Changes in NG2 cells and oligodendrocytes in a new model of intraspinal hemorrhage

Quantifying Intraparenchymal Hemorrhage after Traumatic Spinal Cord Injury: A Review of Methodology

Intraparenchymal hemorrhage (IPH) after a traumatic injury has been associated with poor neurological outcomes. Although IPH may result from the initial mechanical trauma, the blood and its breakdown products have potentially deleterious effects. Further, the degree of IPH has been correlated with injury severity and the extent of subsequent recovery. Therefore, accurate evaluation and quantification of IPH following traumatic spinal cord injury (SCI) is important to define treatments' effects on IPH progression and secondary neuronal injury. Imaging modalities, such as magnetic resonance imaging (MRI) and ultrasound (US), have been explored by researchers for the detection and quantification of IPH following SCI. Both quantitative and semiquantitative MRI and US measurements have been applied to objectively assess IPH following SCI, but the optimal methods for doing so are not well established. Studies in animal SCI models (rodent and porcine) have explored US and histological techniques in evaluating SCI and have demonstrated the potential to detect and quantify IPH. Newer techniques using machine learning algorithms (such as convolutional neural networks [CNN]) have also been studied to calculate IPH volume and have yielded promising results. Despite long-standing recognition of the potential pathological significance of IPH within the spinal cord, quantifying IPH with MRI or US is a relatively new area of research. Further studies are warranted to investigate their potential use. Here, we review the different and emerging quantitative MRI, US, and histological approaches used to detect and quantify IPH following SCI.

TUBB4A mutations result in both glial and neuronal degeneration in an H-ABC leukodystrophy mouse model

Mutations in TUBB4A result in a spectrum of leukodystrophy including Hypomyelination with Atrophy of Basal Ganglia and Cerebellum (H-ABC), a rare hypomyelinating leukodystrophy, often associated with a recurring variant p.Asp249Asn (D249N). We have developed a novel knock-in mouse model harboring heterozygous (Tubb4a^D249N/+) and the homozygous (Tubb4a^D249N/D249N) mutation that recapitulate the progressive motor dysfunction with tremor, dystonia and ataxia seen in H-ABC. Tubb4a^D249N/D249N mice have myelination deficits along with dramatic decrease in mature oligodendrocytes and their progenitor cells. Additionally, a significant loss occurs in the cerebellar granular neurons and striatal neurons in Tubb4a^D249N/D249N mice. In vitro studies show decreased survival and dysfunction in microtubule dynamics in neurons from Tubb4a^D249N/D249N mice. Thus Tubb4a^D249N/D249N mice demonstrate the complex cellular physiology of H-ABC, likely due to independent effects on oligodendrocytes, striatal neurons, and cerebellar granule cells in the context of altered microtubule dynamics, with profound neurodevelopmental deficits.

Transcriptomic analysis of α-synuclein knockdown after T3 spinal cord injury in rats

Background

Endogenous α-synuclein (α-Syn) is involved in many pathophysiological processes in the secondary injury stage after acute spinal cord injury (SCI), and the mechanism governing these functions has not been thoroughly elucidated to date. This research aims to characterize the effect of α-Syn knockdown on transcriptional levels after SCI and to determine the mechanisms underlying α-Syn activity based on RNA-seq.

Result

The establishment of a rat model of lentiviral vector-mediated knockdown of α-Syn in Sprague-Dawley rats with T3 spinal cord contusion (LV_SCI group). The results of the RNA-seq analysis showed that there were 337 differentially expressed genes (DEGs) between the SCI group and the LV_SCI group, and 153 DEGs specific to LV_SCI between the (SCI vs LV_SCI) and (SCI vs CON) comparisons. The top 20 biological transition terms were identified by Gene ontology (GO) analysis. The Kyoto Gene and Genomic Encyclopedia (KEGG) analysis showed that the LV_SCI group significantly upregulated the cholinergic synaptic & nicotine addiction and the neuroactive ligand receptor interaction signaling pathway. Enriched chord analysis analyzes key genes. Further cluster analysis, gene and protein interaction network analysis and RT-qPCR results showed that Chrm2 and Chrnb2 together significantly in both pathways. The proliferation of muscarinic cholinergic receptor subtype 2 (Chrm2) and nicotinic cholinergic receptor subtype β2 (Chrnb2), and the neurogenesis were elevated in the injury site of LV_SCI group by immunofluorescence. Further by subcellular localization, the LV_SCI group enhanced the expression of Chrnb2 at the cell membrane.

