Comparison of AAV2 and AAV5 in gene transfer in the injured spinal cord of mice

The Neuroprotective Effect of Neural Cell Adhesion Molecule L1 in the Hippocampus of Aged Alzheimer's Disease Model Mice

Alzheimer's disease (AD) is a severe neurodegenerative disorder and the most common form of dementia, causing the loss of cognitive function. Our previous study has shown, using a doubly mutated mouse model of AD (APP/PS1), that the neural adhesion molecule L1 directly binds amyloid peptides and decreases plaque load and gliosis when injected as an adeno-associated virus construct (AAV-L1) into APP/PS1 mice. In this study, we microinjected AAV-L1, using a Hamilton syringe, directly into the 3-month-old APP/PS1 mouse hippocampus and waited for a year until significant neurodegeneration developed. We stereologically counted the principal neurons and parvalbumin-positive interneurons in the hippocampus, estimated the density of inhibitory synapses around principal cells, and compared the AAV-L1 injection models with control injections of green fluorescent protein (AAV-GFP) and the wild-type hippocampus. Our results show that there is a significant loss of granule cells in the dentate gyrus of the APP/PS1 mice, which was improved by AAV-L1 injection, compared with the AAV-GFP controls (p < 0.05). There is also a generalized loss of parvalbumin-positive interneurons in the hippocampus of APP/PS1 mice, which is ameliorated by AAV-L1 injection, compared with the AAV-GFP controls (p < 0.05). Additionally, AAV-L1 injection promotes the survival of inhibitory synapses around the principal cells compared with AAV-GFP controls in all three hippocampal subfields (p < 0.01). Our results indicate that L1 promotes neuronal survival and protects the synapses in an AD mouse model, which could have therapeutic implications.

AAV6 mediated Gsx1 expression in neural stem progenitor cells promotes neurogenesis and restores locomotor function after contusion spinal cord injury

Genomic screened homeobox 1 (Gsx1 or Gsh1) is a neurogenic transcription factor required for the generation of excitatory and inhibitory interneurons during spinal cord development. In the adult, lentivirus (LV) mediated Gsx1 expression promotes neural regeneration and functional locomotor recovery in a mouse model of lateral hemisection spinal cord injury (SCI). The LV delivery method is clinically unsafe due to insertional mutations to the host DNA. In addition, the most common clinical case of SCI is contusion/compression. In this study, we identify that adeno-associated virus serotype 6 (AAV6) preferentially infects neural stem/progenitor cells (NSPCs) in the injured spinal cord. Using a rat model of contusion SCI, we demonstrate that AAV6 mediated Gsx1 expression promotes neurogenesis, increases the number of neuroblasts/immature neurons, restores excitatory/inhibitory neuron balance and serotonergic neuronal activity through the lesion core, and promotes locomotor functional recovery. Our findings support that AAV6 preferentially targets NSPCs for gene delivery and confirmed Gsx1 efficacy in clinically relevant rat model of contusion SCI.

L1 Cell Adhesion Molecule Overexpression Down Regulates Phosphacan and Up Regulates Structural Plasticity-Related Genes Rostral and Caudal to the Complete Spinal Cord Transection

L1 cell adhesion molecule (L1CAM) supports spinal cord cellular milieu after contusion and compression lesions, contributing to neuroprotection, promoting axonal outgrowth, and reducing outgrowth-inhibitory molecules in lesion proximity. We extended investigations into L1CAM molecular targets and explored long-distance effects of L1CAM rostral and caudal to complete spinal cord transection (SCT) in adult rats. L1CAM overexpression in neurons and glia after Th10/Th11 SCT was achieved using adeno-associated viral vector serotype 5 (AAV5) injected into an L1-lumbar segment immediately after transection. At 5 weeks, a L1CAM mRNA profound decrease detected rostral and caudal to the transection site was alleviated by AAV5-L1CAM treatment, with increased endogenous L1CAM rostral to the SCT. Transected corticospinal tract fibers showed attenuated retraction after treatment, accompanied by a multi-segmental increase of lesion-reduced expression of adenylate cyclase 1 (Adcy1), synaptophysin, growth-associated protein 43, and myelin basic protein genes caudal to transection, and Adcy1 rostral to transection. In parallel, chondroitin sulfate proteoglycan phosphacan elevated after SCT was downregulated after treatment. Low-molecular L1CAM isoforms generated after spinalization indicated the involvement of sheddases in L1CAM processing and long-distance effects. A disintegrin and metalloproteinase (ADAM)10 sheddase immunoreactivity, stronger in AAV5-L1CAM than AAV5- enhanced green fluorescent protein (EGFP)-transduced motoneurons indicated local ADAM10 upregulation by L1CAM. The results suggest that increased L1CAM availability and penetration of diffusible L1CAM fragments post-lesion induce both local and long-distance neuronal and glial responses toward better neuronal maintenance, neurite growth, and myelination. Despite the fact that intervention promoted beneficial molecular changes, kinematic analysis of hindlimb movements showed minor improvement, indicating that spinalized rats require longer L1CAM treatment to regain locomotor functions.

