Nuclear ASC speck formation in microglia is associated with inflammasome priming and is exacerbated in LRRK2-G2019S Parkinson’s disease

Neuroinflammation is increasingly recognized as a central pathological mechanism in Parkinson’s disease (PD), a progressive neurodegenerative disorder characterized by the selective loss of dopaminergic neurons and variety of motor and non-motor symptoms. The NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome and its adaptor protein ASC play a critical role in initiating and maintaining inflammatory responses in the central nervous system. Although its acute activation is beneficial for host defense and homeostasis, chronic activation of the inflammasome has been associated with the pathogenesis of PD. Another key contributor to neuroinflammation is the leucine-rich repeat kinase 2 (LRRK2), particularly the G2019S mutation associated with PD, which has been shown to exacerbate inflammatory signaling in microglia and peripheral immune cells. However, the interaction between LRRK2 and the NLRP3 inflammasome pathway remains poorly understood. In this study, we investigated the role of LRRK2-G2019S in the priming and activation dynamics of the NLRP3 inflammasome using mouse primary microglia and human monocyte-derived microglia-like cells (hMDMi). We observed that LRRK2-G2019S microglia exhibit increased expression of NLRP3 under basal conditions and spontaneous formation of ASC specks within the nucleus, an unexpected subcellular location not previously reported in microglia. Interestingly, nuclear ASC specks also formed in wild-type microglia and hMDMi after lipopolysaccharide (LPS) priming but only progressed to cytosolic ASC specks and interleukin-1β release after subsequent exposure to canonical NLRP3 activators. These findings suggest that nuclear ASC specks may represent a primed state of inflammasome activation and propose a novel cellular phenotype associated with LRRK2-G2019S. Altogether, our results reveal a new layer of inflammasome regulation in microglia and implicate LRRK2-G2019S in the promotion of a pro-inflammatory state, which may predispose to chronic neuroinflammation in PD. These findings advance our understanding of glial immune regulation and highlight potential therapeutic targets in PD.