A role for MHC class I molecules in synaptic plasticity and regeneration of neurons after axotomy

CD3ζ-Mediated Signaling Protects Retinal Ganglion Cells in Glutamate Excitotoxicity of the Retina

Excessive levels of glutamate activity could potentially damage and kill neurons. Glutamate excitotoxicity is thought to play a critical role in many CNS and retinal diseases. Accordingly, glutamate excitotoxicity has been used as a model to study neuronal diseases. Immune proteins, such as major histocompatibility complex (MHC) class I molecules and their receptors, play important roles in many neuronal diseases, while T-cell receptors (TCR) are the primary receptors of MHCI. We previously showed that a critical component of TCR, CD3ζ, is expressed by mouse retinal ganglion cells (RGCs). The mutation of CD3ζ or MHCI molecules compromises the development of RGC structure and function. In this study, we investigated whether CD3ζ-mediated molecular signaling regulates RGC death in glutamate excitotoxicity. We show that mutation of CD3ζ significantly increased RGC survival in NMDA-induced excitotoxicity. In addition, we found that several downstream molecules of TCR, including Src (proto-oncogene tyrosine-protein kinase) family kinases (SFKs) and spleen tyrosine kinase (Syk), are expressed by RGCs. Selective inhibition of an SFK member, Hck, or Syk members, Syk or Zap70, significantly increased RGC survival in NMDA-induced excitotoxicity. These results provide direct evidence to reveal the underlying molecular mechanisms that control RGC death under disease conditions.

Effects of local and systemic treatment with human natural killer-1 mimetic peptide (HNK-1) after ventral root avulsion and reimplantation in mice

Background

Spinal ventral root injuries generate significant motoneuron degeneration, which hinders full functional recovery. The poor prognosis of functional recovery can be attributed to the use or combination of different therapeutic approaches. Several molecules have been screened as potential treatments in combination with surgical reimplantation of the avulsed roots, the gold standard approach for such injuries. Among the studied molecules, human natural killer-1 (HNK-1) stands out as it is related to the stimulation of motor axon outgrowth. Therefore, we aimed to comparatively investigate the effects of local administration of an HNK-1 mimetic peptide (mp-HNK-1) and systemic treatment with ursolic acid (UA), another HNK-1 mimetic, after ventral root avulsion and reimplantation with heterologous fibrin biopolymer (HFB).

Methods

Female mice of the isogenic strain C57BL/6JUnib were divided into five experimental groups: Avulsion, Reimplantation, mp-HNK-1 (in situ), and UA (systemic treatment). Mice were evaluated 2 and 12 weeks after surgery. Functional assessment was performed every four days using the Catwalk platform. Neuronal survival was analyzed by cytochemistry, and glial reactions and synaptic coverage were evaluated by immunofluorescence.

Results

Treatment with UA elicited long-term neuroprotection, accompanied by a decrease in microglial reactions, and reactive astrogliosis. The neuroprotective effects of UA were preceded by increased glutamatergic and GABAergic inputs in the ventral spinal cord two weeks after injury. However, a single application of mp-HNK-1 had no significant effects. Functional analysis showed that UA treatment led to an improvement in motor and sensory recovery.

Conclusion

Overall, the results indicate that UA is neuroprotective, acting on glial cells and synaptic maintenance, and the combination of these findings led to a better functional recovery.

DLK signaling in axotomized neurons triggers complement activation and loss of upstream synapses

Axotomized spinal motoneurons (MNs) lose presynaptic inputs following peripheral nerve injury; however, the cellular mechanisms that lead to this form of synapse loss are currently unknown. Here, we delineate a critical role for neuronal kinase dual leucine zipper kinase (DLK)/MAP3K12, which becomes activated in axotomized neurons. Studies with conditional knockout mice indicate that DLK signaling activation in injured MNs triggers the induction of phagocytic microglia and synapse loss. Aspects of the DLK-regulated response include expression of C1q first from the axotomized MN and then later in surrounding microglia, which subsequently phagocytose presynaptic components of upstream synapses. Pharmacological ablation of microglia inhibits the loss of cholinergic C boutons from axotomized MNs. Together, the observations implicate a neuronal mechanism, governed by the DLK, in the induction of inflammation and the removal of synapses.

Mild and moderate chronic hypercapnia elicit distinct transcriptomic responses of immune function in cardiorespiratory nuclei

Chronic hypercapnia (CH) is a hallmark of respiratory-related diseases, and the level of hypercapnia can acutely or progressively become more severe. Previously, we have shown time-dependent adaptations in steady-state physiology during mild (arterial Pco2 ∼55 mmHg) and moderate (∼60 mmHg) CH in adult goats, including transient (mild CH) or sustained (moderate CH) suppression of acute chemosensitivity suggesting limitations in adaptive respiratory control mechanisms as the level of CH increases. Changes in specific markers of glutamate receptor plasticity, interleukin-1ß, and serotonergic modulation within key nodes of cardiorespiratory control do not fully account for the physiological adaptations to CH. Here, we used an unbiased approach (bulk tissue RNA sequencing) to test the hypothesis that mild or moderate CH elicits distinct gene expression profiles in important brain stem regions of cardiorespiratory control, which may explain the contrasting responses to CH. Gene expression profiles from the brain regions validated the accuracy of tissue biopsy methodology. Differential gene expression analyses revealed greater effects of CH on brain stem sites compared with the medial prefrontal cortex. Mild CH elicited an upregulation of predominantly immune-related genes and predicted activation of immune-related pathways and functions. In contrast, moderate CH broadly led to downregulation of genes and predicted inactivation of cellular pathways related to the immune response and vascular function. These data suggest that mild CH leads to a steady-state activation of neuroinflammatory pathways within the brain stem, whereas moderate CH drives the opposite response. Transcriptional shifts in immune-related functions may underlie the cardiorespiratory network's capability to respond to acute, more severe hypercapnia when in a state of progressively increased CH.NEW & NOTEWORTHY Mild chronic hypercapnia (CH) broadly upregulated immune-related genes and a predicted activation of biological pathways related to immune cell activity and the overall immune response. In contrast, moderate CH primarily downregulated genes related to major histocompatibility complex signaling and vasculature function that led to a predicted inactivation of pathways involving the immune response and vascular endothelial function. The severity-dependent effect on immune responses suggests that neuroinflammation has an important role in CH and may be important in the maintenance of proper ventilatory responses to acute and chronic hypercapnia.

Neuroprotection by upregulation of the major histocompatibility complex class I (MHC I) in SOD1G93A mice

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that progressively affects motoneurons, causing muscle atrophy and evolving to death. Astrocytes inhibit the expression of MHC-I by neurons, contributing to a degenerative outcome. The present study verified the influence of interferon β (IFN β) treatment, a proinflammatory cytokine that upregulates MHC-I expression, in SOD1G93A transgenic mice. For that, 17 days old presymptomatic female mice were subjected to subcutaneous application of IFN β (250, 1,000, and 10,000 IU) every other day for 20 days. Rotarod motor test, clinical score, and body weight assessment were conducted every third day throughout the treatment period. No significant intergroup variations were observed in such parameters during the pre-symptomatic phase. All mice were then euthanized, and the spinal cords collected for comparative analysis of motoneuron survival, reactive gliosis, synapse coverage, microglia morphology classification, cytokine analysis by flow cytometry, and RT-qPCR quantification of gene transcripts. Additionally, mice underwent Rotarod motor assessment, weight monitoring, and neurological scoring. The results show that IFN β treatment led to an increase in the expression of MHC-I, which, even at the lowest dose (250 IU), resulted in a significant increase in neuronal survival in the ALS presymptomatic period which lasted until the onset of the disease. The treatment also influenced synaptic preservation by decreasing excitatory inputs and upregulating the expression of AMPA receptors by astrocytes. Microglial reactivity quantified by the integrated density of pixels did not decrease with treatment but showed a less activated morphology, coupled with polarization to an M1 profile. Disease progression upregulated gene transcripts for pro- and anti-inflammatory cytokines, and IFN β treatment significantly decreased mRNA expression for IL4. Overall, the present results demonstrate that a low dosage of IFN β shows therapeutic potential by increasing MHC-I expression, resulting in neuroprotection and immunomodulation.

Synaptojanin 1 Modulates Functional Recovery After Incomplete Spinal Cord Injury in Male Apolipoprotein E Epsilon 4 Mice

Apolipoprotein E epsilon 4 (ApoE4) is the second most common variant of ApoE, being present in ∼14% of the population. Clinical reports identify ApoE4 as a genetic risk factor for poor outcomes after traumatic spinal cord injury (SCI) and spinal cord diseases such as cervical myelopathy. To date, there is no intervention to promote recovery of function after SCI/spinal cord diseases that is specifically targeted at ApoE4-associated impairment. Studies in the human and mouse brain link ApoE4 to elevated levels of synaptojanin 1 (synj1), a lipid phosphatase that degrades phosphoinositol 4,5-bisphosphate (PIP2) into inositol 4-monophosphate. Synj1 regulates rearrangements of the cytoskeleton as well as endocytosis and trafficking of synaptic vesicles. We report here that, as compared to ApoE3 mice, levels of synj1 messenger RNA and protein were elevated in spinal cords of healthy ApoE4 mice associated with lower PIP2 levels. Using a moderate-severity model of contusion SCI in mice, we found that genetic reduction of synj1 improved locomotor function recovery at 14 days after SCI in ApoE4 mice without altering spared white matter. Genetic reduction of synj1 did not alter locomotor recovery of ApoE3 mice after SCI. Bulk RNA sequencing revealed that at 14 days after SCI in ApoE4 mice, genetic reduction of synj1 upregulated genes involved in glutaminergic synaptic transmission just above and below the lesion. Overall, our findings provide evidence for a link between synj1 to poor outcomes after SCI in ApoE4 mice, up to 14 days post-injury, through mechanisms that may involve the function of excitatory glutaminergic neurons.

