Signal Exchange through Extracellular Vesicles in Neuromuscular Junction Establishment and Maintenance: From Physiology to Pathology

Treating amyotrophic lateral sclerosis with allogeneic Schwann cell-derived exosomal vesicles: a case report

Schwann cells are essential for the maintenance and function of motor neurons, axonal networks, and the neuromuscular junction. In amyotrophic lateral sclerosis, where motor neuron function is progressively lost, Schwann cell function may also be impaired. Recently, important signaling and potential trophic activities of Schwann cell-derived exosomal vesicles have been reported. This case report describes the treatment of a patient with advanced amyotrophic lateral sclerosis using serial intravenous infusions of allogeneic Schwann cell-derived exosomal vesicles, marking, to our knowledge, the first instance of such treatment. An 81-year-old male patient presented with a 1.5-year history of rapidly progressive amyotrophic lateral sclerosis. After initial diagnosis, the patient underwent a combination of generic riluzole, sodium phenylbutyrate for the treatment of amyotrophic lateral sclerosis, and taurursodiol. The patient volunteered to participate in an FDA-approved single-patient expanded access treatment and received weekly intravenous infusions of allogeneic Schwann cell-derived exosomal vesicles to potentially restore impaired Schwann cell and motor neuron function. We confirmed that cultured Schwann cells obtained from the amyotrophic lateral sclerosis patient via sural nerve biopsy appeared impaired (senescent) and that exposure of the patient's Schwann cells to allogeneic Schwann cell-derived exosomal vesicles, cultured expanded from a cadaver donor improved their growth capacity in vitro. After a period of observation lasting 10 weeks, during which amyotrophic lateral sclerosis Functional Rating Scale-Revised and pulmonary function were regularly monitored, the patient received weekly consecutive infusions of 1.54 × 10 12 (×2), and then consecutive infusions of 7.5 × 10 12 (×6) allogeneic Schwann cell-derived exosomal vesicles diluted in 40 mL of Dulbecco's phosphate-buffered saline. None of the infusions were associated with adverse events such as infusion reactions (allergic or otherwise) or changes in vital signs. Clinical lab serum neurofilament and cytokine levels measured prior to each infusion varied somewhat without a clear trend. A more sensitive in-house assay suggested possible inflammasome activation during the disease course. A trend for clinical stabilization was observed during the infusion period. Our study provides a novel approach to address impaired Schwann cells and possibly motor neuron function in patients with amyotrophic lateral sclerosis using allogeneic Schwann cell-derived exosomal vesicles. Initial findings suggest that this approach is safe.

Neuronal innervation regulates the secretion of neurotrophic myokines and exosomes from skeletal muscle

Myokines and exosomes, originating from skeletal muscle, are shown to play a significant role in maintaining brain homeostasis. While exercise has been reported to promote muscle secretion, little is known about the effects of neuronal innervation and activity on the yield and molecular composition of biologically active molecules from muscle. As neuromuscular diseases and disabilities associated with denervation impact muscle metabolism, we hypothesize that neuronal innervation and firing may play a pivotal role in regulating secretion activities of skeletal muscles. We examined this hypothesis using an engineered neuromuscular tissue model consisting of skeletal muscles innervated by motor neurons. The innervated muscles displayed elevated expression of mRNAs encoding neurotrophic myokines, such as interleukin-6, brain-derived neurotrophic factor, and FDNC5, as well as the mRNA of peroxisome-proliferator-activated receptor γ coactivator 1α, a key regulator of muscle metabolism. Upon glutamate stimulation, the innervated muscles secreted higher levels of irisin and exosomes containing more diverse neurotrophic microRNAs than neuron-free muscles. Consequently, biological factors secreted by innervated muscles enhanced branching, axonal transport, and, ultimately, spontaneous network activities of primary hippocampal neurons in vitro. Overall, these results reveal the importance of neuronal innervation in modulating muscle-derived factors that promote neuronal function and suggest that the engineered neuromuscular tissue model holds significant promise as a platform for producing neurotrophic molecules.