Conclusion

Knockdown of α-Syn after SCI enhance motor function and promote neurogenesis probably through enhancing cholinergic signaling pathways and neuroreceptor interactions. This study not only further clarifies the understanding of the mechanism of knockdown of α-Syn on SCI but also helps to guide the treatment strategy for SCI.

Myelin status and oligodendrocyte lineage cells over time after spinal cord injury: What do we know and what still needs to be unwrapped?

Spinal cord injury (SCI) affects over 17,000 individuals in the United States per year, resulting in sudden motor, sensory and autonomic impairments below the level of injury. These deficits may be due at least in part to the loss of oligodendrocytes and demyelination of spared axons as it leads to slowed or blocked conduction through the lesion site. It has long been accepted that progenitor cells form new oligodendrocytes after SCI, resulting in the acute formation of new myelin on demyelinated axons. However, the chronicity of demyelination and the functional significance of remyelination remain contentious. Here we review work examining demyelination and remyelination after SCI as well as the current understanding of oligodendrocyte lineage cell responses to spinal trauma, including the surprisingly long-lasting response of NG2+ oligodendrocyte progenitor cells (OPCs) to proliferate and differentiate into new myelinating oligodendrocytes for months after SCI. OPCs are highly sensitive to microenvironmental changes, and therefore respond to the ever-changing post-SCI milieu, including influx of blood, monocytes and neutrophils; activation of microglia and macrophages; changes in cytokines, chemokines and growth factors such as ciliary neurotrophic factor and fibroblast growth factor-2; glutamate excitotoxicity; and axon degeneration and sprouting. We discuss how these changes relate to spontaneous oligodendrogenesis and remyelination, the evidence for and against demyelination being an important clinical problem and if remyelination contributes to motor recovery.

MicroRNA-219 Inhibits Proliferation and Induces Differentiation of Oligodendrocyte Precursor Cells after Contusion Spinal Cord Injury in Rats

MicroRNA-219 (miR-219) regulates the proliferation and differentiation of oligodendrocyte precursor cells (OPCs) during central nervous system (CNS) development. OPCs only differentiate into oligodendrocytes (OLs) in the healthy CNS, but can generate astrocytes (As) after injury. We hypothesized that miR-219 may modulate OPC proliferation and differentiation in a cervical C5 contusion spinal cord injury (SCI) model. After injury, we observed a decrease in the miR-219 level and quantity of OLs and an increase in the number of OPCs and As. Silencing of miR-219 by its antagomir in vivo produced similar results, but of greater magnitude. Overexpression of miR-219 by its agomir in vivo increased the number of OLs and suppressed generation of OPCs and As. Luxol fast blue staining confirmed that SCI caused demyelination and that the extent of demyelination was attenuated by miR-219 overexpression, but aggravated by miR-219 reduction. Monocarboxylate transporter 1 (MCT-1) may be implicated in the regulation of OPC proliferation and differentiation mediated by miR-219 following contusion SCI. Collectively, our data suggest that miR-219 may mediate SCI-induced OPC proliferation and differentiation, and MCT-1 may participate in this process as a target of miR-219.

The Biology of Regeneration Failure and Success After Spinal Cord Injury

Since no approved therapies to restore mobility and sensation following spinal cord injury (SCI) currently exist, a better understanding of the cellular and molecular mechanisms following SCI that compromise regeneration or neuroplasticity is needed to develop new strategies to promote axonal regrowth and restore function. Physical trauma to the spinal cord results in vascular disruption that, in turn, causes blood-spinal cord barrier rupture leading to hemorrhage and ischemia, followed by rampant local cell death. As subsequent edema and inflammation occur, neuronal and glial necrosis and apoptosis spread well beyond the initial site of impact, ultimately resolving into a cavity surrounded by glial/fibrotic scarring. The glial scar, which stabilizes the spread of secondary injury, also acts as a chronic, physical, and chemo-entrapping barrier that prevents axonal regeneration. Understanding the formative events in glial scarring helps guide strategies towards the development of potential therapies to enhance axon regeneration and functional recovery at both acute and chronic stages following SCI. This review will also discuss the perineuronal net and how chondroitin sulfate proteoglycans (CSPGs) deposited in both the glial scar and net impede axonal outgrowth at the level of the growth cone. We will end the review with a summary of current CSPG-targeting strategies that help to foster axonal regeneration, neuroplasticity/sprouting, and functional recovery following SCI.

