Glial Metabolic Rewiring Promotes Axon Regeneration and Functional Recovery in the Central Nervous System

Metabolic reprogramming: a new option for the treatment of spinal cord injury

Spinal cord injuries impose a notably economic burden on society, mainly because of the severe after-effects they cause. Despite the ongoing development of various therapies for spinal cord injuries, their effectiveness remains unsatisfactory. However, a deeper understanding of metabolism has opened up a new therapeutic opportunity in the form of metabolic reprogramming. In this review, we explore the metabolic changes that occur during spinal cord injuries, their consequences, and the therapeutic tools available for metabolic reprogramming. Normal spinal cord metabolism is characterized by independent cellular metabolism and intercellular metabolic coupling. However, spinal cord injury results in metabolic disorders that include disturbances in glucose metabolism, lipid metabolism, and mitochondrial dysfunction. These metabolic disturbances lead to corresponding pathological changes, including the failure of axonal regeneration, the accumulation of scarring, and the activation of microglia. To rescue spinal cord injury at the metabolic level, potential metabolic reprogramming approaches have emerged, including replenishing metabolic substrates, reconstituting metabolic couplings, and targeting mitochondrial therapies to alter cell fate. The available evidence suggests that metabolic reprogramming holds great promise as a next-generation approach for the treatment of spinal cord injury. To further advance the metabolic treatment of the spinal cord injury, future efforts should focus on a deeper understanding of neurometabolism, the development of more advanced metabolomics technologies, and the design of highly effective metabolic interventions.

Local glycolysis supports injury-induced axonal regeneration

Successful axonal regeneration following injury requires the effective allocation of energy. How axons withstand the initial disruption in mitochondrial energy production caused by the injury and subsequently initiate regrowth is poorly understood. Transcriptomic data showed increased expression of glycolytic genes after optic nerve crush in retinal ganglion cells with the co-deletion of Pten and Socs3. Using retinal cultures in a multicompartment microfluidic device, we observed increased regrowth and enhanced mitochondrial trafficking in the axons of Pten and Socs3 co-deleted neurons. While wild-type axons relied on mitochondrial metabolism, after injury, in the absence of Pten and Socs3, energy production was supported by local glycolysis. Specific inhibition of lactate production hindered injury survival and the initiation of regrowth while slowing down glycolysis upstream impaired regrowth initiation, axonal elongation, and energy production. Together, these observations reveal that glycolytic ATP, combined with sustained mitochondrial transport, is essential for injury-induced axonal regrowth, providing new insights into the metabolic underpinnings of axonal regeneration.

Renal L-2-hydroxyglutarate dehydrogenase activity promotes hypoxia tolerance and mitochondrial metabolism in Drosophila melanogaster

OBJECTIVES

The mitochondrial enzyme L-2-hydroxyglutarate dehydrogenase (L2HGDH) regulates the abundance of L-2-hydroxyglutarate (L-2HG), a potent signaling metabolite capable of influencing chromatin architecture, mitochondrial metabolism, and cell fate decisions. Loss of L2hgdh activity in humans induces ectopic L-2HG accumulation, resulting in neurodevelopmental defects, altered immune cell function, and enhanced growth of clear cell renal cell carcinomas. To better understand the molecular mechanisms that underlie these disease pathologies, we used the fruit fly Drosophila melanogaster to investigate the endogenous functions of L2hgdh.

METHODS

L2hgdh mutant adult male flies were analyzed under normoxic and hypoxic conditions using a combination of semi-targeted metabolomics and RNA-seq. These multi-omic analyses were complemented by tissue-specific genetic studies that examined the effects of L2hgdh mutations on the Drosophila renal system (Malpighian tubules; MTs).

RESULTS

Our studies revealed that while L2hgdh is not essential for growth or viability under standard culture conditions, L2hgdh mutants are hypersensitive to hypoxia and expire during the reoxygenation phase with severe disruptions of mitochondrial metabolism. Moreover, we find that the fly renal system is a key site of L2hgdh activity, as L2hgdh mutants that express a rescuing transgene within the MTs survive hypoxia treatment and exhibit normal levels of mitochondrial metabolites. We also demonstrate that even under normoxic conditions, L2hgdh mutant MTs experience significant metabolic stress and are sensitized to aberrant growth upon Egfr activation.

CONCLUSIONS

These findings present a model in which renal L2hgdh activity limits systemic L-2HG accumulation, thus indirectly regulating the balance between glycolytic and mitochondrial metabolism, enabling successful recovery from hypoxia exposure, and ensuring renal tissue integrity.

Effect of sodium L-lactate on bioactive properties of chitosan-hydroxyapatite/polycaprolactone conduits for peripheral nerve tissue engineering

Biomaterials and synthetic polymers have been widely used to replicate the regenerative microenvironment of the peripheral nervous system. Chitosan-based conduits have shown promise in the regeneration of nerve injuries. However, to mimic the regenerative microenvironment, the scaffold structure should possess bioactive properties. This can be achieved by the incorporation of biomolecules (e.g., proteins, peptides) or trophic factors that should preferably be aligned and/or released with controlled kinetics to activate the process of positive axon chemotaxis. In this study, sodium L-lactate has been used to enhance the bioactive properties of chitosan-hydroxyapatite/polycaprolactone electrodeposits. Next, two methods have been developed to incorporate NGF-loaded microspheres - Method 1 involves entrapment and co-deposition of NGF-loaded microspheres, while Method 2 is based on absorption of NGF-loaded microspheres. The study shows that modification of chitosan-hydroxyapatite/polycaprolactone conduits by sodium L-lactate significantly improves their bioactive, biological, and physicochemical properties. The obtained implants are cytocompatible, enhancing the neurite regeneration process by stimulating its elongation. The absorption of NGF-loaded microspheres into the conduit structure may be considered more favorable for the stimulation of axonal elongation compared to entrapment, as it allows for trophic factor dose-dependent controlled release. The developed conduits possess properties essential for the successful treatment of peripheral nerve discontinuities.

Targeting Lactate: An Emerging Strategy for Macrophage Regulation in Chronic Inflammation and Cancer

Lactate accumulation and macrophage infiltration are pivotal features of both chronic inflammation and cancer. Lactate, once regarded merely as an aftereffect of glucose metabolism, is now gaining recognition for its burgeoning spectrum of biological roles and immunomodulatory significance. Recent studies have evidenced that macrophages display divergent immunophenotypes in different diseases, which play a pivotal role in disease management by modulating macrophage polarization within the disease microenvironment. The specific polarization patterns of macrophages in a high-lactate environment and their contribution to the progression of chronic inflammation and cancer remain contentious. This review presents current evidence on the crosstalk of lactate and macrophage in chronic inflammation and cancer. Additionally, we provide an in-depth exploration of the pivotal yet enigmatic mechanisms through which lactate orchestrates disease pathogenesis, thereby offering novel perspectives to the development of targeted therapeutic interventions for chronic inflammation and cancer.

