The mTOR cell signaling pathway is crucial to the long-term protective effects of ischemic postconditioning against stroke

Inhibition of PI3K/Akt/mTOR signaling by NDRG2 contributes to neuronal apoptosis and autophagy in ischemic stroke

BACKGROUND

Astrocytic N-myc downstream-regulated gene 2 (NDRG2), a differentiation- and stress-associated molecule, has been involved in the cause of ischemic stroke (IS). However, its downstream effector in IS remains unclear. This study aimed to characterize expression of NDRG2 in IS patients and rats and to investigate the underlying mechanism.

METHODS

The protein expression of NDRG2 and mammalian target of the rapamycin (mTOR) and the extent of mTOR phosphorylation in plasma of IS patients were detected by ELISA. An oxygen-glucose deprivation model was established in mouse neuronal cells CATH.a, followed by cell counting kit-8, flow cytometry, TUNEL, and western blot assays to examine cell viability, apoptosis and autophagy. Finally, the effect of NDRG2-mediated phosphatidylinositol 3-kinase/protein kinase-B/mTOR (PI3K/AKT/mTOR) pathway on neuronal apoptosis and autophagy was verified in rats treated with middle cerebral artery occlusion.

RESULTS

NDRG2 was highly expressed in the plasma of IS patients, while the extent of mTOR phosphorylation was reduced in IS patients. NDRG2 blocked the PI3K/Akt/mTOR signaling through dephosphorylation. Depletion of NDRG2 suppressed apoptosis and autophagy in CATH.a cells, which was reversed by a dual inhibitor of PI3K and mTOR, BEZ235. In vivo experiments confirmed that NDRG2 promoted neuronal apoptosis and autophagy by dephosphorylating and blocking the PI3K/Akt/mTOR signaling.

CONCLUSION

The present study has shown that NDRG2 impairs the PI3K/Akt/mTOR pathway via dephosphorylation to promote neuronal apoptosis and autophagy in IS. These findings provide potential targets for future clinical therapies for IS.

Mesenchymal Stem Cell-Derived Neuron-Like Cell Transplantation Combined with Electroacupuncture Improves Synaptic Plasticity in Rats with Intracerebral Hemorrhage via mTOR/p70S6K Signaling

Previous studies have shown that the combination of mesenchymal stem cell (MSC) transplantation and electroacupuncture (EA) stimulation is a neuroprotective strategy for treating intracerebral hemorrhage (ICH). However, the underlying mechanisms by which the combined treatment promotes neuroprotection remain unclear. This study was designed to investigate the effects of the combined treatment on synaptic plasticity and elucidate their underlying mechanisms. Therefore, rat ICH models were established by injecting collagenase and heparin, and the animals were randomly divided into model control (MC), EA stimulation (EA), MSC-derived neuron-like cell transplantation (MSC-dNLCs), and MSC-dNLC transplantation combined with EA stimulation (MSC-dNLCs+EA) groups. We observed the ultrastructure of the brain and measured the brain water content (BWC) and the levels of the microtubule-associated protein 2 (MAP2), galactocerebrosidase (GALC), and glial fibrillary acidic protein (GFAP) proteins. We also measured the levels of the phosphorylated mammalian target of rapamycin (mTOR) and 70 kDa ribosomal protein S6 kinase (p70S6K) proteins, as well as the expression of synapse-related proteins. The BWC increased in rats after ICH and decreased significantly in ICH rats treated with MSC-dNLC transplantation, EA stimulation, or combined therapy. Meanwhile, after ICH, the number of blood vessels increased more evidently, but only the combined treatment reduced the number of blood vessels among rats receiving the three treatments. Moreover, the levels of MAP2, GALC, postsynaptic density 95 (PSD95), and synaptophysin (SYP) proteins, as well as the levels of the phosphorylated mTOR and p70S6k proteins, increased in the MSC-dNLCs+EA group compared with those in the MSC-dNLCs and EA groups. Compared with the MC group, GFAP expression was significantly reduced in the MSC-dNLCs, EA, and MSC-dNLCs+EA groups, but the differences among the three treatment groups were not significant. In addition, the number of synapses increased only in the MSC-dNLCs+EA group compared to the MC group. Based on these data, the combination of MSC-dNLC transplantation and EA stimulation exerts a synergistic effect on improving the consequences of ICH by relieving cerebral edema and glial scarring, promoting the survival of neurons and oligodendrocytes, and activating mTOR/p70S6K signaling to enhance synaptic plasticity.

The neuroprotective effect and RNA-sequence analysis of postconditioning on the ischemic stroke with diabetes mellitus tree shrew model

INTRODUCTION

Patients with comorbidity of ischemic stroke (IS) and diabetes mellitus (DM) show poor neurological functional recovery, and ischemic postconditioning (IPOC) should be considered a powerful neuroprotective method for IS. However, whether it should be introduced for patients with IS and DM remains controversial. This study established a DM with IS (DMIS) tree shrew model, which was intervened by IPOC to assess its neuroprotective effects and also to analyze the relevant mechanism by RNA-sequence and bioinformatics analysis.

METHODS

Fifty-four tree shrews were randomly divided into a sham operation control group, a DMIS group, and an IPOC group (DMIS model), with 18 tree shrews per group. Triphenyl tetrazolium chloride (TTC), hematoxylin-eosin (HE) staining, transmission electron microscopy (TEM), and RNA-sequence analysis were performed to assess the IPOC effect.

RESULTS

IPOC reduced infarct size and reduced nerve cell injury in IS tree shrews with DM. RNA-seq analysis showed that IPOC significantly increased the expression of the homeobox protein SIX3, while downregulating the expression of HLA class II histocompatibility antigens DQ beta 1 chain, CAS1 domain-containing protein 1, and cytokine receptor-like factor 2. The most downregulated signaling pathways include the NF-κB signaling pathway, TNF signaling pathway, and Fc gamma R-mediated phagocytosis.

