Arginine is a disease modifier for polyQ disease models that stabilizes polyQ protein conformation

A single-center, single-arm, prospective, open-label, and comparative trial to evaluate the safety and tolerability profile of a 90-day oral L-arginine hydrochloride intervention for patients with amyotrophic lateral sclerosis

Weight loss, a key indicator of malnutrition in amyotrophic lateral sclerosis (ALS) patients, negatively impacts patient prognosis. However, effective nutritional interventions have not been adequately established. Research in ALS model mice has shown that L-arginine can prolong survival; however, no human intervention studies have been conducted. We conducted a single-center, single-arm, prospective, open-label, and comparative trial to assess the safety and tolerability of L-arginine hydrochloride in ALS patients. ALS patients were administered 15 g/day L-arginine hydrochloride for 90 days. The primary outcome of safety was evaluated on days 45 and 90. The secondary outcome of efficacy was evaluated by measuring nutritional status, ALS Functional Rating Scale (ALSFRS) scores, and the occurrence of events such as the initiation of tracheostomy positive pressure ventilation (TPPV) and death. The study included 20 patients (40% female; mean age, 62.0 ± 6.9 years; median disease duration, 1.9 years). Six participants (30%) experienced treatment-emergent adverse events (TEAEs), including elevated creatine kinase levels, liver function test abnormalities, glucose tolerance issues, hyperammonemia, anorexia, dysgeusia, and vasculitis. No serious TEAEs were associated with L-arginine hydrochloride. Over the course of three months, the average changes in body weight, body mass index, and the ALSFRS score were - 0.37 kg, -1.1 kg/m2, and - 1.7 points, respectively. There were no events requiring TPPV initiation or deaths. This study demonstrated that the oral administration of L-arginine hydrochloride over three months was well tolerated by ALS patients, with no serious TEAEs or deaths attributed to the study drug.Trial Registration number: Japan Registry of Clinical Trials (jRCTs061230001), first registered 11/04/2023.

Arginine: A potential prophylactic supplement for transthyretin amyloidosis

Transthyretin (TTR) is an amyloidogenic protein associated with TTR amyloidosis (ATTR). Dissociation of TTR tetramers into TTR monomers causes TTR misfolding, resulting in amyloid fibril formation and triggering the onset of ATTR. Low-molecular-weight tetrameric TTR stabilizers are potential therapeutic agents to delay ATTR progression. However, the currently available drugs are expensive and cannot be used for prophylaxis. Therefore, in this study, we aimed to identify a prophylactic supplement that suppresses TTR amyloid formation. We investigated whether arginine, an amyloidogenic protein aggregation inhibitor, stabilizes tetrameric TTR, thereby preventing amyloid fibril formation. Immunoblotting showed that arginine mixed with wild-type TTR (TTRwt), amyloidogenic TTR Val30Met (ATTR V30M), and human serum samples reduced the amount of monomeric TTR but increased the tetramer/monomer ratio of TTR compared to those in the samples without arginine. Additionally, oral administration of arginine (5000 mg for 5 days) to healthy volunteers effectively increased the tetramer/monomer ratio of TTR in the serum. Thioflavin T test, a quantitative analysis method for amyloid fibril formation, showed that amyloid fibril formation was significantly suppressed with arginine compared to that without arginine. As arginine is a common supplement and non-toxic amino acid, it can be used as a promising prophylactic supplement to suppress amyloid fibril formation in ATTR.

Advances in the Differentiation of hiPSCs into Cerebellar Neuronal Cells

The cerebellum has historically been primarily associated with the regulation of precise motor functions. However, recent findings suggest that it also plays a pivotal role in the development of advanced cognitive functions, including learning, memory, and emotion regulation. Pathological changes in the cerebellum, whether congenital hereditary or acquired degenerative, can result in a diverse spectrum of disorders, ranging from genetic spinocerebellar ataxias to psychiatric conditions such as autism, and schizophrenia. While studies in animal models have significantly contributed to our understanding of the genetic networks governing cerebellar development, it is important to note that the human cerebellum follows a protracted developmental timeline compared to the neocortex. Consequently, employing animal models to uncover human-specific molecular events in cerebellar development presents significant challenges. The emergence of human induced pluripotent stem cells (hiPSCs) has provided an invaluable tool for creating human-based culture systems, enabling the modeling and analysis of cerebellar physiology and pathology. hiPSCs and their differentiated progenies can be derived from patients with specific disorders or carrying distinct genetic variants. Importantly, they preserve the unique genetic signatures of the individuals from whom they originate, allowing for the elucidation of human-specific molecular and cellular processes involved in cerebellar development and related disorders. This review focuses on the technical advancements in the utilization of hiPSCs for the generation of both 2D cerebellar neuronal cells and 3D cerebellar organoids.

