Neutrophil extracellular traps exacerbate neurological deficits after traumatic brain injury

Loss of AMPK potentiates inflammation by activating the inflammasome after traumatic brain injury in mice

Traumatic brain injury (TBI) is a significant public health concern characterized by a complex cascade of cellular events. TBI induces adenosine monophosphate-activated protein kinase (AMPK) dysfunction impairs energy balance activates inflammatory cytokines and leads to neuronal damage. AMPK is a key regulator of cellular energy homeostasis during inflammatory responses. Recent research has revealed its key role in modulating the inflammatory process in TBI. Following TBI the activation of AMPK can influence various important pathways and mechanisms including metabolic pathways and inflammatory signaling. Our study investigated the effects of post-TBI loss of AMPK function on functional outcomes inflammasome activation, and inflammatory cytokine production. Male C57BL/6 adult wild-type (WT) and AMPK knockout (AMPK-KO) mice were subjected to a controlled cortical impact (CCI) model of TBI or sham surgery. The mice were tested for behavioral impairment at 24 h post-TBI thereafter, mice were anesthetized, and their brains were quickly removed for histological and biochemical evaluation. In vitro we investigated inflammasome activation in mixed glial cells stimulated with lipopolysaccharides+ Interferon-gamma (LI) (0.1 µg/20 ng/ml LPS/IFNg) for 6 h to induce an inflammatory response. Estimating the nucleotide-binding domain, leucine-rich-containing family pyrin domain containing western blotting ELISA and qRT-PCR performed 3 (NLRP3) inflammasome activation and cytokine production. Our findings suggest that TBI leads to reduced AMPK phosphorylation in WT mice and that the loss of AMPK correlates with worsened behavioral deficits at 24 h post-TBI in AMPK-KO mice as compared to WT mice. Moreover compared with the WT mice AMPK-KO mice exhibit exacerbated NLRP3 inflammasome activation and increased expression of proinflammatory mediators such as IL-1b IL-6 TNF-a iNOS and Cox 2. These results align with the in vitro studies using brain glial cells under inflammatory conditions, demonstrating greater activation of inflammasome components in AMPK-KO mice than in WT mice. Our results highlighted the critical role of AMPK in TBI outcomes. We found that the absence of AMPK worsens behavioral deficits and heightens inflammasome-mediated inflammation thereby exacerbating brain injury after TBI. Restoring AMPK activity after TBI could be a promising therapeutic approach for alleviating TBI-related damage.

Neutrophil Targeting Platform Reduces Neutrophil Extracellular Traps for Improved Traumatic Brain Injury and Stroke Theranostics

Traumatic brain injuries (TBI) and stroke are major causes of morbidity and mortality in both developing and developed countries. The complex and heterogeneous pathophysiology of TBI and cerebral ischemia-reperfusion injury (CIRI), in addition to the blood-brain barrier (BBB) resistance, is a major barrier to the advancement of diagnostics and therapeutics. Clinical data showed that the severity of TBI and stroke is positively correlated with the number of neutrophils in peripheral blood and brain injury sites. Furthermore, neutrophil extracellular traps (NETs) released by neutrophils correlate with worse TBI and stroke outcomes by impairing revascularization and vascular remodeling. Therefore, targeting neutrophils to deliver NETs inhibitors to brain injury sites and reduce the formation of NETs can be an optimal strategy for TBI and stroke therapy. Herein, the study designs and synthesizes a reactive oxygen species (ROS)-responsive neutrophil-targeting delivery system loaded with peptidyl arginine deiminase 4 (PAD4) inhibitor, GSK484, to prevent the formation of NETs in brain injury sites, which significantly inhibited neuroinflammation and improved neurological deficits, and improved the survival rate of TBI and CIRI. This strategy may provide a groundwork for the development of targeted theranostics of TBI and stroke.

Bioinformatics gene analysis for potential biomarkers and therapeutic targets of Parkinson's disease based on neutrophil extracellular traps

Introduction

Neutrophil extracellular traps (NETs) provide key innate immune mechanisms, and studies have shown innate immunity and adaptive immunity are directly linked to Parkinson's disease (PD) pathology. However, limited research has been conducted on NETs in the context of PD.

Methods

A differential analysis was implemented to acquire differentially expressed genes (DEGs) between PD and control as well as between high- and low-score groups determined by a gene set variation analysis (GSVA). Then, the genes within the critical module, obtained through a weighted gene co-expression network analysis (WGCNA), were intersected with the DEGs to identify the overlapping genes. Then, five kinds of algorithms in the protein-protein interaction (PPI) were performed to identify potential biomarkers. Subsequently, a nomogram for forecasting PD probability was created. An enrichment analysis and an immune infiltration analysis were performed on the identified biomarkers. qRT-PCR was performed to validate the expression trends of three biomarkers.

Results

We revealed 798 DEGs between PD and control groups as well as 168 DEGs between high- and low-score groups obtained by differential analyses. The pink module containing 926 genes was identified as the critical module. According to the intersection of these gene sets, a total of 43 overlapping genes were screened out. Furthermore, GPR78, CADM3, and CACNA1E were confirmed as biomarkers. Moreover, we found that biomarkers mainly participated in pathways, such as the 'hydrogen peroxide catabolic process', and 'cell cycle'; five kinds of differential immune cells between PD and control groups were identified. Finally, the qRT-PCR analysis demonstrated the up-regulation of GPR78, CADM3, and CACNA1E in the PD group.

Discussion

Our study authenticated GPR78, CADM3, and CACNA1E as the biomarkers associated with PD. These findings provide an original reference for the diagnosis and treatment of PD.

Single episode of moderate to severe traumatic brain injury leads to chronic neurological deficits and Alzheimer's-like pathological dementia

Traumatic brain injury (TBI) is one of the foremost causes of disability and mortality globally. While the scientific and medical emphasis is to save lives and avoid disability during acute period of injury, a severe health problem can manifest years after injury. For instance, TBI increases the risk of cognitive impairment in the elderly. Remote TBI history was reported to be a cause of the accelerated clinical trajectory of Alzheimer's disease-related dementia (ADRD) resulting in earlier onset of cognitive impairment and increased AD-associated pathological markers like greater amyloid deposition and cortical thinning. It is not well understood whether a single TBI event may increase the risk of dementia. Moreover, the cellular signaling pathways remain elusive for the chronic effects of TBI on cognition. We have hypothesized that a single TBI induces sustained neuroinflammation and disrupts cellular communication in a way that results later in ADRD pathology. To test this, we induced TBI in young adult CD1 mice and assessed the behavioral outcomes after 11 months followed by pathological, histological, transcriptomic, and MRI assessment. On MRI scans, these mice showed significant loss of tissue, reduced CBF, and higher white matter injury compared to sham mice. We found these brains showed progressive atrophy, markers of ADRD, sustained astrogliosis, loss of neuronal plasticity, and growth factors even after 1-year post-TBI. Because of progressive neurodegeneration, these mice had motor deficits, showed cognitive impairments, and wandered randomly in open field. We, therefore, conclude that progressive pathology after adulthood TBI leads to neurodegenerative conditions such as ADRD and impairs neuronal functions.

Neutrophil Extracellular Traps Regulate Surgical Brain Injury by Activating the cGAS-STING Pathway

Surgical brain injury (SBI), induced by neurosurgical procedures or instruments, has not attracted adequate attention. The pathophysiological process of SBI remains sparse compared to that of other central nervous system diseases thus far. Therefore, novel and effective therapies for SBI are urgently needed. In this study, we found that neutrophil extracellular traps (NETs) were present in the circulation and brain tissues of rats after SBI, which promoted neuroinflammation, cerebral edema, neuronal cell death, and aggravated neurological dysfunction. Inhibition of NETs formation by peptidylarginine deiminase (PAD) inhibitor or disruption of NETs with deoxyribonuclease I (DNase I) attenuated SBI-induced damages and improved the recovery of neurological function. We show that SBI triggered the activation of cyclic guanosine monophosphate-adenosine monophosphate synthase stimulator of interferon genes (cGAS-STING), and that inhibition of the cGAS-STING pathway could be beneficial. It is worth noting that DNase I markedly suppressed the activation of cGAS-STING, which was reversed by the cGAS product cyclic guanosine monophosphate-adenosine monophosphate (cGMP-AMP, cGAMP). Furthermore, the neuroprotective effect of DNase I in SBI was also abolished by cGAMP. NETs may participate in the pathophysiological regulation of SBI by acting through the cGAS-STING pathway. We also found that high-dose vitamin C administration could effectively inhibit the formation of NETs post-SBI. Thus, targeting NETs may provide a novel therapeutic strategy for SBI treatment, and high-dose vitamin C intervention may be a promising translational therapy with an excellent safety profile and low cost.

STING-Dependent Signaling in Microglia or Peripheral Immune Cells Orchestrates the Early Inflammatory Response and Influences Brain Injury Outcome

While originally identified as an antiviral pathway, recent work has implicated that cyclic GMP-AMP-synthase-Stimulator of Interferon Genes (cGAS-STING) signaling is playing a critical role in the neuroinflammatory response to traumatic brain injury (TBI). STING activation results in a robust inflammatory response characterized by the production of inflammatory cytokines called interferons, as well as hundreds of interferon stimulated genes (ISGs). Global knock-out (KO) mice inhibiting this pathway display neuroprotection with evidence that this pathway is active days after injury; yet, the early neuroinflammatory events stimulated by STING signaling remain understudied. Furthermore, the source of STING signaling during brain injury is unknown. Using a murine controlled cortical impact (CCI) model of TBI, we investigated the peripheral immune and microglial response to injury utilizing male chimeric and conditional STING KO animals, respectively. We demonstrate that peripheral and microglial STING signaling contribute to negative outcomes in cortical lesion volume, cell death, and functional outcomes postinjury. A reduction in overall peripheral immune cell and neutrophil infiltration at the injury site is STING dependent in these models at 24 h. Transcriptomic analysis at 2 h, when STING is active, reveals that microglia drive an early, distinct transcriptional program to elicit proinflammatory genes including interleukin 1-β (IL-1β), which is lost in conditional knock-out mice. The upregulation of alternative innate immune pathways also occurs after injury in these animals, which supports a complex relationship between brain-resident and peripheral immune cells to coordinate the proinflammatory response and immune cell influx to damaged tissue after injury.

