Lesional accumulation of CD163+ macrophages/microglia in rat traumatic brain injury

TAMing Gliomas: Unraveling the Roles of Iba1 and CD163 in Glioblastoma

Gliomas, the most common type of primary brain tumor, are a significant cause of morbidity and mortality worldwide. Glioblastoma, a highly malignant subtype, is particularly common, aggressive, and resistant to treatment. The tumor microenvironment (TME) of gliomas, especially glioblastomas, is characterized by a distinct presence of tumor-associated macrophages (TAMs), which densely infiltrate glioblastomas, a hallmark of these tumors. This macrophage population comprises both tissue-resident microglia as well as macrophages derived from the walls of blood vessels and the blood stream. Ionized calcium-binding adapter molecule 1 (Iba1) and CD163 are established cellular markers that enable the identification and functional characterization of these cells within the TME. This review provides an in-depth examination of the roles of Iba1 and CD163 in malignant gliomas, with a focus on TAM activation, migration, and immunomodulatory functions. Additionally, we will discuss how recent advances in AI-enhanced cell identification and visualization techniques have begun to transform the analysis of TAMs, promising unprecedented precision in their characterization and providing new insights into their roles within the TME. Iba1 and CD163 appear to have both unique and shared roles in glioma pathobiology, and both have the potential to be targeted through different molecular and cellular mechanisms. We discuss the therapeutic potential of Iba1 and CD163 based on available preclinical (experimental) and clinical (human tissue-based) evidence.

The E3 ligase c-Cbl modulates microglial phenotypes and contributes to Parkinson's disease pathology

Microglial activation, particularly the polarization between classical (M1 phenotype) and alternative (M2 phenotype) states, plays pivotal roles in the immune pathogenesis of Parkinson's disease (PD), with the M1 phenotype exerting neurotoxic effects and the M2 phenotype conferring neuroprotection. Modulating microglial polarization toward the M2 phenotype holds therapeutic potential for PD. This study investigated the role of c-Cbl, an E3 ubiquitin ligase implicated in modulating microglial phenotypes and protecting dopaminergic neurons. Our findings revealed that c-Cbl-/- mice exhibited motor deficits, reduced striatal dopamine levels, and progressive dopaminergic neuron loss in the substantia nigra (SN). Genetic ablation of c-Cbl significantly increased proinflammatory cytokine release and microglial activation in the SN, accompanied by a phenotypic shift from M2 to M1 polarization. Furthermore, stereotaxic c-Cbl knockdown in the SN exacerbated behavioral impairments and accelerated dopaminergic neuron degeneration in the MPTP-induced mouse model of PD. At the molecular level, c-Cbl deletion promoted M1 polarization of microglia through dysregulation of the PI3K/Akt signaling pathway, thereby impairing dopaminergic neuronal survival. Collectively, this study demonstrates that c-Cbl knockout recapitulates PD-like pathology and drives microglial activation. Our results establish that c-Cbl orchestrates the transition from neurotoxic M1 to neuroprotective M2 microglial phenotypes, highlighting its central role in PD immunopathogenesis. These findings suggest c-Cbl as a promising therapeutic target for modulating microglial polarization and alleviating PD symptoms.

Metabolic shift as a compensatory response to impaired hippocampal neurogenesis after developmental exposure to sodium fluoride in rats

Fluoride affects neurodevelopment in children. In this study, we examined the effects of developmental exposure to sodium fluoride (NaF) on hippocampal neurogenesis in rats. Dams were given drinking water containing NaF at 0 (untreated controls), 30 or 100 ppm from gestational day 6 to day 21 post-delivery upon weaning, and offspring were reared until postnatal day (PND) 77. On PND 21, NaF at 100 ppm altered the numbers in subpopulations of granule cell lineages, including a decrease in type-3 neural progenitor cells (NPCs), as well as a compensatory increase in type-1 neural stem cells (NSCs) and type-2a NPCs. NaF exposure tended to increase GluR2+ mossy cells in the hilus of the dentate gyrus (DG) in a dose-dependent manner, suggesting that NaF exposure induces a compensatory neurogenic response. NaF also caused a dose-dependent increase in ARC+ granule cells, and it upregulated Ptgs2 in the DG at 100 ppm, suggesting that NaF exposure increases synaptic plasticity in granule cells. NaF at 100 ppm upregulated granule cell lineage marker genes (Nes, Eomes and Rbfox3) and an anti-apoptotic gene (Bcl2), suggesting ameliorating responses against the impaired neurogenesis during NaF exposure. Moreover, NaF at 100 ppm downregulated oxidative phosphorylation-related genes (Atp5f1b and Sdhd) and upregulated a glycolysis-related gene (Hk3), suggesting a metabolic shift in cells undergoing neurogenesis. By PND 77, the changes in granule cell lineages were no longer detected, and GABAergic interneuron marker genes (Calb2 and Reln) were upregulated, suggesting a persistent protective response in granule cell lineages. Together, these findings suggest that developmental NaF exposure causes transient disruption of hippocampal neurogenesis, which in turn induces a metabolic shift as a compensatory response.

Circulating soluble CD163 is associated with reduced Glasgow Coma Scale Score and 1-year all-cause mortality in traumatized patients

Soluble CD163 (sCD163) is a biomarker of macrophage activation, not previously investigated in the circulation of traumatized patients. A biobank of 398 adult trauma patients was analyzed. Patients with an Injury Severity Score (ISS) >8 served as trauma patients (n = 195) and those with ISS ≤ 8 as trauma controls (n = 203). Serum samples obtained upon admission, 15h and 72h after were analyzed for sCD163 using an in-house ELISA. Multiple linear regression was used to analyze the association between admission levels of sCD163 with, 1: overall trauma severity (ISS), and 2: severity of injury to specified organs using Abbreviated Injury Score (AIS) and Glasgow Coma Scale (GCS). The association between the peak level of sCD163 with 1-year all-cause mortality was analyzed by logistic regression analysis. Median admission levels of sCD163 were higher in trauma patients than trauma controls [2.32 (IQR 1.73 to 2.86) vs. 1.92 (IQR 1.41 to 2.51) mg/L, p < 0.01]. Worsening GCS score was associated with a 10.3% (95% CI: 17.0 to 3.1, p < 0.01) increase in sCD163. Increasing Head-AIS score was associated with a 5.1% (95% CI: -0.5 to 11.0, p = 0.07) increase in sCD163. The remaining AIS scores and ISS were not consistently associated with sCD163 admission levels. Each mg/L increase in sCD163 peak level had an odds ratio 1.34 (95%CI: 0.98 to 1.83), p = 0.06) after adjustment for age, sex, and GCS. Circulating sCD163 is increased in traumatized patients and associated with worsening GCS. Our findings suggest an association between circulating sCD163 levels with 1-year all-cause mortality.

Efficacy of a music-based intervention in a preclinical model of traumatic brain injury: An initial foray into a novel and non-pharmacological rehabilitative therapy

Traumatic brain injury (TBI) causes neurobehavioral and cognitive impairments that negatively impact life quality for millions of individuals. Because of its pernicious effects, numerous pharmacological interventions have been evaluated to attenuate the TBI-induced deficits or to reinstate function. While many such pharmacotherapies have conferred benefits in the laboratory, successful translation to the clinic has yet to be achieved. Given the individual, medical, and societal burden of TBI, there is an urgent need for alternative approaches to attenuate TBI sequelae and promote recovery. Music based interventions (MBIs) may hold untapped potential for improving neurobehavioral and cognitive recovery after TBI as data in normal, non-TBI, rats show plasticity and augmented cognition. Hence, the aim of this study was to test the hypothesis that providing a MBI to adult rats after TBI would improve cognition, neurobehavior, and histological endpoints. Adult male rats received a moderate-to-severe controlled cortical impact injury (2.8 mm impact at 4 m/s) or sham surgery (n = 10-12 per group) and 24 h later were randomized to classical Music or No Music (i.e., ambient room noise) for 3 h/day from 19:00 to 22:00 h for 30 days (last day of behavior). Motor (beam-walk), cognitive (acquisition of spatial learning and memory), anxiety-like behavior (open field), coping (shock probe defensive burying), as well as histopathology (lesion volume), neuroplasticity (BDNF), and neuroinflammation (Iba1, and CD163) were assessed. The data showed that the MBI improved motor, cognitive, and anxiety-like behavior vs. No Music (p's < 0.05). Music also reduced cortical lesion volume and activated microglia but increased resting microglia and hippocampal BDNF expression. These findings support the hypothesis and provide a compelling impetus for additional preclinical studies utilizing MBIs as a potential efficacious rehabilitative therapy for TBI.