MCT1-mediated endothelial cell lactate shuttle as a target for promoting axon regeneration after spinal cord injury

Rationale: Spinal cord injury (SCI)-induced vascular damage causes ischemia and hypoxia at the injury site, which, in turn, leads to profound metabolic disruptions. The effects of these metabolic alterations on neural tissue remodeling and functional recovery have yet to be elucidated. The current study aimed to investigate the consequences of the SCI-induced hypoxic environment at the epicenter of the injury. Methods: This study employed metabolomics to assess changes in energy metabolism after SCI. The use of a lactate sensor identified lactate shuttle between endothelial cells (ECs) and neurons. Reanalysis of single-cell RNA sequencing data demonstrated reduced MCT1 expression in ECs after SCI. Additionally, an adeno-associated virus (AAV) overexpressing MCT1 was utilized to elucidate its role in endothelial-neuronal interactions, tissue repair, and functional recovery. Results: The findings revealed markedly decreased monocarboxylate transporter 1 (MCT1) expression that facilitates lactate delivery to neurons to support their energy metabolism in ECs post-SCI. This decreased expression of MCT1 disrupts lactate transport to neurons, resulting in a metabolic imbalance that impedes axonal regeneration. Strikingly, our results suggested that administering adeno-associated virus specifically to ECs to restore MCT1 expression enhances axonal regeneration and improves functional recovery in SCI mice. These findings indicate a novel link between lactate shuttling from endothelial cells to neurons following SCI and subsequent neural functional recovery. Conclusion: In summary, the current study highlights a novel metabolic pathway for therapeutic interventions in the treatment of SCI. Additionally, our findings indicate the potential benefits of targeting lactate transport mechanisms in recovery from SCI.

Lactate: A New Target for Brain Disorders

Lactate in the brain is produced endogenously and exogenously. The primary functional cells that produce lactate in the brain are astrocytes. Astrocytes release lactate to act on neurons, thereby affecting neuronal function, through a process known as the astrocyte-neuron shuttle. Lactate affects microglial function as well and inhibits microglia-mediated neuroinflammation. Lactate also provides energy, acts as a signaling molecule, and promotes neurogenesis. This article summarizes the role of lactate in cells, animals, and humans. Lactate is a protective molecule against stress in healthy organisms and in the early stages of brain disorders. Thus, lactate may be a potential therapeutic target for brain disorders. Further research on the role of lactate in microglia may have great prospects. This article provides a new perspective and research direction for the study of lacate in brain disorders.

Unleashing metabolic power for axonal regeneration

Axon regeneration requires the mobilization of intracellular resources, including proteins, lipids, and nucleotides. After injury, neurons need to adapt their metabolism to meet the biosynthetic demands needed to achieve axonal regeneration. However, the exact contribution of cellular metabolism to this process remains elusive. Insights into the metabolic characteristics of proliferative cells may illuminate similar mechanisms operating in axon regeneration; therefore, unraveling previously unappreciated roles of metabolic adaptation is critical to achieving neuron regrowth, which is connected to the therapeutic strategies for neurological conditions necessitating nerve repairs, such as spinal cord injury and stroke. Here, we outline the metabolic role in axon regeneration and discuss factors enhancing nerve regrowth, highlighting potential novel metabolic treatments for restoring nerve function.

miR-223 accelerates lipid droplets clearance in microglia following spinal cord injury by upregulating ABCA1

BACKGROUND

Spinal cord injury (SCI) is characterized by extensive demyelination and inflammatory responses. Facilitating the clearance of lipid droplets (LDs) within microglia contributes to creating a microenvironment that favors neural recovery and provides essential materials for subsequent remyelination. Therefore, investigating MicroRNAs (miRNAs) that regulate lipid homeostasis after SCI and elucidating their potential mechanisms in promoting LDs clearance in microglia have become focal points of SCI research.

METHODS

We established a subacute C5 hemicontusion SCI model in mice and performed transcriptomic sequencing on the injury epicenter to identify differentially expressed genes and associated pathways. Confocal imaging was employed to observe LDs accumulation. Multi-omics analyses were conducted to identify differentially expressed mRNA and miRNA post-SCI. Pathway enrichment analysis and protein-protein interaction network construction were performed using bioinformatics methods, revealing miR-223-Abca1 as a crucial miRNA-mRNA pair in lipid metabolism regulation. BV2 microglia cell lines overexpressing miR-223 were engineered, and immunofluorescence staining, western blot, and other techniques were employed to assess LDs accumulation, relevant targets, and inflammatory factor expression, confirming its role in regulating lipid homeostasis in microglia.

RESULTS

Histopathological results of our hemicontusion SCI model confirmed LDs aggregation at the injury epicenter, predominantly within microglia. Our transcriptomic analysis during the subacute phase of SCI in mice implicated ATP-binding cassette transporter A1 (Abca1) as a pivotal gene in lipid homeostasis, cholesterol efflux and microglial activation. Integrative mRNA-miRNA multi-omics analysis highlighted the crucial role of miR-223 in the neuroinflammation process following SCI, potentially through the regulation of lipid metabolism via Abca1. In vitro experiments using BV2 cells overexpressing miR-223 demonstrated that elevated levels of miR-223 enhance ABCA1 expression in myelin debris and LPS-induced BV2 cells. This promotes myelin debris degradation and LDs clearance, and induces a shift toward an anti-inflammatory M2 phenotype.

CONCLUSIONS

In summary, our study unveils the critical regulatory role of miR-223 in lipid homeostasis following SCI. The mechanism by which this occurs involves the upregulation of ABCA1 expression, which facilitates LDs clearance and myelin debris degradation, consequently alleviating the lipid burden, and inhibiting inflammatory polarization of microglia. These findings suggest that strategies to enhance miR-223 expression and target ABCA1, thereby augmenting LDs clearance, may emerge as appealing new clinical targets for SCI treatment.

The NR4A2/VGF pathway fuels inflammation-induced neurodegeneration via promoting neuronal glycolysis

A disturbed balance between excitation and inhibition (E/I balance) is increasingly recognized as a key driver of neurodegeneration in multiple sclerosis (MS), a chronic inflammatory disease of the central nervous system. To understand how chronic hyperexcitability contributes to neuronal loss in MS, we transcriptionally profiled neurons from mice lacking inhibitory metabotropic glutamate signaling with shifted E/I balance and increased vulnerability to inflammation-induced neurodegeneration. This revealed a prominent induction of the nuclear receptor NR4A2 in neurons. Mechanistically, NR4A2 increased susceptibility to excitotoxicity by stimulating continuous VGF secretion leading to glycolysis-dependent neuronal cell death. Extending these findings to people with MS (pwMS), we observed increased VGF levels in serum and brain biopsies. Notably, neuron-specific deletion of Vgf in a mouse model of MS ameliorated neurodegeneration. These findings underscore the detrimental effect of a persistent metabolic shift driven by excitatory activity as a fundamental mechanism in inflammation-induced neurodegeneration.

Progress in The Research of Lactate Metabolism Disruption And Astrocyte-Neuron Lactate Shuttle Impairment in Schizophrenia: A Comprehensive Review

Schizophrenia (SCZ) is a complex neuropsychiatric disorder widely recognized for its impaired bioenergy utilization. The astrocyte-neuron lactate shuttle (ANLS) plays a critical role in brain energy supply. Recent studies have revealed abnormal lactate metabolism in SCZ, which is associated with mitochondrial dysfunction, tissue hypoxia, gastric acid retention, oxidative stress, neuroinflammation, abnormal brain iron metabolism, cerebral white matter hypermetabolic activity, and genetic susceptibility. Furthermore, astrocytes, neurons, and glutamate abnormalities are prevalent in SCZ with abnormal lactate metabolism, which are essential components for maintaining ANLS in the brain. Therefore, an in-depth study of the pathophysiological mechanisms of ANLS in SCZ with abnormal lactate metabolism will contribute to a better understanding of the pathogenesis of SCZ and provide new ideas and approaches for the diagnosis and treatment of SCZ.

