Trazodone rescues dysregulated synaptic and mitochondrial nascent proteomes in prion neurodegeneration

Idebenone improves mitochondrial respiratory activity and attenuates oxidative damage via the SIRT3-SOD2 pathway in a prion disease cell model

Prion diseases are neurodegenerative diseases that are transmitted between humans and animals, which cause spongiform brain degeneration and neuronal death. Prion diseases are difficult to treat. Mitochondrial damage and oxidative stress occurring early in disease progression. Reducing oxidative stress is a therapeutic strategy for disease. Idebenone (IDE) is an antioxidant that enhances electron transfer in the mitochondrial respiratory chain. To investigate IDE protection mechanisms in prion neuron models, we examined IDE effects on apoptosis, mitochondrial dysfunction, cellular respiratory chain damage, and oxidative stress in N2a cells treated with the prion toxic peptide PrP106-126. IDE effectively alleviated apoptosis and mitochondrial dysfunction, reduced mitochondrial reactive oxygen species (ROS), attenuated lipid peroxidation, improved glutathione percentages, increased important antioxidant enzyme (superoxide dismutase (SOD) and catalase) activities, and elevated mitochondrial DNA levels. IDE also modulated SOD2 deacetylation and oxidative damage by regulating SIRT3. Overall, IDE exerted significant antioxidant effects in our prion disease cell model and may have therapeutic applications for prion disease.

A unified model for the origins of spongiform degeneration and other neuropathological features in prion diseases

Decades after their initial observation in prion-infected brain tissues, the identities of virus-like dense particles, varicose tubules, and oval bodies containing parallel bands and fibrils have remained elusive. Our recent work revealed that a phenotype of dilation of the endoplasmic reticulum (ER), most notable for the perinuclear space (PNS), contributes to spongiform degeneration. To assess the significance of this phenotype for the etiology of prion diseases, we explored whether it can be functionally linked to other neuropathological hallmarks observed in these diseases, as this would indicate it to be a central event. Having surveyed the neuropathological record and other distant literature niches, we propose a model in which pathogenic forms of the prion protein poison raft domains, including essential Na+, K+-ATPases (NKAs) embedded within them, thereby triggering an ER-centered cellular rescue program coordinated by the unfolded protein response (UPR). The execution of this program stalls general protein synthesis, causing the deterioration of synaptic spines. As the disease progresses, cells selectively increase sterol biosynthesis, along with ribosome and ER biogenesis. These adaptive rescue attempts cause morphological changes to the ER which manifest as ER dilation or ER hypertrophy in a manner that is influenced by Ca2+ influx into the cell. The nuclear-to-cytoplasmic transport of mRNAs and tRNAs interrupts in late stage disease, thereby depriving ribosomes of supplies and inducing them to aggregate into a paracrystalline form. In support of this model, we share previously reported data, whose features are consistent with the interpretation that 1) the phenotype of ER dilation is observed in major prion diseases, 2) varicose tubules and oval bodies represent ER hypertrophy, and 3) virus-like dense particles are paracrystalline aggregates of inactive ribosomes.

Trazodone, dibenzoylmethane and tauroursodeoxycholic acid do not prevent motor dysfunction and neurodegeneration in Marinesco-Sjögren syndrome mice

There is no cure for Marinesco-Sjögren syndrome (MSS), a genetic multisystem disease linked to loss-of-function mutations in the SIL1 gene, encoding a BiP co-chaperone. Previously, we showed that the PERK kinase inhibitor GSK2606414 delays cerebellar Purkinje cell (PC) degeneration and the onset of ataxia in the woozy mouse model of MSS. However, GSK2606414 is toxic to the pancreas and does not completely rescue the woozy phenotype. The present study tested trazodone and dibenzoylmethane (DBM), which partially inhibit PERK signaling with neuroprotective effects and no pancreatic toxicity. We also tested the chemical chaperone tauroursodeoxycholic acid (TUDCA), which protects MSS patients' cells from stress-induced apoptosis. Mice were chronically treated for five weeks, starting from a presymptomatic stage. Trazodone was given 40 mg/kg daily by intraperitoneal (ip) injection. DBM was given 0.5% in the diet ad libitum. TUDCA was given either 0.4% in the diet, or 500 mg/kg ip every three days. None of the treatments prevented motor dysfunction or PC degeneration in woozy mice, as assessed by beam walking, rotarod test, and calbindin immunohistochemistry. Only trazodone slightly boosted beam walking performance, but this effect was not related to inhibition of PERK signaling. Pharmacokinetic studies excluded that the lack of effect was due to altered drug metabolism in woozy mice. These results indicate that trazodone, DBM and TUDCA, at dosing regimens active in other neurodegenerative disease mouse models, have no disease-modifying effect in a preclinical model of MSS. This underscores the difficulty of translating neuroprotective strategies from other conditions to MSS, highlighting the need for more targeted therapeutic approaches.