Cellular and molecular mechanisms in vascular repair after traumatic brain injury: a narrative review

Traumatic brain injury (TBI) disrupts normal brain function and is associated with high morbidity and fatality rates. TBI is characterized as mild, moderate or severe depending on its severity. The damage may be transient and limited to the dura matter, with only subtle changes in cerebral parenchyma, or life-threatening with obvious focal contusions, hematomas and edema. Blood vessels are often injured in TBI. Even in mild TBI, dysfunctional cerebral vascular repair may result in prolonged symptoms and poor outcomes. Various distinct types of cells participate in vascular repair after TBI. A better understanding of the cellular response and function in vascular repair can facilitate the development of new therapeutic strategies. In this review, we analyzed the mechanism of cerebrovascular impairment and the repercussions following various forms of TBI. We then discussed the role of distinct cell types in the repair of meningeal and parenchyma vasculature following TBI, including endothelial cells, endothelial progenitor cells, pericytes, glial cells (astrocytes and microglia), neurons, myeloid cells (macrophages and monocytes) and meningeal lymphatic endothelial cells. Finally, possible treatment techniques targeting these unique cell types for vascular repair after TBI are discussed.

Insulin-like growth factor-1 receptor controls the function of CNS-resident macrophages and their contribution to neuroinflammation

Signaling by insulin-like growth factor-1 (IGF-1) is essential for the development of the central nervous system (CNS) and regulates neuronal survival and myelination in the adult CNS. In neuroinflammatory conditions including multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE), IGF-1 can regulate cellular survival and activation in a context-dependent and cell-specific manner. Notwithstanding its importance, the functional outcome of IGF-1 signaling in microglia/macrophages, which maintain CNS homeostasis and regulate neuroinflammation, remains undefined. As a result, contradictory reports on the disease-ameliorating efficacy of IGF-1 are difficult to interpret, together precluding its potential use as a therapeutic agent. To fill this gap, we here investigated the role of IGF-1 signaling in CNS-resident microglia and border associated macrophages (BAMs) by conditional genetic deletion of the receptor Igf1r in these cell types. Using a series of techniques including histology, bulk RNA sequencing, flow cytometry and intravital imaging, we show that absence of IGF-1R significantly impacted the morphology of both BAMs and microglia. RNA analysis revealed minor changes in microglia. In BAMs however, we detected an upregulation of functional pathways associated with cellular activation and a decreased expression of adhesion molecules. Notably, genetic deletion of Igf1r from CNS-resident macrophages led to a significant weight gain in mice, suggesting that absence of IGF-1R from CNS-resident myeloid cells indirectly impacts the somatotropic axis. Lastly, we observed a more severe EAE disease course upon Igf1r genetic ablation, thus highlighting an important immunomodulatory role of this signaling pathway in BAMs/microglia. Taken together, our work shows that IGF-1R signaling in CNS-resident macrophages regulates the morphology and transcriptome of these cells while significantly decreasing the severity of autoimmune CNS inflammation.

Retinal microglia protect against vascular damage in a mouse model of retinopathy of prematurity

Retinopathy of prematurity (ROP) is a common cause of blindness in preterm babies. As a hypoxia-induced eye disease characterized by neovascularization, its association with retinal microglia has been noted but not well documented. We performed a comprehensive analysis of retinal microglia and retinal vessels in mouse oxygen-induced retinopathy (OIR), an animal model of ROP. In combination with a pharmacological inhibitory strategy, the role of retinal microglia in vascular network maintenance was investigated. Postnatal day (P) 7 C57BL/6J mouse pups with their nursing mother were exposed to 75% oxygen for 5 days to induce OIR. Age-matched room air-treated pups served as controls. On P12, P17, P21, P25, and P30, retinal microglia and vessels were visualized and quantified based on their location and activation status. Their relationship with retinal vessels was also analyzed. On P5 or P12, retinal microglia inhibition was achieved by intravitreal injection of liposomes containing clodronate (CLD); retinal vasculature and microglia were examined in P12 and P17 OIR retinae. The number of retinal microglia was increased in the superficial areas of OIR retinae on P12, P17, P21, P25, and P30, and most of them displayed an amoeboid (activated) morphology. The increased retinal microglia were associated with increased superficial retinal vessels in OIR retinae. The number of retinal microglia in deep retinal areas of OIR retinae also increased from P17 to P30 with a ramified morphology, which was not associated with reduced retinal vessels. Intravitreal injection of liposomes-CLD caused a significant reduction in retinal microglia. Loss of retinal microglia before hyperoxia treatment resulted in increased vessel obliteration on P12 and subsequent neovascularization on P17 in OIR retinae. Meanwhile, loss of retinal microglia immediately after hyperoxia treatment on P12 also led to more neovascularization in P17 OIR retinae. Our data showed that activated microglia were strongly associated with vascular abnormalities upon OIR. Retinal microglial activation continued throughout OIR and lasted until after retinal vessel recovery. Pharmacological inhibition of retinal microglia in either hyperoxic or hypoxic stage of OIR exacerbated retinal vascular consequences. These results suggested that retinal microglia may play a protective role in retinal vasculature maintenance in the OIR process.

Distinct Phenotypes of Inflammation Associated Macrophages and Microglia in the Prefrontal Cortex Schizophrenia Compared to Controls

Approximately 40% of people with schizophrenia are classified as having "high inflammation." This subgroup has worse neuropathology than patients with "low inflammation." Thus, one would expect the resident microglia and possibly monocyte-derived macrophages infiltrating from the periphery to be "activated" in those with schizophrenia with elevated neuroinflammation. To test whether microglia and/or macrophages are associated with increased inflammatory signaling in schizophrenia, we measured microglia- and macrophage-associated transcripts in the postmortem dorsolateral prefrontal cortex of 69 controls and 72 people with schizophrenia. Both groups were stratified by neuroinflammatory status based on cortical mRNA levels of cytokines and SERPINA3. We found microglial mRNAs levels were either unchanged (IBA1 and Hexb, p > 0.20) or decreased (CD11c, <62% p < 0.001) in high inflammation schizophrenia compared to controls. Conversely, macrophage CD163 mRNA levels were increased in patients, substantially so in the high inflammation schizophrenia subgroup compared to low inflammation subgroup (>250%, p < 0.0001). In contrast, high inflammation controls did not have elevated CD163 mRNA compared to low inflammation controls (p > 0.05). The pro-inflammatory macrophage marker (CD64 mRNA) was elevated (>160%, all p < 0.05) and more related to CD163 mRNA in the high inflammation schizophrenia subgroup compared to high inflammation controls, while anti-inflammatory macrophage and cytokine markers (CD206 and IL-10 mRNAs) were either unchanged or decreased in schizophrenia. Finally, macrophage recruitment chemokine CCL2 mRNA was increased in schizophrenia (>200%, p < 0.0001) and CCL2 mRNA levels positively correlated with CD163 mRNA (r = 0.46, p < 0.0001). Collectively, our findings support the co-existence of quiescent microglia and increased pro-inflammatory macrophages in the cortex of people with schizophrenia.

Effect of exercise from a very early stage after intracerebral hemorrhage on microglial and macrophage reactivity states in rats

OBJECTIVE

This study investigated the effects of exercise, starting very early after intracerebral hemorrhage (ICH), on microglia and macrophages in a rat model. Collagenase solution was injected into the left striatum to induce ICH.

METHODS

Rats were randomly assigned to receive placebo surgery without exercise (sham surgery), ICH without exercise (ICH), or ICH with very early exercise (ICH + VET). The ICH + VET group was subjected to treadmill running 6 h, 24 h, and days 2-6 after ICH. Motor function assessment was performed using the ladder test and rotarod test 3 h, 25 h, and 7 days after ICH. Postexercise brain tissue was collected on day 8 after surgery to investigate the lesion volume. Very early exercise temporarily worsened motor dysfunction. The protein expression levels of the macrophage and microglial markers CD80, CD163, and TMEM119 were analyzed 6 h, 24 h, and 8 days after ICH. Protein analysis of NeuN, GFAP, and PSD95 was also performed on day 8 after ICH.

RESULTS

There was no significant difference in lesion volume between the ICH and ICH + VET groups on day 8 after ICH. Exercise from very early stage prevented elevated CD163 protein expression.

CONCLUSION

Very early exercise may inhibit the activation of anti-inflammatory-associated macrophages/microglia.

Time dependent analysis of rat microglial surface markers in traumatic brain injury reveals dynamics of distinct cell subpopulations

Traumatic brain injury (TBI) results in a cascade of cellular responses, which produce neuroinflammation, partly due to the activation of microglia. Accurate identification of microglial populations is key to understanding therapeutic approaches that modify microglial responses to TBI and improve long-term outcome measures. Notably, previous studies often utilized an outdated convention to describe microglial phenotypes. We conducted a temporal analysis of the response to controlled cortical impact (CCI) in rat microglia between ipsilateral and contralateral hemispheres across seven time points, identified microglia through expression of activation markers including CD45, CD11b/c, and p2y12 receptor and evaluated their activation state using additional markers of CD32, CD86, RT1B, CD200R, and CD163. We identified unique sub-populations of microglial cells that express individual or combination of activation markers across time points. We further portrayed how the size of these sub-populations changes through time, corresponding to stages in TBI response. We described longitudinal changes in microglial population after CCI in two different locations using activation markers, showing clear separation into cellular sub-populations that feature different temporal patterns of markers after injury. These changes may aid in understanding the symptomatic progression following TBI and help define microglial subpopulations beyond the outdated M1/M2 paradigm.

