Pathological stress granules in Alzheimer's disease

Microglial-derived C1q integrates into neuronal ribonucleoprotein complexes and impacts protein homeostasis in the aging brain

Neuroimmune interactions mediate intercellular communication and underlie critical brain functions. Microglia, CNS-resident macrophages, modulate the brain through direct physical interactions and the secretion of molecules. One such secreted factor, the complement protein C1q, contributes to complement-mediated synapse elimination in both developmental and disease models, yet brain C1q protein levels increase significantly throughout aging. Here, we report that C1q interacts with neuronal ribonucleoprotein (RNP) complexes in an age-dependent manner. Purified C1q protein undergoes RNA-dependent liquid-liquid phase separation (LLPS) in vitro, and the interaction of C1q with neuronal RNP complexes in vivo is dependent on RNA and endocytosis. Mice lacking C1q have age-specific alterations in neuronal protein synthesis in vivo and impaired fear memory extinction. Together, our findings reveal a biophysical property of C1q that underlies RNA- and age-dependent neuronal interactions and demonstrate a role of C1q in critical intracellular neuronal processes.

Polysome collapse and RNA condensation fluidize the cytoplasm

The cell interior is packed with macromolecules of mesoscale size, and this crowded milieu significantly influences cellular physiology. Cellular stress responses almost universally lead to inhibition of translation, resulting in polysome collapse and release of mRNA. The released mRNA molecules condense with RNA-binding proteins to form ribonucleoprotein (RNP) condensates known as processing bodies and stress granules. Here, we show that polysome collapse and condensation of RNA transiently fluidize the cytoplasm, and coarse-grained molecular dynamic simulations support this as a minimal mechanism for the observed biophysical changes. Increased mesoscale diffusivity correlates with the efficient formation of quality control bodies (Q-bodies), membraneless organelles that compartmentalize misfolded peptides during stress. Synthetic, light-induced RNA condensation also fluidizes the cytoplasm. Together, our study reveals a functional role for stress-induced translation inhibition and formation of RNP condensates in modulating the physical properties of the cytoplasm to enable efficient response of cells to stress conditions.

SARS-CoV-2 Nucleocapsid Protein Induces Tau Pathological Changes That Can Be Counteracted by SUMO2

Neurologic manifestations are an immediate consequence of SARS-CoV-2 infection, the etiologic agent of COVID-19, which, however, may also trigger long-term neurological effects. Notably, COVID-19 patients with neurological symptoms show elevated levels of biomarkers associated with brain injury, including Tau proteins linked to Alzheimer's pathology. Studies in brain organoids revealed that SARS-CoV-2 alters the phosphorylation and distribution of Tau in infected neurons, but the mechanisms are currently unknown. We hypothesize that these pathological changes are due to the recruitment of Tau into stress granules (SGs) operated by the nucleocapsid protein (NCAP) of SARS-CoV-2. To test this hypothesis, we investigated whether NCAP interacts with Tau and localizes to SGs in hippocampal neurons in vitro and in vivo. Mechanistically, we tested whether SUMOylation, a posttranslational modification of NCAP and Tau, modulates their distribution in SGs and their pathological interaction. We found that NCAP and Tau colocalize and physically interact. We also found that NCAP induces hyperphosphorylation of Tau and causes cognitive impairment in mice infected with NCAP in their hippocampus. Finally, we found that SUMOylation modulates NCAP SG formation in vitro and cognitive performance in infected mice. Our data demonstrate that NCAP induces Tau pathological changes both in vitro and in vivo. Moreover, we demonstrate that SUMO2 ameliorates NCAP-induced Tau pathology, highlighting the importance of the SUMOylation pathway as a target of intervention against neurotoxic insults, such as Tau oligomers and viral infection.

Valosin-Containing Protein (VCP): A Review of Its Diverse Molecular Functions and Clinical Phenotypes

In this review we examine the functionally diverse ATPase associated with various cellular activities (AAA-ATPase), valosin-containing protein (VCP/p97), its molecular functions, the mutational landscape of VCP and the phenotypic manifestation of VCP disease. VCP is crucial to a multitude of cellular functions including protein quality control, endoplasmic reticulum-associated degradation (ERAD), autophagy, mitophagy, lysophagy, stress granule formation and clearance, DNA replication and mitosis, DNA damage response including nucleotide excision repair, ATM- and ATR-mediated damage response, homologous repair and non-homologous end joining. VCP variants cause multisystem proteinopathy, and pathology can arise in several tissue types such as skeletal muscle, bone, brain, motor neurons, sensory neurons and possibly cardiac muscle, with the disease course being challenging to predict.

Protein Compartments Modulate Fibrillar Self-Assembly

A notable feature of complex cellular environments is protein-rich compartments that are formed via liquid-liquid phase separation. Recent studies have shown that these biomolecular condensates can play both promoting and inhibitory roles in fibrillar protein self-assembly, a process that is linked to Alzheimer's, Parkinson's, Huntington's, and various prion diseases. Yet, the exact regulatory role of these condensates in protein aggregation remains unknown. By employing microfluidics to create artificial protein compartments, the self-assembly behavior of the fibrillar protein lysozyme within them can be characterized. It is observed that the volumetric parameters of protein-rich compartments can change the kinetics of protein self-assembly. Depending on the change in compartment parameters, the lysozyme fibrillation process either accelerated or decelerated. Furthermore, the results confirm that the volumetric parameters govern not only the nucleation and growth phases of the fibrillar aggregates but also affect the crosstalk between the protein-rich and protein-poor phases. The appearance of phase-separated compartments in the vicinity of natively folded protein complexes triggers their abrupt percolation into the compartments' core and further accelerates protein aggregation. Overall, the results of the study shed more light on the complex behavior and functions of protein-rich phases and, importantly, on their interaction with the surrounding environment.

SERBP1 interacts with PARP1 and is present in PARylation-dependent protein complexes regulating splicing, cell division, and ribosome biogenesis

RNA binding proteins (RBPs) containing intrinsically disordered regions (IDRs) are present in diverse molecular complexes where they function as dynamic regulators. Their characteristics promote liquid-liquid phase separation (LLPS) and the formation of membraneless organelles such as stress granules and nucleoli. IDR-RBPs are particularly relevant in the nervous system and their dysfunction is associated with neurodegenerative diseases and brain tumor development. SERBP1 is a unique member of this group, being mostly disordered and lacking canonical RNA-binding domains. Using a proteomics approach followed by functional analysis, we defined SERBP1's interactome. We uncovered novel SERBP1 roles in splicing, cell division, and ribosomal biogenesis and showed its participation in pathological stress granules and Tau aggregates in Alzheimer's disease brains. SERBP1 preferentially interacts with other G-quadruplex (G4) binders, implicated in different stages of gene expression, suggesting that G4 binding is a critical component of SERBP1 function in different settings. Similarly, we identified important associations between SERBP1 and PARP1/polyADP-ribosylation (PARylation). SERBP1 interacts with PARP1 and its associated factors and influences PARylation. Moreover, protein complexes in which SERBP1 participates contain mostly PARylated proteins and PAR binders. Based on these results, we propose a feedback regulatory model in which SERBP1 influences PARP1 function and PARylation, while PARylation modulates SERBP1 functions and participation in regulatory complexes.

β-amyloid accumulation enhances microtubule associated protein tau pathology in an APPNL-G-F/MAPTP301S mouse model of Alzheimer's disease

Introduction

The study of the pathophysiology study of Alzheimer's disease (AD) has been hampered by lack animal models that recapitulate the major AD pathologies, including extracellular -amyloid (A) deposition, intracellular aggregation of microtubule associated protein tau (MAPT), inflammation and neurodegeneration.

Methods

The humanized APPNL-G-F knock-in mouse line was crossed to the PS19 MAPTP301S, over-expression mouse line to create the dual APPNL-G-F/PS19 MAPTP301S line. The resulting pathologies were characterized by immunochemical methods and PCR.

