Study Rationale:
LRRK2 is one of the most attractive therapeutic targets in Parkinson's disease (PD); however, chronic doses of LRRK2 inhibitors result in side effects in pre-clinical models. We recently observed that the kinase PAK6 interacts with LRRK2 and negatively affects its activity, mimicking LRRK2 pathological mutations. Furthermore, PAK6 is abnormally activated in PD. Thus, PAK6 appears an appealing target alternative to direct LRRK2 inhibition.
Hypothesis:
Since PAK6 is mostly expressed in the brain and its deletion in pre-clinical models is well tolerated, here, we aim to determine whether inhibition of PAK6 or disruption of the LRRK2-PAK6 pathway is a valid alternative and/or complementary strategy to target LRRK2-linked Parkinson's.
Study Design:
The project has two major goals. The first goal is to understand the mechanism of PAK6-mediated LRRK2 regulation by investigating whether PAK6 kinase activity regulates 14-3-3 binding to LRRK2, which is known to protect LRRK2, and/or the activity of PP1/PP2A phosphatases, which also regulates LRRK2 activity. The second aim is to identify small peptides capable of regulating LRRK2-PAK6 interactions and other pathways.
Impact on Diagnosis/Treatment of Parkinson's disease:
Should PAK6 targeting, by inhibition or by displacing its interaction with LRRK2, result in the reduction of LRRK2-associated toxic phenotypes, this kinase holds the potential to represent a safer approach than direct LRRK2 targeting.
Next Steps for Development:
If successful, this study will lay the groundwork to design specific ATP (cell energy) analogues against PAK6 activity, as well as small cell-permeable peptides that disrupt PAK6-LRRK2 interaction and pathways.
Final Outcome
This project led to the discovery of a new mechanism that controls LRRK2, one of the most attractive therapeutic targets in Parkinson's disease (PD). We demonstrated that PAK6 -- a protein that can modify other proteins -- does modify LRRK2 in a complex series of chemical reactions that take place inside the cell. Importantly, PAK6 may be able to repair cellular defects caused by LRRK2 mutations -- changes in the genes -- that lead to neurodegeneration. Finally, we measured the likelihood of interaction between the LRRK2 and PAK6 proteins. We found that the R1441C mutation -- one of the most prevalent mutations contributing to inherited PD -- reduces the ability of LRRK2 to interact with PAK6, further suggesting the potential relevance of this interaction to PD.
Presentations & Publications
- Manuscript: Civiero L, Cogo S, Kiekens A, et al. PAK6 Phosphorylates 14-3-3γ to Regulate Steady State Phosphorylation of LRRK2. Front Mol Neurosci. 2017;10:417.
- Poster at the Italian Society of Physiology congress (September 2017)
- Invited presentation (Laura Civiero)