NT-3 Combined with TGF-β Signaling Pathway Enhance the Repair of Spinal Cord Injury by Inhibiting Glial Scar Formation and Promoting Axonal Regeneration

This study investigated the mechanism of neurotrophin-3 (NT-3) in promoting spinal cord injury repair through the transforming growth factor-beta (TGF-β) signaling pathway. A mouse model of spinal cord injury was established. Forty C57BL/6J mice were randomized into model, NT-3, NT-3 + TGF-β1 and NT-3 + LY364947 groups. The Basso-Beattie-Bresnahan (BBB) scores of the NT-3 and NT-3 + LY364947 groups were significantly higher than the model group. The BBB score of the NT-3 + TGF-β1 group was significantly lower than NT-3 group. Hematoxylin-eosin staining and transmission electron microscopy showed reduction in myelin sheath injury, more myelinated nerve fibers in the middle section of the catheter, and relatively higher density and more neatly arranged regenerated axons in the NT-3 and NT-3 + LY364947 groups compared with the model and NT-3 + TGF-β1 groups. Immunofluorescence, TUNEL and Western blot analysis showed that compared with model group, the NEUN expression increased, and the apoptosis and Col IV, LN, CSPG, tenascin-C, Sema 3 A, EphB2 and Smad2/3 protein expression decreased significantly in the NT-3 and NT-3 + LY364947 groups; the condition was reversed in the NT-3 + TGF-β1 group compared with the NT-3 group. NT-3 combined with TGF-β signaling pathway promotes astrocyte differentiation, reduces axon regeneration inhibitory molecules, apoptosis and glial scar formation, promotes axon regeneration, and improves spinal cord injury.

The Neurovascular Unit Dysfunction in the Molecular Mechanisms of Epileptogenesis and Targeted Therapy

Epilepsy is a multifaceted neurological syndrome characterized by recurrent, spontaneous, and synchronous seizures. The pathogenesis of epilepsy, known as epileptogenesis, involves intricate changes in neurons, neuroglia, and endothelium, leading to structural and functional disorders within neurovascular units and culminating in the development of spontaneous epilepsy. Although current research on epilepsy treatments primarily centers around anti-seizure drugs, it is imperative to seek effective interventions capable of disrupting epileptogenesis. To this end, a comprehensive exploration of the changes and the molecular mechanisms underlying epileptogenesis holds the promise of identifying vital biomarkers for accurate diagnosis and potential therapeutic targets. Emphasizing early diagnosis and timely intervention is paramount, as it stands to significantly improve patient prognosis and alleviate the socioeconomic burden. In this review, we highlight the changes and molecular mechanisms of the neurovascular unit in epileptogenesis and provide a theoretical basis for identifying biomarkers and drug targets.

The alpha-ketoacid dehydrogenase complexes of Drosophila melanogaster

The conserved family of alpha-ketoacid dehydrogenase complexes (AKDHCs) catalyze essential reactions in central metabolism and their dysregulation is implicated in several human diseases. Drosophila melanogaster provides an excellent model system to study the genetics and functions of these complexes. However, a systematic account of Drosophila AKDHCs and their composition has been lacking. Here, I identify and classify the genes encoding all Drosophila AKDHC subunits, update their functional annotations and integrate this work into the FlyBase database.

Acute Administration of Lactate Exerts Antidepressant-like Effect Through cAMP-dependent Protein Synthesis

Lactate acts as an important metabolic substrate and signalling molecule modulating neural activities in the brain, and recent preclinical and clinical studies have revealed its antidepressant effect after acute or chronic peripheral administration. However, the neural mechanism underlying the antidepressant effect of lactate, in particular when lactate is acutely administered remains largely unknown. In the current study, we focused on forced swimming test (FST) to elucidate the neural mechanisms through which acute intracerebroventricular (ICV) infusion of lactate exerts antidepressant-like effect. A total of 238 male Sprague Dawley rats were used as experimental subjects. Results showed lactate produced antidepressant-like effect, as indicated by reduced immobility, in a dose- and time-dependent manner. Moreover, the antidepressant-like effect of lactate was dependent of new protein synthesis but not new gene expression, lactate's metabolic effect or hydroxy-carboxylic acid receptor 1 (HCAR1) activation. Furthermore, lactate rapidly promoted dephosphorylation of eukaryotic elongation factor 2 (eEF2) and increased brain-derived neurotrophic factor (BDNF) protein synthesis in the hippocampus in a cyclic adenosine monophosphate (cAMP)-dependent manner. Finally, inhibition of cAMP production blocked the antidepressant-like effect of lactate. These findings suggest that acute administration of lactate exerts antidepressant-like effect through cAMP-dependent protein synthesis.

O-GlcNAc signaling increases neuron regeneration through one-carbon metabolism in Caenorhabditis elegans

Cellular metabolism plays an essential role in the regrowth and regeneration of a neuron following physical injury. Yet, our knowledge of the specific metabolic pathways that are beneficial to neuron regeneration remains sparse. Previously, we have shown that modulation of O-linked β-N-acetylglucosamine (O-GlcNAc) signaling, a ubiquitous post-translational modification that acts as a cellular nutrient sensor, can significantly enhance in vivo neuron regeneration. Here, we define the specific metabolic pathway by which O-GlcNAc transferase (ogt-1) loss of function mediates increased regenerative outgrowth. Performing in vivo laser axotomy and measuring subsequent regeneration of individual neurons in C. elegans, we find that glycolysis, serine synthesis pathway (SSP), one-carbon metabolism (OCM), and the downstream transsulfuration metabolic pathway (TSP) are all essential in this process. The regenerative effects of ogt-1 mutation are abrogated by genetic and/or pharmacological disruption of OCM and the SSP linking OCM to glycolysis. Testing downstream branches of this pathway, we find that enhanced regeneration is dependent only on the vitamin B12 independent shunt pathway. These results are further supported by RNA sequencing that reveals dramatic transcriptional changes by the ogt-1 mutation, in the genes involved in glycolysis, OCM, TSP, and ATP metabolism. Strikingly, the beneficial effects of the ogt-1 mutation can be recapitulated by simple metabolic supplementation of the OCM metabolite methionine in wild-type animals. Taken together, these data unearth the metabolic pathways involved in the increased regenerative capacity of a damaged neuron in ogt-1 animals and highlight the therapeutic possibilities of OCM and its related pathways in the treatment of neuronal injury.

Histone methyltransferase Ezh2 coordinates mammalian axon regeneration via regulation of key regenerative pathways

Current treatments for neurodegenerative diseases and neural injuries face major challenges, primarily due to the diminished regenerative capacity of neurons in the mammalian CNS as they mature. Here, we investigated the role of Ezh2, a histone methyltransferase, in regulating mammalian axon regeneration. We found that Ezh2 declined in the mouse nervous system during maturation but was upregulated in adult dorsal root ganglion neurons following peripheral nerve injury to facilitate spontaneous axon regeneration. In addition, overexpression of Ezh2 in retinal ganglion cells in the CNS promoted optic nerve regeneration via both histone methylation-dependent and -independent mechanisms. Further investigation revealed that Ezh2 fostered axon regeneration by orchestrating the transcriptional silencing of genes governing synaptic function and those inhibiting axon regeneration, while concurrently activating various factors that support axon regeneration. Notably, we demonstrated that GABA transporter 2, encoded by Slc6a13, acted downstream of Ezh2 to control axon regeneration. Overall, our study underscores the potential of modulating chromatin accessibility as a promising strategy for promoting CNS axon regeneration.

