Therapeutic reversal of Huntington's disease by in vivo self-assembled siRNAs

Genetically engineered human induced pluripotent stem cells for the production of brain-targeting extracellular vesicles

BACKGROUND

Extracellular vesicles (EVs) are cell-secreted membrane vesicles that have become a promising, natural nanoparticle system for delivering either naturally carried or exogenously loaded therapeutic molecules. Among reported cell sources for EV manufacture, human induced pluripotent stem cells (hiPSCs) offer numerous advantages. However, hiPSC-EVs only have a moderate ability for brain delivery. Herein, we sought to develop a stable hiPSC line for producing EVs with substantially enhanced brain targeting by genetic engineering to overexpress rabies viral glycoprotein (RVG) peptide fused to the N terminus of lysosomal associated membrane protein 2B (RVG-Lamp2B) which has been shown capable of boosting the brain delivery of EVs via the nicotinic acetylcholine receptor.

METHODS

An RVG-Lamp2B-HA expression cassette was knocked into the AAVS1 safe harbor locus of a control hiPSC line using the CRISPR/Cas9-assisted homologous recombination. Western blot was used to detect the expression of RVG-Lamp2B-HA in RVG-edited hiPSCs as well as EVs derived from RVG-edited hiPSCs. Uptake of EVs by SH-SY5Y cells in the presence of various endocytic inhibitors was analyzed using flow cytometry. Biodistribution and brain delivery of intravenously injected control and RVG-modified EVs in wild-type mice were examined using ex vivo fluorescent imaging.

RESULTS

Here we report that an RVG-Lamp2B-HA expression cassette was knocked into the AAVS1 safe harbor locus of a control hiPSC line using the CRISPR/Cas9-assisted homologous recombination. The RVG-edited iPSCs have normal karyotype, express pluripotency markers, and have differentiation potential. Expression of RVG-Lamp2B-HA was detected in total cell extracts as well as EVs derived from RVG-edited (vs. control) hiPSCs. The RVG-modified EVs enter neuronal cells via distinct endocytic pathways, compared with control EVs. The biodistribution study confirmed that EVs derived from RVG-edited hiPSCs possess higher brain delivery efficiency.

CONCLUSION

Taken together, we have established stable, genetically engineered hiPSCs for producing EVs with RVG expression, offering the improved ability for brain-targeted drug delivery.

Nanotechnology used for siRNA delivery for the treatment of neurodegenerative diseases: Focusing on Alzheimer's disease and Parkinson's disease

Neurodegenerative diseases (ND) are often accompanied by dementia, motor dysfunction, or disability. Caring for these patients imposes a significant psychological and financial burden on families. Until now, there are no effective methods for the treatment of NDs. Among them, Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common. Recently, studies have revealed that the overexpression of certain genes may be linked to the occurrence of AD and PD. Small interfering RNAs (siRNAs) are a powerful tool for gene silencing because they can specifically bind to and cleave target mRNA. However, the intrinsic properties of naked siRNA and various physiological barriers limit the application of siRNA in the brain. Nanotechnology is a promising option for addressing these issues. Nanoparticles are not only able to protect siRNA from degradation but also have the advantage of crossing various physiological barriers to reach the brain target of siRNA. In this review, we aim to introduce diverse nanotechnology used for delivering siRNA to treat AD and PD. Finally, we will briefly discuss our perspectives on this promising field.

Extracellular vesicle and CRISPR gene therapy: Current applications in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease

Neurodegenerative diseases are characterized by progressive deterioration of the nervous system. Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD) are prominently life-threatening examples of neurodegenerative diseases. The complexity of the pathophysiology in neurodegenerative diseases causes difficulties in diagnosing. Although the drugs temporarily help to correct specific symptoms including memory loss and degeneration, a complete treatment has not been found yet. New therapeutic approaches have been developed to understand and treat the underlying pathogenesis of neurodegenerative diseases. With this purpose, clustered-regularly interspaced short palindromic repeats/CRISPR-associated protein (CRISPR/Cas) technology has recently suggested a new treatment option. Editing of the genome is carried out by insertion and deletion processes on DNA. Safe delivery of the CRISPR/Cas system to the targeted cells without affecting surrounding cells is frequently investigated. Extracellular vesicles (EVs), that is exosomes, have recently been used in CRISPR/Cas studies. In this review, CRISPR/Cas and EV approaches used for diagnosis and/or treatment in AD, PD, ALS, and HD are reviewed. CRISPR/Cas and EV technologies, which stand out as new therapeutic approaches, may offer a definitive treatment option in neurodegenerative diseases.

In vivo and ex vivo gene therapy for neurodegenerative diseases: a promise for disease modification

Neurodegenerative diseases (NDDs), including AD, PD, HD, and ALS, represent a growing public health concern linked to aging and lifestyle factors, characterized by progressive nervous system damage leading to motor and cognitive deficits. Current therapeutics offer only symptomatic management, highlighting the urgent need for disease-modifying treatments. Gene therapy has emerged as a promising approach, targeting the underlying pathology of diseases with diverse strategies including gene replacement, gene silencing, and gene editing. This innovative therapeutic approach involves introducing functional genetic material to combat disease mechanisms, potentially offering long-term efficacy and disease modification. With advancements in genomics, structural biology, and gene editing tools such as CRISPR/Cas9, gene therapy holds significant promise for addressing the root causes of NDDs. Significant progress in preclinical and clinical studies has demonstrated the potential of in vivo and ex vivo gene therapy to treat various NDDs, offering a versatile and precise approach in comparison to conventional treatments. The current review describes various gene therapy approaches employed in preclinical and clinical studies for the treatment of NDDs, including AD, PD, HD, and ALS, and addresses some of the key translational challenges in this therapeutic approach.

