The unfolded protein response is activated in pretangle neurons in Alzheimer's disease hippocampus

Endoplasmic reticulum stress in diseases

The endoplasmic reticulum (ER) is a key organelle in eukaryotic cells, responsible for a wide range of vital functions, including the modification, folding, and trafficking of proteins, as well as the biosynthesis of lipids and the maintenance of intracellular calcium homeostasis. A variety of factors can disrupt the function of the ER, leading to the aggregation of unfolded and misfolded proteins within its confines and the induction of ER stress. A conserved cascade of signaling events known as the unfolded protein response (UPR) has evolved to relieve the burden within the ER and restore ER homeostasis. However, these processes can culminate in cell death while ER stress is sustained over an extended period and at elevated levels. This review summarizes the potential role of ER stress and the UPR in determining cell fate and function in various diseases, including cardiovascular diseases, neurodegenerative diseases, metabolic diseases, autoimmune diseases, fibrotic diseases, viral infections, and cancer. It also puts forward that the manipulation of this intricate signaling pathway may represent a novel target for drug discovery and innovative therapeutic strategies in the context of human diseases.

NERD-seq: a novel approach of Nanopore direct RNA sequencing that expands representation of non-coding RNAs

Non-coding RNAs (ncRNAs) are frequently documented RNA modification substrates. Nanopore Technologies enables the direct sequencing of RNAs and the detection of modified nucleobases. Ordinarily, direct RNA sequencing uses polyadenylation selection, studying primarily mRNA gene expression. Here, we present NERD-seq, which enables detection of multiple non-coding RNAs, excluded by the standard approach, alongside natively polyadenylated transcripts. Using neural tissues as a proof of principle, we show that NERD-seq expands representation of frequently modified non-coding RNAs, such as snoRNAs, snRNAs, scRNAs, srpRNAs, tRNAs, and rRFs. NERD-seq represents an RNA-seq approach to simultaneously study mRNA and ncRNA epitranscriptomes in brain tissues and beyond.

Histone deacetylase inhibition expands cellular proteostasis repertoires to enhance neuronal stress resilience

Neurons are long-lived, terminally differentiated cells with limited regenerative capacity. Cellular stressors such as endoplasmic reticulum (ER) protein folding stress and membrane trafficking stress accumulate as neurons age and accompany age-dependent neurodegeneration. Current strategies to improve neuronal resilience are focused on using factors to reprogram neurons or targeting specific proteostasis pathways. We discovered a different approach. In an unbiased screen for modifiers of neuronal membrane trafficking defects, we unexpectedly identified a role for histone deacetylases (HDACs) in limiting cellular flexibility in choosing cellular pathways to respond to diverse types of stress. Genetic or pharmacological inactivation of HDACs resulted in improved neuronal health in response to ER protein folding stress and endosomal membrane trafficking stress in C. elegans and mammalian neurons. Surprisingly, HDAC inhibition enabled neurons to activate latent proteostasis pathways tailored to the nature of the individual stress, instead of generalized transcriptional upregulation. These findings shape our understanding of neuronal stress responses and suggest new therapeutic strategies to enhance neuronal resilience.

Bioinformatic analysis of hippocampal histopathology in Alzheimer's disease and the therapeutic effects of active components of traditional Chinese medicine

Background and aim

Pathological changes in the central nervous system (CNS) begin before the clinical symptoms of Alzheimer's Disease (AD) manifest, with the hippocampus being one of the first affected structures. Current treatments fail to alter AD progression. Traditional Chinese medicine (TCM) has shown potential in improving AD pathology through multi-target mechanisms. This study investigates pathological changes in AD hippocampal tissue and explores TCM active components that may alleviate these changes.

Methods

GSE5281 and GSE173955 datasets were downloaded from GEO and normalized to identify differentially expressed genes (DEGs). Key functional modules and hub genes were analyzed using Cytoscape and R. Active TCM components were identified from literature and the Pharmacopoeia of the People's Republic of China. Enrichment analyses were performed on target genes overlapping with DEGs.

Result

From the datasets, 76 upregulated and 363 downregulated genes were identified. Hub genes included SLAMF, CD34, ELN (upregulated) and ATP5F1B, VDAC1, VDAC2, HSPA8, ATP5F1C, PDHA1, UBB, SNCA, YWHAZ, PGK1 (downregulated). Literature review identified 33 active components from 23 herbal medicines. Target gene enrichment and analysis were performed for six components: dihydroartemisinin, berberine, naringenin, calycosin, echinacoside, and icariside II.

Conclusion

Mitochondrial to synaptic vesicle dysfunction pathways were enriched in downregulated genes. Despite downregulation, UBB and SNCA proteins accumulate in AD brains. TCM studies suggest curcumin and echinacoside may improve hippocampal pathology and cognitive impairment in AD. Further investigation into their mechanisms is needed.

Downregulation of ATF-4 Attenuates the Endoplasmic Reticulum Stress-Mediated Neuroinflammation and Cognitive Impairment in Experimentally Induced Alzheimer's Disease Model

Protein aggregation is invariably associated with the inflammation as a factor in Alzheimer's disease (AD). We investigated the interaction between downstream factors of endoplasmic reticulum (ER) stress pathway and inflammation, with implications in cognitive impairment in AD. Amyloid-β (Aβ)(1-42) was administered by bilateral intracerebroventricular (icv) injection in the brain of adult male Wistar rats to experimentally develop AD. The cognitive impairment was assessed by measuring behavioral parameters such as Morris water maze and novel object recognition tests. Levels of pro-inflammatory cytokines such as interleukin (IL)-1β and tumor necrosis factor (TNF)-α and anti-inflammatory cytokines IL-4 and IL-10 were measured by the enzyme-linked immunosorbent assay (ELISA) in different rat brain regions. Inflammatory marker proteins such as cyclo-oxygenase (COX)-2 and phosphorylation of nuclear factor kappa B (NF-КB) (p65) were measured by the western blotting. Gene expression of ER stress downstream factors such as ATF-4, CHOP, and GADD-34 was analyzed by qRT-PCR. Histological studies were performed to check Aβ accumulation and neuronal degeneration. Integrated stress response inhibitor (ISRIB) was used to confirm the specific role of ER stress-mediated inflammation in cognitive impairment. Administration of Aβ(1-42) resulted in alteration in levels of inflammatory cytokines, inflammatory proteins, and mRNA levels of ER stress downstream factors. ISRIB treatment resulted in attenuation of Aβ(1-42)-induced ER stress, inflammation, neurodegeneration, and cognitive impairment in rats. These results indicate that ER stress-mediated inflammation potentiates the cognitive impairment in AD. An understanding of cascade of events, interaction of ER stress which was a hallmark of the present investigation together with inflammation and modulation of downstream signalling factors could serve as potent biomarkers to study AD progression.

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.

Endoplasmic reticulum unfolded protein response transcriptional targets of XBP-1s mediate rescue from tauopathy

Pathological tau disrupts protein homeostasis (proteostasis) within neurons in Alzheimer's disease (AD) and related disorders. We previously showed constitutive activation of the endoplasmic reticulum unfolded protein response (UPRER) transcription factor XBP-1s rescues tauopathy-related proteostatic disruption in a tau transgenic Caenorhabditis elegans (C. elegans) model of human tauopathy. XBP-1s promotes clearance of pathological tau, and loss of function of the ATF-6 branch of the UPRER prevents XBP-1s rescue of tauopathy in C. elegans. We conducted transcriptomic analysis of tau transgenic and xbp-1s transgenic C. elegans and found 116 putative target genes significantly upregulated by constitutively active XBP-1s. Among these were five candidate XBP-1s target genes with human orthologs and a previously known association with ATF6 (csp-1, dnj-28, hsp-4, ckb-2, and lipl-3). We examined the functional involvement of these targets in XBP-1s-mediated tauopathy suppression and found loss of function in any one of these genes completely disrupts XBP-1s suppression of tauopathy. Further, we demonstrate upregulation of HSP-4, C. elegans BiP, partially rescues tauopathy independent of other changes in the transcriptional network. Understanding how the UPRER modulates pathological tau accumulation will inform neurodegenerative disease mechanisms and direct further study in mammalian systems with the long-term goal of identifying therapeutic targets in human tauopathies.

Sephin1 enhances integrated stress response and autophagy to alleviate myocardial ischemia-reperfusion injury in mice

OBJECTIVE

Integrated stress response (ISR) is activated to promote cell survival by maintaining the phosphorylation of eukaryotic translation initiation factor 2 (eIF2α). We investigated whether Sephin1 enhances ISR and attenuates myocardial ischemia-reperfusion (MIR) injury.

METHODS

Male C57BL/6 J mice were injected with Sephin1 (2 mg/kg,i.p.) 30 min before surgery to establish a model of MIR with 45 min ischemia and 180 min reperfusion. In vitro, the H9C2 cell line with hypoxia-reoxygenation (H/R) was used to simulate MIR. Myocardial injury was evaluated by echocardiography, histologic observation after staining with TTC and H&E and electron microscopy. ISR, autophagy and apoptosis in vivo and in vitro were evaluated by immunoblotting, immunohistochemistry, immunofluorescence, and flow cytometry, respectively. Global protein synthesis was determined using a non-radioactive SUnSET Assay based on the puromycin method. Autophinib, an autophagy-specific inhibitor, was used to investigate the correlation between autophagy and apoptosis in the presence of Sephin1.

