Staufen 1 amplifies proapoptotic activation of the unfolded protein response

Dysfunctional RNA binding protein induced neurodegeneration is attenuated by inhibition of the integrated stress response

Dysfunction of the RNA binding protein heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) contributes to neurodegeneration, the primary cause of permanent disability in multiple sclerosis (MS). To better understand the role of hnRNP A1 dysfunction in the pathogenesis of neurodegeneration, we utilized optogenetics-driven hnRNP A1 clustering to model its dysfunction in neuron-like differentiated Neuro-2A cells. hnRNP A1 clustering activates the integrated stress response (ISR) and results in a neurodegenerative phenotype marked by decreased neuronal protein translation and neurite loss. Small molecule inhibition of the ISR with either PERKi (GSK2606414) or ISRIB (integrated stress response inhibitor) attenuated both the decrease in neuronal translation and neurite loss, without affecting hnRNP A1 clustering. We then confirmed a strong association between hnRNP A1 clustering and ISR activation in neurons from MS brains. These data illustrate that hnRNP A1 dysfunction promotes neurodegeneration by activation of the ISR in vitro and in vivo, thus revealing a novel therapeutic target to reduce neurodegeneration and subsequent disability in MS.

Oncoprotein LAMTOR5-mediated CHOP silence via DNA hypermethylation and miR-182/miR-769 in promotion of liver cancer growth

C/EBP homologous protein (CHOP) triggers the death of multiple cancers via endoplasmic reticulum (ER) stress. However, the function and regulatory mechanism of CHOP in liver cancer remain elusive. We have reported that late endosomal/lysosomal adapter, mitogen-activated protein kinase and mTOR activator 5 (LAMTOR5) suppresses apoptosis in various cancers. Here, we show that the transcriptional and posttranscriptional inactivation of CHOP mediated by LAMTOR5 accelerates liver cancer growth. Clinical bioinformatic analysis revealed that the expression of CHOP was low in liver cancer tissues and that its increased expression predicted a good prognosis. Elevated CHOP contributed to destruction of LAMTOR5-induced apoptotic suppression and proliferation. Mechanistically, LAMTOR5-recruited DNA methyltransferase 1 (DNMT1) to the CpG3 region (-559/-429) of the CHOP promoter and potentiated its hypermethylation to block its interaction with general transcription factor IIi (TFII-I), resulting in its inactivation. Moreover, LAMTOR5-enhanced miR-182/miR-769 reduced CHOP expression by targeting its 3'UTR. Notably, lenvatinib, a first-line targeted therapy for liver cancer, could target the LAMTOR5/CHOP axis to prevent liver cancer progression. Accordingly, LAMTOR5-mediated silencing of CHOP via the regulation of ER stress-related apoptosis promotes liver cancer growth, providing a theoretical basis for the use of lenvatinib for the treatment of liver cancer.

RNA-binding protein GIGYF2 orchestrates hepatic insulin resistance through STAU1/PTEN-mediated disruption of the PI3K/AKT signaling cascade

BACKGROUND

Obesity is well-established as a significant contributor to the development of insulin resistance (IR) and diabetes, partially due to elevated plasma saturated free fatty acids like palmitic acid (PA). Grb10-interacting GYF Protein 2 (GIGYF2), an RNA-binding protein, is widely expressed in various tissues including the liver, and has been implicated in diabetes-induced cognitive impairment. Whereas, its role in obesity-related IR remains uninvestigated.

METHODS

In this study, we employed palmitic acid (PA) exposure to establish an in vitro IR model in the human liver cancer cell line HepG2 with high-dose chronic PA treatment. The cells were stained with fluorescent dye 2-NBDG to evaluate cell glucose uptake. The mRNA expression levels of genes were determined by real-time qRT-PCR (RT-qPCR). Western blotting was employed to examine the protein expression levels. The RNA immunoprecipitation (RIP) was used to investigate the binding between protein and mRNA. Lentivirus-mediated gene knockdown and overexpression were employed for gene manipulation. In mice, an IR model induced by a high-fat diet (HFD) was established to validate the role and action mechanisms of GIGYF2 in the modulation of HFD-induced IR in vivo.

