Dysregulation of neurogenesis by neuroinflammation: key differences in neurodevelopmental and neurological disorders

Mesenchymal stem cell-derived exosomes improve neurogenesis and cognitive function of mice with methamphetamine addiction: A novel treatment approach

BACKGROUND

Methamphetamine (METH) is a psychostimulant substance with highly addictive and neurotoxic effects, but no ideal treatment option exists to improve METH-induced neurocognitive deficits. Recently, mesenchymal stem cells (MSCs)-derived exosomes have raised many hopes for treating neurodegenerative sequela of brain disorders. This study aimed to determine the therapeutic potential of MSCs-derived exosomes on cognitive function and neurogenesis of METH-addicted rodents.

METHODS

Male BALB/c mice were subjected to chronic METH addiction, followed by intravenous administration of bone marrow MSCs-derived exosomes. Then, the spatial memory and recognition memory of animals were assessed by the Barnes maze and the novel object recognition test (NORT). The neurogenesis-related factors, including NeuN and DCX, and the expression of Iba-1, a microglial activation marker, were assessed in the hippocampus by immunofluorescence staining. Also, the expression of inflammatory cytokines, including TNF-α and NF-κB, were evaluated by western blotting.

RESULTS

The results showed that BMSCs-exosomes improved the time spent in the target quadrant and correct-to-wrong relative time in the Barnes maze. Also, NORT's discrimination index (DI) and recognition index (RI) were improved following exosome therapy. Additionally, exosome therapy significantly increased the expression of NeuN and DCX in the hippocampus while decreasing the expression of inflammatory cytokines, including TNF-α and NF-κB. Besides, BMSC-exosomes down-regulated the expression of Iba-1.

CONCLUSION

Our findings indicate that BMSC-exosomes mitigated METH-caused cognitive dysfunction by improving neurogenesis and inhibiting neuroinflammation in the hippocampus.

Three Decades of Valproate: A Current Model for Studying Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder with increased prevalence and incidence in recent decades. Its etiology remains largely unclear, but it seems to involve a strong genetic component and environmental factors that, in turn, induce epigenetic changes during embryonic and postnatal brain development. In recent decades, clinical studies have shown that inutero exposure to valproic acid (VPA), a commonly prescribed antiepileptic drug, is an environmental factor associated with an increased risk of ASD. Subsequently, prenatal VPA exposure in rodents has been established as a reliable translational model to study the pathophysiology of ASD, which has helped demonstrate neurobiological changes in rodents, non-human primates, and brain organoids from human pluripotent stem cells. This evidence supports the notion that prenatal VPA exposure is a valid and current model to replicate an idiopathic ASD-like disorder in experimental animals. This review summarizes and describes the current features reported with this animal model of autism and the main neurobiological findings and correlates that help elucidate the pathophysiology of ASD. Finally, we discuss the general framework of the VPA model in comparison to other environmental and genetic ASD models.

Genetically engineered neural stem cells (NSCs) therapy for neurological diseases; state-of-the-art

Neural stem cells (NSCs) are multipotent stem cells with remarkable self-renewal potential and also unique competencies to differentiate into neurons, astrocytes, and oligodendrocytes (ODCs) and improve the cellular microenvironment. In addition, NSCs secret diversity of mediators, including neurotrophic factors (e.g., BDNF, NGF, GDNF, CNTF, and NT-3), pro-angiogenic mediators (e.g., FGF-2 and VEGF), and anti-inflammatory biomolecules. Thereby, NSCs transplantation has become a reasonable and effective treatment for various neurodegenerative disorders by their capacity to induce neurogenesis and vasculogenesis and dampen neuroinflammation and oxidative stress. Nonetheless, various drawbacks such as lower migration and survival and less differential capacity to a particular cell lineage concerning the disease pathogenesis hinder their application. Thus, genetic engineering of NSCs before transplantation is recently regarded as an innovative strategy to bypass these hurdles. Indeed, genetically modified NSCs could bring about more favored therapeutic influences post-transplantation in vivo, making them an excellent option for neurological disease therapy. This review for the first time offers a comprehensive review of the therapeutic capability of genetically modified NSCs rather than naïve NSCs in neurological disease beyond brain tumors and sheds light on the recent progress and prospect in this context.

Minocycline improves autism-related behaviors by modulating microglia polarization in a mouse model of autism

Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental disorder with few pharmacological treatments. Minocycline, a tetracycline derivative that inhibits microglial activation, has been well-identified with anti-inflammatory properties and neuroprotective effects. A growing body of research suggests that ASD is associated with neuroinflammation, abnormal neurotransmitter levels, and neurogenesis. Thus, we hypothesized that minocycline could improve autism-related behaviors by inhibiting microglia activation and altering neuroinflammation. To verify our hypothesis, we used a mouse model of autism, BTBR T + Itpr3tf/J (BTBR). As expected, minocycline administration rescued the sociability and repetitive, stereotyped behaviors of BTBR mice while having no effect in C57BL/6J mice. We also found that minocycline improved neurogenesis and inhibited microglia activation in the hippocampus of BTBR mice. In addition, minocycline treatment inhibited Erk1/2 phosphorylation in the hippocampus of BTBR mice. Our findings show that minocycline administration alleviates ASD-like behaviors in BTBR mice and improves neurogenesis, suggesting that minocycline supplementation might be a potential strategy for improving ASD symptoms.

Differential Effects of the Processed and Unprocessed Garlic (Allium sativum L.) Ethanol Extracts on Neuritogenesis and Synaptogenesis in Rat Primary Hippocampal Neurons

Garlic (Allium sativum L.) is an aromatic herb known for its culinary and medicinal uses for centuries. Both unprocessed (white) and processed (black) garlic are known to protect against the pathobiology of neurological disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD), which has been attributed to their anti-inflammatory and antioxidant properties. The information on the effects of processed and unprocessed garlic on neuronal process outgrowth, maturation, and synaptic development is limited. This study aimed at investigating and comparing the effects of the ethanol extracts of unprocessed (white garlic extract, WGE) and processed (black garlic extract, BGE) garlic on the maturation of primary hippocampal neurons. Neurite outgrowth was stimulated in a dose-dependent manner by both WGE and BGE and the most effective doses were 15 μg/mL and 60 μg/mL, respectively, without showing cytotoxicity. At this optimal concentration, both extracts promoted axonal and dendritic growth and maturation. Furthermore, both extracts substantially increased the formation of functional synapses. However, the effect of WGE was more robust at every developmental stage of neurons. In addition, the gas chromatography and mass spectrometry (GC-MS) analysis revealed a chemical profile of various bioactives in both BGE and WGE. Linalool, a compound that was found in both extracts, has shown neurite outgrowth-promoting activity in neuronal cultures, suggesting that the neurotrophic activity of garlic extracts is attributed, at least in part, to this compound. By using network pharmacology, linalool's role in neuronal development can also be observed through its modulatory effect on the signaling molecules of neurotrophic signaling pathways such as glycogen synthase kinase 3 (GSK3β), extracellular signal-regulated protein kinase (Erk1/2), which was further verified by immunocytochemistry. Overall, these findings provide information on the molecular mechanism of processed and unprocessed garlic for neuronal growth, survival, and memory function which may have the potential for the prevention of several neurological disorders.

A single intranasal dose of human mesenchymal stem cell-derived extracellular vesicles after traumatic brain injury eases neurogenesis decline, synapse loss, and BDNF-ERK-CREB signaling

An optimal intranasal (IN) dose of human mesenchymal stem cell-derived extracellular vesicles (hMSC-EVs), 90 min post-traumatic brain injury (TBI), has been reported to prevent the evolution of acute neuroinflammation into chronic neuroinflammation resulting in the alleviation of long-term cognitive and mood impairments. Since hippocampal neurogenesis decline and synapse loss contribute to TBI-induced long-term cognitive and mood dysfunction, this study investigated whether hMSC-EV treatment after TBI can prevent hippocampal neurogenesis decline and synapse loss in the chronic phase of TBI. C57BL6 mice undergoing unilateral controlled cortical impact injury (CCI) received a single IN administration of different doses of EVs or the vehicle at 90 min post-TBI. Quantifying neurogenesis in the subgranular zone-granule cell layer (SGZ-GCL) through 5'-bromodeoxyuridine and neuron-specific nuclear antigen double labeling at ~2 months post-TBI revealed decreased neurogenesis in TBI mice receiving vehicle. However, in TBI mice receiving EVs (12.8 and 25.6 × 10⁹ EVs), the extent of neurogenesis was matched to naive control levels. A similar trend of decreased neurogenesis was seen when doublecortin-positive newly generated neurons were quantified in the SGZ-GCL at ~3 months post-TBI. The above doses of EVs treatment after TBI also reduced the loss of pre-and post-synaptic marker proteins in the hippocampus and the somatosensory cortex. Moreover, at 48 h post-treatment, brain-derived neurotrophic factor (BDNF), phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), and phosphorylated cyclic AMP response-element binding protein (p-CREB) levels were downregulated in TBI mice receiving the vehicle but were closer to naïve control levels in TBI mice receiving above doses of hMSC-EVs. Notably, improved BDNF concentration observed in TBI mice receiving hMSC-EVs in the acute phase was sustained in the chronic phase of TBI. Thus, a single IN dose of hMSC-EVs at 90 min post-TBI can ease TBI-induced declines in the BDNF-ERK-CREB signaling, hippocampal neurogenesis, and synapses.

