The Neurotoxicity of Vesicles Secreted by ALS Patient Myotubes Is Specific to Exosome-Like and Not Larger Subtypes

Accumulation of Damaging Lipids in the Arf1-Ablated Neurons Promotes Neurodegeneration through Releasing mtDNA and Activating Inflammatory Pathways in Microglia

Lipid metabolism disorders in both neurons and glial cells have been found in neurodegenerative (ND) patients and animal models. However, the pathological connection between lipid droplets and NDs remains poorly understood. The recent work has highlighted the utility of a neuron-specific Arf1-knockout mouse model and corresponding cells for elucidating the nexus between lipid metabolism disorders and amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). In this study, it is found that Arf1 deficiency first induced surplus fatty acid synthesis through the AKT-mTORC1-SREBP1-FASN axis, which further triggered endoplasmic reticulum (ER)-mitochondrial stress cascade via calcium flux. The organelle stress cascade further caused mitochondrial DNA (mtDNA) to be released into cytoplasm. Concurrently, the FASN-driven fatty acid synthesis in the Arf1-deficient neurons might also induce accumulation of sphingolipids in lysosomes that caused dysfunction of autophagy and lysosomes, which further promoted lysosomal stress and mitochondria-derived extracellular vesicles (MDEVs) release. The released MDEVs carried mtDNA into microglia to activate the inflammatory pathways and neurodegeneration. The studies on neuronal lipid droplets (LDs) and recent studies of microglial LDs suggest a unified pathological function of LDs in NDs: activating the inflammatory pathways in microglia. This finding potentially provides new therapeutic strategies for NDs.

Analysis of translatomic changes in the Ubqln2P497S model of ALS reveals that motor neurons express muscle-associated genes in non-disease states

Introduction

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by progressively worsening motor symptoms that lead to eventual fatal paralysis. The number of gene mutations associated with ALS have increased dramatically in recent years, suggesting heterogeneity in the etiology of ALS and the need to develop new models of the disease that encompass these pathologies. In 2011, mutations in the UBQLN2 gene were identified in families with both ALS and frontotemporal dementia (FTD) and have since been linked to ubiquitinated TDP43 inclusion pathology. The involvement of UBQLN2 in ubiquitination and proteasome function suggests an important role in proteostasis, which is reported to be impaired in ALS.

Methods

A UBQLN2 mouse model was generated for the P497S mutation and recapitulates some of the motor symptoms of ALS. We utilized ribosomal profiling followed by mRNA sequencing of associated transcripts to characterize gene expression changes of motor neurons in the Ubqln2P497S model and evaluated ALS phenotypes in these animals.

Results

At 12 months of age, we observed reduced motor neuron survival and neuromuscular junction denervation in these mice that translated into motor deficits observed in locomotor behavioral trials. The sequencing of motor neuron transcripts revealed that Wnt pathways and muscle-related transcripts were downregulated in Ubqln2P497S mice, while metabolic pathways were upregulated.

Discussion

Surprisingly, genes often reported to be muscle-specific, such as Desmin and Acta1, were expressed in motor neurons and were dramatically downregulated in symptomatic Ubqln2P497S mice. The expression of muscle transcripts by motor neurons suggests their potentially supportive role in skeletal muscle maintenance.

New perspectives of the role of skeletal muscle derived extracellular vesicles in the pathogenesis of amyotrophic lateral sclerosis: the 'dying back' hypothesis

Amyotrophic lateral sclerosis (ALS), is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord, and is characterized by muscle weakness, paralysis and ultimately, respiratory failure. The exact causes of ALS are not understood, though it is believed to combine genetic and environmental factors. Until now, it was admitted that motor neurons (MN) in the brain and spinal cord degenerate, leading to muscle weakness and paralysis. However, as ALS symptoms typically begin with muscle weakness or stiffness, a new hypothesis has recently emerged to explain the development of the pathology, that is, the 'dying back hypothesis', suggesting that this degeneration starts at the connections between MN and muscles, resulting in the loss of muscle function. Over time, this damage extends along the length of the MN, ultimately affecting their cell bodies in the spinal cord and brain. While the dying back hypothesis provides a potential framework for understanding the progression of ALS, the exact mechanisms underlying the disease remain complex and not fully understood. In this review, we are positioning the role of extracellular vesicles as new actors in ALS development.

