CSF1R Inhibition Reduces Microglia Proliferation, Promotes Tissue Preservation and Improves Motor Recovery After Spinal Cord Injury

Sex and age differences in glia and myelin in nonhuman primate and human spinal cords: implications for pathology

In a healthy central nervous system, glial cells are influenced by genetic, epigenetic, age, and sex factors. Aging typically causes astrocytes and microglia to undergo changes that reduce their neuroprotective functions and increase harmful activities. Additionally, sex-related differences in glial and myelin functions may impact neurological disorders. Despite this, few studies have investigated glial cells in primates, with most focusing on the brain. This study aims to explore whether glial cells and myelin exhibit age- and sex-related differences in the spinal cord of nonhuman primates and humans. We used immunohistochemistry and myelin staining to analyze healthy spinal cord samples from midlife and aged individuals of both sexes, focusing on Microcebus murinus (a small nonhuman primate) and humans. Primate spinal cords show distinct variations in glial markers and myelin characteristics related to sex and age, with differences varying between species. Notably, GFAP expression is sex-dependent in both primate species. We also observed greater differences in the expression of microglial markers than other glial markers. Overall, we found the opposite pattern for the g-ratio and oligodendrocytic marker between species. These findings suggest that glial cells may play a critical role in age- and sex-related differences in the prevalence and progression of spinal cord diseases.

Microglia Promote Lymphangiogenesis Around the Spinal Cord Through VEGF-C/VEGFR3-Dependent Autophagy and Polarization After Acute Spinal Cord Injury

Reducing secondary injury is a key focus in the field of spinal cord injury (SCI). Recent studies have revealed the role of lymphangiogenesis in reducing secondary damage to central nerve. However, the mechanism of lymphangiogenesis is not yet clear. Macrophages have been shown to play an important role in peripheral tissue lymphangiogenesis. Microglia is believed to play a role similar to macrophages in the central nervous system (CNS); we hypothesized that there was a close relationship between microglia and central nerve system lymphangiogenesis. Herein, we used an in vivo model of SCI to explored the relationship between microglia and spinal cord lymphangiogenesis and further investigated the polarization of microglia and its role in promoting spinal cord lymphangiogenesis by a series of in vitro experiments. The current study elucidated for the first time the relationship between microglia and lymphangiogenesis around the spinal cord after SCI. Classical activated (M1) microglia can promote lymphangiogenesis by secreting VEGF-C which further increases polarization and secretion of lymphatic growth factor by activating VEGFR3. The VEGF-C/VEGFR3 pathway activation downregulates microglia autophagy, thereby regulating the microglia phenotype. These results indicate that M1 microglia promote lymphangiogenesis after SCI, and activated VEGF-C/VEGFR3 signaling promotes M1 microglia polarization by inhibiting autophagy, thereby facilitates lymphangiogenesis.

Chemical Composition, In Vivo, and In Silico Molecular Docking Studies of the Effect of Syzygium aromaticum (Clove) Essential Oil on Ochratoxin A-Induced Acute Neurotoxicity

The aim of our research was to understand the impact of ochratoxin A (OTA) exposure on various physiological and behavioral aspects in adult Wistar rats, and to evaluate the efficacy of a Syzygium aromaticum essential oil (EOC) treatment in restoring the damage caused by this toxin. The essential oils were extracted by hydrodistillation, a yield of 12.70% was obtained for EOC, and the GC-MS characterization of this essential oil revealed that its principal major components are eugenol (80.95%), eugenyl acetate (10.48%), β-caryophyllene (7.21%), and α-humulene (0.87%). Acute OTA intoxication was induced by an intraperitoneal (IP) injection of 289 µg/kg/b.w. every 48 h for 12 doses, resulting in significant reductions in the body and brain weights of exposed rats when compared with controls. The neurobehavioral analysis using several behavioral testing techniques, such as the forced swimming, the dark/light test, the Morris water maze, and the open field test, clearly revealed that OTA exposure causes neurobehavioral disorders, including decreased locomotor activity, a reduced willingness to explore the environment, reflecting a state of stress, anxiety and depression, as well as impaired memory and learning. In addition, OTA intoxication has been associated with metabolic disturbances such as hyperglycemia and hypercortisolemia. However, treatment with EOC mitigated these adverse effects by improving body and brain weights and restoring neurobehavioral function. The in silico analysis revealed significant affinities between clove oils and two tested esterase enzymes (ACh and BuChE) that were more than or similar to the four neurotransmitters "dopamine, serotonin, norepinephrine, and glutamic acid" and the co-crystallized ligands NAG, MES, and GZ5. These results highlight the therapeutic potential of EOC in combating the toxic effects of OTA and pave the way for future research into the mechanisms of action and therapeutic applications of natural compounds in the prevention and treatment of poison-induced diseases.

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

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

Long-term reprogramming of primed microglia after moderate inhibition of CSF1R signaling

In acute neuroinflammation, microglia activate transiently, and return to a resting state later on. However, they may retain immune memory of such event, namely priming. Primed microglia are more sensitive to new stimuli and develop exacerbated responses, representing a risk factor for neurological disorders with an inflammatory component. Strategies to control the hyperactivation of microglia are, hence, of great interest. The receptor for colony stimulating factor 1 (CSF1R), expressed in myeloid cells, is essential for microglia viability, so its blockade with specific inhibitors (e.g. PLX5622) results in significant depletion of microglial population. Interestingly, upon inhibitor withdrawal, new naïve microglia repopulate the brain. Depletion-repopulation has been proposed as a strategy to reprogram microglia. However, substantial elimination of microglia is inadvisable in human therapy. To overcome such drawback, we aimed to reprogram long-term primed microglia by CSF1R partial inhibition. Microglial priming was induced in mice by acute neuroinflammation, provoked by intracerebroventricular injection of neuraminidase. After 3-weeks recovery, low-dose PLX5622 treatment was administrated for 12 days, followed by a withdrawal period of 7 weeks. Twelve hours before euthanasia, mice received a peripheral lipopolysaccharide (LPS) immune challenge, and the subsequent microglial inflammatory response was evaluated. PLX5622 provoked a 40%-50% decrease in microglial population, but basal levels were restored 7 weeks later. In the brain regions studied, hippocampus and hypothalamus, LPS induced enhanced microgliosis and inflammatory activation in neuraminidase-injected mice, while PLX5622 treatment prevented these changes. Our results suggest that PLX5622 used at low doses reverts microglial priming and, remarkably, prevents broad microglial depletion.

Temporal changes of spinal microglia in murine models of neuropathic pain: a scoping review

Neuropathic pain (NP) is an ineffectively treated, debilitating chronic pain disorder that is associated with maladaptive changes in the central nervous system, particularly in the spinal cord. Murine models of NP looking at the mechanisms underlying these changes suggest an important role of microglia, the resident immune cells of the central nervous system, in various stages of disease progression. However, given the number of different NP models and the resource limitations that come with tracking longitudinal changes in NP animals, many studies fail to truly recapitulate the patterns that exist between pain conditions and temporal microglial changes. This review integrates how NP studies are being carried out in murine models and how microglia changes over time can affect pain behavior in order to inform better study design and highlight knowledge gaps in the field. 258 peer-reviewed, primary source articles looking at spinal microglia in murine models of NP were selected using Covidence. Trends in the type of mice, statistical tests, pain models, interventions, microglial markers and temporal pain behavior and microglia changes were recorded and analyzed. Studies were primarily conducted in inbred, young adult, male mice having peripheral nerve injury which highlights the lack of generalizability in the data currently being collected. Changes in microglia and pain behavior, which were both increased, were tested most commonly up to 2 weeks after pain initiation despite aberrant microglia activity also being recorded at later time points in NP conditions. Studies using treatments that decrease microglia show decreased pain behavior primarily at the 1- and 2-week time point with many studies not recording pain behavior despite the involvement of spinal microglia dysfunction in their development. These results show the need for not only studying spinal microglia dynamics in a variety of NP conditions at longer time points but also for better clinically relevant study design considerations.

