of the obtained reference list. Attempts of stimulating neuroregeneration after stroke found in current literature include supporting endogenous neurogenesis, different routes of exogenous stem cells supplying and extracellular vesicles used as a method of particle transport. Although further research in this field is required, post stroke brain recovery supported by exogenous stem cells seems to be promising future therapy revolutionizing modern neurology.

Adult Neurogenesis and Stroke: A Tale of Two Neurogenic Niches.

In the aftermath of an acute stroke, numerous signaling cascades that reshape the brain both in the perilesional zone as well as in more distal regions are activated. Despite continuous improvement in the acute treatment of stroke and the sustained research efforts into the pathophysiology of stroke, we critically lag in our integrated understanding of the delayed and chronic responses to ischemic injury. As such, the beneficial or maladaptive effect of some stroke-induced cellular responses is unclear, restricting the advancement of therapeutic strategies to target long-term complications. A prominent delayed effect of stroke is the robust increase in adult neurogenesis, which raises hopes for a regenerative strategy to counter neurological deficits in stroke survivors. In the adult brain, two regions are known to generate new neurons from endogenous stem cells: the subventricular zone (SVZ) and the dentate subgranular zone (SGZ) of the hippocampus. While both niches respond with an increase in neurogenesis post-stroke, there are significant regional differences in the ensuing stages of survival, migration, and maturation, which may differently influence functional outcome. External interventions such as rehabilitative training add a further layer of complexity by independently modulating the process of adult neurogenesis. In this review we summarize the current knowledge regarding the effects of ischemic stroke on neurogenesis in the SVZ and in the SGZ, and the influence of exogenous stimuli such as motor activity or enriched environment (EE). In addition, we discuss the contribution of SVZ or SGZ post-stroke neurogenesis to sensory, motor and cognitive recovery.

Angiogenin in the Neurogenic Subventricular Zone After Stroke.

Ischemic stroke is a leading cause of death and disability worldwide with effective acute thrombolytic treatments. However, brain repair mechanisms related to spontaneous or rehabilitation-induced recovery are still under investigation, and little is known about the molecules involved. The present study examines the potential role of angiogenin (ANG), a known regulator of cell function and metabolism linked to neurological disorders, focusing in the neurogenic subventricular zone (SVZ). Angiogenin expression was examined in the mouse SVZ and in SVZ-derived neural stem cells (NSCs), which were exposed to exogenous ANG treatment during neurosphere formation as well as in other neuron-like cells (SH-SY5Y). Additionally, male C57Bl/6 mice underwent a distal permanent occlusion of the middle cerebral artery to study endogenous and exercise-induced expression of SVZ-ANG and neuroblast migration. Our results show that SVZ areas are rich in ANG, primarily expressed in DCX+ neuroblasts but not in nestin+NSCs. In vitro, treatment with ANG increased the number of SVZ-derived NSCs forming neurospheres but could not modify SH-SY5Y neurite differentiation. Finally, physical exercise rapidly increased the amount of endogenous ANG in the ipsilateral SVZ niche after ischemia, where DCX-migrating cells increased as part of the post-stroke neurogenesis process. Our findings position for the first time ANG in the SVZ during post-stroke recovery, which could be linked to neurogenesis.

Post-stroke Neurogenesis: Friend or Foe?

The substantial clinical burden and disability after stroke injury urges the need to explore therapeutic solutions. Recent compelling evidence supports that neurogenesis persists in the adult mammalian brain and is amenable to regulation in both physiological and pathological situations. Its ability to generate new neurons implies a potential to contribute to recovery after brain injury. However, post-stroke neurogenic response may have different functional consequences. On the one hand, the capacity of newborn neurons to replenish the damaged tissue may be limited. In addition, aberrant forms of neurogenesis have been identified in several insult settings. All these data suggest that adult neurogenesis is at a crossroads between the physiological and the pathological regulation of the neurological function in the injured central nervous system (CNS). Given the complexity of the CNS together with its interaction with the periphery, we ultimately lack in-depth understanding of the key cell types, cell–cell interactions, and molecular pathways involved in the neurogenic response after brain damage and their positive or otherwise deleterious impact. Here we will review the evidence on the stroke-induced neurogenic response and on its potential repercussions on functional outcome. First, we will briefly describe subventricular zone (SVZ) neurogenesis after stroke beside the main evidence supporting its positive role on functional restoration after stroke. Then, we will focus on hippocampal subgranular zone (SGZ) neurogenesis due to the relevance of hippocampus in cognitive functions; we will outline compelling evidence that supports that, after stroke, SGZ neurogenesis may adopt a maladaptive plasticity response further contributing to the development of post-stroke cognitive impairment and dementia. Finally, we will discuss the therapeutic potential of specific steps in the neurogenic cascade that might ameliorate brain malfunctioning and the development of post-stroke cognitive impairment in the chronic phase.