Ultrastructural Evidence of Synapse Preservation and Axonal Regeneration Following Spinal Root Repair with Fibrin Biopolymer and Therapy with Dimethyl Fumarate

Spinal cord injury causes critical loss in motor and sensory function. Ventral root avulsion is an experimental model in which there is the tearing of the ventral (motor) roots from the surface of the spinal cord, resulting in several morphological changes, including motoneuron degeneration and local spinal cord circuitry rearrangements. Therefore, our goal was to test the combination of surgical repair of lesioned roots with a fibrin biopolymer and the pharmacological treatment with dimethyl fumarate, an immunomodulatory drug. Thus, adult female Lewis rats were subjected to unilateral ventral root avulsion of L4-L6 roots followed by repair with fibrin biopolymer and daily treatment with dimethyl fumarate (15 mg/Kg; gavage) for 4 weeks, the survival time post-surgery being 12 weeks; n = 5/group/technique. Treatments were evaluated by immunofluorescence and transmission electron microscopy, morphometry of the sciatic nerve, and motor function recovery. Our results indicate that the combination between fibrin biopolymer and dimethyl fumarate is neuroprotective since most of the synapses apposed to alfa motoneurons were preserved in clusters. Also, nerve sprouting occurred, and the restoration of the 'g' ratio and large axon diameter was achieved with the combined treatment. Such parameters were combined with up to 50% of gait recovery, observed by the walking track test. Altogether, our results indicate that combining root restoration with fibrin biopolymer and dimethyl fumarate administration can enhance motoneuron survival and regeneration after proximal lesions.

Low T-cell reactivity to TDP-43 peptides in ALS

Background

Dysregulation of the immune system in amyotrophic lateral sclerosis (ALS) includes changes in T-cells composition and infiltration of T cells in the brain and spinal cord. Recent studies have shown that cytotoxic T cells can directly induce motor neuron death in a mouse model of ALS and that T cells from ALS patients are cytotoxic to iPSC-derived motor neurons from ALS patients. Furthermore, a clonal expansion to unknown epitope(s) was recently found in familial ALS and increased peripheral and intrathecal activation of cytotoxic CD8+ T cells in sporadic ALS.

Results

Here, we show an increased activation of peripheral T cells from patients with sporadic ALS by IL-2 treatment, suggesting an increase of antigen-experienced T cells in ALS blood. However, a putative antigen for T-cell activation in ALS has not yet been identified. Therefore, we investigated if peptides derived from TDP-43, a key protein in ALS pathogenesis, can act as epitopes for antigen-mediated activation of human T cells by ELISPOT and flow cytometry. We found that TDP-43 peptides induced only a weak MHCI or MHCII-restricted activation of both naïve and antigen-experienced T cells from healthy controls and ALS patients. Interestingly, we found less activation in T cells from ALS patients to TDP-43 and control stimuli. Furthermore, we found no change in the levels of naturally occurring auto-antibodies against full-length TDP-43 in ALS.

Conclusion

Our data suggests a general increase in antigen-experienced T cells in ALS blood, measured by in-vitro culture with IL-2 for 14 days. Furthermore, it suggests that TDP-43 is a weak autoantigen.

Boldine modulates glial transcription and functional recovery in a murine model of contusion spinal cord injury

Membrane channels such as those formed by connexins (Cx) and P2X7 receptors (P2X7R) are permeable to calcium ions and other small molecules such as adenosine triphosphate (ATP) and glutamate. Release of ATP and glutamate through these channels is a key mechanism driving tissue response to traumas such as spinal cord injury (SCI). Boldine, an alkaloid isolated from the Chilean boldo tree, blocks both Cx and Panx1 hemichannels (HCs). To test if boldine could improve function after SCI, boldine or vehicle was administered to treat mice with a moderate severity contusion-induced SCI. Boldine led to greater spared white matter and increased locomotor function as determined by the Basso Mouse Scale and horizontal ladder rung walk tests. Boldine treatment reduced immunostaining for markers of activated microglia (Iba1) and astrocytic (GFAP) markers while increasing that for axon growth and neuroplasticity (GAP-43). Cell culture studies demonstrated that boldine blocked glial HC, specifically Cx26 and Cx30, in cultured astrocytes and blocked calcium entry through activated P2X7R. RT-qPCR studies showed that boldine treatment reduced expression of the chemokine Ccl2, cytokine IL-6 and microglial gene CD68, while increasing expression of the neurotransmission genes Snap25 and Grin2b, and Gap-43. Bulk RNA sequencing revealed that boldine modulated a large number of genes involved in neurotransmission in spinal cord tissue just caudal from the lesion epicenter at 14 days after SCI. Numbers of genes regulated by boldine was much lower at 28 days after injury. These results indicate that boldine treatment ameliorates injury and spares tissue to increase locomotor function.

Aß Pathology and Neuron-Glia Interactions: A Synaptocentric View

Alzheimer's disease (AD) causes the majority of dementia cases worldwide. Early pathological hallmarks include the accumulation of amyloid-ß (Aß) and activation of both astrocytes and microglia. Neurons form the building blocks of the central nervous system, and astrocytes and microglia provide essential input for its healthy functioning. Their function integrates at the level of the synapse, which is therefore sometimes referred to as the "quad-partite synapse". Increasing evidence puts AD forward as a disease of the synapse, where pre- and postsynaptic processes, as well as astrocyte and microglia functioning progressively deteriorate. Here, we aim to review the current knowledge on how Aß accumulation functionally affects the individual components of the quad-partite synapse. We highlight a selection of processes that are essential to the healthy functioning of the neuronal synapse, including presynaptic neurotransmitter release and postsynaptic receptor functioning. We further discuss how Aß affects the astrocyte's capacity to recycle neurotransmitters, release gliotransmitters, and maintain ion homeostasis. We additionally review literature on how Aß changes the immunoprotective function of microglia during AD progression and conclude by summarizing our main findings and highlighting the challenges in current studies, as well as the need for further research.

Celsr2 Knockout Alleviates Inhibitory Synaptic Stripping and Benefits Motoneuron Survival and Axon Regeneration After Branchial Plexus Avulsion

Axotomy-induced synaptic stripping modulates survival and axon regeneration of injured motoneurons. Celsr2 is supposed to mediate homophilic interactions of neighboring cells during development, and its role in synaptic stripping remains unknow. In a model of brachial plexus avulsion, Celsr2 knockout improved functional recovery, motoneuron survival, and axon regeneration. Celsr2 was indicated to express in spinal motoneurons, excitatory and inhibitory interneurons, astrocytes, and a subset of oligodendrocytes using Celsr2^LacZ mice. Double immunostaining showed that the coverage of inhibitory and excitatory vesicles on injured motoneurons were remarkably reduced after injury, whereas more inhibitory vesicles were maintained in Celsr2^-/- mutants than control mice. In the ultrastructure, the density of inhibitory F-boutons on injured motoneurons was higher in Celsr2^-/- mutants than controls. Conditional knockout of Celsr2 in astrocytes or oligodendrocytes showed the similar axotomy-induced synaptic withdrawal to the control. RNAseq of injured spinal samples identified 12 MHC I molecules with significant changes between Celsr2^-/- and control mice. After injury, expression of MHC I surrounding injured motoneurons was increased, particularly high in Celsr2^-/- mutants. In conclusion, Celsr2 knockout enhances MHC I signaling, alleviates inhibitory synaptic stripping cell-autonomously, and contributes to motoneuron survival and regeneration, and Celsr2 is a potential target for neural repair.

Boldine modulates glial transcription and functional recovery in a murine model of contusion spinal cord injury

Membrane channels such as connexins (Cx), pannexins (Panx) and P2X ₇ receptors (P2X ₇ R) are permeable to calcium ions and other small molecules such as ATP and glutamate. Release of ATP and glutamate through these channels is a key mechanism driving tissue response to traumas such as spinal cord injury (SCI). Boldine, an alkaloid isolated from the Chilean boldo tree, blocks both Cx hemichannels (HC) and Panx. To test if boldine could improve function after SCI, boldine or vehicle was administered to treat mice with a moderate severity contusion-induced SCI. Boldine led to greater spared white matter and increased locomotor function as determined by the Basso Mouse Scale and horizontal ladder rung walk tests. Boldine treatment reduced immunostaining for markers of activated microglia (Iba1) and astrocytic (GFAP) markers while increasing that for axon growth and neuroplasticity (GAP-43). Cell culture studies demonstrated that boldine blocked glial HC, specifically Cx26 and Cx30, in cultured astrocytes and blocked calcium entry through activated P2X ₇ R. RT-qPCR studies showed that boldine treatment reduced expression of the chemokine Ccl2, cytokine IL-6 and microglial gene CD68, while increasing expression of the neurotransmission genes Snap25 and Grin2b, and Gap-43. Bulk RNA sequencing (of the spinal cord revealed that boldine modulated a large number of genes involved in neurotransmission in in spinal cord tissue just below the lesion epicenter at 14 days after SCI. Numbers of genes regulated by boldine was much lower at 28 days after injury. These results indicate that boldine treatment ameliorates injury and spares tissue to increase locomotor function.

