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

Therapeutic potential of natural compounds from herbs and nutraceuticals in spinal cord injury: Regulation of the mTOR signaling pathway

Spinal cord injury (SCI) is a disease in which the spinal cord is subjected to various external forces that cause it to burst, shift, or, in severe cases, injure the spinal tissue, resulting in nerve injury. SCI includes not only acute primary injury but also delayed and persistent spinal tissue injury (i.e., secondary injury). The pathological changes post-SCI are complex, and effective clinical treatment strategies are lacking. The mammalian target of rapamycin (mTOR) coordinates the growth and metabolism of eukaryotic cells in response to various nutrients and growth factors. The mTOR signaling pathway has multiple roles in the pathogenesis of SCI. There is evidence for the beneficial effects of natural compounds and nutraceuticals that regulate the mTOR signaling pathways in a variety of diseases. Therefore, the effects of natural compounds on the pathogenesis of SCI were evaluated by a comprehensive review using electronic databases, such as PubMed, Web of Science, Scopus, and Medline, combined with our expertise in neuropathology. In particular, we reviewed the pathogenesis of SCI, including the importance of secondary nerve injury after the primary mechanical injury, the roles of the mTOR signaling pathways, and the beneficial effects and mechanisms of natural compounds that regulate the mTOR signaling pathway on pathological changes post-SCI, including effects on inflammation, neuronal apoptosis, autophagy, nerve regeneration, and other pathways. This recent research highlights the value of natural compounds in regulating the mTOR pathway, providing a basis for developing novel therapeutic strategies for SCI.

Activating Endogenous Neurogenesis for Spinal Cord Injury Repair: Recent Advances and Future Prospects

After spinal cord injury (SCI), endogenous neural stem cells are activated and migrate to the injury site where they differentiate into astrocytes, but they rarely differentiate into neurons. It is difficult for brain-derived information to be transmitted through the injury site after SCI because of the lack of neurons that can relay neural information through the injury site, and the functional recovery of adult mammals is difficult to achieve. The development of bioactive materials, tissue engineering, stem cell therapy, and physiotherapy has provided new strategies for the treatment of SCI and shown broad application prospects, such as promoting endogenous neurogenesis after SCI. In this review, we focus on novel approaches including tissue engineering, stem cell technology, and physiotherapy to promote endogenous neurogenesis and their therapeutic effects on SCI. Moreover, we explore the mechanisms and challenges of endogenous neurogenesis for the repair of SCI.

The potential of gene therapies for spinal cord injury repair: a systematic review and meta-analysis of pre-clinical studies

Currently, there is no cure for traumatic spinal cord injury but one therapeutic approach showing promise is gene therapy. In this systematic review and meta-analysis, we aim to assess the efficacy of gene therapies in pre-clinical models of spinal cord injury and the risk of bias. In this meta-analysis, registered at PROSPERO (Registration ID: CRD42020185008), we identified relevant controlled in vivo studies published in English by searching the PubMed, Web of Science, and Embase databases. No restrictions of the year of publication were applied and the last literature search was conducted on August 3, 2020. We then conducted a random-effects meta-analysis using the restricted maximum likelihood estimator. A total of 71 studies met our inclusion criteria and were included in the systematic review. Our results showed that overall, gene therapies were associated with improvements in locomotor score (standardized mean difference [SMD]: 2.07, 95% confidence interval [CI]:1.68–2.47, Tau² = 2.13, I² = 83.6%) and axonal regrowth (SMD: 2.78, 95%CI: 1.92–3.65, Tau² = 4.13, I² = 85.5%). There was significant asymmetry in the funnel plots of both outcome measures indicating the presence of publication bias. We used a modified CAMARADES (Collaborative Approach to Meta-Analysis and Review of Animal Data in Experimental Studies) checklist to assess the risk of bias, finding that the median score was 4 (IQR:3–5). In particular, reports of allocation concealment and sample size calculations were lacking. In conclusion, gene therapies are showing promise as therapies for spinal cord injury repair, but there is no consensus on which gene or genes should be targeted.

Extracellular vesicles from human umbilical cord mesenchymal stem cells reduce lipopolysaccharide-induced spinal cord injury neuronal apoptosis by mediating miR-29b-3p/PTEN

OBJECTIVE

This study investigated the molecular mechanism of whether hUC-MSCs-EVs repressed PTEN expression and activated the PI3K/AKT pathway through miR-29b-3p, thus inhibiting LPS-induced neuronal injury.

