STRESS GRANULES AND α-SYNUCLEIN: INTERPLAY BETWEEN CELLULAR STRESS AND PROTEIN AGGREGATION IN PARKINSON’S DISEASE

Zanchi G¹, Novello C¹, Calogero AM², Mazzetti S², Bonaldo B¹, Gomez MCL¹, Rolando C¹, Calandrella D^2,3, Pezzoli G² and Cappelletti G¹ | ¹Department of Biosciences, University of Milan, Milan, Italy ²Fondazione Pezzoli per la Malattia di Parkinson, Milan, Italy ³Parkinson Institute, ASST G. Pini-CTO, Milan, Milan, Italy

Stress granules (SGs) are membraneless organelles that are constituted primarily of untranslated messenger ribonucleoproteins, whose assembly occurs via liquid-liquid phase separation (LLPS) in response to various cellular stressors and that play a critical role in maintaining proteostasis. Increasing evidence indicates that chronic stress can disrupt the tightly regulated dynamics of SGs assembly and disassembly, leading to their persistence. These pathological SGs potentially serve as nucleation sites for aberrant protein aggregation in several neurodegenerative disorders (NDDs)2. Focusing on Parkinson’s disease (PD), current knowledge on the dysregulation of SGs assembly and disassembly in relation to α-Synuclein (α-Syn) aggregation is only based on cellular models, with no evidence from human brain tissue. It is well established that, under specific conditions, α-Syn can form condensates regulated by microtubule dynamics, promoting amyloid fibril formation via LLPS, and that α-Syn interacts with several RNA-binding proteins (RBPs) involved in SGs formation. Based on this we aim to determine whether: i) α-Syn pathology and SGs are associated in post-mortem human brains obtained from PD patients and ii) α-Syn aggregates within SGs under conditions of acute and chronic stress in a neuronal cell model (SH-SY5Y cells) and whether this process affects SGs homeostasis. Immunohistochemical analysis on post-mortem PD brains highlighted a characteristic pattern of small, round RBPs-positive granules in neuronal cell bodies, which also accumulated alongside α- Syn oligomers. Interestingly, different RBPs were found to be involved in Lewy body formation, and quantitative analyses showed a significant RBPs increase in mature compared to undefined aggregates. This suggests that SGs may act as an intermediate for α-Syn aggregation in PD brains. Simultaneously, SH-SY5Y cells exposed to both acute and chronic treatment with the oxidative stress inducer sodium arsenite showed an increase in intracellular aggregates positive for both SGs markers and α-Syn, indicating enhanced recruitment or association of α-Syn with SGs. Future work will aim to explore the impact of both α-Syn aggregation and microtubule dynamics on the homeostasis of SGs in PD pathology, providing further insight into the molecular mechanisms of the disease.