Galectin-1, a β-galactosides-binding protein, is widely expressed in various tissues and exhibits diverse biological activities. We previously obtained following findings; 1) Diosgenin, a steroid sapogenin, promoted axonal regeneration in the brain and recovered memory deficits in a model of Alzheimer\'s disease (AD), 5XFAD mouse; 2) Neuron-specific overexpression of Galectin-1 protein in the hippocampus recovered memory impairment and promoted axonal regeneration in the brain in 5XFAD mice; 3) Secernin-1, a counterpart and axonal guidance molecule for Galectin-1-expressing axons, was secreted from the prefrontal cortical neurons to promote axonal guidance from the hippocampus to the prefrontal cortex. However, it has never been elucidated that diosgenin signaling increase Galectin-1 and Secernin-1 or not. Here, we found that diosgenin treatment upregulated the protein level of Galectin-1 in the hippocampus both in primary cultured neurons and in 5XFAD mouse brains. In addition, diosgenin-induced upregulation of Galectin-1 was diminished by treatment of a neutralizing antibody of 1,25D3-membrane-associated rapid response steroid-binding receptor (1,25D3-MARRS), a direct binding receptor for diosgenin. Importantly, knockdown of Galectin-1 in hippocampal neurons inhibited axonal growth activity of diosgenin. Furthermore, the expression level of Secernin-1 was also increased in prefrontal cortical neurons by administration of diosgenin to 5XFAD mice. These findings suggest that diosgenin is a suitable compound to facilitate Galectin-1-Secernin-1-mediated axonal growth in AD brains.

Fibroblast growth factors (FGFs) are required for the specification and formation of the epibranchial placodes, which give rise to the distal part of the cranial sensory ganglia. However, it remains unclear whether FGFs play a role in regulating the neurite outgrowth of the epibranchial placode-derived ganglia during further development. Previous studies have shown that Fibroblast growth factor 8 (FGF8) promotes neurite outgrowth from the statoacoustic ganglion in vitro. However, these studies did not distinguish between the neural crest- and placode-derived components of the sensory ganglia. In this study, we focused on the petrosal and nodose ganglia as representatives of the epibranchial ganglia and investigated their axonal outgrowth under the influence of FGF8 signaling protein in vitro. To precisely isolate the placode-derived ganglion part, we labeled the placode and its derivatives with enhanced green fluorescent protein (EGFP) through electroporation. The isolated ganglia were then collected for qRT-PCR assay and cultured in a collagen gel with and without FGF8 protein. Our findings revealed that both placode-derived petrosal and nodose ganglia expressed FGFR1 and FGFR2. In culture, FGF8 exerted a neural trophic effect on the axon outgrowth of both ganglia. While the expression levels of FGFR1/2 were similar between the two ganglia, the petrosal ganglion exhibited greater sensitivity to FGF8 compared to the nodose ganglion. This indicates that the placode-derived ganglia have differential responsiveness to FGF8 signaling during axonal extension. Thus, FGF8 is not only required for the early development of the epibranchial placode, as shown in previous studies, but also promotes neurite outgrowth of placode-derived ganglia.

The Krüppel-like factor (KLF) family represents a group of transcription factors (TFs) performing different biological processes that are crucial for proper neuronal function, including neuronal development, synaptic plasticity, and neuronal survival. As reported, genetic variants within the KLF family have been associated with a wide spectrum of neurodevelopmental and psychiatric symptoms. In a patient exhibiting attention deficit hyperactivity disorder (ADHD) combined with both neurodevelopmental and psychiatric symptoms, whole-exome sequencing (WES) analysis revealed a de novo heterozygous variant within the Krüppel-like factor 13 (KLF13) gene, which belongs to the KLF family and regulates axonal growth, development, and regeneration in mice. Moreover, in silico analyses pertaining to the likely pathogenic significance of the variant and the impact of the mutation on the KLF13 protein structure suggested a potential deleterious effect. In fact, the variant was localized in correspondence to the starting residue of the N-terminal domain of KLF13, essential for protein-protein interactions, DNA binding, and transcriptional activation or repression. This study aims to highlight the potential involvement of the KLF13 gene in neurodevelopmental and psychiatric disorders. Nevertheless, we cannot rule out that excluded variants, those undetectable by WES, or the polygenic risk may have contributed to the patient\'s phenotype given ADHD\'s high polygenic risk. However, further functional studies are required to validate its potential contribution to these disorders.

