PD-L1 signaling in reactive astrocytes counteracts neuroinflammation and ameliorates neuronal damage after traumatic brain injury

Linking severe traumatic brain injury to pulmonary Infections: Translocation of intestinal bacteria mediated by nociceptor neurons

The prevalence of bacterial infections significantly increases among patients with severe traumatic brain injury (STBI), leading to a notable rise in mortality rates. While immune dysfunctions are linked to the incidence of pneumonia, our observations indicate that endogenous pathogens manifest in the lungs post-STBI due to the migration of gut commensal bacteria. This translocation involves gut-innervating nociceptor sensory neurons, which are crucial for host defense. Following STBI, the expression of transient receptor potential vanilloid 1 (TRPV1) in dorsal root ganglion (DRG) neurons significantly decreases, despite an initial brief increase. The timing of TRPV1 defects coincides with the occurrence of pulmonary infections post-STBI. This alteration in TRPV1+ neurons diminishes their ability to signal bacterial injuries, weakens defense mechanisms against intestinal bacteria, and increases susceptibility to pulmonary infections via bacterial translocation. Experimental evidence demonstrates that pulmonary infections can be successfully replicated through the chemical ablation and gene interference of TRPV1+ nociceptors, and that these infections can be mitigated by TRPV1 activation, thereby confirming the crucial role of nociceptor neurons in controlling intestinal bacterial migration. Furthermore, TRPV1+ nociceptors regulate the immune response of microfold cells by releasing calcitonin gene-related peptide (CGRP), thereby influencing the translocation of gut bacteria to the lungs. Our study elucidates how changes in nociceptive neurons post-STBI impact intestinal pathogen defense. This new understanding of endogenous risk factors within STBI pathology offers novel insights for preventing and treating pulmonary infections.

Therapeutic implications for the PD-1 axis in cerebrovascular injury

Since the discovery and characterization of the PD-1/PD-L pathway, mounting evidence has emerged regarding its role in regulating neuroinflammation following cerebrovascular injury. Classically, PD-L1 on antigen-presenting cells or tissues binds PD-1 on T cell surfaces resulting in T cell inhibition. In myeloid cells, PD-1 stimulation induces polarization of microglia and macrophages into an anti-inflammatory, restorative phenotype. The therapeutic potential of PD-1 agonism in ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage-related vasospasm, and traumatic brain injury rests on the notion of harnessing the immunomodulatory function of immune checkpoint pathways to temper the harmful effects of immune overactivation and secondary injury while promoting repair and recovery. Immune checkpoint agonism has greater specificity than the wider and non-specific anti-inflammatory effects of other agents, such as steroids. PD-1 agonism has already demonstrated success in clinical trials for rheumatoid arthritis and is being tested in other chronic inflammatory diseases. Further investigation of PD-1 agonism as a therapeutic strategy in cerebrovascular injury can help clarify the mechanisms underlying clinical benefit, develop drugs with optimal pharmacodynamic and pharmacokinetic properties, and mitigate unwanted side effects.

Targeting astrocytic TDAG8 with delayed CO2 postconditioning improves functional outcomes after controlled cortical impact injury in mice

T-cell death-associated gene 8 (TDAG8), a G-protein-coupled receptor sensing physiological or weak acids, regulates inflammatory responses. However, its role in traumatic brain injury (TBI) remains unknown. Our recent study showed that delayed CO2 postconditioning (DCPC) has neuroreparative effects after TBI. We hypothesized that activating astrocytic TDAG8 is a key mechanism for DCPC. WT and TDAG8-/- mice received DCPC daily by transiently inhaling 10% CO2 after controlled cortical impact (CCI). HBAAV2/9-GFAP-m-TDAG8-3xflag-EGFP was used to overexpress TDAG8 in astrocytes. The beam walking test, mNSS, immunofluorescence and Golgi-Cox staining were used to evaluate motor function, glial activation and dendritic plasticity. DCPC significantly improved motor function; increased total dendritic length, neuronal complexity and spine density; inhibited overactivation of astrocytes and microglia; and promoted the expression of astrocytic brain-derived neurotrophic factor in WT but not TDAG8-/- mice. Overexpressing TDAG8 in astrocytes surrounding the lesion in TDAG8-/- mice restored the beneficial effects of DCPC. Although the effects of DCPC on Days 14-28 were much weaker than those of DCPC on Days 3-28 in WT mice, these effects were further enhanced by overexpressing astrocytic TDAG8. Astrocytic TDAG8 is a key target of DCPC for TBI rehabilitation. Its overexpression is a strategy that broadens the therapeutic window and enhances the effects of DCPC.

