Tracking the transcriptional host response from the acute to the regenerative phase of experimental pneumococcal meningitis

Uncovering the neuroprotective effect of vitamin B12 in pneumococcal meningitis: insights into its pleiotropic mode of action at the transcriptional level

Background

The interplay between bacterial virulence factors and the host innate immune response in pneumococcal meningitis (PM) can result in uncontrolled neuroinflammation, which is known to induce apoptotic death of progenitor cells and post-mitotic neurons in the hippocampal dentate gyrus, resulting in cognitive impairment. Vitamin B12 attenuates hippocampal damage and reduces the expression of some key inflammatory genes in PM, by acting as an epidrug that promotes DNA methylation, with increased production of S-adenosyl-methionine, the universal donor of methyl.

Material and methods

Eleven-day-old rats were infected with S. pneumoniae via intracisternal injection and then administered either vitamin B12 or a placebo. After 24 hours of infection, the animals were euthanized, and apoptosis in the hippocampal dentate gyrus, microglia activation, and the inflammatory infiltrate were quantified in one brain hemisphere. The other hemisphere was used for RNA-Seq and RT-qPCR analysis.

Results

In this study, adjuvant therapy with B12 was found to modulate the hippocampal transcriptional signature induced by PM in infant rats, mitigating the effects of the disease in canonical pathways related to the recognition of pathogens by immune cells, signaling via NF-kB, production of pro-inflammatory cytokines, migration of peripheral leukocytes into the central nervous system, and production of reactive species. Phenotypic analysis revealed that B12 effectively inhibited microglia activation in the hippocampus and reduced the inflammatory infiltrate in the central nervous system of the infected animals. These pleiotropic transcriptional effects of B12 that lead to neuroprotection are partly regulated by alterations in histone methylation markings. No adverse effects of B12 were predicted or observed, reinforcing the well-established safety profile of this epidrug.

Conclusion

B12 effectively mitigates the impact of PM on pivotal neuroinflammatory pathways. This leads to reduced microglia activation and inflammatory infiltrate within the central nervous system, resulting in the attenuation of hippocampal damage. The anti-inflammatory and neuroprotective effects of B12 involve the modulation of histone markings in hippocampal neural cells.

Metagenomic Next-Generation Sequencing for Pathogen Detection and Transcriptomic Analysis in Pediatric Central Nervous System Infections

Background

Pediatric central nervous system (CNS) infections are potentially life-threatening and may incur significant morbidity. Identifying a pathogen is important, both in terms of guiding therapeutic management and in characterizing prognosis. Usual care testing by culture and polymerase chain reaction is often unable to identify a pathogen. We examined the systematic application of metagenomic next-generation sequencing (mNGS) for detecting organisms and transcriptomic analysis of cerebrospinal fluid (CSF) in children with central nervous system (CNS) infections.

Methods

We conducted a prospective multisite study that aimed to enroll all children with a CSF pleocytosis and suspected CNS infection admitted to 1 of 3 tertiary pediatric hospitals during the study timeframe. After usual care testing had been performed, the remaining CSF was sent for mNGS and transcriptomic analysis.

Results

We screened 221 and enrolled 70 subjects over a 12-month recruitment period. A putative organism was isolated from CSF in 25 (35.7%) subjects by any diagnostic modality. Metagenomic next-generation sequencing of the CSF samples identified a pathogen in 20 (28.6%) subjects, which were also all identified by usual care testing. The median time to result was 38 hours.

Conclusions

Metagenomic sequencing of CSF has the potential to rapidly identify pathogens in children with CNS infections.

Spread of COVID-19 in China: analysis from a city-based epidemic and mobility model

Understanding the processes and mechanisms of the spatial spread of epidemics is essential for making reasonable judgments on the development trends of epidemics and for adopting effective containment measures. Using multi-agent network technology and big data on population migration, this paper constructed a city-based epidemic and mobility model (CEMM) to stimulate the spatiotemporal of COVID-19. Compared with traditional models, this model is characterized by an urban network perspective and emphasizes the important role of intercity population mobility and high-speed transportation networks. The results show that the model could simulate the inter-city spread of COVID-19 at the early stage in China with high precision. Through scenario simulation, the paper quantitatively evaluated the effect of control measures "city lockdown" and "decreasing population mobility" on containing the spatial spread of the COVID-19 epidemic. According to the simulation, the total number of infectious cases in China would have climbed to 138,824 on February 2020, or 4.46 times the real number, if neither of the measures had been implemented. Overall, the containment effect of the lockdown of cities in Hubei was greater than that of decreasing intercity population mobility, and the effect of city lockdowns was more sensitive to timing relative to decreasing population mobility.

