Lrrk2 alleles modulate inflammation during microbial infection of mice in a sex-dependent manner.

Variants in the leucine-rich repeat kinase-2 (LRRK2) gene are associated with Parkinson's disease, leprosy, and Crohn's disease, three disorders with inflammation as an important component. Because of its high expression in granulocytes and CD68-positive cells, LRRK2 may have a function in innate immunity. We tested this hypothesis in two ways. First, adult mice were intravenously inoculated with Salmonella typhimurium, resulting in sepsis. Second, newborn mouse pups were intranasally infected with reovirus (serotype 3 Dearing), which induced encephalitis. In both mouse models, wild-type Lrrk2 expression was protective and showed a sex effect, with female Lrrk2-deficient animals not controlling infection as well as males. Mice expressing Lrrk2 carrying the Parkinson's disease-linked p.G2019S mutation controlled infection better, with reduced bacterial growth and longer animal survival during sepsis. This gain-of-function effect conferred by the p.G2019S mutation was mediated by myeloid cells and was abolished in animals expressing a kinase-dead Lrrk2 variant, p.D1994S. Mouse pups with reovirus-induced encephalitis that expressed the p.G2019S Lrrk2 mutation showed increased mortality despite lower viral titers. The p.G2019S mutant Lrrk2 augmented immune cell chemotaxis and generated more reactive oxygen species during virulent infection. Reovirus-infected brains from mice expressing the p.G2019S mutant Lrrk2 contained higher concentrations of α-synuclein. Animals expressing one or two p.D1994S Lrrk2 alleles showed lower mortality from reovirus-induced encephalitis. Thus, Lrrk2 alleles may alter the course of microbial infections by modulating inflammation, and this may be dependent on the sex and genotype of the host as well as the type of pathogen.

Parkinson's disease-linked LRRK2 is expressed in circulating and tissue immune cells and upregulated following recognition of microbial structures.

Sequence variants at or near the leucine-rich repeat kinase 2 (LRRK2) locus have been associated with susceptibility to three human conditions: Parkinson's disease (PD), Crohn's disease and leprosy. As all three disorders represent complex diseases with evidence of inflammation, we hypothesized a role for LRRK2 in immune cell functions. Here, we report that full-length Lrrk2 is a relatively common constituent of human peripheral blood mononuclear cells (PBMC) including affinity isolated, CD14(+) monocytes, CD19(+) B cells, and CD4(+) as well as CD8(+) T cells. Up to 26% of PBMC from healthy donors and up to 43% of CD14(+) monocytes were stained by anti-Lrrk2 antibodies using cell sorting. PBMC lysates contained full-length (>260 kDa) and higher molecular weight Lrrk2 species. The expression of LRRK2 in circulating leukocytes was confirmed by microscopy of human blood smears and in sections from normal midbrain and distal ileum. Lrrk2 reactivity was also detected in mesenteric lymph nodes and spleen (including in dendritic cells), but was absent in splenic mononuclear cells from lrrk2-null mice, as expected. In cultured bone marrow-derived macrophages from mice we made three observations: (i) a predominance of higher molecular weight lrrk2; (ii) the reduction of autophagy marker LC3-II in (R1441C)lrrk2-mutant cells (<31%); and (iii) a significant up-regulation of lrrk2 mRNA (>fourfold) and protein after exposure to several microbial structures including bacterial lipopolysaccharide and lentiviral particles. We conclude that Lrrk2 is a constituent of many cell types in the immune system. Following the recognition of microbial structures, stimulated macrophages respond with altered lrrk2 gene expression. In the same cells, lrrk2 appears to co-regulate autophagy. A pattern recognition receptor-type function for LRRK2 could explain its locus' association with Crohn's disease and leprosy risk. We speculate that the role of Lrrk2 in immune cells may also be relevant to the susceptibility of developing PD or its progression.