Date of Award

2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Bioengineering

First Advisor

D. Kacy Cullen

Second Advisor

Jason A. Burdick

Abstract

Parkinson’s disease is a progressive neurodegenerative disease that affects 1-2% of people over 65, causing significant morbidity across a prolonged and escalating disease course. The classic motor deficits of Parkinson’s disease (PD) are caused by degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc), resulting in the loss of their long-distance axonal projections that modulate the striatum. Contemporary treatments only minimize the symptoms of this disconnection, as there is no approach currently capable of replacing the nigrostriatal pathway. In this dissertation, we applied micro-tissue engineering techniques to create living, implantable micro-tissue engineered neural networks (micro-TENNs) that mimic the architecture and function of the nigrostriatal pathway. These constructs consisted of dopaminergic neurons with long axonal tracts encased within hydrogel micro-columns; lumen extracellular matrix (ECM), growth factors, and end targets were varied to optimize cytoarchitecture and neurite length. Immunocytochemistry, fast scan cyclic voltammetry (FSCV), and imaging analysis were used to investigate the functional characteristics of the constructs in vitro, including their ability to release dopamine and integrate with a population of striatal neurons. Finally, the constructs were transplanted to span the nigrostriatal pathway in a rat model of PD. Immunohistochemistry, FSCV, and behavioral tests were conducted to assess the ability of the micro-TENNs to reconstruct the pathway, release dopamine in the striatum, and improve motor deficits. This work confirmed that dopaminergic micro-TENNs demonstrating discrete somatic and axonal regions could be fabricated to span nigrostriatal pathway in rats. Our worked showed that they had the machinery to release dopamine, recycle dopamine, and functionally integrate with striatal neurons in vitro. In vivo studies established that transplanted micro-TENNs could maintain their cytoarchitecture, extend dopaminergic neurites into the host tissue, and release an appropriate concentration of dopamine. In conclusion, this dissertation showed proof of concept for using dopaminergic micro-TENNs to reconstruct the nigrostriatal pathway and laid the groundwork for future optimization studies necessary for clinical translation. This strategy has the potential to provide a transformative solution to replace lost neuroanatomy and alleviate the cause of motor symptoms for patients afflicted by PD.

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