NT-3 Promotes Oligodendrocyte Proliferation and Nerve Function Recovery After Spinal Cord Injury by Inhibiting Autophagy Pathway

Exogenous NT-3 Promotes Phenotype Switch of Resident Macrophages and Improves Sciatic Nerve Injury through AMPK/NF-κB Signaling Pathway

Neurotrophin-3 (NT-3) is an important family of neurotrophic factors with extensive neurotrophic activity, which can maintain the survival and regeneration of nerve cells. However, the mechanism of NT-3 on macrophage phenotype transformation after sciatic nerve injury is not clear. In this study, we constructed a scientific nerve compression injury animal model and administered different doses of NT-3 treatment through osmotic minipump. 7 days after surgery, we collected sciatic nerve tissue and observed the distribution of macrophage phenotype through iNOS and CD206 immunofluorescence. During the experiment, regular postoperative observations were conducted on rats. After the experiment, sciatic nerve tissue was collected for HE staining, myelin staining, immunofluorescence staining, and Western blot analysis. To verify the role of the AMPK/NF-κB pathway, we applied the AMPK inhibitor Compound C and the NF-κB inhibitor BAY11-7082 to repeat the above experiment. Our experimental results reveal that NT-3 promotes sciatic nerve injury repair and polarization of M2 macrophage phenotype, promotes AMPK activation, and inhibits NF-κB activation. The repair effect of high concentration NT-3 on sciatic nerve injury is significantly enhanced compared to low concentration. Compound C administration can weaken the effect of NT-3, while BAY 11-7082 can enhance the effect of NT-3. In short, NT-3 significantly improves sciatic nerve injury in rats, promotes sciatic nerve function repair, accelerates M2 macrophage phenotype polarization, and improves neuroinflammatory response. The protective effects of NT-3 mentioned above are partially related to the AMPK/NF-κB signal axis.

Role of dendritic cells in spinal cord injury

BACKGROUND

Inflammation can worsen spinal cord injury (SCI), with dendritic cells (DCs) playing a crucial role in the inflammatory response. They mediate T lymphocyte differentiation, activate microglia, and release cytokines like NT-3. Moreover, DCs can promote neural stem cell survival and guide them toward neuron differentiation, positively impacting SCI outcomes.

OBJECTIVE

This review aims to summarize the role of DCs in SCI-related inflammation and identify potential therapeutic targets for treating SCI.

METHODS

Literature in PubMed and Web of Science was reviewed using critical terms related to DCs and SCI.

RESULTS

The study indicates that DCs can activate microglia and astrocytes, promote T-cell differentiation, increase neurotrophin release at the injury site, and subsequently reduce secondary brain injury and enhance functional recovery in the spinal cord.

CONCLUSIONS

This review highlights the repair mechanisms of DCs and their potential therapeutic potential for SCI.

The Temporal and Spatial Changes of Autophagy and PI3K Isoforms in Different Neural Cells After Hypoxia/Reoxygenation Injury

There are limited therapeutic options for patient with traumatic spinal cord injury (SCI). Phosphoinositide 3-kinase family (PI3Ks) are the key molecules for regulating cell autophagy, which is a possible way of treating SCI. As we know, PI3K family are composed of eight isoforms, which are distributed into three classes. While the role of PI3Ks in regulating autophagy is controversial and the effects may be in a cell-specific manner. Different isoforms do not distribute in neural cells consistently and it is not clear how the PI3K isoforms regulate and interact with autophagy. Therefore, we explored the distributions and expression of different PI3K isoforms in two key neural cells (PC12 cells and astrocytes). The results showed that the expression of LC3II/I and p62, which are the markers of autophagy, changed in different patterns in PC12 cells and astrocytes after hypoxia/reoxygenation injury (H/R). Furthermore, the mRNA level of eight PI3K isoforms did not change in the same way, and even for the same isoform the mRNA activities are different between PC12 cells and astrocytes. What is more, the results of western blot of PI3K isoforms after H/R were inconsistent with the relevant mRNA. Based on this study, the therapeutic effects of regulating autophagy on SCI are not confirmed definitely, and its molecular mechanisms may be related with different temporal and spatial patterns of activation and distributions of PI3K isoforms.