RESULTS

In hepatocytes, high levels of PA exposure strongly trigger the occurrence of hepatic IR evidenced by reduced glucose uptake and elevated extracellular glucose content, which is remarkably accompanied by up-regulation of GIGYF2. Silencing GIGYF2 ameliorated PA-induced IR and enhanced glucose uptake. Conversely, GIGYF2 overexpression promoted IR, PTEN upregulation, and AKT inactivation. Additionally, PA-induced hepatic IR caused a notable increase in STAU1, which was prevented by depleting GIGYF2. Notably, silencing STAU1 prevented GIGYF2-induced PTEN upregulation, PI3K/AKT pathway inactivation, and IR. STAU1 was found to stabilize PTEN mRNA by binding to its 3'UTR. In liver cells, tocopherol treatment inhibits GIGYF2 expression and mitigates PA-induced IR. In the in vivo mice model, GIGYF2 knockdown and tocopherol administration alleviate high-fat diet (HFD)-induced glucose intolerance and IR, along with the suppression of STAU1/PTEN and restoration of PI3K/AKT signaling.

CONCLUSIONS

Our study discloses that GIGYF2 mediates obesity-related IR by disrupting the PI3K/AKT signaling axis through the up-regulation of STAU1/PTEN. Targeting GIGYF2 may offer a potential strategy for treating obesity-related metabolic diseases, including type 2 diabetes.

Excessive STAU1 condensate drives mTOR translation and autophagy dysfunction in neurodegeneration

The double-stranded RNA-binding protein Staufen1 (STAU1) regulates a variety of physiological and pathological events via mediating RNA metabolism. STAU1 overabundance was observed in tissues from mouse models and fibroblasts from patients with neurodegenerative diseases, accompanied by enhanced mTOR signaling and impaired autophagic flux, while the underlying mechanism remains elusive. Here, we find that endogenous STAU1 forms dynamic cytoplasmic condensate in normal and tumor cell lines, as well as in mouse Huntington's disease knockin striatal cells. STAU1 condensate recruits target mRNA MTOR at its 5'UTR and promotes its translation both in vitro and in vivo, and thus enhanced formation of STAU1 condensate leads to mTOR hyperactivation and autophagy-lysosome dysfunction. Interference of STAU1 condensate normalizes mTOR levels, ameliorates autophagy-lysosome function, and reduces aggregation of pathological proteins in cellular models of neurodegenerative diseases. These findings highlight the importance of balanced phase separation in physiological processes, suggesting that modulating STAU1 condensate may be a strategy to mitigate the progression of neurodegenerative diseases with STAU1 overabundance.

Coding and Non-Coding Transcriptomic Landscape of Aortic Complications in Marfan Syndrome

Marfan syndrome (MFS) is a rare congenital disorder of the connective tissue, leading to thoracic aortic aneurysms (TAA) and dissection, among other complications. Currently, the most efficient strategy to prevent life-threatening dissection is preventive surgery. Periodic imaging applying complex techniques is required to monitor TAA progression and to guide the timing of surgical intervention. Thus, there is an acute demand for non-invasive biomarkers for diagnosis and prognosis, as well as for innovative therapeutic targets of MFS. Unraveling the intricate pathomolecular mechanisms underlying the syndrome is vital to address these needs. High-throughput platforms are particularly well-suited for this purpose, as they enable the integration of different datasets, such as transcriptomic and epigenetic profiles. In this narrative review, we summarize relevant studies investigating changes in both the coding and non-coding transcriptome and epigenome in MFS-induced TAA. The collective findings highlight the implicated pathways, such as TGF-β signaling, extracellular matrix structure, inflammation, and mitochondrial dysfunction. Potential candidates as biomarkers, such as miR-200c, as well as therapeutic targets emerged, like Tfam, associated with mitochondrial respiration, or miR-632, stimulating endothelial-to-mesenchymal transition. While these discoveries are promising, rigorous and extensive validation in large patient cohorts is indispensable to confirm their clinical relevance and therapeutic potential.