Evaluation of neurofilament light chain in the cerebrospinal fluid and blood as a biomarker for neuronal damage in experimental pneumococcal meningitis

Background

Pneumococcal meningitis (PM) remains a global public health concern and affects all age groups. If acquired during infancy or childhood, permanent neurofunctional deficits including cognitive impairment, cerebral palsy, and secondary epilepsy are typical sequelae of neuronal injury. Determination of patients at risk for the development of brain injury and subsequent neurofunctional sequelae could help to identify patients for focused management. Neurofilament light chain (NfL) is an axonal cytoskeletal protein released upon neuronal injury into the cerebrospinal fluid (CSF) and blood. As little is known about the course of neurofilament release in the course of PM, we measured CSF and serum NfL levels longitudinally in experimental PM (ePM).

Methods

Eleven-day-old infant Wistar rats were infected intracisternally with Streptococcus pneumoniae and treated with ceftriaxone. At 18 and 42 h post-infection (hpi), the blood and CSF were sampled for NfL measurements by a single molecule array technology. Inflammatory cytokines and MMP-9 in CSF were quantified by magnetic bead multiplex assay (Luminex®) and by gel zymography, respectively.

Results

In ePM, CSF and serum NfL levels started to increase at 18 hpi and were 26- and 3.5-fold increased, respectively, compared to mock-infected animals at 42 hpi (p < 0.0001). CSF and serum NfL correlated at 18 hpi (p < 0.05, r = 0.4716) and 42 hpi (p < 0.0001, r = 0.8179). Both CSF and serum NfL at 42 hpi strongly correlated with CSF levels of IL-1β, TNF-α, and IL-6 and of MMP-9 depending on their individual kinetics.

Conclusion

Current results demonstrate that during the peak inflammatory phase of ePM, NfL levels in CSF and serum are the highest among CNS disease models studied so far. Given the strong correlation of CSF versus serum NfL, and its CNS-specific signal character, longitudinal measurements to monitor the course of PM could be performed based on blood sample tests, i.e., without the need of repetitive spinal taps. We conclude that NfL in the serum should be evaluated as a biomarker in PM.

Repetitive transcranial magnetic stimulation activates glial cells and inhibits neurogenesis after pneumococcal meningitis

Pneumococcal meningitis (PM) causes damage to the hippocampus, a brain structure critically involved in learning and memory. Hippocampal injury-which compromises neurofunctional outcome-occurs as apoptosis of progenitor cells and immature neurons of the hippocampal dentate granule cell layer thereby impairing the regenerative capacity of the hippocampal stem cell niche. Repetitive transcranial magnetic stimulation (rTMS) harbours the potential to modulate the proliferative activity of this neuronal stem cell niche. In this study, specific rTMS protocols-namely continuous and intermittent theta burst stimulation (cTBS and iTBS)-were applied on infant rats microbiologically cured from PM by five days of antibiotic treatment. Following two days of exposure to TBS, differential gene expression was analysed by whole transcriptome analysis using RNAseq. cTBS provoked a prominent effect in inducing differential gene expression in the cortex and the hippocampus, whereas iTBS only affect gene expression in the cortex. TBS induced polarisation of microglia and astrocytes towards an inflammatory phenotype, while reducing neurogenesis, neuroplasticity and regeneration. cTBS was further found to induce the release of pro-inflammatory cytokines in vitro. We conclude that cTBS intensified neuroinflammation after PM, which translated into increased release of pro-inflammatory mediators thereby inhibiting neuroregeneration.

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.

Inhibition of Hippocampal Regeneration by Adjuvant Dexamethasone in Experimental Infant Rat Pneumococcal Meningitis

