Microglial implication in Parkinson's Disease: studying functional and morphological changes occurring in LRRK2 microglia during PD pathophysiology using a stem cell derived human model

Abstract

[eng] Parkinson’s disease (PD) is an incurable neurodegenerative disease characterized by the loss of neuromelanin (NM)-containing dopamine neurons in Substantia Nigra pars compacta (SNpc) and accumulation of insoluble cytoplasmic protein inclusions known as Lewy bodies. Microglial activation, astrocyte reactivity and lymphocyte infiltration also occur in PD. Here, we hypothesize that PD is initiated years before the emergence of motor dysfunction in response to several mechanisms some of which triggered following microglia activation that impact negatively in neuronal survival. Taking advantage of our human iPSC-based model of PD, we first generated human Microglia-like cells (hMG) from LRRK2-PD and Control iPSCs and confirmed their identity by using specific microglial markers. We then carried out functional studies with pro-inflammatory stimuli such as LPS or NM, which revealed a higher motility, cytokine release and phagocytic activity of LRRK2-PD hMG compared to control hMG. In addition, we found that extracellular NM particles induced microglial activation and increases ROS production in LRRK2-PD microglia. The use of a corrected isogenic PD hMG reverted all previous phenotypes, confirming a LRRK2-dependent activation of hMG. Upon co-culture with LRRK2-PD hMG and in the presence of NM particles, Control Dopaminergic neurons (DAn) displayed morphological signs of neurodegeneration, such as short and few neurites as well as beaded necklace-like neurites, as well as increased neuronal loss. Thus, our findings indicate a critical role for neuromelanin-activated microglia in LRRK2-PD and may serve as a valid human cellular model to test compounds that can lower risk for PD or disease progression.