Prospects for mTOR-mediated functional repair after central nervous system trauma

Spontaneous mutation in 2310061I04Rik results in reduced expression of mitochondrial genes and impaired brain myelination

Here, we describe a spontaneous mouse mutant with a deletion in a predicted gene 2310061I04Rik (Rik) of unknown function located on chromosome 17. A 59 base pair long deletion occurred in the first intron of the Rik gene and disrupted its expression. Riknull mice were born healthy and appeared anatomically normal up to two weeks of age. After that, these mice showed inhibited growth, ataxic gait, and died shortly after postnatal day 24 (P24). Transcriptome analysis at P14 and P23 revealed significantly reduced expression of mitochondrial genes in Riknull brains compared to wild type controls including mt-Nd4, mt-Cytb, mt-Nd2, mt-Co1, mt-Atp6, and others. Similarly, genes specific for myelinating oligodendrocytes also showed reduced expression in P23 Riknull brains compared to controls. Histological examination of anterior thalamic nuclei demonstrated decreased myelination of anteroventral nuclei but not of anterodorsal nuclei in P23 Riknull mice. Myelination of the anterior commissure was also impaired and displayed extensive vacuolation. Consistently with these findings, immunohistochemistry showed reduced expression of Opalin, a glycoprotein expressed in differentiated oligodendrocytes. Taken together, these results suggest that RIK is important for oligodendrocyte maturation and myelination in the developing brain.

Analysis of miRNAs involved in mouse brain injury upon Coxsackievirus A6 infection

Introduction

Coxsackievirus A6 (CV-A6) has emerged as the predominant epidemic strain responsible for hand, foot and mouth disease (HFMD). CV-A6 infection can result in severe clinical manifestations, including encephalitis, meningitis, and potentially life-threatening central nervous system disorders. Our previous research findings demonstrated that neonatal mice infected with CV-A6 exhibited limb weakness, paralysis, and ultimately succumbed to death. However, the underlying mechanism of CV-A6-induced nervous system injury remains elusive. Numerous reports have highlighted the pivotal role of miRNAs in various viral infections.

Methods

Separately established infection and control groups of mice were used to create miRNA profiles of the brain tissues before and after CV-A6 transfection, followed by experimental verification, prediction, and analysis of the results.

Results

At 2 days post-infection (dpi), 4 dpi, and 2dpi vs 4dpi, we identified 175, 198 and 78 significantly differentially expressed miRNAs respectively using qRT-PCR for validation purposes. Subsequently, we predicted target genes of these differentially expressed miRNAs and determined their potential targets through GO (Gene Ontology) enrichment analysis and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis. Finally, we verified the miRNA-mRNA pairing via double luciferase experiments while confirming functional enrichment of target genes through Western Blotting analyses.

Discussion

The results from this study suggest that transcriptional regulation, neuronal necrosis, pro-inflammatory cytokine release, and antiviral immunity are all implicated in the pathogenesis of central nervous system injury in mice infected with CV-A6. Brain injury resulting from CV-A6 infection may involve multiple pathways, including glial cell activation, neuronal necrosis, synaptic destruction, degenerative diseases of the nervous system. It can even encompass destruction of the blood-brain barrier, leading to central nervous system injury. The dysregulated miRNAs and signaling pathways discovered in this study provide valuable insights for further investigations into the pathogenesis of CV-A6.

Matrine exerts its neuroprotective effects by modulating multiple neuronal pathways

Recent evidence suggests that misfolding, clumping, and accumulation of proteins in the brain may be common causes and pathogenic mechanism for several neurological illnesses. This causes neuronal structural deterioration and disruption of neural circuits. Research from various fields supports this idea, indicating that developing a single treatment for several severe conditions might be possible. Phytochemicals from medicinal plants play an essential part in maintaining the brain's chemical equilibrium by affecting the proximity of neurons. Matrine is a tetracyclo-quinolizidine alkaloid derived from the plant Sophora flavescens Aiton. Matrine has been shown to have a therapeutic effect on Multiple Sclerosis, Alzheimer's disease, and various other neurological disorders. Numerous studies have demonstrated that matrine protects neurons by altering multiple signalling pathways and crossing the blood-brain barrier. As a result, matrine may have therapeutic utility in the treatment of a variety of neurocomplications. This work aims to serve as a foundation for future clinical research by reviewing the current state of matrine as a neuroprotective agent and its potential therapeutic application in treating neurodegenerative and neuropsychiatric illnesses. Future research will answer many concerns and lead to fascinating discoveries that could impact other aspects of matrine.

Mesenchymal Stem Cell-Derived Exosomes in Ophthalmology: A Comprehensive Review

Over the past decade, the field of mesenchymal stem cell (MSC) therapy has exhibited rapid growth. Due to their regenerative, reparatory, and immunomodulatory capacities, MSCs have been widely investigated as therapeutic agents in the cell-based treatment of chronic ophthalmic pathologies. However, the applicability of MSC-based therapy is limited by suboptimal biocompatibility, penetration, and delivery to the target ocular tissues. An emerging body of research has elucidated the role of exosomes in the biological functions of MSCs, and that MSC-derived extracellular vesicles (EVs) possess anti-inflammatory, anti-apoptotic, tissue repairing, neuroprotective, and immunomodulatory properties similar to MSCs. The recent advances in MSCs-derived exosomes can serve as solutions to the challenges faced by MSCs-therapy. Due to their nano-dimensions, MSC-derived exosomes can rapidly penetrate biological barriers and reach immune-privileged organs, allowing for efficient delivery of therapeutic factors such as trophic and immunomodulatory agents to ocular tissues that are typically challenging to target by conventional therapy and MSCs transplantation. In addition, the use of EVs minimizes the risks associated with mesenchymal stem cell transplantation. In this literature review, we focus on the studies published between 2017 and 2022, highlighting the characteristics of EVs derived from MSCs and their biological functions in treating anterior and posterior segment ocular diseases. Additionally, we discuss the potential use of EVs in clinical settings. Rapid advancements in regenerative medicine and exosome-based drug delivery, in conjunction with an increased understanding of ocular pathology and pharmacology, hold great promise for the treatment of ocular diseases. The potential of exosome-based therapies is exciting and can revolutionize the way we approach these ocular conditions.

Fidgetin impacts axonal growth and branching in a local mTOR signal dependent manner

Neurons require a constant increase in protein synthesis during axonal growth and regeneration. AKT-mTOR is a central pathway for mammalian cell survival and regeneration. Fidgetin (Fign) is an ATP-dependent microtubule (MT)-severing enzyme whose functions are associated with neurite outgrowth, axon regeneration and cell migration. Although most previous studies have indicated that depletion of Fign is involved in those biological activities by increasing labile MT mass, it remains unknown whether mTOR activation contributes to this process. Here, we showed that depletion of Fign enhanced p-mTOR/p-S6K activation, and the mTOR inhibitor Rapamycin inhibited axon outgrowth and p-rpS6 activation. We then investigated the effects of neuronal-specific Fign deletion in a rat spinal cord hemisection model by injecting syn-GFP Fign shRNA virus. BBB values revealed an improvement in functional recovery. The p-mTOR was activated along with neuronal Fign depletion. The syn-mCherry virus showed more sprouting neurites entering the injury region, which was confirmed by immunostaining GAP43 protein. Further, we showed that Fign siRNA treatment promoted axon outgrowth and branching, whose underlying mechanism was firstly attributed to local activation of the mTOR pathway, and increased MT dynamicity. Finally, considering L-leucine, promotes axonal growth and neuronal survival, we applied L-leucine with Fign depletion after spinal cord injury or in chondroitin sulfate proteoglycan inhibitory molecules. The phenomenon of synergistically augmented axon regeneration was observed. In summary, our results indicated a novel local mTOR pathway for fidgetin to impact axon growth and provided a combined strategy in SCI.