Results

We now report on a double transgenic APPNL-G-F/PS19 MAPTP301S mouse that at 6 months of age exhibits robust A plaque accumulation, intense MAPT pathology, strong inflammation and extensive neurodegeneration. The presence of A pathology potentiated the other major pathologies, including MAPT pathology, inflammation and neurodegeneration. MAPT pathology neither changed levels of amyloid precursor protein nor potentiated A accumulation. Interestingly, study of immunofluorescence in cleared brains indicates that microglial inflammation was generally stronger in the hippocampus, dentate gyrus and entorhinal cortex, which are regions with predominant MAPT pathology. The APPNL-G-F/MAPTP301S mouse model also showed strong accumulation of N6-methyladenosine (m6A), which was recently shown to be elevated in the AD brain. m6A primarily accumulated in neuronal soma, but also co-localized with a subset of astrocytes and microglia. The accumulation of m6A corresponded with increases in METTL3 and decreases in ALKBH5, which are enzymes that add or remove m6A from mRNA, respectively.

Discussion

Our understanding of the pathophysiology of Alzheimer's disease (AD) has been hampered by lack animal models that recapitulate the major AD pathologies, including extracellular -amyloid (A) deposition, intracellular aggregation of microtubule associated protein tau (MAPT), inflammation and neurodegeneration. The APPNL-G-F/MAPTP301S mouse recapitulates many features of AD pathology beginning at 6 months of aging, and thus represents a useful new mouse model for the field.

Mitochondrial dysfunction in neurodegenerative disorders: Potential therapeutic application of mitochondrial transfer to central nervous system-residing cells

Mitochondrial dysfunction is reiteratively involved in the pathogenesis of diverse neurodegenerative diseases. Current in vitro and in vivo approaches support that mitochondrial dysfunction is branded by several molecular and cellular defects, whose impact at different levels including the calcium and iron homeostasis, energetic balance and/or oxidative stress, makes it difficult to resolve them collectively given their multifactorial nature. Mitochondrial transfer offers an overall solution since it contains the replacement of damage mitochondria by healthy units. Therefore, this review provides an introducing view on the structure and energy-related functions of mitochondria as well as their dynamics. In turn, we summarize current knowledge on how these features are deregulated in different neurodegenerative diseases, including frontotemporal dementia, multiple sclerosis, amyotrophic lateral sclerosis, Friedreich ataxia, Alzheimer´s disease, Parkinson´s disease, and Huntington's disease. Finally, we analyzed current advances in mitochondrial transfer between diverse cell types that actively participate in neurodegenerative processes, and how they might be projected toward developing novel therapeutic strategies.

Moyamoya disease-specific extracellular vesicle-derived microRNAs in the cerebrospinal fluid revealed by comprehensive expression analysis through microRNA sequencing

PURPOSE

To examine the specific changes that occur in the expression levels of extracellular vesicle-derived microRNAs (miRNAs) in intracranial cerebrospinal fluid (CSF) in moyamoya disease.

METHODS

Patients with arteriosclerotic cerebral ischemia were used as controls to eliminate the effects of cerebral ischemia. Intracranial CSF was collected from moyamoya disease and control patients during bypass surgery. Extracellular vesicles (EVs) were extracted from the CSF. Comprehensive expression analysis of miRNAs extracted from EVs by next-generation sequencing (NGS) and validation by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was performed.

RESULTS

Experiments were conducted on eight cases of moyamoya disease and four control cases. In the comprehensive miRNA expression analysis, 153 miRNAs were upregulated, and 98 miRNAs were downregulated in moyamoya disease compared to the control cases (q-value < 0.05 and |log2 fold change|> 1). qRT-PCR performed on the four most variable miRNAs (hsa-miR-421, hsa-miR-361-5p, hsa-miR-320a, and hsa-miR-29b-3p) associated with vascular lesions among the differentially expressed miRNAs gave the same results as miRNA sequencing. On gene ontology (GO) analysis for the target genes, cytoplasmic stress granule was the most significant GO term.

CONCLUSIONS

This study is the first comprehensive expression analysis of EV-derived miRNAs in the CSF of moyamoya disease patients using NGS. The miRNAs identified here may be related to the etiology and pathophysiology of moyamoya disease.

mRNA condensation fluidizes the cytoplasm

The intracellular environment is packed with macromolecules of mesoscale size, and this crowded milieu significantly influences cell physiology. When exposed to stress, mRNAs released after translational arrest condense with RNA binding proteins, resulting in the formation of membraneless RNA protein (RNP) condensates known as processing bodies (P-bodies) and stress granules (SGs). However, the impact of the assembly of these condensates on the biophysical properties of the crowded cytoplasmic environment remains unclear. Here, we find that upon exposure to stress, polysome collapse and condensation of mRNAs increases mesoscale particle diffusivity in the cytoplasm. Increased mesoscale diffusivity is required for the efficient formation of Q-bodies, membraneless organelles that coordinate degradation of misfolded peptides that accumulate during stress. Additionally, we demonstrate that polysome collapse and stress granule formation has a similar effect in mammalian cells, fluidizing the cytoplasm at the mesoscale. We find that synthetic, light-induced RNA condensation is sufficient to fluidize the cytoplasm, demonstrating a causal effect of RNA condensation. Together, our work reveals a new functional role for stress-induced translation inhibition and formation of RNP condensates in modulating the physical properties of the cytoplasm to effectively respond to stressful conditions.

Connecting the dots: Neuronal senescence, stress granules, and neurodegeneration

Cellular senescence increases with aging. While senescence is associated with an exit of the cell cycle, there is ample evidence that post-mitotic cells including neurons can undergo senescence as the brain ages, and that senescence likely contributes significantly to the progression of neurodegenerative diseases (ND) such as Alzheimer's Disease (AD) and Amyotrophic Lateral Sclerosis (ALS). Stress granules (SGs) are stress-induced cytoplasmic biomolecular condensates of RNA and proteins, which have been linked to the development of AD and ALS. The SG seeding hypothesis of NDs proposes that chronic stress in aging neurons results in static SGs that progress into pathological aggregates Alterations in SG dynamics have also been linked to senescence, though studies that link SGs and senescence in the context of NDs and the aging brain have not yet been performed. In this Review, we summarize the literature on senescence, and explore the contribution of senescence to the aging brain. We describe senescence phenotypes in aging neurons and glia, and their links to neuroinflammation and the development of AD and ALS. We further examine the relationships of SGs to senescence and to ND. We propose a new hypothesis that neuronal senescence may contribute to the mechanism of SG seeding in ND by altering SG dynamics in aged cells, thereby providing additional aggregation opportunities within aged neurons.

Unconventional Source of Neurotoxic Protein Aggregation from Organelle Off-Target Bax∆2 in Alzheimer's Disease

Protein aggregates are a hallmark of Alzheimer's disease (AD). Extensive studies have focused on β-amyloid plaques and Tau tangles. Here, we illustrate a novel source of protein aggregates in AD neurons from organelle off-target proteins. Bax is a mitochondrial pore-forming pro-death protein. What happens to Bax if it fails to target mitochondria? We previously showed that a mitochondrial target-deficient alternatively spliced variant, Bax∆2, formed large cytosolic protein aggregates and triggered caspase 8-mediated cell death. Bax∆2 protein levels were low in most normal organs and the proteins were quickly degraded in cancer. Here, we found that 85% of AD patients had Bax∆2 required alternative splicing. Increased Bax∆2 proteins were mostly accumulated in neurons of AD-susceptible brain regions. Intracellularly, Bax∆2 aggregates distributed independently of Tau tangles. Interestingly, Bax∆2 aggregates triggered the formation of stress granules (SGs), a large protein-RNA complex involved in AD pathogenesis. Although the functional domains required for aggregation and cell death are the same as in cancer cells, Bax∆2 relied on SGs, not caspase 8, for neuronal cell death. These results imply that the aggregation of organelle off-target proteins, such as Bax∆2, broadens the scope of traditional AD pathogenic proteins that contribute to the neuronal stress responses and AD pathogenesis.