Neurodegenerative diseases associated with the disruption of proteostasis and their therapeutic strategies using chemical chaperones

Aberrant proteostasis is thought to be involved in the pathogenesis of neurodegenerative diseases. Some proteostasis abnormalities are ameliorated by chaperones. Chaperones are divided into three groups: molecular, pharmacological and chemical. Chemical chaperones intended to alleviate stress in organelles, such as the endoplasmic reticulum (ER), are now being administered clinically. Of the chemical chaperones, 4-phenylbutyrate (4-PBA) has been used as a research reagent, and its mechanism of action includes chaperone effects and the inhibition of histone deacetylase. Moreover, it also binds to the B-site of SEC24 and regulates COPII-mediated transport from the ER. Although its therapeutic effect may not be strong, elucidating the mechanism of action of 4-PBA may contribute to the identification of novel therapeutic targets for neurodegenerative diseases.

Why Is Arginine the Only Amino Acid That Inhibits Polyglutamine Monomers from Taking on Toxic Conformations?

Polyglutamine (polyQ) diseases are devastating neurodegenerative disorders characterized by abnormal expansion of glutamine repeats within specific proteins. The aggregation of polyQ proteins is a critical pathological hallmark of these diseases. Arginine was identified as a promising inhibitory compound because it prevents polyQ-protein monomers from forming intra- and intermolecular β-sheet structures and hinders polyQ proteins from aggregating to form oligomers. Such an aggregation inhibitory effect was not observed in other amino acids. However, the underlying molecular mechanism of the aggregation inhibition and the factors that differentiate arginine from other amino acids, in terms of the inhibition of the polyQ-protein aggregation, remain poorly understood. Here, we performed replica-permutation molecular dynamics simulations to elucidate the molecular mechanism by which arginine inhibits the formation of the intramolecular β-sheet structure of a polyQ monomer. We found that the intramolecular β-sheet structure with more than four β-bridges of the polyQ monomer with arginine is more unstable than without any ligand and with lysine. We also found that arginine has 1.6-2.1 times more contact with polyQ than lysine. In addition, we revealed that arginine forms more hydrogen bonds with the main chain of the polyQ monomer than lysine. More hydrogen bonds formed between arginine and polyQ inhibit polyQ from forming the long intramolecular β-sheet structure. It is known that intramolecular β-sheet structure enhances intermolecular β-sheet structure between proteins. These effects are thought to be the reason for the inhibition of polyQ aggregation. This study provides insights into the molecular events underlying arginine's inhibition of polyQ-protein aggregation.

α-Synuclein pathology in Drosophila melanogaster is exacerbated by haploinsufficiency of Rop: connecting STXBP1 encephalopathy with α-synucleinopathies

Syntaxin-binding protein 1 (STXBP1) is a presynaptic protein that plays important roles in synaptic vesicle docking and fusion. STXBP1 haploinsufficiency causes STXBP1 encephalopathy (STXBP1-E), which encompasses neurological disturbances including epilepsy, neurodevelopmental disorders, and movement disorders. Most patients with STXBP1-E present with regression and movement disorders in adulthood, highlighting the importance of a deeper understanding of the neurodegenerative aspects of STXBP1-E. An in vitro study proposed an interesting new role of STXBP1 as a molecular chaperone for α-Synuclein (αSyn), a key molecule in the pathogenesis of neurodegenerative disorders. However, no studies have shown αSyn pathology in model organisms or patients with STXBP1-E. In this study, we used Drosophila models to examine the effects of STXBP1 haploinsufficiency on αSyn-induced neurotoxicity in vivo. We demonstrated that haploinsufficiency of Ras opposite (Rop), the Drosophila ortholog of STXBP1, exacerbates compound eye degeneration, locomotor dysfunction, and dopaminergic neurodegeneration in αSyn-expressing flies. This phenotypic aggravation was associated with a significant increase in detergent-insoluble αSyn levels in the head. Furthermore, we tested whether trehalose, which has neuroprotective effects in various models of neurodegenerative disorders, mitigates αSyn-induced neurotoxicity exacerbated by Rop haploinsufficiency. In flies expressing αSyn and carrying a heterozygous Rop null variant, trehalose supplementation effectively alleviates neuronal phenotypes, accompanied by a decrease in detergent-insoluble αSyn in the head. In conclusion, this study revealed that Rop haploinsufficiency exacerbates αSyn-induced neurotoxicity by altering the αSyn aggregation propensity. This study not only contributes to understanding the mechanisms of neurodegeneration in STXBP1-E patients, but also provides new insights into the pathogenesis of α-synucleinopathies.

