Urinary LRRK2 phosphorylation predicts parkinsonian phenotypes in G2019S LRRK2 carriers

Regulation of LRRK2 by Phosphatases

LRRK2 is a highly phosphorylated protein, and evidence of a physiological role for LRRK2 phosphorylation has accumulated in recent years for cellular phosphosites, many of which are found in the ANK-LRR interdomain region, i.e., the S910/S935/S955/S973 sites as well as recently for autophosphorylation sites, at least one of which has been confirmed in cells, S1292. LRRK2 phosphorylation is modulated in several disease or potential therapy relevant conditions such as in disease mutant variants of LRRK2 or following LRRK2 kinase inhibitor treatment. This chapter will focus on the regulation of LRRK2 phosphorylation and more specifically the role of phosphatases in LRRK2 dephosphorylation. This will include reviewing the conditions in which LRRK2 is found to be dephosphorylated, the molecular partners and phosphatases involved in regulating LRRK2 phosphorylation, as well as discussing how LRRK2 phosphatases may be therapeutic targets or biomarkers in their own right.

Exosomes in Parkinson's Disease

Exosomes, nano-sized extracellular vesicles secreted by most cell types, are found in all kinds of biological fluids and tissues, including the central nervous system (CNS). The proposed functions of these vesicles include roles in cell-cell signaling, removal of cellular debris, and transfer of pathogens between cells. Many studies have revealed that exosomes derived from the CNS occur in the cerebrospinal fluid and peripheral body fluids, and their contents are altered during disease, making them an appealing target for biomarker development in Parkinson's disease (PD). Exosomes have been shown to spread toxic α-synuclein (αsyn) between cells and induce apoptosis, which suggests a key mechanism underlying the spread of αsyn aggregates in the brain and the acceleration of pathology in PD. However, potential neuroprotective roles of exosomes in PD have also been reported. On the treatment side, as drug delivery vehicles, exosomes have been used to deliver small interfering RNAs and catalase to the brain, and have shown clear therapeutic effects in a mouse model of PD. These features of exosomes in PD make them extremely interesting from the point of view of developing novel diagnostic and therapeutic approaches.

Leucine-rich repeat kinase 2 and Parkinson's disease

Leucine-rich repeat kinase 2 (LRRK2) is a large multidomain protein that is expressed in many tissues and participates in numerous biological pathways. Mutations in LRRK2 are recognized as genetic risk factors for familial Parkinson's disease (PD) and may also represent causal factors in the more common sporadic form of PD. The structure of LRRK2 comprises a combination of GTPase, kinase, and scaffolding domains. This functional diversity, combined with a potentially central role in genetic and idiopathic PD motivates significant effort to further credential LRRK2 as a therapeutic target. Here, we review the current understanding for LRRK2 function in normal physiology and PD, with emphasis on insight gained from proteomic approaches.

Ser(P)-1292 LRRK2 in urinary exosomes is elevated in idiopathic Parkinson's disease

BACKGROUND

Mutations in Leucine-rich repeat kinase 2 (LRRK2) enhance levels of the autophosphorylated LRRK2 protein and are the most common known cause of inherited Parkinson's disease (PD). LRRK2 has been further implicated in susceptibility to idiopathic PD in genetic association studies.

OBJECTIVE

The objective of this study was to compare autophosphorylated Ser(P)-1292 LRRK2 levels from biobanked urine samples with clinical data in PD patients and controls.

METHODS

Ser(P)-1292 LRRK2 levels were measured from urine exosome fractions from 79 PD patients and 79 neurologically healthy controls enrolled in the Parkinson Disease Biomarker Program at the University of Alabama at Birmingham.

RESULTS

Ser(P)-1292 LRRK2 levels were higher in men than women (P < .0001) and elevated in PD patients when compared with controls (P = .0014). Ser(P)-1292 LRRK2 levels were higher in PD cases with worse cognition and correlated with poor performance in MoCA (r = -0.2679 [-0.4628 to -0.0482]), MDS-UPDRS subscales 1 and 2 (r = 0.2239 [0.0014-0.4252], 0.3404 [0.1276-0.5233], respectively), Epworth Sleepiness Scale (r = 0.3215 [0.1066-0.5077]), and Modified Schwab and England Activities of Daily Living Scales (r = -0.4455 [-0.6078 to -0.2475]). Ser(P)-1292 LRRK2 levels predicted those with worse cognitive impairment in PD patients with some success (c = 0.73).

CONCLUSIONS

Urinary exosome Ser(P)-1292 LRRK2 levels are elevated in idiopathic PD and correlated with the severity of cognitive impairment and difficultly in accomplishing activities of daily living. These results implicate biochemical changes in LRRK2 in idiopathic PD. © 2016 International Parkinson and Movement Disorder Society.

Phos-tag analysis of Rab10 phosphorylation by LRRK2: a powerful assay for assessing kinase function and inhibitors

Autosomal dominant mutations that activate the leucine-rich repeat kinase 2 (LRRK2) cause inherited Parkinson's disease. Recent work has revealed that LRRK2 directly phosphorylates a conserved threonine/serine residue in the effector-binding switch-II motif of a number of Rab GTPase proteins, including Rab10. Here we describe a facile and robust method to assess phosphorylation of endogenous Rab10 in mouse embryonic fibroblasts (MEFs), lung and spleen-derived B-cells, based on the ability of the Phos-tag reagent to retard the electrophoretic mobility of LRRK2-phosphorylated Rab10. We exploit this assay to show that phosphorylation of Rab10 is ablated in kinase-inactive LRRK2[D2017A] knockin MEFs and mouse lung, demonstrating that LRRK2 is the major Rab10 kinase in these cells/tissue. We also establish that the Phos-tag assay can be deployed to monitor the impact that activating LRRK2 pathogenic (G2019S and R1441G) knockin mutations have on stimulating Rab10 phosphorylation. We show that upon addition of LRRK2 inhibitors, Rab10 is dephosphorylated within 1-2 min, markedly more rapidly than the Ser(935) and Ser(1292) biomarker sites that require 40-80 min. Furthermore, we find that phosphorylation of Rab10 is suppressed in LRRK2[S910A+S935A] knockin MEFs indicating that phosphorylation of Ser(910) and Ser(935) and potentially 14-3-3 binding play a role in facilitating the phosphorylation of Rab10 by LRRK2 in vivo The Rab Phos-tag assay has the potential to significantly aid with evaluating the effect that inhibitors, mutations and other factors have on the LRRK2 signalling pathway.