Extracellular vesicles set the stage for brain plasticity and recovery by multimodal signalling.

Extracellular vesicles (EVs) are extremely versatile naturally occurring membrane particles that convey complex signals between cells. EVs of different cellular sources are capable of inducing striking therapeutic responses in neurological disease models. Differently from pharmacological compounds that act by modulating defined signalling pathways, EV-based therapeutics possess multiple abilities via a variety of effectors, thus allowing the modulation of complex disease processes that may have very potent effects on brain tissue recovery. When applied in vivo in experimental models of neurological diseases, EV-based therapeutics have revealed remarkable effects on immune responses, cell metabolism and neuronal plasticity. This multimodal modulation of neuroimmune networks by EVs profoundly influences disease processes in a highly synergistic and context-dependent way. Ultimately, the EV-mediated restoration of cellular functions helps to set the stage for neurological recovery. With this review we first outline the current understanding of the mechanisms of action of EVs, describing how EVs released from various cellular sources identify their cellular targets and convey signals to recipient cells. Then, mechanisms of action applicable to key neurological conditions such as stroke, multiple sclerosis and neurodegenerative diseases are presented. Pathways that deserve attention in specific disease contexts are discussed. We subsequently showcase considerations about EV biodistribution and delineate genetic engineering strategies aiming at enhancing brain uptake and signalling. By sketching a broad view of EV-orchestrated brain plasticity and recovery, we finally define possible future clinical EV applications and propose necessary information to be provided ahead of clinical trials. Our goal is to provide a steppingstone that can be used to critically discuss EVs as next generation therapeutics for brain diseases.

Succinate Receptor 1: An Emerging Regulator of Myeloid Cell Function in Inflammation.

The rapidly evolving area of immunometabolism has shed new light on the fundamental properties of products and intermediates of cellular metabolism (metabolites), highlighting their key signaling roles in cell-to-cell communication. Recent evidence identifies the succinate-succinate receptor 1 (SUCNR1) axis as an essential regulator of tissue homeostasis. Succinate signaling via SUCNR1 guides divergent responses in immune cells, which are tissue and context dependent. Herein, we explore the main cellular pathways regulated by the succinate-SUCNR1 axis and focus on the biology of SUCNR1 and its roles influencing the function of myeloid cells. Hence, we identify new therapeutic targets and putative therapeutic approaches aimed at resolving detrimental myeloid cell responses in tissues, including those occurring in the persistently inflamed central nervous system (CNS).

Neural stem cells traffic functional mitochondria via extracellular vesicles.

Neural stem cell (NSC) transplantation induces recovery in animal models of central nervous system (CNS) diseases. Although the replacement of lost endogenous cells was originally proposed as the primary healing mechanism of NSC grafts, it is now clear that transplanted NSCs operate via multiple mechanisms, including the horizontal exchange of therapeutic cargoes to host cells via extracellular vesicles (EVs). EVs are membrane particles trafficking nucleic acids, proteins, metabolites and metabolic enzymes, lipids, and entire organelles. However, the function and the contribution of these cargoes to the broad therapeutic effects of NSCs are yet to be fully understood. Mitochondrial dysfunction is an established feature of several inflammatory and degenerative CNS disorders, most of which are potentially treatable with exogenous stem cell therapeutics. Herein, we investigated the hypothesis that NSCs release and traffic functional mitochondria via EVs to restore mitochondrial function in target cells. Untargeted proteomics revealed a significant enrichment of mitochondrial proteins spontaneously released by NSCs in EVs. Morphological and functional analyses confirmed the presence of ultrastructurally intact mitochondria within EVs with conserved membrane potential and respiration. We found that the transfer of these mitochondria from EVs to mtDNA-deficient L929 Rho0 cells rescued mitochondrial function and increased Rho0 cell survival. Furthermore, the incorporation of mitochondria from EVs into inflammatory mononuclear phagocytes restored normal mitochondrial dynamics and cellular metabolism and reduced the expression of pro-inflammatory markers in target cells. When transplanted in an animal model of multiple sclerosis, exogenous NSCs actively transferred mitochondria to mononuclear phagocytes and induced a significant amelioration of clinical deficits. Our data provide the first evidence that NSCs deliver functional mitochondria to target cells via EVs, paving the way for the development of novel (a)cellular approaches aimed at restoring mitochondrial dysfunction not only in multiple sclerosis, but also in degenerative neurological diseases.

