The presence of alpha-synuclein (alpha-SYN) aggregate in Lewy neurites (LNs) and Lewy bodies (LBs), the pathological hallmarks of Parkinson's disease (PD), and mitochondrial dysfunction are two central components in PD pathogenesis. Known physiological roles of alpha-SYN are limited in synaptic terminals, raising the possibility that alpha-SYN mRNA is transported to neurites and its translation is locally controlled. In fact, we have recently found that alpha-SYN mRNA is translocated into neurites of fully differentiated human dopaminergic neuronal cells. We also identified that Pum2, a paralogue of mammalian PUF family RNA binding protein, binds to a PUM binding motif of the alpha-SYN 3'UTR and is responsible for neuritic localization as well as translational repression of alpha-SYN mRNA. Mitochondrial ROS generated by respiratory complex I inhibition led to local translation of alpha-SYN from mRNA associated with mitochondria, suggesting that Pum2 might transmit mitochondrial signal to alpha-SYN translation. Although it is obvious that there is an inter- relationship between mitochondria and alpha-SYN underlying the development of disease, molecular mechanisms governing this cross-talk remain elusive. Our central hypothesis is that Pum2 is responsible for alpha-SYN mRNA transport to the juxta-mitochondrial compartment, alpha-SYN translational regulation and aggregation in neurites. The objectives of this project are to understand the interplay between alpha-SYN and mitochondria in neurites through Pum2-mediated translational regulation of mitochondria-associated alpha-SYN mRNA. To achieve these objectives we propose the following three specific aims:
Aim 1. Examine the role of Pum2 in mitochondrial localization of alpha-SYN mRNA.
Aim 2. Examine how mitochondrial ROS control alpha-SYN translation.
Aim 3. Determine how newly synthesized alpha-SYN near mitochondria affects mitochondrial fragmentation and alpha-SYN aggregation in neurites. The successful completion of the project will bring a paradigm shift in our understanding of molecular mechanisms that control alpha-SYN level in neurites and how mitochondrial ROS contribute to this alpha-SYN regulation. The results expected from the project will open new avenues to understand 1) 3'UTR-dependent posttranscriptional regulation of alpha-SYN in neurites and Pum2's role in this process, 2) intimate crosstalk between alpha-SYN and mitochondria in neurites and 3) its contribution to mitochondrial fragmentation and LN formation.
The presence of Lewy bodies (LBs) and Lewy neurites (LNs), cytoplasmic protein aggregates, and the loss of dopaminergic (DA) neurons are cardinal pathological features of Parkinson's disease (PD). alpha-synuclein (alpha-SYN) protein is a major component of LBs and LNs but precise regulation mechanism of alpha-SYN expression is yet to be elucidated. LNs are frequently observed at the early stage of PD prior to the formation of LBs. The proposed project is aiming to elucidate the novel mechanism of alpha-synuclein expression and aggregation in neurites through Pum2, a RNA binding protein, under mitochondria-derived oxidative stress. The successful completion of the project will bring a paradigm shift in our understanding of molecular mechanisms underlying mitochondria-mediated control of alpha-SYN expression in neurites. This will allow us to develop new therapeutic strategies to reverse the condition.