Exogenous BDNF increases neurogenesis in the hippocampus in experimental Streptococcus pneumoniae meningitis

Visual stimulation and brain-derived neurotrophic factor (BDNF) have protective effects in experimental autoimmune uveoretinitis

AIMS

To investigate the therapeutic potential of visual stimulation (VS) and BDNF in murine experimental autoimmune uveoretinitis (EAU).

MAIN METHODS

Mice were immunized by subcutaneous injection of interphotoreceptor retinoid-binding protein in Freund's complete adjuvant and intravenous injection of pertussis toxin, and were then exposed to high-contrast VS 12 h/day (days 1-14 post-immunization). EAU severity was assessed by examining clinical score, visual acuity, inflammatory markers, and immune cells in the retina. The transcriptome of activated retinal cells was determined by RNA-seq using RNA immunoprecipitated in complex with phosphorylated ribosomal protein S6. The retinal levels of protein products of relevant upregulated genes were quantified. The effect of BDNF on EAU was tested in unstimulated mice by its daily topical ocular administration (days 8-14 post-immunization).

KEY FINDINGS

VS attenuated EAU development and decreased the expression of pro-inflammatory cytokines/chemokines and numbers of immune cells in the retina (n = 10-20 eyes/group for each analysis). In activated retinal cells of control mice (n = 30 eyes/group), VS upregulated genes encoding immunomodulatory neuropeptides, of which BDNF and vasoactive intestinal peptide (VIP) also showed increased mRNA and protein levels in the retina of VS-treated EAU mice (n = 6-10 eyes/group for each analysis). In unstimulated EAU mice, BDNF treatment mimicked the protective effects of VS by modulating the inflammatory and stem cell properties of Müller cells (n = 5 eyes/group for each analysis).

SIGNIFICANCE

VS effectively suppresses EAU, at least through enhancing retinal levels of anti-inflammatory and neuroprotective factors, VIP and BDNF. Our findings also suggest BDNF as a promising therapeutic agent for uveitis treatment.

A review on current advancement in zebrafish models to study chronic inflammatory diseases and their therapeutic targets

Chronic inflammatory diseases are caused due to prolonged inflammation at a specific site of the body. Among other inflammatory diseases, bacterial meningitis, chronic obstructive pulmonary disease (COPD), atherosclerosis and inflammatory bowel diseases (IBD) are primarily focused on because of their adverse effects and fatality rates around the globe in recent times. In order to come up with novel strategies to eradicate these diseases, a clear understanding of the mechanisms of the diseases is needed. Similarly, detailed insight into the mechanisms of commercially available drugs and potent lead compounds from natural sources are also important to establish efficient therapeutic effects. Zebrafish is widely accepted as a model to study drug toxicity and the pharmacokinetic effects of the drug. Moreover, researchers use various inducers to trigger inflammatory cascades and stimulate physiological changes in zebrafish. The effect of these inducers contrasts with the type of zebrafish used in the investigation. Hence, a thorough analysis is required to study the current advancements in the zebrafish model for chronic inflammatory disease suppression. This review presents the most common inflammatory diseases, commercially available drugs, novel therapeutics, and their mechanisms of action for disease suppression. The review also provides a detailed description of various zebrafish models for these diseases. Finally, the future prospects and challenges for the same are described, which can help the researchers understand the potency of the zebrafish model and its further exploration for disease attenuation.

Spatio-temporal brain invasion pattern of Streptococcus pneumoniae and dynamic changes in the cellular environment in bacteremia-derived meningitis

Streptococcus pneumoniae (the pneumococcus) is the major cause of bacterial meningitis globally, and pneumococcal meningitis is associated with increased risk of long-term neurological sequelae. These include several sensorimotor functions that are controlled by specific brain regions which, during bacterial meningitis, are damaged by a neuroinflammatory response and the deleterious action of bacterial toxins in the brain. However, little is known about the invasion pattern of the pneumococcus into the brain. Using a bacteremia-derived meningitis mouse model, we combined 3D whole brain imaging with brain microdissection to show that all brain regions were equally affected during disease progression, with the presence of pneumococci closely associated to the microvasculature. In the hippocampus, the invasion provoked microglial activation, while the neurogenic niche showed increased proliferation and migration of neuroblasts. Our results indicate that, even before the outbreak of symptoms, the bacterial load throughout the brain is high and causes neuroinflammation and cell death, a pathological scenario which ultimately leads to a failing regeneration of new neurons.

An insight into crosstalk among multiple signalling pathways contributing to the pathophysiology of PTSD and depressive disorders

Post-traumatic stress disorder (PTSD) and depressive disorders represent two significant mental health challenges with substantial global prevalence. These are debilitating conditions characterized by persistent, often comorbid, symptoms that severely impact an individual's quality of life. Both PTSD and depressive disorders are often precipitated by exposure to traumatic events or chronic stress. The profound impact of PTSD and depressive disorders on individuals and society necessitates a comprehensive exploration of their shared and distinct pathophysiological features. Although the activation of the stress system is essential for maintaining homeostasis, the ability to recover from it after diminishing the threat stimulus is also equally important. However, little is known about the main reasons for individuals' differential susceptibility to external stressful stimuli. The solution to this question can be found by delving into the interplay of stress with the cognitive and emotional processing of traumatic incidents at the molecular level. Evidence suggests that dysregulation in these signalling cascades may contribute to the persistence and severity of PTSD and depressive symptoms. The treatment strategies available for this disorder are antidepressants, which have shown good efficiency in normalizing symptom severity; however, their efficacy is limited in most individuals. This calls for the exploration and development of innovative medications to address the treatment of PTSD. This review delves into the intricate crosstalk among multiple signalling pathways implicated in the development and manifestation of these mental health conditions. By unravelling the complexities of crosstalk among multiple signalling pathways, this review aims to contribute to the broader knowledge base, providing insights that could inform the development of targeted interventions for individuals grappling with the challenges of PTSD and depressive disorders.

