LRRK2 Ablation Attenuates Αlpha-Synuclein–Induced Neuroinflammation Without Affecting Neurodegeneration or Neuropathology In Vivo

The development of disease-modifying therapies for Parkinson’s disease is a major challenge which would be facilitated by a better understanding of the pathogenesis. Leucine-rich repeat kinase 2 (LRRK2) and α-synuclein are key players in Parkinson’s disease, but their relationship remains incompletely resolved. Previous studies investigating the effect of LRRK2 on α-synuclein–induced neurotoxicity and neuroinflammation in preclinical Parkinson’s disease models have reported conflicting results. Here, we aimed to further explore the functional interaction between α-synuclein and LRRK2 and to evaluate the therapeutic potential of targeting physiological LRRK2 levels. We studied the effects of total LRRK2 protein loss as well as pharmacological LRRK2 kinase inhibition in viral vector–mediated α-synuclein–based Parkinson’s disease models developing early- and late-stage neurodegeneration. Surprisingly, total LRRK2 ablation or in-diet treatment with the LRRK2 kinase inhibitor MLi-2 did not significantly modify α-synuclein–induced motor deficits, dopaminergic cell loss, or α-synuclein pathology. Interestingly, we found a significant effect on α-synuclein–induced neuroinflammatory changes in the absence of LRRK2, with a reduced microglial activation and CD4+ and CD8+ T cell infiltration. This observed lack of protection against α-synuclein–induced toxicity should be well considered in light of the ongoing therapeutic development of LRRK2 kinase inhibitors for idiopathic Parkinson’s disease. Future studies will be crucial to understand the link between these neuroinflammatory processes and disease progression as well as the role of α-synuclein and LRRK2 in these pathological events.