G-quadruplexes and associated proteins in aging and Alzheimer's disease

Aging is a prominent risk factor for many neurodegenerative disorders, such as Alzheimer's disease (AD). Alzheimer's disease is characterized by progressive cognitive decline, memory loss, and neuropsychiatric and behavioral symptoms, accounting for most of the reported dementia cases. This disease is now becoming a major challenge and burden on modern society, especially with the aging population. Over the last few decades, a significant understanding of the pathophysiology of AD has been gained by studying amyloid deposition, hyperphosphorylated tau, synaptic dysfunction, oxidative stress, calcium dysregulation, and neuroinflammation. This review focuses on the role of non-canonical secondary structures of DNA/RNA G-quadruplexes (G4s, G4-DNA, and G4-RNA), G4-binding proteins (G4BPs), and helicases, and their roles in aging and AD. Being critically important for cellular function, G4s are involved in the regulation of DNA and RNA processes, such as replication, transcription, translation, RNA localization, and degradation. Recent studies have also highlighted G4-DNA's roles in inducing DNA double-strand breaks that cause genomic instability and G4-RNA's participation in regulating stress granule formation. This review emphasizes the significance of G4s in aging processes and how their homeostatic imbalance may contribute to the pathophysiology of AD.

Accumulation of m6A exhibits stronger correlation with MAPT than β-amyloid pathology in an APPNL-G-F /MAPTP301S mouse model of Alzheimer's disease

The study for the pathophysiology study of Alzheimer's disease (AD) has been hampered by lack animal models that recapitulate the major AD pathologies, including extracellular β-amyloid (Aβ) deposition, intracellular aggregation of microtubule associated protein tau (MAPT), inflammation and neurodegeneration. We now report on a double transgenic APPNL-G-F MAPTP301S mouse that at 6 months of age exhibits robust Aβ plaque accumulation, intense MAPT pathology, strong inflammation and extensive neurodegeneration. The presence of Aβ pathology potentiated the other major pathologies, including MAPT pathology, inflammation and neurodegeneration. However, MAPT pathology neither changed levels of amyloid precursor protein nor potentiated Aβ accumulation. The APPNL-G-F/MAPTP301S mouse model also showed strong accumulation of N6-methyladenosine (m6A), which was recently shown to be elevated in the AD brain. M6A primarily accumulated in neuronal soma, but also co-localized with a subset of astrocytes and microglia. The accumulation of m6A corresponded with increases in METTL3 and decreases in ALKBH5, which are enzymes that add or remove m6A from mRNA, respectively. Thus, the APPNL-G-F/MAPTP301S mouse recapitulates many features of AD pathology beginning at 6 months of aging.

Accumulation of m6A exhibits stronger correlation with MAPT than β-amyloid pathology in an APPNL-G-F /MAPTP301S mouse model of Alzheimer's disease

The study for the pathophysiology study of Alzheimer's disease (AD) has been hampered by lack animal models that recapitulate the major AD pathologies, including extracellular β-amyloid (Aβ) deposition, intracellular aggregation of microtubule associated protein tau (MAPT), inflammation and neurodegeneration. We now report on a double transgenic APPNL-G-F MAPTP301S mouse that at 6 months of age exhibits robust Aβ plaque accumulation, intense MAPT pathology, strong inflammation and extensive neurodegeneration. The presence of Aβ pathology potentiated the other major pathologies, including MAPT pathology, inflammation and neurodegeneration. However, MAPT pathology neither changed levels of amyloid precursor protein nor potentiated Aβ accumulation. The APPNL-G-F/MAPTP301S mouse model also showed strong accumulation of N6-methyladenosine (m6A), which was recently shown to be elevated in the AD brain. M6A primarily accumulated in neuronal soma, but also co-localized with a subset of astrocytes and microglia. The accumulation of m6A corresponded with increases in METTL3 and decreases in ALKBH5, which are enzymes that add or remove m6A from mRNA, respectively. Thus, the APPNL-G-F/MAPTP301S mouse recapitulates many features of AD pathology beginning at 6 months of aging.

Canonical cellular stress granules are required for arsenite-induced necroptosis mediated by Z-DNA-binding protein 1

Cellular stress granules arise in cells subjected to stress and promote cell survival. A cellular protein that localizes to stress granules is Z-DNA-binding protein 1 (ZBP1), which plays a major role in necroptosis, a programmed cell death pathway mediated by the kinase RIPK3. Here, we showed that the stress granule inducer arsenite activated RIPK3-dependent necroptosis. This pathway required ZBP1, which localized to arsenite-induced stress granules. RIPK3 localized to stress granules in the presence of ZBP1, leading to the formation of ZBP1-RIPK3 necrosomes, phosphorylation of the RIPK3 effector MLKL, and execution of necroptosis. Cells that did not form stress granules did not induce necroptosis in response to arsenite. Together, these results show that arsenite induces ZBP1-mediated necroptosis in a manner dependent on stress granule formation.

Lipoprotein Metabolism, Protein Aggregation, and Alzheimer's Disease: A Literature Review

Alzheimer's disease (AD) is the most common form of dementia. The physiopathology of AD is well described by the presence of two neuropathological features: amyloid plaques and tau neurofibrillary tangles. In the last decade, neuroinflammation and cellular stress have gained importance as key factors in the development and pathology of AD. Chronic cellular stress occurs in degenerating neurons. Stress Granules (SGs) are nonmembranous organelles formed as a response to stress, with a protective role; however, SGs have been noted to turn into pathological and neurotoxic features when stress is chronic, and they are related to an increased tau aggregation. On the other hand, correct lipid metabolism is essential to good function of the brain; apolipoproteins are highly associated with risk of AD, and impaired cholesterol efflux and lipid transport are associated with an increased risk of AD. In this review, we provide an insight into the relationship between cellular stress, SGs, protein aggregation, and lipid metabolism in AD.

The enigma of ultraviolet radiation stress granules: Research challenges and new perspectives

Stress granules (SGs) are non-membrane bound cytoplasmic condensates that form in response to a variety of different stressors. Canonical SGs are thought to have a cytoprotective role, reallocating cellular resources during stress by activation of the integrated stress response (ISR) to inhibit translation and avoid apoptosis. However, different stresses result in compositionally distinct, non-canonical SG formation that is likely pro-apoptotic, though the exact function(s) of both SGs subtypes remain unclear. A unique non-canonical SG subtype is triggered upon exposure to ultraviolet (UV) radiation. While it is generally agreed that UV SGs are bona fide SGs due to their dependence upon the core SG nucleating protein Ras GTPase-activating protein-binding protein 1 (G3BP1), the localization of other key components of UV SGs are unknown or under debate. Further, the dynamics of UV SGs are not known, though unique properties such as cell cycle dependence have been observed. This Perspective compiles the available information on SG subtypes and on UV SGs in particular in an attempt to understand the formation, dynamics, and function of these mysterious stress-specific complexes. We identify key gaps in knowledge related to UV SGs, and examine the unique aspects of their formation. We propose that more thorough knowledge of the distinct properties of UV SGs will lead to new avenues of understanding of the function of SGs, as well as their roles in disease.