Preclinical investigation in FAAH inhibition as a neuroprotective therapy for frontotemporal dementia using TDP-43 transgenic male mice

BACKGROUND

Frontotemporal dementia (FTD) is a heterogeneous group of early onset and progressive neurodegenerative disorders, characterized by degeneration in the frontal and temporal lobes, which causes deterioration in cognition, personality, social behavior and language. Around 45% of the cases are characterized by the presence of aggregates of the RNA-binding protein TDP-43.

METHODS

In this study, we have used a murine model of FTD that overexpresses this protein exclusively in the forebrain (under the control of the CaMKIIα promoter) for several biochemical, histological and pharmacological studies focused on the endocannabinoid system.

RESULTS

These mice exhibited at postnatal day 90 (PND90) important cognitive deficits, signs of emotional impairment and disinhibited social behaviour, which were, in most of cases, maintained during the first year of life of these animals. Motor activity was apparently normal, but FTD mice exhibited higher mortality. Their MRI imaging analysis and their ex-vivo histopathological evaluation proved changes compatible with atrophy (loss of specific groups of pyramidal neurons: Ctip2- and NeuN-positive cells) and inflammatory events (astroglial and microglial reactivities) in both cortical (medial prefrontal cortex) and subcortical (hippocampus) structures at PND90 and also at PND365. The analysis of the endocannabinoid system in these mice proved a decrease in the hydrolysing enzyme FAAH in the prefrontal cortex and the hippocampus, with an increase in the synthesizing enzyme NAPE-PLD only in the hippocampus, responses that were accompanied by modest elevations in anandamide and related N-acylethanolamines. The potentiation of these elevated levels of anandamide after the pharmacological inactivation of FAAH with URB597 resulted in a general improvement in behaviour, in particular in cognitive deterioration, associated with the preservation of pyramidal neurons of the medial prefrontal cortex and the CA1 layer of the hippocampus, and with the reduction of gliosis in both structures.

CONCLUSIONS

Our data confirmed the potential of elevating the endocannabinoid tone as a therapy against TDP-43-induced neuropathology in FTD, limiting glial reactivity, preserving neuronal integrity and improving cognitive, emotional and social deficits.

The Adult Neurogenesis Theory of Alzheimer's Disease

Alzheimer's disease starts in neural stem cells (NSCs) in the niches of adult neurogenesis. All primary factors responsible for pathological tau hyperphosphorylation are inherent to adult neurogenesis and migration. However, when amyloid pathology is present, it strongly amplifies tau pathogenesis. Indeed, the progressive accumulation of extracellular amyloid-β deposits in the brain triggers a state of chronic inflammation by microglia. Microglial activation has a significant pro-neurogenic effect that fosters the process of adult neurogenesis and supports neuronal migration. Unfortunately, this "reactive" pro-neurogenic activity ultimately perturbs homeostatic equilibrium in the niches of adult neurogenesis by amplifying tau pathogenesis in AD. This scenario involves NSCs in the subgranular zone of the hippocampal dentate gyrus in late-onset AD (LOAD) and NSCs in the ventricular-subventricular zone along the lateral ventricles in early-onset AD (EOAD), including familial AD (FAD). Neuroblasts carrying the initial seed of tau pathology travel throughout the brain via neuronal migration driven by complex signals and convey the disease from the niches of adult neurogenesis to near (LOAD) or distant (EOAD) brain regions. In these locations, or in close proximity, a focus of degeneration begins to develop. Then, tau pathology spreads from the initial foci to large neuronal networks along neural connections through neuron-to-neuron transmission.

Development of an Aptamer-Based Molecular Tool for Specifically Targeting Microglia via the CD64 Protein

Microglial dysfunction has been identified as a key factor in the pathology of several traumatic and neurodegenerative diseases in the central nervous system. Due to the importance of microglia in various pathological processes, the development of molecular tools to target microglia may be of significance for the clinical diagnosis and treatment of these disorders. In this study, a DNA aptamer, ZH-1c, that binds microglia with high affinity was developed by cell-SELEX and truncated strategies. ZH-1c exhibits promising binding ability under physiological temperatures, high serum stability after being modified, and can be internalized by microglia. Also, the binding target of ZH-1c on microglia was identified as the transmembrane protein CD64, which increased in response to inflammatory stimulation via lipopolysaccharide and interferon-gamma, thus enhancing the affinity of ZH-1c for activated microglia. Based on the above experiments, the DNA aptamer ZH-1c exhibits great potential for the targeting of activated inflammatory microglia and may be suitable as a novel and effective molecular tool for diagnosis and microglia-targeted therapies.

Recent Advances in Biomaterials-Based Therapies for Alleviation and Regeneration of Traumatic Brain Injury

Traumatic brain injury (TBI), a major public health problem accompanied with numerous complications, usually leads to serve disability and huge financial burden. The adverse and unfavorable pathological environment triggers a series of secondary injuries, resulting in serious loss of nerve function and huge obstacle of endogenous nerve regeneration. With the advances in adaptive tissue regeneration biomaterials, regulation of detrimental microenvironment to reduce the secondary injury and to promote the neurogenesis becomes possible. The adaptive biomaterials could respond and regulate biochemical, cellular, and physiological events in the secondary injury, including excitotoxicity, oxidative stress, and neuroinflammation, to rebuild circumstances suitable for regeneration. In this review, the development of pathology after TBI is discussed, followed by the introduction of adaptive biomaterials based on various pathological characteristics. The adaptive biomaterials carried with neurotrophic factors and stem cells for TBI treatment are then summarized. Finally, the current drawbacks and future perspective of biomaterials for TBI treatment are suggested.

In vivo models to study neurogenesis and associated neurodevelopmental disorders-Microcephaly and autism spectrum disorder

The genesis and functioning of the central nervous system are one of the most intricate and intriguing aspects of embryogenesis. The big lacuna in the field of human CNS development is the lack of accessibility of the human brain for direct observation during embryonic and fetal development. Thus, it is imperative to establish alternative animal models to gain deep mechanistic insights into neurodevelopment, establishment of neural circuitry, and its function. Neurodevelopmental events such as neural specification, differentiation, and generation of neuronal and non-neuronal cell types have been comprehensively studied using a variety of animal models and in vitro model systems derived from human cells. The experimentations on animal models have revealed novel, mechanistic insights into neurogenesis, formation of neural networks, and function. The models, thus serve as indispensable tools to understand the molecular basis of neurodevelopmental disorders (NDDs) arising from aberrations during embryonic development. Here, we review the spectrum of in vivo models such as fruitfly, zebrafish, frog, mice, and nonhuman primates to study neurogenesis and NDDs like microcephaly and Autism Spectrum Disorder. We also discuss nonconventional models such as ascidians and the recent technological advances in the field to study neurogenesis, disease mechanisms, and pathophysiology of human NDDs. This article is categorized under: Cancer > Stem Cells and Development Congenital Diseases > Stem Cells and Development Neurological Diseases > Stem Cells and Development Congenital Diseases > Genetics/Genomics/Epigenetics.

The Dialogue Between Neuroinflammation and Adult Neurogenesis: Mechanisms Involved and Alterations in Neurological Diseases

Adult neurogenesis occurs mainly in the subgranular zone of the hippocampal dentate gyrus and the subventricular zone of the lateral ventricles. Evidence supports the critical role of adult neurogenesis in various conditions, including cognitive dysfunction, Alzheimer's disease (AD), and Parkinson's disease (PD). Several factors can alter adult neurogenesis, including genetic, epigenetic, age, physical activity, diet, sleep status, sex hormones, and central nervous system (CNS) disorders, exerting either pro-neurogenic or anti-neurogenic effects. Compelling evidence suggests that any insult or injury to the CNS, such as traumatic brain injury (TBI), infectious diseases, or neurodegenerative disorders, can provoke an inflammatory response in the CNS. This inflammation could either promote or inhibit neurogenesis, depending on various factors, such as chronicity and severity of the inflammation and underlying neurological disorders. Notably, neuroinflammation, driven by different immune components such as activated glia, cytokines, chemokines, and reactive oxygen species, can regulate every step of adult neurogenesis, including cell proliferation, differentiation, migration, survival of newborn neurons, maturation, synaptogenesis, and neuritogenesis. Therefore, this review aims to present recent findings regarding the effects of various components of the immune system on adult neurogenesis and to provide a better understanding of the role of neuroinflammation and neurogenesis in the context of neurological disorders, including AD, PD, ischemic stroke (IS), seizure/epilepsy, TBI, sleep deprivation, cognitive impairment, and anxiety- and depressive-like behaviors. For each disorder, some of the most recent therapeutic candidates, such as curcumin, ginseng, astragaloside, boswellic acids, andrographolide, caffeine, royal jelly, estrogen, metformin, and minocycline, have been discussed based on the available preclinical and clinical evidence.