Epigenetic Mechanisms Underlying Adult Post Stroke Neurogenesis.

Stroke remains the leading cause of adult disability. Post-stroke neurogenesis contributes to functional recovery. As an intrinsic neurorestorative process, it is important to elucidate the molecular mechanism underlying stroke-induced neurogenesis and to develop therapies designed specifically to augment neurogenesis. Epigenetic mechanisms include DNA methylation, histone modification and its mediation by microRNAs and long-non-coding RNAs. In this review, we highlight how epigenetic factors including DNA methylation, histone modification, microRNAs and long-non-coding RNAs mediate stroke-induced neurogenesis including neural stem cell self-renewal and cell fate determination. We also summarize therapies targeting these mechanisms in the treatment of stroke.

Perlecan Domain-V Enhances Neurogenic Brain Repair After Stroke in Mice

The extracellular matrix fragment perlecan domain V is neuroprotective and functionally restorative following experimental stroke. As neurogenesis is an important component of chronic post-stroke repair, and previous studies have implicated perlecan in developmental neurogenesis, we hypothesized that domain V could have a broad therapeutic window by enhancing neurogenesis after stroke. We demonstrated that domain V is chronically increased in the brains of human stroke patients, suggesting that it is present during post-stroke neurogenic periods. Furthermore, perlecan deficient mice had significantly less neuroblast precursor cells after experimental stroke. Seven-day delayed domain V administration enhanced neurogenesis and restored peri-infarct excitatory synaptic drive to neocortical layer 2/3 pyramidal neurons after experimental stroke. Domain V’s effects were inhibited by blockade of α2β1 integrin, suggesting the importance of α2β1 integrin to neurogenesis and domain V neurogenic effects. Our results demonstrate that perlecan plays a previously unrecognized role in post-stroke neurogenesis and that delayed DV administration after experimental stroke enhances neurogenesis and improves recovery in an α2β1 integrin-mediated fashion. We conclude that domain V is a clinically relevant neuroprotective and neuroreparative novel stroke therapy with a broad therapeutic window.

Sleep-restriction Inhibits Neurogenesis Through Decreasing the Infiltration of CD169+ Macrophages to Ischemic Brain After Stroke

Chronic sleep-restriction (SR) is shown to be correlated with neurodevelopmental disorders. However, the effects of SR during stroke recovery on neurorepair remain unclear. In this study, mice were subjected to 60 min of cerebral ischemia followed by reperfusion. The SR protocol was accomplished by depriving mice of sleep for 20 h/day for 14 days starting at 14 days post-ischemia. We found that SR increased CD169+ macrophages infiltration into the ischemic brain parenchyma and inhibited neurogenesis and functional recovery. SR decreased CD169+ macrophages infiltration into the choroid plexus (CP) and cerebrospinal fluid (CSF), accompanied by increased expression of Chemokine C-X3-C-Motif Ligand 1 (CX3CL1) and intercellular adhesion molecule (ICAM-1) via IFN-γ/IFN-γR signaling in the CP. When splenic CD169+ macrophages sorted from Kaede transgenic mice were administered into CSF of C57BL/6 mice, they homed to the ischemic brain parenchyma. Moreover, blockade of IFN-γ/IFN-γR signaling, CX3CL1 or ICAM-1 decreased CD169+ macrophages infiltration into the CP, CSF and ischemic brain parenchyma, as well as decreasing neurogenesis and functional recovery after SR. The promoting roles of infiltrated CD169+ macrophages in post-stroke neurogenesis were due to increasing regulatory T cells (Tregs) in the ischemic brain parenchyma. Furthermore, dexmedetomidine treatment during SR increased CD169+ macrophages infiltration into the CP, CSF and ischemic brain parenchyma, and promoted neurogenesis and functional recovery. Taken together, our results showed that SR during stroke recovery decreased Tregs in the ischemic brain parenchyma by decreasing CD169+ macrophages infiltration to the ischemic brain parenchyma across the CP, which inhibited neurogenesis and functional recovery.