Chronic glial activation and behavioral alterations induced by acute/subacute pioglitazone treatment in a mouse model of traumatic brain injury

Traumatic brain injury (TBI) is a disabling neurotraumatic condition and the leading cause of injury-related deaths and disability in the United States. Attenuation of neuroinflammation early after TBI is considered an important treatment target; however, while these inflammatory responses can induce secondary brain injury, they are also involved in the repair of the nervous system. Pioglitazone, which activates peroxisome proliferator-activated receptor gamma, has been shown to decrease inflammation acutely after TBI, but the long-term consequences of its use remain unknown. For this reason, the impacts of treatment with pioglitazone during the acute/subacute phase (30 min after injury and each subsequent 24 h for 5 days) after TBI were interrogated during the chronic phase (30- and 274-days post-injury (DPI)) in mice using the controlled cortical impact model of experimental TBI. Acute/subacute pioglitazone treatment after TBI results in long-term deleterious consequences, including disruption of tau homeostasis, chronic glial cell activation, neuronal pathology, and worsened injury severity particularly at 274 DPI, with male mice being more susceptible than female mice. Further, male pioglitazone-treated TBI mice exhibited increased dominant and offensive-like behavior while having a decreased non-social exploring behavior at 274 DPI. After TBI, both sexes exhibited glial activation at 30 DPI when treated with pioglitazone; however, while injury severity was increased in females it was not impacted in male mice. This work reveals that although pioglitazone has been shown to lead to attenuated TBI outcomes acutely, sex-based differences, timing and long-term consequences of treatment with glitazones must be considered and further studied prior to their clinical use for TBI therapy.

Intervention of CXCL5 attenuated neuroinflammation and promoted neurological recovery after traumatic brain injury

Neuroinflammation after traumatic brain injury (TBI) exhibits a strong correlation with neurological impairment, which is a crucial target for improving the prognosis of TBI patients. The involvement of CXCL5/CXCR2 signaling in the regulation of neuroinflammation in brain injury models has been documented. Therefore, the effects of CXCL5 on post-TBI neuroinflammation and its potential mechanisms need to be explored. Following TBI, C57BL/6 mice were administered intraperitoneal injections of a CXCL5 neutralizing antibody (Nab-CXCL5) (5 mg/kg, 2 times/day). Subsequently, the effects on neuroinflammation, nerve injury, and neurological function were assessed. Nab-CXCL5 significantly reduced the release of inflammatory factors, inhibited the formation of inflammatory microglia and astrocytes, and reduced the infiltration of peripheral immune cells in TBI mice. Additionally, this intervention led to a reduction in neuronal impairment and facilitated the restoration of sensorimotor abilities, as well as improvements in learning and memory functions. Peripheral administration of the Nab-CXCL5 to TBI mice could suppress neuroinflammation, reduce neurological damage, and improve neurological function. Our data suggest that neutralizing antibodies against CXCL5 (Nab-CXCL5) may be a promising agent for treating TBI.

Blood-based inflammatory protein biomarker panel for the prediction of relapse and severity in patients with neuromyelitis optica spectrum disorder: A prospective cohort study

BACKGROUND

To date, most existing models for predicting neuromyelitis optica spectrum disorder (NMOSD) are based primarily on clinical characteristics. Blood-based NMOSD severity and prognostic predictive immune- and inflammation-related biomarkers are needed. We aimed to investigate the associations between plasma inflammatory biomarkers and relapse and attack severity in NMOSD.

METHODS

This two-step, single-center prospective cohort study included discovery and validation cohorts. We quantified 92 plasma inflammatory proteins by using Olink's proximity extension assay and identified differentially expressed proteins in the relapse group (relapse within 1 year of follow-up) and severe attack group. To define a new molecular prognostic model, we calculated the risk score of each patient based on the key protein signatures and validated the results in the validation cohort.

RESULTS

The relapse prediction model, including FGF-23, DNER, GDNF, and SLAMF1, predicted the 1-year relapse risk. The severe attack prediction model, including PD-L1 and MCP-2, predicted the severe clinical attack risk. Both the relapse and severe attack prediction models demonstrated good discriminative ability and high accuracy in the validation cohort.

CONCLUSIONS

Our discovered biomarker signature and prediction models may complement current clinical risk stratification approaches. These inflammatory biomarkers could contribute to the discovery of therapeutic interventions and prevent NMOSD progression.