Macrophages coordinate immune response to laser-induced injury via extracellular traps

BACKGROUND

Retinal degeneration results from disruptions in retinal homeostasis due to injury, disease, or aging and triggers peripheral leukocyte infiltration. Effective immune responses rely on coordinated actions of resident microglia and recruited macrophages, critical for tissue remodeling and repair. However, these phagocytes also contribute to chronic inflammation in degenerated retinas, yet the precise coordination of immune response to retinal damage remains elusive. Recent investigations have demonstrated that phagocytic cells can produce extracellular traps (ETs), which are a source of self-antigens that alter the immune response, which can potentially lead to tissue injury.

METHODS

Innovations in experimental systems facilitate real-time exploration of immune cell interactions and dynamic responses. We integrated in vivo imaging with ultrastructural analysis, transcriptomics, pharmacological treatments, and knockout mice to elucidate the role of phagocytes and their modulation of the local inflammatory response through extracellular traps (ETs). Deciphering these mechanisms is essential for developing novel and enhanced immunotherapeutic approaches that can redirect a specific maladaptive immune response towards favorable wound healing in the retina.

RESULTS

Our findings underscore the pivotal role of innate immune cells, especially macrophages/monocytes, in regulating retinal repair and inflammation. The absence of neutrophil and macrophage infiltration aids parenchymal integrity restoration, while their depletion, particularly macrophages/monocytes, impedes vascular recovery. We demonstrate that macrophages/monocytes, when recruited in the retina, release chromatin and granular proteins, forming ETs. Furthermore, the pharmacological inhibition of ETosis support retinal and vascular repair, surpassing the effects of blocking innate immune cell recruitment. Simultaneously, the absence of ETosis reshapes the inflammatory response, causing neutrophils, helper, and cytotoxic T-cells to be restricted primarily in the superficial capillary plexus instead of reaching the damaged photoreceptor layer.

CONCLUSIONS

Our data offer novel insights into innate immunity's role in responding to retinal damage and potentially help developing innovative immunotherapeutic approaches that can shift the immune response from maladaptive to beneficial for retinal regeneration.

An analysis of neutrophil-to-lymphocyte ratios and monocyte-to-lymphocyte ratios with six-month prognosis after cerebral contusions

Background and purpose

Neutrophil-to-lymphocyte ratio (NLR) and monocyte-to-lymphocyte ratio (MLR) have been identified as potential prognostic markers in various conditions, including cancer, cardiovascular disease, and stroke. This study aims to investigate the dynamic changes of NLR and MLR following cerebral contusion and their associations with six-month outcomes.

Methods

Retrospective data were collected from January 2016 to April 2020, including patients diagnosed with cerebral contusion and discharged from two teaching-oriented tertiary hospitals in Southern China. Patient demographics, clinical manifestations, laboratory test results (neutrophil, monocyte, and lymphocyte counts) obtained at admission, 24 hours, and one week after cerebral contusion, as well as outcomes, were analyzed. An unfavorable outcome was defined as a Glasgow Outcome Score (GOS) of 0-3 at six months. Logistic regression analysis was performed to identify independent predictors of prognosis, while receiver characteristic curve analysis was used to determine the optimal cutoff values for NLR and MLR.

Results

A total of 552 patients (mean age 47.40, SD 17.09) were included, with 73.19% being male. Higher NLR at one-week post-cerebral contusion (adjusted OR = 4.19, 95%CI, 1.16 - 15.16, P = 0.029) and higher MLR at admission and at 24 h (5.80, 1.40 - 24.02, P = 0.015; 9.06, 1.45 - 56.54, P = 0.018, respectively) were significantly associated with a 6-month unfavorable prognosis after adjustment for other risk factors by multiple logistic regression. The NLR at admission and 24 hours, as well as the MLR at one week, were not significant predictors for a 6-month unfavorable prognosis. Based on receiver operating characteristic curve analysis, the optimal thresholds of NLR at 1 week and MLR at admission after cerebral contusion that best discriminated a unfavorable outcome at 6-month were 6.39 (81.60% sensitivity and 70.73% specificity) and 0.76 (55.47% sensitivity and 78.26% specificity), respectively.

Conclusion

NLR measured one week after cerebral contusion and MLR measured at admission may serve as predictive markers for a 6-month unfavorable prognosis. These ratios hold potential as parameters for risk stratification in patients with cerebral contusion, complementing established biomarkers in diagnosis and treatment. However, further prospective studies with larger cohorts are needed to validate these findings.

Sex differences in physiological response to increased neuronal excitability in a knockin mouse model of pediatric epilepsy

BACKGROUND

Epilepsy is a common neurological disease; however, few if any of the currently marketed antiseizure medications prevent or cure epilepsy. Discovery of pathological processes in the early stages of epileptogenesis has been challenging given the common use of preclinical models that induce seizures in physiologically normal animals. Moreover, despite known sex dimorphism in neurological diseases, females are rarely included in preclinical epilepsy models.

METHODS

We characterized sex differences in mice carrying a pathogenic knockin variant (p.N1768D) in the Scn8a gene that causes spontaneous tonic-clonic seizures (TCs) at ∼3 months of age and found that heterozygous females are more resilient than males in mortality and morbidity. To investigate the cellular mechanisms that underlie female resilience, we utilized blood-brain barrier (BBB) and hippocampal transcriptomic analyses in heterozygous mice before seizure onset (pre-TC) and in mice that experienced ∼20 TCs (post-TC).

RESULTS

In the pre-TC latent phase, both sexes exhibited leaky BBB; however, patterns of gene expression were sexually dimorphic. Females exhibited enhanced oxidative phosphorylation and protein biogenesis, while males activated gliosis and CREB signaling. After seizure onset (chronic phase), females exhibited a metabolic switch to lipid metabolism, while males exhibited increased gliosis and BBB dysfunction and a strong activation of neuroinflammatory pathways.

CONCLUSION

The results underscore the central role of oxidative stress and BBB permeability in the early stages of epileptogenesis, as well as sex dimorphism in response to increasing neuronal hyperexcitability. Our results also highlight the need to include both sexes in preclinical studies to effectively translate results of drug efficacy studies.

Neuroinflammation and acquired traumatic CNS injury: a mini review

Acquired traumatic central nervous system (CNS) injuries, including traumatic brain injury (TBI) and spinal cord injury (SCI), are devastating conditions with limited treatment options. Neuroinflammation plays a pivotal role in secondary damage, making it a prime target for therapeutic intervention. Emerging therapeutic strategies are designed to modulate the inflammatory response, ultimately promoting neuroprotection and neuroregeneration. The use of anti-inflammatory agents has yielded limited support in improving outcomes in patients, creating a critical need to re-envision novel approaches to both quell deleterious inflammatory processes and upend the progressive cycle of neurotoxic inflammation. This demands a comprehensive exploration of individual, age, and sex differences, including the use of advanced imaging techniques, multi-omic profiling, and the expansion of translational studies from rodents to humans. Moreover, a holistic approach that combines pharmacological intervention with multidisciplinary neurorehabilitation is crucial and must include both acute and long-term care for the physical, cognitive, and emotional aspects of recovery. Ongoing research into neuroinflammatory biomarkers could revolutionize our ability to predict, diagnose, and monitor the inflammatory response in real time, allowing for timely adjustments in treatment regimens and facilitating a more precise evaluation of therapeutic efficacy. The management of neuroinflammation in acquired traumatic CNS injuries necessitates a paradigm shift in our approach that includes combining multiple therapeutic modalities and fostering a more comprehensive understanding of the intricate neuroinflammatory processes at play.

Intravenous Administration of Mesenchymal Stem Cell-Derived Exosome Alleviates Spinal Cord Injury by Regulating Neutrophil Extracellular Trap Formation through Exosomal miR-125a-3p

Spinal cord injury (SCI) leads to devastating sequelae, demanding effective treatments. Recent advancements have unveiled the role of neutrophil extracellular traps (NETs) produced by infiltrated neutrophils in exacerbating secondary inflammation after SCI, making it a potential target for treatment intervention. Previous research has established that intravenous administration of stem cell-derived exosomes can mitigate injuries. While stem cell-derived exosomes have demonstrated the ability to modulate microglial reactions and enhance blood-brain barrier integrity, their impact on neutrophil deactivation, especially in the context of NETs, remains poorly understood. This study aims to investigate the effects of intravenous administration of MSC-derived exosomes, with a specific focus on NET formation, and to elucidate the associated molecular mechanisms. Exosomes were isolated from the cell supernatants of amnion-derived mesenchymal stem cells using the ultracentrifugation method. Spinal cord injuries were induced in Sprague-Dawley rats (9 weeks old) using a clip injury model, and 100 μg of exosomes in 1 mL of PBS or PBS alone were intravenously administered 24 h post-injury. Motor function was assessed serially for up to 28 days following the injury. On Day 3 and Day 28, spinal cord specimens were analyzed to evaluate the extent of injury and the formation of NETs. Flow cytometry was employed to examine the formation of circulating neutrophil NETs. Exogenous miRNA was electroporated into neutrophil to evaluate the effect of inflammatory NET formation. Finally, the biodistribution of exosomes was assessed using 64Cu-labeled exosomes in animal positron emission tomography (PET). Rats treated with exosomes exhibited a substantial improvement in motor function recovery and a reduction in injury size. Notably, there was a significant decrease in neutrophil infiltration and NET formation within the spinal cord, as well as a reduction in neutrophils forming NETs in the circulation. In vitro investigations indicated that exosomes accumulated in the vicinity of the nuclei of activated neutrophils, and neutrophils electroporated with the miR-125a-3p mimic exhibited a significantly diminished NET formation, while miR-125a-3p inhibitor reversed the effect. PET studies revealed that, although the majority of the transplanted exosomes were sequestered in the liver and spleen, a notably high quantity of exosomes was detected in the damaged spinal cord when compared to normal rats. MSC-derived exosomes play a pivotal role in alleviating spinal cord injury, in part through the deactivation of NET formation via miR-125a-3p.