Mesenchymal Stem Cell-based Scaffolds in Regenerative Medicine of Dental Diseases

Biomedical engineering breakthroughs and increased patient expectations and requests for more comprehensive care are propelling the field of regenerative dentistry forward at a fast pace. Stem cells (SCs), bioactive compounds, and scaffolds are the mainstays of tissue engineering, the backbone of regenerative dentistry. Repairing damaged teeth and gums is a significant scientific problem at present. Novel therapeutic approaches for tooth and periodontal healing have been inspired by tissue engineering based on mesenchymal stem cells (MSCs). Furthermore, as a component of the MSC secretome, extracellular vesicles (EVs) have been shown to contribute to periodontal tissue repair and regeneration. The scaffold, made of an artificial extracellular matrix (ECM), acts as a supporting structure for new cell development and tissue formation. To effectively promote cell development, a scaffold must be non-toxic, biodegradable, biologically compatible, low in immunogenicity, and safe. Due to its promising biological characteristics for cell regeneration, dental tissue engineering has recently received much attention for its use of natural or synthetic polymer scaffolds with excellent mechanical properties, such as small pore size and a high surface-to-volume ratio, as a matrix. Moreover, as a bioactive material for carrying MSC-EVs, the combined application of scaffolds and MSC-EVs has a better regenerative effect on dental diseases. In this paper, we discuss how MSCs and MSC-derived EV treatment may be used to regenerate damaged teeth, and we highlight the role of various scaffolds in this process.

Engineered exosomes in emerging cell-free therapy

The discovery and use of exosomes ushered in a new era of cell-free therapy. Exosomes are a subgroup of extracellular vesicles that show great potential in disease treatment. Engineered exosomes. with their improved functions have attracted intense interests of their application in translational medicine research. However, the technology of engineering exosomes still faces many challenges which have been the great limitation for their clinical application. This review summarizes the current status of research on engineered exosomes and the difficulties encountered in recent years, with a view to providing new approaches and ideas for future exosome modification and new drug development.

Cell Type-Specific Extracellular Vesicles and Their Impact on Health and Disease

Extracellular vesicles (EVs), a diverse group of cell-derived exocytosed particles, are pivotal in mediating intercellular communication due to their ability to selectively transfer biomolecules to specific cell types. EVs, composed of proteins, nucleic acids, and lipids, are taken up by cells to affect a variety of signaling cascades. Research in the field has primarily focused on stem cell-derived EVs, with a particular focus on mesenchymal stem cells, for their potential therapeutic benefits. Recently, tissue-specific EVs or cell type-specific extracellular vesicles (CTS-EVs), have garnered attention for their unique biogenesis and molecular composition because they enable highly targeted cell-specific communication. Various studies have outlined the roles that CTS-EVs play in the signaling for physiological function and the maintenance of homeostasis, including immune modulation, tissue regeneration, and organ development. These properties are also exploited for disease propagation, such as in cancer, neurological disorders, infectious diseases, autoimmune conditions, and more. The insights gained from analyzing CTS-EVs in different biological roles not only enhance our understanding of intercellular signaling and disease pathogenesis but also open new avenues for innovative diagnostic biomarkers and therapeutic targets for a wide spectrum of medical conditions. This review comprehensively outlines the current understanding of CTS-EV origins, function within normal physiology, and implications in diseased states.

Extracellular Vesicles in Atherosclerosis: State of the Art

Atherosclerosis is a chronic inflammatory disease driven by lipid accumulation in the arteries, leading to narrowing and thrombosis that causes mortality. Emerging evidence has confirmed that atherosclerosis affects younger people and is involved in the majority of deaths worldwide. EVs are associated with critical steps in atherosclerosis, cholesterol metabolism, immune response, endothelial dysfunction, vascular inflammation, and remodeling. Endothelial cell-derived EVs can interact with platelets and monocytes, thereby influencing endothelial dysfunction, atherosclerotic plaque destabilization, and the formation of thrombus. EVs are potential diagnostic and prognostic biomarkers in atherosclerosis (AS) and cardiovascular disease (CVD). Importantly, EVs derived from stem/progenitor cells are essential mediators of cardiogenesis and cardioprotection and may be used in regenerative medicine and tissue engineering.

