Combined Gene Therapy to Reduce the Neuronal Damage in the Mouse Model of Focal Ischemic Injury

Still in Search for an EAAT Activator: GT949 Does Not Activate EAAT2, nor EAAT3 in Impedance and Radioligand Uptake Assays

Excitatory amino acid transporters (EAATs) are important regulators of amino acid transport and in particular glutamate. Recently, more interest has arisen in these transporters in the context of neurodegenerative diseases. This calls for ways to modulate these targets to drive glutamate transport, EAAT2 and EAAT3 in particular. Several inhibitors (competitive and noncompetitive) exist to block glutamate transport; however, activators remain scarce. Recently, GT949 was proposed as a selective activator of EAAT2, as tested in a radioligand uptake assay. In the presented research, we aimed to validate the use of GT949 to activate EAAT2-driven glutamate transport by applying an innovative, impedance-based, whole-cell assay (xCELLigence). A broad range of GT949 concentrations in a variety of cellular environments were tested in this assay. As expected, no activation of EAAT3 could be detected. Yet, surprisingly, no biological activation of GT949 on EAAT2 could be observed in this assay either. To validate whether the impedance-based assay was not suited to pick up increased glutamate uptake or if the compound might not induce activation in this setup, we performed radioligand uptake assays. Two setups were utilized; a novel method compared to previously published research, and in a reproducible fashion copying the methods used in the existing literature. Nonetheless, activation of neither EAAT2 nor EAAT3 could be observed in these assays. Furthermore, no evidence of GT949 binding or stabilization of purified EAAT2 could be observed in a thermal shift assay. To conclude, based on experimental evidence in the present study GT949 requires specific assay conditions, which are difficult to reproduce, and the compound cannot simply be classified as an activator of EAAT2 based on the presented evidence. Hence, further research is required to develop the tools needed to identify new EAAT modulators and use their potential as a therapeutic target.

Glutamate dehydrogenase: Potential therapeutic targets for neurodegenerative disease

Glutamate dehydrogenase (GDH) is a key enzyme in mammalian glutamate metabolism. It is located at the intersection of multiple metabolic pathways and participates in a variety of cellular activities. GDH activity is strictly regulated by a variety of allosteric compounds. Here, we review the unique distribution and expressions of GDH in the brain nervous system. GDH plays an essential role in the glutamate-glutamine-GABA cycle between astrocytes and neurons. The dysfunction of GDH may induce the occurrence of many neurodegenerative diseases, such as Parkinson's disease, epilepsy, Alzheimer's disease, schizophrenia, and frontotemporal dementia. GDH activators and gene therapy have been found to protect neurons and improve motor disorders in neurodegenerative diseases caused by glutamate metabolism disorders. To date, no medicine has been discovered that specifically targets neurodegenerative diseases, although several potential medicines are used clinically. Targeting GDH to treat neurodegenerative diseases is expected to provide new insights and treatment strategies.

Ultrasound-Mediated Blood-Brain Barrier Opening Improves Whole Brain Gene Delivery in Mice

Gene therapy represents a powerful therapeutic tool to treat diseased tissues and provide a durable and effective correction. The central nervous system (CNS) is the target of many gene therapy protocols, but its high complexity makes it one of the most difficult organs to reach, in part due to the blood-brain barrier that protects it from external threats. Focused ultrasound (FUS) coupled with microbubbles appears as a technological breakthrough to deliver therapeutic agents into the CNS. While most studies focus on a specific targeted area of the brain, the present work proposes to permeabilize the entire brain for gene therapy in several pathologies. Our results show that, after i.v. administration and FUS sonication in a raster scan manner, a self-complementary AAV9-CMV-GFP vector strongly and safely infected the whole brain of mice. An increase in vector DNA (19.8 times), GFP mRNA (16.4 times), and GFP protein levels (17.4 times) was measured in whole brain extracts of FUS-treated GFP injected mice compared to non-FUS GFP injected mice. In addition to this increase in GFP levels, on average, a 7.3-fold increase of infected cells in the cortex, hippocampus, and striatum was observed. No side effects were detected in the brain of treated mice. The combining of FUS and AAV-based gene delivery represents a significant improvement in the treatment of neurological genetic diseases.