METHODS

hUC-MSCs were cultured and then identified. Cell morphology was observed. Alizarin red, oil red O, and alcian blue staining were used for inducing osteogenesis, adipogenesis, and chondrogenesis. EVs were extracted from hUC-MSCs and identified by transmission electron microscope observation and Western blot. SCI neuron model was established by 24h lipopolysaccharide (LPS) induction. After the cells were cultured with EVs without any treatment, uptake of EVs by SCI neurons, miR-29b-3p expression, cell viability, apoptosis, caspase-3, cleaved caspase-3, caspase 9, Bcl-2, PTEN, PI3K, AKT, and p-Akt protein levels, caspase 3 and caspase 9 activities, and inflammatory factors IL-6 and IL-1β levels were detected by immunofluorescence labeling, RT-qPCR, MTT, flow cytometry, Western blot, caspase 3 and caspase 9 activity detection kits, and ELISA. The binding sites between PTEN and miR-29b-3p were predicted by the database and verified by dual-luciferase assay.

RESULTS

LPS-induced SCI cell model was successfully established, and hUC-MSCs-EVs inhibited LPS-induced apoptosis of injured spinal cord neurons. EVs transferred miR-29b-3p into LPS-induced injured neurons. miR-29b-3p silencing reversed EV effects on reducing LPS-induced neuronal apoptosis. miR-29b-3p reduced LPS-induced neuronal apoptosis by targeting PTEN. After EVs-miR-inhi and si-PTEN treatment, inhibition of the PI3K/AKT pathway reversed hUC-MSCs-EVs effects on reducing LPS-induced neuronal apoptosis.

CONCLUSION

hUC-MSCs-EVs activated the PI3K/AKT pathway by carrying miR-29b-3p into SCI neurons and silencing PTEN, thus reducing neuronal apoptosis.

MiRNAs as Promising Translational Strategies for Neuronal Repair and Regeneration in Spinal Cord Injury

Spinal cord injury (SCI) represents a devastating injury to the central nervous system (CNS) that is responsible for impaired mobility and sensory function in SCI patients. The hallmarks of SCI include neuroinflammation, axonal degeneration, neuronal loss, and reactive gliosis. Current strategies, including stem cell transplantation, have not led to successful clinical therapy. MiRNAs are crucial for the differentiation of neural cell types during CNS development, as well as for pathological processes after neural injury including SCI. This makes them ideal candidates for therapy in this condition. Indeed, several studies have demonstrated the involvement of miRNAs that are expressed differently in CNS injury. In this context, the purpose of the review is to provide an overview of the pre-clinical evidence evaluating the use of miRNA therapy in SCI. Specifically, we have focused our attention on miRNAs that are widely associated with neuronal and axon regeneration. “MiRNA replacement therapy” aims to transfer miRNAs to diseased cells and improve targeting efficacy in the cells, and this new therapeutic tool could provide a promising technique to promote SCI repair and reduce functional deficits.

miR-182-5p Regulates Nogo-A Expression and Promotes Neurite Outgrowth of Hippocampal Neurons In Vitro

Nogo-A protein is a key myelin-associated inhibitor of axonal growth, regeneration, and plasticity in the central nervous system (CNS). Regulation of the Nogo-A/NgR1 pathway facilitates functional recovery and neural repair after spinal cord trauma and ischemic stroke. MicroRNAs are described as effective tools for the regulation of important processes in the CNS, such as neuronal differentiation, neuritogenesis, and plasticity. Our results show that miR-182-5p mimic specifically downregulates the expression of the luciferase reporter gene fused to the mouse Nogo-A 3′UTR, and Nogo-A protein expression in Neuro-2a and C6 cells. Finally, we observed that when rat primary hippocampal neurons are co-cultured with C6 cells transfected with miR-182-5p mimic, there is a promotion of the outgrowth of neuronal neurites in length. From all these data, we suggest that miR-182-5p may be a potential therapeutic tool for the promotion of axonal regeneration in different diseases of the CNS.

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.