STAU1 exhibits a dual function by promoting amyloidogenesis and tau phosphorylation in cultured cells

Staufen-1 (STAU1) is a double-stranded RNA-binding protein (RBP) involved in a variety of pathological conditions. In this study, we investigated the potential role of STAU1 in Alzheimer's disease (AD), in which two hallmarks are well-established as cerebral β-amyloid protein (Aβ) deposition and Tau-centered neurofibrillary tangles. We found that STAU1 protein level was significantly increased in cells that stably express full-length APP and the brain of APP/PS1 mice, an animal model of AD. STAU1 knockdown, as opposed to overexpression, significantly decreased the protein levels of β-amyloid converting enzyme 1 (BACE1) and Aβ. We further found that STAU1 extended the half-life of the BACE1 mRNA through binding to the 3' untranslated region (3'UTR). Transcriptome analysis revealed that STAU1 enhanced the expression of growth arrest and DNA damage 45 β (GADD45B) upstream of P38 MAPK signaling, which contributed to STAU1-induced regulation of Tau phosphorylation at Ser396 and Thr181. Together, STAU1 promoted amyloidogenesis by inhibiting BACE1 mRNA decay, and augmented Tau phosphorylation through activating GADD45B in relation to P38 MAPK. Targeting STAU1 that acts on both amyloidogenesis and tauopathy may serve as an optimistic approach for AD treatment.

Aberrant hyper-expression of the RNA binding protein GIGYF2 in endothelial cells modulates vascular aging and function

Vascular endothelial cells (ECs) senescence plays a crucial role in vascular aging that promotes the initiation and progression of cardiovascular disease. The mutation of Grb10-interacting GYF protein 2 (GIGYF2) is strongly associated with the pathogenesis of aging-related diseases, whereas its role in regulating ECs senescence and dysfunction still remains elusive. In this study, we found aberrant hyperexpression of GIGYF2 in senescent human ECs and aortas of old mice. Silencing GIGYF2 in senescent ECs suppressed eNOS-uncoupling, senescence, and endothelial dysfunction. Conversely, in nonsenescent cells, overexpressing GIGYF2 promoted eNOS-uncoupling, cellular senescence, endothelial dysfunction, and activation of the mTORC1-SK61 pathway, which were ablated by rapamycin or antioxidant N-Acetyl-l-cysteine (NAC). Transcriptome analysis revealed that staufen double-stranded RNA binding protein 1 (STAU1) is remarkably downregulated in the GIGYF2-depleted ECs. STAU1 depletion significantly attenuated GIGYF2-induced cellular senescence, dysfunction, and inflammation in young ECs. Furthermore, we disclosed that GIGYF2 acting as an RNA binding protein (RBP) enhances STAU1 mRNA stability, and that the intron region of the late endosomal/lysosomal adaptor MAPK and mTOR activator 4 (LAMTOR4) could bind to STAU1 protein to upregulate LAMTOR4 expression. Immunofluorescence staining showed that GIGYF2 overexpression promoted the translocation of mTORC1 to lysosome. In the mice model, GIGYF2flox/flox Cdh-Cre+ mice protected aged mice from aging-associated vascular endothelium-dependent relaxation and arterial stiffness. Our work discloses that GIGYF2 serving as an RBP enhances the mRNA stability of STAU1 that upregulates LAMTOR4 expression through binding with its intron region, which activates the mTORC1-S6K1 signaling via recruitment of mTORC1 to the lysosomal membrane, ultimately leading to ECs senescence, dysfunction, and vascular aging. Disrupting the GIGYF2-STAU1-mTORC1 signaling cascade may represent a promising therapeutic approach against vascular aging and aging-related cardiovascular diseases.

Staufen Impairs Autophagy in Neurodegeneration

OBJECTIVE

The mechanistic target of rapamycin (mTOR) kinase is one of the master coordinators of cellular stress responses, regulating metabolism, autophagy, and apoptosis. We recently reported that staufen1 (STAU1), a stress granule (SG) protein, was overabundant in fibroblast cell lines from patients with spinocerebellar ataxia type 2 (SCA2), amyotrophic lateral sclerosis, frontotemporal degeneration, Huntington's, Alzheimer's, and Parkinson's diseases as well as animal models, and patient tissues. STAU1 overabundance is associated with mTOR hyperactivation and links SG formation with autophagy. Our objective was to determine the mechanism of mTOR regulation by STAU1.

METHODS

We determined STAU1 abundance with disease- and chemical-induced cellular stressors in patient cells and animal models. We also used RNA-binding assays to contextualize STAU1 interaction with MTOR mRNA.

