Investigation of the Role of PINK1-dependent Phosphorylation of Rab GTPases in Parkinson’s Disease

Study Rationale:
Mutations in the PINK1 gene lead to Parkinson’s disease. PINK1 belongs to a special class of enzymes known as protein kinases. We recently found that PINK1 targets a family of enzymes known as Rab GTPases via site-specific modification (known as phosphorylation). Rabs function as switches in cells to orchestrate a host of functions vital for cellular health and survival. Importantly Rabs have also been shown to be targeted by two other important Parkinson’s genes namely LRRK2 and alpha-synuclein. The exact mechanism by which PINK1 targets Rabs and the key players involved in mediating Rab function upon PINK1 engagement are unknown.

Hypothesis:
We will undertake an in-depth analysis of the mechanism by which PINK1 targets Rabs. We also aim to uncover the key molecules that are required for Rabs to execute their functions upon targeting by PINK1.

Study Design:
We will employ a variety of biochemical methods to determine how PINK1 targeting modifies the properties of Rabs including techniques that will enable us to visualize their structure and form upon targeting by PINK1. We will employ state-of-the-art mass spectrometry technologies in human cell lines to identify the key molecular players that are both required for PINK1 to target Rabs as well as the players that function downstream of Rabs to enable them to execute their biological functions. We will investigate how human mutations of PINK1 disrupt the upstream and downstream functions of Rabs. We will elaborate powerful antibody tools that will enable us to study the PINK1-induced modification of Rabs in complex cells and tissue systems including Parkinson’s-derived tissues to advance understanding on the relevance of the PINK1-Rab pathway to disease.

Impact on Diagnosis/Treatment of Parkinson’s Disease:
Providing clear-cut relevance of the PINK1 regulation of Rabs to Parkinson’s disease mechanisms may provide strong rationale to develop a biomarker based on monitoring modified/phosphorylated version of Rabs by PINK1. This could be valuable to clinicians and pharmaceutical companies currently involved in therapeutic trials in Parkinson’s disease.

Next Steps for Development:

• Develop facile and tractable assays employing phospho-specific antibodies to measure Rab phosphorylation in human samples
• Undertake a large clinical study using these assays to assess their utility as a biomarker for sporadic Parkinson’s disease