Agmatine Mitigates Inflammation-Related Oxidative Stress in BV-2 Cells by Inducing a Pre-Adaptive Response

Neuroinflammation and microglial activation, common components of most neurodegenerative diseases, can be imitated in vitro by challenging microglia cells with Lps. We here aimed to evaluate the effects of agmatine pretreatment on Lps-induced oxidative stress in a mouse microglial BV-2 cell line. Our findings show that agmatine suppresses nitrosative and oxidative burst in Lps-stimulated microglia by reducing iNOS and XO activity and decreasing O₂^- levels, arresting lipid peroxidation, increasing total glutathione content, and preserving GR and CAT activity. In accordance with these results, agmatine suppresses inflammatory NF-kB, and stimulates antioxidant Nrf2 pathway, resulting in decreased TNF, IL-1 beta, and IL-6 release, and reduced iNOS and COX-2 levels. Together with increased ARG1, CD206 and HO-1 levels, our results imply that, in inflammatory conditions, agmatine pushes microglia towards an anti-inflammatory phenotype. Interestingly, we also discovered that agmatine alone increases lipid peroxidation end product levels, induces Nrf2 activation, increases total glutathione content, and GPx activity. Thus, we hypothesize that some of the effects of agmatine, observed in activated microglia, may be mediated by induced oxidative stress and adaptive response, prior to Lps stimulation.

Therapeutic efficacy of rolipram delivered by PgP nanocarrier on secondary injury and motor function in a rat TBI model

Aim: To develop poly(lactide-co-glycolide)-graft-polyethylenimine (PgP) as a nanocarrier for the delivery of rolipram (Rm) and evaluate the therapeutic efficacy of Rm-loaded PgP (Rm-PgP) on secondary injury and motor function in a rat traumatic brain injury (TBI) model. Materials & methods: Rm-PgP was injected in the injured brain lesion immediately after TBI using a microinjection pump. Secondary injury pathologies such as inflammatory response, apoptosis and astrogliosis were assessed by histological analysis and functional recovery was assessed by assorted motor function tests. Results: Rm-PgP restored cyclic adenosine monophosphate level in the injured brain close to the sham level and Rm-PgP treatment reduced lesion volume, neuroinflammation and apoptosis and improved motor function at 7 days post-TBI. Conclusion: One single injection of Rm-PgP can be effective for acute mild TBI treatment.

Immunomodulatory effects of mesenchymal stem cells in peripheral nerve injury

Various immune cells and cytokines are present in the aftermath of peripheral nerve injuries (PNI), and coordination of the local inflammatory response is of great significance for the recovery of PNI. Mesenchymal stem cells (MSCs) exhibit immunosuppressive and anti-inflammatory abilities which can accelerate tissue regeneration and attenuate inflammation, but the role of MSCs in the regulation of the local inflammatory microenvironment after PNI has not been widely studied. Here, we summarize the known interactions between MSCs, immune cells, and inflammatory cytokines following PNI with a focus on the immunosuppressive role of MSCs. We also discuss the immunomodulatory potential of MSC-derived extracellular vesicles as a new cell-free treatment for PNI.

The P2X7 Receptor in Microglial Cells Modulates the Endolysosomal Axis, Autophagy, and Phagocytosis

Microglial cells regulate neural homeostasis by coordinating both immune responses and clearance of debris, and the P2X₇ receptor for extracellular ATP plays a central role in both functions. The P2X₇ receptor is primarily known in microglial cells for its immune signaling and NLRP3 inflammasome activation. However, the receptor also affects the clearance of extracellular and intracellular debris through modifications of lysosomal function, phagocytosis, and autophagy. In the absence of an agonist, the P2X₇ receptor acts as a scavenger receptor to phagocytose material. Transient receptor stimulation induces autophagy and increases LC3-II levels, likely through calcium-dependent phosphorylation of AMPK, and activates microglia to an M1 or mixed M1/M2 state. We show an increased expression of Nos2 and Tnfa and a decreased expression of Chil3 (YM1) from primary cultures of brain microglia exposed to high levels of ATP. Sustained stimulation can reduce lysosomal function in microglia by increasing lysosomal pH and slowing autophagosome-lysosome fusion. P2X₇ receptor stimulation can also cause lysosomal leakage, and the subsequent rise in cytoplasmic cathepsin B activates the NLRP3 inflammasome leading to caspase-1 cleavage and IL-1β maturation and release. Support for P2X₇ receptor activation of the inflammasome following lysosomal leakage comes from data on primary microglia showing IL-1β release following receptor stimulation is inhibited by cathepsin B blocker CA-074. This pathway bridges endolysosomal and inflammatory roles and may provide a key mechanism for the increased inflammation found in age-dependent neurodegenerations characterized by excessive lysosomal accumulations. Regardless of whether the inflammasome is activated via this lysosomal leakage or the better-known K⁺-efflux pathway, the inflammatory impact of P2X₇ receptor stimulation is balanced between the autophagic reduction of inflammasome components and their increase following P2X₇-mediated priming. In summary, the P2X₇ receptor modulates clearance of extracellular debris by microglial cells and mediates lysosomal damage that can activate the NLRP3 inflammasome. A better understanding of how the P2X₇ receptor alters phagocytosis, lysosomal health, inflammation, and autophagy can lead to therapies that balance the inflammatory and clearance roles of microglial cells.

Dwellers and Trespassers: Mononuclear Phagocytes at the Borders of the Central Nervous System

The central nervous system (CNS) parenchyma is enclosed and protected by a multilayered system of cellular and acellular barriers, functionally separating glia and neurons from peripheral circulation and blood-borne immune cells. Populating these borders as dynamic observers, CNS-resident macrophages contribute to organ homeostasis. Upon autoimmune, traumatic or neurodegenerative inflammation, these phagocytes start playing additional roles as immune regulators contributing to disease evolution. At the same time, pathological CNS conditions drive the migration and recruitment of blood-borne monocyte-derived cells across distinct local gateways. This invasion process drastically increases border complexity and can lead to parenchymal infiltration of blood-borne phagocytes playing a direct role both in damage and in tissue repair. While recent studies and technical advancements have highlighted the extreme heterogeneity of these resident and CNS-invading cells, both the compartment-specific mechanism of invasion and the functional specification of intruding and resident cells remain unclear. This review illustrates the complexity of mononuclear phagocytes at CNS interfaces, indicating how further studies of CNS border dynamics are crucially needed to shed light on local and systemic regulation of CNS functions and dysfunctions.

Increased Macrophages and C1qA, C3, C4 Transcripts in the Midbrain of People With Schizophrenia

Increased cytokine and inflammatory-related transcripts are found in the ventral midbrain, a dopamine neuron-rich region associated with schizophrenia symptoms. In fact, half of schizophrenia cases can be defined as having a "high inflammatory/immune biotype." Recent studies implicate both complement and macrophages in cortical neuroinflammation in schizophrenia. Our aim was to determine whether measures of transcripts related to phagocytosis/macrophages (CD163, CD64, and FN1), or related to macrophage adhesion [intercellular adhesion molecule 1 (ICAM1)], or whether CD163+ cell density, as well as protein and/or gene expression of complement pathway activators (C1qA) and mediators (C3 or C4), are increased in the midbrain in schizophrenia, especially in those with a high inflammatory biotype. We investigated whether complement mRNA levels correlate with macrophage and/or microglia and/or astrocyte markers. We found CD163+ cells around blood vessels and in the parenchyma and increases in ICAM1, CD163, CD64, and FN1 mRNAs as well as increases in all complement transcripts in the midbrain of schizophrenia cases with high inflammation. While we found positive correlations between complement transcripts (C1qA and C3) and microglia or astrocyte markers across diagnostic and inflammatory subgroups, the only unique strong positive correlation was between CD163 and C1qA mRNAs in schizophrenia cases with high inflammation. Our study is the first to suggest that more circulating macrophages may be attracted to the midbrain in schizophrenia, and that increased macrophages are linked to increased complement pathway activation in tissue and may contribute to dopamine dysregulation in schizophrenia. Single-cell transcriptomic studies and mechanistic preclinical studies are required to test these possibilities.

The Role of Microglia in Cerebral Traumatic Injury and its Therapeutic Implications

Microglia have a variety of functions in the brain such as synaptic remodeling, damage repair of the central nervous system (CNS), and CNS’ inflammatory response to peripheral infections. The response depends on the type of insult and infection and includes a range of variety of activation states, the duration of which will decide the outcome. In response to traumatic brain injury (TBI), early activation can lead to early restoration of function, while prolonged and continuous activation can cause neurodegeneration states. Current evidence, however, states that this may not be the case. In this article, we discuss this seldom understood topic of microglia response to TBI, and analyze their distribution, function and possible sites of manipulation. Animal studies have allowed genetic and pharmacological manipulations of microglia activation, in order to define their role. Microglia activation can be remote to the site of injury, and thus their manipulation may play a significant role in the response to any trauma.

