Systemic injection of AAV9-GDNF provides modest functional improvements in the SOD1G93A ALS rat but has adverse side effects

Trehalose-based coacervates for local bioactive protein delivery to the central nervous system

Therapeutic outcomes of local biomolecule delivery to the central nervous system (CNS) using bulk biomaterials are limited by inadequate drug loading, neuropil disruption, and severe foreign body responses. Effective CNS delivery requires addressing these issues and developing well-tolerated, highly-loaded carriers that are dispersible within local neural parenchyma. Here, we synthesized biodegradable trehalose-based polyelectrolyte oligomers using facile A2:B3:AR thiol-ene Michael addition reactions that form complex coacervates upon mixing of oppositely charged oligomers. Coacervates permit high concentration loading and controlled release of bioactive growth factors, enzymes, and antibodies, with modular formulation parameters that confer tunable release kinetics. Coacervates are cytocompatible with cultured neural cells in vitro and can be formulated to either direct intracellular protein delivery or sequester media containing proteins and remain extracellular. Coacervates serve as effective vehicles for precisely delivering biomolecules, including bioactive neurotrophins, to the mouse striatum following intraparenchymal injection. These results support the use of trehalose-based coacervates as part of therapeutic protein delivery strategies for CNS disorders.

Intrathecal delivery of AAV-NDNF ameliorates disease progression of ALS mice

Amyotrophic lateral sclerosis (ALS) is a uniformly lethal neurodegenerative disease characterized by progressive deterioration of motor neurons and neuromuscular denervation. Adeno-associated virus (AAV)-mediated delivery of trophic factors is being considered as a potential disease-modifying therapeutic avenue. Here we show a marked effect of AAV-mediated over-expression of neuron-derived neurotrophic factor (NDNF) on SOD1G93A ALS model mice. First, we adopt AAV-PHP.eB capsid to enable widespread expression of target proteins in the brain and spinal cord when delivered intrathecally. Then we tested the effects of AAV-NDNF on SOD1G93A mice at different stages of disease. Interestingly, AAV-NDNF markedly improved motor performance and alleviated weight loss when delivered at early post-symptomatic stage. Injection in the middle post-symptomatic stages still improved the locomotion ability, although it did not alleviate the loss of body weight. Injection in the late stage also extended the life span of SOD1G93A mice. Furthermore, NDNF expression promoted the survival of spinal motoneurons, reduced abnormal protein aggregation, and preserved the innervated neuromuscular functions. We further analyzed the signaling pathways of NDNF expression and found that it activates cell survival and growth-associated mammalian target of rapamycin signaling pathway and downregulates apoptosis-related pathways. Thus, intrathecally AAV-NDNF delivery has provided a potential strategy for the treatment of ALS.

The Key Role of Astrocytes in Amyotrophic Lateral Sclerosis and Their Commitment to Glutamate Excitotoxicity

In the last two decades, there has been increasing evidence supporting non-neuronal cells as active contributors to neurodegenerative disorders. Among glial cells, astrocytes play a pivotal role in driving amyotrophic lateral sclerosis (ALS) progression, leading the scientific community to focus on the "astrocytic signature" in ALS. Here, we summarized the main pathological mechanisms characterizing astrocyte contribution to MN damage and ALS progression, such as neuroinflammation, mitochondrial dysfunction, oxidative stress, energy metabolism impairment, miRNAs and extracellular vesicles contribution, autophagy dysfunction, protein misfolding, and altered neurotrophic factor release. Since glutamate excitotoxicity is one of the most relevant ALS features, we focused on the specific contribution of ALS astrocytes in this aspect, highlighting the known or potential molecular mechanisms by which astrocytes participate in increasing the extracellular glutamate level in ALS and, conversely, undergo the toxic effect of the excessive glutamate. In this scenario, astrocytes can behave as "producers" and "targets" of the high extracellular glutamate levels, going through changes that can affect themselves and, in turn, the neuronal and non-neuronal surrounding cells, thus actively impacting the ALS course. Moreover, this review aims to point out knowledge gaps that deserve further investigation.

Fibroblast growth factor 10 ameliorates neurodegeneration in mouse and cellular models of Alzheimer's disease via reducing tau hyperphosphorylation and neuronal apoptosis

Alzheimer's disease (AD) is characterized with senile plaques formed by Aβ deposition, and neurofibrillary tangles composed of hyperphosphorylated tau protein, which ultimately lead to cognitive impairment. Despite the heavy economic and life burdens faced by the patients with AD, effective treatments are still lacking. Previous studies have reported the neuroprotective effects of FGF10 in CNS diseases, but its role in AD remains unclear. In this study, we demonstrated that FGF10 levels were reduced in the serum of AD patients, as well as in the brains of 3xTg-AD mice and APPswe-transfected HT22 cells, suggesting a close relationship between FGF10 and AD. Further investigations revealed that intranasal delivery of FGF10 improved cognitive functions in 3xTg-AD mice. Additionally, FGF10 treatment reduced tau hyperphosphorylation and neuronal apoptosis, thereby mitigating neuronal cell damage and synaptic deficits in the cortex and hippocampus of 3xTg-AD mice, as well as APPswe-transfected HT22 cells. Furthermore, we evaluated the therapeutic potential of FGF10 gene delivery for treating AD symptoms and pathologies. Tail vein delivery of the FGF10 gene using AAV9 improved cognitive and neuronal functions in 3xTg-AD mice. Similarly, endogenous FGF10 overexpression ameliorated tau hyperphosphorylation and neuronal apoptosis in the cortex and hippocampus of 3xTg-AD mice. Importantly, we confirmed that the FGFR2/PI3K/AKT signaling pathway was activated following intranasal FGF10 delivery and AAV9-mediated FGF10 gene delivery in 3xTg-AD mice and APPswe-transfected HT22 cells. Knockdown of FGFR2 attenuated the protective effect of FGF10. Collectively, these findings suggest that intranasal delivery of FGF10 and AAV9-mediated FGF10 gene delivery could be a promising disease-modifying therapy for AD.