Spinal cord injury: molecular mechanisms and therapeutic interventions

Spinal cord injury (SCI) remains a severe condition with an extremely high disability rate. The challenges of SCI repair include its complex pathological mechanisms and the difficulties of neural regeneration in the central nervous system. In the past few decades, researchers have attempted to completely elucidate the pathological mechanism of SCI and identify effective strategies to promote axon regeneration and neural circuit remodeling, but the results have not been ideal. Recently, new pathological mechanisms of SCI, especially the interactions between immune and neural cell responses, have been revealed by single-cell sequencing and spatial transcriptome analysis. With the development of bioactive materials and stem cells, more attention has been focused on forming intermediate neural networks to promote neural regeneration and neural circuit reconstruction than on promoting axonal regeneration in the corticospinal tract. Furthermore, technologies to control physical parameters such as electricity, magnetism and ultrasound have been constantly innovated and applied in neural cell fate regulation. Among these advanced novel strategies and technologies, stem cell therapy, biomaterial transplantation, and electromagnetic stimulation have entered into the stage of clinical trials, and some of them have already been applied in clinical treatment. In this review, we outline the overall epidemiology and pathophysiology of SCI, expound on the latest research progress related to neural regeneration and circuit reconstruction in detail, and propose future directions for SCI repair and clinical applications.

Neurotrophin-3 (NT-3) as a Potential Biomarker of the Peripheral Nervous System Damage Following Breast Cancer Treatment

Damage to the peripheral nervous system (PNS) is a common complication of breast cancer (BC) treatment, with 60 to 80% of breast cancer survivors experiencing symptoms of PNS damage. In the current study, the levels of brain-derived neurotrophic factor (BDNF), galectin-3 (Gal-3), and neurotrophin-3 (NT-3) were measured in the blood serum of BC patients by ELISA as potential biomarkers that might indicate the PNS damage. Sixty-seven patients were enrolled in this multi-center trial and compared to the aged-matched healthy female volunteers (control group) (n = 25). Intergroup comparison of biomarker levels (i.e., Gal-3 and BDNF) did not show significant differences in any of the studied subgroups. However, intriguingly, NT-3 levels were significantly higher in BC patients as compared to healthy volunteers, constituting 14.85 [10.3; 18.0] and 5.74 [4.56; 13.7] pg/mL, respectively (p < 0.001). In conclusion, NT-3 might be employed as a potential biomarker in BC patients with clinical manifestations of PNS damage. However, further studies to validate its correlation to the degree of peripheral nervous system lesions are of high value.

Effect of selegiline as a monomine oxidase B inhibitor on the expression of neurotrophin mRNA levels in a contusion rat model of spinal cord injury

OBJECTIVE

Spinal cord injury (SCI) is followed by a cascade of events at the site of injury, including vascular ischemia, an increase in free radicals, inflammation, and neuronal death. In these individuals, protection of nerves and supporting cells, as well as prevention of neuronal damage, may improve recovery opportunities. Neurotrophins are a family of polypeptides that regulate nerve differentiation, growth, and survival. Selegiline is a selective monoamine oxidase B (MAO-B) inhibitor used to treat Parkinson's disease. Selegiline has been found to have neuroprotective properties and may be useful for the expression of neurotrophins. The aim of this study was to evaluate the expression levels of neurotrophin genes in spinal cord rats treated with selegiline.

METHODS

Rats were divided into four groups: injury (control), laminectomy, sham (injured rat received 1 ml saline intraperitoneally) and treatment (injured rat received 5 mg/kg selegiline intraperitoneally for 7 days; once a day). The BBB scale (Basso, Beattie and Bresnahan) was performed once a week for 4 weeks to assess motor function after a spinal cord injury. On day 28 after SCI, the rat was sacrificed and the spinal cord lesion removed. A real-time PCR approach was used to assess neurotrophin gene expression.

RESULTS

The results showed that administration of selegiline improves locomotor function and increases mRNA levels of BDNF, GDNF, NT-3, and NT-4.

CONCLUSION

In summary, the results of this study suggest that selegiline may be an appropriate treatment for spinal cord injuries.