Proteomic Assessment of C57BL/6 Hippocampi after Non-Selective Pharmacological Inhibition of Nitric Oxide Synthase Activity: Implications of Seizure-like Neuronal Hyperexcitability Followed by Tauopathy

Nitric oxide (NO) is a small gaseous signaling molecule responsible for maintaining homeostasis in a myriad of tissues and molecular pathways in neurology and the cardiovasculature. In recent years, there has been increasing interest in the potential interaction between arterial stiffness (AS), an independent cardiovascular risk factor, and neurodegenerative syndromes given increasingly epidemiological study reports. For this reason, we previously investigated the mechanistic convergence between AS and neurodegeneration via the progressive non-selective inhibition of all nitric oxide synthase (NOS) isoforms with N(G)-nitro-L-arginine methyl ester (L-NAME) in C57BL/6 mice. Our previous results showed progressively increased AS in vivo and impaired visuospatial learning and memory in L-NAME-treated C57BL/6 mice. In the current study, we sought to further investigate the progressive molecular signatures in hippocampal tissue via LC–MS/MS proteomic analysis. Our data implicate mitochondrial dysfunction due to progressive L-NAME treatment. Two weeks of L-NAME treatment implicates altered G-protein-coupled-receptor signaling in the nerve synapse and associated presence of seizures and altered emotional behavior. Furthermore, molecular signatures implicate the cerebral presence of seizure-related hyperexcitability after short-term (8 weeks) treatment followed by ribosomal dysfunction and tauopathy after long-term (16 weeks) treatment.

Sexually dimorphic RNA helicases DDX3X and DDX3Y differentially regulate RNA metabolism through phase separation

Sex differences are pervasive in human health and disease. One major key to sex-biased differences lies in the sex chromosomes. Although the functions of the X chromosome proteins are well appreciated, how they compare with their Y chromosome homologs remains elusive. Herein, using ensemble and single-molecule techniques, we report that the sex chromosome-encoded RNA helicases DDX3X and DDX3Y are distinct in their propensities for liquid-liquid phase separation (LLPS), dissolution, and translation repression. We demonstrate that the N-terminal intrinsically disordered region of DDX3Y more strongly promotes LLPS than the corresponding region of DDX3X and that the weaker ATPase activity of DDX3Y, compared with DDX3X, contributes to the slower disassembly dynamics of DDX3Y-positive condensates. Interestingly, DDX3Y-dependent LLPS represses mRNA translation and enhances aggregation of FUS more strongly than DDX3X-dependent LLPS. Our study provides a platform for future comparisons of sex chromosome-encoded protein homologs, providing insights into sex differences in RNA metabolism and human disease.

T-Cell Intracellular Antigen 1-Like Protein in Physiology and Pathology

T-cell intracellular antigen 1 (TIA1)-related/like (TIAR/TIAL1) protein is a multifunctional RNA-binding protein (RBP) involved in regulating many aspects of gene expression, independently or in combination with its paralog TIA1. TIAR was first described in 1992 by Paul Anderson’s lab in relation to the development of a cell death phenotype in immune system cells, as it possesses nucleolytic activity against cytotoxic lymphocyte target cells. Similar to TIA1, it is characterized by a subcellular nucleo-cytoplasmic localization and ubiquitous expression in the cells of different tissues of higher organisms. In this paper, we review the relevant structural and functional information available about TIAR from a triple perspective (molecular, cellular and pathophysiological), paying special attention to its expression and regulation in cellular events and processes linked to human pathophysiology.

Phase-Separated Subcellular Compartmentation and Related Human Diseases

In live cells, proteins and nucleic acids can associate together through multivalent interactions, and form relatively isolated phases that undertake designated biological functions and activities. In the past decade, liquid–liquid phase separation (LLPS) has gradually been recognized as a general mechanism for the intracellular organization of biomolecules. LLPS regulates the assembly and composition of dozens of membraneless organelles and condensates in cells. Due to the altered physiological conditions or genetic mutations, phase-separated condensates may undergo aberrant formation, maturation or gelation that contributes to the onset and progression of various diseases, including neurodegenerative disorders and cancers. In this review, we summarize the properties of different membraneless organelles and condensates, and discuss multiple phase separation-regulated biological processes. Based on the dysregulation and mutations of several key regulatory proteins and signaling pathways, we also exemplify how aberrantly regulated LLPS may contribute to human diseases.

Disrupting the HDAC6-ubiquitin interaction impairs infection by influenza and Zika virus and cellular stress pathways

The deacetylase HDAC6 has tandem catalytic domains and a zinc finger domain (ZnF) binding ubiquitin (Ub). While the catalytic domain has an antiviral effect, the ZnF facilitates influenza A virus (IAV) infection and cellular stress responses. By recruiting Ub via the ZnF, HDAC6 promotes the formation of aggresomes and stress granules (SGs), dynamic structures associated with pathologies such as neurodegeneration. IAV subverts the aggresome/HDAC6 pathway to facilitate capsid uncoating during early infection. To target this pathway, we generate designed ankyrin repeat proteins (DARPins) binding the ZnF; one of these prevents interaction with Ub in vitro and in cells. Crystallographic analysis shows that it blocks the ZnF pocket where Ub engages. Conditional expression of this DARPin reversibly impairs infection by IAV and Zika virus; moreover, SGs and aggresomes are downregulated. These results validate the HDAC6 ZnF as an attractive target for drug discovery.

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A small synthetic protein (DARPin) blocks interaction between HDAC6 and ubiquitin

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This DARPin impairs infection by influenza and Zika virus at the uncoating step

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Both viruses contain ubiquitin associated with their capsid

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The DARPin also impacts the formation of aggresomes and stress granules

Proteostasis Perturbations and Their Roles in Causing Sterile Inflammation and Autoinflammatory Diseases

Proteostasis, a portmanteau of the words protein and homeostasis, refers to the ability of eukaryotic cells to maintain a stable proteome by acting on protein synthesis, quality control and/or degradation. Over the last two decades, an increasing number of disorders caused by proteostasis perturbations have been identified. Depending on their molecular etiology, such diseases may be classified into ribosomopathies, proteinopathies and proteasomopathies. Strikingly, most—if not all—of these syndromes exhibit an autoinflammatory component, implying a direct cause-and-effect relationship between proteostasis disruption and the initiation of innate immune responses. In this review, we provide a comprehensive overview of the molecular pathogenesis of these disorders and summarize current knowledge of the various mechanisms by which impaired proteostasis promotes autoinflammation. We particularly focus our discussion on the notion of how cells sense and integrate proteostasis perturbations as danger signals in the context of autoinflammatory diseases to provide insights into the complex and multiple facets of sterile inflammation.

RNA N6-Methyladenosine Modifications and Its Roles in Alzheimer's Disease

The importance of epitranscriptomics in regulating gene expression has received widespread attention. Recently, RNA methylation modifications, particularly N6-methyladenosine (m6A), have received marked attention. m6A, the most common and abundant type of eukaryotic methylation modification in RNAs, is a dynamic reversible modification that regulates nuclear splicing, stability, translation, and subcellular localization of RNAs. These processes are involved in the occurrence and development of many diseases. An increasing number of studies have focused on the role of m6A modification in Alzheimer's disease, which is the most common neurodegenerative disease. This review focuses on the general features, mechanisms, and functions of m6A methylation modification and its role in Alzheimer's disease.

Looking at the Pretty "Phase" of Membraneless Organelles: A View From Drosophila Glia

Membraneless granules assemble in different cell types and cellular loci and are the focus of intense research due to their fundamental importance for cellular organization. These dynamic organelles are commonly assembled from RNA and protein components and exhibit soft matter characteristics of molecular condensates currently characterized with biophysical approaches and super-resolution microscopy imaging. In addition, research on the molecular mechanisms of the RNA-protein granules assembly provided insights into the formation of abnormal granules and molecular aggregates, which takes place during many neurodegenerative disorders including Parkinson's diseases (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and frontotemporal dementia (FTD). While these disorders are associated with formation of abnormal granules, membraneless organelles are normally assembled in neurons and contribute to translational control and affect stability of neuronal RNAs. More recently, a new subtype of membraneless granules was identified in Drosophila glia (glial granules). Interestingly, glial granules were found to contain proteins which are the principal components of the membraneless granules in germ cells (germ granules), indicating some similarity in the functional assembly of these structures in glia and germline. This mini review highlights recent research on glial granules in the context of other membraneless organelles, including their assembly mechanisms and potential functions in the nervous system.