Downregulation of UBE4B promotes CNS axon regrowth and functional recovery after stroke

The limited intrinsic regrowth capacity of corticospinal axons impedes functional recovery after cortical stroke. Although the mammalian target of rapamycin (mTOR) and p53 pathways have been identified as the key intrinsic pathways regulating CNS axon regrowth, little is known about the key upstream regulatory mechanism by which these two major pathways control CNS axon regrowth. By screening genes that regulate ubiquitin-mediated degradation of the p53 proteins in mice, we found that ubiquitination factor E4B (UBE4B) represses axonal regrowth in retinal ganglion cells and corticospinal neurons. We found that axonal regrowth induced by UBE4B depletion depended on the cooperative activation of p53 and mTOR. Importantly, overexpression of UbV.E4B, a competitive inhibitor of UBE4B, in corticospinal neurons promoted corticospinal axon sprouting and facilitated the recovery of corticospinal axon-dependent function in a cortical stroke model. Thus, our findings provide a translatable strategy for restoring corticospinal tract-dependent functions after cortical stroke.

Axonal Regeneration: Underlying Molecular Mechanisms and Potential Therapeutic Targets

Axons in the peripheral nervous system have the ability to repair themselves after damage, whereas axons in the central nervous system are unable to do so. A common and important characteristic of damage to the spinal cord, brain, and peripheral nerves is the disruption of axonal regrowth. Interestingly, intrinsic growth factors play a significant role in the axonal regeneration of injured nerves. Various factors such as proteomic profile, microtubule stability, ribosomal location, and signalling pathways mark a line between the central and peripheral axons' capacity for self-renewal. Unfortunately, glial scar development, myelin-associated inhibitor molecules, lack of neurotrophic factors, and inflammatory reactions are among the factors that restrict axonal regeneration. Molecular pathways such as cAMP, MAPK, JAK/STAT, ATF3/CREB, BMP/SMAD, AKT/mTORC1/p70S6K, PI3K/AKT, GSK-3β/CLASP, BDNF/Trk, Ras/ERK, integrin/FAK, RhoA/ROCK/LIMK, and POSTN/integrin are activated after nerve injury and are considered significant players in axonal regeneration. In addition to the aforementioned pathways, growth factors, microRNAs, and astrocytes are also commendable participants in regeneration. In this review, we discuss the detailed mechanism of each pathway along with key players that can be potentially valuable targets to help achieve quick axonal healing. We also identify the prospective targets that could help close knowledge gaps in the molecular pathways underlying regeneration and shed light on the creation of more powerful strategies to encourage axonal regeneration after nervous system injury.

Bone marrow mesenchymal stem cells and exercise restore motor function following spinal cord injury by activating PI3K/AKT/mTOR pathway

Although many therapeutic interventions have shown promise in treating spinal cord injury, focusing on a single aspect of repair cannot achieve successful and functional regeneration in patients following spinal cord injury . In this study, we applied a combinatorial approach for treating spinal cord injury involving neuroprotection and rehabilitation, exploiting cell transplantation and functional sensorimotor training to promote nerve regeneration and functional recovery. Here, we used a mouse model of thoracic contusive spinal cord injury to investigate whether the combination of bone marrow mesenchymal stem cell transplantation and exercise training has a synergistic effect on functional restoration. Locomotor function was evaluated by the Basso Mouse Scale, horizontal ladder test, and footprint analysis. Magnetic resonance imaging, histological examination, transmission electron microscopy observation, immunofluorescence staining, and western blotting were performed 8 weeks after spinal cord injury to further explore the potential mechanism behind the synergistic repair effect. In vivo, the combination of bone marrow mesenchymal stem cell transplantation and exercise showed a better therapeutic effect on motor function than the single treatments. Further investigations revealed that the combination of bone marrow mesenchymal stem cell transplantation and exercise markedly reduced fibrotic scar tissue, protected neurons, and promoted axon and myelin protection. Additionally, the synergistic effects of bone marrow mesenchymal stem cell transplantation and exercise on spinal cord injury recovery occurred via the PI3K/AKT/mTOR pathway. In vitro, experimental evidence from the PC12 cell line and primary cortical neuron culture also demonstrated that blocking of the PI3K/AKT/mTOR pathway would aggravate neuronal damage. Thus, bone marrow mesenchymal stem cell transplantation combined with exercise training can effectively restore motor function after spinal cord injury by activating the PI3K/AKT/mTOR pathway.

Strategies for Biomaterial-Based Spinal Cord Injury Repair via the TLR4-NF-κB Signaling Pathway

The repair and motor functional recovery after spinal cord injury (SCI) has remained a clinical challenge. Injury-induced gliosis and inflammation lead to a physical barrier and an extremely inhibitory microenvironment, which in turn hinders the recovery of SCI. TLR4-NF-κB is a classic implant-related innate immunomodulation signaling pathway and part of numerous biomaterial-based treatment strategies for SCI. Numerous experimental studies have demonstrated that the regulation of TLR4-NF-κB signaling pathway plays an important role in the alleviation of inflammatory responses, the modulation of autophagy, apoptosis and ferroptosis, and the enhancement of anti-oxidative effect post-SCI. An increasing number of novel biomaterials have been fabricated as scaffolds and carriers, loaded with phytochemicals and drugs, to inhibit the progression of SCI through regulation of TLR4-NF-κB. This review summarizes the empirical strategies for the recovery after SCI through individual or composite biomaterials that mediate the TLR4-NF-κB signaling pathway.

The Role of Tissue Geometry in Spinal Cord Regeneration

Unlike peripheral nerves, axonal regeneration is limited following injury to the spinal cord. While there may be reduced regenerative potential of injured neurons, the central nervous system (CNS) white matter environment appears to be more significant in limiting regrowth. Several factors may inhibit regeneration, and their neutralization can modestly enhance regrowth. However, most investigations have not considered the cytoarchitecture of spinal cord white matter. Several lines of investigation demonstrate that axonal regeneration is enhanced by maintaining, repairing, or reconstituting the parallel geometry of the spinal cord white matter. In this review, we focus on environmental factors that have been implicated as putative inhibitors of axonal regeneration and the evidence that their organization may be an important determinant in whether they inhibit or promote regeneration. Consideration of tissue geometry may be important for developing successful strategies to promote spinal cord regeneration.

Progesterone attenuates neurological deficits and exerts a protective effect on damaged axons via the PI3K/AKT/mTOR-dependent pathway in a mouse model of intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating event with high disability and fatality rates. However, there is a lack of effective treatments for this condition. We aimed to investigate the neuroprotective and axonal regenerative effects of progesterone after ICH. For this purpose, an ICH model was established in adult mice by injecting type VII collagenase into the striatum; the mice were then treated with progesterone (8 mg/kg). Hematoma absorption, neurological scores, and brain water content were evaluated on days one, three, and seven after the ICH. The effect of progesterone on inflammation and axonal regeneration was examined on day three after the ICH using western blotting, immunohistochemistry, immunofluorescence, as well as hematoxylin-eosin, Nissl, and Luxol fast blue staining. In addition, we combined progesterone with the phosphoinositide 3-kinase/serine/threonine-specific protein kinase (PI3K/AKT) inhibitor, LY294002, to explore its potential neuroprotective mechanisms. Administration of progesterone attenuated the neurological deficits and expression of inflammatory cytokines and promoted axonal regeneration after ICH, this effect was blocked by LY294002. Collectively, these results suggest that progesterone could reduce axonal damage and produced partial neuroprotective effects after ICH through the PI3K/AKT/mTOR pathway, providing a new therapeutic target and basis for the treatment of ICH.