Brain Infection by Group B Streptococcus Induces Inflammation and Affects Neurogenesis in the Adult Mouse Hippocampus

Central nervous system infections caused by pathogens crossing the blood-brain barrier are extremely damaging and trigger cellular alterations and neuroinflammation. Bacterial brain infection, in particular, is a major cause of hippocampal neuronal degeneration. Hippocampal neurogenesis, a continuous multistep process occurring throughout life in the adult brain, could compensate for such neuronal loss. However, the high rates of cognitive and other sequelae from bacterial meningitis/encephalitis suggest that endogenous repair mechanisms might be severely affected. In the current study, we used Group B Streptococcus (GBS) strain NEM316, to establish an adult mouse model of brain infection and determine its impact on adult neurogenesis. Experimental encephalitis elicited neurological deficits and death, induced inflammation, and affected neurogenesis in the dentate gyrus of the adult hippocampus by suppressing the proliferation of progenitor cells and the generation of newborn neurons. These effects were specifically associated with hippocampal neurogenesis while subventricular zone neurogenesis was not affected. Overall, our data provide new insights regarding the effect of GBS infection on adult brain neurogenesis.

The salt-inducible kinases inhibitor HG-9-91-01 exhibits antidepressant-like actions in mice exposed to chronic unpredictable mild stress

Major depressive disorder is a frequently occurring neuropsychiatric disorder throughout the world. However, the limited and delayed therapeutic efficacy of monoaminergic medications has led to intensive research efforts to develop novel antidepressants. We have previously demonstrated that hippocampal salt-inducible kinase 2 (SIK2) plays a role in the pathogenesis of depression via regulating the downstream CREB-regulated transcription coactivator 1 (CRTC1)-cAMP response element-binding protein (CREB)-brain derived neurotrophic factor (BDNF) pathway. HG-9-91-01 is a potent and selective inhibitor of salt-inducible kinases (SIKs). The present study aims to explore whether HG-9-91-01 has antidepressant-like actions in male C57BL/6J mice. The chronic unpredictable mild stress (CUMS) model of depression, various behavioral tests, western blotting, co-immunoprecipitation, immunofluorescence, stereotactic infusion, and viral-mediated genetic knockdown were used together. It was found that hippocampal infusion of HG-9-91-01 induced significant antidepressant-like effects in the CUMS model, accompanied with preventing the enhancement of CUMS on the hippocampal SIK2 expression and cytoplasmic translocation of CRTC1. HG-9-91-01 treatment also reversed the decreasing effects of CUMS on the BDNF signaling cascade and adult neurogenesis in the hippocampus. Moreover, the antidepressant-like actions of HG-9-91-01 in mice required the hippocampal CRTC1-CREB-BDNF pathway. In conclusion, HG-9-91-01 has potential of being a novel antidepressant candidate.

Oral Exposure to Lead Acetate for 28 Days Reduces the Number of Neural Progenitor Cells but Increases the Number and Synaptic Plasticity of Newborn Granule Cells in Adult Hippocampal Neurogenesis of Young-Adult Rats

Lead (Pb) causes developmental neurotoxicity. Developmental exposure to Pb acetate (PbAc) induces aberrant hippocampal neurogenesis by increasing or decreasing neural progenitor cell (NPC) subpopulations in the dentate gyrus (DG) of rats. To investigate whether hippocampal neurogenesis is similarly affected by PbAc exposure in a general toxicity study, 5-week-old Sprague-Dawley rats were orally administered PbAc at 0, 4000, and 8000 ppm (w/v) in drinking water for 28 days. After exposure to 4000 or 8000 ppm PbAc, Pb had accumulated in the brains. Neurogenesis was suppressed by 8000 ppm PbAc, which was related to decreased number of type-2b NPCs, although number of mature granule cells were increased by both PbAc doses. Gene expression in the 8000 ppm PbAc group suggested suppressed NPC proliferation and increased apoptosis resulting in suppressed neurogenesis. PbAc exposure increased numbers of metallothionein-I/II⁺ cells and GFAP⁺ astrocytes in the DG hilus, and upregulated Mt1, antioxidant genes (Hmox1 and Gsta5), and Il6 in the DG, suggesting the induction of oxidative stress and neuroinflammation related to Pb accumulation resulting in suppressed neurogenesis. PbAc at 8000 ppm also upregulated Ntrk2 and increased the number of CALB2⁺ interneurons, suggesting the activation of BDNF-TrkB signaling and CALB2⁺ interneuron-mediated signals to ameliorate suppressed neurogenesis resulting in increased number of newborn granule cells. PbAc at both doses increased the number of ARC⁺ granule cells, suggesting the facilitation of synaptic plasticity of newborn granule cells through the activation of BDNF-TrkB signaling. These results suggest that PbAc exposure during the young-adult stage disrupted hippocampal neurogenesis, which had a different pattern from developmental exposure to PbAc. However, the induction of oxidative stress/neuroinflammation and activation of identical cellular signals occurred irrespective of the life stage at PbAc exposure.

