The Development of an Inducible Akt as a Potential Gene Therapy for Parkinson’s Disease

Parkinson’s disease remains a major neurodegenerative disease with prevalence that is second only to Alzheimer’s disease. Despite much advancement in the understanding of the pathogenesis of Parkinson’s disease, current therapeutic options are limited to those that are only symptomatic and are not disease-modifying. Furthermore, due to what seems to be increasingly complex underlying mechanisms of the disease, identifying a broadly applicable therapeutic strategy is difficult. There is much evidence surrounding the role of apoptosis and conversely, dysfunction of anti-apoptotic signaling in the progressive neurodegeneration that causes Parkinson’s disease. In particular, suppressed PI3K signaling has been implicated in the literature as a key event that occurs during neurodegeneration. Thus, regardless of the diverse upstream mechanisms that may lead to the disease, targeting a downstream effector of neuronal survival presents a therapeutic strategy that may be broadly effective against Parkinson’s disease. For this dissertation, we have developed a method to control the levels of active Akt, the main mediator of the PI3K signaling pathway, using an innovative protein destabilizing technique to create an inducible Akt, DD-Akt(E40K). This method permits the control of active Akt levels through a commonly used and blood-brain barrier permeable antibiotic, Trimethoprim. We have successfully established the inducibility of DD-Akt(E40K) across various cellular contexts, including neuronal cell types and conditions with suppressed PI3K signaling. This inducibility was found to be dose-responsive to Trimethoprim, reversible, and able to induce a known downstream substrate, FoxO4, that is an important regulator of cell survival. Importantly, DD-Akt(E40K) was found to inducibly protect neuronal PC12 cells against Parkinson’s disease mimetic toxins as well as growth-factor removal, indicating a proof of principle for the targeting of Akt activity as a protective strategy against Parkinson’s disease. The reported trophic effects of active Akt were also corroborated using our inducible DD-Akt(E40K) system in vivo, demonstrating significant increases in neuronal cell size within the substantia nigra of mice. Intriguingly, the inducibility of DD-Akt(E40K) was found to be dependent on the region of expression in the brain of mice such that the levels of this protective protein were not controllable by Trimethoprim in the substantia nigra but were controllable in the striatum. Taken together, the studies presented in this dissertation establish a new tool for the study of Akt signaling in various cellular and disease contexts and validate Akt as a promising therapeutic target in Parkinson’s disease. Our results also suggest an intriguing mechanism for the underlying pathology and selective degeneration observed in the disease.