Global, Regional, and National Economic Consequences of Stroke.

BACKGROUND: An understanding of global, regional, and national macroeconomic losses caused by stroke is important for allocation of clinical and research resources. The authors investigated the macroeconomic consequences of stroke disease burden in the year 2019 in 173 countries. METHODS: Disability-adjusted life year data for overall stroke and its subtypes (ischemic stroke, intracerebral hemorrhage, and subarachnoid hemorrhage) were collected from the GBD study (Global Burden of Disease) 2019 database. Gross domestic product (GDP, adjusted for purchasing power parity [PPP]) data were collected from the World Bank; GDP and disability-adjusted life year data were combined to estimate macroeconomic losses using a value of lost welfare (VLW) approach. All results are presented in 2017 international US dollars adjusted for PPP. RESULTS: Globally, in 2019, VLW due to stroke was $2059.67 billion or 1.66% of the global GDP. Global VLW/GDP for stroke subtypes was 0.78% (VLW=$964.51 billion) for ischemic stroke, 0.71% (VLW=$882.81 billion) for intracerebral hemorrhage, and 0.17% (VLW=$212.36 billion) for subarachnoid hemorrhage. The Central European, Eastern European, and Central Asian GBD super-region reported the highest VLW/GDP for stroke overall (3.01%), ischemic stroke (1.86%), and for subarachnoid hemorrhage (0.26%). The Southeast Asian, East Asian, and Oceanian GBD super-region reported the highest VLW/GDP for intracerebral hemorrhage (1.48%). CONCLUSIONS: The global macroeconomic consequences related to stroke are vast even when considering stroke subtypes. The present quantification may be leveraged to help justify increased spending of finite resources on stroke in an effort to improve outcomes for patients with stroke globally.

Systematic approach to selecting licensed drugs for repurposing in the treatment of progressive multiple sclerosis.

OBJECTIVE: To establish a rigorous, expert-led, evidence-based approach to the evaluation of licensed drugs for repurposing and testing in clinical trials of people with progressive multiple sclerosis (MS). METHODS: We long-listed licensed drugs with evidence of human safety, blood-brain barrier penetrance and demonstrable efficacy in at least one animal model, or mechanistic target, agreed by a panel of experts and people with MS to be relevant to the pathogenesis of progression. We systematically reviewed the preclinical and clinical literature for each compound, condensed this into a database of summary documents and short-listed drugs by scoring each one of them. Drugs were evaluated for immediate use in a clinical trial, and our selection was scrutinised by a final independent expert review. RESULTS: From a short list of 55 treatments, we recommended four treatments for immediate testing in progressive MS: R-α-lipoic acid, metformin, the combination treatment of R-α-lipoic acid and metformin, and niacin. We also prioritised clemastine, lamotrigine, oxcarbazepine, nimodipine and flunarizine. CONCLUSIONS: We report a standardised approach for the identification of candidate drugs for repurposing in the treatment of progressive MS.

Foxg1 Antagonizes Neocortical Stem Cell Progression to Astrogenesis.

Neocortical astrogenesis follows neuronogenesis and precedes oligogenesis. Among key factors dictating its temporal articulation, there are progression rates of pallial stem cells (SCs) towards astroglial lineages as well as activation rates of astrocyte differentiation programs in response to extrinsic gliogenic cues. In this study, we showed that high Foxg1 SC expression antagonizes astrocyte generation, while stimulating SC self-renewal and committing SCs to neuronogenesis. We found that mechanisms underlying this activity are mainly cell autonomous and highly pleiotropic. They include a concerted downregulation of 4 key effectors channeling neural SCs to astroglial fates, as well as defective activation of core molecular machineries implementing astroglial differentiation programs. Next, we found that SC Foxg1 levels specifically decline during the neuronogenic-to-gliogenic transition, pointing to a pivotal Foxg1 role in temporal modulation of astrogenesis. Finally, we showed that Foxg1 inhibits astrogenesis from human neocortical precursors, suggesting that this is an evolutionarily ancient trait.

