Pathological α-synuclein recruits LRRK2 expressing pro-inflammatory monocytes to the brain

Abstract

Background Leucine rich repeat kinase 2 (LRRK2) and SNCA are genetically linked to late-onset Parkinson’s disease (PD). Aggregated α-synuclein pathologically defines PD. Recent studies identified elevated LRRK2 expression in pro-inflammatory CD16+ monocytes in idiopathic PD, as well as increased phosphorylation of the LRRK2 kinase substrate Rab10 in monocytes in some LRRK2 mutation carriers. Brain-engrafting pro-inflammatory monocytes have been implicated in dopaminergic neurodegeneration in PD models. Here we examine how α-synuclein and LRRK2 interact in monocytes and subsequent neuroinflammatory responses. Methods Human and mouse monocytes were differentiated to distinct transcriptional states resembling macrophages, dendritic cells, or microglia, and exposed to well-characterized human or mouse α-synuclein fibrils. LRRK2 expression and LRRK2-dependent Rab10 phosphorylation were measured with monoclonal antibodies, and myeloid cell responses to α-synuclein fibrils in R1441C-Lrrk2 knock-in mice or G2019S-Lrrk2 BAC mice were evaluated by flow cytometry. Chemotaxis assays were performed with monocyte-derived macrophages stimulated with α-synuclein fibrils and microglia in Boyden chambers. Results α-synuclein fibrils robustly stimulate LRRK2 and Rab10 phosphorylation in human and mouse macrophages and dendritic-like cells. In these cells, α-synuclein fibrils stimulate LRRK2 through JAK-STAT activation and intrinsic LRRK2 kinase activity in a feed-forward pathway that upregulates phosphorylated Rab10. In contrast, LRRK2 expression and Rab10 phosphorylation are both suppressed in microglia-like cells that are otherwise highly responsive to α-synuclein fibrils. Corroborating these results, LRRK2 expression in the brain parenchyma occurs in pro-inflammatory monocytes infiltrating from the periphery, distinct from brain-resident microglia. Mice expressing pathogenic LRRK2 mutations G2019S or R1441C have increased numbers of infiltrating pro-inflammatory monocytes in acute response to α-synuclein fibrils. In primary cultured macrophages, LRRK2 kinase inhibition dampens α-synuclein fibril and microglia-stimulated chemotaxis. Conclusions Pathologic α-synuclein activates LRRK2 expression and kinase activity in monocytes and induces their recruitment to the brain. These results predict that LRRK2 kinase inhibition may attenuate damaging pro-inflammatory monocyte responses in the brain.

Monocyte biomarkers define sargramostim treatment outcomes for Parkinson's disease

“…Over the treatment course, sargramostim resulted in an overall decrease in UPDRS part III (UPDRS III) scores compared to baseline for all subjects. 14 Although, CNS innate immune microglia are comprehensively studied in PD animal models and patients, 3 , 29 , 30 peripheral monocytes have received less attention due to a past perception of immune privileged CNS. Altered monocyte functions have been reported in the periphery and CSF of PD patients.…”

Elevated Urinary Rab10 Phosphorylation in Idiopathic Parkinson Disease

“…Because LRRK2 is linked to iPD, but also to other diseases of inflammation including Crohn's disease and mycobacterial infection, it could be that late systemic inflammation in worsening disease may manifest in increased LRRK2 activity and increased phosphorylated Rab10 (eg, responsive to aggregated α-synuclein as we detected recently in monocytes). 31 Evaluation of LRRK2 markers in other diseases besides iPD would be informative in this regard. Some evidence for systemic LRRK2 changes driving central responses in the brain via inflammation has been observed in mouse models.…”

Structural and functional landscape of α-synuclein fibril conformations amplified from cerebrospinal fluid

“…Microglia HLA-DRα correlates with α-synuclein inclusions in Lewy body dementia 36 . To gain insight into whether the fibril products produced from DLB-CSF amplifications might differ with respect to evoked microglia phenotypes, we differentiated primary human monocytes procured from healthy volunteers to a microglia-like state as previously described 37,38 . Adherent cells here robustly express the microglia-specific receptor P2RY12 receptor, and within minutes the cells internalize exogenous DLB-CSF amplified α-synuclein fibrils ( Fig.…”