Shedding light on functional heterogeneity of dementia-related alpha-synuclein strains

α-突触核蛋白（αS）在脑内的沉积是路易体痴呆（LBD）的主要特征，是路易体痴呆的发病机制

The deposition of α-synuclein (αS) in the brain is a main feature of Lewy bodies dementia (LBD), which is the 2nd most common dementia after Alzheimer’s disease (AD). Both postmortem and experimental evidence showed that the progression of LBD can be driven by pathogenic αS (preformed fibrils, PFF) in a prion-like fashion, and these αS aggregates exhibit distinct strains underling heterogeneity of α-synucleinopathies. In our preliminary studies, we have amplified αS aggregates from patients and found the strains from Parkinson's disease with cognitive impairment (PD-CI) are distinct from those derived from PD with normal cognition (PD- NC) in the cross-sectional analysis. Longitudinal studies of αS strains from the same individuals further indicate a strain conversion when cognition progresses from PD-NC to PD-CI. However, there are two critical knowledge gaps in the current understanding of the heterogeneity of αS strains. First, whether and how distinct αS strains cause different cellular responses in the brain of a living organism are poorly known. It is our vision that interdisciplinary efforts are essential to bring novel insights on the pathogenesis of LBD. We have established the long-term intravital single-cell tracking platform under 2p microscopy, enabling subcellular-resolution imaging of the location, migration, and function of brain cells in live mice for a few weeks. Implementing this tool allows us to address the above-mentioned question by obtaining a dynamic picture about how brain cells respond to αS over time, including temporal responses from neurons and microglia exposed to different strains of αS. The second critical knowledge gap is whether different strains of αS have distinct cell-to-cell propagation dynamics. The gold standard histological methodology for α-synucleinopathies is the immunoreactivity of posttranslational phosphorylation of αS at serine 129 (p129), precluding the possibility to obtain dynamic αS propagation information. To address this issue, we propose to design a novel probe for αS, called the NanoFAST, which has a few inherent advantages over other αS aggregation reporters: (i). detection of untagged αS aggregates; (ii). no need to overexpress αS in cells for the reporter to work; and (iii). the ability to detect either aggregation or disaggregation (bi-directional) process of αS. Overall, we have assembled an interdisciplinary team covering neuroscience, nanobody engineering, biophysics, and clinical practice to address the critical knowledge gaps in the understanding of αS heterogeneity. If we are successful, the long-term intravital cell tracking of the response of neurons/microglia to different αS strains will provide important insights on the mechanism underlying heterogeneity in neurotoxicity from dementia-related αS strains. The NanoFAST may become an enabling tool for exploring αS aggregating and spreading dynamics in cell-based assay or even for in vivo applications, with the potential to be translated to clinic for early diagnosis, progression evaluation or prognosis of LBD to combat these devastating neurodegenerative diseases.