RESULTS

In vivo, Sephin1 significantly reduced myocardial injury and improved the cardiac function in MIR mice. Sephin1 administration prolonged ISR, reduced cell apoptosis, and promoted autophagy. In vitro, Sephin1 increased the number of stress granules (SGs) and autophagic vesicles, enhanced ISR and related protein synthesis suppression, and reduced cell apoptosis. Autophinib partly reversed autophagosome formation and apoptosis in H9c2 cells.

CONCLUSIONS

Sephin1 enhances ISR and related protein synthesis suppression, ameliorates myocardial apoptosis, and promotes autophagy during MIR stress. Sephin1 could act as a noval ISR enhancer for managing acute myocardial ischemia disease.

Caspases in Alzheimer's Disease: Mechanism of Activation, Role, and Potential Treatment

With the aging of the population, treatment of conditions emerging in old age, such as neurodegenerative disorders, has become a major medical challenge. Of these, Alzheimer's disease, leading to cognitive dysfunction, is of particular interest. Neuronal loss plays an important role in the pathophysiology of this condition, and over the years, a great effort has been made to determine the role of various factors in this process. Unfortunately, until now, the exact pathomechanism of this condition remains unknown. However, the most popular theories associate AD with abnormalities in the Tau and β-amyloid (Aβ) proteins, which lead to their deposition and result in neuronal death. Neurons, like all cells, die in a variety of ways, among which pyroptosis, apoptosis, and necroptosis are associated with the activation of various caspases. It is worth mentioning that Tau and Aβ proteins are considered to be one of the caspase activators, leading to cell death. Moreover, the protease activity of caspases influences both of the previously mentioned proteins, Tau and Aβ, converting them into more toxic derivatives. Due to the variety of ways caspases impact the development of AD, drugs targeting caspases could potentially be useful in the treatment of this condition. Therefore, there is a constant need to search for novel caspase inhibitors and evaluate them in preclinical and clinical trials.

Crosstalk between protein misfolding and endoplasmic reticulum stress during ageing and their role in age-related disorders

Maintaining the proteome is crucial to retaining cell functionality and response to multiple intrinsic and extrinsic stressors. Protein misfolding increased the endoplasmic reticulum (ER) stress and activated the adaptive unfolded protein response (UPR) to restore cell homeostasis. Apoptosis occurs when ER stress is prolonged or the adaptive response fails. In healthy young cells, the ratio of protein folding machinery to quantities of misfolded proteins is balanced under normal circumstances. However, the age-related deterioration of the complex systems for handling protein misfolding is accompanied by ageing-related disruption of protein homeostasis, which results in the build-up of misfolded and aggregated proteins. This ultimately results in decreased cell viability and forms the basis of common age-related diseases called protein misfolding diseases. Proteins or protein fragments convert from their ordinarily soluble forms to insoluble fibrils or plaques in many of these disorders, which build up in various organs such as the liver, brain, or spleen. Alzheimer's, Parkinson's, type II diabetes, and cancer are diseases in this group commonly manifest in later life. Thus, protein misfolding and its prevention by chaperones and different degradation paths are becoming understood from molecular perspectives. Proteodynamics information will likely affect future interventional techniques to combat cellular stress and support healthy ageing by avoiding and treating protein conformational disorders. This review provides an overview of the diverse proteostasis machinery, protein misfolding, and ER stress involvement, which activates the UPR sensors. Here, we will discuss the crosstalk between protein misfolding and ER stress and their role in developing age-related diseases.

Genetic Variations in EIF2AK3 are Associated with Neurocognitive Impairment in People Living with HIV

Based on emerging evidence on the role for specific single-nucleotide variants (SNVs) in EIF2AK3 encoding the integrated stress response kinase PERK, in neurodegeneration, we assessed the association of EIF2AK3 SNVs with neurocognitive performance in people with HIV (PWH) using a candidate gene approach. This retrospective study included the CHARTER cohort participants, excluding those with severe neuropsychiatric comorbidities. Genome-wide data previously obtained for 1047 participants and targeted sequencing of 992 participants with available genomic DNA were utilized to interrogate the association of three noncoding and three coding EIF2AK3 SNVs with the continuous global deficit score (GDS) and global neurocognitive impairment (NCI; GDS ≥ 0.5) using univariable and multivariable methods, with demographic, disease-associated, and treatment characteristics as covariates. The cohort characteristics were as follows: median age, 43.1 years; females, 22.8%; European ancestry, 41%; median CD4 + T cell counts, 175/µL (nadir) and 428/µL (current). At first assessment, 70.5% used ART and 68.3% of these had plasma HIV RNA levels ≤ 200 copies/mL. All three noncoding EIF2AK3 SNVs were associated with GDS and NCI (all p < 0.05). Additionally, 30.9%, 30.9%, and 41.2% of participants had at least one risk allele for the coding SNVs rs1805165 (G), rs867529 (G), and rs13045 (A), respectively. Homozygosity for all three coding SNVs was associated with significantly worse GDS (p < 0.001) and more NCI (p < 0.001). By multivariable analysis, the rs13045 A risk allele, current ART use, and Beck Depression Inventory-II value > 13 were independently associated with GDS and NCI (p < 0.001) whereas the other two coding SNVs did not significantly correlate with GDS or NCI after including rs13045 in the model. The coding EIF2AK3 SNVs were associated with worse performance in executive functioning, motor functioning, learning, and verbal fluency. Coding and non-coding SNVs of EIF2AK3 were associated with global NC and domain-specific performance. The effects were small-to-medium in size but present in multivariable analyses, raising the possibility of specific SNVs in EIF2AK3 as an important component of genetic vulnerability to neurocognitive complications in PWH.

Endoplasmic reticulum stress: A possible connection between intestinal inflammation and neurodegenerative disorders

BACKGROUND

Different studies have shown the key role of endoplasmic reticulum (ER) stress in autoimmune and chronic inflammatory disorders, as well as in neurodegenerative diseases. ER stress leads to the formation of misfolded proteins which affect the secretion of different cell types that are crucial for the intestinal homeostasis.

PURPOSE

In this review, we discuss the role of ER stress and its involvement in the development of inflammatory bowel diseases, chronic conditions that can cause severe damage of the gastrointestinal tract, focusing on the alteration of Paneth cells and goblet cells (the principal secretory phenotypes of the intestinal epithelial cells). ER stress is also discussed in the context of neurodegenerative diseases, in which protein misfolding represents the signature mechanism. ER stress in the bowel and consequent accumulation of misfolded proteins might represent a bridge between bowel inflammation and neurodegeneration along the gut-to-brain axis, affecting intestinal epithelial homeostasis and the equilibrium of the commensal microbiota. Targeting intestinal ER stress could foster future studies for designing new biomarkers and new therapeutic approaches for neurodegenerative disorders.

Serotonergic dysfunction may mediate the relationship between alcohol consumption and Alzheimer's disease

The impact of Alzheimer's disease (AD) and its related dementias is rapidly expanding, and its mitigation remains an urgent social and technical challenge. To date there are no effective treatments or interventions for AD, but recent studies suggest that alcohol consumption is correlated with the risk of developing dementia. In this review, we synthesize data from preclinical, clinical, and epidemiological models to evaluate the combined role of alcohol consumption and serotonergic dysfunction in AD, underscoring the need for further research on this topic. We first discuss the limitations inherent to current data-collection methods, and how neuropsychiatric symptoms common among AD, alcohol use disorder, and serotonergic dysfunction may mask their co-occurrence. We additionally describe how excess alcohol consumption may accelerate the development of AD via direct effects on serotonergic function, and we explore the roles of neuroinflammation and proteostasis in mediating the relationship between serotonin, alcohol consumption, and AD. Lastly, we argue for a shift in current research to disentangle the pathogenic effects of alcohol on early-affected brainstem structures in AD.

