Gene transfer to the CNS using recombinant adeno-associated virus

Retro-Orbital Delivery of AAVs for CNS Wide Astrocyte Targeting

Viral vector-mediated astrocyte targeting in live mice is a popular and valuable method to investigate astrocyte function in the context of intact neural circuits and complex brain physiology. Targeted genetic manipulation and functional investigation of this cell population can be accomplished by utilizing cell type-specific promoters to drive adeno-associated virus (AAV)-mediated transgene expression specifically in astrocytes. Here, we provide a comprehensive protocol for non-invasive retro-orbital (RO) administration of blood-brain barrier (BBB)-crossing AAVs in neonatal and adult mice, such as AAV-PHP.B, AAV-PHP.eB, and AAV.CAP-B22, which results in central nervous system (CNS)-wide transduction. Key procedures outlined include the preparation of AAV solutions for injection, a modified two-handed injection technique for precise and consistent RO injections, and a training strategy to practice mock RO injections using non-toxic dyes. This protocol serves as a valuable resource for researchers interested in exploring the roles of astrocytes in brain functions and neurological disorders.

CRISPR-CasRx-mediated disruption of Aqp1/Adrb2/Rock1/Rock2 genes reduces intraocular pressure and retinal ganglion cell damage in mice

Glaucoma affects approximately 80 million individuals worldwide, a condition for which current treatment options are inadequate. The primary risk factor for glaucoma is elevated intraocular pressure. Intraocular pressure is determined by the balance between the secretion and outflow of aqueous humor. Here we show that using the RNA interference tool CasRx based on shH10 adenovirus-associated virus can reduce the expression of the aqueous humor circulation related genes Rock1 and Rock2, as well as aquaporin 1 and β2 adrenergic receptor in female mice. This significantly reduced intraocular pressure in female mice and provided protection to the retina ganglion cells, ultimately delaying disease progression. In addition, we elucidated the mechanisms by which the knockdown of Rock1 and Rock2, or aquaporin 1 and β2 adrenergic receptor in female mice, reduces the intraocular pressure and secures the retina ganglion cells by single-cell sequencing.

A shedding analysis after AAV8 CNS injection revealed fragmented viral DNA without evidence of functional AAV particles in mice

Adeno-associated viruses (AAV) are commonly used in the scientific field due to their diverse application range. However, AAV shedding, the release of virions from the host organism, can impact the safety of AAV-based approaches. An increasing number of authorities require the characterization of vector shedding in clinical trials. Recently, shedding of transduced laboratory animals has also gained attention regarding the necessary disposal measures of their waste products. However, no explicit international regulations for AAV-shedding waste exist. Generating insights into shedding dynamics becomes increasingly relevant to help authorities develop adequate regulations. To date, knowledge of AAV vector shedding in mice is very limited. Moreover, confirmation of functional shed AAV particles in mice is missing. Therefore, we examined feces, urine, and saliva of mice after CNS injection with AAV2/8. It revealed the presence of viral DNA fragments via qPCR for up to 4 days after injection. To examine AAV functionality we performed nested PCR and could not detect full-length viral genomes in any but two collected feces samples. Furthermore, a functional infection assay did not reveal evidence of intact AAV particles. Our findings are supposed to contribute murine shedding data as a foundation to help establish still lacking adequate biosafety regulations in the context of AAV shedding.

No evidence from complementary data sources of a direct glutamatergic projection from the mouse anterior cingulate area to the hippocampal formation

The connectivity and interplay between the prefrontal cortex and hippocampus underpin various key cognitive processes, with changes in these interactions being implicated in both neurodevelopmental and neurodegenerative conditions. Understanding the precise cellular connections through which this circuit is organised is, therefore, vital for understanding these same processes. Overturning earlier findings, a recent study described a novel excitatory projection from anterior cingulate area to dorsal hippocampus. We sought to validate this unexpected finding using multiple, complementary methods: anterograde and retrograde anatomical tracing, using anterograde and retrograde adeno-associated viral vectors, monosynaptic rabies tracing, and the Fast Blue classical tracer. Additionally, an extensive data search of the Allen Projection Brain Atlas database was conducted to find the stated projection within any of the deposited anatomical studies as an independent verification of our own results. However, we failed to find any evidence of a direct, monosynaptic glutamatergic projection from mouse anterior cingulate cortex to the hippocampus proper.

