SOCS3 deletion promotes optic nerve regeneration in vivo

Bidirectional causality of physical exercise in retinal neuroprotection

Physical exercise is recognized as an effective intervention to improve mood, physical performance, and general well-being. It achieves these benefits through cellular and molecular mechanisms that promote the release of neuroprotective factors. Interestingly, reduced levels of physical exercise have been implicated in several central nervous system diseases, including ocular disorders. Emerging evidence has suggested that physical exercise levels are significantly lower in individuals with ocular diseases such as glaucoma, age-related macular degeneration, retinitis pigmentosa, and diabetic retinopathy. Physical exercise may have a neuroprotective effect on the retina. Therefore, the association between reduced physical exercise and ocular diseases may involve a bidirectional causal relationship whereby visual impairment leads to reduced physical exercise and decreased exercise exacerbates the development of ocular disease. In this review, we summarize the evidence linking physical exercise to eye disease and identify potential mediators of physical exercise-induced retinal neuroprotection. Finally, we discuss future directions for preclinical and clinical research in exercise and eye health.

Regeneration of retinal ganglion cell-like cells and reconstruction of visual neural circuits in mice with glaucoma

Glaucoma is an irreversible blinding eye disease characterized by apoptosis of mature neurons-retinal ganglion cells (RGCs), visual field defect and vision loss. Regeneration of RGCs and reconstruction of the neural connections between the retina and the brain is considered an effective strategy to promote visual restoration in patients with glaucoma. However, there are currently no effective methods for regenerating RGCs to restore vision in clinical practice. Microglia are a type of glial cells that regulate the immune response in the retina and central nervous system (CNS), whether they have pluripotency and be reversed into RGCs remains unclear and challenging. This study revealed that the ectopic expression of multiple genes (Brn3b, Sox2, Cbln1, and NP1, referred to as BSCN) in microglia can promote their conversion into RGC-like cells by microglia fate lineage tracing in vivo. The regenerated RGC-like cells project axons to the distant brain and reconstruct the visual neural circuit, restoring the impaired vision in adult mice with acute glaucoma induced by retinal ischemia-reperfusion (I/R) injury. Furthermore, the regenerated RGC-like cells could survive stably for up to one year, and the same regeneration strategy was performed in older mice with acute glaucoma, which confirmed the effectiveness of the BSCN reprogramming to regenerate RGC-like cells. In summary, we have identified the microglia as a new type of reprogramming seed cells, and four key genes were found to be involved in regenerating RGC-like cells to restore vision. These findings highlight a new strategy of RGC-like cell regeneration and provide a theoretical basis for treatment of glaucoma in the future.

The neuroimmune interface in retinal regeneration

Retinal neurodegeneration leads to irreversible blindness due to the mammalian nervous system's inability to regenerate lost neurons. Efforts to regenerate retina involve two main strategies: stimulating endogenous cells to reprogram into neurons or transplanting stem-cell derived neurons into the degenerated retina. However, both approaches must overcome a major barrier in getting new neurons to grow back down the optic nerve and connect to appropriate visual targets in environments that differ significantly from developmental conditions. While immune privilege has historically been associated with the central nervous system, an emerging literature highlights the active role of immune cells in shaping neurodegeneration and regeneration. This review explores the neuroimmune interface in retinal repair, dissecting how immune interactions influence glial reprogramming, transplantation outcomes, and axonal regeneration. By integrating insights from regenerative species with mammalian models, we highlight novel immunomodulatory strategies to optimize retinal regeneration.

Glycoprotein 130 improves repressor element‑1 silencing transcription factor‑related axon regenerative capacity in peripheral nerves with aging

Axon regenerative capacity diminishes with aging and differences in the condition of peripheral nerves between young and elderly individuals have been reported. However, the underlying pathology remains unclear. The expression of repressor element‑1 silencing transcription factor (REST) increases with age and is reported to suppress axon regeneration. The present study investigated the pathology and potential treatment of reduced axon regenerative capacity using REST‑regulated cells and a mouse model. This study examined the molecular expression of the janus kinase 1 (JAK1)/signal transducer and activator of transcription 3 (STAT3) pathway, which is involved in growth‑associated protein 43 (GAP43) expression. In REST‑overexpressed (REST‑OE), glycoprotein 130 (GP130), JAK1 and phosphorylated STAT3 (p‑STAT3) expression was decreased compared with the control (GP130, P=0.004; JAK1, P=0.038; pSTAT3, P=0.015). On the other hand, in REST‑low expressed (siREST), GP130, JAK1 and pSTAT3 expression was increased compared with the control (GP130, P=0.004; JAK1, P=0.003; pSTAT3, P=0.033). It suggested that GP130 plays an important role. Therefore, GP130 agonist was administered to REST‑OE and aged mice and resulted in a significant increase in GAP43 expression (REST‑OE: Protein P=0.018, mRNA P=0.040; aged mice: Protein P=0.016, mRNA P=0.013). The results of this study suggest that the pathology of reduction in peripheral nerve axon regenerative capacity is inhibited by age‑related increase in REST expression, which leads to decreased GP130 expression and inhibition of JAK1/STAT3 pathway activity. These findings suggest that regulating GP130 expression may improve axon regenerative capacity by aging.

Socs3a is Dispensable for Zebrafish Hematopoiesis and is Required for Neuromast Formation

BACKGROUND

Suppressor of cytokine signaling (SOCS)3 is a regulatory protein that participates in an important negative feedback loop downstream of several critical cytokines, especially members of the interleukin-6 (IL-6) family. As a result, SOCS3 has been shown to impact the development and function of blood and immune cells. Zebrafish harbor duplicates of SOCS3, Socs3a and Socs3b, both of which possess conserved functional domains.

METHODS

This study explored the role of zebrafish Socs3a by creating a whole genome knockout using CRISPR/Cas9, with a focus on hematopoiesis and neuromast formation.

RESULTS

A zebrafish Socs3a knockout mutant was successfully generated. Characterization of this mutant revealed that normal hematopoiesis was not impacted nor was neutrophils lacking Socs3a displayed normal responses to injury or their production during emergency granulopoiesis. Neuromast formation was severely impacted in Socs3a knockout zebrafish.

CONCLUSIONS

Zebrafish Socs3a mutants display normal hematopoiesis and myeloid function, but the formation of the lateral line neuromast was affected by the absence of Socs3a.

Roles of Kdm6a and Kdm6b in Regulation of Mammalian Neural Regeneration

Epigenetic regulation of neuronal transcriptomic landscape is emerging to be a key coordinator of mammalian neural regeneration. The roles of two histone 3 lysine 27 (H3K27) demethylases, Kdm6a/b, in controlling neuroprotection and axon regeneration are investigated here. Deleting either Kdm6a or Kdm6b leads to enhanced sensory axon regeneration in the peripheral nervous system (PNS), whereas in the central nervous system (CNS), only deleting Kdm6a in retinal ganglion cells (RGCs) significantly enhances optic nerve regeneration. Moreover, both Kdm6a and Kdm6b function to regulate RGC survival but with different mechanisms. Mechanistically, Kdm6a regulates RGC regeneration via distinct pathway from that of Pten, and co-deleting Kdm6a and Pten results in long distance optic nerve regeneration passing the optic chiasm. In addition, RNA-seq profiling reveals that Kdm6a deletion switches the RGC transcriptomics into a developmental-like state and suppresses several known repressors of neural regeneration. Klf4 is identified as a direct downstream target of Kdm6a-H3K27me3 signaling in both sensory neurons and RGCs to regulate axon regeneration. These findings not only reveal different roles of Kdm6a and Kdm6b in regulation of neural regeneration and their underlying mechanisms, but also identify Kdm6a-mediated histone demethylation signaling as a novel epigenetic target for supporting CNS neural regeneration.