Study of Effector CD8+ T Cell Interactions with Cortical Neurons in Response to Inflammation in Mouse Brain Slices and Neuronal Cultures

Cytotoxic CD8+ T cells contribute to neuronal damage in inflammatory and degenerative CNS disorders, such as multiple sclerosis (MS). The mechanism of cortical damage associated with CD8+ T cells is not well understood. We developed in vitro cell culture and ex vivo brain slice co-culture models of brain inflammation to study CD8+ T cell-neuron interactions. To induce inflammation, we applied T cell conditioned media, which contains a variety of cytokines, during CD8+ T cell polyclonal activation. Release of IFNγ and TNFα from co-cultures was verified by ELISA, confirming an inflammatory response. We also visualized the physical interactions between CD8+ T cells and cortical neurons using live-cell confocal imaging. The imaging revealed that T cells reduced their migration velocity and changed their migratory patterns under inflammatory conditions. CD8+ T cells increased their dwell time at neuronal soma and dendrites in response to added cytokines. These changes were seen in both the in vitro and ex vivo models. The results confirm that these in vitro and ex vivo models provide promising platforms for the study of the molecular details of neuron-immune cell interactions under inflammatory conditions, which allow high-resolution live microscopy and are readily amenable to experimental manipulation.

Hypoimmunogenic human pluripotent stem cells are valid cell sources for cell therapeutics with normal self-renewal and multilineage differentiation capacity

Hypoimmunogenic human pluripotent stem cells (hPSCs) are expected to serve as an unlimited cell source for generating universally compatible "off-the-shelf" cell grafts. However, whether the engineered hypoimmunogenic hPSCs still preserve their advantages of unlimited self-renewal and multilineage differentiation to yield functional tissue cells remains unclear. Here, we systematically studied the self-renewal and differentiation potency of three types of hypoimmunogenic hPSCs, established through the biallelic lesion of B2M gene to remove all surface expression of classical and nonclassical HLA class I molecules (B2Mnull), biallelic homologous recombination of nonclassical HLA-G1 to the B2M loci to knockout B2M while expressing membrane-bound β2m-HLA-G1 fusion proteins (B2MmHLAG), and ectopic expression of soluble and secreted β2m-HLA-G5 fusion proteins in B2MmHLAG hPSCs (B2Mm/sHLAG) in the most widely used WA09 human embryonic stem cells. Our results showed that hypoimmunogenic hPSCs with variable expression patterns of HLA molecules and immune compromising spectrums retained their normal self-renewal capacity and three-germ-layer differentiation potency. More importantly, as exemplified by neurons, cardiomyocytes and hepatocytes, hypoimmunogenic hPSC-derived tissue cells were fully functional as of their morphology, electrophysiological properties, macromolecule transportation and metabolic regulation. Our findings thus indicate that engineered hypoimmunogenic hPSCs hold great promise of serving as an unlimited universal cell source for cell therapeutics.

Viral-induced neuroinflammation: Different mechanisms converging to similar exacerbated glial responses

There is increasing evidence that viral infections are the source/origin of various types of encephalitis, encephalomyelitis, and other neurological and cognitive disorders. While the involvement of certain viruses, such as the Nipah virus and measles virus, is known, the mechanisms of neural invasion and the factors that trigger intense immune reactions are not fully understood. Based on recent publications, this review discusses the role of the immune response, interactions between viruses and glial cells, and cytokine mediators in the development of inflammatory diseases in the central nervous system. It also highlights the significant gaps in knowledge regarding these mechanisms.

Glia as antigen-presenting cells in the central nervous system

The contribution of the cells within the central nervous system (CNS) toward adaptive immune responses is emerging and incompletely understood. Recent findings indicate important functional interactions between T-cells and glial cells within the CNS that may contribute to disease and neuropathology through antigen presentation. Although glia are not classically considered antigen-presenting cell (APC) types, there is growing evidence indicating that glial antigen presentation plays an important role in several neurological diseases. This review discusses these findings which incriminate microglia, astrocytes, and oligodendrocyte lineage cells as CNS-resident APC types with implications for understanding disease.

The Time Course of MHC-I Expression in C57BL/6J and A/J Mice Correlates with the Degree of Retrograde Gliosis in the Spinal Cord following Sciatic Nerve Crush

The pleiotropic role of the major histocompatibility complex class I (MHC-I) reflects the close association between the nervous and immune systems. In turn, MHC-I upregulation postinjury is associated with a better regenerative outcome in isogenic mice following peripheral nerve damage. In the present work, we compared the time course of neuronal, glial, and sensorimotor recovery (1, 3, 5, 7, and 28 days after lesion—dal) following unilateral sciatic nerve crush in A/J and C57BL/6J mice. The A/J strain showed higher expression of MHC-I (7 dal, ** p < 0.01), Iba-1 (microglial reaction, 7 dal, *** p < 0.001), and GFAP (astrogliosis, 5 dal, * p < 0.05) than the C57BL/6J counterpart. Synaptic coverage (synaptophysin) was equivalent in both strains over time. In addition, mRNA expression of microdissected spinal motoneurons revealed an increase in cytoskeleton-associated molecules (cofilin, shp2, and crmp2, * p < 0.05), but not trkB, in C57BL/6J mice. Gait recovery, studied by the sciatic functional index, was faster in the A/J strain, despite the equivalent results of C57BL/6J at 28 days after injury. A similar recovery was also seen for the nociceptive threshold (von Frey test). Interestingly, when evaluating proprioceptive recovery, C57BL/6J animals showed an enlarged base of support, indicating abnormal ambulation postinjury. Overall, the present results reinforce the role of MHC-I expression in the plasticity of the nervous system following axotomy, which in turn correlates with the variable recovery capacity among strains of mice.

The SARS-CoV-2 envelope protein disrupts barrier function in an in vitro human blood-brain barrier model

Patients with coronavirus disease 2019 (COVID-19) have been frequently reported to exhibit neurological manifestations and disruption of the blood-brain barrier (BBB). Among the risk factors for BBB breakdown, the loss of endothelial cells and pericytes has caused widespread concern. Recent studies have revealed that severe acute respiratory syndrome coronavirus 2 envelope (S2E) protein caused cell death. We tested the hypothesis that the S2E protein alone could induce BBB dysfunction. The S2E protein bound to human BBB-related cells and inhibited cell viability in a dose- and time-dependent manner. Importantly, the S2E protein disrupted barrier function in an in vitro BBB model composed of HCMEC/D3 (brain endothelial cell line), HBVP (brain vascular pericyte), and U87MG (astrocyte cell line) cells and suppressed the expression of major genes involved in maintaining endothelial permeability and function. In addition, the S2E protein crossed the HCMEC/D3 monolayer. The S2E protein triggered inflammatory responses in HCMEC/D3 and U87MG cells. Taken together, these results show for the first time that the S2E protein has a negative impact on the BBB. Therapies targeting the S2E protein could protect against and treat central nervous system manifestations in COVID-19 patients.

Delayed onset, immunomodulation, and lifespan improvement of SOD1G93A mice after intravenous injection of human mesenchymal stem cells derived from adipose tissue

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the selective and progressive loss of motor neurons from the spinal cord, brain stem, and motor cortex. Although the hallmark of ALS is motor neuron degeneration, astrocytes, microglia, and T cells actively participate. Pharmacological treatment with riluzole has little effect on the lifespan of the patient. Thus, the development of new therapeutic strategies is of utmost importance. The objective of this study was to verify whether human mesenchymal stem cells (hMSCs) from adipose tissue have therapeutic potential in SOD1^G93A transgenic mice. The treatment was carried out in the asymptomatic phase of the disease (10th week) by a single systemic application of ad-hMSCs (1 ×10⁵ cells). The animals were sacrificed at the 14th week (the initial stage of symptoms) or the end-stage (ES) of the disease. The lumbar spinal cords were dissected and processed for Nissl staining (neuronal survival), immunohistochemistry (gliosis and synaptic preservation), and gene transcript expression (qRT-PCR). Behavioral analyses considering the onset of disease and its progression, neurological score, body weight, and motor control (rotarod test) started on the 10th week and were performed every three days until the ES of the disease. The results revealed that treatment with ad-hMSCs promoted greater neuronal survival (44%) than vehicle treatment. However, no effect was seen at the ES of the disease. Better structural preservation of the ventral horn in animals treated with ad-hMSCs was observed, together with decreased gliosis and greater synapse protection. In line with this, we found that the transcript levels of Hgf1 were upregulated in ad-hMSCs-treated mice. These results corroborate the behavioral data showing that ad-hMSCs had delayed motor deficits and reduced weight loss compared to vehicle animals. Additionally, cell therapy delayed the course of the disease and significantly improved survival by 20 days. Overall, our results indicate that treatment with ad-hMSCs has beneficial effects, enhancing neuronal survival and promoting a less degenerative neuronal microenvironment. Thus, this may be a potential therapy to improve the quality of life and to extend the lifespan of ALS patients.