Role of Neurocellular Endoplasmic Reticulum Stress Response in Alzheimer's Disease and Related Dementias Risk

Currently, more than 55 million people around the world suffer from dementia, and Alzheimer's Disease and Related Dementias (ADRD) accounts for nearly 60-70% of all those cases. The spread of Alzheimer's Disease (AD) pathology and progressive neurodegeneration in the hippocampus and cerebral cortex is strongly correlated with cognitive decline in AD patients; however, the molecular underpinning of ADRD's causality is still unclear. Studies of postmortem AD brains and animal models of AD suggest that elevated endoplasmic reticulum (ER) stress may have a role in ADRD pathology through altered neurocellular homeostasis in brain regions associated with learning and memory. To study the ER stress-associated neurocellular response and its effects on neurocellular homeostasis and neurogenesis, we modeled an ER stress challenge using thapsigargin (TG), a specific inhibitor of sarco/endoplasmic reticulum Ca2+ ATPase (SERCA), in the induced pluripotent stem cell (iPSC)-derived neural stem cells (NSCs) of two individuals from our Mexican American Family Study (MAFS). High-content screening and transcriptomic analysis of the control and ER stress-challenged NSCs showed that the NSCs' ER stress response resulted in a significant decline in NSC self-renewal and an increase in apoptosis and cellular oxidative stress. A total of 2300 genes were significantly (moderated t statistics FDR-corrected p-value ≤ 0.05 and fold change absolute ≥ 2.0) differentially expressed (DE). The pathway enrichment and gene network analysis of DE genes suggests that all three unfolded protein response (UPR) pathways, protein kinase RNA-like ER kinase (PERK), activating transcription factor-6 (ATF-6), and inositol-requiring enzyme-1 (IRE1), were significantly activated and cooperatively regulated the NSCs' transcriptional response to ER stress. Our results show that IRE1/X-box binding protein 1 (XBP1) mediated transcriptional regulation of the E2F transcription factor 1 (E2F1) gene, and its downstream targets have a dominant role in inducing G1/S-phase cell cycle arrest in ER stress-challenged NSCs. The ER stress-challenged NSCs also showed the activation of C/EBP homologous protein (CHOP)-mediated apoptosis and the dysregulation of synaptic plasticity and neurotransmitter homeostasis-associated genes. Overall, our results suggest that the ER stress-associated attenuation of NSC self-renewal, increased apoptosis, and dysregulated synaptic plasticity and neurotransmitter homeostasis plausibly play a role in the causation of ADRD.

Gene-expression profiling of individuals resilient to Alzheimer's disease reveals higher expression of genes related to metallothionein and mitochondrial processes and no changes in the unfolded protein response

Some individuals show a discrepancy between cognition and the amount of neuropathological changes characteristic for Alzheimer's disease (AD). This phenomenon has been referred to as 'resilience'. The molecular and cellular underpinnings of resilience remain poorly understood. To obtain an unbiased understanding of the molecular changes underlying resilience, we investigated global changes in gene expression in the superior frontal gyrus of a cohort of cognitively and pathologically well-defined AD patients, resilient individuals and age-matched controls (n = 11-12 per group). 897 genes were significantly altered between AD and control, 1121 between resilient and control and 6 between resilient and AD. Gene set enrichment analysis (GSEA) revealed that the expression of metallothionein (MT) and of genes related to mitochondrial processes was higher in the resilient donors. Weighted gene co-expression network analysis (WGCNA) identified gene modules related to the unfolded protein response, mitochondrial processes and synaptic signaling to be differentially associated with resilience or dementia. As changes in MT, mitochondria, heat shock proteins and the unfolded protein response (UPR) were the most pronounced changes in the GSEA and/or WGCNA, immunohistochemistry was used to further validate these processes. MT was significantly increased in astrocytes in resilient individuals. A higher proportion of the mitochondrial gene MT-CO1 was detected outside the cell body versus inside the cell body in the resilient compared to the control group and there were higher levels of heat shock protein 70 (HSP70) and X-box-binding protein 1 spliced (XBP1s), two proteins related to heat shock proteins and the UPR, in the AD donors. Finally, we show evidence for putative sex-specific alterations in resilience, including gene expression differences related to autophagy in females compared to males. Taken together, these results show possible mechanisms involving MTs, mitochondrial processes and the UPR by which individuals might maintain cognition despite the presence of AD pathology.

An increase in ER stress and unfolded protein response in iPSCs-derived neuronal cells from neuronopathic Gaucher disease patients

Gaucher disease (GD) is a lysosomal storage disorder caused by a mutation in the GBA1 gene, responsible for encoding the enzyme Glucocerebrosidase (GCase). Although neuronal death and neuroinflammation have been observed in the brains of individuals with neuronopathic Gaucher disease (nGD), the exact mechanism underlying neurodegeneration in nGD remains unclear. In this study, we used two induced pluripotent stem cells (iPSCs)-derived neuronal cell lines acquired from two type-3 GD patients (GD3-1 and GD3-2) to investigate the mechanisms underlying nGD by biochemical analyses. These iPSCs-derived neuronal cells from GD3-1 and GD3-2 exhibit an impairment in endoplasmic reticulum (ER) calcium homeostasis and an increase in unfolded protein response markers (BiP and CHOP), indicating the presence of ER stress in nGD. A significant increase in the BAX/BCL-2 ratio and an increase in Annexin V-positive cells demonstrate a notable increase in apoptotic cell death in GD iPSCs-derived neurons, suggesting downstream signaling after an increase in the unfolded protein response. Our study involves the establishment of iPSCs-derived neuronal models for GD and proposes a possible mechanism underlying nGD. This mechanism involves the activation of ER stress and the unfolded protein response, ultimately leading to apoptotic cell death in neurons.

Redox changes and cellular senescence in Alzheimer's disease

The redox process and cellular senescence are involved in a range of essential physiological functions. However, they are also implicated in pathological processes underlying age-related neurodegenerative disorders, including Alzheimer's disease (AD). Elevated levels of reactive oxygen species (ROS) are generated as a result of abnormal accumulation of beta-amyloid peptide (Aβ), tau protein, and heme dyshomeostasis and is further aggravated by mitochondria dysfunction and endoplasmic reticulum (ER) stress. Excessive ROS damages vital cellular components such as proteins, DNA and lipids. Such damage eventually leads to impaired neuronal function and cell death. Heightened oxidative stress can also induce cellular senescence via activation of the senescence-associated secretory phenotype to further exacerbate inflammation and tissue dysfunction. In this review, we focus on how changes in the redox system and cellular senescence contribute to AD and how they are affected by perturbations in heme metabolism and mitochondrial function. While potential therapeutic strategies targeting such changes have received some attention, more research is necessary to bring them into clinical application.

Transgenic Dendra2::tau expression allows in vivo monitoring of tau proteostasis in Caenorhabditis elegans

Protein homeostasis is perturbed in aging-related neurodegenerative diseases called tauopathies, which are pathologically characterized by aggregation of the microtubule-associated protein tau (encoded by the human MAPT gene). Transgenic Caenorhabditis elegans serve as a powerful model organism to study tauopathy disease mechanisms, but moderating transgenic expression level has proven problematic. To study neuronal tau proteostasis, we generated a suite of transgenic strains expressing low, medium or high levels of Dendra2::tau fusion proteins by comparing integrated multicopy transgene arrays with single-copy safe-harbor locus strains generated by recombinase-mediated cassette exchange. Multicopy Dendra2::tau strains exhibited expression level-dependent neuronal dysfunction that was modifiable by known genetic suppressors or an enhancer of tauopathy. Single-copy Dendra2::tau strains lacked distinguishable phenotypes on their own but enabled detection of enhancer-driven neuronal dysfunction. We used multicopy Dendra2::tau strains in optical pulse-chase experiments measuring tau turnover in vivo and found that Dendra2::tau turned over faster than the relatively stable Dendra2. Furthermore, Dendra2::tau turnover was dependent on the protein expression level and independent of co-expression with human TDP-43 (officially known as TARDBP), an aggregating protein interacting with pathological tau. We present Dendra2::tau transgenic C. elegans as a novel tool for investigating molecular mechanisms of tau proteostasis.

Protein translation: biological processes and therapeutic strategies for human diseases

Protein translation is a tightly regulated cellular process that is essential for gene expression and protein synthesis. The deregulation of this process is increasingly recognized as a critical factor in the pathogenesis of various human diseases. In this review, we discuss how deregulated translation can lead to aberrant protein synthesis, altered cellular functions, and disease progression. We explore the key mechanisms contributing to the deregulation of protein translation, including functional alterations in translation factors, tRNA, mRNA, and ribosome function. Deregulated translation leads to abnormal protein expression, disrupted cellular signaling, and perturbed cellular functions- all of which contribute to disease pathogenesis. The development of ribosome profiling techniques along with mass spectrometry-based proteomics, mRNA sequencing and single-cell approaches have opened new avenues for detecting diseases related to translation errors. Importantly, we highlight recent advances in therapies targeting translation-related disorders and their potential applications in neurodegenerative diseases, cancer, infectious diseases, and cardiovascular diseases. Moreover, the growing interest lies in targeted therapies aimed at restoring precise control over translation in diseased cells is discussed. In conclusion, this comprehensive review underscores the critical role of protein translation in disease and its potential as a therapeutic target. Advancements in understanding the molecular mechanisms of protein translation deregulation, coupled with the development of targeted therapies, offer promising avenues for improving disease outcomes in various human diseases. Additionally, it will unlock doors to the possibility of precision medicine by offering personalized therapies and a deeper understanding of the molecular underpinnings of diseases in the future.