Oleuropein enhances proteasomal activity and reduces mutant huntingtin-induced cytotoxicity

Introduction

Huntington's disease (HD) is a hereditary neurodegenerative disorder that primarily affects the striatum, a brain region responsible for movement control. The disease is characterized by the mutant huntingtin (mHtt) proteins with an extended polyQ stretch, which are prone to aggregation. These mHtt aggregates accumulate in neurons and are the primary cause of the neuropathology associated with HD. To date, no effective cure for HD has been developed.

Methods

The immortalized STHdh Q111/Q111 striatal cell line, the mHtt-transfected wild-type STHdh Q7/Q7 striatal cell line, and N2a cells were used as Huntington's disease cell models. Flow cytometry was used to assess cellular reactive oxygen species and transfection efficiency. The CCK-8 assay was used to measure cell viability, while fluorescence microscopy was used to quantify aggregates. Immunoblotting analyses were used to evaluate the effects on protein expression.

Results

Polyphenols are natural antioxidants that offer neuroprotection in neurological disorders. In this study, we provide evidence that oleuropein, the primary polyphenol in olive leaves and olive oil, enhances cell viability in HD cell models, including. STHdh Q7/Q7 STHdh Q7/Q7 striatal cells, N2a cells ectopically expressing the truncated mHtt, and STHdh Q111/Q111 striatal cells expressing the full-length mHtt. Oleuropein effectively reduced both soluble and aggregated forms of mHtt protein in these HD model cells. Notably, the reduction of mHtt aggregates associated with oleuropein was linked to increased proteasome activity rather than changes in autophagic flux. Oleuropein seems to modulate proteasome activity through an unidentified pathway, as it did not affect the 20S proteasome catalytic β subunits, the proteasome regulator PA28γ, or multiple MAPK pathways.

Discussion

We demonstrated that oleuropein enhances the degradation of mHtt by increasing proteasomal protease activities and alleviates mHtt-induced cytotoxicity. Hence, we propose that oleuropein and potentially other polyphenols hold promise as a candidate for alleviating Huntington's disease.

MSC-Derived Extracellular Vesicles Alleviate NLRP3/GSDMD-Mediated Neuroinflammation in Mouse Model of Sporadic Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease, with sporadic form being the predominant type. Neuroinflammation plays a critical role in accelerating pathogenic processes in AD. Mesenchymal stem cell (MSC)-derived small extracellular vesicles (MSC-sEVs) regulate inflammatory responses and show great promise for treating AD. Induced pluripotent stem cell (iPSC)-derived MSCs are similar to MSCs and exhibit low immunogenicity and heterogeneity, making them promising cell sources for clinical applications. This study examined the anti-inflammatory effects of MSC-sEVs in a streptozotocin-induced sporadic mouse model of AD (sAD). The intracisternal administration of iPSC-MSC-sEVs alleviated NLRP3/GSDMD-mediated neuroinflammation, decreased amyloid deposition and neuronal apoptosis, and mitigated cognitive dysfunction. Furthermore, it explored the role of miR-223-3p in the iPSC-MSC-sEVs-mediated anti-inflammatory effects in vitro. miR-223-3p directly targeted NLRP3, whereas inhibiting miR-223-3p almost completely reversed the suppression of NLRP3 by MSC-sEVs, suggesting that miR-223-3p may, at least partially, account for MSC-sEVs-mediated anti-inflammation. Results obtained suggest that intracisternal administration of iPSC-MSC-sEVs can reduce cognitive impairment by inhibiting NLRP3/GSDMD neuroinflammation in a sAD mouse model. Therefore, the present study provides a proof-of-principle for applying iPSC-MSC-sEVs to target neuroinflammation in sAD.

Exosomes for neurodegenerative diseases: diagnosis and targeted therapy

PURPOSE OF REVIEW

Neurodegenerative diseases are still challenging clinical issues, with no curative interventions available and early, accurate diagnosis remaining difficult. Finding solutions to them is of great importance. In this review, we discuss possible exosomal diagnostic biomarkers and explore current explorations in exosome-targeted therapy for some common neurodegenerative diseases, offering insights into the clinical transformation of exosomes in this field.

RECENT FINDINGS

The burgeoning research on exosomes has shed light on their potential applications in disease diagnosis and treatment. As a type of extracellular vesicles, exosomes are capable of crossing the blood - brain barrier and exist in various body fluids, whose components can reflect pathophysiological changes in the brain. In addition, they can deliver specific drugs to brain tissue, and even possess certain therapeutic effects themselves. And the recent advancements in engineering modification technology have further enabled exosomes to selectively target specific sites, facilitating the possibility of targeted therapy for neurodegenerative diseases. The unique properties of exosomes give them great potential in the diagnosis and treatment of neurodegenerative diseases, and provide novel ideas for dealing with such diseases.

Advances on the Mechanisms and Therapeutic Strategies in Non-coding CGG Repeat Expansion Diseases

Non-coding CGG repeat expansions within the 5' untranslated region are implicated in a range of neurological disorders, including fragile X-associated tremor/ataxia syndrome, oculopharyngeal myopathy with leukodystrophy, and oculopharyngodistal myopathy. This review outlined the general characteristics of diseases associated with non-coding CGG repeat expansions, detailing their clinical manifestations and neuroimaging patterns, which often overlap and indicate shared pathophysiological traits. We summarized the underlying molecular mechanisms of these disorders, providing new insights into the roles that DNA, RNA, and toxic proteins play. Understanding these mechanisms is crucial for the development of targeted therapeutic strategies. These strategies include a range of approaches, such as antisense oligonucleotides, RNA interference, genomic DNA editing, small molecule interventions, and other treatments aimed at correcting the dysregulated processes inherent in these disorders. A deeper understanding of the shared mechanisms among non-coding CGG repeat expansion disorders may hold the potential to catalyze the development of innovative therapies, ultimately offering relief to individuals grappling with these debilitating neurological conditions.