The Role of Microglia in Neuroinflammation of the Spinal Cord after Peripheral Nerve Injury

Peripheral nerve injuries induce a pronounced immune reaction within the spinal cord, largely governed by microglia activation in both the dorsal and ventral horns. The mechanisms of activation and response of microglia are diverse depending on the location within the spinal cord, type, severity, and proximity of injury, as well as the age and species of the organism. Thanks to recent advancements in neuro-immune research techniques, such as single-cell transcriptomics, novel genetic mouse models, and live imaging, a vast amount of literature has come to light regarding the mechanisms of microglial activation and alluding to the function of microgliosis around injured motoneurons and sensory afferents. Herein, we provide a comparative analysis of the dorsal and ventral horns in relation to mechanisms of microglia activation (CSF1, DAP12, CCR2, Fractalkine signaling, Toll-like receptors, and purinergic signaling), and functionality in neuroprotection, degeneration, regeneration, synaptic plasticity, and spinal circuit reorganization following peripheral nerve injury. This review aims to shed new light on unsettled controversies regarding the diversity of spinal microglial-neuronal interactions following injury.

Accumulation of misfolded SOD1 outlines distinct patterns of motor neuron pathology and death during disease progression in a SOD1G93A mouse model of amyotrophic lateral sclerosis

Early misfolded superoxide dismutase 1 (mfSOD1) accumulation, motor neuron (MN) degeneration, and microgliosis are hallmark pathological features in SOD1^G93A amyotrophic lateral sclerosis (ALS) mice. Because of the different vulnerabilities of distinct MN subtypes, degenerating and surviving MNs coexist in different proportions during disease progression. By examining the expression of misfolded conformers of SOD1 using specific antibodies, we defined distinct MN phenotypes that were evaluated during disease progression and the local neuroinflammatory reaction. The most severe phenotype corresponded to somata of fast‐twitch subtype MNs, which exhibited highly positive mfSOD1 immunostaining and an extreme degree of vacuolar degeneration. Vacuoles, which are of mitochondrial origin, contain mfSOD1 in conjunction with nonmitochondrial proteins, such as chromogranin, CD81, and flotillin. The fusion of ER‐derived vesicles enriched in mfSOD1 with outer mitochondrial membranes is thought to be the primary mechanism for vacuole formation. In addition, the ulterior coalescence of enlarged mitochondria may lead to the formation of giant vacuoles. Vacuolar degeneration is a transient degenerative process occurring early during the presymptomatic stages of the disease in ALS mice. Some vacuolated MNs are also positive for pMLKL, the effector protein of necroptosis. This indicates a newly described mechanism in which extracellular vesicles derived from damaged MNs, via cellular secretion or necroptotic disruption, may be the triggers for initiating neuroinflammation, glial‐mediated neurotoxicity, and disease spreading. Furthermore, as MN degeneration in mutant SOD1 mice is noncell autonomous, the effects of experimentally increasing or decreasing the microglial response on the expression of MN phenotypes were also evaluated, demonstrating bidirectional cross talk signaling between the degree of expression of mfSOD1 and local neuroinflammation. More detailed knowledge regarding these processes occurring long before the end stages of the disease is necessary to identify novel molecular targets for future preclinical testing.

Reversible CD8 T cell-neuron cross-talk causes aging-dependent neuronal regenerative decline

Aging is associated with increased prevalence of axonal injuries characterized by poor regeneration and disability. However, the underlying mechanisms remain unclear. In our experiments, RNA sequencing of sciatic dorsal root ganglia (DRG) revealed significant aging-dependent enrichment in T cell signaling both before and after sciatic nerve injury (SNI) in mice. Lymphotoxin activated the transcription factor NF-κB, which induced expression of the chemokine CXCL13 by neurons. This in turn recruited CXCR5+CD8+ T cells to injured DRG neurons overexpressing major histocompatibility complex class I. CD8+ T cells repressed the axonal regeneration of DRG neurons via caspase 3 activation. CXCL13 neutralization prevented CXCR5+CD8+ T cell recruitment to the DRG and reversed aging-dependent regenerative decline, thereby promoting neurological recovery after SNI. Thus, axonal regeneration can be facilitated by antagonizing cross-talk between immune cells and neurons.

(-)-Epigallocatechin Gallate Attenuates Spinal Motoneuron Death Induced by Brachial Plexus Root Avulsion in Rats

Background:

Recent studies have indicated that epigallocatechin gallate (EGCG) benefits a variety of neurological insults. This study was performed to investigate the neuroprotective effect of EGCG after brachial plexus root avulsion in SD rats.

Methods:

One hundred twenty SD rats were randomized into the following three groups: an EGCG group, an Avulsion group, and a Sham group. There were 40 rats in each group. EGCG (100 mg/kg, i.p.) or normal saline was administered to rats immediately following the injuries. The treatment was continued from day 1 to day 7, and the animals were sacrificed on days 3, 7, 14 and 28 post-surgery for the harvesting of spinal cord samples for Nissl staining, immunohistochemistry (caspase-3, p-JNK, p-c-Jun) and western blot analysis (p-JNK, JNK, p-c-Jun, c-Jun).

Results:

EGCG treatment caused significant increases in the percentage of surviving motoneurons at days 14 and 28 (P<0.05) compared to the control animals. At days 3 and 7 after avulsion, the numbers of caspase-3-positive motoneurons in the EGCG-treated animals were significantly fewer than in the control animals (P<0.05). The numbers of p-JNK-positive motoneurons and the ratio of p-JNK/JNK were no significant differences between the Avulsion group and the EGCG-treated group after injury at any time point. The numbers of p-c-Jun-positive motoneurons and the ratio of p-c-Jun/c-Jun were significantly lower in EGCG-treated group compared with the Avulsion group at 3d and 7d after injury (p<0.05).

Conclusions:

Our results indicated that motoneurons were protected by EGCG against the cell death induced by brachial plexus root avulsion, and this effect was correlated with inhibiting c-Jun phosphorylation.

Mice lacking 5-lipoxygenase display motor deficits associated with cortical and hippocampal synapse abnormalities

Neural-immune interactions are related to the synapse plasticity and other dynamic processes in the nervous system. The absence or dysfunction of cellular/molecular elements from the immune system lead to impairments in the central and peripheral nervous system with behavior consequences such as cognitive, sensory, and locomotor deficits as well as social disabilities and anxiety disturbances. Cellular interactions between immune cells such as macrophages, microglia, and neutrophils with glial or neuronal cells have been of increasing interest over the last years. However, little is known about the role of immune-derived soluble factors in the context of homeostasis of the nervous system. Leukotrienes (LTs) are lipid mediators derived from the oxidation of arachidonic acid by 5-lipoxygenase (5-LO), and are classically involved in inflammation, allergies, and asthma. Here, we demonstrated that adult mice lacking 5-LO (5-LO^-/-) showed motor deficits in rotarod test and increased repetitive behavior (marble burying test). These behavioral changes are accompanied by increased levels of synapse proteins (PSD95 and synaptophysin) at the motor cortex and hippocampus, but not with BDNF alterations. No changes in microglial cell density or morphology were seen in the brains of 5-LO^-/- mice. Furthermore, expression of fractalkine receptor CX3CR1 was increased and of its ligand CX3CL1 was decreased in the cortex of 5-LO^-/- mice. Here we provide evidence for the involvement of 5-LO products structuring synapses network with motor behavior consequences. We suggest that the absence of 5-LO products lead to modified microglial/neuron interaction, reducing microglial pruning.

Brain Mast Cells in Sleep and Behavioral Regulation

The function of mast cells in the brain for the mediation of neurobehavior is largely unknown. Mast cells are a heterogeneous population of granulocytic cells in the immune system. Mast cells contain numerous mediators, such as histamine, serotonin, cytokines, chemokines, and lipid-derived factors. Mast cells localize not only in the periphery but are also resident in the brain of mammalians. Mast cells in the brain are constitutively active, releasing their contents gradually or rapidly by anaphylactic degranulation. Their activity is also increased by a wide range of stimuli including both immune and non-immune signals. Brain mast cell neuromodulation may thus be involved in various neurobehavior in health and diseases.Using Kit mutant mast cell deficient mice (Kit^W/Kit^W-v), we obtained results indicating that brain mast cells regulate sleep/wake and other behavioral phenotypes and that histamine from brain mast cells promotes wakefulness. These findings were also confirmed using a newer inducible and Kit-independent mast cell deficient Mas-TRECK (toxin receptor knockout) mouse. Injections of diphtheria toxin (DT) selectively deplete mast cells and reduce wakefulness during the periods of mast cell depletion.We recently introduced a mouse model for chronic sleep loss associated with diabetes. The mice reared on the wire net for 3 weeks (i.e., mild stress [MS]) showed decreased amount of non-rapid eye movement (NREM) sleep, increased sleep fragmentation, and abnormal glucose tolerance test [GTT] and insulin tolerance test [ITT], phenotypes which mirror human chronic insomnia. Interestingly, these mice with insomnia showed an increased number of mast cells in both the brain and adipose tissue. Mast cell deficient mice (Kit^W/Kit^W-v) and inhibition of mast cell functions with cromolyn or a histamine H1 receptor antagonist administration ameliorated both insomnia and abnormal glycometabolism. Mast cells may therefore represent an important pathophysiological mediator in sleep impairments and abnormal glycometabolism associated with chronic insomnia.