A Potential Role for Neuroinflammation in ADHD

Attention deficit hyperactivity disorder (ADHD) is a neurobehavioural disorder in children and adolescents. Although increases in oxidative stress and disturbances of neurotransmitter system such as the dopaminergic and abnormalities in several brain regions have been demonstrated, the pathophysiology of ADHD is not fully understood. Nevertheless, ADHD involves several factors that have been associated with an increase in neuroinflammation. This chapter presents an overview of factors that may increase neuroinflammation and play a potential role in the development and pathophysiology of ADHD. The altered immune response, polymorphisms in inflammatory-related genes, ADHD comorbidity with autoimmune and inflammatory disorders and prenatal exposure to inflammation are associated with alterations in offspring brain development and are a risk factor; genetic and environmental risk factors that may increase the risk for ADHD and medications can increase neuroinflammation. Evidence of an association between these factors has been an invaluable tool for research on inflammation in ADHD. Therefore, evidence studies have made it possible to generate alternative therapeutic interventions using natural products as anti-inflammatories that could have great potential against neuroinflammation in ADHD.

The impact of maternal immune activation on embryonic brain development

The adult brain is a complex structure with distinct functional sub-regions, which are generated from an initial pool of neural epithelial cells within the embryo. This transition requires a number of highly coordinated processes, including neurogenesis, i.e., the generation of neurons, and neuronal migration. These take place during a critical period of development, during which the brain is particularly susceptible to environmental insults. Neurogenesis defects have been associated with the pathogenesis of neurodevelopmental disorders (NDDs), such as autism spectrum disorder and schizophrenia. However, these disorders have highly complex multifactorial etiologies, and hence the underlying mechanisms leading to aberrant neurogenesis continue to be the focus of a significant research effort and have yet to be established. Evidence from epidemiological studies suggests that exposure to maternal infection in utero is a critical risk factor for NDDs. To establish the biological mechanisms linking maternal immune activation (MIA) and altered neurodevelopment, animal models have been developed that allow experimental manipulation and investigation of different developmental stages of brain development following exposure to MIA. Here, we review the changes to embryonic brain development focusing on neurogenesis, neuronal migration and cortical lamination, following MIA. Across published studies, we found evidence for an acute proliferation defect in the embryonic MIA brain, which, in most cases, is linked to an acceleration in neurogenesis, demonstrated by an increased proportion of neurogenic to proliferative divisions. This is accompanied by disrupted cortical lamination, particularly in the density of deep layer neurons, which may be a consequence of the premature neurogenic shift. Although many aspects of the underlying pathways remain unclear, an altered epigenome and mitochondrial dysfunction are likely mechanisms underpinning disrupted neurogenesis in the MIA model. Further research is necessary to delineate the causative pathways responsible for the variation in neurogenesis phenotype following MIA, which are likely due to differences in timing of MIA induction as well as sex-dependent variation. This will help to better understand the underlying pathogenesis of NDDs, and establish therapeutic targets.

Photobiomodulation Attenuated Cognitive Dysfunction and Neuroinflammation in a Prenatal Valproic Acid-Induced Autism Spectrum Disorder Mouse Model

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by social communication and interaction disorders, as well as repetitive and restrictive behaviors. To date, no effective treatment strategies have been identified. However, photobiomodulation (PBM) is emerging as a promising treatment for neurological and neuropsychiatric disorders. We used mice exposed to valproic acid (VPA) as a model of ASD and found that pathological behavioral and histological changes that may have been induced by VPA were attenuated by PBM treatment. Pregnant mice that had been exposed to VPA were treated with PBM three times. Thereafter, we evaluated the offspring for developmental disorders, motor function, hyperactivity, repetitive behaviors, and cognitive impairment. PBM attenuated many of the pathological behaviors observed in the VPA-induced ASD mouse model. In addition, pathophysiological analyses confirmed that the increase in activated microglia and astrocytes observed in the VPA-induced ASD mouse model was attenuated by PBM treatment. This suggests that PBM can counteract the behavioral changes caused by neuroinflammation in ASD. Therefore, our data show that PBM has therapeutic potential and may reduce the prevalence of neurodevelopmental disorders such as ASD.

Role of neuroinflammation mediated potential alterations in adult neurogenesis as a factor for neuropsychiatric symptoms in Post-Acute COVID-19 syndrome-A narrative review

Persistence of symptoms beyond the initial 3 to 4 weeks after infection is defined as post-acute COVID-19 syndrome (PACS). A wide range of neuropsychiatric symptoms like anxiety, depression, post-traumatic stress disorder, sleep disorders and cognitive disturbances have been observed in PACS. The review was conducted based on PRISMA-S guidelines for literature search strategy for systematic reviews. A cytokine storm in COVID-19 may cause a breach in the blood brain barrier leading to cytokine and SARS-CoV-2 entry into the brain. This triggers an immune response in the brain by activating microglia, astrocytes, and other immune cells leading to neuroinflammation. Various inflammatory biomarkers like inflammatory cytokines, chemokines, acute phase proteins and adhesion molecules have been implicated in psychiatric disorders and play a major role in the precipitation of neuropsychiatric symptoms. Impaired adult neurogenesis has been linked with a variety of disorders like depression, anxiety, cognitive decline, and dementia. Persistence of neuroinflammation was observed in COVID-19 survivors 3 months after recovery. Chronic neuroinflammation alters adult neurogenesis with pro-inflammatory cytokines supressing anti-inflammatory cytokines and chemokines favouring adult neurogenesis. Based on the prevalence of neuropsychiatric symptoms/disorders in PACS, there is more possibility for a potential impairment in adult neurogenesis in COVID-19 survivors. This narrative review aims to discuss the various neuroinflammatory processes during PACS and its effect on adult neurogenesis.

Increased immune cell and altered microglia and neurogenesis transcripts in an Australian schizophrenia subgroup with elevated inflammation

We previously identified a subgroup of schizophrenia cases (~40 %) with heightened inflammation in the neurogenic subependymal zone (SEZ) (North et al., 2021b). This schizophrenia subgroup had changes indicating reduced microglial activity, increased peripheral immune cells, increased stem cell dormancy/quiescence and reduced neuronal precursor cells. The present follow-up study aimed to replicate and extend those novel findings in an independent post-mortem cohort of schizophrenia cases and controls from Australia. RNA was extracted from SEZ tissue from 20 controls and 22 schizophrenia cases from the New South Wales Brain Tissue Resource Centre, and gene expression analysis was performed. Cluster analysis of inflammation markers (IL1B, IL1R1, SERPINA3 and CXCL8) revealed a high-inflammation schizophrenia subgroup comprising 52 % of cases, which was a significantly greater proportion than the 17 % of high-inflammation controls. Consistent with our previous report (North et al., 2021b), those with high-inflammation and schizophrenia had unchanged mRNA expression of markers for steady-state and activated microglia (IBA1, HEXB, CD68), decreased expression of phagocytic microglia markers (P2RY12, P2RY13), but increased expression of markers for macrophages (CD163), monocytes (CD14), natural killer cells (FCGR3A), and the adhesion molecule ICAM1. Similarly, the high-inflammation schizophrenia subgroup emulated increased quiescent stem cell marker (GFAPD) and decreased neuronal progenitor (DLX6-AS1) and immature neuron marker (DCX) mRNA expression; but also revealed a novel increase in a marker of immature astrocytes (VIM). Replicating primary results in an independent cohort demonstrates that inflammatory subgroups in the SEZ in schizophrenia are reliable, robust and enhance understanding of neuropathological heterogeneity when studying schizophrenia.

Alzheimer’s Disease and Inflammaging

Alzheimer’s disease is one of the most common age-related neurodegenerative disorders. The main theory of Alzheimer’s disease progress is the amyloid-β cascade hypothesis. However, the initial mechanisms of insoluble forms of amyloid-β formation and hyperphosphorylated tau protein in neurons remain unclear. One of the factors, which might play a key role in senile plaques and tau fibrils generation due to Alzheimer’s disease, is inflammaging, i.e., systemic chronic low-grade age-related inflammation. The activation of the proinflammatory cell phenotype is observed during aging, which might be one of the pivotal mechanisms for the development of chronic inflammatory diseases, e.g., atherosclerosis, metabolic syndrome, type 2 diabetes mellitus, and Alzheimer’s disease. This review discusses the role of the inflammatory processes in developing neurodegeneration, activated during physiological aging and due to various diseases such as atherosclerosis, obesity, type 2 diabetes mellitus, and depressive disorders.

Wnt family member 1 (Wnt1) overexpression-induced M2 polarization of microglia alleviates inflammation-sensitized neonatal brain injuries

Intrauterine infection induces inflammation-mediated microglial activation and brain injury. This study aimed to explore the regulatory mechanism of Wnt family member 1 (Wnt1) in intrauterine infection-mediated microglial polarization. The cell counting kit-8 (CCK-8) assay was used to determine the viability of microglia, and cytokine expression levels were determined using enzyme linked immunosorbent assay (ELISA) kits and real-time quantitative PCR (RT-qPCR). The number of CD206⁺ and CD16/32⁺ cells was determined by flow cytometry. Wnt1 expression was analyzed using western blotting and immunofluorescence. Moreover, an in vivo assay was performed to verify the role of WNT1 in inflammation-sensitized brain injury in newborn mice. Lipopolysaccharide (LPS) exposure resulted in a decrease in microglial cell viability while increasing the expression levels of inflammatory cytokines (TNF-α, IL-6, and IL-1β), simultaneously promoting M1-type microglial conversion. However, these effects were rescued by overexpression of Wnt1, which was expressed less in microglia exposed to LPS in vitro and in vivo. Here, we found that Wnt1 activated the LKB1-AMPK pathway, and the inhibition of LKB1 attenuated the rescue effects of Wnt1. In addition, LPS exposure reduced the autophagy of microglia, and Wnt1 overexpression enhanced the autophagy, but this effect was reversed by treatment with an LKB1 inhibitor. Wnt1 activated LKB1 to suppress inflammation-mediated activation of microglia, promote M2-type microglia conversion via the AMPK pathway, and alleviate inflammation-sensitized neonatal brain injuries. This provides a potential avenue for the treatment of neonatal brain injuries.

