Downregulation of the Repressor Element 1-Silencing Transcription Factor (REST) Is Associated with Akt-mTOR and Wnt-β-Catenin Signaling in Prion Diseases Models

Lipopolysaccharides from Porphyromonas gingivalis indirectly induce neuronal GSK3β-dependent synaptic defects and cause cognitive decline in a low-amyloid-β-concentration environment in Alzheimer's disease

BackgroundLipopolysaccharides from Porphyromonas gingivalis (P.gLPS) are involved in the pathology of Alzheimer's disease (AD). However, the effect of P.gLPS on synaptic defects remains unclear.ObjectiveIn this study, we tested our hypothesis that P.gLPS induces synaptic defects in a low-amyloid-beta (Aβ)-concentration environment.MethodsMG6 microglia or N2a neurons was treated with P.gLPS (0.1 μg/mL), soluble Aβ42 (0.1 μM) or AL (combined P.gLPS and soluble Aβ42 at 0.1 μM).ResultsIn cultured MG6 microglia, increased the mRNA expression of TNF-α, IL-1β and IL-6 and the TNF-α release in parallel with increased NF-κB activation. In cultured N2a neurons, treatment with Aβ42, P.gLPS, and AL did not affect the mRNA expression of synapsin1 (SYN1) or post-synaptic density protein-95 (PSD-95). However, the treatment with conditioned medium from AL-exposed MG6 microglia (AL-MCM) significantly reduced the mRNA and protein expression of SYN1, PSD-95, and nuclear translocation of repressor element-1 silencing transcription factor (REST) but significantly increased the mRNA expression of TNF receptor type I (at 48 h) and glycogen synthase kinase (GSK)3β (at 24 h). TWS119 pretreatment (5 μM), a GSK3β specific inhibitor, significantly reversed the AL-MCM-induced reduction in the mRNA expression of SYN1 and PSD-95 and nuclear translocation of REST in cultured N2a neurons. In APPNL-F/NL-F mice, the immunofluorescence intensity of SYN1 and PSD-95 in cortical neurons was positively correlated with the index of the memory test but negatively correlated with that of TNF-α-positive microglia.ConclusionsThese observations demonstrate that P.gLPS induces neuronal GSK3β-dependent synaptic defects in a low-Aβ concentration environment via microglial activation.

REST and RCOR genes display distinct expression profiles in neurons and astrocytes using 2D and 3D human pluripotent stem cell models

Repressor element-1 silencing transcription factor (REST) is a transcriptional repressor involved in neurodevelopment and neuroprotection. REST forms a complex with the REST corepressors, CoREST1, CoREST2, or CoREST3 (encoded by RCOR1, RCOR2, and RCOR3, respectively). Emerging evidence suggests that the CoREST family can target unique genes independently of REST, in various neural and glial cell types during different developmental stages. However, there is limited knowledge regarding the expression and function of the CoREST family in human neurodevelopment. To address this gap, we employed 2D and 3D human pluripotent stem cell (hPSC) models to investigate REST and RCOR gene expression levels. Our study revealed a significant increase in RCOR3 expression in glutamatergic cortical and GABAergic ventral forebrain neurons, as well as mature functional NGN2-induced neurons. Additionally, a simplified astrocyte transdifferentiation protocol resulted in a significant decrease in RCOR2 expression following differentiation. REST expression was notably reduced in mature neurons and cerebral organoids. In summary, our findings provide the first insights into the cell-type-specific expression patterns of RCOR genes in human neuronal and glial differentiation. Specifically, RCOR3 expression increases in neurons, while RCOR2 levels decrease in astrocytes. The dynamic expression patterns of REST and RCOR genes during hPSC neuronal and glial differentiation underscore the potential distinct roles played by REST and CoREST proteins in regulating the development of these cell types in humans.