Glial fibrillary acidic protein is pathologically modified in Alexander disease

Here, we describe pathological events potentially involved in the disease pathogenesis of Alexander disease (AxD). This is a primary genetic disorder of astrocyte caused by dominant gain-of-function mutations in the gene coding for an intermediate filament protein glial fibrillary acidic protein (GFAP). Pathologically, this disease is characterized by the upregulation of GFAP and its accumulation as Rosenthal fibers. Although the genetic basis linking GFAP mutations with Alexander disease has been firmly established, the initiating events that promote GFAP accumulation and the role of Rosenthal fibers (RFs) in the disease process remain unknown. Here, we investigate the hypothesis that disease-associated mutations promote GFAP aggregation through aberrant posttranslational modifications. We found high molecular weight GFAP species in the RFs of AxD brains, indicating abnormal GFAP crosslinking as a prominent pathological feature of this disease. In vitro and cell-based studies demonstrate that cystine-generating mutations promote GFAP crosslinking by cysteine-dependent oxidation, resulting in defective GFAP assembly and decreased filament solubility. Moreover, we found GFAP was ubiquitinated in RFs of AxD patients and rodent models, supporting this modification as a critical factor linked to GFAP aggregation. Finally, we found that arginine could increase the solubility of aggregation-prone mutant GFAP by decreasing its ubiquitination and aggregation. Our study suggests a series of pathogenic events leading to AxD, involving interplay between GFAP aggregation and abnormal modifications by GFAP ubiquitination and oxidation. More important, our findings provide a basis for investigating new strategies to treat AxD by targeting abnormal GFAP modifications.

Polyglutamine disorders: Pathogenesis and potential drug interventions

Polyglutamine/poly(Q) diseases are a group nine hereditary neurodegenerative disorders caused due to abnormally expanded stretches of CAG trinucleotide in functionally distinct genes. All human poly(Q) diseases are characterized by the formation of microscopically discernable poly(Q) positive aggregates, the inclusion bodies. These toxic inclusion bodies are responsible for the impairment of several cellular pathways such as autophagy, transcription, cell death, etc., that culminate in disease manifestation. Although, these diseases remain largely without treatment, extensive research has generated mounting evidences that various events of poly(Q) pathogenesis can be developed as potential drug targets. The present review article briefly discusses the key events of disease pathogenesis, model system-based investigations that support the development of effective therapeutic interventions against pathogenesis of human poly(Q) disorders, and a comprehensive list of pharmacological and bioactive compounds that have been experimentally shown to alleviate poly(Q)-mediated neurotoxicity. Interestingly, due to the common cause of pathogenesis, all poly(Q) diseases share etiology, thus, findings from one disease can be potentially extrapolated to other poly(Q) diseases as well.

[Recent clinical advances in hereditary spinocerebellar degeneration]

Spinocerebellar degeneration (SCD) is a neurodegenerative disorder characterized by cerebellar ataxia and other multisystem manifestations, such as Parkinsonism and pyramidal tract symptoms. No effective treatment is available for SCD. Approximately one-third of the cases of SCD are inherited, and the remaining two-third are sporadic, including multiple system atrophy. This article provides an overview of hereditary SCD, its clinical features, recent treatment advances, biomarkers, role of genomic medicine, and future treatment prospects.

