Abolition of aberrant neurogenesis ameliorates cognitive impairment after stroke in mice

Exosomes as a therapeutic tool to promote neurorestoration and cognitive function in neurological conditions: Achieve two ends with a single effort

Exosomes possess a significant role in intercellular communications. In the nervous system, various neural cells release exosomes that not only own a role in intercellular communications but also eliminate the waste of cells, maintain the myelin sheath, facilitate neurogenesis, and specifically assist in normal cognitive function. In neurological conditions including Parkinson's disease (PD), Alzheimer's disease (AD), traumatic brain injury (TBI), and stroke, exosomal cargo like miRNAs take part in the sequela of conditions and serve as a diagnostic tool of neurological disorders, too. Exosomes are not only a diagnostic tool but also their inhibition or administration from various sources like mesenchymal stem cells and serum, which have shown a worthy potential to treat multiple neurological disorders. In addition to neurodegenerative manifestations, cognitive deficiencies are an integral part of neurological diseases, and applying exosomes in improving both aspects of these diseases has been promising. This review discusses the status of exosome therapy in improving neurorestorative and cognitive function following neurological disease.

The role of gut microbiota in cerebrovascular disease and related dementia

In recent years, increasing evidence suggests that commensal microbiota may play an important role not only in health but also in disease including cerebrovascular disease. Gut microbes impact physiology, at least in part, by metabolizing dietary factors and host-derived substrates and then generating active compounds including toxins. The purpose of this current review is to highlight the complex interplay between microbiota, their metabolites. and essential functions for human health, ranging from regulation of the metabolism and the immune system to modulation of brain development and function. We discuss the role of gut dysbiosis in cerebrovascular disease, specifically in acute and chronic stroke phases, and the possible implication of intestinal microbiota in post-stroke cognitive impairment and dementia, and we identify potential therapeutic opportunities of targeting microbiota in this context. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Periplaneta Americana (L.) extract activates the ERK/CREB/BDNF pathway to promote post-stroke neuroregeneration and recovery of neurological functions in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Periplaneta americana (L.) (PA) has been used in traditional Chinese medicine for thousands of years for the effect of invigorating blood circulation and removing blood stasis. Modern pharmacological research shown that PA extract exhibits promising effects in promoting wound healing and regeneration, as well as in brain diseases such as Parkinson's disease (PD). However, whether it is effective for neuroregeneration and neurological function recovery after stroke still unknown.

AIM OF THE STUDY

This study aims to investigate the potential effect of PA extract to promote brain remodeling through the activation of endogenous neurogenesis and angiogenesis, in addition, preliminary exploration of its regulatory mechanism.

METHODS

Firstly, BrdU proliferation assay and immunofluorescence (IF) staining were used to evaluate the effect of PA extract on the neurogenesis and angiogenesis in vitro and in vivo. Subsequently, the effects of PA extract on brain injury in stroke rats were assessed by TTC and HE. While mNSS score, adhesive removal test, rota-rod test, and morris water maze test were used to assess the impact of PA extract on neurological function in post-stroke rats. Finally, the molecular mechanisms of PA extract regulation were explored by RNA-Seq and western blotting.

RESULTS

The number of BrdU+ cells in C17.2 cells, NSCs and BMECs dramatically increased, as well as the expression of astrocyte marker protein GFAP and neuronal marker protein Tuj-1 in C17.2 and NSCs. Moreover, PA extract also increased the number of BrdU+DCX+, BrdU+GFAP+, BrdU+CD31+ cells in the SGZ area of transient middle cerebral artery occlusion model (tMCAO) rats. TTC and HE staining revealed that PA extract significantly reduced the infarction volume and ameliorated the pathological damage. Behavioral tests demonstrated that treatment with PA extract reduced the mNSS score and the time required to remove adhesive tape, while increasing the time spent on the rotarod. Additionally, in the morris water maze test, the frequency of crossing platform and the time spent in the platform quadrant increased. Finally, RNA-Seq and Western blot revealed that PA extract increased the expression of p-ERK, p-CREB and BDNF. Importantly, PA extract mediated proliferation and differentiation of C17.2 and NSCs reversed by the ERK inhibitor SCH772984 and the BDNF inhibitor ANA-12, respectively.

CONCLUSION

Our study demonstrated that PA extract promoted neurogenesis and angiogenesis by activating the CREB/ERK signaling pathway and upregulating BDNF expression, thereby recovering neurological dysfunction in post-stroke.

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.

Absence in CX3CR1 receptor signaling promotes post-ischemic stroke cognitive function recovery through suppressed microglial pyroptosis in mice

BACKGROUND

Post-stroke cognitive impairment (PSCI) is a major source of morbidity and mortality after stroke, but the pathological mechanisms remain unclear. Previous studies have demonstrated that the CX3CR1 receptor plays a crucial role in maintaining an early protective microenvironment after stroke, but whether it persistently influences cognitive dysfunction in the chronic phase requires further investigation.

METHODS

Mouse was used to establish a middle cerebral artery occlusion (MCAO)/reperfusion model to study PSCI. Cognitive function was assessed by the Morris water maze (MWM) and the novel object recognition test. Neurogenesis was assessed by immunofluorescence staining with Nestin+ /Ki67+ and DCX+ /BrdU+ double-positive cells. The cerebral damage was monitored by [18 F]-DPA-714 positron emission tomography, Nissel, and TTC staining. The pyroptosis was histologically, biochemically, and electron microscopically examined.

RESULTS

Upon MCAO, at 28 to 35 days, CX3CR1 knockout (CX3CR1-/- ) mice had better cognitive behavioral performance both in MWM and novel object recognition test than their CX3CR1+/- counterparts. Upon MCAO, at 7 days, CX3CR1-/- mice increased the numbers of Nestin+ /Ki67+ and DCX+ /BrdU+ cells, and meanwhile it decreased the protein expression of GSDMD, NLRP3 inflammasome subunit, caspase-1, mature IL-1β/IL-18, and p-P65 in the hippocampus as compared with CX3CR1+/- mice. In addition, CX3CR1-/- mice could reverse infarct volume in the hippocampus region post-stroke.

CONCLUSION

Our study demonstrated that CX3CR1 gene deletion was beneficial to PSCI recovery. The mechanism might lie in inhibited pyroptosis and enhanced neurogenesis. CX3CR1 receptor may serve as a therapeutic target for improving the PSCI.

Stroke and Vascular Cognitive Impairment: The Role of Intestinal Microbiota Metabolite TMAO

The gut microbiome interacts with the brain bidirectionally through the microbiome-gutbrain axis, which plays a key role in regulating various nervous system pathophysiological processes. Trimethylamine N-oxide (TMAO) is produced by choline metabolism through intestinal microorganisms, which can cross the blood-brain barrier to act on the central nervous system. Previous studies have shown that elevated plasma TMAO concentrations increase the risk of major adverse cardiovascular events, but there are few studies on TMAO in cerebrovascular disease and vascular cognitive impairment. This review summarized a decade of research on the impact of TMAO on stroke and related cognitive impairment, with particular attention to the effects on vascular cognitive disorders. We demonstrated that TMAO has a marked impact on the occurrence, development, and prognosis of stroke by regulating cholesterol metabolism, foam cell formation, platelet hyperresponsiveness and thrombosis, and promoting inflammation and oxidative stress. TMAO can also influence the cognitive impairment caused by Alzheimer's disease and Parkinson's disease via inducing abnormal aggregation of key proteins, affecting inflammation and thrombosis. However, although clinical studies have confirmed the association between the microbiome-gut-brain axis and vascular cognitive impairment (cerebral small vessel disease and post-stroke cognitive impairment), the molecular mechanism of TMAO has not been clarified, and TMAO precursors seem to play the opposite role in the process of poststroke cognitive impairment. In addition, several studies have also reported the possible neuroprotective effects of TMAO. Existing therapies for these diseases targeted to regulate intestinal flora and its metabolites have shown good efficacy. TMAO is probably a new target for early prediction and treatment of stroke and vascular cognitive impairment.

