Molecular neurobiology of mTOR

Erdheim-Chester disease: a comprehensive review from the ophthalmologic perspective

Erdheim-Chester disease (ECD) is a rare clonal histiocytic neoplasm with less than 1200 documented cases to date. The disease is life-threatening and difficult to recognize, although increasing awareness as well as the integration of clinical, imaging, pathology information , and genetic studies have led to a recent exponential increase in new reported cases. ECD affects multiple organs and systems, including skeletal, neurologic, and cardiovascular. Pulmonary, retroperitoneal, and cutaneous lesions have also been reported in various combinations. Until the discovery that more than half of ECD patients harbor the BRAF-V600E mutation or other mutations in the mitogen-activated protein kinase (MAPK) and RAS pathways, Interferon-a was the first-line treatment. Nowadays BRAF and MEK-inhibitors targeted therapies are the mainstay of treatment. Ophthalmologic involvement occurs in 25% -30% of ECD cases, usually in the form of orbital involvement presenting with exophthalmos and ophthalmoplegia. Other ophthalmologic manifestations include palpebral xanthelasmas, anterior uveitis and vitritis, optic disk edema, choroidal infiltration, recurrent serous retinal detachment, retinal drusen-like deposits and retinal pigment epithelial changes. ECD patients can also present with ocular symptoms as a result of adverse effects of the treatment regimens. In some cases with smoldering or protean symptoms, the emergence of eye manifestations triggered the diagnosis. Ophthalmologists have to be aware of the disease, recognize the constellation of ECD symptoms, and contribute to the diagnosis, treatment, and follow-up of ECD patients.

mTOR controls endoplasmic reticulum-Golgi apparatus trafficking of VSVg in specific cell types

BACKGROUND

Mammalian/mechanistic target of rapamycin (mTOR) complexes are essential for cell proliferation, growth, differentiation, and survival. mTORC1 hyperactivation occurs in the tuberous sclerosis complex (TSC). mTORC1 localizes to the surface of lysosomes, where Rheb activates it. However, mTOR was also found on the endoplasmic reticulum (ER) and Golgi apparatus (GA). Recent studies showed that the same inputs regulate ER-to-GA cargo transport and mTORC1 (e.g., the level of amino acids or energy status of the cell). Nonetheless, it remains unknown whether mTOR contributes to the regulation of cargo passage through the secretory pathway.

METHODS

The retention using selective hooks (RUSH) approach was used to image movement of model cargo (VSVg) between the ER and GA in various cell lines in which mTOR complexes were inhibited. We also investigated VSVg trafficking in TSC patient fibroblasts.

RESULTS

We found that mTOR inhibition led to the overall enhancement of VSVg transport through the secretory pathway in PC12 cells and primary human fibroblasts. Also, in TSC1-deficient cells, VSVg transport was enhanced.

CONCLUSIONS

Altogether, these data indicate the involvement of mTOR in the regulation of ER-to-GA cargo transport and suggest that impairments in exocytosis may be an additional cellular process that is disturbed in TSC.

Cross talk between autophagy and oncogenic signaling pathways and implications for cancer therapy

Autophagy is a highly conserved metabolic process involved in the degradation of intracellular components including proteins and organelles. Consequently, it plays a critical role in recycling metabolic energy for the maintenance of cellular homeostasis in response to various stressors. In cancer, autophagy either suppresses or promotes cancer progression depending on the stage and cancer type. Epithelial-mesenchymal transition (EMT) and cancer metastasis are directly mediated by oncogenic signal proteins including SNAI1, SLUG, ZEB1/2, and NOTCH1, which are functionally correlated with autophagy. In this report, we discuss the crosstalk between oncogenic signaling pathways and autophagy followed by possible strategies for cancer treatment via regulation of autophagy. Although autophagy affects EMT and cancer metastasis, the overall signaling pathways connecting cancer progression and autophagy are still illusive. In general, autophagy plays a critical role in cancer cell survival by providing a minimum level of energy via self-digestion. Thus, cancer cells face nutrient limitations and challenges under stress during EMT and metastasis. Conversely, autophagy acts as a potential cancer suppressor by degrading oncogenic proteins, which are essential for cancer progression, and by removing damaged components such as mitochondria to enhance genomic stability. Therefore, autophagy activators or inhibitors represent possible cancer therapeutics. We further discuss the regulation of autophagy-dependent degradation of oncogenic proteins and its functional correlation with oncogenic signaling pathways, with potential applications in cancer therapy.

ZNRF2 attenuates focal cerebral ischemia/reperfusion injury in rats by inhibiting mTORC1-mediated autophagy

Zinc and ring finger 2 (ZNRF2), an E3 ubiquitin ligase, plays a crucial role in many diseases. However, its role in cerebral ischemia/reperfusion injury (CIRI) still remains unknown. In this study, the function and molecular mechanism of ZNRF2 in CIRI in vivo and vitro was studied. ZNRF2 was found to be dramatically downregulated in CIRI. Overexpression of ZNRF2 could significantly reduce the neurological deficit, brain infarct volume and histopathological damage of cortex in middle cerebral artery occlusion/reperfusion. Concomitantly, overexpression of ZNRF2 increased the primary neuronal viability and decreased the neuronal apoptosis induced by oxygen-glucose deprivation and reoxygenation (OGD/R). Mechanistically, overexpression of ZNRF2 inhibited the over-induction of autophagy induced by OGD/R which was abolished by mTORC1 inhibitor rapamycin. It can be concluded that ZNRF2 plays a protective effect in CIRI and the underlying mechanism may be related to the inhibition of mTORC1-mediated autophagy.

Tanc2-mediated mTOR inhibition balances mTORC1/2 signaling in the developing mouse brain and human neurons

mTOR signaling, involving mTORC1 and mTORC2 complexes, critically regulates neural development and is implicated in various brain disorders. However, we do not fully understand all of the upstream signaling components that can regulate mTOR signaling, especially in neurons. Here, we show a direct, regulated inhibition of mTOR by Tanc2, an adaptor/scaffolding protein with strong neurodevelopmental and psychiatric implications. While Tanc2-null mice show embryonic lethality, Tanc2-haploinsufficient mice survive but display mTORC1/2 hyperactivity accompanying synaptic and behavioral deficits reversed by mTOR-inhibiting rapamycin. Tanc2 interacts with and inhibits mTOR, which is suppressed by mTOR-activating serum or ketamine, a fast-acting antidepressant. Tanc2 and Deptor, also known to inhibit mTORC1/2 minimally affecting neurodevelopment, distinctly inhibit mTOR in early- and late-stage neurons. Lastly, Tanc2 inhibits mTORC1/2 in human neural progenitor cells and neurons. In summary, our findings show that Tanc2 is a mTORC1/2 inhibitor affecting neurodevelopment.

Current Approaches and Future Directions for the Treatment of mTORopathies

The mechanistic target of rapamycin (mTOR) is a kinase at the center of an evolutionarily conserved signaling pathway that orchestrates cell growth and metabolism. mTOR responds to an array of intra- and extracellular stimuli and in turn controls multiple cellular anabolic and catabolic processes. Aberrant mTOR activity is associated with numerous diseases, with particularly profound impact on the nervous system. mTOR is found in two protein complexes, mTOR complex 1 (mTORC1) and 2 (mTORC2), which are governed by different upstream regulators and have distinct cellular actions. Mutations in genes encoding for mTOR regulators result in a collection of neurodevelopmental disorders known as mTORopathies. While these disorders can affect multiple organs, neuropsychiatric conditions such as epilepsy, intellectual disability, and autism spectrum disorder have a major impact on quality of life. The neuropsychiatric aspects of mTORopathies have been particularly challenging to treat in a clinical setting. Current therapeutic approaches center on rapamycin and its analogs, drugs that are administered systemically to inhibit mTOR activity. While these drugs show some clinical efficacy, adverse side effects, incomplete suppression of mTOR targets, and lack of specificity for mTORC1 or mTORC2 may limit their utility. An increased understanding of the neurobiology of mTOR and the underlying molecular, cellular, and circuit mechanisms of mTOR-related disorders will facilitate the development of improved therapeutics. Animal models of mTORopathies have helped unravel the consequences of mTOR pathway mutations in specific brain cell types and developmental stages, revealing an array of disease-related phenotypes. In this review, we discuss current progress and potential future directions for the therapeutic treatment of mTORopathies with a focus on findings from genetic mouse models.