Abstract 110: RNA Sequencing Reveals Novel Macrophage Transcriptome Favoring Neurovascular Plasticity After Ischemic Stroke

Introduction: Blood monocytes/macrophages (MΦ) infiltrate the brain in massive numbers after ischemic stroke, but their functional roles in the post-stroke brain remain elusive. Methods: We sorted CD11b + CD45 high monocytes/MΦ from mouse blood and brain 5d after distal MCAO (dMCAO) and investigated their transcriptomic profiles by RNA-seq (n=3/group). Results: Robust genomic changes occurred in MΦ invading the post-dMCAO brain compared to their counterparts in the blood (3196 differentially expressed genes with >2 fold changes; FDR<0.05). In addition to their canonical role in immune responses, brain MΦ expressed unique transcriptomic programs which may favor post-stroke neurovascular repair. Functional enrichment analysis of brain MΦ transcriptome revealed significant overrepresentation (p<0.01) of 110 biological processes linked to neurovascular remodeling and plasticity (e.g., angiogenesis and axonal regeneration), suggesting a previously underappreciated role for MΦ in post-stroke brain repair. Upstream Regulator analysis predicted PPARγ as a master regulator (z-score=2.64, p<10 -15 ) that drives the transcriptional reprogramming in post-stroke brain MΦ and dictates their functional phenotype. Accordingly, tamoxifen-induced, myeloid cell-specific PPARγ knockout mice demonstrated less post-stroke angiogenesis (BrdU+CD31 staining) and neurogenesis (BrdU+NeuN) than WT mice (n=9/group, p<0.01), which correlated significantly with the exacerbation of neurological deficits in these mice (n=9/group, p<0.01 vs WT in foot fault and adhesive removal tests) at 35d after dMCAO. Conclusions: Our study reveals a novel repair-enhancing transcriptome in brain MΦ during post-stroke neurovascular remodeling. As a master molecule controlling genomic reprogramming, PPARγ is a rational therapeutic target for promoting beneficial MΦ functions, and facilitating neurorestoration and long term functional recovery after ischemic stroke.

Region-specific and activity-dependent regulation of SVZ neurogenesis and recovery after stroke

Stroke is the leading cause of adult disability. Neurogenesis after stroke is associated with repair; however, the mechanisms regulating poststroke neurogenesis and its functional effect remain unclear. Here, we investigate multiple mechanistic routes of induced neurogenesis in the poststroke brain, using both a forelimb overuse manipulation that models a clinical neurorehabilitation paradigm, as well as local manipulation of cellular activity in the peri-infarct cortex. Increased activity in the forelimb peri-infarct cortex via either modulation drives increased subventricular zone (SVZ) progenitor proliferation, migration, and neuronal maturation in peri-infarct cortex. This effect is sensitive to competition from neighboring brain regions. By using orthogonal tract tracing and rabies virus approaches in transgenic SVZ-lineage-tracing mice, SVZ-derived neurons synaptically integrate into the peri-infarct cortex; these effects are enhanced with forelimb overuse. Synaptic transmission from these newborn SVZ-derived neurons is critical for spontaneous recovery after stroke, as tetanus neurotoxin silencing specifically of the SVZ-derived neurons disrupts the formation of these synaptic connections and hinders functional recovery after stroke. SVZ-derived neurogenesis after stroke is activity-dependent, region-specific, and sensitive to modulation, and the synaptic connections formed by these newborn cells are functionally critical for poststroke recovery.

Hyperforin Promotes Post-stroke Neuroangiogenesis via Astrocytic IL-6-Mediated Negative Immune Regulation in the Ischemic Brain.