Drivers of Chronic Pathology Following Ischemic Stroke: A Descriptive Review

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

Bioinformatics analysis identifies the protective targets of omentin in mice with focal cerebral ischemia injury

Omentin is known to play a protective role in ischemic stroke. However, its regulatory networks and downstream targets in the pathogenesis of IS are incompletely revealed now. In this study, the model of photochemical brain ischemia was constructed after omentin over-expression. 8 key differentially expressed genes (DEGs) were obtained and analyzed by transcriptome analysis. These DEGs were mainly related to the negative regulation of hormone secretion, cellular phosphate ion homeostasis, and other pathways. Moreover, the mRNA expression of predicted gene 3435 (Gm3435), ankyrin repeat domain 53 (Ankrd53), fibroblast growth factor 23 (Fgf23) and the Fgf23 protein expression were down-regulated after omentin over-expression in HT22 cells injured by oxygen-glucose deprivation (OGD). In conclusion, our findings identified 8 key DEGs regulated by omentin after IS. In vitro models, the Gm3435, Ankrd53, Fgf23 mRNA expression and the Fgf23 protein expression were further verified to consistent with the transcriptomics results.

Targeting BACE1-mediated production of amyloid beta improves hippocampal synaptic function in an experimental model of ischemic stroke

Post-stroke cognitive impairment and dementia (PSCID) affects many survivors of large vessel cerebral ischemia. The molecular pathways underlying PSCID are poorly defined but may overlap with neurodegenerative pathophysiology. Specifically, synaptic dysfunction after stroke may be directly mediated by alterations in the levels of amyloid beta (Aβ), the peptide that accumulates in the brains of Alzheimer's disease (AD) patients. In this study, we use the transient middle cerebral artery occlusion (MCAo) model in young adult mice to evaluate if a large vessel stroke increases brain soluble Aβ levels. We show that soluble Aβ40 and Aβ42 levels are increased in the ipsilateral hippocampus in MCAo mice 7 days after the injury. We also analyze the level and activity of β-site amyloid precursor protein cleaving enzyme 1 (BACE1), an enzyme that generates Aβ in the brain, and observe that BACE1 activity is increased in the ipsilateral hippocampus of the MCAo mice. Finally, we highlight that treatment of MCAo mice with a BACE1 inhibitor during the recovery period rescues stroke-induced deficits in hippocampal synaptic plasticity. These findings support a molecular pathway linking ischemia to alterations in BACE1-mediated production of Aβ, and encourage future studies that evaluate whether targeting BACE1 activity improves the cognitive deficits seen with PSCID.

Possible involvement of inflammasomes on the post-stroke cognitive impairment in a mouse model of embolic cerebral infarct

Post-stroke cognitive impairment (PSCI) of the complications after stroke has been shown to be involved in brain proinflammatory cytokines such as interleukin (IL)-1β (IL-lβ) and IL-18. In the present study, we examined using acetic acid-induced embolic cerebral infarct (ECI) mice whether post-stroke inflammasome activation is involved in the development of PSCI. In behavioral tests, long-term learning and memory assessed using the passive avoidance test were impaired after ECI. On the other hand, the impairment of short-term learning and memory assessed using the Y-maze test was not observed. Furthermore, the phosphorylated α-amino-3hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit glutamate receptor 1 (GluR1) at Ser 831 and Ser 845 protein was found to be significantly decreased in the dorsal hippocampus of ECI mice. In addition, the expression levels of ionized calcium-binding adapter protein 1 (Iba1), glial fibrillary acidic protein (GFAP), apoptosis-associated speck-like protein containing a caspase recruitment domain / target of methylation-induced silencing 1 (ASC/TMS1), Caspase-1, IL-1β, IL-18 and tumor necrosis factor-α (TNF-α) were significantly increased in the dorsal hippocampus of ECI mice. These results indicate that development of PSCI after embolic cerebral infarction is due to a decrease in AMPA receptor subunit GluR1 at Ser831 and Ser845 through the inflammasome activation pathway in the dorsal hippocampus.

Ipsilesional Hippocampal GABA Is Elevated and Correlates With Cognitive Impairment and Maladaptive Neurogenesis After Cortical Stroke in Mice

BACKGROUND

Cognitive dysfunction is a frequent stroke sequela, but its pathogenesis and treatment remain unresolved. Involvement of aberrant hippocampal neurogenesis and maladaptive circuitry remodeling has been proposed, but their mechanisms are unknown. Our aim was to evaluate potential underlying molecular/cellular events implicated.

METHODS

Stroke was induced by permanent occlusion of the middle cerebral artery occlusion in 2-month-old C57BL/6 male mice. Hippocampal metabolites/neurotransmitters were analyzed longitudinally by in vivo magnetic resonance spectroscopy. Cognitive function was evaluated with the contextual fear conditioning test. Microglia, astrocytes, neuroblasts, interneurons, γ-aminobutyric acid (GABA), and c-fos were analyzed by immunofluorescence.

RESULTS

Approximately 50% of mice exhibited progressive post-middle cerebral artery occlusion cognitive impairment. Notably, immature hippocampal neurons in the impaired group displayed more severe aberrant phenotypes than those from the nonimpaired group. Using magnetic resonance spectroscopy, significant bilateral changes in hippocampal metabolites, such as myo-inositol or N-acetylaspartic acid, were found that correlated, respectively, with numbers of glia and immature neuroblasts in the ischemic group. Importantly, some metabolites were specifically altered in the ipsilateral hippocampus suggesting its involvement in aberrant hippocampal neurogenesis and remodeling processes. Specifically, middle cerebral artery occlusion animals with higher hippocampal GABA levels displayed worse cognitive outcome. Implication of GABA in this setting was supported by the amelioration of ischemia-induced memory deficits and aberrant hippocampal neurogenesis after blocking pharmacologically GABAergic neurotransmission, an intervention which was ineffective when neurogenesis was inhibited. These data suggest that GABA exerts its detrimental effect, at least partly, by affecting morphology and integration of newborn neurons into the hippocampal circuits.

CONCLUSIONS

Hippocampal GABAergic neurotransmission could be considered a novel diagnostic and therapeutic target for poststroke cognitive impairment.

Defective hippocampal neurogenesis underlies cognitive impairment by carotid stenosis-induced cerebral hypoperfusion in mice

Chronic cerebral hypoperfusion due to carotid artery stenosis is a major cause of vascular cognitive impairment and dementia (VCID). Bilateral carotid artery stenosis (BCAS) in rodents is a well-established model of VCID where most studies have focused on white matter pathology and subsequent cognitive deficit. Therefore, our aim was to study the implication of adult hippocampal neurogenesis in hypoperfusion-induced VCID in mice, and its relationship with cognitive hippocampal deficits. Mice were subjected to BCAS; 1 and 3 months later, hippocampal memory and neurogenesis/cell death were assessed, respectively, by the novel object location (NOL) and spontaneous alternation performance (SAP) tests and by immunohistology. Hypoperfusion was assessed by arterial spin labeling-magnetic resonance imaging (ASL-MRI). Hypoperfused mice displayed spatial memory deficits with decreased NOL recognition index. Along with the cognitive deficit, a reduced number of newborn neurons and their aberrant morphology indicated a remarkable impairment of the hippocampal neurogenesis. Both increased cell death in the subgranular zone (SGZ) and reduced neuroblast proliferation rate may account for newborn neurons number reduction. Our data demonstrate quantitative and qualitative impairment of adult hippocampal neurogenesis disturbances associated with cerebral hypoperfusion-cognitive deficits in mice. These findings pave the way for novel diagnostic and therapeutic targets for VCID.