High-resolution and differential analysis of rat microglial markers in traumatic brain injury: conventional flow cytometric and bioinformatics analysis

Traumatic brain injury (TBI) results in a cascade of cellular responses, which produce neuroinflammation, partly due to microglial activation. Transforming from surveying to primed phenotypes, microglia undergo considerable molecular changes. However, specific microglial profiles in rat remain elusive due to tedious methodology and limited availability of reagents. Here, we present a flow cytometry-based analysis of rat microglia 24 h after TBI using the controlled cortical impact model, validated with a bioinformatics approach. Isolated microglia are analyzed for morphological changes and their expression of activation markers using flow cytometry, traditional gating-based analysis methods and support the data by employing bioinformatics statistical tools. We use CD45, CD11b/c, and p2y12 receptor to identify microglia and evaluate their activation state using CD32, CD86, RT1B, CD200R, and CD163. The results from logic-gated flow cytometry analysis was validated with bioinformatics-based analysis and machine learning algorithms to detect quantitative changes in morphology and marker expression in microglia due to activation following TBI.

Loss of homeostatic microglial phenotype in CSF1R-related Leukoencephalopathy

Microglia are resident macrophages of the central nervous system, and their unique molecular signature is dependent upon CSF-1 signaling. Previous studies have demonstrated the importance of CSF-1R in survival and development of microglia in animal models, but the findings are of uncertain relevance to understanding the influence of CSF-1R on microglia in humans. Hereditary diffuse leukoencephalopathy with spheroids (HDLS) [also known as adult onset leukoencephalopathy with spheroids and pigmented glia (ALSP)] is a neurodegenerative disorder primarily affecting cerebral white matter, most often caused by mutations of CSF1R. Therefore, we hypothesized that the molecular profile of microglia may be affected in HDLS. Semi-quantitative immunohistochemistry and quantitative transcriptomic profiling revealed reduced expression of IBA-1 and P2RY12 in both white and gray matter microglia of HDLS. In contrast, there was increased expression of CD68 and CD163 in microglia in affected white matter. In addition, expression of selective and specific microglial markers, including P2RY12, CX3CR1 and CSF-1R, were reduced in affected white matter. These results suggest that microglia in white matter in HDLS lose their homeostatic phenotype. Supported by gene ontology analysis, it is likely that an inflammatory phenotype is a key pathogenic feature of microglia in vulnerable brain regions of HDLS. Our findings suggest a potential mechanism of disease pathogenesis by linking aberrant CSF-1 signaling to altered microglial phenotype. They also support the idea that HDLS may be a primary microgliopathy. We observed increased expression of CSF-2 in gray matter compared to affected white matter, which may contribute to selective vulnerability of white matter in HDLS. Our findings suggest that methods that restore the homeostatic phenotype of microglia might be considered treatment approaches in HDLS.

Brain injury-induced dysfunction of the blood brain barrier as a risk for dementia

The blood-brain barrier (BBB) is a complex and dynamic physiological interface between brain parenchyma and cerebral vasculature. It is composed of closely interacting cells and signaling molecules that regulate movement of solutes, ions, nutrients, macromolecules, and immune cells into the brain and removal of products of normal and abnormal brain cell metabolism. Dysfunction of multiple components of the BBB occurs in aging, inflammatory diseases, traumatic brain injury (TBI, severe or mild repetitive), and in chronic degenerative dementing disorders for which aging, inflammation, and TBI are considered risk factors. BBB permeability changes after TBI result in leakage of serum proteins, influx of immune cells, perivascular inflammation, as well as impairment of efflux transporter systems and accumulation of aggregation-prone molecules involved in hallmark pathologies of neurodegenerative diseases with dementia. In addition, cerebral vascular dysfunction with persistent alterations in cerebral blood flow and neurovascular coupling contribute to brain ischemia, neuronal degeneration, and synaptic dysfunction. While the idea of TBI as a risk factor for dementia is supported by many shared pathological features, it remains a hypothesis that needs further testing in experimental models and in human studies. The current review focusses on pathological mechanisms shared between TBI and neurodegenerative disorders characterized by accumulation of pathological protein aggregates, such as Alzheimer's disease and chronic traumatic encephalopathy. We discuss critical knowledge gaps in the field that need to be explored to clarify the relationship between TBI and risk for dementia and emphasize the need for longitudinal in vivo studies using imaging and biomarkers of BBB dysfunction in people with single or multiple TBI.

Defining molecular identity and fates of CNS-border associated macrophages after ischemic stroke in rodents and humans

Central nervous system (CNS)-border associated macrophages (BAMs) maintain their steady-state population during adulthood and are not replaced by circulating monocytes under physiological conditions. Their roles in CNS integrity and functions under pathological conditions remain largely unknown. Until recently, BAMs and microglia could not be unequivocally distinguished due to expression of common macrophage markers. We investigated the transcriptional profiles of immunosorted BAMs from rat sham-operated and ischemic brains using RNA sequencing. We found that BAMs express the distinct transcriptional signature than microglia and infiltrating macrophages. The enrichment of functional groups associated with the cell cycle in CD163⁺ cells isolated 3 days after the ischemic injury indicates the proliferative capacity of these cells. The increased number of CD163⁺ cells 3 days post-ischemia was corroborated by flow cytometry and detecting the increased number of CD163⁺ cells positive for a proliferation marker Ki67 at perivascular spaces. CD163⁺ cells in the ischemic brains up-regulated many inflammatory genes and parenchymal CD163+ cells expressed iNOS, which indicates acquisition of a pro-inflammatory phenotype. In mice, BAMs typically express CD206 and we found a subset of these cells expressing CD169. Chimeric mice generated by transplanting bone marrow of donor Cx3cr1^gfpCCR2^rfp mice to wild type hosts showed an increased number of CX3CR1⁺CD169⁺ perivascular macrophages 3 days post-ischemia. Furthermore, these cells accumulated in the brain parenchyma and we detected replacement of perivascular macrophages by peripheral monocytic cells in the sub-acute phase of stroke. In line with the animal results, post-mortem brain samples from human ischemic stroke cases showed time-dependent accumulation of CD163⁺ cells in the ischemic parenchyma. Our findings indicate a unique transcriptional signature of BAMs, their local proliferation and migration of inflammatory BAMs to the brain parenchyma after stroke in animal models and humans.

Brain perivascular macrophages: Recent advances and implications in health and diseases

Brain perivascular macrophages (PVMs) belong to a distinct population of brain‐resident myeloid cells located within the perivascular space surrounding arterioles and venules. Their characterization depends on the combination of anatomical localization, phagocytic capacity, and molecular markers. Under physiological status, they provide structural and functional support for maintaining brain homeostasis, including facilitation of blood‐brain barrier integrity and lymphatic drainage, and exertion of immune functions such as phagocytosis and antigen presentation. Increasing evidence also implicates their specific roles in diseased brain, ranging from cerebrovascular diseases, Aβ pathologies, infections, and autoimmunity. Collectively, PVMs are key components of the brain‐resident immune system, actively participate in a broad‐spectrum of processes in normal and diseased status. Details of the processes are largely underexplored. Targeting PVMs would lead to new insights and be a promising strategy for a broad array of human diseases.

Blood-Related Toxicity after Traumatic Brain Injury: Potential Targets for Neuroprotection

Emergency visits, hospitalizations, and deaths due to traumatic brain injury (TBI) have increased significantly over the past few decades. While the primary early brain trauma is highly deleterious to the brain, the secondary injury post-TBI is postulated to significantly impact mortality. The presence of blood, particularly hemoglobin, and its breakdown products and key binding proteins and receptors modulating their clearance may contribute significantly to toxicity. Heme, hemin, and iron, for example, cause membrane lipid peroxidation, generate reactive oxygen species, and sensitize cells to noxious stimuli resulting in edema, cell death, and increased morbidity and mortality. A wide range of other mechanisms such as the immune system play pivotal roles in mediating secondary injury. Effective scavenging of all of these pro-oxidant and pro-inflammatory metabolites as well as controlling maladaptive immune responses is essential for limiting toxicity and secondary injury. Hemoglobin metabolism is mediated by key molecules such as haptoglobin, heme oxygenase, hemopexin, and ferritin. Genetic variability and dysfunction affecting these pathways (e.g., haptoglobin and heme oxygenase expression) have been implicated in the difference in susceptibility of individual patients to toxicity and may be target pathways for potential therapeutic interventions in TBI. Ongoing collaborative efforts are required to decipher the complexities of blood-related toxicity in TBI with an overarching goal of providing effective treatment options to all patients with TBI.