GDF-11 Protects the Traumatically Injured Spinal Cord by Suppressing Pyroptosis and Necroptosis via TFE3-Mediated Autophagy Augmentation

Spinal cord injury (SCI) refers to a major worldwide cause of accidental death and disability. However, the complexity of the pathophysiological mechanism can result in less-effective clinical treatment. Growth differentiation factor 11 (GDF-11), an antiageing factor, was reported to affect the development of neurogenesis and exert a neuroprotective effect after cerebral ischaemic injury. The present work is aimed at investigating the influence of GDF-11 on functional recovery following SCI, in addition to the potential mechanisms involved. We employed a mouse model of spinal cord contusion injury and assessed functional outcomes via the Basso Mouse Scale and footprint analysis following SCI. Using western blot assays and immunofluorescence, we analysed the levels of pyroptosis, autophagy, necroptosis, and molecules related to the AMPK-TRPML1-calcineurin signalling pathway. The results showed that GDF-11 noticeably optimized function-related recovery, increased autophagy, inhibited pyroptosis, and alleviated necroptosis following SCI. Furthermore, the conducive influences exerted by GDF-11 were reversed with the application of 3-methyladenine (3MA), an autophagy suppressor, indicating that autophagy critically impacted the therapeutically related benefits of GDF-11 on recovery after SCI. In the mechanistic study described herein, GDF-11 stimulated autophagy improvement and subsequently inhibited pyroptosis and necroptosis, which were suggested to be mediated by TFE3; this effect resulted from the activity of TFE3 through the AMPK-TRPML1-calcineurin signalling cascade. Together, GDF-11 protects the injured spinal cord by suppressing pyroptosis and necroptosis via TFE3-mediated autophagy augmentation and is a potential agent for SCI therapy.

Macrophage-mediated degradable gelatin-coated mesoporous silica nanoparticles carrying pirfenidone for the treatment of rat spinal cord injury

The treatment of spinal cord injury is still a challenge worldwide; there is still no effective method. Our strategy is to devise a macrophage-mediated degradable gelatin coated mesoporous silica nanoparticles, which could carry pirfenidone and realize spatiotemporal control of pirfenidone release in the lesion site. For the in vivo experiment, three groups of SD rats subjected to spinal cord contusion injury were injected with GNS-PFD, PFD or PBS. Spinal cord functions were observed. In vitro, we investigated the expression of inflammatory and anti-inflammatory factors. Spinal cord function and recovery were better in the GSN-PFD and PFD than the control group. In the in vitro study, the MMPs after SCI in lesion site were lower in the experimental group. Moreover, the expression of anti-inflammatory and inflammatory factors showed better in the experimental group. The inflammatory response of the PFD to time and space can be achieved with the loading of macrophage-mediated degradable gelatin coated mesoporous silica nanoparticles.

Peripheral Macrophage-derived Exosomes promote repair after Spinal Cord Injury by inducing Local Anti-inflammatory type Microglial Polarization via Increasing Autophagy

Treatment for spinal cord injury (SCI) remains a challenge worldwide, and inflammation is a major cause of secondary injury after SCI. Peripheral macrophages (PMs) have been verified as a key factor that exert anti-inflammatory effects after SCI, but the mechanism is unidentified. As local macrophages, microglia also exert significant effects after SCI, especially polarization. Exosomes show source cell-like biological functions to target cells and have been the subject of much research in recent years. Thus, we hypothesized the PM-derived exosomes (PM-Exos) play an important role in signal transmission with local microglia and can be used therapeutic agents for SCI in a series of in vivo and in vitro studies. For the in vivo experiment, three groups of Sprague-Dawley (SD) rats subjected to spinal cord contusion injury were injected with 200 µg/ml PM-Exos, 20 µg/ml PM-Exos or PBS via the tail vein. Recovery of the rats and of spinal cord function were observed. In vitro, we investigated the potential anti-inflammatory mechanism of PM-Exos and evaluated microglial autophagy, anti-inflammatory type microglia polarization and the upstream signaling pathway. The results showed that spinal cord function and recovery were better in the PM-Exo groups than the control group. In the in vitro study, microglial autophagy levels and the expression of anti-inflammatory type microglia were higher in the experimental groups than the control group. Moreover, the expression of proteins related to the PI3K/AKT/mTOR autophagic signaling pathway was suppressed in the PM-Exo groups. PM-Exos have a beneficial effect in SCI, and activation of microglial autophagy via inhibition of the PI3K/AKT/mTOR signaling pathway, enhancing the polarization of anti-inflammatory type microglia, that may play a major role in the anti-inflammatory process.