Neonatal Brain Injury Triggers Niche-Specific Changes to Cellular Biogeography

Preterm infants are at risk for brain injury and neurodevelopmental impairment due, in part, to white matter injury following chronic hypoxia exposure. However, the precise molecular mechanisms by which neonatal hypoxia disrupts early neurodevelopment are poorly understood. Here, we constructed a brain-wide map of the regenerative response to newborn brain injury using high-resolution imaging-based spatial transcriptomics to analyze over 800,000 cells in a mouse model of chronic neonatal hypoxia. Additionally, we developed a new method for inferring condition-associated differences in cell type spatial proximity, enabling the identification of niche-specific changes in cellular architecture. We observed hypoxia-associated changes in region-specific cell states, cell type composition, and spatial organization. Importantly, our analysis revealed mechanisms underlying reparative neurogenesis and gliogenesis, while also nominating pathways that may impede circuit rewiring following neonatal hypoxia. Altogether, our work provides a comprehensive description of the molecular response to newborn brain injury.

High-Efficiency, Prevascularization-Free Macroencapsulation System for Subcutaneous Transplantation of Pancreatic Islets for Enhanced Diabetes Treatment

Pancreatic islet macroencapsulation systems for subcutaneous transplantation have garnered significant attention as a therapy for Type I diabetes due to their minimal invasiveness and low complication rates. However, the low vascular density of subcutaneous tissue threatens the long-term survival of islets. To address this issue, prevascularized systems are introduced but various challenges remain, including system complexity and vascular-cell immunogenicity. Here, a novel prevasculature-free macroencapsulation system designed as a multilayer sheet, which ensures sufficient mass transport even in regions with sparse vasculature, is presented. Islets are localized in top/bottom micro-shell layers (≈300 µm thick) to maximize proximity to the surrounding host vasculature. These sheets, fabricated via bioprinting using rat islets and alginate-based bio-ink, double islet viability and optimize islet density, improving insulin secretion function by 240%. The subcutaneous transplantation of small islet masses (≈250 islet equivalent) into diabetic nude mice enable rapid (<1 day) recovery of blood glucose, which remain stable for >120 days. Additionally, antifibrotic drug-loaded multilayer sheets facilitate blood glucose regulation by rat islets at the subcutaneous sites of diabetic immunocompetent mice for >35 days. Thus, this macroencapsulation system can advance the treatment of Type I diabetes and is also effective for islet xenotransplantation in subcutaneous tissue.

Regenerative medicine approaches for the treatment of spinal cord injuries: Progress and challenges

Spinal cord injury (SCI) is a profound medical condition that significantly hampers motor function, imposing substantial limitations on daily activities and exerting a considerable financial burden on patients and their families. The constrained regenerative capacity of endogenous spinal cord tissue, exacerbated by the inflammatory response following the initial trauma, poses a formidable obstacle to effective therapy. Recent advancements in the field, stem cells, biomaterials, and molecular therapy, show promising outcomes. This review provides a comprehensive analysis of tissue engineering and regenerative medicine approaches for SCI treatment, including cell transplantation, tissue-engineered construct implantation, and other potential therapeutic strategies. Additionally, it sheds light on preclinical animal studies and recent clinical trials incorporating these modalities, providing a glimpse into the evolving landscape of SCI management. STATEMENT OF SIGNIFICANCE: The investigation into spinal cord injury (SCI) treatments focuses on reducing long-term impacts by targeting scar inhibition and enhancing regeneration through stem cells, with or without growth factors. Induced pluripotent stem cells (iPSCs) show promise for autologous use, with clinical trials confirming their safety. Challenges include low cell viability and difficulty in targeted differentiation. Biomaterial scaffolds hold potential for improving cell viability and integration, and extracellular vesicles (EVs) are emerging as a novel therapy. While EV research is in its early stages, stem cell trials demonstrate safety and potential recovery. Advancing tissue engineering approaches with biomaterial scaffolds is crucial for human trials.

Neuromodulation with transcranial direct current stimulation contributes to motor function recovery via microglia in spinal cord injury

Spinal cord injury (SCI) is damage or trauma to the spinal cord, which often results in loss of function, sensation, or mobility below the injury site. Transcranial direct current stimulation (tDCS) is a non-invasive and affordable brain stimulation technique used to modulate neuronal circuits, which changes the morphology and activity of microglia in the cerebral cortex. However, whether similar morphological changes can be observed in the spinal cord remains unclear. Therefore, we evaluated neuronal population activity in layer 5 (L5) of M1 following SCI and investigated whether changes in the activities of L5 neurons affect microglia-axon interactions using C57BL/6J mice. We discovered that L5 of the primary motor cortex (corticospinal neurons) exhibited reduced synchronized activity after SCI that correlates with microglial morphology, which was recovered using tDCS. This indicates that tDCS promotes changes in the morphological properties and recovery of microglia after SCI. Combining immunotherapy with tDCS may be effective in treating SCI.

CSF1R blockade slows progression of cerebral hemorrhage by reducing microglial proliferation and increasing infiltration of CD8 + CD122+ T cells into the brain

Microglia play a pivotal role in the neuroinflammatory response after brain injury, and their proliferation is dependent on colony-stimulating factors. In the present study, we investigated the effect of inhibiting microglia proliferation on neurological damage post intracerebral hemorrhage (ICH) in a mouse model, an aspect that has never been studied before. Using a colony-stimulating factor-1 receptor antagonist (GW2580), we observed that inhibition of microglia proliferation significantly ameliorated neurobehavioral deficits, attenuated cerebral edema, and reduced hematoma volume after ICH. This intervention was associated with a decrease in pro-inflammatory factors in microglia and an increased infiltration of peripheral regulatory CD8 + CD122+ T cells into the injured brain tissue. The CXCR3/CXCL10 axis is the mechanism of brain homing of regulatory CD8 + CD122+ T cells, and the high expression of IL-10 is the hallmark of their synergistic anti-inflammatory effect with microglia. And activated astrocytes around the insult site are a prominent source of CXCL10. Thus, inhibition of microglial proliferation offers a new perspective for clinical translation. The cross-talk between multiple cells involved in the regulation of the inflammatory response highlights the comprehensive nature of neuroimmunomodulation.

Human Glial Cells as Innovative Targets for the Therapy of Central Nervous System Pathologies

In vitro and preclinical in vivo research in the last 35 years has clearly highlighted the crucial physiopathological role of glial cells, namely astrocytes/microglia/oligodendrocytes and satellite glial cells/Schwann cells in the central and peripheral nervous system, respectively. Several possible pharmacological targets to various neurodegenerative disorders and painful conditions have therefore been successfully identified, including receptors and enzymes, and mediators of neuroinflammation. However, the translation of these promising data to a clinical setting is often hampered by both technical and biological difficulties, making it necessary to perform experiments on human cells and models of the various diseases. In this review we will, therefore, summarize the most relevant data on the contribution of glial cells to human pathologies and on their possible pharmacological modulation based on data obtained in post-mortem tissues and in iPSC-derived human brain cells and organoids. The possibility of an in vivo visualization of glia reaction to neuroinflammation in patients will be also discussed.

Allogenic microglia replacement: A novel therapeutic strategy for neurological disorders

Microglia are resident immune cells in the central nervous system (CNS) that play vital roles in CNS development, homeostasis and disease pathogenesis. Genetic defects in microglia lead to microglial dysfunction, which in turn leads to neurological disorders. The correction of the specific genetic defects in microglia in these disorders can lead to therapeutic effects. Traditional genetic defect correction approaches are dependent on viral vector-based genetic defect corrections. However, the viruses used in these approaches, including adeno-associated viruses, lentiviruses and retroviruses, do not primarily target microglia; therefore, viral vector-based genetic defect corrections are ineffective in microglia. Microglia replacement is a novel approach to correct microglial genetic defects via replacing microglia of genetic defects with allogenic healthy microglia. In this paper, we systematically review the history, rationale and therapeutic perspectives of microglia replacement, which would be a novel strategy for treating CNS disorders.