Assessments of dentate gyrus function: discoveries and debates

There has been considerable speculation regarding the function of the dentate gyrus (DG) - a subregion of the mammalian hippocampus - in learning and memory. In this Perspective article, we compare leading theories of DG function. We note that these theories all critically rely on the generation of distinct patterns of activity in the region to signal differences between experiences and to reduce interference between memories. However, these theories are divided by the roles they attribute to the DG during learning and recall and by the contributions they ascribe to specific inputs or cell types within the DG. These differences influence the information that the DG is thought to impart to downstream structures. We work towards a holistic view of the role of DG in learning and memory by first developing three critical questions to foster a dialogue between the leading theories. We then evaluate the extent to which previous studies address our questions, highlight remaining areas of conflict, and suggest future experiments to bridge these theories.

Fluoxetine Can Cause Epileptogenesis and Aberrant Neurogenesis in Male Wild-Type Mice

Antidepressants in general, and fluoxetine in particular, increase adult hippocampal neurogenesis (AHN) in mice. Here we asked how the antidepressant fluoxetine affects behavior and AHN in a corticosterone model of depression. In three groups of adult male C57BL/6j mice, we administered either vehicle (VEH), corticosterone (CORT) treatment to induce a depression-like state, or corticosterone plus a standard dose of fluoxetine (CORT+FLX). Following treatment, mice performed the open field test, the novelty suppressed feeding (NSF) test, and the splash test. Neurogenesis was assessed by means of immunohistochemistry using BrdU and neuronal maturation markers. Unexpectedly, 42% of the CORT+FLX-treated mice exhibited severe weight loss, seizures, and sudden death. As expected, the CORT-treated group had altered behaviors compared to the VEH group, but the CORT+FLX mice that survived did not show any behavioral improvement compared to the CORT group. Antidepressants generally increase neurogenesis and here we also found that compared to CORT mice, CORT+FLX mice that survived had a significantly greater density of BrdU+, BrdU+DCX+, and BrdU+NeuN+ cells, suggesting increased neurogenesis. Moreover, the density of BrdU+NeuN+ cells was increased in an aberrant location, the hilus, of CORT+FLX mice, similar to previous studies describing aberrant neurogenesis following seizures. In conclusion, fluoxetine could induce considerable adverse effects in wild-type mice, including seizure-like activity. Fluoxetine-induced neurogenesis increases could be related to this activity; therefore, proneurogenic effects of fluoxetine and other antidepressants, especially in the absence of any behavioral therapeutic effects, should be interpreted with caution.

Brain-Derived Estrogen Regulates Neurogenesis, Learning and Memory with Aging in Female Rats

Although 17β-estradiol (E2) can be locally synthesized in the brain, whether and how brain-derived E2 (BDE2) impacts neurogenesis with aging is largely unclear. In this study, we examined the hippocampal neural stem cells, neurogenesis, and gliogenesis of 1, 3, 6, 14, and 18-month (Mon) female rats. Female forebrain neuronal aromatase knockout (FBN-ARO-KO) rats and letrozole-treated rats were also employed. We demonstraed that (1) the number of neural stem cells declined over 14-Mon age, and the differentiation of astrocytes and microglia markedly elevated and exhibited excessive activation. KO rats showed declines in astrocyte A2 subtype and elevation in A1 subtype at 18 Mon; (2) neurogenesis sharply dropped from 1-Mon age; (3) KO suppressed dentate gyrus (DG) neurogenesis at 1, 6 and 18 Mon. Additionally, KO and letrozole treatment led to declined neurogenesis at 1-Mon age, compared to age-matched WT controls; (4) FBN-ARO-KO inhibited CREB-BDNF activation, and decreased protein levels of neurofilament, spinophilin and PSD95. Notably, hippocampal-dependent spatial learning and memory was impaired in juvenile (1 Mon) and adulthood (6 Mon) KO rats. Taken together, we demonstrated that BDE2 plays a pivotal role for hippocampal neurogenesis, as well as learning and memory during female aging, especially in juvenile and middle age.

Neural Circuit Changes in Neurological Disorders: Evidence from in vivo Two-photon Imaging

Neural circuits, such as synaptic plasticity and neural activity, are critical components of healthy brain function. The consequent dynamic remodeling of neural circuits is an ongoing procedure affecting neuronal activities. Disruption of this essential process results in diseases. Advanced microscopic applications such as two-photon laser scanning microscopy have recently been applied to understand neural circuit changes during disease since it can visualize fine structural and functional cellular activation in living animals. In this review, we have summarized the latest work assessing the dynamic rewiring of postsynaptic dendritic spines and modulation of calcium transients in neurons of the intact living brain, focusing on their potential roles in neurological disorders (e.g. Alzheimer's disease, stroke, and epilepsy). Understanding the fine changes that occurred in the brain during disease is crucial for future clinical intervention developments.

Migratory Response of Cells in Neurogenic Niches to Neuronal Death: The Onset of Harmonic Repair?

Harmonic mechanisms orchestrate neurogenesis in the healthy brain within specific neurogenic niches, which generate neurons from neural stem cells as a homeostatic mechanism. These newly generated neurons integrate into existing neuronal circuits to participate in different brain tasks. Despite the mechanisms that protect the mammalian brain, this organ is susceptible to many different types of damage that result in the loss of neuronal tissue and therefore in alterations in the functionality of the affected regions. Nevertheless, the mammalian brain has developed mechanisms to respond to these injuries, potentiating its capacity to generate new neurons from neural stem cells and altering the homeostatic processes that occur in neurogenic niches. These alterations may lead to the generation of new neurons within the damaged brain regions. Notwithstanding, the activation of these repair mechanisms, regeneration of neuronal tissue within brain injuries does not naturally occur. In this review, we discuss how the different neurogenic niches respond to different types of brain injuries, focusing on the capacity of the progenitors generated in these niches to migrate to the injured regions and activate repair mechanisms. We conclude that the search for pharmacological drugs that stimulate the migration of newly generated neurons to brain injuries may result in the development of therapies to repair the damaged brain tissue.

Neuroprotection of NAD+ and NBP against ischemia/reperfusion brain injury is associated with restoration of sirtuin-regulated metabolic homeostasis

Background: Ischemic stroke seriously threatens human health because of high rates of morbidity, mortality and disability. This study compared the effects of nicotinamide adenine dinucleotide (NAD+) and butylphthalide (NBP) on in vitro and in vivo ischemic stroke models.

Methods: Transient middle cerebral artery occlusion/reperfusion (t-MCAO/R) model was established in mice, and the cultured primary cortical neurons were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R). Cerebral infarct volume, neurobehavioral indices, antioxidant activity, ATP level and lactic acid content were determined. The neuroprotective effects of NAD+ or NBP were compared using sirtuin inhibitor niacinamide (NAM).

Results: Intraperitoneal injection of NBP within 4 h or intravenous injection of NAD+ within 1 h after t-MCAO/R significantly reduced the volume of infarcts, cerebral edema, and neurological deficits. Administration of NAD+ and NBP immediately after t-MCAO/R in mice showed similar neuroprotection against acute and long-term ischemic injury. Both NAD+ and NBP significantly inhibited the accumulation of MDA and H2O2 and reduced oxidative stress. NAD+ was superior to NBP in inhibiting lipid oxidation and DNA damage. Furthermore, although both NAD+ and NBP improved the morphology of mitochondrial damage induced by ischemia/reperfusion, NAD+ more effectively reversed the decrease of ATP and increase of lactic acid after ischemia/reperfusion compared with NBP. NAD+ but not NBP treatment significantly upregulated SIRT3 in the brain, but the sirtuin inhibitor NAM could abolish the protective effect of NAD+ and NBP by inhibiting SIRT1 or SIRT3.