Elevated SLC7A2 expression is associated with an abnormal neuroinflammatory response and nitrosative stress in Huntington's disease

We previously identified solute carrier family 7 member 2 (SLC7A2) as one of the top upregulated genes when normal Huntingtin was deleted. SLC7A2 has a high affinity for L-arginine. Arginine is implicated in inflammatory responses, and SLC7A2 is an important regulator of innate and adaptive immunity in macrophages. Although neuroinflammation is clearly demonstrated in animal models and patients with Huntington's disease (HD), the question of whether neuroinflammation actively participates in HD pathogenesis is a topic of ongoing research and debate. Here, we studied the role of SLC7A2 in mediating the neuroinflammatory stress response in HD cells. RNA sequencing (RNA-seq), quantitative RT-PCR and data mining of publicly available RNA-seq datasets of human patients were performed to assess the levels of SLC7A2 mRNA in different HD cellular models and patients. Biochemical studies were then conducted on cell lines and primary mouse astrocytes to investigate arginine metabolism and nitrosative stress in response to neuroinflammation. The CRISPR-Cas9 system was used to knock out SLC7A2 in STHdhQ7 and Q111 cells to investigate its role in mediating the neuroinflammatory response. Live-cell imaging was used to measure mitochondrial dynamics. Finally, exploratory studies were performed using the Enroll-HD periodic human patient dataset to analyze the effect of arginine supplements on HD progression. We found that SLC7A2 is selectively upregulated in HD cellular models and patients. HD cells exhibit an overactive response to neuroinflammatory challenges, as demonstrated by abnormally high iNOS induction and NO production, leading to increased protein nitrosylation. Depleting extracellular Arg or knocking out SLC7A2 blocked iNOS induction and NO production in STHdhQ111 cells. We further examined the functional impact of protein nitrosylation on a well-documented protein target, DRP-1, and found that more mitochondria were fragmented in challenged STHdhQ111 cells. Last, analysis of Enroll-HD datasets suggested that HD patients taking arginine supplements progressed more rapidly than others. Our data suggest a novel pathway that links arginine uptake to nitrosative stress via upregulation of SLC7A2 in the pathogenesis and progression of HD. This further implies that arginine supplements may potentially pose a greater risk to HD patients.

Metabolic deregulation associated with aging modulates protein aggregation in the yeast model of Huntington's disease

Huntington's disease is associated with increased CAG repeat resulting in an expanded polyglutamine tract in the protein Huntingtin (HTT) leading to its aggregation resulting in neurodegeneration. Previous studies have shown that N-terminal HTT with 46Q aggregated in the stationary phase but not the logarithmic phase in the yeast model of HD. We carried out a metabolomic analysis of logarithmic and stationary phase yeast model of HD expressing different polyQ lengths attached to N-terminal HTT tagged with enhanced green fluorescent protein (EGFP). The results show significant changes in the metabolic profile and deregulated pathways in stationary phase cells compared to logarithmic phase cells. Comparison of metabolic pathways obtained from logarithmic phase 46Q versus 25Q with those obtained for presymptomatic HD patients from our previous study and drosophila model of HD showed considerable overlap. The arginine biosynthesis pathway emerged as one of the key pathways that is common in stationary phase yeast compared to logarithmic phase and HD patients. Treatment of yeast with arginine led to a significant decrease, while transfer to arginine drop-out media led to a significant increase in the size of protein aggregates in both logarithmic and stationary phase yeast model of HD. Knockout of arginine transporters in the endoplasmic reticulum and vacuole led to a significant decrease in mutant HTT aggregation. Overall our results highlight arginine as a critical metabolite that modulates the aggregation of mutant HTT and disease progression in HD.Communicated by Ramaswamy H. Sarma.

Efficacy of l-Arginine treatment in patients with HTLV-1-associated neurological disease

OBJECTIVE

HTLV-1 infection causes HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), resulting in loss of motor function. In this Phase 2 trial, we assessed the efficacy and safety of l-arginine in patients with HAM/TSP.

METHODS

This open-label, single-arm, Phase 2 study enrolled patients diagnosed with HAM/TSP. Patients received l-arginine at a dose of 20 g orally for 1 week and were followed-up for 3 weeks. The primary endpoint was change in walking speed in the 10-m walk test (10MWT). The main secondary endpoints were change in Timed Up and Go Test (TUGT) time, improvement in inflammatory markers in cerebrospinal fluid (CSF), safety, and tolerability.