MicroRNA-92a-3p enhances functional recovery and suppresses apoptosis after spinal cord injury via targeting phosphatase and tensin homolog

Spinal cord injury (SCI) is a neurological disease commonly caused by traumatic events on spinal cords. MiRNA-92a-3p is reported to be down-regulated after SCI. Our study investigated the effects of up-regulated miR-92a-3p on SCI and the underlying mechanisms. SCI mice model was established to evaluate the functional recovery of hindlimbs of mice through open-field locomotion and scored by Basso, Beattie, and Bresnahan (BBB) locomotion scale. Apoptosis of spinal cord cells was determined by flow cytometry. The effects of miR-92a-3p on SCI were detected by intrathecally injecting miR-92a-3p agomiR (agomiR-92) into the mice prior to the establishment of SCI. Phosphatase and tensin homolog (PTEN) was predicted as a target of miR-29a-3p by TargetScan. We further assessed the effects of agomiR-92 or/and overexpressed PTEN on apoptosis rates and apoptotic protein expressions in SCI mice. Moreover, the activation of protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling was determined by Western blot. The results showed that compared with the sham-operated mice, SCI mice had much lower BBB scores, and theapoptosis rate of spinal cord cells was significantly increased. After SCI, the expression of miR-92a-3p was down-regulated, and increased expression of miR-92a-3p induced by agomiR-92 further significantly increased the BBB score and decreased apoptosis. PTEN was specifically targeted by miR-92a-3p. In addition, the phosphorylation levels of Akt and mTOR were up-regulated under the treatment of agomiR-92. Our data demonstrated that the neuroprotective effects of miR-92a-3p on spinal cord safter SCI were highly associated with the activation of the PTEN/AKT/mTOR pathway.

Promoting functions of microRNA-29a/199B in neurological recovery in rats with spinal cord injury through inhibition of the RGMA/STAT3 axis

Background

The prognostic and therapeutic potential of microRNAs (miRNAs) in spinal cord injury (SCI) has aroused increasing concerns. This study aims to research the functions of miR-29a/199B in the neurological function recovery after SCI and the mechanical mechanism.

Methods

A rat model with SCI was induced with sham-operated ones as control. The locomotor function and coordination of rat hindlimbs were determined by a Basso, Beattie, and Bresnahan (BBB) locomotor rating scale and a ladder-climbing test, respectively. Expression of a neurofilament protein NF-200 and synaptophysin in gray matter of rats was determined to evaluate neuronal recovery in a cellular perspective. Binding relationships between miR-29a/199B with RGMA were predicted and validated using luciferase assays. Altered expression of miR-29a/199B and RGMA was introduced to explore their functions in rat neurological functions. The protein level and phosphorylation of STAT3 in gray matter were measured by western blot analysis.

Results

miR-29a and miR-199B were poorly expressed, while RGMA was abundantly expressed in gray matter at injury sites. Either miR-29a or miR-199B could bind to RGMA. Overexpression of miR-29a/199B or silencing of RGMA led to an increase in BBB locomotor scores, hindlimb coordination ability, and the expression of NF-200 and synaptophysin in gray matter. Further inhibition in miR-29a/199B blocked the promoting roles of RGMA silencing in neurological recovery. Upregulation of miR-29a/199B or downregulation of RGMA suppressed the phosphorylation of STAT3.

Conclusion

This study evidenced that miR-29a and miR-199B negatively regulated RGMA to suppress STAT3 phosphorylation, therefore promoting the neurological function recovery in rats following SCI.

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.

Silencing of Long Non-Coding RNA (lncRNA) Nuclear Paraspeckle Assembly Transcript 1 (NEAT1) Protects PC-12 Cells from LPS-Induced Injury via Targeting miR-29a

Background

Spinal cord injury (SCI) is a debilitating neuropathological condition that significantly affects the quality of life. The present study is basic research examining the underlying mechanisms of NEAT1 and miR-29a in regulating LPS-induced PC-12 cell injury.

