Parkinson’s disease (PD) is a common neurodegenerative disorder symptomatically characterized by motor dysfunction caused by the selective loss of nigral dopamine neurons within midbrain. The pathogenesis of PD remains unclear. Although, originally thought to be sporadic, about ten percent of PD is familial. The recent elucidation of mutations in genes linked to the disease has offered potential for new animal models and understanding of PD pathogenesis. DJ-1 and LRRK2 are genes linked to autosomal recessive juvenile-onset PD and autosomal-dominant late onset PD, respectively. How mutations in these two genes leads to PD remains uncertain and is plagued by poor murine models that do not recapitulate the human condition. The following dissertation attempts to characterize both mouse and fly models of DJ-1 and LRRK2 mediated PD and elucidate other genetic modifiers that may contribute to PD. Firstly, the DJ-1 null mouse model, which lacks cell death, was improved by backcrossing to a pure C57-Bl6 background. These DJ-1 null mice display a robust and progressive unilateral-to-bilateral loss of nigral neurons accompanied by motor deficits in aged mice. Secondly, a large scale screen was performed in Drosophila to determine genes that modify mutant LRRK2 toxicity in both the eye and dopaminergic neurons of the fly. The screen revealed 36 genetic interactors that either suppressed or enhanced LRRK2 induced cell death in the fly. One of these interactors was SCAR (human WAVE-2). Due to the role WAVE-2 is known to have in immune cell phagocytic function, we demonstrate that LRRK2 deficient/G2019S murine myeloid cells have impaired/enhanced phagocytic activity which is correlated with a decrease/increase in WAVE-2 protein, respectively. We furthermore suggest that LRRK2 and WAVE-2 may bind directly and that LRRK2 phosphorylates WAVE-2 to maintain its stability. Finally, as a proof of concept, we constructed a novel animal model of LRRK2 in flies by limiting LRRK2 over expression to central phagocytes of the Drosophila brain. This causes lifespan deficits and motor dysfunction that can be rescued by down-regulation of SCAR. Collectively, this body of work helped create the first germ-line, genetic model of PD that recapitulates nigral loss and elucidated LRRK2 interactors in the fly. Furthermore, we demonstrate that one of these interactors mediated LRRK2’s modulation of phagocytic activity that may contribute to the pathogenesis of PD.

Parkinson’s disease (PD) is the most common movement neurodegenerative disease affecting approximately 1% of the population over 60. Though originally thought to be sporadic in nature, a genetic component is increasingly being linked to the disease. Of these genes, mutations in DJ-1 (PARK7) cause early onset autosomal recessive PD. Initial workup of the DJ-1 protein has suggested that it may act in the cell by combatting oxidative stress though the mechanism by which it does so is unclear. Thus, though much work has attempted to elucidate a function at the biochemical, cellular and organismal level, the overt physiological role of DJ-1 remains elusive. In this dissertation, we explore the mechanisms through which DJ-1 confers neuroprotection, particularly in the case of oxidative stress insult. We demonstrate that DJ-1 acts through the pro-survival protein AKT to accomplish its neuroprotective function. Moreover, we note that DJ-1 likely serves its role as an antioxidant through the NRF2 master antioxidant regulator pathway a pathway that is, itself, likely to be regulated by AKT. Together, our results demonstrate that neuroprotection by DJ-1 is done through a signaling pathway involving both AKT and NRF2 and that disruption of the former in PD likely results in abolishing this signaling pathway. Finally, to generate a better animal model of PD, we demonstrate that backcrossing DJ-1 null mice - which originally did not demonstrate any gross histopathological or behavioral phenotypes – display unilateral dopaminergic degeneration that progresses to bilateral degeneration with aging, a feature reminiscent of classical PD progression. Collectively, this thesis takes a two-sided approach to address the biochemical and physiological functions of DJ-1 within the cell and the mouse in hopes of elucidating mechanisms of neuronal death to devise better translational therapies.

