Enzyme replacement in the CSF to treat metachromatic leukodystrophy in mouse model using single intracerebroventricular injection of self-complementary AAV1 vector

In Silico Structural Modeling and Binding Site Analysis of Cerebroside Sulfotransferase (CST): A Therapeutic Target for Developing Substrate Reduction Therapy for Metachromatic Leukodystrophy

Cerebroside sulfotransferase (CST) is emerging as an important therapeutic target to develop substrate reduction therapy (SRT) for metachromatic leukodystrophy (MLD), a rare neurodegenerative lysosomal storage disorder. MLD develops with progressive impairment and destruction of the myelin sheath as a result of accumulation of sulfatide around the nerve cells in the absence of its recycling mechanism with deficiency of arylsulfatase A (ARSA). Sulfatide is the product of the catalytic action of cerebroside sulfotransferase (CST), which needs to be regulated under pathophysiological conditions by inhibitor development. To carry out in silico-based preliminary drug screening or for designing new drug candidates, a high-quality three-dimensional (3D) structure is needed in the absence of an experimentally derived three-dimensional crystal structure. In this study, a 3D model of the protein was developed using a primary sequence with the SWISS-MODEL server by applying the top four GMEQ score-based templates belonging to the sulfotransferase family as a reference. The 3D model of CST highlights the features of the protein responsible for its catalytic action. The CST model comprises five β-strands, which are flanked by ten α-helices from both sides as well as form the upside cover of the catalytic pocket of CST. CST has two catalytic regions: PAPS (-sulfo donor) binding and galactosylceramide (-sulfo acceptor) binding. The catalytic action of CST was proposed via molecular docking and molecular dynamic (MD) simulation with PAPS, galactosylceramide (GC), PAPS-galactosylceramide, and PAP. The stability of the model and its catalytic action were confirmed using molecular dynamic simulation-based trajectory analysis. CST response against the inhibition potential of the experimentally reported competitive inhibitor of CST was confirmed via molecular docking and molecular dynamics simulation, which suggested the suitability of the CST model for future drug discovery to strengthen substrate reduction therapy for MLD.

A comprehensive review on structural and therapeutical insight of Cerebroside sulfotransferase (CST) - An important target for development of substrate reduction therapy against metachromatic leukodystrophy

This review is an effort towards the development of substrate reduction therapy using cerebroside sulfotransferase (CST) as a target protein for the development of inhibitors intended to treat pathophysiological condition resulting from the accumulation of sulfatide, a product from the catalytic action of CST. Accumulation of sulfatides leads to progressive impairment and destruction of the myelin structure, disruption of normal physiological transmission of electrical impulse between nerve cells, axonal loss in the central and peripheral nervous system and cumulatively gives a clinical manifestation of metachromatic leukodystrophy. Thus, there is a need to develop specific and potent CST inhibitors to positively control sulfatide accumulation. Structural similarity and computational studies revealed that LYS85, SER172 and HIS141 are key catalytic residues that determine the catalytic action of CST through the transfer of sulfuryl group from the donor PAPS to the acceptor galactosylceramide. Computational studies revealed catalytic site of CST consists two binding site pocket including PAPS binding pocket and substrate binding pocket. Specific substrate site residues in CST can be targeted to develop specific CST inhibitors. This review also explores the challenges of CST-directed substrate reduction therapy as well as the opportunities available in natural products for inhibitor development.

Treadmill Exercise Reduces Neuroinflammation, Glial Cell Activation and Improves Synaptic Transmission in the Prefrontal Cortex in 3 × Tg-AD Mice