Neurotrophic factors in the physiology of motor neurons and their role in the pathobiology and therapeutic approach to amyotrophic lateral sclerosis

The discovery of the neurotrophins and their potent survival and trophic effects led to great enthusiasm about their therapeutic potential to rescue dying neurons in neurodegenerative diseases. The further discovery that brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) and glial cell line-derived neurotrophic factor (GDNF) had potent survival-promoting activity on motor neurons led to the proposal for their use in motor neuron diseases such as amyotrophic lateral sclerosis (ALS). In this review we synthesize the literature pertaining to the role of NGF, BDNF, CNTF and GDNF on the development and physiology of spinal motor neurons, as well as the preclinical studies that evaluated their potential for the treatment of ALS. Results from the clinical trials of these molecules will also be described and, with the aid of decades of hindsight, we will discuss what can reasonably be concluded and how this information can inform future clinical development of neurotrophic factors for ALS.

Human iPSC-derived neural progenitor cells secreting GDNF provide protection in rodent models of ALS and retinal degeneration

Human induced pluripotent stem cells (iPSCs) are a renewable cell source that can be differentiated into neural progenitor cells (iNPCs) and transduced with glial cell line-derived neurotrophic factor (iNPC-GDNFs). The goal of the current study is to characterize iNPC-GDNFs and test their therapeutic potential and safety. Single-nuclei RNA-seq show iNPC-GDNFs express NPC markers. iNPC-GDNFs delivered into the subretinal space of the Royal College of Surgeons rodent model of retinal degeneration preserve photoreceptors and visual function. Additionally, iNPC-GDNF transplants in the spinal cord of SOD1G93A amyotrophic lateral sclerosis (ALS) rats preserve motor neurons. Finally, iNPC-GDNF transplants in the spinal cord of athymic nude rats survive and produce GDNF for 9 months, with no signs of tumor formation or continual cell proliferation. iNPC-GDNFs survive long-term, are safe, and provide neuroprotection in models of both retinal degeneration and ALS, indicating their potential as a combined cell and gene therapy for various neurodegenerative diseases.

Protective effects of intrathecal injection of AAV9-RabGGTB-GFP+ in SOD1G93A mice

Introduction

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that widely affects motor neurons of the CNS. About 20% of patients with ALS have familial ALS (fALS). One of the classic models of ALS are SOD1G93A mice. Misfolded SOD1 protein can be overexpressed in motor neurons, which results in progressive paralysis of the limbs of mice. There is still no effective treatment for ALS. In recent years, the treatment of ALS by regulating autophagy has become a research hotspot. Autophagy obstacles have been confirmed to be one of the early pathological events of ALS. Rab7 is a member of the Ras superfamily and plays a key role in the late stage of autophagy. In our previous studies, we found that prenoylation of Rab7 was inhibited in the ALS model. Prenylation is a post-translational modification in which farnesyl or geranylgeranyl groups are covalently linked to target proteins. Based on these findings, we proposed the novel idea that the regulation of RabGGTB (the β-subunit of RabGGTase) mediated prenylation modification of Rab7, and that this can be used as a prevention and treatment of ALS associated with abnormal protein accumulation.

Methods

In the present study, RabGGTB was overexpressed in mouse spinal cord motoneurons by using adeno-associated virus as vector. Then immunofluorescence quantitative analysis was used for pathological study. The body weight, footprint analysis, the accelerating rotarod test, and neurological deficits score were used to evaluate animal behavior.

Results

Our results show that the protein level of RabGGTB was significantly increased in the lumbar and thoracic regions of spinal cord motoneurons of injected mice. Furthermore, the onset time and survival time of SOD1G93A mice injected with AAV9-RabGGTB-GFP+ were delayed compared with those of mice without overexpression. At the same time, we also observed a decrease in SOD1 misfolded and glial overactivation in the lumbar spinal cord of these SOD1G93A mice.

Conclusion

The findings reported here show that RabGGTB plays a significant role in the pathogenesis of SOD1G93A mice and with great therapeutic potential for reducing abnormal aggregation of SOD1 in ALS.