Toll-like receptors 2 and 4 differentially regulate the self-renewal and differentiation of spinal cord neural precursor cells

BACKGROUND

Toll-like receptors (TLRs) represent critical effectors in the host defense response against various pathogens; however, their known function during development has also highlighted a potential role in cell fate determination and neural differentiation. While glial cells and neural precursor cells (NPCs) of the spinal cord express both TLR2 and TLR4, their influence on self-renewal and cell differentiation remains incompletely described.

METHODS

TLR2, TLR4 knock-out and the wild type mice were employed for spinal cord tissue analysis and NPCs isolation at early post-natal stage. Sox2, FoxJ1 and Ki67 expression among others served to identify the undifferentiated and proliferative NPCs; GFAP, Olig2 and β-III-tubulin markers served to identify astrocytes, oligodendrocytes and neurons respectively after NPC spontaneous differentiation. Multiple comparisons were analyzed using one-way ANOVA, with appropriate corrections such as Tukey's post hoc tests used for comparisons.

RESULTS

We discovered that the deletion of TLR2 or TLR4 significantly reduced the number of Sox2-expressing NPCs in the neonatal mouse spinal cord. While TLR2-knockout NPCs displayed enhanced self-renewal, increased proliferation and apoptosis, and delayed neural differentiation, the absence of TLR4 promoted the neural differentiation of NPCs without affecting proliferation, producing long projecting neurons. TLR4 knock-out NPCs showed significantly higher expression of Neurogenin1, that would be involved in the activation of this neurogenic program by a ligand and microenvironment-independent mechanism. Interestingly, the absence of both TLR2 and TLR4, which induces also a significant reduction in the expression of TLR1, in NPCs impeded oligodendrocyte precursor cell maturation to a similar degree.

CONCLUSIONS

Our data suggest that Toll-like receptors are needed to maintain Sox2 positive neural progenitors in the spinal cord, however possess distinct regulatory roles in mouse neonatal spinal cord NPCs-while TLR2 and TLR4 play a similar role in oligodendrocytic differentiation, they differentially influence neural differentiation.

SARS-CoV-2-Mediated Neuropathogenesis, Deterioration of Hippocampal Neurogenesis and Dementia

A significant portion of COVID-19 patients and survivors display marked clinical signs of neurocognitive impairments. SARS-CoV-2-mediated peripheral cytokine storm and its neurotropism appear to elicit the activation of glial cells in the brain proceeding to neuroinflammation. While adult neurogenesis has been identified as a key cellular basis of cognitive functions, neuroinflammation-induced aberrant neuroregenerative plasticity in the hippocampus has been implicated in progressive memory loss in ageing and brain disorders. Notably, recent histological studies of post-mortem human and experimental animal brains indicate that SARS-CoV-2 infection impairs neurogenic process in the hippocampus of the brain due to neuroinflammation. Considering the facts, this article describes the prominent neuropathogenic characteristics and neurocognitive impairments in COVID-19 and emphasizes a viewpoint that neuroinflammation-mediated deterioration of hippocampal neurogenesis could contribute to the onset and progression of dementia in COVID-19. Thus, it necessitates the unmet need for regenerative medicine for the effective management of neurocognitive deficits in COVID-19.

A schizophrenia subgroup with elevated inflammation displays reduced microglia, increased peripheral immune cell and altered neurogenesis marker gene expression in the subependymal zone

Inflammation regulates neurogenesis, and the brains of patients with schizophrenia and bipolar disorder have reduced expression of neurogenesis markers in the subependymal zone (SEZ), the birthplace of inhibitory interneurons. Inflammation is associated with cortical interneuron deficits, but the relationship between inflammation and reduced neurogenesis in schizophrenia and bipolar disorder remains unexplored. Therefore, we investigated inflammation in the SEZ by defining those with low and high levels of inflammation using cluster analysis of IL6, IL6R, IL1R1 and SERPINA3 gene expression in 32 controls, 32 schizophrenia and 29 bipolar disorder cases. We then determined whether mRNAs for markers of glia, immune cells and neurogenesis varied with inflammation. A significantly greater proportion of schizophrenia (37%) and bipolar disorder cases (32%) were in high inflammation subgroups compared to controls (10%, p < 0.05). Across the high inflammation subgroups of psychiatric disorders, mRNAs of markers for phagocytic microglia were reduced (P2RY12, P2RY13), while mRNAs of markers for perivascular macrophages (CD163), pro-inflammatory macrophages (CD64), monocytes (CD14), natural killer cells (FCGR3A) and adhesion molecules (ICAM1) were increased. Specific to high inflammation schizophrenia, quiescent stem cell marker mRNA (GFAPD) was reduced, whereas neuronal progenitor (ASCL1) and immature neuron marker mRNAs (DCX) were decreased compared to low inflammation control and schizophrenia subgroups. Thus, a heightened state of inflammation may dampen microglial response and recruit peripheral immune cells in psychiatric disorders. The findings elucidate differential neurogenic responses to inflammation within psychiatric disorders and highlight that inflammation may impair neuronal differentiation in the SEZ in schizophrenia.

Saponins from Panax japonicus attenuate cognitive impairment in ageing rats through regulating microglial polarisation and autophagy

CONTEXT

Panax japonicus is the dried rhizome of Panax japonicus C.A. Mey. (Araliaceae). Saponins from Panax japonicus (SPJ) exhibit anti-inflammatory and antioxidative effects.

OBJECTIVE

To explore the neuroprotective effect of SPJ on natural ageing of rat.

MATERIALS AND METHODS

Sprague-Dawley (SD) rats 18-month-old were divided into ageing control, ageing treated with SPJ 10 or 30 mg/kg (n = 8). Five-month-old rats were taken as the adult control (n = 8). Rats were fed regular feed or feed containing SPJ for 4 months. Cognitive level was evaluated by Morris water maze (MWM) test. The mechanisms of SPJ's neuroprotection were evaluated by transmission electron microscope, western blot analysis, and immunofluorescence in vivo and in vitro.

RESULTS

SPJ attenuated ageing-induced cognitive impairment as indicated by elevated number of times crossing the target platform (from 1.63 to 3.5) and longer time spent in the target platform quadrant (from 1.33 to 1.98). Meanwhile, SPJ improved the morphology of microglia and synapse, and activated M2 microglia polarisation including increased hippocampus levels of CD206 (from 0.98 to 1.47) and YM-1 (from 0.67 to 1.1), and enhanced autophagy-related proteins LC3B (from 0.48 to 0.82), Beclin1 (from 0.32 to 0.51), Atg5 (from 0.22 to 0.89) whereas decreased p62 level (from 0.71 to 0.45) of ageing rats. In vitro study also showed that SPJ regulated the microglial polarisation and autophagy.

DISCUSSION AND CONCLUSIONS

SPJ improved cognitive deficits of ageing rats through attenuating microglial inflammation and enhancing microglial autophagy, which could be used to treat neurodegenerative disorders.

MicroRNAs as Potential Orchestrators of Alzheimer's Disease-Related Pathologies: Insights on Current Status and Future Possibilities

Alzheimer's disease (AD) is a progressive and deleterious neurodegenerative disease, strongly affecting the cognitive functions and memory of seniors worldwide. Around 58% of the affected patients live in low and middle-income countries, with estimates of increasing deaths caused by AD in the coming decade. AD is a multifactor pathology. Mitochondrial function declines in AD brain and is currently emerging as a hallmark of this disease. It has been considered as one of the intracellular processes severely compromised in AD. Many mitochondrial parameters decline already during aging; mitochondrial efficiency for energy production, reactive oxygen species (ROS) metabolism and the de novo synthesis of pyrimidines, to reach an extensive functional failure, concomitant with the onset of neurodegenerative conditions. Besides its impact on cognitive functions, AD is characterized by loss of synapses, extracellular amyloid plaques composed of the amyloid-β peptide (Aβ), and intracellular aggregates of hyperphosphorylated Tau protein, accompanied by drastic sleep disorders, sensory function alterations and pain sensitization. Unfortunately, till date, effective management of AD-related disorders and early, non-invasive AD diagnostic markers are yet to be found. MicroRNAs (miRNAs) are small non-coding nucleic acids that regulate key signaling pathway(s) in various disease conditions. About 70% of experimentally detectable miRNAs are expressed in the brain where they regulate neurite outgrowth, dendritic spine morphology, and synaptic plasticity. Increasing studies suggest that miRNAs are intimately involved in synaptic function and specific signals during memory formation. This has been the pivotal key for considering miRNAs crucial molecules to be studied in AD. MicroRNAs dysfunctions are increasingly acknowledged as a pivotal contributor in AD via deregulating genes involved in AD pathogenesis. Moreover, miRNAs have been proved to control pain sensitization processes and regulate circadian clock system that affects the sleep process. Interestingly, the differential expression of miRNA panels implies their emerging potential as diagnostic AD biomarkers. In this review, we will present an updated analysis of miRNAs role in regulating signaling processes that are involved in AD-related pathologies. We will discuss the current challenges against wider use of miRNAs and the future promising capabilities of miRNAs as diagnostic and therapeutic means for better management of AD.