Neural Stem Cell Grafts Promote Astroglia-Driven Neurorestoration in the Aged Parkinsonian Brain via Wnt/ß-Catenin Signaling.

During aging-one the most potent risk factors for Parkinson's disease (PD)-both astrocytes and microglia undergo functional changes that ultimately hamper homoeostasis, defense, and repair of substantia nigra pars compacta (SNpc) midbrain dopaminergic (mDA) neurons. We tested the possibility of rejuvenating the host microenvironment and boosting SNpc DA neuronal plasticity via the unilateral transplantation of syngeneic neural stem/progenitor cells (NSCs) in the SNpc of aged mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced experimental PD. Transplanted NSCs within the aged SNpc engrafted and migrated in large proportions to the tegmental aqueduct mDA niche, with 30% acquiring an astroglial phenotype. Both graft-derived exogenous (ex-Astro) and endogenous astrocytes (en-Astro) expressed Wnt1. Both ex-Astro and en-Astro were key triggers of Wnt/ß-catenin signaling in SNpc-mDA neurons and microglia, which was associated with mDA neurorescue and immunomodulation. At the aqueduct-ventral tegmental area level, NSC grafts recapitulated a genetic Wnt1-dependent mDA developmental program, inciting the acquisition of a mature Nurr1+ TH+ neuronal phenotype. Wnt/ß-catenin signaling antagonism abolished mDA neurorestoration and immune modulatory effects of NSC grafts. Our work implicates an unprecedented therapeutic potential for somatic NSC grafts in the restoration of mDA neuronal function in the aged Parkinsonian brain. Stem Cells 2018;36:1179-1197.

Extracellular vesicles are independent metabolic units with asparaginase activity.

Extracellular vesicles (EVs) are membrane particles involved in the exchange of a broad range of bioactive molecules between cells and the microenvironment. Although it has been shown that cells can traffic metabolic enzymes via EVs, much remains to be elucidated with regard to their intrinsic metabolic activity. Accordingly, herein we assessed the ability of neural stem/progenitor cell (NSC)-derived EVs to consume and produce metabolites. Our metabolomics and functional analyses both revealed that EVs harbor L-asparaginase activity, catalyzed by the enzyme asparaginase-like protein 1 (Asrgl1). Critically, we show that Asrgl1 activity is selective for asparagine and is devoid of glutaminase activity. We found that mouse and human NSC EVs traffic Asrgl1. Our results demonstrate, for the first time, that NSC EVs function as independent metabolic units that are able to modify the concentrations of critical nutrients, with the potential to affect the physiology of their microenvironment.

Neural Stem Cell Transplantation Induces Stroke Recovery by Upregulating Glutamate Transporter GLT-1 in Astrocytes.

Ischemic stroke is the leading cause of disability, but effective therapies are currently widely lacking. Recovery from stroke is very much dependent on the possibility to develop treatments able to both halt the neurodegenerative process as well as to foster adaptive tissue plasticity. Here we show that ischemic mice treated with neural precursor cell (NPC) transplantation had on neurophysiological analysis, early after treatment, reduced presynaptic release of glutamate within the ipsilesional corticospinal tract (CST), and an enhanced NMDA-mediated excitatory transmission in the contralesional CST. Concurrently, NPC-treated mice displayed a reduced CST degeneration, increased axonal rewiring, and augmented dendritic arborization, resulting in long-term functional amelioration persisting up to 60 d after ischemia. The enhanced functional and structural plasticity relied on the capacity of transplanted NPCs to localize in the peri-ischemic and ischemic area, to promote the upregulation of the glial glutamate transporter 1 (GLT-1) on astrocytes and to reduce peri-ischemic extracellular glutamate. The upregulation of GLT-1 induced by transplanted NPCs was found to rely on the secretion of VEGF by NPCs. Blocking VEGF during the first week after stroke reduced GLT-1 upregulation as well as long-term behavioral recovery in NPC-treated mice. Our results show that NPC transplantation, by modulating the excitatory-inhibitory balance and stroke microenvironment, is a promising therapy to ameliorate disability, to promote tissue recovery and plasticity processes after stroke. SIGNIFICANCE STATEMENT: Tissue damage and loss of function occurring after stroke can be constrained by fostering plasticity processes of the brain. Over the past years, stem cell transplantation for repair of the CNS has received increasing interest, although underlying mechanism remain elusive. We here show that neural stem/precursor cell transplantation after ischemic stroke is able to foster axonal rewiring and dendritic plasticity and to induce long-term functional recovery. The observed therapeutic effect of neural precursor cells seems to underlie their capacity to upregulate the glial glutamate transporter on astrocytes through the vascular endothelial growth factor inducing favorable changes in the electrical and molecular stroke microenvironment. Cell-based approaches able to influence plasticity seem particularly suited to favor poststroke recovery.