Extracellular vesicles as nanotheranostic platforms for targeted neurological disorder interventions

Central Nervous System (CNS) disorders represent a profound public health challenge that affects millions of people around the world. Diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and traumatic brain injury (TBI) exemplify the complexities and diversities that complicate their early detection and the development of effective treatments. Amid these challenges, the emergence of nanotechnology and extracellular vesicles (EVs) signals a new dawn for treating and diagnosing CNS ailments. EVs are cellularly derived lipid bilayer nanosized particles that are pivotal in intercellular communication within the CNS and have the potential to revolutionize targeted therapeutic delivery and the identification of novel biomarkers. Integrating EVs with nanotechnology amplifies their diagnostic and therapeutic capabilities, opening new avenues for managing CNS diseases. This review focuses on examining the fascinating interplay between EVs and nanotechnology in CNS theranostics. Through highlighting the remarkable advancements and unique methodologies, we aim to offer valuable perspectives on how these approaches can bring about a revolutionary change in disease management. The objective is to harness the distinctive attributes of EVs and nanotechnology to forge personalized, efficient interventions for CNS disorders, thereby providing a beacon of hope for affected individuals. In short, the confluence of EVs and nanotechnology heralds a promising frontier for targeted and impactful treatments against CNS diseases, which continue to pose significant public health challenges. By focusing on personalized and powerful diagnostic and therapeutic methods, we might improve the quality of patients.

Recent Progress of Small Interfering RNA Delivery on the Market and Clinical Stage

Small interfering RNAs (siRNAs) are promising therapeutic strategies, and five siRNA drugs have been approved by the Food and Drug Administration (FDA) and the European Commission (EC). This marks a significant milestone in the development of siRNA for clinical applications. The approved siRNA agents can effectively deliver siRNAs to the liver and treat liver-related diseases. Currently, researchers have developed diverse delivery platforms for transporting siRNAs to different tissues such as the brain, lung, muscle, and others, and a large number of siRNA drugs are undergoing clinical trials. Here, these delivery technologies and the latest advancements in clinical applications are summarized, and this Review provides a concise overview of the strategies employed for siRNA delivery to both hepatic and extrahepatic tissues.

Antisense therapy: a potential breakthrough in the treatment of neurodegenerative diseases

Neurodegenerative diseases are a group of disorders characterized by the progressive degeneration of neurons in the central or peripheral nervous system. Currently, there is no cure for neurodegenerative diseases and this means a heavy burden for patients and the health system worldwide. Therefore, it is necessary to find new therapeutic approaches, and antisense therapies offer this possibility, having the great advantage of not modifying cellular genome and potentially being safer. Many preclinical and clinical studies aim to test the safety and effectiveness of antisense therapies in the treatment of neurodegenerative diseases. The objective of this review is to summarize the recent advances in the development of these new technologies to treat the most common neurodegenerative diseases, with a focus on those antisense therapies that have already received the approval of the U.S. Food and Drug Administration.

Preferential cleavage of upstream targets in concatenated miRNA/siRNA target sites support a 5'-3' scanning model for RISC target recognition

RNA interference (RNAi) is becoming medicine for curing human diseases. Still, we lack a thorough understanding of some fundamental aspects of RNAi that affect its efficiency and accuracy. One such question is how RNA-induced silencing complex (RISC) can efficiently find its targets. To address this question, we developed a strategy that involves the expression of mRNAs containing concatenations of identical miRNA/siRNA target sites. These mRNAs were cleaved by co-expressed miRNAs in plant cells or by co-transfected siRNAs in mammalian cells. The mRNA cleavage events were then detected using the 5'RACE assay. Using this strategy, we found that RISCs preferentially cleave the upstream ones of concatenated target sites, consistent with a model that RISC scans mRNA in 5'→3' direction to approach its target sites. The stability of the cleaved mRNA fragments correlates with the complementarity between siRNA and its target sequence. When siRNA perfectly complements its target sequence, the cleaved mRNA fragment becomes stable and may be cleaved in a second round. Our findings have practical implications for designing siRNAs with increased efficiency and reduced off-target effects.

Huntington's Disease: Complex Pathogenesis and Therapeutic Strategies

Huntington's disease (HD) arises from the abnormal expansion of CAG repeats in the huntingtin gene (HTT), resulting in the production of the mutant huntingtin protein (mHTT) with a polyglutamine stretch in its N-terminus. The pathogenic mechanisms underlying HD are complex and not yet fully elucidated. However, mHTT forms aggregates and accumulates abnormally in neuronal nuclei and processes, leading to disruptions in multiple cellular functions. Although there is currently no effective curative treatment for HD, significant progress has been made in developing various therapeutic strategies to treat HD. In addition to drugs targeting the neuronal toxicity of mHTT, gene therapy approaches that aim to reduce the expression of the mutant HTT gene hold great promise for effective HD therapy. This review provides an overview of current HD treatments, discusses different therapeutic strategies, and aims to facilitate future therapeutic advancements in the field.

Chemically Modified Platforms for Better RNA Therapeutics

RNA-based therapies have catalyzed a revolutionary transformation in the biomedical landscape, offering unprecedented potential in disease prevention and treatment. However, despite their remarkable achievements, these therapies encounter substantial challenges including low stability, susceptibility to degradation by nucleases, and a prominent negative charge, thereby hindering further development. Chemically modified platforms have emerged as a strategic innovation, focusing on precise alterations either on the RNA moieties or their associated delivery vectors. This comprehensive review delves into these platforms, underscoring their significance in augmenting the performance and translational prospects of RNA-based therapeutics. It encompasses an in-depth analysis of various chemically modified delivery platforms that have been instrumental in propelling RNA therapeutics toward clinical utility. Moreover, the review scrutinizes the rationale behind diverse chemical modification techniques aiming at optimizing the therapeutic efficacy of RNA molecules, thereby facilitating robust disease management. Recent empirical studies corroborating the efficacy enhancement of RNA therapeutics through chemical modifications are highlighted. Conclusively, we offer profound insights into the transformative impact of chemical modifications on RNA drugs and delineates prospective trajectories for their future development and clinical integration.