Neural Stem Cells: What Happens When They Go Viral?

Viruses that infect the central nervous system (CNS) are associated with developmental abnormalities as well as neuropsychiatric and degenerative conditions. Many of these viruses such as Zika virus (ZIKV), cytomegalovirus (CMV), and herpes simplex virus (HSV) demonstrate tropism for neural stem cells (NSCs). NSCs are the multipotent progenitor cells of the brain that have the ability to form neurons, astrocytes, and oligodendrocytes. Viral infections often alter the function of NSCs, with profound impacts on the growth and repair of the brain. There are a wide spectrum of effects on NSCs, which differ by the type of virus, the model system, the cell types studied, and the age of the host. Thus, it is a challenge to predict and define the consequences of interactions between viruses and NSCs. The purpose of this review is to dissect the mechanisms by which viruses can affect survival, proliferation, and differentiation of NSCs. This review also sheds light on the contribution of key antiviral cytokines in the impairment of NSC activity during a viral infection, revealing a complex interplay between NSCs, viruses, and the immune system.

The dysfunction of parvalbumin interneurons mediated by microglia contributes to cognitive impairment induced by lipopolysaccharide challenge

BACKGROUND

The mechanisms underlying cognitive impairments induced by systemic inflammation remain unclear. Increasing evidence has suggested that parvalbumin (PV) interneurons play an important role in regulating cognitive behaviors and its dysfunction is implicated in many neurological disorders. Thus, the present study was aimed to detect whether the destruction of PV interneurons mediates cognitive impairment associated with systemic inflammation.

METHODS

Male wild-type C57BL/6J mice (12-14 weeks old) received lipopolysaccharide (LPS 2 mg/kg i.p.) injection to establish the systemic inflammation model. For the suppression of microglial activation, minocycline (50 mg/kg i.p.) was applied. Animal behavior tests were conducted on day 3 post-LPS injection including the open field test, fear conditioning test and Y maze test. The PV expression in hippocampus was detected by Western blot and immunofluorescence. The number of perisomatic boutons around the NeuN-positive cells and microglia in hippocampus was detected by immunofluorescence.

RESULTS

LPS induced hippocampus-dependent memory and working memory impairment, coinciding with decreased PV expression, reduced perisomatic boutons around the NeuN-positive cells and activated microglia in the hippocampus. Notably, the treatment of minocycline suppressed the microglial activation and rescued the PV expression as well as the perisomatic boutons around the NeuN-positive cells in the hippocampus, contributing to improved cognitive function.

CONCLUSION

Our study suggests that the dysfunction of parvalbumin interneurons mediated by microglia plays a key role in LPS-induced cognitive impairments, which may serve a therapeutic strategy for cognitive disorders associated with systemic inflammation.

COVID-19 and Parkinson's disease: Defects in neurogenesis as the potential cause of olfactory system impairments and anosmia

Anosmia, a neuropathogenic condition of loss of smell, has been recognized as a key pathogenic hallmark of the current pandemic SARS-CoV-2 infection responsible for COVID-19. While the anosmia resulting from olfactory bulb (OB) pathology is the prominent clinical characteristic of Parkinson's disease (PD), SARS-CoV-2 infection has been predicted as a potential risk factor for developing Parkinsonism-related symptoms in a significant portion of COVID-19 patients and survivors. SARS-CoV-2 infection appears to alter the dopamine system and induce the loss of dopaminergic neurons that have been known to be the cause of PD. However, the underlying biological basis of anosmia and the potential link between COVID-19 and PD remains obscure. Ample experimental studies in rodents suggest that the occurrence of neural stem cell (NSC) mediated neurogenesis in the olfactory epithelium (OE) and OB is important for olfaction. Though the occurrence of neurogenesis in the human forebrain has been a subject of debate, considerable experimental evidence strongly supports the incidence of neurogenesis in the human OB in adulthood. To note, various viral infections and neuropathogenic conditions including PD with olfactory dysfunctions have been characterized by impaired neurogenesis in OB and OE. Therefore, this article describes and examines the recent reports on SARS-CoV-2 mediated OB dysfunctions and defects in the dopaminergic system responsible for PD. Further, the article emphasizes that COVID-19 and PD associated anosmia could result from the regenerative failure in the replenishment of the dopaminergic neurons in OB and olfactory sensory neurons in OE.

Cell Adhesion Molecules Involved in Neurodevelopmental Pathways Implicated in 3p-Deletion Syndrome and Autism Spectrum Disorder

Autism spectrum disorder (ASD) is characterized by impaired social interaction, language delay and repetitive or restrictive behaviors. With increasing prevalence, ASD is currently estimated to affect 0.5–2.0% of the global population. However, its etiology remains unclear due to high genetic and phenotypic heterogeneity. Copy number variations (CNVs) are implicated in several forms of syndromic ASD and have been demonstrated to contribute toward ASD development by altering gene dosage and expression. Increasing evidence points toward the p-arm of chromosome 3 (chromosome 3p) as an ASD risk locus. Deletions occurring at chromosome 3p result in 3p-deletion syndrome (Del3p), a rare genetic disorder characterized by developmental delay, intellectual disability, facial dysmorphisms and often, ASD or ASD-associated behaviors. Therefore, we hypothesize that overlapping molecular mechanisms underlie the pathogenesis of Del3p and ASD. To investigate which genes encoded in chromosome 3p could contribute toward Del3p and ASD, we performed a comprehensive literature review and collated reports investigating the phenotypes of individuals with chromosome 3p CNVs. We observe that high frequencies of CNVs occur in the 3p26.3 region, the terminal cytoband of chromosome 3p. This suggests that CNVs disrupting genes encoded within the 3p26.3 region are likely to contribute toward the neurodevelopmental phenotypes observed in individuals affected by Del3p. The 3p26.3 region contains three consecutive genes encoding closely related neuronal immunoglobulin cell adhesion molecules (IgCAMs): Close Homolog of L1 (CHL1), Contactin-6 (CNTN6), and Contactin-4 (CNTN4). CNVs disrupting these neuronal IgCAMs may contribute toward ASD phenotypes as they have been associated with key roles in neurodevelopment. CHL1, CNTN6, and CNTN4 have been observed to promote neurogenesis and neuronal survival, and regulate neuritogenesis and synaptic function. Furthermore, there is evidence that these neuronal IgCAMs possess overlapping interactomes and participate in common signaling pathways regulating axon guidance. Notably, mouse models deficient for these neuronal IgCAMs do not display strong deficits in axonal migration or behavioral phenotypes, which is in contrast to the pronounced defects in neuritogenesis and axon guidance observed in vitro. This suggests that when CHL1, CNTN6, or CNTN4 function is disrupted by CNVs, other neuronal IgCAMs may suppress behavioral phenotypes by compensating for the loss of function.

Expression of NLRP3 Inflammasomes in Neurogenic Niche Contributes to the Effect of Spatial Learning in Physiological Conditions but Not in Alzheimer's Type Neurodegeneration

A common feature of neurodegenerative disorders, in particular Alzheimer's disease (AD), is a chronic neuroinflammation associated with aberrant neuroplasticity. Development of neuroinflammation affects efficacy of stem and progenitor cells proliferation, differentiation, migration, and integration of newborn cells into neural circuitry. However, precise mechanisms of neurogenesis alterations in neuroinflammation are not clear yet. It is well established that expression of NLRP3 inflammasomes in glial cells marks neuroinflammatory events, but less is known about contribution of NLRP3 to deregulation of neurogenesis within neurogenic niches and whether neural stem cells (NSCs), neural progenitor cells (NPCs) or immature neuroblasts may express inflammasomes in (patho)physiological conditions. Thus, we studied alterations of neurogenesis in rats with the AD model (intra-hippocampal injection of Aβ1-42). We found that in Aβ-affected brain, number of CD133+ cells was elevated after spatial training in the Morris water maze. The number of PSA-NCAM+ neuroblasts diminished by Aβ injection was completely restored by subsequent spatial learning. Spatial training leads to elevated expression of NLRP3 inflammasomes in the SGZ (subgranular zones): CD133+ and PSA-NCAM+ cells started to express NLRP3 in sham-operated, but not AD rats. Taken together, our data suggest that expression of NLRP3 inflammasomes in CD133+ and PSA-NCAM+ cells may contribute to stimulation of adult neurogenesis in physiological conditions, whereas Alzheimer's type neurodegeneration abolishes stimuli-induced overexpression of NLRP3 within the SGZ neurogenic niche.