PHB2 Alleviates Neurotoxicity of Prion Peptide PrP106-126 via PINK1/Parkin-Dependent Mitophagy

Prion diseases are a group of neurodegenerative diseases characterized by mitochondrial dysfunction and neuronal death. Mitophagy is a selective form of macroautophagy that clears injured mitochondria. Prohibitin 2 (PHB2) has been identified as a novel inner membrane mitophagy receptor that mediates mitophagy. However, the role of PHB2 in prion diseases remains unclear. In this study, we isolated primary cortical neurons from rats and used the neurotoxic prion peptide PrP106-126 as a cell model for prion diseases. We examined the role of PHB2 in PrP106-126-induced mitophagy using Western blotting and immunofluorescence microscopy and assessed the function of PHB2 in PrP106-126-induced neuronal death using the cell viability assay and the TUNEL assay. The results showed that PrP106-126 induced mitochondrial morphological abnormalities and mitophagy in primary cortical neurons. PHB2 was found to be indispensable for PrP106-126-induced mitophagy and was involved in the accumulation of PINK1 and recruitment of Parkin to mitochondria in primary neurons. Additionally, PHB2 depletion exacerbated neuronal cell death induced by PrP106-126, whereas the overexpression of PHB2 alleviated PrP106-126 neuronal toxicity. Taken together, this study demonstrated that PHB2 is indispensable for PINK1/Parkin-mediated mitophagy in PrP106-126-treated neurons and protects neurons against the neurotoxicity of the prion peptide.

Cardiolipin externalization mediates prion protein (PrP) peptide 106-126-associated mitophagy and mitochondrial dysfunction

Proper mitochondrial performance is imperative for the maintenance of normal neuronal function to prevent the development of neurodegenerative diseases. Persistent accumulation of damaged mitochondria plays a role in prion disease pathogenesis, which involves a chain of events that culminate in the generation of reactive oxygen species and neuronal death. Our previous studies have demonstrated that PINK1/Parkin-mediated mitophagy induced by PrP^106-126 is defective and leads to an accumulation of damaged mitochondria after PrP^106-126 treatment. Externalized cardiolipin (CL), a mitochondria-specific phospholipid, has been reported to play a role in mitophagy by directly interacting with LC3II at the outer mitochondrial membrane. The involvement of CL externalization in PrP^106-126-induced mitophagy and its significance in other physiological processes of N2a cells treated with PrP^106-126 remain unknown. We demonstrate that the PrP^106-126 peptide caused a temporal course of mitophagy in N2a cells, which gradually increased and subsequently decreased. A similar trend in CL externalization to the mitochondrial surface was seen, resulting in a gradual decrease in CL content at the cellular level. Inhibition of CL externalization by knockdown of CL synthase, responsible for de novo synthesis of CL, or phospholipid scramblase-3 and NDPK-D, responsible for CL translocation to the mitochondrial surface, significantly decreased PrP^106-126-induced mitophagy in N2a cells. Meanwhile, the inhibition of CL redistribution significantly decreased PINK1 and DRP1 recruitment in PrP^106-126 treatment but had no significant decrease in Parkin recruitment. Furthermore, the inhibition of CL externalization resulted in impaired oxidative phosphorylation and severe oxidative stress, which led to mitochondrial dysfunction. Our results indicate that CL externalization induced by PrP^106-126 on N2a cells plays a positive role in the initiation of mitophagy, leading to the stabilization of mitochondrial function.

Comprehensive Analysis of REST/NRSF Gene in Glioma and Its ceRNA Network Identification

We sought to clarify the clinical relationship between REST/NRSF expression and the prognosis of glioma and explore the REST-associated competitive endogenous RNA (ceRNA) network in glioma. We downloaded RNA-seq, miRNA-seq and correlated clinical data of 670 glioma patients from The Cancer Genome Atlas and analyzed the correlation between REST expression, clinical characteristics and prognosis. Differentially expressed genes (DEGs) were identified with DESeq2 and analyzed with Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) using the Profiler package. Starbase was used to explore the regulatory interaction between REST and miRNAs or LncRNAs. The lncRNA-miRNA-REST ceRNA network was constructed with Cytoscape. RT-qPCR, WB, CCK8, wound-healing, and luciferase assays were performed to validate the ceRNA network. Results showed that REST expression was significantly higher in glioma patients than normal samples. Higher REST expression was significantly associated with worse overall survival, progression-free interval, and worse disease-specific survival in glioma patients. The DEGs of mRNA, miRNA, and lncRNA were identified, and GO and KEGG enrichment analyses were performed. Finally, REST-associated ceRNA networks, including NR2F2-AS1-miR129-REST and HOTAIRM1-miR137-REST, were experimentally validated. Thus, REST may be a prognostic biomarker and therapeutic target in glioma, and its regulatory network validated in this study may provide insights into glioma's molecular regulatory mechanisms.

