Interrogating Parkinson's disease LRRK2 kinase pathway activity by assessing Rab10 phosphorylation in human neutrophils

There is compelling evidence for the role of the leucine-rich repeat kinase 2 (LRRK2) and in particular its kinase function in Parkinson's disease. Orally bioavailable, brain penetrant and potent LRRK2 kinase inhibitors are in the later stages of clinical development. Here, we describe a facile and robust assay to quantify LRRK2 kinase pathway activity by measuring LRRK2-mediated phosphorylation of Rab10 in human peripheral blood neutrophils. We use the selective MJFF-pRab10 monoclonal antibody recognising the Rab10 Thr73 phospho-epitope that is phosphorylated by LRRK2. We highlight the feasibility and practicability of using our assay in the clinical setting by studying a few patients with G2019S LRRK2 associated and sporadic Parkinson's as well as healthy controls. We suggest that peripheral blood neutrophils are a valuable resource for LRRK2 research and should be considered for inclusion in Parkinson's bio-repository collections as they are abundant, homogenous and express relatively high levels of LRRK2 as well as Rab10. In contrast, the widely used peripheral blood mononuclear cells are heterogeneous and only a minority of cells (monocytes and contaminating neutrophils) express LRRK2. While our LRRK2 kinase pathway assay could assist in patient stratification based on LRRK2 kinase activity, we envision that it may find greater utility in pharmacodynamic and target engagement studies in future LRRK2 inhibitor trials.