Inositol Polyphosphate-5-Phosphatase K (Inpp5k) Enhances Sprouting of Corticospinal Tract Axons after CNS Trauma

Failure of CNS neurons to mount a significant growth response after trauma contributes to chronic functional deficits after spinal cord injury. Activator and repressor screening of embryonic cortical neurons and retinal ganglion cells in vitro and transcriptional profiling of developing CNS neurons harvested in vivo have identified several candidates that stimulate robust axon growth in vitro and in vivo Building on these studies, we sought to identify novel axon growth activators induced in the complex adult CNS environment in vivo We transcriptionally profiled intact sprouting adult corticospinal neurons (CSNs) after contralateral pyramidotomy (PyX) in nogo receptor-1 knock-out mice and found that intact CSNs were enriched in genes in the 3-phosphoinositide degradation pathway, including six 5-phosphatases. We explored whether inositol polyphosphate-5-phosphatase K (Inpp5k) could enhance corticospinal tract (CST) axon growth in preclinical models of acute and chronic CNS trauma. Overexpression of Inpp5k in intact adult CSNs in male and female mice enhanced the sprouting of intact CST terminals after PyX and cortical stroke and sprouting of CST axons after acute and chronic severe thoracic spinal contusion. We show that Inpp5k stimulates axon growth in part by elevating the density of active cofilin in labile growth cones, thus stimulating actin polymerization and enhancing microtubule protrusion into distal filopodia. We identify Inpp5k as a novel CST growth activator capable of driving compensatory axon growth in multiple complex CNS injury environments and underscores the veracity of using in vivo transcriptional screening to identify the next generation of cell-autonomous factors capable of repairing the damaged CNS.SIGNIFICANCE STATEMENT Neurologic recovery is limited after spinal cord injury as CNS neurons are incapable of self-repair post-trauma. In vitro screening strategies exploit the intrinsically high growth capacity of embryonic CNS neurons to identify novel axon growth activators. While promising candidates have been shown to stimulate axon growth in vivo, concomitant functional recovery remains incomplete. We identified Inpp5k as a novel axon growth activator using transcriptional profiling of intact adult corticospinal tract (CST) neurons that had initiated a growth response after pyramidotomy in plasticity sensitized nogo receptor-1-null mice. Here, we show that Inpp5k overexpression can stimulate CST axon growth after pyramidotomy, stroke, and acute and chronic contusion injuries. These data support in vivo screening approaches to identify novel axon growth activators.

CD82 protects against glaucomatous axonal transport deficits via mTORC1 activation in mice

Glaucoma is a leading cause of irreversible blindness worldwide and is characterized by progressive optic nerve degeneration and retinal ganglion cell loss. Axonal transport deficits have been demonstrated to be the earliest crucial pathophysiological changes underlying axonal degeneration in glaucoma. Here, we explored the role of the tetraspanin superfamily member CD82 in an acute ocular hypertension model. We found a transient downregulation of CD82 after acute IOP elevation, with parallel emergence of axonal transport deficits. The overexpression of CD82 with an AAV2/9 vector in the mouse retina improved optic nerve axonal transport and ameliorated subsequent axon degeneration. Moreover, the CD82 overexpression stimulated optic nerve regeneration and restored vision in a mouse optic nerve crush model. CD82 exerted a protective effect through the upregulation of TRAF2, which is an E3 ubiquitin ligase, and activated mTORC1 through K63-linked ubiquitylation and intracellular repositioning of Raptor. Therefore, our study offers deeper insight into the tetraspanin superfamily and demonstrates a potential neuroprotective strategy in glaucoma treatment.

mTOR pathway: A potential therapeutic target for spinal cord injury

Spinal cord injury (SCI) is the most common disabling spinal injury, and the complex pathological process can eventually lead to severe neurological dysfunction. Many studies have reported that the mammalian target of rapamycin (mTOR) signaling pathway plays an important role in synaptogenesis, neuron growth, differentiation, and survival after central nervous system injury. It is also involved in various traumatic and central nervous system diseases, including traumatic brain injury, neonatal hypoxic-ischemic brain injury, Alzheimer's disease, Parkinson's disease, and cerebral apoplexy. mTOR has also been reported to play an important regulatory role in various pathophysiological processes following SCI. Activation of mTOR signals after SCI can regulate physiological and pathological processes, such as proliferation and differentiation of neural stem cells, regeneration of nerve axons, neuroinflammation, and glial scar formation, through various pathways. Inhibition of mTOR activity has been confirmed to promote repair in SCI. At present, many studies have reported that Chinese herbal medicine can inhibit the SCI-activated mTOR pathway to improve the microenvironment and promote nerve repair after SCI. Due to the role of the mTOR pathway in SCI, it may be a potential therapeutic target for SCI. This review is focused on the pathophysiological process of SCI, characteristics of the mTOR pathway, role of the mTOR pathway in SCI, role of inhibition of mTOR on SCI, and role and significance of inhibition of mTOR by related Chinese herbal medicine inhibitors in SCI. In addition, the review discusses the deficiencies and solutions to mTOR and SCI research shortcomings. This study hopes to provide reference for mTOR and SCI research and a theoretical basis for SCI biotherapy.

Therapeutic effects of mesenchymal stem cells-derived extracellular vesicles' miRNAs on retinal regeneration: a review

Extracellular vesicles (EVs), which consist of microvesicles and exosomes, are secreted from all cells to transform vital information in the form of lipids, proteins, mRNAs and small RNAs such as microRNAs (miRNAs). Many studies demonstrated that EVs' miRNAs have effects on target cells. Numerous people suffer from the blindness caused by retinal degenerations. The death of retinal neurons is irreversible and creates permanent damage to the retina. In the absence of acceptable cures for retinal degenerative diseases, stem cells and their paracrine agents including EVs have become a promising therapeutic approach. Several studies showed that the therapeutic effects of stem cells are due to the miRNAs of their EVs. Considering the effects of microRNAs in retinal cells development and function and studies which provide the possible roles of mesenchymal stem cells-derived EVs miRNA content on retinal diseases, we focused on the similarities between these two groups of miRNAs that could be helpful for promoting new therapeutic techniques for retinal degenerative diseases.

HBO-PC Promotes Locomotor Recovery by Reducing Apoptosis and Inflammation in SCI Rats: The Role of the mTOR Signaling Pathway

Hyperbaric oxygen preconditioning (HBO-PC) has beneficial effects on the promotion of locomotor recovery by reducing apoptosis and inflammation after traumatic spinal cord injury (SCI). The mammalian target of rapamycin (mTOR) signaling pathway has been implicated in apoptosis and inflammation in many pathophysiological conditions. However, whether HBO-PC improves traumatic SCI-induced locomotor dysfunction by regulating the mTOR signaling pathway and its downstream molecules remains unknown. In the present study, we found that HBO-PC significantly promoted SCI-induced hind-limb locomotor recovery and increased the amplitude and potential of motor evoked potential. Magnetic resonance imaging showed that spinal cavitation or atrophy caused by SCI was obviously alleviated by HBO-PC therapy. Histological analysis showed that the changes in spinal cord neural structure in SCI rats were markedly restored by HBO-PC treatment. Western blot analysis showed that the SCI-induced enhanced levels of p-mTOR, inflammatory cytokines and apoptosis in the spinal cord were abrogated after administration of HBO-PC. Furthermore, intrathecal administration of an mTOR agonist reversed the effects of HBO-PC on locomotor function recovery, p-NF-κB p65 and p-p70S6K levels, inflammation and apoptosis. These findings indicated a new mechanism by which HBO-PC therapy suppressed inflammation and apoptosis through inactivation of the mTOR signaling pathway, which contributed to motor disability in SCI rats.