NLRP3 exacerbates EAE severity through ROS-dependent NET formation in the mouse brain

BACKGROUND

Neutrophil extracellular trap (NET) has been implicated in the pathology of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). However, the specific contributions of NLRP3, a NET-associated molecule, to EAE pathogenesis and its regulatory role in NET formation remain unknown.

METHODS

To investigate the detrimental effect of NETs supported by NLRP3 in MS pathogenesis, we induced EAE in WT and NLRP3 KO mice and monitored the disease severity. At the peak of the disease, NET formation was assessed by flow cytometry, immunoblotting, and immunofluorescence staining. To further identify the propensity of infiltrated neutrophils, NET-related chemokine receptors, degranulation, ROS production, and PAD4 expression levels were evaluated by flow cytometry. In some experiments, mice were injected with DNase-1 to eliminate the formed NETs.

RESULTS

Our data revealed that neutrophils significantly infiltrate the brain and spinal cord and form NETs during EAE pathogenesis. NLRP3 significantly elevates NET formation, primarily in the brain. NLRP3 also modulated the phenotypes of brain-infiltrated and circulating neutrophils, augmenting CXCR2 and CXCR4 expression, thereby potentially enhancing NET formation. NLRP3 facilitates NET formation in a ROS-dependent and PAD4-independent manner in brain-infiltrated neutrophils. Finally, NLRP3-supported NET formation exacerbates disease severity, triggering Th1 and Th17 cells recruitment.

CONCLUSIONS

Collectively, our findings suggest that NLRP3-supported NETs may be an etiological factor in EAE pathogenesis, primarily in the brain. This study provides evidence that targeting NLRP3 could be a potential therapeutic strategy for MS, specifically by attenuating NET formation.

Gut microbial regulation of innate and adaptive immunity after traumatic brain injury

Acute care management of traumatic brain injury is focused on the prevention and reduction of secondary insults such as hypotension, hypoxia, intracranial hypertension, and detrimental inflammation. However, the imperative to balance multiple clinical concerns simultaneously often results in therapeutic strategies targeted to address one clinical concern causing unintended effects in other remote organ systems. Recently the bidirectional communication between the gastrointestinal tract and the brain has been shown to influence both the central nervous system and gastrointestinal tract homeostasis in health and disease. A critical component of this axis is the microorganisms of the gut known as the gut microbiome. Changes in gut microbial populations in the setting of central nervous system disease, including traumatic brain injury, have been reported in both humans and experimental animal models and can be further disrupted by off-target effects of patient care. In this review article, we will explore the important role gut microbial populations play in regulating brain-resident and peripheral immune cell responses after traumatic brain injury. We will discuss the role of bacterial metabolites in gut microbial regulation of neuroinflammation and their potential as an avenue for therapeutic intervention in the setting of traumatic brain injury.

Association between neutrophil-to-albumin ratio and long-term mortality of aneurysmal subarachnoid hemorrhage

OBJECTIVE

The prognosis of aneurysmal subarachnoid hemorrhage (aSAH) survivors is concerning. The goal of this study was to investigate and demonstrate the relationship between the neutrophil-to-albumin ratio (NAR) and long-term mortality of aSAH survivors.

METHODS

A retrospective observational cohort study was conducted at Sichuan University West China Hospital between January 2009 and June 2019. The investigation of relationship between NAR and long-term mortality was conducted using univariable and multivariable Cox regression models. To demonstrate the predictive performance of different biomarkers over time, time-dependent receiver operating characteristic curve (ROC) analysis and decision curve analysis (DCA) were created.

RESULTS

In total, 3173 aSAH patients were included in this study. There was a strong and continuous relationship between NAR levels and long-term mortality (HR 3.23 95% CI 2.75-3.79, p < 0.001). After adjustment, the result was still significant (adjusted HR 1.78 95% CI 1.49-2.12). Compared with patients with the lowest quartile (< 0.15) of NAR levels, the risk of long-term mortality in the other groups was higher (0.15-0.20: adjusted HR 1.30 95% CI 0.97-1.73; 0.20-0.28: adjusted HR 1.37 95% CI 1.03-1.82; >0.28: adjusted HR 1.74 95% CI 1.30-2.32). Results in survivors were found to be still robust. Moreover, out of all the inflammatory markers studied, NAR demonstrated the highest correlation with long-term mortality.

CONCLUSIONS

A high level of NAR was associated with increased long-term mortality among patients with aSAH. NAR was a promising inflammatory marker for long-term mortality of aSAH.

The Role of Neutrophil Extracellular Traps in Early Microthrombosis and Brain Injury After Subarachnoid Hemorrhage in Mice

Microthrombosis plays an important role in secondary brain injury after experimental subarachnoid hemorrhage (SAH), but the specific mechanism of microthrombosis remains unclear. The purpose of this study was to investigate the role of neutrophil extracellular traps (NETs) in microthrombosis after SAH. SAH was induced in male C57BL/6 mice using an endovascular perforation technique. The marker protein of NETs, citrullinated histone H3 (CitH3), was significantly elevated in the cerebral cortex after SAH, and was co-labeled with microthrombi. Both depletion of neutrophils by anti-Ly6G antibody and DNase I treatment significantly reduced the formation of NETs and microthrombi, and ameliorated neurological deficits, brain edema, BBB disruption, and neuronal injury at 24 h after SAH induction. Cerebral hypoperfusion in the first hours after SAH is a major determinant of poor neurological outcome; in this study, we found that DNase I treatment significantly improved the restoration of early cortical perfusion after SAH. In addition, DNase I treatment also significantly attenuated cerebrospinal fluid (CSF) flow after SAH, which was associated with the diffusion barrier caused by microthrombi in the paravascular space after SAH. In conclusion, NETs are associated with early microthrombosis after SAH; they may be a novel therapeutic target for early brain injury (EBI) after SAH.

Inhibition of neutrophil extracellular trap formation ameliorates neuroinflammation and neuronal apoptosis via STING-dependent IRE1α/ASK1/JNK signaling pathway in mice with traumatic brain injury

BACKGROUND

Neuroinflammation is one of the most important pathogeneses in secondary brain injury after traumatic brain injury (TBI). Neutrophil extracellular traps (NETs) forming neutrophils were found throughout the brain tissue of TBI patients and elevated plasma NET biomarkers correlated with worse outcomes. However, the biological function and underlying mechanisms of NETs in TBI-induced neural damage are not yet fully understood. Here, we used Cl-amidine, a selective inhibitor of NETs to investigate the role of NETs in neural damage after TBI.

METHODS

Controlled cortical impact model was performed to establish TBI. Cl-amidine, 2'3'-cGAMP (an activator of stimulating Interferon genes (STING)), C-176 (a selective STING inhibitor), and Kira6 [a selectively phosphorylated inositol-requiring enzyme-1 alpha [IRE1α] inhibitor] were administrated to explore the mechanism by which NETs promote neuroinflammation and neuronal apoptosis after TBI. Peptidyl arginine deiminase 4 (PAD4), an essential enzyme for neutrophil extracellular trap formation, is overexpressed with adenoviruses in the cortex of mice 1 day before TBI. The short-term neurobehavior tests, magnetic resonance imaging (MRI), laser speckle contrast imaging (LSCI), Evans blue extravasation assay, Fluoro-Jade C (FJC), TUNEL, immunofluorescence, enzyme-linked immunosorbent assay (ELISA), western blotting, and quantitative-PCR were performed in this study.

RESULTS

Neutrophils form NETs presenting in the circulation and brain at 3 days after TBI. NETs inhibitor Cl-amidine treatment improved short-term neurological functions, reduced cerebral lesion volume, reduced brain edema, and restored cerebral blood flow (CBF) after TBI. In addition, Cl-amidine exerted neuroprotective effects by attenuating BBB disruption, inhibiting immune cell infiltration, and alleviating neuronal death after TBI. Moreover, Cl-amidine treatment inhibited microglia/macrophage pro-inflammatory polarization and promoted anti-inflammatory polarization at 3 days after TBI. Mechanistically, STING ligand 2'3'-cGAMP abolished the neuroprotection of Cl-amidine via IRE1α/ASK1/JNK signaling pathway after TBI. Importantly, overexpression of PAD4 promotes neuroinflammation and neuronal death via the IRE1α/ASK1/JNK signaling pathway after TBI. However, STING inhibitor C-176 or IRE1α inhibitor Kira6 effectively abolished the neurodestructive effects of PAD4 overexpression after TBI.

CONCLUSION

Altogether, we are the first to demonstrate that NETs inhibition with Cl-amidine ameliorated neuroinflammation, neuronal apoptosis, and neurological deficits via STING-dependent IRE1α/ASK1/JNK signaling pathway after TBI. Thus, Cl-amidine treatment may provide a promising therapeutic approach for the early management of TBI.