Upregulation of Extracellular Vesicles-Encapsulated miR-132 Released From Mesenchymal Stem Cells Attenuates Ischemic Neuronal Injury by Inhibiting Smad2/c-jun Pathway via Acvr2b Suppression

Ischemic cerebrovascular disease is a significant and common public health issue worldwide. The emerging roles of mesenchymal stem cells (MSCs)-derived extracellular vesicles (EVs) in ischemic neuronal injury continue to be investigated. The current study aimed to investigate the role of EV-derived miR-132 from MSCs in ischemic neuronal injury. EVs were initially isolated from bone MSCs (BMSCs) and subsequently evaluated. A middle cerebral artery occlusion (MCAO) mouse model was constructed with the neurological function evaluated through a series of neurological scores, a pole test, and a foot fault test. Histopathological changes, neuron viability, and apoptosis, as well as cerebral infarction, were detected by hematoxylin and eosin (HE) staining and 2,3,5-triphenyltetrazolium hydrochloride (TTC) staining. The targeting relationship between microRNA (miR)-132 and Activin receptor type IIB (Acvr2b) was further confirmed based on dual-luciferase reporter gene assay results. Loss- and gain-of-function assays were conducted to elucidate the role of miR-132, EV-derived miR-132, Acvr2b, and Smad2 in oxygen-glucose deprivation (OGD)-treated neurons, and in mice models. Neuronal cell viability and apoptosis were evaluated via Cell Counting kit-8 (CCK-8) and flow cytometry. Our results indicated that Acvr2b was highly expressed, while miR-132 was poorly expressed in the MCAO mice and OGD-treated neurons. Acvr2b silencing or upregulation of miR-132 led to an elevation in neuronal activity, decreased neuronal apoptosis, reduced expression of Bax, and cleaved-caspase 3, as well as increased Bcl-2 expression. Acvr2b expression was targeted and inhibited by miR-132. EV-derived Acvr2b promoted activation of phosphorylated-Smad2 (p-Smad2)/c-jun signaling pathway, ultimately inducing neuronal injury. Our study provides evidence demonstrating that the overexpression of c-jun inhibits the protective role of MSCs-derived EV-miR-132 in neuronal injury. Upregulation of EV-derived miR-132 released from MSCs attenuates ischemic neuronal injury by inhibiting Smad2/c-jun pathways via the suppression of Acvr2b.

Genes to treat excitotoxicity ameliorate the symptoms of the disease in mice models of multiple system atrophy

Multiple system atrophy (MSA) is a sporadic neurodegenerative disorder characterized by striatonigral degeneration and olivopontocerebellar atrophy. The main hallmark of MSA is the aggregation of alpha-synuclein in oligodendrocytes, which contributes to the dysfunction and death of the oligodendrocytes, followed by neurodegeneration. Studies suggested that oxidative-excitatory pathway is associated with the progression of the disease. The aim of the current study was to test this concept by overexpression of excitatory amino acid transporter 2, glutamate dehydrogenase and nuclear factor (erythroid-derived 2)-related factor 2 genes in the striatum of two established mouse models of MSA. To induce the first model, we injected the mitochondrial neurotoxin, 3-nitropropionic acid (3-NP), unilaterally into the right striatum in 2-month-old C57BL/6 male mice. We demonstrate a significant improvement in two drug-induced rotational behavior tests, following unilateral injection the three genes. For the second model, we used transgenic mice expressing the alpha-synuclein gene under the proteolipid protein, in the age of 7 months, boosted with 3-NP to enhance the motor deficits and neurodegeneration. We show that the overexpression of the three genes attenuated the motor-related deficit in the elevated bridge and pole tests. Thus, our study indicates that glutamate excito-oxidative toxicity plays a major role in this MSA model and our gene therapy approach might suggest a novel strategy for MSA treatment.