Neuroprotection and gliosis attenuation by intravenous application of human mesenchymal stem cells (hMSC) following ventral root crush in mice

Rupture and stretching of spinal roots are common incidents that take place in high-energy accidents. The proximal axotomy of motoneurons by crushing of ventral roots is directly related to the degeneration of half of the lesioned population within the first two weeks. Moreover, only a small percentage of surviving motoneurons can successfully achieve regeneration after such a proximal lesion, and new treatments are necessary to improve this scenario. In this sense, mesenchymal stem cells (MSC) are of great interest once they secrete a broad spectrum of bioactive molecules that are immunomodulatory and can restore the environment after a lesion. The present work aimed at studying the effects of human mesenchymal stem cells (hMSC) therapy after ventral root crush (VRC) in mice. We evaluated motoneuron survival, glial reaction, and synapse preservation at the ventral horn. For this purpose, C57BL/6 J were submitted to a crush procedure of L4 to L6 ventral roots and treated with a single intravenous injection of adipose-derived hMSC. Evaluation of the results was carried out at 7, 14, and 28 days after injury. Analysis of motoneuron survival and astrogliosis showed that hMSC treatment resulted in higher motoneuron preservation (motoneuron survival ipsi/contralateral ratio: VRC group = 53%, VRC + hMSC group = 66%; p < 0.01), combined with reduction of astrogliosis (ipsi/contralateral GFAP immunolabeling: VRC group = 470%, VRC + hMSC group = 250%; p < 0.001). The morphological classification and Sholl analysis of microglial activation revealed that hMSC treatment reduced type V and increased type II profiles, indicating an enhancement of surveying over activated microglial cells. The glial reactivity modulation directly influenced synaptic inputs in apposition to axotomized motoneurons. In the hMSC-treated group, synaptic maintenance was increased (ipsi/contralateral synaptophysin immunolabeling: VRC group = 53%, VRC + hMSC group = 64%; p < 0.05). Overall, the present data show that intravenous injection of hMSC has neuroprotective and anti-inflammatory effects, decreasing reactive astrogliosis, and microglial reaction. Also, such cell therapy results in motoneuron preservation, combined with significant maintenance of spinal cord circuits, in particular those related to the ventral horn.

Short and long-term neuroprotective effects of cannabidiol after neonatal peripheral nerve axotomy

Neonatal rat sciatic nerve crush mimics obstetric axonotmesis, leading to extensive loss of motor and sensory neurons. The present study aimed to investigate the neuroprotective potential of cannabidiol (CBD) and the role of cannabinoid receptors after sciatic nerve crush in neonatal rats. For that, two-day-old Wistar rats were used, organized into the following experimental groups: sciatic nerve crush plus CBD treatment (CBD), crush plus vehicle treatment (VE), crush + CBD + AM251 treatment (AM251 - CB1 inverse agonist), crush + CBD + AM630 treatment (AM630 - CB2 antagonist). Spinal motoneuron survival was evaluated by Nissl staining of the lumbar spinal cord, 5- and 56-days following injury. CBD treatment enhanced neuronal survival by ~54 % both 5 days and 8 weeks after injury. However, AM251 and AM630 treatment decreased neuronal rescue by 30 % when compared to the CBD group, suggesting that CBD acts partially through such pathways. However, in the long term, only the CB1 blockade reverted CBD positive results. Synaptic preservation was evaluated by anti-synaptophysin immunolabeling. Five days after the lesion, CBD treatment preserved ~35 % of synapses in the ventral horn, and such effect was partially reversed by CB1 inactivation. Additionally, CBD treatment reduced astroglial reaction both at 5 days (39 %, compared to VE) and 8 weeks (31 %, compared to VE) after lesion. The microglial response was acutely reduced by 62 % after CBD treatment. Overall, the results herein show that CBD is neuroprotective, increasing neuronal survival and reducing glial reaction after neonatal axotomy. Such effects require CB1 and CB2 receptors to be effective, in turn influencing neuroprotection, glial reactivity, and functional recovery.

3D-printed nerve guidance conduits multi-functionalized with canine multipotent mesenchymal stromal cells promote neuroregeneration after sciatic nerve injury in rats

Background

Nerve injuries are debilitating, leading to long-term motor deficits. Remyelination and axonal growth are supported and enhanced by growth factor and cytokines. Combination of nerve guidance conduits (NGCs) with adipose-tissue-derived multipotent mesenchymal stromal cells (AdMSCs) has been performing promising strategy for nerve regeneration.

Methods

3D-printed polycaprolactone (PCL)-NGCs were fabricated. Wistar rats subjected to critical sciatic nerve damage (12-mm gap) were divided into sham, autograft, PCL (empty NGC), and PCL + MSCs (NGC multi-functionalized with 10⁶ canine AdMSCs embedded in heterologous fibrin biopolymer) groups. In vitro, the cells were characterized and directly stimulated with interferon-gamma to evaluate their neuroregeneration potential. In vivo, the sciatic and tibial functional indices were evaluated for 12 weeks. Gait analysis and nerve conduction velocity were analyzed after 8 and 12 weeks. Morphometric analysis was performed after 8 and 12 weeks following lesion development. Real-time PCR was performed to evaluate the neurotrophic factors BDNF, GDNF, and HGF, and the cytokine and IL-10. Immunohistochemical analysis for the p75^NTR neurotrophic receptor, S100, and neurofilament was performed with the sciatic nerve.

Results

The inflammatory environment in vitro have increased the expression of neurotrophins BDNF, GDNF, HGF, and IL-10 in canine AdMSCs. Nerve guidance conduits multi-functionalized with canine AdMSCs embedded in HFB improved functional motor and electrophysiological recovery compared with PCL group after 12 weeks. However, the results were not significantly different than those obtained using autografts. These findings were associated with a shift in the regeneration process towards the formation of myelinated fibers. Increased immunostaining of BDNF, GDNF, and growth factor receptor p75^NTR was associated with the upregulation of BDNF, GDNF, and HGF in the spinal cord of the PCL + MSCs group. A trend demonstrating higher reactivity of Schwann cells and axonal branching in the sciatic nerve was observed, and canine AdMSCs were engrafted at 30 days following repair.

Conclusions

3D-printed NGCs multi-functionalized with canine AdMSCs embedded in heterologous fibrin biopolymer as cell scaffold exerted neuroregenerative effects. Our multimodal approach supports the trophic microenvironment, resulting in a pro-regenerative state after critical sciatic nerve injury in rats.

Microglial recruitment and mechanisms involved in the disruption of afferent synaptic terminals on spinal cord motor neurons after acute peripheral nerve injury

Peripheral nerve section with subsequent disconnection of motor neuron (MN) cell bodies from their skeletal muscle targets leads to a rapid reactive response involving the recruitment and activation of microglia. In addition, the loss of afferent synapses on MNs occurs in concomitance with microglial reaction by a process described as synaptic stripping. However, the way in which postaxotomy-activated microglia adjacent to MNs are involved in synaptic removal is less defined. Here, we used confocal and electron microscopy to examine interactions between recruited microglial cells and presynaptic terminals in axotomized MNs between 1 and 15 days after sciatic nerve transection in mice. We did not observe any bulk engulfment of synaptic boutons by microglia. Instead, microglial cells internalized small membranous-vesicular fragments which originated from the acute disruption of synaptic terminals involving the activation of the necroptotic pathway. The presence of abundant extracellular vesicles in the perineuronal space after axotomy, together with the increased expression of phospho-mixed lineage kinase domain-like protein and, later, of extracellular vesicle markers, such as CD9, CD63, and flotillin, indicate that the vesicles mainly originated in synapses and were transferred to microglia. The upregulation of Rab7 and Rab10 in microglia interacting with injured MNs, indicated the activation of endocytosis. As activated microglia and synaptic boutons displayed positive C1q immunoreactivity, a complement-mediated opsonization may also contribute to microglial-mediated synaptic disruption. In addition to the relevance of our data in the context of neuroinflammation and MN disease, they should also be taken into account for understanding functional recovery after peripheral nerve injury.

The Human ApoE4 Variant Reduces Functional Recovery and Neuronal Sprouting After Incomplete Spinal Cord Injury in Male Mice

Spinal cord injury (SCI) is a devastating form of neurotrauma. Patients who carry one or two apolipoprotein E (ApoE)4 alleles show worse functional outcomes and longer hospital stays after SCI, but the cellular and molecular underpinnings for this genetic link remain poorly understood. Thus, there is a great need to generate animal models to accurately replicate the genetic determinants of outcomes after SCI to spur development of treatments that improve physical function. Here, we examined outcomes after a moderate contusion SCI of transgenic mice expressing human ApoE3 or ApoE4. ApoE4 mice have worse locomotor function and coordination after SCI. Histological examination revealed greater glial staining in ApoE4 mice after SCI associated with reduced levels of neuronal sprouting markers. Bulk RNA sequencing revealed that subcellular processes (SCPs), such as extracellular matrix organization and inflammatory responses, were highly ranked among upregulated genes at 7 days after SCI in ApoE4 variants. Conversely, SCPs related to neuronal action potential and neuron projection development were increased in ApoE3 mice at 21 days. In summary, our results reveal a clinically relevant SCI mouse model that recapitulates the influence of ApoE genotypes on post SCI function in individuals who carry these alleles and suggest that the mechanisms underlying worse recovery for ApoE4 animals involve glial activation and loss of sprouting and synaptic activity.