Crosstalk between exosomes and autophagy in spinal cord injury: fresh positive target for therapeutic application

Spinal cord injury (SCI) is a very serious clinical traumatic illness with a very high disability rate. It not only causes serious functional disorders below the injured segment, but also causes unimaginable economic burden to social development. Exosomes are nano-sized cellular communication carriers that exist stably in almost all organisms and cell types. Because of their capacity to transport proteins, lipids, and nucleic acids, they affect various physiological and pathological functions of recipient cells and parental cells. Autophagy is a process that relies on the lysosomal pathway to degrade cytoplasmic proteins and organelles and involves a variety of pathophysiological processes. Exosomes and autophagy play critical roles in cellular homeostasis following spinal cord injury. Presently, the coordination mechanism of exosomes and autophagy has attracted much attention in the early efficacy of spinal cord injury. In this review, we discussed the interaction of autophagy and exosomes from the perspective of molecular mechanisms, which might provide novel insights for the early therapeutic application of spinal cord injury.

Neurotrophic Factors in Experimental Cerebral Acanthamoebiasis

To date, no studies have addressed the role of neurotrophins (NTs) in Acanthamoeba spp. infections in the brain. Thus, to clarify the role of NTs in the cerebral cortex and hippocampus during experimental acanthamoebiasis in relation to the host immune status, the purpose of this study was to determine whether Acanthamoeba spp. may affect the concentration of brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4) in brain structures. Our results suggest that at the beginning of infection in immunocompetent hosts, BDNF and NT-3 may reflect an endogenous attempt at neuroprotection against Acanthamoeba spp. infection. We also observed a pro-inflammatory effect of NGF during acanthamoebiasis in immunosuppressed hosts. This may provide important information for understanding the development of cerebral acanthamoebiasis related to the immunological status of the host. However, the pathogenesis of brain acanthamoebiasis is still poorly understood and documented and, therefore, requires further research.

Novel Strategies for Spinal Cord Regeneration

A spinal cord injury (SCI) is one of the most devastating lesions, as it can damage the continuity and conductivity of the central nervous system, resulting in complex pathophysiology. Encouraged by the advances in nanotechnology, stem cell biology, and materials science, researchers have proposed various interdisciplinary approaches for spinal cord regeneration. In this respect, the present review aims to explore the most recent developments in SCI treatment and spinal cord repair. Specifically, it briefly describes the characteristics of SCIs, followed by an extensive discussion on newly developed nanocarriers (e.g., metal-based, polymer-based, liposomes) for spinal cord delivery, relevant biomolecules (e.g., growth factors, exosomes) for SCI treatment, innovative cell therapies, and novel natural and synthetic biomaterial scaffolds for spinal cord regeneration.

Homeodomain Interacting Protein Kinase 2-Modified Rat Spinal Astrocytes Affect Neurofunctional Recovery After Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) is regarded as an acute neurological disorder, and astrocytes play a role in the progression of SCI.

OBJECTIVE

Herein, we investigated the roles of homeodomain-interacting protein kinase 2 (HIPK2)- modified rat spinal astrocytes in neurofunctional recovery after SCI.

METHODS

Rat spinal astrocytes were cultured, isolated, and then identified through microscopic observation and immunofluorescence staining. Astrocytes were infected with the adenovirus vector overexpressing HIPK2 for modification, and proliferation and apoptosis of astrocytes were examined using Cell Counting Kit-8 method and flow cytometry. SCI rat models were established and treated with astrocytes or HIPK2-modified astrocytes. Subsequently, rat motor ability was analyzed via the Basso-Beattie-Bresnahan (BBB) scoring and inclined-plane test, and the damage to spinal cord tissues and neuronal survival were observed via Hematoxylin-eosin staining and Nissl staining. The levels of HIPK2, brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and nuclear factor erythroid 2- related transcription factor 2 (Nrf2)/antioxidant response element (ARE) pathway-related proteins were detected.

RESULTS

Rat spinal astrocytes were harvested successfully. HIPK2 overexpression accelerated the proliferation and repressed the apoptosis of rat spinal astrocytes. Rat spinal astrocytes treatment increased BBB points and the maximum angle at which SCI rats remained stable, ameliorated damage to spinal cord tissues, increased the number of neurons, and attenuated neural damage and inflammation, while the treatment of HIPK2-modified rat spinal astrocytes imparted more pronounced effects to the neurofunctional recovery of SCI rats. Meanwhile, HIPK2-modified rat spinal astrocytes further activated the Nrf2/ARE pathway.

