Neuroimmunology of Traumatic Brain Injury: Time for a Paradigm Shift

Microglial polarization pathways and therapeutic drugs targeting activated microglia in traumatic brain injury

Traumatic brain injury can be categorized into primary and secondary injuries. Secondary injuries are the main cause of disability following traumatic brain injury, which involves a complex multicellular cascade. Microglia play an important role in secondary injury and can be activated in response to traumatic brain injury. In this article, we review the origin and classification of microglia as well as the dynamic changes of microglia in traumatic brain injury. We also clarify the microglial polarization pathways and the therapeutic drugs targeting activated microglia. We found that regulating the signaling pathways involved in pro-inflammatory and anti-inflammatory microglia, such as the Toll-like receptor 4 /nuclear factor-kappa B, mitogen-activated protein kinase, Janus kinase/signal transducer and activator of transcription, phosphoinositide 3-kinase/protein kinase B, Notch, and high mobility group box 1 pathways, can alleviate the inflammatory response triggered by microglia in traumatic brain injury, thereby exerting neuroprotective effects. We also reviewed the strategies developed on the basis of these pathways, such as drug and cell replacement therapies. Drugs that modulate inflammatory factors, such as rosuvastatin, have been shown to promote the polarization of anti-inflammatory microglia and reduce the inflammatory response caused by traumatic brain injury. Mesenchymal stem cells possess anti-inflammatory properties, and clinical studies have confirmed their significant efficacy and safety in patients with traumatic brain injury. Additionally, advancements in mesenchymal stem cell-delivery methods-such as combinations of novel biomaterials, genetic engineering, and mesenchymal stem cell exosome therapy-have greatly enhanced the efficiency and therapeutic effects of mesenchymal stem cells in animal models. However, numerous challenges in the application of drug and mesenchymal stem cell treatment strategies remain to be addressed. In the future, new technologies, such as single-cell RNA sequencing and transcriptome analysis, can facilitate further experimental studies. Moreover, research involving non-human primates can help translate these treatment strategies to clinical practice.

Counteracting immunodepression by extracellular matrix hydrogel to promote brain tissue remodeling and neurological function recovery after traumatic brain injury

Traumatic brain injury (TBI), an intractable disorder of the central nervous system (CNS), is a leading cause of long-term disability and mortality in humans worldwide. However, there is still no effective therapy for TBI, and an important reason for this is TBI-induced immunodepression, which renders TBI patients with low resistance to infections and aggravated brain damage. In this study, a multifunctional extracellular matrix hydrogel was constructed for the treatment of TBI in terms of both counteracting the immunodepression and enhancing neurogenesis. The stromal cell-derived factor-1α (SDF-1α)-loaded hyaluronic acid (HA)/decellularized brain extracellular matrix (BM) hydrogel (SDF@HA/BM) not only mimicked the composition and the biological cues of brain extracellular matrix, but also exhibited the injectability, self-healing, and mechanical properties close to those of brain tissue. The SDF@HA/BM hydrogel protected activated immune cells from dysfunction during the acute phase of TBI for normal levels of inflammatory cytokines, thereby creating a favorable immune microenvironment for subsequent neurogenesis. The SDF-1α and the BM synergistically promoted neurogenesis after TBI by recruiting endogenous neural stem/progenitor cells and inducing their differentiation into neurons. In vivo results demonstrated that the SDF@HA/BM hydrogel exhibited desirable therapeutic effects in severe TBI mice through facilitating brain tissue remodeling and neurological function recovery, including limb balance, autonomous locomotion, and spatial learning and memory abilities, and relieving depression and anxiety. Our work provides a novel strategy for TBI treatment in terms of restoring immune homeostasis and enhancing neurogenesis using advanced biomaterials.

Microglial NOX2 as a therapeutic target in traumatic brain injury: Mechanisms, consequences, and potential for neuroprotection

Traumatic brain injury (TBI) is a leading cause of long-term disability worldwide, with secondary injury mechanisms, including neuroinflammation and oxidative stress, driving much of its chronic pathology. While NADPH oxidase 2 (NOX2)-mediated reactive oxygen species (ROS) production is a recognized factor in TBI, the specific role of microglial NOX2 in perpetuating oxidative and inflammatory damage remains underexplored. Addressing this gap is critical, as current therapeutic approaches primarily target acute symptoms and fail to interrupt the persistent neuroinflammation that contributes to progressive neurodegeneration. Besides NOX, other ROS-generating enzymes, such as CYP1B1, COX2, and XO, also play crucial roles in triggering oxidative stress and neuroinflammatory conditions in TBI. However, this review highlights the pathophysiological role of microglial NOX2 in TBI, focusing on its activation following injury and its impact on ROS generation, neuroinflammatory signaling, and neuronal loss. These insights reveal NOX2 as a critical driver of secondary injury, linked to worsened outcomes, particularly in aged individuals where NOX2 activation is more pronounced. In addition, this review evaluates emerging therapeutic approaches targeting NOX2, such as GSK2795039 and other selective NOX2 inhibitors, which show potential in reducing ROS levels, limiting neuroinflammation, and preserving neurological functions. By highlighting the specific role of NOX2 in microglial ROS production and secondary neurodegeneration, this study advocates for NOX2 inhibition as a promising strategy to improve TBI outcomes by addressing the unmet need for therapies targeting long-term inflammation and neuroprotection. Our review highlights the potential of NOX2-targeted interventions to disrupt the cycle of oxidative stress and inflammation, ultimately offering a pathway to mitigate the chronic impact of TBI.

3-Deoxysappanchalcone attenuates LPS-induced neuroinflammation in microglia cell culture and ameliorates cognitive impairment in traumatic brain injury

BACKGROUND

As one of the major public health security problems, traumatic brain injury (TBI) is characterized by cerebral dysfunction. The following neuroinflammation is considered as the main secondary injury factor. Targeting the expression of inflammatory cytokines could be effective in alleviating TBI-induced neuroinflammation. The anti-inflammatory role of natural products is increasingly receiving attention. 3-Deoxysappanchalcone (3-DSC) is a bioactive compound from Caesalpinia sappan L.

METHODS

The present study was designed to investigate the impact of 3-DSC on neuroinflammation in primary microglia and TBI models. To assess cytotoxicity, cell viability tests were conducted with varying concentrations of 3-DSC ranging from 5 to 20 μM. Quantitative PCR (qPCR) and Enzyme-Linked Immunosorbent Assay (ELISA) were utilized to measure the production of inflammatory cytokines in LPS-activated primary microglia treated with or without 3-DSC (at 10 μM). Immune blotting arrays were used to examine the activation of canonical inflammation signaling pathways. To further elucidate the anti-inflammation effect of 3-DSC, RNA-seq was carried out between LPS and LPS + 3-DSC group. In vitro co-culture experiments were carried out to evaluate the protective effect of 3-DSC on neurons against inflammation-mediated apoptosis. Additionally, in vivo experiments were performed to observe the impact of 3-DSC on TBI-induced microglia activation and spatial memory impairment. 3-DSC (160 μg/kg, 320 μg/kg) were administered via the tail vein at day 1 after TBI (n = 6). Behavioral tests were conducted 7 days after traumatic brain injury (TBI) to detect the spatial memory ability of rats.

RESULTS

The cell viability results revealed that within the concentration range of 5-20 μM, 3-DSC did not cause significant cytotoxicity. In the qPCR and ELISA assays, it was found that 3-DSC at 10 μM led to a reduction in the production of inflammatory cytokines. The immune blotting arrays demonstrated that 3-DSC inhibited the activation of NF-kB and MAPK signaling pathways. The results of RNA sequencing revealed the altered signaling pathways and key hub genes. The in vitro co-culture outcomes indicated that 3-DSC could safeguard neurons from apoptosis caused by neuroinflammation. Finally, the in vivo experiments showed that 3-DSC was effective in alleviating TBI-induced microglia activation and spatial memory impairment.

DISCUSSION

Collectively, these findings suggest that 3-DSC holds promise as a potential compound for the development of therapeutic and preventive agents aimed at treating neuroinflammation-related disorders. It offers a new avenue for further research and potential clinical applications in the context of TBI and neuroinflammation related disorders.

Impact of galanin receptors 2 and 3 double-knockout on neuroinflammation and functional recovery following traumatic brain injury

Traumatic brain injury (TBI) is one of the world's leading causes of death and disability in young individuals and the mechanism underlying TBI-associated neuroinflammation is poorly understood. The regulatory neuropeptide galanin (GAL) and its three receptors (GAL1-3R) are assumed to modulate the neuroinflammatory response following TBI, especially by signalling via GAL2R and GAL3R. Therefore, the role of GALRs in acute neuroinflammation and functional recovery following moderate Controlled Cortical Impact TBI was studied using GAL2/3R-double-KO (GAL2/3R-KO) mice. Brains and cerebrospinal fluid (CSF) were collected at day 1 and 30 days post TBI. Functional recovery post TBI was assessed by the modified Neurological Severity Score (mNSS), Elevated Plus Maze (EPM) and Morris Water Maze (MWM) test. Post TBI (day 1 to 28 post injury), neurological dysfunction was more severe in GAL2/3R-KO mice than in WT mice. At 1 day post TBI, inflammatory markers and several nerve growth factors significantly increased in the ipsilateral hemisphere, compared to the contralateral hemisphere in both GAL2/3R-KO and WT mice. At 4 days post surgery, TBI mice entered significantly more frequent the open-arms in the EPM compared to Sham-operated mice, suggestive of increased exploratory behaviour in TBI mice. At 30 days post TBI, immunostaining of brain sections revealed significant differences in vascularisation and glial scarring in the cortex when comparing TBI and Sham-operated mice, but genotypes were similar. In summary, the results indicate that GAL2R and/or GAL3R have a neuroprotective role following moderate TBI, as the severity was significantly lower in their presence than in their absence.