Deplete and repeat: microglial CSF1R inhibition and traumatic brain injury

Traumatic brain injury (TBI) is a public health burden affecting millions of people. Sustained neuroinflammation after TBI is often associated with poor outcome. As a result, increased attention has been placed on the role of immune cells in post-injury recovery. Microglia are highly dynamic after TBI and play a key role in the post-injury neuroinflammatory response. Therefore, microglia represent a malleable post-injury target that could substantially influence long-term outcome after TBI. This review highlights the cell specific role of microglia in TBI pathophysiology. Microglia have been manipulated via genetic deletion, drug inhibition, and pharmacological depletion in various pre-clinical TBI models. Notably, colony stimulating factor 1 (CSF1) and its receptor (CSF1R) have gained much traction in recent years as a pharmacological target on microglia. CSF1R is a transmembrane tyrosine kinase receptor that is essential for microglia proliferation, differentiation, and survival. Small molecule inhibitors targeting CSF1R result in a swift and effective depletion of microglia in rodents. Moreover, discontinuation of the inhibitors is sufficient for microglia repopulation. Attention is placed on summarizing studies that incorporate CSF1R inhibition of microglia. Indeed, microglia depletion affects multiple aspects of TBI pathophysiology, including neuroinflammation, oxidative stress, and functional recovery with measurable influence on astrocytes, peripheral immune cells, and neurons. Taken together, the data highlight an important role for microglia in sustaining neuroinflammation and increasing risk of oxidative stress, which lends to neuronal damage and behavioral deficits chronically after TBI. Ultimately, the insights gained from CSF1R depletion of microglia are critical for understanding the temporospatial role that microglia develop in mediating TBI pathophysiology and recovery.

Colony Stimulating Factor-1 Receptor: An emerging target for neuroinflammation PET imaging and AD therapy

Although neuroinflammation is a significant pathogenic feature of many neurologic disorders, its precise function in-vivo is still not completely known. PET imaging enables the longitudinal examination, quantification, and tracking of different neuroinflammation biomarkers in living subjects. Particularly, PET imaging of Microglia, specialised dynamic immune cells crucial for maintaining brain homeostasis in central nervous system (CNS), is crucial for staging the neuroinflammation. Colony Stimulating Factor- 1 Receptor (CSF-1R) PET imaging is a novel method for the quantification of neuroinflammation. CSF-1R is mainly expressed on microglia, and neurodegenerative disorders greatly up-regulate its expression. The present review primarily focuses on the development, pros and cons of all the CSF-1R PET tracers reported for neuroinflammation imaging. Apart from neuroinflammation imaging, CSF-1R inhibitors are also reported for the therapy of neurodegenerative diseases such as Alzheimer's disease (AD). AD is a prevalent, advancing, and fatal neurodegenerative condition that have the characteristic feature of persistent neuroinflammation and primarily affects the elderly. The aetiology of AD is profoundly influenced by amyloid-beta (Aβ) plaques, intracellular neurofibrillary tangles, and microglial dysfunction. Increasing evidence suggests that CSF-1R inhibitors (CSF-1Ri) can be helpful in preclinical models of neurodegenerative diseases. This review article also summarises the most recent developments of CSF-1Ri-based therapy for AD.

Inhibiting CSF1R alleviates cerebrovascular white matter disease and cognitive impairment

White matter abnormalities, related to poor cerebral perfusion, are a core feature of small vessel cerebrovascular disease, and critical determinants of vascular cognitive impairment and dementia. Despite this importance there is a lack of treatment options. Proliferation of microglia producing an expanded, reactive population and associated neuroinflammatory alterations have been implicated in the onset and progression of cerebrovascular white matter disease, in patients and in animal models, suggesting that targeting microglial proliferation may exert protection. Colony-stimulating factor-1 receptor (CSF1R) is a key regulator of microglial proliferation. We found that the expression of CSF1R/Csf1r and other markers indicative of increased microglial abundance are significantly elevated in damaged white matter in human cerebrovascular disease and in a clinically relevant mouse model of chronic cerebral hypoperfusion and vascular cognitive impairment. Using the mouse model, we investigated long-term pharmacological CSF1R inhibition, via GW2580, and demonstrated that the expansion of microglial numbers in chronic hypoperfused white matter is prevented. Transcriptomic analysis of hypoperfused white matter tissue showed enrichment of microglial and inflammatory gene sets, including phagocytic genes that were the predominant expression modules modified by CSF1R inhibition. Further, CSF1R inhibition attenuated hypoperfusion-induced white matter pathology and rescued spatial learning impairments and to a lesser extent cognitive flexibility. Overall, this work suggests that inhibition of CSF1R and microglial proliferation mediates protection against chronic cerebrovascular white matter pathology and cognitive deficits. Our study nominates CSF1R as a target for the treatment of vascular cognitive disorders with broader implications for treatment of other chronic white matter diseases.

Highly dynamic inflammatory and excitability transcriptional profiles in hippocampal CA1 following status epilepticus

Transient brain insults including status epilepticus (SE) can initiate a process termed 'epileptogenesis' that results in chronic temporal lobe epilepsy. As a consequence, the entire tri-synaptic circuit of the hippocampus is fundamentally impaired. A key role in epileptogenesis has been attributed to the CA1 region as the last relay station in the hippocampal circuit and as site of aberrant plasticity, e.g. mediated by acquired channelopathies. The transcriptional profiles of the distinct hippocampal neurons are highly dynamic during epileptogenesis. Here, we aimed to elucidate the early SE-elicited mRNA signature changes and the respective upstream regulatory cascades in CA1. RNA sequencing of CA1 was performed in the mouse pilocarpine-induced SE model at multiple time points ranging from 6 to 72 h after the initial insult. Bioinformatics was used to decipher altered gene expression, signalling cascades and their corresponding cell type profiles. Robust transcriptomic changes were detected at 6 h after SE and at subsequent time points during early epileptogenesis. Major differentially expressed mRNAs encoded primarily immediate early and excitability-related gene products, as well as genes encoding immune signalling factors. Binding sites for the transcription factors Nfkb1, Spi1, Irf8, and two Runx family members, were enriched within promoters of differentially expressed genes related to major inflammatory processes, whereas the transcriptional repressors Suz12, Nfe2l2 and Rest were associated with hyperexcitability and GABA / glutamate receptor activity. CA1 quickly responds to SE by inducing transcription of genes linked to inflammation and excitation stress. Transcription factors mediating this transcriptomic switch represent targets for new highly selected, cell type and time window-specific anti-epileptogenic strategies.

CSF1R inhibition at chronic stage after spinal cord injury modulates microglia proliferation

Traumatic spinal cord injury (SCI) induces irreversible autonomic and sensory-motor impairments. A large number of patients exhibit chronic SCI and no curative treatment is currently available. Microglia are predominant immune players after SCI, they undergo highly dynamic processes, including proliferation and morphological modification. In a translational aim, we investigated whether microglia proliferation persists at chronic stage after spinal cord hemisection and whether a brief pharmacological treatment could modulate microglial responses. We first carried out a time course analysis of SCI-induced microglia proliferation associated with morphological analysis up to 84 days post-injury (dpi). Second, we analyzed outcomes on microglia of an oral administration of GW2580, a colony stimulating factor-1 receptor tyrosine kinase inhibitor reducing selectively microglia proliferation. After SCI, microglia proliferation remains elevated at 84 dpi. The percentage of proliferative microglia relative to proliferative cells increases over time reaching almost 50% at 84 dpi. Morphological modifications of microglia processes are observed up to 84 dpi and microglia cell body area is transiently increased up to 42 dpi. A transient post-injury GW2580-delivery at two chronic stages after SCI (42 and 84 dpi) reduces microglia proliferation and modifies microglial morphology evoking an overall limitation of secondary inflammation. Finally, transient GW2580-delivery at chronic stage after SCI modulates myelination processes. Together our study shows that there is a persistent microglia proliferation induced by SCI and that a pharmacological treatment at chronic stage after SCI modulates microglial responses. Thus, a transient oral GW2580-delivery at chronic stage after injury may provide a promising therapeutic strategy for chronic SCI patients.

Microglia/macrophages are ultrastructurally altered by their proximity to spinal cord injury in adult female mice

Traumatic spinal cord injury can cause immediate physical damage to the spinal cord and result in severe neurological deficits. The primary, mechanical tissue damage triggers a variety of secondary damage mechanisms at the injury site which significantly contribute to a larger lesion size and increased functional damage. Inflammatory mechanisms which directly involve both microglia (MG) and monocyte-derived macrophages (MDM) play important roles in the post-injury processes, including inflammation and debris clearing. In the current study, we investigated changes in the structure and function of MG/MDM in the injured spinal cord of adult female mice, 7 days after a thoracic contusion SCI. With the use of chip mapping scanning electron microscopy, which allows to image large samples at the nanoscale, we performed an ultrastructural comparison of MG/MDM located near the lesion vs adjacent regions to provide novel insights into the mechanisms at play post-injury. We found that MG/MDM located near the lesion had more mitochondria overall, including mitochondria with and without morphological alterations, and had a higher proportion of altered mitochondria. MG/MDM near the lesion also showed an increased number of phagosomes, including phagosomes containing myelin and partiallydigested materials. MG/MDM near the injury interacted differently with the spinal cord parenchyma, as shown by their reduced number of direct contacts with synaptic elements, axon terminals and dendritic spines. In this study, we characterized the ultrastructural changes of MG/MDM in response to spinal cord tissue damage in mice, uncovering changes in phagocytic activity, mitochondrial ultrastructure, and inter-cellular interactions within the spinal cord parenchyma.