Exosomes: potential targets for the diagnosis and treatment of neuropsychiatric disorders

The field of neuropsychiatry is considered a middle ground between neurological and psychiatric disorders, thereby bridging the conventional boundaries between matter and mind, consciousness, and function. Neuropsychiatry aims to evaluate and treat cognitive, behavioral, and emotional disorders in individuals with neurological conditions. However, the pathophysiology of these disorders is not yet fully understood, and objective biological indicators for these conditions are currently lacking. Treatment options are also limited due to the blood-brain barrier, which results in poor treatment effects. Additionally, many drugs, particularly antipsychotic drugs, have adverse reactions, which make them difficult to tolerate for patients. As a result, patients often abandon treatment owing to these adverse reactions. Since the discovery of exosomes in 1983, they have been extensively studied in various diseases owing to their potential as nanocellulators for information exchange between cells. Because exosomes can freely travel between the center and periphery, brain-derived exosomes can reflect the state of the brain, which has considerable advantages in diagnosis and treatment. In addition, administration of engineered exosomes can improve therapeutic efficacy, allow lesion targeting, ensure drug stability, and prevent systemic adverse effects. Therefore, this article reviews the source and biological function of exosomes, relationship between exosomes and the blood-brain barrier, relationship between exosomes and the pathological mechanism of neuropsychiatric disorders, exosomes in the diagnosis and treatment of neuropsychiatric disorders, and application of engineered exosomes in neuropsychiatric disorders.

Current progression in application of extracellular vesicles in central nervous system diseases

Early diagnosis and pharmacological treatment of central nervous system (CNS) diseases has been a long-standing challenge for clinical research due to the presence of the blood-brain barrier. Specific proteins and RNAs in brain-derived extracellular vesicles (EVs) usually reflect the corresponding state of brain disease, and therefore, EVs can be used as diagnostic biomarkers for CNS diseases. In addition, EVs can be engineered and fused to target cells for delivery of cargo, demonstrating the great potential of EVs as a nanocarrier platform. We review the progress of EVs as markers and drug carriers in the diagnosis and treatment of neurological diseases. The main areas include visual imaging, biomarker diagnosis and drug loading therapy for different types of CNS diseases. It is hoped that increased knowledge of EVs will facilitate their clinical translation in CNS diseases.

A Comprehensive Review of Small Interfering RNAs (siRNAs): Mechanism, Therapeutic Targets, and Delivery Strategies for Cancer Therapy

Small interfering RNA (siRNA) delivery by nanocarriers has been identified as a promising strategy in the study and treatment of cancer. Short nucleotide sequences are synthesized exogenously to create siRNA, which triggers RNA interference (RNAi) in cells and silences target gene expression in a sequence-specific way. As a nucleic acid-based medicine that has gained popularity recently, siRNA exhibits novel potential for the treatment of cancer. However, there are still many obstacles to overcome before clinical siRNA delivery devices can be developed. In this review, we discuss prospective targets for siRNA drug design, explain siRNA drug properties and benefits, and give an overview of the current clinical siRNA therapeutics for the treatment of cancer. Additionally, we introduce the siRNA chemical modifications and delivery systems that are clinically sophisticated and classify bioresponsive materials for siRNA release in a methodical manner. This review will serve as a reference for researchers in developing more precise and efficient targeted delivery systems, promoting ongoing advances in clinical applications.

Synthesizing biomaterials in living organisms

Living organisms fabricate biomacromolecules such as DNA, RNA, and proteins by the self-assembly process. The research on the mechanism of biomacromolecule formation also inspires the exploration of in vivo synthesized biomaterials. By elaborate design, artificial building blocks or precursors can self-assemble or polymerize into functional biomaterials within living organisms. In recent decades, these so-called in vivo synthesized biomaterials have achieved extensive applications in cell-fate manipulation, disease theranostics, bioanalysis, cellular surface engineering, and tissue regeneration. In this review, we classify strategies for in vivo synthesis into non-covalent, covalent, and genetic types. The development of these approaches is based on the chemical principles of supramolecular chemistry and synthetic chemistry, biological cues such as enzymes and microenvironments, and the means of synthetic biology. By summarizing the design principles in detail, some insights into the challenges and opportunities in this field are provided to  enlighten further research.

Exploration of the Noncoding Genome for Human-Specific Therapeutic Targets-Recent Insights at Molecular and Cellular Level

While it is well known that 98-99% of the human genome does not encode proteins, but are nevertheless transcriptionally active and give rise to a broad spectrum of noncoding RNAs [ncRNAs] with complex regulatory and structural functions, specific functions have so far been assigned to only a tiny fraction of all known transcripts. On the other hand, the striking observation of an overwhelmingly growing fraction of ncRNAs, in contrast to an only modest increase in the number of protein-coding genes, during evolution from simple organisms to humans, strongly suggests critical but so far essentially unexplored roles of the noncoding genome for human health and disease pathogenesis. Research into the vast realm of the noncoding genome during the past decades thus lead to a profoundly enhanced appreciation of the multi-level complexity of the human genome. Here, we address a few of the many huge remaining knowledge gaps and consider some newly emerging questions and concepts of research. We attempt to provide an up-to-date assessment of recent insights obtained by molecular and cell biological methods, and by the application of systems biology approaches. Specifically, we discuss current data regarding two topics of high current interest: (1) By which mechanisms could evolutionary recent ncRNAs with critical regulatory functions in a broad spectrum of cell types (neural, immune, cardiovascular) constitute novel therapeutic targets in human diseases? (2) Since noncoding genome evolution is causally linked to brain evolution, and given the profound interactions between brain and immune system, could human-specific brain-expressed ncRNAs play a direct or indirect (immune-mediated) role in human diseases? Synergistic with remarkable recent progress regarding delivery, efficacy, and safety of nucleic acid-based therapies, the ongoing large-scale exploration of the noncoding genome for human-specific therapeutic targets is encouraging to proceed with the development and clinical evaluation of novel therapeutic pathways suggested by these research fields.