RESULTS

The study enrolled 20 patients (13 [65%] female) with a mean age of 67.8 years (95% CI 62.3 to 73.3). Although the primary endpoint, the changes in 10MWT time between baseline (Day 0) and Day 7, did not reach statistical significance (mean percent change in time -3.5%, 95% CI -10.8% to 3.7%; P = 0.32), a significant improvement was detected between baseline and Day 14 (-9.4%, 95% CI -16.6% to -2.2%; P = 0.01). Significant improvements were also observed in selected secondary endpoints, including in TUGT time (-9.1%, 95% CI -15.5% to -2.7%; P < 0.01), and in neopterin concentration in CSF (-2.1 pmol/mL, 95% CI -3.8 to -0.5; P = 0.01). Adverse events were infrequent, mild, and resolved rapidly.

INTERPRETATION

l-arginine therapy improved motor function and decreased CSF inflammatory markers. l-arginine thus represents a promising therapeutic option for patients with HAM/TSP.

TRIAL REGISTRATION NUMBER

UMIN000023854.

Mechanism underlying liquid-to-solid phase transition in fused in sarcoma liquid droplets

The RNA-binding protein fused in sarcoma (FUS) forms ribonucleoprotein granules via liquid-liquid phase separation (LLPS) in the cytoplasm. The phase separation of FUS accelerates aberrant liquid-solid phase separation and leads to the onset of familial amyotrophic lateral sclerosis (ALS). We previously found that FUS forms two types of liquid condensates in equilibrium, specifically LP-LLPS (i.e., normal type) and HP-LLPS (i.e., aberrant type), each with different partial molar volumes. However, it is unclear how liquid condensates are converted to the pathogenic solid phase. Here, we report a mechanism underlying the aberrant liquid-to-solid phase transition of FUS liquid condensates and the inhibition of this transition with small molecules. We found that the liquid condensate formed via HP-LLPS had greatly reduced dynamics, which is a common feature of aged wild-type FUS droplets and the droplet-like assembly of the ALS patient-type FUS variant. The longer FUS remained on the HP-LLPS, the harder it was to transform it into a mixed state (i.e., one-phase). These results indicate that liquid-to-solid phase transition, namely the aging of droplets, is accelerated with HP-LLPS. Interestingly, arginine suppressed the aging of droplets and HP-LLPS formation more strongly than LP-LLPS formation. These data indicate that the formation of HP-LLPS via the one-phase state or LP-LLPS is a pathway leading to irreversible solid aggregates. Dopamine and pyrocatechol also suppressed HP-LLPS formation. Our data highlight the potential of HP-LLPS to be used as a therapeutic target and arginine as a plausible drug candidate for ALS-causing FUS.

Exploring the Role of Posttranslational Modifications in Spinal and Bulbar Muscular Atrophy

Spinal and Bulbar Muscular Atrophy (SBMA) is an X-linked adult-onset progressive neuromuscular disease that affects the spinal and bulbar motor neurons and skeletal muscles. SBMA is caused by expansion of polymorphic CAG trinucleotide repeats in the Androgen Receptor (AR) gene, resulting in expanded glutamine tract in the AR protein. Polyglutamine (polyQ) expansion renders the mutant AR protein toxic, resulting in the formation of mutant protein aggregates and cell death. This classifies SBMA as one of the nine known polyQ diseases. Like other polyQ disorders, the expansion of the polyQ tract in the AR protein is the main genetic cause of the disease; however, multiple other mechanisms besides the polyQ tract expansion also contribute to the SBMA disease pathophysiology. Posttranslational modifications (PTMs), including phosphorylation, acetylation, methylation, ubiquitination, and SUMOylation are a category of mechanisms by which the functionality of AR has been found to be significantly modulated and can alter the neurotoxicity of SBMA. This review summarizes the different PTMs and their effects in regulating the AR function and discusses their pathogenic or protective roles in context of SBMA. This review also includes the therapeutic approaches that target the PTMs of AR in an effort to reduce the mutant AR-mediated toxicity in SBMA.