Single-Cell Sequencing Reveals the Optimal Time Window for Anti-Inflammatory Treatment in Spinal Cord Injury

Though the occurrence of neuroinflammation after spinal cord injury (SCI) is essential for antigen clearance and tissue repair, excessive inflammation results in cell death and axon dieback. The effect of anti-inflammatory medicine used in clinical treatment remains debatable owing to the inappropriate therapeutic schedule that does not align with the biological process of immune reaction. A better understanding of the immunity process is critical to promote effective anti-inflammatory therapeutics. However, cellular heterogeneity, which results in complex cellular functions, is a major challenge. This study performs single-cell RNA sequencing by profiling the tissue proximity to the injury site at different time points after SCI. Depending on the analysis of single-cell data and histochemistry observation, an appropriate time window for anti-inflammatory medicine treatment is proposed. This work also verifies the mechanism of typical anti-inflammatory medicine methylprednisolone sodium succinate (MPSS), which is found attributable to the activation inhibition of cells with pro-inflammatory phenotype through the downregulation of pathways such as TNF, IL2, and MIF. These pathways can also be provided as targets for anti-inflammatory treatment. Collectively, this work provides a therapeutic schedule of 1-3 dpi (days post injury) to argue against classical early pulse therapy and provides some pathways for target therapy in the future.

Organization of collagen fibers and tissue hardening: Markers of fibrotic scarring after spinal cord injury in mice revealed by multiphoton-atomic force microscopy imaging

Spinal cord injury is a dramatic disease leading to severe motor, sensitive and autonomic impairments. After injury the axonal regeneration is partly inhibited by the glial scar, acting as a physical and chemical barrier. The scarring process involves microglia, astrocytes and extracellular matrix components, such as collagen, constructing the fibrotic component of the scar. To investigate the role of collagen, we used a multimodal label-free imaging approach combining multiphoton and atomic force microscopy. The second harmonic generation signal exhibited by fibrillar collagen enabled to specifically monitor it as a biomarker of the lesion. An increase in collagen density and the formation of more tortuous fibers over time after injury are observed. Nano-mechanical investigations revealed a noticeable hardening of the injured area, correlated with collagen fibers' formation. These observations indicate the concomitance of important structural and mechanical modifications during the fibrotic scar evolution.

CSF-1 and Notch signaling cooperate in macrophage instruction and tissue repair during peripheral limb ischemia

Ischemia causes an inflammatory response featuring monocyte-derived macrophages (MF) involved in angiogenesis and tissue repair. Angiogenesis and ischemic macrophage differentiation are regulated by Notch signaling via Notch ligand Delta-like 1 (Dll1). Colony stimulating factor 1 (CSF-1) is an essential MF lineage factor, but its role in ischemic macrophage development and the interaction with Notch signaling is so far unclear. Using a mouse model of hind limb ischemia with CSF-1 inhibitor studies and Dll1 heterozygous mice we show that CSF-1 is induced in the ischemic niche by a subpopulation of stromal cells expressing podoplanin, which was paralleled by the development of ischemic macrophages. Inhibition of CSF-1 signaling with small molecules or blocking antibodies impaired macrophage differentiation but prolonged the inflammatory response, resulting in impaired perfusion recovery and tissue regeneration. Yet, despite high levels of CSF-1, macrophage maturation and perfusion recovery were impaired in mice with Dll1 haploinsufficiency, while inflammation was exaggerated. In vitro, CSF-1 was not sufficient to induce full MF differentiation from donor monocytes in the absence of recombinant DLL1, while the presence of DLL1 in a dose-dependent manner stimulated MF differentiation in combination with CSF-1. Thus, CSF-1 is an ischemic niche factor that cooperates with Notch signaling in a non-redundant fashion to instruct macrophage cell fate and maturation, which is required for ischemic perfusion recovery and tissue repair.

The Role of Microglial Depletion Approaches in Pathological Condition of CNS

Microglia are the primary immune cells of the central nervous system (CNS) that comprise about 5-12% of all cells in the brain. These cells are the first line of defense that protects the CNS from damage and attacking pathogens. Microglia originate from yolk sac macrophages and migrate to the brain before the blood-brain barrier formation. Microglia show key roles in healthy CNS including promoting neurogenesis, synaptic sculpting, and maintaining homeostasis but in pathological conditions of CNS, microglial activation may exacerbate diseases. Thus, microglial depletion of the CNS is a novel approach that could be a useful tool to understand the microglial functions in neurodegenerative and neuroinflammatory diseases. There are methods for microglial ablation and reduction such as genetic tools and pharmacological inhibitors. In this study, we review recent studies that used different microglial ablation models for microglial reduction and repopulation after depletion in pathological states of CNS. Recently, studies showed that microglial depletion as a potential therapeutic application has benefits (such as inflammatory factors reduction, increase synaptogenesis, astrogliosis preventation) in CNS. For these reasons, the inhibition of microglia with these models was considered a therapeutic approach for neurodegenerative disease treatment.

Temporal dynamics of microglia-astrocyte interaction in neuroprotective glial scar formation after intracerebral hemorrhage

The role of glial scar after intracerebral hemorrhage (ICH) remains unclear. This study aimed to investigate whether microglia-astrocyte interaction affects glial scar formation and explore the specific function of glial scar. We used a pharmacologic approach to induce microglial depletion during different ICH stages and examine how ablating microglia affects astrocytic scar formation. Spatial transcriptomics (ST) analysis was performed to explore the potential ligand-receptor pair in the modulation of microglia-astrocyte interaction and to verify the functional changes of astrocytic scars at different periods. During the early stage, sustained microglial depletion induced disorganized astrocytic scar, enhanced neutrophil infiltration, and impaired tissue repair. ST analysis indicated that microglia-derived insulin like growth factor 1 (IGF1) modulated astrocytic scar formation via mechanistic target of rapamycin (mTOR) signaling activation. Moreover, repopulating microglia (RM) more strongly activated mTOR signaling, facilitating a more protective scar formation. The combination of IGF1 and osteopontin (OPN) was necessary and sufficient for RM function, rather than IGF1 or OPN alone. At the chronic stage of ICH, the overall net effect of astrocytic scar changed from protective to destructive and delayed microglial depletion could partly reverse this. The vital insight gleaned from our data is that sustained microglial depletion may not be a reasonable treatment strategy for early-stage ICH. Inversely, early-stage IGF1/OPN treatment combined with late-stage PLX3397 treatment is a promising therapeutic strategy. This prompts us to consider the complex temporal dynamics and overall net effect of microglia and astrocytes, and develop elaborate treatment strategies at precise time points after ICH.

The Role of Mesenchymal Stromal Cells and Their Products in the Treatment of Injured Spinal Cords

Spinal cord injury (SCI) is a destructive condition that results in lasting neurological damage resulting in disruption of the connection between the central nervous system and the rest of the body. Currently, there are several approaches in the treatment of a damaged spinal cord; however, none of the methods allow the patient to return to the original full-featured state of life before the injury. Cell transplantation therapies show great potential in the treatment of damaged spinal cords. The most examined type of cells used in SCI research are mesenchymal stromal cells (MSCs). These cells are at the center of interest of scientists because of their unique properties. MSCs regenerate the injured tissue in two ways: (i) they are able to differentiate into some types of cells and so can replace the cells of injured tissue and (ii) they regenerate tissue through their powerful known paracrine effect. This review presents information about SCI and the treatments usually used, aiming at cell therapy using MSCs and their products, among which active biomolecules and extracellular vesicles predominate.