3-Nitrotyrosine (3-NT), a byproduct of oxidative and nitrosative stress, is implicated in age-related neurodegenerative disorders. Current literature suggests that free 3-NT becomes integrated into the carboxy-terminal domain of α-tubulin via the tyrosination/detyrosination cycle. Independently of this integration, 3-NT has been associated with the cell death of dopaminergic neurons. Given the critical role of tyrosination/detyrosination in governing axonal morphology and function, the substitution of tyrosine with 3-NT in this process may potentially disrupt axonal homeostasis, although this aspect remains underexplored. In this study, we examined the impact of 3-NT on the axons of cerebellar granule neurons, which is used as a model for non-dopaminergic neurons. Our observations revealed axonal shortening, which correlated with the incorporation of 3-NT into α-tubulin. Importantly, this axonal effect was observed prior to the onset of cellular death. Furthermore, 3-NT was found to diminish mitochondrial motility within the axon, leading to a subsequent reduction in mitochondrial membrane potential. The suppression of syntaphilin, a protein responsible for anchoring mitochondria to microtubules, restored the mitochondrial motility and axonal elongation that were inhibited by 3-NT. These findings underscore the inhibitory role of 3-NT in axonal elongation by impeding mitochondrial movement, suggesting its potential involvement in axonal dysfunction within non-dopaminergic neurons.

GRT-X, which targets both the mitochondrial translocator protein (TSPO) and the Kv7.2/3 (KCNQ2/3) potassium channels, has been shown to efficiently promote recovery from cervical spine injury. In the present work, we investigate the role of GRT-X and its two targets in the axonal growth of dorsal root ganglion (DRG) neurons. Neurite outgrowth was quantified in DRG explant cultures prepared from wild-type C57BL6/J and TSPO-KO mice. TSPO was pharmacologically targeted with the agonist XBD173 and the Kv7 channels with the activator ICA-27243 and the inhibitor XE991. GRT-X efficiently stimulated DRG axonal growth at 4 and 8 days after its single administration. XBD173 also promoted axonal elongation, but only after 8 days and its repeated administration. In contrast, both ICA27243 and XE991 tended to decrease axonal elongation. In dissociated DRG neuron/Schwann cell co-cultures, GRT-X upregulated the expression of genes associated with axonal growth and myelination. In the TSPO-KO DRG cultures, the stimulatory effect of GRT-X on axonal growth was completely lost. However, GRT-X and XBD173 activated neuronal and Schwann cell gene expression after TSPO knockout, indicating the presence of additional targets warranting further investigation. These findings uncover a key role of the dual mode of action of GRT-X in the axonal elongation of DRG neurons.

Spinal cord injury (SCI) induces the disruption of the blood-spinal cord barrier (BSCB) and the failure of axonal growth. SCI activates a complex series of responses, including cell apoptosis and endoplasmic reticulum (ER) stress. Pericytes play a critical role in maintaining BSCB integrity and facilitating tissue growth and repair. However, the roles of pericytes in SCI and the potential mechanisms underlying the improvements in functional recovery in SCI remain unclear. Recent evidence indicates that irisflorentin exerts neuroprotective effects against Parkinson\'s disease; however, whether it has potential protective roles in SCI or not is still unknown. In this study, we found that the administration of irisflorentin significantly inhibited pericyte apoptosis, protected BSCB integrity, promoted axonal growth, and ultimately improved locomotion recovery in a rat model of SCI. In vitro, we found that the positive effects of irisflorentin on axonal growth were likely to be mediated by regulating the crosstalk between pericytes and neurons. Furthermore, irisflorentin effectively ameliorated ER stress caused by incubation with thapsigargin (TG) in pericytes. Meanwhile, the protective effect of irisflorentin on BSCB disruption is strongly related to the reduction of pericyte apoptosis via inhibition of ER stress. Collectively, our findings demonstrate that irisflorentin is beneficial for functional recovery after SCI and that pericytes are a valid target of interest for future SCI therapies.