The molecular pathogenesis of repeat expansion diseases

Expanded short tandem repeats in the genome cause various monogenic diseases, particularly neurological disorders. Since the discovery of a CGG repeat expansion in the FMR1 gene in 1991, more than 40 repeat expansion diseases have been identified to date. In the coding repeat expansion diseases, in which the expanded repeat sequence is located in the coding regions of genes, the toxicity of repeat polypeptides, particularly misfolding and aggregation of proteins containing an expanded polyglutamine tract, have been the focus of investigation. On the other hand, in the non-coding repeat expansion diseases, in which the expanded repeat sequence is located in introns or untranslated regions, the toxicity of repeat RNAs has been the focus of investigation. Recently, these repeat RNAs were demonstrated to be translated into repeat polypeptides by the novel mechanism of repeat-associated non-AUG translation, which has extended the research direction of the pathological mechanisms of this disease entity to include polypeptide toxicity. Thus, a common pathogenesis has been suggested for both coding and non-coding repeat expansion diseases. In this review, we briefly outline the major pathogenic mechanisms of repeat expansion diseases, including a loss-of-function mechanism caused by repeat expansion, repeat RNA toxicity caused by RNA foci formation and protein sequestration, and toxicity by repeat polypeptides. We also discuss perturbation of the physiological liquid-liquid phase separation state caused by these repeat RNAs and repeat polypeptides, as well as potential therapeutic approaches against repeat expansion diseases.

Upstream open reading frame with NOTCH2NLC GGC expansion generates polyglycine aggregates and disrupts nucleocytoplasmic transport: implications for polyglycine diseases

Neuronal intranuclear inclusion disease (NIID) is neurodegenerative disease characterized by widespread inclusions. Despite the identification of GGC repeat expansion in 5'UTR of NOTCH2NLC gene in adult-onset NIIDs, its pathogenic mechanism remains unclear. Gain-of-function poly-amino-acid proteins generated by unconventional translation have been revealed in nucleotide repeat expansion disorders, inspiring us to explore the possibility of unconventional translation in NIID. Here we demonstrated that NOTCH2NLC 5'UTR triggers the translation of a polyglycine (polyG)-containing protein, N2NLCpolyG. N2NLCpolyG accumulates in p62-positive inclusions in cultured cells, mouse models, and NIID patient tissues with NOTCH2NLC GGC expansion. Translation of N2NLCpolyG is initiated by an upstream open reading frame (uORF) embedding the GGC repeats. N2NLCpolyG tends to aggregate with the increase of GGC repeat units, and displays phase separation properties. N2NLCpolyG aggregation impairs nuclear lamina and nucleocytoplasmic transport but does not necessarily cause acute death on neuronal cells. Our study suggests a similarity of pathogenic mechanisms between NIID and another GGC-repeat disease, fragile X-associated tremor ataxia syndrome. These findings expand our knowledge of protein gain-of-function in NIID, and further highlight evidence for a novel spectrum of diseases caused by aberrant polyG protein aggregation, namely the polyG diseases.

Arginine and Arginine-Rich Peptides as Modulators of Protein Aggregation and Cytotoxicity Associated With Alzheimer's Disease

A substantial body of evidence indicates cationic, arginine-rich peptides (CARPs) are effective therapeutic compounds for a range of neurodegenerative pathologies, with beneficial effects including the reduction of excitotoxic cell death and mitochondrial dysfunction. CARPs, therefore, represent an emergent class of promising neurotherapeutics with multimodal mechanisms of action. Arginine itself is a known chaotrope, able to prevent misfolding and aggregation of proteins. The putative role of proteopathies in chronic neurodegenerative diseases such as Alzheimer's disease (AD) warrants investigation into whether CARPs could also prevent the aggregation and cytotoxicity of amyloidogenic proteins, particularly amyloid-beta and tau. While monomeric arginine is well-established as an inhibitor of protein aggregation in solution, no studies have comprehensively discussed the anti-aggregatory properties of arginine and CARPs on proteins associated with neurodegenerative disease. Here, we review the structural, physicochemical, and self-associative properties of arginine and the guanidinium moiety, to explore the mechanisms underlying the modulation of protein aggregation by monomeric and multimeric arginine molecules. Arginine-rich peptide-based inhibitors of amyloid-beta and tau aggregation are discussed, as well as further modulatory roles which could reduce proteopathic cytotoxicity, in the context of therapeutic development for AD.

