Manipulating mitochondrial dynamics as a potential therapeutic strategy for Parkinson's disease

The debilitating movement symptoms in patients with Parkinson's disease (PD) are primarily caused by the death of a type of brain cell that produces the chemical called dopamine. Understanding why these nerve cells die or do not work properly may lead to new therapies for PD. It has been proposed for decades that the small structures inside the cell known as mitochondria are very important to keep nerves healthy and working properly in PD. Mitochondria, the power generators of the cell, have many important functions such as to supply energy and to maintain chemical balances in brain cells.

Mitochondria are highly dynamic and they undergo frequent changes in shape, size, number and location. These dynamic processes can be controlled by mitochondrial fission (a process that leads to multiple smaller mitochondria) or fusion (which results in larger mitochondria). Recent studies, including our own, have shown that manipulating these processes has considerable potential for treating human neurological conditions and has led us to hypothesize that promoting mitochondrial fusion will be beneficial to controlling PD. The overall objectives of this proposal are to first, use pharmaceutical and gene-therapy approaches to test whether enhancing mitochondrial fusion will result in more functional mitochondria and protecting nerve cells of parkinsonian rodents from dying. Second, we will also investigate the ways by which promoting mitochondrial fusion is beneficial in these animals. To achieve these objectives, we have assembled a team of investigators from four independent laboratories in the UK and France. If successful, this work will provide critical information regarding how non-functional mitochondria affect dopamine release and cell loss in PD and offer insights into a potential novel therapeutic strategy for PD.

Mitochondria are dynamic organelles that can be controlled by fission (Drp1 and hFis1) and fusion (OPA1 and Mfn1/2) proteins. Imbalances in fission/fusion can result in synaptic dysfunction and neurodegeneration. This research will use two novel animal models of Parkinson's disease to evaluate the therapeutic effects of promoting mitochondrial fusion. The virally-transduced alpha-synuclein rats represent a human relevant genetic model with neurodegeneration. Because regular wild type mice do not display striatal damage, the novel Oct3-knockout mice will be used to model paraquat neurotoxicity. We hypothesize that blocking Drp1 or promoting OPA1 function will attenuate neurodegeneration and synaptic deficits in these animal models. To test these hypotheses in vivo, we will use rigorous state-of-the art techniques such as: 1) in vivo microdialysis in freely moving mice followed by HPLC to quantify evoked striatal dopamine release; 2) Electrophysiology performed in acute slices to further investigate synaptic activities in these animals; 3) The Seahorse XF24 extracellular flux analyzer to measure striatal synaptosomal mitochondrial respiration; 4) Laser capture microdissection followed by single cell RT-PCR to quantify mitochondrial DNA mutations in nigral dopaminergic neurons; 5) rAAV-mediated gene transfer to inhibit Drp1 function or promote mitochondrial fusion. To complement our genetic approach, we will systemically inject a Drp1 inhibitor. 6) Animal locomotor activities (using the highly sensitive force-plate actometer) and neuropathology (stereological cell counting, striatal DA terminal density and total striatal DA content as well as protein aggregation) will be assessed.

Our proposal addresses a key area of high strategic importance for the MRC: to prevent disability and promote wellbeing. If successful, our therapeutic strategies and mechanistic studies will have a wide range of beneficiaries as outlined below:

1) PD patients and health care providers. It has been estimated that up to 10 million people worldwide are affected by PD and approximately 100,000 people in the UK are living with this debilitating disease. People who suffer from PD will benefit the most from this research, if this research is funded and the neuroprotective data in our animal models are subsequently validated in human studies. As demonstrated from our preliminary data, our proposal of targeting mitochondrial dynamics has considerable potential for PD treatment. By being able to provide effective treatments to patients, health care providers also benefit from this research.

2) Society and policy makers. The economic burden of this disease is enormous. PD is estimated to have a staggering economic burden of £3.3 billion annually in the UK. Therefore, it does not come as a surprise that PD has an effect on health, social and economic policy. By providing an effective treatment of PD over the long term, if successful, this research will likely reduce the societal and economic burden being impacted by PD.

3) MRC and the UK. The role of mitochondrial dysfunction is being intensively investigated by various laboratories worldwide because of its high potential to shed light on the pathogenic mechanisms of PD and to serve as a target for this incurable disease. In recent years, perturbed mitochondrial dynamics provides another perspective on how to restore mitochondrial function in PD. If successful, the UK is positioned as an ideal place to conduct world-class research and MRC is recognized for supporting this novel and translational research.

4) Commercial private sector. We believe our therapeutic approaches have high translational values. The mechanistic and therapeutic knowledge gained from pre-clinical studies in this project will potentially lead to new drug development, which will be of great interest to the pharmaceutical industry. Economic development and scientific competitiveness will benefit from the commercialization of this research.

5) Trainees. The post-doctoral research associate, the graduate and undergraduate students who are involved in this project will gain new and improved skills, experience and publications.