Alterations in the LRRK2-Rab pathway in urinary extracellular vesicles as Parkinson’s disease and pharmacodynamic biomarkers

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Abstract Levels of expression or of phosphorylation of leucine-rich repeat kinase 2 (LRRK2) and its Rab substrates have the potential for use as disease or pharmacodynamic biomarkers. LRRK2 phosphorylation levels at the S910-S935-S955-S973 phosphosites are reduced for most disease mutant forms of LRRK2, while for phospho-S1292, phospho-T72-Rab8 and phospho-T73-Rab10 levels are increased for most mutants. In addition, all of these 5 phosphosites on LRRK2 are rapidly dephosphorylated upon LRRK2 inhibitor treatment, considered potential therapeutics. The main objective of this study is therefore to characterize leucine-rich repeat kinase 2 (LRRK2) and Rab8/10 in human, non-human primate and rat urine for use as potential disease or pharmacodynamic biomarkers. With urine collected from human subjects as well as animals, we have applied an ultracentrifugation based fractionation protocol to isolate small extracellular vesicles (EVs). We used western blot with antibodies directed against LRRK2, LRRK2 phosphorylation sites as well as Rab8 and Rab10 total and phosphorylated proteins in order to measure these LRRK2 and Rab epitopes in urinary EVs (uEVs). We confirm the presence of LRRK2 and Rab8/10 in human and non-human primate (NHP) uEVs, including total LRRK2 as well phosphorylated forms of LRRK2 pS910, pS935, pS955, pS973, pS1292 and phosphorylated Rab8 and Rab10. We also confirm LRRK2 and Rab expression in rodent uEVs. We quantified LRRK2 and Rab epitopes in human cohorts and found in a first cohort that pS1292-LRRK2 levels were elevated in individuals carrying the LRRK2 G2019S mutation, but did not differ significantly between healthy and PD groups, whether for LRRK2 G2019S carriers or not. In a second cohort, we found that PD was associated to an increase in Rab8 levels and a decrease in S910-LRRK2 and S935-LRRK2 phosphorylation rates. In animals, we found that acute treatment with LRRK2 kinase inhibitor led to decreases in Rab10 phosphorylation rates and to a decrease in pS935-LRRK2 rates in uEVs from NHPs. The identification of changes in LRRK2 phosphorylation at heterologous phosphorylation sites in uEVs of PD patients further reinforces the potential of the LRRK2-Rab pathway as a source of PD biomarkers in uEVs.

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