Engineered exosomes for tissue regeneration: from biouptake, functionalization and biosafety to applications

Exosomes are increasingly recognized as important effector molecules that regulate intercellular signaling pathways. Notably, certain types of exosomes can induce therapeutic responses, including cell proliferation, angiogenesis, and tissue repair. The use of exosomes in therapy is a hot spot in current research, especially in regenerative medicine. Despite the therapeutic potential, problems have hindered their success in clinical applications. These shortcomings include low concentration, poor targeting and limited loading capability. To fully realize their therapeutic potential, certain modifications are needed in native exosomes. In the present review, we summarize the exosome modification and functionalization strategies. In addition, we provide an overview of potential clinical applications and highlight the issues associated with the biosafety and biocompatibility of engineered exosomes in applications.

RNA therapeutics for neurological diseases

INTRODUCTION

Ribonucleic acid (RNA) therapeutics are a new class of drugs whose importance is highlighted by the growing number of molecules in the clinic.

SOURCES OF DATA

We focus on RNA therapeutics for neurogenetic disorders, which are broadly defined as diseases with a genetic background and with at least one clinical sign affecting the nervous system. A systematic search identified 14 RNA drugs approved by FDA and many others in development.

AREAS OF AGREEMENT

The field of RNA therapeutics is changing the therapeutic scenario across many disorders.

AREAS OF CONTROVERSY

Despite its recent successes, RNA therapeutics encountered several hurdles and some clinical failures. Delivery to the brain represents the biggest challenge.

GROWING POINTS

The many advantages of RNA drugs make the development of these technologies a worthwhile investment.

AREAS TIMELY FOR DEVELOPING RESEARCH

Clinical failures stress the importance of implementing clinical trial design and optimizing RNA molecules to hold the promise of revolutionizing the treatment of human diseases.

Ferroptosis-Regulated Cell Death as a Therapeutic Strategy for Neurodegenerative Diseases: Current Status and Future Prospects

Ferroptosis is increasingly being recognized as a key element in the pathogenesis of diverse diseases. Recent studies have highlighted the intricate links between iron metabolism and neurodegenerative disorders. Emerging evidence suggests that iron homeostasis, oxidative stress, and neuroinflammation all contribute to the regulation of both ferroptosis and neuronal health. However, the precise molecular mechanisms underlying the involvement of ferroptosis in the pathological processes of neurodegeneration and its impact on neuronal dysfunction remain incompletely understood. In our Review, we provide a comprehensive analysis and summary of the potential molecular mechanisms underlying ferroptosis in neurodegenerative diseases, aiming to elucidate the disease progression of neurodegeneration. Additionally, we discuss potential therapeutic agents that modulate ferroptosis with the goal of identifying novel drug molecules for the treatment of neurodegenerative disorders.

In situ stimulus-responsive self-assembled nanomaterials for drug delivery and disease treatment

The individual motifs that respond to specific stimuli for the self-assembly of nanomaterials play important roles. In situ constructed nanomaterials are formed spontaneously without human intervention and have promising applications in bioscience. However, due to the complex physiological environment of the human body, designing stimulus-responsive self-assembled nanomaterials in vivo is a challenging problem for researchers. In this article, we discuss the self-assembly principles of various nanomaterials in response to the tissue microenvironment, cell membrane, and intracellular stimuli. We propose the applications and advantages of in situ self-assembly in drug delivery and disease diagnosis and treatment, with a focus on in situ self-assembly at the lesion site, especially in cancer. Additionally, we introduce the significance of introducing exogenous stimulation to construct self-assembly in vivo. Based on this foundation, we put forward the prospects and possible challenges in the field of in situ self-assembly. This review uncovers the relationship between the structure and properties of in situ self-assembled nanomaterials and provides new ideas for innovative drug molecular design and development to solve the problems in the targeted delivery and precision medicine.

Nucleic acid-based therapeutics for the treatment of central nervous system disorders

Nucleic acid-based therapeutics (NBTs) are an emerging class of drugs with potential for the treatment of a wide range of central nervous system conditions. To date, pertaining to CNS indications, there are two commercially available NBTs and a large number of ongoing clinical trials. However, these NBTs are applied directly to the brain due to very low blood brain barrier permeability. In this review, we outline recent advances in chemical modifications of NBTs and NBT delivery techniques intended to promote brain exposure, efficacy, and possible future systemic application.

Where should siRNAs go: applicable organs for siRNA drugs

RNA interference mediated by small interfering RNAs (siRNAs) has been exploited for the development of therapeutics. siRNAs can be a powerful therapeutic tool because the working mechanisms of siRNAs are straightforward. siRNAs determine targets based on their sequence and specifically regulate the gene expression of the target gene. However, efficient delivery of siRNAs to the target organ has long been an issue that needs to be solved. Tremendous efforts regarding siRNA delivery have led to significant progress in siRNA drug development, and from 2018 to 2022, a total of five siRNA drugs were approved for the treatment of patients. Although all FDA-approved siRNA drugs target the hepatocytes of the liver, siRNA-based drugs targeting different organs are in clinical trials. In this review, we introduce siRNA drugs in the market and siRNA drug candidates in clinical trials that target cells in multiple organs. The liver, eye, and skin are the preferred organs targeted by siRNAs. Three or more siRNA drug candidates are in phase 2 or 3 clinical trials to suppress gene expression in these preferred organs. On the other hand, the lungs, kidneys, and brain are challenging organs with relatively few clinical trials. We discuss the characteristics of each organ related to the advantages and disadvantages of siRNA drug targeting and strategies to overcome the barriers in delivering siRNAs based on organ-specific siRNA drugs that have progressed to clinical trials.