Role of Ciliary Neurotrophic Factor in Angiotensin II-Induced Hypertension

BACKGROUND

Ciliary neurotrophic factor (CNTF), mainly known for its neuroprotective properties, belongs to the IL-6 (interleukin-6) cytokine family. In contrast to IL-6, the effects of CNTF on the vasculature have not been explored. Here, we examined the role of CNTF in AngII (angiotensin II)-induced hypertension.

METHODS

Hypertension was chronically induced with AngII (1000 ng/kg per minute, osmotic mini-pumps, 14 days) in CNTF-knockout and wild-type mice (with or without nephrectomy and 1% NaCl drinking water). Blood pressure was measured by tail-cuff and radiotelemetry. Effects of CNTF on vascular function and the JAK2/STAT3 pathway were measured in vivo, in the isolated perfused kidney, and in mouse and human vascular smooth muscle cells.

RESULTS

At baseline, systolic blood pressure was similar between both groups. During AngII infusion, blood pressure increase was significantly attenuated and hypertensive heart and kidney damage was significantly attenuated in CNTF-knockout compared with wild-type mice. Accordingly, renal pressor response to AngII but not KCl or phenylephrine was significantly decreased in CNTF-knockout compared with wild-type mice. Acute CNTF (5 µmol/L) administration nearly restored the AngII-dependent renal pressor response. Chronic CNTF treatment in CNTF-knockout mice increased blood pressure response to AngII to levels observed in wild-type mice. CNTF augments AngII-induced activation of the JAK2/STAT3 pathway in vitro in vascular smooth muscle cells. The significance of this interaction was shown, as the increase in renal pressor response by CNTF was abolished by JAK2/STAT3 inhibitors.

CONCLUSIONS

Our results demonstrate a major impact of CNTF on blood pressure regulation by modulating AngII-induced pressor response via a JAK2/STAT3-dependent mechanism and indicate that CNTF is an important regulatory cytokine in hypertension.

Neuroprotective Mechanisms of Ciliary Neurotrophic Factor in Retinal Ganglion Cells: Insights from Microarray Analysis

PURPOSE

This study investigated the changes in gene expression in retinal ganglion cells (RGCs) following ciliary neurotrophic factor (CNTF) treatment to elucidate the underlying mechanisms contributing to its neuroprotective effects.

METHODS

RGCs isolated from Sprague-Dawley rat pups were treated with recombinant CNTF. Gene expression was analyzed via microarray. Differentially expressed genes (DEGs) were defined as those with a fold change greater than 2 or less than -2. The DEGs were further explored using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses.

RESULTS

Our analysis identified 71 upregulated and 58 downregulated genes. A2m exhibited the highest increase, with a fold change of 4.97, whereas Rho displayed the most significant decrease in expression, with a fold change of -6.38. GO and KEGG pathway analyses revealed substantial involvement in sensory organ development and the phototransduction pathway.

CONCLUSIONS

This study provides new insights into the impact of CNTF on gene expression in RGCs, suggesting broader neuroprotective mechanisms that could inform future therapeutic strategies for retinal degenerative diseases. Our findings emphasize the importance of further investigation into the complex gene network responses to CNTF treatment.

Advances in Regenerative Medicine, Cell Therapy, and 3D Bioprinting for Glaucoma and Retinal Diseases

Regenerative medicine, cell therapy, and 3D bioprinting represent promising advancements in addressing retinal and glaucomatous diseases. These conditions, including diabetic retinopathy (DR), age-related macular degeneration (AMD), inherited retinal degenerations (IRDs), and glaucomatous optic neuropathy, have complex pathophysiologies that involve neurodegeneration, oxidative stress, and vascular dysfunction. Despite significant progress in conventional therapies, including anti-VEGF injections, laser photocoagulation, and intraocular pressure (IOP)-lowering interventions, these approaches remain limited in reversing disease progression and restoring lost visual function.This chapter explores the potential of emerging regenerative therapies to fill these critical gaps. For retinal diseases, cell replacement strategies using human embryonic stem cells (hESCs), induced pluripotent stem cells (iPSCs), and mesenchymal stem cells (MSCs) have demonstrated encouraging outcomes in clinical trials, though challenges in delivery and long-term integration persist. Similarly, neuroprotective strategies and the use of retinal progenitor cells hold promise for preserving and restoring vision in degenerative retinal conditions. Advances in 3D bioprinting and retinal organoids further augment these efforts, offering innovative tools for disease modeling and therapy development.In glaucoma, regenerative approaches targeting trabecular meshwork (TM) dysfunction and retinal ganglion cell (RGC) loss are gaining traction. Stem cell-based therapies have shown potential in restoring TM functionality and providing neuroprotection, while innovative delivery systems and bioengineered platforms aim to enhance therapeutic efficacy and safety.This chapter provides an overview of the evolving landscape of regenerative therapies for retinal and glaucomatous diseases, highlighting current advancements, ongoing challenges, and future directions in the field. These approaches, while still emerging, hold the potential to transform the management of these complex ocular diseases.

Predicting the Regenerative Potential of Retinal Ganglion Cells Based on Developmental Growth Trajectories

Retinal ganglion cells in the mammalian central nervous system fail to regenerate following injury, with the capacity to survive and regrow varying by cell type. This variability may be linked to differences in developmental programs that overlap with the genetic pathways that mediate regeneration. To explore this correlation, we compared the structural changes in mouse retinal ganglion cells during development with those occurring after axonal injury. The dendritic trees of over 1,000 ganglion cells were reconstructed at different developmental stages, revealing that each cell type follows a distinct timeline. ON-sustained (sONα) cells reach maturity by P14, whereas ON-transient (tONα) cells achieve their maximum dendritic size by P10. Modeling of the dendritic changes indicate that while sONα and tONα follow similar growth programs the onset of growth was later in sONα. After optic nerve crush, the remodeling of dendritic architecture differed between the two cell-types. sONα cells exhibited rapid dendritic shrinkage, while tONα cells shrank more gradually with changes in branching features. Following injury, sONα cells reverted to an earlier developmental state than tONα cells. In addition, after co-deletion of PTEN and SOC3, neurons appeared to regress further back in developmental time. Our results provide evidence that a ganglion cell's resilience to injury and regenerative potential is predicted by its maturation timeline. Understanding these intrinsic differences could inform targeted neuroprotective interventions.

Unlocking the potential for optic nerve regeneration over long distances: a multi-therapeutic intervention

Retinal ganglion cells (RGCs) generally fail to regenerate axons, resulting in irreversible vision loss after optic nerve injury. While many studies have shown that modulating specific genes can enhance RGCs survival and promote optic nerve regeneration, inducing long-distance axon regeneration in vivo through single-gene manipulation remains challenging. Nevertheless, combined multi-gene therapies have proven effective in significantly enhancing axonal regeneration. At present, research on promoting optic nerve regeneration remains slow, with most studies unable to achieve axonal growth beyond the optic chiasm or reestablish connections with the brain. Future research priorities include directing axonal growth along correct pathways, facilitating synapse formation and myelination, and modifying the inhibitory microenvironment. These strategies are crucial not only for optic nerve regeneration but also for broader applications in central nervous system repair. In this review, we discuss multifactors therapeutic strategies for optic nerve regeneration, offering insights into advancing nerve regeneration research.

