Utility of poly(ethylene glycol) based hydrogels for improved neural cell culture and cell delivery systems

Cell transplant therapy is a very promising treatment for patients afflicted with neurodegenerative diseases and involves replacing dying neurons with fresh fetal tissue that is composed of both new neurons and multipotent neural precursor cells (NPCs). Unfortunately, this therapy is not clinically feasible given the scarcity of fresh donor fetal tissue. The NPCs present in fetal tissue may be a promising renewable cell source because they can be instructed to divide indefinitely in culture, expanding the number of NPCs that are available. Importantly, NPCs can also be instructed to differentiate into the therapeutic neurons needed to treat patients. However, when NPCs are expanded in culture, they increasingly differentiate into glial cells. Glial cell contamination not only introduces many uncharacterized signals into NSC cultures, but when transplanted into the brain, glia can contribute to inflammation and glial scarring. The goal of this project is to identify in vitro culture conditions that can be used to expand fresh NPCs while completely avoiding glial differentiation, only allowing the generation of neuronal progeny with therapeutic potential. The culture system used in this work was chosen carefully, and after exploring the utility of standard neural cell culture systems such as monolayer, neurosphere, and three-dimensional fibrin matrices, an advantageous culture system was identified. The chosen culture system is a synthetic, degradable, photo-polymerizable, poly (ethylene) glycocl (PEG) hydrogel. This thesis experimentally demonstrates advantages of PEG hydrogel culture over the other culture systems including enrichment of the initial cell population for NPCs, clonal expansion capabilities, increased potency of proliferation-stimulating mitogens, decreased reactivity and growth of glial cells, and control over the initiation and orientation of neural process growth. PEG hydrogels were used to directly assess the influence of various ECM proteins and cell cell contacts on NPC fate decisions as they expanded in vitro, and it was determined that cell:cell contacts were the critical culture parameter that needed to be inhibited in order to expand NPCs while completely avoiding glial cell differentiation. Identification of this culture parameter is an important step towards achieving the large-scale production NPCs useful for treating the millions of patients afflicted by neurodegenerative diseases.