Continuous Exposure to Alpha-Glycosyl Isoquercitrin from Gestation Ameliorates Disrupted Hippocampal Neurogenesis in Rats Induced by Gestational Injection of Valproic Acid

This study examined the ameliorating effect of alpha-glycosyl isoquercitrin (AGIQ), an antioxidant, on disrupted hippocampal neurogenesis in the dentate gyrus (DG) in a rat model of autism spectrum disorder induced by prenatal valproic acid (VPA) exposure. Dams were intraperitoneally injected with 500 mg/kg VPA on gestational day 12. AGIQ was administered in the diet at 0.25 or 0.5% to dams from gestational day 13 until weaning at postnatal day (PND) 21 and then to pups until PND 63. At PND 21, VPA-exposed offspring showed decreased numbers of type-2a and type-3 neural progenitor cells (NPCs) among granule cell lineage subpopulations. AGIQ treatment at both doses rescued the reduction in type-3 NPCs. AGIQ upregulated Reln and Vldlr transcript levels in the DG at 0.5% and ≥ 0.25%, respectively, and increased the number of reelin⁺ interneurons in the DG hilus at 0.5%. AGIQ at 0.25% and/or 0.5% also upregulated Ntrk2, Cntf, Igf1, and Chrnb2. At PND 63, there were no changes in the granule cell lineage subpopulations in response to VPA or AGIQ. AGIQ at 0.25% increased the number of FOS⁺ granule cells, accompanied by Gria2 and Gria3 upregulation and increasing trend in the number of FOS⁺ granule cells at 0.5%. There was no definitive evidence of VPA-induced oxidative stress in the hippocampus throughout postnatal life. These results indicate that AGIQ ameliorates the VPA-induced disruption of hippocampal neurogenesis at weaning involving reelin, BDNF-TrkB, CNTF, and IGF1 signaling, and enhances FOS-mediated synaptic plasticity in adulthood, potentially through AMPA-receptor upregulation. The ameliorating effects of AGIQ may involve direct interactions with neural signaling cascades rather than antioxidant capacity.

Interactions Among Brain-Derived Neurotrophic Factor and Neuroimmune Pathways Are Key Components of the Major Psychiatric Disorders

The purpose of this review is to summarize the current knowledge regarding the reciprocal associations between brain-derived neurotrophic factor (BDNF) and immune-inflammatory pathways and how these links may explain the involvement of this neurotrophin in the immune pathophysiology of mood disorders and schizophrenia. Toward this end, we delineated the protein-protein interaction (PPI) network centered around BDNF and searched PubMed, Scopus, Google Scholar, and Science Direct for papers dealing with the involvement of BDNF in the major psychosis, neurodevelopment, neuronal functions, and immune-inflammatory and related pathways. The PPI network was built based on the significant interactions of BDNF with neurotrophic (NTRK2, NTF4, and NGFR), immune (cytokines, STAT3, TRAF6), and cell-cell junction (CTNNB, CDH1) DEPs (differentially expressed proteins). Enrichment analysis shows that the most significant terms associated with this PPI network are the tyrosine kinase receptor (TRKR) and Src homology region two domain-containing phosphatase-2 (SHP2) pathways, tyrosine kinase receptor signaling pathways, positive regulation of kinase and transferase activity, cytokine signaling, and negative regulation of the immune response. The participation of BDNF in the immune response and its interactions with neuroprotective and cell-cell adhesion DEPs is probably a conserved regulatory process which protects against the many detrimental effects of immune activation and hyperinflammation including neurotoxicity. Lowered BDNF levels in mood disorders and schizophrenia (a) are associated with disruptions in neurotrophic signaling and activated immune-inflammatory pathways leading to neurotoxicity and (b) may interact with the reduced expression of other DEPs (CTNNB1, CDH1, or DISC1) leading to multiple aberrations in synapse and axonal functions.

Clathrin-nanoparticles deliver BDNF to hippocampus and enhance neurogenesis, synaptogenesis and cognition in HIV/neuroAIDS mouse model

Brain derived neurotrophic factor (BDNF) promotes the growth, differentiation, maintenance and survival of neurons. These attributes make BDNF a potentially powerful therapeutic agent. However, its charge, instability in blood, and poor blood brain barrier (BBB) penetrability have impeded its development. Here, we show that engineered clathrin triskelia (CT) conjugated to BDNF (BDNF-CT) and delivered intranasally increased hippocampal BDNF concentrations 400-fold above that achieved previously with intranasal BDNF alone. We also show that BDNF-CT targeted Tropomyosin receptor kinase B (TrkB) and increased TrkB expression and downstream signaling in iTat mouse brains. Mice were induced to conditionally express neurotoxic HIV Transactivator-of-Transcription (Tat) protein that decreases BDNF. Down-regulation of BDNF is correlated with increased severity of HIV/neuroAIDS. BDNF-CT enhanced neurorestorative effects in the hippocampus including newborn cell proliferation and survival, granule cell neurogenesis, synaptogenesis and increased dendritic integrity. BDNF-CT exerted cognitive-enhancing effects by reducing Tat-induced learning and memory deficits. These results show that CT bionanoparticles efficiently deliver BDNF to the brain, making them potentially powerful tools in regenerative medicine.

Hippocampal MSK1 regulates the behavioral and biological responses of mice to chronic social defeat stress: Involving of the BDNF-CREB signaling and neurogenesis

Depression is one of the most common psychiatric diseases in the 21st century, while its pathogenesis is not yet fully understood. Currently, besides to the monoaminergic system, the brain-derived neurotrophic factor (BDNF)-cAMP response element-binding protein (CREB) signaling is one of the most attractive signaling pathways for treating depression. Mitogen and stress-activated kinase (MSK) 1 and 2 are nuclear proteins activated downstream of the ERK1/2 or p38 MAPK pathways, and it has been demonstrated that MSKs are involved in the BDNF-CREB signaling. Here we assumed that MSKs may play a role in depression, and various methods including the chronic social defeat stress (CSDS) model of depression, western blotting, immunofluorescence and virus-mediated gene transfer were used together. It was found that CSDS fully enhanced the expression of both phosphorylated MSK1 and total MSK1 in the hippocampus but not the medial prefrontal cortex (mPFC). CSDS did not influence the expression of phosphorylated MSK2 and total MSK2 in the two brain regions. Genetic over-expression of hippocampal MSK1 fully prevented not only the CSDS-induced depressive-like behaviors but also the CSDS-induced dysfunction in the hippocampal BDNF-CREB signaling and neurogenesis in mice, while genetic knockdown of hippocampal MSK1 aggravated the CSDS-induced depressive-like symptomatology in mice. Our results collectively suggest that although CSDS evidently enhances the activity of hippocampal MSK1, it is not a contributor to the CSDS-induced dysfunction in the brain but a defensive feedback regulator which protects against CSDS. Therefore, hippocampal MSK1 participates in the pathogenesis of depression and is a feasible and potential antidepressant target.