Human iPSC-Derived Neurons as A Platform for Deciphering the Mechanisms behind Brain Aging

With an increased life expectancy among humans, aging has recently emerged as a major focus in biomedical research. The lack of in vitro aging models-especially for neurological disorders, where access to human brain tissues is limited-has hampered the progress in studies on human brain aging and various age-associated neurodegenerative diseases at the cellular and molecular level. In this review, we provide an overview of age-related changes in the transcriptome, in signaling pathways, and in relation to epigenetic factors that occur in senescent neurons. Moreover, we explore the current cell models used to study neuronal aging in vitro, including immortalized cell lines, primary neuronal culture, neurons directly converted from fibroblasts (Fib-iNs), and iPSC-derived neurons (iPSC-iNs); we also discuss the advantages and limitations of these models. In addition, the key phenotypes associated with cellular senescence that have been observed by these models are compared. Finally, we focus on the potential of combining human iPSC-iNs with genome editing technology in order to further our understanding of brain aging and neurodegenerative diseases, and discuss the future directions and challenges in the field.

Repressor element 1 silencing transcription factor /neuron-restrictive silencing factor (REST/NRSF) in social stress and depression

Extreme stress is closely linked with symptoms of depression. Chronic social stress can cause structural and functional changes in the brain. These changes are associated with dysfunction of neuroprotective signalling that is necessary for cell survival, growth, and maturation. Reduced neuronal numbers and volume of brain regions have been found in depressed patients, which may be caused by decreased cell survival and increased cell death. Elucidating the mechanism underlying the degeneration of the neuroprotective system in social stress-induced depression is important for developing neuroprotective measures. The Repressor Element 1 Silencing Transcription Factor (REST) also known as Neuron-Restrictive Silencing Factor (NRSF) has been reported as a neuroprotective molecule in certain neurological disorders. Decreased expression levels of REST/NRSF in the nucleus can induce death-related gene expression, leading to neuronal death. Under physiological stress conditions, REST/NRSF over expression is known to activate neuronal survival in the brain. Alterations in REST/NRSF expression in the brain has been reported in stressed animal models and in the post-mortem brain of patients with depression. Here, we highlight the neuroprotective function of REST/NRSF and discuss dysregulation of REST/NRSF and neuronal damage during social stress and depression.

More than a Corepressor: The Role of CoREST Proteins in Neurodevelopment

The molecular mechanisms governing normal neurodevelopment are tightly regulated by the action of transcription factors. Repressor element 1 (RE1) silencing transcription factor (REST) is widely documented as a regulator of neurogenesis that acts by recruiting corepressor proteins and repressing neuronal gene expression in non-neuronal cells. The REST corepressor 1 (CoREST1), CoREST2, and CoREST3 are best described for their role as part of the REST complex. However, recent evidence has shown the proteins have the ability to repress expression of distinct target genes in a REST-independent manner. These findings indicate that each CoREST paralogue may have distinct and critical roles in regulating neurodevelopment and are more than simply “REST corepressors,” whereby they act as independent repressors orchestrating biological processes during neurodevelopment.