Non-invasive therapeutics for neurotrauma: a mechanistic overview

Traumatic brain injury is a leading cause of death and a major risk factor for the development of both memory and motor disorders. To date, there are no proven interventions to improve patient outcome after neurotrauma. A promising avenue of treatment has emerged in the use of non-invasive therapies for recovery after brain injury. A number of non-invasive brain stimulation techniques have been developed, such as transcranial direct current stimulation, transcranial magnetic stimulation and vagus nerve stimulation, as well as low intensity ultrasound stimulation and photobiomodulation therapy. However, standardized treatment regimens have not been developed. There is a clear need to better understand the underlying mechanisms of non-invasive therapeutics on brain injury pathology so as to more effectively guide treatment strategy. Here we review the current literature of non-invasive therapies in preclinical neurotrauma and offer insight into the potential mechanism of action and novel targets for the treatment of traumatic brain injury.

Mitochondria: the hidden engines of traumatic brain injury-driven neurodegeneration

Mitochondria play a critical role in brain energy metabolism, cellular signaling, and homeostasis, making their dysfunction a key driver of secondary injury progression in traumatic brain injury (TBI). This review explores the relationship between mitochondrial bioenergetics, metabolism, oxidative stress, and neuroinflammation in the post-TBI brain. Mitochondrial dysfunction disrupts adenosine triphosphate (ATP) production, exacerbates calcium dysregulation, and generates reactive oxygen species, triggering a cascade of neuronal damage and neurodegenerative processes. Moreover, damaged mitochondria release damage-associated molecular patterns (DAMPs) such as mitochondrial DNA (mtDNA), Cytochrome C, and ATP, triggering inflammatory pathways that amplify tissue injury. We discuss the metabolic shifts that occur post-TBI, including the transition from oxidative phosphorylation to glycolysis and the consequences of metabolic inflexibility. Potential therapeutic interventions targeting mitochondrial dynamics, bioenergetic support, and inflammation modulation are explored, highlighting emerging strategies such as mitochondrial-targeted antioxidants, metabolic substrate supplementation, and pharmacological regulators of mitochondrial permeability transition pores. Understanding these mechanisms is crucial for developing novel therapeutic approaches to mitigate neurodegeneration and enhance recovery following brain trauma.

Regulated cell death and DAMPs as biomarkers and therapeutic targets in normothermic perfusion of transplant organs. Part 1: their emergence from injuries to the donor organ

This Part 1 of a bipartite review commences with a succinct exposition of innate alloimmunity in light of the danger/injury hypothesis in Immunology. The model posits that an alloimmune response, along with the presentation of alloantigens, is driven by DAMPs released from various forms of regulated cell death (RCD) induced by any severe injury to the donor or the donor organ, respectively. To provide a strong foundation for this review, which examines RCD and DAMPs as biomarkers and therapeutic targets in normothermic regional perfusion (NRP) and normothermic machine perfusion (NMP) to improve outcomes in organ transplantation, key insights are presented on the nature, classification, and functions of DAMPs, as well as the signaling mechanisms of RCD pathways, including ferroptosis, necroptosis, pyroptosis, and NETosis. Subsequently, a comprehensive discussion is provided on major periods of injuries to the donor or donor organs that are associated with the induction of RCD and DAMPs and precede the onset of the innate alloimmune response in recipients. These periods of injury to donor organs include conditions associated with donation after brain death (DBD) and donation after circulatory death (DCD). Particular emphasis in this discussion is placed on the different origins of RCD-associated DAMPs in DBD and DCD and the different routes they use within the circulatory system to reach potential allografts. The review ends by addressing another particularly critical period of injury to donor organs: their postischemic reperfusion following implantation into the recipient-a decisive factor in determining transplantation outcome. Here, the discussion focuses on mechanisms of ischemia-induced oxidative injury that causes RCD and generates DAMPs, which initiate a robust innate alloimmune response.

The interplay between thyrotropic axis, neurological complications, and rehabilitation outcomes in patients with traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of mortality and long-term disability, with its pathophysiology encompassing both primary mechanical damage and secondary neuroinflammatory, metabolic, and biochemical alterations. These complex mechanisms contribute to the observed heterogeneous clinical outcomes, including neuroendocrine dysfunctions, post-traumatic seizures, and disorders of consciousness (DoC). Thyroid hormones (THs) play essential roles in synaptic plasticity, neurogenesis and neuronal homeostasis, and the hypothalamic-pituitary-thyroid (HPT) axis has recently emerged as a potential acute and chronic modulator of neurological and functional recovery following TBI, thereby hinting at the potential involvement of THs in post-TBI outcomes. While evidence suggests that alterations in the HPT axis may influence susceptibility to seizures, progression of DoC, and rehabilitation outcomes, an increased blood-brain barrier permeability in concert with dysregulated deiodinase activity and expanding oxidative stress have all been proposed as mechanisms linking THs to post-TBI neurological complications. This review aims to summarize current evidence on the potential role of the thyrotropic axis in neurological and rehabilitation outcomes following TBI.

4,4'-Dimethoxychalcone Mitigates Neuroinflammation Following Traumatic Brain Injury Through Modulation of the TREM2/PI3K/AKT/NF-κB Signaling Pathway

Research on 4,4'-dimethoxychalcone (DMC) in the context of traumatic brain injury (TBI) is extremely limited, and no effective clinical treatments are available to improve outcomes for individuals with TBI. Our study aims to investigate the underlying mechanisms by which DMC may alleviate neuroinflammation and neuronal damage following TBI. This study seeks to provide a theoretical foundation for the development of future pharmacological therapies for TBI. A moderate TBI model was established using the fluid percussion injury (FPI) method. The recovery of neuromotor function following TBI was evaluated using the modified neurological severity score (mNSS), the Morris water maze test, and analysis of cerebral edema. Gene and protein expression levels were quantified using cell viability assays, quantitative real-time polymerase chain reaction (qRT-PCR), Western blotting, enzyme-linked immunosorbent assay (ELISA), immunohistochemistry, and immunofluorescence. Network pharmacology was employed to predict potential targets of DMC, and gene ontology (GO) analysis along with KEGG pathway enrichment was conducted to predict signaling pathways affected by DMC.DMC treatment significantly improved neuromotor deficits in mice after TBI. In both in vivo and in vitro experiments, DMC suppressed microglial activation and decreased the production and release of inflammatory factors. Additionally, DMC reduced neuronal lesions after TBI. DMC notably decreased the elevated expression of triggering receptor expressed on myeloid cells 2 (TREM2) following TBI. Network pharmacological analysis indicated that DMC's therapeutic effects may be mediated through the PI3K/AKT signaling cascade. These findings indicate that DMC has therapeutic potential for TBI, with significant anti-inflammatory and neuroprotective properties likely mediated by the TREM2/PI3K/AKT/NF-κB signaling cascade.

Danshen-Chuanxiong-Honghua ameliorates neurological function and inflammation in traumatic brain injury in rats via modulating Ghrelin/GHSR

ETHNOPHARMACOLOGICAL RELEVANCE

Guanxin II, proposed by Chen Keji (National master of traditional Chinese medicine), possesses neuroprotective effect. Interestingly, its simplified prescription Danshen-Chuanxiong-Honghua (DCH) can also clinically ameliorate cerebral impairment and improve spatial cognitive deficits, similar to the function of original formula.

AIM OF THE STUDY

We aimed to elucidate the rationality of DCH's natural existence, qualitatively identify DCH-derived phytochemicals, thereby to validate cerebral protective effect, and expose the potential mechanism of DCH and its main absorbed compound ferulic acid (FA).

MATERIALS AND METHODS

The natural rationality of DCH's existence for treating TBI was verified using data mining. The qualitative analysis of DCH extract-derived phytochemicals was conducted through liquid chromatography with mass spectrometry (LC-MS). Controlled cortical impact (CCI) was chosen to establish TBI model. Neurological behavior tests, blood-brain barrier (BBB) permeability test, brain water content measurement, and proinflammatory factors consisting of IL-6, IL-1β, and TNF-α of plasma, and HPA axis-related hormone levels of DA, NA, 5-HT, ghrelin, and BDNF in hippocampus were analyzed by enzyme-linked immunosorbent assay. Network pharmacology was employed to predict potential targets and pathways of DCH intervening TBI. Growth hormone secretagogue receptor (GHSR) antagonist [D-Lys3]-GHRP-6 (D-Lys3) was injected intraperitoneally in TBI rats after waking up. Molecular docking and pharmacological experiment with D-Lys3 were used to verify the pathway.

RESULTS

Twenty-six phytochemicals were identified based on LC-MS. FA, as the primary contributor of DCH, alleviated disruption of BBB and reduced brain edema, suppressed the secretion of proinflammatory factors, such as IL-6, IL-1β, TNF-α, as well as HPA axis-related hormones such as DA, NA, and 5-HT, and ghrelin, and BDNF by regulating the Ghrelin/GHSR pathway. These results were validated by GHSR receptor antagonist, as well as molecule docking.