Chronic Administration of Thymoquinone Enhances Adult Hippocampal Neurogenesis and Improves Memory in Rats Via Regulating the BDNF Signaling Pathway

Thymoquinone is a pharmacologically active component of Nigella sativa Linn. seeds. Despite the diverse neuropharmacological attributes of TQ, limited reports related to adult neurogenesis and memory research are available. In this study, we investigated the effects of TQ on the proliferation and neural differentiation of cultured neural stem/progenitor cells (NSCs/NPCs). We also investigated the effect of TQ chronic administration on neurogenesis and memory in adult rats. Under proliferation conditions, TQ (0.05-0.3 μM) significantly increased NSCs/NPCs viability, neurosphere diameter, and cell count. TQ treatment under differentiation conditions increased the proportion of cells positive for Tuj1 (a neuronal marker). Furthermore, chronic oral administration of TQ (25 mg/kg/day for 12 weeks) to adult rats increased the number of bromodeoxyuridine (BrdU)-immunopositive cells double-stained with a mature neuronal marker, neuronal nuclei (NeuN), and a proliferation marker, doublecortin (Dcx), in the dentate gyrus of the hippocampus. TQ-administered rats showed a profound beneficial effect on avoidance-related learning ability, associated with an increase in the hippocampal mRNA and protein levels of brain-derived neurotrophic factor (BDNF), as measured by both real-time PCR and ELISA. Western blot analysis revealed that TQ stimulates the phosphorylation of cAMP-response element-binding protein (CREB), the upstream signaling molecule in the BDNF pathway. Furthermore, chronic administration of TQ decreased lipid peroxide and reactive oxygen species levels in the hippocampus. Taken together, our results suggest that TQ plays a role in memory improvement in adult rats and that the CREB/BDNF signaling pathways are involved in mediating the actions of TQ in hippocampal neurogenesis.

Regulation of the p75 neurotrophin receptor attenuates neuroinflammation and stimulates hippocampal neurogenesis in experimental Streptococcus pneumoniae meningitis

Background

Streptococcus pneumoniae meningitis is a destructive central nervous system (CNS) infection with acute and long-term neurological disorders. Previous studies suggest that p75NTR signaling influences cell survival, apoptosis, and proliferation in brain-injured conditions. However, the role of p75NTR signaling in regulating pneumococcal meningitis (PM)-induced neuroinflammation and altered neurogenesis remains largely to be elucidated.

Methods

p75NTR signaling activation in the pathological process of PM was assessed. During acute PM, a small-molecule p75NTR modulator LM11A-31 or vehicle was intranasally administered for 3 days prior to S. pneumoniae exposure. At 24 h post-infection, clinical severity, histopathology, astrocytes/microglia activation, neuronal apoptosis and necrosis, inflammation-related transcription factors and proinflammatory cytokines/mediators were evaluated. Additionally, p75NTR was knocked down by the adenovirus-mediated short-hairpin RNA (shRNA) to ascertain the role of p75NTR in PM. During long-term PM, the intranasal administration of LM11A-31 or vehicle was continued for 7 days after successfully establishing the PM model. Dynamic changes in inflammation and hippocampal neurogenesis were assessed.

Results

Our results revealed that both 24 h (acute) and 7, 14, 28 day (long-term) groups of infected rats showed increased p75NTR expression in the brain. During acute PM, modulation of p75NTR through pretreatment of PM model with LM11A-31 significantly alleviated S. pneumoniae-induced clinical severity, histopathological injury and the activation of astrocytes and microglia. LM11A-31 pretreatment also significantly ameliorated neuronal apoptosis and necrosis. Moreover, we found that blocking p75NTR with LM11A-31 decreased the expression of inflammation-related transcription factors (NF-κBp65, C/EBPβ) and proinflammatory cytokines/mediators (IL-1β, TNF-α, IL-6 and iNOS). Furthermore, p75NTR knockdown induced significant changes in histopathology and inflammation-related transcription factors expression. Importantly, long-term LM11A-31 treatment accelerated the resolution of PM-induced inflammation and significantly improved hippocampal neurogenesis.

Conclusion

Our findings suggest that the p75NTR signaling plays an essential role in the pathogenesis of PM. Targeting p75NTR has beneficial effects on PM rats by alleviating neuroinflammation and promoting hippocampal neurogenesis. Thus, the p75NTR signaling may be a potential therapeutic target to improve the outcome of PM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02294-w.