Conclusions: These results confirmed the protective effects of NAD+ and NBP on cerebral ischemic injury. NBP and NAD+ showed similar antioxidant effects, while NAD+ had better ability in restoring energy metabolism, possibly through upregulating the activity of SIRT1 and SIRT3. The protection provided by NBP against cerebral ischemia/reperfusion may be achieved through SIRT1.

Post-Stroke Environmental Enrichment Improves Neurogenesis and Cognitive Function and Reduces the Generation of Aberrant Neurons in the Mouse Hippocampus

Ischemic lesions stimulate adult neurogenesis in the dentate gyrus, however, this is not associated with better cognitive function. Furthermore, increased neurogenesis is associated with the formation of aberrant neurons. In a previous study, we showed that a running task after a stroke not only increases neurogenesis but also the number of aberrant neurons without improving general performance. Here, we determined whether stimulation in an enriched environment after a lesion could increase neurogenesis and cognitive function without enhancing the number of aberrant neurons. After an ischemic stroke induced by MCAO, animals were transferred to an enriched environment containing a running wheel, tunnels and nest materials. A GFP-retroviral vector was delivered on day 3 post-stroke and a modified water maze test was performed 6 weeks after the lesion. We found that the enriched environment significantly increased the number of new neurons compared with the unstimulated stroke group but not the number of aberrant cells after a lesion. Increased neurogenesis after environmental enrichment was associated with improved cognitive function. Our study showed that early placement in an enriched environment after a stroke lesion markedly increased neurogenesis and flexible learning but not the formation of aberrant neurons, indicating that rehabilitative training, as a combination of running wheel training and enriched environment housing, improved functional and structural outcomes after a stroke.

Blockade of D-serine signaling and adult hippocampal neurogenesis attenuates remote contextual fear memory following multiple memory retrievals in male mice

The retrieval of fear memories induces two opposing processes, reconsolidation, and extinction. The memory reconsolidation is an active process that involves gene expression and updates an existing memory. It is hypothesized that blockade of reconsolidation by manipulating the neurobiological factors, which are mechanistically involved in the process, could weaken or disrupt the original fear memory. The N-methyl-D-aspartate (NMDA) receptor and hippocampal neurogenesis play crucial roles in hippocampus-dependent memory processes, including reconsolidation. Using contextual fear conditioning paradigm with multiple retrievals, we attempted to weaken the original contextual fear memory by repeatedly disrupting retrieval-induced reconsolidation via downregulation of NMDA receptor signaling and inhibition of neurogenesis. In the first experiment, prior to fear conditioning, NMDA receptor signaling was downregulated by the genetic reduction of its co-agonist, D-serine, and the neurogenesis was dampened by focal X-ray irradiation on the hippocampus. We found that simultaneous D-serine reduction and neurogenesis dampening resulted in a progressive decrease in freezing following each retrieval, leading to an attenuation of remote contextual fear memory on day 28. In the second experiment using the same behavioral protocols, after conditioning, pharmacological approaches were conducted to simultaneously block D-serine signaling and neurogenesis, resulting in a similar suppressive effect on the remote fear memory. The present findings provide insights for understanding the role of D-serine-mediated NMDA receptor signaling and neurogenesis in memory retrieval and the maintenance of remote fear memory, and improving the efficacy of exposure-based therapy for the treatment of post-traumatic stress disorder (PTSD).

Forsythoside B ameliorates diabetic cognitive dysfunction by inhibiting hippocampal neuroinflammation and reducing synaptic dysfunction in ovariectomized mice

BACKGROUND

Diabetes-associated cognitive impairment (DACI) is a common complication of diabetes, and studies have shown that DACI is more severe in postmenopausal patients with diabetes. Forsythoside B (FTS⋅B) can inhibit inflammation and reduce synaptic dysfunction, which can improve cognitive function. However, it has not been confirmed whether FTS⋅B has a reversing or retarding effect on postmenopausal diabetic encephalopathy.

METHODS

Seven days after bilateral ovariectomy (OVX) or sham surgery, adult female C57 mice (n = 15/group) received intraperitoneal injection of streptozotocin (60 mg/kg/day/L) and citrate buffer for 5 consecutive days to induce diabetes mellitus (DM). Fourteen days later, ovariectomized diabetic mice were given intraperitoneal injection of FTS⋅B (100, 150 mg/kg/day/L) and subcutaneous injection of 17β-estradiol (1 mg/kg) for 8 weeks [OVX + DM + low-FTS⋅B group (L-F), OVX + DM + high-FTS⋅B group (H-F), and OVX + DM + 17β-estradiol (ER)]. In addition, the following control groups were defined: Sham, OVX, DM, and OVX + DM (O + D). Fasting plasma glucose, body weight and blood insulin levels were determined in each group of mice. Next, their cognitive function was tested through behavioral experiments. Hematoxylin & eosin (H&E) and Nissl staining were used to detect the morphological changes in the hippocampus. The aggregation of amyloid beta (Aβ) and the hyperaggregation of p-tau were assessed by immunohistochemistry. Interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), brain-derived neurotrophic factor (BDNF), post-synaptic density-95 (PSD-95), synaptophysin, and synapsin-1 expression in the hippocampus was detected by real-time polymerase chain reaction (RT-PCR) and western blot analysis.

RESULTS

FTS⋅B can decrease fasting glucose and blood insulin level. Behavioral results showed that cognitive decline was the most severe in the O + D group, and the ER, L-F, and H-F groups revised the cognitive decline. Compared to the O + D group, more normal morphology, which has obvious nucleoli and clear nuclear membrane, was observed by H&E and Nissl staining in the ER, L-F, and H-F groups. FTS⋅B alleviated DACI by reducing the aggregation of Aβ and the hyperaggregation of p-tau in the hippocampus. Moreover, the protein and mRNA expression showed that FTS⋅B not only inhibited inflammation by decreasing IL-1β, IL-6, and TNF-α but also modulated synaptic plasticity by increasing BDNF, PSD-95, synaptophysin, and synapsin-1.

CONCLUSION

These results suggest that FTS⋅B may be a novel therapeutic target for postmenopausal diabetic encephalopathy treatment.

Pathological Nuclear Hallmarks in Dentate Granule Cells of Alzheimer’s Patients: A Biphasic Regulation of Neurogenesis

The dentate gyrus (DG) of the human hippocampus is a complex and dynamic structure harboring mature and immature granular neurons in diverse proliferative states. While most mammals show persistent neurogenesis through adulthood, human neurogenesis is still under debate. We found nuclear alterations in granular cells in autopsied human brains, detected by immunohistochemistry. These alterations differ from those reported in pyramidal neurons of the hippocampal circuit. Aging and early AD chromatin were clearly differentiated by the increased epigenetic markers H3K9me3 (heterochromatin suppressive mark) and H3K4me3 (transcriptional euchromatin mark). At early AD stages, lamin B2 was redistributed to the nucleoplasm, indicating cell-cycle reactivation, probably induced by hippocampal nuclear pathology. At intermediate and late AD stages, higher lamin B2 immunopositivity in the perinucleus suggests fewer immature neurons, less neurogenesis, and fewer adaptation resources to environmental factors. In addition, senile samples showed increased nuclear Tau interacting with aged chromatin, likely favoring DNA repair and maintaining genomic stability. However, at late AD stages, the progressive disappearance of phosphorylated Tau forms in the nucleus, increased chromatin disorganization, and increased nuclear autophagy support a model of biphasic neurogenesis in AD. Therefore, designing therapies to alleviate the neuronal nuclear pathology might be the only pathway to a true rejuvenation of brain circuits.

