LRRK2 contributes to monocyte dysregulation in Parkinson’s disease

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common cause of familial Parkinson’s disease (PD) [20, 32]. Common polymorphisms in LRRK2 have been shown to modulate the risk for sporadic PD [6, 23, 24] strengthening the idea that inherited and sporadic PD share common underlying pathways. Although LRRK2 has been associated with a variety of cellular functions, including autophagy [1], mitochondrial function/dynamics [30] and microtubule/cytoskeletal dynamics [12], the overall physiological function of LRRK2 and its role in PD are only partially understood. Relatively recent studies also support a role for LRRK2 as regulator of inflammation. Substantial levels of LRRK2 protein and mRNA have been reported in immune cells like peripheral blood mononuclear cells (PBMCs), including B-cells, monocytes/macrophages, and dendritic cells [9, 13, 16, 29]. Moreover, LRRK2 has been shown to be involved in the activation and maturation of immune cells [29], in controlling the radical burst against pathogens in macrophages [9] and in modulating neuroinflammation by cytokine signaling [10, 19]. Remarkably, elevated levels of serum cytokines (IL-2, IL-4, IL-6, IL-10, TNFα) in PD patients [4, 22, 27] point to an involvement of the peripheral immune system in the pathogenesis of PD. Recently, we found an enrichment of “classical” CD14CD16 monocyte subpopulation in the peripheral blood of PD patients together with a dysregulation of inflammatory pathways, phagocytosis deficits as well as hyperactivation of PD monocytes in response to LPS treatment, which correlated to PD severity [11]. Here, we sought to study the contribution of LRRK2 to the dysregulation of monocytes in Parkinson’s disease. We set out to obtain a comprehensive picture of LRRK2 levels in circulating monocyte subpopulations as well as in lymphoid B-cells in PD patients. To determine the intracellular LRRK2 protein levels in the different immune cells we established a flow cytometry-based technique for intracellular LRRK2 staining. To verify the specificity of the anti-LRRK2 antibody used in this study [Novus Biologicals (NB300-268AF647)] isolated murine spleen cells from LRRK2 knockout (KO) mice [14] and mice overexpressing human wild-type (WT) LRRK2 (LRRK2 WT-OX mice) [17, 28] were processed, stained and analyzed as described in the supplementary material and method section (Additional file 1). While we found a highly LRRK2-positive population with the Novus antibody in spleen samples of LRRK2 WT-OX mice (black histogram Fig. 1a) no unspecific staining was found in LRRK2 KO mice (dark grey histogram Fig. 1a) or with the isotype control (IgG ctrl.) in spleen samples of LRRK2 WT-OX mice (light grey histogram Fig. 1a). We used a combination of our well established five-color FACS analysis strategy [5, 11] to distinguish “classical” CD14CD16 (hereinafter referred to as CD14) monocytes and “non-classical” CD14CD16 (hereinafter referred to as CD16) monocytes together with the intracellular LRRK2 staining. We found that both monocyte subpopulations were LRRK2 positive (orange histograms Fig. 1b), while the IgG and unstained controls did not show any significant staining (dark and light grey histograms Fig. 1b). Strikingly, we found significantly higher LRRK2 protein levels in CD16 monocytes (upper panel Fig. 1c) as well as in CD14 monocytes (lower panel Fig. 1c) of PD patients (n = 26; mean age 71.0 years) compared to ageand sex matched healthy controls (n = 26; mean age 68.7 years). Of note, * Correspondence: [email protected] Department of Neurology, Ulm University, Albert Einstein Allee 11, 89081 Ulm, Germany Full list of author information is available at the end of the article