CONCLUSIONS

Taken together, DCH, when prescribed for the treatment of TBI, has a certain degree of reasonableness. FA, as the main absorbed component, demonstrated a similar function to DCH in improving the blood-brain barrier, promoting neural recovery, and anti-inflammatory effects in TBI rats, primarily via modulating Ghrelin/GHSR.

Balancing Anti-Inflammation and Neurorepair: The Role of Mineralocorticoid Receptor in Regulating Microglial Phenotype Switching After Traumatic Brain Injury

BACKGROUND

As potent anti-inflammatory agents, glucocorticoids (GCs) have been widely used in the treatment of traumatic brain injury (TBI). However, their use remains controversial. Our previous study indicated that although dexamethasone (DEX) exerted anti-inflammatory effects and protected the blood-brain barrier (BBB) by activating the glucocorticoid receptor (GR) after TBI, it also impeded tissue repair processes due to excessive anti-inflammation. Conversely, fludrocortisone, acting as a specific mineralocorticoid receptor (MR) agonist, has shown potential in controlling neuroinflammation and promoting neurorepair, but the underlying mechanisms need further exploration.

OBJECTIVE

This study aimed to explore the impact of the MR agonist fludrocortisone on microglia polarization, angiogenesis, functional rehabilitation, and associated mechanisms after TBI.

METHODS

We established a mice controlled cortical impact model, and then immunofluorescence staining, western blot, rt-PCR, and MRI were performed to investigate microglia polarization, angiogenesis, and brain edema in the ipsilateral hemisphere after TBI and fludrocortisone treatment. Subsequently, functional tests including morris water maze, sucrose preference test, and forced swimming test were conducted to evaluate the effects of fludrocortisone treatment on neurofunction after TBI.

RESULTS

Our results revealed that fludrocortisone suppressed neuroinflammation, enhanced angiogenesis and neuronal survival, and promoted functional rehabilitation by inducing a shift in microglia phenotype from M1 to M2 via the JAK/STAT6/PPARγ pathway. Additionally, the PI3K/Akt/HIF-1α pathway was involved in VEGF expression and in the process of angiogenesis.

CONCLUSION

Fludrocortisone, the specific MR agonist, exerted anti-neuroinflammatory and neuroprotective effects by regulating phenotypic switching of microglia from M1 to M2 rather than suppressing all types of microglia. Our study provided a theoretical basis for the therapeutic strategy of GCs targeting neuroinflammation after TBI.

Inhibition of S100A8/A9 ameliorates neuroinflammation by blocking NET formation following traumatic brain injury

Traumatic brain injury (TBI) triggers a robust inflammatory response that is closely linked to worsened clinical outcomes. S100A8/A9, also known as calprotectin or myeloid-related protein-8/14 (MRP8/14), is an alarmin primarily secreted by activated neutrophils with potent pro-inflammatory property. In this study, we explored the roles of S100A8/A9 in modulating neuroinflammation and influencing TBI outcomes, delving into the underlying mechanisms. S100A8/A9-enriched neutrophils were present in the injured brain tissue of TBI patients, and elevated plasma levels of S100A8/A9 were correlated with poorer neurological function. Furthermore, using a TBI mouse model, we demonstrated that treatment with the selective S100A8/A9 inhibitor Paquinimod significantly mitigated neuroinflammation and neuronal death, thereby improving the prognosis of TBI mice. Mechanistically, we found that S100A8/A9, in conjunction with neutrophil activation and infiltration into the brain, enhances reactive oxygen species (ROS) production within neutrophils, accelerating PAD4-mediated neutrophil extracellular trap (NET) formation, which in turn exacerbates neuroinflammation. These findings suggest that S100A8/A9 amplifies neuroinflammatory responses by promoting NET formation in neutrophils. Inhibition of S100A8/A9 effectively attenuated NET-mediated neuroinflammation; however, when PAD4 was overexpressed in the brain using adenovirus, leading to an increased formation of NET in the brain, the anti-inflammatory effects of S100A8/A9 inhibition were markedly diminished. Further experiments with PAD4 knockout mice confirmed that the reduction of NETs could substantially alleviate S100A8/A9-driven neuroinflammation. Finally, we established that the suppression of NET formation by S100A8/A9 inhibition is primarily mediated through the AMPK/Nrf2/HO-1 signaling pathway. These findings underscore the critical pathological role of S100A8/A9 in TBI and emphasize the need for further exploration of S100A8/A9 inhibitor Paquinimod as a potential therapeutic strategy for TBI.

Astrocytes, reactive astrogliosis, and glial scar formation in traumatic brain injury

Traumatic brain injury is a global health crisis, causing significant death and disability worldwide. Neuroinflammation that follows traumatic brain injury has serious consequences for neuronal survival and cognitive impairments, with astrocytes involved in this response. Following traumatic brain injury, astrocytes rapidly become reactive, and astrogliosis propagates from the injury core to distant brain regions. Homeostatic astroglial proteins are downregulated near the traumatic brain injury core, while pro-inflammatory astroglial genes are overexpressed. This altered gene expression is considered a pathological remodeling of astrocytes that produces serious consequences for neuronal survival and cognitive recovery. In addition, glial scar formed by reactive astrocytes is initially necessary to limit immune cell infiltration, but in the long term impedes axonal reconnection and functional recovery. Current therapeutic strategies for traumatic brain injury are focused on preventing acute complications. Statins, cannabinoids, progesterone, beta-blockers, and cerebrolysin demonstrate neuroprotective benefits but most of them have not been studied in the context of astrocytes. In this review, we discuss the cell signaling pathways activated in reactive astrocytes following traumatic brain injury and we discuss some of the potential new strategies aimed to modulate astroglial responses in traumatic brain injury, especially using cell-targeted strategies with miRNAs or lncRNA, viral vectors, and repurposed drugs.

Developmental deletion of amyloid precursor protein precludes transcriptional and proteomic responses to brain injury

INTRODUCTION

Amyloid precursor protein (APP) undergoes striking changes following traumatic brain injury (TBI). Considering its role in the control of gene expression, we investigated whether APP regulates transcription and translation following TBI.

METHODS

We assessed brain morphology (n = 4-9 mice/group), transcriptome (n = 3 mice/group), proteome (n = 3 mice/group), and behavior (n = 17-27 mice/group) of wild-type (WT) and APP knock-out (KO) mice either untreated or 10-weeks following TBI.

RESULTS

After TBI, WT mice displayed transcriptional programs consistent with late stages of brain repair, hub genes were predicted to impact translation and brain proteome showed subtle changes. APP KO mice largely replicated this transcriptional repertoire, but showed no transcriptional nor translational response to TBI.

DISCUSSION

The similarities between WT mice following TBI and APP KO mice suggest that developmental APP deficiency induces a condition reminiscent of late stages of brain repair, hampering the control of gene expression in response to injury.

HIGHLIGHTS

10-weeks after TBI, brains exhibit transcriptional profiles consistent with late stage of brain repair. Developmental APP deficiency maintains brains perpetually in an immature state akin to late stages of brain repair. APP responds to TBI by changes in gene expression at a transcriptional and translational level. APP deficiency precludes molecular brain changes in response to TBI.

Extracellular particles: emerging insights into central nervous system diseases

Extracellular particles (EPs), including extracellular vesicles (EVs) and non-vesicular extracellular particles (NVEPs), are multimolecular biomaterials released by cells that play a crucial role in intercellular communication. Recently, new subtypes of EPs associated with central nervous system (CNS), such as exophers and supermeres have been identified. These EPs provide new perspectives for understanding the pathological progression of CNS disorders and confer potential diagnostic value for liquid biopsies in neurodegenerative diseases (NDs). Moreover, EPs have emerged as promising drug delivery vehicles and targeted platforms for CNS-specific therapies. In this review, we delineate the landscape of EP subtypes and their roles in the pathophysiology of CNS diseases. We also review the recent advances of EP-based diagnosis in NDs and highlight the importance of analytical platforms with single-particle resolution in the exploitation of potential biomarkers. Furthermore, we summarize the application of engineered EVs in the treatment of CNS diseases and outline the underexplored potential of NVEPs as novel therapeutic agents.

A post-injury immune challenge with lipopolysaccharide following adult traumatic brain injury alters neuroinflammation and the gut microbiome acutely, but has little effect on chronic outcomes

Patients with a traumatic brain injury (TBI) are susceptible to hospital-acquired infections, presenting a significant challenge to an already-compromised immune system. The consequences and mechanisms by which this dual insult worsens outcomes are poorly understood. This study aimed to explore how a systemic immune stimulus (lipopolysaccharide, LPS) influences outcomes following experimental TBI in young adult mice. Male and female C57Bl/6J mice underwent controlled cortical impact or sham surgery, followed by 1 mg/kg i.p. LPS or saline-vehicle at 4 days post-TBI, before behavioral assessment and tissue collection at 6 h, 24 h, 7 days or 6 months. LPS induced acute sickness behaviors including weight loss, transient hypoactivity, and increased anxiety-like behavior. Early systemic immune activation by LPS was confirmed by increased spleen weight and serum cytokines. In brain tissue, gene expression analysis revealed a time course of inflammatory immune activation in TBI or LPS-treated mice (e.g., IL-1β, IL-6, CCL2, TNFα), which was exacerbated in TBI + LPS mice. This group also presented with fecal microbiome dysbiosis at 24 h post-LPS, with reduced bacterial diversity and changes in the relative abundance of key bacterial genera associated with sub-acute neurobehavioral and immune changes. Chronically, TBI induced hyperactivity and cognitive deficits, brain atrophy, and increased seizure susceptibility, similarly in vehicle and LPS-treated groups. Together, findings suggest that an immune challenge with LPS early after TBI, akin to a hospital-acquired infection, alters the acute neuroinflammatory response to injury, but has no lasting effects. Future studies could consider more clinically-relevant models of infection to build upon these findings.