Transplantation of human neural progenitor cells secreting GDNF into the spinal cord of patients with ALS: a phase 1/2a trial

Amyotrophic lateral sclerosis (ALS) involves progressive motor neuron loss, leading to paralysis and death typically within 3–5 years of diagnosis. Dysfunctional astrocytes may contribute to disease and glial cell line-derived neurotrophic factor (GDNF) can be protective. Here we show that human neural progenitor cells transduced with GDNF (CNS10-NPC-GDNF) differentiated to astrocytes protected spinal motor neurons and were safe in animal models. CNS10-NPC-GDNF were transplanted unilaterally into the lumbar spinal cord of 18 ALS participants in a phase 1/2a study (NCT02943850). The primary endpoint of safety at 1 year was met, with no negative effect of the transplant on motor function in the treated leg compared with the untreated leg. Tissue analysis of 13 participants who died of disease progression showed graft survival and GDNF production. Benign neuromas near delivery sites were common incidental findings at post-mortem. This study shows that one administration of engineered neural progenitors can provide new support cells and GDNF delivery to the ALS patient spinal cord for up to 42 months post-transplantation.

A phase 1/2a study shows that human neural progenitor cells modified to release the growth factor GDNF are safely transplanted into the spinal cord of patients with ALS, with cell survival and GDNF production for over 3 years.

Bimodal regulation of axonal transport by the GDNF-RET signalling axis in healthy and diseased motor neurons

Deficits in axonal transport are one of the earliest pathological outcomes in several models of amyotrophic lateral sclerosis (ALS), including SOD1G93A mice. Evidence suggests that rescuing these deficits prevents disease progression, stops denervation, and extends survival. Kinase inhibitors have been previously identified as transport enhancers, and are being investigated as potential therapies for ALS. For example, inhibitors of p38 mitogen-activated protein kinase and insulin growth factor receptor 1 have been shown to rescue axonal transport deficits in vivo in symptomatic SOD1G93A mice. In this work, we investigated the impact of RET, the tyrosine kinase receptor for glial cell line-derived neurotrophic factor (GDNF), as a modifier of axonal transport. We identified the fundamental interplay between RET signalling and axonal transport in both wild-type and SOD1G93A motor neurons in vitro. We demonstrated that blockade of RET signalling using pharmacological inhibitors and genetic knockdown enhances signalling endosome transport in wild-type motor neurons and uncovered a divergence in the response of primary motor neurons to GDNF compared with cell lines. Finally, we showed that inhibition of the GDNF-RET signalling axis rescues in vivo transport deficits in early symptomatic SOD1G93A mice, promoting RET as a potential therapeutic target in the treatment of ALS.

Endothelium-targeted delivery of PPARδ by adeno-associated virus serotype 1 ameliorates vascular injury induced by hindlimb ischemia in obese mice

Diabetic vasculopathy is a major health problem worldwide. Peripheral arterial disease (PAD), and in its severe form, critical limb ischemia is a major form of diabetic vasculopathy with limited treatment options. Existing literature suggested an important role of PPARδ in vascular homeostasis. It remains elusive for using PPARδ as a potential therapeutic target due to mostly the side effects of PPARδ agonists. To explore the roles of PPARδ in endothelial homeostasis, endothelial cell (EC) selective Ppard knockout and controlled mice were subjected to hindlimb ischemia (HLI) injury. The muscle ECs were sorted for single-cell RNA sequencing (scRNA-seq) analysis. HLI was also performed in high fat diet (HFD)-induced obese mice to examine the function of PPARδ in obese mice with delayed vascular repair. Adeno-associated virus type 1 (AAV1) carrying ICAM2 promoter to target endothelium for overexpressing PPARδ was injected into the injured muscles of normal chow- and HFD-fed obese mice before HLI surgery was performed. scRNA-seq analysis of ECs in ischemic muscles revealed a pivotal role of PPARδ in endothelial homeostasis. PPARδ expression was diminished both after HLI injury, and also in obese mice, which showed further delayed vascular repair. Endothelium-targeted delivery of PPARδ by AAV1 improved perfusion recovery, increased capillary density, restored endothelial integrity, suppressed vascular inflammation, and promoted muscle regeneration in ischemic hindlimbs of both lean and obese mice. Our study indicated the effectiveness of endothelium-targeted PPARδ overexpression for restoring functional vasculature after ischemic injury, which might be a promising option of gene therapy to treat PAD and CLI.

Approaches to Gene Modulation Therapy for ALS

Amyotrophic lateral sclerosis (ALS) is a devastating motor neuron disease for which there is currently no robust therapy. Recent progress in understanding ALS disease mechanisms and genetics in combination with innovations in gene modulation strategies creates promising new options for the development of ALS therapies. In recent years, six gene modulation therapies have been tested in ALS patients. These target gain-of-function pathology of the most common ALS genes, SOD1, C9ORF72, FUS, and ATXN2, using adeno-associated virus (AAV)-mediated microRNAs and antisense oligonucleotides (ASOs). Here, we review the latest clinical and preclinical advances in gene modulation approaches for ALS, including gene silencing, gene correction, and gene augmentation. These techniques have the potential to positively impact the direction of future research trials and transform ALS treatments for this grave disease.