Astragalus polysaccharides promote neural stem cells-derived oligodendrogenesis through attenuating CD8+T cell infiltration in experimental autoimmune encephalomyelitis

Endogenous neural stem cells (NSCs) have the potential to generate remyelinating oligodendrocytes, which play an important role in multiple sclerosis (MS). However, the differentiation of NSCs into oligodendrocytes is insufficient, which is considered a major cause of remyelination failure. Our previous work reported that Astragalus polysaccharides (APS) had a neuroprotective effect on experimental autoimmune encephalomyelitis (EAE) mice. However, it remains unclear whether APS regulate NSCs differentiation in EAE mice. In this study, our data illustrated that APS administration could promote NSCs in the subventricular zone (SVZ) to differentiate into oligodendrocytes. Furthermore, we found that APS significantly improved neuroinflammation and inhibited CD8+T cell infiltration into SVZ of EAE mice. We also found that MOG35-55-specific CD8+T cells suppressed NSCs differentiation into oligodendrocytes by secreting IFN-γ, and APS facilitated the differentiation of NSCs into oligodendrocytes which was related to decreased IFN-γ secretion. In addition, APS treatment did not show a better effect on the NSCs-derived oligodendrogenesis after CD8+T cell depletion. This present study demonstrated that APS alleviated neuroinflammation and CD8+T cell infiltration into SVZ to induce oligodendroglial differentiation, and thus exerted neuroprotective effect. Our findings revealed that reducing the infiltration of CD8+T cells might contribute to enhancing NSCs-derived neurogenesis. And APS might be a promising drug candidate to treat MS.

Lactate metabolism in neurodegenerative diseases

Lactate, a byproduct of glycolysis, was thought to be a metabolic waste until the discovery of the Warburg effect. Lactate not only functions as a metabolic substrate to provide energy but can also function as a signaling molecule to modulate cellular functions under pathophysiological conditions. The Astrocyte-Neuron Lactate Shuttle has clarified that lactate plays a pivotal role in the central nervous system. Moreover, protein lactylation highlights the novel role of lactate in regulating transcription, cellular functions, and disease development. This review summarizes the recent advances in lactate metabolism and its role in neurodegenerative diseases, thus providing optimal perspectives for future research.

All hands on deck: Adipocytes lept-in to drive nerve regeneration

The glial metabolic state instructs nerve regeneration. In this issue of Cell Metabolism, Sundaram, Schütza, Schröter, et al. demonstrate that nerve injury induces adipocytes-glia signaling via leptin, thereby modulating glial metabolism and driving nerve regeneration.

Retinal ganglion cell repopulation for vision restoration in optic neuropathy: a roadmap from the RReSTORe Consortium

Retinal ganglion cell (RGC) death in glaucoma and other optic neuropathies results in irreversible vision loss due to the mammalian central nervous system's limited regenerative capacity. RGC repopulation is a promising therapeutic approach to reverse vision loss from optic neuropathies if the newly introduced neurons can reestablish functional retinal and thalamic circuits. In theory, RGCs might be repopulated through the transplantation of stem cell-derived neurons or via the induction of endogenous transdifferentiation. The RGC Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration (RReSTORe) Consortium was established to address the challenges associated with the therapeutic repair of the visual pathway in optic neuropathy. In 2022, the RReSTORe Consortium initiated ongoing international collaborative discussions to advance the RGC repopulation field and has identified five critical areas of focus: (1) RGC development and differentiation, (2) Transplantation methods and models, (3) RGC survival, maturation, and host interactions, (4) Inner retinal wiring, and (5) Eye-to-brain connectivity. Here, we discuss the most pertinent questions and challenges that exist on the path to clinical translation and suggest experimental directions to propel this work going forward. Using these five subtopic discussion groups (SDGs) as a framework, we suggest multidisciplinary approaches to restore the diseased visual pathway by leveraging groundbreaking insights from developmental neuroscience, stem cell biology, molecular biology, optical imaging, animal models of optic neuropathy, immunology & immunotolerance, neuropathology & neuroprotection, materials science & biomedical engineering, and regenerative neuroscience. While significant hurdles remain, the RReSTORe Consortium's efforts provide a comprehensive roadmap for advancing the RGC repopulation field and hold potential for transformative progress in restoring vision in patients suffering from optic neuropathies.

Decellularised spinal cord matrix manipulates glial niche into repairing phase via serglycin-mediated signalling pathway

Astrocytes are the most abundant and widespread glial cells in the central nervous system. The heterogeneity of astrocytes plays an essential role in spinal cord injury (SCI) repair. Decellularised spinal cord matrix (DSCM) is advantageous for repairing SCI, but little is known regarding the exact mechanisms and niche alterations. Here, we investigated the DSCM regulatory mechanism of glial niche in the neuro-glial-vascular unit using single-cell RNA sequencing. Our single cell sequencing, molecular and biochemical experiments validated that DSCM facilitated the differentiation of neural progenitor cells through increasing the number of immature astrocytes. Upregulation of mesenchyme-related genes, which maintained astrocyte immaturity, causing insensitivity to inflammatory stimuli. Subsequently, we identified serglycin (SRGN) as a functional component of DSCM, which involves inducing CD44-AKT signalling to trigger human spinal cord-derived primary astrocytes (hspASCs) proliferation and upregulation of genes related to epithelial-mesenchymal transition, thus impeding astrocyte maturation. Finally, we verified that SRGN-COLI and DSCM had similar functions in the human primary cell co-culture system to mimic the glia niche. In conclusion, our work revealed that DSCM reverted astrocyte maturation and altered the glia niche into the repairing phase through the SRGN-mediated signalling pathway.

Lactate-dependent transcriptional regulation controls mammalian eye morphogenesis

Mammalian retinal metabolism favors aerobic glycolysis. However, the role of glycolytic metabolism in retinal morphogenesis remains unknown. We report that aerobic glycolysis is necessary for the early stages of retinal development. Taking advantage of an unbiased approach that combines the use of eye organoids and single-cell RNA sequencing, we identify specific glucose transporters and glycolytic genes in retinal progenitors. Next, we determine that the optic vesicle territory of mouse embryos displays elevated levels of glycolytic activity. At the functional level, we show that removal of Glucose transporter 1 and Lactate dehydrogenase A gene activity from developing retinal progenitors arrests eye morphogenesis. Surprisingly, we uncover that lactate-mediated upregulation of key eye-field transcription factors is controlled by the epigenetic modification of histone H3 acetylation through histone deacetylase activity. Our results identify an unexpected bioenergetic independent role of lactate as a signaling molecule necessary for mammalian eye morphogenesis.

A newly-synthesized compound CP-07 alleviates microglia-mediated neuroinflammation and ischemic brain injury via inhibiting STAT3 phosphorylation

Background and Objectives

Overactivated glial cells, especially microglia, are core components in the progression of pathologic neuroinflammation, and the application of anti-inflammatory reagents has been regarded as a potential therapy in the management of infarction/reperfusion (I/R) brain injury. This research aims to clarify the anti-inflammatory efect of a novel lipophilic compound N-(2-[4-tert-butylphenyl]-2-[pyrrolidine-1-yl]ethyl)-7-methyl-4-oxo-4H-chromene-2-carboxamide (named CP-07 in this study) in LPS-stimulated BV2 cell line and primary mouse microglia, and its therapeutic effect on I/R brain injury.