Functional Magnetic Resonance Imaging of Rats with Experimental Autoimmune Encephalomyelitis Reveals Brain Cortex Remodeling.

Cortical reorganization occurring in multiple sclerosis (MS) patients is thought to play a key role in limiting the effect of structural tissue damage. Conversely, its exhaustion may contribute to the irreversible disability that accumulates with disease progression. Several aspects of MS-related cortical reorganization, including the overall functional effect and likely modulation by therapies, still remain to be elucidated. The aim of this work was to assess the extent of functional cortical reorganization and its brain structural/pathological correlates in Dark Agouti rats with experimental autoimmune encephalomyelitis (EAE), a widely accepted preclinical model of chronic MS. Morphological and functional MRI (fMRI) were performed before disease induction and during the relapsing and chronic phases of EAE. During somatosensory stimulation of the right forepaw, fMRI demonstrated that cortical reorganization occurs in both relapsing and chronic phases of EAE with increased activated volume and decreased laterality index versus baseline values. Voxel-based morphometry demonstrated gray matter (GM) atrophy in the cerebral cortex, and both GM and white matter atrophy were assessed by ex vivo pathology of the sensorimotor cortex and corpus callosum. Neuroinflammation persisted in the relapsing and chronic phases, with dendritic spine density in the layer IV sensory neurons inversely correlating with the number of cluster of differentiation 45-positive inflammatory lesions. Our work provides an innovative experimental platform that may be pivotal for the comprehension of key mechanisms responsible for the accumulation of irreversible brain damage and for the development of innovative therapies to reduce disability in EAE/MS. SIGNIFICANCE STATEMENT: Since the early 2000s, functional MRI (fMRI) has demonstrated profound modifications in the recruitment of cortical areas during motor, cognitive, and sensory tasks in multiple sclerosis (MS) patients. Experimental autoimmune encephalomyelitis (EAE) represents a reliable model of the chronic-progressive variant of MS. fMRI studies in EAE have not been performed extensively up to now. This paper reports fMRI studies in a rat model of MS with somatosensory stimulation of the forepaw. We demonstrated modifications in the recruitment of cortical areas consistent with data from MS patients. To the best of our knowledge, this is the first report of cortical remodeling in a preclinical in vivo model of MS.

Metabolic determinants of the immune modulatory function of neural stem cells.