Time-dependent hemeoxygenase-1, lipocalin-2 and ferritin induction after non-contusion traumatic brain injury

Traumatic brain injury (TBI) often presents with focal contusion and parenchymal bleeds, activating heme oxygenase (HO) to degrade released hemoglobin. Here we show that diffuse, midline fluid percussion injury causes time-dependent induction of HO-1 and iron binding proteins within both hemorrhagic neocortex and non-hemorrhagic hippocampus. Rats subjected to midline fluid percussion injury (FPI) survived 1-15d postinjury and tissue was collected for Western blot and immunohistochemical assays. HO-1 was elevated 1d after FPI, peaked at 3d, and returned to control baseline 7-15d. Iron management proteins lipocalin 2 (LCN2) and ferritin (FTL) exhibited distinct postinjury time courses, where peak LCN2 response preceded, and FTL followed that of HO-1. LCN2 elevation supported not only its role in iron transport, but also mediation of matrix metalloproteinase 9 (MMP9) activity. Upregulation of FTL for intracellular iron sequestration was delayed relative to both HO-1 and LCN2 induction. In the neocortex IBA-1+ microglia around the injury core expressed HO-1, but astrocytes co-localized with HO-1 in perilesional parenchyma. Non-hemorrhagic dentate gyrus showed predominant HO-1 labeling in hilar microglia and in molecular layer astrocytes. At 1d postinjury, LCN2 and HO-1 co-localized in a subpopulation of reactive glia within both brain regions. Notably, FTL was distributed within cells around injured vessels, damaged subcortical white matter, and along vessels of the hippocampal fissure. Together these results confirm that even the moderate, non-contusional insult of diffuse midline FPI can significantly activate postinjury HO-1 heme processing pathways and iron management proteins. Moreover, this activation is time-dependent and occurs in the absence of overt hemorrhage.

Haemoglobin scavenging in intracranial bleeding: biology and clinical implications

Haemoglobin is released into the CNS during the breakdown of red blood cells after intracranial bleeding. Extracellular free haemoglobin is directly neurotoxic. Haemoglobin scavenging mechanisms clear haemoglobin and reduce toxicity; these mechanisms include erythrophagocytosis, haptoglobin binding of haemoglobin, haemopexin binding of haem and haem oxygenase breakdown of haem. However, the capacity of these mechanisms is limited in the CNS, and they easily become overwhelmed. Targeting of haemoglobin toxicity and scavenging is, therefore, a rational therapeutic strategy. In this Review, we summarize the neurotoxic mechanisms of extracellular haemoglobin and the peculiarities of haemoglobin scavenging pathways in the brain. Evidence for a role of haemoglobin toxicity in neurological disorders is discussed, with a focus on subarachnoid haemorrhage and intracerebral haemorrhage, and emerging treatment strategies based on the molecular pathways involved are considered. By focusing on a fundamental biological commonality between diverse neurological conditions, we aim to encourage the application of knowledge of haemoglobin toxicity and scavenging across various conditions. We also hope that the principles highlighted will stimulate research to explore the potential of the pathways discussed. Finally, we present a consensus opinion on the research priorities that will help to bring about clinical benefits.

Protective effects of delayed intraventricular TLR7 agonist administration on cerebral white and gray matter following asphyxia in the preterm fetal sheep

Preterm brain injury is highly associated with inflammation, which is likely related in part to sterile responses to hypoxia-ischemia. We have recently shown that neuroprotection with inflammatory pre-conditioning in the immature brain is associated with induction of toll-like receptor 7 (TLR7). We therefore tested the hypothesis that central administration of a synthetic TLR7 agonist, gardiquimod (GDQ), after severe hypoxia-ischemia in preterm-equivalent fetal sheep would improve white and gray matter recovery. Fetal sheep at 0.7 of gestation received sham asphyxia or asphyxia induced by umbilical cord occlusion for 25 minutes, followed by a continuous intracerebroventricular infusion of GDQ or vehicle from 1 to 4 hours (total dose 1.8 mg/kg). Sheep were killed 72 hours after asphyxia for histology. GDQ significantly improved survival of immature and mature oligodendrocytes (2′,3′-cyclic-nucleotide 3′-phosphodiesterase, CNPase) and total oligodendrocytes (oligodendrocyte transcription factor 2, Olig-2) within the periventricular and intragyral white matter. There were reduced numbers of cells showing cleaved caspase-3 positive apoptosis and astrogliosis (glial fibrillary acidic protein, GFAP) in both white matter regions. Neuronal survival was increased in the dentate gyrus, caudate and medial thalamic nucleus. Central infusion of GDQ was associated with a robust increase in fetal plasma concentrations of the anti-inflammatory cytokines, interferon-β (IFN-β) and interleukin-10 (IL-10), with no significant change in the concentration of the pro-inflammatory cytokine, tumor necrosis factor-α (TNF-α). In conclusion, delayed administration of the TLR7 agonist, GDQ, after severe hypoxia-ischemia in the developing brain markedly ameliorated white and gray matter damage, in association with upregulation of anti-inflammatory cytokines. These data strongly support the hypothesis that modulation of secondary inflammation may be a viable therapeutic target for injury of the preterm brain.

Transplantation of mesenchymal stem cells genetically engineered to overexpress interleukin-10 promotes alternative inflammatory response in rat model of traumatic brain injury

Background

Traumatic brain injury (TBI) is a major cause for long-term disability, yet the treatments available that improve outcomes after TBI limited. Neuroinflammatory responses are key contributors to determining patient outcomes after TBI. Transplantation of mesenchymal stem cells (MSCs), which release trophic and pro-repair cytokines, represents an effective strategy to reduce inflammation after TBI. One such pro-repair cytokine is interleukin-10 (IL-10), which reduces pro-inflammatory markers and trigger alternative inflammatory markers, such as CD163. In this study, we tested the therapeutic effects of MSCs that were engineered to overexpress IL-10 when transplanted into rats following TBI in the medial frontal cortex.

Methods

Thirty-six hours following TBI, rats were transplanted with MSCs and then assessed for 3 weeks on a battery of behavioral tests that measured motor and cognitive abilities. Histological evaluation was then done to measure the activation of the inflammatory response. Additionally, immunomodulatory effects were evaluated by immunohistochemistry and Western blot analyses.

Results

A significant improvement in fine motor function was observed in rats that received transplants of MSCs engineered to overexpress IL-10 (MSCs + IL-10) or MSCs alone compared to TBI + vehicle-treated rats. Although tissue spared was unchanged, anti-inflammatory effects were revealed by a reduction in the number of glial fibrillary acidic protein cells and CD86 cells in both TBI + MSCs + IL-10 and TBI + MSC groups compared to TBI + vehicle rats. Microglial activation was significantly increased in the TBI + MSC group when compared to the sham + vehicle group. Western blot data suggested a reduction in tumor necrosis factor-alpha in the TBI + MSCs + IL-10 group compared to TBI + MSC group. Immunomodulatory effects were demonstrated by a shift from classical inflammation expression (CD86) to an alternative inflammation state (CD163) in both treatments with MSCs and MSCs + IL-10. Furthermore, co-labeling of both CD86 and CD163 was detected in the same cells, suggesting a temporal change in macrophage expression.

Conclusions

Overall, our findings suggest that transplantation of MSCs that were engineered to overexpress IL-10 can improve functional outcomes by providing a beneficial perilesion environment. This improvement may be explained by the shifting of macrophage expression to a more pro-repair state, thereby providing a possible new therapy for treating TBI.

Role of the End-Point Mediators of Sympathoadrenal and Sympathoneural Stress Axes in the Pathogenesis of Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis

The role of stress effector systems in the initiation and progression of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), the most commonly used experimental model of MS, has strongly been suggested. To corroborate this notion, alterations in activity of the sympathoadrenal and sympathoneural axes of sympathoadrenal system (a major communication pathway between the central nervous system and the immune system), mirrored in altered release of their end-point mediators (adrenaline and noradrenaline, respectively), are shown to precede (in MS) and/or occur during development of MS and EAE in response to immune cell activation (in early phase of disease) and disease-related damage of sympathoadrenal system neurons and their projections (in late phase of disease). To add to the complexity, innate immunity cells and T-lymphocytes synthesize noradrenaline that may be implicated in a local autocrine/paracrine self-amplifying feed-forward loop to enhance myeloid-cell synthesis of proinflammatory cytokines and inflammatory injury. Furthermore, experimental manipulations targeting noradrenaline/adrenaline action are shown to influence clinical outcome of EAE, in a disease phase-specific manner. This is partly related to the fact that virtually all types of cells involved in the instigation and progression of autoimmune inflammation and target tissue damage in EAE/MS express functional adrenoceptors. Although catecholamines exert majority of immunomodulatory effects through β₂-adrenoceptor, a role for α-adrenoceptors in EAE pathogenesis has also been indicated. In this review, we summarize all aforementioned aspects of immunopathogenetic action of catecholamines in EAE/MS as possibly important for designing new strategies targeting their action to prevent/mitigate autoimmune neuroinflammation and tissue damage.

HO-1 protects the nerves of rats with cerebral hemorrhage by regulating the PI3K/AKT signaling pathway

Objective: This study aimed to investigate the neuroprotective effect of heme oxygenase-1 (HO-1) on the PI3K/AKT signaling pathway in rats with cerebral hemorrhage. Materials and methods: Adult male Sprague-Dawley rats were randomly divided into: a sham group, a model group and an HO-1 inhibitor group (ZnPP group). Functional defects after surgery were scored according to the Longa5 standard. Hemotoxylin and eosin staining was used to detect whether the model was constructed successfully. Superoxide dismutase (SOD) vitality and malondialdehyde (MDA) content were calculated by the xanthine oxidase method and thiobarbituric acid method, respectively. Blood-brain barrier permeability was measured by Evans Blue. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay. The expression of Bcl-2 and BAX was evaluated by immunohistochemistry and the expression of PI3K, p-PI3K, AKT and p-AKT was tested by Western blotting. Results: The rat intracerebral hemorrhage model was successfully constructed. Compared with the model group, the bleeding in the ZnPP group was more serious, the cell edema and deformation were aggravated, and the neurological deficit score in the rat was significantly increased. In addition, the content of Evans blue, MDA, the number of apoptotic cells, the water content of brain tissue and the expression of BAX were significantly increased, while the SOD activity and the expressions of Bcl-2, p-PI3K and p-AKT protein were decreased. Conclusion: HO-1 could protect the nerves of rats with cerebral hemorrhage by regulating the PI3K/AKT signaling pathway.

