Presymptomatic neuroanatomical and cognitive biomarkers of alpha-synuclein propagation in a mouse model of synucleinopathy

Abstract

There is significant evidence suggesting aggregated misfolded alpha-synuclein, a major component of Lewy bodies, propagates in a prion-like manner contributing to disease progression in Parkinson's disease (PD) and other synucleinopathies. Animal models are essential for understanding and developing treatments for these diseases. However, despite modelling human pathology, most endpoints studied in mice do not translate to humans. Furthermore, the progression by which alpha-synuclein misfolding affects human-relevant measures such as brain volume and underlying subtle, high-level cognitive deficits is poorly understood. Here we used a mouse model of synucleinopathy; hemizygous M83 human A53T alpha-synuclein transgenic mice inoculated with recombinant human alpha-synuclein preformed fibrils (PFF) injected in the right striatum to initiate alpha-synuclein misfolding and aggregation. We examined alpha-synuclein-induced atrophy at 90 days post-injection using ex vivo magnetic resonance imaging as well as high-level cognition and motor function, as biomarkers of alpha-synuclein toxicity. We observed widespread atrophy in bilateral regions that project to or receive input from the injection site, highlighting a network of regions that are consistent with structural changes observed in humans with PD. Moreover, we detected early deficits in reversal learning with touchscreen testing in PFF-injected mice prior to motor dysfunction, consistent with the pathology observed in cortical-striatal and thalamic loops. We show, using translational approaches in mice, that progression of prion-like spreading of alpha-synuclein causes selective atrophy via connected brain regions leading to high-level cognitive deficits. We propose that precise imaging and cognitive biomarkers can provide a more direct and human-relevant measurement of alpha-synuclein-induced toxicity in pre-clinical testing.

Sex-focused analyses of M83 A53T hemizygous mouse model with recombinant human alpha-synuclein preformed fibril injection identifies female resilience to disease progression: A combined magnetic resonance imaging and behavioural study

“…Healthy 3 to 4-month-old hemizygous M83 mice were injected with Hu-PFF or phosphate-buffered saline (PBS) in the right dorsal striatum, consistent with previous work modelling known disease epicentres of spreading (Bétemps et al, 2014; Luk et al, 2012a; Mougenot et al, 2012; Tullo et al, 2023). Groups were randomly assigned, with an equal number of mice across injection assignment and sex.…”

“…Evidence for the prion-like spreading of aSyn emerged from post-mortem analysis of patients’ brains that received fetal dopaminergic cell transplantation in the substantia nigra pars compacta (Kordower et al, 2008; Li et al, 2008) showing host-to-graft aSyn transfer. Subsequent cellular assays of aSyn cell-to-cell transfer (Bétemps et al, 2014; Desplats et al, 2009; Fares et al, 2016; Panattoni et al, 2018; Tapias et al, 2017; Volpicelli-Daley et al, 2014) and animal models of aSyn spreading (Froula et al, 2019; Lackie et al, 2022; Luk et al, 2012a; Luk et al, 2012b; Masuda-Suzukake et al, 2013; Masuda-Suzukake et al, 2014; Mougenot et al, 2012; Sacino et al, 2014; Sorrentino et al, 2022; Tullo et al, 2023; Watts et al, 2013) further support the prion-like hypothesis.…”

“…The experimental timeline is shown in Figure 1 and group numbers in Supplementary Table S1. We examined groups receiving Hu-PFF or PBS in the right dorsal striatum at 7 days prior to the injection (−7 dpi) for a baseline assessment, 30 dpi (earliest signs of aSyn Lewy-body like pathology (Luk et al, 2012)), 90 dpi (when motor symptomatology onset is typically observed (∼ 90-100 dpi) (Bétemps et al, 2014; Luk et al, 2012a; Sacino et al, 2014; Sorrentino et al, 2022; Tullo et al, 2023; Watts et al, 2013)), and 120 dpi (when the mice are fully symptomatic and nearing the end stage of the disease. Mice were studied at specified time points ± 2 days.…”

“…This is not altogether surprising as sex is often neglected as a biological variable in preclinical research (Galea et al, 2020; Galea & Parekh 2023; Galea et al, 2023). This limitation extends to using the M83 mouse model, harbouring an A53T mutation in the human aSyn transgene, that is commonly used to examine the prion-like spreading hypothesis (Bétemps et al, 2014; Froula et al, 2019; Lackie et al, 2022; Luk et al, 2012a; Luk et al, 2012b; Masuda-Suzukake et al, 2013; Masuda-Suzukake et al, 2014; Mougenot et al, 2012; Sacino et al, 2014; Sorrentino et al, 2022; Tullo et al, 2023; Watts et al, 2013). Aside from a recent study that used intramuscular injection (Sorrentino et al, 2022) and a magnetic resonance imaging (MRI) study from our group (Tullo et al, 2023), few others using the M83 mouse line have explicitly explored sex differences.…”

“…This limitation extends to using the M83 mouse model, harbouring an A53T mutation in the human aSyn transgene, that is commonly used to examine the prion-like spreading hypothesis (Bétemps et al, 2014; Froula et al, 2019; Lackie et al, 2022; Luk et al, 2012a; Luk et al, 2012b; Masuda-Suzukake et al, 2013; Masuda-Suzukake et al, 2014; Mougenot et al, 2012; Sacino et al, 2014; Sorrentino et al, 2022; Tullo et al, 2023; Watts et al, 2013). Aside from a recent study that used intramuscular injection (Sorrentino et al, 2022) and a magnetic resonance imaging (MRI) study from our group (Tullo et al, 2023), few others using the M83 mouse line have explicitly explored sex differences. Given the cross-sectional nature of our recent work, it is likely that a longitudinal design may be more sensitive to inter-individual variation that results in sex differences (Lerch et al 2012; Valiquette et al 2023).…”