DJ-1 and neurodegeneration: its roles in mitochondria and in protein misfolding

Parkinson's disease (PD), the second most common neurodegenerative disorder after Alzheimer's disease, is characterized by loss of dopaminergic neurons and the accumulation of misfolded alpha-synuclein in the form of Lewy bodies. The clinical symptoms include muscle rigidity, resting tremor, bradykinesia and postural instability as a result of the loss of dopaminergic neurons in the substantia nigra pars compacta. At later stages, the etiology of neuronal loss in sporadic PD is unknown, although aberrant alpha-synuclein aggregation and oxidative stress may contribute to the death of specific neuronal populations. Although little is known about the pathogenesis of PD, the detailed study of several genes associated with familial PD is enhancing the understanding of the molecular mechanisms associated with the disease. Mutations in one of these genes - PARK7 - accounts for ~1-2% of the sporadic cases of early onset recessive PD. PARK7 encodes for DJ-1, a small conserved protein which is broadly expressed and primarily localized to the cytoplasm, but also found in the nucleus and associated with mitochondria. Despite the importance of this protein, the role of DJ-1 in in formation of PD remains unclear. Several functions have been suggested for DJ-1, including an oxidative stress sensor, a chaperone which deals with misfolded protein in the cells, and a regulator of mitochondrial function. In this project we seek to clarify how DJ-1 contributes to mitochondrial function and protein misfolding, and ultimately how defects in these cellular processes due to DJ-1 mutations contribute to pathogenesis in PD. For these studies we plan to implement immortalized cell lines, primary cells from mice, as well as fruit flies.

In preliminary experiments we have observed that mutations in DJ-1 alter its ability to localize to mitochondria in mammalian cells under oxidative stress conditions. We thus now seek to further characterize this effect with varied oxidants, and also in the context of alpha-synuclein overexpression. In addition, we plan to investigate the impact of these mutants on both morphology and function of mitochondria in mouse cells, as well as the effects on mitochondrial gene expression. Finally we plan to extend this approach by studying the effect of DJ-1 mutants on the structure and function of mitochondria in fruit flies.

Next we seek to further explore the role of DJ-1 in protein misfolding by investigating the relationship between DJ-1 and the Tau protein, which has been implicated in several neurodegenerative disorders. The Tau protein is involved in the pathogenesis of Alzheimer's disease and is a major component of neurofibrillary tangles present in this disorder. The gene encoding Tau has recently been genetically linked to PD. In addition, DJ-1 co-localizes with Tau inclusions in Alzheimer's disease and other brain disorders. However any possible physical/functional interactions between DJ-1 and Tau have not been studied and their relationship in the context of PD has not been explored. Thus we propose to study the interaction between DJ-1 and Tau in living mammalian cells, and to what extent, if any, this alters Tau toxicity or formation of fibers. Furthermore, we plan to extend this work to a fruit fly model of Tauopathies, to ascertain whether DJ-1 modulates disease-relevant "symptoms" in these animals. In preliminary work we have observed that DJ-1 and Tau directly interaction when expressed in mammalian cells.

Thus, our work will better define the role of DJ-1 in mitochondrial function and in protein misfolding which will help clarify its pathogenic role in PD. This added insight into DJ-1 biology may ultimately help inform therapeutic strategies for this, and other, neurodegenerative disorders.

Parkinson's disease (PD), the second most common neurodegenerative disorder, presents with loss of dopaminergic neurons and the accumulation of misfolded alpha-synuclein (aSyn) in Lewy bodies. The study of genes associated with familial PD - such as PARK7 which encodes for DJ-1 - is elucidating the mechanisms underlying this disease. DJ-1 has several roles in the cell: oxidative stress sensor, protein chaperone, and a regulator of mitochondrial function. Here we seek to clarify how DJ-1 contributes to mitochondrial function and protein misfolding, and how these roles contribute to pathogenesis in PD.

In initial work we have found that mutations in DJ-1 modulate its relocalization to mitochondria in mammalian cells with paraquat treatment. We thus seek to further characterize this effect with a range of disease-causing and functional mutants, additional oxidants, and in the context of aSyn expression. We also plan to investigate how DJ-1 mutations affect function and morphology of mitochondria. Finally we plan to extend this approach by studying how DJ-1 mutants modulate the structure and function of mitochondria in fruit flies.

We will also explore the relationship between DJ-1 and the Tau protein, which is involved in the pathogenesis of Alzheimer's disease (AD), is a major component of neurofibrillary tangles, and has been recently genetically linked to PD. DJ-1 modulates misfolding/toxicity of several aggregation-prone proteins and co-localizes with Tau inclusions in AD and other brain disorders. Interactions between DJ-1 and Tau have not been studied, and their relationship in the context of PD has not been explored. Thus we propose to study the interaction between DJ-1 and Tau in living mammalian cells using bimolecular fluorescence complementation, and to what extent, if any, this alters Tau toxicity or formation of fibers. We will extend this work to a fruit fly model of Tauopathies, to ascertain whether DJ-1 modulates disease-relevant phenotypes.

The common neurodegenerative disorders affect more than 700,000 people in the UK, and cases are predicted to double in the next 25 years, costing the UK economy a staggering £50 billion. Thus, in addition to the obvious patient benefits, the identification of effective treatments for neurodegenerative disorders could dramatically cut these expenditures world-wide. This proposal is focused on dissecting the cellular roles of DJ-1, a protein directly linked to familial cases of Parkinson's disease (PD), which is the second most common neurodegenerative disorder after Alzheimer's disease (AD). Futhermore, we plan to explore the relationship between DJ-1 and the Tau protein, which is involved in the pathogenesis of AD and other brain disorders, and has recently been genetically linked to PD. Thus, this proposal has implications for individuals suffering from PD, and likely AD as well, and their families. Much research has been directed toward uncovering novel therapeutics for these devastating disorders, but nevertheless, to date, the options for treatment are limited. By determining the cellular role of proteins linked to neurodegenerative disease we can enhance our understanding of the molecular mechanisms associated with pathogenesis. Ultimately, these approaches may aid in the identification of novel candidate targets and therapeutic approaches for PD and other devastating brain disorders. Therefore, this will work will directly impact upon patients suffering from PD and their families, as well as researchers and clinicians focused upon this and related disorders.