Trazodone rescues dysregulated synaptic and mitochondrial nascent proteomes in prion neurodegeneration

The unfolded protein response (UPR) is rapidly gaining momentum as a therapeutic target for protein misfolding neurodegenerative diseases, in which its overactivation results in sustained translational repression leading to synapse loss and neurodegeneration. In mouse models of these disorders, from Alzheimer's to prion disease, modulation of the pathway-including by the licensed drug, trazodone-restores global protein synthesis rates with profound neuroprotective effects. However, the precise nature of the translational impairment, in particular the specific proteins affected in disease, and their response to therapeutic UPR modulation are poorly understood. We used non-canonical amino acid tagging (NCAT) to measure de novo protein synthesis in the brains of prion-diseased mice with and without trazodone treatment, in both whole hippocampus and cell-specifically. During disease the predominant nascent proteome changes occur in synaptic, cytoskeletal and mitochondrial proteins in both hippocampal neurons and astrocytes. Remarkably, trazodone treatment for just 2 weeks largely restored the whole disease nascent proteome in the hippocampus to that of healthy, uninfected mice, predominantly with recovery of proteins involved in synaptic and mitochondrial function. In parallel, trazodone treatment restored the disease-associated decline in synapses and mitochondria and their function to wild-type levels. In conclusion, this study increases our understanding of how translational repression contributes to neurodegeneration through synaptic and mitochondrial toxicity via depletion of key proteins essential for their function. Further, it provides new insights into the neuroprotective mechanisms of trazodone through reversal of this toxicity, relevant for the treatment of neurodegenerative diseases via translational modulation.

UBXN1 maintains ER proteostasis and represses UPR activation by modulating translation

ER protein homeostasis (proteostasis) is essential for proper folding and maturation of proteins in the secretory pathway. Loss of ER proteostasis can lead to the accumulation of misfolded or aberrant proteins in the ER and triggers the unfolded protein response (UPR). In this study, we find that the p97 adaptor UBXN1 is an important negative regulator of the UPR. Loss of UBXN1 sensitizes cells to ER stress and activates the UPR. This leads to widespread upregulation of the ER stress transcriptional program. Using comparative, quantitative proteomics we show that deletion of UBXN1 results in a significant enrichment of proteins involved in ER-quality control processes including those involved in protein folding and import. Notably, we find that loss of UBXN1 does not perturb p97-dependent ER-associated degradation (ERAD). Our studies indicate that loss of UBXN1 increases translation in both resting and ER-stressed cells. Surprisingly, this process is independent of p97 function. Taken together, our studies have identified a new role for UBXN1 in repressing translation and maintaining ER proteostasis in a p97 independent manner.

Oxidative damage in neurodegeneration: roles in the pathogenesis and progression of Alzheimer disease

Alzheimer disease (AD) is associated with multiple etiologies and pathological mechanisms, among which oxidative stress (OS) appears as a major determinant. Intriguingly, OS arises in various pathways regulating brain functions, and it seems to link different hypotheses and mechanisms of AD neuropathology with high fidelity. The brain is particularly vulnerable to oxidative damage, mainly because of its unique lipid composition, resulting in an amplified cascade of redox reactions that target several cellular components/functions ultimately leading to neurodegeneration. The present review highlights the "OS hypothesis of AD," including amyloid beta-peptide-associated mechanisms, the role of lipid and protein oxidation unraveled by redox proteomics, and the antioxidant strategies that have been investigated to modulate the progression of AD. Collected studies from our groups and others have contributed to unraveling the close relationships between perturbation of redox homeostasis in the brain and AD neuropathology by elucidating redox-regulated events potentially involved in both the pathogenesis and progression of AD. However, the complexity of AD pathological mechanisms requires an in-depth understanding of several major intracellular pathways affecting redox homeostasis and relevant for brain functions. This understanding is crucial to developing pharmacological strategies targeting OS-mediated toxicity that may potentially contribute to slow AD progression as well as improve the quality of life of persons with this severe dementing disorder.

ApoER2-Dab1 disruption as the origin of pTau-associated neurodegeneration in sporadic Alzheimer's disease

In sporadic Alzheimer's disease (sAD) specific regions, layers and neurons accumulate hyperphosphorylated Tau (pTau) and degenerate early while others remain unaffected even in advanced disease. ApoER2-Dab1 signaling suppresses Tau phosphorylation as part of a four-arm pathway that regulates lipoprotein internalization and the integrity of actin, microtubules, and synapses; however, the role of this pathway in sAD pathogenesis is not fully understood. We previously showed that multiple ApoER2-Dab1 pathway components including ApoE, Reelin, ApoER2, Dab1, pP85αTyr607, pLIMK1Thr508, pTauSer202/Thr205 and pPSD95Thr19 accumulate together within entorhinal-hippocampal terminal zones in sAD, and proposed a unifying hypothesis wherein disruption of this pathway underlies multiple aspects of sAD pathogenesis. However, it is not yet known whether ApoER2-Dab1 disruption can help explain the origin(s) and early progression of pTau pathology in sAD. In the present study, we applied in situ hybridization and immunohistochemistry (IHC) to characterize ApoER2 expression and accumulation of ApoER2-Dab1 pathway components in five regions known to develop early pTau pathology in 64 rapidly autopsied cases spanning the clinicopathological spectrum of sAD. We found that (1) these selectively vulnerable neuron populations strongly express ApoER2; and (2) multiple ApoER2-Dab1 components representing all four arms of this pathway accumulate in abnormal neurons and neuritic plaques in mild cognitive impairment (MCI) and sAD cases and correlate with histological progression and cognitive deficits. Multiplex-IHC revealed that Dab1, pP85αTyr607, pLIMK1Thr508, pTauSer202/Thr205 and pPSD95Thr19 accumulate together within many of the same ApoER2-expressing neurons and in the immediate vicinity of ApoE/ApoJ-enriched extracellular plaques. Collective findings reveal that pTau is only one of many ApoER2-Dab1 pathway components that accumulate in multiple neuroanatomical sites in the earliest stages of sAD and provide support for the concept that ApoER2-Dab1 disruption drives pTau-associated neurodegeneration in human sAD.

Protein retention in the endoplasmic reticulum rescues Aβ toxicity in Drosophila

Amyloid β (Aβ) accumulation is a hallmark of Alzheimer's disease. In adult Drosophila brains, human Aβ overexpression harms climbing and lifespan. It's uncertain whether Aβ is intrinsically toxic or activates downstream neurodegeneration pathways. Our study uncovers a novel protective role against Aβ toxicity: intra-endoplasmic reticulum (ER) protein accumulation with a focus on laminin and collagen subunits. Despite high Aβ, laminin B1 (LanB1) overexpression robustly counters toxicity, suggesting a potential Aβ resistance mechanism. Other laminin subunits and collagen IV also alleviate Aβ toxicity; combining them with LanB1 augments the effect. Imaging reveals ER retention of LanB1 without altering Aβ secretion. LanB1's rescue function operates independently of the IRE1α/XBP1 ER stress response. ER-targeted GFP overexpression also mitigates Aβ toxicity, highlighting broader ER protein retention advantages. Proof-of-principle tests in murine hippocampal slices using mouse Lamb1 demonstrate ER retention in transduced cells, indicating a conserved mechanism. Though ER protein retention generally harms, it could paradoxically counter neuronal Aβ toxicity, offering a new therapeutic avenue for Alzheimer's disease.

Exploring the Role of Neuroplasticity in Development, Aging, and Neurodegeneration

Neuroplasticity refers to the ability of the brain to reorganize and modify its neural connections in response to environmental stimuli, experience, learning, injury, and disease processes. It encompasses a range of mechanisms, including changes in synaptic strength and connectivity, the formation of new synapses, alterations in the structure and function of neurons, and the generation of new neurons. Neuroplasticity plays a crucial role in developing and maintaining brain function, including learning and memory, as well as in recovery from brain injury and adaptation to environmental changes. In this review, we explore the vast potential of neuroplasticity in various aspects of brain function across the lifespan and in the context of disease. Changes in the aging brain and the significance of neuroplasticity in maintaining cognitive function later in life will also be reviewed. Finally, we will discuss common mechanisms associated with age-related neurodegenerative processes (including protein aggregation and accumulation, mitochondrial dysfunction, oxidative stress, and neuroinflammation) and how these processes can be mitigated, at least partially, by non-invasive and non-pharmacologic lifestyle interventions aimed at promoting and harnessing neuroplasticity.

Single-cell transcriptomic and neuropathologic analysis reveals dysregulation of the integrated stress response in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a sporadic neurodegenerative tauopathy variably affecting brainstem and cortical structures and characterized by tau inclusions in neurons and glia. The precise mechanism whereby these protein aggregates lead to cell death remains unclear. To investigate the contribution of these different cellular abnormalities to PSP pathogenesis, we performed single-nucleus RNA sequencing and analyzed 45,559 high quality nuclei targeting the subthalamic nucleus and adjacent structures from human post-mortem PSP brains with varying degrees of pathology compared to controls. Cell-type specific differential expression and pathway analysis identified both common and discrete changes in numerous pathways previously implicated in PSP and other neurodegenerative disorders. This included EIF2 signaling, an adaptive pathway activated in response to diverse stressors, which was the top activated pathway in vulnerable cell types. Using immunohistochemistry, we found that activated eIF2α was positively correlated with tau pathology burden in vulnerable brain regions. Multiplex immunofluorescence localized activated eIF2α positivity to hyperphosphorylated tau (p-tau) positive neurons and ALDH1L1-positive astrocytes, supporting the increased transcriptomic EIF2 activation observed in these vulnerable cell types. In conclusion, these data provide insights into cell-type-specific pathological changes in PSP and support the hypothesis that failure of adaptive stress pathways play a mechanistic role in the pathogenesis and progression of PSP.