Runx2 Suppresses Astrocyte Activation and Astroglial Scar Formation After Spinal Cord Injury in Mice

After spinal cord injury, astrocytes undergo a reactive process and form an astroglial scar, which impedes the regeneration of axons. The role of Runx2 in promoting the transformation of astrocytes in the central nervous system is well-established. However, it remains unclear whether Runx2 also plays a role in the development of astroglial scar, and the precise underlying mechanism has yet to be identified. Recently, our study using cell culture and animal models has demonstrated that Runx2 actually suppresses astrocyte activation and the formation of astroglial scar following injury. The initial results demonstrated an increase in the expression of Runx2 in astrocytes following in vivo injury. Subsequently, the overexpression of Runx2 resulted in the inhibition of astrocyte activation, reduction in the total area of astroglial scar, and restoration of neural function after 14 days of injury. However, these effects were reversed by CADD522. These findings indicate that Runx2 could potentially serve as a therapeutic intervention for spinal cord injury (SCI). Furthermore, our findings suggest that the Nuclear-matrix-targeting signal (NMTS) of Runx2 is associated with its effect. In summary, the study's results propose that targeting Runx2 may be a promising treatment approach for reactive astrocytes and astroglial scar in the recovery of SCI.

Research hotspots and trends of microRNAs in spinal cord injury: a comprehensive bibliometric analysis

Background

Spinal cord injury (SCI) is a nervous system disease leading to motor and sensory dysfunction below the injury level, and can result in paralysis. MicroRNAs (miRNAs) play a key role in SCI treatment, and related research provides insights for SCI diagnosis and treatment. Bibliometrics is an important tool for literature statistics and evaluation, objectively summarizing multidimensional information. This study comprehensively overviews the field through bibliometric analysis of miRNA and SCI research, providing contemporary resources for future collaboration and clinical treatment.

Materials and methods

In this study, we searched the Web of Science Core Collection (WOSCC) database. After careful screening and data import, we extracted annual publications, citation counts, countries, institutions, authors, journals, highly cited articles, co-cited articles, keywords, and H-index. Bibliometrics and visualization analyses employed VOSviewer, CiteSpace, the R package "bibliometrix," and online analytic platforms. Using Arrowsmith, we determined miRNA-SCI relationships and discussed potential miRNA mechanisms in SCI.

Results

From 2008 to 2024, the number of related papers increased annually, reaching 754. The number of yearly publications remained high and entered a period of rapid development. Researchers from 50 countries/regions, 802 institutions, 278 journals, and 3,867 authors participated in the field. Currently, China has advantages in the number of national papers, citations, institutions, and authors. However, it is necessary to strengthen cooperation among different authors, institutions, and countries to promote the production of important academic achievements. The research in the field currently focuses on nerve injury, apoptosis, and gene expression. Future research directions mainly involve molecular mechanisms, clinical trials, exosomes, and inflammatory reactions.

Conclusion

Overall, this study comprehensively analyzes the research status and frontier of miRNAs in SCI. A systematic summary provides a complete and intuitive understanding of the relationship between SCI and miRNAs. The presented findings establish a basis for future research and clinical application in this field.

Effect of CTLA-4 Inhibition on Inflammation and Apoptosis After Spinal Cord Injury

Spinal cord injury (SCI) encompasses various pathological processes, notably neuroinflammation and apoptosis, both of which play significant roles. CTLA-4, a well-known immune molecule that suppresses T cell-mediated immune responses, is a key area of research and a focal point for targeted therapy development in treating tumors and autoimmune disorders. Despite its prominence, the impact of CTLA-4 inhibition on inflammation and apoptosis subsequent to SCI remains unexplored. This study aimed to investigate the influence of CTLA-4 on SCI. A weight-drop technique was used to establish a rat model of SCI. To examine the safeguarding effect of CTLA-4 on the restoration of motor function in rats with SCI, the Basso-Beattie-Bresnahan (BBB) scale and inclined plane test were employed to assess locomotion. Neuronal degeneration and apoptosis were assessed using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) and Fluoro-Jade B labeling, respectively, and the activity of microglial cells was examined by immunofluorescence. To evaluate the impact of CTLA4 on SCI, the levels of inflammatory markers were measured. After treatment with the CTLA-4 inhibitor ipilimumab, the rats showed worse neurological impairment and more severe neuroinflammation after SCI. Furthermore, the combination therapy with ipilimumab and durvalumab after SCI had more pronounced effects than treatment with either inhibitor alone. These findings indicate that CTLA-4 contributes to neuroinflammation and apoptosis after SCI, presenting a promising new therapeutic target for this traumatic condition.