Recombinant human DNase-I improves acute respiratory distress syndrome via neutrophil extracellular trap degradation

BACKGROUND

Respiratory failure is the primary cause of death in patients with COVID-19, whereas coagulopathy is associated with excessive inflammation and multiorgan failure. Neutrophil extracellular traps (NETs) may exacerbate inflammation and provide a scaffold for thrombus formation.

OBJECTIVES

The goal of this study was to determine whether degradation of NETs by recombinant human DNase-I (rhDNase), a safe, Food and Drug Administration-approved drug, reduces excessive inflammation, reverses aberrant coagulation, and improves pulmonary perfusion after experimental acute respiratory distress syndrome (ARDS).

METHODS

Intranasal poly(I:C), a synthetic double-stranded RNA, was administered to adult mice for 3 consecutive days to simulate a viral infection, and these subjects were randomized to treatment arms, which received either an intravenous placebo or rhDNase. The effects of rhDNase on immune activation, platelet aggregation, and coagulation were assessed in mice and donor human blood.

RESULTS

NETs were observed in bronchoalveolar lavage fluid and within regions of hypoxic lung tissue after experimental ARDS. The administration of rhDNase mitigated peribronchiolar, perivascular, and interstitial inflammation induced by poly(I:C). In parallel, rhDNase degraded NETs, attenuated platelet-NET aggregates, reduced platelet activation, and normalized the clotting time to improve regional perfusion, as observed using gross morphology, histology, and microcomputed tomographic imaging in mice. Similarly, rhDNase reduced NETs and attenuated platelet activation in human blood.

CONCLUSION

NETs exacerbate inflammation and promote aberrant coagulation by providing a scaffold for aggregated platelets after experimental ARDS. Intravenous administration of rhDNase degrades NETs and attenuates coagulopathy in ARDS, providing a promising translational approach to improve pulmonary structure and function after ARDS.

Brain alarm by self-extracellular nucleic acids: from neuroinflammation to neurodegeneration

Neurological disorders such as stroke, multiple sclerosis, as well as the neurodegenerative diseases Parkinson's or Alzheimer's disease are accompanied or even powered by danger associated molecular patterns (DAMPs), defined as endogenous molecules released from stressed or damaged tissue. Besides protein-related DAMPs or "alarmins", numerous nucleic acid DAMPs exist in body fluids, such as cell-free nuclear and mitochondrial DNA as well as different species of extracellular RNA, collectively termed as self-extracellular nucleic acids (SENAs). Among these, microRNA, long non-coding RNAs, circular RNAs and extracellular ribosomal RNA constitute the majority of RNA-based DAMPs. Upon tissue injury, necrosis or apoptosis, such SENAs are released from neuronal, immune and other cells predominantly in association with extracellular vesicles and may be translocated to target cells where they can induce intracellular regulatory pathways in gene transcription and translation. The majority of SENA-induced signaling reactions in the brain appear to be related to neuroinflammatory processes, often causally associated with the onset or progression of the respective disease. In this review, the impact of the diverse types of SENAs on neuroinflammatory and neurodegenerative diseases will be discussed. Based on the accumulating knowledge in this field, several specific antagonistic approaches are presented that could serve as therapeutic interventions to lower the pathological outcome of the indicated brain disorders.

Extracellular histones as damage-associated molecular patterns in neuroinflammatory responses

The four core histones H2A, H2B, H3, H4, and the linker histone H1 primarily bind DNA and regulate gene expression within the nucleus. Evidence collected mainly from the peripheral tissues illustrates that histones can be released into the extracellular space by activated or damaged cells. In this article, we first summarize the innate immune-modulatory properties of extracellular histones and histone-containing complexes, such as nucleosomes, and neutrophil extracellular traps (NETs), described in peripheral tissues. There, histones act as damage-associated molecular patterns (DAMPs), which are a class of endogenous molecules that trigger immune responses by interacting directly with the cellular membranes and activating pattern recognition receptors (PRRs), such as toll-like receptors (TLR) 2, 4, 9 and the receptor for advanced glycation end-products (RAGE). We then focus on the available evidence implicating extracellular histones as DAMPs of the central nervous system (CNS). It is becoming evident that histones are present in the brain parenchyma after crossing the blood-brain barrier (BBB) or being released by several types of brain cells, including neurons, microglia, and astrocytes. However, studies on the DAMP-like effects of histones on CNS cells are limited. For example, TLR4 is the only known molecular target of CNS extracellular histones and their interactions with other PRRs expressed by brain cells have not been observed. Nevertheless, extracellular histones are implicated in the pathogenesis of a variety of neurological disorders characterized by sterile neuroinflammation; therefore, detailed studies on the role these proteins and their complexes play in these pathologies could identify novel therapeutic targets.

The Extracellular Vesicle Citrullinome and Signature in a Piglet Model of Neonatal Seizures

Neonatal seizures are commonly associated with acute perinatal brain injury, while understanding regarding the downstream molecular pathways related to seizures remains unclear. Furthermore, effective treatment and reliable biomarkers are still lacking. Post-translational modifications can contribute to changes in protein function, and post-translational citrullination, which is caused by modification of arginine to citrulline via the calcium-mediated activation of the peptidylarginine deiminase (PAD) enzyme family, is being increasingly linked to neurological injury. Extracellular vesicles (EVs) are lipid-bilayer structures released from cells; they can be isolated from most body fluids and act as potential liquid biomarkers for disease conditions and response to treatment. As EVs carry a range of genetic and protein cargo that can be characteristic of pathological processes, the current study assessed modified citrullinated protein cargo in EVs isolated from plasma and CSF in a piglet neonatal seizure model, also following phenobarbitone treatment. Our findings provide novel insights into roles for PAD-mediated changes on EV signatures in neonatal seizures and highlight the potential of plasma- and CSF-EVs to monitor responses to treatment.

Neutrophil extracellular traps aggravate neuronal endoplasmic reticulum stress and apoptosis via TLR9 after traumatic brain injury

Endoplasmic reticulum (ER) stress and ER stress-mediated apoptosis play an important role during secondary brain damage after traumatic brain injury (TBI). Increased neutrophil extracellular traps (NETs) formation has been demonstrated to be associated with neurological damage after TBI. However, the correlation between ER stress and NETs remains unclear, and the specific function of NETs in neurons has not been defined. In this study, we found that the levels of NETs circulating biomarkers were remarkably elevated in the plasma of TBI patients. We then inhibited NETs formation by peptidylarginine deiminase 4 (PAD4, a critical enzyme for NETs formation) deficiency and discovered that ER stress activation and ER stress-mediated neuronal apoptosis were reduced. The degradation of NETs via DNase I showed similar outcomes. Furthermore, overexpression of PAD4 aggravated neuronal ER stress and ER stress-associated apoptosis, while TLR9 antagonist administration abrogated the damage caused by NETs. In addition to in vivo experiments, in vitro experiments revealed that treatment with a TLR9 antagonist alleviated NETs-induced ER stress and apoptosis in HT22 cells. Collectively, our results indicated that ER stress as well as the accompanying neuronal apoptosis can be ameliorated by disruption of NETs and that suppression of the TLR9-ER stress signaling pathway may contribute to positive outcomes after TBI.

NLRP3 Exacerbate NETosis-Associated Neuroinflammation in an LPS-Induced Inflamed Brain

Neutrophil extracellular traps (NETs) exert a novel function of trapping pathogens. Released NETs can accumulate in inflamed tissues, be recognized by other immune cells for clearance, and lead to tissue toxicity. Therefore, the deleterious effect of NET is an etiological factor, causing several diseases directly or indirectly. NLR family pyrin domain containing 3 (NLRP3) in neutrophils is pivotal in signaling the innate immune response and is associated with several NET-related diseases. Despite these observations, the role of NLRP3 in NET formation in neuroinflammation remains elusive. Therefore, we aimed to explore NET formation promoted by NLRP3 in an LPS-induced inflamed brain. Wild-type and NLRP3 knockout mice were used to investigate the role of NLRP3 in NET formation. Brain inflammation was systemically induced by administering LPS. In such an environment, the NET formation was evaluated based on the expression of its characteristic indicators. DNA leakage and NET formation were analyzed in both mice through Western blot, flow cytometry, and in vitro live cell imaging as well as two-photon imaging. Our data revealed that NLRP3 promotes DNA leakage and facilitates NET formation accompanied by neutrophil death. Moreover, NLRP3 is not involved in neutrophil infiltration but is predisposed to boost NET formation, which is accompanied by neutrophil death in the LPS-induced inflamed brain. Furthermore, either NLRP3 deficiency or neutrophil depletion diminished pro-inflammatory cytokine, IL-1β, and alleviated blood-brain barrier damage. Overall, the results suggest that NLRP3 exacerbates NETosis in vitro and in the inflamed brain, aggravating neuroinflammation. These findings provide a clue that NLRP3 would be a potential therapeutic target to alleviate neuroinflammation.

USP30 impairs mitochondrial quality control and aggravates oxidative damage after traumatic brain injury

Clinical progress in the treatment of traumatic brain injury (TBI) is hindered by the poor understanding of the molecular mechanisms that underlie secondary brain injury (SBI). USP30, a mitochondrial deubiquitinase, has been implicated in the pathological progress of various diseases. However, the precise role of USP30 in TBI-induced SBI remains unclear. In this study, we found that USP30 was differentially upregulated after TBI in humans and mice. Immunofluorescence staining further revealed that the enhanced USP30 mainly localized in neurons. Neuron-specific knockout of USP30 reduced lesion volumes, mitigated brain edema, and attenuated neurological deficits after TBI in mice. Additionally, we found that USP30 deficiency effectively suppressed oxidative stress and neuronal apoptosis in TBI. Those protective effects of USP30 loss may be attributed, at least partially, to the reduction of TBI-induced impairment of mitochondrial quality control, including mitochondrial dynamics, function, and mitophagy. Collectively, our findings identify a previously undisclosed role of USP30 in the pathophysiology of TBI and lay a preliminary foundation for future research in this field.

