Pathogenic LRRK2 variants are gain-of-function mutations that enhance LRRK2-mediated repression of β-catenin signaling

Abstract

Background LRRK2 mutations and risk variants increase susceptibility to inherited and idiopathic Parkinson’s disease, while recent studies have identified potential protective variants. This, and the fact that LRRK2 mutation carriers develop symptoms and brain pathology almost indistinguishable from idiopathic Parkinson’s disease, has led to enormous interest in this protein. LRRK2 has been implicated in a range of cellular events, but key among them is canonical Wnt signalling, which results in increased levels of transcriptionally active β-catenin. This pathway is critical for the development and survival of the midbrain dopaminergic neurones typically lost in Parkinson’s disease.MethodsHere we use Lrrk2 knockout mice and fibroblasts to investigate the effect of loss of Lrrk2 on canonical Wnt signalling in vitro and in vivo. Micro-computed tomography was used to study predicted tibial strength, while pulldown assays were employed to measure brain β-catenin levels. A combination of luciferase assays, immunofluorescence and co-immunoprecipitation were performed to measure canonical Wnt activity and investigate the relationship between LRRK2 and β-catenin. TOPflash assays are also used to study the effects of LRRK2 kinase inhibition and pathogenic and protective LRRK2 mutations on Wnt signalling. Data were tested by Analysis of Variance.ResultsLoss of Lrrk2 causes a dose-dependent increase in the levels of transcriptionally active β-catenin in the brain, and alters tibial bone architecture, decreasing the predicted risk of fracture. Lrrk2 knockout cells display increased TOPflash and Axin2 promoter activities, both basally and following Wnt activation. Consistently, over-expressed LRRK2 was found to bind β-catenin and repress TOPflash activation. Some pathogenic LRRK2 mutations and risk variants further suppressed TOPflash, whereas the protective R1398H variant increased Wnt signalling activity. LRRK2 kinase inhibitors affected canonical Wnt signalling differently due to off-targeting; however, specific LRRK2 inhibition reduced canonical Wnt signalling similarly to pathogenic mutations.ConclusionsLoss of LRRK2 causes increased canonical Wnt activity in vitro and in vivo. In agreement, over-expressed LRRK2 binds and represses β-catenin, suggesting LRRK2 may act as part of the β-catenin destruction complex. Since some pathogenic LRRK2 mutations enhance this effect while the protective R1398H variant relieves it, our data strengthen the notion that decreased canonical Wnt activity is central to Parkinson’s disease pathogenesis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13024-017-0153-4) contains supplementary material, which is available to authorized users.

Parkinson's disease, aging and adult neurogenesis: Wnt/β‐catenin signalling as the key to unlock the mystery of endogenous brain repair

“…Activation of Wnt signalling plays a role in producing regionally homogeneous populations of NSCs and neurons. For instance, pivotal genes whose mutations are linked to PD negatively impact on WβC‐signalling (Berwick and Harvey, , Berwick et al, ), resulting in an inhibition of the ability of human induced pluripotent cells (iPSCs) to differentiate into DAergic neurons (Awad et al, ; Momcilovic et al, ; Moya et al, ). Specifically, downregulation of WβC‐signalling in iPSC‐derived NSCs due to a GBA1 mutation resulted in a dramatic decrease in the survival of DAergic progenitors (Awad et al, ) .…”

Microglia Polarization, Gene-Environment Interactions and Wnt/β-Catenin Signaling: Emerging Roles of Glia-Neuron and Glia-Stem/Neuroprogenitor Crosstalk for Dopaminergic Neurorestoration in Aged Parkinsonian Brain

“…Finally, the crucial link between inflammation and PD is further exemplified by the fact that key PD-associated genes, such as α-Syn (SNCA), PARK2, deglycase (DJ-1), leucine-rich repeat kinase 2 (LRRK2), and glucocerebrosidase (GBA) are all expressed in immune cells, suggesting their potential to modulate inflammation (Dzamko et al, 2015 ). Reciprocally, an increasing number of PD-related genes including LRRK2, VPS35, PINK1, UCHL-1, Parkin, ATP6AP2, and GBA modulate the canonical Wnt pathway (Berwick et al, 2017 and Refs. therein), further underlinying a critical Wnt/inflammatory connection in PD (Marchetti and Pluchino, 2013 ).…”

Leucine-Rich Repeat Kinase 2 in Parkinson’s Disease: Updated from Pathogenesis to Potential Therapeutic Target

“…Despite evidence of the relationship between LRRK2 and Wnt signaling, the specific effects of LRRK2 on downstream components remain unclear. Recently, Berwick et al [52] reported that the primary role of LRRK2 in the canonical Wnt signaling pathway is β-catenin repression: loss of LRRK2 increases Wnt/β-catenin activity, whereas overexpressed LRRK2 binds and represses β-catenin. Another study assessing the effect of LRRK2 on Wnt/planar cell polarity (PCP) signaling indicated that LRRK2 activates this pathway via interactions with multiple Wnt/PCP signaling components [53].…”