A review of highly sensitive electrochemical genosensors for microRNA detection: A novel diagnostic platform for neurodegenerative diseases diagnostics

The significant role of microRNAs in regulating gene expression and in disease tracking has handed the possibility of robust and accurate diagnosis of various diseases. Measurement of these biomarkers has also had a significant impact on the preparation of natural samples. Discovery of miRNAs is a major challenge due to their small size in the real sample and their short length, which is generally measured by complex and expensive methods. Electrochemical nanobiosensors have made significant progress in this field. Due to the delicate nature of nerve tissue repair and the significance of rapid-fire feature of neurodegenerative conditions, these biosensors can be reliably promising. This review presents advances in the field of neurodegenerative diseases diagnostics. At the same time, there are still numerous openings in this field that are a bright prospect for researchers in the rapid-fire opinion of neurological diseases and indeed nerve tissue repair.

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.

Skin cell-derived extracellular vesicles: a promising therapeutic strategy for cutaneous injury

Wound healing refers to the healing process that occurs after the skin and other tissues are separated or damaged by internal or external forces. It is a complex combination of tissue regeneration, granulation tissue hyperplasia, and scar formation, and shows the synergistic effects of these processes. After skin damage, the environment around the wound and the cells at site of the damage respond immediately, and a range of cytokines and growth factors are released. In cutaneous injury, extracellular vesicle (EV) signaling plays a vital role in the healing process via paracrine and endocrine mechanisms. EVs are natural intercellular and inter-organ communication tools that carry various bioactive substances for message exchange. Stem cells and stem cell EVs facilitate tissue repair, showing promising potential in regenerative medicine. Nevertheless, EVs derived from specific skin tissue cells, such as epidermal cells, fibroblasts, vascular endothelial cells and inflammatory cells, also play important roles in cutaneous tissue repair. Here, we describe the characteristics of wound healing, concentrating on the production and functions of EVs derived from specific skin cells, and provide new ideas for wound therapy using EVs.

Molecular mechanisms by which targeted muscle reinnervation improves the microenvironment of spinal cord motor neurons and target muscles

Targeted muscle reinnervation is a clinically valuable nerve transfers technology used to reconstruct the information sources reconstruct the motor nerve information sources lost because of nerve injury. This study aimed to investigate the effects and underlying molecular mechanisms of hind limb TMR on motor neurons and target muscles in rats after tibial nerve transection (TNT). Immunohistochemistry was performed to detect acetylcholinesterase expression in the target muscles and myelin basic protein, neuregulin-1 (NRG1), and ErbB2 expression in the tibial nerve of rats. Masson's trichrome staining was performed to observe fibrillar collagen expression in the target muscles. Western blot analysis was used to detect the protein expression of NRG1 and its receptor, ErbB2, in the target muscles. TMR significantly enhanced NRG1, ErbB2, and myelin basic protein expression in nerve fibers compared with those in the TNT group and exerted a protective effect on the maintenance of a large number of nerve fibers and myelin sheath thickness. The above results indicated that TMR can regulate NRG1 and ErbB2 expression in residual nerve fibers and protect the integrity of the myelin sheath, thus improving the functional status of the target muscles, which is beneficial for restoring hind limb motor function after TNT.