On the therapeutic targets and pharmacological treatments for pain relief following spinal cord injury: A mechanistic review

Spinal cord injury (SCI) is globally considered as one of the most debilitating disorders, which interferes with daily activities and life of the affected patients. Despite many developments in related recognizing and treating procedures, post-SCI neuropathic pain (NP) is still a clinical challenge for clinicians with no distinct treatments. Accordingly, a comprehensive search was conducted in PubMed, Medline, Scopus, Web of Science, and national database (SID and Irandoc). The relevant articles regarding signaling pathways, therapeutic targets and pharmacotherapy of post-SCI pain were also reviewed. Data were collected with no time limitation until November 2020. The present study provides the findings on molecular mechanisms and therapeutic targets, as well as developing the critical signaling pathways to introduce novel neuroprotective treatments of post-SCI pain. From the pathophysiological mechanistic point of view, post-SCI inflammation activates the innate immune system, in which the immune cells elicit secondary injuries. So, targeting the critical signaling pathways for pain management in the SCI population has significant importance in providing new treatments. Indeed, several receptors, ion channels, excitatory neurotransmitters, enzymes, and key signaling pathways could be used as therapeutic targets, with a pivotal role of n-methyl-D-aspartate, gamma-aminobutyric acid, and inflammatory mediators. The current review focuses on conventional therapies, as well as crucial signaling pathways and promising therapeutic targets for post-SCI pain to provide new insights into the clinical treatment of post-SCI pain. The need to develop innovative delivery systems to treat SCI is also considered.

Convergent and Divergent Mechanisms of Epileptogenesis in mTORopathies

Hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1) due to mutations in genes along the PI3K-mTOR pathway and the GATOR1 complex causes a spectrum of neurodevelopmental disorders (termed mTORopathies) associated with malformation of cortical development and intractable epilepsy. Despite these gene variants’ converging impact on mTORC1 activity, emerging findings suggest that these variants contribute to epilepsy through both mTORC1-dependent and -independent mechanisms. Here, we review the literature on in utero electroporation-based animal models of mTORopathies, which recapitulate the brain mosaic pattern of mTORC1 hyperactivity, and compare the effects of distinct PI3K-mTOR pathway and GATOR1 complex gene variants on cortical development and epilepsy. We report the outcomes on cortical pyramidal neuronal placement, morphology, and electrophysiological phenotypes, and discuss some of the converging and diverging mechanisms responsible for these alterations and their contribution to epileptogenesis. We also discuss potential therapeutic strategies for epilepsy, beyond mTORC1 inhibition with rapamycin or everolimus, that could offer personalized medicine based on the gene variant.

Revisiting Brain Tuberous Sclerosis Complex in Rat and Human: Shared Molecular and Cellular Pathology Leads to Distinct Neurophysiological and Behavioral Phenotypes

Tuberous sclerosis complex (TSC) is a dominant autosomal genetic disorder caused by loss-of-function mutations in TSC1 and TSC2, which lead to constitutive activation of the mammalian target of rapamycin C1 (mTORC1) with its decoupling from regulatory inputs. Because mTORC1 integrates an array of molecular signals controlling protein synthesis and energy metabolism, its unrestrained activation inflates cell growth and division, resulting in the development of benign tumors in the brain and other organs. In humans, brain malformations typically manifest through a range of neuropsychiatric symptoms, among which mental retardation, intellectual disabilities with signs of autism, and refractory seizures, which are the most prominent. TSC in the rat brain presents the first-rate approximation of cellular and molecular pathology of the human brain, showing many instructive characteristics. Nevertheless, the developmental profile and distribution of lesions in the rat brain, with neurophysiological and behavioral manifestation, deviate considerably from humans, raising numerous research and translational questions. In this study, we revisit brain TSC in human and Eker rats to relate their histopathological, electrophysiological, and neurobehavioral characteristics. We discuss shared and distinct aspects of the pathology and consider factors contributing to phenotypic discrepancies. Given the shared genetic cause and molecular pathology, phenotypic deviations suggest an incomplete understanding of the disease. Narrowing the knowledge gap in the future should not only improve the characterization of the TSC rat model but also explain considerable variability in the clinical manifestation of the disease in humans.

The role of G-CSF neuroprotective effects in neonatal hypoxic-ischemic encephalopathy (HIE): current status

Hypoxic-ischemic encephalopathy (HIE) is an important cause of permanent damage to central nervous system (CNS) that may result in neonatal death or manifest later as mental retardation, epilepsy, cerebral palsy, or developmental delay. The primary cause of this condition is systemic hypoxemia and/or reduced cerebral blood flow with long-lasting neurological disabilities and neurodevelopmental impairment in neonates. About 20 to 25% of infants with HIE die in the neonatal period, and 25-30% of survivors are left with permanent neurodevelopmental abnormalities. The mechanisms of hypoxia-ischemia (HI) include activation and/or stimulation of myriad of cascades such as increased excitotoxicity, oxidative stress, N-methyl-D-aspartic acid (NMDA) receptor hyperexcitability, mitochondrial collapse, inflammation, cell swelling, impaired maturation, and loss of trophic support. Different therapeutic modalities have been implicated in managing neonatal HIE, though translation of most of these regimens into clinical practices is still limited. Therapeutic hypothermia, for instance, is the most widely used standard treatment in neonates with HIE as studies have shown that it can inhibit many steps in the excito-oxidative cascade including secondary energy failure, increases in brain lactic acid, glutamate, and nitric oxide concentration. Granulocyte-colony stimulating factor (G-CSF) is a glycoprotein that has been implicated in stimulation of cell survival, proliferation, and function of neutrophil precursors and mature neutrophils. Extensive studies both in vivo and ex vivo have shown the neuroprotective effect of G-CSF in neurodegenerative diseases and neonatal brain damage via inhibition of apoptosis and inflammation. Yet, there are still few experimentation models of neonatal HIE and G-CSF's effectiveness, and extrapolation of adult stroke models is challenging because of the evolving brain. Here, we review current studies and/or researches of G-CSF's crucial role in regulating these cytokines and apoptotic mediators triggered following neonatal brain injury, as well as driving neurogenesis and angiogenesis post-HI insults.

Deletion of hippocampal Glucocorticoid receptors unveils sex-biased microRNA expression and neuronal morphology alterations in mice

Sex differences in the brain have prompted many researchers to investigate the underlying molecular actors, such as the glucocorticoid receptor (GR). This nuclear receptor controls gene expression, including microRNAs (miRNAs), in non-neuronal cells. Here, we investigated sex-biased effects of GR on hippocampal miRNA expression and neuronal morphology by generating a neuron-specific GR knockout mouse (Emx1-Nr3c1^−/−). The levels of 578 mature miRNAs were assessed using NanoString technology and, in contrast to males, female Emx1-Nr3c1^−/− mice showed a substantially higher number of differentially expressed miRNAs, confirming a sex-biased effect of GR ablation. Based on bioinformatic analyses we identified several transcription factors potentially involved in miRNA regulation. Functional enrichment analyses of the miRNA-mRNA interactions revealed pathways related to neuronal arborization and both spine morphology and density in both sexes. Two recognized regulators of dendritic morphology, CAMKII-α and GSK-3β, increased their protein levels by GR ablation in female mice hippocampus, without changes in males. Additionally, sex-specific effects of GR deletion were observed on CA1 neuronal arborization and dendritic spine features. For instance, a reduced density of mushroom spines in apical dendrites was evidenced only in females, while a decreased length in basal dendrites was noted only in males. However, length and arborization of apical dendrites were reduced by GR ablation irrespective of the sex. Overall, our study provides new insights into the sex-biased GR actions, especially in terms of miRNAs expression and neuronal morphology in the hippocampus.

G3BPs tether the TSC complex to lysosomes and suppress mTORC1 signaling

Ras GTPase-activating protein-binding proteins 1 and 2 (G3BP1 and G3BP2, respectively) are widely recognized as core components of stress granules (SGs). We report that G3BPs reside at the cytoplasmic surface of lysosomes. They act in a non-redundant manner to anchor the tuberous sclerosis complex (TSC) protein complex to lysosomes and suppress activation of the metabolic master regulator mechanistic target of rapamycin complex 1 (mTORC1) by amino acids and insulin. Like the TSC complex, G3BP1 deficiency elicits phenotypes related to mTORC1 hyperactivity. In the context of tumors, low G3BP1 levels enhance mTORC1-driven breast cancer cell motility and correlate with adverse outcomes in patients. Furthermore, G3bp1 inhibition in zebrafish disturbs neuronal development and function, leading to white matter heterotopia and neuronal hyperactivity. Thus, G3BPs are not only core components of SGs but also a key element of lysosomal TSC-mTORC1 signaling.