Gene expression in the epileptic (EL) mouse hippocampus

The neuropathology of hippocampal seizure foci in human temporal lobe epilepsy (TLE) and several animal models of epilepsy reveal extensive neuronal loss along with astrocyte and microglial activation. Studies of these models have advanced hypotheses that propose both pathological changes are essential for seizure generation. However, some seizure foci in human TLE show an extreme loss of neurons in all hippocampal fields, giving weight to hypotheses that favor neuroglia as major players. The epileptic (EL) mouse is a seizure model in which there is no observable neuron loss but associated proliferation of microglia and astrocytes and provides a good model to study the role of activated neuroglia in the presence of an apparently normal population of neurons. While many studies have been carried out on the EL mouse, there is a paucity of studies on the molecular changes in the EL mouse hippocampus, which may provide insight on the role of neuroglia in epileptogenesis. In this paper we have applied high throughput gene expression analysis to identify the molecular changes in the hippocampus that may explain the pathological processes. We have observed several classes of genes whose expression levels are changed. It is hypothesized that the upregulation of heat shock proteins (HSP70, HSP72, FOSL2 (HSP40), and their molecular chaperones BAG3 and DNAJB5 along with the down regulated gene MALAT1 may contribute to the neuroprotection observed. The increased expression of BDNF along with immediate early gene expression (FosB, JunB, ERG4, NR4A1, NR4A2, FBXO3) and the down regulation of GABRD, DBP and MALAT1 it is hypothesized may contribute to the hyperexcitability of the hippocampal neurons in this model. Activated astrocytes and microglia may also contribute to excitability pathomechanisms. Activated astrocytes in the ELS mouse are deficient in glutamine synthetase and thus reduce the clearance of extracellular glutamate. Activated microglia which may be associated with C1Q and MHC class I molecules we propose may mediate a process of selective removal of defective GABAergic synapses through a process akin to trogocytosis that may reduce neuronal inhibition and favor hyperexcitability.

Neuroprotection by dimethyl fumarate following ventral root crush in C57BL/6J mice

CNS lesions usually result in permanent loss of function and are an important problem in the medical field. In order to investigate neuroprotection/degeneration mechanisms and the synaptic plasticity of motoneurons, in addition to the potential for a variety of treatments, different experimental models of axonal injury have been proposed. Recent studies have tested the immunomodulatory drug dimethyl fumarate (DMF) for the treatment of neurodegenerative diseases and have shown promising outcomes. Therefore, in this work, we investigated the effects of DMF with regard to neuroprotection and its influence on the glial response in C57BL/6J animals subjected to crushing of the motor roots in the lumbar intumescence of the spinal cord. The animals were divided into a vehicle-treated injury group (0.08 % methylcellulose solution control group, n = 7) and injured groups treated with DMF at different doses (15, 30, 45, 90 and 180 mg/kg; n = 6-7 per dose). The 90 mg/kg dose showed the best neuroprotective results, so it was used for treatment over a period of eight weeks. Neuronal survival was assessed through Nissl staining, and functional recovery was evaluated with the CatWalk system (walking track test) and the von Frey test (mechanoreception). Immunohistochemistry was used to assess synaptic coverage and astroglial and microglial reactivity using the primary antibodies anti-synaptophysin (pre-synaptic terminal pan marker), GAD65 (GABAergic pre-synaptic terminations - inhibitory), and VGLUT1 (glutamatergic pre-synaptic terminations - excitatory). Glial reactions were evaluated with anti-IBA1 (microglia) and GFAP (astrocytes). Gene transcript levels of IL-3, IL-4, TNF-α, IL-6, TGF-β, iNOS-M1, and arginase-M2 were quantified by RT-qPCR. The results indicated that treatment with DMF, at a dose of 90 mg/kg, promoted neuroprotection and immunomodulation towards an anti-inflammatory response. It also resulted in greater preservation of inhibitory synapses and reduced astroglial reactivity, providing a more favorable environment for sensorimotor recovery.

Co-transplantation of bone marrow mesenchymal stem cells and monocytes in the brain stem to repair the facial nerve axotomy

After the facial nerve axotomy (FNA), the distal end of the axon would gradually decay and disappear. Accumulated evidence shows that transplantation of bone marrow mesenchymal stem cells (BMSCs) reveals potential in the treatment of nervous system diseases or injuries. This study is aimed at investigating the therapeutic effects of co-transplantation of BMSCs and monocytes in FNA. We found that co-culture significantly elevated the CD4+/CD8+ ratio and CD4+ CD25+ T cell proportion compared with monocytes transplantation, and enhanced the differentiation of BMSCs into neurons. After the cell transplantation, the lowest apoptosis in the facial nerve nucleus was found in the co-transplantation group 2 (BMSCs:monocytes= 1:30). Moreover, the lowest expression levels of pro-inflammatory cytokines and the highest expression levels of anti-inflammatory cytokines were observed in the co-transplantation group 2 (BMSCs: monocytes= 1:30). The highest expression levels of protein in the JAK/STAT6 pathway and the SDF-1/CXCR4 axis were found in the co-transplantation group 2. BMSC/monocyte co-transplantation significantly improves the microenvironment in the facial nerve nucleus in FNA rats; therefore these findings suggest that it could promote the anti-/pro-inflammatory balance shift towards the anti-inflammatory microenvironment, alleviating survival conditions for BMSCs, regulating BMSC the chemotaxis homing, differentiation, and the section of BMSCs, and finally reducing the neuronal apoptosis. These findings might provide essential evidence for the in-hospital treatment of FNA with co-transplantation of BMSCs and monocytes.

Microglia Dynamics and Interactions with Motoneurons Axotomized After Nerve Injuries Revealed By Two-Photon Imaging

The significance of activated microglia around motoneurons axotomized after nerve injuries has been intensely debated. In particular, whether microglia become phagocytic is controversial. To resolve these issues we directly observed microglia behaviors with two-photon microscopy in ex vivo spinal cord slices from CX3CR1-GFP mice complemented with confocal analyses of CD68 protein. Axotomized motoneurons were retrogradely-labeled from muscle before nerve injuries. Microglia behaviors close to axotomized motoneurons greatly differ from those within uninjured motor pools. They develop a phagocytic phenotype as early as 3 days after injury, characterized by frequent phagocytic cups, high phagosome content and CD68 upregulation. Interactions between microglia and motoneurons changed with time after axotomy. Microglia first extend processes that end in phagocytic cups at the motoneuron surface, then they closely attach to the motoneuron while extending filopodia over the cell body. Confocal 3D analyses revealed increased microglia coverage of the motoneuron cell body surface with time after injury and the presence of CD68 granules in microglia surfaces opposed to motoneurons. Some microglia formed macroclusters associated with dying motoneurons. Microglia in these clusters display the highest CD68 expression and associate with cytotoxic T-cells. These observations are discussed in relation to current theories on microglia function around axotomized motoneurons.

Neuroprotection and immunomodulation by dimethyl fumarate and a heterologous fibrin biopolymer after ventral root avulsion and reimplantation

Background:

Ventral root avulsion (VRA) is an experimental approach in which there is an abrupt separation of the motor roots from the surface of the spinal cord. As a result, most of the axotomized motoneurons degenerate by the second week after injury, and the significant loss of synapses and increased glial reaction triggers a chronic inflammatory state. Pharmacological treatment associated with root reimplantation is thought to overcome the degenerative effects of VRA. Therefore, treatment with dimethyl fumarate (DMF), a drug with neuroprotective and immunomodulatory effects, in combination with a heterologous fibrin sealant/biopolymer (FS), a biological glue, may improve the regenerative response.

Methods:

Adult female Lewis rats were subjected to VRA of L4-L6 roots followed by reimplantation and daily treatment with DMF for four weeks. Survival times were evaluated 1, 4 or 12 weeks after surgery. Neuronal survival assessed by Nissl staining, glial reactivity (anti-GFAP for astrocytes and anti-Iba-1 for microglia) and synapse preservation (anti-VGLUT1 for glutamatergic inputs and anti-GAD65 for GABAergic inputs) evaluated by immunofluorescence, gene expression (pro- and anti-inflammatory molecules) and motor function recovery were measured.

Results:

Treatment with DMF at a dose of 15 mg/kg was found to be neuroprotective and immunomodulatory because it preserved motoneurons and synapses and decreased astrogliosis and microglial reactions, as well as downregulated the expression of pro-inflammatory gene transcripts.

Conclusion:

The pharmacological benefit was further enhanced when associated with root reimplantation with FS, in which animals recovered at least 50% of motor function, showing the efficacy of employing multiple regenerative approaches following spinal cord root injury.