Adeno-Associated Viral Vectors as Versatile Tools for Neurological Disorders: Focus on Delivery Routes and Therapeutic Perspectives

It is without doubt that the gene therapy field is currently in the spotlight for the development of new therapeutics targeting unmet medical needs. Thus, considering the gene therapy scenario, neurological diseases in general and neurodegenerative disorders in particular are emerging as the most appealing choices for new therapeutic arrivals intended to slow down, stop, or even revert the natural progressive course that characterizes most of these devastating neurodegenerative processes. Since an extensive coverage of all available literature is not feasible in practical terms, here emphasis was made in providing some advice to beginners in the field with a narrow focus on elucidating the best delivery route available for fulfilling any given AAV-based therapeutic approach. Furthermore, it is worth nothing that the number of ongoing clinical trials is increasing at a breath-taking speed. Accordingly, a landscape view of preclinical and clinical initiatives is also provided here in an attempt to best illustrate what is ongoing in this quickly expanding field.

Current knowledge and challenges associated with targeted delivery of neurotrophic factors into the central nervous system: focus on available approaches

During the last decades, numerous basic and clinical studies have been conducted to assess the delivery efficiency of therapeutic agents into the brain and spinal cord parenchyma using several administration routes. Among conventional and in-progress administrative routes, the eligibility of stem cells, viral vectors, and biomaterial systems have been shown in the delivery of NTFs. Despite these manifold advances, the close association between the delivery system and regeneration outcome remains unclear. Herein, we aimed to discuss recent progress in the delivery of these factors and the pros and cons related to each modality.

Histamine, Neuroinflammation and Neurodevelopment: A Review

The biogenic amine, histamine, has been shown to critically modulate inflammatory processes as well as the properties of neurons and synapses in the brain, and is also implicated in the emergence of neurodevelopmental disorders. Indeed, a reduction in the synthesis of this neuromodulator has been associated with the disorders Tourette's syndrome and obsessive-compulsive disorder, with evidence that this may be through the disruption of the corticostriatal circuitry during development. Furthermore, neuroinflammation has been associated with alterations in brain development, e.g., impacting synaptic plasticity and synaptogenesis, and there are suggestions that histamine deficiency may leave the developing brain more vulnerable to proinflammatory insults. While most studies have focused on neuronal sources of histamine it remains unclear to what extent other (non-neuronal) sources of histamine, e.g., from mast cells and other sources, can impact brain development. The few studies that have started exploring this in vitro, and more limited in vivo, would indicate that non-neuronal released histamine and other preformed mediators can influence microglial-mediated neuroinflammation which can impact brain development. In this Review we will summarize the state of the field with regard to non-neuronal sources of histamine and its impact on both neuroinflammation and brain development in key neural circuits that underpin neurodevelopmental disorders. We will also discuss whether histamine receptor modulators have been efficacious in the treatment of neurodevelopmental disorders in both preclinical and clinical studies. This could represent an important area of future research as early modulation of histamine from neuronal as well as non-neuronal sources may provide novel therapeutic targets in these disorders.

Systemic mastocytosis: The roles of histamine and its receptors in the central nervous system disorders

Mastocytosis is a rare disease of clonal hematological disorders characterized by a pathological accumulation of Mast Cells (MCs) in different tissues, with variable symptomatology and prognosis. Signs and symptoms of Systemic Mastocytosis (SM) are due to pathological infiltration of MCs and to the release of chemical mediators, mainly histamine. Patients with SM may also present with neurological symptoms or complications. The pathophysiology of these neurological disorders remains uncertain to this day, but it can be associated with the infiltration of tissue mastocytes, release of mastocytes' mediators or both. Moreover, there is a lot to understand about the role of neurological symptoms in SM and knowing, for example, what is the real frequency of neurological disorders in SM and if is present a relation between other SM subtypes, because it has been noted that the alteration of the histamine expression may be an initiating factor for susceptibility, gravity and progression of the epigenetic disease. In this review we explain the possible pathophysiological mechanism about neurological symptomatology found in some patients affected by SM, describing the role of histamine and its receptors in the nervous system and, in light of the results, what the future prospects may be for a more specific course of treatment.

Highlighting the protective or degenerative role of AMPK activators in dementia experimental models

AMP-activated protein kinase (AMPK) is a serine/threonine kinase and a driving or deterrent factor in the development of neurodegenerative diseases and dementia. AMPK affects intracellular proteins like the mammalian target of rapamycin (mTOR). Peroxisome proliferator-activated receptor-γ coactivator 1-α (among others) contributes to a wide range of intracellular activities based on its downstream molecules such as energy balancing (ATP synthesis), extracellular inflammation, cell growth, and neuronal cell death (such as apoptosis, necrosis, and necroptosis). Several studies have looked at the dual role of AMPK in neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington disease (HD) but the exact effect of this enzyme on dementia, stroke, and motor neuron dysfunction disorders has not been elucidated yet. In this article, we review current research on the effects of AMPK on the brain to give an overview of the relationship. More specifically, we review the neuroprotective or neurodegenerative effects of AMPK or AMPK activators like metformin, resveratrol, and 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside on neurological diseases and dementia, which exert through the intracellular molecules involved in neuronal survival or death.