EGB761 ameliorates chronic cerebral hypoperfusion-induced cognitive dysfunction and synaptic plasticity impairment

Chronic cerebral hypoperfusion (CCH) may lead to the cognitive dysfunction, but the underlying mechanisms are unclear. EGB761, extracted from Ginkgo biloba and as a phytomedicine widely used in the world, has been showed to have various neuroprotective roles and mechanisms, and therapeutic effects in Alzheimer’s disease and other cognitive dysfunctions. However, improvements in cognitive function after CCH, following treatment with EGB761, have not been ascertained yet. In this study, we used the behavior test, electrophysiology, neurobiochemistry, and immunohistochemistry to investigate the EGB761’s effect on CCH-induced cognitive dysfunction and identify its underlying mechanisms. The results showed that EGB761 ameliorates spatial cognitive dysfunction occurring after CCH. It may also improve impairment of the long-term potentiation, field excitable potential, synaptic transmission, and the transmission synchronization of neural circuit signals between the entorhinal cortex and hippocampal CA1. EGB761 may also reverse the inhibition of neural activity and the degeneration of dendritic spines and synaptic structure after CCH; it also prevents the downregulation of synaptic proteins molecules and pathways related to the formation and stability of dendritic spines structures. EGB761 may inhibit axon demyelination and ameliorate the inhibition of the mTOR signaling pathway after CCH to improve protein synthesis. In conclusion, EGB761 treatment after CCH may improve spatial cognitive function by ameliorating synaptic plasticity impairment, synapse degeneration, and axon demyelination by rectifying the inhibition of the mTOR signaling pathway.

Amentoflavone Ameliorates Memory Deficits and Abnormal Autophagy in Aβ25-35-Induced Mice by mTOR Signaling

Alzheimer's disease (AD) is a neurodegenerative disease in which autophagy plays a crucial role. Amentoflavone is a flavonoid obtained from various plants and has been shown to have AD-resistant neuroprotective effects. This study investigated the role of amentoflavone on memory impairment and abnormal autophagy in amyloid-β25-35 (Aβ_25-35)-induced mice to elucidate the mechanisms by which it exerts neuroprotective effects. In this experiment, the AD mouse model was established by intracerebroventricular (ICV) injection of Aβ_25-35 peptides, and amentoflavone was administered orally for 4 weeks. Behavioral changes in mice and pathological changes in the hippocampus were observed, and levels of inflammation, oxidative stress, and autophagy in the brain were detected and analyzed. PC-12 and APPswe-N2a cells were used in vitro to further investigate the effect of amentoflavone on the level of intracellular autophagy. Molecular docking was used to determine the action sites of amentoflavone. The results showed that amentoflavone improved memory function, eased anxiety symptoms in Aβ_25-35-induced mice, and reduced atrophic degeneration of neurons in the hippocampus. Moreover, amentoflavone lessened the oxidative stress and inflammation in the brains of mice. Through in vivo and in vitro experiments, we found that amentoflavone may enhance autophagy, by way of binding to the ATP site of the mTOR protein kinase domain. Amentoflavone not only interacted with mTOR, but also improved Aβ_25-35-induced cognitive dysfunction in mice by enhancing autophagy, attenuating levels of inflammation and oxidative stress, and reducing apoptosis in brain cells.

Mechanism of Intermittent Theta-Burst Stimulation in Synaptic Pathology in the Prefrontal Cortex in an Antidepressant-Resistant Depression Rat Model

Intermittent theta-burst stimulation (iTBS), a form of repetitive transcranial magnetic stimulation, is considered a potential therapy for treatment-resistant depression. The synaptic mechanism of iTBS has long been known to be an effective method to induce long-term potentiation (LTP)-like plasticity in humans. However, there is limited evidence as to whether the antidepressant effect of iTBS is associated with change in synaptic function in the prefrontal cortex (PFC) in preclinical study. Hence, we applied an antidepressant (i.e., fluoxetine)-resistant depression rat model induced by severe foot-shocks to investigate the antidepressant efficacy of iTBS in the synaptic pathology. The results showed that iTBS treatment improved not only the impaired LTP, but also the aberrant long-term depression in the PFC of antidepressant-resistant depression model rats. Moreover, the mechanism of LTP improvement by iTBS involved downstream molecules of brain-derived neurotrophic factor, while the mechanism of long-term depression improvement by iTBS involved downstream molecules of proBDNF. The aberrant spine morphology was also improved by iTBS treatment. This study demonstrated that the mechanism of the iTBS paradigm is complex and may regulate not only excitatory but also inhibitory synaptic effects in the PFC.

The neuroprotective effects of activated α7 nicotinic acetylcholine receptor against mutant copper-zinc superoxide dismutase 1-mediated toxicity

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the selective and progressive loss of motor neurons. Although many drugs have entered clinical trials, few have shown effectiveness in the treatment of ALS. Other studies have shown that the stimulation of α7 nicotinic acetylcholine receptor (nAChR) can have neuroprotective effects in some models of neurodegenerative disease, as well as prevent glutamate-induced motor neuronal death. However, the effect of α7 nAChR agonists on ALS-associated mutant copper-zinc superoxide dismutase 1 (SOD1) aggregates in motor neurons remains unclear. In the present study, we examined whether α7 nAChR activation had a neuroprotective effect against SOD1^G85R-induced toxicity in a cellular model for ALS. We found that α7 nAChR activation by PNU282987, a selective agonist of α7 nAChR, exhibited significant neuroprotective effects against SOD1^G85R-induced toxicity via the reduction of intracellular protein aggregates. This reduction also correlated with the activation of autophagy through the AMP-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR) signaling pathway. Furthermore, the activation of α7 nAChRs was found to increase the biogenesis of lysosomes by inducing translocation of the transcription factor EB (TFEB) into the nucleus. These results support the therapeutic potential of α7 nAChR activation in diseases that are characterized by SOD1^G85R aggregates, such as ALS.

Mammalian Target of Rapamycin-RhoA Signaling Impairments in Direct Striatal Projection Neurons Induce Altered Behaviors and Striatal Physiology in Mice

BACKGROUND

As an integrator of molecular pathways, mTOR (mammalian target of rapamycin) has been associated with diseases including neurodevelopmental, psychiatric, and neurodegenerative disorders such as autism spectrum disorder, schizophrenia, and Huntington's disease. An important brain area involved in all these diseases is the striatum. However, the mechanisms behind how mTOR is involved in striatal physiology and its relative role in distinct neuronal populations in these striatal-related diseases still remain to be clarified.

METHODS

Using Drd1-Cre mTOR-conditional knockout male mice, we combined behavioral, biochemical, electrophysiological, and morphological analysis aiming to untangle the role of mTOR in direct pathway striatal projection neurons and how this would impact on striatal physiology.

RESULTS

Our results indicate deep behavioral changes in absence of mTOR in Drd1-expressing neurons such as decreased spontaneous locomotion, impaired social interaction, and decreased marble-burying behavior. These alterations were accompanied by a Kv1.1-induced increase in the fast phase of afterhyperpolarization and coincident decreased distal spine density in striatal direct pathway striatal projection neurons. The physiological changes were mechanistically independent of protein synthesis but sensitive to pharmacological blockade of transforming protein RhoA activity.

CONCLUSIONS

These results identify mTOR signaling as an important regulator of striatal functions through an intricate mechanism involving RhoA and culminating in Kv1.1 overfunction, which could be targeted to treat striatal-related monogenic disorders associated with the mTOR signaling pathway.