Pneumococcal meningitis (PM) causes neurological sequelae in up to half of surviving patients. Neuronal damage associated with poor outcome is largely mediated by the inflammatory host response. Dexamethasone (DXM) is used as an adjuvant therapy in adult PM, but its efficacy in the treatment of pneumococcal meningitis in children is controversially discussed. While DXM has previously been shown to enhance hippocampal apoptosis in experimental PM, its impact on hippocampal cell proliferation is not known. This study investigated the impact of DXM on hippocampal proliferation in infant rat PM. Eleven-day-old nursing Wistar rats (n = 90) were intracisternally infected with Streptococcus pneumoniae to induce experimental meningitis. Treatment with DXM or vehicle was started 18 h after infection, concomitantly with antibiotics (ceftriaxone 100 mg/kg of body weight twice a day [b.i.d.]). Clinical parameters were monitored, and the amount of cells with proliferating activity was assessed using in vivo incorporation of bromodeoxyuridine (BrdU) and an in vitro neurosphere culture system at 3 and 4 d postinfection. DXM significantly worsened weight loss and survival. Density of BrdU-positive cells, as an index of cells with proliferating activity, was significantly lower in DXM-treated animals compared to vehicle controls (P < 0.0001). In parallel, DXM reduced neurosphere formation as an index for stem/progenitor cell density compared to vehicle treatment (P = 0.01). Our findings provide clear evidence that DXM exerts an antiproliferative effect on the hippocampus in infant rat PM. We conclude that an impairment of regenerative hippocampal capacity should be taken into account when considering adjuvant DXM in the therapeutic regimen for PM in children.

The antidepressant fluoxetine protects the hippocampus from brain damage in experimental pneumococcal meningitis

BACKGROUND

High mortality and morbidity rates are observed in patients with bacterial meningitis (BM) and urge for new adjuvant treatments in addition to standard antibiotic therapies. In BM the hippocampal dentate gyrus is injured by apoptosis while in cortical areas ischemic necrosis occurs. Experimental therapies aimed at reducing the inflammatory response and brain damage have successfully been evaluated in animal models of BM. Fluoxetine (FLX) is an anti-depressant of the selective serotonin reuptake inhibitors (SSRI) and was previously shown to be neuroprotective in vitro and in vivo. We therefore assessed the neuroprotective effect of FLX in experimental pneumococcal meningitis.

METHODS

Infant rats were infected intracisternally with live Streptococcus pneumoniae. Intraperitoneal treatment with FLX (10mgkg(-1)d(-1)) or an equal volume of NaCl was initiated 15min later. 18, 27, and 42h after infection, the animals were clinically (weight, clinical score, mortality) evaluated and subject to a cisternal puncture and inflammatory parameters (i.e., cyto-/chemokines, myeloperoxidase activity, matrix metalloproteinase concentrations) were measured in cerebrospinal fluid (CSF) samples. At 42h after infection, animals were sacrificed and the brains collected for histomorphometrical analysis of brain damage.

RESULTS

A significant lower number of animals treated with FLX showed relevant hippocampal apoptosis when compared to littermates (9/19 animals vs 18/23, P=0.038). A trend for less damage in cortical areas was observed in FLX-treated animals compared to controls (13/19 vs 13/23, P=ns). Clinical and inflammatory parameters were not affected by FLX treatment.

CONCLUSION

A significant neuroprotective effect of FLX on the hippocampus was observed in acute pneumococcal meningitis in infant rats.

The mood-stabilizer lithium prevents hippocampal apoptosis and improves spatial memory in experimental meningitis

Pneumococcal meningitis is associated with high morbidity and mortality rates. Brain damage caused by this disease is characterized by apoptosis in the hippocampal dentate gyrus, a morphological correlate of learning deficits in experimental paradigms. The mood stabilizer lithium has previously been found to attenuate brain damage in ischemic and inflammatory diseases of the brain. An infant rat model of pneumococcal meningitis was used to investigate the neuroprotective and neuroregenerative potential of lithium. To assess an effect on the acute disease, LiCl was administered starting five days prior to intracisternal infection with live Streptococcus pneumoniae. Clinical parameters were recorded, cerebrospinal fluid (CSF) was sampled, and the animals were sacrificed 42 hours after infection to harvest the brain and serum. Cryosections of the brains were stained for Nissl substance to quantify brain injury. Hippocampal gene expression of Bcl-2, Bax, p53, and BDNF was analyzed. Lithium concentrations were measured in serum and CSF. The effect of chronic lithium treatment on spatial memory function and cell survival in the dentate gyrus was evaluated in a Morris water maze and by quantification of BrdU incorporation after LiCl treatment during 3 weeks following infection. In the hippocampus, LiCl significantly reduced apoptosis and gene expression of Bax and p53 while it increased expression of Bcl-2. IL-10, MCP-1, and TNF were significantly increased in animals treated with LiCl compared to NaCl. Chronic LiCl treatment improved spatial memory in infected animals. The mood stabilizer lithium may thus be a therapeutic alternative to attenuate neurofunctional deficits as a result of pneumococcal meningitis.

