Snca-GFP knock-in mice reflect patterns of endogenous expression and pathological seeding

Abstract

Alpha-synuclein (aSyn) participates in synaptic vesicle trafficking and synaptic transmission, but its misfolding is also strongly implicated in Parkinsons disease (PD) and other neurodegenerative disorders known as synucleinopathies where misfolded aSyn accumulates in different regions of the central and peripheral nervous systems. Although increased aSyn expression levels or altered aggregation propensities likely underlie familial PD with SNCA amplification or mutations, the majority of synucleinopathies arise sporadically, indicating that disease can develop under normal levels of wildtype aSyn. We report here the development and characterization of a mouse line expressing an aSyn-GFP fusion protein under the control of native Snca regulatory elements. Regional and subcellular localization of the aSyn-GFP fusion protein in brains and peripheral tissues of knock-in (KI) mice are indistinguishable from that of wildtype littermates. Importantly, similar to wildtype aSyn, aSyn-GFP disperses from synaptic vesicles upon membrane depolarization, indicating that the tag does not alter normal aSyn dynamics at synapses. In addition, intracerebral injection of aSyn pre-formed fibrils into KI mice induced the formation of aSyn-GFP inclusions with a distribution pattern similar to that observed in wildtype mice, albeit with attenuated kinetics due to the GFP tag. We anticipate that this new mouse model will facilitate in vitro and in vivo studies requiring in situ detection of endogenous aSyn, therefore providing new insights into aSyn function in health and disease. Significance StatementAlpha-synuclein (aSyn) participates in synaptic vesicle function and represents a major component of the Lewy pathology found in Parkinsons and related neurodegenerative diseases. The function of aSyn and the sequence of events leading to its aggregation and neurotoxicity are not fully understood. Here we present a new mouse model in which Enhanced Green Fluorescence Protein (GFP) has been knocked-in at the C-terminal of the Snca gene. The resulting fusion protein shows identical expression and localization to that of wildtype animals, is functional, and is incorporated into pathological aggregates in vitro and in vivo. This new tool allows for monitoring aSyn under a variety of physiological and pathological conditions, and may uncover additional insights into its function and dysfunction.