Small extracellular vesicles: a novel drug delivery system for neurodegenerative disorders

Neurodegenerative diseases (NDs) have a slow onset and are usually detected late during disease. NDs are often difficult to cure due to the presence of the blood-brain barrier (BBB), which makes it difficult to find effective treatments and drugs, causing great stress and financial burden to families and society. Currently, small extracellular vesicles (sEVs) are the most promising drug delivery systems (DDSs) for targeted delivery of molecules to specific sites in the brain as a therapeutic vehicle due to their low toxicity, low immunogenicity, high stability, high delivery efficiency, high biocompatibility and trans-BBB functionality. Here, we review the therapeutic application of sEVs in several NDs, including Alzheimer's disease, Parkinson's disease, and Huntington's disease, discuss the current barriers associated with sEVs and brain-targeted DDS, and suggest future research directions.

Emergence of Small Interfering RNA-Based Gene Drugs for Various Diseases

Small molecule, peptide, and protein-based drugs have been developed over decades to treat various diseases. The importance of gene therapy as an alternative to traditional drugs has increased after the discovery of gene-based drugs such as Gendicine for cancer and Neovasculgen for peripheral artery disease. Since then, the pharma sector is focusing on developing gene-based drugs for various diseases. After the discovery of the RNA interference (RNAi) mechanism, the development of siRNA-based gene therapy has been accelerated immensely. siRNA-based treatment for hereditary transthyretin-mediated amyloidosis (hATTR) using Onpattro and acute hepatic porphyria (AHP) by Givlaari and three more FDA-approved siRNA drugs has set up a milestone and further improved the confidence for the development of gene therapeutics for a spectrum of diseases. siRNA-based gene drugs have more advantages over other gene therapies and are under study to treat different types of diseases such as viral infections, cardiovascular diseases, cancer, and many more. However, there are a few bottlenecks to realizing the full potential of siRNA-based gene therapy. They include chemical instability, nontargeted biodistribution, undesirable innate immune responses, and off-target effects. This review provides a comprehensive view of siRNA-based gene drugs: challenges associated with siRNA delivery, their potential, and future prospects.

Exosomes in brain diseases: Pathogenesis and therapeutic targets

Exosomes are extracellular vesicles with diameters of about 100 nm that are naturally secreted by cells into body fluids. They are derived from endosomes and are wrapped in lipid membranes. Exosomes are involved in intracellular metabolism and intercellular communication. They contain nucleic acids, proteins, lipids, and metabolites from the cell microenvironment and cytoplasm. The contents of exosomes can reflect their cells' origin and allow the observation of tissue changes and cell states under disease conditions. Naturally derived exosomes have specific biomolecules that act as the "fingerprint" of the parent cells, and the contents changed under pathological conditions can be used as biomarkers for disease diagnosis. Exosomes have low immunogenicity, are small in size, and can cross the blood-brain barrier. These characteristics make exosomes unique as engineering carriers. They can incorporate therapeutic drugs and achieve targeted drug delivery. Exosomes as carriers for targeted disease therapy are still in their infancy, but exosome engineering provides a new perspective for cell-free disease therapy. This review discussed exosomes and their relationship with the occurrence and treatment of some neuropsychiatric diseases. In addition, future applications of exosomes in the diagnosis and treatment of neuropsychiatric disorders were evaluated in this review.

The Potential of Edible and Medicinal Resource Polysaccharides for Prevention and Treatment of Neurodegenerative Diseases

As natural medicines in complementary and alternative medicine, edible and medicinal resources are being gradually recognized throughout the world. According to statistics from the World Health Organization, about 80% of the worldwide population has used edible and medicinal resource products to prevent and treat diseases. Polysaccharides, one of the main effective components in edible and medicinal resources, are considered ideal regulators of various biological responses due to their high effectiveness and low toxicity, and they have a wide range of possible applications for the development of functional foods for the regulation of common, frequently occurring, chronic and severe diseases. Such applications include the development of polysaccharide products for the prevention and treatment of neurodegenerative diseases that are difficult to control by a single treatment, which is of great value to the aging population. Therefore, we evaluated the potential of polysaccharides to prevent neurodegeneration by their regulation of behavioral and major pathologies, including abnormal protein aggregation and neuronal damage caused by neuronal apoptosis, autophagy, oxidative damage, neuroinflammation, unbalanced neurotransmitters, and poor synaptic plasticity. This includes multi-target and multi-pathway regulation involving the mitochondrial pathway, MAPK pathway, NF-κB pathway, Nrf2 pathway, mTOR pathway, PI3K/AKT pathway, P53/P21 pathway, and BDNF/TrkB/CREB pathway. In this paper, research into edible and medicinal resource polysaccharides for neurodegenerative diseases was reviewed in order to provide a basis for the development and application of polysaccharide health products and promote the recognition of functional products of edible and medicinal resources.

