LRRK2 in Drosophila Melanogaster Model: Insights into Cellular Dysfunction and Neuroinflammation in Parkinson's Disease

Abstract

Parkinson's disease (PD) is a fatal neurodegenerative disease for which there are no still effective treatments able to stop or slow down neurodegeneration. To date, pathological mutations in the leucine-rich repeat kinase 2 (LRRK2) gene have been identified as the major genetic cause of PD, although the molecular mechanism responsible for the loss of dopaminergic neurons is still cryptic. In this review, we explore the contribution of Drosophila models to the elucidation of LRRK2 function in different cellular pathways in either neurons or glial cells. Importantly, recent studies have shown that LRRK2 is highly expressed in immunocompetent cells, including astrocytes and microglia in the brain, compared to neuronal expression. LRRK2 mutations are also strongly associated with the development of inflammatory diseases and the production of inflammatory molecules. Using Drosophila models, this paper shows that a genetic reduction of the inflammatory response protects flies from the neurodegeneration induced by LRRK2 pathological mutant expression.

Keywords: Attacin-A; Drosophila; LRRK2; Parkinson’s disease.

Figure 1

Schematic representation of the functional domains of human LRRK2 (hLRRK2) compared to Drosophila LRRK (dLRRK). The key functional domains are highly conserved between human and Drosophila, including the aminoacidic residues mutated in the human pathological variants (R114C, Y1669C, and G2019S). Armadillo (ARM), Ankyrin (ANK), Leucine-rich-repeat (LRR), Ras of complex proteins (ROC), C-terminal of ROC (COR), Kinase, and WD40 domains.

Figure 2

Analysis of AttA RNAi expression on the toxic phenotype due to LRRK2 R1441C expression under the control of actin-GAL4 driver. Transgenic lines used: Actin-GAL4-White (White), Actin-GAL4-UAS-LRRK2 R1441C (R1441C), Actin-GAL4-UAS AttA RNAi (AttA RNAi), Actin-GAL4-UAS-LRRK2 R1441C; UAS-AttA RNAi (R1441C; AttA RNAi). (A) Evaluation of LRRK2 and phospho-RAB10 expression by western blot analysis in head protein extracts of the indicated genotypes in 7-day-old animals. Anti-Tubulin antibody was used to normalize the different protein samples. (B) Evaluation of AttA expression by Real-Time PCR using RNA extracted from the heads of the different genotypes in 7-day-old animals. L32 was used as control to normalize the different samples. * p < 0.05 and ** p < 0.005. (C) Evaluation by climbing assay of locomotor activity of the different 45-day-old Drosophila lines. *** p < 0.001. (D) Schematic representation of PPL1 cluster localization in Drosophila brain and staining of dopaminergic neurons in PPL1 cluster of 45-day-old Drosophila lines of the different genotypes by immunofluorescence on whole brains using anti-TH antibody. (E) Quantification of dopaminergic neuronal number in the PPL1 cluster of the different genotypes. ** p < 0.005.

Figure 3

LRRK2 is highly expressed in glial cells compared to neurons. Several experimental results, in neurons, indicate an important role for LRRK2 in vesicle trafficking, autophagy, lysosome function, and protein translation. In glial cells, in addition to alterations in these molecular pathways, an alteration in the production of inflammatory molecules or molecules/proteins involved in neuronal-glial cell communication has been demonstrated. In addition, LRRK2 is significantly induced by immunoregulatory proteins such as by interferon-γ, further supporting the role of LRRK2 at the interface between neuronal and non-neuronal cells.