Human Tissue-Engineered Nigrostriatal Pathway Encased In Hyaluronic Acid For Axon Tract Reconstruction In Parkinson\u27s Disease

The motor symptoms of Parkinson’s disease (PD) are caused by the loss of dopamine in the striatum that occurs after the death of dopaminergic neurons in the substantia nigra and their axon fibers along the nigrostriatal pathway. The ideal treatment strategy would rebuild the neuronal and axonal structure of the pathway in an anatomically correct way, which may lead to better restoration of basal ganglia connectivity and dopamine regulation. We developed a reconstruction strategy termed the tissue-engineered nigrostriatal pathway (TE-NSP), which consists of a tubular hydrogel with a collagen/laminin core that encases an aggregate of dopaminergic neurons and their axon tracts. The TE-NSPs are fabricated in vitro to resemble the nigrostriatal pathway for subsequent implantation to restore the pathway. Here we sought to advance the TE-NSPs in terms of their hydrogel encasement, cell source, and clinical translatability. The TE-NSPs were fabricated with hyaluronic acid (HA) hydrogels as a more bioactive and tunable encasement, human iPSC-derived dopaminergic neurons as a clinical cell source, and dimensions fit for various cell densities and axon lengths. We implanted these human TE-NSPs in a rat model of PD and characterized the animals with histology, voltammetry for striatal dopamine release, and motor function tests. HA hydrogels and human iPSC-derived neurons could be used to create TE-NSPs that had a nigrostriatal-like cytoarchitecture, dimensions matching rat brain scales and clinical design criteria, proper dopaminergic phenotypes, and the capacity for dopamine release and innervation of striatal neurons. Implanted TE-NSPs exhibited robust survival, preservation of axon tract integrity, and dopamine release functionality even after 6 months. Rat-scale TE-NSPs led to localized improvements in dopamine and innervation in the dorsal striatum, while constructs with quasi-human dimensions exhibited significant growth into the striatum at 6 months. Further work is needed to show definitive therapeutic benefits and to understand the mechanism of reconstruction with TE-NSPs. Still, this dissertation represents the first demonstration of the replacement of a long-distance brain pathway in a preclinical model using engineered micro-tissue made with human cells