REST: An epigenetic regulator of neuronal stress responses in the young and ageing brain

The transcriptional repressor REST (Repressor Element-1 Silencing Transcription factor) is a key modulator of the neuronal epigenome and targets genes involved in neuronal differentiation, axonal growth, vesicular transport, ion channel conductance and synaptic plasticity. Whilst its gene expression-modifying properties have been examined extensively in neuronal development, REST's response towards stress-induced neuronal insults has only recently been explored. Overall, REST appears to be an ideal candidate to fine-tune neuronal gene expression following different forms of cellular, neuropathological, psychological and physical stressors. Upregulation of REST is reportedly protective against premature neural stem cell depletion, neuronal hyperexcitability, oxidative stress, neuroendocrine system dysfunction and neuropathology. In contrast, neuronal REST activation has also been linked to neuronal dysfunction and neurodegeneration. Here, we highlight key findings and discrepancies surrounding our current understanding of REST's function in neuronal adaptation to stress and explore its potential role in neuronal stress resilience in the young and ageing brain.

Epigenetic modifications induced by exercise: Drug-free intervention to improve cognitive deficits associated with obesity

Obesity and metabolic disorders are increasing worldwide and are associated with brain atrophy and dysfunction, which are risk factors for late-onset dementia and Alzheimer's disease. Epidemiological studies demonstrated that changes in lifestyle, including the frequent practice of physical exercise are able to prevent and treat not only obesity/metabolic disorders, but also to improve cognitive function and dementia. Several biochemical pathways and epigenetic mechanisms have been proposed to understand the beneficial effects of physical exercise on cognition. This manuscript revised central ongoing research on epigenetic mechanisms induced by exercise and the beneficial effects on obesity-associated cognitive decline, highlighting potential mechanistic mediators.

Brain aging: A Ianus-faced player between health and neurodegeneration

Neurodegenerative diseases are incurable debilitating disorders characterized by structural and functional neuronal loss. Approximately 30 million people are affected worldwide, and this number is predicted to reach more than 150 million by 2050. Neurodegenerative disorders include Alzheimer's, Parkinson's, and prion diseases among others. These disorders are characterized by the accumulation of aggregating proteins forming amyloid, responsible for the disease-associated pathological lesions. The aggregation of amyloidogenic proteins can result either in gaining of toxic functions, derived from the damage provoked by these deposits in affected tissue, or in a loss of functions, due to the sequestration and the consequent inability of the aggregating protein to ensure its physiological role. While it is widely accepted that aging represents the main risk factor for neurodegeneration, there is still no clear cut-off line between the two conditions. Indeed, many of the pathways that are commonly altered in neurodegeneration-misfolded protein accumulation, chronic inflammation, mitochondrial dysfunction, impaired iron homeostasis, epigenetic modifications-have been often correlated also with healthy aging. This overlap could be explained by the fact that the continuous accumulation of cellular damages, together with a progressive decline in metabolic efficiency during aging, makes the neurons more vulnerable to toxic injuries. When a given threshold is exceeded, all these alterations might give rise to pathological phenotypes that ultimately lead to neurodegeneration.

Context-dependent expression of a conditionally-inducible form of active Akt

Akt kinases are key signaling components in proliferation-competent and post-mitotic cells. Here, we sought to create a conditionally-inducible form of active Akt for both in vitro and in vivo applications. We fused a ligand-responsive Destabilizing Domain (DD) derived from E. coli dihydrofolate reductase to a constitutively active mutant form of Akt1, Akt(E40K). Prior work indicated that such fusion proteins may be stabilized and induced by a ligand, the antibiotic Trimethoprim (TMP). We observed dose-dependent, reversible induction of both total and phosphorylated/active DD-Akt(E40K) by TMP across several cellular backgrounds in culture, including neurons. Phosphorylation of FoxO4, an Akt substrate, was significantly elevated after DD-Akt(E40K) induction, indicating the induced protein was functionally active. The induced Akt(E40K) protected cells from apoptosis evoked by serum deprivation and was neuroprotective in two cellular models of Parkinson's disease (6-OHDA and MPP⁺ exposure). There was no significant protection without induction. We also evaluated Akt(E40K) induction by TMP in mouse substantia nigra and striatum after neuronal delivery via an AAV1 adeno-associated viral vector. While there was significant induction in striatum, there was no apparent induction in substantia nigra. To explore the possible basis for this difference, we examined DD-Akt(E40K) induction in cultured ventral midbrain neurons. Both dopaminergic and non-dopaminergic neurons in the cultures showed DD-Akt(E40K) induction after TMP treatment. However, basal DD-Akt(E40K) expression was 3-fold higher for dopaminergic neurons, resulting in a significantly lower induction by TMP in this population. Such findings suggest that dopaminergic neurons may be relatively inefficient in protein degradation, a property that could relate to their lack of apparent DD-Akt(E40K) induction in vivo and to their selective vulnerability in Parkinson's disease. In summary, we generated an inducible, biologically active form of Akt. The degree of inducibility appears to reflect cellular context that will inform the most appropriate applications for this and related reagents.