Method

Cell Counting Kit-8 assay was used to determine the maximal nontoxic dose of CP-07. The mRNA levels of representative proinflammatory cytokines were determined by quantitative real-time polymerase chain reaction both in vitro and in vivo. TTC staining was performed to calculate infarct volumes while behavioral tests were used to assess the neurological deficits at 24 h after middle cerebral artery occlusion (MCAO). Flow cytometry analysis and immunofluorescence staining were performed to calculate the percentage of pro-inflammatory microglia in vivo.A selective JAK2/STAT3 pathway inhibitor, AG490 was used to block STAT3 phosphorylation before the CP-07 anti-inflammation tests in vitro.

Results

CP-07 could effectively suppress the mRNA levels of IL-6, IL-1β, iNOS and TNF-α induced by lipopolysaccharide (LPS) in vitro, and markedly block the evaluation of the fluorescence intensity of Iba-1 in primary mouse microglia. In middle cerebral arteryocclusion models, intraperitoneal injection with 1 mg/kg CP-07 significantly reduced cerebral infarct volumes at 24 h after surgery compared with vehicle treatment group, and promoted the recovery of neurological functions in MCAO mice. Further studies validated that CP-07 administration reduced the percentage of CD86 positive microglia after I/R injury, and the expression level of p-STAT3 was also markedly reduced in both microglial cells and the penumbra tissues. Blocking STAT3 phosphorylation with AG490 could completely eliminate the anti-inflammatory effects of CP-07, at least in vitro.

Conclusion

We showed that a newly synthesized compound, CP-07, could effectively reduce the inflammatory responses in LPS-stimulated BV2 cells and primary mouse microglia, and overproduction of cytokines in middle cerebral artery occlusion mouse models by inhibiting STAT3 phosphorylation, leading to a neuroprotective effect on I/R brain injury.

Construction and optimization of a coculture system of mouse brain microvascular endothelial cells and myelin debris

Microvascular endothelial cells are a newly discovered cell type involved in the phagocytosis of myelin debris, which play a key role in the repair of spinal cord injuries. Several methods for the preparation of myelin debris and parameters for constructing a coculture system of microvascular endothelial cells and myelin debris are available, but no systematic studies have yet been conducted, which hinders further exploration of the mechanisms of demyelinating disease repair. Herein, we aimed to develop a standardized method for this process. Myelin debris of different sizes was obtained from the brains of C57BL/6 mice by stripping the brains under aseptic conditions, multiple grinding, gradient centrifugation, etc. Transmission electron microscopy and nanoparticle size analysis were used to characterize myelin debris. Microvascular endothelial cells were cultured on a matrix gel, and myelin debris of different sizes (fluorescently labeled using CFSE) was placed in coculture after forming a vascular-like structure. Subsequently, myelin debris of different concentrations was cocultured in the vascular-like structure, and phagocytosis of myelin debris by microvascular endothelial cells was detected using immunofluorescence staining and flow cytometry. We found that myelin debris could be successfuly obtained from the mouse brain with secondary grinding and other steps and cocultured with microvascular endothelial cells at a concentration of 2 mg/mL, which promoted the phagocytosis of microvascular endothelial cells. In conclusion, we provide a reference for the protocol of a coculture system of microvascular endothelial cells and myelin debris.

Next-generation RNA sequencing elucidates transcriptomic signatures of pathophysiologic nerve regeneration

The cellular and molecular underpinnings of Wallerian degeneration have been robustly explored in laboratory models of successful nerve regeneration. In contrast, there is limited interrogation of failed regeneration, which is the challenge facing clinical practice. Specifically, we lack insight on the pathophysiologic mechanisms that lead to the formation of neuromas-in-continuity (NIC). To address this knowledge gap, we have developed and validated a novel basic science model of rapid-stretch nerve injury, which provides a biofidelic injury with NIC development and incomplete neurologic recovery. In this study, we applied next-generation RNA sequencing to elucidate the temporal transcriptional landscape of pathophysiologic nerve regeneration. To corroborate genetic analysis, nerves were subject to immunofluorescent staining for transcripts representative of the prominent biological pathways identified. Pathophysiologic nerve regeneration produces substantially altered genetic profiles both temporally and in the mature neuroma microenvironment, in contrast to the coordinated genetic signatures of Wallerian degeneration and successful regeneration. To our knowledge, this study presents as the first transcriptional study of NIC pathophysiology and has identified cellular death, fibrosis, neurodegeneration, metabolism, and unresolved inflammatory signatures that diverge from pathways elaborated by traditional models of successful nerve regeneration.

Optimizing spinal cord injury in zebrafish larvae: effects of age on the injury response

Zebrafish are an increasingly popular model to study spinal cord injury (SCI) regeneration. The transparency of larval zebrafish makes them ideal to study cellular processes in real time. Standardized approaches, including age of injury, are not readily available making comparisons of the results with other models challenging. In this study, we systematically examined the response to spinal cord transection of larval zebrafish at three different ages (3-7 days post fertilization or dpf) to determine whether the developmental complexity of the central nervous system affects the overall response to SCI. We then used imaging and behavioral analysis to evaluate whether differences existed based on the age of injury. All ages of larval zebrafish upregulated the required genes for glial bridge formation, ctgfa and gfap, at the site of injury, consistent with studies from adult zebrafish. Though all larval ages upregulated factors required to promote glial bridging, young larval zebrafish (3 dpf) were better able to regenerate axons independent of the glial bridge, unlike older zebrafish (7 dpf). Consistent with this data, locomotor experiments demonstrated that some swimming behavior occurs independent of glial bridge formation, further highlighting the need for standardization of this model and recovery assays. Overall, we found subtle cellular differences based on the age of transection in zebrafish, underlining the importance of considering age when designing experiments aimed at understanding regeneration.

Therapeutic Potential of Chinese Medicine for Endogenous Neurogenesis: A Promising Candidate for Stroke Treatment

Strokes are a leading cause of morbidity and mortality in adults worldwide. Extensive preclinical studies have shown that neural-stem-cell-based treatments have great therapeutic potential for stroke. Several studies have confirmed that the effective components of traditional Chinese medicine can protect and maintain the survival, proliferation, and differentiation of endogenous neural stem cells through different targets and mechanisms. Therefore, the use of Chinese medicines to activate and promote endogenous nerve regeneration and repair is a potential treatment option for stroke patients. Here, we summarize the current knowledge regarding neural stem cell strategies for ischemic strokes and the potential effects of these Chinese medicines on neuronal regeneration.

Emerging roles of mitochondria in animal regeneration

The regeneration capacity after an injury is critical to the survival of living organisms. In animals, regeneration ability can be classified into five primary types: cellular, tissue, organ, structure, and whole-body regeneration. Multiple organelles and signaling pathways are involved in the processes of initiation, progression, and completion of regeneration. Mitochondria, as intracellular signaling platforms of pleiotropic functions in animals, have recently gained attention in animal regeneration. However, most studies to date have focused on cellular and tissue regeneration. A mechanistic understanding of the mitochondrial role in large-scale regeneration is unclear. Here, we reviewed findings related to mitochondrial involvement in animal regeneration. We outlined the evidence of mitochondrial dynamics across different animal models. Moreover, we emphasized the impact of defects and perturbation in mitochondria resulting in regeneration failure. Ultimately, we discussed the regulation of aging by mitochondria in animal regeneration and recommended this for future study. We hope this review will serve as a means to advocate for more mechanistic studies of mitochondria related to animal regeneration on different scales.