Timing of neurosurgical interventions for intracranial hypertension: the intensivists' and neurosurgeons' view

PURPOSE OF REVIEW

The aim of this study was to highlight clinical considerations regarding medical versus surgical management of elevated intracranial pressure (ICP), describe limitations of medical management, and summarize evidence regarding timing of neurosurgical interventions.

RECENT FINDINGS

The optimal ICP management strategy remains elusive, and substantial practice variations exist. Common risks of medical treatments include hypotension/shock, cardiac arrhythmias and heart failure, acute renal failure, volume overload, hypoxemia, and prolonged mechanical ventilation.In traumatic brain injury (TBI), recent randomized controlled trials (RCT) did not demonstrate outcome benefits for early, prophylactic decompressive craniectomy, but indicate a role for secondary decompressive craniectomy in patients with refractory elevated ICP. A recent meta-analysis suggested that when an extraventricular drain is required, insertion 24 h or less post-TBI may result in better outcomes.In large ischemic middle cerebral artery strokes, pooled analyses of three RCTs showed functional outcome benefits in patients less than 60 years who underwent prophylactic DC within less than 48 h. In intracranial hemorrhage, a recent RCT suggested outcome benefits for minimally invasive hematoma evacuation within less than 24 h.

SUMMARY

More data are needed to guide ICP targets, treatment modalities, predictors of herniation, and surgical triggers; clinical decisions should consider individual patient characteristics, and account for risks of medical and surgical treatments.

Itaconate restrains acute proinflammatory activation of microglia after traumatic brain injury in mice

Traumatic brain injury (TBI) rapidly triggers proinflammatory activation of microglia, contributing to secondary brain damage post-TBI. Although the governing role of energy metabolism in shaping the inflammatory phenotype and function of immune cells has been increasingly recognized, the specific alterations in microglial bioenergetics post-TBI remain poorly understood. Itaconate, a metabolite produced by the enzyme aconitate decarboxylase 1 [IRG1; encoded by immune responsive gene 1 (Irg1)], is a pivotal metabolic regulator in immune cells, particularly in macrophages. Because microglia are macrophages of the brain parenchyma, the IRG1/itaconate pathway likely modulates microglial inflammatory responses. In this study, we explored the role of the IRG1/itaconate pathway in regulating microglial bioenergetics and inflammatory activation post-TBI using a mouse controlled cortical impact (CCI) model. We isolated microglia before and 4 and 12 hours after TBI and observed a swift but transient increase in glycolysis coupled with a prolonged disruption of mitochondrial metabolism after injury. Despite an up-regulation of Irg1 expression, itaconate in microglia declined after TBI. Microglia-specific Irg1 gene knockout (Irg1-Mi-KO) exacerbated metabolic changes, intensified proinflammatory activation and neurodegeneration, and worsened certain long-term neurological deficits. Supplementation with 4-octyl itaconate (OI) reinstated the use and oxidative metabolism of glucose, glutamine, and fatty acid, thereby enhancing microglial bioenergetics post-TBI. OI supplementation also attenuated proinflammatory activation and neurodegeneration and improved long-term neurological outcomes. These results suggest that therapeutically targeting the itaconate pathway could improve microglial energy metabolism and neurological outcomes after TBI.

Zipper-interacting protein kinase mediates neuronal cell death and cognitive dysfunction in traumatic brain injury via regulating DEDD

Neuronal cell death is a causative process in traumatic brain injury (TBI)-induced structural and functional impairment of the central nervous system. However, the upstream trigger of TBI-induced neuronal loss and the underlying molecular pathways remain unclear. Zipper-interacting protein kinase (ZIPK) has been shown to be upregulated in Alzheimer's disease and ischemic stroke and to play a role in cellular apoptosis, while its pathological significance in TBI has not been reported. Herein, we discovered for the first time that ZIPK expression was markedly elevated in neurons after TBI and that ZIPK caused massive neuronal apoptosis in peri-contusional brain regions. Zipk haploinsufficiency antagonized neuronal cell death and reversed several typical neuropathological changes induced by TBI. Mechanistically, we found that ZIPK affected neuronal viability by modulating death effector domain-containing DNA binding protein (DEDD) and caspase-3 pathway. Specifically, ZIPK could bind to and phosphorylate DEDD at the S9 residue, thus enhancing the stability of DEDD, and leading to the activation of caspase-3-mediated apoptotic cascade in neurons. The rescue of neuronal loss by ZIPK downregulation effectively alleviated TBI-induced behavioral deficits by preserving motor and cognitive abilities in vivo, supporting the decisive role of ZIPK dysregulation in TBI-associated neuronal dysfunctions by modulating neuronal survival. Furthermore, pharmacological suppression of ZIPK activity by a specific inhibitor prior to TBI protected neurons from brain injury-induced cell death and neuronal degeneration in vitro and in vivo by preventing DEDD upregulation and caspase-3 activation. In conclusion, our data reveal the essential contribution of ZIPK to TBI-induced neuronal cell death through the DEDD/caspase-3 cascade, and suggest the potential of targeting ZIPK as an effective strategy for treating TBI-related neuropathologies.

Nasal anti-CD3 monoclonal antibody ameliorates traumatic brain injury, enhances microglial phagocytosis and reduces neuroinflammation via IL-10-dependent Treg-microglia crosstalk

Neuroinflammation plays a crucial role in traumatic brain injury (TBI), contributing to both damage and recovery, yet no effective therapy exists to mitigate central nervous system (CNS) injury and promote recovery after TBI. In the present study, we found that nasal administration of an anti-CD3 monoclonal antibody ameliorated CNS damage and behavioral deficits in a mouse model of contusional TBI. Nasal anti-CD3 induced a population of interleukin (IL)-10-producing regulatory T cells (Treg cells) that migrated to the brain and closely contacted microglia. Treg cells directly reduced chronic microglia inflammation and regulated their phagocytic function in an IL-10-dependent manner. Blocking the IL-10 receptor globally or specifically on microglia in vivo abrogated the beneficial effects of nasal anti-CD3. However, the adoptive transfer of IL-10-producing Treg cells to TBI-injured mice restored these beneficial effects by enhancing microglial phagocytic capacity and reducing microglia-induced neuroinflammation. These findings suggest that nasal anti-CD3 represents a promising new therapeutic approach for treating TBI and potentially other forms of acute brain injury.

CPCGI Alleviates Neural Damage by Modulating Microglial Pyroptosis After Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) is a major global cause of mortality and long-term disability, with limited therapeutic options. Microglial pyroptosis, a form of programmed cell death associated with inflammation, has been implicated in exacerbating neuroinflammation and secondary injury following TBI. Compound porcine cerebroside ganglioside injection (CPCGI) has shown anti-inflammatory and antioxidant properties, but its effects on pyroptosis remain unexplored. This study investigates the role of CPCGI in TBI and its underlying mechanisms.

METHODS

A controlled cortical impact (CCI) model was utilized to establish TBI in vivo, while lipopolysaccharide (LPS) was used in vitro to induce microglial activation that mimicked TBI conditions. The effects of CPCGI on microglial pyroptosis and inflammatory cytokines were analyzed through immunofluorescence, flow cytometry, western blotting, and quantitative real-time PCR (qRT-PCR). The involvement of the NLRP3 inflammasome in CPCGI's mechanism was examined using NLRP3 overexpression or the NLRP3 agonist BMS-986299. A microglia-neuron interaction model was created, and neuronal injury was assessed with the Cell Counting Kit-8 and Fluoro-Jade C (FJC).

RESULTS

Treatment with CPCGI resulted in significant improvement in the neurobehavioral outcomes, reduced lesion volume, and decreased neuronal loss following TBI. Notably, TBI induced microglial pyroptosis and the release of pro-inflammatory cytokines, while CPCGI inhibited microglial pyroptosis, thereby mitigating the inflammatory response and reducing neuronal damage. Mechanistically, overexpression of NLRP3 in microglial cells reversed the inhibitory effects of CPCGI on microglial pyroptosis, indicating that CPCGI's inhibition of microglial pyroptosis may be mediated by the NLRP3 inflammasome. Furthermore, NLRP3 overexpression or administration of the NLRP3 agonist BMS-986299 negated the neuroprotective effects of CPCGI in vivo and in vitro.

CONCLUSION

These findings suggest that CPCGI provides neuroprotection in TBI by targeting NLRP3 inflammasome-mediated microglial pyroptosis, thereby improving the neuroinflammatory microenvironment and promoting neurological recovery. This underscores its potential as a promising candidate for TBI treatment.

Chronic traumatic brain injury induces neurodegeneration, neuroinflammation, and cognitive deficits in a T cell-dependent manner

Traumatic brain injury (TBI) can lead to chronic neuroinflammation, and neurodegeneration associated with long-term cognitive deficits. Following TBI, the acute neuroinflammatory response involves microglial activation and the release of proinflammatory cytokines and chemokines which induce the recruitment of peripheral immune cells such as monocytes and ultimately T cells. Persistent innate and adaptive immune cell responses can lead to chronic neurodegeneration and functional deficits. Therefore, understanding the dynamic interaction between chronic immune responses and TBI-related pathogenesis and progression of the disease is crucial. We hypothesized that T cells have an essential role in TBI severity and recovery. We used generic T cell deletion mice (TCRβ-/-δ-/-) vs Wild-type mice that underwent controlled cortical impact assessing behavioral, histological, and immune system response outcomes at 3 months post-TBI. The absence of T cells reduced neurodegeneration and was associated with improved neurological outcomes 3 months post-injury. Furthermore, the absence of T cells enhanced an anti-inflammatory phenotype in peripheral myeloid cells in the injured brain. Collectively, these data indicate that T cells promote persistent neuropathology and functional impairments chronically after TBI.

