Pathogenic LRRK2 requires secondary factors to induce cellular toxicity

Evy Lobbestael,Veerle Baekelandt,Chris Van Den Haute,Francesca Macchi,Jean-Marc Taymans

doi:10.1042/bsr20202225

Abstract

Pathogenic mutations in the leucine-rich repeat kinase 2 (LRRK2) gene belong to the most common genetic causes of inherited Parkinson’s disease (PD) and variations in its locus increase the risk to develop sporadic PD. Extensive research efforts aimed at understanding how changes in the LRRK2 function result in molecular alterations that ultimately lead to PD. Cellular LRRK2-based models revealed several potential pathophysiological mechanisms including apoptotic cell death, LRRK2 protein accumulation and deficits in neurite outgrowth. However, highly variable outcomes between different cellular models have been reported. Here, we have investigated the effect of different experimental conditions, such as the use of different tags and gene transfer methods, in various cellular LRRK2 models. Readouts included cell death, sensitivity to oxidative stress, LRRK2 relocalization, α-synuclein aggregation and neurite outgrowth in cell culture, as well as neurite maintenance in vivo. We show that overexpression levels and/or the tag fused to LRRK2 affect the relocalization of LRRK2 to filamentous and skein-like structures. We found that overexpression of LRRK2 per se is not sufficient to induce cellular toxicity or to affect α-synuclein-induced toxicity and aggregate formation. Finally, neurite outgrowth/retraction experiments in cell lines and in vivo revealed that secondary, yet unknown, factors are required for the pathogenic LRRK2 effects on neurite length. Our findings stress the importance of technical and biological factors in LRRK2-induced cellular phenotypes and hence imply that conclusions based on these types of LRRK2-based assays should be interpreted with caution.

Highlights

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of genetic forms of Parkinson’s disease (PD) known to date [1,2]
To assess whether LRRK2 overexpression affects the sensitivity of cells to oxidative stress, cells with stable overexpression of LRRK2 WT, K1906M or G2019S were treated with a range of H2O2 concentrations
The assumption that a gain of function underlies the pathogenic mechanism of LRRK2 mutations has incited many groups to overexpress LRRK2 variants in cell culture, in order to generate a representative cellular PD model and obtain insight in the mechanisms by which LRRK2 mutations can induce neurodegeneration

Summary

Introduction

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of genetic forms of Parkinson’s disease (PD) known to date [1,2]. Association studies have identified variations in the LRRK2 locus as a risk factor for sporadic PD [3,4,5,6]. Since its identification in 2004, intense investigations have focused on identifying the mechanisms by which pathogenic mutations in LRRK2 affect its physiological function(s) that lead to neurodegeneration. Overexpression of pathogenic variants of LRRK2 in cell culture or primary neuronal cells has been reported to induce relevant phenotypes, including cell toxicity, increased sensitivity to oxidative stress, disturbed neurites and protein inclusion formation. These phenotypes could not always be replicated in independent studies [8]

Objectives

Methods

Results

Conclusion