Dysregulation of DPYSL2 expression by mTOR signaling in schizophrenia: Multi-level study of postmortem brain

The mechanistic target of rapamycin (mTOR)-signaling and dihydropyrimidinase-like 2 (DPYSL2), which are increasingly gaining attention as potential therapeutic targets for schizophrenia, are connected via Cap-dependent translation of the 5'TOP motif. We quantified the expression of molecules constituting the mTOR-signaling and DPYSL2 in the prefrontal cortex (PFC) and superior temporal gyrus (STG) of postmortem brain tissue samples from 24 patients with schizophrenia and 32 control individuals and conducted association analysis to examine abnormal regulation of DPYSL2 expression by the mTOR-signaling in schizophrenia. The average ribosomal protein S6 (S6) levels in the PFC and STG were lower in patients with schizophrenia (p < 0.01). DPYSL2 expression showed a significant positive correlation with phospho-S6 expression levels, which were effectors of mTOR translational regulation, and the correlation slope between phospho-S6 and DPYSL2 expressions differed between cases and controls. Association analyses of these mTOR-signaling and DPYSL2 alterations with genetic polymorphisms and the clinical profile suggested that certain genetic variants of DPYSL2 require high mTOR-signaling activity. Thus, the findings confirmed decreased S6 expression levels in schizophrenia and supported the relationship between the mTOR-signaling and DPYSL2 via 5'TOP Cap-dependent translation, thus providing insights connecting the two major schizophrenia treatment strategies associated with the mTOR-signaling and DPYSL2.

miR-29a and the PTEN-GSK3β axis are involved in aluminum-induced damage to primary hippocampal neuronal networks

We previously reported that aluminum (Al) can cause a range of neurotoxic injuries including progressive irreversible synaptic structural damage and synaptic dysfunction, and eventually neuronal deaths. Mechanism of Al-induced electrophysiological and neuronal connectivity changes in neurons may indicate damage to the neuronal network. Here, mouse primary hippocampal neurons were cultured on micro-electrode array (MEA)- and high-content analysis (HCA)-related plates, showing that Al exposure significantly inhibited hippocampal neuronal electrical spike activity and neurite outgrowth characterized by a reduction in neurite branching and a decrease in the average total neurite length in relation to both Al dose and time of incubation. In recent years, miR-29a/ phosphatase and tensin homolog (PTEN) have been found to play pivotal roles in the morphogenesis of neurons, it has been confirmed in vitro and in vivo that the PTEN-Glycogen synthase kinase-3β (GSK-3β) axis regulates neurite outgrowth. The present study demonstrated that increases in Al exposure and dose gradually reduce miR-29a expression. Up-regulation of miR-29a in the hippocampal neurons by lentivirus transfection reversed the decrease in electrical spike activity and the reduction in both neurite branching and length induced by Al. Moreover, miR-29a suppressed the expression of PTEN and increased the level of phosphorylated Protein Kinase B (p-AKT) and p-GSK-3β which were inhibited by the Al treatment. This suggests that miR-29a is critically involved in the functional and structural neuronal damage induced by Al and is a potential target for Al neurotoxicity. Moreover, the reduction of neurite length and branching induced by Al exposure was regulated by miR-29a and its target neuronal PTEN-GSK3β signaling pathway, which also represents a possible mechanism of Al-induced the inhibition of the electrical activity. Collectively, Al-induced damage to the neuronal network occurred through miR-29a-mediated alterations of the PTEN-GSK3β signaling pathway.

L-leucine promotes axonal outgrowth and regeneration via mTOR activation

Discovering safe and effective drugs that promote neuron regeneration is an essential strategy for the recovery of central nervous system injuries. In this study, we found that L-leucine, an essential amino acid obtained from both supplements and food sources, could dramatically boost axonal outgrowth and regeneration. First, the effects of L-leucine on neurons were evaluated by cell apoptosis, survival, and death assays, and the results showed no changes in these processes after treatment. By live cell imaging, L-leucine was found to remarkably increase axonal length and growth velocity after axotomy. We also verified that L-leucine enhanced p-mTOR/p-S6K activation in neurons by testing with an mTOR inhibitor, rapamycin. Thereafter, we investigated the effects of L-leucine on the spinal cord injury in vivo. A mouse model of spinal cord hemi-section was established, and L-leucine was administered by tail intravenous injection. Basso mouse scale values revealed that L-leucine could improve functional recovery after injury. It was also notable that L-leucine treatment promoted axon growth across chondroitin sulfate proteoglycan (CSPG) areas. Furthermore, we used CSPGs as inhibitory environmental cues and clarified that L-leucine significantly enhanced axonal outgrowth and regeneration by promoting p-mTOR and p-S6K activation. Therefore, our study is the first to report that L-leucine promotes axonal regeneration in vitro and in vivo and could be candidate drug for axonal re-growth and nervous functional recovery.

miRNA Changes in Retinal Ganglion Cells after Optic Nerve Crush and Glaucomatous Damage

The purpose of this study was to characterize the miRNA profile of purified retinal ganglion cells (RGC) from healthy and diseased rat retina. Diseased retina includes those after a traumatic optic nerve crush (ONC), and after ocular hypertension/glaucoma. Rats were separated into four groups: healthy/intact, 7 days after laser-induced ocular hypertension, 2 days after traumatic ONC, and 7 days after ONC. RGC were purified from rat retina using microbeads conjugated to CD90.1/Thy1. RNA were sequenced using Next Generation Sequencing. Over 100 miRNA were identified that were significantly different in diseased retina compared to healthy retina. Considerable differences were seen in the miRNA expression of RGC 7 days after ONC, whereas after 2 days, few changes were seen. The miRNA profiles of RGC 7 days after ONC and 7 days after ocular hypertension were similar, but discrete miRNA differences were still seen. Candidate mRNA showing different levels of expression after retinal injury were manipulated in RGC cultures using mimics/AntagomiRs. Of the five candidate miRNA identified and subsequently tested for therapeutic efficacy, miR-194 inhibitor and miR-664-2 inhibitor elicited significant RGC neuroprotection, whereas miR-181a mimic and miR-181d-5p mimic elicited significant RGC neuritogenesis.

Exosomal miR-92b-3p Promotes Chemoresistance of Small Cell Lung Cancer Through the PTEN/AKT Pathway

Resistance to first-line chemotherapy drugs has become an obstacle to improving the clinical prognosis of patients with small cell lung cancer (SCLC). Exosomal microRNAs have been shown to play pro- and anti-chemoresistant roles in various cancers, but their role in SCLC chemoresistance has never been explored. In this study, we observed that the expression of exosomal miR-92b-3p was significantly increased in patients who developed chemoresistance. Luciferase reporter analysis confirmed that PTEN was a target gene of miR-92b-3p. The PTEN/AKT regulatory network was related to miR-92b-3p-mediated cell migration and chemoresistance in vitro and in vivo in SCLC. Importantly, exosomes isolated from the conditioned medium of SBC-3 cells overexpressing miR-92b-3p could promote SCLC chemoresistance and cell migration. Furthermore, we found that plasma miR-92b-3p levels were significantly higher in patients with chemoresistant SCLC than in those with chemosensitive SCLC, but the levels were down-regulated in patients who achieved remission. Kaplan–Meier analysis showed that SCLC patients with high miR-92b-3p expression were associated with shorter progression-free survival. Overall, our results suggested that exosomal miR-92b-3p is a potential dynamic biomarker to monitor chemoresistance in SCLC and represents a promising therapeutic target for chemoresistant SCLC.