RESULTS

STAU1 and mTOR were overabundant in bacterial artificial chromosome (BAC)-C9ORF72, ATXN2Q127 , and Thy1-TDP-43 transgenic mouse models. Reducing STAU1 levels in these mice normalized mTOR levels and activity and autophagy-related marker proteins. We also saw increased STAU1 levels in HEK293 cells transfected to express C9ORF72-relevant dipeptide repeats (DPRs). Conversely, DPR accumulations were not observed in cells treated by STAU1 RNA interference (RNAi). Overexpression of STAU1 in HEK293 cells increased mTOR levels through direct MTOR mRNA interaction, activating downstream targets and impairing autophagic flux. Targeting mTOR by rapamycin or RNAi normalized STAU1 abundance in an SCA2 cellular model.

INTERPRETATION

STAU1 interaction with mTOR drives its hyperactivation and inhibits autophagic flux in multiple models of neurodegeneration. Staufen, therefore, constitutes a novel target to modulate mTOR activity and autophagy, and for the treatment of neurodegenerative diseases. ANN NEUROL 2023;93:398-416.

Endogenous retroelements as alarms for disruptions to cellular homeostasis

Endogenous retroelements are DNA sequences which can duplicate and move to new locations in the genome. Actively moving endogenous retroelements can be disruptive to the host, and their expression is therefore often repressed. Interestingly, drugs that disrupt the repression of endogenous retroelements show promise for treating cancer. Expressed endogenous retroelements can activate innate immune receptors that activate the antiviral response, potentially leading to the death of cancer cells. We discuss disruptions to cellular processes which can lead to activation of the antiviral state from endogenous retroelements, and present the 'fire alarm hypothesis', where we argue that endogenous retroelements act as alarms for disruptions to these cellular processes. Furthermore, we discuss the properties of endogenous retroelements which make them suitable as alarms.

RNA-binding protein signaling in adult neurogenesis

The process of neurogenesis in the brain, including cell proliferation, differentiation, survival, and maturation, results in the formation of new functional neurons. During embryonic development, neurogenesis is crucial to produce neurons to establish the nervous system, but the process persists in certain brain regions during adulthood. In adult neurogenesis, the production of new neurons in the hippocampus is accomplished via the division of neural stem cells. Neurogenesis is regulated by multiple factors, including gene expression at a temporal scale and post-transcriptional modifications. RNA-binding Proteins (RBPs) are known as proteins that bind to either double- or single-stranded RNA in cells and form ribonucleoprotein complexes. The involvement of RBPs in neurogenesis is crucial for modulating gene expression changes and posttranscriptional processes. Since neurogenesis affects learning and memory, RBPs are closely associated with cognitive functions and emotions. However, the pathways of each RBP in adult neurogenesis remain elusive and not clear. In this review, we specifically summarize the involvement of several RBPs in adult neurogenesis, including CPEB3, FXR2, FMRP, HuR, HuD, Lin28, Msi1, Sam68, Stau1, Smaug2, and SOX2. To understand the role of these RBPs in neurogenesis, including cell proliferation, differentiation, survival, and maturation as well as posttranscriptional gene expression, we discussed the protein family, structure, expression, functional domain, and region of action. Therefore, this narrative review aims to provide a comprehensive overview of the RBPs, their function, and their role in the process of adult neurogenesis as well as to identify possible research directions on RBPs and neurogenesis.

A quantitative high-throughput screen identifies compounds that lower expression of the SCA2-and ALS-associated gene ATXN2