MicroRNA-335-5p suppresses voltage-gated sodium channel expression and may be a target for seizure control

There remains an urgent need for new therapies for treatment-resistant epilepsy. Sodium channel blockers are effective for seizure control in common forms of epilepsy, but loss of sodium channel function underlies some genetic forms of epilepsy. Approaches that provide bidirectional control of sodium channel expression are needed. MicroRNAs (miRNA) are small noncoding RNAs which negatively regulate gene expression. Here we show that genome-wide miRNA screening of hippocampal tissue from a rat epilepsy model, mice treated with the antiseizure medicine cannabidiol, and plasma from patients with treatment-resistant epilepsy, converge on a single target-miR-335-5p. Pathway analysis on predicted and validated miR-335-5p targets identified multiple voltage-gated sodium channels (VGSCs). Intracerebroventricular injection of antisense oligonucleotides against miR-335-5p resulted in upregulation of Scn1a, Scn2a, and Scn3a in the mouse brain and an increased action potential rising phase and greater excitability of hippocampal pyramidal neurons in brain slice recordings, consistent with VGSCs as functional targets of miR-335-5p. Blocking miR-335-5p also increased voltage-gated sodium currents and SCN1A, SCN2A, and SCN3A expression in human induced pluripotent stem cell-derived neurons. Inhibition of miR-335-5p increased susceptibility to tonic-clonic seizures in the pentylenetetrazol seizure model, whereas adeno-associated virus 9-mediated overexpression of miR-335-5p reduced seizure severity and improved survival. These studies suggest modulation of miR-335-5p may be a means to regulate VGSCs and affect neuronal excitability and seizures. Changes to miR-335-5p may reflect compensatory mechanisms to control excitability and could provide biomarker or therapeutic strategies for different types of treatment-resistant epilepsy.

A genetic tool for the longitudinal study of a subset of post-inflammatory reactive astrocytes

Astrocytes are vital support cells that ensure proper brain function. In brain disease, astrocytes reprogram into a reactive state that alters many of their cellular roles. A long-standing question in the field is whether downregulation of reactive astrocyte (RA) markers during resolution of inflammation is because these astrocytes revert back to a non-reactive state or die and are replaced. This has proven difficult to answer mainly because existing genetic tools cannot distinguish between healthy versus RAs. Here we describe the generation of an inducible genetic tool that can be used to specifically target and label a subset of RAs. Longitudinal analysis of an acute inflammation model using this tool revealed that the previously observed downregulation of RA markers after inflammation is likely due to changes in gene expression and not because of cell death. Our findings suggest that cellular changes associated with astrogliosis after acute inflammation are largely reversible.

Leucine-Rich Repeats and Transmembrane Domain 2 Controls Protein Sorting in the Striatal Projection System and Its Deficiency Causes Disturbances in Motor Responses and Monoamine Dynamics

The striatum is involved in action selection, and its disturbance can cause movement disorders. Here, we show that leucine-rich repeats and transmembrane domain 2 (Lrtm2) controls protein sorting in striatal projection systems, and its deficiency causes disturbances in monoamine dynamics and behavior. The Lrtm2 protein was broadly detected in the brain, but it was enhanced in the olfactory bulb and dorsal striatum. Immunostaining revealed a strong signal in striatal projection output, including GABAergic presynaptic boutons of the SNr. In subcellular fractionation, Lrtm2 was abundantly recovered in the synaptic plasma membrane fraction, synaptic vesicle fraction, and microsome fraction. Lrtm2 KO mice exhibited altered motor responses in both voluntary explorations and forced exercise. Dopamine metabolite content was decreased in the dorsal striatum and hypothalamus, and serotonin turnover increased in the dorsal striatum. The prefrontal cortex showed age-dependent changes in dopamine metabolites. The distribution of glutamate decarboxylase 67 (GAD67) protein and gamma-aminobutyric acid receptor type B receptor 1 (GABA_BR1) protein was altered in the dorsal striatum. In cultured neurons, wild-type Lrtm2 protein enhanced axon trafficking of GAD67-GFP and GABA_BR1-GFP whereas such activity was defective in sorting signal-abolished Lrtm2 mutant proteins. The topical expression of hemagglutinin-epitope-tag (HA)-Lrtm2 and a protein sorting signal abolished HA-Lrtm2 mutant differentially affected GABA_BR1 protein distribution in the dorsal striatum. These results suggest that Lrtm2 is an essential component of striatal projection neurons, contributing to a better understanding of striatal pathophysiology.