BMP7 Attenuates Neuroinflammation after Spinal Cord Injury by Suppressing the Microglia Activation and Inducing Microglial Polarization Via the STAT3 Pathway

Excessive activation of pro-inflammatory (M1) microglia phenotypes after spinal cord injury (SCI) disrupts tissue repair and increases the risk of secondary SCI. We previously reported that adeno-associated virus (AAV) mediated delivery of bone morphogenetic protein 7 (BMP7) promotes functional recovery after SCI by reducing oligodendrocyte loss and demyelination; however, little is known about the early effects of BMP7 in ameliorating neuroinflammation in the acute SCI phase. Herein, we demonstrate that treatment with recombinant human BMP7 (rhBMP7) suppresses the viability of LPS-induced HMC3 microglia cells and increases the proportion with the M2 phenotype. Consistently, in a rat SCI model, rhBMP7 decreases the activation of microglia and promotes M2 polarization. After rhBMP7 administration, the STAT3 signaling pathway was activated in LPS-induced HMC3 cells and microglia in spinal cord lesions. Furthermore, the levels of TNF-α and IL-1β were significantly decreased in cell culture supernatants, lesion sites of injured spinal cords, and cerebrospinal fluid circulation after rhBMP7 administration, thus reducing neuron loss in the injured spinal cord and promoting functional recovery after SCI. These results provide insight into the immediate early mechanisms by which BMP7 may ameliorate the inflammation response to secondary SCI.

Syk inhibitors protect against microglia-mediated neuronal loss in culture

Microglia are brain macrophages and play beneficial and/or detrimental roles in many brain pathologies because of their inflammatory and phagocytic activity. Microglial inflammation and phagocytosis are thought to be regulated by spleen tyrosine kinase (Syk), which is activated by multiple microglial receptors, including TREM2 (Triggering Receptor Expressed on Myeloid Cells 2), implicated in neurodegeneration. Here, we have tested whether Syk inhibitors can prevent microglia-dependent neurodegeneration induced by lipopolysaccharide (LPS) in primary neuron-glia cultures. We found that the Syk inhibitors BAY61-3606 and P505-15 (at 1 and 10 μM, respectively) completely prevented the neuronal loss induced by LPS, which was microglia-dependent. Syk inhibition also prevented the spontaneous loss of neurons from older neuron-glia cultures. In the absence of LPS, Syk inhibition depleted microglia from the cultures and induced some microglial death. However, in the presence of LPS, Syk inhibition had relatively little effect on microglial density (reduced by 0-30%) and opposing effects on the release of two pro-inflammatory cytokines (IL-6 decreased by about 45%, TNFα increased by 80%). Syk inhibition also had no effect on the morphological transition of microglia exposed to LPS. On the other hand, inhibition of Syk reduced microglial phagocytosis of beads, synapses and neurons. Thus, Syk inhibition in this model is most likely neuroprotective by reducing microglial phagocytosis, however, the reduced microglial density and IL-6 release may also contribute. This work adds to increasing evidence that Syk is a key regulator of the microglial contribution to neurodegenerative disease and suggests that Syk inhibitors may be used to prevent excessive microglial phagocytosis of synapses and neurons.

Up-Regulation of Astrocytic Fgfr4 Expression in Adult Mice after Spinal Cord Injury

Spinal cord injury (SCI) leads to persistent neurological deficits without available curative treatment. After SCI astrocytes within the lesion vicinity become reactive, these undergo major morphological, and molecular transformations. Previously, we reported that following SCI, over 10% of resident astrocytes surrounding the lesion spontaneously transdifferentiate towards a neuronal phenotype. Moreover, this conversion is associated with an increased expression of fibroblast growth factor receptor 4 (Fgfr4), a neural stem cell marker, in astrocytes. Here, we evaluate the therapeutic potential of gene therapy upon Fgfr4 over-expression in mature astrocytes following SCI in adult mice. We found that Fgfr4 over-expression in astrocytes immediately after SCI improves motor function recovery; however, it may display sexual dimorphism. Improved functional recovery is associated with a decrease in spinal cord lesion volume and reduced glial reactivity. Cell-specific transcriptomic profiling revealed concomitant downregulation of Notch signaling, and up-regulation of neurogenic pathways in converting astrocytes. Our findings suggest that gene therapy targeting Fgfr4 over-expression in astrocytes after injury is a feasible therapeutic approach to improve recovery following traumatism of the spinal cord. Moreover, we stress that a sex-dependent response to astrocytic modulation should be considered for the development of effective translational strategies in other neurological disorders.

Construction of a searchable database for gene expression changes in spinal cord injury experiments

Spinal cord injury (SCI) is a debilitating disease resulting in an estimated 18,000 new cases in the United States on an annual basis. Significant behavioral research on animal models has led to a large amount of data, some of which has been catalogued in the Open Data Commons for Spinal Cord Injury (ODC-SCI). More recently, high throughput sequencing experiments have been utilized to understand molecular mechanisms associated with SCI, with nearly 6,000 samples from over 90 studies available in the Sequence Read Archive. However, to date, no resource is available for efficiently mining high throughput sequencing data from SCI experiments. Therefore, we have developed a protocol for processing RNA-Seq samples from high-throughput sequencing experiments related to SCI resulting in both raw and normalized data that can be efficiently mined for comparisons across studies as well as homologous discovery across species. We have processed 1,196 publicly available RNA-seq samples from 50 bulk RNA-Seq studies across nine different species, resulting in an SQLite database that can be used by the SCI research community for further discovery. We provide both the database as well as a web-based front-end that can be used to query the database for genes of interest, differential gene expression, genes with high variance, and gene set enrichments.

Transplanting Microglia for Treating CNS Injuries and Neurological Diseases and Disorders, and Prospects for Generating Exogenic Microglia

Microglia are associated with a wide range of both neuroprotective and neuroinflammatory functions in the central nervous system (CNS) during development and throughout lifespan. Chronically activated and dysfunctional microglia are found in many diseases and disorders, such as Alzheimer's disease, Parkinson's disease, and CNS-related injuries, and can accelerate or worsen the condition. Transplantation studies designed to replace and supplement dysfunctional microglia with healthy microglia offer a promising strategy for addressing microglia-mediated neuroinflammation and pathologies. This review will cover microglial involvement in neurological diseases and disorders and CNS-related injuries, current microglial transplantation strategies, and different approaches and considerations for generating exogenic microglia.

Implications of fractalkine on glial function, ablation and glial proteins/receptors/markers—understanding its therapeutic usefulness in neurological settings: a narrative review

Background

Fractalkine (CX3CL1) is a chemokine predominantly released by neurons. As a signaling molecule, CX3CL1 facilitates talk between neurons and glia. CX3CL1 is considered as a potential target which could alleviate neuroinflammation. However, certain controversial results and ambiguous role of CX3CL1 make it inexorable to decipher the overall effects of CX3CL1 on the physiopathology of glial cells.

Main body of the abstract

Implications of cross-talk between CX3CL1 and different glial proteins/receptors/markers will give a bird eye view of the therapeutic significance of CX3CL1. Keeping with the need, this review identifies the effects of CX3CL1 on glial physiopathology, glial ablation, and gives a wide coverage on the effects of CX3CL1 on certain glial proteins/receptors/markers.

Short conclusion

Pinpoint prediction of the therapeutic effect of CX3CL1 on neuroinflammation needs further research. This is owing to certain obscure roles and implications of CX3CL1 on different glial proteins/receptors/markers, which are crucial under neurological settings. Further challenges are imposed due to the dichotomous roles played by CX3CL1. The age-old chemokine shows many newer scopes of research in near future. Thus, overall assessment of the effect of CX3CL1 becomes crucial prior to its administration in neuroinflammation.

Bioelectronic cell-based device provides a strategy for the treatment of the experimental model of multiple sclerosis

Wireless powered optogenetic cell-based implant provides a strategy to deliver subcutaneously therapeutic proteins. Immortalize Human Mesenchymal Stem Cells (hMSC-TERT) expressing the bacteriophytochrome diguanylate cyclase (DGCL) were validated for optogenetic controlled interferon-β delivery (Optoferon cells) in a bioelectronic cell-based implant. Optoferon cells transcriptomic profiling was used to elaborate an in-silico model of the recombinant interferon-β production. Wireless optoelectronic device integration was developed using additive manufacturing and injection molding. Implant cell-based optoelectronic interface manufacturing was established to integrate industrial flexible compact low-resistance screen-printed Near Field Communication (NFC) coil antenna. Optogenetic cell-based implant biocompatibility, and device performances were evaluated in the Experimental Autoimmune Encephalomyelitis (EAE) mouse model of multiple sclerosis.