NINJ1-mediated plasma membrane rupture of pyroptotic endothelial cells exacerbates blood-brain barrier destruction caused by neutrophil extracellular traps in traumatic brain injury

Brain endothelial cell (bEC) dysfunction is the main factor of blood-brain barrier (BBB) breakdown, which triggers a vicious cycle of aggravating traumatic brain injury (TBI) pathogenesis. Previous studies have revealed that neutrophil extracellular traps (NETs) released by neutrophils can lead to BBB disruption, but there is a lack of research on the underlying mechanisms after TBI. Here, excessive NETs were found in both contused brain tissue and circulation following TBI. We found that NETs could activate the TLR4/NF-κB pathway to induce bEC pyroptosis, which led to BBB disruption after TBI. During this process, ninjurin-1 (NINJ1) was activated in pyroptotic bECs, and it mediated the release of high mobility group box 1 protein (HMGB1) via plasma membrane rupture (PMR) to promote NET formation. NINJ1-mediated release of HMGB1 aggravated NET accumulation by forming a vicious circle following TBI. Knockdown of NINJ1 rescued NET formation, attenuated BBB leakage, and improved neurological outcomes after TBI. NINJ1 may represent a promising target for alleviating NET-induced BBB destruction and other related injuries after TBI.

Microglial Autophagic Dysregulation in Traumatic Brain Injury: Molecular Insights and Therapeutic Avenues

Traumatic brain injury (TBI) is a complex and multifaceted condition that can result in cognitive and behavioral impairments. One aspect of TBI that has received increasing attention in recent years is the role of microglia, the brain-resident immune cells, in the pathophysiology of the injury. Specifically, increasing evidence suggests that dysfunction in microglial autophagy, the process by which cells degrade and recycle their own damaged components, may contribute to the development and progression of TBI-related impairments. Here, we unravel the pathways by which microglia autophagic dysregulation predisposes the brain to secondary damage and neurological deficits following TBI. An overview of the role of autophagic dysregulation in perpetuation and worsening of the inflammatory response, neuroinflammation, and neuronal cell death in TBI follows. Further, we have evaluated several signaling pathways and processes that contribute to autophagy dysfunction-mediated inflammation, neurodegeneration, and poor outcome in TBI. Additionally, a discussion on the small molecule therapeutics employed to modulate these pathways and mechanisms to treat TBI have been presented. However, additional research is required to fully understand the processes behind these underlying pathways and uncover potential therapeutic targets for restoring microglial autophagic failure in TBI.

β2 integrin regulates neutrophil trans endothelial migration following traumatic brain injury

Neutrophils are the first responders among peripheral immune cells to infiltrate the central nervous system following a traumatic brain injury (TBI), triggering neuroinflammation that can exacerbate secondary tissue damage. The precise molecular controls that dictate the inflammatory behavior of neutrophils post-TBI, however, remain largely elusive. Our comprehensive analysis of the molecular landscape surrounding the trauma in TBI mice has revealed a significant alteration in the abundance of β2 integrin (ITGB2), predominantly expressed by neutrophils and closely associated with immune responses. Using the fluid percussion injury (FPI) mouse model, we investigated the therapeutic efficacy of Rovelizumab, an agent that blocks ITGB2. The treatment has demonstrated significant improvements in neurologic function in TBI mice, attenuating blood-brain barrier permeability, mitigating oxidative stress and inflammatory mediator release, and enhancing cerebral perfusion. Moreover, ITGB2 blockade has effectively limited the adherence, migration, and infiltration of neutrophils, and has impeded the formation of neutrophil extracellular traps (NETs) upon their activation. Finally, it was demonstrated that ITGB2 mediates these effects mainly through its interaction with intercellular adhesion molecule-1 (ICAM 1) of endotheliocyte. These findings collectively illuminate ITGB2 as a crucial molecular switch that governs the adverse effects of neutrophils post-TBI and could be targeted to improve clinical outcome in patients.

Mapping Inflammatory Markers in Cerebrospinal Fluid Following Aneurysmal Subarachnoid Hemorrhage: An Age- and Sex-Matched Analysis

Despite extensive research on aneurysm treatment and neurocritical care, aneurysmal subarachnoid hemorrhage (SAH) is still a life-threatening disease, often leaving survivors with lasting neurological and cognitive impairments. Early brain injury (EBI) and delayed cerebral ischemia (DCI) are the main contributors to brain damage, with neuroinflammation being a critical shared pathophysiological process. While numerous inflammatory markers and their temporal profiles in cerebrospinal fluid (CSF) have already been identified, comparisons with age- and sex-matched controls are limited. This study analyzed CSF from 17 SAH patients requiring an external ventricular drain (EVD) due to symptomatic hydrocephalus, sampled on days 4 and 10 post-ictus. An age- and sex-matched control group included 17 cerebrovascularly healthy patients requiring lumbar drains during aortic surgery. Chemokines and cytokines were quantified using immunoassays. Significantly elevated markers in SAH patients across both time points included MCP-1, CXCL-13, Eotaxin-1, CXCL-10, IL-8, and MIF. MIP-1α and MIP-1β showed significant differences at particular time points, indicating a distinct temporal profile for each parameter. These findings highlight neuroinflammation's key role in intracranial and systemic pathophysiology following SAH, emphasizing its complexity and individual variability. Knowing demographic factors impact the specific manifestations of pathophysiological processes, the comparison with an age- and sex-matched control group is meaningful.

Relationship between alcohol use and traumatic brain injury: evidence from Mendelian randomization

BACKGROUND

Observational studies suggest that alcohol consumption increases the risk of traumatic brain injury (TBI); however, the causality of this association remains unclear.

OBJECTIVES

This study aimed to identify which drinking pattern is the primary factor influencing TBI.

METHOD

Two-sample Mendelian randomization (MR) was used to assess whether drinking patterns (alcohol consumption, abuse, and intake frequency) are causally associated with TBI risk.

RESULTS

MR analysis revealed causal effects of alcohol intake frequency [odds ratio (OR) 0.806, 95% confidence interval (CI): 0.665-0.978, p = 0.028, beta: -0.215, se: 0.098], alcohol drinks per week (OR 1.772, 95% CI: 1.140-2.753, p = 0.011, beta: 0.572, se: 0.225), and alcohol abuse (OR 1.095, 95% CI: 1.006-1.192, p = 0.035, beta: 0.091, se: 0.043) on TBI. Additionally, no causal effect of alcohol consumption (OR 0.730, 95% CI: 0.264-2.025, p = 0.546, beta: -0.314, se: 0.520) or average monthly alcohol intake (OR 1.138, 95% CI: 0.805-1.609, p = 0.463, beta: 0.130, se: 0.177) on TBI was observed. Similarly, the effects of TBI on alcohol intake were statistically non-significant.

CONCLUSION

Drinking patterns, including alcohol intake frequency and abuse, influence TBI, whereas TBI rarely influences drinking patterns.

The Flavonoid Agathisflavone Attenuates Glia Activation After Mechanical Injury of Cortical Tissue and Negatively Regulates Both NRLP3 and IL-1β Expression

Traumatic brain injury (TBI) has a complex and multifactorial pathology and is a major cause of death and disability for humans. Immediately after TBI, astrocytes and microglia react with complex morphological and functional changes known as reactive gliosis to form a glial scar in the area immediately adjacent to the lesion, which is the major barrier to neuronal regeneration. The flavonoid agathisflavone (bis-apigenin), present in Poincianella pyramidalis leaves, has been shown to have neuroprotective, neurogenic, and anti-inflammatory effects, demonstrated in vitro models of glutamate-induced toxicity, neuroinflammation, and demyelination. In this study, we evaluated the effect and mechanisms of agathisflavone in neuronal integrity and in the modulation of gliosis in an ex vivo model of TBI. For this, microdissections from the encephalon of Wistar rats (P6-8) were prepared and subjected to mechanical injury (MI) and treated or not with daily agathisflavone (5 μM) for 3 days. Astrocyte reactivity was investigated by measuring mRNA and expression of GFAP protein in the lesioned area by immunofluorescence and Western blot. The proportion of microglia was determined by immunofluorescence for Iba-1; mRNA expression for inflammasome NRPL3 and interleukin-1 beta (IL-1β) was determined by RT-qPCR. It was observed that lesions in the cortical tissue induced astrocytes overexpressing GFAP in the typical glial scar formed and that agathisflavone modulated GFAP expression at the transcriptional and post-transcriptional levels, which was associated with a reduction of the glial scar. MI induced an increase in the proportion of microglia (Iba-1+), which was not observed in agathisflavone-treated cultures. Moreover, the flavonoid modulated negatively both the NRLP3 and IL-1β mRNA expression that was increased in the lesioned area of the tissue. These findings support the regulatory properties of agathisflavone in the control of the inflammatory response in glial cells, which can impact neuroprotection and should be considered for future studies for TB and other pathological conditions of the central nervous system.