Electric field stimulation directs target-specific axon regeneration and partial restoration of vision after optic nerve crush injury

Failure of central nervous system (CNS) axons to regenerate after injury results in permanent disability. Several molecular neuro-protective and neuro-regenerative strategies have been proposed as potential treatments but do not provide the directional cues needed to direct target-specific axon regeneration. Here, we demonstrate that applying an external guidance cue in the form of electric field stimulation to adult rats after optic nerve crush injury was effective at directing long-distance, target-specific retinal ganglion cell (RGC) axon regeneration to native targets in the diencephalon. Stimulation was performed with asymmetric charged-balanced (ACB) waveforms that are safer than direct current and more effective than traditional, symmetric biphasic waveforms. In addition to partial anatomical restoration, ACB waveforms conferred partial restoration of visual function as measured by pattern electroretinogram recordings and local field potential recordings in the superior colliculus-and did so without the need for genetic manipulation. Our work suggests that exogenous electric field application can override cell-intrinsic and cell-extrinsic barriers to axon regeneration, and that electrical stimulation performed with specific ACB waveforms may be an effective strategy for directing anatomical and functional restoration after CNS injury.

Emerging therapeutic strategies for optic nerve regeneration

The optic nerve, comprising axons from retinal ganglion cells (RGCs), is a component of the central nervous system (CNS) that generally exhibits a limited regeneration capacity following injury in mature mammals, resulting in permanent vision loss. Here, we summarize recent advances in interventions targeting cell-intrinsic and cell-extrinsic mechanisms to enhance RGC axon regeneration. Additionally, we summarize strategies for guiding the reconnection of regenerating axons with brain visual targets, aiming to restore partial visual function. Given the advent of high-throughput screening techniques and multiomics analyses, we discuss how these emerging methodologies deepen our understanding of regenerative mechanisms and expedite the development of innovative therapeutic approaches. Lastly, we explore the translational potential of these strategies in achieving clinically meaningful vision recovery.

The IL-33/ST2 Axis Protects Retinal Ganglion Cells by Modulating the Astrocyte Response After Optic Nerve Injury

IL-33 and its receptor ST2 play crucial roles in tissue repair and homeostasis. However, their involvement in optic neuropathy due to trauma and glaucoma remains unclear. Here, we report that IL-33 and ST2 were highly expressed in the mouse optic nerve and retina. Deletion of IL-33 or ST2 exacerbated retinal ganglion cell (RGC) loss, retinal thinning, and nerve fiber degeneration following optic nerve (ON) injury. This heightened retinal neurodegeneration correlated with increased neurotoxic astrocytes in Il33-/- mice. In vitro, rIL-33 mitigated the neurotoxic astrocyte phenotype and reduced the expression of pro-inflammatory factors, thereby alleviating the RGC death induced by neurotoxic astrocyte-conditioned medium in retinal explants. Exogenous IL-33 treatment improved RGC survival in Il33-/- and WT mice after ON injury, but not in ST2-/- mice. Our findings highlight the role of the IL-33/ST2 axis in modulating reactive astrocyte function and providing neuroprotection for RGCs following ON injury.

Marcks overexpression in retinal ganglion cells promotes optic nerve regeneration

Regeneration of injured central nervous system (CNS) axons is highly restricted, leading to permanent neurological deficits. The myristoylated alanine-rich C-kinase substrate (MARCKS) is a membrane-associated protein kinase C (PKC) substrate ubiquitously expressed in eukaryotic cells, plays critical roles in development, brain plasticity, and tissues regeneration. However, little is known about the role of Marcks in CNS axon regeneration. Here we show that Marcks overexpression promotes robust axon regeneration either before or after optic nerve crush, but insignificantly impacts neuronal survival. Notably, immunostaining and RNA sequencing demonstrate that Marcks overexpression does not affect known regeneration-associated genes and pathways. Furthermore, combining CNTF which activates the JAK-STAT3 pathway and Marcks overexpression further enhances axon regeneration. Finally, we demonstrate functionally essential effector domain (ED) of MARCKS has similar effects on inducing axon regeneration in RGCs. These results suggest that manipulating Marcks and its ED may become a therapeutic approach to promote axon regeneration after CNS injury.

Axon guidance during mouse central nervous system regeneration is required for specific brain innervation

Reconstructing functional neuronal circuits is one major challenge of central nervous system repair. Through activation of pro-growth signaling pathways, some neurons achieve long-distance axon regrowth. Yet, functional reconnection has hardly been obtained, as these regenerating axons fail to resume their initial trajectory and reinnervate their proper target. Axon guidance is considered to be active only during development. Here, using the mouse visual system, we show that axon guidance is still active in the adult brain in regenerative conditions. We highlight that regenerating retinal ganglion cell axons avoid one of their primary targets, the suprachiasmatic nucleus (SCN), due to Slit/Robo repulsive signaling. Together with promoting regeneration, silencing Slit/Robo in vivo enables regenerating axons to enter the SCN and form active synapses. The newly formed circuit is associated with neuronal activation and functional recovery. Our results provide evidence that axon guidance mechanisms are required to reconnect regenerating axons to specific brain nuclei.

Axon regeneration: an issue of translation

In the mammalian central nervous system (CNS), adult neurons fail to regenerate spontaneously upon axon injury, which leads to a permanent and irreversible loss of neuronal functions. For more than 15 years, much effort was invested to unlock axon regrowth programs based on extensive transcriptomic characterization. However, it is now well described that mRNA and protein levels correlate only partially in cells, and that the transcription process (from DNA to mRNA) may not directly reflect protein expression. Conversely, the translation process (from mRNA to protein) provides an additional layer of gene regulation. This aspect has been overlooked in CNS regeneration. In this review, we discuss the limitations of transcriptomic approaches to promote CNS regeneration and we provide the rationale to investigate translational regulation in this context, and notably the regulatory role of the translational complex. Finally, we summarize our and others’ recent findings showing how variations in the translational complex composition regulate selective (mRNA-specific) translation, thereby controlling CNS axon regrowth.

Clickable, Thermally Responsive Hydrogels Enabled by Recombinant Spider Silk Protein and Spy Chemistry for Sustained Neurotrophin Delivery

The ability to deliver protein therapeutics in a minimally invasive, safe, and sustained manner, without resorting to viral delivery systems, will be crucial for treating a wide range of chronic injuries and diseases. Among these challenges, achieving axon regeneration and functional recovery post-injury or disease in the central nervous system remains elusive to most clinical interventions, constantly calling for innovative solutions. Here, a thermally responsive hydrogel system utilizing recombinant spider silk protein (spidroin) is developed. The protein solution undergoes rapid sol-gel transition at an elevated temperature (37 °C) following brief sonication. This thermally triggered gelation confers injectability to the system. Leveraging SpyTag/SpyCatcher chemistry, the hydrogel, composed of SpyTag-fusion spidroin, can be functionalized with diverse SpyCatcher-fusion bioactive motifs, such as neurotrophic factors (e.g., ciliary neurotrophic factor) and cell-binding ligands (e.g., laminin), rendering it well-suited for neuronal culturing. More importantly, the intravitreous injection of the protein materials decorated with SpyCatcher-fusion CNTF into the vitreous body after optic nerve injury leads to prolonged JAK/STAT3 signaling, increased neuronal survival, and enhanced axon regeneration. This study illustrates a generalizable material system for injectable and sustained delivery of protein therapeutics for neuroprotection and regeneration, with the potential for extension to other chronic diseases and injuries.

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.