Gelatin methacrylate hydrogel loaded with brain-derived neurotrophic factor enhances small molecule-induced neurogenic differentiation of stem cells from apical papilla

The limited neurogenic potential of adult stem cells and their non-specific lineage differentiation pose major challenges in cell-replacement therapy for neurological disorders. In our previous study, we demonstrated that the neurogenic potential of stem cells from apical papilla (SCAPs) was significantly improved upon induction with a small molecule cocktail. This study attempted to investigate whether neuronal differentiation of SCAPs induced by a small molecule cocktail can be further enhanced in a three-dimensional gelatin methacrylate hydrogel loaded with brain-derived neurotrophic factor (BDNF-GelMA). The physiological properties and neural differentiation of SCAPs treated with a combination of small molecules and BDNF-GelMA were evaluated by CCK8, Live/Dead assay, quantitative reverse transcription-polymerase chain reaction, western blot and immunocytochemistry. SCAPs embedded in BDNF-GelMA displayed superior morphological characteristics when induced by a small molecule cocktail, similar to neuronal phenotypes as compared to pure GelMA. There was significant upregulation of neural markers including Tuj1 and MAP2 by SCAPs embedded in BDNF-GelMA, as compared to pure GelMA. Hence, GelMA hydrogel loaded with a potent neurotrophic factor (BDNF) provides a conducive scaffold that can further enhance the differentiation of small molecule-treated SCAPs into neuronal-like cells, which may provide a therapeutic platform for the management of neurological disorders.

Selective Loss of Brain-Derived Neurotrophic Factor Exacerbates Brain Injury by Enhancing Neuroinflammation in Experimental Streptococcus pneumoniae Meningitis

Streptococcus pneumoniae meningitis is a life-threatening bacterial infection of the central nervous system (CNS), and its unfavorable prognosis usually results from an intense inflammatory response. Recent studies have shown that brain-derived neurotrophic factor (BDNF) mediates anti-inflammatory and neuroprotective effects in CNS diseases; however, the distinct contribution of BDNF to pneumococcal meningitis (PM) remains unknown. In this study, we sought to investigate the effects of endogenous BDNF on the inflammatory response and brain damage in experimental PM. We used Camk2a-CreERT2 mice to delete Bdnf from the cerebral cortex and hippocampus, and meningitis was induced by intracisternal infection with S. pneumoniae. Clinical parameters were assessed during acute meningitis. At 24 h post-infection, histopathology, neutrophil granulocytes infiltration, and microglia/macrophage proliferation of brain tissues were evaluated. Additionally, cortical damage and hippocampal apoptosis were assessed using Nissl staining and terminal deoxynucleotidyl transferase dUTP-nick-end labeling (TUNEL), respectively. Pro-inflammatory cytokine levels were determined using real-time polymerase chain reaction (RT-PCR). Key molecules associated with the related signaling pathways were analyzed by RT-PCR and western blot. To investigate the role of microglia/macrophage in infected BDNF conditional knockout mice, GW2580 was used for microglia/macrophage depletion. Here, we, for the first time, found that BDNF conditional knockouts exhibited more profound clinical impairment, pathological severity, and neuron injury and enhanced microglia/macrophage proliferation than were observed in their littermate controls. Furthermore, the BDNF conditional knockouts showed an obviously increase in the expression of pro-inflammatory factors (Tnf-α, Il-1β, and Il-6). Mechanistically, loss of BDNF activated TLR2- and NOD2-mediated downstream nuclear factor kappa B (NF-κB) p65 and p38 mitogen-activated protein kinase (MAPK) pathways associated with S. pneumoniae infection. Furthermore, targeted depletion of microglia/macrophage population decreased the resistance of mice to PM with diminishing neuroinflammation in BDNF conditional knockouts. Our findings suggest that loss of BDNF may enhance the inflammatory response and contribute to brain injury during PM at least partially by modulating TLR2- and NOD2-mediated signaling pathways, thereby providing a potential therapeutic target for future interventions in bacterial meningitis pathologies.

Effect of Different Frequencies of Electroacupuncture on Post-Stroke Dysphagia in Mice

The aim of this study was to determine the optimum frequency of electroacupuncture (EA) for the treatment of dysphagia after stroke. Male C57BL/6 J mice were randomly divided into five groups: normal, model, 2 Hz, 50 Hz, and 100 Hz groups. All mice received a photochemical ischemia, except the normal group. The EA parameters were 1 mA for 15 min, with different frequencies (2, 50, and 100 Hz) applied. After a three day treatment, neuronal activation was detected by the expression of c-Fos. A multi-channel electrophysiological technique was used to assess the discharge of contralateral neurons and the neuron types in each group. The concentration of brain-derived neurotrophic factor (BDNF) in the contralateral neurons was also examined. In addition, the dysfunction of swallowing in mice was calculated according to the lick counts and the lick-lick interval within a certain period of time. The number of c-Fos neurons (P < 0.05) and the expression of BDNF (P < 0.05) increased after the 2 Hz EA treatment. The total frequency of neuron discharge in the 2 Hz group increased compared with the model group (P < 0.05). The pattern of sorted neuron populations was similar between the normal and 2 Hz groups. Consistent with these results, the lick counts increased (P < 0.05) and the lick-lick interval decreased after the 2 Hz EA treatment, which indicated a functional improvement in swallowing. These results indicated that the 2 Hz EA treatment had a good effect on dysphagia after stroke.

Notch1 Signaling Pathway Promotes Proliferation and Mediates Differentiation Direction in Hippocampus of Streptococcus pneumonia Meningitis Rats

BACKGROUND

Streptococcus pneumonia meningitis (PM) is a major cause of childhood neurological deficits. Although the Notch1 signaling pathway regulates neurogenesis and neuroinflammation, we know little about its expression or influence on hippocampal neurogenesis and gliogenesis during PM.

METHODS

We used immunofluorescence and Western blots to detect Notch1 signaling expression during experimental PM. Through double-labeling immunofluorescence, we investigated proliferation and differentiation in the dentate gyrus (DG) in PM before and after treatment with exogenous Notch1 activator (Jagged1) and inhibitor (IMR-1).