Cell-Type-Specific Protein Metabolic Labeling and Identification Using the Methionine Subrogate ANL in Cells Expressing a Mutant Methionyl-tRNA Synthetase

The study of protein homeostasis in vivo is crucial for our understanding of the functions of cells and organisms. However, complex organisms, such as mammals, are built from heterogeneous tissues and cell-types. These cell-types are often specialized and react in different ways to the same physiological or pathological stimulus. Therefore, a major challenge in proteomics is the identification of proteomes and their behavior in a cell-type-specific manner. In this protocol, we describe a technique to label, enrich, and identify proteins from specific cell types. This technique is based on the expression of a mutant methionyl-tRNA synthetase (MetRS*) for incorporation of a bioorthogonal analog of methionine (ANL) into proteins. ANL can be subsequently bound to an alkyne by click-chemistry, which is used as a bait for protein purification followed by mass spectrometry identification.

The integrated stress response in brain diseases: A double-edged sword for proteostasis and synapses

The integrated stress response (ISR) is a highly conserved biochemical pathway that regulates protein synthesis. The ISR is activated in response to diverse stressors to restore cellular homeostasis. As such, the ISR is implicated in a wide range of diseases, including brain disorders. However, in the brain, the ISR also has potent influence on processes beyond proteostasis, namely synaptic plasticity, learning and memory. Thus, in the setting of brain diseases, ISR activity may have dual effects on proteostasis and synaptic function. In this review, we consider the ISR's contribution to brain disorders through the lens of its potential effects on synaptic plasticity. From these examples, we illustrate that at times ISR activity may be a "double-edged sword". We also highlight its potential as a therapeutic target to improve circuit function in brain diseases independent of its role in disease pathogenesis.

The ketamine metabolite (2R,6R)-hydroxynorketamine rescues hippocampal mRNA translation, synaptic plasticity and memory in mouse models of Alzheimer's disease

INTRODUCTION

Impaired brain protein synthesis, synaptic plasticity, and memory are major hallmarks of Alzheimer's disease (AD). The ketamine metabolite (2R,6R)-hydroxynorketamine (HNK) has been shown to modulate protein synthesis, but its effects on memory in AD models remain elusive.

METHODS

We investigated the effects of HNK on hippocampal protein synthesis, long-term potentiation (LTP), and memory in AD mouse models.

RESULTS

HNK activated extracellular signal-regulated kinase 1/2 (ERK1/2), mechanistic target of rapamycin (mTOR), and p70S6 kinase 1 (S6K1)/ribosomal protein S6 signaling pathways. Treatment with HNK rescued hippocampal LTP and memory deficits in amyloid-β oligomers (AβO)-infused mice in an ERK1/2-dependent manner. Treatment with HNK further corrected aberrant transcription, LTP and memory in aged APP/PS1 mice.

DISCUSSION

Our findings demonstrate that HNK induces signaling and transcriptional responses that correct synaptic and memory deficits in AD mice. These results raise the prospect that HNK could serve as a therapeutic approach in AD.

HIGHLIGHTS

The ketamine metabolite HNK activates hippocampal ERK/mTOR/S6 signaling pathways. HNK corrects hippocampal synaptic and memory defects in two mouse models of AD. Rescue of synaptic and memory impairments by HNK depends on ERK signaling. HNK corrects aberrant transcriptional signatures in APP/PS1 mice.