BACKGROUND: Neural stem cells (NSCs) display tissue trophic and immune modulatory therapeutic activities after transplantation in central nervous system disorders. The intercellular interplay between stem cells and target immune cells is increased in NSCs exposed to inflammatory cues. Here, we hypothesize that inflammatory cytokine signalling leads to metabolic reprogramming of NSCs regulating some of their immune modulatory effects. METHODS: NSC lines were prepared from the subventricular zone (SVZ) of 7-12-week-old mice. Whole secretome-based screening and analysis of intracellular small metabolites was performed in NSCs exposed to cocktails of either Th1-like (IFN-γ, 500 U/ml; TNF-α, 200 U/ml; IL-1ß, 100 U/ml) or Th2-like (IL-4, IL-5 and IL-13; 10 ng/ml) inflammatory cytokines for 16 h in vitro. Isotopologues distribution of arginine and downstream metabolites was assessed by liquid chromatography/mass spectrometry in NSCs incubated with U-(13)C6 L-arginine in the presence or absence of Th1 or Th2 cocktails (Th1 NSCs or Th2 NSCs). The expression of arginase I and II was investigated in vitro in Th1 NSCs and Th2 NSCs and in vivo in the SVZ of mice with experimental autoimmune encephalomyelitis, as prototypical model of Th1 cell-driven brain inflammatory disease. The effects of the inflammatory cytokine signalling were studied in NSC-lymph node cells (LNC) co-cultures by flow cytometry-based analysis of cell proliferation following pan-arginase inhibition with N(ω)-hydroxy-nor-arginine (nor-NOHA). RESULTS: Cytokine-primed NSCs showed significantly higher anti-proliferative effect in co-cultures vs. control NSCs. Metabolomic analysis of intracellular metabolites revealed alteration of arginine metabolism and increased extracellular arginase I activity in cytokine-primed NSCs. Arginase inhibition by nor-NOHA partly rescued the anti-proliferative effects of cytokine-primed NSCs. CONCLUSIONS: Our work underlines the use of metabolic profiling as hypothesis-generating tools that helps unravelling how stem cell-mediated mechanisms of tissue restoration become affected by local inflammatory responses. Among different therapeutic candidates, we identify arginase signalling as novel metabolic determinant of the NSC-to-immune system communication.

Defining minor symptoms in acute ischemic stroke.

BACKGROUND: Thrombolysis is often withheld from acute ischemic stroke patients presenting with mild symptoms; however, up to 40% of these patients end up with a poor outcome when left untreated. Since there is lack of consensus on the definition of minor symptoms, we aimed at addressing this issue by looking for features that would better predict functional outcomes at 3 months. METHODS: Among all acute ischemic stroke patients admitted to our Stroke Unit (n = 1,229), we selected a cohort of patients who arrived within 24 hours from symptoms onset, with baseline NIHSS ≤6, not treated with thrombolysis (n = 304). Epidemiological data, comorbidities, radiological features and clinical presentation (NIHSS items) were collected to identify predictors of outcome. Our cohort was tested against minor stroke definitions selected from the literature and a newly proposed one. RESULTS: Three months after stroke onset, 97 patients (31.9%) had mRS ≥ 2. Independent predictors of poor outcome were age (OR 0.97 [95% CI 0.95-9.99]) and baseline NIHSS score (OR 0.79 [95% CI 0.67-0.94]), while cardioembolic aetiology was negatively associated (OR 3.29 [95% CI 1.51-7.14]). Items of NIHSS associated with poor outcome were impairment of right motor arm (OR 0.49 [95% CI 0.27-0.91]) or the involvement of any of the motor items (OR 0.69 [95% CI 0.48-0.99]). The definition of minor stroke as NIHSS ≤3 and the new proposed definition had the highest sensitivity and accuracy and were independent predictors of outcome. CONCLUSIONS: Our study confirmed that in spite of a low NIHSS score, one third of patients had poor outcome. As already described, age and NIHSS score remained independent predictors of poor outcome even in mild stroke. Also, motor impairment appeared a major determinant of poor outcome. The new proposed definition of minor stroke featured the NIHSS score and the NIHSS items that better predicted functional outcome. Awareness that even minor stroke can yield to poor outcome should sensitize patients to arrive early to the ED and neurologists to administer rt-PA.

Metabolic Control of Microglia.

Microglia, immune sentinels of the central nervous system (CNS), play a critical role in maintaining its health and integrity. This chapter delves into the concept of immunometabolism, exploring how microglial metabolism shapes their diverse immune functions. It examines the impact of cell metabolism on microglia during various CNS states, including homeostasis, development, aging, and inflammation. Particularly in CNS inflammation, the chapter discusses how metabolic rewiring in microglia can initiate, resolve, or perpetuate inflammatory responses. The potential of targeting microglial metabolism as a therapeutic strategy for chronic CNS disorders with prominent innate immune cell activation is also explored.