The Unfolded Protein Response in a Murine Model of Alzheimer's Disease: Looking for Predictors

Alzheimer's disease (AD) represents the most frequent type of dementia worldwide, and aging is the most important risk factor for the sporadic form of the pathology. The endoplasmic reticulum (ER), the main cellular actor involved in proteostasis, appears significantly compromised in AD due to the accumulation of the β-amyloid (Aβ) protein and the phosphorylated Tau protein. Increasing protein misfolding activates a specific cellular response known as Unfolded Protein Response (UPR), which orchestrates the recovery of ER function. The aim of the present study was to investigate the role of UPR in a murine model of AD induced by intracerebroventricular (i.c.v.) injection of Aβ1-42 oligomers at 3 or 18 months. The oligomer injection in aged animals induced memory impairment, oxidative stress, and the depletion of glutathione reserve. Furthermore, the RNA sequencing and the bioinformatic analysis performed showed the enrichment of several pathways involved in neurodegeneration and protein regulations. The analysis highlighted the significant dysregulation of the protein kinase RNA-like ER kinase (PERK), inositol-requiring protein 1α (IRE1α) and activating transcription factor 6 (ATF-6). In turn, ER stress affected the PI3K/Akt/Gsk3β and MAPK/ERK pathways, highlighting Mapkapk5 as a potential marker, whose regulation could lead to the definition of new pharmacological and neuroprotective strategies to counteract AD.

A neurodegeneration checkpoint mediated by REST protects against the onset of Alzheimer's disease

Many aging individuals accumulate the pathology of Alzheimer's disease (AD) without evidence of cognitive decline. Here we describe an integrated neurodegeneration checkpoint response to early pathological changes that restricts further disease progression and preserves cognitive function. Checkpoint activation is mediated by the REST transcriptional repressor, which is induced in cognitively-intact aging humans and AD mouse models at the onset of amyloid β-protein (Aβ) deposition and tau accumulation. REST induction is mediated by the unfolded protein response together with β-catenin signaling. A consequence of this response is the targeting of REST to genes involved in key pathogenic pathways, resulting in downregulation of gamma secretase, tau kinases, and pro-apoptotic proteins. Deletion of REST in the 3xTg and J20 AD mouse models accelerates Aβ deposition and the accumulation of misfolded and phosphorylated tau, leading to neurodegeneration and cognitive decline. Conversely, viral-mediated overexpression of REST in the hippocampus suppresses Aβ and tau pathology. Thus, REST mediates a neurodegeneration checkpoint response with multiple molecular targets that may protect against the onset of AD.

Adaptive responses of neuronal cells to chronic endoplasmic reticulum (ER) stress

Accumulation of misfolded proteins or perturbation of calcium homeostasis leads to endoplasmic reticulum (ER) stress and is linked to the pathogenesis of neurodegenerative diseases. Hence, understanding the ability of neuronal cells to cope with chronic ER stress is of fundamental interest. Interestingly, several brain areas uphold functions that enable them to resist challenges associated with neurodegeneration. Here, we established novel clonal mouse hippocampal (HT22) cell lines that are resistant to prolonged (chronic) ER stress induced by thapsigargin (TgR) or tunicamycin (TmR) as in vitro models to study the adaption to ER stress. Morphologically, we observed a significant increase in vesicular und autophagosomal structures in both resistant lines and 'giant lysosomes', especially striking in TgR cells. While autophagic activity increased under ER stress, lysosomal function appeared slightly impaired; in both cell lines, we observed enhanced ER-phagy. However, proteomic analyses revealed that various protein clusters and signaling pathways were differentially regulated in TgR versus TmR cells in response to chronic ER stress. Additionally, bioenergetic analyses in both resistant cell lines showed a shift toward aerobic glycolysis ('Warburg effect') and a defective complex I of the oxidative phosphorylation (OXPHOS) machinery. Furthermore, ER stress-resistant cells differentially activated the unfolded protein response (UPR) comprising IRE1α and ATF6 pathways. These findings display the wide portfolio of adaptive responses of neuronal cells to chronic ER stress. ER stress-resistant neuronal cells could be the basis to uncover molecular modulators of adaptation, resistance, and neuroprotection as potential pharmacological targets for preventing neurodegeneration.

The Preventive Effects of Salubrinal against Pyrethroid-Induced Disruption of Adult Hippocampal Neurogenesis in Mice

Environmental factors, including pesticide exposure, have been identified as substantial contributors to neurodegeneration and cognitive impairments. Previously, we demonstrated that repeated exposure to deltamethrin induces endoplasmic reticulum (ER) stress, reduces hippocampal neurogenesis, and impairs cognition in adult mice. Here, we investigated the potential relationship between ER stress and hippocampal neurogenesis following exposure to deltamethrin, utilizing both pharmacological and genetic approaches. To investigate whether ER stress is associated with inhibition of neurogenesis, mice were given two intraperitoneal injections of eIf2α inhibitor salubrinal (1 mg/kg) at 24 h and 30 min prior to the oral administration of deltamethrin (3 mg/kg). Salubrinal prevented hippocampal ER stress, as indicated by decreased levels of C/EBP-homologous protein (CHOP) and transcription factor 4 (ATF4) and attenuated deltamethrin-induced reductions in BrdU-, Ki-67-, and DCX-positive cells in the dentate gyrus (DG) of the hippocampus. To further explore the relationship between ER stress and adult neurogenesis, we used caspase-12 knockout (KO) mice. The caspase-12 KO mice exhibited significant protection against deltamethrin-induced reduction of BrdU-, Ki-67-, and DCX-positive cells in the hippocampus. In addition, deltamethrin exposure led to a notable upregulation of CHOP and caspase-12 expression in a significant portion of BrdU- and Ki-67-positive cells in WT mice. Conversely, both salubrinal-treated mice and caspase-12 KO mice exhibited a considerably lower number of CHOP-positive cells in the hippocampus. Together, these findings suggest that exposure to the insecticide deltamethrin triggers ER stress-mediated suppression of adult hippocampal neurogenesis, which may subsequently contribute to learning and memory deficits in mice.

Modulating endoplasmic reticulum stress in APP/PS1 mice by Gomisin B and Osthole in Bushen-Yizhi formula: Synergistic effects and therapeutic implications for Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder with no effective cure. Targeting endoplasmic reticulum (ER) stress pathway may offer a novel approach to ameliorate cognitive deficits in AD. Bushen-Yizhi formula (BSYZ), a traditional Chinese medicine (TCM) prescription, has shown potential benefits for AD. To facilitate the development of new therapeutic agents for AD, it is important to identify the active components and the underlying mechanisms of BSYZ against AD.

PURPOSE

The aim of this study was to systematically screen the active components of BSYZ that could improve learning and memory impairment in AD by modulating ER stress pathway.

METHODS

A drug-target (D-T) network was constructed to analyze the herbal components of BSYZ. Network proximity method was used to identify the potential anti-AD components that targeted ER stress and evaluate their synergistic effects. The absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties and the literature evidence were considered to select promising candidates for further validation. The selected components were tested in vitro using an AD cell model (APPswe-SH-SY5Y). In vivo anti-AD effects of the components were assessed in APP/PS1 double-transgenic mice.

RESULTS

58 potential anti-AD components targeting ER stress were detected by network proximity analysis, and 13 out of them were selected based on ADMET properties and literature evidence. In vitro experiments confirmed that 5 components, namely gomisin B, β-Carotene, imperatorin, chrysophanol, and osthole (OST), exhibited anti-AD effects on the APPswe-SH-SY5Y model. Moreover, network proximity analysis suggested that OST and Gomisin B might have synergistic effects on modulating ER stress. In vivo experiments demonstrated that OST, Gomisin B, OST+Gomisin B, and BSYZ all improved learning and memory function in APP/PS1 mice. Gomisin B and OST also restored cellular morphology and tissue structure in APP/PS1 mice. Thioflavine-S (Th-S) staining revealed that they reduced amyloid plaque deposition in the brain tissue of AD model mice. The qPCR results indicated that BSYZ, OST, and Gomisin B differentially regulated IRE1α, PERK, EIF2α, DDIT3, and Caspase 12 expression levels, while the OST and Gomisin B co-administration group showed better efficacy. This trend was further confirmed by immunofluorescence experiments.

CONCLUSION

This study identified the active components of BSYZ that could ameliorate learning and memory impairment in AD by targeting ER stress pathway. OST and Gomisin B exhibited synergistic effects on modulating ER stress and reducing amyloid plaque deposition in vivo. Overall, our study elucidated the molecular mechanisms of BSYZ and its active components in attenuating AD symptoms which suggested the therapeutic potential of TCM for AD.

