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

Metabolomic and Proteomic Profiling of Serum-Derived Extracellular Vesicles from Early-Stage Amyotrophic Lateral Sclerosis Patients

The identification of reliable biomarkers for amyotrophic lateral sclerosis (ALS) is an unmet medical need for the development of diagnostic and therapeutic strategies. Brain-derived extracellular vesicles (EVs) have been described in peripheral blood serum and used as a direct readout of the status of the central nervous system. Here, we aimed to explore exosome-enriched EVs (referred to simply as EVs) from ALS patients via omics analysis at an early disease stage. Serum EVs were obtained from 9 healthy controls and 9 ALS patients. After EV purification, proteomic (LC‒MS/MS followed by TimsTOF Pro Mass Spectrometry) and metabolomic (Q Exactive mass spectrometer) analyses were performed. No differences in the size or concentration of EVs were observed between the controls and ALS patients. Proteomic analysis revealed 45 proteins differentially expressed in the EVs of ALS patients compared with those of controls. Metabolomic analysis revealed several distinctly represented metabolites involved in the citrate cycle and complex lipid metabolism between patients and controls. Interomics correlation analysis revealed 2 modules that were strongly associated with ALS and included several lipid metabolism-related proteins and metabolites. This study is the first to evaluate EVs by integrated proteomics and metabolomics in early-stage ALS patients, highlighting the technological progress in global inter-omics explorations of small biological samples. The differences observed in the levels of several exosomal proteins and metabolites, including phospholipids, could be used to identify serum biomarkers and novel players involved in ALS pathogenesis.

Role of Retroelements in Frontotemporal Dementia Development

Frontotemporal dementia (FTD) develops in proteinopathies involving TDP-43 (transactive response DNA-binding protein 43 kDa), tau, and FUS (fused in sarcoma) proteins, which possess antiviral properties and exert inhibitory effects on human transposable elements. Viruses and aging have been suggested to trigger FTD by activating specific retroelements. FTD is associated with multiple single nucleotide polymorphisms (SNPs), most located in intergenic and regulatory regions where many transposable element genes are found. Therefore, genetic predisposition to FTD may influence the interaction between retroelements and the TDP-43, tau, and FUS proteins, causing pathological conformation changes and aggregate formation. Subsequently, these aggregates lose their ability to inhibit retroelements, leading to the activation of transposable elements. This creates a harmful negative feedback loop in which TDP-43, tau, and FUS protein expressions are further enhanced by retroelement transcripts and proteins, resulting in protein aggregate accumulation and pathological disease progression. Hence, epigenetic inhibition of pathologically activated retroelements using micro-ribonucleic acids (microRNAs) derived from transposable elements has been proposed as a potential treatment for FTD. Finally, a review of the current scientific literature identified 13 appropriate microRNAs (miR-1246, -181c, -330, -345-5p, -361, -548a-3p, -548b-5p, -548c-5p, -571, -588, -659-3p, -708-3p, -887).

Intraventricular Administration of Exosomes from Patients with Amyotrophic Lateral Sclerosis Provokes Motor Neuron Disease in Mice

Amyotrophic lateral sclerosis (ALS) is a severe disease of the central nervous system (CNS) characterized by motor neuron damage leading to death from respiratory failure. The neurodegenerative process in ALS is characterized by an accumulation of aberrant proteins (TDP-43, SOD1, etc.) in CNS cells. The trans-synaptic transmission of these proteins via exosomes may be one of the mechanisms through which the pathology progresses. The aim of this work was to study the effect of an intraventricular injection of exosomes obtained from the cerebrospinal fluid (CSF) of ALS patients on the motor activity and CNS pathomorphology of mice. The exosomes were obtained from two ALS patients and a healthy donor. Exosome suspensions at high and low concentrations were injected into the lateral brain ventricles of male BALB/c mice (n = 45). Motor activity and physiological parameters were evaluated twice a month; morphological examination of the spinal cord was performed 14 months after the start of the experiment. Nine months after administration of exosomes from the ALS patients, the animals started exhibiting a pathological motor phenotype; i.e., altered locomotion with paresis of hind limbs, coordination impairment, and increasing episodes of immobility. The motor symptoms accelerated after administration of a higher concentration of exosomes. The experimental group showed a significant decrease in motor neuron density in the ventral horns of the spinal cord, a significant increase in the number of microglial cells, and microglia activation. The TDP43 protein in the control animals was localized in the nuclei of motor neurons. TDP43 mislocation with its accumulation in the cytoplasm was observed in the experimental group. Thus, the triggering effect of the exosomal proteins derived from the CSF of ALS patients in the development of a motor neuron pathology in the experimental animals was established. This confirms the pathogenetic role of exosomes in neurodegenerative progression and makes it possible to identify a new target for ALS therapy.