Synaptic Plasticity on Motoneurons After Axotomy: A Necessary Change in Paradigm

Motoneurons axotomized by peripheral nerve injuries experience profound changes in their synaptic inputs that are associated with a neuroinflammatory response that includes local microglia and astrocytes. This reaction is conserved across different types of motoneurons, injuries, and species, but also displays many unique features in each particular case. These reactions have been amply studied, but there is still a lack of knowledge on their functional significance and mechanisms. In this review article, we compiled data from many different fields to generate a comprehensive conceptual framework to best interpret past data and spawn new hypotheses and research. We propose that synaptic plasticity around axotomized motoneurons should be divided into two distinct processes. First, a rapid cell-autonomous, microglia-independent shedding of synapses from motoneuron cell bodies and proximal dendrites that is reversible after muscle reinnervation. Second, a slower mechanism that is microglia-dependent and permanently alters spinal cord circuitry by fully eliminating from the ventral horn the axon collaterals of peripherally injured and regenerating sensory Ia afferent proprioceptors. This removes this input from cell bodies and throughout the dendritic tree of axotomized motoneurons as well as from many other spinal neurons, thus reconfiguring ventral horn motor circuitries to function after regeneration without direct sensory feedback from muscle. This process is modulated by injury severity, suggesting a correlation with poor regeneration specificity due to sensory and motor axons targeting errors in the periphery that likely render Ia afferent connectivity in the ventral horn nonadaptive. In contrast, reversible synaptic changes on the cell bodies occur only while motoneurons are regenerating. This cell-autonomous process displays unique features according to motoneuron type and modulation by local microglia and astrocytes and generally results in a transient reduction of fast synaptic activity that is probably replaced by embryonic-like slow GABA depolarizations, proposed to relate to regenerative mechanisms.

CD4+ T cell expression of the IL-10 receptor is necessary for facial motoneuron survival after axotomy

Background

After peripheral nerve transection, facial motoneuron (FMN) survival depends on an intact CD4+ T cell population and a central source of interleukin-10 (IL-10). However, it has not been determined previously whether CD4+ T cells participate in the central neuroprotective IL-10 cascade after facial nerve axotomy (FNA).

Methods

Immunohistochemical labeling of CD4+ T cells, pontine vasculature, and central microglia was used to determine whether CD4+ T cells cross the blood-brain barrier and enter the facial motor nucleus (FMNuc) after FNA. The importance of IL-10 signaling in CD4+ T cells was assessed by performing adoptive transfer of IL-10 receptor beta (IL-10RB)-deficient CD4+ T cells into immunodeficient mice prior to injury. Histology and qPCR were utilized to determine the impact of IL-10RB-deficient T cells on FMN survival and central gene expression after FNA. Flow cytometry was used to determine whether IL-10 signaling in T cells was necessary for their differentiation into neuroprotective subsets.

Results

CD4+ T cells were capable of crossing the blood-brain barrier and associating with reactive microglial nodules in the axotomized FMNuc. Full induction of central IL-10R gene expression after FNA was dependent on CD4+ T cells, regardless of their own IL-10R signaling capability. Surprisingly, CD4+ T cells lacking IL-10RB were incapable of mediating neuroprotection after axotomy and promoted increased central expression of genes associated with microglial activation, antigen presentation, T cell co-stimulation, and complement deposition. There was reduced differentiation of IL-10RB-deficient CD4+ T cells into regulatory CD4+ T cells in vitro.

Conclusions

These findings support the interdependence of IL-10- and CD4+ T cell-mediated mechanisms of neuroprotection after axotomy. CD4+ T cells may potentiate central responsiveness to IL-10, while IL-10 signaling within CD4+ T cells is necessary for their ability to rescue axotomized motoneuron survival. We propose that loss of IL-10 signaling in CD4+ T cells promotes non-neuroprotective autoimmunity after FNA.

Zika virus infection causes temporary paralysis in adult mice with motor neuron synaptic retraction and evidence for proximal peripheral neuropathy

Clinical evidence is mounting that Zika virus can contribute to Guillain-Barré syndrome which causes temporary paralysis, yet the mechanism is unknown. We investigated the mechanism of temporary acute flaccid paralysis caused by Zika virus infection in aged interferon αβ-receptor knockout mice used for their susceptibility to infection. Twenty-five to thirty-five percent of mice infected subcutaneously with Zika virus developed motor deficits including acute flaccid paralysis that peaked 8-10 days after viral challenge. These mice recovered within a week. Despite Zika virus infection in the spinal cord, motor neurons were not destroyed. We examined ultrastructures of motor neurons and synapses by transmission electron microscopy. The percent coverage of motor neurons by boutons was reduced by 20%; more specifically, flattened-vesicle boutons were reduced by 46%, and were normalized in recovering mice. Using electromyographic procedures employed in people to help diagnose Guillain-Barré syndrome, we determined that nerve conduction velocities between the sciatic notch and the gastrocnemius muscle were unchanged in paralyzed mice. However, F-wave latencies were increased in paralyzed mice, which suggests that neuropathy may exist between the sciatic notch to the nerve rootlets. Reversible synaptic retraction may be a previously unrecognized cofactor along with peripheral neuropathy for the development of Guillain-Barré syndrome during Zika virus outbreaks.

Toll-like receptor 4 (TLR4) influences the glial reaction in the spinal cord and the neural response to injury following peripheral nerve crush

After peripheral axotomy, there is a selective retraction of synaptic terminals in contact with injured motoneurons. This process, which actively involves glial cells, is influenced by the expression of immune-related molecules. Since toll-like receptors (TLRs) are upregulated by astrocytes and microglia following lesions, they might be involved in synaptic plasticity processes. Therefore, we administered lipopolysaccharide (LPS) to enhance TLR4 expression in mice and studied retrograde changes in the spinal cord ventral horn following sciatic nerve crush. To this end, adult C57BL/6J male mice were subjected to unilateral sciatic nerve crush at the mid-thigh level and, after a survival time of seven and forty days (acute and chronic phases, respectively), the spinal cords were paraformaldehyde-fixed and dissected out for immunolabeling for synaptophysin, glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (Iba1). The results show that TLR4 upregulation leads to synaptophysin downregulation close to spinal motoneuron cell bodies, indicating increased synaptic elimination. LPS exposure also further increases astrogliosis and microglial reactions in the both ventral and dorsal horns, especially ipsilateral to nerve axotomy, compared to those in untreated mice. Notably, LPS administration to TLR4^-/- mice produces results similar to those observed in untreated wild-type counterparts, reinforcing the role of this receptor in the glial response to injury. Therefore, our results suggest that the overexpression of the TLR4 receptor results in augmented astrogliosis/microglial reactions and the excessive loss of synapses postinjury, which may, in turn, affect the motoneuronal regenerative response and functionality. Additionally, treatment with LPS increases the expression of β2-microglobulin, a subcomponent of MHC I. Importantly, the absence of TLR4 results in imbalanced axonal regeneration, inducing subsequent improvements and setbacks. In conclusion, our results show the involvement of TLR4 in the process of synaptic remodeling, indicating a new target for future research aimed at developing therapies for CNS and PNS repair.

Tempol improves neuroinflammation and delays motor dysfunction in a mouse model (SOD1G93A) of ALS

BACKGROUND

The development of new therapeutic strategies to treat amyotrophic lateral sclerosis (ALS) is of utmost importance. The use of cyclic nitroxides such as tempol may provide neuroprotection and improve lifespan. We investigated whether tempol (50 mg/kg) presents therapeutic potential in SOD1^G93A transgenic mice.

METHODS

Tempol treatment began at the asymptomatic phase of the disease (10th week) and was administered every other day until week 14, after which it was administered twice a week until the final stage of the disease. The animals were sacrificed at week 14 (initial stage of symptoms-ISS) and at the end stage (ES) of the disease. The lumbar spinal cord of the animals was dissected and processed for use in the following techniques: Nissl staining to evaluate neuronal survival; immunohistochemistry to evaluate astrogliosis and microgliosis (ISS and ES); qRT-PCR to evaluate the expression of neurotrophic factors and pro-inflammatory cytokines (ISS); and transmission electron microscopy to evaluate the alpha-motoneurons (ES). Behavioral analyses considering the survival of animals, bodyweight loss, and Rotarod motor performance test started on week 10 and were performed every 3 days until the end-stage of the disease.

RESULTS

The results revealed that treatment with tempol promoted greater neuronal survival (23%) at ISS compared to untreated animals, which was maintained until ES. The intense reactivity of astrocytes and microglia observed in vehicle animals was reduced in the lumbar spinal cords of the animals treated with tempol. In addition, the groups treated with tempol showed reduced expression of proinflammatory cytokines (IL1β and TNFα) and a three-fold decrease in the expression of TGFβ1 at ISS compared with the group treated with vehicle.

CONCLUSIONS

Altogether, our results indicate that treatment with tempol has beneficial effects, delaying the onset of the disease by enhancing neuronal survival and decreasing glial cell reactivity during ALS progression in SOD1^G93A mice.

Temporal gene expression changes after acute and delayed ventral root avulsion-reimplantation

BACKGROUND

In a model of injured spinal motor neurons where the avulsed spinal nerve is surgically reimplanted, useful regrowth of the injured nerve follows, both in animal experiments and clinical cases. This has led to surgical reimplantation strategies with subsequent partial functional motoric recovery. Still, the ideal time point for successful regeneration after reimplantation and the specific genetic profile of this time point is not known.

OBJECTIVE

To explore the temporal gene expression of the whole genome in the ventral spinal cord after reimplantation at different time points after avulsion.

METHODS

Totally 18 adult rats were subjected to avulsion of the left L5 root only (N = 3), avulsion followed by acute spinal reimplantation (N = 3), avulsion followed by 24 h (N = 3) or 48 h (N = 3) delayed reimplantation. Animals were allowed to survive 24 h after their respective surgery whereafter the ventral quadrant of the spinal cord at the operated side was harvested, processed for and analysed with Affymetrix Rat Gene ST 1.0 array followed by statistical analysis of gene expression patternsResults:Specific gene expression patterns were found at different time points after avulsion and reimplantation. Over all, early reimplantation seemed to diminish inflammatory response and support gene regulation related to neuronal activity compared to avulsion only or delayed reimplantation. In addition did gene activity after avulsion-reimplantation correspond to regeneration-associated genes typical for regeneration in the peripheral nervous system.