Insights into Potential Targets for Therapeutic Intervention in Epilepsy

Epilepsy is a chronic brain disease that affects approximately 65 million people worldwide. However, despite the continuous development of antiepileptic drugs, over 30% patients with epilepsy progress to drug-resistant epilepsy. For this reason, it is a high priority objective in preclinical research to find novel therapeutic targets and to develop effective drugs that prevent or reverse the molecular mechanisms underlying epilepsy progression. Among these potential therapeutic targets, we highlight currently available information involving signaling pathways (Wnt/β-catenin, Mammalian Target of Rapamycin (mTOR) signaling and zinc signaling), enzymes (carbonic anhydrase), proteins (erythropoietin, copine 6 and complement system), channels (Transient Receptor Potential Vanilloid Type 1 (TRPV1) channel) and receptors (galanin and melatonin receptors). All of them have demonstrated a certain degree of efficacy not only in controlling seizures but also in displaying neuroprotective activity and in modifying the progression of epilepsy. Although some research with these specific targets has been done in relation with epilepsy, they have not been fully explored as potential therapeutic targets that could help address the unsolved issue of drug-resistant epilepsy and develop new antiseizure therapies for the treatment of epilepsy.

p62-Nrf2-p62 Mitophagy Regulatory Loop as a Target for Preventive Therapy of Neurodegenerative Diseases

Turnover of the mitochondrial pool due to coordinated processes of mitochondrial biogenesis and mitophagy is an important process in maintaining mitochondrial stability. An important role in this process is played by the Nrf2/ARE signaling pathway, which is involved in the regulation of the expression of genes responsible for oxidative stress protection, regulation of mitochondrial biogenesis, and mitophagy. The p62 protein is a multifunctional cytoplasmic protein that functions as a selective mitophagy receptor for the degradation of ubiquitinated substrates. There is evidence that p62 can positively regulate Nrf2 by binding to its negative regulator, Keap1. However, there is also strong evidence that Nrf2 up-regulates p62 expression. Thereby, a regulatory loop is formed between two important signaling pathways, which may be an important target for drugs aimed at treating neurodegeneration. Constitutive activation of p62 in parallel with Nrf2 would most likely result in the activation of mTORC1-mediated signaling pathways that are associated with the development of malignant neoplasms. The purpose of this review is to describe the p62-Nrf2-p62 regulatory loop and to evaluate its role in the regulation of mitophagy under various physiological conditions.

Venlafaxine protects against chronic stress-related behaviors in mice by activating the mTORC1 signaling cascade

BACKGROUND

Recent studies have suggested the role of mammalian target of rapamycin complex 1 (mTORC1) in the pathophysiology of depression. Although venlafaxine was thought to be a serotonin and norepinephrine reuptake inhibitor (SNRI), its pharmacological mechanism remain elusive. In this study, the effects of venlafaxine on the mTORC1 system were studied in both chronic unpredictable mild stress (CUMS) and chronic social defeat stress (CSDS) models.

METHOD

First, we examined whether repeated venlafaxine treatment reversed the effects of CUMS and CSDS on the mTORC1 signaling cascade in both the hippocampus and medial prefrontal cortex (mPFC). Second, several selective pharmacological inhibitors of the mTORC1 system, including rapamycin, LY294002 and U0126, were used together to determine whether the protective effects of venlafaxine against the CUMS and CSDS models were prevented by mTORC1 system blockade. Finally, genetic knockdown of mTORC1 by mTORC1-shRNA was further adopted to test whether mTORC1 was necessary for the anti-stress effects of venlafaxine in mice.

RESULT

Our results showed that the decreasing effects of CUMS and CSDS on the mTORC1 signaling cascade in the hippocampus and mPFC were restored by venlafaxine, and the use of rapamycin, LY294002, U0126 and mTORC1-shRNA fully abolished the anti-stress actions of venlafaxine in mice.

CONCLUSION

The mTORC1 system is involved in the pharmacological mechanism of venlafaxine.

Hypoxia-Induced Glioma-Derived Exosomal miRNA-199a-3p Promotes Ischemic Injury of Peritumoral Neurons by Inhibiting the mTOR Pathway

The underlying molecular mechanisms that the hypoxic microenvironment could aggravate neuronal injury are still not clear. In this study, we hypothesized that the exosomes, exosomal miRNAs, and the mTOR signaling pathway might be involved in hypoxic peritumoral neuronal injury in glioma. Multimodal radiological images, HE, and HIF-1α staining of high-grade glioma (HGG) samples revealed that the peritumoral hypoxic area overlapped with the cytotoxic edema region and directly contacted with normal neurons. In either direct or indirect coculture system, hypoxia could promote normal mouse hippocampal neuronal cell (HT22) injury, and the growth of HT22 cells was suppressed by C6 glioma cells under hypoxic condition. For administrating hypoxia-induced glioma-derived exosomes (HIGDE) that could aggravate oxygen-glucose deprivation (OGD)/reperfusion neuronal injury, we identified that exosomes may be the communication medium between glioma cells and peritumoral neurons, and we furtherly found that exosomal miR-199a-3p mediated the OGD/reperfusion neuronal injury process by suppressing the mTOR signaling pathway. Moreover, the upregulation of miRNA-199a-3p in exosomes from glioma cells was induced by hypoxia-related HIF-1α activation. To sum up, hypoxia-induced glioma-derived exosomal miRNA-199a-3p can be upregulated by the activation of HIF-1α and is able to increase the ischemic injury of peritumoral neurons by inhibiting the mTOR pathway.

MiRNAs as Noninvasive Biomarkers and Therapeutic Agents of Pituitary Adenomas

Pituitary adenoma (PA) accounts for 10-15% of all intracranial neoplasms. Even though most pituitary adenomas are benign, it is known that almost 35% of them exhibit an aggressive clinical course, including rapid proliferative activity and invasion of neighboring tissues. MicroRNAs (miRNAs) are short single-stranded RNA molecules that can influence post-transcriptional regulation by controlling target genes. Based on research data on miRNAs over the past 20 years, more than 60% of genes encoding human proteins are regulated by miRNAs, which ultimately control basic cellular mechanisms, including cell proliferation, differentiation, and apoptosis. Dysregulation of miRNAs has been observed in a number of diseases, especially tumors like PA. A majority of miRNAs are expressed within the cells themselves. However, the circulating miRNAs can be detected in several biological fluids of the human body. The identification of circulating miRNAs as new molecular markers may increase the ability to detect a tumor, predict the course of a disease, plan to choose suitable treatment, and diagnose at the earliest signs of impending neoplastic transformation. Therapy of PAs with aggressive behavior is a complex task. When surgery and chemotherapy fail, radiotherapy becomes the treatment of choice against PAs. Therefore, the possibility of implementing circulating miRNAs as innovative diagnostic and therapeutic agents for PA is one of the main exciting ideas.

Tuberous Sclerosis Complex as Disease Model for Investigating mTOR-Related Gliopathy During Epileptogenesis

Tuberous sclerosis complex (TSC) represents the prototypic monogenic disorder of the mammalian target of rapamycin (mTOR) pathway dysregulation. It provides the rational mechanistic basis of a direct link between gene mutation and brain pathology (structural and functional abnormalities) associated with a complex clinical phenotype including epilepsy, autism, and intellectual disability. So far, research conducted in TSC has been largely neuron-oriented. However, the neuropathological hallmarks of TSC and other malformations of cortical development also include major morphological and functional changes in glial cells involving astrocytes, oligodendrocytes, NG2 glia, and microglia. These cells and their interglial crosstalk may offer new insights into the common neurobiological mechanisms underlying epilepsy and the complex cognitive and behavioral comorbidities that are characteristic of the spectrum of mTOR-associated neurodevelopmental disorders. This review will focus on the role of glial dysfunction, the interaction between glia related to mTOR hyperactivity, and its contribution to epileptogenesis in TSC. Moreover, we will discuss how understanding glial abnormalities in TSC might give valuable insight into the pathophysiological mechanisms that could help to develop novel therapeutic approaches for TSC or other pathologies characterized by glial dysfunction and acquired mTOR hyperactivation.

The analgesic effects of pioglitazone in the bone cancer pain rats via regulating the PPARγ/PTEN/mTOR signaling pathway in the spinal dorsal horn

BACKGROUND AND OBJECTIVES

Bone cancer pain (BCP) remains a difficult clinical problem. This study examined whether pioglitazone, a peroxisome proliferator-activated receptor gamma (PPARγ) agonist, is effective for attenuating BCP, and investigated the interaction between activation of PPARγ and phosphatase and tensin homolog deleted from chromosome 10 (PTEN) / mammalian target of rapamycin (mTOR) signal in the spinal dorsal horn (SDH) of BCP rats.

METHODS

We tested the effects of intrathecal (i.t.) injection of adenovirus-mediated PTEN (Ad-PTEN), PTEN antisense oligonucleotide (Ad-antisense PTEN), mTOR inhibitor rapamycin, pioglitazone and PPARγ antagonist GW9662 on bone cancer-induced mechanical allodynia by measuring the paw withdrawal threshold (PWT). Western blot or immunofluorescence examined the expression of spinal PPARγ, PTEN, mTOR, p-mTOR and p-S6K1.