Fluoride induces neutrophil extracellular traps and aggravates brain inflammation by disrupting neutrophil calcium homeostasis and causing ferroptosis

Endemic fluorosis (EF) has been listed as one of the serious public health problems in many countries. Long-term exposure to high fluoride can lead to severe neuropathological damage to the brain. Although long-term research has revealed the mechanism of some brain inflammation caused by excessive fluoride, the role of intercellular interactions, especially immune cells, in brain damage is still unclear. Fluoride can induce ferroptosis and inflammation in the brain in our study. A co-culture system of neutrophil extranets and primary neuronal cells showed that fluoride can aggravate neuronal cell inflammation by causing neutrophil extranets (NETs). In terms of the mechanism of action, we found that fluoride leads to the opening of calcium ion channels by causing neutrophil calcium imbalance, which in turn leads to the opening of L-type calcium ion channels (LTCC). Extracellular free iron enters the cell from the open LTCC, leading to neutrophil ferroptosis, which releases NETs. Blocking LTCC (nifedipine) rescued neutrophil ferroptosis and reduced the generation of NETs. Inhibition of ferroptosis (Fer-1) did not block cellular calcium imbalance. In summary, our study explores the role of NETs in fluoride-induced brain inflammation and suggests that blocking calcium channels may be one of the possibilities to rescue fluoride-induced ferroptosis.

Neuroimmunomodulatory properties of polysialic acid

Polymeric sialic acid (polysialic acid, polySia) is a remarkable posttranslational modification of only few select proteins. The major, and most prominent polySia protein carrier is the neural cell adhesion molecule NCAM. Here, the key functions of polySia are to regulate interactions of NCAM and to balance cellular interactions in brain development and plasticity. During recent years, however, increasing evidence points towards a role of polySia in the modulation of immune responses. These immunomodulatory functions can be mediated by polySia on proteins other than NCAM, presented either on the cell surface or released into the extracellular space. This perspective review summarizes our current knowledge and addresses major open questions on polySia and polySia receptors in modulating innate immune responses in the brain.

Inflammaging, cellular senescence, and cognitive aging after traumatic brain injury

Traumatic brain injury (TBI) is associated with mortality and morbidity worldwide. Accumulating pre-clinical and clinical data suggests TBI is the leading extrinsic cause of progressive neurodegeneration. Neurological deterioration after either a single moderate-severe TBI or repetitive mild TBI often resembles dementia in aged populations; however, no currently approved therapies adequately mitigate neurodegeneration. Inflammation correlates with neurodegenerative changes and cognitive dysfunction for years post-TBI, suggesting a potential association between immune activation and both age- and TBI-induced cognitive decline. Inflammaging, a chronic, low-grade sterile inflammation associated with natural aging, promotes cognitive decline. Cellular senescence and the subsequent development of a senescence associated secretory phenotype (SASP) promotes inflammaging and cognitive aging, although the functional association between senescent cells and neurodegeneration is poorly defined after TBI. In this mini-review, we provide an overview of the pre-clinical and clinical evidence linking cellular senescence with poor TBI outcomes. We also discuss the current knowledge and future potential for senotherapeutics, including senolytics and senomorphics, which kill and/or modulate senescent cells, as potential therapeutics after TBI.

Neutrophil extracellular traps contribute to coagulopathy after traumatic brain injury

Coagulopathy contributes to the majority of deaths and disabilities associated with traumatic brain injury (TBI). Whether neutrophil extracellular traps (NETs) contribute to an abnormal coagulation state in the acute phase of TBI remains unknown. Our objectives were to demonstrate the definitive role of NETs in coagulopathy in TBI. We detected NET markers in 128 TBI patients and 34 healthy individuals. Neutrophil-platelet aggregates were detected in blood samples from TBI patients and healthy individuals using flow cytometry and staining for CD41 and CD66b. Endothelial cells were incubated with isolated NETs and we detected the expression of vascular endothelial cadherin, syndecan-1, thrombomodulin, von Willebrand factor, phosphatidylserine, and tissue factor. In addition, we established a TBI mouse model to determine the potential role of NETs in TBI-associated coagulopathy. NET generation was mediated by high mobility group box 1 (HMGB1) from activated platelets and contributed to procoagulant activity in TBI. Furthermore, coculture experiments indicated that NETs damaged the endothelial barrier and caused these cells to assume a procoagulant phenotype. Moreover, the administration of DNase I before or after brain trauma markedly reduced coagulopathy and improved the survival and clinical outcome of mice with TBI.

Early DNase-I therapy delays secondary brain damage after traumatic brain injury in adult mice

Traumatic brain injury (TBI) causes the release of danger-associated molecular patterns (DAMP) from damaged or dead cells, which contribute to secondary brain damage after TBI. Cell-free DNA (cfDNA) is a DAMP known to cause disruption of the blood-brain barrier (BBB), promote procoagulant processes, brain edema, and neuroinflammation. This study tested the hypothesis that administration of deoxyribonuclease-I (DNase-I) has a beneficial effect after TBI. Mice (n = 84) were subjected to controlled cortical impact (CCI) and posttraumatic intraperitoneal injections of low dose (LD) or high dose (HD) of DNase-I or vehicle solution at 30 min and 12 h after CCI. LD was most effective to reduce lesion volume (p = 0.003), brain water content (p < 0.0001) and to stabilize BBB integrity (p = 0.019) 1 day post-injury (dpi). At 6 h post injury LD-treated animals showed less cleavage of fibrin (p = 0.0014), and enhanced perfusion as assessed by micro-computer-tomography (p = 0.027). At 5 dpi the number of Iba1-positive cells (p = 0.037) were reduced, but the number of CD45-positive cells, motoric function and brain lesion volume was not different. Posttraumatic-treatment with DNase-I therefore stabilizes the BBB, reduces the formation of brain edema, immune response, and delays secondary brain damage. DNase-I might be a new approach to extend the treatment window after TBI.

Altered endocannabinoid metabolism compromises the brain-CSF barrier and exacerbates chronic deficits after traumatic brain injury in mice

Endocannabinoids [2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (AEA)], endogenously produced arachidonate-based lipids, are anti-inflammatory physiological ligands for two known cannabinoid receptors, CB1 and CB2, yet the molecular and cellular mechanisms underlying their effects after brain injury are poorly defined. In the present study, we hypothesize that traumatic brain injury (TBI)-induced loss of endocannabinoids exaggerates neurovascular injury, compromises brain-cerebrospinal fluid (CSF) barriers (BCB) and causes behavioral dysfunction. Preliminary analysis in human CSF and plasma indicates changes in endocannabinoid levels. This encouraged us to investigate the levels of endocannabinoid-metabolizing enzymes in a mouse model of controlled cortical impact (CCI). Reductions in endocannabinoid (2-AG and AEA) levels in plasma were supported by higher expression of their respective metabolizing enzymes, monoacylglycerol lipase (MAGL), fatty acid amide hydrolase (FAAH), and cyclooxygenase 2 (Cox-2) in the post-TBI mouse brain. Following increased metabolism of endocannabinoids post-TBI, we observed increased expression of CB2, non-cannabinoid receptor Transient receptor potential vanilloid-1 (TRPV1), aquaporin 4 (AQP4), ionized calcium binding adaptor molecule 1 (IBA1), glial fibrillary acidic protein (GFAP), and acute reduction in cerebral blood flow (CBF). The BCB and pericontusional cortex showed altered endocannabinoid expressions and reduction in ventricular volume. Finally, loss of motor functions and induced anxiety behaviors were observed in these TBI mice. Taken together, our findings suggest endocannabinoids and their metabolizing enzymes play an important role in the brain and BCB integrity and highlight the need for more extensive studies on these mechanisms.

Degradable Poly(amino acid) Vesicles Modulate DNA-Induced Inflammation after Traumatic Brain Injury

Following brain trauma, secondary injury from molecular and cellular changes causes progressive cerebral tissue damage. Acute/chronic neuroinflammation following traumatic brain injury (TBI) is a key player in the development of secondary injury. Rapidly elevated cell-free DNAs (cfDNAs) due to cell death could lead to production of inflammatory cytokines that aggravate TBI. Herein, we designed poly(amino acid)-based cationic nanoparticles (cNPs) and applied them intravenously in a TBI mice model with the purpose of scavenging cfDNA in the brain and suppressing the acute inflammation. In turn, these cNPs could effectively eliminate endogenous cfDNA, inhibit excessive activation of inflammation, and promote neural functional recovery.