Physical exercise improves memory and cognition in physiological aging and Alzheimer's disease (AD), but the mechanisms remain poorly understood. Here, we test the hypothesis that Aβ oligomer accumulation, neuroinflammation, and glial cell activation may lead to disruption of synaptic transmission in the prefrontal cortex of 3 × Tg-AD Mice, resulting in impairment of learning and memory. On the other hand, treadmill exercise could prevent the pathogenesis and exert neuroprotective effects. Here, we used immunohistochemistry, western blotting, enzyme-linked immunosorbent assay, and slice electrophysiology to analyze the levels of GSK3β, Aβ oligomers (Aβ dimers and trimers), pro-inflammatory cytokines (IL-1β, IL-6, and TNFα), the phosphorylation of CRMP2 at Thr514, and synaptic currents in pyramidal neurons in the prefrontal cortex. We show that 12-week treadmill exercise beginning in three-month-old mice led to the inhibition of GSK3β kinase activity, decreases in the levels of Aβ oligomers, pro-inflammatory cytokines (IL-1β, IL-6, and TNFα), and the phosphorylation of CRMP2 at Thr514, reduction of microglial and astrocyte activation, and improvement of excitatory and inhibitory synaptic transmission of pyramidal neurons in the prefrontal cortex of 3 × Tg-AD Mice. Thus, treadmill exercise reduces neuroinflammation, glial cell activation and improves synaptic transmission in the prefrontal cortex in 3 × Tg-AD mice, possibly related to the inhibition of GSK3β kinase activity.

CNS gene therapy: present developments and emerging trends accelerating industry-academia pathways

The recent success of first central nervous system gene therapies has reinvigorated the growing community of gene therapy researchers and strengthened the field's market position. We are witnessing an increase of clinical trials with long-term efficiency mainly for neurometabolic, neurodegenerative and neurodevelopmental diseases caused by loss-of-function mutations. The ever-expanding knowledge and accessibility to the most advanced tools allow enrichment of applications to more complex diseases. This gradually contributes towards sealing the gap between top diseases impacting current global health and those towards which gene therapy development is currently aimed. Here, we highlight innovative therapeutic approaches that have reached the clinics and outline the latest improvements of vector design and targeting. Finally, we address the pressing challenges faced by clinical trials and the direction they are heading.

Mammalian Sulfatases: Biochemistry, Disease Manifestation, and Therapy

Sulfatases are enzymes that catalyze the removal of sulfate from biological substances, an essential process for the homeostasis of the body. They are commonly activated by the unusual amino acid formylglycine, which is formed from cysteine at the catalytic center, mediated by a formylglycine-generating enzyme as a post-translational modification. Sulfatases are expressed in various cellular compartments such as the lysosome, the endoplasmic reticulum, and the Golgi apparatus. The substrates of mammalian sulfatases are sulfolipids, glycosaminoglycans, and steroid hormones. These enzymes maintain neuronal function in both the central and the peripheral nervous system, chondrogenesis and cartilage in the connective tissue, detoxification from xenobiotics and pharmacological compounds in the liver, steroid hormone inactivation in the placenta, and the proper regulation of skin humidification. Human sulfatases comprise 17 genes, 10 of which are involved in congenital disorders, including lysosomal storage disorders, while the function of the remaining seven is still unclear. As for the genes responsible for pathogenesis, therapeutic strategies have been developed. Enzyme replacement therapy with recombinant enzyme agents and gene therapy with therapeutic transgenes delivered by viral vectors are administered to patients. In this review, the biochemical substrates, disease manifestation, and therapy for sulfatases are summarized.

Prokineticin-2 prevents neuronal cell deaths in a model of traumatic brain injury

Prokineticin-2 (Prok2) is an important secreted protein likely involved in the pathogenesis of several acute and chronic neurological diseases through currently unidentified regulatory mechanisms. The initial mechanical injury of neurons by traumatic brain injury triggers multiple secondary responses including various cell death programs. One of these is ferroptosis, which is associated with dysregulation of iron and thiols and culminates in fatal lipid peroxidation. Here, we explore the regulatory role of Prok2 in neuronal ferroptosis in vitro and in vivo. We show that Prok2 prevents neuronal cell death by suppressing the biosynthesis of lipid peroxidation substrates, arachidonic acid-phospholipids, via accelerated F-box only protein 10 (Fbxo10)-driven ubiquitination, degradation of long-chain-fatty-acid-CoA ligase 4 (Acsl4), and inhibition of lipid peroxidation. Mice injected with adeno-associated virus-Prok2 before controlled cortical impact injury show reduced neuronal degeneration and improved motor and cognitive functions, which could be inhibited by Fbxo10 knockdown. Our study shows that Prok2 mediates neuronal cell deaths in traumatic brain injury via ferroptosis.

