Transplantable Micro-Tissue Engineered Neural Networks to Restore the Nigrostriatal Pathway in Parkinson's Disease

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ABSTRACT Parkinson's disease (PD) is a progressive neurodegenerative disease that affects 1-2% of people over 65. The classic motor symptoms of PD result from selective degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc), resulting in a loss of their long-projecting axonal inputs to the striatum. Current treatment strategies [e.g., dopamine replacement, deep brain stimulation (DBS)] can only minimize the symptoms of nigrostriatal degeneration, not directly replace the lost pathway. Therefore, we propose a novel regenerative medicine solution, whereby custom-built micro-tissue engineered neural networks (TENNs) are transplanted to physically replace the axonal connections from the SNpc to the striatum. Specifically, micro- TENNs will be transplanted in rodent and porcine models of PD to directly replace SNpc neurons, restore axonal inputs to the striatum, and ameliorate motor deficits. Our overarching hypothesis is that preformed micro-TENNs comprised of dopaminergic neurons and long-projecting axonal tracts will survive, synaptically integrate, and thereby physically reconstruct the nigrostriatal pathway to restore motor function in models of nigrostriatal deafferentation. To test this hypothesis, we propose three aims: (1) Determine optimal in vitro techniques to create dopaminergic micro-TENNs, using both differentiated neurons as well as stem-cell derived neurons; (2) Assess micro-TENN capabilities to reconstruct the nigrostriatal pathway, restore dopaminergic inputs, and ameliorate motor symptoms rodents; (3) Apply human-scale micro-TENNs to reconstruct the nigrostriatal pathway in swine. Living dopaminergic micro-TENNs will be constructed with an architecture consisting of a discrete population of neurons with unidirectional long-projecting axonal tracts. Micro-TENN health, phenotype, structure, and function will be optimized in vitro. To enable clinical translation, we will construct human-scale micro-TENNs using human stem cell derived dopaminergic neurons. Preformed constructs will be stereotactically microinjected into neurodegenerative PD rat and pig models to assess circuit reconstruction and motor symptom amelioration. Nigrostriatal pathway reconstruction will be assessed using behavioral, imaging, electrophysiological, and histological outcomes. The proposed work will establish the future clinical potential of personalized micro-TENNs to ameliorate PD motor symptoms by restoring the dopaminergic nigrostriatal pathway. Our micro-tissue engineering strategy addresses a crucial gap in clinical treatment by providing a means to directly replace the nigrostriatal pathway and, as a result, restore motor function following PD neurodegeneration. By virtue of their long axonal tracts, micro-TENNs may be capable of replacing degenerated circuitry to restore dopaminergic inputs to the striatum. Our custom process to generate micro-TENNs enables a precisely engineered structure where the number of neurons and generation of dopamine can be known prior to implantation, thus, alleviating issues of inconsistency historically seen in fetal tissue grafts. Therefore, micro-TENNs may provide a transformative and scalable solution to permanently replace lost neuroanatomy and alleviate the cause of motor symptoms for the millions of patient afflicted by PD.