CONCLUSIONS

Our study reveal that genetic profiling after this kind of injury is possible, that specific and distinct expression patterns can be found with early reimplantation being favourable over late and that regenerative activity in this kind of injury bears hallmark typical for peripheral nerve regeneration. These findings can be useful in elucidating specific genetic expression typical for successful nerve regeneration, hopefully not only in this specific model but in the nervous system in general.

Removal of the Potassium Chloride Co-Transporter from the Somatodendritic Membrane of Axotomized Motoneurons Is Independent of BDNF/TrkB Signaling But Is Controlled by Neuromuscular Innervation

The potassium-chloride cotransporter (KCC2) maintains the low intracellular chloride found in mature central neurons and controls the strength and direction of GABA/glycine synapses. We found that following axotomy as a consequence of peripheral nerve injuries (PNIs), KCC2 protein is lost throughout the somatodendritic membrane of axotomized spinal cord motoneurons after downregulation of kcc2 mRNA expression. This large loss likely depolarizes the reversal potential of GABA/glycine synapses, resulting in GABAergic-driven spontaneous activity in spinal motoneurons similar to previous reports in brainstem motoneurons. We hypothesized that the mechanism inducing KCC2 downregulation in spinal motoneurons following peripheral axotomy might be mediated by microglia or motoneuron release of BDNF and TrkB activation as has been reported on spinal cord dorsal horn neurons after nerve injury, motoneurons after spinal cord injury (SCI), and in many other central neurons throughout development or a variety of pathologies. To test this hypothesis, we used genetic approaches to interfere with microglia activation or delete bdnf from specifically microglia or motoneurons, as well as pharmacology (ANA-12) and pharmacogenetics (F616A mice) to block TrkB activation. We show that KCC2 dysregulation in axotomized motoneurons is independent of microglia, BDNF, and TrkB. KCC2 is instead dependent on neuromuscular innervation; KCC2 levels are restored only when motoneurons reinnervate muscle. Thus, downregulation of KCC2 occurs specifically while injured motoneurons are regenerating and might be controlled by target-derived signals. GABAergic and glycinergic synapses might therefore depolarize motoneurons disconnected from their targets and contribute to augment motoneuron activity known to promote motor axon regeneration.

Neural circuit repair by low-intensity magnetic stimulation requires cellular magnetoreceptors and specific stimulation patterns

Although electromagnetic brain stimulation is a promising treatment in neurology and psychiatry, clinical outcomes are variable, and underlying mechanisms are ill-defined, which impedes the development of new effective stimulation protocols. Here, we show, in vivo and ex vivo, that repetitive transcranial magnetic stimulation at low-intensity (LI-rTMS) induces axon outgrowth and synaptogenesis to repair a neural circuit. This repair depends on stimulation pattern, with complex biomimetic patterns being particularly effective, and the presence of cryptochrome, a putative magnetoreceptor. Only repair-promoting LI-rTMS patterns up-regulated genes involved in neuronal repair; almost 40% of were cryptochrome targets. Our data open a new framework to understand the mechanisms underlying structural neuroplasticity induced by electromagnetic stimulation. Rather than neuronal activation by induced electric currents, we propose that weak magnetic fields act through cryptochrome to activate cellular signaling cascades. This information opens new routes to optimize electromagnetic stimulation and develop effective treatments for different neurological diseases.

Role of MHC-I Expression on Spinal Motoneuron Survival and Glial Reactions Following Ventral Root Crush in Mice

Lesions to the CNS/PNS interface are especially severe, leading to elevated neuronal degeneration. In the present work, we establish the ventral root crush model for mice, and demonstrate the potential of such an approach, by analyzing injury evoked motoneuron loss, changes of synaptic coverage and concomitant glial responses in β2-microglobulin knockout mice (β2m KO). Young adult (8-12 weeks old) C57BL/6J (WT) and β2m KO mice were submitted to a L4-L6 ventral roots crush. Neuronal survival revealed a time-dependent motoneuron-like cell loss, both in WT and β2m KO mice. Along with neuronal loss, astrogliosis increased in WT mice, which was not observed in β2m KO mice. Microglial responses were more pronounced during the acute phase after lesion and decreased over time, in WT and KO mice. At 7 days after lesion β2m KO mice showed stronger Iba-1+ cell reaction. The synaptic inputs were reduced over time, but in β2m KO, the synaptic loss was more prominent between 7 and 28 days after lesion. Taken together, the results herein demonstrate that ventral root crushing in mice provides robust data regarding neuronal loss and glial reaction. The retrograde reactions after injury were altered in the absence of functional MHC-I surface expression.

Major Histocompatibility Complex (MHC) Genes and Disease Resistance in Fish

Fascinating about classical major histocompatibility complex (MHC) molecules is their polymorphism. The present study is a review and discussion of the fish MHC situation. The basic pattern of MHC variation in fish is similar to mammals, with MHC class I versus class II, and polymorphic classical versus nonpolymorphic nonclassical. However, in many or all teleost fishes, important differences with mammalian or human MHC were observed: (1) The allelic/haplotype diversification levels of classical MHC class I tend to be much higher than in mammals and involve structural positions within but also outside the peptide binding groove; (2) Teleost fish classical MHC class I and class II loci are not linked. The present article summarizes previous studies that performed quantitative trait loci (QTL) analysis for mapping differences in teleost fish disease resistance, and discusses them from MHC point of view. Overall, those QTL studies suggest the possible importance of genomic regions including classical MHC class II and nonclassical MHC class I genes, whereas similar observations were not made for the genomic regions with the highly diversified classical MHC class I alleles. It must be concluded that despite decades of knowing MHC polymorphism in jawed vertebrate species including fish, firm conclusions (as opposed to appealing hypotheses) on the reasons for MHC polymorphism cannot be made, and that the types of polymorphism observed in fish may not be explained by disease-resistance models alone.

Cytotoxic CD8+ T lymphocytes expressing ALS-causing SOD1 mutant selectively trigger death of spinal motoneurons

CD8⁺ T lymphocytes, which are typically devoted to eliminate malignant and infected cells, have been described in the central nervous system (CNS) of patients and mice with amyotrophic lateral sclerosis (ALS). However, their role in ALS pathogenesis has yet to be unraveled. Here, we show that ablation of CD8⁺ T cells in ALS mice increased the number of surviving motoneurons. CD8⁺ T cells expressing the ALS-causing superoxide dismutase-1 mutant protein recognize and selectively kill motoneurons in vitro. To exert their cytotoxic function, mutant CD8⁺ T cells required presentation of the antigen-MHC-I complex at the surface of the motoneurons. Analysis of T cell receptor diversity supports the evidence that self-reactive CD8⁺ T lymphocytes infiltrate the CNS of ALS mice to exert cytotoxic function.

Adaptive immune response is part of the dynamic changes that accompany motoneuron loss in amyotrophic lateral sclerosis (ALS). CD4⁺ T cells that regulate a protective immunity during the neurodegenerative process have received the most attention. CD8⁺ T cells are also observed in the spinal cord of patients and ALS mice although their contribution to the disease still remains elusive. Here, we found that activated CD8⁺ T lymphocytes infiltrate the central nervous system (CNS) of a mouse model of ALS at the symptomatic stage. Selective ablation of CD8⁺ T cells in mice expressing the ALS-associated superoxide dismutase-1 (SOD1)^G93A mutant decreased spinal motoneuron loss. Using motoneuron-CD8⁺ T cell coculture systems, we found that mutant SOD1-expressing CD8⁺ T lymphocytes selectively kill motoneurons. This cytotoxicity activity requires the recognition of the peptide-MHC-I complex (where MHC-I represents major histocompatibility complex class I). Measurement of interaction strength by atomic force microscopy-based single-cell force spectroscopy demonstrated a specific MHC-I-dependent interaction between motoneuron and SOD1^G93A CD8⁺ T cells. Activated mutant SOD1 CD8⁺ T cells produce interferon-γ, which elicits the expression of the MHC-I complex in motoneurons and exerts their cytotoxic function through Fas and granzyme pathways. In addition, analysis of the clonal diversity of CD8⁺ T cells in the periphery and CNS of ALS mice identified an antigen-restricted repertoire of their T cell receptor in the CNS. Our results suggest that self-directed immune response takes place during the course of the disease, contributing to the selective elimination of a subset of motoneurons in ALS.

The Role of BDNF in Peripheral Nerve Regeneration: Activity-Dependent Treatments and Val66Met

Despite the ability of peripheral nerves to spontaneously regenerate after injury, recovery is generally very poor. The neurotrophins have emerged as an important modulator of axon regeneration, particularly brain derived neurotrophic factor (BDNF). BDNF regulation and signaling, as well as its role in activity-dependent treatments including electrical stimulation, exercise, and optogenetic stimulation are discussed here. The importance of a single nucleotide polymorphism in the BDNF gene, Val66Met, which is present in 30% of the human population and may hinder the efficacy of these treatments in enhancing regeneration after injury is considered. Preliminary data are presented on the effectiveness of one such activity-dependent treatment, electrical stimulation, in enhancing axon regeneration in mice expressing the met allele of the Val66Met polymorphism.