Hyperforin has been shown to be capable of promoting angiogenesis and functional recovery after ischemic stroke in our previous study. However, the exact mechanisms involved are not fully elucidated. In this study, adult male mice were subjected to 60-min transient middle cerebral artery occlusion followed by reperfusion for 28 days. Hyperforin was administrated to MCAO mice every 24 h for 2 weeks starting at 14 days post-ischemia (dpi). Then flow cytometry, quantitative Real-time PCR (RT-qPCR), western blotting, immunohistochemistry, and functional assays were performed to explore the molecular mechanisms in vivo and in vitro. Our data showed that hyperforin increased astrocytic interleukin (IL)-6 in the ischemic hemisphere via TLR4 at 28 dpi. The astrocytic IL-6 was essential to the promoting effects of hyperforin on the neural precursor cells proliferation, neuronal differentiation, angiogenesis, and functional recovery after stroke. Furthermore, hyperforin promoted the infiltration of regulatory T cells (Tregs) to the ischemic hemisphere and increased Tregs-derived cytokine IL-10 and transforming growth factor-β (TGF-β) in a manner that was dependent on astrocytic IL-6. Astrocytic IL-6 was critical to the role of hyperforin in promoting the infiltration of T-helper (Th) type 2 cells to the ischemic hemisphere and Th2-derived cytokine IL-4, relative to Th1 and Th1-derived cytokine interferon-γ (IFN-γ), which decreased during stroke recovery. After depletion of CD25+ Tregs, the promoting effects of hyperforin on post-stroke neurogenesis was attenuated. Moreover, blockade of IL-4 and TGF-β abrogated the promoting role of hyperforin in post-stroke neurogenesis, angiogenesis and functional recovery. Our results reveal a previously uncharacterized role of astrocytic IL-6-mediated negative immune regulation in the promoting effects of hyperforin on post-stroke neurovascular regeneration and functional recovery.

HDAC6 dysfunction contributes to impaired maturation of adult neurogenesis in vivo: vital role on functional recovery after ischemic stroke

BackgroundPromoting post-stroke neurogenesis has long been proposed to be a therapeutic strategy for the enhancement of functional recovery after cerebral ischemic stroke. Despite numerous approaches have been widely reported the proliferation or differentiation of the neurogenic population therapeutic strategies by targeting adult neurogenesis not yet to be successfully clarified in clinical settings. Here, we hypothesized that alterations in microenvironment of the ischemic brain might impede the functional maturation of adult newly generated neurons that limits functional recovery after stroke.MethodsThe in vivo retroviral based labeling model was applied to directly birth-date and trace the maturation process of adult newly generating neurons after hypoxic challenge. A rehabilitation therapy procedure was adopted through the combination of task-specific motor rehabilitating training with environmental enrichment to promote functional recovery after stroke. In addition, a pharmacological or genetic suppression of HDAC6 was performed to evaluate the functional significance of HDAC6 in the pathology of ischemic stroke induced deficits.ResultsSerial morphological analyses at multiple stages along the maturation process showed significant retardation of the dendritic maturation on the newly generated neurons after stroke. Subsequent biochemical analyses revealed an aberrant nuclear translocation of HDAC6 that leads to the hyper-acetylation of α-tubulin (an indication of over-stabilized microtubules) after hypoxic challenge was observed at different time points after stroke. Furthermore, the mimicry experiments with either pharmacological or genetic suppression of HDAC6, phenocopied the stroke induced retardation in dendritic maturation of newly generating neurons in vivo. More importantly, we provide direct evidence showing the proper function of HDAC6 is required for rehabilitation therapy induced therapeutic benefits after stroke.ConclusionTogether, our current study unravels that dysfunction of HDAC6 contributes to stroke induced deficits in neurogenesis and provides an innovative therapeutic strategy that targets HDAC6 for promoting functional recovery toward the patients with stroke in clinic.

Abolition of aberrant neurogenesis ameliorates cognitive impairment after stroke in mice

Poststroke cognitive impairment is considered one of the main complications during the chronic phase of ischemic stroke. In the adult brain, the hippocampus regulates both encoding and retrieval of new information through adult neurogenesis. Nevertheless, the lack of predictive models and studies based on the forgetting processes hinders the understanding of memory alterations after stroke. Our aim was to explore whether poststroke neurogenesis participates in the development of long-term memory impairment. Here, we show a hippocampal neurogenesis burst that persisted 1 month after stroke and that correlated with an impaired contextual and spatial memory performance. Furthermore, we demonstrate that the enhancement of hippocampal neurogenesis after stroke by physical activity or memantine treatment weakened existing memories. More importantly, stroke-induced newborn neurons promoted an aberrant hippocampal circuitry remodeling with differential features at ipsi- and contralesional levels. Strikingly, inhibition of stroke-induced hippocampal neurogenesis by temozolomide treatment or using a genetic approach (Nestin-CreERT2/NSE-DTA mice) impeded the forgetting of old memories. These results suggest that hippocampal neurogenesis modulation could be considered as a potential approach for treatment of poststroke cognitive impairment.