Exosomes derived from miR-26a-modified MSCs promote axonal regeneration via the PTEN/AKT/mTOR pathway following spinal cord injury

Background

Exosomes derived from the bone marrow mesenchymal stem cell (MSC) have shown great potential in spinal cord injury (SCI) treatment. This research was designed to investigate the therapeutic effects of miR-26a-modified MSC-derived exosomes (Exos-26a) following SCI.

Methods

Bioinformatics and data mining were performed to explore the role of miR-26a in SCI. Exosomes were isolated from miR-26a-modified MSC culture medium by ultracentrifugation. A series of experiments, including assessment of Basso, Beattie and Bresnahan scale, histological evaluation, motor-evoked potential recording, diffusion tensor imaging, and western blotting, were performed to determine the therapeutic influence and the underlying molecular mechanisms of Exos-26a in SCI rats.

Results

Exos-26a was shown to promote axonal regeneration. Furthermore, we found that exosomes derived from miR-26a-modified MSC could improve neurogenesis and attenuate glial scarring through PTEN/AKT/mTOR signaling cascades.

Conclusions

Exosomes derived from miR-26a-modified MSC could activate the PTEN-AKT-mTOR pathway to promote axonal regeneration and neurogenesis and attenuate glia scarring in SCI and thus present great potential for SCI treatment.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02282-0.

Protective effects of human umbilical cord mesenchymal stem cells on retinal ganglion cells in mice with acute ocular hypertension

AIM

To observe the protective effect of human umbilical cord mesenchymal stem cells (hucMSCs) on retinal ganglion cells (RGCs) injury in mice with acute ocular hypertension (AOH).

METHODS

Fifty-six adult male C57BL/6 mice were randomly divided into four groups: normal group, AOH group, hucMSCs group, normal saline (NS) group. Left eye of mice was induced by 90 mm Hg intraocular pressure for 1h to establish AOH model. hucMSCs 1×10⁵/µL, 1 µL or NS 1 µL was injected into the vitreous body the next day. CM-Dil fluorescent dye was used to label the 3^rd generation of hucMSCs, for tracing the cells in the vitreous cavity of mice. Seven days after the model established, hematoxylin-eosin (HE) staining was used to observe the thickness of the inner retina layer in four groups. Numbers and loss rate of RGCs were evaluated by counting Brn-3a positive cells stained by immunofluorescencein.

RESULTS

On the 7^th day after AOH established, labeled hucMSCs were found in the vitreous cavity. HE staining showed that the thickness of retinal inner layer in AOH group was significantly lower than that in normal group and hucMSCs group (P<0.05), same as that in NS group (P>0.05). Compared with AOH group, the RGCs in normal group was significantly higher; RGCs number increased in hucMSCs group and the loss rate was lower (P<0.05). Injection of NS had no protective effect on RGCs.

CONCLUSION

In AOH mouse model, vitreous injection of hucMSCs have shown a protection for RGCs.

Elevated miR-29a Contributes to Axonal Outgrowth and Neurological Recovery After Intracerebral Hemorrhage via Targeting PTEN/PI3K/Akt Pathway

Spontaneous intracerebral hemorrhage (ICH) is a clinical challenge with high disability and lacks an effective treatment. miR-29a strongly expressed in the brain has been implicated in various neurological disorders. In this study, we investigated the biological roles of miR-29a in axonal outgrowth and neurological outcomes after ICH and relevant molecular mechanism. The rat model of ICH was established by injection of autologous whole blood into the right basal ganglia. First, a significant decrease in miR-29a level was found in perihematomal brain tissues and cerebrospinal fluid (CSF) after ICH in vivo and hemin-treated neurons in vitro. Further study documented that lentivirus-mediated miR-29a overexpression could remarkably attenuate hemorrhagic brain injury, promoted regenerative outgrowth of injured axons and improved neurobehavioral and cognitive impairments after ICH in rats. In addition, we also identified that overexpression of miR-29a obviously alleviated neuronal damage and mitochondrial dysfunctions, and facilitated neurite outgrowth in cultured neurons exposed to hemin in vitro. Furthermore, luciferase reporter assay showed that miR-29a directly targeted the 3'-UTR region of phosphatase and tensin homolog (PTEN) mRNA and negatively regulated its expression. More importantly, pharmacological inhibition of PTEN has similar neuroprotective effects as miR-29a overexpression involving activation of the PI3K/Akt pathway after hemorrhagic stroke. Collectively, these results suggested that elevated miR-29a could contribute to axonal outgrowth and neurological recovery through targeting PTEN/PI3K/Akt pathway after ICH, thereby providing a potential therapeutic target for patients with ICH.

Viral delivery of multiple miRNAs promotes retinal ganglion cell survival and functional preservation after optic nerve crush injury

Bone marrow mesenchymal stem cell (BMSC)-derived small extracellular vesicles (sEV) but not fibroblast sEV provide retinal ganglion cell (RGC) neuroprotection both in vitro and in vivo, with miRNAs playing an essential role. More than 40 miRNAs were more abundant in BMSC-sEV than in fibroblast-sEV. The purpose of this study was to test the in vitro and in vivo neuroprotective and axogenic properties of six candidate miRNAs (miR-26a, miR-17, miR-30c-2, miR-92a, miR-292, and miR-182) that were more abundant in BMSC-sEV than in fibroblast-sEV. Adeno-associated virus 2 (AAV2) expressing a combination of three of the above candidate miRNAs were added to heterogenous adult rat retinal cultures or intravitreally injected into rat eyes one week before optic nerve crush (ONC) injury. Survival and neuritogenesis of βIII-tubulin⁺ RGCs was assessed in vitro, as well as the survival of RBPMS⁺ RGCs and regeneration of their axons in vivo. Retinal nerve fiber layer thickness (RNFL) was measured to assess axonal density whereas positive scotopic threshold response electroretinography amplitudes provided a readout of RGC function. Qualitative retinal expression of PTEN, a target of several of the above miRNAs, was used to confirm successful miRNA activity. AAV2 reliably transduced RGCs in vitro and in vivo. Viral delivery of miRNAs in vitro showed a trend towards neuroprotection but remained insignificant. Delivery of selected combinations of miRNAs (miR-17-5p, miR-30c-2 and miR-92a; miR-92a, miR-292 and miR-182) before ONC provided significant therapeutic benefits according to the above measurable endpoints. However, no single miRNA appeared to be responsible for the effects observed, whilst positive effects observed appeared to coincide with successful qualitative reduction in PTEN immunofluorescence in the retina. Viral delivery of miRNAs provides a possible neuroprotective strategy for injured RGCs that is conducive to therapeutic manipulation.

