Phosphorylated pS1292 LRRK2 to Total LRRK2 Concentration Ratio in Urine Exosomes Distinguishes LRRK2-PD and Idiopathic PD (S7.002)

Objective: To measure total LRRK2 and phosphorylated pS1292-LRRK2 levels in urine exosomes of LRRK2 G2019S carriers with PD (LRRK2+/PD+), and non-carriers with (LRRK2-/PD+), and without PD (LRRK2-/PD-). Background: LRRK2 G2019S mutations may increase Parkinson’s disease (PD) risk through a gain of kinase function including autophosphorylation at the serine-1292 residue near the LRRK2 GTPase domain. Phosphorylated pS1292-LRRK2 may reflect LRRK2 kinase activity. Methods: 14 Male participants included LRRK2+/PD+ (n=7), LRRK2-/PD+ (n=4), and LRRK2-/PD- (n=3). Fresh urine was collected and frozen in a -80oC freezer. Urinary exosomes were purified from ~40 ml samples. Monoclonal anti-LRRK2/Dardarin clone acquired from NeuroMab were used to measure total LRRK2, and novel polyclonal antibodies generated in rabbits against pS1292-LRRK2 were used to quantify total-LRRK2 and pS1292-LRRK2 in Western blots. Total LRRK2, pS1292-LRRK2 and the ratio between total LRRK2 and pS1292-LRRK2 were compared between G2019S carriers with PD and non-carriers with and without PD. Results: All three groups were similar in age (mean=67.0; SD=7.5). The ratio of pS1292-LRRK2 to total LRRK2 was significantly different between LRRK2+/PD+ (mean=0.90; SD=0.28; range 0.60-1.46) and both LRRK2-/PD+ (mean=0.20; SD=0.03; range 0.16-0.24, p<0.001) and LRRK2-/PD- (mean=0.19; SD=0.09; range 0.10-0.29; p<0.001). The values did not overlap. Conclusion: A ratio of phosphorylated pS1292-LRRK2 to total LRRK2 in urine may distinguish between LRRK2+/PD+ and non-carriers with and without PD. Future studies are required to confirm that this ratio signifies LRRK2 autophosphorylation activity in the brain and to test if the elevated ratio is associated with disease characteristics in men and women. Disclosure: Dr. Alcalay has nothing to disclose. Dr. Fraser has nothing to disclose. Dr. West has nothing to disclose.