CPEB alteration and aberrant transcriptome-polyadenylation lead to a treatable SLC19A3 deficiency in Huntington's disease

[Figure: see text].

TAR RNA Mediated Folding of a Single-Arginine-Mutant HIV-1 Tat Protein within HeLa Cells Experiencing Intracellular Crowding

The various effects of native protein folding on the stability and folding rate of intrinsically disordered proteins (IDPs) in crowded intracellular environments are important in biomedicine. Although most studies on protein folding have been conducted in vitro, providing valuable insights, studies on protein folding in crowded intracellular environments are scarce. This study aimed to explore the effects of intracellular molecular crowding on the folding of mutant transactivator HIV-1 Tat based on intracellular interactions, including TAR RNA, as proof of the previously reported chaperna-RNA concept. Considering that the Tat-TAR RNA motif binds RNA, we assessed the po tential function of TAR RNA as a chaperna for the refolding of R52Tat, a mutant in which the argi nine (R) residues at R52 have been replaced with alanine (A) by site-directed mutagenesis. We mon itored Tat-EGFP and Tat folding in HeLa cells via time-lapse fluorescence microscopy and biolayer interferometry using EGFP fusion as an indicator for folding status. These results show that the refolding of R52A Tat was stimulated well at a 0.3 μM TAR RNA concentration; wild-type Tat refolding was essentially abolished because of a reduction in the affinity for TAR RNA at that con centration. The folding and refolding of R52Tat were mainly promoted upon stimulation with TAR RNA. Our findings provide novel insights into the therapeutic potential of chaperna-mediated fold ing through the examination of as-yet-unexplored RNA-mediated protein folding as well as viral genetic variants that modulate viral evolutionary linkages for viral diseases inside a crowded intra cellular environment.

Advances and impact of arginine-based materials in wound healing

In studies on wound-dressing materials, bioactive materials have been developed rapidly to accelerate wound healing. In recent years, scientists have studied arginine as a bioactive component due to its excellent biosafety, antimicrobial properties and therapeutic effects on wound healing. Surprisingly, arginine therapy is also used under specific pathological conditions, such as diabetes and trauma/hemorrhagic shock. Due to the broad utilization of arginine-assisted therapy, we present the unique properties of arginine for healing lesions of damaged tissue and examined multiple arginine-based systems for the application of wound healing. This review shows that arginine-based therapy can be separated in two categories: direct supplemental approaches of free arginine, and indirect approaches based on arginine derivatives in which modified arginine can be released after biodegradation. Using these two pathways, arginine-based therapy may prove to be a promising strategy in the development of wound curative treatments.

New Perspectives of Gene Therapy on Polyglutamine Spinocerebellar Ataxias: From Molecular Targets to Novel Nanovectors

Seven of the most frequent spinocerebellar ataxias (SCAs) are caused by a pathological expansion of a cytosine, adenine and guanine (CAG) trinucleotide repeat located in exonic regions of unrelated genes, which in turn leads to the synthesis of polyglutamine (polyQ) proteins. PolyQ proteins are prone to aggregate and form intracellular inclusions, which alter diverse cellular pathways, including transcriptional regulation, protein clearance, calcium homeostasis and apoptosis, ultimately leading to neurodegeneration. At present, treatment for SCAs is limited to symptomatic intervention, and there is no therapeutic approach to prevent or reverse disease progression. This review provides a compilation of the experimental advances obtained in cell-based and animal models toward the development of gene therapy strategies against polyQ SCAs, providing a discussion of their potential application in clinical trials. In the second part, we describe the promising potential of nanotechnology developments to treat polyQ SCA diseases. We describe, in detail, how the design of nanoparticle (NP) systems with different physicochemical and functionalization characteristics has been approached, in order to determine their ability to evade the immune system response and to enhance brain delivery of molecular tools. In the final part of this review, the imminent application of NP-based strategies in clinical trials for the treatment of polyQ SCA diseases is discussed.