The role of astrocyte in neuroinflammation in traumatic brain injury

Traumatic brain injury (TBI), a significant contributor to mortality and morbidity worldwide, is a devastating condition characterized by initial mechanical damage followed by subsequent biochemical processes, including neuroinflammation. Astrocytes, the predominant glial cells in the central nervous system, play a vital role in maintaining brain homeostasis and supporting neuronal function. Nevertheless, in response to TBI, astrocytes undergo substantial phenotypic alternations and actively contribute to the neuroinflammatory response. This article explores the multifaceted involvement of astrocytes in neuroinflammation subsequent to TBI, with a particular emphasis on their activation, release of inflammatory mediators, modulation of the blood-brain barrier, and interactions with other immune cells. A comprehensive understanding the dynamic interplay between astrocytes and neuroinflammation in the condition of TBI can provide valuable insights into the development of innovative therapeutic approaches aimed at mitigating secondary damage and fostering neuroregeneration.

PD-1 deficiency aggravates spinal cord injury by regulating the reprogramming of NG2 glia and activating the NgR/RhoA/ROCK signaling pathway

Spinal cord injury (SCI) is a devastating disorder and a leading cause of disability in adults worldwide. Multiple studies have reported the upregulation of programmed cell death 1 (PD-1) following SCI. However, the underlying mechanism of PD-1 deficiency in SCI is not well established. Therefore, we aimed to investigate the role and potential mechanism of PD-1 in SCI pathogenesis. PD-1 Knockout (KO) SCI mouse model was established, and PD-1 expression was evaluated in tissue samples by western blot assay. We then used a series of function gain-and-loss assays to determine the role of PD-1 in SCI pathogenesis. Moreover, mechanistic assays were performed to explore the association between PD-1, neuron-glia antigen-2 (NG2) glia cells, and miR-23b-5p and then investigated the involved signaling pathway. Results illustrated that PD-1 deficiency enhanced the inflammatory response, neuron loss, and functional impairment induced by SCI. We found that NG2 glia depletion aggravated inflammation, reduced neural survival, and suppressed locomotor recovery in murine SCI model. Further analysis indicated that NG2+ cells were increased in the spinal cord of SCI mice, and PD-1 deficiency increased the number of NG2+ cells by activating the Nogo receptor/ras homolog family member A/Rho kinase (NgR/RhoA/ROCK) signaling. Mechanistically, miR-23b-5p was identified as the negative regulator of PD-1 in NG2 glia. MiR-23b-5p deficiency reduced the expression of inflammatory cytokines, enhanced neural survival, and promoted locomotor recovery in SCI mice, which was counteracted by PD-1 deficiency. In conclusion, PD-1 deficiency exacerbates SCI in vivo by regulating reprogramming of NG2 glia and activating the NgR/RhoA/ROCK signaling.

Exploring the landscape of drug resistance in gastrointestinal cancer immunotherapy: A review

Gastrointestinal (GI) cancers pose a significant challenge due to high prevalence and mortality. While advancements in detection and conventional treatments have been made, prognosis often remains poor, particularly for advanced-stage cancers. Immunotherapy has emerged as a transformative approach, leveraging the body immune system against cancer, including immune checkpoint inhibitors (ICIs), cancer vaccines, and adoptive cell transfer. These modalities have shown promise, achieving sustained responses and improved survival in some patients. However, their efficacy in GI cancers is less pronounced, hindered by drug resistance mechanisms that are either intrinsic or acquired over time. This review examines the latest understanding of immunotherapy in GI cancers, focusing on ICIs, cancer vaccines, and adoptive cell transfer, along with their associated outcomes and limitations. It delves into the mechanisms behind drug resistance, including alterations in immune checkpoints, the immunosuppressive tumor microenvironment, and genetic/epigenetic changes. The role of the gut microbiome is also considered as an emerging factor in resistance. To combat drug resistance, strategies such as enhancing immune response, targeting the tumor microenvironment, and modulating resistance mechanisms are explored. The review underscores the potential of ferroptosis induction as a novel approach. Looking forward, it highlights the need for personalized immunotherapies, understanding the influence of the gut microbiome, and further exploration of ferroptosis in overcoming resistance. While challenges persist, the continuous evolution in GI cancer immunotherapy research promises innovative treatments that could significantly improve patient outcomes.