Delivering gene therapy for mucopolysaccharide diseases

Mucopolysaccharide diseases are a group of paediatric inherited lysosomal storage diseases that are caused by enzyme deficiencies, leading to a build-up of glycosaminoglycans (GAGs) throughout the body. Patients have severely shortened lifespans with a wide range of symptoms including inflammation, bone and joint, cardiac, respiratory and neurological disease. Current treatment approaches for MPS disorders revolve around two main strategies. Enzyme replacement therapy (ERT) is efficacious in treating somatic symptoms but its effect is limited for neurological functions. Haematopoietic stem cell transplant (HSCT) has the potential to cross the BBB through monocyte trafficking, however delivered enzyme doses limit its use almost exclusively to MPSI Hurler. Gene therapy is an emerging therapeutic strategy for the treatment of MPS disease. In this review, we will discuss the various vectors that are being utilised for gene therapy in MPS as well as some of the most recent gene-editing approaches undergoing pre-clinical and clinical development.

Chemogenetics drives paradigm change in the investigation of behavioral circuits and neural mechanisms underlying drug action

Recent developments in chemogenetic approaches to the investigation of brain function have ushered in a paradigm change in the strategy for drug and behavior research and clinical drug-based medications. As the nature of the drug action is based on humoral regulation, it is a challenge to identify the neuronal mechanisms responsible for the expression of certain targeted behavior induced by drug application. The development of chemogenetic approaches has allowed researchers to control neural activities in targeted neurons through a toolbox, including engineered G protein-coupled receptors or ligand-gated ion channels together with exogenously inert synthetic ligands. This review provides a brief overview of the chemogenetics toolbox with an emphasis on the DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) technique used in rodent models, which is applicable to the investigation of how specific neural circuits regulate behavioral processes. The use of chemogenetics has had a significant impact on basic neuroscience for a better understanding of the relationships between brain activity and the expression of behaviors with cell- and circuit-specific orders. Furthermore, chemogenetics is potentially a useful tool to deconstruct the neuropathological mechanisms of mental diseases and its regulation by drug, and provide us with transformative therapeutics with medication. We also review recent findings in the use of chemogenetic techniques to uncover functional circuit connections of serotonergic neurons in rodent models.

SP1 activated-lncRNA SNHG1 mediates the development of epilepsy via miR-154-5p/TLR5 axis

BACKGROUND

Epilepsy is a one of the most frequent serious neurological disorders characterized by enduring and unprovoked seizures. The treatments to epilepsy are very limited and many patients are even resistant to current medications due to the elusive pathogenesis. Here, we sought to investigate the functions of lncRNA SNHG1 and miR-154-5p in epilepsy.

METHODS

We employed both in vivo mouse model and in vitro cell model to study epilepsy. H&E staining and Nissl staining were used to examine the morphology of hippocampus and measure neuronal injury, respectively. TUNEL staining and flow cytometry were performed to determine cell apoptosis. Caspase-3 activity assay kit was used to assess caspase-3 activity. RT-qPCR and western blot were conducted to measure the levels of SNHG1, miR-154-5p, TLR5, and SP1, respectively. Dual luciferase reporter assay was employed to validate the binding relationship of SNHG1/miR-154-5p and miR-154-5p/TLR5. ChIP assay was performed to confirm the transcriptional regulation of SP1 on SNHG1.

RESULTS

Elevated SNHG1 and decreased miR-154-5p were observed in both in vivo mouse model and in vitro cell model of epilepsy. Knockdown of SNHG1 or transfection with miR-154-5p mimics significantly ameliorated Mg2+ free-induced neuronal injury in SH-SY5Y cells. SNHG1 acted as a sponge of miR-154-5p. Moreover, SNHG1 promoted neuronal injury via acting as a miR-154-5p sponge to disinhibit TLR5. Additionally, SP1 activated the transcriptional activity of SNHG1.

CONCLUSION

In summary, SP1 transcriptionally activated-SNHG1 contributes to the development of epilepsy via directly regulating miR-154-5p/TLR5 axis, which provides novel targets in treatment of epilepsy.

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.