To Be or Not to Be: Environmental Factors that Drive Myelin Formation during Development and after CNS Trauma

Oligodendrocytes are specialized glial cells that myelinate central nervous system (CNS) axons. Historically, it was believed that the primary role of myelin was to compactly ensheath axons, providing the insulation necessary for rapid signal conduction. However, mounting evidence demonstrates the dynamic importance of myelin and oligodendrocytes, including providing metabolic support to neurons and regulating axon protein distribution. As such, the development and maintenance of oligodendrocytes and myelin are integral to preserving CNS homeostasis and supporting proper functioning of widespread neural networks. Environmental signals are critical for proper oligodendrocyte lineage cell progression and their capacity to form functional compact myelin; these signals are markedly disturbed by injury to the CNS, which may compromise endogenous myelin repair capabilities. This review outlines some key environmental factors that drive myelin formation during development and compares that to the primary factors that define a CNS injury milieu. We aim to identify developmental factors disrupted after CNS trauma as well as pathogenic factors that negatively impact oligodendrocyte lineage cells, as these are potential therapeutic targets to promote myelin repair after injury or disease.

Sub-cellular In-situ Characterization of Ferritin(iron) in a Rodent Model of Spinal Cord Injury

Iron (Fe) is an essential metal involved in a wide spectrum of physiological functions. Sub-cellular characterization of the size, composition, and distribution of ferritin(iron) can provide valuable information on iron storage and transport in health and disease. In this study we employ magnetic force microscopy (MFM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS) to characterize differences in ferritin(iron) distribution and composition across injured and non-injured tissues by employing a rodent model of spinal cord injury (SCI). Our biophysical and ultrastructural analyses provide novel insights into iron distribution which are not obtained by routine biochemical stains. In particular, ferritin(iron) rich lysosomes revealed increased heterogeneity in MFM signal from tissues of SCI animals. Ultrastructural analysis using TEM elucidated that both cytosolic and lysosomal ferritin(iron) density was increased in the injured (spinal cord) and non-injured (spleen) tissues of SCI as compared to naïve animals. In-situ EELs analysis revealed that ferritin(iron) was primarily in Fe³⁺ oxidation state in both naïve and SCI animal tissues. The insights provided by this study and the approaches utilized here can be applied broadly to other systemic problems involving iron regulation or to understand the fate of exogenously delivered iron-oxide nanoparticles.

Intraspinal TLR4 activation promotes iron storage but does not protect neurons or oligodendrocytes from progressive iron-mediated damage

Iron is essential for basic cellular functions but in excess is highly toxic. For this reason, free iron and iron storage are controlled in the periphery by elaborate regulatory mechanisms. In contrast, iron regulation in the central nervous system (CNS) is not well defined. Given that excess iron is present after trauma, hemorrhagic stroke and neurodegeneration, understanding normal iron regulation and promoting iron uptake in CNS pathology is crucial. Peripherally, toll-like receptor 4 (TLR4) activation promotes iron sequestration by macrophages. Notably, iron-rich sites of CNS pathology typically contain TLR4 agonists, which may promote iron uptake. Indeed, our recent work showed impaired iron storage after acute spinal cord injury in mice with TLR4 deficiency. Here we used a reductionist model to ask if TLR4 activation in the CNS stimulates iron uptake and promotes neuroprotection from iron-induced toxicity. For this, we measured the ability of microglia/macrophages to sequester exogenous iron and prevent pathology with and without concomitant intraspinal TLR4 activation. Results show that, similar to the periphery, activating intraspinal TLR4 via focal LPS injection increased mRNA encoding iron uptake and storage proteins and promoted iron sequestration into ferritin-expressing macrophages. However, this did not prevent oligodendrocyte and neuron loss. Moreover, replacement of oligodendrocytes by progenitor cells - a normally robust response to in vivo macrophage TLR4 activation - was significantly reduced if iron was present concomitant with TLR4 activation. Thus, while TLR4 signaling promotes CNS iron uptake, future work needs to determine ways to enhance iron removal without blocking the reparative effects of innate immune receptor signaling.