Pharmacological Regulation of Endoplasmic Reticulum Structure and Calcium Dynamics: Importance for Neurodegenerative Diseases

The endoplasmic reticulum (ER) is the largest organelle of the cell, composed of a continuous network of sheets and tubules, and is involved in protein, calcium (Ca2+), and lipid homeostasis. In neurons, the ER extends throughout the cell, both somal and axodendritic compartments, and is highly important for neuronal functions. A third of the proteome of a cell, secreted and membrane-bound proteins, are processed within the ER lumen and most of these proteins are vital for neuronal activity. The brain itself is high in lipid content, and many structural lipids are produced, in part, by the ER. Cholesterol and steroid synthesis are strictly regulated in the ER of the blood-brain barrier protected brain cells. The high Ca2+ level in the ER lumen and low cytosolic concentration is needed for Ca2+-based intracellular signaling, for synaptic signaling and Ca2+ waves, and for preparing proteins for correct folding in the presence of high Ca2+ concentrations to cope with the high concentrations of extracellular milieu. Particularly, ER Ca2+ is controlled in axodendritic areas for proper neurito- and synaptogenesis and synaptic plasticity and remodeling. In this review, we cover the physiologic functions of the neuronal ER and discuss it in context of common neurodegenerative diseases, focusing on pharmacological regulation of ER Ca2+ Furthermore, we postulate that heterogeneity of the ER, its protein folding capacity, and ensuring Ca2+ regulation are crucial factors for the aging and selective vulnerability of neurons in various neurodegenerative diseases. SIGNIFICANCE STATEMENT: Endoplasmic reticulum (ER) Ca2+ regulators are promising therapeutic targets for degenerative diseases for which efficacious drug therapies do not exist. The use of pharmacological probes targeting maintenance and restoration of ER Ca2+ can provide restoration of protein homeostasis (e.g., folding of complex plasma membrane signaling receptors) and slow down the degeneration process of neurons.

The PERK pathway: beneficial or detrimental for neurodegenerative diseases and tumor growth and cancer

Protein kinase R (PKR)-like endoplasmic reticulum (ER) kinase (PERK) is one of the three major sensors in the unfolded protein response (UPR). The UPR is involved in the modulation of protein synthesis as an adaptive response. Prolonged PERK activity correlates with the development of diseases and the attenuation of disease severity. Thus, the current debate focuses on the role of the PERK signaling pathway either in accelerating or preventing diseases such as neurodegenerative diseases, myelin disorders, and tumor growth and cancer. In this review, we examine the current findings on the PERK signaling pathway and whether it is beneficial or detrimental for the above-mentioned disorders.

Protein disulfide isomerases as CSF biomarkers for the neuronal response to tau pathology

INTRODUCTION

Cerebrospinal fluid (CSF) biomarkers for specific cellular disease processes are lacking for tauopathies. In this translational study we aimed to identify CSF biomarkers reflecting early tau pathology-associated unfolded protein response (UPR) activation.

METHODS

We employed mass spectrometry proteomics and targeted immunoanalysis in a combination of biomarker discovery in primary mouse neurons in vitro and validation in patient CSF from two independent large multicentre cohorts (EMIF-AD MBD, n = 310; PRIDE, n = 771).

RESULTS

First, we identify members of the protein disulfide isomerase (PDI) family in the neuronal UPR-activated secretome and validate secretion upon tau aggregation in vitro. Next, we demonstrate that PDIA1 and PDIA3 levels correlate with total- and phosphorylated-tau levels in CSF. PDIA1 levels are increased in CSF from AD patients compared to controls and patients with tau-unrelated frontotemporal and Lewy body dementia (LBD).

HIGHLIGHTS

Neuronal unfolded protein response (UPR) activation induces the secretion of protein disulfide isomerases (PDIs) in vitro. PDIA1 is secreted upon tau aggregation in neurons in vitro. PDIA1 and PDIA3 levels correlate with total and phosphorylated tau levels in CSF. PDIA1 levels are increased in CSF from Alzheimer's disease (AD) patients compared to controls. PDIA1 levels are not increased in CSF from tau-unrelated frontotemporal dementia (FTD) and Lewy body dementia (LBD) patients.

The proteomic effects of ketone bodies: implications for proteostasis and brain proteinopathies

A growing body of evidence supports the beneficial effects of the ketone bodies (KBs), acetoacetate and β-hydroxybutyrate (BHB), on diverse physiological processes and diseases. Hence, KBs have been suggested as therapeutic tools for neurodegenerative diseases. KBs are an alternative fuel during fasting and starvation as they can be converted to Ac-CoA to produce ATP. A ketogenic diet (KD), enriched in fats and low in carbohydrates, induces KB production in the liver and favors their use in the brain. BHB is the most abundant KB in the circulation; in addition to its role as energy fuel, it exerts many actions that impact the set of proteins in the cell and tissue. BHB can covalently bind to proteins in lysine residues as a new post-translational modification (PTM) named β-hydroxybutyrylation (Kbhb). Kbhb has been identified in many proteins where Kbhb sites can be critical for binding to other proteins or cofactors. Kbhb is mostly found in proteins involved in chromatin structure, DNA repair, regulation of spliceosome, transcription, and oxidative phosphorylation. Histones are the most studied family of proteins with this PTM, and H3K9bhb is the best studied histone mark. Their target genes are mainly related to cell metabolism, chromatin remodeling and the control of circadian rhythms. The role of Kbhb on physiological processes is poorly known, but it might link KB metabolism to cell signaling and genome regulation. BHB also impacts the proteome by influencing proteostasis. This KB can modulate the Unfolded Protein Response (UPR) and autophagy, two processes involved in the maintenance of protein homeostasis through the clearance of accumulated unfolded and damaged proteins. BHB can support proteostasis and regulate the UPR to promote metabolism adaptation in the liver and prevent cell damage in the brain. Also, BHB stimulates autophagy aiding to the degradation of accumulated proteins. Protein aggregation is common to proteinopathies like Alzheimer's (AD) and Parkinson's (PD) diseases, where the KD and BHB treatment have shown favorable effects. In the present review, the current literature supporting the effects of KBs on proteome conformation and proteostasis is discussed, as well as its possible impact on AD and PD.

Structurally and Morphologically Distinct Pathological Tau Assemblies Differentially Affect GVB Accumulation

Tau aggregation is central to the pathogenesis of a large group of neurodegenerative diseases termed tauopathies, but it is still unclear in which way neurons respond to tau pathology and how tau accumulation leads to neurodegeneration. A striking neuron-specific response to tau pathology is presented by granulovacuolar degeneration bodies (GVBs), lysosomal structures that accumulate specific cargo in a dense core. Here we employed different tau aggregation models in primary neurons to investigate which properties of pathological tau assemblies affect GVB accumulation using a combination of confocal microscopy, transmission electron microscopy, and quantitative automated high-content microscopy. Employing GFP-tagged and untagged tau variants that spontaneously form intraneuronal aggregates, we induced pathological tau assemblies with a distinct subcellular localization, morphology, and ultrastructure depending on the presence or absence of the GFP tag. The quantification of the GVB load in the different models showed that an increased GVB accumulation is associated with the untagged tau aggregation model, characterized by shorter and more randomly distributed tau filaments in the neuronal soma. Our data indicate that tau aggregate structure and/or subcellular localization may be key determinants of GVB accumulation.

ApoER2-Dab1 disruption as the origin of pTau-related neurodegeneration in sporadic Alzheimer's disease

BACKGROUND

Sporadic Alzheimer's disease (sAD) is not a global brain disease. Specific regions, layers and neurons degenerate early while others remain untouched even in advanced disease. The prevailing model used to explain this selective neurodegeneration-prion-like Tau spread-has key limitations and is not easily integrated with other defining sAD features. Instead, we propose that in humans Tau hyperphosphorylation occurs locally via disruption in ApoER2-Dab1 signaling and thus the presence of ApoER2 in neuronal membranes confers vulnerability to degeneration. Further, we propose that disruption of the Reelin/ApoE/ApoJ-ApoER2-Dab1-P85α-LIMK1-Tau-PSD95 (RAAAD-P-LTP) pathway induces deficits in memory and cognition by impeding neuronal lipoprotein internalization and destabilizing actin, microtubules, and synapses. This new model is based in part on our recent finding that ApoER2-Dab1 disruption is evident in entorhinal-hippocampal terminal zones in sAD. Here, we hypothesized that neurons that degenerate in the earliest stages of sAD (1) strongly express ApoER2 and (2) show evidence of ApoER2-Dab1 disruption through co-accumulation of multiple RAAAD-P-LTP components.

METHODS

We applied in situ hybridization and immunohistochemistry to characterize ApoER2 expression and accumulation of RAAAD-P-LTP components in five regions that are prone to early pTau pathology in 64 rapidly autopsied cases spanning the clinicopathological spectrum of sAD.

RESULTS

We found that: (1) selectively vulnerable neuron populations strongly express ApoER2; (2) numerous RAAAD-P-LTP pathway components accumulate in neuritic plaques and abnormal neurons; and (3) RAAAD-P-LTP components were higher in MCI and sAD cases and correlated with histological progression and cognitive deficits. Multiplex-IHC revealed that Dab1, pP85αTyr607, pLIMK1Thr508, pTau and pPSD95Thr19 accumulated together within dystrophic dendrites and soma of ApoER2-expressing neurons in the vicinity of ApoE/ApoJ-enriched extracellular plaques. These observations provide evidence for molecular derangements that can be traced back to ApoER2-Dab1 disruption, in each of the sampled regions, layers, and neuron populations that are prone to early pTau pathology.