Current status and new avenues of stem cell-based preclinical and therapeutic approaches in amyotrophic lateral sclerosis

INTRODUCTION

Cell therapy development represents a critical challenge in amyotrophic lateral sclerosis (ALS) research. Despite more than 20 years of basic and clinical research, no definitive safety and efficacy results of cell-based therapies for ALS have been published.

AREAS COVERED

This review summarizes advances using stem cells (SCs) in pre-clinical studies to promote clinical translation and in clinical trials to treat ALS. New technologies have been developed and new experimental in vitro and animal models are now available to facilitate pre-clinical research in this field and to determine the most promising approaches to pursue in patients. New clinical trial designs aimed at developing personalized SC-based treatment with biological endpoints are being defined.

EXPERT OPINION

Knowledge of the basic biology of ALS and on the use of SCs to study and potentially treat ALS continues to grow. However, a consensus has yet to emerge on how best to translate these results into therapeutic applications. The selection and follow-up of patients should be based on clinical, biological, and molecular criteria. Planning of SC-based clinical trials should be coordinated with patient profiling genetically and molecularly to achieve personalized treatment. Much work within basic and clinical research is still needed to successfully transition SC therapy in ALS.

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.

ALS-linked SOD1 mutations impair mitochondrial-derived vesicle formation and accelerate aging

Oxidative stress (OS) is regarded as the dominant theory for aging. While compelling correlative data have been generated to support the OS theory, a direct cause-and-effect relationship between the accumulation of oxidation-mediated damage and aging has not been firmly established. Superoxide dismutase 1 (SOD1) is a primary antioxidant in all cells. It is, however, susceptible to oxidation due to OS and gains toxic properties to cells. This study investigates the role of oxidized SOD1 derived from amyotrophic lateral sclerosis (ALS) linked SOD1 mutations in cell senescence and aging. Herein, we have shown that the cell line NSC34 expressing the G93A mutation of human SOD1 (hSOD1G93A) entered premature senescence as evidenced by a decreased number of the 5-ethynyl-2'-deoxyuridine (EdU)-positive cells. There was an upregulation of cellular senescence markers compared to cells expressing the wild-type human SOD1 (hSOD1WT). Transgenic mice carrying the hSOD1G93A gene showed aging phenotypes at an early age (135 days) with high levels of P53 and P16 but low levels of SIRT1 and SIRT6 compared with age-matched hSOD1WT transgenic mice. Notably, the levels of oxidized SOD1 were significantly elevated in both the senescent NSC34 cells and 135-day hSOD1G93A mice. Selective removal of oxidized SOD1 by our CT4-directed autophagy significantly decelerated aging, indicating that oxidized SOD1 is a causal factor of aging. Intriguingly, mitochondria malfunctioned in both senescent NSC34 cells and middle-aged hSODG93A transgenic mice. They exhibited increased production of mitochondrial-derived vesicles (MDVs) in response to mild OS in mutant humanSOD1 (hSOD1) transgenic mice at a younger age; however, the mitochondrial response gradually declined with aging. In conclusion, our data show that oxidized SOD1 derived from ALS-linked SOD1 mutants is a causal factor for cellular senescence and aging. Compromised mitochondrial responsiveness to OS may serve as an indicator of premature aging.