White Matter Injury after Intracerebral Hemorrhage: Pathophysiology and Therapeutic Strategies

Intracerebral hemorrhage (ICH) accounts for 10%–30% of all types of stroke. Bleeding within the brain parenchyma causes gray matter (GM) destruction as well as proximal or distal white matter (WM) injury (WMI) due to complex pathophysiological mechanisms. Because WM has a distinct cellular architecture, blood supply pattern and corresponding function, and its response to stroke may vary from that of GM, a better understanding of the characteristics of WMI following ICH is essential and may shed new light on treatment options. Current evidence using histological, radiological and chemical biomarkers clearly confirms the spatio-temporal distribution of WMI post- ICH. Although certain types of pathological damage such as inflammatory, oxidative and neuro-excitotoxic injury to WM have been identified, the exact molecular mechanisms remain unclear. In this review article, we briefly describe the constitution and physiological function of brain WM, summarize evidence regarding WMI, and focus on the underlying pathophysiological mechanisms and therapeutic strategies.

Understanding the NG2 Glial Scar after Spinal Cord Injury

NG2 cells, also known as oligodendrocyte progenitor cells, are located throughout the central nervous system and serve as a pool of progenitors to differentiate into oligodendrocytes. In response to spinal cord injury (SCI), NG2 cells increase their proliferation and differentiation into remyelinating oligodendrocytes. While astrocytes are typically associated with being the major cell type in the glial scar, many NG2 cells also accumulate within the glial scar but their function remains poorly understood. Similar to astrocytes, these cells hypertrophy, upregulate expression of chondroitin sulfate proteoglycans, inhibit axon regeneration, contribute to the glial-fibrotic scar border, and some even differentiate into astrocytes. Whether NG2 cells also have a role in other astrocyte functions, such as preventing the spread of infiltrating leukocytes and expression of inflammatory cytokines, is not yet known. Thus, NG2 cells are not only important for remyelination after SCI but are also a major component of the glial scar with functions that overlap with astrocytes in this region. In this review, we describe the signaling pathways important for the proliferation and differentiation of NG2 cells, as well as the role of NG2 cells in scar formation and tissue repair.

Cognitive deficits develop 1month after diffuse brain injury and are exaggerated by microglia-associated reactivity to peripheral immune challenge

Traumatic brain injury (TBI) elicits immediate neuroinflammatory events that contribute to acute cognitive, motor, and affective disturbance. Despite resolution of these acute complications, significant neuropsychiatric and cognitive issues can develop and progress after TBI. We and others have provided novel evidence that these complications are potentiated by repeated injuries, immune challenges and stressors. A key component to this may be increased sensitization or priming of glia after TBI. Therefore, our objectives were to determine the degree to which cognitive deterioration occurred after diffuse TBI (moderate midline fluid percussion injury) and ascertain if glial reactivity induced by an acute immune challenge potentiated cognitive decline 30 days post injury (dpi). In post-recovery assessments, hippocampal-dependent learning and memory recall were normal 7 dpi, but anterograde learning was impaired by 30 dpi. Examination of mRNA and morphological profiles of glia 30 dpi indicated a low but persistent level of inflammation with elevated expression of GFAP and IL-1β in astrocytes and MHCII and IL-1β in microglia. Moreover, an acute immune challenge 30 dpi robustly interrupted memory consolidation specifically in TBI mice. These deficits were associated with exaggerated microglia-mediated inflammation with amplified (IL-1β, CCL2, TNFα) and prolonged (TNFα) cytokine/chemokine expression, and a marked reactive morphological profile of microglia in the CA3 of the hippocampus. Collectively, these data indicate that microglia remain sensitized 30 dpi after moderate TBI and a secondary inflammatory challenge elicits robust microglial reactivity that augments cognitive decline.

STATEMENT OF SIGNIFICANCE

Traumatic brain injury (TBI) is a major risk factor in development of neuropsychiatric problems long after injury, negatively affecting quality of life. Mounting evidence indicates that inflammatory processes worsen with time after a brain injury and are likely mediated by glia. Here, we show that primed microglia and astrocytes developed in mice 1 month following moderate diffuse TBI, coinciding with cognitive deficits that were not initially evident after injury. Additionally, TBI-induced glial priming may adversely affect the ability of glia to appropriately respond to immune challenges, which occur regularly across the lifespan. Indeed, we show that an acute immune challenge augmented microglial reactivity and cognitive deficits. This idea may provide new avenues of clinical assessments and treatments following TBI.