Combination Immunotherapy with Vaccine and Oncolytic HSV Virotherapy Is Time Dependent.

Oncolytic virotherapy or immunovirotherapy is a strategy that utilizes viruses to selectively infect and kill tumor cells while also stimulating an immune response against the tumor. Early clinical trials in both pediatric and adult patients using oncolytic herpes simplex viruses (oHSV) have demonstrated safety and promising efficacy; however, combinatorial strategies designed to enhance oncolysis while also promoting durable T-cell responses for sustaining disease remission are likely required. We hypothesized that combining the direct tumor cell killing and innate immune stimulation by oHSV with a vaccine that promotes T cell-mediated immunity may lead to more durable tumor regression. To this end, we investigated the preclinical efficacy and potential synergy of combining oHSV with a self-assembling nanoparticle vaccine codelivering peptide antigens and Toll-like receptor 7 and 8 agonists (referred to as SNAPvax),which induces robust tumor-specific T-cell immunity. We then assessed how timing of the treatments (i.e., vaccine before or after oHSV) impacts T-cell responses, viral replication, and preclinical efficacy. The sequence of treatments was critical, as survival was significantly enhanced when the SNAPvax vaccine was given prior to oHSV. Increased clinical efficacy was associated with reduced tumor volume and increases in virus replication and tumor antigen-specific CD8+ T cells. These findings substantiate the criticality of combination immunotherapy timing and provide preclinical support for combining SNAPvax with oHSV as a promising treatment approach for both pediatric and adult tumors.

Integrated multi-omics analysis reveals molecular changes associated with chronic lipid accumulation following contusive spinal cord injury.

Functional and pathological recovery after spinal cord injury (SCI) is often incomplete due to the limited regenerative capacity of the central nervous system (CNS), which is further impaired by several mechanisms that sustain tissue damage. Among these, the chronic activation of immune cells can cause a persistent state of local CNS inflammation and damage. However, the mechanisms that sustain this persistent maladaptive immune response in SCI have not been fully clarified yet. In this study, we integrated histological analyses with proteomic, lipidomic, transcriptomic, and epitranscriptomic approaches to study the pathological and molecular alterations that develop in a mouse model of cervical spinal cord hemicontusion. We found significant pathological alterations of the lesion rim with myelin damage and axonal loss that persisted throughout the late chronic phase of SCI. This was coupled by a progressive lipid accumulation in myeloid cells, including resident microglia and infiltrating monocyte-derived macrophages. At tissue level, we found significant changes of proteins indicative of glycolytic, tricarboxylic acid cycle (TCA), and fatty acid metabolic pathways with an accumulation of triacylglycerides with C16:0 fatty acyl chains in chronic SCI. Following transcriptomic, proteomic, and epitranscriptomic studies identified an increase of cholesterol and m6A methylation in lipid-droplet-accumulating myeloid cells as a core feature of chronic SCI. By characterizing the multiple metabolic pathways altered in SCI, our work highlights a key role of lipid metabolism in the chronic response of the immune and central nervous system to damage.

Dark Microglia Are Abundant in Normal Postnatal Development, where they Remodel Synapses via Phagocytosis and Trogocytosis, and Are Dependent on TREM2.

This study examined dark microglia-a state linked to central nervous system pathology and neurodegeneration-during postnatal development in the mouse ventral hippocampus, finding that dark microglia interact with blood vessels and synapses and perform trogocytosis of pre-synaptic axon terminals. Furthermore, we found that dark microglia in development notably expressed C-type lectin domain family 7 member A (CLEC7a), lipoprotein lipase (LPL) and triggering receptor expressed on myeloid cells 2 (TREM2) and required TREM2, differently from other microglia, suggesting a link between their role in remodeling during development and central nervous system pathology. Together, these results point towards a previously under-appreciated role for dark microglia in synaptic pruning and plasticity during normal postnatal development.

Increased cholesterol synthesis drives neurotoxicity in patient stem cell-derived model of multiple sclerosis.