CAG repeat expansions in the ATXN2 (ataxin-2) gene can cause the autosomal dominant disorder spinocerebellar ataxia type 2 (SCA2) as well as increase the risk of ALS. Abnormal molecular, motor, and neurophysiological phenotypes in SCA2 mouse models are normalized by lowering ATXN2 transcription, and reduction of nonmutant Atxn2 expression has been shown to increase the life span of mice overexpressing the TDP-43 (transactive response DNA-binding protein 43 kDa) ALS protein, demonstrating the potential benefits of targeting ATXN2 transcription in humans. Here, we describe a quantitative high-throughput screen to identify compounds that lower ATXN2 transcription. We screened 428,759 compounds in a multiplexed assay using an ATXN2-luciferase reporter in human embryonic kidney 293 (HEK-293) cells and identified a diverse set of compounds capable of lowering ATXN2 transcription. We observed dose-dependent reductions of endogenous ATXN2 in HEK-293 cells treated with procillaridin A, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), and heat shock protein 990 (HSP990), known inhibitors of HSP90 and Na+/K+-ATPases. Furthermore, HEK-293 cells expressing polyglutamine-expanded ATXN2-Q58 treated with 17-DMAG had minimally detectable ATXN2, as well as normalized markers of autophagy and endoplasmic reticulum stress, including STAU1 (Staufen 1), molecular target of rapamycin, p62, LC3-II (microtubule-associated protein 1A/1B-light chain 3II), CHOP (C/EBP homologous protein), and phospho-eIF2α (eukaryotic initiation factor 2α). Finally, bacterial artificial chromosome ATXN2-Q22 mice treated with 17-DMAG or HSP990 exhibited highly reduced ATXN2 protein abundance in the cerebellum. Taken together, our study demonstrates inhibition of HSP90 or Na+/K+-ATPases as potentially effective therapeutic strategies for treating SCA2 and ALS.

Phosphomimicry on STAU1 Serine 20 Impairs STAU1 Posttranscriptional Functions and Induces Apoptosis in Human Transformed Cells

Staufen 1 (STAU1) is an RNA-binding protein that is essential in untransformed cells. In cancer cells, it is rather STAU1 overexpression that impairs cell proliferation. In this paper, we show that a modest increase in STAU1 expression in cancer cells triggers apoptosis as early as 12 h post-transfection and impairs proliferation in non-apoptotic cells for several days. Interestingly, a mutation that mimics the phosphorylation of STAU1 serine 20 is sufficient to cause these phenotypes, indicating that serine 20 is at the heart of the molecular mechanism leading to apoptosis. Mechanistically, phosphomimicry on serine 20 alters the ability of STAU1 to regulate translation and the decay of STAU1-bound mRNAs, indicating that the posttranscriptional regulation of mRNAs by STAU1 controls the balance between proliferation and apoptosis. Unexpectedly, the expression of RBD2S20D, the N-terminal 88 amino acids with no RNA-binding activity, is sufficient to induce apoptosis via alteration, in trans, of the posttranscriptional functions of endogenous STAU1. These results suggest that STAU1 is a sensor that controls the balance between cell proliferation and apoptosis, and, therefore, may be considered as a novel therapeutic target against cancer.

Consensus Paper: Strengths and Weaknesses of Animal Models of Spinocerebellar Ataxias and Their Clinical Implications

Spinocerebellar ataxias (SCAs) represent a large group of hereditary degenerative diseases of the nervous system, in particular the cerebellum, and other systems that manifest with a variety of progressive motor, cognitive, and behavioral deficits with the leading symptom of cerebellar ataxia. SCAs often lead to severe impairments of the patient's functioning, quality of life, and life expectancy. For SCAs, there are no proven effective pharmacotherapies that improve the symptoms or substantially delay disease progress, i.e., disease-modifying therapies. To study SCA pathogenesis and potential therapies, animal models have been widely used and are an essential part of pre-clinical research. They mainly include mice, but also other vertebrates and invertebrates. Each animal model has its strengths and weaknesses arising from model animal species, type of genetic manipulation, and similarity to human diseases. The types of murine and non-murine models of SCAs, their contribution to the investigation of SCA pathogenesis, pathological phenotype, and therapeutic approaches including their advantages and disadvantages are reviewed in this paper. There is a consensus among the panel of experts that (1) animal models represent valuable tools to improve our understanding of SCAs and discover and assess novel therapies for this group of neurological disorders characterized by diverse mechanisms and differential degenerative progressions, (2) thorough phenotypic assessment of individual animal models is required for studies addressing therapeutic approaches, (3) comparative studies are needed to bring pre-clinical research closer to clinical trials, and (4) mouse models complement cellular and invertebrate models which remain limited in terms of clinical translation for complex neurological disorders such as SCAs.

