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Central nervous system (CNS) injury, including stroke, spinal cord injury, and traumatic brain injury, causes severe neurological symptoms such as sensory and motor deficits. Currently, there is no effective therapeutic method to restore neurological function because the adult CNS has limited capacity to regenerate after injury. Many efforts have been made to understand the molecular and cellular mechanisms underlying CNS regeneration and to establish novel therapeutic methods based on these mechanisms, with a variety of strategies including cell transplantation, modulation of cell intrinsic molecular mechanisms, and therapeutic targeting of the pathological nature of the extracellular environment in CNS injury. In this review, we will focus on the mechanisms that regulate CNS regeneration, highlighting the history, recent efforts, and questions left unanswered in this field.

Glial cells play crucial roles in brain homeostasis and pathogenesis of central nervous system (CNS) injuries and diseases. However, the roles of these cells and the molecular mechanisms toward regeneration in the CNS have not been fully understood, especially the capacity of them toward demyelinating diseases. Therefore, there are still very limited therapeutic strategies to restore the function of adult CNS in diseases such as multiple sclerosis (MS). Remyelination, a spontaneous regeneration process in the CNS, requires the involvement of multiple cellular and extracellular components. Promoting remyelination by therapeutic interventions is a promising novel approach to restore the CNS function. Herein, we review the role of glial cells in CNS diseases and injuries. Particularly, we discuss the roles of glia and their functional interactions and regulatory mechanisms in remyelination, as well as the current therapeutic strategies for MS.

Astrocytes have a beneficial role in tissue repair after central nervous system (CNS) injury. Although astrocyte proliferation is activated in response to injury, the intracellular mechanisms of astrocyte proliferation during acute phase of injury are not fully clarified. In this study, by functionally screening the highly expressed genes in the pathological state of spinal astrocytes, heterogeneous nuclear ribonucleoprotein U (Hnrnpu) is identified as a potential endogenous molecule that regulates astrocyte proliferation and the following scar formation. Inhibition of Hnrnpu in astrocytes impairs the formation of astrocytic glial scar, motor function recovery, and neuronal regeneration after spinal cord injury (SCI) in mice. In human astrocytes, HNRNPU knockdown downregulates the genes related to the astrocyte functions in scar formation and neuronal regeneration. These findings uncover that modulation of endogenous astrocytic function would be a promising therapeutic avenue to restore neurological function after CNS injury.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the white matter degeneration. Although changes in blood lipids are involved in the pathogenesis of neurological diseases, the pathological role of blood lipids in ALS remains unclear. We performed lipidome analysis on the plasma of ALS model mice, mutant superoxide dismutase 1 (SOD1 ) mice, and found that the concentration of free fatty acids (FFAs), including oleic acid (OA) and linoleic acid (LA), decreased prior to disease onset. An study revealed that OA and LA directly inhibited glutamate-induced oligodendrocytes cell death via free fatty acid receptor 1 (FFAR1). A cocktail containing OA/LA suppressed oligodendrocyte cell death in the spinal cord of SOD1 mice. These results suggested that the reduction of FFAs in the plasma is a pathogenic biomarker for ALS in the early stages, and supplying a deficiency in FFAs is a potential therapeutic approach for ALS by preventing oligodendrocyte cell death.

Brain pericytes play essential roles in vascular homeostasis, including capillary stabilization and maintenance of the blood–brain barrier. Lipopolysaccharide (LPS), a component of the outer membrane of Gram-negative bacteria, is known to trigger inflammatory responses not only systemically but also within the central nervous system. In this study, we investigated the effects of LPS on the phenotype and transcriptome of brain vascular pericytes. LPS promoted bromodeoxyuridine incorporation in the primary culture of human brain pericytes as well as increased the number of Ki67-positive cells, indicating enhanced pericyte proliferation. Morphological analysis revealed that LPS decreased the cellular aspect ratio, suggesting altered cellular elongation. Transcriptomic profiling showed that LPS-induced differentially expressed genes were enriched for terms related to cell proliferation, angiogenesis, and blood–brain barrier function. Because pericytes critically regulate neurovascular coupling and metabolic support for active neurons, these LPS-induced alterations may ultimately perturb the microvascular control of neural circuits. These results suggest that LPS has the potential to regulate brain vascular function by inducing morphological and functional changes in pericytes.