Microtubule stabilization is critical for axonal growth and regeneration, and many microtubule-associated proteins are involved in this process. In this study, we found that the knockdown of echinoderm microtubule-associated protein-like 1 (EML1) hindered axonal growth in cultured cortical and dorsal root ganglion neurons. We further revealed that EML1 facilitated the acetylation of microtubules and that the impairment of axonal growth due to EML1 inhibition could be restored by treatment with deacetylase inhibitors, suggesting that EML1 affected tubulin acetylation. Moreover, we verified an interaction between EML1 and the alpha-tubulin acetyltransferase 1, which is responsible for the acetylation of alpha-tubulin. We thus proposed that EML1 might regulate microtubule acetylation and stabilization via alpha-tubulin acetyltransferase 1 and then promote axon growth. Finally, we verified that the knockdown of EML1 in vivo also inhibited sciatic nerve regeneration. Our findings revealed a novel effect of EML1 on microtubule acetylation during axonal regeneration.

Oxygen is compulsory for mitochondrial function and energy supply, but it has numerous more nuanced roles. The different roles of oxygen in peripheral nerve regeneration range from energy supply, inflammation, phagocytosis, and oxidative cell destruction in the context of reperfusion injury to crucial redox signaling cascades that are necessary for effective axonal outgrowth. A fine balance between reactive oxygen species production and antioxidant activity draws the line between physiological and pathological nerve regeneration. There is compelling evidence that redox signaling mediated by the Nox family of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases plays an important role in peripheral nerve regeneration. Further research is needed to better characterize the role of Nox in physiological and pathological circumstances, but the available data suggest that the modulation of Nox activity fosters great therapeutic potential. One of the promising approaches to enhance nerve regeneration by modulating the redox environment is hyperbaric oxygen therapy. In this review, we highlight the influence of various oxygenation states, i.e., hypoxia, physoxia, and hyperoxia, on peripheral nerve repair and regeneration. We summarize the currently available data and knowledge on the effectiveness of using hyperbaric oxygen therapy to treat nerve injuries and discuss future directions.

Mesenchymal stem cell-based therapies have been studied for spinal cord injury (SCI) treatment due to their paracrine action upon damaged tissues. MSCs neuroregenerative role may relate to the contents of their secretome in anti-inflammatory cytokines and growth-permissive factors. We propose using the secretome of MSCs isolated from the adipose tissue-adipose tissue-derived stem cells (ASCs) as a cell-free based therapy for SCI. In vivo studies were conducted in two SCI models, Xenopus laevis and mice, after complete spinal cord transection. Our results on both models demonstrated positive impacts of ASC secretome on their functional recovery which were correlated with histopathological markers of regeneration. Furthermore, in our mice study, secretome induced white matter preservation together with modulation of the local and peripheral inflammatory response. Altogether, these results demonstrate the neuroregenerative and potential for inflammatory modulation of ASC secretome suggesting it as a good candidate for cell-free therapeutic strategies for SCI.

OBJECTIVE: Neurotransmitters have been extensively studied as neural communication molecules. Genetic associations discovered, and indirect intervention studies in Humans and mammals have led to a general proposition that neurotransmitters have a role in structuring of neuronal network during development. olf413 is a Drosophila gene annotated as coding for dopamine beta-monooxygenase enzyme with a predicted function in octopaminergic pathway. The biological function of this gene is very little worked out. In this study we investigate the requirement of olf413 gene function for octopamine biogenesis and developmental patterning of embryonic nervous system.
RESULTS: In our study we have used the newly characterized neuronal specific allele olf413SG1.1, and the gene disruption strain olf413MI02014 to dissect out the function of olf413. olf413 has an enhancer activity as depicted by reporter GFP expression, in the embryonic ventral nerve cord, peripheral nervous system and the somatic muscle bundles. Homozygous loss of function mutants show reduced levels of octopamine, and this finding supports the proposed function of the gene in octopamine biogenesis. Further, loss of function of olf413 causes embryonic lethality. FasII staining of these embryos reveal a range of phenotypes in the central and peripheral motor nerves, featuring axonal growth, pathfinding, branching and misrouting defects. Our findings are important as they implicate a key functional requirement of this gene in precise axonal patterning events, a novel developmental role imparted for an octopamine biosynthesis pathway gene in structuring of embryonic nervous system.