Vitamin B6 reduces hippocampal apoptosis in experimental pneumococcal meningitis

BACKGROUND

Bacterial meningitis caused by Streptococcus pneumoniae leads to death in up to 30% of patients and leaves up to half of the survivors with neurological sequelae. The inflammatory host reaction initiates the induction of the kynurenine pathway and contributes to hippocampal apoptosis, a form of brain damage that is associated with learning and memory deficits in experimental paradigms. Vitamin B6 is an enzymatic cofactor in the kynurenine pathway and may thus limit the accumulation of neurotoxic metabolites and preserve the cellular energy status. The aim of this study in a pneumococcal meningitis model was to investigate the effect of vitamin B6 on hippocampal apoptosis by histomorphology, by transcriptomics and by measurement of cellular nicotine amide adenine dinucleotide content.

METHODS AND RESULTS

Eleven day old Wistar rats were infected with 1x10(6) cfu/ml of S. pneumoniae and randomized for treatment with vitamin B6 or saline as controls. Vitamin B6 led to a significant (p > 0.02) reduction of hippocampal apoptosis. According to functional annotation based clustering, vitamin B6 led to down-regulation of genes involved in processes of inflammatory response, while genes encoding for processes related to circadian rhythm, neuronal signaling and apoptotic cell death were mostly up-regulated.

CONCLUSIONS

Our results provide evidence that attenuation of apoptosis by vitamin B6 is multi-factorial including down-modulation of inflammation, up-regulation of the neuroprotective brain-derived neurotrophic factor and prevention of the exhaustion of cellular energy stores. The neuroprotective effect identifies vitamin B6 as a potential target for the development of strategies to attenuate brain injury in bacterial meningitis.

Microglial activation and expression of immune-related genes in a rat ex vivo nervous system model after infection with Listeria monocytogenes

A wide variety of microorganisms has previously been identified as causes of brain infection. Among them, Listeria monocytogenes has a particular tropism for the central nervous system. To gain knowledge about the immune response elicited by L. monocytogenes in the brain, we used a rat ex vivo organotypic nervous system culture as a model for Listeria infection. Scanning electron microscopy (SEM) revealed that activated microglial cells showing a typical amoeboid morphology are quickly recruited to the surface of the explants after the infection. After bacterial engulfment, these cells appear to act as Trojan horses, releasing the engulfed bacteria inside the brain tissue. We describe cycles of microglial phagocytosis, necrotic cell death and the subsequent removal of cell debris for the first time. Furthermore, we used this ex vivo model to assess the expression profiles of immune relevant genes up to 24 h postinfection by means of q-PCR-arrays, finding that a number of inflammation-promoting genes are upregulated. Shortly after infection by L. monocytogenes, upregulated genes were those that encoded molecules involved in Th1 responses, being the Ccl2 chemokine and members of the interleukin1-β family the most abundant immunomodulatory signals expressed. After 5 h of infection, L. monocytogenes caused a substantial increase in the expression of TLR1 and TLR2 genes, as well as in several downstream genes of the TLR signaling pathways.

Host response transcriptional profiling reveals extracellular components and ABC (ATP-binding cassette) transporters gene enrichment in typhoid fever-infected Nigerian children

Background

Salmonella enterica serovar Typhi (S. Typhi) is a human-specific pathogen that causes typhoid fever, and remains a global health problem especially in developing countries. Its pathogenesis is complex and host response is poorly understood. In Africa, typhoid fever can be a major cause of morbidity in young infected children. The onset of the illness is insidious and clinical diagnosis is often unreliable. Gold standard blood culture diagnostic services are limited, thus rapid, sensitive, and affordable diagnostic test is essential in poor-resourced clinical settings. Routine typhoid fever vaccination is highly recommended but currently licensed vaccines provide only 55-75% protection. Recent epidemiological studies also show the rapid emergence of multi-drug resistant S. Typhi strains. High-throughput molecular technologies, such as microarrays, can dissect the molecular mechanisms of host responses which are S. Typhi-specific to provide a comprehensive genomic component of immunological responses and suggest new insights for diagnosis and treatment.

Methods

Global transcriptional profiles of S. Typhi-infected young Nigerian children were obtained from their peripheral blood and compared with that of other bacteremic infections using Agilent gene expression microarrays. The host-response profiles of the same patients in acute vs. convalescent phases were also determined. The top 96-100 differentially-expressed genes were identified and four genes were validated by quantitative real-time PCR. Gene clusters were obtained and functional pathways were predicted by DAVID (Database for Annotation, Visualization and Integrated Discovery).