Regulation of MicroRNAs-Mediated Autophagic Flux: A New Regulatory Avenue for Neurodegenerative Diseases With Focus on Prion Diseases

Prion diseases are fatal neurological disorders affecting various mammalian species including humans. Lack of proper diagnostic tools and non-availability of therapeutic remedies are hindering the control strategies for prion diseases. MicroRNAs (miRNAs) are abundant endogenous short non-coding essential RNA molecules that negatively regulate the target genes after transcription. Several biological processes depend on miRNAs, and altered profiles of these miRNAs are potential biomarkers for various neurodegenerative diseases, including prion diseases. Autophagic flux degrades the misfolded prion proteins to reduce chronic endoplasmic reticulum stress and enhance cell survival. Recent evidence suggests that specific miRNAs target and regulate the autophagic mechanism, which is critical for alleviating cellular stress. miRNAs-mediated regulation of these specific proteins involved in the autophagy represents a new target with highly significant therapeutic prospects. Here, we will briefly describe the biology of miRNAs, the use of miRNAs as potential biomarkers with their credibility, the regulatory mechanism of miRNAs in major neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and prion diseases, degradation pathways for aggregated prion proteins, the role of autophagy in prion diseases. Finally, we will discuss the miRNAs-modulated autophagic flux in neurodegenerative diseases and employ them as potential therapeutic intervention strategy in prion diseases.

Prion protein is essential for the RE1 silencing transcription factor (REST)-dependent developmental switch in synaptic NMDA receptors

It is important that the correct amounts of GluN2 subunits are maintained, as they determine NMDAR functional properties, which are crucial to neuronal communication, synaptogenesis and cognitive function. The transcriptional repressor RE1 silencing transcription factor (REST) is critical for the postnatal developmental switch in NMDARs. However, the mechanisms triggering REST and the link between NMDARs and REST are unclear. Here we show a new physiological essential role for cellular prion protein (PrPC) in REST-dependent homeostasis and the developmental switch of NMDARs. REST and REST-associated proteins were overactivated in the hippocampi of Prnp knockout mice (Prnp 0/0 ) compared with wild-type Prnp (Prnp +/+ ) mice. This coincided with the disruption of the normal developmental switch from GluN2B-to-GluN2A in vivo. PrPC co-located with REST under physiological environments and mediated the translocation of REST in conditioners of NMDARs in vitro in Prnp +/+ hippocampal neurons. Regardless of whether REST was knocked down or overexpressed, deletion of PrPC not only disrupted REST-mediated distribution of mitochondria, but also prevented REST-regulated expression of GluN2B and GluN2A in Prnp 0/0 . Importantly, these effects were rescued after overexpression of full-length PrPC through restoration of NMDAR2 subunits and their distributions in dendritic processes in Prnp 0/0 . Consistently, knockdown of PrPC in Prnp +/+ had a similar effect on Prnp 0/0 . Furthermore, PrPC colocalized with both GluN2B and GluN2A in Prnp +/+ . For the first time, we demonstrate that PrPC is essential for REST-regulated NMDARs. Confirming the regulation of NMDAR-modulating mechanisms could provide novel therapeutic targets against dysfunctions of glutamatergic transmission in the nervous system.