Gene Therapy for Lysosomal Storage Disorders: Ongoing Studies and Clinical Development

Rare monogenic disorders such as lysosomal diseases have been at the forefront in the development of novel treatments where therapeutic options are either limited or unavailable. The increasing number of successful pre-clinical and clinical studies in the last decade demonstrates that gene therapy represents a feasible option to address the unmet medical need of these patients. This article provides a comprehensive overview of the current state of the field, reviewing the most used viral gene delivery vectors in the context of lysosomal storage disorders, a selection of relevant pre-clinical studies and ongoing clinical trials within recent years.

Dirty Fish Versus Squeaky Clean Mice: Dissecting Interspecies Differences Between Animal Models of Interferonopathy

Autoimmune and autoinflammatory diseases are rare but often devastating disorders, underpinned by abnormal immune function. While some autoimmune disorders are thought to be triggered by a burden of infection throughout life, others are thought to be genetic in origin. Among these heritable disorders are the type I interferonopathies, including the rare Mendelian childhood-onset encephalitis Aicardi-Goutières syndrome. Patients with Aicardi Goutières syndrome are born with defects in enzymes responsible for nucleic acid metabolism and develop devastating white matter abnormalities resembling congenital cytomegalovirus brain infection. In some cases, common infections preceded the onset of the disease, suggesting immune stimulation as a potential trigger. Thus, the antiviral immune response has been actively studied in an attempt to provide clues on the pathological mechanisms and inform on the development of therapies. Animal models have been fundamental in deciphering biological mechanisms in human health and disease. Multiple rodent and zebrafish models are available to study type I interferonopathies, which have advanced our understanding of the human disease by identifying key pathological pathways and cellular drivers. However, striking differences in phenotype have also emerged between these vertebrate models, with zebrafish models recapitulating key features of the human neuropathology often lacking in rodents. In this review, we compare rodent and zebrafish models, and summarize how they have advanced our understanding of the pathological mechanisms in Aicardi Goutières syndrome and similar disorders. We highlight recent discoveries on the impact of laboratory environments on immune stimulation and how this may inform the differences in pathological severity between mouse and zebrafish models of type I interferonopathies. Understanding how these differences arise will inform the improvement of animal disease modeling to accelerate progress in the development of therapies for these devastating childhood disorders.

Genetic disorders with central nervous system white matter abnormalities: An update

Several genetic disorders have variable degree of central nervous system white matter abnormalities. We retrieved and reviewed 422 genetic conditions with prominent and consistent involvement of white matter from the literature. We herein describe the current definitions, classification systems, clinical spectrum, neuroimaging findings, genomics, and molecular mechanisms of these conditions. Though diagnosis for most of these disorders relies mainly on genomic tests, specifically exome sequencing, we collate several clinical and neuroimaging findings still relevant in diagnosis of clinically recognizable disorders. We also review the current understanding of pathophysiology and therapeutics of these disorders.

Viral-Mediated Gene Replacement Therapy in the Developing Central Nervous System: Current Status and Future Directions

The past few years have witnessed rapid developments in viral-mediated gene replacement therapy for pediatric central nervous system neurogenetic disorders. Here, we provide pediatric neurologists with an up-to-date, comprehensive overview of these developments and note emerging trends for future research. This review presents the different types of viral vectors used in viral-mediated gene replacement therapy; the fundamental properties of viral-mediated gene replacement therapy; the challenges associated with the use of this therapy in the central nervous system; the pathway for therapy development, from translational basic science studies to clinical trials; and an overview of the therapies that have reached clinical trials in patients. Current viral platforms under investigation include adenovirus vectors, adeno-associated viral vectors, lentiviral/retroviral vectors, and herpes simplex virus type 1 vectors. This review also presents an in-depth analysis of numerous studies that investigated these viral platforms in cultured cells and in transgenic animal models for pediatric neurogenetic disorders. Viral vectors have been applied to clinical trials for many different pediatric neurogenetic disorders, including Canavan disease, metachromatic leukodystrophy, neuronal ceroid lipofuscinosis, mucopolysaccharidosis III, spinal muscular atrophy, and aromatic l-amino acid decarboxylase deficiency. Of these diseases, only spinal muscular atrophy has a viral-mediated gene replacement therapy approved for marketing. Despite significant progress in therapy development, many challenges remain. Surmounting these challenges is critical to advancing the current status of viral-mediated gene replacement therapy for pediatric central nervous system neurogenetic disorders.