Effect of Electroacupuncture Treatment at Dazhui (GV14) and Mingmen (GV4) Modulates the PI3K/AKT/mTOR Signaling Pathway in Rats after Spinal Cord Injury

Electroacupuncture (EA) is widely recognized as clinical treatment of spinal cord injury (SCI). The purpose of this study is to elucidate whether and how the PI3K/AKT/mTOR signaling pathway plays any role in EA treating SCI. Rats were randomly divided into four equal groups: Control Group, Sham-operation Group, Model Group, and EA Group, then further randomly divided into the following subgroups: 1-day (n = 12), 1-day rapamycin (n = 6), 14-day (n = 18), and 28-day (n = 18). A rat model of SCI was established by a modified Allen's weight-drop method. In the EA Group, rats were stimulated on Dazhui (GV14) and Mingmen (GV4) for 20 min by sterilized stainless steel needles. In the EA Group, the Basso, Beattie, and Bresnahan locomotor rating scale showed obvious improved locomotor function, and hematoxylin-eosin staining and magnetic resonance imaging showed that the histological morphology change of injured spinal cord tissue was obviously alleviated. Also, blocking spinal mTOR by injection of rapamycin showed that mTOR existed in the injured spinal cord, and EA could significantly activate mTOR in SCI rats. And immunohistochemistry and western blot analysis on the PI3K/AKT/mTOR signaling pathway showed that levels of PI3K, AKT, mTOR, and p70S6K in the injured spinal cord tissue were greatly increased in the EA Group, while the levels of PTEN and caspase 3 were decreased. The present study suggests that EA could affect cell growth, apoptosis, and autophagy through the PI3K/AKT/mTOR signaling pathway.

Nystatin Regulates Axonal Extension and Regeneration by Modifying the Levels of Nitric Oxide

Nystatin is a pharmacological agent commonly used for the treatment of oral, mucosal and cutaneous fungal infections. Nystatin has also been extensively applied to study the cellular function of cholesterol-enriched structures because of its ability to bind and extract cholesterol from mammalian membranes. In neurons, cholesterol level is tightly regulated, being essential for synapse and dendrite formation, and axonal guidance. However, the action of Nystatin on axon regeneration has been poorly evaluated. Here, we examine the effect of Nystatin on primary cultures of hippocampal neurons, showing how acute dose (minutes) of Nystatin increases the area of growth cones, and chronic treatment (days) enhances axon length, axon branching, and axon regeneration post-axotomy. We describe two alternative signaling pathways responsible for the observed effects and activated at different concentrations of Nystatin. At elevated concentrations, Nystatin promotes growth cone expansion through phosphorylation of Akt; whereas, at low concentrations, Nystatin enhances axon length and regrowth by increasing nitric oxide levels. Together, our findings indicate new signaling pathways of Nystatin and propose this compound as a novel regulator of axon regeneration.

Activation of the BMP4/Smad1 Pathway Promotes Retinal Ganglion Cell Survival and Axon Regeneration

Purpose

We investigate if the BMP4/Smad1 intracellular signaling pathway is neuroprotective and axogenic in adult rodent retinal ganglion cells (RGC) in vivo and in vitro.

Methods

Adult retinal cultures were prepared from intact and after optic nerve crush (ONC) injured rats that have been stimulated to survive and regenerate using an intravitreal peripheral nerve (PN) graft. Laser capture microdissection (LCM) then was used to isolate RGC with and without neurites. Quantitative RT-PCR determined changes in BMP4/Smad1 signaling pathway mRNA. Immunohistochemistry confirmed localization of BMP4 and activation of Smad1 in ONC+PN-stimulated RGC in vivo. BMP4 peptide was used to stimulate RGC survival and neurite/axon regeneration in vitro and in vivo. Finally, the rapamycin sensitivity of the effects was determined in BMP4-stimulated RGC in vitro and in vivo.

Results

In retinal cultures prepared from intact and ONC+PN-stimulated rats, RGC with neurites had upregulated regeneration-related and BMP4/Smad1 signaling pathway mRNA levels, while low levels of these mRNAs were present in RGC isolated without neurites. An optimal dose of 200 ng/mL BMP4 peptide in vitro promoted approximately 30% RGC survival and disinhibited RGC neurite outgrowth, despite the presence of inhibitory CNS myelin extracts. BMP4 also promoted approximately 30% RGC survival in vivo and stimulated significant RGC axon regeneration at 100, 200, and 400 μm beyond the lesion site. Finally, the response of RGC to BMP4 treatment in vitro and in vivo was rapamycin-insensitive.

Conclusions

Activation of the BMP4/Smad1 pathway promotes survival and axon regeneration independent of mTOR and, therefore, may be of therapeutic interest.

Intrinsic mechanisms of neuronal axon regeneration

Permanent disabilities following CNS injuries result from the failure of injured axons to regenerate and rebuild functional connections with their original targets. By contrast, injury to peripheral nerves is followed by robust regeneration, which can lead to recovery of sensory and motor functions. This regenerative response requires the induction of widespread transcriptional and epigenetic changes in injured neurons. Considerable progress has been made in recent years in understanding how peripheral axon injury elicits these widespread changes through the coordinated actions of transcription factors, epigenetic modifiers and, to a lesser extent, microRNAs. Although many questions remain about the interplay between these mechanisms, these new findings provide important insights into the pivotal role of coordinated gene expression and chromatin remodelling in the neuronal response to injury.

Network-centric medicine for peripheral nerve injury: Treating the whole to boost endogenous mechanisms of neuroprotection and regeneration

Peripheral nerve injuries caused by accidents may lead to paralysis, sensory disturbances, anaesthesia, and lack of autonomic functions. Functional recovery after disconnection of the motoneuronal soma from target tissue with proximal rupture of axons is determined by several factors: motoneuronal soma viability, proper axonal sprouting across inhibitory zones and elongation toward specific muscle, effective synapse contact rebuilding, and prevention of muscle atrophy. Therapies, such as adjuvant drugs with pleiotropic effects, that promote functional recovery after peripheral nerve injury are needed. Toward this aim, we designed a drug discovery workflow based on a network-centric molecular vision using unbiased proteomic data and neural artificial computational tools. Our focus is on boosting intrinsic capabilities of neurons for neuroprotection; this is in contrast to the common approach based on suppression of a pathobiological pathway known to be associated with disease condition. Using our workflow, we discovered neuroheal, a combination of two repurposed drugs that promotes motoneuronal soma neuroprotection, is anti-inflammatory, enhances axonal regeneration after axotomy, and reduces muscle atrophy. This drug discovery workflow has thus yielded a therapy that is close to its clinical application.

Lentivirus-Mediated Overexpression of miR-29a Promotes Axonal Regeneration and Functional Recovery in Experimental Spinal Cord Injury via PI3K/Akt/mTOR Pathway

MicroRNAs as a novel class of endogenous small non-coding RNAs, modulate negative gene expression at the post-transcriptional level. Our previous work has demonstrated that miR-29a reduces PTEN expression by directly targeting the 3'-UTRs (untranslated regions) of its mRNA, thus promoting neurite outgrowth. To further confirm the role of miR-29a in the recovery of SCI and its potential mechanisms, a recombinant lentiviral vector was used to promote miR-29a expression in the injured spinal cord. As compared with the LV-eGFP group and normal saline group, a significantly increased level of miR-29a expression and a markedly decreased level of PTEN expression were observed in the LV-miR-29a group. Overexpression of miR-29a increased the phosphorylation of two proteins (Akt and S6) of PI3K-AKT-mTOR signaling pathway and the expression of axonal regeneration associated key marker protein (neurofiament-200). Moreover, quantitative imaging analysis was performed to confirm that LV-miR-29a group expressed axonal regeneration at 4.0 ± 0.2-fold as much as the other two groups. Besides, miR-29a overexpression promoted hindlimb motor functional recovery. Collectively, these results suggested that miR-29a may be an important regulator for axon regeneration, and a potential therapeutic target for SCI recovery.