Long-term administration of salvianolic acid A promotes endogenous neurogenesis in ischemic stroke rats through activating Wnt3a/GSK3β/β-catenin signaling pathway

Stroke is the major cause of death and disability worldwide. Most stroke patients who survive in the acute phase of ischemia display various extents of neurological deficits. In order to improve the prognosis of ischemic stroke, promoting endogenous neurogenesis has attracted great attention. Salvianolic acid A (SAA) has shown neuroprotective effects against ischemic diseases. In the present study, we investigated the neurogenesis effects of SAA in ischemic stroke rats, and explored the underlying mechanisms. An autologous thrombus stroke model was established by electrocoagulation. The rats were administered SAA (10 mg/kg, ig) or a positive drug edaravone (5 mg/kg, iv) once a day for 14 days. We showed that SAA administration significantly decreased infarction volume and vascular embolism, and ameliorated pathological injury in the hippocampus and striatum as well as the neurological deficits as compared with the model rats. Furthermore, we found that SAA administration significantly promoted neural stem/progenitor cells (NSPCs) proliferation, migration and differentiation into neurons, enhanced axonal regeneration and diminished neuronal apoptosis around the ipsilateral subventricular zone (SVZ), resulting in restored neural density and reconstructed neural circuits in the ischemic striatum. Moreover, we revealed that SAA-induced neurogenesis was associated to activating Wnt3a/GSK3β/β-catenin signaling pathway and downstream target genes in the hippocampus and striatum. Edaravone exerted equivalent inhibition on neuronal apoptosis in the SVZ, as SAA, but edaravone-induced neurogenesis was weaker than that of SAA. Taken together, our results demonstrate that long-term administration of SAA improves neurological function through enhancing endogenous neurogenesis and inhibiting neuronal apoptosis in ischemic stroke rats via activating Wnt3a/GSK3β/β-catenin signaling pathway. SAA may be a potential therapeutic drug to promote neurogenesis after stroke.

Neural recovery after cortical injury: Effects of MSC derived extracellular vesicles on motor circuit remodeling in rhesus monkeys

Reorganization of motor circuits in the cortex and corticospinal tract are thought to underlie functional recovery after cortical injury, but the mechanisms of neural plasticity that could be therapeutic targets remain unclear. Recent work from our group have shown that systemic treatment with mesenchymal stem cell derived (MSCd) extracellular vesicles (EVs) administered after cortical damage to the primary motor cortex (M1) of rhesus monkeys resulted in a robust recovery of fine motor function and reduced chronic inflammation. Here, we used immunohistochemistry for cfos, an activity-dependent intermediate early gene, to label task-related neurons in the surviving primary motor and premotor cortices, and markers of axonal and synaptic plasticity in the spinal cord. Compared to vehicle, EV treatment was associated with a greater density of cfos⁺ pyramidal neurons in the deep layers of M1, greater density of cfos⁺ inhibitory interneurons in premotor areas, and lower density of synapses on MAP2+ lower motor neurons in the cervical spinal cord. These data suggest that the anti-inflammatory effects of EVs may reduce injury-related upper motor neuron damage and hyperexcitability, as well as aberrant compensatory re-organization in the cervical spinal cord to improve motor function.

Brain‐associated innate leukocytes display diverse inflammatory states following experimental stroke

Previous studies investigating innate leukocyte recruitment into the brain after cerebral ischemia have shown conflicting results. Using distinct cell surface and intracellular markers, the current study evaluated the contributions of innate immune cells to the poststroke brain following 1‐h middle cerebral artery occlusion (tMCAO) or permanent MCAO (pMCAO), and assessed whether these cells ascribed to an inflammatory state. Moreover, we examined whether there is evidence for leukocyte infiltration into the contralateral (CL) hemisphere despite the absence of stroke infarct. We observed the recruitment of peripheral neutrophils, monocytes and macrophages into the hemisphere ipsilateral (IL) to the ischemic brain infarct at 24 and 96 h following both tMCAO and pMCAO. In addition, we found evidence of increased leukocyte recruitment to the CL hemisphere but to a lesser extent than the IL hemisphere after stroke. Robust production of intracellular cytokines in the innate immune cell types examined was most evident at 24 h after pMCAO. Specifically, brain‐associated neutrophils, monocytes and macrophages demonstrated stroke‐induced production of tumor necrosis factor‐α (TNF‐α) and interleukin (IL)‐1β, while only monocytes and macrophages exhibit a significant expression of arginase 1 (Arg1) after stroke. At 96 h after stroke, brain‐resident microglia demonstrated production of TNF‐α and IL‐1β following both tMCAO and pMCAO. At this later timepoint, neutrophils displayed TNF‐α production and brain‐associated macrophages exhibited elevation of IL‐1β and Arg1 after tMCAO. Further, pMCAO induced significant expression of Arg1 and IL‐1β in monocytes and macrophages at 96 h, respectively. These results revealed that brain‐associated innate immune cells display various stroke‐induced inflammatory states that are dependent on the experimental stroke setting.

Neurogenesis mediated plasticity is associated with reduced neuronal activity in CA1 during context fear memory retrieval

Postnatal hippocampal neurogenesis has been demonstrated to affect learning and memory in numerous ways. Several studies have now demonstrated that increased neurogenesis can induce forgetting of memories acquired prior to the manipulation of neurogenesis and, as a result of this forgetting can also facilitate new learning. However, the mechanisms mediating neurogenesis-induced forgetting are not well understood. Here, we used a subregion-based analysis of the immediate early gene c-Fos as well as in vivo fiber photometry to determine changes in activity corresponding with neurogenesis induced forgetting. We found that increasing neurogenesis led to reduced CA1 activity during context memory retrieval. We also demonstrate here that perineuronal net expression in areas CA1 is bidirectionally altered by the levels or activity of postnatally generated neurons in the dentate gyrus. These results suggest that neurogenesis may induce forgetting by disrupting perineuronal nets in CA1 which may otherwise protect memories from degradation.

Immune Pathways in Etiology, Acute Phase, and Chronic Sequelae of Ischemic Stroke

Inflammation and immune mechanisms are crucially involved in the pathophysiology of the development, acute damage cascades, and chronic course after ischemic stroke. Atherosclerosis is an inflammatory disease, and, in addition to classical risk factors, maladaptive immune mechanisms lead to an increased risk of stroke. Accordingly, individuals with signs of inflammation or corresponding biomarkers have an increased risk of stroke. Anti-inflammatory drugs, such as IL (interleukin)-1β blockers, methotrexate, or colchicine, represent attractive treatment strategies to prevent vascular events and stroke. Lately, the COVID-19 pandemic shows a clear association between SARS-CoV2 infections and increased risk of cerebrovascular events. Furthermore, mechanisms of both innate and adaptive immune systems influence cerebral damage cascades after ischemic stroke. Neutrophils, monocytes, and microglia, as well as T and B lymphocytes each play complex interdependent roles that synergize to remove dead tissue but also can cause bystander injury to intact brain cells and generate maladaptive chronic inflammation. Chronic systemic inflammation and comorbid infections may unfavorably influence both outcome after stroke and recurrence risk for further stroke. In addition, stroke triggers specific immune depression, which in turn can promote infections. Recent research is now increasingly addressing the question of the extent to which immune mechanisms may influence long-term outcome after stroke and, in particular, cause specific complications such as poststroke dementia or even poststroke depression.