ZFP36 protects against oxygen-glucose deprivation/reoxygenation-induced mitochondrial fragmentation and neuronal apoptosis through inhibiting NOX4-DRP1 pathway

The imbalance of mitochondrial dynamics plays an important role in the pathogenesis of cerebral ischemia/reperfusion (I/R) injury. Zinc-finger protein 36 (ZFP36) has been documented to have neuroprotective effects, however, whether ZFP36 is involved in the regulation of neuronal survival during cerebral I/R injury remains unknown. In this study, we found that the transcriptional and translational levels of ZFP36 were increased in immortalized hippocampal HT22 neuronal cells after oxygen-glucose deprivation/reoxygenation (OGD/R) treatment. ZFP36 gene silencing exacerbated OGD/R-induced dynamin-related protein 1 (DRP1) activity, mitochondrial fragmentation, oxidative stress and neuronal apoptosis, whereas ZFP36 overexpression exhibited the opposite effects. Besides, we found that NADPH oxidase 4 (NOX4) was upregulated by OGD/R, and NOX4 inhibition remarkably attenuated OGD/R-instigated DRP1 activity, mitochondrial fragmentation and neuronal apoptosis. Further study demonstrated that ZFP36 targeted NOX4 mRNA directly by binding to the AU-rich elements (AREs) in the NOX4 3'-untranslated regions (3'-UTR) and inhibited NOX4 expression. Taken together, our data indicate that ZFP36 protects against OGD/R-induced neuronal injury by inhibiting NOX4-mediated DRP1 activation and excessive mitochondrial fission. Pharmacological targeting of ZFP36 to suppress excessive mitochondrial fission may provide new therapeutic strategies in the treatment of cerebral I/R injury.

G3BP2 regulates oscillatory shear stress-induced endothelial dysfunction

GTPase-activating SH3 domain-binding protein 2 (G3BP2) is a mediator that responds to environmental stresses through stress granule formation and is involved in the progression of chronic diseases. However, no studies have examined the contribution of G3BP2 in the oscillatory shear stress (OSS)-induced endothelial dysfunction. Here we assessed the effects of G3BP2 in endothelial cells (ECs) function and investigated the underlying mechanism. Using shear stress apparatus and partial ligation model, we identified that stress granule-related genes in ECs could be induced by OSS with RNA-seq, and then confirmed that G3BP2 was highly and specifically expressed in athero-susceptible endothelia in the OSS regions. G3bp2^–/–Apoe^–/– mice had significantly decreased atherosclerotic lesions associated with deficiency of G3BP2 in protecting endothelial barrier function, decreasing monocyte adhesion to ECs and inhibiting the proinflammatory cytokine levels. Furthermore, loss of G3BP2 diminished OSS-induced inflammation in ECs by increasing YAP nucleocytoplasmic shuttling and phosphorylation. These data demonstrate that G3BP2 is a critical OSS regulated gene in regulating ECs function and that G3BP2 inhibition in ECs is a promising atheroprotective therapeutic strategy.

The potential role of Piper guineense (black pepper) in managing geriatric brain aging: a review

Brain aging is one of the unavoidable aspects of geriatric life. As one ages, changes such as the shrinking of certain parts (particularly the frontal cortex, which is vital to learning and other complex mental activities) of the brain may occur. Consequently, communications between neurons are less effective, and blood flow to the brain could also decrease. Efforts made at the biological level for repair become inadequate, leading to the accumulation of β-amyloid peptide in the brain faster than its probable degradation mechanism, resulting in cognitive malfunction. Subsequent clinical usage of drugs in battling related brain-aging ailments has been associated with several undesirable side effects. However, recent research has investigated the potential use of natural compounds from food in combating such occurrences. This review provides information about the use of Piper guineense (black pepper) as a possible agent in managing brain aging because of its implications for practical brain function. P. guineense contains an alkaloid (piperine) reported to be an antioxidant, anti-depressant, and central nervous system stimulant. This alkaloid and other related compounds are neuroprotective agents that reduce lipid oxidation and inhibit tangles in the brain tissues.

Melatonin: Regulation of Biomolecular Condensates in Neurodegenerative Disorders

Biomolecular condensates are membraneless organelles (MLOs) that form dynamic, chemically distinct subcellular compartments organizing macromolecules such as proteins, RNA, and DNA in unicellular prokaryotic bacteria and complex eukaryotic cells. Separated from surrounding environments, MLOs in the nucleoplasm, cytoplasm, and mitochondria assemble by liquid-liquid phase separation (LLPS) into transient, non-static, liquid-like droplets that regulate essential molecular functions. LLPS is primarily controlled by post-translational modifications (PTMs) that fine-tune the balance between attractive and repulsive charge states and/or binding motifs of proteins. Aberrant phase separation due to dysregulated membrane lipid rafts and/or PTMs, as well as the absence of adequate hydrotropic small molecules such as ATP, or the presence of specific RNA proteins can cause pathological protein aggregation in neurodegenerative disorders. Melatonin may exert a dominant influence over phase separation in biomolecular condensates by optimizing membrane and MLO interdependent reactions through stabilizing lipid raft domains, reducing line tension, and maintaining negative membrane curvature and fluidity. As a potent antioxidant, melatonin protects cardiolipin and other membrane lipids from peroxidation cascades, supporting protein trafficking, signaling, ion channel activities, and ATPase functionality during condensate coacervation or dissolution. Melatonin may even control condensate LLPS through PTM and balance mRNA- and RNA-binding protein composition by regulating N6-methyladenosine (m6A) modifications. There is currently a lack of pharmaceuticals targeting neurodegenerative disorders via the regulation of phase separation. The potential of melatonin in the modulation of biomolecular condensate in the attenuation of aberrant condensate aggregation in neurodegenerative disorders is discussed in this review.

RNA Dynamics in Alzheimer's Disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder that heavily burdens healthcare systems worldwide. There is a significant requirement to understand the still unknown molecular mechanisms underlying AD. Current evidence shows that two of the major features of AD are transcriptome dysregulation and altered function of RNA binding proteins (RBPs), both of which lead to changes in the expression of different RNA species, including microRNAs (miRNAs), circular RNAs (circRNAs), long non-coding RNAs (lncRNAs), and messenger RNAs (mRNAs). In this review, we will conduct a comprehensive overview of how RNA dynamics are altered in AD and how this leads to the differential expression of both short and long RNA species. We will describe how RBP expression and function are altered in AD and how this impacts the expression of different RNA species. Furthermore, we will also show how changes in the abundance of specific RNA species are linked to the pathology of AD.

Stress Granules and Neurodegenerative Disorders: A Scoping Review

Cytoplasmic ribonucleoproteins called stress granules (SGs) are considered as one of the main cellular solutions against stress. Their temporary presence ends with stress relief. Any factor such as chronic stress or mutations in the structure of the components of SGs that lead to their permanent presence can affect their interactions with pathological aggregations and increase the degenerative effects. SGs involved in RNA mechanisms are important factors in the pathophysiology of neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS), frontotemporal degeneration (FTD), and Alzheimer's diseases (AD). Although many studies have been performed in the field of SGs and neurodegenerative disorders, so far, no systematic studies have been executed in this field. The purpose of this study is to provide a comprehensive perspective of all studies about the role of SGs in the pathogenesis of neurodegenerative disorders with a focus on the protein ingredients of these granules. This scoping review is based on a six-stage methodology structure and the PRISMA guideline. A systematic search of seven databases for qualified articles was conducted until December 2020. Publications were screened independently by two reviewers and quantitative and qualitative analysis was performed on the extracted data. Bioinformatics analysis was used to plot the network and predict interprotein interactions. In addition, GO analysis was performed. A total of 48 articles were identified that comply the inclusion criteria. Most studies on neurodegenerative diseases have been conducted on ALS, AD, and FTD using human post mortem tissues. Human derived cell line studies have been used only in ALS. A total 29 genes of protein components of SGs have been studied, the most important of which are TDP-43, TIA-1, PABP-1. Bioinformatics studies have predicted 15 proteins to interact with the protein components of SGs, which may be the constituents of SGs. Understanding the interactions between SGs and pathological aggregations in neurodegenerative diseases can provide new targets for treatment of these disorders.