Neutrophil Extracellular Traps Release following Hypoxic-Ischemic Brain Injury in Newborn Rats Treated with Therapeutic Hypothermia

The peripheral immune system plays a critical role in neuroinflammation of the central nervous system after an insult. Hypoxic-ischemic encephalopathy (HIE) induces a strong neuroinflammatory response in neonates, which is often associated with exacerbated outcomes. In adult models of ischemic stroke, neutrophils infiltrate injured brain tissue immediately after an ischemic insult and aggravate inflammation via various mechanisms, including neutrophil extracellular trap (NETs) formation. In this study, we used a neonatal model of experimental hypoxic-ischemic (HI) brain injury and demonstrated that circulating neutrophils were rapidly activated in neonatal blood. We observed an increased infiltration of neutrophils in the brain after exposure to HI. After treatment with either normothermia (NT) or therapeutic hypothermia (TH), we observed a significantly enhanced expression level of the NETosis marker Citrullinated H3 (Cit-H3), which was significantly more pronounced in animals treated with TH than in those treated with NT. NETs and NLR family pyrin domain containing 3 (NLRP-3) inflammasome assembly are closely linked in adult models of ischemic brain injury. In this study, we observed an increase in the activation of the NLRP-3 inflammasome at the time points analyzed, particularly immediately after TH, when we observed a significant increase in NETs structures in the brain. Together, these results suggest the important pathological functions of early arriving neutrophils and NETosis following neonatal HI, particularly after TH treatment, which is a promising starting point for the development of potential new therapeutic targets for neonatal HIE.

ROLE OF PEPTIDYLARGININE DEIMINASE AND NEUTROPHIL EXTRACELLULAR TRAPS IN INJURIES: FUTURE NOVEL DIAGNOSTICS AND THERAPEUTIC TARGETS

ABSTRACT

Injuries lead to an early systemic inflammatory state with innate immune system activation. Neutrophil extracellular traps (NETs) are a complex of chromatin and proteins released from the activated neutrophils. Although initially described as a response to bacterial infections, NETs have also been identified in the sterile postinjury inflammatory state. Peptidylarginine deiminases (PADs) are a group of isoenzymes that catalyze the conversion of arginine to citrulline, termed citrullination or deimination. PAD2 and PAD4 have been demonstrated to play a role in NET formation through citrullinated histone 3. PAD2 and PAD4 have a variety of substrates with variable organ distribution. Preclinical and clinical studies have evaluated the role of PADs and NETs in major trauma, hemorrhage, burns, and traumatic brain injury. Neutrophil extracellular trap formation and PAD activation have been shown to contribute to the postinjury inflammatory state leading to a detrimental effect on organ systems. This review describes our current understanding of the role of PAD and NET formation following injury and burn. This is a new field of study, and the emerging data appear promising for the future development of targeted biomarkers and therapies in trauma.

Extracellular traps formation following cervical spinal cord injury

Spinal cord injuries involve a primary injury that can lead to permanent loss of function and a secondary injury associated with pathologic and inflammatory processes. Extracellular traps are extracellular structures expressed by immune cells that are primarily composed of chromatin, granular enzymes and histones. Extracellular traps are known to induce tissue damage when overexpressed and could be associated in the occurrence of secondary damage. In the present study, we used flow cytometry to demonstrate that at 1 day following a C2 spinal cord lateral hemisection in male Swiss mice, resident microglia form vital microglia extracellular traps, and infiltrating neutrophils form vital neutrophil extracellular traps. We also used immunolabelling to show that microglia near the lesion area are most likely to form these microglia extracellular traps. As expected, infiltrating neutrophils are located at the site of injury, though only some of them engage in post-injury extracellular trap formation. We also observed the formation of microglia and neutrophil extracellular traps in our sham animal models of durotomy, but formation was less frequent than following the C2 hemisection. Our results demonstrate for the first time that microglia form extracellular traps in the spinal cord following injury and durotomy. It remains however to determine the exact mechanisms and kinetics of neutrophil and microglia extracellular traps formation following spinal cord injury. This information would allow to better mitigate this inflammatory process that may contribute to secondary injury and to effectively target extracellular traps to improve functional outcomes following spinal cord injury.

GPR109A controls neutrophil extracellular traps formation and improve early sepsis by regulating ROS/PAD4/Cit-H3 signal axis

BACKGROUND

Neutrophil extracellular traps (NETs) is the key means for neutrophils to resist bacterial invasion. Sepsis is a systemic inflammatory response syndrome caused by infection.

METHODS

In our study, qRT-PCR was used to detect the gene expression in neutrophils, Western blot was used to detect the protein expression in mouse tissues and neutrophils, flow cytometry was used to detect the purity of neutrophils in the whole blood and immunofluorescence was used to detect the NETs formation.

RESULTS

In this study, we analyzed the NETs formation in the blood of patients with sepsis. The results showed that a large number of NETs appeared. And the expression of GPR109A in neutrophils of patients with sepsis was significantly up regulated. Then we collected neutrophils from WT mice and GPR109A^-/- mice and found that GPR109A knockout could significantly inhibit the early NETs formation of neutrophils. The results also showed that knockout of GPR109A or inhibition of the NETs formation could increase the inflammatory response of liver, spleen, lung and kidney in mice, thus affecting the disease process of sepsis. Then we observed the death of mice in 16 days. The results showed that inhibiting the NETs formation could significantly affect the early mortality of mice, while knocking out GPR109A could directly affect the mortality of the whole period.

CONCLUSIONS

This study confirmed the regulatory effect of GPR109A on early NETs formation for the first time, and provided a new target for the treatment of sepsis.

Neutrophil extracellular traps in central nervous system pathologies: A mini review

Neutrophils are the first cells to be recruited to sites of acute inflammation and contribute to host defense through phagocytosis, degranulation and neutrophil extracellular traps (NETs). Neutrophils are rarely found in the brain because of the highly selective blood-brain barrier (BBB). However, several diseases disrupt the BBB and cause neuroinflammation. In this regard, neutrophils and NETs have been visualized in the brain after various insults, including traumatic (traumatic brain injury and spinal cord injury), infectious (bacterial meningitis), vascular (ischemic stroke), autoimmune (systemic lupus erythematosus), neurodegenerative (multiple sclerosis and Alzheimer's disease), and neoplastic (glioma) causes. Significantly, preventing neutrophil trafficking into the central nervous system or NET production in these diseases alleviates brain pathology and improves neurocognitive outcomes. This review summarizes the major studies on the contribution of NETs to central nervous system (CNS) disorders.

Tackling Neuroinflammation After Traumatic Brain Injury: Complement Inhibition as a Therapy for Secondary Injury

Traumatic brain injury (TBI) is a leading cause of mortality, sensorimotor morbidity, and neurocognitive disability. Neuroinflammation is one of the key drivers causing secondary brain injury after TBI. Therefore, attenuation of the inflammatory response is a potential therapeutic goal. This review summarizes the most important neuroinflammatory pathophysiology resulting from TBI and the clinical trials performed to attenuate neuroinflammation. Studies show that non-selective attenuation of the inflammatory response, in the early phase after TBI, might be detrimental and that there is a gap in the literature regarding pharmacological trials targeting specific pathways. The complement system and its crosstalk with the coagulation system play an important role in the pathophysiology of secondary brain injury after TBI. Therefore, regaining control over the complement cascades by inhibiting overshooting activation might constitute useful therapy. Activation of the complement cascade is an early component of neuroinflammation, making it a potential target to mitigate neuroinflammation in TBI. Therefore, we have described pathophysiological aspects of complement inhibition and summarized animal studies targeting the complement system in TBI. We also present the first clinical trial aimed at inhibition of complement activation in the early days after brain injury to reduce the risk of morbidity and mortality following severe TBI.

Inhibition of neutrophil extracellular trap formation attenuates NLRP1-dependent neuronal pyroptosis via STING/IRE1α pathway after traumatic brain injury in mice

Introduction

Increased neutrophil extracellular trap (NET) formation has been reported to be associated with cerebrovascular dysfunction and neurological deficits in traumatic brain injury (TBI). However, the biological function and underlying mechanisms of NETs in TBI-induced neuronal cell death are not yet fully understood.

Methods

First, brain tissue and peripheral blood samples of TBI patients were collected, and NETs infiltration in TBI patients was detected by immunofluorescence staining and Western blot. Then, a controlled cortical impact device was used to model brain trauma in mice, and Anti-Ly6G, DNase, and CL-amidine were given to reduce the formation of neutrophilic or NETs in TBI mice to evaluate neuronal death and neurological function. Finally, the pathway changes of neuronal pyroptosis induced by NETs after TBI were investigated by administration of peptidylarginine deiminase 4 (a key enzyme of NET formation) adenovirus and inositol-requiring enzyme-1 alpha (IRE1α) inhibitors in TBI mice.

Results

We detected that both peripheral circulating biomarkers of NETs and local NETs infiltration in the brain tissue were significantly increased and had positive correlations with worse intracranial pressure (ICP) and neurological dysfunction in TBI patients. Furthermore, the depletion of neutrophils effectively reduced the formation of NET in mice subjected to TBI. we found that degradation of NETs or inhibition of NET formation significantly inhibited nucleotide-binding oligomerization domain (NOD)-like receptor pyrin domain containing 1 (NLRP1) inflammasome-mediated neuronal pyroptosis after TBI, whereas these inhibitory effects were abolished by cyclic GMP-AMP (cGAMP), an activator of stimulating Interferon genes (STING). Moreover, overexpression of PAD4 in the cortex by adenoviruses could aggravate NLRP1-mediated neuronal pyroptosis and neurological deficits after TBI, whereas these pro-pyroptotic effects were rescued in mice also receiving STING antagonists. Finally, IRE1α activation was significantly upregulated after TBI, and NET formation or STING activation was found to promote this process. Notably, IRE1α inhibitor administration significantly abrogated NETs-induced NLRP1 inflammasome-mediated neuronal pyroptosis in TBI mice.

Discussion

Our findings indicated that NETs could contribute to TBI-induced neurological deficits and neuronal death by promoting NLRP1-mediated neuronal pyroptosis. Suppression of the STING/ IRE1α signaling pathway can ameliorate NETs-induced neuronal pyroptotic death after TBI.

