Transgenic SOD1 mice as a model for developing amyotrophic lateral sclerosis therapies

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by a loss of motor neurons in the brain (brainstem and cortex) and the spinal cord that leads to a motor neurological symptomatology. Approximately 10% of ALS cases have a familial form of ALS. Among the familial cases, 20% are caused by dominantly inherited mutations (around 100 different mutations) in the protein Cu/Zn superoxide dismutase (SOD1). To date, genetic ALS models on mutated SOD1 (SOD1G93A, SOD1G85R and SOD1G37R) transgenesis in rodents have been successful in recapitulating the main features of the human pathology, especially the loss of spinal or facial motoneurons, the increased astrogliosis, the activation of microglia and the cellular and molecular disruptions in motoneurons. The therapies toward a treatment or cure for ALS have been met with limited success. In the present study, SOD1G93A transgenic mice have been used to test new gene therapies to slow disease progression and pharmacological approach to obtain a better comprehension of the pathological process, more precisely, to define the involvement of microglial activation in the spread of the disease. For the approach by gene therapy, injection of viral vectors in a localized region of central nervous system (CNS) constitutes an excellent tool for the development of new therapies. In the present study, the viral-mediated expression of potential neuroprotective factors was explored in the lumbar spinal cord or facial nucleus of SOD1G93A transgenic mice. As HIV-1-derived lentiviral vectors can efficiently transduce neurons in CNS, these retroviral vectors were used to over-express the neurotrophic factor GDNF (glial cell line-derived neurotrophic factor) to supply a trophic support to lumbar and facial motoneurons, or RNAi molecules specifically targeting the SOD1G93A gene to inhibit the mutant SOD1 expression, the cause of the disease, in the lumbar spinal cord of SOD1G93A transgenic mice. For the study of the level of microglial involvement in the pathology, SOD1G93A transgenic mice had a daily pharmacological treatment with an inhibitor of microglial activation, the minocycline. The present thesis demonstrates that, on the one hand, at the difference of laboratories that delayed the disease progression by intramuscular injection of adenoviral vectors or adenoassociated vectors encoding for GDNF, the intraspinal injection of lentivirus encoding for GDNF did not lead to a protection of lumbar motoneurons and a delay of the disease. But this study showed a significantly rescue of facial motoneurons by the injection of lentivirus encoding for GDNF directly in facial nucleus. A selective vulnerability between motoneurons in facial nucleus and these in lumbar spinal cord has been therefore underlined. On the other hand, we showed that the therapeutic approach to inhibit the mutant SOD1 expression look as the most effective to delay the progression of the ALS pathology. Both studies of gene therapy, compared to others studies using the same therapeutic factors, demonstrated clearly that to optimize a therapeutic treatment, it seems better to act at muscular junction level with a retrograde transport form muscle to motoneuronal bodies of the therapeutic molecule or viral vector. Nevertheless, motoneuron-restricted silencing of mutant SOD1 would be useful for better understanding of neuronal and glial cellular mechanism mediating ALS-linked mutated SOD1 toxicity. Regarding the involvement of microglia in the pathological process, the inhibition of microglial activation by the minocycline treatment, suggests, on the one hand, that microglial activation do not initiate the pathological process and that this microgliosis might be a consequence and triggered by multiple disruptions. On the other hand, that minocycline could protect completely facial motoneurons and partially spinal motoneurons by its anti-apoptotic property. Therapeutic approaches aiming to act directly on the cause of the disease as well as a better comprehension of the role of non-neuronal cells in the pathological process may therefore open new perspectives for the treatment of ALS pathology.

AAV based gene therapy for rare diseases

Cylia Cloé Rochat

Of the seven thousand diseases that are described as rare, 80% of them have an identified genetic cause. With this in the mind, the development of technologies, such as gene therapy, to address the genetic factors involved in these pathologies, might be a game-changing therapeutic approach. Viral delivery of transgenes for RNA interference, DNA editing, or protein overexpression may offer opportunities for novel treatments. In this thesis, we developed adeno-associated virus (AAV) vector systems to tackle two rare diseases: Amyotrophic lateral sclerosis (ALS) caused by gain-of-function mutations in the superoxide dismutase 1 (SOD1) gene and inherited hearing loss disorder caused by mutation in the transmembrane channel-like 1 (TMC1) gene. ALS is a fatal neurodegenerative disease caused by the progressive degeneration of motoneurons (MN). Glial cells have been shown to importantly contribute to the disease. Silencing of the human pathogenic mutated SOD1 protein (SOD1G93A) in MN and/or astrocytes by AAV-mediated expression of microRNA targeting SOD1 has been shown to provide therapeutic benefits in a mouse model which is overexpressing SOD1G93A. However, in order to have an effective treatment, it is important to understand the influence of the therapy on several relevant ALS cell types. In this work, we determined the effects of lowering SOD1G93A expression in astrocytes using an AAV serotype 9, in combination with an astrocyte-specific promoter, in order to express a microRNA targeting SOD1. In the treated mice, we observed a significant improvement of the neuromuscular function and a partial protection of the vulnerable fast-fatigable MN. SOD1 silencing also induced a significant re-innervation of the neuromuscular junctions (NMJ) in the gastrocnemius muscle, observed after the initial phase of denervation, occurring around the age of 60 days. Re-innervation was associated with a grouping of the muscle fibers from the same type, consistent with enhanced axonal plasticity in the treated SOD1G93A mice. Overall, we demonstrated that silencing of SOD1 in astrocytes has an impact on MN plasticity at the level of NMJ, which translates into improved neuromuscular function towards the end stage of the disease. Mutations in the TMC1 gene lead to either complete deafness at birth, or to progressive hearing loss beginning in childhood, depending on the mode of inheritance (autosomal recessive or dominant, respectively). TMC1 is likely a component of the mechanotransduction channel, which is responsible for the transformation of mechanical sound-induced stimuli into electrical signals. This protein has been found to be expressed in the stereociliae of hair cells. In the second part of the thesis, we report on the development of viral tools to deliver a functional copy of the TMC1 gene, or its related paralog TMC2, into hair cells. We engineered several AAV vectors, in combination with different promoters, to identify a suitable combination able to restore TMC expression in the mouse cochlear hair cells, both in vitro and in vivo. We demonstrated, in collaboration with the lab of J. Holt, that when injected in TMC-null mice at birth, these vectors could partially restore loss of auditory function in this mouse model otherwise completely deaf. Overall we showed that AAV-based gene therapy is a promising approach to treat rare genetic disease.