Extracellular vesicle-based delivery of silencing sequences for the treatment of Machado-Joseph disease/spinocerebellar ataxia type 3

Machado-Joseph disease (MJD)/spinocerebellar ataxia type 3 (SCA3) is the most common autosomal dominantly inherited ataxia worldwide. It is caused by an over-repetition of the trinucleotide CAG within the ATXN3 gene, which confers toxic properties to ataxin-3 (ATXN3) species. RNA interference technology has shown promising therapeutic outcomes but still lacks a non-invasive delivery method to the brain. Extracellular vesicles (EVs) emerged as promising delivery vehicles due to their capacity to deliver small nucleic acids, such as microRNAs (miRNAs). miRNAs were found to be enriched into EVs due to specific signal motifs designated as ExoMotifs. In this study, we aimed at investigating whether ExoMotifs would promote the packaging of artificial miRNAs into EVs to be used as non-invasive therapeutic delivery vehicles to treat MJD/SCA3. We found that miRNA-based silencing sequences, associated with ExoMotif GGAG and ribonucleoprotein A2B1 (hnRNPA2B1), retained the capacity to silence mutant ATXN3 (mutATXN3) and were 3-fold enriched into EVs. Bioengineered EVs containing the neuronal targeting peptide RVG on the surface significantly decreased mutATXN3 mRNA in primary cerebellar neurons from MJD YAC 84.2 and in a novel dual-luciferase MJD mouse model upon daily intranasal administration. Altogether, these findings indicate that bioengineered EVs carrying miRNA-based silencing sequences are a promising delivery vehicle for brain therapy.

Potential for Therapeutic-Loaded Exosomes to Ameliorate the Pathogenic Effects of α-Synuclein in Parkinson's Disease

Pathogenic forms of α-synuclein (α-syn) are transferred to and from neurons, astrocytes, and microglia, which spread α-syn pathology in the olfactory bulb and the gut and then throughout the Parkinson's disease (PD) brain and exacerbate neurodegenerative processes. Here, we review attempts to minimize or ameliorate the pathogenic effects of α-syn or deliver therapeutic cargo into the brain. Exosomes (EXs) have several important advantages as carriers of therapeutic agents including an ability to readily cross the blood-brain barrier, the potential for targeted delivery of therapeutic agents, and immune resistance. Diverse cargo can be loaded via various methods, which are reviewed herein, into EXs and delivered into the brain. Genetic modification of EX-producing cells or EXs and chemical modification of EX have emerged as powerful approaches for the targeted delivery of therapeutic agents to treat PD. Thus, EXs hold great promise for the development of next-generation therapeutics for the treatment of PD.

Biodistribution and delivery of oligonucleotide therapeutics to the central nervous system: Advances, challenges, and future perspectives

Considerable advances have been made in the research and development of oligonucleotide therapeutics (OTs) for treating central nervous system (CNS) diseases, such as psychiatric and neurodegenerative disorders, because of their promising mode of action. However, due to the tight barrier function and complex physiological structure of the CNS, the efficient delivery of OTs to target the brain has been a major challenge, and intensive efforts have been made to overcome this limitation. In this review, we summarize the representative methodologies and current knowledge of biodistribution, along with the pharmacokinetic/pharmacodynamic (PK/PD) relationship of OTs in the CNS, which are critical elements for the successful development of OTs for CNS diseases. First, quantitative bioanalysis methods and imaging-based approaches for the evaluation of OT biodistribution are summarized. Next, information available on the biodistribution profile, distribution pathways, quantitative PK/PD modeling, and simulation of OTs following intrathecal or intracerebroventricular administration are reviewed. Finally, the latest knowledge on the drug delivery systems to the brain via intranasal or systemic administration as noninvasive routes for improved patient quality of life is reviewed. The aim of this review is to enrich research on the successful development of OTs by clarifying OT distribution profiles and pathways to the target brain regions or cells, and by identifying points that need further investigation for a mechanistic approach to generate efficient OTs.

Nucleic acid drug vectors for diagnosis and treatment of brain diseases

Nucleic acid drugs have the advantages of rich target selection, simple in design, good and enduring effect. They have been demonstrated to have irreplaceable superiority in brain disease treatment, while vectors are a decisive factor in therapeutic efficacy. Strict physiological barriers, such as degradation and clearance in circulation, blood-brain barrier, cellular uptake, endosome/lysosome barriers, release, obstruct the delivery of nucleic acid drugs to the brain by the vectors. Nucleic acid drugs against a single target are inefficient in treating brain diseases of complex pathogenesis. Differences between individual patients lead to severe uncertainties in brain disease treatment with nucleic acid drugs. In this Review, we briefly summarize the classification of nucleic acid drugs. Next, we discuss physiological barriers during drug delivery and universal coping strategies and introduce the application methods of these universal strategies to nucleic acid drug vectors. Subsequently, we explore nucleic acid drug-based multidrug regimens for the combination treatment of brain diseases and the construction of the corresponding vectors. In the following, we address the feasibility of patient stratification and personalized therapy through diagnostic information from medical imaging and the manner of introducing contrast agents into vectors. Finally, we take a perspective on the future feasibility and remaining challenges of vector-based integrated diagnosis and gene therapy for brain diseases.

Extracellular Vesicle-Based Therapeutics in Neurological Disorders

Neurological diseases remain some of the major causes of death and disability in the world. Few types of drugs and insufficient delivery across the blood-brain barrier limit the treatment of neurological disorders. The past two decades have seen the rapid development of extracellular vesicle-based therapeutics in many fields. As the physiological and pathophysiological roles of extracellular vesicles are recognized in neurological diseases, they have become promising therapeutics and targets for therapeutic interventions. Moreover, advanced nanomedicine technologies have explored the potential of extracellular vesicles as drug delivery systems in neurological diseases. In this review, we discussed the preclinical strategies for extracellular vesicle-based therapeutics in neurological disorders and the struggles involved in their clinical application.