Metabolites as signalling molecules

Traditional views of cellular metabolism imply that it is passively adapted to meet the demands of the cell. It is becoming increasingly clear, however, that metabolites do more than simply supply the substrates for biological processes; they also provide critical signals, either through effects on metabolic pathways or via modulation of other regulatory proteins. Recent investigation has also uncovered novel roles for several metabolites that expand their signalling influence to processes outside metabolism, including nutrient sensing and storage, embryonic development, cell survival and differentiation, and immune activation and cytokine secretion. Together, these studies suggest that, in contrast to the prevailing notion, the biochemistry of a cell is frequently governed by its underlying metabolism rather than vice versa. This important shift in perspective places common metabolites as key regulators of cell phenotype and behaviour. Yet the signalling metabolites, and the cognate targets and transducers through which they signal, are only beginning to be uncovered. In this Review, we discuss the emerging links between metabolism and cellular behaviour. We hope this will inspire further dissection of the mechanisms through which metabolic pathways and intermediates modulate cell function and will suggest possible drug targets for diseases linked to metabolic deregulation.

Epigenetic Alterations of Brain Non-Neuronal Cells in Major Mental Diseases

The tissue-specific expression and epigenetic dysregulation of many genes in cells derived from the postmortem brains of patients have been reported to provide a fundamental biological framework for major mental diseases such as autism, schizophrenia, bipolar disorder, and major depression. However, until recently, the impact of non-neuronal brain cells, which arises due to cell-type-specific alterations, has not been adequately scrutinized; this is because of the absence of techniques that directly evaluate their functionality. With the emergence of single-cell technologies, such as RNA sequencing (RNA-seq) and other novel techniques, various studies have now started to uncover the cell-type-specific expression and DNA methylation regulation of many genes (e.g., TREM2, MECP2, SLC1A2, TGFB2, NTRK2, S100B, KCNJ10, and HMGB1, and several complement genes such as C1q, C3, C3R, and C4) in the non-neuronal brain cells involved in the pathogenesis of mental diseases. Additionally, several lines of experimental evidence indicate that inflammation and inflammation-induced oxidative stress, as well as many insidious/latent infectious elements including the gut microbiome, alter the expression status and the epigenetic landscapes of brain non-neuronal cells. Here, we present supporting evidence highlighting the importance of the contribution of the brain's non-neuronal cells (in particular, microglia and different types of astrocytes) in the pathogenesis of mental diseases. Furthermore, we also address the potential impacts of the gut microbiome in the dysfunction of enteric and brain glia, as well as astrocytes, which, in turn, may affect neuronal functions in mental disorders. Finally, we present evidence that supports that microbiota transplantations from the affected individuals or mice provoke the corresponding disease-like behavior in the recipient mice, while specific bacterial species may have beneficial effects.

Coordinated Regulation of Myelination by Growth Factor and Amino-acid Signaling Pathways

Myelin-forming oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS) are essential for structural and functional homeostasis of nervous tissue. Albeit with certain similarities, the regulation of CNS and PNS myelination is executed differently. Recent advances highlight the coordinated regulation of oligodendrocyte myelination by amino-acid sensing and growth factor signaling pathways. In this review, we discuss novel insights into the understanding of differential regulation of oligodendrocyte and Schwann cell biology in CNS and PNS myelination, with particular focus on the roles of growth factor-stimulated RHEB-mTORC1 and GATOR2-mediated amino-acid sensing/signaling pathways. We also discuss recent progress on the metabolic regulation of oligodendrocytes and Schwann cells and the impact of their dysfunction on neuronal function and disease.

Glycolytic System in Axons Supplement Decreased ATP Levels after Axotomy of the Peripheral Nerve

Wallerian degeneration (WD) occurs in the early stages of numerous neurologic disorders, and clarifying WD pathology is crucial for the advancement of neurologic therapies. ATP is acknowledged as one of the key pathologic substances in WD. The ATP-related pathologic pathways that regulate WD have been defined. The elevation of ATP levels in axon contributes to delay WD and protects axons. However, ATP is necessary for the active processes to proceed WD, given that WD is stringently managed by auto-destruction programs. But little is known about the bioenergetics during WD. In this study, we made sciatic nerve transection models for GO-ATeam2 knock-in rats and mice. We presented the spatiotemporal ATP distribution in the injured axons with in vivo ATP imaging systems, and investigated the metabolic source of ATP in the distal nerve stump. A gradual decrease in ATP levels was observed before the progression of WD. In addition, the glycolytic system and monocarboxylate transporters (MCTs) were activated in Schwann cells following axotomy. Interestingly, in axons, we found the activation of glycolytic system and the inactivation of the tricarboxylic acid (TCA) cycle. Glycolytic inhibitors, 2-deoxyglucose (2-DG) and MCT inhibitors, a-cyano-4-hydroxycinnamic acid (4-CIN) decreased ATP and enhanced WD progression, whereas mitochondrial pyruvate carrier (MPC) inhibitors (MSDC-0160) did not change. Finally, ethyl pyruvate (EP) increased ATP levels and delayed WD. Together, our findings suggest that glycolytic system, both in Schwann cells and axons, is the main source of maintaining ATP levels in the distal nerve stump.

Advances in molecular therapies for targeting pathophysiology in spinal cord injury

INTRODUCTION

Spinal cord injury (SCI) affects 25,000-50,000 people around the world each year and there is no cure for SCI patients currently. The primary injury damages spinal cord tissues and secondary injury mechanisms, including ischemia, apoptosis, inflammation, and astrogliosis, further exacerbate the lesions to the spinal cord. Recently, researchers have designed various therapeutic approaches for SCI by targeting its major cellular or molecular pathophysiology.

AREAS COVERED

Some strategies have shown promise in repairing injured spinal cord for functional recoveries, such as administering neuroprotective reagents, targeting specific genes to promote robust axon regeneration of disconnected spinal fiber tracts, targeting epigenetic factors to enhance cell survival and neural repair, and facilitating neuronal relay pathways and neuroplasticity for restoration of function after SCI. This review focuses on the major advances in preclinical molecular therapies for SCI reported in recent years.

EXPERT OPINION

Recent progress in developing novel and effective repairing strategies for SCI is encouraging, but many challenges remain for future design of effective treatments, including developing highly effective neuroprotectants for early interventions, stimulating robust neuronal regeneration with functional synaptic reconnections among disconnected neurons, maximizing the recovery of lost neural functions with combination strategies, and translating the most promising therapies into human use.

Aging and memory are altered by genetically manipulating lactate dehydrogenase in the neurons or glia of flies

The astrocyte-neuron lactate shuttle hypothesis posits that glial-generated lactate is transported to neurons to fuel metabolic processes required for long-term memory. Although studies in vertebrates have revealed that lactate shuttling is important for cognitive function, it is uncertain if this form of metabolic coupling is conserved in invertebrates or is influenced by age. Lactate dehydrogenase (Ldh) is a rate limiting enzyme that interconverts lactate and pyruvate. Here we genetically manipulated expression of Drosophila melanogaster lactate dehydrogenase (dLdh) in neurons or glia to assess the impact of altered lactate metabolism on invertebrate aging and long-term courtship memory at different ages. We also assessed survival, negative geotaxis, brain neutral lipids (the core component of lipid droplets) and brain metabolites. Both upregulation and downregulation of dLdh in neurons resulted in decreased survival and memory impairment with age. Glial downregulation of dLdh expression caused age-related memory impairment without altering survival, while upregulated glial dLdh expression lowered survival without disrupting memory. Both neuronal and glial dLdh upregulation increased neutral lipid accumulation. We provide evidence that altered lactate metabolism with age affects the tricarboxylic acid (TCA) cycle, 2-hydroxyglutarate (2HG), and neutral lipid accumulation. Collectively, our findings indicate that the direct alteration of lactate metabolism in either glia or neurons affects memory and survival but only in an age-dependent manner.