The expression mechanism of programmed cell death 1 ligand 1 and its role in immunomodulatory ability of mesenchymal stem cells

Programmed cell death 1 ligand 1 (PD-L1) is an important immunosuppressive molecule, which inhibits the function of T cells and other immune cells by binding to the receptor programmed cell death-1. The PD-L1 expression disorder plays an important role in the occurrence, development, and treatment of sepsis or other inflammatory diseases, and has become an important target for the treatment of these diseases. Mesenchymal stem cells (MSCs) are a kind of pluripotent stem cells with multiple differentiation potential. In recent years, MSCs have been found to have a strong immunosuppressive ability and are used to treat various inflammatory insults caused by hyperimmune diseases. Moreover, PD-L1 is deeply involved in the immunosuppressive events of MSCs and plays an important role in the treatment of various diseases. In this review, we will summarize the main regulatory mechanism of PD-L1 expression, and discuss various biological functions of PD-L1 in the immune regulation of MSCs.

The implication of targeting PD-1:PD-L1 pathway in treating sepsis through immunostimulatory and anti-inflammatory pathways

Sepsis currently remains a major contributor to mortality in the intensive care unit (ICU), with 48.9 million cases reported globally and a mortality rate of 22.5% in 2017, accounting for almost 20% of all-cause mortality worldwide. This highlights the urgent need to improve the understanding and treatment of this condition. Sepsis is now recognized as a dysregulation of the host immune response to infection, characterized by an excessive inflammatory response and immune paralysis. This dysregulation leads to secondary infections, multiple organ dysfunction syndrome (MODS), and ultimately death. PD-L1, a co-inhibitory molecule expressed in immune cells, has emerged as a critical factor in sepsis. Numerous studies have found a significant association between the expression of PD-1/PD-L1 and sepsis, with a particular focus on PD-L1 expressed on neutrophils recently. This review explores the role of PD-1/PD-L1 in immunostimulatory and anti-inflammatory pathways, illustrates the intricate link between PD-1/PD-L1 and sepsis, and summarizes current therapeutic approaches against PD-1/PD-L1 in the treatment and prognosis of sepsis in preclinical and clinical studies.

PD-L1 positive astrocytes attenuate inflammatory functions of PD-1 positive microglia in models of autoimmune neuroinflammation

Multiple Sclerosis (MS) is a chronic autoimmune inflammatory disorder of the central nervous system (CNS). Current therapies mainly target inflammatory processes during acute stages, but effective treatments for progressive MS are limited. In this context, astrocytes have gained increasing attention as they have the capacity to drive, but also suppress tissue-degeneration. Here we show that astrocytes upregulate the immunomodulatory checkpoint molecule PD-L1 during acute autoimmune CNS inflammation in response to aryl hydrocarbon receptor and interferon signaling. Using CRISPR-Cas9 genetic perturbation in combination with small-molecule and antibody-mediated inhibition of PD-L1 and PD-1 both in vivo and in vitro, we demonstrate that astrocytic PD-L1 and its interaction with microglial PD-1 is required for the attenuation of autoimmune CNS inflammation in acute and progressive stages in a mouse model of MS. Our findings suggest the glial PD-L1/PD-1 axis as a potential therapeutic target for both acute and progressive MS stages.

Neurological adverse events associated with PD-1/PD-L1 immune checkpoint inhibitors

Immunotherapy is a promising method for cancer treatment. Among them, immune checkpoint inhibitors targeting PD-1/PD-L1 are increasingly used for certain cancers. However, with the widespread use of such drugs, reports of immune-related adverse events (irAEs) are also increasing. Neurological adverse events (nAEs) are one of the irAEs that affect the peripheral and central nervous systems. They are characterized by low incidence, hard to diagnose, and life-threatening risks, which have a significant impact on the prognosis of patients. Biomarker-based early diagnosis and subsequent treatment strategies are worthy of attention, and comprehensive management of irAEs is important for optimizing patients' quality of life and long-term outcomes. In this review, we summarized the mechanisms, common symptoms, early biomarkers, treatments, and future research directions of nAEs, in order to provide a comprehensive overview of immune checkpoint inhibitor-related nAEs targeting PD-1/PD-L1.