CD163, a novel therapeutic target, regulates the proliferation and stemness of glioma cells via casein kinase 2

Glioma is a devastating cancer with a dismal prognosis and there is an urgent need to discover novel glioma-specific antigens for glioma therapy. Previous studies have identified CD163-positive tumour cells in certain solid tumours, but CD163 expression in glioma remains unknown. In this study, via an analysis of public datasets, we demonstrated that CD163 overexpression in glioma specimens correlated with an unfavourable patient prognosis. CD163 expression was increased in glioma cells, especially primary glioma cells. The loss of CD163 expression inhibited both cell cycle progression and the proliferation of glioblastoma multiforme (GBM) cell lines and primary glioma cells. CD163 interacted directly with casein kinase 2 (CK2) and CD163 silencing reduced AKT/GSK3β/β-catenin/cyclin D1 pathway activity via CK2. Moreover, CD163 was upregulated in CD133-positive glioma stem cells (GSCs), and CD163 downregulation decreased the expression of GSC markers, including CD133, ALDH1A1, NANOG and OCT4. The knockdown of CD163 impaired GSC stemness by inhibiting the CK2/AKT/GSK3β/β-catenin pathway. Finally, a CD163 antibody successfully induced complement-dependent cytotoxicity against glioma cells. Our findings indicate that CD163 contributes to gliomagenesis via CK2 and provides preclinical evidence that CD163 and the CD163 pathway might serve as a therapeutic target for glioma.

The absence of the CD163 receptor has distinct temporal influences on intracerebral hemorrhage outcomes

Hemoglobin (Hb) toxicity precipitates secondary brain damage following intracerebral hemorrhage (ICH). CD163 is an anti-inflammatory Hb scavenger receptor and CD163-positive macrophages/microglia locally accumulate post-bleed, yet no studies have investigated the role of CD163 after ICH. ICH was induced in wildtype and CD163^-/- mice and various anatomical and functional outcomes were assessed. At 3 d, CD163^-/- mice have 43.4 ± 5.0% (p = 0.0002) and 34.8 ± 3.4% (p = 0.0003) less hematoma volume and tissue injury, respectively. Whereas, at 10 d, CD163^-/- mice have 49.2 ± 15.0% larger lesions (p = 0.0385). An inflection point was identified, where CD163^-/- mice perform better on neurobehavioral testing and have less mortality before 4 d, but increased mortality and worse function after 4 d (p = 0.0389). At 3 d, CD163^-/- mice have less Hb, iron, and blood-brain barrier dysfunction, increased astrogliosis and neovascularization, and no change in heme oxygenase 1 (HO1) expression. At 10 d, CD163^-/- mice have increased iron and VEGF immunoreactivity, but no significant change in HO1 or astrogliosis. These novel findings reveal that CD163 deficiency has distinct temporal influences following ICH, with early beneficial properties but delayed injurious effects. While it is unclear why CD163 deficiency is initially beneficial, the late injurious effects are consistent with the key anti-inflammatory role of CD163 in the recovery phase of tissue damage.

Ganoderma Lucidum Protects Rat Brain Tissue Against Trauma-Induced Oxidative Stress

Objective

Traumatic brain injury causes tissue damage, breakdown of cerebral blood flow and metabolic regulation. This study aims to investigate the protective influence of antioxidant Ganoderma lucidum (G. lucidum) polysaccharides (GLPs) on brain injury in brain-traumatized rats.

Methods

Sprague-Dawley conducted a head-traumatized method on rats by dropping off 300 g weight from 1 m height. Groups were categorized as control, G. lucidum, trauma, trauma+ G. lucidum (20 mL/kg per day via gastric gavage). Brain tissues were dissected from anesthetized rats 7 days after injury. For biochemical analysis, malondialdehyde, glutathione and myeloperoxidase values were measured.

Results

In histopathological examination, neuronal damage in brain cortex and changes in blood brain barrier were observed. In the analysis of immunohistochemical and western blot, p38 mitogen-activated protein kinase, vascular endothelial growth factor and cluster of differentiation 68 expression levels were shown. These analyzes demonstrated the beneficial effects of GLPs on brain injury.

Conclusion

We propose that GLPs treatment after brain injury could be an alternative treatment to decraseing inflammation and edema, preventing neuronal and glial cells degeneration if given in appropriate dosage and in particular time intervals.

A neuropeptide, Substance-P, directly induces tissue-repairing M2 like macrophages by activating the PI3K/Akt/mTOR pathway even in the presence of IFNγ

Macrophage polarization plays an important role in tissue damage and repair. In this study, we show that Substance-P (SP) can directly induce M2 polarization of inflammatory macrophages. SP induced the differentiation of GM-CSF-differentiated pro-inflammatory macrophages into alternatively activated phagocytic M2 like macrophages (M2^SP) through direct activation of the PI3K/Akt/mTOR/S6kinase pathway and induction of Arginase-1, CD163, and CD206, all of which were nullified by pretreatment with the neurokinin-1 receptor (NK-1R) antagonist RP67580 and specific signaling pathway inhibitors. M2^SP were distinct from IL-4/IL-13-induced M2a and IL-10-induced M2c subtypes; they did not show STAT activation and exhibited high phagocytic and endothelial adhesive activity. Furthermore, SP had a dominant effect on M2 polarization over Interferon gamma (IFNγ), a potent M1-skewing cytokine, and effectively induced the M2 phenotype in monocytes and the human THP-1 cell line. Finally, adoptively transferred M2^SP migrated to a spinal cord injury (SCI) lesion site and improved functional recovery. Collectively, our findings show that SP, a neuropeptide, plays a role as a novel cytokine by inducing tissue-repairing M2^SP macrophages and thus may be developed for pharmacological intervention in diseases involving chronic inflammation and acute injury.

Brain perivascular macrophages: characterization and functional roles in health and disease

Perivascular macrophages (PVM) are a distinct population of resident brain macrophages characterized by a close association with the cerebral vasculature. PVM migrate from the yolk sac into the brain early in development and, like microglia, are likely to be a self-renewing cell population that, in the normal state, is not replenished by circulating monocytes. Increasing evidence implicates PVM in several disease processes, ranging from brain infections and immune activation to regulation of the hypothalamic-adrenal axis and neurovascular-neurocognitive dysfunction in the setting of hypertension, Alzheimer disease pathology, or obesity. These effects involve crosstalk between PVM and cerebral endothelial cells, interaction with circulating immune cells, and/or production of reactive oxygen species. Overall, the available evidence supports the idea that PVM are a key component of the brain-resident immune system with broad implications for the pathogenesis of major brain diseases. A better understanding of the biology and pathobiology of PVM may lead to new insights and therapeutic strategies for a wide variety of brain diseases.

Response of the cerebral vasculature following traumatic brain injury

The critical role of the vasculature and its repair in neurological disease states is beginning to emerge particularly for stroke, dementia, epilepsy, Parkinson's disease, tumors and others. However, little attention has been focused on how the cerebral vasculature responds following traumatic brain injury (TBI). TBI often results in significant injury to the vasculature in the brain with subsequent cerebral hypoperfusion, ischemia, hypoxia, hemorrhage, blood-brain barrier disruption and edema. The sequalae that follow TBI result in neurological dysfunction across a host of physiological and psychological domains. Given the importance of restoring vascular function after injury, emerging research has focused on understanding the vascular response after TBI and the key cellular and molecular components of vascular repair. A more complete understanding of vascular repair mechanisms are needed and could lead to development of new vasculogenic therapies, not only for TBI but potentially vascular-related brain injuries. In this review, we delineate the vascular effects of TBI, its temporal response to injury and putative biomarkers for arterial and venous repair in TBI. We highlight several molecular pathways that may play a significant role in vascular repair after brain injury.

Ionizing Radiation-Induced Immune and Inflammatory Reactions in the Brain

Radiation-induced late brain injury consisting of vascular abnormalities, demyelination, white matter necrosis, and cognitive impairment has been described in patients subjected to cranial radiotherapy for brain tumors. Accumulating evidence suggests that various degrees of cognitive deficit can develop after much lower doses of ionizing radiation, as well. The pathophysiological mechanisms underlying these alterations are not elucidated so far. A permanent deficit in neurogenesis, chronic microvascular alterations, and blood–brain barrier dysfunctionality are considered among the main causative factors. Chronic neuroinflammation and altered immune reactions in the brain, which are inherent complications of brain irradiation, have also been directly implicated in the development of cognitive decline after radiation. This review aims to give a comprehensive overview on radiation-induced immune alterations and inflammatory reactions in the brain and summarizes how these processes can influence cognitive performance. The available data on the risk of low-dose radiation exposure in the development of cognitive impairment and the underlying mechanisms are also discussed.