Single cell profiling of CD45+ spinal cord cells reveals microglial and B cell heterogeneity and crosstalk following spinal cord injury

Background

Immune cells play crucial roles after spinal cord injury (SCI). However, incomplete knowledge of immune contributions to injury and repair hinders development of SCI therapies. We leveraged single-cell observations to describe key populations of immune cells present in the spinal cord and changes in their transcriptional profiles from uninjured to subacute and chronic stages of SCI.

Methods

Deep-read single-cell sequencing was performed on CD45+ cells from spinal cords of uninjured and injured Swiss-webster mice. After T9 thoracic contusion, cells were collected 3-, 7-, and 60-day post-injury (dpi). Subpopulations of CD45+ immune cells were identified informatically, and their transcriptional responses characterized with time. We compared gene expression in spinal cord microglia and B cell subpopulations with those in published models of disease and injury. Microglia were compared with Disease Associated Microglia (DAM) and Injury Responsive Microglia (IRM). B cells were compared to developmental lineage states and to an Amyotrophic Lateral Sclerosis (ALS) model.

Results

In uninjured and 7 dpi spinal cord, most CD45+ cells isolated were microglia while chronically B cells predominated. B cells accumulating in the spinal cord following injury included immature B to mature stages and were predominantly found in the injury zone. We defined diverse subtypes of microglia and B cells with altered gene expression with time after SCI. Spinal cord microglia gene expression indicates differences from brain microglia at rest and in inflammatory states. Expression analysis of signaling ligand–receptor partners identified microglia–B cell interactions at acute and chronic stages that may be involved in B cell recruitment, retention, and formation of ectopic lymphoid follicles.

Conclusions

Immune cell responses to SCI have region-specific aspects and evolve with time. Developmentally diverse populations of B cells accumulate in the spinal cord following injury. Microglia at subacute stages express B cell recruitment factors, while chronically, they express factors predicted to reduce B cell inflammatory state. In the injured spinal cord, B cells create ectopic lymphoid structures, and express secreted factors potentially acting on microglia. Our study predicts previously unidentified crosstalk between microglia and B cells post-injury at acute and chronic stages, revealing new potential targets of inflammatory responses for SCI repair warranting future functional analyses.

Long-term microglia depletion impairs synapse elimination and auditory brainstem function

Specialized sound localization circuit development requires synapse strengthening, refinement, and pruning. Many of these functions are carried out by microglia, immune cells that aid in regulating neurogenesis, synaptogenesis, apoptosis, and synaptic removal. We previously showed that postnatal treatment with BLZ945 (BLZ), an inhibitor of colony stimulating factor 1 receptor (CSF1R), eliminates microglia in the brainstem and disables calyceal pruning and maturation of astrocytes in the medial nucleus of the trapezoid body (MNTB). BLZ treatment results in elevated hearing thresholds and delayed signal propagation as measured by auditory brainstem responses (ABR). However, when microglia repopulate the brain following the cessation of BLZ, most of the deficits are repaired. It is unknown whether this recovery is achievable without the return of microglia. Here, we induced sustained microglial elimination with a two-drug approach using BLZ and PLX5622 (PLX). We found that BLZ/PLX treated mice had impaired calyceal pruning, diminished astrocytic GFAP in the lateral, low frequency, region of MNTB, and elevated glycine transporter 2 (GLYT2) levels. BLZ/PLX treated mice had elevated hearing thresholds, diminished peak amplitudes, and altered latencies and inter-peak latencies. These findings suggest that microglia are required to repopulate the brain in order to rectify deficits from their ablation.

Microglial depletion impairs glial scar formation and aggravates inflammation partly by inhibiting STAT3 phosphorylation in astrocytes after spinal cord injury

Astrocytes and microglia play an orchestrated role following spinal cord injury; however, the molecular mechanisms through which microglia regulate astrocytes after spinal cord injury are not yet fully understood. Herein, microglia were pharmacologically depleted and the effects on the astrocytic response were examined. We further explored the potential mechanisms involving the signal transducers and activators of transcription 3 (STAT3) pathway. For in vivo experiments, we constructed a contusion spinal cord injury model in C57BL/6 mice. To deplete microglia, all mice were treated with colony-stimulating factor 1 receptor inhibitor PLX3397, starting 2 weeks prior to surgery until they were sacrificed. Cell proliferation was examined by 5-ethynyl-2-deoxyuridine (EdU) and three pivotal inflammatory cytokines were detected by a specific Bio-Plex Pro^TM Reagent Kit. Locomotor function, neuroinflammation, astrocyte activation and phosphorylated STAT3 (pSTAT3, a maker of activation of STAT3 signaling) levels were determined. For in vitro experiments, a microglia and astrocyte coculture system was established, and the small molecule STA21, which blocks STAT3 activation, was applied to investigate whether STAT3 signaling is involved in mediating astrocyte proliferation induced by microglia. PLX3397 administration disrupted glial scar formation, increased inflammatory spillover, induced diffuse tissue damage and impaired functional recovery after spinal cord injury. Microglial depletion markedly reduced EdU⁺ proliferating cells, especially proliferating astrocytes at 7 days after spinal cord injury. RNA sequencing analysis showed that the JAK/STAT3 pathway was downregulated in mice treated with PLX3397. Double immunofluorescence staining confirmed that PLX3397 significantly decreased STAT3 expression in astrocytes. Importantly, in vitro coculture of astrocytes and microglia showed that microglia-induced astrocyte proliferation was abolished by STA21 administration. These findings suggest that microglial depletion impaired astrocyte proliferation and astrocytic scar formation, and induced inflammatory diffusion partly by inhibiting STAT3 phosphorylation in astrocytes following spinal cord injury.

The limitations of investigating appetite through circuit manipulations: are we biting off more than we can chew?

Disordered eating can underpin a number of debilitating and prevalent chronic diseases, such as obesity. Broader advances in psychopharmacology and biology have motivated some neuroscientists to address diet-induced obesity through reductionist, pre-clinical eating investigations on the rodent brain. Specifically, chemogenetic and optogenetic methods developed in the 21st century allow neuroscientists to perform in vivo, region-specific/projection-specific/promoter-specific circuit manipulations and immediately assess the impact of these manipulations on rodent feeding. These studies are able to rigorously conclude whether a specific neuronal population regulates feeding behaviour in the hope of eventually developing a mechanistic neuroanatomical map of appetite regulation. However, an artificially stimulated/inhibited rodent neuronal population that changes feeding behaviour does not necessarily represent a pharmacological target for treating eating disorders in humans. Chemogenetic/optogenetic findings must therefore be triangulated with the array of theories that contribute to our understanding of appetite. The objective of this review is to provide a wide-ranging discussion of the limitations of chemogenetic/optogenetic circuit manipulation experiments in rodents that are used to investigate appetite. Stepping into and outside of medical science epistemologies, this paper draws on philosophy of science, nutrition, addiction biology and neurophilosophy to prompt more integrative, transdisciplinary interpretations of chemogenetic/optogenetic appetite data. Through discussing the various technical and epistemological limitations of these data, we provide both an overview of chemogenetics and optogenetics accessible to non-neuroscientist obesity researchers, as well as a resource for neuroscientists to expand the number of lenses through which they interpret their circuit manipulation findings.

The Mechanical Microenvironment Regulates Axon Diameters Visualized by Cryo-Electron Tomography

Axonal varicosities or swellings are enlarged structures along axon shafts and profoundly affect action potential propagation and synaptic transmission. These structures, which are defined by morphology, are highly heterogeneous and often investigated concerning their roles in neuropathology, but why they are present in the normal brain remains unknown. Combining confocal microscopy and cryo-electron tomography (Cryo-ET) with in vivo and in vitro systems, we report that non-uniform mechanical interactions with the microenvironment can lead to 10-fold diameter differences within an axon of the central nervous system (CNS). In the brains of adult Thy1-YFP transgenic mice, individual axons in the cortex displayed significantly higher diameter variation than those in the corpus callosum. When being cultured on lacey carbon film-coated electron microscopy (EM) grids, CNS axons formed varicosities exclusively in holes and without microtubule (MT) breakage, and they contained mitochondria, multivesicular bodies (MVBs), and/or vesicles, similar to the axonal varicosities induced by mild fluid puffing. Moreover, enlarged axon branch points often contain MT free ends leading to the minor branch. When the axons were fasciculated by mimicking in vivo axonal bundles, their varicosity levels reduced. Taken together, our results have revealed the extrinsic regulation of the three-dimensional ultrastructures of central axons by the mechanical microenvironment under physiological conditions.