CONCLUSION

HIPK2-modified rat spinal astrocytes facilitated neurofunctional recovery and activated the Nrf2/ARE pathway after SCI.

Biomimetic nerve guidance conduit containing engineered exosomes of adipose-derived stem cells promotes peripheral nerve regeneration

BACKGROUND

Efficient and stable delivery of neurotrophic factors (NTFs) is crucial to provide suitable microenvironment for peripheral nerve regeneration. Neurotrophin-3 (NT-3) is an important NTF during peripheral nerve regeneration which is scarce in the first few weeks of nerve defect. Exosomes are nanovesicles and have been served as promising candidate for biocarrier. In this work, NT-3 mRNA was encapsulated in adipose-derived stem cell (ADSC)-derived exosomes (Exo^NT-3). These engineered exosomes were applied as NT-3 mRNA carrier and then were loaded in nerve guidance conduit (Exo^NT-3-NGC) to bridge rat sciatic nerve defect.

METHOD

NT-3 mRNA was encapsulated in exosomes by forcedly expression of NT-3 mRNA in the donor ADSCs. Exo^NT-3 were co-cultured with SCs in vitro; after 24 h of culture, the efficiency of NT-3 mRNA delivery was evaluated by qPCR, western blotting and ELISA. Then, Exo^NT-3 were loaded in alginate hydrogel to construct the nerve guidance conduits (Exo^NT-3-NGC). Exo^NT-3-NGC were implanted in vivo to reconstruct 10 mm rat sciatic nerve defect. The expression of NT-3 was measured 2 weeks after the implantation operation. The sciatic nerve functional index (SFI) was examined at 2 and 8 weeks after the operation. Moreover, the therapeutic effect of Exo^NT-3-NGC was also evaluated by morphology assay, immunofluorescence staining of regenerated nerves, function evaluation of gastrocnemius muscles after 8 weeks of implantation.

RESULTS

The engineered exosomes could deliver NT-3 mRNA to the recipient cells efficiently and translated into functional protein. The constructed NGC could realize stable release of exosomes at least for 2 weeks. After NGC implantation in vivo, Exo^NT-3-NGC group significantly promote nerve regeneration and improve the function recovery of gastrocnemius muscles compared with control exosomes (Exo^empty-NGC) group.

CONCLUSION

In this work, NGC was constructed to allow exosome-mediated NT-3 mRNA delivery. After Exo^NT-3-NGC implantation in vivo, the level of NT-3 could restore which enhance the nerve regeneration. Our study provide a potential approach to improve nerve regeneration.

Autophagy and ALS: mechanistic insights and therapeutic implications

Mechanisms of protein homeostasis are crucial for overseeing the clearance of misfolded and toxic proteins over the lifetime of an organism, thereby ensuring the health of neurons and other cells of the central nervous system. The highly conserved pathway of autophagy is particularly necessary for preventing and counteracting pathogenic insults that may lead to neurodegeneration. In line with this, mutations in genes that encode essential autophagy factors result in impaired autophagy and lead to neurodegenerative conditions such as amyotrophic lateral sclerosis (ALS). However, the mechanistic details underlying the neuroprotective role of autophagy, neuronal resistance to autophagy induction, and the neuron-specific effects of autophagy-impairing mutations remain incompletely defined. Further, the manner and extent to which non-cell autonomous effects of autophagy dysfunction contribute to ALS pathogenesis are not fully understood. Here, we review the current understanding of the interplay between autophagy and ALS pathogenesis by providing an overview of critical steps in the autophagy pathway, with special focus on pivotal factors impaired by ALS-causing mutations, their physiologic effects on autophagy in disease models, and the cell type-specific mechanisms regulating autophagy in non-neuronal cells which, when impaired, can contribute to neurodegeneration. This review thereby provides a framework not only to guide further investigations of neuronal autophagy but also to refine therapeutic strategies for ALS and related neurodegenerative diseases.Abbreviations: ALS: amyotrophic lateral sclerosis; Atg: autophagy-related; CHMP2B: charged multivesicular body protein 2B; DPR: dipeptide repeat; FTD: frontotemporal dementia; iPSC: induced pluripotent stem cell; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; PINK1: PTEN induced kinase 1; RNP: ribonuclear protein; sALS: sporadic ALS; SPHK1: sphingosine kinase 1; TARDBP/TDP-43: TAR DNA binding protein; TBK1: TANK-binding kinase 1; TFEB: transcription factor EB; ULK: unc-51 like autophagy activating kinase; UPR: unfolded protein response; UPS: ubiquitin-proteasome system; VCP: valosin containing protein.