CONCLUSION

Findings support the RAAAD-P-LTP hypothesis, a unifying model that implicates dendritic ApoER2-Dab1 disruption as the major driver of both pTau accumulation and neurodegeneration in sAD. This model provides a new conceptual framework to explain why specific neurons degenerate and identifies RAAAD-P-LTP pathway components as potential mechanism-based biomarkers and therapeutic targets for sAD.

Knockout of PERK protects rat Müller glial cells against OGD-induced endoplasmic reticulum stress-related apoptosis

BACKGROUND

The pathological basis for many retinal diseases, retinal ischemia is also one of the most common causes of visual impairment. Numerous ocular diseases have been linked to Endoplasmic reticulum(ER)stress. However, there is still no clear understanding of the relationship between ER stress and Müller glial cells during retinal ischemia and hypoxia. This study examined the effects of ER stress on autophagy and apoptosis-related proteins, as well as the microtubule-related protein tau in rMC-1 cells.

METHODS

rMC-1 cells were cultured in vitro. RT-PCR、immunofluorescence and Western blotting revealed the expression levels of associated mRNAs and proteins, and the CCK-8 and flow cytometry assays detected cell apoptosis.

RESULTS

The results showed that under OGD(Oxygen-glucose deprivation) conditions, the number of rMC-1 cells was decreased, the PERK/eIF2a pathway was activated, and the expressions of p-tau, LC3、Beclin1 and Caspase-12 proteins were increased. After the PERK knockout, the expression of the above proteins was decreased, and the apoptosis was also decreased.

CONCLUSION

According to the findings of this study, specific downregulation of PERK expression had an anti-apoptotic effect on OGD-conditioned rMC-1 cells. There is a possibility that this is one of the mechanisms of MG cell apoptosis during retinal ischemic injury.

Soluble and insoluble protein aggregates, endoplasmic reticulum stress, and vascular dysfunction in Alzheimer's disease and cardiovascular diseases

Dementia refers to a particular group of symptoms characterized by difficulties with memory, language, problem-solving, and other thinking skills that affect a person's ability to perform everyday activities. Alzheimer's disease (AD) is the most common form of dementia, affecting about 6.2 million Americans aged 65 years and older. Likewise, cardiovascular diseases (CVDs) are a major cause of disability and premature death, impacting 126.9 million adults in the USA, a number that increases with age. Consequently, CVDs and cardiovascular risk factors are associated with an increased risk of AD and cognitive impairment. They share important age-related cardiometabolic and lifestyle risk factors, that make them among the leading causes of death. Additionally, there are several premises and hypotheses about the mechanisms underlying the association between AD and CVD. Although AD and CVD may be considered deleterious to health, the study of their combination constitutes a clinical challenge, and investigations to understand the mechanistic pathways for the cause-effect and/or shared pathology between these two disease constellations remains an active area of research. AD pathology is propagated by the amyloid β (Aβ) peptides. These peptides give rise to small, toxic, and soluble Aβ oligomers (SPOs) that are nonfibrillar, and it is their levels that show a robust correlation with the extent of cognitive impairment. This review will elucidate the interplay between the effects of accumulating SPOs in AD and CVDs, the resulting ER stress response, and their role in vascular dysfunction. We will also address the potential underlying mechanisms, including the possibility that SPOs are among the causes of vascular injury in CVD associated with cognitive decline. By revealing common mechanistic underpinnings of AD and CVD, we hope that novel experimental therapeutics can be designed to reduce the burden of these devastating diseases. Graphical abstract Alzheimer's disease (AD) pathology leads to the release of Aβ peptides, and their accumulation in the peripheral organs has varying effects on various components of the cardiovascular system including endoplasmic reticulum (ER) stress and vascular damage. Image created with BioRender.com.

Early and late chaperone intervention therapy boosts XBP1s and ADAM10, restores proteostasis, and rescues learning in Alzheimer's Disease mice

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder that is pervasive among the aging population. Two distinct phenotypes of AD are deficits in cognition and proteostasis, including chronic activation of the unfolded protein response (UPR) and aberrant Aβ production. It is unknown if restoring proteostasis by reducing chronic and aberrant UPR activation in AD can improve pathology and cognition. Here, we present data using an APP knock-in mouse model of AD and several protein chaperone supplementation paradigms, including a late-stage intervention. We show that supplementing protein chaperones systemically and locally in the hippocampus reduces PERK signaling and increases XBP1s, which is associated with increased ADAM10 and decreased Aβ42. Importantly, chaperone treatment improves cognition which is correlated with increased CREB phosphorylation and BDNF. Together, this data suggests that chaperone treatment restores proteostasis in a mouse model of AD and that this restoration is associated with improved cognition and reduced pathology.

One-sentence summary

Chaperone therapy in a mouse model of Alzheimer's disease improves cognition by reducing chronic UPR activity.

ApoER2-Dab1 disruption as the origin of pTau-related neurodegeneration in sporadic Alzheimer's disease

BACKGROUND

Sporadic Alzheimer's disease (sAD) is not a global brain disease. Specific regions, layers and neurons degenerate early while others remain untouched even in advanced disease. The prevailing model used to explain this selective neurodegeneration-prion-like Tau spread-has key limitations and is not easily integrated with other defining sAD features. Instead, we propose that in humans Tau hyperphosphorylation occurs locally via disruption in ApoER2-Dab1 signaling and thus the presence of ApoER2 in neuronal membranes confers vulnerability to degeneration. Further, we propose that disruption of the Reelin/ApoE/ApoJ-ApoER2-Dab1-P85α-LIMK1-Tau-PSD95 (RAAAD-P-LTP) pathway induces deficits in memory and cognition by impeding neuronal lipoprotein internalization and destabilizing actin, microtubules, and synapses. This new model is based in part on our recent finding that ApoER2-Dab1 disruption is evident in entorhinal-hippocampal terminal zones in sAD. Here, we hypothesized that neurons that degenerate in the earliest stages of sAD (1) strongly express ApoER2 and (2) show evidence of ApoER2-Dab1 disruption through co-accumulation of multiple RAAAD-P-LTP components.

METHODS

We applied in situ hybridization and immunohistochemistry to characterize ApoER2 expression and accumulation of RAAAD-P-LTP components in five regions that are prone to early pTau pathology in 64 rapidly autopsied cases spanning the clinicopathological spectrum of sAD.

RESULTS

We found that: (1) selectively vulnerable neuron populations strongly express ApoER2; (2) numerous RAAAD-P-LTP pathway components accumulate in neuritic plaques and abnormal neurons; and (3) RAAAD-P-LTP components were higher in MCI and sAD cases and correlated with histological progression and cognitive deficits. Multiplex-IHC revealed that Dab1, pP85αTyr607, pLIMK1Thr508, pTau and pPSD95Thr19 accumulated together within dystrophic dendrites and soma of ApoER2-expressing neurons in the vicinity of ApoE/ApoJ-enriched extracellular plaques. These observations provide evidence for molecular derangements that can be traced back to ApoER2-Dab1 disruption, in each of the sampled regions, layers, and neuron populations that are prone to early pTau pathology.

CONCLUSION

Findings support the RAAAD-P-LTP hypothesis, a unifying model that implicates dendritic ApoER2-Dab1 disruption as the major driver of both pTau accumulation and neurodegeneration in sAD. This model provides a new conceptual framework to explain why specific neurons degenerate and identifies RAAAD-P-LTP pathway components as potential mechanism-based biomarkers and therapeutic targets for sAD.

Proteostasis failure exacerbates neuronal circuit dysfunction and sleep impairments in Alzheimer's disease

Failed proteostasis is a well-documented feature of Alzheimer's disease, particularly, reduced protein degradation and clearance. However, the contribution of failed proteostasis to neuronal circuit dysfunction is an emerging concept in neurodegenerative research and will prove critical in understanding cognitive decline. Our objective is to convey Alzheimer's disease progression with the growing evidence for a bidirectional relationship of sleep disruption and proteostasis failure. Proteostasis dysfunction and tauopathy in Alzheimer's disease disrupts neurons that regulate the sleep-wake cycle, which presents behavior as impaired slow wave and rapid eye movement sleep patterns. Subsequent sleep loss further impairs protein clearance. Sleep loss is a defined feature seen early in many neurodegenerative disorders and contributes to memory impairments in Alzheimer's disease. Canonical pathological hallmarks, β-amyloid, and tau, directly disrupt sleep, and neurodegeneration of locus coeruleus, hippocampal and hypothalamic neurons from tau proteinopathy causes disruption of the neuronal circuitry of sleep. Acting in a positive-feedback-loop, sleep loss and circadian rhythm disruption then increase spread of β-amyloid and tau, through impairments of proteasome, autophagy, unfolded protein response and glymphatic clearance. This phenomenon extends beyond β-amyloid and tau, with interactions of sleep impairment with the homeostasis of TDP-43, α-synuclein, FUS, and huntingtin proteins, implicating sleep loss as an important consideration in an array of neurodegenerative diseases and in cases of mixed neuropathology. Critically, the dynamics of this interaction in the neurodegenerative environment are not fully elucidated and are deserving of further discussion and research. Finally, we propose sleep-enhancing therapeutics as potential interventions for promoting healthy proteostasis, including β-amyloid and tau clearance, mechanistically linking these processes. With further clinical and preclinical research, we propose this dynamic interaction as a diagnostic and therapeutic framework, informing precise single- and combinatorial-treatments for Alzheimer's disease and other brain disorders.

