LRRK2 interactions with α-synuclein in Parkinson's disease brains and in cell models

Mutations in the genes encoding leucine-rich repeat kinase 2 (LRRK2) and alpha-synuclein are associated with both autosomal dominant and idiopathic forms of Parkinson's disease (PD). alpha-Synuclein is the main protein in Lewy bodies, hallmark inclusions present in both sporadic and familial PD. We show that in PD brain tissue, the levels of LRRK2 are positively related to the increase in alpha-synuclein phosphorylation and aggregation in affected brain regions (amygdala and anterior cingulate cortex), but not in the unaffected visual cortex. In disease-affected regions, we show co-localization of these two proteins in neurons and Lewy body inclusions. Further, in vitro experiments show a molecular interaction between alpha-synuclein and LRRK2 under endogenous and over-expression conditions. In a cell culture model of alpha-synuclein inclusion formation, LRRK2 co-localizes with the alpha-synuclein inclusions, and knocking down LRRK2 increases the number of smaller inclusions. In addition to providing strong evidence for an interaction between LRRK2 and alpha-synuclein, our results shed light on the complex relationship between these two proteins in the brains of patients with PD and the underlying molecular mechanisms of the disease.