Long Non-coding RNA ANRIL Downregulation Alleviates Neuroinflammation in an Ischemia Stroke Model via Modulation of the miR-671-5p/NF-κB Pathway

The aim of this study was to investigate the role and underlying mechanism of the long non-coding RNA ANRIL (antisense noncoding RNA in the INK4 locus, ANRIL) in ischemia stroke (IS) injury. Downregulation of ANRIL by right intracerebroventricular injected si-ANRIL in middle cerebral artery occlusion-reperfusion (MCAO/R) C57/BL6 mice and by transferring si-ANRIL in oxygen glucose deprivation/reperfusion (OGD/R) HT22 cells. The results showed that ANRIL levels increased in IS model, downregulation of ANRIL reduced infract area, neurological deficit scores and injured cells, and prolong fall latency time in MCAO/R mice, improved cell viability and reduced cell cytotoxicity in OGD/R cells. Fluorescence in Situ Hybridization detected that there were both ANRIL and miR-671-5p in neurons; miranda v3.3a and dual luciferase reporter assay demonstrated that miR-671-5p was one of direct target of ANRIL; and our previously published research demonstrated that NF-κB was one of direct target of miR-671-5p. Downregulation of ANRIL alleviated neuroinflammation and reduced p-NF-κB, NF-κB, pro-inflammatory cytokines (IL-1β, IL-6, TNF-a), and iNOS, which diminished by miR-671-5p antagomir both in in vivo and in vitro IS models. Downregulation of ANRIL alleviated disruption of blood brain barrier, and protected against tight junction (ZO-1, occludin and claudin 5) disorder in MCAO/R mice. This work clarified that downregulation of ANRIL reduced neuroinflammation by negatively regulating miR-671-5p to inhibit NF-κB in IS models, which provided a theoretical foundation for the protective effect of downregulating ANRIL for IS patients.

Targeting the Erk1/2 and autophagy signaling easily improved the neurobalst differentiation and cognitive function after young transient forebrain ischemia compared to old gerbils

The hippocampal neurogenesis occurs constitutively throughout adulthood in mammalian species, but declines with age. In this study, we overtly found that the neuroblast proliferation and differentiation in the subgranular zone and the maturation into fully functional and integrated neurons in the granule-cell layer in young gerbils following cerebral ischemia/reperfusion was much more than those in old gerbils. The neurological function and cognitive and memory-function rehabilitation in the young gerbils improved faster than those in the old one. These results demonstrated that, during long term after cerebral ischemia/reperfusion, the ability of neurogenesis and recovery of nerve function in young animals were significantly higher than that in the old animals. We found that, after 14- and 28-day cerebral ischemia/reperfusion, the phosphorylation of MEK1/2, ERK1/2, p90RSK, and MSK1/2 protein levels in the hippocampus of young gerbils was significantly much higher than that of old gerbils. The levels of autophagy-related proteins, including Beclin-1, Atg3, Atg5, and LC3 in the hippocampus were effectively maintained and elevated at 28 days after cerebral ischemia/reperfusion in the young gerbils compared with those in the old gerbils. These results indicated that an increase or maintenance of the phosphorylation of ERK1/2 signal pathway and autophagy-related proteins was closely associated with the neuroblast proliferation and differentiation and the process of maturation into neurons. Further, we proved that neuroblast proliferation and differentiation in the dentate gyrus and cognitive function were significantly reversed in young cerebral ischemic gerbils by administering the ERK inhibitor (U0126) and autophagy inhibitor (3MA). In brief, following experimental young ischemic stroke, the long-term promotion of the neurogenesis in the young gerbil’s hippocampal dentate gyrus by upregulating the phosphorylation of ERK signaling pathway and maintaining autophagy-related protein levels, it overtly improved the neurological function and cognitive and memory function.

Forgetting as a form of adaptive engram cell plasticity

One leading hypothesis suggests that memories are stored in ensembles of neurons (or 'engram cells') and that successful recall involves reactivation of these ensembles. A logical extension of this idea is that forgetting occurs when engram cells cannot be reactivated. Forms of 'natural forgetting' vary considerably in terms of their underlying mechanisms, time course and reversibility. However, we suggest that all forms of forgetting involve circuit remodelling that switches engram cells from an accessible state (where they can be reactivated by natural recall cues) to an inaccessible state (where they cannot). In many cases, forgetting rates are modulated by environmental conditions and we therefore propose that forgetting is a form of neuroplasticity that alters engram cell accessibility in a manner that is sensitive to mismatches between expectations and the environment. Moreover, we hypothesize that disease states associated with forgetting may hijack natural forgetting mechanisms, resulting in reduced engram cell accessibility and memory loss.

Androgens and Adult Neurogenesis in the Hippocampus

Adult neurogenesis in the hippocampus is modulated by steroid hormones, including androgens, in male rodents. In this review, we summarize research showing that chronic exposure to androgens, such as testosterone and dihydrotestosterone, enhances the survival of new neurons in the dentate gyrus of male, but not female, rodents, via the androgen receptor. However, the neurogenesis promoting the effect of androgens in the dentate gyrus may be limited to younger adulthood as it is not evident in middle-aged male rodents. Although direct exposure to androgens in adult or middle age does not significantly influence neurogenesis in female rodents, the aromatase inhibitor letrozole enhances neurogenesis in the hippocampus of middle-aged female mice. Unlike other androgens, androgenic anabolic steroids reduce neurogenesis in the hippocampus of male rodents. Collectively, the research indicates that the ability of androgens to enhance hippocampal neurogenesis in adult rodents is dependent on dose, androgen type, sex, duration, and age. We discuss these findings and how androgens may be influencing neuroprotection, via neurogenesis in the hippocampus, in the context of health and disease.

Voluntary Exercise Increases Neurogenesis and Mediates Forgetting of Complex Paired Associates Memories

The hippocampus is a critical structure involved in many forms of learning and memory. It is also one of the only regions in the mammalian brain that continues to generate new neurons throughout adulthood. This process of adult neurogenesis may increase the plasticity of the hippocampus which could be beneficial for learning but has also been demonstrated to decrease the stability of previously acquired memories. Here we test whether exposure to voluntary running (which increases the production of new neurons) following the formation of a gradually acquired paired associates task will result in forgetting of this type of memory. We trained mice in a touchscreen-based object/location task and then increased neurogenesis using voluntary running. Our results indicate that running increased neurogenesis and resulted in poor recall of the previously established memory. When subsequently exposed to a reversal task we also show that running reduced the number of correction trials required to acquire the new task contingencies. This suggests that prior forgetting reduces perseveration on the now outdated memory. Together our results add to a growing body of literature which indicates the important role of adult neurogenesis in destabilizing previously acquired memories to allow for flexible encoding of new memories.