RESULTS

Our results showed that Notch1 was activated after 24 hours in PM. Compared with the phosphate-buffered saline (PBS) control, Jagged1 increased the proliferation of neural stem cells and progenitor cells (NS/PCs) in DG. After 14 and 28 days of meningitis, astrocyte differentiation increased compared with control. Astrocyte differentiation was higher in the Jagged1 versus the PBS group. In contrast, IMR-1 increased neuronal differentiation but decreased astrocyte differentiation compared with dimethyl sulfoxide treatment.

CONCLUSIONS

Under PM, Notch1 signaling promotes NS/PC proliferation and astrocyte differentiation in DG, while decreasing neuronal differentiation. Transient activation of the Notch1 signaling pathway explains the reactive gliogenesis and limited neuronal differentiation observed in PM.

Acute Bacterial Meningitis: Challenges to Better Antibiotic Therapy

Bacterial meningitis is a medical emergency requiring highly bactericidal antibiotics to achieve cure. Many challenges exist to achieving optimal patient outcome. First, antibiotics must pass the blood brain barrier. Once in the subarachnoid space, achieving bactericidal therapy involves circumventing antibiotic resistance and, more commonly, antibiotic tolerance arising from the slow growth of bacteria in the nutrient poor cerebrospinal fluid. Finally, bactericidal therapy is most often bacteriolytic, and debris from lysis is highly inflammatory. Controlling damage from lytic products may require adjunctive therapy to prevent neuronal death. These challenges are an extreme example of the different requirements for treating infections in different body sites.

Metformin mediates neuroprotection and attenuates hearing loss in experimental pneumococcal meningitis

Background

Pneumococcal meningitis is associated with high risk of neurological sequelae such as cognitive impairment and hearing loss. These sequelae are due to parenchymal brain and inner ear damage primarily induced by the excessive inflammatory reaction in response to bacterial brain invasion. Metformin—a biguanide drug to treat diabetes mellitus type 2—was recently found to suppress neuroinflammation and induce neuroregeneration. This study evaluated the effect of metformin adjunctive to antibiotics on neuroinflammation, brain and inner ear damage, and neurofunctional outcome in experimental pediatric pneumococcal meningitis.

Methods

Eleven-day-old Wistar rats were infected intracisternally with 5.22 ± 1.27 × 10³ CFU Streptococcus pneumoniae and randomized for treatment with metformin (50 mg/kg, i.p., once daily for 3 weeks) plus ceftriaxone (100 mg/kg, i.p., bid, n = 61) or ceftriaxone monotherapy (n = 79). Cortical damage and hippocampal apoptosis were evaluated histomorphometrically 42 h post infection. Cerebrospinal fluid cytokine levels were analyzed during acute infection. Five weeks post infection, auditory brainstem responses were measured to determine hearing thresholds. Spiral ganglion neuron density and abundance of recently proliferated and integrated hippocampal granule neurons were assessed histologically. Additionally, the anti-inflammatory effect of metformin was studied in primary rat astroglial cells in vitro.

Results

Upon pneumococcal infection, metformin treatment significantly reduced levels of inflammatory cytokines and nitric oxide production in cerebrospinal fluid and in astroglial cell cultures in vitro (p < 0.05). Compared to animals receiving ceftriaxone monotherapy, adjunctive metformin significantly reduced cortical necrosis (p < 0.02) during acute infection and improved median click-induced hearing thresholds (60 dB vs. 100 dB, p < 0.002) 5 weeks after infection. Adjuvant metformin significantly improved pure tone hearing thresholds at all assessed frequencies compared to ceftriaxone monotherapy (p < 0.05) and protected from PM-induced spiral ganglion neuron loss in the inner ear (p < 0.05).

Conclusion

Adjuvant metformin reduces brain injury during pneumococcal meningitis by decreasing the excessive neuroinflammatory response. Furthermore, it protects spiral ganglion neurons in the inner ear and improves hearing impairments after experimental pneumococcal meningitis. These results identify adjuvant metformin as a promising therapeutic option to improve the outcome after pediatric pneumococcal meningitis.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1549-6) contains supplementary material, which is available to authorized users.

Novel and preclinical treatment strategies in pneumococcal meningitis

PURPOSE OF REVIEW

Pneumococcal meningitis is the most frequent form of bacterial meningitis in Europe and the United States. Although early antimicrobial and adjuvant therapy with dexamethasone have helped to improve disease outcome in adults, mortality and morbidity rates remain unsatisfactorily high, emphasizing the need for additional treatment options. Promising targets for adjuvant therapy have been identified recently and will be the focus of this review.

RECENT FINDINGS

Brain disease in pneumococcal meningitis is caused by direct bacterial toxicity and excessive meningeal inflammation. Accordingly, promising targets for adjuvant therapy comprise limiting the release of toxic bacterial products and suppressing inflammation in a way that maximally protects against tissue injury without hampering pathogen eradication by antibiotics. Among the agents tested so far in experimental models, complement inhibitors, matrix-metalloproteinase inhibitors, and nonbacteriolytic antibiotics or a combination of the above have the potential to more efficiently protect the brain either alone (e.g., in children and outside the high-income settings) or in addition to adjuvant dexamethasone. Additionally, new protein-based pneumococcal vaccines are being developed that promise to improve disease prevention, namely by addressing the increasing problem of serotype replacement seen with pneumococcal conjugate vaccines.

SUMMARY

Pneumococcal meningitis remains a life-threatening disease requiring early antibiotic and targeted anti-inflammatory therapy. New adjuvant therapies showed promising results in animal models but need systematic clinical testing.