Neurotrophins as Key Regulators of Cell Metabolism: Implications for Cholesterol Homeostasis

Neurotrophins constitute a family of growth factors initially characterized as predominant mediators of nervous system development, neuronal survival, regeneration and plasticity. Their biological activity is promoted by the binding of two different types of receptors, leading to the generation of multiple and variegated signaling cascades in the target cells. Increasing evidence indicates that neurotrophins are also emerging as crucial regulators of metabolic processes in both neuronal and non-neuronal cells. In this context, it has been reported that neurotrophins affect redox balance, autophagy, glucose homeostasis and energy expenditure. Additionally, the trophic support provided by these secreted factors may involve the regulation of cholesterol metabolism. In this review, we examine the neurotrophins' signaling pathways and their effects on metabolism by critically discussing the most up-to-date information. In particular, we gather experimental evidence demonstrating the impact of these growth factors on cholesterol metabolism.

Neurotrophin-3 Promotes the Neuronal Differentiation of BMSCs and Improves Cognitive Function in a Rat Model of Alzheimer's Disease

Transplantation of bone marrow-derived mesenchymal stem cells (BMSCs) has the potential to be developed into an effective treatment for neurodegenerative diseases such as Alzheimer's disease (AD). However, the therapeutic effects of BMSCs are limited by their low neural differentiation rate. We transfected BMSCs with neurotrophin-3 (NT-3), a neurotrophic factor that promotes neuronal differentiation, and investigated the effects of NT-3 gene overexpression on the differentiation of BMSCs into neurons in vitro and in vivo. We further studied the possible molecular mechanisms. We found that overexpression of NT-3 promoted the differentiation of BMSCs into neurons in vitro and in vivo and improved cognitive function in rats with experimental AD. By contrast, silencing NT-3 inhibited the differentiation of BMSCs and decreased cognitive function in rats with AD. The Wnt/β-catenin signaling pathway was involved in the mechanism by which NT-3 gene modification influenced the neuronal differentiation of BMSCs in vitro and in vivo. Our findings support the prospect of using NT-3-transduced BMSCs for the development of novel therapies for AD.

Neurotrophin-3 stimulates stem Leydig cell proliferation during regeneration in rats

Neurotrophin‐3 (NT‐3) acts as an important growth factor to stimulate and control tissue development. The NT‐3 receptor, TRKC, is expressed in rat testis. Its function in regulation of stem Leydig cell development and its underlying mechanism remain unknown. Here, we reported the role of NT‐3 to regulate stem Leydig cell development in vivo and in vitro. Ethane dimethane sulphonate was used to kill all Leydig cells in adult testis, and NT‐3 (10 and 100 ng/testis) was injected intratesticularly from the 14th day after ethane dimethane sulphonate injection for 14 days. NT‐3 significantly reduced serum testosterone levels at doses of 10 and 100 ng/testis without affecting serum luteinizing hormone and follicle‐stimulating hormone levels. NT‐3 increased CYP11A1‐positive Leydig cell number at 100 ng/testis and lowered Leydig cell size and cytoplasmic size at doses of 10 and 100 ng/testis. After adjustment by the Leydig cell number, NT‐3 significantly down‐regulated the expression of Leydig cell genes (Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, Hsd11b1, Insl3, Trkc and Nr5a1) and the proteins. NT‐3 increased the phosphorylation of AKT1 and mTOR, decreased the phosphorylation of 4EBP, thereby increasing ATP5O. In vitro study showed that NT‐3 dose‐dependently stimulated EdU incorporation into stem Leydig cells and inhibited stem Leydig cell differentiation into Leydig cells, thus leading to lower medium testosterone levels and lower expression of Lhcgr, Scarb1, Trkc and Nr5a1 and their protein levels. NT‐3 antagonist Celitinib can antagonize NT‐3 action in vitro. In conclusion, the present study demonstrates that NT‐3 stimulates stem Leydig cell proliferation but blocks the differentiation via TRKC receptor.