Gene therapy for ALS: A review

Amyotrophic lateral sclerosis (ALS) has historically posed unique challenges for gene-therapy-based approaches, due to a paucity of therapeutic targets as well as the difficulty of accessing both the brain and spinal cord. Recent advances in our understanding of disease mechanism and ALS genetics, however, have combined with tremendous strides in CNS targeting, gene delivery, and gene editing and knockdown techniques to open new horizons of therapeutic possibility. Gene therapy clinical trials are currently underway for ALS patients with SOD1 mutations, C9orf72 hexanucleotide repeat expansions, ATXN2 trinucleotide expansions, and FUS mutations, as well as sporadic disease without known genetic cause. In this review, we provide an in-depth exploration of the state of ALS-directed gene therapy, including antisense oligonucleotides, RNA interference, CRISPR, adeno-associated virus (AAV)-mediated trophic support, and antibody-based methods. We discuss how each of these approaches has been implemented across known genetic causes as well as sporadic ALS, reviewing preclinical studies as well as completed and ongoing human clinical trials. We highlight the transformative potential of these evolving technologies as the gene therapy field advances toward a true disease-modifying treatment for this devastating illness.

Specific Expression of Glial-Derived Neurotrophic Factor in Muscles as Gene Therapy Strategy for Amyotrophic Lateral Sclerosis

Glial cell line-derived neurotrophic factor (GDNF) is a powerful neuroprotective growth factor. However, systemic or intrathecal administration of GDNF is associated with side effects. Here, we aimed to avoid this by restricting the transgene expression to the skeletal muscle by gene therapy. To specifically target most skeletal muscles in the mouse model of amyotrophic lateral sclerosis (ALS), SOD1G93A transgenic mice were intravenously injected with adeno-associated vectors coding for GDNF under the control of the desmin promoter. Treated and control SOD1G93A mice were evaluated by rotarod and nerve conduction tests from 8 to 20 weeks of age, and then histological and molecular analyses were performed. Muscle-specific GDNF expression delayed the progression of the disease in SOD1G93A female and male mice by preserving the neuromuscular function; increasing the number of innervated neuromuscular junctions, the survival of spinal motoneurons; and reducing glial reactivity in treated SOD1G93A mice. These beneficial actions are attributed to a paracrine protective mechanism from the muscle to the motoneurons by GDNF. Importantly, no adverse secondary effects were detected. These results highlight the potential of muscle GDNF-targeted expression for ALS therapy.

Therapeutic Potential of AAV1-Rheb(S16H) Transduction against Neurodegenerative Diseases

Neurotrophic factors (NTFs) are essential for cell growth, survival, synaptic plasticity, and maintenance of specific neuronal population in the central nervous system. Multiple studies have demonstrated that alterations in the levels and activities of NTFs are related to the pathology and symptoms of neurodegenerative disorders, such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and Huntington’s disease. Hence, the key molecule that can regulate the expression of NTFs is an important target for gene therapy coupling adeno-associated virus vector (AAV) gene. We have previously reported that the Ras homolog protein enriched in brain (Rheb)–mammalian target of rapamycin complex 1 (mTORC1) axis plays a vital role in preventing neuronal death in the brain of AD and PD patients. AAV transduction using a constitutively active form of Rheb exerts a neuroprotective effect through the upregulation of NTFs, thereby promoting the neurotrophic interaction between astrocytes and neurons in AD conditions. These findings suggest the role of Rheb as an important regulator of the regulatory system of NTFs to treat neurodegenerative diseases. In this review, we present an overview of the role of Rheb in neurodegenerative diseases and summarize the therapeutic potential of AAV serotype 1 (AAV1)-Rheb(S16H) transduction in the treatment of neurodegenerative disorders, focusing on diseases, such as AD and PD.

Overview of stem cells therapy in amyotrophic lateral sclerosis

Background: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease of upper and lower motor neurons with high burden on society. Despite tremendous efforts over the last several decades, there is still no definite cure for ALS. Up to now, only two disease-modifying agents, riluzole and edaravone, are approved by U.S. Food and Drug Administration (FDA) for ALS treatment, which only modestly improves survival and disease progression. Major challenging issues to find an effective therapy are heterogeneity in the pathogenesis and genetic variability of ALS. As such, stem cell therapy has been recently a focus of both preclinical and clinical investigations of ALS. This is because stem cells have multifaceted features that can potentially target multiple pathogenic mechanisms in ALS even though its underlying mechanisms are not completely elucidated. Methods & Results: Here, we will have an overview of stem cell therapy in ALS, including their therapeutic mechanisms, the results of recent clinical trials as well as ongoing clinical trials. In addition, we will further discuss complications and limitations of stem cell therapy in ALS. Conclusion: The determination of whether stem cells offer a viable treatment strategy for ALS rests on well-designed and appropriately powered future clinical trials. Randomized, double-blinded, and sham-controlled studies would be valuable.