Retinal Ganglion Cell Replacement in Glaucoma Therapy: A Narrative Review

Glaucoma is a leading cause of irreversible blindness worldwide. It leads to the progressive degeneration of retinal ganglion cells (RGCs), the axons of which form the optic nerve. Enormous RGC apoptosis causes a lack of transfer of visual information to the brain. The RGC loss typical of the central nervous system is irreversible, and when glaucoma progresses, the total amount of RGCs in the retina enormously diminishes. The successful treatment in glaucoma patients is a direct neuroprotection by decreasing the intraocular pressure, which enables RGC protection but does not revive the lost ones. The intriguing new therapy for advanced glaucoma is the possibility of RGC replacement with new healthy cells. In this review article, the strategies regarding RGC replacement therapy are presented with the latest advances in the technique and the obstacles that it meets.

Engineered bio-functional material-based nerve guide conduits for optic nerve regeneration: a view from the cellular perspective, challenges and the future outlook

Nerve injuries can be tantamount to severe impairment, standard treatment such as the use of autograft or surgery comes with complications and confers a shortened relief. The mechanism relevant to the regeneration of the optic nerve seems yet to be fully uncovered. The prevailing rate of vision loss as a result of direct or indirect insult on the optic nerve is alarming. Currently, the use of nerve guide conduits (NGC) to some extent has proven reliable especially in rodents and among the peripheral nervous system, a promising ground for regeneration and functional recovery, however in the optic nerve, this NGC function seems quite unfamous. The insufficient NGC application and the unabridged regeneration of the optic nerve could be a result of the limited information on cellular and molecular activities. This review seeks to tackle two major factors (i) the cellular and molecular activity involved in traumatic optic neuropathy and (ii) the NGC application for the optic nerve regeneration. The understanding of cellular and molecular concepts encompassed, ocular inflammation, extrinsic signaling and intrinsic signaling for axon growth, mobile zinc role, Ca2+ factor associated with the optic nerve, alternative therapies from nanotechnology based on the molecular information and finally the nanotechnological outlook encompassing applicable biomaterials and the use of NGC for regeneration. The challenges and future outlook regarding optic nerve regenerations are also discussed. Upon the many approaches used, the comprehensive role of the cellular and molecular mechanism may set grounds for the efficient application of the NGC for optic nerve regeneration.

Molecular signaling predicts corticospinal axon growth state and muscle response plasticity induced by neuromodulation

Electrical motor cortex stimulation can produce corticospinal system plasticity and enhance motor function after injury. We investigate molecular mechanisms of structural and physiological plasticity following electrical neuromodulation, focusing on identifying molecular predictors, or biomarkers, for durable plasticity. We used two neuromodulation protocols, repetitive multipulse stimulation (rMPS) and patterned intermittent theta burst stimulation (iTBS), incorporating different stimulation durations and follow-up periods. We compared neuromodulation efficacy in promoting corticospinal tract (CST) sprouting, motor cortex muscle evoked potential (MEP) LTP-like plasticity, and their associated molecular underpinnings. Only iTBS produced CST sprouting after short-term neuromodulation (1 d of stimulation; 9-d survival for sprouting expression); both iTBS and rMPS produced sprouting with long-term (10-d) neuromodulation. Significant mTOR signaling activation and phosphatase and tensin homolog (PTEN) protein deactivation predicted axon growth across all neuromodulation conditions that produced significant sprouting. Both neuromodulation protocols, regardless of duration, were effective in producing MEP enhancement. However, persistent LTP-like enhancement of MEPs at 30 d was only produced by long-term iTBS. Statistical modeling suggests that Stat3 signaling is the key mediator of MEP enhancement. Cervical spinal cord injury (SCI) alone did not affect baseline molecular signaling. Whereas iTBS and rMPS after SCI produced strong mTOR activation and PTEN deactivation, only iTBS produced Stat3 activation. Our findings support differential molecular biomarkers for neuromodulation-dependent structural and physiological plasticity and show that motor cortex epidural neuromodulation produces molecular changes in neurons that support axonal growth after SCI. iTBS may be more suitable for repair after SCI because it promotes molecular signaling for both CST growth and MEP plasticity.

The injured axon: intrinsic mechanisms driving axonal regeneration

Injury to the central nervous system (CNS) often results in permanent neurological impairments because axons fail to regenerate and re-establish lost synaptic contacts. By contrast, peripheral neurons can activate a pro-regenerative program and regenerate following a nerve lesion. This relies on an intricate intracellular communication system between the severed axon and the cell body. Locally activated signaling molecules are retrogradely transported to the soma to promote the epigenetic and transcriptional changes required for the injured neuron to regain growth competence. These signaling events rely heavily on intra-axonal translation and mitochondrial trafficking into the severed axon. Here, we discuss the interplay between these mechanisms and the main intrinsic barriers to axonal regeneration. We also examine the potential of manipulating these processes for driving CNS repair.

A miR-383-5p Signaling Hub Coordinates the Axon Regeneration Response to Inflammation

Neuroinflammation can positively influence axon regeneration following injury in the central nervous system. Inflammation promotes the release of neurotrophic molecules and stimulates intrinsic proregenerative molecular machinery in neurons, but the detailed mechanisms driving this effect are not fully understood. We evaluated how microRNAs are regulated in retinal neurons in response to intraocular inflammation to identify their potential role in axon regeneration. We found that miR-383-5p is downregulated in retinal ganglion cells in response to zymosan-induced intraocular inflammation. MiR-383-5p downregulation in neurons is sufficient to promote axon growth in vitro, and the intravitreal injection of a miR-383-5p inhibitor into the eye promotes axon regeneration following optic nerve crush. MiR-383-5p directly targets ciliary neurotrophic factor (CNTF) receptor components, and miR-383-5p inhibition sensitizes adult retinal neurons to the outgrowth-promoting effects of CNTF. Interestingly, we also demonstrate that CNTF treatment is sufficient to reduce miR-383-5p levels in neurons, constituting a positive-feedback module, whereby initial CNTF treatment reduces miR-383-5p levels, which then disinhibits CNTF receptor components to sensitize neurons to the ligand. Additionally, miR-383-5p inhibition derepresses the mitochondrial antioxidant protein peroxiredoxin-3 (PRDX3) which was required for the proregenerative effects associated with miR-383-5p loss-of-function in vitro. We have thus identified a positive-feedback mechanism that facilitates neuronal CNTF sensitivity in neurons and a new molecular signaling module that promotes inflammation-induced axon regeneration.

Glial cell derived pathway directs regenerating optic nerve axons toward the CNS midline

Several RGC intrinsic signaling pathways have been shown to enhance RGC survival and RGC axonal growth after optic nerve injury. Yet an unresolved challenge for regenerating RGC axons is to properly navigate the optic chiasm located at the Central Nervous System midline. Here, we use live-cell imaging in larval zebrafish to show that regrowing RGC axons initiate growth toward the midline and extend along a trajectory similar to their original projection. From a candidate genetic screen, we identify the glycosyltransferase Lh3 to be required during the process of regeneration to direct regrowing RGC axons toward the midline. Moreover, we find that mutants in collagen 18a1 (col18a1), a putative Lh3 substrate, display RGC axonal misguidance phenotypes similar to those we observe in lh3 mutants, suggesting that lh3 may act through col18a1 during regeneration. Finally, we show that transgenic lh3 expression in sox10+ presumptive olig2+ oligodendrocytes located near the optic chiasm restores directed axonal growth. Combined these data identify lh3 and col18a1 as part of a glial derived molecular pathway critical for guiding in vivo regenerating RGC axons towards and across the optic chiasm.