Human Traumatic Brain Injury Results in Oligodendrocyte Death and Increases the Number of Oligodendrocyte Progenitor Cells

Oligodendrocyte (OL) death may contribute to white matter pathology, a common cause of network dysfunction and persistent cognitive problems in patients with traumatic brain injury (TBI). Oligodendrocyte progenitor cells (OPCs) persist throughout the adult CNS and may replace dead OLs. OL death and OPCs were analyzed by immunohistochemistry of human brain tissue samples, surgically removed due to life-threatening contusions and/or focal brain swelling at 60.6 ± 75 hours (range 4-192 hours) postinjury in 10 severe TBI patients (age 51.7 ± 18.5 years). Control brain tissue was obtained postmortem from 5 age-matched patients without CNS disorders. TUNEL and CC1 co-labeling was used to analyze apoptotic OLs, which were increased in injured brain tissue (p < 0.05), without correlation with time from injury until surgery. The OPC markers Olig2, A2B5, NG2, and PDGFR-α were used. In contrast to the number of single-labeled Olig2, A2B5, NG2, and PDGFR-α-positive cells, numbers of Olig2 and A2B5 co-labeled cells were increased in TBI samples (p < 0.05); this was inversely correlated with time from injury to surgery (r = -0.8, p < 0.05). These results indicate that severe focal human TBI results in OL death and increases in OPCs postinjury, which may influence white matter function following TBI.

Lipopolysaccharide Upregulates the Expression of CINC-3 and LIX in Primary NG2 Cells

Numerous NG2 cells, also called oligodendrocyte progenitor cells (OPCs), exist ubiquitously in the gray and white matter in the adult central nervous system (CNS). Although NG2 cells could become active by upregulation of NG2 expression and hypertrophy or extension of their processes under various neuropathological conditions, their actual role in the brain remains to be illustrated. In view of the fact that the synergy of cytokine and chemokine networks plays an important role in CNS inflammation and immunity, we have assumed that the NG2 cells might take part in brain inflammation and immunity by making a contribution to the pool of cytokines or chemokines. In the current study, NG2-expressing OPCs were prepared from cerebral hemispheres of postnatal day 0 or 1 Sprague-Dawley rats. Our results showed that NG2-expressing OPCs, verified by immunohistological staining of anti-NG2 antibody and anti-platelet-derived growth factor receptor alpha (PDGFRα) antibody, presented binding affinity to lipopolysaccharide (LPS), a commonly used stimulator in a neuroinflammatory model. Using cytokine antibody array, QPCR and ELISA, we have further shown that LPS could upregulate the expression of cytokine induced neutrophil chemoattractant-3 (CINC-3) and LPS induced CXC chemokine (LIX) in primary NG2-expressing OPCs, without the alteration in cell number of NG2-expressing OPCs. In addition, the cells bearing the receptor for these two cytokines included microglia and OPCs. Taken together, our results suggest that NG2-expressing OPCs could response to LPS and may take part in neuroinflammatory process, through secreting cytokines and chemokines to exert an effect on target cells (OPCs and microglia).

Oligodendrocyte Precursor Cells in Spinal Cord Injury: A Review and Update

Spinal cord injury (SCI) is a devastating condition to individuals, families, and society. Oligodendrocyte loss and demyelination contribute as major pathological processes of secondary damages after injury. Oligodendrocyte precursor cells (OPCs), a subpopulation that accounts for 5 to 8% of cells within the central nervous system, are potential sources of oligodendrocyte replacement after SCI. OPCs react rapidly to injuries, proliferate at a high rate, and can differentiate into myelinating oligodendrocytes. However, posttraumatic endogenous remyelination is rarely complete, and a better understanding of OPCs' characteristics and their manipulations is critical to the development of novel therapies. In this review, we summarize known characteristics of OPCs and relevant regulative factors in both health and demyelinating disorders including SCI. More importantly, we highlight current evidence on post-SCI OPCs transplantation as a potential treatment option as well as the impediments against regeneration. Our aim is to shed lights on important knowledge gaps and to provoke thoughts for further researches and the development of therapeutic strategies.

Impact of vasculature damage on the outcome of spinal cord injury: a novel collagenase-induced model may give new insights into the mechanisms involved

The deleterious effect of vasculature damage on the outcome of spinal cord injury has long been recognized, and numerous clinical studies have shown that the presence of hemorrhage into the spinal cord is directly associated with a poorer neurological outcome. Vascular damage leads to decreased blood flow to the cord and the release of potentially toxic blood-borne components. Here we consider the mechanisms that may be contributing to hemorrhage-induced damage and discuss the utility of a new model of spinal cord hemorrhage, which was urgently required as most of our current understanding has been extrapolated from intracerebral hemorrhage studies.