How to Build and to Protect the Neuromuscular Junction: The Role of the Glial Cell Line-Derived Neurotrophic Factor

The neuromuscular junction (NMJ) is at the crossroad between the nervous system (NS) and the muscle. Following neurotransmitter release from the motor neurons (MNs), muscle contraction occurs and movement is generated. Besides eliciting muscle contraction, the NMJ represents a site of chemical bidirectional interplay between nerve and muscle with the active participation of Schwann cells. Indeed, signals originating from the muscle play an important role in synapse formation, stabilization, maintenance and function, both in development and adulthood. We focus here on the contribution of the Glial cell line-Derived Neurotrophic Factor (GDNF) to these processes and to its potential role in the protection of the NMJ during neurodegeneration. Historically related to the maintenance and survival of dopaminergic neurons of the substantia nigra, GDNF also plays a fundamental role in the peripheral NS (PNS). At this level, it promotes muscle trophism and it participates to the functionality of synapses. Moreover, compared to the other neurotrophic factors, GDNF shows unique peculiarities, which make its contribution essential in neurodegenerative disorders. While describing the known structural and functional changes occurring at the NMJ during neurodegeneration, we highlight the role of GDNF in the NMJ–muscle cross-talk and we review its therapeutic potential in counteracting the degenerative process occurring in the PNS in progressive and severe diseases such as Alzheimer’s disease (AD), Amyotrophic Lateral Sclerosis (ALS) and Spinal Muscular Atrophy (SMA). We also describe functional 3D neuromuscular co-culture systems that have been recently developed as a model for studying both NMJ formation in vitro and its involvement in neuromuscular disorders.

Mild traumatic brain injury exacerbates Parkinson's disease induced hemeoxygenase-2 expression and brain pathology: Neuroprotective effects of co-administration of TiO2 nanowired mesenchymal stem cells and cerebrolysin

Mild traumatic brain injury (mTBI) is one of the leading predisposing factors in the development of Parkinson's disease (PD). Mild or moderate TBI induces rapid production of tau protein and alpha synuclein (ASNC) in the cerebrospinal fluid (CSF) and in several brain areas. Enhanced tau-phosphorylation and ASNC alters the molecular machinery of the brain leading to PD pathology. Recent evidences show upregulation of constitutive isoform of hemeoxygenase (HO-2) in PD patients that correlates well with the brain pathology. mTBI alone induces profound upregulation of HO-2 immunoreactivity. Thus, it would be interesting to explore whether mTBI exacerbates PD pathology in relation to tau, ASNC and HO-2 expression. In addition, whether neurotrophic factors and stem cells known to reduce brain pathology in TBI could induce neuroprotection in PD following mTBI. In this review role of mesenchymal stem cells (MSCs) and cerebrolysin (CBL), a well-balanced composition of several neurotrophic factors and active peptide fragments using nanowired delivery in PD following mTBI is discussed based on our own investigation. Our results show that mTBI induces concussion exacerbates PD pathology and nanowired delivery of MSCs and CBL induces superior neuroprotection. This could be due to reduction in tau, ASNC and HO-2 expression in PD following mTBI, not reported earlier. The functional significance of our findings in relation to clinical strategies is discussed.

Small Molecules and Peptides Targeting Glial Cell Line-Derived Neurotrophic Factor Receptors for the Treatment of Neurodegeneration

Glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs) are able to promote the survival of multiple neuronal populations in the body and, therefore, hold considerable promise for disease-modifying treatments of diseases and conditions caused by neurodegeneration. Available data reveal the potential of GFLs for the therapy of Parkinson's disease, neuropathic pain and diseases caused by retinal degeneration but, also, amyotrophic lateral sclerosis and, possibly, Alzheimer's disease. Despite promising data collected in preclinical models, clinical translation of GFLs is yet to be conducted. The main reasons for the limited success of GFLs clinical development are the poor pharmacological characteristics of GFL proteins, such as the inability of GFLs to cross tissue barriers, poor diffusion in tissues, biphasic dose-response and activation of several receptors in the organism in different cell types, along with ethical limitations on patients' selection in clinical trials. The development of small molecules selectively targeting particular GFL receptors with improved pharmacokinetic properties can overcome many of the difficulties and limitations associated with the clinical use of GFL proteins. The current review lists several strategies to target the GFL receptor complex with drug-like molecules, discusses their advantages, provides an overview of available chemical scaffolds and peptides able to activate GFL receptors and describes the effects of these molecules in cultured cells and animal models.

Alternative Anesthesia of Neonatal Mice for Global rAAV Delivery in the Brain With Non-detectable Behavioral Interference in Adults

Viral-transduced gene expression is the current standard for cell-type-specific labeling and cell tacking in experimental neuroscience. To achieve widespread gene expression, a viral delivery method to neonatal rodents was introduced more than two decades ago. Most of those neonatal viral vector injection-based gene transduction methods in mice used deep hypothermia for anesthesia, which was reported to be associated with behavioral impairments. To explore other options for neonatal viral applications, we applied a combination of Medetomidine, Midazolam, and Fentanyl (MMF), each of which can be antagonized by a specific antagonist. Later in their adulthood, we found that adult mice, that received the MMF-induced anesthesia, combined with virus-injected into the brain at postnatal day 2, showed similar performance in all behavioral tasks tested, including tasks for motor coordination, anxiety-related tasks, and spatial memory when compared to adult naïve littermates. This demonstrates that MMF anesthesia could be safely applied to mice for neonatal viral transduction at P2.