Enriched housing promotes post-stroke neurogenesis through calpain 1-STAT3/HIF-1α/VEGF signaling

Enriched environment (EE) has been shown to promote neurogenesis and functional recovery after ischemic stroke. However, the underlying molecular mechanisms are not fully understood. In this study, C57BL/6 mice underwent middle cerebral artery occlusion (60 min) followed by reperfusion, after which mice were housed in either standard environment (SE) or EE and allowed to survive for 3, 4, 6 or 10 weeks. Ipsilateral subventricular zone (SVZ) or striatum cells were dissociated from ischemic hemispheric brains of enriched mice at 14 days post-ischemia (dpi) and cultured in vitro. Our data showed that post-ischemic EE inhibited calpain 1 activity, and increased the expression of phosphorylated signal transducer and activator of transcription 3 (p-STAT3) in the ischemic hemisphere of enriched mice at 21 dpi. Calpain 1-specific inhibitor PD151746 further increased p-STAT3 expression and augmented the promoting effects of EE on post-stroke SVZ neural precursor cells (NPCs) proliferation and functional recovery. EE also increased the expression of hypoxia-inducible factor 1-alpha (HIF-1α) and vascular endothelial growth factor (VEGF) in the ischemic hemisphere at 21 dpi. Inhibition of the JAK/STAT3 pathway with AG490 decreased the expression of HIF-1α and VEGF. Furthermore, inhibition of HIF-1α with 2-methoxyestradiol robustly abolished EE-induced elevation of VEGF l expression. Furthermore, VEGF-A promoted the production and secretion of high mobility group box-1 protein (HMGB1) from reactive astrocytes in vitro. Culture supernatant from reactive astrocytes treated with VEGF-A promoted the proliferation and differentiation of NPCs. Glycyrrhizin reversed the promoting effects of EE on post-stroke neurorepair and functional recovery in vivo. Taken together, our data indicate that EE promotes post-stroke functional recovery through the inhibition of calpain 1 activity, and subsequent STAT3-HIF-1α-VEGF-mediated neurogenesis.

Enriched environment promotes post-stroke neurogenesis through NF-κB-mediated secretion of IL-17A from astrocytes

Enriched environment (EE) has been shown to promote post-stroke neurogenesis and functional recovery. However, the underlying molecular mechanisms remains poorly understood. Male C57BL/6 mice underwent 60-min middle cerebral artery occlusion (MCAO) followed by reperfusion, after which mice were housed in either standard environment (SE) or EE. We found that post-ischemic EE exhibited reduced protein level of nuclear factor κB (NF-κB)/p65 in cytoplasm and increased its expression correspondingly in nucleus at 28 days post-ischemia (dpi). However, post-ischemic EE had no effects on terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL)-positive cells in ischemic hemisphere at 28dpi. EE mice treated with NF-kB inhibitor Bay11-7082 had decreased subventricular zone (SVZ) neural precursor cells (NPCs) proliferation, neuronal differentiation and subsequent functional recovery after stroke at 28dpi. Bay11-7082 treatment attenuated the promoting effects of post-ischemic EE on interleukin 17A (IL-17A) messenger RNA (mRNA) and protein expression at 28dpi. Furthermore, our in vitro data revealed that in primary astrocyte cultures addition of Bay11-7082 markedly decreased the expression of IL-17A in both the cell lysate and culture supernatant of activated astrocytes. Blockade of IL-17A with neutralizing antibody abrogated the promoting role of EE in NPCs proliferation derived from SVZ, neuronal differentiation and subsequent functional recovery after stroke. Thus, our results reveal a previously uncharacterized property of NF-κB/IL-17A signaling pathway in EE-mediated neurogenesis and functional recovery after ischemic stroke.