Exacerbated cellular senescence in human dopaminergic neurons along with an increase in LRRK2 kinase activity

Abstract

Background: Parkinson’s disease (PD) is a common neurodegenerative disease, characterized by symptoms like tremors, muscle rigidity, and slow movement. The main cause of these symptoms is the loss of dopamine-producing neurons in a brain area called the substantia nigra. Various genetic and environmental factors contribute to this neuronal loss. Once symptoms of PD begin, they worsen with age, which also impacts several critical cellular processes. Leucine-rich repeat kinase 2 (LRRK2) is a gene associated with PD. Certain mutations in LRRK2, such as G2019S, increase its activity, disrupting cellular mechanisms necessary for healthy neuron function, including autophagy and lysosomal activity. Exposure to rotenone (RTN) promotes LRRK2 activity in neurons and contributes to cellular senescence and α-syn accumulation. Methods: In this study, human dopaminergic progenitor cells were reprogrammed to study the effects of RTN with the co-treatment of LRRK2 inhibitor on cellular senescence. We measured the cellular senescence using quantifying proteins of senescence markers, such as p53, p21, Rb, phosphory-lated Rb, and β-galatocidase, and the enzymatic activity of senescence-associated β-galatocidase. And we estimated the levels of accumulated α-synuclein (α-syn), which is increased via the impaired autophagy-lysosomal pathway by cellular senescence. Then, we evaluated the association of the G2019S LRRK2 mutation and senescence-associated β-galatocidase and the levels of accumulated or secreted α-syn, and the neuroinflammatory responses mediated by the secreted α-syn in rat primary microglia were determined using the release of pro-inflammatory cytokines. Results: RTN raised senescence markers and affected the phosphorylation of Rab10, a substrate of LRRK2. The inhibiting agent MLI2 reduced these senescence markers and Rab10 phosphorylations. Additionally, RTN increased α-syn levels in the neurons, while MLI2 aided in degrading it. When focusing on cells from PD patients with the G2019S mutation, an increase in cellular senescence and release of α-syn was observed, provoking neuroinflammation. Treatment with the LRRK2 inhibitor MLI2 decreased both cellular senescence and α-syn secretion, thereby mitigating inflammatory responses. Conclusion: Overall, inhibiting LRRK2 may provide a beneficial strategy for managing PD.