Roles of Kdm6a and Kdm6b in regulation of mammalian neural regeneration

Epigenetic regulation of neuronal transcriptomic landscape is emerging to be a key coordinator of mammalian neural regeneration. Here we investigated roles of two histone 3 lysine 27 (H3K27) demethylases Kdm6a/b in controlling neuroprotection and axon regeneration. Deleting either Kdm6a or Kdm6b led to enhanced sensory axon regeneration in PNS, whereas in the CNS only deleting Kdm6a in retinal ganglion cells (RGCs) significantly enhanced optic nerve regeneration. Moreover, both Kdm6a and Kdm6b functioned to regulate RGC survival but with different mechanisms. Mechanistically, Kdm6a regulates RGC regeneration via distinct pathway from that of Pten and co-deleting Kdm6a and Pten resulted in long distance optic nerve regeneration passing the optic chiasm. In addition, RNA-seq profiling revealed that Kdm6a deletion switched the RGC transcriptomics into a developmental-like state and suppressed several known repressors of neural regeneration. Klf4 was identified as a direct downstream target of Kdm6a-H3K27me3 signaling in both sensory neurons and RGCs to regulate axon regeneration. These findings not only revealed different roles of Kdm6a and Kdm6b in regulation of neural regeneration and their underlying mechanisms, but also identified Kdm6a-mediated histone demethylation signaling as a novel epigenetic target for supporting CNS neural regeneration.

Lipin1 depletion coordinates neuronal signaling pathways to promote motor and sensory axon regeneration after spinal cord injury

Adult central nervous system (CNS) neurons down-regulate growth programs after injury, leading to persistent regeneration failure. Coordinated lipids metabolism is required to synthesize membrane components during axon regeneration. However, lipids also function as cell signaling molecules. Whether lipid signaling contributes to axon regeneration remains unclear. In this study, we showed that lipin1 orchestrates mechanistic target of rapamycin (mTOR) and STAT3 signaling pathways to determine axon regeneration. We established an mTOR-lipin1-phosphatidic acid/lysophosphatidic acid-mTOR loop that acts as a positive feedback inhibitory signaling, contributing to the persistent suppression of CNS axon regeneration following injury. In addition, lipin1 knockdown (KD) enhances corticospinal tract (CST) sprouting after unilateral pyramidotomy and promotes CST regeneration following complete spinal cord injury (SCI). Furthermore, lipin1 KD enhances sensory axon regeneration after SCI. Overall, our research reveals that lipin1 functions as a central regulator to coordinate mTOR and STAT3 signaling pathways in the CNS neurons and highlights the potential of lipin1 as a promising therapeutic target for promoting the regeneration of motor and sensory axons after SCI.

Deleting PTEN, but not SOCS3 or myelin inhibitors, robustly boosts BRAF-elicited intraspinal regeneration of peripheral sensory axons

Primary sensory axons fail to regenerate into the spinal cord following dorsal root injury leading to permanent sensory deficits. Re-entry is prevented at the dorsal root entry zone (DREZ), the CNS-PNS interface. Current approaches for promoting DR regeneration across the DREZ have had some success, but sustained, long-distance regeneration, particularly of large-diameter myelinated axons, still remains a formidable challenge. We have previously shown that induced expression of constitutively active B-RAF (kaBRAF) enhanced the regenerative competence of injured DRG neurons in adult mice. In this study, we investigated whether robust intraspinal regeneration can be achieved after a cervical DR injury by selective expression of kaBRAF alone or in combination with deletion of the myelin-associated inhibitors or neuron-intrinsic growth suppressors (PTEN or SOCS3). We found that kaBRAF promoted some axon regeneration across the DREZ but did not produce significant functional recovery by two months. Supplementary deletion of Nogo, MAG, and OMgp only modestly improved kaBRAF-induced regeneration. Deletion of PTEN or SOCS3 individually or in combination failed to promote any growth across the DREZ. In marked contrast, simultaneous deletion of PTEN, but not SOCS3, dramatically enhanced kaBRAF-mediated regeneration enabling many more axons to penetrate the DREZ and grow deep into the spinal cord. This study shows that dual activation of BRAF-MEK-ERK and PI3K-Akt-mTOR signaling is an effective strategy to stimulate robust intraspinal DR regeneration.

microRNA-2184 orchestrates Mauthner-cell axon regeneration in zebrafish via syt3 modulation

MicroRNAs (miRNAs) play a significant role in axon regeneration following spinal cord injury. However, the functions of numerous miRNAs in axon regeneration within the central nervous system (CNS) remain largely unexplored. Here, we elucidate the positive role of microRNA-2184 (miR-2184) in axon regeneration within zebrafish Mauthner cells (M-cells). The upregulation of miR-2184 in a single M-cell can facilitate axon regeneration, while the specific sponge-induced silencing of miR-2184 leads to impeded regeneration. We show that syt3, a downstream target of miR-2184, negatively regulates axon regeneration, and the regeneration suppression modulated by syt3 depends on its binding to Ca2+. Furthermore, pharmacological stimulation of the cAMP/PKA pathway suggests that changes in the readily releasable pool may affect axon regeneration. Our data indicate that miR-2184 promotes axon regeneration of M-cells within the CNS by modulating the downstream target syt3, providing valuable insights into potential therapeutic strategies.

Molecular mechanisms of spinal cord injury repair across vertebrates: A comparative review

In humans and other adult mammals, axon regeneration is difficult in axotomized neurons. Therefore, spinal cord injury (SCI) is a devastating event that can lead to permanent loss of locomotor and sensory functions. Moreover, the molecular mechanisms of axon regeneration in vertebrates are not very well understood, and currently, no effective treatment is available for SCI. In striking contrast to adult mammals, many nonmammalian vertebrates such as reptiles, amphibians, bony fishes and lampreys can spontaneously resume locomotion even after complete SCI. In recent years, rapid progress in the development of next-generation sequencing technologies has offered valuable information on SCI. In this review, we aimed to provide a comparison of axon regeneration process across classical model organisms, focusing on crucial genes and signalling pathways that play significant roles in the regeneration of individually identifiable descending neurons after SCI. Considering the special evolutionary location and powerful regenerative ability of lamprey and zebrafish, they will be the key model organisms for ongoing studies on spinal cord regeneration. Detailed study of SCI in these model organisms will help in the elucidation of molecular mechanisms of neuron regeneration across species.

TET3 Contributes to Exercise-Induced Functional Axon Regeneration and Visual Restoration

Axons have intrinsically poor regenerative capacity in the mature central nervous system (CNS), leading to permanent neurological impairments in individuals. There is growing evidence that exercise is a powerful physiological intervention that can obviously enhance cell rejuvenate capacity, but its molecular mechanisms that mediate the axonal regenerative benefits remain largely unclear. Using the eye as the CNS model, here it is first indicated that placing mice in an exercise stimulation environment induced DNA methylation patterns and transcriptomes of retinal ganglion cell, promoted axon regeneration after injury, and reversed vision loss in aged mice. These beneficial effects are dependent on the DNA demethylases TET3-mediated epigenetic effects, which increased the expression of genes associated with the regenerative growth programs, such as STAT3, Wnt5a, Klf6. Exercise training also shows with the improved mitochondrial and metabolic dysfunction in retinas and optic nerves via TET3. Collectively, these results suggested that the increased regenerative capacity induced by enhancing physical activity is mediated through epigenetic reprogramming in mouse model of optic nerve injury and in aged mouse. Understanding the molecular mechanism underlying exercise-dependent neuronal plasticity led to the identification of novel targets for ameliorating pathologies associated with etiologically diverse diseases.