RESULTS

Bone cancer did not alter total mTOR expression but caused significant downregulation of PTEN and upregulation of p-mTOR and p-S6K1 in spinal neurons. Rapamycin markedly reduced BCP. Upregulation of spinal PTEN by i.t. Ad-PTEN significantly relieved BCP and downregulated p-mTOR and p-S6K1; while i.t. Ad-antisense PTEN led to the opposite effects of Ad-PTEN. Spinal PPARγ expression increased in BCP rats, co-localizing mainly with neurons and a few astrocytes, but not in microglia. Pioglitazone (500 μg/day i.t. for one week, from 7 days after surgery) attenuated BCP, further increased expression of PPARγ, and inhibited downregulation of PTEN and upregulation of p-mTOR and p-S6K1 in the SDH. Pioglitazone's analgesic effect was enhanced by Ad-PTEN and attenuated by Ad-antisense PTEN. Blockade of PPARγ with GW9662 (300 μg i.t. 15 min prior to pioglitazone) reversed the effects of pioglitazone on BCP and regulations of PPARγ/PTEN/mTOR signal.

CONCLUSIONS

Intrathecal pioglitazone administration alleviates BCP by regulating the PPARγ/PTEN/mTOR signal in the SDH. Our data provided new insight in the therapeutic strategy in BCP management.

Niacin inhibits the synthesis of milk fat in BMECs through the GPR109A-mediated downstream signalling pathway

AIMS

Previous studies have shown the effect of niacin on dairy cow production, but no study on the role of niacin in milk fat synthesis has been performed. Therefore, the purpose of this study was to examine the effect of niacin on milk fat synthesis and its specific mechanism in BMECs.

MAIN METHODS

In this study, 0.5 mM niacin, a GPR109A-inhibiting plasmid, and an AMPK inhibitor were added to BMECs. Milk fat was measured by a triglyceride kit and BODIPY staining. The protein expression of GPR109A, FASN, SREBP1, AMPK, ACC, mTOR and S6K was measured by Western blotting. The gene expression of GPR109A, FASN, and SREBP1 was analysed by RT-PCR.

KEY FINDINGS

Our results showed that 0.5 mM niacin could significantly reduce milk fat synthesis in BMECs and activate the AMPK/ACC signalling pathway by stimulating GPR109A, reducing the protein expression of p-mTOR and p-S6K, and reducing the expression of SREBP1 and FASN in BMECs.

SIGNIFICANCE

The present study clarified the effect of niacin on milk fat synthesis. The results show that niacin inhibits the synthesis of milk fat in BMECs through the downstream signalling pathway mediated by GPR109A. The function of niacin has been expanded, and knowledge of the new mechanism and signalling pathway will help improve the biosynthesis of milk fat.

Novel brain permeant mTORC1/2 inhibitors are as efficacious as rapamycin or everolimus in mouse models of acquired partial epilepsy and tuberous sclerosis complex

Mechanistic target of rapamycin (mTOR) regulates cell proliferation, growth and survival, and is activated in cancer and neurological disorders, including epilepsy. The rapamycin derivative ("rapalog") everolimus, which allosterically inhibits the mTOR pathway, is approved for the treatment of partial epilepsy with spontaneous recurrent seizures (SRS) in individuals with tuberous sclerosis complex (TSC). In contrast to the efficacy in TSC, the efficacy of rapalogs on SRS in other types of epilepsy is equivocal. Furthermore, rapalogs only poorly penetrate into the brain and are associated with peripheral adverse effects, which may compromise their therapeutic efficacy. Here we compare the antiseizure efficacy of two novel, brain-permeable ATP-competitive and selective mTORC1/2 inhibitors, PQR620 and PQR626, and the selective dual pan-PI3K/mTORC1/2 inhibitor PQR530 in two mouse models of chronic epilepsy with SRS, the intrahippocampal kainate (IHK) mouse model of acquired temporal lobe epilepsy and Tsc1^GFAP CKO mice, a well-characterized mouse model of epilepsy in TSC. During prolonged treatment of IHK mice with rapamycin, everolimus, PQR620, PQR626, or PQR530; only PQR620 exerted a transient antiseizure effect on SRS, at well tolerated doses whereas the other compounds were ineffective. In contrast, all of the examined compounds markedly suppressed SRS in Tsc1^GFAP CKO mice during chronic treatment at well tolerated doses. Thus, against our expectation, no clear differences in antiseizure efficacy were found across the three classes of mTOR inhibitors examined in mouse models of genetic and acquired epilepsies. The main advantage of the novel 1,3,5-triazine derivatives is their excellent tolerability compared to rapalogs, which would favor their development as new therapies for TORopathies such as TSC.

Vascular endothelial growth factor receptor-3 regulates astroglial glutamate transporter-1 expression via mTOR activation in reactive astrocytes following pilocarpine-induced status epilepticus

Recent evidence has shown that the vascular endothelial growth factor (VEGF) system plays a crucial role in several neuropathological processes. We previously reported an upregulation of VEGF-C and its receptor, VEGFR-3, in reactive astrocytes after the onset of status epilepticus (SE). However, it remains unknown, which molecules act as downstream signals following VEGFR-3 upregulation, and are involved in reactive astrogliosis after SE. Therefore, we investigated whether VEGFR-3 upregulation within reactive astrocytes is associated with the activation of mammalian target of rapamycin (mTOR) signaling, which we confirmed by assaying for the phosphorylated form of S6 protein (pS6), and whether VEGFR-3-mediated mTOR activation induces astroglial glutamate transporter-1 (GLT-1) expression in the hippocampus after pilocarpine-induced SE. We found that spatiotemporal expression of pS6 was consistent with VEGFR-3 expression in the hippocampus after SE, and that both pS6 and VEGFR-3 were highly expressed in SE-induced reactive astrocytes. Treatment with the mTOR inhibitor rapamycin decreased astroglial VEGFR-3 expression and GLT-1 expression after SE. Treatment with a selective inhibitor for VEGFR-3 attenuated astroglial pS6 expression as well as suppressed GLT-1 expression and astroglial reactivity in the hippocampus after SE. These findings demonstrate that VEGFR-3-mediated mTOR activation could contribute to the regulation of GLT-1 expression in reactive astrocytes during the subacute phase of epilepsy. In conclusion, the present study suggests that VEGFR-3 upregulation in reactive astrocytes may play a role in preventing hyperexcitability induced by continued seizure activity.

RAB39B's role in membrane traffic, autophagy, and associated neuropathology

Neuropathological disorders are increasingly associated with dysfunctions in neuronal membrane traffic and autophagy, with defects among members of the Rab family of small GTPases implicated. Mutations in the human Xq28 localized gene RAB39B have been associated with X-linked neurodevelopmental defects including macrocephaly, intellectual disability, autism spectrum disorder (ASD), as well as rare cases of early-onset Parkinson's disease (PD). Despite the finding that RAB39B regulates GluA2 trafficking and could thus influence synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit composition, reasons for the wide-ranging neuropathological consequences associated with RAB39B defects have been unclear. Recent studies have now unraveled possible mechanisms underlying the neuropathological roles of this brain-enriched small GTPase. Studies in RAB39B knockout mice showed that RAB39B interacts with components of Class I phosphatidylinositol-3-kinase (PI3K) signaling. In its absence, the PI3K-AKT-mechanistic target of rapamycin signaling pathway in neural progenitor cells (NPCs) is hyperactivated, which promotes NPC proliferation, leading to macrocephaly and ASD. Pertaining to early-onset PD, a complex of C9orf72, Smith-Magenis syndrome chromosome region candidate 8 and WD repeat domain 41 that functions in autophagy has been identified as a guanine nucleotide exchange factor of RAB39B. Here, recent findings that have shed light on our mechanistic understanding of RAB39B's role in neurodevelopmental and neurodegenerative pathologies are reviewed. Caveats and unanswered questions are also discussed, and future perspectives outlined.