Extracellular vesicles in neurodegenerative, mental, and other neurological disorders: Perspectives into mechanisms, biomarker potential, and therapeutic implications

Extracellular vesicles (EVs) are produced, secreted, and targeted by most human cells, including cells that compose nervous system tissues. EVs carry several types of biomolecules, such as lipids, proteins and microRNA, and can function as signaling agents in physiological and pathological processes. In this chapter, we will focus on EVs and their cargo secreted by brain cells, especially neurons and glia, and how these aspects are affected in pathological conditions. The chapter covers neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis, as well as several psychiatric disorders, namely schizophrenia, autism spectrum disorder and major depressive disorder. This chapter also addresses other types of neurological dysfunctions, epilepsy and traumatic brain injury. EVs can cross the blood brain barrier, and thus brain EVs may be detected in more accessible peripheral tissue, such as circulating blood. Alterations in EV composition and contents can therefore impart valuable clues into the molecular etiology of these disorders, and serve biomarkers regarding disease prevalence, progression and treatment. EVs can also be used to carry drugs and biomolecules into brain tissue, considered as a promising drug delivery agent for neurological diseases. Therefore, although this area of research is still in its early development, it offers great potential in further elucidating and in treating neurological disorders.

Aberrant evoked calcium signaling and nAChR cluster morphology in a SOD1 D90A hiPSC-derived neuromuscular model

Familial amyotrophic lateral sclerosis (ALS) is a progressive neuromuscular disorder that is due to mutations in one of several target genes, including SOD1. So far, clinical records, rodent studies, and in vitro models have yielded arguments for either a primary motor neuron disease, or a pleiotropic pathogenesis of ALS. While mouse models lack the human origin, in vitro models using human induced pluripotent stem cells (hiPSC) have been recently developed for addressing ALS pathogenesis. In spite of improvements regarding the generation of muscle cells from hiPSC, the degree of maturation of muscle cells resulting from these protocols has remained limited. To fill these shortcomings, we here present a new protocol for an enhanced myotube differentiation from hiPSC with the option of further maturation upon coculture with hiPSC-derived motor neurons. The described model is the first to yield a combination of key myogenic maturation features that are consistent sarcomeric organization in association with complex nAChR clusters in myotubes derived from control hiPSC. In this model, myotubes derived from hiPSC carrying the SOD1 D90A mutation had reduced expression of myogenic markers, lack of sarcomeres, morphologically different nAChR clusters, and an altered nAChR-dependent Ca2+ response compared to control myotubes. Notably, trophic support provided by control hiPSC-derived motor neurons reduced nAChR cluster differences between control and SOD1 D90A myotubes. In summary, a novel hiPSC-derived neuromuscular model yields evidence for both muscle-intrinsic and nerve-dependent aspects of neuromuscular dysfunction in SOD1-based ALS.

Recent Advances in Extracellular Vesicles in Amyotrophic Lateral Sclerosis and Emergent Perspectives

Amyotrophic lateral sclerosis (ALS) is a severe and incurable neurodegenerative disease characterized by the progressive death of motor neurons, leading to paralysis and death. It is a rare disease characterized by high patient-to-patient heterogeneity, which makes its study arduous and complex. Extracellular vesicles (EVs) have emerged as important players in the development of ALS. Thus, ALS phenotype-expressing cells can spread their abnormal bioactive cargo through the secretion of EVs, even in distant tissues. Importantly, owing to their nature and composition, EVs' formation and cargo can be exploited for better comprehension of this elusive disease and identification of novel biomarkers, as well as for potential therapeutic applications, such as those based on stem cell-derived exosomes. This review highlights recent advances in the identification of the role of EVs in ALS etiopathology and how EVs can be promising new therapeutic strategies.

