The Emory ALS Center: Molecular and Cellular Motor Neuron Neurosurgery
Boulis Laboratory
The Boulis Laboratory is particularly interested in providing neurosurgical
approaches to the treatment of the brain, spinal cord, and nerves of patients with motor neuron disease. To date these approaches have largely focused on gene therapy and cell transplantation. Gene Therapy projects have attempted to define novel methods for the delivery of therapeutic genes to motor neurons, as well as testing specific genes for motor neuron protection and axonal regeneration.
Attempts to deliver genes to motor neurons have spanned molecular and surgical approaches. Our laboratory originally tested the distribution of gene expression following direct spinal cord injection of viruses genetically engineered to safely deliver genes. Investigations have involved adenoviral vectors, adeno-associated viral vectors, and lentiviral vectors. We have gone on to develop devices that enable the injection of vectors into the human lumbar and cervical spinal cord. These devices have been tested together with novel techniques borrowed from deep brain mapping to target the spinal cord ventral horn where motor neurons dwell. We have shown that spinal cord injection can be accomplished safely with the use of these techniques and devices. Current modifications of the devices are ongoing (Figure 1).
Parallel attempts have been made to leverage axonal transport to deliver therapeutic genes to motor neurons through peripheral nerve and muscle injections. We originally described the tendency of non-neurotropic vectors to undergo this process (Figure 2). The failure of initial attempts to scale this approach up for application to humans has led to the attempts to engineer the coat of viral vectors to enhance their uptake into motor neuron axons. Vectors have been constructed that link to the targeting domain of tetanus toxin, hence improving binding and uptake into axon terminals. Further work in this area led to the discovery of novel small peptides that mimic the binding properties of tetanus. The genetic code for these peptides have since been inserted into the DNA encoding the coat of adeno-associated virus, enhancing the ability of the virus to deliver therapy to motor neurons (Figure 3). Currently, we are refining these techniques of molecular vector engineering in collaboration with the Universities of North Carolina and Ohio.
Our attempts to protect motor neurons through gene delivery have spanned a variety of approaches. Our work has largely employed the genes for neural growth factors and intracellular proteins proven to prevent programmed cell death (apoptosis). In particular, we have shown that the delivery of the IGF-I gene can prolong motor neuron survival and axonal regeneration in cell culture models. In addition, we have shown that the genes for Bcl-xL and XIAP, both intracellular inhibitors of programmed cell death can protect motor neurons in culture. More recent work has examined the potential to employ these strategies in rodent models of ALS. This work has been done in collaboration with Ceregene Inc and Sangamo Biosciences. Sangamo’s technology provides a new approach that uses zinc finger proteins to increase the production of the bodies own growth factor genes.
Finally, in collaboration with the University of Wisconsin has allowed our laboratory to begin testing our techniques for direct spinal cord injection as a means for the delivery of therapeutic cells. These cells include astrocytes derived from human neural progenitors that have been engineered to secrete neural growth factors. More recent collaborations have attempted to assist in the development of transplant strategies for human motor neurons manufactured from embryonic stem cells.