A Simple, Two-Step, Small-Scale Purification of Recombinant Adeno-Associated Viruses

Recombinant adeno-associated viruses (rAAVs) are robust and versatile tools for in vivo gene delivery. Natural and designer capsid variations in rAAVs allow for targeted gene delivery to specific cell types. Low immunogenicity and lack of pathogenesis also add to the popularity of this virus as an innocuous gene delivery vector for gene therapy. rAAVs are routinely used to express recombinases, sensors, detectors, CRISPR-Cas9 components, or to simply overexpress a gene of interest for functional studies. High production demand has given rise to multiple platforms for the production and purification of rAAVs. However, most platforms rely heavily on large amounts of starting material and multiple purification steps to produce highly purified viral particles. Often, researchers require several small-scale purified rAAVs. Here, we describe a simple and efficient technique for purification of recombinant rAAVs from small amounts of starting material in a two-step purification method. In this method, rAAVs are released into the packaging cell medium using high salt concentration, pelleted by ultracentrifugation to remove soluble impurities. Then, the resuspended pellet is purified using a protein spin-concentrator. In this protocol, we modify the conventional rAAV purification methods to eliminate the need for fraction collection and the labor-intensive steps for evaluating the titer and purity of individual fractions. The resulting rAAV preparations are comparable in titer and purity to commercially available samples. This simplified process can be used to generate highly purified rAAV particles on a small scale, thereby saving resources, generating less waste, and reducing a laboratory's environmental footprint.

Adeno-Associated Virus Technologies and Methods for Targeted Neuronal Manipulation

Cell-type-specific expression of molecular tools and sensors is critical to construct circuit diagrams and to investigate the activity and function of neurons within the nervous system. Strategies for targeted manipulation include combinations of classical genetic tools such as Cre/loxP and Flp/FRT, use of cis-regulatory elements, targeted knock-in transgenic mice, and gene delivery by AAV and other viral vectors. The combination of these complex technologies with the goal of precise neuronal targeting is a challenge in the lab. This report will discuss the theoretical and practical aspects of combining current technologies and establish best practices for achieving targeted manipulation of specific cell types. Novel applications and tools, as well as areas for development, will be envisioned and discussed.

Fluorescent Biosensors for Neurotransmission and Neuromodulation: Engineering and Applications

Understanding how neuronal activity patterns in the brain correlate with complex behavior is one of the primary goals of modern neuroscience. Chemical transmission is the major way of communication between neurons, however, traditional methods of detection of neurotransmitter and neuromodulator transients in mammalian brain lack spatiotemporal precision. Modern fluorescent biosensors for neurotransmitters and neuromodulators allow monitoring chemical transmission in vivo with millisecond precision and single cell resolution. Changes in the fluorescent biosensor brightness occur upon neurotransmitter binding and can be detected using fiber photometry, stationary microscopy and miniaturized head-mounted microscopes. Biosensors can be expressed in the animal brain using adeno-associated viral vectors, and their cell-specific expression can be achieved with Cre-recombinase expressing animals. Although initially fluorescent biosensors for chemical transmission were represented by glutamate biosensors, nowadays biosensors for GABA, acetylcholine, glycine, norepinephrine, and dopamine are available as well. In this review, we overview functioning principles of existing intensiometric and ratiometric biosensors and provide brief insight into the variety of neurotransmitter-binding proteins from bacteria, plants, and eukaryotes including G-protein coupled receptors, which may serve as neurotransmitter-binding scaffolds. We next describe a workflow for development of neurotransmitter and neuromodulator biosensors. We then discuss advanced setups for functional imaging of neurotransmitter transients in the brain of awake freely moving animals. We conclude by providing application examples of biosensors for the studies of complex behavior with the single-neuron precision.

Global CNS transduction of adult mice by intravenously delivered rAAVrh.8 and rAAVrh.10 and nonhuman primates by rAAVrh.10

Some recombinant adeno-associated viruses (rAAVs) can cross the neonatal blood-brain barrier (BBB) and efficiently transduce cells of the central nervous system (CNS). However, in the adult CNS, transduction levels by systemically delivered rAAVs are significantly reduced, limiting their potential for CNS gene therapy. Here, we characterized 12 different rAAVEGFPs in the adult mouse CNS following intravenous delivery. We show that the capability of crossing the adult BBB and achieving widespread CNS transduction is a common character of AAV serotypes tested. Of note, rAAVrh.8 is the leading vector for robust global transduction of glial and neuronal cell types in regions of clinical importance such as cortex, caudate-putamen, hippocampus, corpus callosum, and substantia nigra. It also displays reduced peripheral tissue tropism compared to other leading vectors. Additionally, we evaluated rAAVrh.10 with and without microRNA (miRNA)-regulated expressional detargeting from peripheral tissues for systemic gene delivery to the CNS in marmosets. Our results indicate that rAAVrh.8, along with rh.10 and 9, hold the best promise for developing novel therapeutic strategies to treat neurological diseases in the adult patient population. Additionally, systemically delivered rAAVrh.10 can transduce the CNS efficiently, and its transgene expression can be limited in the periphery by endogenous miRNAs in adult marmosets.