Mitogen and Stress-activated Protein Kinase 1 Negatively Regulates Hippocampal Neurogenesis

Neurogenesis in the subgranular zone (SGZ) of the adult hippocampus can be stimulated by a variety of means, including via exposure of experimental animals to an enriched environment that provides additional sensory, social, and motor stimulation. Tangible health and cognitive benefits accrue in enriched animals, including the amelioration of signs modelling psychiatric, neurological and neurodegenerative conditions that affect humans, which may in part be due to enhanced production of neurons. A key factor in the neuronal response to enrichment is the release of brain-derived neurotrophic factor (BDNF) and the activation of the Mitogen-Activated Protein Kinase (MAPK) cascade, which can lead to the stimulation of neurogenesis. Mitogen- and Stress-Activated protein Kinase 1 (MSK1) is a nuclear enzyme downstream of BDNF and MAPK that regulates transcription. MSK1 has previously been implicated in both basal and stimulated neurogenesis on the basis of studies with mice lacking MSK1 protein. In the present study, using mice in which only the kinase activity of MSK1 is lacking, we show that the rate of cellular proliferation in the SGZ (Ki-67 staining) is unaffected by the MSK1 kinase-dead (KD) mutation, and no different from controls levels after five weeks of enrichment. However, compared to wild-type mice, the number of doublecortin (DCX)-positive cells was greater in both standard-housed and enriched MSK1 KD mice. These observations suggest that, while MSK1 does not influence the basal rate of proliferation of neuronal precursors, MSK1 negatively regulates the number of cells destined to become neurons, potentially as a homeostatic control on the number of new neurons integrating into the dentate gyrus.

Microglial Density Alters Measures of Axonal Integrity and Structural Connectivity

Diffusion tensor imaging (DTI) has fundamentally transformed how we interrogate diseases and disorders of the brain in neuropsychiatric illness. DTI and recently developed multicompartment diffusion-weighted imaging (MC-DWI) techniques, such as NODDI (neurite orientation dispersion and density imaging), measure diffusion anisotropy presuming a static neuroglial environment; however, microglial morphology and density are highly dynamic in psychiatric illness, and how alterations in microglial density might influence intracellular measures of diffusion anisotropy in DTI and MC-DWI brain microstructure is unknown. To address this question, DTI and MC-DWI studies of murine brains depleted of microglia were performed, revealing significant alterations in axonal integrity and fiber tractography in DTI and in commonly used MC-DWI models. With accumulating evidence of the role of microglia in neuropsychiatric illness, our findings uncover the unexpected contribution of microglia to measures of axonal integrity and structural connectivity and provide unanticipated insights into the potential influence of microglia in diffusion imaging studies of neuropsychiatric disease.

A 20-Year Journey from Axonal Injury to Neurodegenerative Diseases and the Prospect of Immunotherapy for Combating Alzheimer's Disease

The understanding of the dialogue between the brain and the immune system has undergone dramatic changes over the last two decades, with immense impact on the perception of neurodegenerative diseases, mental dysfunction, and many other brain pathologic conditions. Accumulated results have suggested that optimal function of the brain is dependent on support from the immune system, provided that this immune response is tightly controlled. Moreover, in contrast to the previous prevailing dogma, it is now widely accepted that circulating immune cells are needed for coping with brain pathologies and that their optimal effect is dependent on their type, location, and activity. In this perspective, we describe our own scientific journey, reviewing the milestones in attaining this understanding of the brain-immune axis integrated with numerous related studies by others. We then explain their significance in demonstrating the possibility of harnessing the immune system in a well-controlled manner for the treatment of neurodegenerative diseases.

Therapeutic potential of neurogenesis and melatonin regulation in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by the hallmark pathologies of amyloid-beta plaques and neurofibrillary tangles. Symptoms of this devastating disease include behavioral changes and deterioration of higher cognitive functions. Impairment of neurogenesis has also been shown to occur in AD, which adversely impacts new neuronal cell growth, differentiation, and survival. This impairment possibly results from the cumulative effects of the various pathologies of AD. Preclinical studies have suggested that the administration of melatonin-the pineal hormone primarily responsible for the regulation of the circadian rhythm-targets the effects of AD pathologies and improves cognitive impairment. It is postulated that by mitigating the effect of these pathologies, melatonin can also rescue neurogenesis impairment. This review aims to explore the effect of AD pathologies on neurogenesis, as well as the mechanisms by which melatonin is able to ameliorate AD pathologies to potentially promote neurogenesis.

A complement-microglial axis driving inhibitory synapse related protein loss might contribute to systemic inflammation-induced cognitive impairment

Systemic inflammation induces cognitive impairments via unclear mechanisms. Increasing evidence has suggested complement C3/C3a receptor signaling, a key component of innate immune pathogen defense, plays an important role in cognition and neurodegeneration, whereas its dysfunction is implicated in many neurological disorders. However, it remains unclear whether complement C3/C3a receptor signaling was involved in systemic inflammation-induced cognitive impairments. In the present study, we showed that hippocampal complement C3 levels in astrocytes and C3a receptor expressions in microglia were specifically up-regulated after lipopolysaccharide (LPS) injection. Interestingly, LPS selectively induced inhibitory but not excitatory synapse related protein loss. Notably, C3a receptor antagonist SB290157 trifluoroacetate attenuated LPS-induced hippocampal neuroinflammation and inhibitory synapse related protein loss, contributing to improved cognitive function. In conclusion, our study suggests that complement C3/C3a receptor signaling plays a key role in LPS-induced cognitive impairments, which may serve a therapeutic target for systemic inflammation related cognitive disorders.

Cortical Gray Matter Injury in Encephalopathy of Prematurity: Link to Neurodevelopmental Disorders

Preterm-born infants frequently suffer from an array of neurological damage, collectively termed encephalopathy of prematurity (EoP). They also have an increased risk of presenting with a neurodevelopmental disorder (e.g., autism spectrum disorder; attention deficit hyperactivity disorder) later in life. It is hypothesized that it is the gray matter injury to the cortex, in addition to white matter injury, in EoP that is responsible for the altered behavior and cognition in these individuals. However, although it is established that gray matter injury occurs in infants following preterm birth, the exact nature of these changes is not fully elucidated. Here we will review the current state of knowledge in this field, amalgamating data from both clinical and preclinical studies. This will be placed in the context of normal processes of developmental biology and the known pathophysiology of neurodevelopmental disorders. Novel diagnostic and therapeutic tactics required integration of this information so that in the future we can combine mechanism-based approaches with patient stratification to ensure the most efficacious and cost-effective clinical practice.

Shifting equilibriums in Alzheimer's disease: the complex roles of microglia in neuroinflammation, neuronal survival and neurogenesis

Alzheimer's disease is the leading cause of dementia. Its increased prevalence in developed countries, due to the sharp rise in ageing populations, presents one of the costliest challenges to modern medicine. In order to find disease-modifying therapies to confront this challenge, a more complete understanding of the pathogenesis of Alzheimer's disease is necessary. Recent studies have revealed increasing evidence for the roles played by microglia, the resident innate immune system cells of the brain. Reflecting the well-established roles of microglia in reacting to pathogens and inflammatory stimuli, there is now a growing literature describing both protective and detrimental effects for individual cytokines and chemokines produced by microglia in Alzheimer's disease. A smaller but increasing number of studies have also addressed the divergent roles played by microglial neurotrophic and neurogenic factors, and how their perturbation may play a key role in the pathogenesis of Alzheimer's disease. Here we review recent findings on the roles played by microglia in neuroinflammation, neuronal survival and neurogenesis in Alzheimer's disease. In each case, landmark studies have provided evidence for the divergent ways in which microglia can either promote neuronal function and survival, or perturb neuronal function, leading to cell death. In many cases, the secreted molecules of microglia can lead to divergent effects depending on the magnitude and context of microglial activation. This suggests that microglial functions must be maintained in a fine equilibrium, in order to support healthy neuronal function, and that the cellular microenvironment in the Alzheimer's disease brain disrupts this fine balance, leading to neurodegeneration. Thus, an understanding of microglial homeostasis, both in health and across the trajectory of the disease state, will improve our understanding of the pathogenic mechanisms underlying Alzheimer's disease, and will hopefully lead to the development of microglial-based therapeutic strategies to restore equilibrium in the Alzheimer's disease brain.

The role of microglia in neuroprogressive disorders: mechanisms and possible neurotherapeutic effects of induced ketosis

A comprehensive review of molecular mechanisms involved in the promotion and maintenance of distinct microglia phenotypes is provided. The acquisition and perpetuation of predominantly pro-inflammatory microglial phenotypes have been implicated in the pathophysiology of several neuroprogressive diseases and is associated with reduced ATP production via oxidative phosphorylation, increased ATP generation by glycolysis, elevated oxidative and nitrosative stress and other metabolic, inflammatory and hormonal insults. Microglia can also adopt a predominantly anti-inflammatory phenotypes with neuroprotective properties. Strategies that promote and maintain a predominantly anti-inflammatory phenotype may hold promise as novel therapeutic opportunities for neuroprogressive illness. Induced ketosis may promote a transition towards predominantly anti-inflammatory microglial states/phenotypes by several mechanisms, including inhibition of glycolysis and increased NAD⁺ production; engagement of microglial GPR109A receptors; histone deacetylase inhibition; and elevated n-3 polyunsaturated fatty acids levels. Since microglia activation can now be assessed in vivo, these data provide a clear rationale for the design of transdiagnostic randomized controlled trials of the ketogenic diet and other ketosis-inducing strategies for neuroprogressive diseases, which may also provide mechanistic insights through the assessment of "target engagement".