Structure and Function of the Mammalian Neuromuscular Junction

The mammalian neuromuscular junction (NMJ) comprises a presynaptic terminal, a postsynaptic receptor region on the muscle fiber (endplate), and the perisynaptic (terminal) Schwann cell. As with any synapse, the purpose of the NMJ is to transmit signals from the nervous system to muscle fibers. This neural control of muscle fibers is organized as motor units, which display distinct structural and functional phenotypes including differences in pre- and postsynaptic elements of NMJs. Motor units vary considerably in the frequency of their activation (both motor neuron discharge rate and duration/duty cycle), force generation, and susceptibility to fatigue. For earlier and more frequently recruited motor units, the structure and function of the activated NMJs must have high fidelity to ensure consistent activation and continued contractile response to sustain vital motor behaviors (e.g., breathing and postural balance). Similarly, for higher force less frequent behaviors (e.g., coughing and jumping), the structure and function of recruited NMJs must ensure short-term reliable activation but not activation sustained for a prolonged period in which fatigue may occur. The NMJ is highly plastic, changing structurally and functionally throughout the life span from embryonic development to old age. The NMJ also changes under pathological conditions including acute and chronic disease. Such neuroplasticity often varies across motor unit types. © 2022 American Physiological Society. Compr Physiol 12:1-36, 2022.

Adaptive Remodeling of the Neuromuscular Junction with Aging

Aging is associated with gradual degeneration, in mass and function, of the neuromuscular system. This process, referred to as “sarcopenia”, is considered a disease by itself, and it has been linked to a number of other serious maladies such as type II diabetes, osteoporosis, arthritis, cardiovascular disease, and even dementia. While the molecular causes of sarcopenia remain to be fully elucidated, recent findings have implicated the neuromuscular junction (NMJ) as being an important locus in the development and progression of that malady. This synapse, which connects motor neurons to the muscle fibers that they innervate, has been found to degenerate with age, contributing both to senescent-related declines in muscle mass and function. The NMJ also shows plasticity in response to a number of neuromuscular diseases such as amyotrophic lateral sclerosis (ALS) and Lambert-Eaton myasthenic syndrome (LEMS). Here, the structural and functional degradation of the NMJ associated with aging and disease is described, along with the measures that might be taken to effectively mitigate, if not fully prevent, that degeneration.

An Emerging Role for Epigenetics in Cerebral Palsy

Cerebral palsy is a set of common, severe, motor disabilities categorized by a static, nondegenerative encephalopathy arising in the developing brain and associated with deficits in movement, posture, and activity. Spastic CP, which is the most common type, involves high muscle tone and is associated with altered muscle function including poor muscle growth and contracture, increased extracellular matrix deposition, microanatomic disruption, musculoskeletal deformities, weakness, and difficult movement control. These muscle-related manifestations of CP are major causes of progressive debilitation and frequently require intensive surgical and therapeutic intervention to control. Current clinical approaches involve sophisticated consideration of biomechanics, radiologic assessments, and movement analyses, but outcomes remain difficult to predict. There is a need for more precise and personalized approaches involving omics technologies, data science, and advanced analytics. An improved understanding of muscle involvement in spastic CP is needed. Unfortunately, the fundamental mechanisms and molecular pathways contributing to altered muscle function in spastic CP are only partially understood. In this review, we outline evidence supporting the emerging hypothesis that epigenetic phenomena play significant roles in musculoskeletal manifestations of CP.

Extracellular Vesicles in Regenerative Medicine: Potentials and Challenges

The ultimate goal of regenerative medicine is to regain or restore the damaged or lost function of tissues and organs. Several therapeutic strategies are currently being explored to achieve this goal. From the point of view of regenerative medicine, extracellular vesicles (EVs) are exceptionally attractive due to the fact that they can overcome the limitations faced by many cell therapies and can be engineered according to their purpose through various technical modifications. EVs are biological nanoscale vesicles naturally secreted by all forms of living organisms, including prokaryotes and eukaryotes, and act as vehicles of communication between cells and their surrounding environment. Over the past decade, EVs have emerged as a new therapeutic agent for various diseases and conditions owing to their multifaceted biological functions. This is reflected by the number of publications on this subject found in the Web of Science database, which currently exceeds 12,300, over 85% of which were published within the last decade, demonstrating the increasing global trends of this innovative field. The reviews collected in this special issue provide an overview of the different approaches being explored in the use of EVs for regenerative medicine.