Polyglutamine diseases

Polyglutamine diseases are a collection of nine CAG trinucleotide expansion disorders, presenting with a spectrum of neurological and clinical phenotypes. Recent human, mouse and cell studies of Huntington's disease have highlighted the role of DNA repair genes in somatic expansion of the CAG repeat region, modifying disease pathogenesis. Incomplete splicing of the HTT gene has also been shown to occur in humans, with the resulting exon 1 fragment most probably contributing to the Huntington's disease phenotype. In the spinocerebellar ataxias, studies have converged on transcriptional dysregulation of ion channels as a key disease modifier. In addition, advances have been made in understanding how increased levels of toxic, polyglutamine-expanded proteins can arise in the spinocerebellar ataxias through post-transcriptional and -translational modifications and autophagic mechanisms. Recent studies in spinal and bulbar muscular atrophy implicate similar pathogenic pathways to the more common polyglutamine diseases, highlighting autophagy stimulation as a potential therapeutic target. Finally, the therapeutic use of antisense oligonucleotides in several polyglutamine diseases has shown preclinical benefits and serves as potential future therapies in humans.

High Level of Staufen1 Expression Confers Longer Recurrence Free Survival to Non-Small Cell Lung Cancer Patients by Promoting THBS1 mRNA Degradation

Stau1 is a pluripotent RNA-binding protein that is responsible for the post-transcriptional regulation of a multitude of transcripts. Here, we observed that lung cancer patients with a high Stau1 expression have a longer recurrence free survival. Strikingly, Stau1 did not impair cell proliferation in vitro, but rather cell migration and cell adhesion. In vivo, Stau1 depletion favored tumor progression and metastases development. In addition, Stau1 depletion strongly impaired vessel maturation. Among a panel of candidate genes, we specifically identified the mRNA encoding the cell adhesion molecule Thrombospondin 1 (THBS1) as a new target for Staufen-mediated mRNA decay. Altogether, our results suggest that regulation of THBS1 expression by Stau1 may be a key process involved in lung cancer progression.

RNA-binding protein dysfunction in neurodegeneration

Protein homeostasis (proteostasis) is a prerequisite for cellular viability and plasticity. In particular, post-mitotic cells such as neurons rely on a tightly regulated safeguard system that allows for regulated protein expression. Previous investigations have identified RNA-binding proteins (RBPs) as crucial regulators of protein expression in nerve cells. However, during neurodegeneration, their ability to control the proteome is progressively disrupted. In this review, we examine the malfunction of key RBPs such as TAR DNA-binding protein 43 (TDP-43), Fused in Sarcoma (FUS), Staufen, Pumilio and fragile-X mental retardation protein (FMRP). Therefore, we focus on two key aspects of RBP dysfunctions in neurodegeneration: protein aggregation and dysregulation of their target RNAs. Moreover, we discuss how the chaperone system responds to changes in the RBP-controlled transcriptome. Based on recent findings, we propose a two-hit model in which both, harmful RBP deposits and target mRNA mistranslation contribute to neurodegeneration observed in RBPathologies.

The multifunctional RNA-binding protein Staufen1: an emerging regulator of oncogenesis through its various roles in key cellular events

The double-stranded multifunctional RNA-binding protein (dsRBP) Staufen was initially discovered in insects as a regulator of mRNA localization. Later, its mammalian orthologs have been described in different organisms, including humans. Two human orthologues of Staufen, named Staufen1 (STAU1) and Staufen2 (STAU2), share some structural and functional similarities. However, given their different spatio-temporal expression patterns, each of these orthologues plays distinct roles in cells. In the current review, we focus on the role of STAU1 in cell functions and cancer development. Since its discovery, STAU1 has mostly been studied for its involvement in various aspects of RNA metabolism. Given the pivotal role of RNA metabolism within cells, recent studies have explored the mechanistic impact of STAU1 in a wide variety of cell functions ranging from cell growth to cell death, as well as in various disease states. In particular, there has been increasing attention on the role of STAU1 in neuromuscular disorders, neurodegeneration, and cancer. Here, we provide an overview of the current knowledge on the role of STAU1 in RNA metabolism and cell functions. We also highlight the link between STAU1-mediated control of cellular functions and cancer development, progression, and treatment. Hence, our review emphasizes the potential of STAU1 as a novel biomarker and therapeutic target for cancer diagnosis and treatment, respectively.