Microglia coordinate cellular interactions during spinal cord repair in mice

Traumatic spinal cord injury (SCI) triggers a neuro-inflammatory response dominated by tissue-resident microglia and monocyte derived macrophages (MDMs). Since activated microglia and MDMs are morphologically identical and express similar phenotypic markers in vivo, identifying injury responses specifically coordinated by microglia has historically been challenging. Here, we pharmacologically depleted microglia and use anatomical, histopathological, tract tracing, bulk and single cell RNA sequencing to reveal the cellular and molecular responses to SCI controlled by microglia. We show that microglia are vital for SCI recovery and coordinate injury responses in CNS-resident glia and infiltrating leukocytes. Depleting microglia exacerbates tissue damage and worsens functional recovery. Conversely, restoring select microglia-dependent signaling axes, identified through sequencing data, in microglia depleted mice prevents secondary damage and promotes recovery. Additional bioinformatics analyses reveal that optimal repair after SCI might be achieved by co-opting key ligand-receptor interactions between microglia, astrocytes and MDMs.

Restorative therapy using microglial depletion and repopulation for central nervous system injuries and diseases

Microglia are important resident immune cells in the central nervous system (CNS) and play an important role in its development, homeostasis, and disease treatments. Activated microglia perform diverse functions in mouse models of CNS neurodegenerative diseases or deficits. In humans, microglia have been linked to various neurodegenerative diseases. Following brain or spinal cord injury, microglia express pro- and anti-inflammatory phenotypes at different stages of recovery. With the development of pharmacological and genetic tools for microglial depletion, studies have demonstrated that microglial depletion exerts both positive and negative effects in the treatment of CNS diseases. Notably, microglial depletion provides an empty niche that stimulates production of new microglia. Microglial depletion and repopulation can not only treat diseases by eliminating dysfunctional microglia but can also provide an indication of the molecular mechanisms of diseases. Although this approach has shown impressive results, its use is still in its infancy. In this review, we summarize the current pharmacological and genetic tools for microglial depletion and highlight recent advances in microglial repopulation therapy for the treatment and functional recovery of neurological diseases and deficits. Finally, we briefly discuss the therapeutic challenges and prospective uses of microglial repopulation therapy.

Perinatal arsenic exposure-induced sustained microglial activation leads to impaired cognitive response in BALB/c mice

Arsenic is infamous for its adverse health effects worldwide. It is known to induce cognitive impairment in experimental model animals and children in the arsenic-affected area. Although the effect of arsenic on neuronal health is well studied, but the involvement of the brain immune component, microglia, has not been well explored. The present study is focused on examining the role of microglia in arsenic-induced cognitive impairment. We have used balb/c mice for the study. Pregnant dams were gavaged with sodium arsenite (0.38 mg/kg body weight) from gestational day 5 (GD5) till postnatal day 22 (PND22). Mice were sacrificed on PND 7, 14, 22 and isolated brains were used for various assays. The study reveals that perinatal arsenic exposure keeps the microglia activated and skews them towards the M1 phenotype. Increased microglial proliferation, ROS, NO, higher levels of proinflammatory cytokines and chemokines were observed in the arsenic exposed group. Enhanced phagocytosis and phagocytic receptor TREM2, along with decreased expression of SNAP25 and PSD95, were correlated for enhanced neuronal pruning leading to impaired learning and memory response. Taken together, the study reveals an association between arsenic exposure and altered cognitive response where enhanced neuronal pruning by arsenic-activated microglia plays an important role in developing mice.

Emerging Roles of Microglia Depletion in the Treatment of Spinal Cord Injury

Microglia, as the resident immune cells and first responder to neurological insults, play an extremely important role in the pathophysiological process of spinal cord injury. On the one hand, microglia respond rapidly and gather around the lesion in the early stage of injury to exert a protective role, but with the continuous stimulation of the injury, the excessive activated microglia secrete a large number of harmful substances, aggravate the injury of spinal cord tissue, and affect functional recovery. The effects of microglia depletion on the repair of spinal cord injury remain unclear, and there is no uniformly accepted paradigm for the removal methods and timing of microglia depletion, but different microglia depletion strategies greatly affect the outcomes after spinal cord injury. Therefore, this review summarizes the physiological and pathological roles of microglia, especially the effects of microglia depletion on spinal cord injury-sustained microglial depletion would aggravate injury and impair functional recovery, while the short-term depletion of microglial population in diseased conditions seems to improve tissue repair and promote functional improvement after spinal cord injury. Furthermore, we discuss the advantages and disadvantages of major strategies and timing of microglia depletion to provide potential strategy for the treatment of spinal cord injury.

Inhibition of colony stimulating factor-1 receptor (CSF-1R) as a potential therapeutic strategy for neurodegenerative diseases: opportunities and challenges

Microglia are specialized dynamic immune cells in the central nervous system (CNS) that plays a crucial role in brain homeostasis and in disease states. Persistent neuroinflammation is considered a hallmark of many neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS) and primary progressive multiple sclerosis (MS). Colony stimulating factor 1-receptor (CSF-1R) is predominantly expressed on microglia and its expression is significantly increased in neurodegenerative diseases. Cumulative findings have indicated that CSF-1R inhibitors can have beneficial effects in preclinical neurodegenerative disease models. Research using CSF-1R inhibitors has now been extended into non-human primates and humans. This review article summarizes the most recent advances using CSF-1R inhibitors in different neurodegenerative conditions including AD, PD, HD, ALS and MS. Potential challenges for translating these findings into clinical practice are presented.

Redefining microglia states: Lessons and limits of human and mouse models to study microglia states in neurodegenerative diseases

Microglia are resident macrophages of the brain parenchyma and play an essential role in various aspects of brain development, plasticity, and homeostasis. With recent advances in single-cell RNA-sequencing, heterogeneous microglia transcriptional states have been identified in both animal models of neurodegenerative disorders and patients. However, the functional roles of these microglia states remain unclear; specifically, the question of whether individual states or combinations of states are protective or detrimental (or both) in the context of disease progression. To attempt to answer this, the field has largely relied on studies employing mouse models, human in vitro and chimeric models, and human post-mortem tissue, all of which have their caveats, but used in combination can enable new biological insight and validation of candidate disease pathways and mechanisms. In this review, we summarize our current understanding of disease-associated microglia states and phenotypes in neurodegenerative disorders, discuss important considerations when comparing mouse and human microglia states and functions, and identify areas of microglia biology where species differences might limit our understanding of microglia state.

The preventive effects of colony-stimulating factor 1 receptor (CSF-1R) inhibition on bladder outlet obstruction induced remodeling

INTRODUCTION

Bladder outlet obstruction (BOO) is a common problem that can affect bladder structure and function. Currently, there is no effective drugs available to prevent BOO-induced remodeling. Previous reports have demonstrated that the pathogenesis of BOO is associated with macrophage infiltration and polarization, which is physiologically dependent on colony-stimulating factor 1 receptor (CSF-1R) activation. Here we utilized a highly selective CSF-1R inhibitor, GW2580, to determine its preventive effects on BOO-induced remodeling.

METHODS

A total of 24 Sprague-Dawley rats were randomly divided into sham, BOO + vehicle, and BOO + GW2580 group. GW2580 or vehicle control was administrated by oral gavage at daily doses of 40 mg/kg for 6 weeks. Bladder samples were collected for histopathology, immunohistochemistry, immunofluorescence, western blotting, and flow cytometry analysis.

RESULTS

Our results demonstrated that bladder fibrosis was ameliorated by GW2580 compared with the vehicle group (22.01% ± 5.13% vs. 32.15% ± 7.24%, p < 0.01). Furthermore, treatment with GW2580 induced an inhibition of macrophage infiltration (4.41% ± 1.28% vs. 13.57% ± 3.42%, p < 0.001) and M2 macrophage polarization (10.67% ± 4.15% vs. 28.59% ± 6.38%, p < 0.001). There was also a decrease of profibrotic F4/80⁺  α-smooth muscle actin⁺ (α-SMA⁺ ) macrophage to myofibroblast transition (9.11% ± 2.58% vs. 17.33% ± 4.01%, p < 0.001) and CD163⁺ TGF-β1⁺ cells (7.68% ± 2.10% vs. 14.17% ± 4.09%, p < 0.01) in the GW2580 group when compared with the vehicle group.

CONCLUSIONS

In summary, our findings showed that GW2580 is a worthwhile candidate for a follow-up study to test in the treatment of BOO-induced remodeling.