The glymphatic system delivery enhances the transduction efficiency of AAV1 to brain endothelial cells in adult mice

BACKGROUND

Recombinant adeno-associated virus (rAAV) is increasingly applied in neuroscience research or gene therapy. However, there is no simple and efficient tool for specific transfection of rAAV into cerebrovascular tissues. It has been reported that fluorescent tracers or beta-amyloid protein can enter the brain through perivascular spaces, named as "glymphatic system". The purpose of this study was to explore whether rAAV could transduce the cerebral vasculature through the glymphatic pathway.

NEW METHOD

An AAV1-GFP vector suspension (15 μL) was injected into the intracisternal space of anesthetized mice (n = 2) and 5 μl was injected into the bulbus medullae (n = 2). As controls, 15 μl of artificial cerebrospinal fluid (aCSF) was injected into the cisterna magna. The endothelial specific transduction was verified by Glut1 or PDGFRβ immunofluorescent staining. Immunofluorescence images for all groups were captured with a laser microscope.

RESULTS

It was observed that infection with rAAV1 vectors encoding green fluorescence protein resulted in a successful cerebrovascular transduction when injected into cisterna magna, compared to aCSF or intra-parenchymal injection at 30 days post-transduction in adult mice. In addition, GFP was co-localized with Glut1 based on immuno-fluorescence. These results indicate that glymphatic system delivery enhances the transduction efficiency of AAV1 to brain endothelial cells.

COMPARISON WITH EXISTING METHODS

The AAV1 vector can simply and efficiently transduce the cerebral endothelial cells through the glymphatic pathway.

CONCLUSION

The findings of this study reveal that rAAV1-based vectors have high application potential for endothelial-targeted neurologic disease research or gene-based therapies.

Gene suppressing therapy for Pelizaeus-Merzbacher disease using artificial microRNA

Copy number increase or decrease of certain dosage-sensitive genes may cause genetic diseases with distinct phenotypes, conceptually termed genomic disorders. The most common cause of Pelizaeus-Merzbacher disease (PMD), an X-linked hypomyelinating leukodystrophy, is genomic duplication encompassing the entire proteolipid protein 1 (PLP1) gene. Although the exact molecular and cellular mechanisms underlying PLP1 duplication, which causes severe hypomyelination in the central nervous system, remain largely elusive, PLP1 overexpression is likely the fundamental cause of this devastating disease. Here, we investigated if adeno-associated virus-mediated (AAV-mediated) gene-specific suppression may serve as a potential cure for PMD by correcting quantitative aberrations in gene products. We developed an oligodendrocyte-specific Plp1 gene suppression therapy using artificial microRNA under the control of human CNP promoter in a self-complementary AAV (scAAV) platform. A single direct brain injection achieved widespread oligodendrocyte-specific Plp1 suppression in the white matter of WT mice. AAV treatment in Plp1-transgenic mice, a PLP1 duplication model, ameliorated cytoplasmic accumulation of Plp1, preserved mature oligodendrocytes from degradation, restored myelin structure and gene expression, and improved survival and neurological phenotypes. Together, our results provide evidence that AAV-mediated gene suppression therapy can serve as a potential cure for PMD resulting from PLP1 duplication and possibly for other genomic disorders.

Efficient Gene Transfer to the Central Nervous System by Single-Stranded Anc80L65

Adeno-associated viral vectors (AAVs) have demonstrated potential in applications for neurologic disorders, and the discovery that some AAVs can cross the blood-brain barrier (BBB) after intravenous injection has further expanded these opportunities for non-invasive brain delivery. Anc80L65, a novel AAV capsid designed from in silico reconstruction of the viral evolutionary lineage, has previously demonstrated robust transduction capabilities after local delivery in various tissues such as liver, retina, or cochlea, compared with conventional AAVs. Here, we compared the transduction efficacy of Anc80L65 with conventional AAV9 in the CNS after intravenous, intracerebroventricular (i.c.v.), or intraparenchymal injections. Anc80L65 was more potent at targeting the brain and spinal cord after intravenous injection than AAV9, and mostly transduced astrocytes and a wide range of neuronal subpopulations. Although the efficacy of Anc80L65 and AAV9 is similar after direct intraparenchymal injection in the striatum, Anc80L65's diffusion throughout the CNS was more extensive than AAV9 after i.c.v. infusion, leading to widespread EGFP expression in the cerebellum. These findings demonstrate that Anc80L65 is a highly efficient gene transfer vector for the murine CNS. Systemic injection of Anc80L65 leads to notable expression in the CNS that does not rely on a self-complementary genome. These data warrant further testing in larger animal models.