Vascular network disruption caused by spinal cord injury (SCI) exacerbates secondary neuronal damage. Although vascular barrier disruption naturally restores over time, its underlying mechanism is not fully clarified. Here, we found that blood factors promote the proliferation of endothelial cells (ECs), which are essential for revascularization in the repair process after SCI. In vivo, endogenous IgG leakage into the spinal cord initiates EC proliferation at the lesion after injury. In vitro, adult mouse serum promotes mouse ECs proliferation through beta-2-microglobulin (B2M) via transforming growth factor beta receptor 2 (TGFBR2). Under EC-specific knockdown of Tgfbr2 in vivo, we observed exacerbated blood extravasation and increased inflammatory cell infiltration compared to controls. Additionally, suppression of endothelial Tgfbr2 impaired motor function recovery, axon regrowth, and regeneration in injured mice. These findings suggest that targeting the B2M-TGFBR2 axis could be a potential therapeutic approach to promoting functional recovery against vascular disruption after SCI.

Remyelination requires the precise wrapping of axons by oligodendrocyte processes, a critical step for restoring neural circuit function. However, a lack of quantitative systems that recapitulate axonal geometry and chemistry has limited mechanistic and pharmacological insights into myelin wrapping. Here, we present a bioengineered microfiber platform that mimics neurite architecture and surface chemistry, enabling high-content quantification of oligodendrocyte wrapping. Through compound screening, we identified dimemorfan, a clinically used sigma-1 receptor agonist, as a potent enhancer of myelin wrapping. Dimemorfan treatment accelerated remyelination and functional recovery in demyelinated mice and promoted myelin wrapping by human induced pluripotent stem cell (iPSC)-derived oligodendrocytes. Moreover, population-level magnetic resonance imaging (MRI) analyses revealed increased white matter volume in dimemorfan-administered individuals. This study establishes a biomimetic materials platform for myelin quantification and regeneration-oriented drug discovery, providing mechanistic and translational insights into sigma-1 receptor-mediated control of myelin wrapping.

Background CRISPR/Cas9 system is a powerful method to investigate the role of genes by introducing a mutation selectively and efficiently to specific genome positions in cell and animal lines. However, in primary neuron cultures, this method is affected by the issue that the effectiveness of CRISPR/Cas9 is different in each neuron. Here, we report an easy, quick and reliable method to identify mutants induced by the CRISPR/Cas9 system at a single neuron level, using immunocytochemistry (ICC) and fluorescence imaging. Results Dissociated cortical cells were transfected with CRISPR/Cas9 plasmids targeting the transcription factor cAMP-response element binding protein (CREB). Fluorescence ICC with CREB antibody and quantitative analysis of fluorescence intensity demonstrated that CREB expression disappeared in a fraction of the transfected neurons. The downstream FOS expression was also decreased in accordance with suppressed CREB expression. Moreover, dendritic arborization was decreased in the transfected neurons which lacked CREB immunoreactivity. Conclusions Detection of protein expression is efficient to identify individual postmitotic neurons with CRISPR/Cas9-mediated gene disruption in primary cortical cultures. The present method composed of CRISPR/Cas9 system, ICC and fluorescence imaging is applicable to study the function of various genes at a single-neuron level.

Demyelination is a common pathological feature of central nervous system (CNS) diseases, and its early detection is important for the diagnosis of neurological disorders; therefore, simple detection methods are in high demand. In this study, we found that both age-related myelin loss and demyelination in disease model mice can be predicted through integrative analysis of multiple respiratory parameters. Changes in some respiratory parameters correlated with myelin levels with aging; however, integrative analysis using conventional models further enabled the prediction of age-related myelin changes. In cuprizone-induced demyelination models, average respiratory values did not differ between demyelinated and control mice. However, the integrative analysis of the respiratory parameter set successfully distinguished demyelinated mice. Our study showed that respiratory function data may be used as a non-invasive method to predict brain conditions in mice, although translation to humans will require further validation. This approach shows promise as a potential method for early disease prediction and diagnostic support for CNS diseases.

Age-related regeneration failure in the central nervous system can occur as a result of a decline in remyelination efficacy. The responsiveness of myelin-forming cells to signals for remyelination is affected by aging-related epigenetic modification; however, the molecular mechanism is not fully clarified. In the present study, we report that the apelin receptor (APJ) mediates remyelination efficiency with age. APJ expression in myelin-forming cells is correlated with age-associated changes in remyelination efficiency, and the activation of APJ promotes remyelination through the translocation of myelin regulatory factor. APJ signaling activation promoted remyelination in both aged mice with toxin-induced demyelination and mice with experimental autoimmune encephalomyelitis. In human cells, APJ activation enhanced the expression of remyelination markers. Impaired oligodendrocyte function in aged animals can be reversibly reactivated; thus, the results demonstrate that dysfunction of the apelin-APJ system mediates remyelination failure in aged animals, and that their myelinating function can be reactivated by APJ activation.