Cell Responsive Hydrogels to Improve Functional Recovery after Spinal Cord Injury

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 DESCRIPTION (provided by applicant): Throughout tissue development and homeostasis, cells dynamically interact with the extracellular matrix (ECM). However, most materials developed to regulate stem cell fate and facilitate tissue regeneration are primarily cell-instructive, providing mechanical and biochemical signals to cells, and are not cell-responsive, that is they do not respond to the changes elicited in the delivered cells. The majority of materials that are cell-responsive simply degrade in response to cell-secreted proteases. A material that reacts to specific phenotypic changes elicited upon stem cell differentiation, such as those that occur during development, remains to be developed. A potential therapeutic target for such a material is spinal cord injury (SCI). SCI often results in severely debilitating conditins for patients, with limited clinically available treatment options. Nerve regeneration is limited by the body's natural inflammatory response that rapidly replaces injured spinal cord tissue with scar tissue. Furthermore, this inflammatory process results in significant oxidative damage to the surviving neurons, which further hampers regeneration. The goal of this project is to remediate the damage caused by this inflammation by delivering neural stem cells (NSCs) at the injury site within a material that is both cell-instructive, facilitating engraftment and differentiation of the delivered cells, and cell-responsive, releasing a neuroprotective peptide in response to neuronal differentiation. In Specific Aim 1, I will synthesize a material that dynamically responds to NSC differentiation by releasing a neuroprotective peptide. The peptide will be conjugated to an elastin-like protein (ELP) via a proteolytically cleavable linker using azide-alkyne "click" chemistry. Urokinase plasminogen activator (uPA) is a serine protease known to play a role in neuronal development, as it is secreted from the growth cones of axons. I hypothesize that neuronal differentiation of NSCs cultured in ELP hydrogels will result in increased uPA activity, which in turn will selectively release the neuroprotective peptide upon neuronal differentiation. In Specific Aim 2, I will develop a computational model to refine the cel-responsive material design. A reaction-diffusion model with Michaelis-Menten kinetics will be used to simulate the release of the neuroprotective peptide, and the relevant parameters will be experimentally determined. The model will be validated by culturing and differentiating NSCs in the cell-responsive ELP hydrogels and subjecting the cells to oxidative stress. In Specific Aim 3, I will deliver NSCs in the cell-responsive hydrogels to injury sites in rodent SCI contusion models and evaluate functional recovery. Material retention will be assessed with live-animal imaging, and NSC survival, engraftment, and differentiation will be assessed by histology. Recovery will be evaluated by tracing the regenerating nerves and through behavioral testing. I hypothesize that the cell-responsive material will improve the viability of the transplanted NSCs, resulting in improved functional recovery in animals treated with the cell-responsive materials.