Interactions between astrocytes and extracellular matrix structures contribute to neuroinflammation-associated epilepsy pathology

Often considered the "housekeeping" cells of the brain, astrocytes have of late been rising to the forefront of neurodegenerative disorder research. Identified as crucial components of a healthy brain, it is undeniable that when astrocytes are dysfunctional, the entire brain is thrown into disarray. We offer epilepsy as a well-studied neurological disorder in which there is clear evidence of astrocyte contribution to diseases as evidenced across several different disease models, including mouse models of hippocampal sclerosis, trauma associated epilepsy, glioma-associated epilepsy, and beta-1 integrin knockout astrogliosis. In this review we suggest that astrocyte-driven neuroinflammation, which plays a large role in the pathology of epilepsy, is at least partially modulated by interactions with perineuronal nets (PNNs), highly structured formations of the extracellular matrix (ECM). These matrix structures affect synaptic placement, but also intrinsic neuronal properties such as membrane capacitance, as well as ion buffering in their immediate milieu all of which alters neuronal excitability. We propose that the interactions between PNNs and astrocytes contribute to the disease progression of epilepsy vis a vis neuroinflammation. Further investigation and alteration of these interactions to reduce the resultant neuroinflammation may serve as a potential therapeutic target that provides an alternative to the standard anti-seizure medications from which patients are so frequently unable to benefit.

Glial cells: an important switch for the vascular function of the central nervous system

In this review, we first describe the current understanding of glial-mediated vascular function affecting the role of the blood-brain barrier (BBB) in central nervous system (CNS) disorders. BBB, mainly composed of glial and endothelial cells (ECs), is the protective structure that orchestrates the transport of substances, including ions, molecules, and cells from brain vessels into or out of the CNS. Then, we display the multiple communication between glial and vascular function based on angiogenesis, vascular wrapping, and blood perfusion in the brain. Glial can support microvascular ECs to form a blood network connecting to neurons. Astrocytes, microglia, and oligodendrocytes are the common types of glial surrounding the brain vessel. Glial-vessel interaction is required for the permeability and integrity of BBB. Glial cells surrounding the cerebral blood vessels can transmit communication signals to ECs and regulate the activity of vascular endothelial growth factor (VEGF) or Wnt-dependent endothelial angiogenesis mechanism. In addition, these glial cells monitor the blood flow in the brain via Ca2+/K+-dependent pathways. Finally, we provide a potential research direction for the glial-vessel axis in CNS disorders. Microglial activation can trigger astrocyte activation, which suggests that microglia-astrocyte interaction may play a key role in monitoring cerebral blood flow. Thus, microglia-astrocyte interaction can be the key point of follow-up studies focusing on the microglia-blood mechanism. More investigations focus on the mechanism of how oligodendrocyte progenitor cells communicate and interact with ECs. The direct role of oligodendrocytes in modulating vascular function needs to be explored in the future.

Immune regulation in neurovascular units after traumatic brain injury

Traumatic brain injury (TBI) is a major cause of death and disability worldwide. Survivors may experience movement disorders, memory loss, and cognitive deficits. However, there is a lack of understanding of the pathophysiology of TBI-mediated neuroinflammation and neurodegeneration. The immune regulation process of TBI involves changes in the peripheral and central nervous system (CNS) immunity, and intracranial blood vessels are essential communication centers. The neurovascular unit (NVU) is responsible for coupling blood flow with brain activity, and comprises endothelial cells, pericytes, astrocyte end-feet, and vast regulatory nerve terminals. A stable NVU is the basis for normal brain function. The concept of the NVU emphasizes that cell-cell interactions between different types of cells are essential for maintaining brain homeostasis. Previous studies have explored the effects of immune system changes after TBI. The NVU can help us further understand the immune regulation process. Herein, we enumerate the paradoxes of primary immune activation and chronic immunosuppression. We describe the changes in immune cells, cytokines/chemokines, and neuroinflammation after TBI. The post-immunomodulatory changes in NVU components are discussed, and research exploring immune changes in the NVU pattern is also described. Finally, we summarize immune regulation therapies and drugs after TBI. Therapies and drugs that focus on immune regulation have shown great potential for neuroprotection. These findings will help us further understand the pathological processes after TBI.