Stress granules, RNA-binding proteins and polyglutamine diseases: too much aggregation?

Stress granules (SGs) are membraneless cell compartments formed in response to different stress stimuli, wherein translation factors, mRNAs, RNA-binding proteins (RBPs) and other proteins coalesce together. SGs assembly is crucial for cell survival, since SGs are implicated in the regulation of translation, mRNA storage and stabilization and cell signalling, during stress. One defining feature of SGs is their dynamism, as they are quickly assembled upon stress and then rapidly dispersed after the stress source is no longer present. Recently, SGs dynamics, their components and their functions have begun to be studied in the context of human diseases. Interestingly, the regulated protein self-assembly that mediates SG formation contrasts with the pathological protein aggregation that is a feature of several neurodegenerative diseases. In particular, aberrant protein coalescence is a key feature of polyglutamine (PolyQ) diseases, a group of nine disorders that are caused by an abnormal expansion of PolyQ tract-bearing proteins, which increases the propensity of those proteins to aggregate. Available data concerning the abnormal properties of the mutant PolyQ disease-causing proteins and their involvement in stress response dysregulation strongly suggests an important role for SGs in the pathogenesis of PolyQ disorders. This review aims at discussing the evidence supporting the existence of a link between SGs functionality and PolyQ disorders, by focusing on the biology of SGs and on the way it can be altered in a PolyQ disease context.

The Integral Role of RNA in Stress Granule Formation and Function

Stress granules (SGs) are phase-separated, membraneless, cytoplasmic ribonucleoprotein (RNP) assemblies whose primary function is to promote cell survival by condensing translationally stalled mRNAs, ribosomal components, translation initiation factors, and RNA-binding proteins (RBPs). While the protein composition and the function of proteins in the compartmentalization and the dynamics of assembly and disassembly of SGs has been a matter of study for several years, the role of RNA in these structures had remained largely unknown. RNA species are, however, not passive members of RNA granules in that RNA by itself can form homo and heterotypic interactions with other RNA molecules leading to phase separation and nucleation of RNA granules. RNA can also function as molecular scaffolds recruiting multivalent RBPs and their interactors to form higher-order structures. With the development of SG purification techniques coupled to RNA-seq, the transcriptomic landscape of SGs is becoming increasingly understood, revealing the enormous potential of RNA to guide the assembly and disassembly of these transient organelles. SGs are not only formed under acute stress conditions but also in response to different diseases such as viral infections, cancer, and neurodegeneration. Importantly, these granules are increasingly being recognized as potential precursors of pathological aggregates in neurodegenerative diseases. In this review, we examine the current evidence in support of RNA playing a significant role in the formation of SGs and explore the concept of SGs as therapeutic targets.

Heat shock proteins-driven stress granule dynamics: yet another avenue for cell survival

Heat shock proteins (HSPs) are evolutionary conserved 'stress-response' proteins that facilitate cell survival against various adverse conditions. HSP-mediated cytoprotection was hitherto reported to occur principally in two ways. Firstly, HSPs interact directly or indirectly with apoptosis signaling components and suppress apoptosis. Secondly, through chaperon activity, HSPs suppress proteotoxicity and maintain protein-homeostasis. Recent studies highlight the interaction of HSPs with cytoplasmic stress granules (SGs). SGs are conserved cytoplasmic mRNPs granules that aid in cell survival under stressful conditions. We primarily aim to describe the distinct cell survival strategy mediated by HSPs as the crucial regulators of SGs assembly and disassembly. Based on the growing evidence, HSPs and associated co-chaperones act as important determinants of SG assembly, composition and dissolution. Under cellular stress, as a 'stress-coping mechanism', the formation of SGs reprograms protein translation machinery and modulates signaling pathways indispensable for cell survival. Besides their role in suppressing apoptosis, HSPs also regulate protein-homeostasis by their chaperone activity as well as by their tight regulation of SG dynamics. The intricate molecular signaling in and around the nexus of HSPs-SGs and its importance in diseases has to be unearthed. These studies have significant implications in the management of chronic diseases such as cancer and neurodegenerative diseases where SGs possess pathological functions.

Stress granules in Ciona robusta: First evidences of TIA-1-related nucleolysin and tristetraprolin gene expression under metal exposure

Stress granules are non-membranous cytoplasmic foci, composed of non-translating messenger ribonucleoproteins, translational initiation factors and other additional proteins. They represent a primary mechanism to rapidly modulate gene expression when cells are subjected to adverse environmental conditions. Very few works have been devoted to study the presence of the molecular components of stress granules in invertebrates. In this work, we characterized the transcript sequences for two important protein components of stress granules, TIA-1-related nucleolysin (TIAR) and tristetraprolin (TTP), in the solitary ascidian Ciona robusta, an invertebrate chordate, and carried out the first studies on their gene expression under stress conditions induced by metals (Cu, Zn and Cd). Data on mRNA expression levels, provided by qRT-PCR analyses, show a generalized decrease at the second day of metal-exposure for both tiar and ttp, suggesting that metal accumulation induces acute stress and the inhibition of the transcription for the two studied proteins. In-situ hybridization analyses demonstrate that TIAR and TTP antisense riboprobes recognize circulating granular amoebocytes in the hemolymph, in both blood lacunae and tunic. The results obtained in this work increase our knowledge on the evolution of anti-stress proteins in metazoans and emphasize the importance of the transcription of tiar and ttp, which represents an efficient physiological response allowing organisms to survive in the environment under stress conditions.

Saturated fatty acids entrap PDX1 in stress granules and impede islet beta cell function

AIMS/HYPOTHESIS

Failure of pancreatic and duodenal homeobox factor 1 (PDX1) to localise in the nucleus of islet beta cells under high-fat diet (HFD) conditions may be an early functional defect that contributes to beta cell failure in type 2 diabetes; however, the mechanism of PDX1 intracellular mislocalisation is unclear. Stress granules (SGs) are membrane-less cytoplasmic structures formed under stress that impair nucleocytoplasmic transport by sequestering nucleocytoplasmic transport factors and components of the nuclear pore complex. In this study, we investigated the stimulators that trigger SG formation in islet beta cells and the effects of SGs on PDX1 localisation and beta cell function.

METHODS

The effect of palmitic acid (PA) on nucleocytoplasmic transport was investigated by using two reporters, S-tdTomato and S-GFP. SG assembly in rat insulinoma cell line INS1 cells, human islets under PA stress, and the pancreas of diet-induced obese mice was analysed using immunofluorescence and immunoblotting. SG protein components were identified through mass spectrometry. SG formation was blocked by specific inhibitors or genetic deletion of essential SG proteins, and then PDX1 localisation and beta cell function were investigated in vitro and in vivo.

RESULTS

We showed that saturated fatty acids (SFAs) are endogenous stressors that disrupted nucleocytoplasmic transport and stimulated SG formation in pancreatic beta cells. Using mass spectrometry approaches, we revealed that several nucleocytoplasmic transport factors and PDX1 were localised to SGs after SFA treatment, which inhibited glucose-induced insulin secretion. Furthermore, we found that SFAs induced SG formation in a phosphoinositide 3-kinase (PI3K)/eukaryotic translation initiation factor 2α (EIF2α) dependent manner. Disruption of SG assembly by PI3K/EIF2α inhibitors or genetic deletion of T cell restricted intracellular antigen 1 (TIA1) in pancreatic beta cells effectively suppressed PA-induced PDX1 mislocalisation and ameliorated HFD-mediated beta cell dysfunction.

CONCLUSIONS/INTERPRETATION

Our findings suggest a link between SG formation and beta cell dysfunction in the presence of SFAs. Preventing SG formation may be a potential therapeutic strategy for treating obesity and type 2 diabetes.