BVR-A Deficiency Leads to Autophagy Impairment through the Dysregulation of AMPK/mTOR Axis in the Brain-Implications for Neurodegeneration

Biliverdin reductase-A (BVR-A) impairment is associated with increased accumulation of oxidatively-damaged proteins along with the impairment of autophagy in the brain during neurodegenerative disorders. Reduced autophagy inhibits the clearance of misfolded proteins, which then form neurotoxic aggregates promoting neuronal death. The aim of our study was to clarify the role for BVR-A in the regulation of the mTOR/autophagy axis by evaluating age-associated changes (2, 6 and 11 months) in cerebral cortex samples collected from BVR-A knock-out (BVR-A^−/−) and wild-type (WT) mice. Our results show that BVR-A deficiency leads to the accumulation of oxidatively-damaged proteins along with mTOR hyper-activation in the cortex. This process starts in juvenile mice and persists with aging. mTOR hyper-activation is associated with the impairment of autophagy as highlighted by reduced levels of Beclin-1, LC3β, LC3II/I ratio, Atg5–Atg12 complex and Atg7 in the cortex of BVR-A^−/− mice. Furthermore, we have identified the dysregulation of AMP-activated protein kinase (AMPK) as a critical event driving mTOR hyper-activation in the absence of BVR-A. Overall, our results suggest that BVR-A is a new player in the regulation of autophagy, which may be targeted to arrive at novel therapeutics for diseases involving impaired autophagy.

Haploinsufficiency of Tsc2 Leads to Hyperexcitability of Medial Prefrontal Cortex via Weakening of Tonic GABAB Receptor-mediated Inhibition

Loss-of-function mutation in one of the tumor suppressor genes TSC1 or TSC2 is associated with several neurological and psychiatric diseases, including autism spectrum disorders (ASDs). As an imbalance between excitatory and inhibitory neurotransmission, E/I ratio is believed to contribute to the development of these disorders, we investigated synaptic transmission during the first postnatal month using the Tsc2+/- mouse model. Electrophysiological recordings were performed in acute brain slices of medial prefrontal cortex. E/I ratio at postnatal day (P) 15-19 is increased in Tsc2+/- mice as compared with wildtype (WT). At P25-30, facilitated GABAergic transmission reduces E/I ratio to the WT level, but weakening of tonic GABAB receptor (GABABR)-mediated inhibition in Tsc2+/- mice leads to hyperexcitability both at single cell and neuronal network level. Short (1 h) preincubation of P25-30 Tsc2+/- slices with baclofen restores the GABABR-mediated inhibition and reduces network excitability. Interestingly, the same treatment at P15-19 leads to weakening of GABABR-mediated inhibition. We hypothesize that a dysfunction of tonic GABABR-mediated inhibition might contribute to the development of ASD symptoms and suggest that GABABR activation within an appropriate time window may be considered as a therapeutic target in ASD.

PI3K isoform-selective inhibition in neuron-specific PTEN-deficient mice rescues molecular defects and reduces epilepsy-associated phenotypes

Epilepsy affects all ages, races, genders, and socioeconomic groups. In about one third of patients, epilepsy is uncontrolled with current medications, leaving a vast need for improved therapies. The causes of epilepsy are diverse and not always known but one gene mutated in a small subpopulation of patients is phosphatase and tensin homolog (PTEN). Moreover, focal cortical dysplasia, which constitutes a large fraction of refractory epilepsies, has been associated with signaling defects downstream of PTEN. So far, most preclinical attempts to reverse PTEN deficiency-associated neurological deficits have focused on mTOR, a signaling hub several steps downstream of PTEN. Phosphoinositide 3-kinases (PI3Ks), by contrast, are the direct enzymatic counteractors of PTEN, and thus may be alternative treatment targets. PI3K activity is mediated by four different PI3K catalytic isoforms. Studies in cancer, where PTEN is commonly mutated, have demonstrated that inhibition of only one isoform, p110β, reduces progression of PTEN-deficient tumors. Importantly, inhibition of a single PI3K isoform leaves critical functions of general PI3K signaling throughout the body intact. Here, we show that this disease mechanism-targeted strategy borrowed from cancer research rescues or ameliorates neuronal phenotypes in male and female mice with neuron-specific PTEN deficiency. These phenotypes include cell signaling defects, protein synthesis aberrations, seizures, and cortical dysplasia. Of note, p110β is also dysregulated and a promising treatment target in the intellectual disability Fragile X syndrome, pointing towards a shared biological mechanism that is therapeutically targetable in neurodevelopmental disorders of different etiologies. Overall, this work advocates for further assessment of p110β inhibition not only in PTEN deficiency-associated neurodevelopmental diseases but also other brain disorders characterized by defects in the PI3K/mTOR pathway.

mTORC1 and mTORC2 expression in inner retinal neurons and glial cells

The retina is one of the most metabolically active tissues, yet the processes that control retinal metabolism remains poorly understood. The mTOR complex (mTORC) that drives protein and lipid biogenesis and autophagy has been studied extensively in regards to retinal development and responses to optic nerve injury but the processes that regulate homeostasis in the adult retina have not been determined. We previously demonstrated that normal adult retina has high rates of protein synthesis compared to skeletal muscle, associated with high levels of mechanistic target of rapamycin (mTOR), a kinase that forms multi-subunit complexes that sense and integrate diverse environmental cues to control cell and tissue physiology. This study was undertaken to: 1) quantify expression of mTOR complex 1 (mTORC1)- and mTORC2-specific partner proteins in normal adult rat retina, brain and liver; and 2) to localize these components in normal human, rat, and mouse retinas. Immunoblotting and immunoprecipitation studies revealed greater expression of raptor (exclusive to mTORC1) and rictor (exclusive for mTORC2) in normal rat retina relative to liver or brain, as well as the activating mTORC components, pSIN1 and pPRAS40. By contrast, liver exhibits greater amounts of the mTORC inhibitor, DEPTOR. Immunolocalization studies for all three species showed that mTOR, raptor, and rictor, as well as most other known components of mTORC1 and mTORC2, were primarily localized in the inner retina with mTORC1 primarily in retinal ganglion cells (RGCs) and mTORC2 primarily in glial cells. In addition, phosphorylated ribosomal protein S6, a direct target of the mTORC1 substrate ribosomal protein S6 kinase beta-1 (S6K1), was readily detectable in RGCs, indicating active mTORC1 signaling, and was preserved in human donor eyes. Collectively, this study demonstrates that the inner retina expresses high levels of mTORC1 and mTORC2 and possesses active mTORC1 signaling that may provide cell- and tissue-specific regulation of homeostatic activity. These findings help to define the physiology of the inner retina, which is key for understanding the pathophysiology of optic neuropathies, glaucoma and diabetic retinopathy.

Ultrasound Stimulation Increases Neurite Regeneration in Injured Dorsal Root Ganglion Neurons through Mammalian Target of Rapamycin Activation

Ultrasound stimulation (US) is reported to be a safe and useful technology for improving injured nerve regeneration. However, the intracellular mechanisms underlying its stimulatory effects are only partially understood. Mammalian target of rapamycin (mTOR) signaling is involved in neuronal survival and axonal outgrowth. In this study, we investigated the effect of US on regeneration of injured dorsal root ganglion (DRG) neurons and activation of the mTOR pathway. We showed that US significantly increased neurite regeneration and enhanced mTOR activation. Moreover, the expression of growth-associated protein-43 (GAP-43), a crucial factor for axonal outgrowth and regeneration in neurons, was significantly increased by US. These data suggest that US-induced neurite regeneration is mediated by upregulation of mTOR activity, which promotes the regeneration of injured DRG neurons.

Energy-Sensing Pathways in Ischemia: The Counterbalance Between AMPK and mTORC

Stroke is an important cause of death and disability, and it is the second leading cause of death worldwide. In humans, middle cerebral artery occlusion (MCAO) is the most common cause of ischemic stroke. The damage occurs due to the lack of nutrients and oxygen contributed by the blood flow. The present review aims to analyze to what extent the lack of each of the elements of the system leads to damage and which mechanisms are unaffected by this deficiency. We believe that the specific analysis of the effect of lack of each component could lead to the emergence of new therapeutic targets for this important brain pathology.

The effect of intrauterine inflammation on mTOR signaling in mouse fetal brain

Fetuses exposed to an inflammatory environment are predisposed to long-term adverse neurological outcomes. However, the mechanism by which intrauterine inflammation (IUI) is responsible for abnormal fetal brain development is not fully understood. The mechanistic target of rapamycin (mTOR) signaling pathway is closely associated with fetal brain development. We hypothesized that mTOR signaling might be involved in fetal brain injury and malformation when fetuses are exposed to the IUI environment. A well-established IUI model was utilized by intrauterine injection of lipopolysaccharide (LPS) to explore the effect of IUI on mTOR signaling in mouse fetal brains. We found that microglia activation in LPS fetal brains was increased, as demonstrated by elevated Iba-1 protein level and immunofluorescence density. LPS fetal brains also showed reduced neuronal cell counts, decreased cell proliferation demonstrated by low Ki67-positive density, and elevated neuron apoptosis evidenced by high expression of cleaved Caspase 3. Furthermore, we found that mTOR signaling in LPS fetal brains was elevated at 2 hr after LPS treatment, declined at 6 hr and showed overall inhibition at 24 hr. In summary, our study revealed that LPS-induced IUI leads to increased activation of microglia cells, neuronal damage, and dynamic alterations in mTOR signaling in the mouse fetal brain. Our findings indicate that abnormal changes in mTOR signaling may underlie the development of future neurological complications in offspring exposed to prenatal IUI.