Trends in Understanding the Pathological Roles of TDP-43 and FUS Proteins

Following the discovery of TDP-43 and FUS involvement in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar dementia (FTLD), the major challenge in the field has been to understand their physiological functions, both in normal and disease conditions. The hope is that this knowledge will improve our understanding of disease and lead to the development of effective therapeutic options. Initially, the focus has been directed at characterizing the role of these proteins in the control of RNA metabolism, because the main function of TDP-43 and FUS is to bind coding and noncoding RNAs to regulate their life cycle within cells. As a result, we now have an in-depth picture of the alterations that occur in RNA metabolism following their aggregation in various ALS/FTLD models and, to a somewhat lesser extent, in patients' brains. In parallel, progress has been made with regard to understanding how aggregation of these proteins occurs in neurons, how it can spread in different brain regions, and how these changes affect various metabolic cellular pathways to result in neuronal death. The aim of this chapter will be to provide a general overview of the trending topics in TDP-43 and FUS investigations and to highlight what might represent the most promising avenues of research in the years to come.

Uniting homeostatic plasticity and exosome biology: A revision of the conceptual framework for drug discovery in neurodegenerative diseases?

Neurodegenerative diseases (NDDs) are in need of new drug discovery approaches. Our previous systematic analyses of Huntington's Disease (HD) literature for protein-protein interactors (PPIs) and modifiers of mutant Huntingtin-driven phenotypes revealed enrichment for PPIs of genes required for homeostatic synaptic plasticity (HSP) and exosome (EV) function and exosomal proteins, which in turn highly overlapped each other and with PPIs of genes associated with other NDDs. We proposed that HSP and EVs are linked to each other and are also involved in NDD pathophysiology. Recent studies showed that HSP is indeed altered in HD and AD, and that presynaptic homeostatic plasticity in motoneurons compensates for ALS pathology. Eliminating it causes earlier degeneration and death. If this holds true in other NDDs, drug discovery in animal models should then include elucidation of homeostatic compensation that either masks phenotypes of physiologically expressed mutant genes or are overridden by their overexpression. In this new conceptual framework, enhancing such underlying homeostatic compensation forms the basis for novel therapeutic strategies to slow progression of NDDs. Moreover, if EVs are linked to HSP, then their ability to penetrate the brain, target cell types, deliver miRNA and other molecules can be leveraged to develop attractive drug modalities. Testing this new framework is posed as four questions on model development and mechanistic studies progressing from higher throughput platforms to mouse models. Similar approaches may apply to other CNS disorders including schizophrenia, autism, Rett and Fragile X syndromes due to potential links of their susceptibility genes to HSP and EVs.

Engineering Smart Targeting Nanovesicles and Their Combination with Hydrogels for Controlled Drug Delivery

Smart engineered and naturally derived nanovesicles, capable of targeting specific tissues and cells and delivering bioactive molecules and drugs into them, are becoming important drug delivery systems. Liposomes stand out among different types of self-assembled nanovesicles, because of their amphiphilicity and non-toxic nature. By modifying their surfaces, liposomes can become stimulus-responsive, releasing their cargo on demand. Recently, the recognized role of exosomes in cell-cell communication and their ability to diffuse through tissues to find target cells have led to an increase in their usage as smart delivery systems. Moreover, engineering "smarter" delivery systems can be done by creating hybrid exosome-liposome nanocarriers via membrane fusion. These systems can be loaded in naturally derived hydrogels to achieve sustained and controlled drug delivery. Here, the focus is on evaluating the smart behavior of liposomes and exosomes, the fabrication of hybrid exosome-liposome nanovesicles, and the controlled delivery and routes of administration of a hydrogel matrix for drug delivery systems.