Heterogeneous Nuclear Ribonucleoproteins: Implications in Neurological Diseases

Heterogenous nuclear ribonucleoproteins (hnRNPs) are a complex and functionally diverse family of RNA binding proteins with multifarious roles. They are involved, directly or indirectly, in alternative splicing, transcriptional and translational regulation, stress granule formation, cell cycle regulation, and axonal transport. It is unsurprising, given their heavy involvement in maintaining functional integrity of the cell, that their dysfunction has neurological implications. However, compared to their more established roles in cancer, the evidence of hnRNP implication in neurological diseases is still in its infancy. This review aims to consolidate the evidences for hnRNP involvement in neurological diseases, with a focus on spinal muscular atrophy (SMA), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), multiple sclerosis (MS), congenital myasthenic syndrome (CMS), and fragile X-associated tremor/ataxia syndrome (FXTAS). Understanding more about hnRNP involvement in neurological diseases can further elucidate the pathomechanisms involved in these diseases and perhaps guide future therapeutic advances.

Hypusination of Eif5a regulates cytoplasmic TDP-43 aggregation and accumulation in a stress-induced cellular model

TAR DNA-binding protein 43 (TDP-43) is a nuclear RNA/DNA binding protein involved in mRNA metabolism. Aberrant mislocalization to the cytoplasm and formation of phosphorylated/aggregated TDP-43 inclusions remains the hallmark pathology in a spectrum of neurodegenerative diseases, including frontotemporal disorders and Alzheimer's disease. Eukaryotic Translation Initiation Factor 5A undergoes a unique post-translation modification of lysine to hypusine (K50), which determines eIF5A binding partners. We used a sodium arsenite-induced cellular stress model to investigate the role of hypusinated eIF5A (eIF5AHypK50) in governing TDP-43 cytoplasmic mislocalization and accumulation in stress granule. Our proteomics and functional data provide evidence that eIF5A interacts with TDP-43 in a hypusine-dependent manner. Additionally, we showed that following stress TDP-43 interactions with eIF5AHypK50 were induced both in the cytoplasm and stress granules. Pharmacological reduction of hypusination or mutations of lysine residues within the hypusine loop decreased phosphorylated and insoluble TDP-43 levels. The proteomic and biochemical analysis also identified nuclear pore complex importins KPNA1/2, KPNB1, and RanGTP as interacting partners of eIF5AHypK50. These findings are the first to provide a novel pathway and potential therapeutic targets that require further investigation in models of TDP-43 proteinopathies.

Pharmacological inhibition of DEAD-Box RNA Helicase 3 attenuates stress granule assembly

Stress granules (SGs) are non-membranous cytosolic protein-RNA aggregates that process mRNAs through stalled translation initiation in response to cellular stressors and in disease. DEAD-Box RNA helicase 3 (DDX3) is an active target of drug development for the treatment of viral infections, cancers, and neurodegenerative diseases. DDX3 plays a critical role in RNA metabolism, including SGs, but the role of DDX3 enzymatic activity in SG dynamics is not well understood. Here, we address this question by determining the effects of DDX3 inhibition on the dynamics of SG assembly and disassembly. We use two small molecule inhibitors of DDX3, RK33 and 16D, with distinct inhibitory mechanisms that target DDX3's ATPase activity and RNA helicase site, respectively. We find that both DDX3 inhibitors reduce the assembly of SGs, with a more pronounced reduction from RK-33. In contrast, both compounds only marginally affect the disassembly of SGs. RNA-mediated knockdown of DDX3 caused a similar reduction in SG assembly and minimal effect on SG disassembly. Collectively, these results reveal that the enzymatic activity of DDX3 is required for the assembly of SGs and pharmacological inhibition of DDX3 could be relevant for the treatment of SG-dependent pathologies.

Tristetraprolin destabilizes NOX2 mRNA and protects dopaminergic neurons from oxidative damage in Parkinson's disease

Tristetraprolin (TTP), an RNA-binding protein encoded by the ZFP36 gene, is vital for neural differentiation; however, its involvement in neurodegenerative diseases such as Parkinson's disease (PD) remains unclear. To explore the role of TTP in PD, an in vitro 1-methyl-4-phenylpyridinium (MPP⁺ ) cell model and an in vivo 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) of PD were used. Transfection of small interfering (si)-TTP RNA upregulated pro-oxidative NOX2 expression and ROS formation, downregulated anti-oxidative GSH and SOD activity；si-TTP upregulated pro-apoptotic cleaved-caspase-3 expression, and downregulated antiapoptotic Bcl-2 expression; while overexpression (OE)-TTP lentivirus caused opposite effects. Through database prediction, luciferase experiment, RNA immunoprecipitation (RIP), and mRNA stability analysis, we evaluated the potential binding sites of TTP to 3'-untranslated regions (3'-UTR) of NOX2 mRNA. TTP affected the NOX2 luciferase activity by binding to two sites in the NOX2 3'-UTR. RIP-qPCR confirmed TTP binding to both sites, with a higher affinity for site-2. In addition, TTP reduced the NOX2 mRNA stability. si-NOX2 and antioxidant N-acetyl cysteine (NAC) reversed si-TTP-induced cell apoptosis. In MPTP-treated mice, TTP expression increased and was co-located with dopaminergic neurons. TTP also inhibited NOX2 and decreased the oxidative stress in vivo. In conclusion, TTP protects against dopaminergic oxidative injury by promoting NOX2 mRNA degradation in the MPP⁺ /MPTP model of PD, suggesting that TTP could be a potential therapeutic target for regulating the oxidative stress in PD.

Mammalian stress granules and P bodies at a glance

Stress granules (SGs) and processing bodies (PBs) are membraneless ribonucleoprotein-based cellular compartments that assemble in response to stress. SGs and PBs form through liquid-liquid phase separation that is driven by high local concentrations of key proteins and RNAs, both of which dynamically shuttle between the granules and the cytoplasm. SGs uniquely contain certain translation initiation factors and PBs are uniquely enriched with factors related to mRNA degradation and decay, although recent analyses reveal much broader protein commonality between these granules. Despite detailed knowledge of their composition and dynamics, the function of SGs and PBs remains poorly understood. Both, however, contain mRNAs, implicating their assembly in the regulation of RNA metabolism. SGs may also serve as hubs that rewire signaling events during stress. By contrast, PBs may constitute RNA storage centers, independent of mRNA decay. The aberrant assembly or disassembly of these granules has pathological implications in cancer, viral infection and neurodegeneration. Here, we review the current concepts regarding the formation, composition, dynamics, function and involvement in disease of SGs and PBs.

Functional Mammalian Amyloids and Amyloid-Like Proteins

Amyloids are highly ordered fibrous cross-β protein aggregates that are notorious primarily because of association with a variety of incurable human and animal diseases (termed amyloidoses), including Alzheimer’s disease (AD), Parkinson’s disease (PD), type 2 diabetes (T2D), and prion diseases. Some amyloid-associated diseases, in particular T2D and AD, are widespread and affect hundreds of millions of people all over the world. However, recently it has become evident that many amyloids, termed “functional amyloids,” are involved in various activities that are beneficial to organisms. Functional amyloids were discovered in diverse taxa, ranging from bacteria to mammals. These amyloids are involved in vital biological functions such as long-term memory, storage of peptide hormones and scaffolding melanin polymerization in animals, substrate attachment, and biofilm formation in bacteria and fungi, etc. Thus, amyloids undoubtedly are playing important roles in biological and pathological processes. This review is focused on functional amyloids in mammals and summarizes approaches used for identifying new potentially amyloidogenic proteins and domains.

