Assessing whether the adult neocortex can incorporate new projection neurons. The neocortex is the seat of our highest cognitive functions. Neocortical projection neurons can be lost due to neurodegenerative diseases and once lost they are not normally replaced, leading to permanent functional deficits. There are a number of therapies in development to alleviate the symptoms and retard the onset of neurodegenerative diseases, such as Alzheimer's, in which neocortical projection neurons are lost. However, additional treatment, such as the replacement of cortical projection neurons, will eventually be necessary to return patients to pre-disease states. Developing strategies to replace lost projection neurons is a daunting task because of the complexity and size of the neocortex. Previous attempts at replacing projection neurons in the neocortex using several types of transplanted neural stem or precursor cells have not provided viable strategies. One reason for the limited integration of new neurons is that thus far transplanted cells have remained primarily in a clump at the transplant site. To achieve the goal of functionally integrating new projection neurons throughout broad areas of the neocortex, a novel strategy is required that takes into account cell dispersion. The central aim of this proposal is to develop an approach for introducing new, widely dispersed, projection neurons in the adult neocortex, providing a paradigm for testing whether they can functionally integrate. Our preliminary data suggest that we can achieve the wide dispersion of precursors in the adult neocortex and that new neurons can extend long projections along their normal tracks and to their normal targets. In a first aim, we are engineering precursors, which have a natural ability to disperse in the adul neocortex, with doxycycline-inducible transcription factors that will, once the precursors have dispersed, allow their reprogramming to a cortical projection neuron fate. In a second aim, we will test the electrophysiological response of new neurons in the barrel cortex to stimulation of thalamic neurons and to whisker stimulation;we will also test the ability of new neurons in the premotor cortex to stimulate striatal neurons. For both aims, we will assess the ability of transplanted neuronal cells to disperse and integrate in a healthy environment compared with one in which projection neurons are degenerating.
Although there are a number of therapies in the works to alleviate the symptoms and retard the onset of neurodegenerative diseases, such as Alzheimer's disease (AD), there is currently no way to replace the lost neurons and return afflicted individuals to a pre-disease state. Strategies using neural stem cells to replace lost neurons in the neocortex, an area of the brain in which neurons degenerate in AD for example, have thus far not been successful. One key impediment to success has been the inability of the transplanted stem or precursor cells to disperse throughout the neocortex. The first goal of this proposal is to explore the possibility of using a novel cell replacement strategy that overcomes the problem of dispersal, and is potentially applicable to a wide range of neurodegenerative disorders. We will use a subtype of neural precursors (MGE cells) that are attracted to the neocortex and disperse widely throughout it. These precursors, however, give rise to a type of neuron that is different than the ones that are primarily lost in AD and other diseases. Therefore, we will engineer these MGE precursor cells so that once they have dispersed throughout the neocortex, they generate the appropriate type of neuron to replace the lost ones. We are testing this approach using a mouse model. The second goal is to begin to assess the potential of new neurons to physiologically integrate into the adult neocortex, either healthy ones or those undergoing neuronal degeneration. Achieving our aims will pave the way for further studies examining whether newly introduced neurons can remedy cortical-based behavioral deficits in animal models and finally for treating disorders in human patients in which neocortical neurons are lost.
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