Senescent neural progenitor cells have been identified in brain lesions of people with progressive multiple sclerosis (PMS). However, their role in disease pathobiology and contribution to the lesion environment remains unclear. By establishing directly induced neural stem/progenitor cell (iNSC) lines from PMS patient fibroblasts, we studied their senescent phenotype in vitro. Senescence was strongly associated with inflammatory signaling, hypermetabolism, and the senescence-associated secretory phenotype (SASP). PMS-derived iNSCs displayed increased glucose-dependent fatty acid and cholesterol synthesis, which resulted in the accumulation of lipid droplets. A 3-hydroxy-3-methylglutaryl (HMG)-coenzyme A (CoA) reductase (HMGCR)-mediated lipogenic state was found to induce a SASP in PMS iNSCs via cholesterol-dependent transcription factors. SASP from PMS iNSC lines induced neurotoxicity in mature neurons, and treatment with the HMGCR inhibitor simvastatin altered the PMS iNSC SASP, promoting cytoprotective qualities and reducing neurotoxicity. Our findings suggest a disease-associated, cholesterol-related, hypermetabolic phenotype of PMS iNSCs that leads to neurotoxic signaling and is rescuable pharmacologically.

Safety and efficacy of transcranial direct current stimulation in acute experimental ischemic stroke.

BACKGROUND AND PURPOSE: Transcranial direct current stimulation is emerging as a promising tool for the treatment of several neurological conditions, including cerebral ischemia. The therapeutic role of this noninvasive treatment is, however, limited to chronic phases of stroke. We thus ought to investigate whether different stimulation protocols could also be beneficial in the acute phase of experimental brain ischemia. METHODS: The influence of both cathodal and anodal transcranial direct current stimulation in modifying brain metabolism of healthy mice was first tested by nuclear magnetic resonance spectroscopy. Then, mice undergoing transient proximal middle cerebral artery occlusion were randomized and treated acutely with anodal, cathodal, or sham transcranial direct current stimulation. Brain metabolism, functional outcomes, and ischemic lesion volume, as well as the inflammatory reaction and blood brain barrier functionality, were analyzed. RESULTS: Cathodal stimulation was able, if applied in the acute phase of stroke, to preserve cortical neurons from the ischemic damage, to reduce inflammation, and to promote a better clinical recovery compared with sham and anodal treatments. This finding was attributable to the significant decrease of cortical glutamate, as indicated by nuclear magnetic resonance spectroscopy. Conversely, anodal stimulation induced an increase in the postischemic lesion volume and augmented blood brain barrier derangement. CONCLUSIONS: Our data indicate that transcranial direct current stimulation exerts a measurable neuroprotective effect in the acute phase of stroke. However, its timing and polarity should be carefully identified on the base of the pathophysiological context to avoid potential harmful side effects.

Time-resolved single-cell RNAseq profiling identifies a novel Fabp5+ subpopulation of inflammatory myeloid cells with delayed cytotoxic profile in chronic spinal cord injury.

Traumatic spinal cord injuries (SCI) are a group of highly debilitating pathologies affecting thousands annually, and adversely affecting quality of life. Currently, no fully restorative therapies exist, and SCI still results in significant personal, societal and financial burdens. Inflammation plays a major role in the evolution of SCI, with myeloid cells, including bone marrow derived macrophages (BMDMs) and microglia (MG) being primary drivers of both early secondary pathogenesis and delayed wound healing events. The precise role of myeloid cell subsets is unclear as upon crossing the blood-spinal cord barrier, infiltrating bone marrow derived macrophages (BMDMs) may take on the morphology of resident microglia, and upregulate canonical microglia markers, thus making the two populations difficult to distinguish. Here, we used time-resolved scRNAseq and transgenic fate-mapping to chart the transcriptional profiles of tissue-resident and -infiltrating myeloid cells in a mouse model of thoracic contusion SCI. Our work identifies a novel subpopulation of foam cell-like inflammatory myeloid cells with increased expression of Fatty Acid Binding Protein 5 (Fabp5) and comprise both tissue-resident and -infiltrating cells. Fabp5+ inflammatory myeloid cells display a delayed cytotoxic profile that is predominant at the lesion epicentre and extends into the chronic phase of SCI.