Peli1 Contributions in Microglial Activation, Neuroinflammatory Responses and Neurological Deficits Following Experimental Subarachnoid Hemorrhage

Early brain injury (EBI) following subarachnoid hemorrhage (SAH) is closely associated with neuroinflammation. Microglial activation is an early event that leads to neuroinflammation after SAH. Peli1 is an E3 ubiquitin ligase that mediates the induction of pro-inflammatory cytokines in microglia. Here we report Peli1 contributions in SAH mediated brain pathology. An SAH model was induced by endovascular perforation in adult male C57BL/6J mice. Peli1 was markedly induced in mice brains in a time-dependent manner and was predominantly expressed in CD16/32-positive microglia after SAH. Using genetic approaches, we demonstrated that decreased Peli1 significantly improved neurological deficits, attenuated brain edema, reduced over-expression of pro-inflammatory cytokine IL-6 and modified apoptotic/antiapoptotic biomarkers. In addition, Peli1 downregulation suppressed ERK and JNK phosphorylation levels via the downregulation of cIAP1/2 expression, subsequently reducing inducible nitric oxide synthase (iNOS) expression after SAH. Therefore, these findings demonstrate that Peli1 contributes to microglia-mediated neuroinflammation in EBI by mediating cIAP1/2 activation, thus promoting the activation of MyD88-dependent MAPK pathway after experimental SAH. Our findings also showed that Peli1 could promote the expression of M1 microglia polarization biomarker CD16/32 and iNOS after SAH. Targeting Peli1 exerts neuroprotective effects during EBI after SAH, thus could provide potential option for prevention-therapy in high-risk individuals.

Mef2C restrains microglial inflammatory response and is lost in brain ageing in an IFN-I-dependent manner

During ageing, microglia acquire a phenotype that may negatively affect brain function. Here we show that ageing microglial phenotype is largely imposed by interferon type I (IFN-I) chronically present in aged brain milieu. Overexpression of IFN-β in the CNS of adult wild-type mice, but not of mice lacking IFN-I receptor on their microglia, induces an ageing-like transcriptional microglial signature, and impairs cognitive performance. Furthermore, we demonstrate that age-related IFN-I milieu downregulates microglial myocyte-specific enhancer factor 2C (Mef2C). Immune challenge in mice lacking Mef2C in microglia results in an exaggerated microglial response and has an adverse effect on mice behaviour. Overall, our data indicate that the chronic presence of IFN-I in the brain microenvironment, which negatively affects cognitive function, is mediated via modulation of microglial activity. These findings may shed new light on other neurological conditions characterized by elevated IFN-I signalling in the brain.Microglia cells in the brain regulate immune responses, but in ageing can negatively affect brain function. Here the authors show that the chronic presence of type I interferon in aged mouse brain impedes cognitive ability by altering microglia transcriptome and limiting Mef2C, a microglia 'off' signal.

Childhood leukodystrophies: A literature review of updates on new definitions, classification, diagnostic approach and management

Childhood leukodystrophies are a growing category of neurological disorders in pediatric neurology practice. With the help of new advanced genetic studies such as whole exome sequencing (WES) and whole genome sequencing (WGS), the list of childhood heritable white matter disorders has been increased to more than one hundred disorders. During the last three decades, the basic concepts and definitions, classification, diagnostic approach and medical management of these disorders much have changed. Pattern recognition based on brain magnetic resonance imaging (MRI), has played an important role in this process. We reviewed the last Global Leukodystrophy Initiative (GLIA) expert opinions in definition, new classification, diagnostic approach and medical management including emerging treatments for pediatric leukodystrophies.