Increased blood neutrophil extracellular traps (NETs) associated with early life stress: translational findings in recent-onset schizophrenia and rodent model

Higher levels of interleukin (IL)-6 and elevated neutrophil counts are consistently reported in the blood of patients with schizophrenia. Stressors during childhood and/or adolescence are major socioenvironmental risk factors for schizophrenia and may contribute to immune dysregulation. Previous studies using blood cytokines to stratify patients with schizophrenia suggest that only a subset presents a low-grade inflammatory state. However, these studies have not addressed whether environmental factors such as childhood maltreatment contributed to identifying inflammatory clusters. Moreover, a neutrophil-related mechanism (Neutrophil Extracellular Traps; NETs) central to both the initiation and chronicity of autoimmune and inflammatory diseases has never been investigated in psychiatry. Elevated NETs in schizophrenia may predispose patients to inflammatory and autoimmune diseases resulting in reduced life expectancy. We, therefore, investigated NETs as a novel mechanism and biological target in early schizophrenia and their role together with IL-6 and childhood maltreatment in identifying cluster subgroups. We found increased NETs in the plasma of patients with early schizophrenia (n = 78) compared to both their unaffected siblings (n = 25) and community controls (n = 78), irrespective of sex, body mass index, psychoactive drug use, or tobacco smoking. Increased NETs in patients were unrelated to antipsychotic treatment, which was further tested in vitro using fresh neutrophils. By applying unsupervised two-step clustering analysis, we integrated values of NETs, IL-6, and childhood maltreatment scores. We identified two main clusters; childhood maltreatment scores and NETs were the most important variables contributing to cluster separation (high-CL1 and low-CL2), while IL-6 was the least contributor. Patients allocated in the high-CL1 (61.5%) had significantly higher childhood maltreatment scores, NETs, and IL-6 levels than the remaining groups (patients low-CL2, siblings, and controls high-CL1 and low-CL2). We complemented these findings with a rat model based on stress exposure during adolescence that results in several schizophrenia-like changes in adulthood. We found that adolescent stressed rats had higher NETs and IL-6 levels in serum compared to non-stressed rats with a tendency to produce more NETs from the bone marrow. Altogether, this study brings a novel cellular-based mechanism in schizophrenia that, combined with early-stress, could be useful to identify subgroups for more personalised treatments.

Increased formation of neutrophil extracellular traps in patients with anti-N-methyl-d-aspartate receptor encephalitis

Background

Neutrophil extracellular traps (NETs) have been found to play an important role in several nervous system diseases. However, their role in anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis remains unclear. The purpose of this study was to examine the possible role of NETs in anti-NMDAR encephalitis.

Materials and methods

Eleven patients with anti-NMDAR encephalitis and ten healthy participants were enrolled. Plasma NETs levels were detected using an immunofluorescence assay and enzyme-linked immunosorbent assay. Additionally, we examined 10 plasma cytokines in patients with anti-NMDAR encephalitis and analyzed the correlation between citrullinated histone 3 levels and cytokine release.

Results

Peripheral blood neutrophils from patients with anti-NMDAR encephalitis were more susceptible to NET generation. When compared with controls, cases of anti-NMDAR encephalitis showed elevated levels of IL-1 α, IL-6, IL-8, IL-13, MCP-1, and TNF-α (p < 0.05). Moreover, IL-6, IL-8, and TNF-α levels were positively correlated with H3Cit levels.

Conclusion

We provide evidence that NETs may play a role in anti-NMDAR encephalitis, providing clues for elucidation of the pathogenesis of this disease.

Immune modulation after traumatic brain injury

Traumatic brain injury (TBI) induces instant activation of innate immunity in brain tissue, followed by a systematization of the inflammatory response. The subsequent response, evolved to limit an overwhelming systemic inflammatory response and to induce healing, involves the autonomic nervous system, hormonal systems, and the regulation of immune cells. This physiological response induces an immunosuppression and tolerance state that promotes to the occurrence of secondary infections. This review describes the immunological consequences of TBI and highlights potential novel therapeutic approaches using immune modulation to restore homeostasis between the nervous system and innate immunity.

Macrophage Extracellular Traps Exacerbate Secondary Spinal Cord Injury by Modulating Macrophage/Microglia Polarization via LL37/P2X7R/NF-κB Signaling Pathway

Persistent inflammation in the secondary spinal cord injury (SCI) is an important reason for the failure of nerve repair, which is partly due to the continuous activation of local M1-like macrophage/microglia. It is reported that extracellular trap (ET) has been a new way of cell death, which can be released by macrophages and named macrophage extracellular trap (Met). Furthermore, it exists widely in the pathophysiological process of many diseases, but it has been rarely studied in the field of SCI. In this study, we constructed a spinal cord contusion model and assessed the function outcome of SCI rats. We used immunofluorescence, flow cytometry, and transmission electron microscope (TEM) to demonstrate the existence of Mets. Besides, some related experiments had also been employed to explore the relationship between Mets and M1 polarization of macrophage/microglia. We also performed Co-IP and Western blotting to reveal a new extracellular proinflammatory signal pathway. Finally, we made a linear regression analysis between the concentrations of specific markers of Mets in human serum and ASIA scores. Briefly, our results suggested that macrophages infiltrated in SCI area could induce macrophage/microglia to differentiate into M1-like cells by releasing Mets, which may be achieved partly through LL37-P2X37-NF-κB signal pathway. However, limiting Mets could effectively inhibit M1 polarization and promote function recovery. In addition, the concentrations of Met related proteins in human serum showed high correlation with ASIA scores and could be applied to reflect the severity of SCI. In conclusion, Mets may be a new target for SCI therapy and a promising index for SCI assessment.

Genetic deletion of Krüppel-like factor 11 aggravates traumatic brain injury

Background

The long-term functional recovery of traumatic brain injury (TBI) is hampered by pathological events, such as parenchymal neuroinflammation, neuronal death, and white matter injury. Krüppel-like transcription factor 11 (KLF 11) belongs to the zinc finger family of transcription factors and actively participates in various pathophysiological processes in neurological disorders. Up to now, the role and molecular mechanisms of KLF11 in regulating the pathogenesis of brain trauma is poorly understood.

Methods

KLF11 knockout (KO) and wild-type (WT) mice were subjected to experimental TBI, and sensorimotor and cognitive functions were evaluated by rotarod, adhesive tape removal, foot fault, water maze, and passive avoidance tests. Brain tissue loss/neuronal death was examined by MAP2 and NeuN immunostaining, and Cresyl violet staining. White matter injury was assessed by Luxol fast blue staining, and also MBP/SMI32 and Caspr/Nav1.6 immunostaining. Activation of cerebral glial cells and infiltration of blood-borne immune cells were detected by GFAP, Iba-1/CD16/32, Iba-1/CD206, Ly-6B, and F4/80 immunostaining. Brian parenchymal inflammatory cytokines were measured with inflammatory array kits.

Results

Genetic deletion of KLF11 worsened brain trauma-induced sensorimotor and cognitive deficits, brain tissue loss and neuronal death, and white matter injury in mice. KLF11 genetic deficiency in mice also accelerated post-trauma astrocytic activation, promoted microglial polarization to a pro-inflammatory phenotype, and increased the infiltration of peripheral neutrophils and macrophages into the brain parenchyma. Mechanistically, loss-of-KLF11 function was found to directly increase the expression of pro-inflammatory cytokines in the brains of TBI mice.

Conclusion

KLF11 acts as a novel protective factor in TBI. KLF11 genetic deficiency in mice aggravated the neuroinflammatory responses, grey and white matter injury, and impaired long-term sensorimotor and cognitive recovery. Elucidating the functional importance of KLF11 in TBI may lead us to discover novel pharmacological targets for the development of effective therapies against brain trauma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02638-0.

Specific signature biomarkers highlight the potential mechanisms of circulating neutrophils in aneurysmal subarachnoid hemorrhage

Background: Aneurysmal subarachnoid hemorrhage (aSAH) is a devastating hemorrhagic stroke with high disability and mortality. Neuroinflammation and the immunological response after aSAH are complex pathophysiological processes that have not yet been fully elucidated. Therefore, attention should be paid to exploring the inflammation-related genes involved in the systemic response to the rupture of intracranial aneurysms.

Methods: The datasets of gene transcriptomes were downloaded from the Gene Expression Omnibus database. We constructed a gene co-expression network to identify cluster genes associated with aSAH and screened out differentially expressed genes (DEGs). The common gene was subsequently applied to identify hub genes by protein-protein interaction analysis and screen signature genes by machine learning algorithms. CMap analysis was implemented to identify potential small-molecule compounds. Meanwhile, Cibersort and ssGSEA were used to evaluate the immune cell composition, and GSEA reveals signal biological pathways.

Results: We identified 602 DEGs from the GSE36791. The neutrophil-related module associated with aSAH was screened by weighted gene co-expression network analysis (WGCNA) and functional enrichment analysis. Several small molecular compounds were predicted based on neutrophil-related genes. MAPK14, ITGAM, TLR4, and FCGR1A have been identified as crucial genes involved in the peripheral immune activation related to neutrophils. Six significant genes (CST7, HSP90AB1, PADI4, PLBD1, RAB32, and SLAMF6) were identified as signature biomarkers by performing the LASSO analysis and SVM algorithms. The constructed machine learning model appears to be robust by receiver-operating characteristic curve analysis. The immune feature analysis demonstrated that neutrophils were upregulated post-aSAH and PADI4 was positively correlated with neutrophils. The NETs pathway was significantly upregulated in aSAH.

Conclusion: We identified core regulatory genes influencing the transcription profiles of circulating neutrophils after the rupture of intracranial aneurysms using bioinformatics analysis and machine learning algorithms. This study provides new insight into the mechanism of peripheral immune response and inflammation after aSAH.