Regulation of axonal regeneration after mammalian spinal cord injury

One hundred years ago, Ramón y Cajal, considered by many as the founder of modern neuroscience, stated that neurons of the adult central nervous system (CNS) are incapable of regenerating. Yet, recent years have seen a tremendous expansion of knowledge in the molecular control of axon regeneration after CNS injury. We now understand that regeneration in the adult CNS is limited by (1) a failure to form cellular or molecular substrates for axon attachment and elongation through the lesion site; (2) environmental factors, including inhibitors of axon growth associated with myelin and the extracellular matrix; (3) astrocyte responses, which can both limit and support axon growth; and (4) intraneuronal mechanisms controlling the establishment of an active cellular growth programme. We discuss these topics together with newly emerging hypotheses, including the surprising finding from transcriptomic analyses of the corticospinal system in mice that neurons revert to an embryonic state after spinal cord injury, which can be sustained to promote regeneration with neural stem cell transplantation. These gains in knowledge are steadily advancing efforts to develop effective treatment strategies for spinal cord injury in humans.

Drosophila Laser Axotomy Injury Model to Investigate RNA Repair and Splicing in Axon Regeneration

The limited axon regeneration capacity of mature neurons often leads to insufficient functional recovery after damage to the central nervous system (CNS). To promote CNS nerve repair, there is an urgent need to understand the regeneration machinery in order to develop effective clinical therapies. To this aim, we developed a Drosophila sensory neuron injury model and the accompanying behavioral assay to examine axon regeneration competence and functional recovery after injury in the peripheral and central nervous systems. Specifically, we used a two-photon laser to induce axotomy and performed live imaging to assess axon regeneration, combined with the analysis of the thermonociceptive behavior as a readout of functional recovery. Using this model, we found that the RNA 3'-terminal phosphate cyclase (Rtca), which acts as a regulator for RNA repair and splicing, responds to injury-induced cellular stress and impedes axon regeneration after axon breakage. Here we describe how we utilize our Drosophila model to assess the role of Rtca during neuroregeneration.

Increased white matter glycolysis in humans with cerebral small vessel disease

White matter lesions in cerebral small vessel disease are related to ischemic injury and increase the risk of stroke and cognitive decline. Pathological changes due to cerebral small vessel disease are increasingly recognized outside of discrete lesions, but the metabolic alterations in nonlesional tissue has not been described. Aerobic glycolysis is critical to white matter myelin homeostasis and repair. In this study, we examined cerebral metabolism of glucose and oxygen as well as blood flow in individuals with and without cerebral small vessel disease using multitracer positron emission tomography. We show that glycolysis is relatively elevated in nonlesional white matter in individuals with small vessel disease relative to healthy, age-matched controls. On the other hand, in young healthy individuals, glycolysis is relatively low in areas of white matter susceptible to lesion formation. These results suggest that increased white matter glycolysis is a marker of pathology associated with small vessel disease.

A shear-thinning, ROS-scavenging hydrogel combined with dental pulp stem cells promotes spinal cord repair by inhibiting ferroptosis

Spinal cord injury (SCI) is a serious clinical disease. Due to the deformability and fragility of the spinal cord, overly rigid hydrogels cannot be used to treat SCI. Hence, we used TPA and Laponite to develop a hydrogel with shear-thinning ability. This hydrogel exhibits good deformation, allowing it to match the physical properties of the spinal cord; additionally, this hydrogel scavenges ROS well, allowing it to inhibit the lipid peroxidation caused by ferroptosis. According to the in vivo studies, the TPA@Laponite hydrogel could synergistically inhibit ferroptosis by improving vascular function and regulating iron metabolism. In addition, dental pulp stem cells (DPSCs) were introduced into the TPA@Laponite hydrogel to regulate the ratios of excitatory and inhibitory synapses. It was shown that this combination biomaterial effectively reduced muscle spasms and promoted recovery from SCI.

Alterations in gut microbiota are related to metabolite profiles in spinal cord injury

Studies have shown that gut microbiota metabolites can enter the central nervous system via the blood-spinal cord barrier and cause neuroinflammation, thus constituting secondary injury after spinal cord injury. To investigate the correlation between gut microbiota and metabolites and the possible mechanism underlying the effects of gut microbiota on secondary injury after spinal cord injury, in this study, we established mouse models of T8-T10 traumatic spinal cord injury. We used 16S rRNA gene amplicon sequencing and metabolomics to reveal the changes in gut microbiota and metabolites in fecal samples from the mouse model. Results showed a severe gut microbiota disturbance after spinal cord injury, which included marked increases in pro-inflammatory bacteria, such as Shigella, Bacteroides, Rikenella, Staphylococcus, and Mucispirillum and decreases in anti-inflammatory bacteria, such as Lactobacillus, Allobaculum, and Sutterella. Meanwhile, we identified 27 metabolites that decreased and 320 metabolites that increased in the injured spinal cord. Combined with pathway enrichment analysis, five markedly differential amino acids (L-leucine, L-methionine, L-phenylalanine, L-isoleucine and L-valine) were screened out, which play a pivotal role in activating oxidative stress and inflammatory responses following spinal cord injury. Integrated correlation analysis indicated that the alteration of gut microbiota was related to the differences in amino acids, which suggests that disturbances in gut microbiota might participate in the secondary injury through the accumulation of partial metabolites that activate oxidative stress and inflammatory responses. Findings from this study provide a new theoretical basis for improving the secondary injury after spinal cord injury through fecal microbial transplantation.

Capacity of astrocytes to promote axon growth in the injured mammalian central nervous system

Understanding the regulation of axon growth after injury to the adult central nervous system (CNS) is crucial to improve neural repair. Following acute focal CNS injury, astrocytes are one cellular component of the scar tissue at the primary lesion that is traditionally associated with inhibition of axon regeneration. Advances in genetic models and experimental approaches have broadened knowledge of the capacity of astrocytes to facilitate injury-induced axon growth. This review summarizes findings that support a positive role of astrocytes in axon regeneration and axon sprouting in the mature mammalian CNS, along with potential underlying mechanisms. It is important to recognize that astrocytic functions, including modulation of axon growth, are context-dependent. Evidence suggests that the local injury environment, neuron-intrinsic regenerative potential, and astrocytes’ reactive states determine the astrocytic capacity to support axon growth. An integrated understanding of these factors will optimize therapeutic potential of astrocyte-targeted strategies for neural repair.

A cAMP Sensor Based on Ligand-Dependent Protein Stabilization

cAMP is a ubiquitous second messenger with many functions in diverse organisms. Current cAMP sensors, including Föster resonance energy transfer (FRET)-based and single-wavelength-based sensors, allow for real time visualization of this small molecule in cultured cells and in some cases in vivo. Nonetheless the observation of cAMP in living animals is still difficult, typically requiring specialized microscopes and ex vivo tissue processing. Here we used ligand-dependent protein stabilization to create a new cAMP sensor. This sensor allows specific and sensitive detection of cAMP in living zebrafish embryos, which may enable new understanding of the functions of cAMP in living vertebrates.