Gene therapy targeting oligodendrocytes provides therapeutic benefit in a leukodystrophy model

Pelizaeus-Merzbacher-like disease or hypomyelinating leukodystrophy-2 is an autosomal recessively inherited leukodystrophy with childhood onset resulting from mutations in the gene encoding the gap junction protein connexin 47 (Cx47, encoded by GJC2). Cx47 is expressed specifically in oligodendrocytes and is crucial for gap junctional communication throughout the central nervous system. Previous studies confirmed that a cell autonomous loss-of-function mechanism underlies hypomyelinating leukodystrophy-2 and that transgenic oligodendrocyte-specific expression of another connexin, Cx32 (GJB1), can restore gap junctions in oligodendrocytes to achieve correction of the pathology in a disease model. To develop an oligodendrocyte-targeted gene therapy, we cloned the GJC2/Cx47 gene under the myelin basic protein promoter and used an adeno-associated viral vector (AAV.MBP.Cx47myc) to deliver the gene to postnatal Day 10 mice via a single intracerebral injection in the internal capsule area. Lasting Cx47 expression specifically in oligodendrocytes was detected in Cx47 single knockout and Cx32/Cx47 double knockout mice up to 12 weeks post-injection, including the corpus callosum and the internal capsule but also in more distant areas of the cerebrum and in the spinal cord. Application of this oligodendrocyte-targeted somatic gene therapy at postnatal Day 10 in groups of double knockout mice, a well characterized model of hypomyelinating leukodystrophy-2, resulted in significant improvement in motor performance and coordination at 1 month of age in treated compared to mock-treated mice, as well as prolonged survival. Furthermore, immunofluorescence and morphological analysis revealed improvement in demyelination, oligodendrocyte apoptosis, inflammation, and astrogliosis, all typical features of this leukodystrophy model in both brain and spinal cord. Functional dye transfer analysis confirmed the re-establishment of oligodendrocyte gap junctional connectivity in treated as opposed to untreated mice. These results provide a significant advance in the development of oligodendrocyte-cell specific gene therapy. Adeno-associated viral vectors can be used to target therapeutic expression of a myelin gene to oligodendrocytes. We show evidence for the first somatic gene therapy approach to treat hypomyelinating leukodystrophy-2 preclinically, providing a potential treatment for this and similar forms of leukodystrophies.

Tailored transgene expression to specific cell types in the central nervous system after peripheral injection with AAV9

The capacity of certain adeno-associated virus (AAV) vectors to cross the blood–brain barrier after intravenous delivery offers a unique opportunity for noninvasive brain delivery. However, without a well-tailored system, the use of a peripheral route injection may lead to undesirable transgene expression in nontarget cells or organs. To refine this approach, the present study characterizes the transduction profiles of new self-complementary AAV9 (scAAV9) expressing the green fluorescent protein (GFP) either under an astrocyte (glial fibrillary acidic (GFA) protein) or neuronal (Synapsin (Syn)) promoter, after intravenous injection of adult mice (2 × 10¹³ vg/kg). ScAAV9-GFA-GFP and scAAV9-Syn-GFP robustly transduce astrocytes (11%) and neurons (17%), respectively, without aberrant expression leakage. Interestingly, while the percentages of GFP-positive astrocytes with scAAV9-GFA-GFP are similar to the performances observed with scAAV9-CBA-GFP (broadly active promoter), significant higher percentages of neurons express GFP with scAAV9-Syn-GFP. GFP-positive excitatory as well as inhibitory neurons are observed, as well as motor neurons in the spinal cord. Additionally, both activated (GFAP-positive) and resting astrocytes (GFAP-negative) express the reporter gene after scAAV9-GFA-GFP injection. These data thoroughly characterize the gene expression specificity of AAVs fitted with neuronal and astrocyte-selective promoters after intravenous delivery, which will prove useful for central nervous system (CNS) gene therapy approaches in which peripheral expression of transgene is a concern.

Adeno-Associated Virus-Based Gene Therapy for CNS Diseases

Gene therapy is at the cusp of a revolution for treating a large spectrum of CNS disorders by providing a durable therapeutic protein via a single administration. Adeno-associated virus (AAV)-mediated gene transfer is of particular interest as a therapeutic tool because of its safety profile and efficiency in transducing a wide range of cell types. The purpose of this review is to describe the most notable advancements in preclinical and clinical research on AAV-based CNS gene therapy and to discuss prospects for future development based on a new generation of vectors and delivery.