mTOR/AMPK signaling in the brain: Cell metabolism, proteostasis and survival

The mechanistic (or mammalian) target of rapamycin (mTOR) and the adenosine monophosphate-activated protein kinase (AMPK) regulate cell survival and metabolism in response to diverse stimuli such as variations in amino acid content, changes in cellular bioenergetics, oxygen levels, neurotrophic factors and xenobiotics. This Opinion paper aims to discuss the current state of knowledge regarding how mTOR and AMPK regulate the metabolism and survival of brain cells and the close interrelationship between both signaling cascades. It is now clear that both mTOR and AMPK pathways regulate cellular homeostasis at multiple levels. Studies so far demonstrate that dysregulation in these two pathways is associated with neuronal injury, degeneration and neurotoxicity, but the mechanisms involved remain unclear. Most of the work so far has been focused on their antagonistic regulation of autophagy, but recent findings highlight that changes in protein synthesis, metabolism and mitochondrial function are likely to play a role in the regulatory effects of both mTOR and AMPK on neuronal health. Understanding the role and relationship between these two master regulators of cell metabolism is crucial for future therapeutic approaches to counteract alterations in cell metabolism and survival in brain injury and disease.

miRNA in spinal muscular atrophy pathogenesis and therapy

Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disease characterized by the selective death of lower motor neurons in the brain stem and spinal cord. SMA is caused by mutations in the survival motor neuron 1 gene (SMN1), leading to the reduced expression of the full-length SMN protein. microRNAs (miRNAs) are small RNAs that regulate post-transcriptional gene expression. Recent findings have suggested an important role for miRNAs in the pathogenesis of motor neuron diseases, including SMA. Motor neuron-specific miRNA dysregulation in SMA might be implicated in their selective vulnerability. In this study, we discuss recent findings regarding the consequences of SMN defects on miRNAs and their target mRNAs in motor neurons. Taken together, these data suggest that cell-specific changes in miRNAs are not only involved in the SMA motor neuron phenotype but can also be used as biomarkers and therapeutic targets.

"mTOR Signaling Pathway": A Potential Target of Curcumin in the Treatment of Spinal Cord Injury

The purpose of this review is to discuss the possibility of the treatment of spinal cord injury (SCI) with curcumin via regulating the mTOR signaling pathway, which may provide another strong support for curcumin to be a promising medicine applied to the treatment of SCI. Curcumin is termed as a multifunctional targeting therapy drug that regulates the mTOR signaling pathway in the treatment of numerous diseases. Previous research has already revealed that mTOR signaling pathway plays a vital role in prognosis, which involves the axon regeneration and autophagy. This review discusses a potential mechanism that curcumin suppresses the activation of this pathway and ameliorates the microenvironment of axons regeneration which would provide a new way that induces autophagy appropriately.

Restricting the induction of NGF in ovarian stroma engenders selective follicular activation through the mTOR signaling pathway

In mammalian ovaries, primordial follicles remain in a quiescent state until activation by the surrounding microenvironment. Ovarian intervention, for example, ovarian cystectomy, ovarian wedge resection or laser drilling therapies for polycystic ovarian syndrome, has long been reported to change follicular development by an unknown mechanism(s). Herein, we established a murine model with partial ovarian resection of one ovary unilaterally, with the contralateral ovary undamaged. We found the injury accelerated follicular activation and development through the mTORC1 signaling pathway. Moreover, the stimulation of primordial follicles was restricted near the incision site where the mTORC1 pathway showed sequential activation beginning at the interstitial cells and proceeding to the primordial follicles. Total and polysome-associated RNA-seq revealed the increase of the nerve growth factor (NGF) family member, in both two fractions and immunostaining showed the restricted induction of NGF near the incision site. In cultured newborn ovaries, NGF demonstrated increase of follicular activation, and moreover, the NGF inhibitor K252a effectively blocked activation of primordial follicles stimulated by the surgery. We liken ovulation in mammals to minor tissue trauma, which happens naturally and cyclically in the body. As the increase in NGF accompanied the accumulation of activated primordial follicles after ovulation, our study may represent a common mechanism for selective follicular activation induced by a localized increase in NGF in interstitial cells and mediated via the mTOR signaling pathway. In addition, the NGF inhibitor K252a and the mTOR inhibitor rapamycin constitute good candidates for protecting follicular reserve against over exhaustion after ovarian surgery.

Matrine promotes oligodendrocyte development in CNS autoimmunity through the PI3K/Akt signaling pathway

AIMS

Matrine (MAT), a quinolizidine alkaloid derived from the herb Radix Sophorae flavescens, has been recently found to be beneficial in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, mainly through its anti-inflammatory effect. In the present study, we tested the effect of MAT on ongoing EAE and defined possible mechanisms underlying its effects on myelination and oligodendrocytes.

MAIN METHODS

EAE was induced in C57BL/6 mice and MAT treatment was started at disease onset. Clinical scores were monitored daily; spinal cords and the corpus callosum brain region of mice were harvested on day 23 p.i. for inflammatory infiltration and demyelination of the central nervous system. Myelin content and the development of oligodendrocytes and their precursors were determined by immunostaining, and expression of p-Akt, p-mTOR, p-PI3K, and p-P70S6 was determined by Western blot.

KEY FINDINGS

MAT effectively suppressed EAE severity and increased the expression of proteolipid protein, a myelin protein that is a marker of CNS myelin. MAT treatment largely increased the number of mature oligodendrocytes, and significantly activated the PI3K/Akt/mTOR signaling pathway, which is required for oligodendrocyte survival and axon myelination.

SIGNIFICANCE

These findings demonstrate a beneficial effect of MAT on oligodendrocyte differentiation and myelination during EAE, most likely through activating the PI3K/Akt/mTOR signaling pathway.

MotomiRs: miRNAs in Motor Neuron Function and Disease

MiRNAs are key regulators of the mammalian transcriptome that have been increasingly linked to degenerative diseases of the motor neurons. Although many of the miRNAs currently incriminated as participants in the pathogenesis of these diseases are also important to the normal development and function of motor neurons, at present there is no knowledge of the complete miRNA profile of motor neurons. In this review, we examine the current understanding with respect to miRNAs that are specifically required for motor neuron development, function and viability, and provide evidence that these should be considered as a functional network of miRNAs which we have collectively termed MotomiRs. We will also summarize those MotomiRs currently known to be associated with both amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA), and discuss their potential use as biomarkers.

Molecular neurobiology of mTOR

Mammalian/mechanistic target of rapamycin (mTOR) is a serine-threonine kinase that controls several important aspects of mammalian cell function. mTOR activity is modulated by various intra- and extracellular factors; in turn, mTOR changes rates of translation, transcription, protein degradation, cell signaling, metabolism, and cytoskeleton dynamics. mTOR has been repeatedly shown to participate in neuronal development and the proper functioning of mature neurons. Changes in mTOR activity are often observed in nervous system diseases, including genetic diseases (e.g., tuberous sclerosis complex, Pten-related syndromes, neurofibromatosis, and Fragile X syndrome), epilepsy, brain tumors, and neurodegenerative disorders (Alzheimer's disease, Parkinson's disease, and Huntington's disease). Neuroscientists only recently began deciphering the molecular processes that are downstream of mTOR that participate in proper function of the nervous system. As a result, we are gaining knowledge about the ways in which aberrant changes in mTOR activity lead to various nervous system diseases. In this review, we provide a comprehensive view of mTOR in the nervous system, with a special focus on the neuronal functions of mTOR (e.g., control of translation, transcription, and autophagy) that likely underlie the contribution of mTOR to nervous system diseases.