The far-reaching scope of neuroinflammation after traumatic brain injury

The 'silent epidemic' of traumatic brain injury (TBI) has been placed in the spotlight as a result of clinical investigations and popular press coverage of athletes and veterans with single or repetitive head injuries. Neuroinflammation can cause acute secondary injury after TBI, and has been linked to chronic neurodegenerative diseases; however, anti-inflammatory agents have failed to improve TBI outcomes in clinical trials. In this Review, we therefore propose a new framework of targeted immunomodulation after TBI for future exploration. Our framework incorporates factors such as the time from injury, mechanism of injury, and secondary insults in considering potential treatment options. Structuring our discussion around the dynamics of the immune response to TBI - from initial triggers to chronic neuroinflammation - we consider the ability of soluble and cellular inflammatory mediators to promote repair and regeneration versus secondary injury and neurodegeneration. We summarize both animal model and human studies, with clinical data explicitly defined throughout this Review. Recent advances in neuroimmunology and TBI-responsive neuroinflammation are incorporated, including concepts of inflammasomes, mechanisms of microglial polarization, and glymphatic clearance. Moreover, we highlight findings that could offer novel therapeutic targets for translational and clinical research, assimilate evidence from other brain injury models, and identify outstanding questions in the field.

Immortalization of primary microglia: a new platform to study HIV regulation in the central nervous system

The major reservoirs for HIV in the CNS are in the microglia, perivascular macrophages, and to a lesser extent, astrocytes. To study the molecular events controlling HIV expression in the microglia, we developed a reliable and robust method to immortalize microglial cells from primary glia from fresh CNS tissues and commercially available frozen glial cells. Primary human cells, including cells obtained from adult brain tissue, were transformed with lentiviral vectors expressing SV40 T antigen or a combination of SVR40 T antigen and hTERT. The immortalized cells have microglia-like morphology and express key microglial surface markers including CD11b, TGFβR, and P2RY12. Importantly, these cells were confirmed to be of human origin by sequencing. The RNA expression profiles identified by RNA-seq are also characteristic of microglial cells. Furthermore, the cells demonstrate the expected migratory and phagocytic activity, and the capacity to mount an inflammatory response characteristic of primary microglia. The immortalization method has also been successfully applied to a wide range of microglia from other species (macaque, rat, and mouse). To investigate different aspects of HIV molecular regulation in CNS, the cells have been superinfected with HIV reporter viruses and latently infected clones have been selected that reactive HIV in response to inflammatory signals. The cell lines we have developed and rigorously characterized will provide an invaluable resource for the study of HIV infection in microglial cells as well as studies of microglial cell function.

Anti-Inflammatory Modulation of Microglia via CD163-Targeted Glucocorticoids Protects Dopaminergic Neurons in the 6-OHDA Parkinson's Disease Model

Increasing evidence supports a decisive role for inflammation in the neurodegenerative process of Parkinson's disease (PD). The immune response in PD seems to involve, not only microglia, but also other immune cells infiltrated into the brain. Indeed, we observed here the infiltration of macrophages, specifically CD163+ macrophages, into the area of neurodegeneration in the 6-hydroxydopamine (6-OHDA) PD model. Therefore, we investigated the therapeutic potential of the infiltrated CD163+ macrophages to modulate local microglia in the brain to achieve neuroprotection. To do so, we designed liposomes targeted for the CD163 receptor to deliver dexamethasone (Dexa) into the CD163+ macrophages in the 6-OHDA PD model. Our data show that a fraction of the CD163-targeted liposomes were carried into the brain after peripheral intravenous injection. The 6-OHDA-lesioned rats that received repeated intravenous CD163-targeted liposomes with Dexa for 3 weeks exhibited better motor performance than the control groups and had minimal glucocorticoid-driven side effects. Furthermore, these animals showed better survival of dopaminergic neurons in substantia nigra and an increased number of microglia expressing major histocompatibility complex II. Therefore, rats receiving CD163-targeted liposomes with Dexa were partially protected against 6-OHDA-induced dopaminergic neurodegeneration, which correlated with a distinctive microglia response. Altogether, our data support the use of macrophages for the modulation of brain neurodegeneration and specifically highlight the potential of CD163-targeted liposomes as a therapeutic tool in PD.

SIGNIFICANCE STATEMENT

The immune response now evident in the progression of Parkinson's disease comprises both local microglia and other immune cells. We provide evidence that CD163+ macrophages can be a target to modulate brain immune response to achieve neuroprotection in the 6-hydroxydopamine model. To do so, we targeted the CD163+ population, which to a low but significant extent infiltrated in the neurodegenerating area of the brain. Specially designed liposomes targeted for the CD163 receptor were loaded with glucocorticoids and injected peripherally to modify the infiltrated CD163 cells toward an anti-inflammatory profile. This modification of the CD163 population resulted in a distinctive microglial response that correlated with decreased dopaminergic cell death and better motor performance.

Age-Dependent Effects of Haptoglobin Deletion in Neurobehavioral and Anatomical Outcomes Following Traumatic Brain Injury

Cerebral hemorrhages are common features of traumatic brain injury (TBI) and their presence is associated with chronic disabilities. Recent clinical and experimental evidence suggests that haptoglobin (Hp), an endogenous hemoglobin-binding protein most abundant in blood plasma, is involved in the intrinsic molecular defensive mechanism, though its role in TBI is poorly understood. The aim of this study was to investigate the effects of Hp deletion on the anatomical and behavioral outcomes in the controlled cortical impact model using wildtype (WT) C57BL/6 mice and genetically modified mice lacking the Hp gene (Hp(-∕-)) in two age cohorts [2-4 mo-old (young adult) and 7-8 mo-old (older adult)]. The data obtained suggest age-dependent significant effects on behavioral and anatomical TBI outcomes and recovery from injury. Moreover, in the adult cohort, neurological deficits in Hp(-∕-) mice at 24 h were significantly improved compared to WT, whereas there were no significant differences in brain pathology between these genotypes. In contrast, in the older adult cohort, Hp(-∕-) mice had significantly larger lesion volumes compared to WT, but neurological deficits were not significantly different. Immunohistochemistry for ionized calcium-binding adapter molecule 1 (Iba1) and glial fibrillary acidic protein (GFAP) revealed significant differences in microglial and astrocytic reactivity between Hp(-∕-) and WT in selected brain regions of the adult but not the older adult-aged cohort. In conclusion, the data obtained in the study provide clarification on the age-dependent aspects of the intrinsic defensive mechanisms involving Hp that might be involved in complex pathways differentially affecting acute brain trauma outcomes.

Organotypic Hippocampal Slices as Models for Stroke and Traumatic Brain Injury

Organotypic hippocampal slice cultures (OHSCs) have been used as a powerful ex vivo model for decades. They have been used successfully in studies of neuronal death, microglial activation, mossy fiber regeneration, neurogenesis, and drug screening. As a pre-animal experimental phase for physiologic and pathologic brain research, OHSCs offer outcomes that are relatively closer to those of whole-animal studies than outcomes obtained from cell culture in vitro. At the same time, mechanisms can be studied more precisely in OHSCs than they can be in vivo. Here, we summarize stroke and traumatic brain injury research that has been carried out in OHSCs and review classic experimental applications of OHSCs and its limitations.

Cerebrospinal Fluid Markers of Macrophage and Lymphocyte Activation After Traumatic Brain Injury in Children

OBJECTIVES

The magnitude and role of the cellular immune response following pediatric traumatic brain injury remains unknown. We tested the hypothesis that macrophage/microglia and T-cell activation occurs following pediatric traumatic brain injury by measuring cerebrospinal fluid levels of soluble cluster of differentiation 163 and ferritin and soluble interleukin-2 receptor α, respectively, and determined whether these biomarkers were associated with relevant clinical variables and outcome.

DESIGN

Retrospective analysis of samples from an established, single-center cerebrospinal fluid bank.

SETTING

PICU in a tertiary children's hospital.