Systemic whole transcriptome analysis identified underlying molecular characteristics and regulatory networks implicated in the retina following optic nerve injury

Optic nerve injuries are severely disrupt the structural and functional integrity of the retina, often leading to visual impairment or blindness. Despite the profound impact of these injuries, the molecular mechanisms involved remain poorly understood. In this study, we performed a comprehensive whole-transcriptome analysis of mouse retina samples after optic nerve crush (ONC) to elucidate changes in gene expression and regulatory networks. Transcriptome analysis revealed a variety of molecular alterations, including 256 mRNAs, 530 lncRNAs, and 37 miRNAs, associated with metabolic, inflammatory, signaling, and biosynthetic pathways in the injured retina. The integrated analysis of co-expression and protein-protein interactions identified an active interconnected module comprising 5 co-expressed proteins (Fga, Serpina1a, Hpd, Slc38a4, and Ahsg) associated with the complement and coagulation cascades. Finally, 5 mRNAs (Fga, Serpinala, Hpd, Slc38a4, and Ahsg), 2 miRNAs (miR-671-5p and miR-3057-5p), and 6 lncRNAs (MSTRG. 1830.1, Gm10814, A530013C23Rik, Gm40634, MSTRG.9514.1, A330023F24Rik) were identified by qPCR in the injured retina, and some of them were validated as critical components of a ceRNA network active in 661W and HEK293T cells through dual-luciferase reporter assays. In conclusion, our study provides comprehensive insight into the complex and dynamic biological mechanisms involved in retinal injury responses and highlights promising potential targets to enhance neuroprotection and restore vision.

The top 100 most cited articles on axon regeneration from 2003 to 2023: a bibliometric analysis

Objective

In this study, we used a bibliometric and visual analysis to evaluate the characteristics of the 100 most cited articles on axon regeneration.

Methods

The 100 most cited papers on axon regeneration published between 2003 and 2023 were identified by searching the Web of Science Core Collection database. The extracted data included the title, author, keywords, journal, publication year, country, and institution. A bibliometric analysis was subsequently undertaken.

Results

The examined set of 100 papers collectively accumulated a total of 39,548 citations. The number of citations for each of the top 100 articles ranged from 215 to 1,604, with a median value of 326. The author with the most contributions to this collection was He, Zhigang, having authored eight papers. Most articles originated in the United States (n = 72), while Harvard University was the institution with the most cited manuscripts (n = 19). Keyword analysis unveiled several research hotspots, such as chondroitin sulfate proteoglycan, alternative activation, exosome, Schwann cells, axonal protein synthesis, electrical stimulation, therapeutic factors, and remyelination. Examination of keywords in the articles indicated that the most recent prominent keyword was "local delivery."

Conclusion

This study offers bibliometric insights into axon regeneration, underscoring that the United States is a prominent leader in this field. Our analysis highlights the growing relevance of local delivery systems in axon regeneration. Although these systems have shown promise in preclinical models, challenges associated with long-term optimization, agent selection, and clinical translation remain. Nevertheless, the continued development of local delivery technologies represents a promising pathway for achieving axon regeneration; however, additional research is essential to fully realize their potential and thereby enhance patient outcomes.

Repurposing development genes for axonal regeneration following injury: Examining the roles of Wnt signaling

In this review, we explore the connections between developmental embryology and axonal regeneration. Genes that regulate embryogenesis and central nervous system (CNS) development are discussed for their therapeutic potential to induce axonal and cellular regeneration in adult tissues after neuronal injury. Despite substantial differences in the tissue environment in the developing CNS compared with the injured CNS, recent studies have identified multiple molecular pathways that promote axonal growth in both scenarios. We describe various molecular cues and signaling pathways involved in neural development, with an emphasis on the versatile Wnt signaling pathway. We discuss the capacity of developmental factors to initiate axonal regrowth in adult neural tissue within the challenging environment of the injured CNS. Our discussion explores the roles of Wnt signaling and also examines the potential of other embryonic genes including Pax, BMP, Ephrin, SOX, CNTF, PTEN, mTOR and STAT3 to contribute to axonal regeneration in various CNS injury model systems, including spinal cord and optic crush injuries in mice, Xenopus and zebrafish. Additionally, we describe potential contributions of Müller glia redifferentiation to neuronal regeneration after injury. Therefore, this review provides a comprehensive summary of the state of the field, and highlights promising research directions for the potential therapeutic applications of specific embryologic molecular pathways in axonal regeneration in adults.

Lhx2 promotes axon regeneration of adult retinal ganglion cells and rescues neurodegeneration in mouse models of glaucoma

The axons of retinal ganglion cells (RGCs) form the optic nerve, transmitting visual information from the eye to the brain. Damage or loss of RGCs and their axons is the leading cause of visual functional defects in traumatic injury and degenerative diseases such as glaucoma. However, there are no effective clinical treatments for nerve damage in these neurodegenerative diseases. Here, we report that LIM homeodomain transcription factor Lhx2 promotes RGC survival and axon regeneration in multiple animal models mimicking glaucoma disease. Furthermore, following N-methyl-D-aspartate (NMDA)-induced excitotoxicity damage of RGCs, Lhx2 mitigates the loss of visual signal transduction. Mechanistic analysis revealed that overexpression of Lhx2 supports axon regeneration by systematically regulating the transcription of regeneration-related genes and inhibiting transcription of Semaphorin 3C (Sema3C). Collectively, our studies identify a critical role of Lhx2 in promoting RGC survival and axon regeneration, providing a promising neural repair strategy for glaucomatous neurodegeneration.

Macrophages modulate fibrosis during newt lens regeneration

BACKGROUND

Previous studies have suggested that macrophages are present during lens regeneration in newts, but their role in the process is yet to be elucidated.

METHODS

Here we generated a transgenic reporter line using the newt, Pleurodeles waltl, that traces macrophages during lens regeneration. Furthermore, we assessed early changes in gene expression during lens regeneration using two newt species, Notophthalmus viridescens and Pleurodeles waltl. Finally, we used clodronate liposomes to deplete macrophages during lens regeneration in both species and tested the effect of a subsequent secondary injury after macrophage recovery.

RESULTS

Macrophage depletion abrogated lens regeneration, induced the formation of scar-like tissue, led to inflammation, decreased iris pigment epithelial cell (iPEC) proliferation, and increased rates of apoptosis in the eye. Some of these phenotypes persisted throughout the last observation period of 100 days and could be attenuated by exogenous FGF2 administration. A distinct transcript profile encoding acute inflammatory effectors was established for the dorsal iris. Reinjury of the newt eye alleviated the effects of macrophage depletion, including the resolution of scar-like tissue, and re-initiated the regeneration process.

CONCLUSIONS

Together, our findings highlight the importance of macrophages for facilitating a pro-regenerative environment in the newt eye by regulating fibrotic responses, modulating the overall inflammatory landscape, and maintaining the proper balance of early proliferation and late apoptosis of the iPECs.

Stat3 Has a Different Role in Axon Growth During Development Than It Does in Axon Regeneration After Injury

Signal transducer and activator of transcription 3 (STAT3) is essential for neural development and regeneration as a key transcription factor and mitochondrial activator. However, the mechanism of Stat3 in axon development and regeneration has not been fully understood. In this study, using zebrafish posterior lateral line (PLL) axons, we demonstrate that Stat3 plays distinct roles in PLL axon embryonic growth and regeneration. Our experiments indicate that stat3 is required for PLL axon extension. In stat3 mutant zebrafish, the PLL axon ends were stalled at the level of the cloaca, and expression of stat3 rescues the PLL axon growth in a cell-autonomous manner. Jak/Stat signaling inhibition did not affect PLL axon growth indicating Jak/Stat was dispensable for PLL axon growth. In addition, we found that Stat3 was co-localized with mitochondria in PLL axons and important for the mitochondrial membrane potential and ATPase activity. The PLL axon growth defect of stat3 mutants was mimicked and rescued by rotenone and DCHC treatment, respectively, which suggests that Stat3 regulates PLL axon growth through mitochondrial Stat3. By contrast, mutation of stat3 or Jak/Stat signaling inhibition retarded PLL axon regeneration. Meanwhile, we also found Schwann cell migration was also inhibited in stat3 mutants. Taken together, Stat3 is required for embryonic PLL axon growth by regulating the ATP synthesis efficiency of mitochondria, whereas Stat3 stimulates PLL axon regeneration by regulating Schwann cell migration via Jak/Stat signaling. Our findings show a new mechanism of Stat3 in axon growth and regeneration.