EPFL2017

Adeno-Associated Virus-Mediated Gene Delivery for the Treatment of Amyotrophic Lateral Sclerosis and other Motor Neuron Disorders

Christopher Towne

The delivery of molecules and genes to the central nervous system (CNS) poses a major challenge for the treatment of neurodegenerative diseases. CNS disorders require long-term intervention and the presence of the blood-brain barrier (BBB) restricts the penetration of conventional drugs to the desired target cells. One approach towards stable delivery of therapeutic agents to the CNS is based on the transfer of DNA to target cells using viral vectors; a strategy known as gene therapy. Although viral vectors have provided encouraging results in CNS gene therapy trials for disorders such as Parkinson's disease, the small diffusion of the vector following direct injection into the brain region is not amenable to motor neuron (MN) disorders, such as amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy, that have cells distributed across fifty centimeters of spinal cord. The aim of this thesis was to explore non-invasive approaches for gene delivery to MNs of the spinal cord using adeno-associated viruses (AAV). AAV vectors are powerful gene transfer vehicles due to their low pathogenicity and ability to express genes in neurons for long periods of time. The first part of the thesis focused on ALS, an incurable paralytic disease resulting from a global death of MNs. Using a mouse model of ALS expressing a mutant form of superoxide dismutase 1 (SOD1) that causes the disease in humans, we have delivered genetic silencing instructions that act to degrade the SOD1 messenger RNA prior to its translation into the toxic protein. AAV serotype 6 was used to deliver the SOD1-silencing cassette through noninvasive peripheral routes to target relevant cell types in disease. The vector was administered intravenously following the hypothesis that AAV could infect MNs from the vasculature through traversing the peripheral axons that connect the MNs to the muscle fibers, a process known as retrograde transport. This resulted in infection of MNs across the spinal cord and brain stem, as well as almost total infection of skeletal muscle, another cell type implicated in ALS. Direct injections into multiple muscle groups were also performed, capitalizing on the retrograde transport capability of AAVs, to result in even higher levels of MN infection. These injections demonstrated that AAV serotype 6 could successfully deliver genes to MNs across the breadth of the spinal cord and resulted in protection of individual MN pools from ALS-mediated death. Curiously, however, despite the impressive infection profiles and neuroprotection at various spinal cord levels, neither of the techniques altered the disease course of the animals. These results stress the complexity of gene delivery and suggest that critical thresholds of SOD1-silencing and transduction across various cell types are required to rescue this particular disease model. The second component of the thesis concentrated purely on gene delivery to spinal cord neurons. AAV serotype 6 was injected directly into the muscles of Green African monkeys to determine whether the vector could undergo retrograde transport in larger animals. Indeed, efficient infection of MNs occurred, suggesting that this peripheral non-invasive delivery route is applicable to primates. These findings are not only relevant for human ALS therapy, but considering the similar dimensions of the injected monkeys with human newborns, directly relevant for treatment of infantile disease, spinal muscular atrophy. The last part of the thesis examined the ability of AAV serotype 6 to deliver genes to sensory neurons of spinal cord dorsal root ganglia in a mouse model of chronic pain. This study was initiated following the fortuitous observation of sensory neuron infection in the previous ALS mouse experiments. We examined various administration routes and found that AAV serotype 6 could efficiently deliver genes to sensory neurons in the context of chronic pain, demonstrating that the vector can be used to dissect mechanisms behind this disorder in rodents, and potentially serve as a vehicle for gene therapy towards intractable pain. In conclusion, the present thesis demonstrates that AAV serotype 6 is a powerful gene transfer vehicle for the CNS. Combined with future advances in AAV technology and delivery methods, the work presented here may one day facilitate gene therapy across the spinal cord for the treatment of devastating MN diseases, such as ALS and spinal muscular atrophy, as well as sensory neuron disorders, such as chronic pain.

EPFL2010

Lentiviral and Adeno-Associated Vector-Based Therapy for Motor Neuron Disease Through RNAi

Patrick Aebischer, Christopher Towne

RNAi holds promise for neurodegenerative disorders caused by gain-of-function mutations. We and others have demonstrated proof-of-principle for viral-mediated RNAi in a mouse model of motor neuron disease. Lentivirus and adeno-associated virus have been used to knockdown levels of mutated superoxide dismutase 1 (SOD1) in the G93A SOD1 mouse model of familial amyotrophic lateral sclerosis (fALS) to result in beneficial therapeutic outcomes. This chapter describes the design, production, and titration of lentivirus and adeno-associated virus capable of mediating SOD1 knockdown in vivo. The delivery of the virus to the spinal cord directly, through intraspinal injection, or indirectly, through intramuscular injection, is also described, as well as the methods pertaining to the analysis of spinal cord transduction, SOD1 silencing, and determination of motor neuron protection