The inflammatory response and neuronal injury in Streptococcus suis meningitis

BACKGROUND

Many of the currently used models of bacterial meningitis have limitations due to direct inoculation of pathogens into the cerebrospinal fluid or brain and a relatively insensitive assessment of long-term sequelae. The present study evaluates the utility of a Streptococcus (S.) suis intranasal infection model for the investigation of experimental therapies in meningitis.

METHODS

We examined the brains of 10 piglets with S. suis meningitis as well as 14 control piglets by histology, immunohistochemistry and in-situ tailing for morphological alterations in the hippocampal dentate gyrus and microglial activation in the neocortex.

RESULTS

In piglets with meningitis, the density of apoptotic neurons was significantly higher than in control piglets. Moreover, scoring of microglial morphology revealed a significant activation of these cells during meningitis. The slight increase in the density of dividing cells, young neurons and microglia observed in piglets suffering from meningitis was not statistically significant, probably because of the short time frame between onset of clinical signs and organ sampling.

CONCLUSIONS

The morphological changes found during S. suis meningitis are in accordance with abnormalities in other animal models and human autopsy cases. Therefore, the pig should be considered as a model for evaluating effects of experimental therapeutic approaches on neurological function in bacterial meningitis.

Mycobacterium smegmatis Induces Neurite Outgrowth and Differentiation in an Autophagy-Independent Manner in PC12 and C17.2 Cells

Both pathogenic and non-pathogenic Mycobacteria can induce the differentiation of immune cells into dendritic cells (DC) or DC-like cells. In addition, pathogenic Mycobacteria is found to stimulate cell differentiation in the nerves system. Whether non-pathogenic Mycobacteria interacts with nerve cells remains unknown. In this study, we found that co-incubation with fast-growing Mycobacteria smegmatis induced neuron-like morphological changes of PC12 and C17.2 cells. Moreover, the M. smegmatis culture supernatant which was ultrafiltrated through a membrane with a 10 kDa cut-off, induced neurite outgrowth and differentiation in an autophagy-independent pathway in PC12 and C17.2 cells. Further analysis showed that IFN-γ production and activation of the PI3K-Akt signaling pathway were involved in the neural differentiation. In conclusion, our finding demonstrated that non-pathogenic M. smegmatis was able to promote neuronal differentiation by its extracellular proteins, which might provide a novel therapeutic strategy for the treatment of neurodegenerative disorders.

Using biomaterials to modulate chemotactic signaling for central nervous system repair

Chemotaxis enables cellular communication and movement within the body. This review focuses on exploiting chemotaxis as a tool for repair of the central nervous system (CNS) damaged from injury and/or degenerative diseases. Chemokines and factors alone may initiate repair following CNS injury/disease, but exogenous administration may enhance repair and promote regeneration. This review will discuss critical chemotactic molecules and factors that may promote neural regeneration. Additionally, this review highlights how biomaterials can impact the presentation and delivery of chemokines and growth factors to alter the regenerative response.

Estrogen receptor-β of microglia underlies sexual differentiation of neuronal protection via ginsenosides in mice brain

AIMS

Streptococcus pneumoniae infection in acute bacterial meningitis can lead to widespread brain damage and mortality. Inflammatory responses by immune cells in the brain are thought to determine the degree of brain injury. Yet, the mechanisms underlying host responses to pneumococcal meningitis are largely unknown. To explore host responses as a potential therapeutic target for preventing brain injury after pneumococcal meningitis.

METHODS

We evaluated signaling mechanisms that minimize neuronal damage caused by pneumococcal infection; specifically, we assessed pathways related to neuronal survival after enhancing estrogen receptor-β (ER-β) expression using a natural therapeutic substance known as ginsenoside Rb1 and Rg3 enhanced ginseng.

RESULTS

Tissue damage caused by bacterial infection was reduced in Rb1/Rg3-treated mice as a result of microglial activation and the inhibition of apoptosis. Furthermore, Rb1 upregulated the expression of brain-derived neurotrophic factor (BDNF) as well as anti-apoptotic factors including Bcl-2 and Bcl-xL. Using BV2 microglial cells in vitro, Rb1 treatment inhibited microglial apoptosis in a manner associated with JAK2/STAT5 phosphorylation.

CONCLUSION

After S. pneumoniae infection in mice, particularly in female mice, Rb1-containing ginseng increased bacterial clearance and survival. These findings inform our understanding of the host immune response to pneumococcal meningitis.

The effect of different frequencies of electroacupuncture on BDNF and NGF expression in the hippocampal CA3 area of the ischemic hemisphere in cerebral ischemic rats

OBJECTIVE

The aim of this study was to observe the effects of different frequencies of electroacupuncture (EA) on expression of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the hippocampal CA3 region of cerebral ischemic rats.

METHODS

Middle cerebral artery occlusion was successfully introduced to simulate cerebral infarction in 48 healthy male Sprague-Dawley rats. Totally, 48 rats were randomly divided into three groups: the control group, the EA 5-Hz group, and the EA 50-Hz group, 16 in each group. The rats in the control group were placed in an ordinary cage and fed normally without any treatment. EA treatment was given at a certain frequency 24 hours after surgery in the EA 5-Hz group and EA 50-Hz group. Morris water maze test was used to measure the learning and memory abilities of rats in each group after 14-day treatment with EA. Immunohistochemical staining was used to detect the expression of BDNF- and NGF-positive cells in the ischemic hippocampal CA3 area of the rats.

RESULTS

The EA 5-Hz group and EA 50-Hz group had significantly improved learning and memory ability compared with the control group according to Morris water maze findings (P<0.05). The number of BDNF- and NGF-positive cells in the hippocampal CA3 region of the ischemic hemisphere in the 5-Hz group and 50-Hz EA group was significantly more than that in the control group after EA treatment (P<0.05), and the difference in the 50-Hz group was more obvious than that in the 5-Hz group. The difference was statistically significant (P<0.05).