Parkinson’s disease (PD) is the most common movement neurodegenerative disease affecting approximately 1% of the population over 60. Though originally thought to be sporadic in nature, a genetic component is increasingly being linked to the disease. Of these genes, mutations in DJ-1 (PARK7) cause early onset autosomal recessive PD. Initial workup of the DJ-1 protein has suggested that it may act in the cell by combatting oxidative stress though the mechanism by which it does so is unclear. Thus, though much work has attempted to elucidate a function at the biochemical, cellular and organismal level, the overt physiological role of DJ-1 remains elusive. In this dissertation, we explore the mechanisms through which DJ-1 confers neuroprotection, particularly in the case of oxidative stress insult. We demonstrate that DJ-1 acts through the pro-survival protein AKT to accomplish its neuroprotective function. Moreover, we note that DJ-1 likely serves its role as an antioxidant through the NRF2 master antioxidant regulator pathway a pathway that is, itself, likely to be regulated by AKT. Together, our results demonstrate that neuroprotection by DJ-1 is done through a signaling pathway involving both AKT and NRF2 and that disruption of the former in PD likely results in abolishing this signaling pathway. Finally, to generate a better animal model of PD, we demonstrate that backcrossing DJ-1 null mice - which originally did not demonstrate any gross histopathological or behavioral phenotypes – display unilateral dopaminergic degeneration that progresses to bilateral degeneration with aging, a feature reminiscent of classical PD progression. Collectively, this thesis takes a two-sided approach to address the biochemical and physiological functions of DJ-1 within the cell and the mouse in hopes of elucidating mechanisms of neuronal death to devise better translational therapies.

Oxidative stress and mutations in DJ-1, a redox sensitive protein, are linked to Parkinson's Disease. The protective mechanism of DJ-1 is unclear. I hypothesized that: 1) DJ-1 mediates protection by translocating to mitochondria after oxidative stress and, 2) when DJ-1 is downregulated, apoptotic pathways regulated by calcineurin are also downregulated. In PC12 cells and rat cortical neurons, oxidative stress resulted in the upregulation of DJ-1 and increased DJ-1 in the nucleus, but did not increase mitochondrial translocation of DJ-1. In cortical neurons and wildtype mouse embryonic fibroblasts, H2O2 induced cleavage of CnA into an inactive fragment. DJ-1 knockout fibroblasts had less nuclear localization of the transcription factor NFATc4, a substrate of calcineurin involved in apoptosis. H2O2 increased CnA cleavage in DJ-1 knockout fibroblasts, but NFATc4 localization was unchanged. These results suggest that the downregulation of apoptotic pathways regulated by calcineurin may be a compensatory response to the downregulation of DJ-1.

Oxidative stress and mutations in DJ-1, a redox sensitive protein, are linked to Parkinson's Disease. The protective mechanism of DJ-1 is unclear. I hypothesized that: 1) DJ-1 mediates protection by translocating to mitochondria after oxidative stress and, 2) when DJ-1 is downregulated, apoptotic pathways regulated by calcineurin are also downregulated. In PC12 cells and rat cortical neurons, oxidative stress resulted in the upregulation of DJ-1 and increased DJ-1 in the nucleus, but did not increase mitochondrial translocation of DJ-1. In cortical neurons and wildtype mouse embryonic fibroblasts, H2O2 induced cleavage of CnA into an inactive fragment. DJ-1 knockout fibroblasts had less nuclear localization of the transcription factor NFATc4, a substrate of calcineurin involved in apoptosis. H2O2 increased CnA cleavage in DJ-1 knockout fibroblasts, but NFATc4 localization was unchanged. These results suggest that the downregulation of apoptotic pathways regulated by calcineurin may be a compensatory response to the downregulation of DJ-1.

Parkinson’s disease (PD) is the most common movement neurodegenerative disease affecting approximately 1% of the population over 60. Though originally thought to be sporadic in nature, a genetic component is increasingly being linked to the disease. Of these genes, mutations in DJ-1 (PARK7) cause early onset autosomal recessive PD. Initial workup of the DJ-1 protein has suggested that it may act in the cell by combatting oxidative stress though the mechanism by which it does so is unclear. Thus, though much work has attempted to elucidate a function at the biochemical, cellular and organismal level, the overt physiological role of DJ-1 remains elusive. In this dissertation, we explore the mechanisms through which DJ-1 confers neuroprotection, particularly in the case of oxidative stress insult. We demonstrate that DJ-1 acts through the pro-survival protein AKT to accomplish its neuroprotective function. Moreover, we note that DJ-1 likely serves its role as an antioxidant through the NRF2 master antioxidant regulator pathway a pathway that is, itself, likely to be regulated by AKT. Together, our results demonstrate that neuroprotection by DJ-1 is done through a signaling pathway involving both AKT and NRF2 and that disruption of the former in PD likely results in abolishing this signaling pathway. Finally, to generate a better animal model of PD, we demonstrate that backcrossing DJ-1 null mice - which originally did not demonstrate any gross histopathological or behavioral phenotypes – display unilateral dopaminergic degeneration that progresses to bilateral degeneration with aging, a feature reminiscent of classical PD progression. Collectively, this thesis takes a two-sided approach to address the biochemical and physiological functions of DJ-1 within the cell and the mouse in hopes of elucidating mechanisms of neuronal death to devise better translational therapies.