Clioquinol improves motor and non-motor deficits in MPTP-induced monkey model of Parkinson's disease through AKT/mTOR pathway

Despite decades of research into the pathology mechanisms of Parkinson’s disease (PD), disease-modifying therapy of PD is scarce. Thus, searching for new drugs or more effective neurosurgical treatments has elicited much interest. Clioquinol (CQ) has been shown to have therapeutic benefits in rodent models of neurodegenerative disorders. However, it’s neuroprotective role and mechanisms in PD primate models and PD patients, especially in the advanced stages, are not fully understood. Furthermore, issues such as spontaneous recovery of motor function and high symptom variability in different monkeys after the same toxic protocol, has not been resolved before the present study. In this study, we designed a chronic and long-term progressive protocol to generate a stabilized PD monkey model showed with classic motor and non-motor deficits, followed by treatment analysis of CQ. We found that CQ could remarkably improve the motor and non-motor deficits, which were based on the reduction of iron content and ROS level in the SN and further improvement in pathology. Meanwhile, we also showed that ferroptosis was probably involved in the pathogenesis of PD. In addition, the study shows a positive effect of CQ on AKT/mTOR survival pathway and a blocking effect on p53 medicated cell death in vivo and in vitro.

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.

Deep Brain Stimulation Improves Motor Function in Rats with Spinal Cord Injury by Increasing Synaptic Plasticity

OBJECTIVE

To investigate the effect of deep brain stimulation (DBS) on rats with spinal cord injury (SCI) and its possible molecular mechanism.

METHODS

A rat SCI model was prepared using a modified Allen method. The animals were randomly divided into 3 groups (n = 12 per group): the sham group, the SCI group, and the SCI + DBS group. Then, DBS was applied to the rats in the SCI + DBS group for half an hour per day for 4 weeks. Basso, Beattie, and Bresnahan scores were used to assess spinal function.

RESULTS

DBS significantly improved hindlimb motor function in SCI rats, and the protein expression levels of brain-derived neurotrophic factor, the mammalian target of rapamycin, tropomyosin-related kinase B, protein kinase B, p70 ribosomal S6 protein kinase, postsynaptic density protein 95, and synaptophysin increased correspondingly.

CONCLUSIONS

DBS improves motor function in rats with SCI by increasing synaptic plasticity via tropomyosin-related kinase B-protein kinase B-mammalian target of rapamycin pathway.

Early 5-HT6 receptor blockade prevents symptom onset in a model of adolescent cannabis abuse

Cannabis abuse during adolescence confers an increased risk for developing later in life cognitive deficits reminiscent of those observed in schizophrenia, suggesting common pathological mechanisms that remain poorly characterized. In line with previous findings that revealed a role of 5-HT6 receptor-operated mTOR activation in cognitive deficits of rodent developmental models of schizophrenia, we show that chronic administration of ∆9-tetrahydrocannabinol (THC) to mice during adolescence induces a long-lasting activation of mTOR in prefrontal cortex (PFC), alterations of excitatory/inhibitory balance, intrinsic properties of layer V pyramidal neurons, and long-term depression, as well as cognitive deficits in adulthood. All are prevented by administrating a 5-HT6 receptor antagonist or rapamycin, during adolescence. In contrast, they are still present 2 weeks after the same treatments delivered at the adult stage. Collectively, these findings suggest a role of 5-HT6 receptor-operated mTOR signaling in abnormalities of cortical network wiring elicited by THC at a critical period of PFC maturation and highlight the potential of 5-HT6 receptor antagonists as early therapy to prevent cognitive symptom onset in adolescent cannabis abusers.

PHF23 negatively regulates the autophagy of chondrocytes in osteoarthritis

AIM

Osteoarthritis (OA) is the main cause of disability and joint replacement surgery in the elderly. As a crucial cell survival mechanism, autophagy has been reported to decrease in OA. PHF23 is a new autophagy inhibitor which was first reported by us previously. This study aimed to explore the anti-autophagic mechanism of PHF23 to make it a possible therapeutic target of OA.

MAIN METHOD

Lentiviral vectors specific to PHF23 were used on chondrocytes (C28/I2) to establish PHF23 overexpressed or knockdown stable cell strains. Interleukin (IL)-1β (10 ng/mL) and chloroquine (CQ, 25 uM) were used as an inducer of OA and inhibitor of lysosome, respectively. Autophagy was evaluated by autophagosome formation using transmission electron microscopy (TEM) and western blot analysis of P62 and LC3B on different groups of cells. Effects of PHF23 on OA were evaluated by collagen II immunofluorescent staining and western blot analysis of OA-associated proteins MMP13 and ADAMTS5. Effects of PHF23 on AMPK and mTOR/S6K pathways and mitophagy were determined by western blot analysis.

KEY FINDINGS

Knockdown of PHF23 enhanced IL-1β-induced autophagy, while overexpression of PHF23 exerted the opposite effect. Knockdown of PHF23 protected chondrocytes against IL-1β-induced OA by decreasing the levels of OA-associated proteins and increasing expression of Collagen II. Knockdown of PHF23 also increased mitophagy level and altered the phosphorylation levels of AMPK, mTOR, and S6K.

SIGNIFICANCE

PHF23 downregulates autophagy, mitophagy in IL-1β-induced OA-like chondrocytes and alters the activities of AMPK and mTOR/S6K, which suggests that PHF23 may be a possible therapeutic target for OA.

An update on the central nervous system manifestations of tuberous sclerosis complex

The autosomal dominant disorder tuberous sclerosis complex (TSC) is characterized by an array of manifestations both within and outside of the central nervous system (CNS), including hamartomas and other malformations. TSC is caused by mutations in the TSC1 or TSC2 gene resulting in activation of the mechanistic target of rapamycin (mTOR) signaling pathway. Study of TSC has shed light on the critical role of the mTOR pathway in neurodevelopment. This update reviews the genetic basis of TSC, its cardinal phenotypic CNS features, and recent developments in the field of TSC and other mTOR-altered disorders.

G-CSF attenuates neuroinflammation and neuronal apoptosis via the mTOR/p70SK6 signaling pathway in neonatal Hypoxia-Ischemia rat model

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is an important cause of permanent damage to the central nervous system, associated with long-lasting neurological disabilities and neurodevelopmental impairment in neonates. Granulocyte-colony stimulating factor (G-CSF) has been shown to have neuroprotective activity in a variety of experimental brain injury models and G-CSF is a standard treatment in chemotherapeutic-induced neutropenia. The underlying mechanisms are still unclear. The mTOR (mammalian target of rapamycin) signaling pathway is a master regulator of cell growth and proliferation in the nervous system. However, the effects of G-CSF treatment on the mTOR signaling pathway have not been elucidated in neonates with hypoxic-ischemic (HI) brain injury. Our study investigated the neuroprotective effect of G-CSF on neonates with hypoxic-ischemic (HI) brain injury and the possible mechanism involving the mTOR/p70S6K pathway.

METHODS

Sprague-Dawley rat pups at postnatal day 7 (P7) were subjected to right unilateral carotid artery ligation followed by hypoxic (8% oxygen and balanced nitrogen) exposure for 2.5 h or sham surgery. Pups received normal saline, G-CSF, G-CSF combined with rapamycin or ethanol (vehicle for rapamycin) intraperitoneally. On postnatal day 9 (P9), TTC staining for infarct volume, and Nissl and TUNEL staining for neuronal cell injury were conducted. Activation of mTOR/p70S6K pathway, cleaved caspase-3 (CC3), Bax and Bcl-2 and cytokine expression levels were determined by western blotting.