Repeated oxytocin treatment during abstinence inhibited context- or restraint stress-induced reinstatement of methamphetamine-conditioned place preference and promoted adult hippocampal neurogenesis in mice

Propensity to relapse, even after long-term abstinence, is a crucial feature of methamphetamine (METH) abuse. We and other laboratories have reported that acute treatment of oxytocin (OXT), a hormone and neuropeptide, could inhibit reinstatement of METH seeking in animal studies. However, the effects of repeated OXT treatment on METH reinstatement as well as underlying mechanisms are still unclear. In the present study, the effects of repeated OXT treatment during abstinence on context- or restraint stress-induced reinstatement were investigated using the mice conditioned place preference (CPP) paradigm. After three intermittent injections of METH (2 mg/kg, i.p.) to induce CPP, mice received a daily bilateral intra-hippocampus injection of OXT (0.625, 1.25 or 2.5 μg) for 8 consecutive days before the context- or restraint stress-induced reinstatement test. Meanwhile, adult hippocampal neurogenesis (AHN) level was detected using immunostaining. To further clarify the role of AHN underlying OXT's effects on METH-CPP reinstatement, temozolomide (TMZ, 25 mg/kg, i.p.) was employed to deplete AHN prior to OXT treatment. The data showed that repeated OXT treatment (1.25 and 2.5 μg, intra-hippocampus) significantly inhibited both context- and restraint stress-induced METH-CPP reinstatement and concomitantly promoted AHN in a dose-dependent manner. Notably, TMZ pre-treatment markedly abolished all the above-mentioned effects of OXT, suggesting that AHN was closely involved in OXT's inhibition on reinstatement induced by both triggers. Taken together, the present study indicated that repeated OXT treatment during abstinence could inhibit both context- and restraint stress-induced METH-CPP reinstatement possibly by promoting AHN in mice, which provided a better understanding for OXT's beneficial effects on METH addiction.

Consequences of adolescent alcohol use on adult hippocampal neurogenesis and hippocampal integrity

Alcohol is the most commonly used drug among adolescents. Their decreased sensitivity to self-regulating cues to stop drinking coincides with an enhanced vulnerability to negative outcomes of excessive drinking. In adolescents, the hippocampus is one brain region that is particularly susceptible to alcohol-induced neurodegeneration. While cell death is causal, alcohol effects on adult neurogenesis also impact hippocampal structure and function. This review describes what little is known about adolescent-specific effects of alcohol on adult neurogenesis and its relationship to hippocampal integrity. For example, alcohol intoxication inhibits neurogenesis persistently in adolescents but produces aberrant neurogenesis after alcohol dependence. Little is known, however, about the role of adolescent-born neurons in hippocampal integrity or the mechanisms of these effects. Understanding the role of neurogenesis in adolescent alcohol use and misuse is critical to our understanding of adolescent susceptibility to alcohol pathology and increased likelihood of developing alcohol problems in adulthood.

Delayed rFGF21 Administration Improves Cerebrovascular Remodeling and White Matter Repair After Focal Stroke in Diabetic Mice

Type 2 diabetes mellitus (T2DM) is a major comorbidity exacerbating ischemic brain injury and impairing post-stroke recovery. Our previous study suggested that recombinant human fibroblast growth factor (rFGF) 21 might be a potent therapeutic targeting multiple aspects of pathophysiology in T2DM stroke. This study aims to evaluate the potential effects of rFGF21 on cerebrovascular remodeling after T2DM stroke. Permanent distal middle cerebral artery occlusion was performed in heterozygous non-diabetic db/ + and homozygous diabetic db/db mice. Daily rFGF21 administration was initiated 1 week after stroke induction and maintained for up to 2 weeks thereafter. Multiple markers associated with post-stroke recovery, including angiogenesis, oligodendrogenesis, white matter integrity, and neurogenesis, were assessed up to 3 weeks after stroke. Our results showed an impairment in post-stroke vascular remodeling under T2DM condition, reflected by the decreased expression of trophic factors in brain microvessels and impairments of angiogenesis. The defected cerebrovascular remodeling was accompanied by the decreased oligodendrogenesis and neurogenesis. However, delayed rFGF21 administration normalized post-stroke hyperglycemia and improved neurological outcomes, which may partially be via the promotion of pro-angiogenic trophic factor expression in brain microvessels and cerebrovascular remodeling. The better cerebrovascular remodeling may also contribute to oligodendrogenesis, white matter integrity, and neurogenesis after T2DM stroke. Therefore, delayed rFGF21 administration may improve neurological outcomes in T2DM stroke mice, at least in part by normalizing the metabolic abnormalities and promoting cerebrovascular remodeling and white matter repair.

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.

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

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

Association between Blood Pressure, Blood Pressure Variability, and Post-Stroke Cognitive Impairment

After stroke, dynamic changes take place from necrotic-apoptotic continuum, inflammatory response to poststroke neurogenesis, and remodeling of the network. These changes and baseline brain pathology such as small vessel disease (SVD) and amyloid burden may be associated with the occurrence of early or late poststroke cognitive impairment (PSCI) or dementia (PSD), which affect not only stroke victims but also their families and even society. We reviewed the current concepts and understanding of the pathophysiology for PSCI/PSD and identified useful tools for the diagnosis and the prediction of PSCI in serological, CSF, and image characteristics. Then, we untangled their relationships with blood pressure (BP) and blood pressure variability (BPV), important but often overlooked risk factors for PSCI/PSD. Finally, we provided evidence for the modifying effects of BP and BPV on PSCI as well as pharmacological and non-pharmacological interventions and life style modification for PSCI/PSD prevention and treatment.

Adult neurogenesis mediates forgetting of multiple types of memory in the rat

The formation and retention of hippocampus-dependent memories is impacted by neurogenesis, a process that involves the production of new neurons in the dentate gyrus of the hippocampus. Recent studies demonstrate that increasing neurogenesis after memory formation induces forgetting of previously acquired memories. Neurogenesis-induced forgetting was originally demonstrated in mice, but a recent report suggests that the same effect may be absent in rats. Although a general species difference is possible, other potential explanations for these incongruent findings are that memories which are more strongly reinforced become resilient to forgetting or that perhaps only certain types of memories are affected. Here, we investigated whether neurogenesis-induced forgetting occurs in rats using several hippocampus-dependent tasks including contextual fear conditioning (CFC), the Morris Water Task (MWT), and touchscreen paired associates learning (PAL). Neurogenesis was increased following training using voluntary exercise for 4 weeks before recall of the previous memory was assessed. We show that voluntary running causes forgetting of context fear memories in a neurogenesis-dependent manner, and that neurogenesis-induced forgetting is present in rats across behavioral tasks despite differences in complexity or reliance on spatial, context, or object memories. In addition, we asked whether stronger memories are less susceptible to forgetting by varying the strength of training. Even with a very strong training protocol in the CFC task, we still observed enhanced forgetting related to increased neurogenesis. These results suggest that forgetting due to neurogenesis is a conserved mechanism that aids in the clearance of memories.

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.

Remote memory of drug experiences coexists with cognitive decline and abnormal adult neurogenesis in an animal model of cocaine-altered cognition

Cocaine addiction is a chronic disorder in which the person loses control over drug use. The past memories of the stimuli associated with the drug are a relevant clinical problem, since they trigger compulsive drug-seeking and drug-taking habits. Furthermore, these persistent drug-related memories seemingly coexist with cognitive decline that predicts worse therapeutic output. Here, we use a new animal model of cocaine-altered cognition that allowed to observe these events in the same individual and study their relationship. Mice were chronically administered cocaine in a conditioned place preference (CPP) apparatus for 14 days, and control mice received saline. After 28 days of cocaine withdrawal, animals were tested for retrieval of remote drug-associated memory as well as for cognitive performance in a battery of tests, including novel object and place recognition and spatial memory. The cocaine-withdrawn mice showed persistent CPP memory while impaired in the cognitive tasks, displaying deficits in reference memory acquisition and working memory. However, the CPP expression was not associated with the defective cognitive performance, indicating that they were concomitant but independent occurrences. After completion of the experiment, adult hippocampal neurogenesis (AHN) was studied as a relevant neurobiological correlate due to its potential role in both learning and drug addiction. Results suggested a preserved basal AHN in the cocaine-withdrawn mice but an aberrant learning-induced regulation of these neurons. This paradigm may be useful to investigate maladaptive cognition in drug addiction as well as related therapies.