Regenerative Strategies for Retinal Neurons: Novel Insights in Non-Mammalian Model Organisms

A detailed knowledge of the status of the retina in neurodegenerative conditions is a crucial point for the development of therapeutics in retinal pathologies and to translate eye research to CNS disease. In this context, manipulating signaling pathways that lead to neuronal regeneration offers an excellent opportunity to substitute damaged cells and, thus, restore the tissue functionality. Alternative systems and methods are increasingly being considered to replace/reduce in vivo approaches in the study of retina pathophysiology. Herein, we present recent data obtained from the zebrafish (Danio rerio) and the fruit fly Drosophila melanogaster that bring promising advantages into studying and modeling, at a preclinical level, neurodegeneration and regenerative approaches in retinal diseases. Indeed, the regenerative ability of vertebrate model zebrafish is particularly appealing. In addition, the fruit fly is ideal for regenerative studies due to its high degree of conservation with vertebrates and the broad spectrum of genetic variants achievable. Furthermore, a large part of the drosophila brain is dedicated to sight, thus offering the possibility of studying common mechanisms of the visual system and the brain at once. The knowledge acquired from these alternative models may help to investigate specific well-conserved factors of interest in human neuroregeneration after injuries or during pathologies.

Regenerative Role of T Cells in Nerve Repair and Functional Recovery

The immune system is essential in the process of nerve repair after injury. Successful modulation of the immune response is regarded as an effective approach to improving treatment outcomes. T cells play an important role in the immune response of the nervous system, and their beneficial roles in promoting regeneration have been increasingly recognized. However, the diversity of T-cell subsets also delivers both neuroprotective and neurodegenerative functions. Therefore, this review mainly discusses the beneficial impact of T-cell subsets in the repair of both peripheral nervous system and central nervous system injuries and introduces studies on various therapies based on T-cell regulation. Further discoveries in T-cell mechanisms and multifunctional biomaterials will provide novel strategies for nerve regeneration.

Crosstalk of Astrocytes and Other Cells during Ischemic Stroke

Stroke is a leading cause of death and long-term disability worldwide. Astrocytes structurally compose tripartite synapses, blood–brain barrier, and the neurovascular unit and perform multiple functions through cell-to-cell signaling of neurons, glial cells, and vasculature. The crosstalk of astrocytes and other cells is complicated and incompletely understood. Here we review the role of astrocytes in response to ischemic stroke, both beneficial and detrimental, from a cell–cell interaction perspective. Reactive astrocytes provide neuroprotection through antioxidation and antiexcitatory effects and metabolic support; they also contribute to neurorestoration involving neurogenesis, synaptogenesis, angiogenesis, and oligodendrogenesis by crosstalk with stem cells and cell lineage. In the meantime, reactive astrocytes also play a vital role in neuroinflammation and brain edema. Glial scar formation in the chronic phase hinders functional recovery. We further discuss astrocyte enriched microRNAs and exosomes in the regulation of ischemic stroke. In addition, the latest notion of reactive astrocyte subsets and astrocytic activity revealed by optogenetics is mentioned. This review discusses the current understanding of the intimate molecular conversation between astrocytes and other cells and outlines its potential implications after ischemic stroke. “Neurocentric” strategies may not be sufficient for neurological protection and recovery; future therapeutic strategies could target reactive astrocytes.

Microglial voltage-gated proton channel Hv1 in spinal cord injury

After spinal cord injury, microglia as the first responders to the lesion display both beneficial and detrimental characteristics. Activated microglia phagocyte and eliminate cell debris, release cytokines to recruit peripheral immune cells to the injury site. Excessively activated microglia can aggravate the secondary damage by producing extravagant reactive oxygen species and pro-inflammatory cytokines. Recent studies demonstrated that the voltage-gated proton channel Hv1 is selectively expressed in microglia and regulates microglial activation upon injury. In mouse models of spinal cord injury, Hv1 deficiency ameliorates microglia activation, resulting in alleviated production of reactive oxygen species and pro-inflammatory cytokines. The reduced secondary damage subsequently decreases neuronal loss and correlates with improved locomotor recovery. This review provides a brief historical perspective of advances in investigating voltage-gated proton channel Hv1 and home in on microglial Hv1. We discuss recent studies on the roles of Hv1 activation in pathophysiological activities of microglia, such as production of NOX-dependent reactive oxygen species, microglia polarization, and tissue acidosis, particularly in the context of spinal cord injury. Further, we highlight the rationale for targeting Hv1 for the treatment of spinal cord injury and related disorders.

Beyond Genetics: The Role of Metabolism in Photoreceptor Survival, Development and Repair

Vision commences in the retina with rod and cone photoreceptors that detect and convert light to electrical signals. The irreversible loss of photoreceptors due to neurodegenerative disease leads to visual impairment and blindness. Interventions now in development include transplanting photoreceptors, committed photoreceptor precursors, or retinal pigment epithelial (RPE) cells, with the latter protecting photoreceptors from dying. However, introducing exogenous human cells in a clinical setting faces both regulatory and supply chain hurdles. Recent work has shown that abnormalities in central cell metabolism pathways are an underlying feature of most neurodegenerative disorders, including those in the retina. Reversal of key metabolic alterations to drive retinal repair thus represents a novel strategy to treat vision loss based on cell regeneration. Here, we review the connection between photoreceptor degeneration and alterations in cell metabolism, along with new insights into how metabolic reprogramming drives both retinal development and repair following damage. The potential impact of metabolic reprogramming on retinal regeneration is also discussed, specifically in the context of how metabolic switches drive both retinal development and the activation of retinal glial cells known as Müller glia. Müller glia display latent regenerative properties in teleost fish, however, their capacity to regenerate new photoreceptors has been lost in mammals. Thus, re-activating the regenerative properties of Müller glia in mammals represents an exciting new area that integrates research into developmental cues, central metabolism, disease mechanisms, and glial cell biology. In addition, we discuss this work in relation to the latest insights gleaned from other tissues (brain, muscle) and regenerative species (zebrafish).

Quantifying Glial-Glial Tiling Using Automated Image Analysis in Drosophila

Not only do glia form close associations with neurons throughout the central nervous system (CNS), but glial cells also interact closely with other glial cells. As these cells mature, they undergo a phenomenon known as glial tiling, where they grow to abut one another, often without invading each other’s boundaries. Glial tiling occurs throughout the animal kingdom, from fruit flies to humans; however, not much is known about the glial-glial interactions that lead to and maintain this tiling. Drosophila provide a strong model to investigate glial-glial tiling, where tiling occurs both among individual glial cells of the same subtype, as well as between those of different subtypes. Furthermore, the spatial segregation of the CNS allows for the unique ability to visualize and manipulate inter-subtype interactions. Previous work in Drosophila has suggested an interaction between cortex glia and astrocytes, where astrocytes cross the normal neuropil-cortex boundary in response to dysfunctional cortex glia. Here, we further explore this interaction by implementing an automated pipeline to more fully characterize this astrocyte-cortex glial relationship. By quantifying and correlating the extent of cortex glial dysfunction and aberrant astrocyte infiltration using automated analysis, we maximize the size of the quantified dataset to reveal subtle patterns in astrocyte-cortex glial interactions. We provide a guide for creating and validating a fully-automated image analysis pipeline for exploring these interactions, and implement this pipeline to describe a significant correlation between cortex glial dysfunction and aberrant astrocyte infiltration, as well as demonstrate variations in their relationship across different regions of the CNS.