Skull bone marrow and skull meninges channels: redefining the landscape of central nervous system immune surveillance

The understanding of neuroimmune function has evolved from concepts of immune privilege and protection to a new stage of immune interaction. The discovery of skull meninges channels (SMCs) has opened new avenues for understanding central nervous system (CNS) immunity. Here, we characterize skull bone marrow and SMCs by detailing the anatomical structures adjacent to the skull, the differences between skull and peripheral bone marrow, mainstream animal processing methods, and the role of skull bone marrow in monitoring various CNS diseases. Additionally, we highlight several unresolved issues based on current research findings, aiming to guide future research directions.

Evidence Suggesting Prolonged Neuroinflammation in a Subset of Children after Moderate/Severe TBI: A UCLA RAPBI Study

Traumatic brain injury (TBI) presents a public health concern as a leading cause of death and disability in children. Pediatric populations are particularly vulnerable to adverse outcomes following TBI due to periods of rapid growth, synaptic pruning, and myelination. Pediatric patients with moderate-severe TBI (msTBI) and healthy controls were evaluated from the post-acute (2-5 months) to chronic phase (13-19 months) of recovery using diffusion magnetic resonance imaging (dMRI) and interhemispheric transfer time (IHTT), which is an event-related potential measure the speed of information transfer across the corpus callosum. We previously identified two subgroups of patients based on IHTT, with one group showing a significantly slower IHTT (TBI-slow), poorer cognitive performance, and progressive structural damage. In contrast, the other group (TBI-normal) did not differ from controls on IHTT or cognitive performance and showed relative structural recovery over time. Here, we examined group differences in restricted diffusion imaging (RDI), which is a dMRI metric sensitive to inflammation. Comparing TBI-slow, TBI-normal, and controls on RDI cross-sectionally, dMRI connectometry analysis revealed higher RDI across the white matter in the TBI-slow group compared to both the control and TBI-normal groups. Longitudinal analyses indicated that while both TBI groups exhibited a decrease in RDI over time, suggesting resolution of neuroinflammation and recovery, the decreases in the TBI-slow group were smaller. The differences in RDI between TBI-slow and TBI-normal suggest that inflammation may play a key role in the prolonged recovery, including brain structure, cognitive performance, and symptom reports, of pediatric patients with msTBI.

Animal Models of Non-Respiratory, Post-Acute Sequelae of COVID-19

Post-acute sequelae of COVID-19 (PASC) are a diverse set of symptoms and syndromes driven by dysfunction of multiple organ systems that can persist for years and negatively impact the quality of life for millions of individuals. We currently lack specific therapeutics for patients with PASC, due in part to an incomplete understanding of its pathogenesis, especially for non-pulmonary sequelae. Here, we discuss three animal models that have been utilized to investigate PASC: non-human primates (NHPs), hamsters, and mice. We focus on neurological, gastrointestinal, and cardiovascular PASC and highlight advances in mechanistic insight that have been made using these animal models, as well as discussing the sequelae that warrant continued and intensive research.

Neuroprotective effects of hypidone hydrochloride (YL-0919) after traumatic brain injury in mice

BACKGROUND

Neurological dysfunction is a common complication of traumatic brain injury (TBI), and early treatments are critical for the long-term prognosis. This study aimed to investigate whether hypidone hydrochloride (YL-0919) improves neurological function impairment in mice with TBI.

METHODS

TBI was induced in adult male C57BL/6J mice using the controlled cortical impact (CCI) method. First, the modified neurological severity score (mNSS), rotarod test, and Morris water maze (MWM) test were conducted to assess the impact of YL-0919 on neurological function in mice with TBI. Next, immunofluorescence and laser speckle contrast imaging were utilized to measure the number and activation of microglia and cerebral blood flow (CBF) after TBI. Enzyme-linked immunosorbent assays (ELISAs) were employed to assess the inflammatory factors. Finally, Western blotting was performed to measure the expression of proteins. Golgi-Cox staining was utilized to investigate the structure of pyramidal neurons.

RESULTS

YL-0919 significantly alleviated neurological dysfunction in TBI+YL-0919 mice compared with TBI+Vehicle mice, increased the time spent on the rotarod (F = 1.297, P <0.05), and partially relieved cognitive dysfunction in TBI mice (for mNSS, F = 5.540, P <0.01; for MWM test, F = 30.78, P <0.05). Additionally, YL-0919 effectively inhibited the proliferation and activation of microglia (both P <0.01), promoted the recovery of CBF around the brain injury site and inhibited the expression of tumor necrosis factor-α (F = 9.142, P <0.05) and IL-1β (F = 4.662, P <0.05), and increased the concentration of IL-4 (F = 5.172, P <0.05). Furthermore, continuous gavage of YL-0919 (2.5 mg/kg) for seven days effectively increased the protein expression of brain-derived neurotrophic factor (BDNF), promoted the phosphorylation of mammalian target of rapamycin (mTOR), increased postsynaptic density protein 95 (PSD95) and synapsin1 levels, and increased the neuronal dendritic complexity and the dendritic spine density around the brain injury site (all P <0.05).

CONCLUSIONS

Our findings indicated that YL-0919 can ameliorate neurological dysfunction in mice after TBI through the suppression of inflammation and the stimulation of the BDNF-mTOR signaling pathway. These findings provide an insightful perspective on the potential pharmacological mechanism involved in the neuroprotective effect of YL-0919.

Blood leukocyte-based clusters in patients with traumatic brain injury

Background

Leukocytes play an important role in inflammatory response after a traumatic brain injury (TBI). We designed this study to identify TBI phenotypes by clustering blood levels of various leukocytes.

Methods

TBI patients from the Medical Information Mart for Intensive Care-III (MIMIC-III) database were included. Blood levels of neutrophils, lymphocytes, monocytes, basophils, and eosinophils were collected by analyzing the first blood sample within 24 h since admission. Overall, TBI patients were divided into clusters following the K-means clustering method using blood levels of five types of leukocytes. The correlation between identified clusters and mortality was tested by univariate and multivariate logistic regression analyses. The Kaplan-Meier method was used to verify the survival difference between identified TBI clusters.

Results

A total of 172 (cluster 1), 791 (cluster 2), and 636 (cluster 3) TBI patients were divided into three clusters with the following percentages, 10.8%, 49.5%, and 39.8%, respectively. Cluster 1 had the lowest Glasgow Coma Scale (GCS) and the highest Injury Severity Score (ISS) while cluster 2 had the highest GCS and the lowest ISS. The mortality rates of the three clusters were 25.6%, 13.3%, and 18.1%, respectively. The multivariate logistic regression indicated that cluster 1 had a higher mortality risk (OR = 2.211, p = 0.003) than cluster 2, while cluster 3 did not show a significantly higher mortality risk than cluster 2 (OR = 1.285, p = 0.163). Kapan-Meier analysis showed that cluster 1 had shorter survival than cluster 2 and cluster 3.

Conclusion

Three TBI phenotypes with different inflammatory statuses and mortality rates were identified based on blood levels of leukocytes. This classification is helpful for physicians to evaluate the prognosis of TBI patients.

A Roadmap of Peptide-Based Materials in Neural Regeneration

Injuries to the nervous system lead to irreversible damage and limited functional recovery. The peripheral nervous system (PNS) can self-regenerate to some extent for short nerve gaps. In contrast, the central nervous system (CNS) has an intrinsic limitation to self-repair owing to its convoluted neural microenvironment and inhibitory response. The primary phase of CNS injury, happening within 48 h, results from external impacts like mechanical stress. Afterward, the secondary phase of the injury occurs, originating from neuronal excitotoxicity, mitochondrial dysfunction, and neuroinflammation. No golden standard to treat injured neurons exists, and conventional medicine serves only as a protective approach to alleviating the symptoms of chronic injury. Synthetic peptides provide a promising approach for neural repair, either as soluble drugs or by using their intrinsic self-assembly propensity to serve as an extracellular matrix (ECM) mimic for cell adhesion and to incorporate bioactive epitopes. In this review, an overview of nerve injury models, common in vitro models, and peptide-based therapeutics such as ECM mimics is provided. Due to the complexity of treating neuronal injuries, a multidisciplinary collaboration between biologists, physicians, and material scientists is paramount. Together, scientists with complementary expertise will be required to formulate future therapeutic approaches for clinical use.

Unraveling the complexity of microglial responses in traumatic brain and spinal cord injury

Microglia, the resident innate immune cells of the central nervous system (CNS), play an important role in neuroimmune signaling, neuroprotection, and neuroinflammation. In the healthy CNS, microglia adopt a surveillant and antiinflammatory phenotype characterized by a ramified scanning morphology that maintains CNS homeostasis. In response to acquired insults, such as traumatic brain injury (TBI) or spinal cord injury (SCI), microglia undergo a dramatic morphologic and functional switch to that of a reactive state. This microglial switch is initially protective and supports the return of the injured tissue to a physiologic homeostatic state. However, there is now a significant body of evidence that both TBI and SCI can result in a chronic state of microglial activation, which contributes to neurodegeneration and impairments in long-term neurologic outcomes in humans and animal models. In this review, we discuss the complex role of microglia in the pathophysiology of TBI and SCI, and recent advancements in knowledge of microglial phenotypic states in the injured CNS. Furthermore, we highlight novel therapeutic strategies targeting chronic microglial responses in experimental models and discuss how they may ultimately be translated to the clinic for human brain and SCI.