CONCLUSIONS

IPOCs have a neuroprotective effect in a DMIS animal model that reduces infarct size and nerve cell injury. This mechanism might be related to reducing inflammation and stress responses that decreases the activity of TNF and NF-κB signaling pathways.

Systematic Study of Immune Cell Diversity in ischemic postconditioning Using High-Dimensional Single-Cell Analysis with Mass Cytometry

Ischemic postconditioning (IPostC) is a concept of ischemic stroke treatment, in which several cycles of brief reocclusion after reperfusion are repeated. It is essential to have an accurate understanding of the immune response in IPostC. By using high parametric single-cell mass cytometry, immune cell subsets and characterize their unique functions from ischemic brain and peripheral blood were identified after IPostC. This study enabled us to better understand the immune cell phenotypical and functional characteristics in ischemic brain and peripheral blood at the single-cell and protein levels. Since some cell surface markers can serve as functional markers, reflecting the degree of inflammation, the cell surface marker intensity among different groups was analyzed. The results showed that downregulation of 4E-BP1 and p38 of Microglia and MoDM in the ischemic brain was involved in IPostC-induced protection. In the peripheral blood, downregulation of P38 of CD4 T cell and Treg has also participated in IPostC-induced protection.

Dichloromethane extraction from Piper nigrum L. and P. longum L. to mitigate ischemic stroke by activating the AKT/mTOR signaling pathway to suppress autophagy

Dichloromethane fraction (DF) of Piper nigrum L. and P. longum L. (PnL and PlL), has been found to exert a protective effect against ischemic stroke in rats. However, the regulatory mechanism exerted by PnL and PIL have not been fully elucidated. In this study, we found that DF greatly ameliorated cerebral ischemic injury in a rat model of permanent middle cerebral artery occlusion (pMCAO). The neurological score, behavioral assessment, brain infarct volume, phosphorylation of AKT (p-AKT), phosphorylation mTOR (p-mTOR), and Atg7 protein levels were determined. Additionally, we discovered that DF pretreatment reduced infarct volume, neurological score, and brain damage. Furthermore, DF therapy caused the downregulation of Atg7 and p-AKT expression, as well as the upregulation of p-mTOR expression. In conclusion, our findings indicated that DF treatment can reduce brain damage and inhibit apoptosis and autophagy by activating the Akt-mTOR signaling pathway in ischemic stroke.

Inhibition of mTOR Alleviates Early Brain Injury After Subarachnoid Hemorrhage Via Relieving Excessive Mitochondrial Fission

The mammalian target of rapamycin (mTOR) was reported to regulate cell autophagy and outcomes of several neurological diseases. Mitochondria, which serve as critical organelles in neurons. are also involved in the pathology of neurological diseases. However, the role of mTOR in mitochondrial morphology has not been clarified especially in subarachnoid hemorrhage (SAH). In this study, we established SAH models both in vivo and in vitro. Rapamycin and 3-methyl adenine (3-MA) were then administered to alter mTOR activity. Post-SAH assessment included SAH grading, neurological evaluation, blood-brain barrier (BBB) permeability, brain water content, mitochondrial membrane potential (MMP), mitochondrial morphology, ATP content, cell viability, cytotoxicity, and expression of proteins related to apoptosis and mitochondrial fission. The results showed that (1) neurological deficits, BBB permeability, and brain edema were increased after SAH and that cell viability was exacerbated in brain tissue. (2) Excessive mitochondrial fission was evident based on changes in mitochondrial morphology, while MMP and ATP content were decreased in neurons after SAH. (3) Administration of rapamycin improved the excessive mitochondrial fission and restored mitochondrial function, which subsequently reduced apoptosis. (4) 3-MA showed an adverse effect on mitochondria and aggravated excessive mitochondrial fission and dysfunction in SAH. Neurological deficits and neuronal viability were also exacerbated following the administration of 3-MA. Therefore, our study suggests that mTOR inhibition has neuroprotective effects against neuronal injury after SAH via alleviating excessive mitochondrial fission.

CD4 T cell deficiency attenuates ischemic stroke, inhibits oxidative stress, and enhances Akt/mTOR survival signaling pathways in mice

Background

Inhibition of CD4 T cells reduces stroke-induced infarction by inhibiting neuroinflammation in the ischemic brain in experimental stroke. Nevertheless, little is known about its effects on neuronal survival signaling pathways. In this study, we investigated the effects of CD4 T cell deficits on oxidative stress and on the Akt/mTOR cell signaling pathways after ischemic stroke in mice.

Methods

MHC II gene knockout C57/BL6 mice, with significantly decreased CD4 T cells, were used. Stroke was induced by 60-min middle cerebral artery (MCA) occlusion. Ischemic brain tissues were harvested for Western blotting.

Results

The impairment of CD4 T cell production resulted in smaller infarction. The Western blot results showed that iNOS protein levels robustly increased at 5 h and 24 h and then returned toward baseline at 48 h in wild-type mice after stroke, and gene KO inhibited iNOS at 5 h and 24 h. In contrast, the anti-inflammatory marker, arginase I, was found increased after stroke in WT mice, which was further enhanced in the KO mice. In addition, stroke resulted in increased phosphorylated PTEN, Akt, PRAS40, P70S6, and S6 protein levels in WT mice, which were further enhanced in the animals whose CD4 T cells were impaired.

Conclusion

The impairment of CD4 T cell products prevents ischemic brain injury, inhibits inflammatory signals, and enhances the Akt/mTOR cell survival signaling pathways.