Increased serum QUIN/KYNA is a reliable biomarker of post-stroke cognitive decline

BACKGROUND

Strokes are becoming less severe due to increased numbers of intensive care units and improved treatments. As patients survive longer, post-stroke cognitive impairment (PSCI) has become a major health public issue. Diabetes has been identified as an independent predictive factor for PSCI. Here, we characterized a clinically relevant mouse model of PSCI, induced by permanent cerebral artery occlusion in diabetic mice, and investigated whether a reliable biomarker of PSCI may emerge from the kynurenine pathway which has been linked to inflammatory processes.

METHODS

Cortical infarct was induced by permanent middle cerebral artery occlusion in male diabetic mice (streptozotocin IP). Six weeks later, cognitive assessment was performed using the Barnes maze, hippocampi long-term potentiation using microelectrodes array recordings, and neuronal death, white matter rarefaction and microglia/macrophages density assessed in both hemispheres using imunohistochemistry. Brain and serum metabolites of the kynurenin pathway were measured using HPLC and mass fragmentography. At last, these same metabolites were measured in the patient's serum, at the acute phase of stroke, to determine if they could predict PSCI 3 months later.

RESULTS

We found long-term spatial memory was impaired in diabetic mice 6 weeks after stroke induction. Synaptic plasticity was completely suppressed in both hippocampi along with increased neuronal death, white matter rarefaction in both striatum, and increased microglial/macrophage density in the ipsilateral hemisphere. Brain and serum quinolinic acid concentrations and quinolinic acid over kynurenic acid ratios were significantly increased compared to control, diabetic and non-diabetic ischemic mice, where PSCI was absent. These putative serum biomarkers were strongly correlated with degradation of long-term memory, neuronal death, microglia/macrophage infiltration and white matter rarefaction. Moreover, we identified these same serum biomarkers as potential predictors of PSCI in a pilot study of stroke patients.

CONCLUSIONS

we have established and characterized a new model of PSCI, functionally and structurally, and we have shown that the QUIN/KYNA ratio could be used as a surrogate biomarker of PSCI, which may now be tested in large prospective studies of stroke patients.

Phosphofructokinase-1 Inhibition Promotes Neuronal Differentiation of Neural Stem Cells and Functional Recovery After Stroke

Ischemic stroke is a major cause of long-term disability. Neuronal differentiation of neural stem cells (NSCs) is crucial for brain repair after stroke. However, the underlying mechanisms remain unclear. Here, the role and potential mechanisms of phosphofructokinase-1 (PFK-1), the rate-limiting enzyme of glycolysis, was investigated in stroke using middle cerebral artery occlusion (MCAO) and oxygen-glucose deprivation models. We found that stroke increased the PFK-1 expression of NSCs. However, PFK-1 inhibition promoted neuronal differentiation of NSCs and facilitated the dendritic maturation of newborn neurons in vitro and in vivo. Moreover, PFK-1 inhibition also improved the spatial memory performance of MCAO rats. Additionally, we proved that the effect of PFK-1 inhibition above might be achieved by promoting β-catenin nuclear translocation and activating its downstream signaling, independent of Wnt signaling. Thus, these observations reveal a critical role of PFK-1 in stroke, which may provide a novel target for regenerative repair after stroke.

High-Frequency rTMS Improves Cognitive Function by Regulating Synaptic Plasticity in Cerebral Ischemic Rats

Poststroke cognitive impairment (PSCI) is one of the most severe sequelae of stroke and lacks effective treatment. Previous studies have shown that high-frequency repetitive transcranial magnetic stimulation (rTMS) may be a promising PSCI therapeutic approach, but the underlying mechanism is unclear. To uncover the effect of rTMS on PSCI, a transient middle cerebral artery occlusion (tMCAO) model was established. Modified Neurological Severity Score (mNSS) test and Morris Water Maze (MWM) test were performed to assess the neurological and cognitive function of rats. Furthermore, to explore the underlying mechanism, differentially expressed genes (DEGs) in the hippocampus of rats in the rTMS group and tMCAO group were compared using RNA sequencing. Then, bioinformatics analysis, including gene ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and protein-protein interaction (PPI) network analysis, was conducted to elaborate these DEGs. Our results indicated that high-frequency rTMS could significantly improve neurological and cognitive function, according to mNSS and MWM tests. We found 85 DEGs, including 71 upregulated genes and 14 downregulated genes, between the rTMS group and tMCAO group. The major functional category was related to chemical synaptic transmission modulation and several DEGs were significantly upregulated in processes related to synaptic plasticity, such as glutamatergic synapses. Calb2, Zic1, Kcnk9, and Grin3a were notable in PPI analysis. These results demonstrate that rTMS has a beneficial effect on PSCI, and its mechanism may be related to the regulation of synaptic plasticity and functional genes such as Calb2, Zic1, Kcnk9, and Grin3a in the hippocampus.

Neurogenesis After Stroke: A Therapeutic Perspective

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

Immunological mechanisms in poststroke dementia

PURPOSE OF REVIEW

To review new evidence on links between poststroke dementia and inflammation.

RECENT FINDINGS

Although there are still no treatments for poststroke dementia, recent evidence has improved our understanding that stroke increases the risk of incident dementia and worsens cognitive trajectory for at least a decade afterwards. Within approximately the first year dementia onset is associated with stroke severity and location, whereas later absolute risk is associated with more traditional dementia risk factors, such as age and imaging findings. The molecular mechanisms that underlie increased risk of incident dementia in stroke survivors remain unproven; however new data in both human and animal studies suggests links between cognitive decline and inflammation. These point to a model where chronic brain inflammation, provoked by inefficient clearance of myelin debris and a prolonged innate and adaptive immune response, causes poststroke dementia. These localized immune events in the brain may themselves be influenced by the peripheral immune state at key times after stroke.

SUMMARY

This review recaps clinical evidence on poststroke dementia, new mechanistic links between the chronic inflammatory response to stroke and poststroke dementia, and proposes a model of immune-mediated neurodegeneration after stroke.

Recovery of Hippocampal-Dependent Learning Despite Blunting Reactive Adult Neurogenesis After Alcohol Dependence

Background:

The excessive alcohol drinking that occurs in alcohol use disorder (AUD) causes neurodegeneration in regions such as the hippocampus, though recovery may occur after a period of abstinence. Mechanisms of recovery are not clear, though reactive neurogenesis has been observed in the hippocampal dentate gyrus following alcohol dependence and correlates to recovery of granule cell number.

Objective:

We investigated the role of neurons born during reactive neurogenesis in the recovery of hippocampal learning behavior after 4-day binge alcohol exposure, a model of an AUD. We hypothesized that reducing reactive neurogenesis would impair functional recovery.

Methods:

Adult male rats were subjected to 4-day binge alcohol exposure and two approaches were tested to blunt reactive adult neurogenesis, acute doses of alcohol or the chemotherapy drug, temozolomide (TMZ).

Results:

Acute 5 g/kg doses of EtOH gavaged T6 and T7 days post binge did not inhibit significantly the number of Bromodeoxyuridine-positive (BrdU+) proliferating cells in EtOH animals receiving 5 g/kg EtOH versus controls. A single cycle of TMZ inhibited reactive proliferation (BrdU+ cells) and neurogenesis (NeuroD+ cells) to that of controls. However, despite this blunting of reactive neurogenesis to basal levels, EtOH-TMZ rats were not impaired in their recovery of acquisition of the Morris water maze (MWM), learning similarly to all other groups 35 days after 4-day binge exposure.

Conclusions:

These studies show that TMZ is effective in decreasing reactive proliferation/neurogenesis following 4-day binge EtOH exposure, and baseline levels of adult neurogenesis are sufficient to allow recovery of hippocampal function.