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by the selective loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc). PD affects ~1% of the population over 65, as demonstrated by characteristic symptoms such as tremor, rigidity, and bradykinesia. While the majority of PD cases are idiopathic, some cases are familial, including those caused by homozygous loss-of-function mutations in DJ-1 (PARK7), which lead to early onset PD. Although the physiological role of DJ-1 is not fully understood, DJ-1’s neuroprotective role against oxidative stress is well documented. DJ-1 is required for AKT-mediated neuroprotective effects, however the mechanism by which DJ-1 affects membrane localization/activation of AKT is unknown and is likely a critical aspect of DJ-1 function. In this thesis we explore the mechanism through which DJ-1 confers neuroprotection through AKT membrane recruitment, particularly in the case of oxidative stress insult. We demonstrate here that DJ-1 interacts with PHLDA3, a negative regulator of AKT, and loss of DJ-1 leads to hypersensitivity of neurons to PHLDA3-mediated death. Additionally, we demonstrate that in the absence of DJ-1, PHLDA3 localization at the membrane is increased, and overexpression of PHLDA3 causes reduced AKT phosphorylation in DJ-1 KO MEFs in response to oxidative stress. Taken together, these studies provide a potential novel mechanism by which DJ-1 regulates the activity of AKT, a critical neuronal survival pathway. Elucidation of these mechanisms may provide insight into the design of neuroprotective therapies for PD.

Indiana University-Purdue University Indianapolis (IUPUI) / Parkinson’s disease (PD) is a neurodegenerative disorder characterized by progressive loss of motor function resulting from dopaminergic neuronal death in the substantia nigra pars compacta leading to subsequent decreased striatal dopamine levels. The majority of PD cases are diagnosed as sporadic in nature, however 10% - 15% of patients show a positive family history of the disease. While many genes have been found to be implicated in the familial form of PD, early-onset autosomal recessive PD has been associated with mutations in PARK7, a gene which codes for the protein DJ-1. While there are many proposed roles of DJ-1 across numerous systems, the function of DJ-1 in relation to the development and progression of PD remains largely unclear. A first step towards determining this function is the creation of biologically relevant cell models of PD. The goal of this work was to design a representative cell model of DJ-1-associated PD in order to further study DJ-1 with the intention of elucidating its relevant function in relation of PD pathogenesis.

No description available.

Parkinson's disease (PD) is the most common neurodegenerative motor disorder, whose clinical features are rest tremor, bradykinesia, muscular rigidity and postural instability. Although most reported cases are sporadic, a handful of familial cases and their causative genes have been identified. Loss-of-function mutations in DJ-1, one of these genes, are responsible for 1% of familial PD cases. Our laboratory has previously reported that DJ-1- lacking neurons are sensitive to oxidative stress, induced by hydrogen peroxide or the neurotoxin MPTP. To investigate the possible mechanisms through which DJ-1 protects against oxidative stress, we performed a proteomic screen and identified Von Hippel Lindau (VHL) and Paraoxonase2 (PON2) as potential DJ-1 interacting partners. VHL is an E3 ubiquitin ligase which, in normal conditions, poly-ubiquitinates HIF-1 , a subunit of a master hypoxic/oxidative stress transcription factor, whose function is protective in oxidative and hypoxic stresses. In the present study, we provided further evidence of interaction of DJ-1 with VHL. We also demonstrated that HIF-1 protein level, as an indicator of VHL activity, is lower in cells lacking DJ-1, suggesting the inhibitory role of DJ-1 on VHL. Our in vitro studies also showed that DJ-1 inhibits ubiquitin ligase activity of VHL on HIF-1 by reducing the VHL-HIF-1 interaction. Importantly, accumulation of HIF-1 protects embryonic cortical neurons against MPP+ induced neuronal death. Finally, we confirmed the impairment of HIF-1 response to oxidative stress in human lymphoblastoids of DJ-1-linked PD cases. In the second part of this study, we demonstrated the interaction of DJ-1 and PON2. Interestingly, PON2 lactonase activity is reduced in DJ-1 deficient cells which could be rescued by re-introduction of DJ-1, suggesting a modulating role of DJ-1 on PON2 activity. In addition, PON2 deficiency, like DJ-1 deficiency, hypersensitizes neurons to MPP+, which could be rescued by over-expression of PON2 in both cases. Taken together, our data provide evidence that DJ-1 exerts its protective role by inhibiting VHL activity, enhancing HIF-1 stability, and increasing PON2 pro-survival function in PD models.