The AKT modulator A-443654 reduces α-synuclein expression and normalizes ER stress and autophagy

Accumulation of α-synuclein is a main underlying pathological feature of Parkinson's disease and α-synucleinopathies, for which lowering expression of the α-synuclein gene (SNCA) is a potential therapeutic avenue. Using a cell-based luciferase reporter of SNCA expression we performed a quantitative high-throughput screen of 155,885 compounds and identified A-443654, an inhibitor of the multiple functional kinase AKT, as a potent inhibitor of SNCA. HEK-293 cells with CAG repeat expanded ATXN2 (ATXN2-Q58 cells) have increased levels of α-synuclein. We found that A-443654 normalized levels of both SNCA mRNA and α-synuclein monomers and oligomers in ATXN2-Q58 cells. A-443654 also normalized levels of α-synuclein in fibroblasts and iPSC-derived dopaminergic neurons from a patient carrying a triplication of the SNCA gene. Analysis of autophagy and endoplasmic reticulum stress markers showed that A-443654 successfully prevented α-synuclein toxicity and restored cell function in ATXN2-Q58 cells, normalizing the levels of mTOR, LC3-II, p62, STAU1, BiP, and CHOP. A-443654 also decreased the expression of DCLK1, an inhibitor of α-synuclein lysosomal degradation. Our study identifies A-443654 and AKT inhibition as a potential strategy for reducing SNCA expression and treating Parkinson's disease pathology.

The Staufen1-dependent cell cycle regulon or how a misregulated RNA-binding protein leads to cancer

In recent years, an increasing number of reports have linked the RNA-binding protein Staufen1 (STAU1) to the control of cell decision making. In non-transformed cells, STAU1 balances the expression of messenger RNA (mRNA) regulons that regulate differentiation and well-ordered cell division. Misregulation of STAU1 expression and/or functions changes the fragile balance in the expression of pro- and anti-proliferative and apoptotic genes and favours a novel equilibrium that supports cell proliferation and cancer development. The misregulation of STAU1 functions causes multiple coordinated modest effects in the post-transcriptional regulation of many RNA targets that code for cell cycle regulators, leading to dramatic consequences at the cellular level. The new tumorigenic equilibrium in STAU1-mediated gene regulation observed in cancer cells can be further altered by a slight increase in STAU1 expression that favours expression of pro-apoptotic genes and cell death. The STAU1-dependent cell cycle regulon is a good model to study how abnormal expression of an RNA-binding protein promotes cell growth and provides an advantageous selection of malignant cells in the first step of cancer development.

Staufen1 in Human Neurodegeneration

OBJECTIVE

Mutations in the ATXN2 gene (CAG expansions ≥32 repeats) can be a rare cause of Parkinson's disease and amyotrophic lateral sclerosis (ALS). We recently reported that the stress granule (SG) protein Staufen1 (STAU1) was overabundant in neurodegenerative disorder spinocerebellar ataxia type 2 (SCA2) patient cells, animal models, and ALS-TDP-43 fibroblasts, and provided a link between SG formation and autophagy. We aimed to test if STAU1 overabundance has a role in the pathogenesis of other neurodegenerative diseases.

METHODS

With multiple neurodegenerative patient-derived cell models, animal models, and human postmortem ALS tissue, we evaluate STAU1 function using biochemical and immunohistological analyses.

RESULTS

We demonstrate STAU1 overabundance and increased total and phosphorylated mammalian target of rapamycin (mTOR) in fibroblast cells from patients with ALS with mutations in TDP-43, patients with dementia with PSEN1 mutations, a patient with parkinsonism with MAPT mutation, Huntington's disease (HD) mutations, and SCA2 mutations. Increased STAU1 levels and mTOR activity were seen in human ALS spinal cord tissues as well as in animal models. Changes in STAU1 and mTOR protein levels were post-transcriptional. Exogenous expression of STAU1 in wildtype cells was sufficient to activate mTOR and downstream targets and form SGs. Targeting STAU1 by RNAi normalized mTOR, suggesting a potential role for therapy in diseases associated with STAU1 overabundance.

INTERPRETATION

STAU1 overabundance in neurodegeneration is a common phenomenon associated with hyperactive mTOR. Targeting STAU1 with ASOs or miRNA viral vectors may represent a novel, efficacious therapy for neurodegenerative diseases characterized by overabundant STAU1. ANN NEUROL 2021;89:1114-1128.