Remote Ischemic Post-Conditioning (RIC) Mediates Anti-Inflammatory Signaling via Myeloid AMPKα1 in Murine Traumatic Optic Neuropathy (TON)

Traumatic optic neuropathy (TON) has been regarded a vision-threatening condition caused by either ocular or blunt/penetrating head trauma, which is characterized by direct or indirect TON. Injury happens during sports, vehicle accidents and mainly in military war and combat exposure. Earlier, we have demonstrated that remote ischemic post-conditioning (RIC) therapy is protective in TON, and here we report that AMPKα1 activation is crucial. AMPKα1 is the catalytic subunit of the heterotrimeric enzyme AMPK, the master regulator of cellular energetics and metabolism. The α1 isoform predominates in immune cells including macrophages (Mφs). Myeloid-specific AMPKα1 KO mice were generated by crossing AMPKα1Flox/Flox and LysMcre to carry out the study. We induced TON in mice by using a controlled impact system. Mice (mixed sex) were randomized in six experimental groups for Sham (mock); Sham (RIC); AMPKα1F/F (TON); AMPKα1F/F (TON+RIC); AMPKα1F/F LysMCre (TON); AMPKα1F/F LysMCre (TON+RIC). RIC therapy was given every day (5-7 days following TON). Data were generated by using Western blotting (pAMPKα1, ICAM1, Brn3 and GAP43), immunofluorescence (pAMPKα1, cd11b, TMEM119 and ICAM1), flow cytometry (CD11b, F4/80, CD68, CD206, IL-10 and LY6G), ELISA (TNF-α and IL-10) and transmission electron microscopy (TEM, for demyelination and axonal degeneration), and retinal oxygenation was measured by a Unisense sensor system. First, we observed retinal morphology with funduscopic images and found TON has vascular inflammation. H&E staining data suggested that TON increased retinal inflammation and RIC attenuates retinal ganglion cell death. Immunofluorescence and Western blot data showed increased microglial activation and decreased retinal ganglion cell (RGCs) marker Brn3 and axonal regeneration marker GAP43 expression in the TON [AMPKα1F/F] vs. Sham group, but TON+RIC [AMPKα1F/F] attenuated the expression level of these markers. Interestingly, higher microglia activation was observed in the myeloid AMPKα1F/F KO group following TON, and RIC therapy did not attenuate microglial expression. Flow cytometry, ELISA and retinal tissue oxygen data revealed that RIC therapy significantly reduced the pro-inflammatory signaling markers, increased anti-inflammatory macrophage polarization and improved oxygen level in the TON+RIC [AMPKα1F/F] group; however, RIC therapy did not reduce inflammatory signaling activation in the myeloid AMPKα1 KO mice. The transmission electron microscopy (TEM) data of the optic nerve showed increased demyelination and axonal degeneration in the TON [AMPKα1F/F] group, and RIC improved the myelination process in TON [AMPKα1F/F], but RIC had no significant effect in the AMPKα1 KO mice. The myeloid AMPKα1c deletion attenuated RIC induced anti-inflammatory macrophage polarization, and that suggests a molecular link between RIC and immune activation. Overall, these data suggest that RIC therapy provided protection against inflammation and neurodegeneration via myeloid AMPKα1 activation, but the deletion of myeloid AMPKα1 is not protective in TON. Further investigation of RIC and AMPKα1 signaling is warranted in TON.

Unveiling the predictive power of biomarkers in traumatic brain injury: A narrative review focused on clinical outcomes

Traumatic brain injury (TBI) has long-term consequences, including neurodegenerative disease risk. Current diagnostic tools are limited in detecting subtle brain damage. This review explores emerging biomarkers for TBI, including those related to neuronal injury, inflammation, EVs, and ncRNAs, evaluating their potential to predict clinical outcomes like mortality, recovery, and cognitive impairment. It addresses challenges and opportunities for implementing biomarkers in clinical practice, aiming to improve TBI diagnosis, prognosis, and treatment.

Temporal differential effects of post-injury alcohol consumption in a mouse model of blast-induced traumatic brain injury

Traumatic brain injury is a prevalent condition that affects millions worldwide with no clear understanding or effective therapeutic management available. Military soldiers have a high risk of exposure to blast-induced traumatic brain injury (bTBI). Furthermore, alcohol drinking is common in this population, and studies have shown that post-TBI alcohol exposure can result in memory loss. Hence, it is possible that alcohol could contribute to the overall pathological outcome of brain trauma. However, such a possibility has not been explored in detail. Here, we combined a mild bTBI (mbTBI) model with the drinking-in-the-dark (DID) paradigm to investigate the pathological synergy between mbTBI and alcohol consumption by examining brain oxidative stress levels and behavioral alterations in mice. The results revealed the anxiolytic and short-term memory improvement effects of post-trauma alcohol drinking examined at an early timepoint post mbTBI. However, extended alcohol drinking for up to three weeks post mbTBI impaired long-term memory and was accompanied by intensified oxidative stress in brain regions associated with memory and anxiety. These findings, as well as those from previous in vitro TBI/alcohol studies, suggest a pathological synergy of physical force and post-impact alcohol exposure. This knowledge could potentially aid in establishing guidelines for TBI victims to avoid further injury to their brains as well as to help maximize their recovery following TBI.

Vaccines for immunological defense against traumatic brain injury

Traumatic brain injury (TBI) and subsequent neurodegeneration is partially driven by chronic inflammation both locally and systemically. Yet, current clinical intervention strategies do not mitigate inflammation sequalae necessitating the development of innovative approaches to reduce inflammation and minimize deleterious effects of TBI. Herein, a subcutaneous formulation based on polymer of alpha-ketoglutarate (paKG) delivering glycolytic inhibitor PFK15 (PFKFB3 inhibitor, a rate limiting step in glycolysis), alpha-ketoglutarate (to fuel Krebs cycle) and peptide antigen from myelin proteolipid protein (PLP139-151) was utilized as the prophylactic immunosuppressive formulation in a mouse model of TBI. In vitro, the paKG(PFK15+PLP) vaccine formulation stimulated proliferation of immunosuppressive regulatory T cells and induced generation of T helper-2 cells. When given subcutaneously in the periphery to two weeks prior to mice sustaining a TBI, the active vaccine formulation increased frequency of immunosuppressive macrophages and dendritic cells in the periphery and the brain at day 7 post- TBI and by 28 days post-TBI enhanced PLP-specific immunosuppressive cells infiltrated the brain. While immunohistology measurements of neuroinflammation were not altered 28 days post-TBI, the vaccine formulation improved motor function and enhanced autophagy mediated genes in a spatial manner in the brain. Overall, these data suggest that the TBI vaccine formulation successfully induced an anti-inflammatory profile and decreased TBI-associated inflammation.

Teaser

In this study, a vaccine formulation was generated to develop central nervous specific immunosuppressive responses for TBI.

Immune Response in Traumatic Brain Injury

PURPOSE OF REVIEW

This review aims to comprehensively examine the immune response following traumatic brain injury (TBI) and how its disruption can impact healing and recovery.

RECENT FINDINGS

The immune response is now considered a key element in the pathophysiology of TBI, with consequences far beyond the acute phase after injury. A delicate equilibrium is crucial for a healthy recovery. When this equilibrium is disrupted, chronic inflammation and immune imbalance can lead to detrimental effects on survival and disability. Globally, traumatic brain injury (TBI) imposes a substantial burden in terms of both years of life lost and years lived with disability. Although its epidemiology exhibits dynamic trends over time and across regions, TBI disproportionally affects the younger populations, posing psychosocial and financial challenge for communities and families. Following the initial trauma, the primary injury is succeeded by an inflammatory response, primarily orchestrated by the innate immune system. The inflammasome plays a pivotal role during this stage, catalyzing both programmed cell death pathways and the up-regulation of inflammatory cytokines and transcription factors. These events trigger the activation and differentiation of microglia, thereby intensifying the inflammatory response to a systemic level and facilitating the migration of immune cells and edema. This inflammatory response, initially originated in the brain, is monitored by our autonomic nervous system. Through the vagus nerve and adrenergic and cholinergic receptors in various peripheral lymphoid organs and immune cells, bidirectional communication and regulation between the immune and nervous systems is established.

Activation of Microglia and Astroglia in Unilateral Focal Traumatic Brain Injury in Rats

The number of microglia cells and astrocytes in layer V of the cerebral cortex was estimated on day 7 after damage caused by a unilateral focal traumatic brain injury of the left hemisphere sensorimotor cortex. Quantitative assessment was performed by counting immunocytochemically stained microglia cells (Iba1 marker) and activated astrocytes (GFAP) at different distances from the lesion site. Activation of microglial and astroglial cells was observed not only in the marginal zone of the lesion of the left hemisphere, but also in the intact hemisphere. The data obtained indicate the dissemination of inflammation in focal traumatic brain injury.

Development of citric acid-based biomaterials for biomedical applications

The development of bioactive materials with controllable preparation is of great significance for biomedical engineering. Citric acid-based biomaterials are one of the few bioactive materials with many advantages such as simple synthesis, controllable structure, biocompatibility, biomimetic viscoelastic mechanical behavior, controllable biodegradability, and further functionalization. In this paper, we review the development of multifunctional citrate-based biomaterials for biomedical applications, and summarize their multifunctional properties in terms of physical, chemical, and biological aspects, and finally the applications of citrate-based biomaterials in biomedical engineering, including bone tissue engineering, skin tissue engineering, drug/cell delivery, vascular and neural tissue engineering, and bioimaging.