Material/Methods

The model of cell injury was induced by the treatment of PC-12 cells with LPS. The expressions of NEAT1, miR-29a, and inflammatory cytokines were measured by real-time quantitative polymerase chain reactions (RT-qPCR). Cell proliferation and apoptosis were evaluated by CCK-8 and flow cytometry, respectively. Finally, the target between miR-29a and NEAT1 as well as miR-29a and BCL2L11 was investigated by luciferase and RNA pull-down assays.

Results

Knockdown of NEAT1 can inhibit inflammatory cytokine expression and PC-12 cell apoptosis and promote PC-12 cell proliferation by targeting miR-29a. However, the variation caused by NEAT1 knockdown can be reversed by the silencing of miR-29a and the overexpression of BCL2L11, which is the direct target gene of miR-29a.

Conclusions

High NEAT1 levels can increase LPS-induced injury in PC-12 cells through the miR-29a/BCL2L11 pathway. lncRNA NEAT1 may, therefore, be a promising target for SCI treatment.

[Research progress on intrinsic signaling pathways in axon regeneration]

The intrinsic regrowth ability of injured neurons is essential for axon regeneration and functional recovery. Recently, numerous intrinsic pathways that regulate axon regeneration have been discovered, among which the mitogen-activated protein kinase (MAPK) pathway and the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway are arguably the best characterized examples. MAPK signaling pathway is involved in multiple processes including sensing injury signals, initiating and promoting axonal regrowth through regulating cytoskeleton dynamics and protein synthesis. The PI3K/Akt signaling pathway regulates axon regeneration mainly through gene transcription and translation. Combinatory manipulation of multiple regeneration-promoting signals can further improve the extend of axonal regrowth. This paper summarizes current progresses on axon regeneration studies in various organisms and discuss their potentials in promoting functional recovery in vivo.

miR-29a promotes pathological cardiac hypertrophy by targeting the PTEN/AKT/mTOR signalling pathway and suppressing autophagy

AIM

Although miR-29 has emerged as a crucial non-coding RNA in the regulation of pathological cardiac hypertrophy, further exploration of its specific mechanisms is necessary to resolve controversy about its major role in this condition. This study therefore evaluated the role of miR-29a and whether it acts through the PTEN/AKT/mTOR pathway.

METHODS

In this study, a rat model of pressure-induced cardiac hypertrophy was established by transverse aortic constriction and verified by echocardiography, histological analysis and quantitative RT-PCR. At the cellular level, we explored the role of miR-29a in angiotensin II-stimulated hypertrophic H9c2 cardiomyoblasts by transfecting the cells with miR-29a inhibitor and mimic. The relationship between miR-29a and the signalling pathway was investigated with dual luciferase reporter assays, immunofluorescence analysis and Western blotting. We also examined whether autophagy is involved in the regulatory mechanism of miR-29a through transmission electron microscopy and detection of autophagy-associated proteins.

RESULTS

The results showed that miR-29a was upregulated both in rats 4 weeks after surgery and in 10^-6  M angiotensin II-stimulated cells. In contrast, inhibition of miR-29a partially attenuated angiotensin II-induced hypertrophy. Additionally, bioinformatics analysis revealed that PTEN was one of the target genes of miR-29a, which was also verified by luciferase assay. The results of immunofluorescence and Western blotting indicated that overexpression of miR-29a inhibited the expression of PTEN, activated the AKT/mTOR pathway and suppressed autophagy, which ultimately led to cardiac hypertrophy.

CONCLUSION

In pathological cardiac hypertrophy, miR-29a was overexpressed and promoted cardiac hypertrophy by regulating the PTEN/AKT/mTOR pathway and suppressing autophagy.

Different Approaches to Modulation of Microglia Phenotypes After Spinal Cord Injury

Microglial cells, which are highly plastic, immediately respond to any change in the microenvironment by becoming activated and shifting the phenotype toward neurotoxicity or neuroprotection. The polarization of microglia/macrophages after spinal cord injury (SCI) seems to be a dynamic process and can change depending on the microenvironment, stage, course, and severity of the posttraumatic process. Effective methods to modulate microglia toward a neuroprotective phenotype in order to stimulate neuroregeneration are actively sought for. In this context, available approaches that can selectively impact the polarization of microglia/macrophages regulate synthesis of trophic factors and cytokines/chemokines in them, and their phagocytic function and effects on the course and outcome of SCI are discussed in this review.