Current Knowledge of Microglia in Traumatic Spinal Cord Injury

Microglia are the resident immune cells in the central nervous system (CNS). After traumatic spinal cord injury (SCI), microglia undergo activation, proliferation, and changes in gene and protein expression and morphology, with detrimental and beneficial effects. Activated microglia cause secondary neuronal injury via the production of proinflammatory cytokines, reactive oxygen species, and proteases. However, activated microglia also promote neuronal repair through the secretion of anti-inflammatory growth factors and cytokines. Proinflammatory cytokines increase endothelial permeability, promote A1 astrocyte activation and axonal demyelination, and reduce neural stem/progenitor cells (NSPCs), leading to the exacerbation of neuronal injury. In contrast, anti-inflammatory factors facilitate angiogenesis, reduce reactive astrocytes, and promote axonal remyelination and the propagation of NSPCs, contributing to tissue repair and locomotor recovery. Due to its limited regenerative capacity, the CNS requires beneficial microglia for continuous protection against injury. Understanding and regulating microglial activation status are beneficial to reducing detrimental effects and promoting repair behaviors and to obtain more information on efficient therapies for traumatic SCI. This review discusses microglial activation and the differences between microglia and similar immune cells, microglial interactions with other cells in the spinal cord, and the progress in the development of therapies targeting microglia in SCI.

Hacking macrophages to combat cancer and inflammatory diseases-Current advances and challenges

Recently, immunotherapy has been served as the treatment of choice for various human pathophysiologies, including inflammatory diseases and cancer. Though most of the current approaches target the lymphoid compartment, macrophages intimately implicated in the induction or resolution of inflammation have rationally gained their place into the therapeutics arena. In this review, I discuss the past and novel groundbreaking strategies focusing on macrophages in different human diseases and highlight the current challenges and considerations underlying their translational potentials.

Spleen tyrosine kinase facilitates neutrophil activation and worsens long-term neurologic deficits after spinal cord injury

Background

Spinal cord injury elicits widespread inflammation that can exacerbate long-term neurologic deficits. Neutrophils are the most abundant immune cell type to invade the spinal cord in the early acute phase after injury, however, their role in secondary pathogenesis and functional recovery remains unclear. We have previously shown that neutrophil functional responses during inflammation are augmented by spleen tyrosine kinase, Syk, a prominent intracellular signaling enzyme. In this study, we evaluated the contribution of Syk towards neutrophil function and long-term neurologic deficits after spinal cord injury.

Methods

Contusive spinal cord injury was performed at thoracic vertebra level 9 in mice with conditional deletion of Syk in neutrophils (Syk^f/fMRP8-Cre). Hindlimb locomotor recovery was evaluated using an open-field test for 35 days following spinal cord injury. Long-term white matter sparing was assessed using eriochrome cyanide staining. Blood-spinal cord barrier disruption was evaluated by immunoblotting. Neutrophil infiltration, activation, effector functions, and cell death were determined by flow cytometry. Cytokine and chemokine expression in neutrophils was assessed using a gene array.

Results

Syk deficiency in neutrophils improved long-term functional recovery after spinal cord injury, but did not promote long-term white matter sparing. Neutrophil activation, cytokine expression, and cell death in the acutely injured spinal cord were attenuated by the genetic loss of Syk while neutrophil infiltration and effector functions were not affected. Acute blood-spinal cord barrier disruption was also unaffected by Syk deficiency in neutrophils.

Conclusions

Syk facilitates specific neutrophil functional responses to spinal cord injury including activation, cytokine expression, and cell death. Long-term neurologic deficits are exacerbated by Syk signaling in neutrophils independent of acute blood-spinal cord barrier disruption and long-term white matter sparing. These findings implicate Syk in pathogenic neutrophil activities that worsen long-term functional recovery after spinal cord injury.

Treatment With the CSF1R Antagonist GW2580, Sensitizes Microglia to Reactive Oxygen Species

Microglia activation and proliferation are hallmarks of many neurodegenerative disorders and may contribute to disease pathogenesis. Neurons actively regulate microglia survival and function, in part by secreting the microglia mitogen interleukin (IL)-34. Both IL-34 and colony stimulating factor (CSF)-1 bind colony stimulating factor receptor (CSFR)1 expressed on microglia. Systemic treatment with central nervous system (CNS) penetrant, CSFR1 antagonists, results in microglia death in a dose dependent matter, while others, such as GW2580, suppress activation during disease states without altering viability. However, it is not known how treatment with non-penetrant CSF1R antagonists, such as GW2580, affect the normal physiology of microglia. To determine how GW2580 affects microglia function, C57BL/6J mice were orally gavaged with vehicle or GW2580 (80mg/kg/d) for 8 days. Body weights and burrowing behavior were measured throughout the experiment. The effects of GW2580 on circulating leukocyte populations, brain microglia morphology, and the transcriptome of magnetically isolated adult brain microglia were determined. Body weights, burrowing behavior, and circulating leukocytes were not affected by treatment. Analysis of Iba-1 stained brain microglia indicated that GW2580 treatment altered morphology, but not cell number. Analysis of RNA-sequencing data indicated that genes related to reactive oxygen species (ROS) regulation and survival were suppressed by treatment. Treatment of primary microglia cultures with GW2580 resulted in a dose-dependent reduction in viability only when the cells were concurrently treated with LPS, an inducer of ROS. Pre-treatment with the ROS inhibitor, YCG063, blocked treatment induced reductions in viability. Finally, GW2580 sensitized microglia to hydrogen peroxide induced cell death. Together, these data suggest that partial CSF1R antagonism may render microglia more susceptible to reactive oxygen and nitrogen species.

Unlike Brief Inhibition of Microglia Proliferation after Spinal Cord Injury, Long-Term Treatment Does Not Improve Motor Recovery

Microglia are major players in scar formation after an injury to the spinal cord. Microglia proliferation, differentiation, and survival are regulated by the colony-stimulating factor 1 (CSF1). Complete microglia elimination using CSF1 receptor (CSF1R) inhibitors worsens motor function recovery after spinal injury (SCI). Conversely, a 1-week oral treatment with GW2580, a CSF1R inhibitor that only inhibits microglia proliferation, promotes motor recovery. Here, we investigate whether prolonged GW2580 treatment further increases beneficial effects on locomotion after SCI. We thus assessed the effect of a 6-week GW2580 oral treatment after lateral hemisection of the spinal cord on functional recovery and its outcome on tissue and cellular responses in adult mice. Long-term depletion of microglia proliferation after SCI failed to improve motor recovery and had no effect on tissue reorganization, as revealed by ex vivo diffusion-weighted magnetic resonance imaging. Six weeks after SCI, GW2580 treatment decreased microglial reactivity and increased astrocytic reactivity. We thus demonstrate that increasing the duration of GW2580 treatment is not beneficial for motor recovery after SCI.

Inhibiting microglia proliferation after spinal cord injury improves recovery in mice and nonhuman primates

No curative treatment is available for any deficits induced by spinal cord injury (SCI). Following injury, microglia undergo highly diverse activation processes, including proliferation, and play a critical role on functional recovery.

In a translational objective, we investigated whether a transient pharmacological reduction of microglia proliferation after injury is beneficial for functional recovery after SCI in mice and nonhuman primates.

Methods: The colony stimulating factor-1 receptor (CSF1R) regulates proliferation, differentiation, and survival of microglia. We orally administrated GW2580, a CSF1R inhibitor that inhibits microglia proliferation. In mice and nonhuman primates, we then analyzed treatment outcomes on locomotor function and spinal cord pathology. Finally, we used cell-specific transcriptomic analysis to uncover GW2580-induced molecular changes in microglia.

Results: First, transient post-injury GW2580 administration in mice improves motor function recovery, promotes tissue preservation and/or reorganization (identified by coherent anti-stokes Raman scattering microscopy), and modulates glial reactivity.

Second, post-injury GW2580-treatment in nonhuman primates reduces microglia proliferation, improves motor function recovery, and promotes tissue protection.

Finally, GW2580-treatment in mice induced down-regulation of proliferation-associated transcripts and inflammatory associated genes in microglia that may account for reduced neuroinflammation and improved functional recovery following SCI.

Conclusion: Thus, a transient oral GW2580 treatment post-injury may provide a promising therapeutic strategy for SCI patients and may also be extended to other central nervous system disorders displaying microglia activation.