MRI-Guided, Noninvasive Delivery of Magneto-Electric Drug Nanocarriers to the Brain in a Nonhuman Primate

A magnetically guided brain delivery method previously demonstrated in mice has not yet been translated for clinical applications due to the mismatch of available static magnet dimensions in relation to the human brain size and shape. To develop a human-compatible methodology, we explored magnetic resonance imaging (MRI) as a tool for the delivery of magneto-electric nanoparticles (MENPs) into the brain of a baboon, as a proof-of-concept study. MRI brain image analysis showed a reduction in T2* value at the basal ganglia, hemisphere, and vertex, thereby confirming successful MENP delivery to the brain. The observation of well-integrated morphologically healthy tissues and no blood toxicity over the study duration confirmed the biocompatibility of MENPs and the delivery procedure. Outcomes of this research present MRI-assisted delivery of MENPs to the brain as a safe and noninvasive method in larger species such as baboons and one step closer to human translation. This MENP-based nanomedicine delivery method can be used for clinical application in order to investigate effective central nervous system (CNS) therapies.

AAV-Mediated Gene Transfer Restores a Normal Muscle Transcriptome in a Canine Model of X-Linked Myotubular Myopathy

Multiple clinical trials employing recombinant adeno-associated viral (rAAV) vectors have been initiated for neuromuscular disorders, including Duchenne and limb-girdle muscular dystrophies, spinal muscular atrophy, and recently X-linked myotubular myopathy (XLMTM). Our previous work on a canine model of XLMTM showed that a single rAAV8-cMTM1 systemic infusion corrected structural abnormalities within the muscle and restored contractile function, with affected dogs surviving more than 4 years post injection. This remarkable therapeutic efficacy presents a unique opportunity to identify the downstream molecular drivers of XLMTM pathology and to what extent the whole muscle transcriptome is restored to normal after gene transfer. Herein, RNA-sequencing was used to examine the transcriptomes of the Biceps femoris and Vastus lateralis in a previously described canine cohort that showed dose-dependent clinical improvements after rAAV8-cMTM1 gene transfer. Our analysis confirmed several dysregulated genes previously observed in XLMTM mice but also identified transcripts linked to XLMTM pathology. We demonstrated XLMTM transcriptome remodeling and dose-dependent normalization of gene expression after gene transfer and created metrics to pinpoint potential biomarkers of disease progression and correction.

Past and Future of Neurotrophic Growth Factors Therapies in ALS: From Single Neurotrophic Growth Factor to Stem Cells and Human Platelet Lysates

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that typically results in death within 3–5 years after diagnosis. To date, there is no curative treatment and therefore an urgent unmet need of neuroprotective and/or neurorestorative treatments. Due to their spectrum of capacities in the central nervous system—e.g., development, plasticity, maintenance, neurogenesis—neurotrophic growth factors (NTF) have been exploited for therapeutic strategies in ALS for decades. In this review we present the initial strategy of using single NTF by different routes of administration to the use of stem cells transplantation to express a multiple NTFs-rich secretome to finally focus on a new biotherapy based on the human platelet lysates, the natural healing system containing a mix of pleitropic NTF and having immunomodulatory function. This review highlights that this latter treatment may be crucial to power the neuroprotection and/or neurorestoration therapy requested in this devastating disease.

Risk Factors and Emerging Therapies in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal progressive neurodegenerative disease characterized by a permanent degeneration of both upper and lower motor neurons. Many different genes and pathophysiological processes contribute to this disease, however its exact cause remains unclear. Therefore, it is necessary to understand this heterogeneity to find effective treatments. In this review, we focus on selected environmental and genetic risk factors predisposing to ALS and highlight emerging treatments in ALS therapy. Of numerous defective genes associated with ALS, we focus on four principal genes that have been identified as definite causes of ALS: the SOD1 gene, C9orf72, TDP-43, as well as the recently identified TBK1. We also provide up-to-date information on selected environmental factors that have historically been considered as key players in ALS development and pathogenesis. In parallel to our survey of known risk factors, we also discuss emerging ALS stem cell therapies and experimental medicines currently undergoing phase II and III clinical trials.

Emerging antisense oligonucleotide and viral therapies for amyotrophic lateral sclerosis

PURPOSE OF REVIEW

Amyotrophic lateral sclerosis (ALS) is a rapidly fatal disease for which there is currently no effective therapy. The present review describes the current progress of existing molecular therapies in the clinical trial pipeline and highlights promising future antisense oligonucleotide (ASO) and viral therapeutic strategies for treating ALS.

RECENT FINDINGS

The immense progress in the design of clinical trials and generation of ASO therapies directed towards superoxide dismutase-1 (SOD1) and chromosome 9 open reading frame 72 (C9orf72) repeat expansion related disease have been propelled by fundamental work to identify the genetic underpinnings of familial ALS and develop relevant disease models. Preclinical studies have also identified promising targets for sporadic ALS (sALS). Moreover, encouraging results in adeno-associated virus (AAV)-based therapies for spinal muscular atrophy (SMA) provide a roadmap for continued improvement in delivery and design of molecular therapies for ALS.

SUMMARY

Advances in preclinical and clinical studies of ASO and viral directed approaches to neuromuscular disease, particularly ALS, indicate that these approaches have high specificity and are relatively well tolerated.