C9orf72-associated arginine-rich dipeptide repeats induce RNA-dependent nuclear accumulation of Staufen in neurons

RNA-binding proteins (RBPs) play essential roles in diverse cellular processes through post-transcriptional regulation of RNAs. The subcellular localization of RBPs is thus under tight control, the breakdown of which is associated with aberrant cytoplasmic accumulation of nuclear RBPs such as TDP-43 and FUS, well-known pathological markers for amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). Here, we report in Drosophila model for ALS/FTD that nuclear accumulation of a cytoplasmic RBP Staufen may be a new pathological feature. We found that in Drosophila C4da neurons expressing PR36, one of the arginine-rich dipeptide repeat proteins (DPRs), Staufen accumulated in the nucleus in Importin- and RNA-dependent manner. Notably, expressing Staufen with exogenous NLS—but not with mutated endogenous NLS—potentiated PR-induced dendritic defect, suggesting that nuclear-accumulated Staufen can enhance PR toxicity. PR36 expression increased Fibrillarin staining in the nucleolus, which was enhanced by heterozygous mutation of stau (stau^+/−), a gene that codes Staufen. Furthermore, knockdown of fib, which codes Fibrillarin, exacerbated retinal degeneration mediated by PR toxicity, suggesting that increased amount of Fibrillarin by stau^+/− is protective. stau^+/− also reduced the amount of PR-induced nuclear-accumulated Staufen and mitigated retinal degeneration and rescued viability of flies expressing PR36. Taken together, our data show that nuclear accumulation of Staufen in neurons may be an important pathological feature contributing to the pathogenesis of ALS/FTD.

Noncoding RNAs implication in cardiovascular diseases in the COVID-19 era

COronaVIrus Disease 19 (COVID-19) is caused by the infection of the Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2). Although the main clinical manifestations of COVID-19 are respiratory, many patients also display acute myocardial injury and chronic damage to the cardiovascular system. Understanding both direct and indirect damage caused to the heart and the vascular system by SARS-CoV-2 infection is necessary to identify optimal clinical care strategies. The homeostasis of the cardiovascular system requires a tight regulation of the gene expression, which is controlled by multiple types of RNA molecules, including RNA encoding proteins (messenger RNAs) (mRNAs) and those lacking protein-coding potential, the noncoding-RNAs. In the last few years, dysregulation of noncoding-RNAs has emerged as a crucial component in the pathophysiology of virtually all cardiovascular diseases. Here we will discuss the potential role of noncoding RNAs in COVID-19 disease mechanisms and their possible use as biomarkers of clinical use.

Effects of Embryonic Inflammation and Adolescent Psychosocial Environment on Cognition and Hippocampal Staufen in Middle-Aged Mice

Accumulating evidence has indicated that embryonic inflammation could accelerate age-associated cognitive impairment, which can be attributed to dysregulation of synaptic plasticity-associated proteins, such as RNA-binding proteins (RBPs). Staufen is a double-stranded RBP that plays a critical role in the modulation of synaptic plasticity and memory. However, relatively few studies have investigated how embryonic inflammation affects cognition and neurobiology during aging, or how the adolescent psychosocial environment affects inflammation-induced remote cognitive impairment. Consequently, the aim of this study was to investigate whether these adverse factors can induce changes in Staufen expression, and whether these changes are correlated with cognitive impairment. In our study, CD-1 mice were administered lipopolysaccharides (LPS, 50 μg/kg) or an equal amount of saline (control) intraperitoneally during days 15–17 of gestation. At 2 months of age, male offspring were randomly exposed to stress (S), an enriched environment (E), or not treated (CON) and then assigned to five groups: LPS, LPS+S, LPS+E, CON, and CON+S. Mice were evaluated at 3-month-old (young) and 15-month-old (middle-aged). Cognitive function was assessed using the Morris water maze test, while Staufen expression was examined at both the protein and mRNA level using immunohistochemistry/western blotting and RNAscope technology, respectively. The results showed that the middle-aged mice had worse cognitive performance and higher Staufen expression than young mice. Embryonic inflammation induced cognitive impairment and increased Staufen expression in the middle-aged mice, whereas adolescent stress/an enriched environment would accelerated/mitigated these effects. Meanwhile, Staufen expression was closely correlated with cognitive performance. Our findings suggested embryonic inflammation can accelerate age-associated learning and memory impairments, and these effects may be related to the Staufen expression.