CONCLUSION

EA stimulation of "Baihui" and "Dazhui" can promote the expression of BDNF and NGF in the hippocampal CA3 region of cerebral ischemic rats, and the 50-Hz EA stimulation effect is more obvious.

Brain-derived neurotrophic factor reduces inflammation and hippocampal apoptosis in experimental Streptococcus pneumoniae meningitis

BACKGROUND

Streptococcus pneumoniae meningitis is a serious inflammatory disease of the central nervous system (CNS) and is associated with high morbidity and mortality rates. The inflammatory processes initiated by recognition of bacterial components contribute to apoptosis in the hippocampal dentate gyrus. Brain-derived neurotrophic factor (BDNF) has long been recommended for the treatment of CNS diseases due to its powerful neuro-survival properties, as well as its recently reported anti-inflammatory and anti-apoptotic effects in vitro and in vivo.

METHODS

In this study, we investigated the effects of BDNF-related signaling on the inflammatory response and hippocampal apoptosis in experimental models of pneumococcal meningitis. Pretreatment with exogenous BDNF or the tropomyosin-receptor kinase B (TrkB) inhibitor k252a was performed to assess the activation or inhibition of the BDNF/TrkB-signaling axis prior to intracisternal infection with live S. pneumoniae. At 24 h post-infection, rats were assessed for clinical severity and sacrificed to harvest the brains. Paraffin-embedded brain sections underwent hematoxylin and eosin staining to evaluate pathological severity, and cytokine and chemokine levels in the hippocampus and cortex were evaluated by enzyme-linked immunosorbent assay. Additionally, apoptotic neurons were detected in the hippocampal dentate gyrus by terminal deoxynucleotidyl transferase dUTP-nick-end labeling, key molecules associated with the related signaling pathway were analyzed by real-time polymerase chain reaction and western blot, and the DNA-binding activity of nuclear factor kappa B (NF-κB) was measured by electrophoretic mobility shift assay.

RESULTS

Rats administered BDNF exhibited reduced clinical impairment, pathological severity, and hippocampal apoptosis. Furthermore, BDNF pretreatment suppressed the expression of inflammatory factors, including tumor necrosis factor α, interleukin (IL)-1β, and IL-6, and increased the expression of the anti-inflammatory factor IL-10. Moreover, BDNF pretreatment increased TrkB expression, activated downstream phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling, and inhibited the myeloid differentiation primary response gene 88 (MyD88)/NF-κB-signaling pathway.

CONCLUSIONS

These data suggested that BDNF administration exerted anti-inflammatory and anti-apoptotic effects on an experimental pneumococcal meningitis model via modulation of MyD88/NF-κB- and PI3K/AKT-signaling pathways. Our results indicated that treatment with exogenous BDNF might constitute a potential therapeutic strategy for the treatment of bacterial meningitis.

Decreased hippocampal brain-derived neurotrophic factor and impaired cognitive function by hypoglossal nerve transection in rats

The hypoglossal nerve controls tongue movements, and damages of it result in difficulty in mastication and food intake. Mastication has been reported to maintain hippocampus‐dependent cognitive function. This study was conducted to examine the effect of tongue motor loss on the hippocampus‐dependent cognitive function and its underlying mechanism. Male Sprague Dawley rats were subjected to the initial training of Morris water maze task before or after the bilateral transection of hypoglossal nerves (Hx). When the initial training was given before the surgery, the target quadrant dwelling time during the probe test performed at a week after the surgery was significantly reduced in Hx rats relative to sham‐operated controls. When the initial training was given after the surgery, Hx affected the initial and reversal trainings and probe tests. Brain‐derived neurotrophic factor (BDNF) expression, cell numbers and long‐term potentiation (LTP) were examined in the hippocampus on the 10^th day, and BrdU and doublecortin staining on the 14^th day, after the surgery. Hx decreased the hippocampal BDNF and cells in the CA1/CA3 regions and impaired LTP. BrdU and doublecortin staining was decreased in the dentate gyrus of Hx rats. Results suggest that tongue motor loss impairs hippocampus‐dependent cognitive function, and decreased BDNF expression in the hippocampus may be implicated in its underlying molecular mechanism in relation with decreased neurogenesis/proliferation and impaired LTP.

Brain-derived neurotrophic factor is regulated via MyD88/NF-κB signaling in experimental Streptococcus pneumoniae meningitis

Streptococcus pneumoniae meningitis is an intractable disease of the central nervous system (CNS). Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophic family and found to participate in the immune inflammatory response. In this study, we investigated if activation of the classical inflammatory signaling pathway, myeloid differentiation factor 88 (MyD88)/nuclear factor-kappa B (NF-κB), regulates BDNF expression in experimental S. pneumoniae meningitis. MyD88 knockout (myd88-/-) mice and wild-type littermates were infected intracisternally with S. pneumoniae suspension. Twenty-four hours after inoculation, histopathology of brains was evaluated. Cytokine and chemokine in brains and spleens was analyzed using ELISA. NF-κB activation was evaluated using EMSA. Cortical and hippocampal BDNF was assessed using RT-PCR and ELISA, respectively. BDNF promoter activity was evaluated using ChIP-PCR. myd88-/- mice showed an obviously weakened inflammatory host response. This diminished inflammation was consistent with worse clinical parameters, neuron injury, and apoptosis. Deficiency in MyD88 was associated with decreased BDNF expression. Furthermore, we identified a valid κB-binding site in the BDNF promoter, consistent with activation of NF-κB induced by inflammation. To sum up, MyD88/NF-κB signaling has a crucial role in up-regulating BDNF, which might provide potential therapeutic targets for S. pneumoniae meningitis.