Results

Transcriptional profiles from S. Typhi-infected children could be distinguished from those of other bacteremic infections. Enriched gene clusters included genes associated with extracellular peptides/components such as lipocalin (LCN2) and systemic immune response which is atypical in bacterial invasion. Distinct gene expression profiles can also be obtained from acute vs. convalescent phase during typhoid fever infection. We found novel down-regulation of ABC (ATP-binding cassette) transporters genes such as ABCA7, ABCC5, and ABCD4 and ATPase activity as the highest enriched pathway.

Conclusions

We identified unique extracellular components and ABC transporters gene enrichments in typhoid fever-infected Nigerian children, which have never been reported. These enriched gene clusters may represent novel targeted pathways to improve diagnostic, prognostic, therapeutic and next-generation vaccine strategies for typhoid fever in Africa.

Adjunctive dexamethasone affects the expression of genes related to inflammation, neurogenesis and apoptosis in infant rat pneumococcal meningitis

Streptococcus pneumoniae is the most common pathogen causing non-epidemic bacterial meningitis worldwide. The immune response and inflammatory processes contribute to the pathophysiology. Hence, the anti-inflammatory dexamethasone is advocated as adjuvant treatment although its clinical efficacy remains a question at issue. In experimental models of pneumococcal meningitis, dexamethasone increased neuronal damage in the dentate gyrus. Here, we investigated expressional changes in the hippocampus and cortex at 72 h after infection when dexamethasone was given to infant rats with pneumococcal meningitis. Nursing Wistar rats were intracisternally infected with Streptococcus pneumoniae to induce experimental meningitis or were sham-infected with pyrogen-free saline. Besides antibiotics, animals were either treated with dexamethasone or saline. Expressional changes were assessed by the use of GeneChip® Rat Exon 1.0 ST Arrays and quantitative real-time PCR. Protein levels of brain-derived neurotrophic factor, cytokines and chemokines were evaluated in immunoassays using Luminex xMAP® technology. In infected animals, 213 and 264 genes were significantly regulated by dexamethasone in the hippocampus and cortex respectively. Separately for the cortex and the hippocampus, Gene Ontology analysis identified clusters of biological processes which were assigned to the predefined categories "inflammation", "growth", "apoptosis" and others. Dexamethasone affected the expression of genes and protein levels of chemokines reflecting diminished activation of microglia. Dexamethasone-induced changes of genes related to apoptosis suggest the downregulation of the Akt-survival pathway and the induction of caspase-independent apoptosis. Signalling of pro-neurogenic pathways such as transforming growth factor pathway was reduced by dexamethasone resulting in a lack of pro-survival triggers. The anti-inflammatory properties of dexamethasone were observed on gene and protein level in experimental pneumococcal meningitis. Further dexamethasone-induced expressional changes reflect an increase of pro-apoptotic signals and a decrease of pro-neurogenic processes. The findings may help to identify potential mechanisms leading to apoptosis by dexamethasone in experimental pneumococcal meningitis.

Microarray analyses of THP-1 cells infected with Streptococcus suis serotype 2

Streptococcus suis serotype 2 (S. suis 2) is a pathogen responsible for several diseases in both pigs and humans. To gain more insight into the pathogenesis of this organism, an oligonucleotide (oligo)-based microarray was used to investigate gene expression changes in human monocytic cells (THP-1) in response to exposure to S. suis 2 strain SC19. A total of 328 differentially expressed genes were identified. These differentially expressed genes belonged to a variety of functional categories, including genes involved in apoptosis, immunity, signal transduction, chemokine production and the ubiquitin-proteasome system. Our findings can be of interest for future research.

Meningitis in neonates: bench to bedside

The clinical outcome of central nervous system infection is determined by the characteristics of the pathogen and the brain's response to the invading bacteria. How infection leads to brain injury remains unresolved. An impediment to progress is the complexity of pathophysiologic processes. Some of the mechanisms involved have been identified in experimental models, providing insights into the molecular basis of brain injury and regeneration, and hinting at targets for therapy. Adjuvant therapies have been proposed. Interventions that protect the brain are evaluated for their potential to preserve neuro-integrative functions in long-term survivors of bacterial meningitis. This article summarizes current studies evaluating pharmacologic interventions in experimental models of bacterial meningitis and discusses how the knowledge gathered could translate into more effective therapies.