Optic nerve regeneration: Potential treatment approaches

The optic nerve, predominantly constituted by the axons of retinal ganglion cells (RGCs), lacks the ability to regenerate and re-establish function after injury. RGCs are crucial for visual function, and thus, RGC death contributes to the development of numerous progressive neurodegenerative optic neuropathies including glaucoma, ischemic optic neuropathy, and optic neuritis. Regenerating optic nerve axons poses numerous challenges due to factors such as the intricate and inhibitory conditions that exist within their environment, intrinsic breaks to regeneration, and the geometric tortuosity that offers physical hindrance to axon growth. However, recent research advancements offer hope for clinically meaningful regeneration for those who suffer from optic nerve damage. In this review, we highlight the current treatment approaches for optic nerve axon regeneration.

Role of RNA polymerase III transcription and regulation in ischaemic stroke

Ischaemic stroke is a leading cause of death and life-long disability due to neuronal cell death resulting from interruption of glucose and oxygen supplies. RNA polymerase III (Pol III)-dependent transcription plays a central role in protein synthesis that is necessary for normal cerebral neuronal functions, and the survival and recovery under pathological conditions. Notably, Pol III transcription is highly sensitive to ischaemic stress that is known to rapidly shut down Pol III transcriptional activity. However, its precise role in ischaemic stroke, especially during the acute and recovery phases, remains poorly understood. The microenvironment within the ischaemic brain undergoes dynamic changes in different phases after stroke. Emerging evidence highlights the distinct roles of Pol III transcription in neuroprotection during the acute phase and repair during the recovery phase of stroke. Additionally, investigations into the mTOR-MAF1 signalling pathway, a conserved regulator of Pol-III transcription, reveal its therapeutic potential in enhancing acute phase neuroprotection and recovery phase repair.

Tafluprost promotes axon regeneration after optic nerve crush via Zn2+-mTOR pathway

PURPOSE

To investigate whether Tafluprost could promote optic nerve regeneration in mice after optic nerve crush (ONC) and determine the underlying molecular mechanism.

METHODS

Tafluprost was injected into the vitreous body immediately after ONC. The level of Zn2+ in the inner plexiform layer (IPL) of the retina was stained using autometallography (AMG). The number of survival retinal ganglion cells (RGCs) was determined via dual staining with RGC markers Tuj1 and RBPMS. Individual axons that regenerated to 0.25, 0.5, 0.75 and 1 mm were manually counted in the whole-mount optic nerve labeled by cholera toxin B fragment (CTB). Immunofluorescence and Western blot were performed to detect protein expression levels. Pattern electroretinogram was used to evaluate RGCs function.

RESULTS

Tafluprost promoted RGC survival in a dose-dependent manner with an optimal concentration of 1 μM. Tafluprost significantly decreased ZnT-3 expression and Zn2+ accumulation in the IPL of retina. Tafluprost stimulated intense axonal regeneration and maintained RGCs function compared to control. Mechanistically, Tafluprost and Zn2+ elimination treatment (TPEN or ZnT-3 deletion) can activate the mTOR pathway with an improved percentage of pS6+ RGCs in the retina. However, rapamycin, a specific inhibitor of the mTOR1, inhibited the activation of the mTOR pathway and abolished the regenerative effect mediated by Tafluprost. Tafluprost also inhibited the upregulation of p62, LC3 and Beclin-1, attenuated the overactivation of microglia/macrophages and downregulated the expression of TNFα and IL-1β.

CONCLUSIONS

Our results suggest that Tafluprost promoted axon regeneration via regulation of the Zn2+-mTOR pathway, and provide novel research directions for glaucomatous optic nerve injury mechanisms.

Genetic rodent models of glaucoma in representing disease phenotype and insights into the pathogenesis

Genetic rodent models are widely used in glaucoma related research. With vast amount of information revealed by human studies about genetic correlations with glaucoma, use of these models is relevant and required. In this review, we discuss the glaucoma endophenotypes and importance of their representation in an experimental animal model. Mice and rats are the most popular animal species used as genetic models due to ease of genetic manipulations in these animal species as well as the availability of their genomic information. With technological advances, induction of glaucoma related genetic mutations commonly observed in human is possible to achieve in rodents in a desirable manner. This approach helps to study the pathobiology of the disease process with the background of genetic abnormalities, reveals potential therapeutic targets and gives an opportunity to test newer therapeutic options. Various genetic manipulation leading to appearance of human relevant endophenotypes in rodents indicate their relevance in glaucoma pathology and the utility of these rodent models for exploring various aspects of the disease related to targeted mutation. The molecular pathways involved in the pathophysiology of glaucoma leading to elevated intraocular pressure and the disease hallmark, apoptosis of retinal ganglion cells and optic nerve degeneration, have been extensively explored in genetic rodent models. In this review, we discuss the consequences of various genetic manipulations based on the primary site of pathology in the anterior or the posterior segment. We discuss how these genetic manipulations produce features in rodents that can be considered a close representation of disease phenotype in human. We also highlight several molecular mechanisms revealed by using genetic rodent models of glaucoma including those involved in increased aqueous outflow resistance, loss of retinal ganglion cells and optic neuropathy. Lastly, we discuss the limitations of the use of genetic rodent models in glaucoma related research.

Neuroinflammation: Breaking barriers and bridging gaps

Neurons are the cells of the nervous system and are responsible for every thought, movement and perception. Immune cells are the cells of the immune system, constantly protecting from foreign pathogens. Understanding the interaction between the two systems is especially important in disease states such as autoimmune or neurodegenerative disease. Unfortunately, this interaction is typically detrimental to the host. However, recent efforts have focused on how neurons and immune cells interact, either directly or indirectly, following traumatic injury to the nervous system. The outcome of this interaction can be beneficial - leading to successful neural repair, or detrimental - leading to functional deficits, depending on where the injury occurs. This review will discuss our understanding of neuron-immune cell interactions after traumatic injury to both the peripheral and central nervous system.

Macrophages modulate fibrosis during newt lens regeneration

Background

Previous studies indicated that macrophages play a role during lens regeneration in newts, but their function has not been tested experimentally.

Methods

Here we generated a transgenic newt reporter line in which macrophages can be visualized in vivo. Using this new tool, we analyzed the location of macrophages during lens regeneration. We uncovered early gene expression changes using bulk RNAseq in two newt species, Notophthalmus viridescens and Pleurodeles waltl. Next, we used clodronate liposomes to deplete macrophages, which inhibited lens regeneration in both newt species.

Results

Macrophage depletion induced the formation of scar-like tissue, an increased and sustained inflammatory response, an early decrease in iris pigment epithelial cell (iPEC) proliferation and a late increase in apoptosis. Some of these phenotypes persisted for at least 100 days and could be rescued by exogenous FGF2. Re-injury alleviated the effects of macrophage depletion and re-started the regeneration process.

Conclusions

Together, our findings highlight the importance of macrophages in facilitating a pro-regenerative environment in the newt eye, helping to resolve fibrosis, modulating the overall inflammatory landscape and maintaining the proper balance of early proliferation and late apoptosis.

