Promising Outcomes of Original Grant:
The objective of our Rapid Response Innovation Awards-supported project was to identify the parkin domain that interacts with Stomatin-like protein 2 (SLP-2), a mitochondrial protein we recently identified as being able to interact with parkin. We believe this interaction is important for maintaining healthy mitochondria and thus set out to examine the effects of this interaction on mitochondrial function in different cell types including induced pluripotent stem cell (iPSC)-derived neurons of parkin mutation carriers. We have successfully confirmed the interaction between these two proteins in skin fibroblasts and iPSC-derived neurons and have identified the parkin domains that seem important for the interaction with SLP-2. Furthermore, we have observed that this binding is weakened in patient fibroblasts harboring different types of parkin mutations. We believe this ultimately leads to some of the compromised mitochondrial function that we have measured in iPSC-derived neurons of patients.
Objectives for Supplemental Investigation:
Based on the results obtained during this one year of funding, we will now proceed with further studies to identify a small sequence of parkin with a high binding affinity for SLP-2 and to test the possibility to rescue the weakened binding between parkin and SLP-2 in parkin mutation carriers and see whether this helps restore mitochondrial health. We would like to investigate whether small fragments of parkin (peptides) that can interact with SLP-2 can be put in cells, are able to get to the mitochondria and whether this can positively influence several measures of mitochondrial function. Should that be the case, we might be able to use these to test whether they are also able to slow markers of disease progress in cells from patients with parkin mutations.
Importance of This Research for the Development of a New PD Therapy:
We believe our findings so far have opened up new avenues for better understanding how parkin regulates mitochondrial health under physiological conditions in neurons. We believe the interaction with SLP-2 helps promote the role of SLP-2 to maintain healthy mitochondrial function. The results with small parkin peptides able to rescue this function in the presence of compromised parkin could form the basis of a novel therapeutic approach based on parkin peptidomimetics.
Protein parkin prevents cell death by breaking down damaged mitochondria, cell's energy generators, and loosing this ability leads to Parkinson's disease (PD). We discovered that parkin interacts with stomatin-like protein 2 (SLP-2) inside mitochondria, which helps to keep mitochondria healthy. We hypothesized that missing or dysfunctional parkin might negatively influence the function of SLP-2. We also hypothesized that fragments of parkin that interact with SLP-2 might be able to remove damaged mitochondria in people whose parkin is missing or does not function as expected.
In this project, we sought to identify such parkin fragments. We also aimed to test whether making the cell manufacture such fragments can substitute for the whole parkin and restore mitochondrial function in people with damaged parkin. We have identified the RING0 fragment of parkin as most likely to interact with SLP-2. The results of the evaluation of this fragment were encouraging. When cells lacking parkin were modified to produce the RING0 fragment, their mitochondrial function improved. Taking this further, we identified parts of the RING0 fragment that influence the binding of parkin to SLP-2. We have engineered parkin minipeptides -- miniature proteins -- containing these RING0 parts to test whether, like RING0, they may be able to improve mitochondrial function. The results of in vivo studies and studies conducted in nerve cells from a person with parkin mutations (genetic changes) indicate that parkin minipeptides are likely to restore mitochondrial function worsened by parkin mutations. These studies lay the foundation for the development of a new, peptide-based or peptide-mimicking therapeutic approach.
Presentations & Publications
- Identification of the Parkin-binding domain for SLP-2, a novel Parkin-interactor. Poster presented at: Multifaceted Mitochondria; July, 2015; Chicago, IL.
- Identification of the Parkin-binding domain for SLP-2, a novel Parkin-interactor, as a potential therapeutic target. Poster presented at: Mitochondrial Medicine: Developing New Treatments for Mitochondrial Disease congress; May, 2016; Hinxton Cambridge, UK.
- Datablitz presentation at: GEoPD meeting; October, 2016; Luxembourg.