Δ8-THC Protects against Amyloid Beta Toxicity Modulating ER Stress In Vitro: A Transcriptomic Analysis

Alzheimer’s disease (AD) represents the most common form of dementia, characterized by amyloid β (Aβ) plaques and neurofibrillary tangles (NFTs). It is characterized by neuroinflammation, the accumulation of misfolded protein, ER stress and neuronal apoptosis. It is of main importance to find new therapeutic strategies because AD prevalence is increasing worldwide. Cannabinoids are arising as promising neuroprotective phytocompounds. In this study, we evaluated the neuroprotective potential of Δ8-THC pretreatment in an in vitro model of AD through transcriptomic analysis. We found that Δ8-THC pretreatment restored the loss of cell viability in retinoic acid-differentiated neuroblastoma SH-SY5Y cells treated with Aβ1-42. Moreover, the transcriptomic analysis provided evidence that the enriched biological processes of gene ontology were related to ER functions and proteostasis. In particular, Aβ1-42 upregulated genes involved in ER stress and unfolded protein response, leading to apoptosis as demonstrated by the increase in Bax and the decrease in Bcl-2 both at gene and protein expression levels. Moreover, genes involved in protein folding and degradation were also deregulated. On the contrary, Δ8-THC pretreatment reduced ER stress and, as a consequence, neuronal apoptosis. Then, the results demonstrated that Δ8-THC might represent a new neuroprotective agent in AD.

The endoplasmic reticulum stress and unfolded protein response in Alzheimer's disease: a calcium dyshomeostasis perspective

Protein misfolding is prominent in early cellular pathology of Alzheimer's disease (AD), implicating pathophysiological significance of endoplasmic reticulum stress/unfolded protein response (ER stress/UPR) and highlighting it as a target for drug development. Experimental data from animal AD models and observations on human specimens are, however, inconsistent. ER stress and associated UPR are readily observed in in vitro AD cellular models and in some AD model animals. In the human brain, components and markers of ER stress as well as UPR transducers are observed at Braak stages III-VI associated with severe neuropathology and neuronal death. The picture, however, is further complicated by the brain region- and cell type-specificity of the AD-related pathology. Terms 'disturbed' or 'non-canonical' ER stress/UPR were used to describe the discrepancies between experimental data and the classic ER stress/UPR cascade. Here we discuss possible 'disturbing' or 'interfering' factors which may modify ER stress/UPR in the early AD pathogenesis. We focus on the dysregulation of the ER Ca²⁺ homeostasis, store-operated Ca²⁺ entry, and the interaction between the ER and mitochondria. We suggest that a detailed study of the CNS cell type-specific alterations of Ca²⁺ homeostasis in early AD may deepen our understanding of AD-related dysproteostasis.

The potential roles of ATF family in the treatment of Alzheimer's disease

Activating transcription factors, ATFs, is a family of transcription factors that activate gene expression and transcription by recognizing and combining the cAMP response element binding proteins (CREB). It is present in various viruses as a cellular gene promoter. ATFs is involved in regulating the mammalian gene expression that is associated with various cell physiological processes. Therefore, ATFs play an important role in maintaining the intracellular homeostasis. ATF2 and ATF3 is mostly involved in mediating stress responses. ATF4 regulates the oxidative metabolism, which is associated with the survival of cells. ATF5 is presumed to regulate apoptosis, and ATF6 is involved in the regulation of endoplasmic reticulum stress (ERS). ATFs is actively studied in oncology. At present, there has been an increasing amount of research on ATFs for the treatment of neurological diseases. Here, we have focused on the different types of ATFs and their association with Alzheimer's disease (AD). The level of expression of different ATFs have a significant difference in AD patients when compared to healthy control. Recent studies have suggested that ATFs are implicated in the pathogenesis of AD, such as neuronal repair, maintenance of synaptic activity, maintenance of cell survival, inhibition of apoptosis, and regulation of stress responses. In this review, the potential role of ATFs for the treatment of AD has been highlighted. In addition, we have systematically reviewed the progress of research on ATFs in AD. This review will provide a basic and innovative understanding on the pathogenesis and treatment of AD.

The unique neuropathological vulnerability of the human brain to aging

Alzheimer's disease (AD)-related neurofibrillary tangles (NFT), argyrophilic grain disease (AGD), aging-related tau astrogliopathy (ARTAG), limbic predominant TDP-43 proteinopathy (LATE), and amygdala-predominant Lewy body disease (LBD) are proteinopathies that, together with hippocampal sclerosis, progressively appear in the elderly affecting from 50% to 99% of individuals aged 80 years, depending on the disease. These disorders usually converge on the same subject and associate with additive cognitive impairment. Abnormal Tau, TDP-43, and α-synuclein pathologies progress following a pattern consistent with an active cell-to-cell transmission and abnormal protein processing in the host cell. However, cell vulnerability and transmission pathways are specific for each disorder, albeit abnormal proteins may co-localize in particular neurons. All these alterations are unique or highly prevalent in humans. They all affect, at first, the archicortex and paleocortex to extend at later stages to the neocortex and other regions of the telencephalon. These observations show that the phylogenetically oldest areas of the human cerebral cortex and amygdala are not designed to cope with the lifespan of actual humans. New strategies aimed at reducing the functional overload of the human telencephalon, including optimization of dream repair mechanisms and implementation of artificial circuit devices to surrogate specific brain functions, appear promising.

Defective proteostasis in Alzheimer's disease

The homeostasis of cellular proteins, or proteostasis, is critical for neuronal function and for brain processes, including learning and memory. Increasing evidence indicates that defective proteostasis contributes to the progression of neurodegenerative disorders, including Alzheimer's disease (AD), the most prevalent form of dementia in the elderly. Proteostasis comprises a set of cellular mechanisms that control protein synthesis, folding, post-translational modification and degradation, all of which are deregulated in AD. Importantly, deregulation of proteostasis plays a key role in synapse dysfunction and in memory impairment, the major clinical manifestation of AD. Here, we discuss molecular pathways involved in protein synthesis and degradation that are altered in AD, and possible pharmacological approaches to correct these defects.

Chaperone-Dependent Mechanisms as a Pharmacological Target for Neuroprotection

Modern pharmacotherapy of neurodegenerative diseases is predominantly symptomatic and does not allow vicious circles causing disease development to break. Protein misfolding is considered the most important pathogenetic factor of neurodegenerative diseases. Physiological mechanisms related to the function of chaperones, which contribute to the restoration of native conformation of functionally important proteins, evolved evolutionarily. These mechanisms can be considered promising for pharmacological regulation. Therefore, the aim of this review was to analyze the mechanisms of endoplasmic reticulum stress (ER stress) and unfolded protein response (UPR) in the pathogenesis of neurodegenerative diseases. Data on BiP and Sigma1R chaperones in clinical and experimental studies of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease are presented. The possibility of neuroprotective effect dependent on Sigma1R ligand activation in these diseases is also demonstrated. The interaction between Sigma1R and BiP-associated signaling in the neuroprotection is discussed. The performed analysis suggests the feasibility of pharmacological regulation of chaperone function, possibility of ligand activation of Sigma1R in order to achieve a neuroprotective effect, and the need for further studies of the conjugation of cellular mechanisms controlled by Sigma1R and BiP chaperones.

Protein quality control and aggregation in the endoplasmic reticulum: From basic to bedside

Endoplasmic reticulum (ER) is the largest membrane-bound compartment in all cells and functions as a key regulator in protein biosynthesis, lipid metabolism, and calcium balance. Mammalian endoplasmic reticulum has evolved with an orchestrated protein quality control system to handle defective proteins and ensure endoplasmic reticulum homeostasis. Nevertheless, the accumulation and aggregation of misfolded proteins in the endoplasmic reticulum may occur during pathological conditions. The inability of endoplasmic reticulum quality control system to clear faulty proteins and aggregates from the endoplasmic reticulum results in the development of many human disorders. The efforts to comprehensively understand endoplasmic reticulum quality control network and protein aggregation will benefit the diagnostics and therapeutics of endoplasmic reticulum storage diseases. Herein, we overview recent advances in mammalian endoplasmic reticulum protein quality control system, describe protein phase transition model, and summarize the approaches to monitor protein aggregation. Moreover, we discuss the therapeutic applications of enhancing endoplasmic reticulum protein quality control pathways in endoplasmic reticulum storage diseases.