PATIENTS

Sixty-six pediatric patients after severe traumatic brain injury (Glasgow Coma Scale score < 8) who were 1 month to 16 years old and 17 control patients who were 1 month to 14 years old.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Cerebrospinal fluid levels of soluble cluster of differentiation 163, ferritin, and soluble interleukin-2 receptor α were determined by enzyme-linked immunosorbent assay at two time points (t1 = 17 ± 10 hr; t2 = 72 ± 15 hr) for each traumatic brain injury patient. Cerebrospinal fluid levels of soluble cluster of differentiation 163, ferritin, and soluble interleukin-2 receptor α after traumatic brain injury were compared with controls and analyzed for associations with age, patient sex, initial Glasgow Coma Scale score, diagnosis of abusive head trauma, the presence of hemorrhage on CT scan, and Glasgow Outcome Scale score. Cerebrospinal fluid level of soluble cluster of differentiation 163 was increased in traumatic brain injury patients at t2 versus t1 and controls (median, 95.4 ng/mL [interquartile range, 21.8-134.0 ng/mL] vs 31.0 ng/mL [5.7-77.7 ng/mL] and 27.8 ng/mL [19.1-43.1 ng/mL], respectively; p < 0.05). Cerebrospinal fluid level of ferritin was increased in traumatic brain injury patients at t2 and t1 versus controls (8.3 ng/mL [<7.5-19.8 ng/mL] and 8.9 ng/mL [<7.5-26.7 ng/mL] vs <7.5 ng/mL below lower limit of detection, respectively; p < 0.05). Cerebrospinal fluid levels of soluble interleukin-2 receptor α in traumatic brain injury patients at t2 and t1 were not different versus controls. Multivariate regression revealed associations between high ferritin and age 4 years or younger, lower Glasgow Coma Scale score, abusive head trauma, and unfavorable Glasgow Outcome Scale score.

CONCLUSIONS

Children with traumatic brain injury demonstrate evidence for macrophage activation after traumatic brain injury, and in terms of cerebrospinal fluid ferritin, this appears more prominent with young age, initial injury severity, abusive head trauma, and unfavorable outcome. Further study is needed to determine whether biomarkers of macrophage activation may be used to discriminate between aberrant and adaptive immune responses and whether inflammation represents a therapeutic target after traumatic brain injury.

Microglial HO-1 induction by curcumin provides antioxidant, antineuroinflammatory, and glioprotective effects

SCOPE

We have studied if curcumin can protect glial cells under an oxidative stress and inflammatory environment, which is known to be deleterious in neurodegeneration.

METHODS AND RESULTS

Primary rat glial cultures exposed to the combination of an oxidative (rotenone/oligomycin A) and a proinflammatory LPS stimuli reduced by 50% glial viability. Under these experimental conditions, curcumin afforded significant glial protection and reduction of reactive oxygen species; these effects were blocked by the HO-1 inhibitor tin protoporphyrin-IX (SnPP). These findings correlate with the observation that curcumin induced the antioxidative protein HO-1. Most interesting was the observation that the glial protective effects related to HO-1 induction were microglial specific as shown in glial cultures from LysM(Cre) Hmox(∆/∆) mice where curcumin lost its protective effect. Under LPS conditions, curcumin reduced the microglial proinflammatory markers iNOS and tumor necrosis factor, but increased the anti-inflammatory cytokine IL4. Analysis of the microglial phenotype showed that curcumin favored a ramified morphology toward a microglial alternative activated state against LPS insult also by a HO-1-dependent mechanism.

CONCLUSION

The curry constituent curcumin protects glial cells and promotes a microglial anti-inflammatory phenotype by a mechanism that implicates HO-1 induction; these effects may have impact on brain protection under oxidative and inflammatory conditions.

Alternatively activated microglia and macrophages in the central nervous system

Macrophages are important players in the fight against viral, bacterial, fungal and parasitic infections. From a resting state they may undertake two activation pathways, the classical known as M1, or the alternative known as M2. M1 markers are mostly mediators of pro-inflammatory responses whereas M2 markers emerge for resolution and cleanup. Microglia exerts in the central nervous system (CNS) a function similar to that of macrophages in the periphery. Microglia activation and proliferation occurs in almost any single pathology affecting the CNS. Often microglia activation has been considered detrimental and drugs able to stop microglia activation were considered for the treatment of a variety of diseases. Cumulative evidence shows that microglia may undergo the alternative activation pathway, express M2-type markers and contribute to neuroprotection. This review focuses on details about the role of M2 microglia and in the approaches available for its identification. Approaches to drive the M2 phenotype and data on its potential in CNS diseases are also reviewed.

Heme oxygenase-1 dysregulation in the brain: implications for HIV-associated neurocognitive disorders

Heme oxygenase-1 (HO-1) is a highly inducible and ubiquitous cellular enzyme that subserves cytoprotective responses to toxic insults, including inflammation and oxidative stress. In neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis, HO-1 expression is increased, presumably reflecting an endogenous neuroprotective response against ongoing cellular injury. In contrast, we have found that in human immunodeficiency virus (HIV) infection of the brain, which is also associated with inflammation, oxidative stress and neurodegeneration, HO-1 expression is decreased, likely reflecting a unique role for HO-1 deficiency in neurodegeneration pathways activated by HIV infection. We have also shown that HO-1 expression is significantly suppressed by HIV replication in cultured macrophages which represent the primary cellular reservoir for HIV in the brain. HO-1 deficiency is associated with release of neurotoxic levels of glutamate from both HIV-infected and immune-activated macrophages; this glutamate-mediated neurotoxicity is suppressed by pharmacological induction of HO-1 expression in the macrophages. Thus, HO-1 induction could be a therapeutic strategy for neuroprotection against HIV infection and other neuroinflammatory brain diseases. Here, we review various stimuli and signaling pathways regulating HO-1 expression in macrophages, which could promote neuronal survival through HO-1-modulation of endogenous antioxidant and immune modulatory pathways, thus limiting the oxidative stress that can promote HIV disease progression in the CNS. The use of pharmacological inducers of endogenous HO-1 expression as potential adjunctive neuroprotective therapeutics in HIV infection is also discussed.

M1 and M2 immune activation in Parkinson's Disease: Foe and ally?

Parkinson's Disease (PD) is a chronic and progressive neurodegenerative disorder of unknown etiology. Autopsy findings, genetics, retrospective studies, and molecular imaging all suggest a role for inflammation in the neurodegenerative process. However, relatively little is understood about the causes and implications of neuroinflammation in PD. Understanding how inflammation arises in PD, in particular the activation state of cells of the innate immune system, may provide an exciting opportunity for novel neuroprotective therapeutics. We analyze the evidence of immune system involvement in PD susceptibility, specifically in the context of M1 and M2 activation states. Tracking and modulating these activation states may provide new insights into both PD etiology and therapeutic strategies.

Redox control of microglial function: molecular mechanisms and functional significance

Neurodegenerative diseases are characterized by chronic microglial over-activation and oxidative stress. It is now beginning to be recognized that reactive oxygen species (ROS) produced by either microglia or the surrounding environment not only impact neurons but also modulate microglial activity. In this review, we first analyze the hallmarks of pro-inflammatory and anti-inflammatory phenotypes of microglia and their regulation by ROS. Then, we consider the production of reactive oxygen and nitrogen species by NADPH oxidases and nitric oxide synthases and the new findings that also indicate an essential role of glutathione (γ-glutamyl-l-cysteinylglycine) in redox homeostasis of microglia. The effect of oxidant modification of macromolecules on signaling is analyzed at the level of oxidized lipid by-products and sulfhydryl modification of microglial proteins. Redox signaling has a profound impact on two transcription factors that modulate microglial fate, nuclear factor kappa-light-chain-enhancer of activated B cells, and nuclear factor (erythroid-derived 2)-like 2, master regulators of the pro-inflammatory and antioxidant responses of microglia, respectively. The relevance of these proteins in the modulation of microglial activity and the interplay between them will be evaluated. Finally, the relevance of ROS in altering blood brain barrier permeability is discussed. Recent examples of the importance of these findings in the onset or progression of neurodegenerative diseases are also discussed. This review should provide a profound insight into the role of redox homeostasis in microglial activity and help in the identification of new promising targets to control neuroinflammation through redox control of the brain.

Macrophage subsets and microglia in multiple sclerosis

Along with microglia and monocyte-derived macrophages, macrophages in the perivascular space, choroid plexus, and meninges are the principal effector cells in neuroinflammatory and neurodegenerative disorders. These phagocytes are highly heterogeneous cells displaying spatial- and temporal-dependent identities in the healthy, injured, and inflamed CNS. In the last decade, researchers have debated on whether phagocytes subtypes and phenotypes are pathogenic or protective in CNS pathologies. In the context of this dichotomy, we summarize and discuss the current knowledge on the spatiotemporal physiology of macrophage subsets and microglia in the healthy and diseased CNS, and elaborate on factors regulating their behavior. In addition, the impact of macrophages present in lymphoid organs on CNS pathologies is defined. The prime focus of this review is on multiple sclerosis (MS), which is characterized by inflammation, demyelination, neurodegeneration, and CNS repair, and in which microglia and macrophages have been extensively scrutinized. On one hand, microglia and macrophages promote neuroinflammatory and neurodegenerative events in MS by releasing inflammatory mediators and stimulating leukocyte activity and infiltration into the CNS. On the other hand, microglia and macrophages assist in CNS repair through the production of neurotrophic factors and clearance of inhibitory myelin debris. Finally, we define how microglia and macrophage physiology can be harnessed for new therapeutics aimed at suppressing neuroinflammatory and cytodegenerative events, as well as promoting CNS repair. We conclude that microglia and macrophages are highly dynamic cells displaying disease stage and location-specific fates in neurological disorders. Changing the physiology of divergent phagocyte subsets at particular disease stages holds promise for future therapeutics for CNS pathologies.