Fetuin-A alleviates neuroinflammation against traumatic brain injury-induced microglial necroptosis by regulating Nrf-2/HO-1 pathway

BACKGROUND

The microglia-mediated inflammatory response is a vital mechanism of secondary damage following traumatic brain injury (TBI), but the underlying mechanism of microglial activation is unclear.

METHODS

Controlled cortical impact (CCI) was induced in adult male C57BL/6J mice, and glutamate was used to construct a classical in vitro injury model in the primary microglia. Microglial activation was determined by western blot and immunostaining. The inflammatory factors were measured by enzyme-linked immunosorbent assay. The oxidative stress marker and mitochondrial reactive oxygen species (ROS) were measured by immunoblotting and MitoSox Red staining. Transmission electron microscopy was used to observe the typical morphology of necroptotic cells.

RESULTS

Our quantitative proteomics identified 2499 proteins; 157 were significantly differentially expressed in brain tissue between the 6 h after CCI (CCI6h) group and sham group, and 109 were significantly differentially expressed between the CCI24h and sham groups. Moreover, compared with the sham group, the terms "acute-phase response", "inflammation", and "protein binding" were significantly enriched in CCI groups. Fetuin-A, a liver-secreted acute-phase glycoprotein, was involved in these biological processes. Using an experimental TBI model, we found that the Fetuin-A level peaked at 6 h and then decreased gradually. Importantly, we showed that administration of Fetuin-A reduced the cortical lesion volume and edema area and inhibited the inflammatory response, which was associated with suppressing microglial necroptosis, thus decreasing microglial activation. Furthermore, administration of Fetuin-A attenuated mitochondrial oxidative stress in glutamate-treated microglial cells, which is a critical mechanism of necroptosis suppression. In addition, we demonstrated that Fetuin-A treatment promoted translocation of nuclear factor erythroid 2-related factor 2 (Nrf-2) from the cytoplasm to the nucleus in vivo; however, the Nrf-2 inhibitor ML385 and si-heme oxygenase-1 (si-HO-1) disrupted the regulation of oxidative stress by Fetuin-A and induced increased ROS levels and necroptosis in glutamate-treated microglial cells. Fetuin-A also protected neurons from adverse factors in vivo and in vitro.

CONCLUSIONS

Our results demonstrated that Fetuin-A activated Nrf-2/HO-1, suppressed oxidative stress and necroptosis levels, and thereby attenuates the abnormal inflammatory response following TBI. The findings suggest a potential therapeutic strategy for TBI treatment.

Differential, Stage Dependent Detection of Peptidylarginine Deiminases and Protein Deimination in Lewy Body Diseases-Findings from a Pilot Study

Over 10 million people worldwide live with Parkinson's disease (PD) and 4% of affected people are diagnosed before the age of 50. Research on early PD-related pathways is therefore of considerable importance. Peptidylarginine deiminases (PADs) are a family of calcium-activated enzymes that, through post-translational deimination of arginine to citrulline, contribute to changes in protein function, including in pathological processes. Recent studies have highlighted roles for PADs in a range of neurological disorders including PD, but overall, investigations on PADs in Lewy body disease (LBD), including PD, are still scarce. Hence, the current pilot study aimed at performing an immunohistochemistry screen of post-mortem human brain sections from Braak stages 4-6 from PD patients, as well as patients with incidental LBD (ILBD). We assessed differences in PAD isozyme detection (assessing all five PADs), in total protein deimination/citrullination and histone H3 deimination-which is an indicator of epigenetic changes and extracellular trap formation (ETosis), which can elicit immune responses and has involvement in pathogenic conditions. The findings of our pilot study indicate that PADs and deimination are increased in cingulate cortex and hippocampus, particularly in earlier stages of the disease. PAD2 and PAD3 were the most strongly upregulated PAD isozymes, with some elevation also observed for PAD1, while PAD4 and PAD6 increase was less marked in PD brains. Total protein deimination and histone H3 deimination were furthermore increased in PD brains, with a considerable increase at earlier Braak stages, compared with controls. Our findings point to a significant contribution of PADs, which may further aid early disease biomarker discovery, in PD and other LBDs.

Neutrophil-derived interleukin-17A participates in neuroinflammation induced by traumatic brain injury

After brain injury, infiltration and abnormal activation of neutrophils damages brain tissue and worsens inflammation, but the mediators that connect activated neutrophils with neuroinflammation have not yet been fully clarified. To identify regulators of neutrophil-mediated neuroinflammation after traumatic brain injury, a mouse model of traumatic brain injury was established by controlled cortical impact. At 7 days post-injury (sub-acute phase), genome-wide transcriptomic data showed that interleukin 17A-associated signaling pathways were markedly upregulated, suggesting that interleukin 17A may be involved in neuroinflammation. Double immunofluorescence staining showed that interleukin 17A was largely secreted by neutrophils rather than by glial cells and neurons. Furthermore, nuclear factor-kappaB and Stat3, both of which are important effectors in interleukin 17A-mediated proinflammatory responses, were significantly activated. Collectively, our findings suggest that neutrophil-derived interleukin 17A participates in neutrophil-mediated neuroinflammation during the subacute phase of traumatic brain injury. Therefore, interleukin 17A may be a promising therapeutic target for traumatic brain injury.

Neutrophils delay repair process in Wallerian degeneration by releasing NETs outside the parenchyma

Neutrophils accumulate at the epineurium in Wallerian degeneration (WD) and inhibit macrophage infiltration from the epineurium into the parenchyma by releasing neutrophil extracellular traps, resulting in the delay of repair processes in WD.

Although inflammation is indispensable for the repair process in Wallerian degeneration (WD), the role of neutrophils in the WD repair process remains unclear. After peripheral nerve injury, neutrophils accumulate at the epineurium but not the parenchyma in the WD region because of the blood–nerve barrier. An increase or decrease in the number of neutrophils delayed or promoted macrophage infiltration from the epineurium into the parenchyma and the repair process in WD. Abundant neutrophil extracellular traps (NETs) were formed around neutrophils, and its inhibition dramatically increased macrophage infiltration into the parenchyma. Furthermore, inhibition of either MIF or its receptor, CXCR4, in neutrophils decreased NET formation, resulting in enhanced macrophage infiltration into the parenchyma. Moreover, inhibiting MIF for just 2 h after peripheral nerve injury promoted the repair process. These findings indicate that neutrophils delay the repair process in WD from outside the parenchyma by inhibiting macrophage infiltration via NET formation and that neutrophils, NETs, MIF, and CXCR4 are therapeutic targets for peripheral nerve regeneration.

Histones of Neutrophil Extracellular Traps Induce CD11b Expression in Brain Pericytes Via Dectin-1 after Traumatic Brain Injury

The brain pericyte is a unique and indispensable part of the blood-brain barrier (BBB), and contributes to several pathological processes in traumatic brain injury (TBI). However, the cellular and molecular mechanisms by which pericytes are regulated in the damaged brain are largely unknown. Here, we show that the formation of neutrophil extracellular traps (NETs) induces the appearance of CD11b+ pericytes after TBI. These CD11b+ pericyte subsets are characterized by increased permeability and pro-inflammatory profiles compared to CD11b- pericytes. Moreover, histones from NETs by Dectin-1 facilitate CD11b induction in brain pericytes in PKC-c-Jun dependent manner, resulting in neuroinflammation and BBB dysfunction after TBI. These data indicate that neutrophil-NET-pericyte and histone-Dectin-1-CD11b are possible mechanisms for the activation and dysfunction of pericytes. Targeting NETs formation and Dectin-1 are promising means of treating TBI.

Neutrophil modulation of behavior and cognition in health and disease: The unexplored role of an innate immune cell

Behavior and cognition are multifaceted processes influenced by genetics, synaptic plasticity, and neuronal connectivity. Recent reports have demonstrated that peripheral inflammation and peripheral immune cells play important roles in the preservation and deterioration of behavior/cognition under various conditions. Indeed, several studies show that the activity of peripheral immune cells can be critical for normal cognitive function. Neutrophils are the most abundant immune cells in the mammalian system. Their activation is critical to the initiation of the inflammatory process and critical for wound healing. Neutrophils are the first cells to be activated and recruited to the central nervous system in both injury and disease. However, our understanding of the role these cells play in behavior and cognition is limited. The present review will summarize what is currently known about the effect the activation of these cells has on various behaviors and cognitive processes.

Downregulation of Sepina3n Aggravated Blood-Brain Barrier Disruption after Traumatic Brain Injury by Activating Neutrophil Elastase in Mice

Traumatic brain injury (TBI) is the leading cause of death in young adults and the main cause of mortality and disability across all ages worldwide. We previously analyzed the expression profile data of TBI models obtained from the Gene Expression Omnibus (GEO) database and found that the seripina3n mRNA was markedly upregulated in the acute phase of TBI in four mRNA expression profile data sets, indicating that serpina3n may be involved in the pathophysiological process of TBI. Therefore, we further investigated the biological role and molecular mechanism of serpina3n in traumatic brain injury in this study. As a result, the endogenous level of sepina3n was markedly elevated in the cortex around the contusion sit in mice at day 1 and day 3 after TBI. Inhibiting the expression of serpina3n caused aggravation of neutrophil elastase (NE) expression, BBB disruption, and neurological deficit. With the inactivation of NE, even if serpina3n was silenced, the disruption of the BBB was not further aggravated. In vitro experiments further proved that recombinant serpina3n dose-dependently inhibited the activity of recombinant NE. Based on the above, this study demonstrated that the endogenous level of sepina3n was significantly elevated in the cortex around the contusion sit after TBI in mice, which reduced the secondary blood-brain barrier disruption by inhibiting the activity of neutrophil elastase.