Navigating the landscape of the unfolded protein response in CD8+ T cells

Endoplasmic reticulum stress occurs due to large amounts of misfolded proteins, hypoxia, nutrient deprivation, and more. The unfolded protein is a complex intracellular signaling network designed to operate under this stress. Composed of three individual arms, inositol-requiring enzyme 1, protein kinase RNA-like ER kinase, and activating transcription factor-6, the unfolded protein response looks to resolve stress and return to proteostasis. The CD8+ T cell is a critical cell type for the adaptive immune system. The unfolded protein response has been shown to have a wide-ranging spectrum of effects on CD8+ T cells. CD8+ T cells undergo cellular stress during activation and due to environmental insults. However, the magnitude of the effects this response has on CD8+ T cells is still understudied. Thus, studying these pathways is important to unraveling the inner machinations of these powerful cells. In this review, we will highlight the recent literature in this field, summarize the three pathways of the unfolded protein response, and discuss their roles in CD8+ T cell biology and functionality.

Post-translational modifications in prion diseases

More than 650 reversible and irreversible post-translational modifications (PTMs) of proteins have been listed so far. Canonical PTMs of proteins consist of the covalent addition of functional or chemical groups on target backbone amino-acids or the cleavage of the protein itself, giving rise to modified proteins with specific properties in terms of stability, solubility, cell distribution, activity, or interactions with other biomolecules. PTMs of protein contribute to cell homeostatic processes, enabling basal cell functions, allowing the cell to respond and adapt to variations of its environment, and globally maintaining the constancy of the milieu interieur (the body's inner environment) to sustain human health. Abnormal protein PTMs are, however, associated with several disease states, such as cancers, metabolic disorders, or neurodegenerative diseases. Abnormal PTMs alter the functional properties of the protein or even cause a loss of protein function. One example of dramatic PTMs concerns the cellular prion protein (PrPC), a GPI-anchored signaling molecule at the plasma membrane, whose irreversible post-translational conformational conversion (PTCC) into pathogenic prions (PrPSc) provokes neurodegeneration. PrPC PTCC into PrPSc is an additional type of PTM that affects the tridimensional structure and physiological function of PrPC and generates a protein conformer with neurotoxic properties. PrPC PTCC into PrPSc in neurons is the first step of a deleterious sequence of events at the root of a group of neurodegenerative disorders affecting both humans (Creutzfeldt-Jakob diseases for the most representative diseases) and animals (scrapie in sheep, bovine spongiform encephalopathy in cow, and chronic wasting disease in elk and deer). There are currently no therapies to block PrPC PTCC into PrPSc and stop neurodegeneration in prion diseases. Here, we review known PrPC PTMs that influence PrPC conversion into PrPSc. We summarized how PrPC PTCC into PrPSc impacts the PrPC interactome at the plasma membrane and the downstream intracellular controlled protein effectors, whose abnormal activation or trafficking caused by altered PTMs promotes neurodegeneration. We discussed these effectors as candidate drug targets for prion diseases and possibly other neurodegenerative diseases.

Therapeutic potential of trazodone in trigeminal neuralgia based on inflammation and oxidative stress: an in vitro experimental study

Trigeminal neuralgia (TN) is a debilitating condition affecting the patients' life quality. New therapeutic approaches and novel drugs are required to treat TN. Trazodone being a serotonin antagonist and reuptake inhibitor (SARI) provides neuroprotection, however its role and underlying mechanism in TN in vitro or in vivo are not clear. This study was aimed to investigate the trazodone impact on glial BV-2 cells regarding TN. It was found that trazodone inhibited the BV-2 cells growth and suppressed the inflammation and oxidative stress in Lipopolysaccharide (LPS)-treated BV-2 cells. Trazodone treatment specifically decreased the levels of Tumor Necrosis Factor-alpha (TNF-α), Interleukin-6 (IL-6), Interleukin-1 beta (IL-1β) (p < 0.05), and Reactive Oxygen Species (ROS) (p < 0.01). Moreover, trazodone suppressed the Mitogen-Activated Protein Kinase (MAPK) pathway in LPS-treated BV-2 cells. These outcomes demonstrate that trazodone suppressed glial cell hyperproliferation, inflammation, and oxidative stress through MAPK pathway activation.