Roles of Astrocytic Endothelin ETB Receptor in Traumatic Brain Injury

Traumatic brain injury (TBI) is an intracranial injury caused by accidents, falls, or sports. The production of endothelins (ETs) is increased in the injured brain. ET receptors are classified into distinct types, including ET_A receptor (ET_A-R) and ET_B receptor (ET_B-R). ET_B-R is highly expressed in reactive astrocytes and upregulated by TBI. Activation of astrocytic ET_B-R promotes conversion to reactive astrocytes and the production of astrocyte-derived bioactive factors, including vascular permeability regulators and cytokines, which cause blood-brain barrier (BBB) disruption, brain edema, and neuroinflammation in the acute phase of TBI. ET_B-R antagonists alleviate BBB disruption and brain edema in animal models of TBI. The activation of astrocytic ET_B receptors also enhances the production of various neurotrophic factors. These astrocyte-derived neurotrophic factors promote the repair of the damaged nervous system in the recovery phase of patients with TBI. Thus, astrocytic ET_B-R is expected to be a promising drug target for TBI in both the acute and recovery phases. This article reviews recent observations on the role of astrocytic ET_B receptors in TBI.

Revisiting the immune landscape post spinal cord injury: More than black and white

Spinal cord injury (SCI) induced catastrophic neurological disability is currently incurable, especially in elderly patients. Due to the limited axon regeneration capacity and hostile microenvironment in the lesion site, essential neural network reconstruction remains challenging. Owing to the blood-spinal cord barrier (BSCB) created immune cells and cytokines isolation, the immune elements were incorrectly recognized as innocent bystanders during the SCI pathological process traditionally. Emerging evidence demonstrated that the central nervous system (CNS) is an "immunological quiescent" rather than "immune privileged" area, and the CNS-associated immune response played mixed roles which dedicate beneficial and detrimental contributions throughout the SCI process. Consequently, coordinating double-edged immunomodulation is vital to promote tissue repair and neurological recovery post-SCI. The comprehensive exploration and understanding of the immune landscape post-SCI are essential in establishing new avenues for further basic and clinical studies. In this context, this review summarizes the recent significant breakthroughs in key aspects of SCI-related immunomodulation, including innate and adaptive immune response, immune organ changes, and holistic immune status modification. Moreover, the currently existing immune-oriented therapies for SCI will be outlined.

Injury programs shape glioblastoma

Glioblastoma is the most common and aggressive primary brain cancer in adults and is almost universally fatal due to its stark therapeutic resistance. During the past decade, although survival has not substantially improved, major advances have been made in our understanding of the underlying biology. It has become clear that these devastating tumors recapitulate features of neurodevelopmental hierarchies which are influenced by the microenvironment. Emerging evidence also highlights a prominent role for injury responses in steering cellular phenotypes and contributing to tumor heterogeneity. This review highlights how the interplay between injury and neurodevelopmental programs impacts on tumor growth, invasion, and treatment resistance, and discusses potential therapeutic considerations in view of these findings.

Targetability of the neurovascular unit in inflammatory diseases of the central nervous system

The blood-brain barrier (BBB) is a selectively permeable barrier separating the periphery from the central nervous system (CNS). The BBB restricts the flow of most material into and out of the CNS, including many drugs that could be used as potent therapies. BBB permeability is modulated by several cells that are collectively called the neurovascular unit (NVU). The NVU consists of specialized CNS endothelial cells (ECs), pericytes, astrocytes, microglia, and neurons. CNS ECs maintain a complex "seal" via tight junctions, forming the BBB; breakdown of these tight junctions leads to BBB disruption. Pericytes control the vascular flow within capillaries and help maintain the basal lamina. Astrocytes control much of the flow of material that has moved beyond the CNS EC layer and can form a secondary barrier under inflammatory conditions. Microglia survey the border of the NVU for noxious material. Neuronal activity also plays a role in the maintenance of the BBB. Since astrocytes, pericytes, microglia, and neurons are all able to modulate the permeability of the BBB, understating the complex contributions of each member of the NVU will potentially uncover novel and effective methods for delivery of neurotherapies to the CNS.

Mesenchymal stromal cell secretome for traumatic brain injury: Focus on immunomodulatory action

