All ETDs from UAB

Advisory Committee Chair

Jianhua Zhang

Advisory Committee Members

Aimee Landar

Scott Ballinger

Guangjie Cheng

Talene Yacoubian

Document Type

Dissertation

Date of Award

2014

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Parkinson's disease (PD) is the second most common neurodegenerative disorder. Two major factors in both familial and sporadic PD are mitochondrial dysfunction and insufficient autophagy. My thesis research focuses on the interplay between these activities in PD. To investigate the common and differential effects of PD-inducing neurotoxins on mitochondrial bioenergetics and their relationships to cell survival, we used an in vitro culture system, differentiated dopaminergic SH-SY5Y neuroblastoma cells. We found that the neurotoxins rotenone, 1-methyl-4- phenylyridinium (MPP+) and 6-hydroxydopamine (6-OHDA), decreased mitochondrial respiration and induced cell death in these cells. The extent and characteristics of mitochondrial dysfunction in response to LD50 of these neurotoxins are drastically different. Rotenone inhibits mitochondrial function at nM concentrations, and this inhibition was directly related to cell death. MPP+ only induces cell death at concentrations that are significantly higher than what was needed to inhibit mitochondrial function. In contrast, 6-OHDA significantly induced cell death at concentrations which had little effects on mitochondrial respiration. The relative proportions of inhibition of ATP-linked, Proton Leak, Maximal, Reserve capacity, and non-mitochondrial oxygen consumption rates are also remarkably different among these neurotoxins, indicating different mechanisms of action. Rotenone induced cell death had the most direct relationship in its induction of mitochondrial dysfunction, and it has been linked to increased PD risk today as it is still used as a pesticide. Dysfunctional mitochondria are cleared by autophagy; therefore it is important to determine the autophagic activities after exposure to rotenone. We found that rotenone at nM doses immediately inhibited mitochondrial function in primary neurons. Doses which decreased mitochondrial function at 2 hrs caused cell death at 24 hrs. Using the 24 hr LD50 of 10 nM rotenone, overall autophagic flux was found to be decreased at both 2 and 24 hrs, whereas autophagy of mitochondria was increased at 24 hrs. We found that upregulation of autophagy by rapamycin protected against cell death and mitochondrial dysfunction while inhibition of autophagy by 3MA exacerbated cell death. Together, this thesis provides novel information regarding mitochondrial dysfunction in response to PD related neurotoxins and the role of autophagy and mitophagy in neuronal survival.

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