Protein Aggregation Inhibitors as Disease-Modifying Therapies for Polyglutamine Diseases

The polyglutamine (polyQ) diseases are a group of inherited neurodegenerative diseases caused by the abnormal expansion of a CAG trinucleotide repeat that are translated into an expanded polyQ stretch in the disease-causative proteins. The expanded polyQ stretch itself plays a critical disease-causative role in the pathomechanisms underlying polyQ diseases. Notably, the expanded polyQ stretch undergoes a conformational transition from the native monomer into the β-sheet-rich monomer, followed by the formation of soluble oligomers and then insoluble aggregates with amyloid fibrillar structures. The intermediate soluble species including the β-sheet-rich monomer and oligomers exhibit substantial neurotoxicity. Therefore, protein conformation stabilization and aggregation inhibition that target the upstream of the insoluble aggregate formation would be a promising approach toward the development of disease-modifying therapies for polyQ diseases. PolyQ aggregation inhibitors of different chemical categories, such as intrabodies, peptides, and small chemical compounds, have been identified through intensive screening methods. Among them, recent advances in the brain delivery methods of several peptides and the screening of small chemical compounds have brought them closer to clinical utility. Notably, the recent discovery of arginine as a potent conformation stabilizer and aggregation inhibitor of polyQ proteins both in vitro and in vivo have paved way to the clinical trial for the patients with polyQ diseases. Meanwhile, expression reduction of expanded polyQ proteins per se would be another promising approach toward disease modification of polyQ diseases. Gene silencing, especially by antisense oligonucleotides (ASOs), have succeeded in reducing the expression of polyQ proteins in the animal models of various polyQ diseases by targeting the aberrant mRNA with expanded CAG repeats. Of note, some of these ASOs have recently been translated into clinical trials. Here we overview and discuss these recent advances toward the development of disease modifying therapies for polyQ diseases. We envision that combination therapies using aggregation inhibitors and gene silencing would meet the needs of the patients with polyQ diseases and their caregivers in the near future to delay or prevent the onset and progression of these currently intractable diseases.

Polyglutamine spinocerebellar ataxias: emerging therapeutic targets

INTRODUCTION

Six of the most frequent dominantly inherited spinocerebellar ataxias (SCAs) worldwide - SCA1, SCA2, SCA3, SCA6, SCA7, and SCA17 - are caused by an expansion of a polyglutamine (polyQ) tract in the corresponding proteins. While the identification of the causative mutation has advanced knowledge on the pathogenesis of polyQ SCAs, effective therapeutics able to mitigate the severe clinical manifestation of these highly incapacitating disorders are not yet available.

AREAS COVERED

This review provides a comprehensive and critical perspective on well-established and emerging therapeutic targets for polyQ SCAs; it aims to inspire prospective drug discovery efforts.

EXPERT OPINION

The landscape of polyQ SCAs therapeutic targets and strategies includes (1) the mutant genes and proteins themselves, (2) enhancement of endogenous protein quality control responses, (3) abnormal protein-protein interactions of the mutant proteins, (4) disturbed neuronal function, (5) mitochondrial function, energy availability and oxidative stress, and (6) glial dysfunction, growth factor or hormone imbalances. Challenges include gaining a clearer definition of therapeutic targets for the drugs in clinical development, the discovery of novel drug-like molecules for challenging key targets, and the attainment of a stronger translation of preclinical findings to the clinic.

Generation of Common Marmoset Model Lines of Spinocerebellar Ataxia Type 3

Animal models are indispensable tools in the development of innovative treatments for rare and incurable diseases. To date, there is almost no effective treatment for neurodegenerative diseases, and animal models that properly simulate human disease pathologies are eagerly anticipated to identify disease biomarkers and develop therapeutic methods and agents. Among experimental animals, non-human primates are the most suitable animal models for the study of neurodegenerative diseases with human-specific higher brain dysfunction and late-onset and slowly progressing symptoms. With the rapid development of novel therapies such as oligonucleotide therapeutics and genome editing technologies, non-human primate models for neurodegenerative diseases will be essential for preclinical studies and active interventional trials. In a previous publication, we reported the generation of the first transgenic marmoset model of spinocerebellar ataxia type 3 and successful obtainment of subsequent generations with stable disease onset. Moreover, we generated transgenic marmosets in which the transgene was controlled by the tetracycline-inducible gene expression system. In this mini-review, we summarize the research on our marmoset model of spinocerebellar ataxia type 3.