RESULTS

The G-CSF treated group was associated with significantly reduced infarction volume and decreased TUNEL positive neuronal cells compared to the HI group treated with saline. The expression levels of TNF-α and IL-1ß were significantly decreased in the G-CSF treated group, while IL-10 expression level was increased. The relative immunoreactivity of p-mTOR and p-p70S6K was significantly reduced in the HI group compared to sham. The HI group treated with G-CSF showed significant upregulated protein expression for p-mTOR and p-p70S6K levels compared to the HI group treated with saline. Furthermore, G-CSF treatment increased Bcl-2 expression levels and decreased CC3 and Bax expression levels in the ipsilateral hemispheres of the HI brain. The effects induced by G-CSF were all reversed by rapamycin.

CONCLUSION

Treatment with G-CSF decreases inflammatory mediators and apoptotic factors, attenuating neuroinflammation and neuronal apoptosis via the mTOR/p70S6K signalling pathway, which represents a potential target for treating HI induced brain damage in neonatal HIE.

Pathological mTOR mutations impact cortical development

Several mosaic mutations of the mammalian/mechanistic target of rapamycin (mTOR) have recently been found in patients with cortical malformations, such as hemimegalencephaly (HME) and focal cortical dysplasia (FCD). Although all of them should activate mTOR signaling, comparisons of the impact of different mTOR mutations on brain development have been lacking. Also it remains unknown if any potential differences these mutations may have on cortical development are directly related to a degree of mTOR signaling increase. The present study assessed levels of mTORC1 pathway activity in cell lines and rat primary neurons overexpressing several mTOR mutants that were previously found in HME, FCD, cancer patients and in vitro mutagenesis screens. Next we introduced the mutants, enhancing mTORC1 signaling most potently, into developing mouse brains and assessed electroporated cell morphology and migratory phenotype using immunofluorescent staining. We observed the differential inhibition of neuronal progenitor cortical migration, which partly corresponded with a degree of mTORC1 signaling enhancement these mutants induced in cultured cells. The most potent quadruple mutant prevented most of the progenitors from entering the cortical plate. Cells that expressed less potent, single-point, mTOR mutants entered the cortical plate but failed to reach its upper layers and had enlarged soma. Our findings suggest a correlation between the potency of mTOR mutation to activate mTORC1 pathway and disruption of cortical migration.

Crosstalk between the mTOR and Nrf2/ARE signaling pathways as a target in the improvement of long-term potentiation

In recent years, a significant progress was made in understanding molecular mechanisms of long-term memory. Long-term memory formation requires strengthening of neuronal connections (LTP, long-term potentiation) associated with structural rearrangement of neurons. The key role in the synthesis of proteins essential for these rearrangements belong to mTOR (mammalian target of rapamycin) complexes and signaling pathways involved in mTOR regulation. Suppression of mTOR activity may impair synaptic plasticity and long-term memory, while mTOR activation inhibits autophagy, thereby potentiating amyloidosis and development of Alzheimer's disease (AD) accompanied by irreversible memory loss. Because of this, suppression/inhibition of mTOR might have unpredictable consequences on memory. The Nrf2/ARE signaling pathway affects almost all mitochondrial processes. The activation of this pathway improves memory and exhibits therapeutic effect in AD. In this review, we discuss the crosstalk between the Nrf2/ARE signaling and mTOR in the maintenance of synaptic plasticity. Nrf2 pathway can be activated by pharmacological agents and by changes in mitochondria functioning accompanying various neuronal dysfunctions.

Chronic mTORC1 inhibition rescues behavioral and biochemical deficits resulting from neuronal Depdc5 loss in mice

DEPDC5 is now recognized as one of the genes most often implicated in familial/inherited focal epilepsy and brain malformations. Individuals with pathogenic variants in DEPDC5 are at risk for epilepsy, associated neuropsychiatric comorbidities and sudden unexplained death in epilepsy. Depdc5flox/flox-Syn1Cre (Depdc5cc+) neuronal-specific Depdc5 knockout mice exhibit seizures and neuronal mTORC1 hyperactivation. It is not known if Depdc5cc+ mice have a hyperactivity/anxiety phenotype, die early from terminal seizures or whether mTOR inhibitors rescue DEPDC5-related seizures and associated comorbidities. Herein, we report that Depdc5cc+ mice were hyperactive in open-field testing but did not display anxiety-like behaviors on the elevated-plus maze. Unlike many other mTOR-related models, Depdc5cc+ mice had minimal epileptiform activity and rare seizures prior to seizure-induced death, as confirmed by video-EEG monitoring. Treatment with the mTORC1 inhibitor rapamycin starting after 3 weeks of age significantly prolonged the survival of Depdc5cc+ mice and partially rescued the behavioral hyperactivity. Rapamycin decreased the enlarged brain size of Depdc5cc+ mice with corresponding decrease in neuronal soma size. Loss of Depdc5 led to a decrease in the other GATOR1 protein levels (NPRL2 and NPRL3). Rapamycin failed to rescue GATOR1 protein levels but rather rescued downstream mTORC1 hyperactivity as measured by phosphorylation of S6. Collectively, our data provide the first evidence of behavioral alterations in mice with Depdc5 loss and support mTOR inhibition as a rational therapeutic strategy for DEPDC5-related epilepsy in humans.

Repurposed molecules for antiepileptogenesis: Missing an opportunity to prevent epilepsy?

Prevention of epilepsy is a great unmet need. Acute central nervous system (CNS) insults such as traumatic brain injury (TBI), cerebrovascular accidents (CVA), and CNS infections account for 15%-20% of all epilepsy. Following TBI and CVA, there is a latency of days to years before epilepsy develops. This allows treatment to prevent or modify postinjury epilepsy. No such treatment exists. In animal models of acquired epilepsy, a number of medications in clinical use for diverse indications have been shown to have antiepileptogenic or disease-modifying effects, including medications with excellent side effect profiles. These include atorvastatin, ceftriaxone, losartan, isoflurane, N-acetylcysteine, and the antiseizure medications levetiracetam, brivaracetam, topiramate, gabapentin, pregabalin, vigabatrin, and eslicarbazepine acetate. In addition, there are preclinical antiepileptogenic data for anakinra, rapamycin, fingolimod, and erythropoietin, although these medications have potential for more serious side effects. However, except for vigabatrin, there have been almost no translation studies to prevent or modify epilepsy using these potentially "repurposable" medications. We may be missing an opportunity to develop preventive treatment for epilepsy by not evaluating these medications clinically. One reason for the lack of translation studies is that the preclinical data for most of these medications are disparate in terms of types of injury, models within different injury type, dosing, injury-treatment initiation latencies, treatment duration, and epilepsy outcome evaluation mode and duration. This makes it difficult to compare the relative strength of antiepileptogenic evidence across the molecules, and difficult to determine which drug(s) would be the best to evaluate clinically. Furthermore, most preclinical antiepileptogenic studies lack information needed for translation, such as dose-blood level relationship, brain target engagement, and dose-response, and many use treatment parameters that cannot be applied clinically, for example, treatment initiation before or at the time of injury and dosing higher than tolerated human equivalent dosing. Here, we review animal and human antiepileptogenic evidence for these medications. We highlight the gaps in our knowledge for each molecule that need to be filled in order to consider clinical translation, and we suggest a platform of preclinical antiepileptogenesis evaluation of potentially repurposable molecules or their combinations going forward.

Caffeine Potentiates Ethanol-Induced Neurotoxicity Through mTOR/p70S6K/4E-BP1 Inhibition in SH-SY5Y Cells

Caffeine is a popular psychostimulant, which is frequently consumed with ethanol. However, the effects of caffeine on neuronal cells constantly exposed to ethanol have not been investigated. Apoptosis and oxidative stress occurring in ethanol-induced neurotoxicity were previously associated with decreased phosphorylation of the mTOR/p70S6K/4E-BP1 signaling proteins. Evidence also suggested that caffeine inhibits the mTOR pathway. In this study, human SH-SY5Y neuroblastoma cells were exposed to caffeine after pretreatment for 24 hours with ethanol. Results indicated that both ethanol and caffeine caused neuronal cell death in a dose- and time-dependent manner. Exposure to 20-mM caffeine for 24 hours magnified reduced cell viability and enhanced apoptotic cell death induced by 200 mM of ethanol pretreatment. The phosphorylation of mTOR, p70S6K, and 4E-BP1 markedly decreased in cells exposed to caffeine after ethanol pretreatment, associated with a decrease of the mitochondrial membrane potential (ΔΨm). These findings suggested that caffeine treatment after neuronal cells were exposed to ethanol resulted in marked cell damages, mediated through enhanced inhibition of mTOR/p70S6K/4E-BP1 signaling leading to impaired ΔΨm and, eventually, apoptotic cell death.