A blood miRNA signature associates with sporadic Creutzfeldt-Jakob disease diagnosis

Sporadic Creutzfeldt-Jakob disease (sCJD) presents as a rapidly progressive dementia which is usually fatal within six months. No clinical blood tests are available for diagnosis or disease monitoring. Here, we profile blood microRNA (miRNA) expression in sCJD. Sequencing of 57 sCJD patients, and healthy controls reveals differential expression of hsa-let-7i-5p, hsa-miR-16-5p, hsa-miR-93-5p and hsa-miR-106b-3p. Downregulation of hsa-let-7i-5p, hsa-miR-16-5p and hsa-miR-93-5p replicates in an independent cohort using quantitative PCR, with concomitant upregulation of four mRNA targets. Absence of correlation in cross-sectional analysis with clinical phenotypes parallels the lack of association between rate of decline in miRNA expression, and rate of disease progression in a longitudinal cohort of samples from 21 patients. Finally, the miRNA signature shows a high level of accuracy in discriminating sCJD from Alzheimer’s disease. These findings highlight molecular alterations in the periphery in sCJD which provide information about differential diagnosis and improve mechanistic understanding of human prion diseases.

Sporadic Creutzfeldt-Jakob disease (sCJD) is a rapidly progressive dementia. No clinical blood tests are available for diagnosis. The authors identified three miRNAs in whole-blood that are downregulated in sCJD patients, and discriminate sCJD from Alzheimer’s disease patients and healthy controls.

Current advances in the development of novel polymeric nanoparticles for the treatment of neurodegenerative diseases

Effective intervention is essential to combat the coming epidemic of neurodegenerative (ND) diseases. Nanomedicine can overcome restrictions of CNS delivery imposed by the blood-brain barrier, and thus be instrumental in preclinical discovery and therapeutic intervention of ND diseases. Polymeric nanoparticles (PNPs) have shown great potential and versatility to encapsulate several compounds simultaneously in controlled drug-delivery systems and target them to the deepest brain regions. Here, we critically review recent advances in the development of drugs incorporated into PNPs and summarize the molecular changes and functional effects achieved in preclinical models of the most common ND disorders. We also briefly discuss the many challenges remaining to translate these findings and technological advances successfully to current clinical settings.

Changing faces of stress: Impact of heat and arsenite treatment on the composition of stress granules

Stress granules (SGs), hallmarks of the cellular adaptation to stress, promote survival, conserve cellular energy, and are fully dissolved upon the cessation of stress treatment. Different stresses can initiate the assembly of SGs, but arsenite and heat are the best studied of these stresses. The composition of SGs and posttranslational modifications of SG proteins differ depending on the type and severity of the stress insult, methodology used, cell line, and presence of overexpressed and tagged proteins. A group of 18 proteins showing differential localization to SGs in heat- and arsenite-stressed mammalian cell lines is described. Upon severe and prolonged stress, physiological SGs transform into more solid protein aggregates that are no longer reversible and do not contain mRNA. Similar pathological inclusions are hallmarks of neurodegenerative diseases. SGs induced by heat stress are less dynamic than SGs induced by arsenite and contain a set of unique proteins and linkage-specific polyubiquitinated proteins. The same types of ubiquitin linkages have been found to contribute to the development of neurodegenerative disorders such as Parkinson disease, Alzheimer disease, and amyotrophic lateral sclerosis (ALS). We propose heat stress-induced SGs as a possible model of an intermediate stage along the transition from dynamic, fully reversible arsenite stress-induced SGs toward aberrant SGs, the hallmark of neurodegenerative diseases. Stress- and methodology-specific differences in the compositions of SGs and the transition of SGs to aberrant protein aggregates are discussed. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Export and Localization > RNA Localization.

Reduction of the RNA Binding Protein TIA1 Exacerbates Neuroinflammation in Tauopathy

Neuroinflammatory processes play an integral role in the exacerbation and progression of pathology in tauopathies, a class of neurodegenerative disease characterized by aggregation of hyperphosphorylated tau protein. The RNA binding protein (RBP) T-cell Intracellular Antigen 1 (TIA1) is an important regulator of the innate immune response in the periphery, dampening cytotoxic inflammation and apoptosis during cellular stress, however, its role in neuroinflammation is unknown. We have recently shown that TIA1 regulates tau pathophysiology and toxicity in part through the binding of phospho-tau oligomers into pathological stress granules, and that haploinsufficiency of TIA1 in the P301S mouse model of tauopathy results in reduced accumulation of toxic tau oligomers, pathologic stress granules, and the development of downstream pathological features of tauopathy. The putative role of TIA1 as a regulator of the peripheral immune response led us to investigate the effects of TIA1 on neuroinflammation in the context of tauopathy, a chronic stressor in the neural environment. Here, we evaluated indicators of neuroinflammation including; reactive microgliosis and phagocytosis, pro-inflammatory cytokine release, and oxidative stress in hippocampal neurons and glia of wildtype and P301S transgenic mice expressing TIA1+/+, TIA1+/-, and TIA1-/- in both early (5 month) and advanced (9 month) disease states through biochemical, ultrastructural, and histological analyses. Our data show that both TIA1 haploinsufficiency and TIA1 knockout exacerbate neuroinflammatory processes in advanced stages of tauopathy, suggesting that TIA1 dampens the immune response in the central nervous system during chronic stress.

Dysfunctional RNA-binding protein biology and neurodegeneration in experimental autoimmune encephalomyelitis in female mice

Altered stress granule (SG) and RNA-binding protein (RBP) biology have been shown to contribute to the pathogenesis of several neurodegenerative diseases, yet little is known about their role in multiple sclerosis (MS). Pathological features associated with dysfunctional RBPs include RBP mislocalization from its normal nuclear location to the cytoplasm and the formation of chronic SGs. We tested the hypothesis that altered SG and RBP biology might contribute to the neurodegeneration in experimental autoimmune encephalomyelitis (EAE). C57BL/6 female mice were actively immunized with MOG_35-55 to induce EAE. Spinal cords were examined for mislocalization of the RBPs, heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) and TAR-DNA binding protein-43 (TDP-43), SGs, neurodegeneration (SMI-32), T cells (CD3), and macrophages (CD68). In contrast to naive mice, mice with EAE showed SG formation (p < 0.0001) and mislocalization of hnRNP A1 (p < 0.05) in neurons of the ventral spinal cord gray matter, which correlated with clinical score (R = 0.8104, p = 0.0253). In these same areas, there was a neuronal loss (p < 0.0001) and increased SMI-32 immunoreactivity (both markers of neurodegeneration) and increased staining for CD3⁺ T cells and IFN-gamma. These findings recapitulate the SG and RBP biology and markers of neurodegeneration in MS tissues and suggest that altered SG and RBP biology contribute to the neurodegeneration in EAE, which might also apply to the pathogenesis of MS.

Heat resilience in embryonic zebrafish revealed using an in vivo stress granule reporter

Although the regulation of stress granules has become an intensely studied topic, current investigations of stress granule assembly, disassembly and dynamics are mainly performed in cultured cells. Here, we report the establishment of a stress granule reporter to facilitate the real-time study of stress granules in vivo. Using CRISPR/Cas9, we fused a green fluorescence protein (GFP) to endogenous G3BP1 in zebrafish. The GFP–G3BP1 reporter faithfully and robustly responded to heat stress in zebrafish embryos and larvae. The induction of stress granules varied by brain regions under the same stress condition, with the midbrain cells showing the highest efficiency and dynamics. Furthermore, pre-conditioning using lower heat stress significantly limited stress granule formation during subsequent higher heat stress. More interestingly, stress granule formation was much more robust in zebrafish embryos than in larvae and coincided with significantly elevated levels of phosphorylated eIF2α and enhanced heat resilience. Therefore, these findings have generated new insights into stress response in zebrafish during early development and demonstrated that the GFP–G3BP1 knock-in zebrafish could be a valuable tool for the investigation of stress granule biology.

This article has an associated First Person interview with the first author of the paper.

Summary: Establishment of a new transgenic zebrafish line with knock-in GFP-G3BP1 to visualize stress granule dynamics in live animals in real time.