Transplantation of Neural Progenitor Cells Expressing Glial Cell Line-Derived Neurotrophic Factor into the Motor Cortex as a Strategy to Treat Amyotrophic Lateral Sclerosis

Early dysfunction of cortical motor neurons may underlie the initiation of amyotrophic lateral sclerosis (ALS). As such, the cortex represents a critical area of ALS research and a promising therapeutic target. In the current study, human cortical-derived neural progenitor cells engineered to secrete glial cell line-derived neurotrophic factor (GDNF) were transplanted into the SOD1^G93A ALS rat cortex, where they migrated, matured into astrocytes, and released GDNF. This protected motor neurons, delayed disease pathology and extended survival of the animals. These same cells injected into the cortex of cynomolgus macaques survived and showed robust GDNF expression without adverse effects. Together this data suggests that introducing cortical astrocytes releasing GDNF represents a novel promising approach to treating ALS. Stem Cells 2018;36:1122-1131.

Histamine upregulates the expression of histamine receptors and increases the neuroprotective effect of astrocytes

BACKGROUND

Astrocytes have attracted increasing attention over recent decades for their role in neuroinflammation. Histamine, a major aminergic brain neurotransmitter, has an important influence on the main activities of astrocytes, such as ion homeostasis, energy metabolism, and neurotransmitter clearance. However, little is known about the impact of histamine on astrocyte immunomodulatory function.

METHODS

The expression of all known histamine receptor subtypes was examined in primary astrocytes. Then, primary astrocytes were pretreated with selective histamine receptor antagonists and stimulated with histamine. Cellular activation, proinflammatory cytokine production, and expression of neurotrophic factors were assessed.

RESULTS

Astrocytes could constitutively express three histamine receptors (H1R, H2R, and H3R), and these three histamine receptors could be selectively upregulated to varying degrees upon histamine treatment. Histamine also dose-dependently stimulated astrocyte activation and subsequent production of glial cell-derived neurotrophic factor (GDNF), whereas it suppressed the secretion of the proinflammatory factors tumor necrosis factor-alpha (TNF-α) and interleukin-1β (IL-1β). The effects of histamine were completely abolished by either an H1R or H3R antagonist, while an H2R antagonist attenuated the effects partly.

CONCLUSIONS

The present study identified the expression of H1R, H2R, and H3R on astrocytes. We also demonstrated that negative regulation of astrocytic TNF-α and IL-1β production and the enhancement of astrocytic GDNF stimulated by histamine were receptor-mediated processes in which all three of the expressed histamine receptors (H1R, H2R, and H3R) were involved. These findings may further clarify the involvement and mechanism of astrocyte activation in neuroinflammation.

AAV gene delivery to the spinal cord: serotypes, methods, candidate diseases, and clinical trials

INTRODUCTION

Adeno-associated viral (AAV) vector-mediated gene delivery to the spinal cord has finally entered the pathway towards regulatory approval. Phase 1 clinical trials using AAV gene therapy for pediatric disorders - spinal muscular atrophy (SMA) and giant axonal neuropathy (GAN) - are now underway.

AREAS COVERED

This review addresses the latest progress in the field of AAV gene delivery to the spinal cord, particularly focusing on the most prominent AAV serotypes and delivery methodologies to the spinal cord. Candidate diseases and scaling up experiments in large animals are also discussed.

EXPERT OPINION

Intravenous (IV) and intrathecal (IT) deliveries seem to undoubtedly be the preferred routes of administration for diffuse spinal cord delivery of therapeutic AAV vectors that can cross the blood-brain barrier (BBB) and correct inherited genetic disorders. Conversely, intraparenchymal delivery is still an undervalued but very viable approach for segmental therapy in afflictions such as ALS or Pompe Disease as a means to prevent respiratory dysfunction.

Motor Neuron Gene Therapy: Lessons from Spinal Muscular Atrophy for Amyotrophic Lateral Sclerosis

Spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS) are severe nervous system diseases characterized by the degeneration of lower motor neurons. They share a number of additional pathological, cellular, and genetic parallels suggesting that mechanistic and clinical insights into one disorder may have value for the other. While there are currently no clinical ALS gene therapies, the splice-switching antisense oligonucleotide, nusinersen, was recently approved for SMA. This milestone was achieved through extensive pre-clinical research and patient trials, which together have spawned fundamental insights into motor neuron gene therapy. We have thus tried to distil key information garnered from SMA research, in the hope that it may stimulate a more directed approach to ALS gene therapy. Not only must the type of therapeutic (e.g., antisense oligonucleotide vs. viral vector) be sensibly selected, but considerable thought must be applied to the where, which, what, and when in order to enhance treatment benefit: to where (cell types and tissues) must the drug be delivered and how can this be best achieved? Which perturbed pathways must be corrected and can they be concurrently targeted? What dosing regime and concentration should be used? When should medication be administered? These questions are intuitive, but central to identifying and optimizing a successful gene therapy. Providing definitive solutions to these quandaries will be difficult, but clear thinking about therapeutic testing is necessary if we are to have the best chance of developing viable ALS gene therapies and improving upon early generation SMA treatments.