Considerations related to the use of short neuropeptide promoters in viral vectors targeting hypothalamic neurons

Targeting specific neuronal cell types is a major challenge for unraveling their function and utilizing specific cells for gene therapy strategies. Viral vector tools are widely used to target specific cells or circuits for these purposes. Here, we use viral vectors with short promoters of neuropeptide genes to target distinct neuronal populations in the hypothalamus of rats and mice. We show that lowering the amount of genomic copies is effective in increasing specificity of a melanin-concentrating hormone promoter. However, since too low titers reduce transduction efficacy, there is an optimal titer for achieving high specificity and sufficient efficacy. Other previously identified neuropeptide promoters as those for oxytocin and orexin require further sequence optimization to increase target specificity. We conclude that promoter-driven viral vectors should be used with caution in order to target cells specifically.

Remodeling of lumbar motor circuitry remote to a thoracic spinal cord injury promotes locomotor recovery

Retrogradely-transported neurotrophin signaling plays an important role in regulating neural circuit specificity. Here we investigated whether targeted delivery of neurotrophin-3 (NT-3) to lumbar motoneurons (MNs) caudal to a thoracic (T10) contusive spinal cord injury (SCI) could modulate dendritic patterning and synapse formation of the lumbar MNs. In vitro, Adeno-associated virus serotype two overexpressing NT-3 (AAV-NT-3) induced NT-3 expression and neurite outgrowth in cultured spinal cord neurons. In vivo, targeted delivery of AAV-NT-3 into transiently demyelinated adult mouse sciatic nerves led to the retrograde transportation of NT-3 to the lumbar MNs, significantly attenuating SCI-induced lumbar MN dendritic atrophy. NT-3 enhanced sprouting and synaptic formation of descending serotonergic, dopaminergic, and propriospinal axons on lumbar MNs, parallel to improved behavioral recovery. Thus, retrogradely transported NT-3 stimulated remodeling of lumbar neural circuitry and synaptic connectivity remote to a thoracic SCI, supporting a role for retrograde transport of NT-3 as a potential therapeutic strategy for SCI.

Controlling AAV Tropism in the Nervous System with Natural and Engineered Capsids

More than one hundred naturally occurring variants of adeno-associated virus (AAV) have been identified, and this library has been further expanded by an array of techniques for modification of the viral capsid. AAV capsid variants possess unique antigenic profiles and demonstrate distinct cellular tropisms driven by differences in receptor binding. AAV capsids can be chemically modified to alter tropism, can be produced as hybrid vectors that combine the properties of multiple serotypes, and can carry peptide insertions that introduce novel receptor-binding activity. Furthermore, directed evolution of shuffled genome libraries can identify engineered variants with unique properties, and rational modification of the viral capsid can alter tropism, reduce blockage by neutralizing antibodies, or enhance transduction efficiency. This large number of AAV variants and engineered capsids provides a varied toolkit for gene delivery to the CNS and retina, with specialized vectors available for many applications, but selecting a capsid variant from the array of available vectors can be difficult. This chapter describes the unique properties of a range of AAV variants and engineered capsids, and provides a guide for selecting the appropriate vector for specific applications in the CNS and retina.

Adeno-associated virus (AAV) gene therapy for neurological disease

Diseases of the central nervous system (CNS) have provided enormous opportunities for the therapeutic application of viral vector gene transfer. Adeno-associated virus (AAV) has been the vector of choice in recent clinical trials of neurological disease, including Parkinson's and Alzheimer's disease, due to the safety, efficacy, and stability of AAV gene transfer to the CNS. This review highlights the strategies employed for improving direct and peripheral targeting of therapeutic vectors to CNS tissue, and considers the significance of cellular and tissue transduction specificity, transgene regulation, and other variables that influence achievement of successful therapeutic goals. This article is part of the Special Issue entitled 'New Targets and Approaches to the Treatment of Epilepsy'.