The severity and long-term consequences of brain damage in traumatic brain injured (TBI) patients urgently calls for better neuroprotective/neuroreparative strategies for this devastating disorder. Mesenchymal stromal cells (MSCs) hold great promise and have been shown to confer neuroprotection in experimental TBI, mainly through paracrine mechanisms via secreted bioactive factors (i.e. secretome), which indicates significant potential for a cell-free neuroprotective approach. The secretome is composed of cytokines, chemokines, growth factors, proteins, lipids, nucleic acids, metabolites, and extracellular vesicles; it may offer advantages over MSCs in terms of delivery, safety, and variability of therapeutic response for brain injury. Immunomodulation by molecular factors secreted by MSCs is considered to be a key mechanism involved in their multi-potential therapeutic effects. Regulated neuroinflammation is required for healthy remodeling of central nervous system during development and adulthood. Moreover, immune cells and their secreted factors can also contribute to tissue repair and neurological recovery following acute brain injury. However, a chronic and maladaptive neuroinflammatory response can exacerbate TBI and contribute to progressive neurodegeneration and long-term neurological impairments. Here, we review the evidence for MSC-derived secretome as a therapy for TBI. Our framework incorporates a detailed analysis of in vitro and in vivo studies investigating the effects of the secretome on clinically relevant neurological and histopathological outcomes. We also describe the activation of immune cells after TBI and the immunomodulatory properties exerted by mediators released in the secretome. We then describe how ageing modifies central and systemic immune responses to TBI and discuss challenges and opportunities of developing secretome based neuroprotective therapies for elderly TBI populations. Finally, strategies aimed at modulating the secretome in order to boost its efficacy for TBI will also be discussed.

Role of statins in regulating molecular pathways following traumatic brain injury: A system pharmacology study

Traumatic brain injury (TBI) is a serious disorder with debilitating physical and psychological complications. Previous studies have indicated that genetic factors have a critical role in modulating the secondary phase of injury in TBI. Statins have interesting pleiotropic properties such as antiapoptotic, antioxidative, and anti-inflammatory effects, which make them a suitable class of drugs for repurposing in TBI. In this study, we aimed to explore how statins modulate proteins and pathways involved in TBI using system pharmacology. We first explored the target associations with statins in two databases to discover critical clustering groups, candidate hub and critical hub genes in the network of TBI, and the possible connections of statins with TBI-related genes. Our results showed 1763 genes associated with TBI. Subsequently, the analysis of centralities in the PPI network displayed 55 candidate hub genes and 15 hub genes. Besides, MCODE analysis based on threshold score:10 determined four modular clusters. Intersection analysis of genes related to TBI and statins demonstrated 204 shared proteins, which suggested that statins influence 31 candidate hub and 9 hub genes. Moreover, statins had the highest interaction with MCODE1. The biological processes of the 31 shared proteins are related to gene expression, inflammation, antioxidant activity, and cell proliferation. Biological enriched pathways showed Programmed Cell Death proteins, AGE-RAGE signaling pathway, C-type lectin receptor signalling pathway, and MAPK signaling pathway as top clusters. In conclusion, statins could target several critical post-TBI genes mainly involved in inflammation and apoptosis, supporting the previous research results as a potential therapeutic agent.

PD-1/PD-L Axis in Neuroinflammation: New Insights

The approval of immune checkpoint inhibitors (ICIs) by the Food and Drug Administration (FDA) led to an improvement in the treatment of several types of cancer. The main targets of these drugs are cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death protein-1/programmed death-ligand 1 pathway (PD-1/PD-L1), which are important inhibitory molecules for the immune system. Besides being generally safer than common chemotherapy, the use of ICIs has been associated with several immune-related adverse effects (irAEs). Although rare, neurological adverse effects are reported within the irAEs in clinical trials, particularly in patients treated with anti-PD-1 antibodies or a combination of both anti-CTLA-4 and PD-1 drugs. The observations obtained from clinical trials suggest that the PD-1 axis may play a remarkable role in the regulation of neuroinflammation. Moreover, numerous studies in preclinical models have demonstrated the involvement of PD-1 in several neurological disorders. However, a comprehensive understanding of these cellular mechanisms remains elusive. Our review aims to summarize the most recent evidence concerning the regulation of neuroinflammation through PD-1/PD-L signaling, focusing on cell populations that are involved in this pathway.

Enteric Glial Cells in Immunological Disorders of the Gut

Enteric glial cells (EGCs) are one of the major cell types of neural crest lineage distributed in the gastrointestinal tract. EGCs represent an integral part of the enteric nervous system (ENS) and significantly outnumber ENS neurons. Studies have suggested that EGCs would exert essential roles in supporting the survival and functions of the ENS neurons. Notably, recent evidence has begun to reveal that EGCs could possess multiple immune functions and thereby may participate in the immune homeostasis of the gut. In this review article, we will summarize the current evidence supporting the potential involvement of EGCs in several important immunological disorders, including inflammatory bowel disease, celiac disease, and autoimmune enteropathy. Further, we highlight critical questions on the immunological aspects of EGCs that warrant future research attention.