Regulation of the JAK/STAT signaling pathway in spinal cord injury: an updated review

Cytokines are involved in neural homeostasis and pathological processes associated with neuroinflammation after spinal cord injury (SCI). The biological effect of cytokines, including those associated with acute or chronic SCI pathologies, are the result of receptor-mediated signaling through the Janus kinases (JAKs) as well as the signal transducers and activators of transcription (STAT) DNA-binding protein families. Although therapies targeting at cytokines have led to significant changes in the treatment of SCI, they present difficulties in various aspects for the direct use by patients themselves. Several small-molecule inhibitors of JAKs, which may affect multiple pro-inflammatory cytokine-dependent pathways, as well as STATs, are in clinical development for the treatment of SCI. This review describes the current understanding of the JAK-STAT signaling in neuroendocrine homeostasis and diseases, together with the rationale for targeting at this pathway for the treatment of SCI.

Inflammatory Mediators of Axon Regeneration in the Central and Peripheral Nervous Systems

Although most pathways in the mature central nervous system cannot regenerate when injured, research beginning in the late 20th century has led to discoveries that may help reverse this situation. Here, we highlight research in recent years from our laboratory identifying oncomodulin (Ocm), stromal cell-derived factor (SDF)-1, and chemokine CCL5 as growth factors expressed by cells of the innate immune system that promote axon regeneration in the injured optic nerve and elsewhere in the central and peripheral nervous systems. We also review the role of ArmC10, a newly discovered Ocm receptor, in mediating many of these effects, and the synergy between inflammation-derived growth factors and complementary strategies to promote regeneration, including deleting genes encoding cell-intrinsic suppressors of axon growth, manipulating transcription factors that suppress or promote the expression of growth-related genes, and manipulating cell-extrinsic suppressors of axon growth. In some cases, combinatorial strategies have led to unprecedented levels of nerve regeneration. The identification of some similar mechanisms in human neurons offers hope that key discoveries made in animal models may eventually lead to treatments to improve outcomes after neurological damage in patients.

Electrical stimulation alters DNA methylation and promotes neurite outgrowth

Electrical stimulation (ES) influences neural regeneration and functionality. We here investigate whether ES regulates DNA demethylation, a critical epigenetic event known to influence nerve regeneration. Retinal ganglion cells (RGCs) have long served as a standard model for central nervous system neurons, whose growth and disease development are reportedly affected by DNA methylation. The current study focuses on the ability of ES to rescue RGCs and preserve vision by modulating DNA demethylation. To evaluate DNA demethylation pattern during development, RGCs from mice at different stages of development, were analyzed using qPCR for ten-eleven translocation (TETs) and immunostained for 5 hydroxymethylcytosine (5hmc) and 5 methylcytosine (5mc). To understand the effect of ES on neurite outgrowth and DNA demethylation, cells were subjected to ES at 75 µAmp biphasic ramp for 20 min and cultured for 5 days. ES increased TETs mediated neurite outgrowth, DNA demethylation, TET1 and growth associated protein 43 levels significantly. Immunostaining of PC12 cells following ES for histone 3 lysine 9 trimethylation showed cells attained an antiheterochromatin configuration. Cultured mouse and human retinal explants stained with β-III tubulin exhibited increased neurite growth following ES. Finally, mice subjected to optic nerve crush injury followed by ES exhibited improved RGCs function and phenotype as validated using electroretinogram and immunohistochemistry. Our results point to a possible therapeutic regulation of DNA demethylation by ES in neurons.

Customization of the translational complex regulates mRNA-specific translation to control CNS regeneration

In the adult mammalian central nervous system (CNS), axons fail to regenerate spontaneously after injury because of a combination of extrinsic and intrinsic factors. Despite recent advances targeting the intrinsic regenerative properties of adult neurons, the molecular mechanisms underlying axon regeneration are not fully understood. Here, we uncover a regulatory mechanism that controls the expression of key proteins involved in regeneration at the translational level. Our results show that mRNA-specific translation is critical for promoting axon regeneration. Indeed, we demonstrate that specific ribosome-interacting proteins, such as the protein Huntingtin (HTT), selectively control the translation of a specific subset of mRNAs. Moreover, modulating the expression of these translationally regulated mRNAs is crucial for promoting axon regeneration. Altogether, our findings highlight that selective translation through the customization of the translational complex is a key mechanism of axon regeneration with major implications in the development of therapeutic strategies for CNS repair.

Factors Affecting Stem Cell-Based Regenerative Approaches in Retinal Degeneration

Inherited and age-associated vision loss is often associated with degeneration of the cells of the retina, the light-sensitive layer at the back of the eye. The mammalian retina, being a postmitotic neural tissue, does not have the capacity to repair itself through endogenous regeneration. There has been considerable excitement for the development of cell replacement approaches since the isolation and development of culture methods for human pluripotent stem cells, as well as the generation of induced pluripotent stem cells. This has now been combined with novel three-dimensional organoid culture systems that closely mimic human retinal development in vitro. In this review, we cover the current state of the field, with emphasis on the cell delivery challenges, role of the recipient immunological microenvironment, and challenges related to connectivity between transplanted cells and host circuitry both locally and centrally to the different areas of the brain.

Recent progress and challenges in the treatment of spinal cord injury

Spinal cord injury (SCI) disrupts the structural and functional connectivity between the higher center and the spinal cord, resulting in severe motor, sensory, and autonomic dysfunction with a variety of complications. The pathophysiology of SCI is complicated and multifaceted, and thus individual treatments acting on a specific aspect or process are inadequate to elicit neuronal regeneration and functional recovery after SCI. Combinatory strategies targeting multiple aspects of SCI pathology have achieved greater beneficial effects than individual therapy alone. Although many problems and challenges remain, the encouraging outcomes that have been achieved in preclinical models offer a promising foothold for the development of novel clinical strategies to treat SCI. In this review, we characterize the mechanisms underlying axon regeneration of adult neurons and summarize recent advances in facilitating functional recovery following SCI at both the acute and chronic stages. In addition, we analyze the current status, remaining problems, and realistic challenges towards clinical translation. Finally, we consider the future of SCI treatment and provide insights into how to narrow the translational gap that currently exists between preclinical studies and clinical practice. Going forward, clinical trials should emphasize multidisciplinary conversation and cooperation to identify optimal combinatorial approaches to maximize therapeutic benefit in humans with SCI.

Transcriptomic Profiling after In Vitro Δ8-THC Exposure Shows Cytoskeletal Remodeling in Trauma-Injured NSC-34 Cell Line

Neuronal cell death is a physiological process that, when uncontrollable, leads to neurodegenerative disorders like spinal cord injury (SCI). SCI represents one of the major causes of trauma and disabilities worldwide for which no effective pharmacological intervention exists. Herein, we observed the beneficial effects of Δ8-Tetrahydrocannabinol (Δ8-THC) during neuronal cell death recovery. We cultured NSC-34 motoneuron cell line performing three different experiments. A traumatic scratch injury was caused in two experiments. One of the scratched was pretreated with Δ8-THC to observe the role of the cannabinoid following the trauma. An experimental control group was neither scratched nor pretreated. All the experiments underwent RNA-seq analysis. The effects of traumatic injury were observed in scratch against control comparison. Comparison of scratch models with or without pretreatment highlighted how Δ8-THC counteracts the traumatic event. Our results shown that Δ8-THC triggers the cytoskeletal remodeling probably due to the activation of the Janus Kinase Signal Transducer and Activator of Transcription (JAK/STAT) signaling pathway and the signaling cascade operated by the Mitogen-Activated Protein (MAP) Kinase signaling pathway. In light of this evidence, Δ8-THC could be a valid pharmacological approach in the treatment of abnormal neuronal cell death occurring in motoneuron cells.