Intranasal delivery: An attractive route for the administration of nucleic acid based therapeutics for CNS disorders

The etiologies of several cardiovascular, inflammatory, neurological, hereditary disorders, cancer, and infectious diseases have implicated changes in the genetic set up or genetic mutations as the root cause. Nucleic acid based therapeutics (NBTs) is a new class of biologics that are known to regulate gene expression at the transcriptional and post-transcriptional level. The NBTs include oligonucleotides, nucleosides, antisense RNA, small interfering RNAs, micro RNA etc. In recent times, this new category of biologics has found enormous potential in the management of cardiovascular, inflammatory, neurological disorders, cancer, infectious diseases and organ transplantation. However, the delivery of NBTs is highly challenging in terms of target specificity (intracellular delivery), mononuclear phagocyte system uptake, stability and biodistribution. Additionally, management of the above mentioned disorders require regular and intrusive therapy making non-invasive routes preferable in comparison to invasive routes like parenteral. The nasal route is garnering focus in delivery of NBTs to the brain in the management of several CNS disorders due to the associated merits such as non-invasiveness, possibility of chronic delivery, improved patient compliance, avoidance of hepatic and gastrointestinal metabolism as well as ability to bypass the BBB. Hence in recent times, this route has been sought by the reserachers as an alternative to parenteral therapy for the delivery of several NBTs. This review shall focus on an array of NBTs delivered through nasal route, their challenges, applications and opportunities. The novel delivery systems for incorporating NBTs; their targeting strategies shall be critically reviewed. The challenges towards regulatory approvals and commercialization shall also be discussed at large. Comparison of learnings derived from the success and barriers in nasal delivery of NBTs will help in identification of futuristic opportunities for their translation from bench to bedside.

A Novel Perspective on Ischemic Stroke: A Review of Exosome and Noncoding RNA Studies

Ischemic stroke is a life-threatening condition that also frequently results in long-term disability. Currently, intravenous thrombolysis with tissue plasminogen activator and mechanical thrombectomy is the most popular treatment. However, the narrow time window and related complications limit the treatment benefits. Exosomes have recently emerged as ideal therapeutic candidates for ischemic stroke with the ability to pass through the blood_brain barrier and mediate intercellular communication, in addition, exosomes and their contents can be bioengineered to implement targeted delivery. In the last two decades, exosomes and exosomal noncoding RNAs have been found to be involved in the pathophysiological progression of ischemic stroke, including atherosclerosis, apoptosis, inflammation, oxidative stress, and neurovascular remodeling. In this review, we describe the latest progress regarding the role of exosomal long noncoding RNAs and circular RNAs in the occurrence, progression, and recovery of ischemic stroke. Exploration of exosomal noncoding RNAs and their correlated effects in ischemic stroke may facilitate accurate diagnosis, and they may serve as new therapeutic targets for the disease.

Benefits and limitations of nanomedicine treatment of brain cancers and age-dependent neurodegenerative disorders

The treatment of central nervous system (CNS) malignancies, including brain cancers, is limited by a number of obstructions, including the blood-brain barrier (BBB), the heterogeneity and high invasiveness of tumors, the inaccessibility of tissues for early diagnosis and effective surgery, and anti-cancer drug resistance. Therapies employing nanomedicine have been shown to facilitate drug penetration across the BBB and maintain biodistribution and accumulation of therapeutic agents at the desired target site. The application of lipid-, polymer-, or metal-based nanocarriers represents an advanced drug delivery system for a growing group of anti-cancer chemicals. The nanocarrier surface is designed to contain an active ligand (cancer cell marker or antibody)-binding structure which can be modified to target specific cancer cells. Glioblastoma, ependymoma, neuroblastoma, medulloblastoma, and primary CNS lymphomas were recently targeted by easily absorbed nanocarriers. The metal- (such as transferrin drug-loaded systems), polymer- (nanocapsules and nanospheres), or lipid- (such as sulfatide-containing nanoliposomes)-based nano-vehicles were loaded with apoptosis- and/or ferroptosis-stimulating agents and demonstrated promising anti-cancer effects. This review aims to discuss effective nanomedicine approaches designed to overcome the current limitations in the therapy of brain cancers and age-dependent neurodegenerative disorders. To accent current obstacles for successful CNS-based cancer therapy, we discuss nanomedicine perspectives and limitations of nanodrug use associated with the specificity of nervous tissue characteristics and the effects nanocarriers have on cognition.

[Principles of translational gene therapy for neuromuscular diseases]

BACKGROUND

In recent years the theoretical hope has become reality and the first hereditary neuromuscular diseases have become causally treatable. Neuromuscular diseases have thus become the pacemaker of this form of therapy for the whole of neurology.

AIMS

This article describes the principles of precision gene therapy for neurogenetic diseases using examples of neuromuscular diseases.

DISCUSSION

Various strategies of gene therapy have become established and are being tested in preclinical and clinical trials and evaluated as approved forms for long-term efficacy. The aim of every gene therapy is the modification or introduction of the target gene with initiation of a degradation of dysfunctional proteins. Various techniques, such as gene transfer, gene substitution or gene editing in vivo and ex vivo are now usable. For example, a modification of the pre-mRNA using antisense oligonucleotides or RNA interference (siRNA) can be used for exon skipping. An initiation of gene expression to produce the target protein can be based on a modification of the DNA by means of gene replacement, cell-based therapy (iPS cells), regulation by compensatory proteins or pharmacological treatment with so-called small molecules. Each method has advantages and complex disadvantages that must be individually evaluated. Phenotypic peculiarities of a rare disease often only become apparent through specific translational therapy. It is already becoming obvious that a very early point in timing of gene therapy is probably the most effective. Newborn screening is therefore gaining additional importance as early diagnosis can achieve the best possible success of therapies, possibly even preventively.

Hitching a ride on exosomes: a new approach for the delivery of siRNA-mediated therapies

This scientific commentary refers to ‘Therapeutic reversal of Huntington’s disease by in vivo self-assembled siRNAs’ by Zhang et al. (doi:10.1093/brain/awab354).