The Cellular and Molecular Signature of ALS in Muscle

Amyotrophic lateral sclerosis is a disease affecting upper and lower motor neurons. Although motor neuron death is the core event of ALS pathology, it is increasingly recognized that other tissues and cell types are affected in the disease, making potentially major contributions to the occurrence and progression of pathology. We review here the known cellular and molecular characteristics of muscle tissue affected by ALS. Evidence of toxicity in skeletal muscle tissue is considered, including metabolic dysfunctions, impaired proteostasis, and deficits in muscle regeneration and RNA metabolism. The role of muscle as a secretory organ, and effects on the skeletal muscle secretome are also covered, including the increase in secretion of toxic factors or decrease in essential factors that have consequences for neuronal function and survival.

Natural product-based pharmacological studies for neurological disorders

Central nervous system (CNS) disorders and diseases are expected to rise sharply in the coming years, partly because of the world's aging population. Medicines for the treatment of the CNS have not been successfully made. Inadequate knowledge about the brain, pharmacokinetic and dynamic errors in preclinical studies, challenges with clinical trial design, complexity and variety of human brain illnesses, and variations in species are some potential scenarios. Neurodegenerative diseases (NDDs) are multifaceted and lack identifiable etiological components, and the drugs developed to treat them did not meet the requirements of those who anticipated treatments. Therefore, there is a great demand for safe and effective natural therapeutic adjuvants. For the treatment of NDDs and other memory-related problems, many herbal and natural items have been used in the Ayurvedic medical system. Anxiety, depression, Parkinson's, and Alzheimer's diseases (AD), as well as a plethora of other neuropsychiatric disorders, may benefit from the use of plant and food-derived chemicals that have antidepressant or antiepileptic properties. We have summarized the present level of knowledge about natural products based on topological evidence, bioinformatics analysis, and translational research in this review. We have also highlighted some clinical research or investigation that will help us select natural products for the treatment of neurological conditions. In the present review, we have explored the potential efficacy of phytoconstituents against neurological diseases. Various evidence-based studies and extensive recent investigations have been included, which will help pharmacologists reduce the progression of neuronal disease.

The Role of Sphingomyelin and Ceramide in Motor Neuron Diseases

Amyotrophic Lateral Sclerosis (ALS), Spinal Bulbar Muscular Atrophy (SBMA), and Spinal Muscular Atrophy (SMA) are motor neuron diseases (MNDs) characterised by progressive motor neuron degeneration, weakness and muscular atrophy. Lipid dysregulation is well recognised in each of these conditions and occurs prior to neurodegeneration. Several lipid markers have been shown to predict prognosis in ALS. Sphingolipids are complex lipids enriched in the central nervous system and are integral to key cellular functions including membrane stability and signalling pathways, as well as being mediators of neuroinflammation and neurodegeneration. This review highlights the metabolism of sphingomyelin (SM), the most abundant sphingolipid, and of its metabolite ceramide, and its role in the pathophysiology of neurodegeneration, focusing on MNDs. We also review published lipidomic studies in MNDs. In the 13 studies of patients with ALS, 12 demonstrated upregulation of multiple SM species and 6 demonstrated upregulation of ceramides. SM species also correlated with markers of clinical progression in five of six studies. These data highlight the potential use of SM and ceramide as biomarkers in ALS. Finally, we review potential therapeutic strategies for targeting sphingolipid metabolism in neurodegeneration.

Pathogenic Extracellular Vesicle (EV) Signaling in Amyotrophic Lateral Sclerosis (ALS)

Extracellular vesicles (EVs), once considered a pathway for cells to remove waste, have now emerged as an important mechanism for intercellular communication. EVs are particularly appealing in understanding the central nervous system (CNS) communication, given that there are very diverse cell types in the CNS and constant communications among various cells to respond to the frequently changing environment. While they are heterogeneous and new vesicles are continuously to be discovered, EVs are primarily classified as plasma membrane-derived microvesicles (MVs) and endosome-derived exosomes. Secretion of EVs has been shown from all CNS cell types in vitro and intercellular EV signaling has been implicated in neural development, axon integrity, neuron to glia communication, and propagation of protein aggregates formed by disease pathogenic proteins. However, significant hurdles remain to be tackled in understanding their physiological and pathological roles as well as how they can be developed as biomarkers or new therapeutics. Here we provide our summary on the known cell biology of EVs and discuss opportunities and challenges in understanding EV biology in the CNS and particularly their involvement in ALS pathogenesis.