Fisetin exerts neuroprotective effects in vivo and in vitro by inhibiting ferroptosis and oxidative stress after traumatic brain injury

Traumatic brain injury (TBI) is an important cause of disability and mortality, and identifying effective neuroprotective drugs and targets after TBI is an urgent public concern. Ferroptosis, an iron dependent, novel form of cell death associated with lipid peroxidation, has recently been shown to participate in secondary injury processes after TBI. Fisetin is a natural and relatively safe at general dosages flavonoid compound with neuroprotective properties. This study aimed to investigate the molecular mechanism of ferroptosis in TBI and the role of fisetin in neuroprotection by regulating ferroptosis and oxidative stress following TBI. Through in vivo experiments, a mouse model of repetitive mild closed head injury was established to determine that fisetin could reduce post-TBI injury and exert neuroprotective effects as determined by the Neurobehavioral Severity Scale score, brain water content, Nissl staining, hematoxylin-eosin staining, TUNEL staining and water maze experiment results. Fisetin was proven to be capable of inhibiting the changes in post-TBI ferroptosis proteins, activating the PI3K/AKT/NRF2 signaling pathway, and reducing oxidative stress, as confirmed by Western blotting. Via in vitro experiments, cell death models of ferroptosis were established with glutamate and erastin. As determined by MTT assay, fisetin improved the survival of cells with induced ferroptosis. The morphological alterations of ferroptotic cells were ascertained with a microscope. Fisetin similarly inhibited the changes in multiple ferroptosis-associated proteins induced by glutamate and erastin, reduced ROS and peroxidation products, and increased the level of antioxidants. In conclusion, fisetin exerts neuroprotective effects in TBI through multiple pathways, thereby alleviating tissue damage and cognitive dysfunction.

The FGFR inhibitor Rogaratinib reduces microglia reactivity and synaptic loss in TBI

Background

Traumatic brain injury (TBI) induces an acute reactive state of microglia, which contribute to secondary injury processes through phagocytic activity and release of cytokines. Several receptor tyrosine kinases (RTK) are activated in microglia upon TBI, and their blockade may reduce the acute inflammation and decrease the secondary loss of neurons; thus, RTKs are potential therapeutic targets. We have previously demonstrated that several members of the Fibroblast Growth Factor Receptor (FGFR) family are transiently phosporylated upon TBI; the availability for drug repurposing of FGFR inhibitors makes worthwhile the elucidation of the role of FGFR in the acute phases of the response to TBI and the effect of FGFR inhibition.

Methods

A closed, blunt, weight-drop mild TBI protocol was employed. The pan-FGFR inhibitor Rogaratinib was administered to mice 30min after the TBI and daily up to 7 days post injury. Phosphor-RTK Arrays and proteomic antibody arrays were used to determine target engagement and large-scale impact of the FGFR inhibitor. pFGFR1 and pFGFR3 immunostaining were employed for validation. As outcome parameters of the TBI injury immunostainings for NeuN, VGLUT1, VGAT at 7dpi were considered.

Results

Inhibition of FGFR during TBI restricted phosphorylation of FGFR1, FGFR3, FGFR4 and ErbB4. Phosphorylation of FGFR1 and FGFR3 during TBI was traced back to Iba1+ microglia. Rogaratinib substantially dowregulated the proteomic signature of the neuroimmunological response to trauma, including the expression of CD40L, CXCR3, CCL4, CCR4, ILR6, MMP3 and OPG. Prolonged Rogaratinib treatment reduced neuronal loss upon TBI and prevented the loss of excitatory (vGLUT+) synapses.

Conclusion

The FGFR family is involved in the early induction of reactive microglia in TBI. FGFR inhibition selectively prevented FGFR phosphorylation in the microglia, dampened the overall neuroimmunological response and enhanced the preservation of neuronal and synaptic integrity. Thus, FGFR inhibitors may be relevant targets for drug repurposing aimed at modulating microglial reactivity in TBI.

Fluid biomarkers of chronic traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of long-term disability across the world. Evidence for the usefulness of imaging and fluid biomarkers to predict outcomes and screen for the need to monitor complications in the acute stage is steadily increasing. Still, many people experience symptoms such as fatigue and cognitive and motor dysfunction in the chronic phase of TBI, where objective assessments for brain injury are lacking. Consensus criteria for traumatic encephalopathy syndrome, a clinical syndrome possibly associated with the neurodegenerative disease chronic traumatic encephalopathy, which is commonly associated with sports concussion, have been defined only recently. However, these criteria do not fit all individuals living with chronic consequences of TBI. The pathophysiology of chronic TBI shares many similarities with other neurodegenerative and neuroinflammatory conditions, such as Alzheimer disease. As with Alzheimer disease, advancements in fluid biomarkers represent one of the most promising paths for unravelling the chain of pathophysiological events to enable discrimination between these conditions and, with time, provide prediction modelling and therapeutic end points. This Review summarizes fluid biomarker findings in the chronic phase of TBI (≥6 months after injury) that demonstrate the involvement of inflammation, glial biology and neurodegeneration in the long-term complications of TBI. We explore how the biomarkers associate with outcome and imaging findings and aim to establish mechanistic differences in biomarker patterns between types of chronic TBI and other neurodegenerative conditions. Finally, current limitations and areas of priority for future fluid biomarker research are highlighted.

Traumatic brain injury: Advances in coagulopathy (Review)

Trauma is a prevalent cause of coagulopathy, with traumatic brain injury (TBI) accompanied by coagulation disorders particularly linked to adverse outcomes. TBI is distinguished by minimal bleeding volume and unique injury sites, which precipitate complex coagulation disturbances. Historically, research into trauma-induced coagulopathy has primarily concentrated on the molecular biology and pathophysiology of endogenous anticoagulation and inflammation. Nonetheless, recognizing that cells are the fundamental units of structure and function in all living organisms, the present review aimed to distill our understanding of coagulopathy post-TBI by elucidating the intricate cellular mechanisms involving endothelial cells, neutrophils and platelets. Additionally, this study evaluates the strengths and weaknesses of various diagnostic tools and discusses the characteristics of pharmacological treatments and potential therapies for patients with TBI and coagulation disorders. The aim of this review is to amalgamate recent updates in mechanistic research and innovative diagnostic and therapeutic methodologies, thereby fostering the progression of precision medicine within this specialized domain.

Anti-CD49d Ab treatment ameliorates age-associated inflammatory response and mitigates CD8+ T-cell cytotoxicity after traumatic brain injury

Patients aged 65 years and older account for an increasing proportion of patients with traumatic brain injury (TBI). Older TBI patients experience increased morbidity and mortality compared to their younger counterparts. Our prior data demonstrated that by blocking α4 integrin, anti-CD49d antibody (aCD49d Ab) abrogates CD8+ T-cell infiltration into the injured brain, improves survival, and attenuates neurocognitive deficits. Here, we aimed to uncover how aCD49d Ab treatment alters local cellular responses in the aged mouse brain. Consequently, mice incur age-associated toxic cytokine and chemokine responses long-term post-TBI. aCD49d Ab attenuates this response along with a T helper (Th)1/Th17 immunological shift and remediation of overall CD8+ T cell cytotoxicity. Furthermore, aCD49d Ab reduces CD8+ T cells exhibiting higher effector status, leading to reduced clonal expansion in aged, but not young, mouse brains with chronic TBI. Together, aCD49d Ab is a promising therapeutic strategy for treating TBI in the older people.

Long-term mesoscale imaging of 3D intercellular dynamics across a mammalian organ

A comprehensive understanding of physio-pathological processes necessitates non-invasive intravital three-dimensional (3D) imaging over varying spatial and temporal scales. However, huge data throughput, optical heterogeneity, surface irregularity, and phototoxicity pose great challenges, leading to an inevitable trade-off between volume size, resolution, speed, sample health, and system complexity. Here, we introduce a compact real-time, ultra-large-scale, high-resolution 3D mesoscope (RUSH3D), achieving uniform resolutions of 2.6 × 2.6 × 6 μm3 across a volume of 8,000 × 6,000 × 400 μm3 at 20 Hz with low phototoxicity. Through the integration of multiple computational imaging techniques, RUSH3D facilitates a 13-fold improvement in data throughput and an orders-of-magnitude reduction in system size and cost. With these advantages, we observed premovement neural activity and cross-day visual representational drift across the mouse cortex, the formation and progression of multiple germinal centers in mouse inguinal lymph nodes, and heterogeneous immune responses following traumatic brain injury-all at single-cell resolution, opening up a horizon for intravital mesoscale study of large-scale intercellular interactions at the organ level.

Neuroimmune and neuroinflammation response for traumatic brain injury

Traumatic brain injury (TBI) is one of the major diseases leading to mortality and disability, causing a serious disease burden on individuals' ordinary lives as well as socioeconomics. In primary injury, neuroimmune and neuroinflammation are both responsible for the TBI. Besides, extensive and sustained injury induced by neuroimmune and neuroinflammation also prolongs the course and worsens prognosis of TBI. Therefore, this review aims to explore the role of neuroimmune, neuroinflammation and factors associated them in TBI as well as the therapies for TBI. Thus, we conducted by searching PubMed, Scopus, and Web of Science databases for articles published between 2010 and 2023. Keywords included "traumatic brain injury," "neuroimmune response," "neuroinflammation," "astrocytes," "microglia," and "NLRP3." Articles were selected based on relevance and quality of evidence. On this basis, we provide the cellular and molecular mechanisms of TBI-induced both neuroimmune and neuroinflammation response, as well as the different factors affecting them, are introduced based on physiology of TBI, which supply a clear overview in TBI-induced chain-reacting, for a better understanding of TBI and to offer more thoughts on the future therapies for TBI.