Long non-coding RNA CRNDE deteriorates intrauterine infection-induced neonatal brain injury

BACKGROUND

This study aimed to test the hypothesis that long non-coding RNA (lncRNA) colorectal neoplasia differentially expressed (CRNDE) could exacerbate brain injury caused by intrauterine infection in neonatal rats.

METHODS

Intrauterine infection was induced in pregnant rats by lipopolysaccharide (LPS). After delivery, newborn rats with brain injury caused by intrauterine infection were randomly divided into control, control shRNA, and CRNDE shRNA groups. CRNDE expression in serum and amniotic fluid of pregnant rats and neonatal brain tissues were determined by quantitative real-time PCR (qRT-PCR). Morris water maze (MWM) task was used to test the spatial learning and memory ability. Histological examination and apoptosis detection were performed by hematoxylin and eosin (H&E) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, respectively. Immunohistochemistry was conducted to evaluate the activation of astrocytes and microglia.

RESULTS

LncRNA CRNDE was highly expressed in serum and amniotic fluid of maternal rats and in brain tissues of offspring rats. Furthermore, shRNA-mediated CRNDE downregulation could rescue the spatial learning and memory ability, improve brain histopathological changes and cell death, and inhibit the activation of astrocytes and microglia caused by LPS.

CONCLUSION

CRNDE silencing possessed a cerebral protective effect in neonatal rats with brain injury caused by interauterine infection.

The unique expression profile of FAM19A1 in the mouse brain and its association with hyperactivity, long-term memory and fear acquisition

Neurodevelopment and mature brain function are spatiotemporally regulated by various cytokines and chemokines. The chemokine-like neuropeptide FAM19A1 is a member of family with sequence similarity 19 (FAM19), which is predominantly expressed in the brain. Its highly conserved amino acid sequence among vertebrates suggests that FAM19A1 may play important physiological roles in neurodevelopment and brain function. Here we used a LacZ reporter gene system to map the expression pattern of the FAM19A1 gene in the mouse brain. The FAM19A1 expression was observed in several brain regions starting during embryonic brain development. As the brain matured, the FAM19A1 expression was detected in the pyramidal cells of cortical layers 2/3 and 5 and in several limbic areas, including the hippocampus and the amygdala. FAM19A1-deficient mice were used to evaluate the physiological contribution of FAM19A1 to various brain functions. In behavior analysis, FAM19A1-deficient mice exhibited several abnormal behaviors, including hyperactive locomotor behavior, long-term memory deficits and fear acquisition failure. These findings provide insight into the potential contributions of FAM19A1 to neurodevelopment and mature brain function.

Interleukin-1 receptor antagonist ameliorates the pain hypersensitivity, spinal inflammation and oxidative stress induced by systemic lipopolysaccharide in neonatal rats

Perinatal inflammation-induced reduction in pain threshold may alter pain sensitivity to hyperalgesia or allodynia which may persist into adulthood. In this study, we investigated the anti-inflammatory protective effect of interleukin-1 receptor antagonist (IL-1ra), an anti-inflammatory cytokine, on systemic lipopolysaccharide (LPS)-induced spinal cord inflammation and oxidative stress, thermal hyperalgesia, and mechanical allodynia in neonatal rats. Intraperitoneal (i.p.) injection of LPS (2 mg/kg) or sterile saline was performed in postnatal day 5 (P5) rat pups, and IL-1ra (100 mg/kg) or saline was administered (i.p.) 5 min after LPS injection. Pain reflex behavior, spinal cord inflammation and oxidative stress were examined 24 h after LPS administration. Systemic LPS exposure led to a reduction of tactile threshold in the von Frey filament tests (mechanical allodynia) and pain response latency in the tail-flick test (thermal hyperalgesia) of P6 neonatal rats. Spinal cord inflammation was indicated by the increased numbers of activated glial cells including microglia (Iba1+) and astrocytes (GFAP+), and elevated levels of pro-inflammatory cytokine interleukin-1β (IL-1β), cyclooxygenase-2 (COX-2), and prostaglandin E2 (PGE2) 24 h after LPS treatment. LPS treatment induced spinal oxidative stress as evidenced by the increase in thiobarbituric acid reactive substances (TBARS) content in the spinal cord. LPS exposure also led to a significant increase in oligodendrocyte lineage population (Olig2+) and mature oligodendrocyte cells (APC+) in the neonatal rat spinal cord. IL-1ra treatment significantly reduced LPS-induced effects including hyperalgesia, allodynia, the increased number of activated microglia, astrocytes and oligodendrocytes, and elevated levels of IL-1β, COX-2, PGE2, and lipid peroxidation (TBARS) in the neonatal rat spinal cord. These data suggest that IL-1ra provides a protective effect against the development of pain hypersensitivity, spinal cord inflammation and oxidative stress in the neonatal rats following LPS exposure, which may be associated with the blockade of LPS-induced pro-inflammatory cytokine IL-1β.

Polyphenols from Food and Natural Products: Neuroprotection and Safety

Polyphenols are naturally occurring micronutrients that are present in many food sources. Besides being potent antioxidants, these molecules may also possess anti-inflammatory properties. Many studies have highlighted their potential role in the prevention and treatment of various pathological conditions connected to oxidative stress and inflammation (e.g., cancer, and cardiovascular and neurodegenerative disorders). Neurodegenerative diseases are globally one of the main causes of death and represent an enormous burden in terms of human suffering, social distress, and economic costs. Recent data expanded on the initial antioxidant-based mechanism of polyphenols’ action by showing that they are also able to modulate several cell-signaling pathways and mediators. The proposed benefits of polyphenols, either as protective/prophylactic substances or as therapeutic molecules, may be achieved by the consumption of a natural polyphenol-enriched diet, by their use as food supplements, or with formulations as pharmaceutical drugs/nutraceuticals. It has also been proved that the health effects of polyphenols depend on the consumed amount and their bioavailability. However, their overconsumption may raise safety concerns due to the accumulation of high levels of these molecules in the organism, particularly if we consider the loose regulatory legislation regarding the commercialization and use of food supplements. This review addresses the main beneficial effects of food polyphenols, and focuses on neuroprotection and the safety issues related to overconsumption.

Dihydrolipoic Acid-Gold Nanoclusters Regulate Microglial Polarization and Have the Potential To Alter Neurogenesis

Microglia-mediated neuroinflammation is one of the most significant features in a variety of central nervous system (CNS) disorders such as traumatic brain injury, stroke, and many neurodegenerative diseases. Microglia become polarized upon stimulation. The two extremes of the polarization are the neuron-destructive proinflammatory M1-like and the neuron-regenerative M2-like phenotypes. Thus, manipulating microglial polarization toward the M2 phenotype is a promising therapeutic approach for CNS repair and regeneration. It has been reported that nanoparticles are potential tools for regulating microglial polarization. Gold nanoclusters (AuNCs) could penetrate the blood-brain barrier and have neuroprotective effects, suggesting the possibility of utilizing AuNCs to regulate microglial polarization and improve neuronal regeneration in CNS. In the current study, AuNCs functionalized with dihydrolipoic acid (DHLA-AuNCs), an antioxidant with demonstrated neuroprotective roles, were prepared, and their effects on polarization of a microglial cell line (BV2) were examined. DHLA-AuNCs effectively suppressed proinflammatory processes in BV2 cells by inducing polarization toward the M2-like phenotype. This was associated with a decrease in reactive oxygen species and reduced NF-kB signaling and an improvement in cell survival coupled with enhanced autophagy and inhibited apoptosis. Conditioned medium from DHLA-AuNC-treated BV2 cells was able to enhance neurogenesis in both the neuronal cell line N2a and in an ex vivo brain slice stroke model. The direct treatment of brain slices with DHLA-AuNCs also ameliorated stroke-related tissue injury and reduced astrocyte activation (astrogliosis). This study suggests that by regulating neuroinflammation to improve neuronal regeneration, DHLA-AuNCs could be a potential therapeutic agent in CNS disorders.

Pathways of Prevention: A Scoping Review of Dietary and Exercise Interventions for Neurocognition

Alzheimer's disease and related dementias (ADRD) represent an increasingly urgent public health concern, with an increasing number of baby boomers now at risk. Due to a lack of efficacious therapies among symptomatic older adults, an increasing emphasis has been placed on preventive measures that can curb or even prevent ADRD development among middle-aged adults. Lifestyle modification using aerobic exercise and dietary modification represents one of the primary treatment modalities used to mitigate ADRD risk, with an increasing number of trials demonstrating that exercise and dietary change, individually and together, improve neurocognitive performance among middle-aged and older adults. Despite several optimistic findings, examination of treatment changes across lifestyle interventions reveals a variable pattern of improvements, with large individual differences across trials. The present review attempts to synthesize available literature linking lifestyle modification to neurocognitive changes, outline putative mechanisms of treatment improvement, and discuss discrepant trial findings. In addition, previous mechanistic assumptions linking lifestyle to neurocognition are discussed, with a focus on potential solutions to improve our understanding of individual neurocognitive differences in response to lifestyle modification. Specific recommendations include integration of contemporary causal inference approaches for analyzing parallel mechanistic pathways and treatment-exposure interactions. Methodological recommendations include trial multiphase optimization strategy (MOST) design approaches that leverage individual differences for improved treatment outcomes.