Bone Marrow-Derived Mesenchymal Stem Cells-Derived Exosomes Promote Survival of Retinal Ganglion Cells Through miRNA-Dependent Mechanisms

The loss of retinal ganglion cells (RGC) and their axons is one of the leading causes of blindness and includes traumatic (optic neuropathy) and degenerative (glaucoma) eye diseases. Although no clinical therapies are in use, mesenchymal stem cells (MSC) have demonstrated significant neuroprotective and axogenic effects on RGC in both of the aforementioned models. Recent evidence has shown that MSC secrete exosomes, membrane enclosed vesicles (30–100 nm) containing proteins, mRNA and miRNA which can be delivered to nearby cells. The present study aimed to isolate exosomes from bone marrow‐derived MSC (BMSC) and test them in a rat optic nerve crush (ONC) model. Treatment of primary retinal cultures with BMSC‐exosomes demonstrated significant neuroprotective and neuritogenic effects. Twenty‐one days after ONC and weekly intravitreal exosome injections; optical coherence tomography, electroretinography, and immunohistochemistry was performed. BMSC‐derived exosomes promoted statistically significant survival of RGC and regeneration of their axons while partially preventing RGC axonal loss and RGC dysfunction. Exosomes successfully delivered their cargo into inner retinal layers and the effects were reliant on miRNA, demonstrated by the diminished therapeutic effects of exosomes derived from BMSC after knockdown of Argonaute‐2, a key miRNA effector molecule. This study supports the use of BMSC‐derived exosomes as a cell‐free therapy for traumatic and degenerative ocular disease. Stem Cells Translational Medicine2017;6:1273–1285

Warming Up to New Possibilities with the Capsaicin Receptor TRPV1: mTOR, AMPK, and Erythropoietin

BACKGROUND

Transient receptor potential (TRP) channels are a superfamily of ion channels termed after the trp gene in Drosophila that are diverse in structure and control a wide range of biological functions including cell development and growth, thermal regulation, and vascular physiology. Of significant interest is the transient receptor potential cation channel subfamily V member 1 (TRPV1) receptor, also known as the capsaicin receptor and the vanilloid receptor 1, that is a non-selective cation channel sensitive to a host of external stimuli including capsaicin and camphor, venoms, acid/basic pH changes, and temperature.

METHODS

Given the multiple modalities that TRPV1 receptors impact in the body, we examined and discussed the role of these receptors in vasomotor control, metabolic disorders, cellular injury, oxidative stress, apoptosis, autophagy, and neurodegenerative disorders and their overlap with other signal transduction pathways that impact trophic factors.

RESULTS

Surprisingly, TRPV1 receptors do not rely entirely upon calcium signaling to affect cellular biology, but also have a close relationship with the mechanistic target of rapamycin (mTOR), AMP activated protein kinase (AMPK), and protein kinase B (Akt) that have roles in pain sensitivity, stem cell development, cellular survival, and cellular metabolism. These pathways with TRPV1 converge in the signaling of growth factors with recent work highlighting a relationship with erythropoietin (EPO). Angiogenesis and endothelial tube formation controlled by EPO requires, in part, the activation of TRPV1 receptors in conjunction with Akt and AMPK pathways.

CONCLUSION

TRPV1 receptors could prove to become vital to target disorders of vascular origin and neurodegeneration. Broader and currently unrealized implementations for both EPO and TRPV1 receptors can be envisioned for for the development of novel therapeutic strategies in multiple systems of the body.

Novel nervous and multi-system regenerative therapeutic strategies for diabetes mellitus with mTOR

Throughout the globe, diabetes mellitus (DM) is increasing in incidence with limited therapies presently available to prevent or resolve the significant complications of this disorder. DM impacts multiple organs and affects all components of the central and peripheral nervous systems that can range from dementia to diabetic neuropathy. The mechanistic target of rapamycin (mTOR) is a promising agent for the development of novel regenerative strategies for the treatment of DM. mTOR and its related signaling pathways impact multiple metabolic parameters that include cellular metabolic homeostasis, insulin resistance, insulin secretion, stem cell proliferation and differentiation, pancreatic β-cell function, and programmed cell death with apoptosis and autophagy. mTOR is central element for the protein complexes mTOR Complex 1 (mTORC1) and mTOR Complex 2 (mTORC2) and is a critical component for a number of signaling pathways that involve phosphoinositide 3-kinase (PI 3-K), protein kinase B (Akt), AMP activated protein kinase (AMPK), silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), Wnt1 inducible signaling pathway protein 1 (WISP1), and growth factors. As a result, mTOR represents an exciting target to offer new clinical avenues for the treatment of DM and the complications of this disease. Future studies directed to elucidate the delicate balance mTOR holds over cellular metabolism and the impact of its broad signaling pathways should foster the translation of these targets into effective clinical regimens for DM.

Charting a course for erythropoietin in traumatic brain injury

Traumatic brain injury (TBI) is a severe public health problem that impacts more than four million individuals in the United States alone and is increasing in incidence on a global scale. Importantly, TBI can result in acute as well as chronic impairments for the nervous system leaving individuals with chronic disability and in instances of severe trauma, death becomes the ultimate outcome. In light of the significant negative health consequences of TBI, multiple therapeutic strategies are under investigation, but those focusing upon the cytokine and growth factor erythropoietin (EPO) have generated a great degree of enthusiasm. EPO can control cell death pathways tied to apoptosis and autophagy as well oversees processes that affect cellular longevity and aging. In vitro studies and experimental animal models of TBI have shown that EPO can restore axonal integrity, promote cellular proliferation, reduce brain edema, and preserve cellular energy homeostasis and mitochondrial function. Clinical studies for neurodegenerative disorders that involve loss of cognition or developmental brain injury support a positive role for EPO to prevent or reduce injury in the nervous system. However, recent clinical trials with EPO and TBI have not produced such clear conclusions. Further clinical studies are warranted to address the potential efficacy of EPO during TBI, the concerns with the onset, extent, and duration of EPO therapeutic strategies, and to focus upon the specific downstream pathways controlled by EPO such as protein kinase B (Akt), mechanistic target of rapamycin (mTOR), AMP activated protein kinase (AMPK), sirtuins, wingless pathways, and forkhead transcription factors for improved precision against the detrimental effects of TBI.

Erythropoietin and mTOR: A "One-Two Punch" for Aging-Related Disorders Accompanied by Enhanced Life Expectancy

Life expectancy continues to increase throughout the world, but is accompanied by a rise in the incidence of non-communicable diseases. As a result, the benefits of an increased lifespan can be limited by aging-related disorders that necessitate new directives for the development of effective and safe treatment modalities. With this objective, the mechanistic target of rapamycin (mTOR), a 289-kDa serine/threonine protein, and its related pathways of mTOR Complex 1 (mTORC1), mTOR Complex 2 (mTORC2), proline rich Akt substrate 40 kDa (PRAS40), AMP activated protein kinase (AMPK), Wnt signaling, and silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), have generated significant excitement for furthering novel therapies applicable to multiple systems of the body. Yet, the biological and clinical outcome of these pathways can be complex especially with oversight of cell death mechanisms that involve apoptosis and autophagy. Growth factors, and in particular erythropoietin (EPO), are one avenue under consideration to implement control over cell death pathways since EPO can offer potential treatment for multiple disease entities and is intimately dependent upon mTOR signaling. In experimental and clinical studies, EPO appears to have significant efficacy in treating several disorders including those involving the developing brain. However, in mature populations that are affected by aging-related disorders, the direction for the use of EPO to treat clinical disease is less clear that may be dependent upon a number of factors including the understanding of mTOR signaling. Continued focus upon the regulatory elements that control EPO and mTOR signaling could generate critical insights for targeting a broad range of clinical maladies.