Abstract

Leucine-rich repeat kinase 2 (LRRK2) encodes a complex protein that includes kinase and GTPase domains. Genome-wide association studies have identified dominant LRRK2 alleles that predispose their carriers to late-onset idiotypic Parkinson's disease (PD) and also to autoimmune disorders such as Crohn's disease. Considerable evidence indicates that PD initiation and progression involve activation of innate immune functions in microglia, which are brain-resident macrophages. Here we asked whether LRRK2 modifies inflammatory signaling and how this modification might contribute to PD and Crohn's disease. We used RNA-Seq–based high-resolution transcriptomics to compare gene expression in activated primary macrophages derived from WT and Lrrk2 knockout mice. Remarkably, expression of a single gene, Rap guanine nucleotide exchange factor 3 (Rapgef3), was strongly up-regulated in the absence of LRRK2 and down-regulated in its presence. We observed similar regulation of Rapgef3 expression in cells treated with a highly specific inhibitor of LRRK2 protein kinase activity. Rapgef3 encodes an exchange protein, activated by cAMP 1 (EPAC-1), a guanine nucleotide exchange factor that activates the small GTPase Rap-1. Rap-1 mediates cell adhesion, polarization, and directional motility, and our results indicate that LRRK2 modulates chemotaxis of microglia and macrophages. Dominant PD-associated LRRK2 alleles may suppress EPAC-1 activity, further restricting motility and preventing efficient migration of microglia to sites of neuronal damage. Functional analysis in vivo in a subclinical infection model also indicated that Lrrk2 subtly modifies the inflammatory response. These results indicate that LRRK2 modulates the expression of genes involved in murine immune cell chemotaxis.

Highlights

  • Leucine-rich repeat kinase 2 (LRRK2) encodes a complex protein that includes kinase and GTPase domains

  • Rap-1 mediates cell adhesion, polarization, and directional motility, and our results indicate that LRRK2 modulates chemotaxis of microglia and macrophages

  • We investigated how Lrrk2 modifies inflammatory signaling mediated by LPS and muramyl dipeptide (MDP)

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Summary

Edited by Alex Toker

Leucine-rich repeat kinase 2 (LRRK2) encodes a complex protein that includes kinase and GTPase domains. Functional analysis in vivo in a subclinical infection model indicated that Lrrk subtly modifies the inflammatory response These results indicate that LRRK2 modulates the expression of genes involved in murine immune cell chemotaxis. The most common mutation in the LRRK2 gene results in a change from glycine to serine at amino acid 2019 (G2019S) This SNP is the highest known risk factor for development of Parkinson’s disease, accounting for 5%–7% of autosomal dominant familial cases [4, 5] and 1%–2% of sporadic cases in Western populations [6]. We used high-resolution transcriptomics to compare gene expression in primary macrophages derived from WT and Lrrk2-deficient mice. This analysis reveals that LRRK2 modulates the expression of a small subset of genes that are involved in chemotaxis and membrane remodeling

Results
Differential gene expression
Gene Symbol
Discussion
Experimental procedures
Animal infection and data collection
Flow cytometry
Immunofluorescence microscopy
Full Text
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