NEIL1 stimulates neurogenesis and suppresses neuroinflammation after stress

Cellular exposure to ionizing radiation leads to oxidatively generated DNA damage, which has been implicated in neurodegenerative diseases. DNA damage is repaired by the evolutionarily conserved base excision repair (BER) system. Exposure of mice to ionizing radiation affects neurogenesis and neuroinflammation. However, the consequences of deficient DNA repair on adult neurogenesis and neuroinflammation are poorly understood despite their potential relevance for homeostasis. We previously reported that loss of NEIL1, an important DNA glycosylase involved in BER, is associated with deficiencies in spatial memory, olfaction, and protection against ischemic stroke in mice. Here, we show that Neil1^-/- mice display an anxiety-mediated behavior in the open field test, a deficient recognitive memory in novel object recognition and increased neuroinflammatory response under basal conditions. Further, mice lacking NEIL1 have decreased neurogenesis and deficient resolution of neuroinflammation following gamma irradiation (IR)-induced stress compared to WT mice. Neil1^-/- IR-exposed mice also exhibit increased DNA damage and apoptosis in the hippocampus. Interestingly, behavioral tests two weeks after IR showed impaired stress response in the Neil1^-/- mice. Our data indicate that NEIL1 plays an important role in adult neurogenesis and in the resolution of neuroinflammation.

The detrimental effects of lipopolysaccharide-induced neuroinflammation on adult hippocampal neurogenesis depend on the duration of the pro-inflammatory response

Adult hippocampal neurogenesis is a finely tuned process regulated by extrinsic factors. Neuroinflammation is a hallmark of several pathological conditions underlying dysregulation of neurogenesis. In animal models, lipopolysaccharide (LPS)-induced neuroinflammation leads to a neurogenic decrease mainly associated to the early inflammatory response. However, it is not well understood how the neuroinflammatory response progresses over time and if neurogenesis continues to be diminished during the late neuroinflammatory response. Moreover, it is unknown if repeated intermittent administration of LPS along time induces a greater reduction in neurogenesis. We administered one single intraperitoneal injection of LPS or saline or four repeated injections (one per week) of LPS or saline to young-adult mice. A cohort of new cells was labeled with three 5-bromo-2-deoxyuridine injections (one per day) 4 days after the last LPS injection. We evaluated systemic and neuroinflammation-associated parameters and compared the effects of the late neuroinflammatory response on neurogenesis induced by each protocol. Our results show that 1) a single LPS injection leads to a late pro-inflammatory response characterized by microglial activation, moderate astrocytic reaction and increased interleukin-6 levels. This response correlates in time with decreased neurogenesis and 2) a repeated intermittent injection of LPS does not elicit a late pro-inflammatory response although activated microglia persists. The latter profile is not accompanied by a continued long-term hippocampal neurogenic decrease. Hereby, we provide evidence that the neuroinflammatory response is a dynamic process that progresses in a milieu-dependent manner and does not necessarily lead to a neurogenic decrease, highlighting the complex interaction between the immune system and neurogenesis.

Role of Prefrontal Cortex Anti- and Pro-inflammatory Cytokines in the Development of Abnormal Behaviors Induced by Disconnection of the Ventral Hippocampus in Neonate Rats

Neonatal disconnection of ventral hippocampus (VH) outputs in rats has been reported to lead to post-pubertal behavioral and synaptic changes of relevance to schizophrenia. Increased oxidative and inflammatory load in the prefrontal cortex (PFC) has been suggested to mediate some of the effects of neonatal VH lesion (NVHL). In this study, we hypothesized that developmental imbalance of anti- and pro-inflammatory factors within the PFC might affect synaptic development thus contributing to the adult NVHL-induced behavioral deficits. Ibotenic acid-induced excitotoxic NVHL was performed in postnatal day (PD) 7 male Sprague-Dawley rats and the mRNA levels of select pro- and anti-inflammatory cytokines were measured in the medial PFC (mPFC) at two developmental time points (PD15 and PD60). We observed a development-specific increase of pro-inflammatory cytokine, interleukin (IL)-1β mRNA at PD15, and an overall reduction in the expression and signaling of transforming growth factor beta 1 (TGF-β1), an anti-inflammatory cytokine, at both PD15 and PD60 in the NVHL animals. These cytokine changes were not seen in the somatosensory cortex (SSC) or tissue surrounding the lesion site. Daily administration of systemic recombinant TGF-β1 from PD7-14 prevented the appearance of hyperlocomotion, deficits in prepulse inhibition (PPI) of startle and social interaction (SI) in post-pubertal (PD60) NVHL rats. Neonatal supplementation of TGF-β1 was also able to attenuate dendritic spine loss in the layer 3 mPFC pyramidal neurons of NVHL animals. These results suggest that early damage of the VH has long-lasting inflammatory consequences in distant connected structures, and that TGF-β1 has potential to confer protection against the deleterious effects of developmental hippocampal damage.

Trigonelline mitigates lipopolysaccharide-induced learning and memory impairment in the rat due to its anti-oxidative and anti-inflammatory effect

Brain inflammation is associated with cognitive dysfunction, especially in elderly. Trigonelline is a plant alkaloid and a major component of coffee and fenugreek with anti-diabetic, antioxidant, anti-inflammatory, and neuroprotective effects. In this study, the beneficial effect of trigonelline against lipopolysaccharide (LPS)-induced cognitive decline was assessed in the rat. LPS was injected i.p. at a dose of 500 μg/kg to induce neuroinflammation and trigonelline was administered p.o. at doses of 20, 40, or 80 mg/kg/day 1 h after LPS that continued for one week. Trigonelline-treated LPS-challenged rats showed improved spatial recognition memory in Y maze, discrimination ratio in novel object discrimination test, and retention and recall in passive avoidance paradigm. Additionally, trigonelline lowered hippocampal malondialdehyde (MDA) and acetylcholinesterase (AChE) activity and improved superoxide dismutase (SOD), catalase, and glutathione (GSH). Furthermore, trigonelline depressed hippocampal nuclear factor-kappaB (NF-κB), toll-like receptor 4 (TLR4), and tumor necrosis factor α (TNF α) in LPS-challenged rats. All of the effects of trigonelline followed a dose-dependent pattern and in some aspects, it acted even better than the routinely-used anti-inflammatory drug dexamethasone. Collectively, trigonelline is capable to diminish LPS-induced cognitive decline via suppression of hippocampal oxidative stress and inflammation and appropriate modulation of NF-κB/TLR4 and AChE activity.

Soy isoflavone genistein attenuates lipopolysaccharide-induced cognitive impairments in the rat via exerting anti-oxidative and anti-inflammatory effects

Systemic inflammation during infectious disorders usually accompanies chronic complications including cognitive dysfunction. Neuroinflammation and cognitive deficit are also observed in some debilitating neurological disorders like Alzheimer's and Parkinson's diseases. Genistein is a soy isoflavone with multiple beneficial effects including anti-inflammatory, anti-oxidative, and protective properties. In this research study, the effect of genistein in prevention of lipopolysaccharide (LPS)-induced cognitive dysfunction was investigated. LPS was given i.p. (500 μg/kg/day) and genistein was orally given (10, 50, or 100 mg/kg) for one week. Findings showed that genistein could dose-dependently attenuate spatial recognition, discrimination, and memory deficits. Additionally, genistein treatment of LPS-challenged group lowered hippocampal level of malondialdehyde (MDA) and increased activity of superoxide dismutase (SOD) and catalase and glutathione (GSH) level. Furthermore, genistein ameliorated hippocampal acetylcholinesterase (AChE) activity in LPS-challenged rats. Furthermore, genistein administration to LPS-injected group lowered hippocampal level of interleukin 6 (IL-6), nuclear factor-kappaB (NF-κB) p65, toll-like receptor 4 (TLR4), tumor necrosis factor α (TNFα), cyclooxygenase-2 (COX2), inducible nitric oxide synthase (iNOS), glial fibrillary acidic protein (GFAP), and increased hippocampal level of antioxidant element nuclear factor (erythroid-derived 2)-like 2 (Nrf2). In conclusion, genistein alleviated LPS-induced cognitive dysfunctions and neural inflammation attenuation of oxidative stress and AChE activity and appropriate modulation of Nrf2/NF-κB/IL-6/TNFα/COX2/iNOS/TLR4/GFAP.

MicroRNAs of microglia: Wrestling with central nervous system disease

Microglia serve as brain-resident myeloid cells that affect cerebral development, ischemia, neurodegeneration, and neuro-viral infection. MicroRNAs play a key role in central nervous system disease through post-transcriptional regulation. Indeed, evidence shows that microRNAs are one of the most important regulators mediating microglial activation, polarization, and autophagy, and subsequently affecting neuroinflammation and the outcome of central nervous system disease. In this review, we provide insight into the function of microRNAs, which may be an attractive strategy and influential treatment for microglia-related central nervous system dysfunction. Moreover, we comprehensively describe how microglia fight against central nervous system disease via multiple functional microRNAs.