Trans-synaptic and retrograde axonal spread of Lewy pathology following pre-formed fibril injection in an in vivo A53T alpha-synuclein mouse model of synucleinopathy

(2020) 8:150 Schaser et al. acta neuropathol commun https://doi.org/10.1186/s40478-020-01026-0 Open Access RESEARCH Trans‑synaptic and retrograde axonal spread of Lewy pathology following pre‑formed fibril injection in an in vivo A53T alpha‑synuclein mouse model of synucleinopathy Allison J. Schaser1, Teresa L. Stackhouse1, Leah J. Weston1, Patrick C. Kerstein2, Valerie R. Osterberg1, Claudia S. López3, Dennis W. Dickson4, Kelvin C. Luk5, Charles K. Meshul6,7, Randall L. Woltjer8 and Vivek K. Unni1,9* Abstract It is necessary to develop an understanding of the specific mechanisms involved in alpha-synuclein aggregation and propagation to develop disease modifying therapies for age-related synucleinopathies, including Parkinson’s disease and Dementia with Lewy Bodies. To adequately address this question, we developed a new transgenic mouse model of synucleinopathy that expresses human A53T SynGFP under control of the mouse prion protein promoter. Our characterization of this mouse line demonstrates that it exhibits several distinct advantages over other, currently available, mouse models. This new model allows rigorous study of the initial location of Lewy pathology formation and propagation in the living brain, and strongly suggests that aggregation begins in axonal structures with retrograde propagation to the cell body. This model also shows expeditious development of alpha-synuclein pathology following induction with small, in vitro-generated alpha-synuclein pre-formed fibrils (PFFs), as well as accelerated cell death of inclusion-bearing cells. Using this model, we found that aggregated alpha-synuclein somatic inclusions developed first in neurons, but later showed a second wave of inclusion formation in astrocytes. Interestingly, astrocytes appear to survive much longer after inclusion formation than their neuronal counterparts. This model also allowed careful study of peripheral-to-central spread of Lewy pathology after PFF injection into the hind limb musculature. Our results clearly show evidence of progressive, retrograde trans-synaptic spread of Lewy pathology through known neuroanatomically connected pathways in the motor system. As such, we have developed a promising tool to understand the biology of neurodegeneration associated with alpha-synuclein aggregation and to discover new treatments capable of altering the neurodegenerative disease course of synucleinopathies. Keywords: Synucleinopathies, Parkinson’s disease, Dementia with Lewy bodies, Alpha-synuclein, Lewy body, Transsynaptic spread, Neurodegeneration *Correspondence: 1 Department of Neurology and Jungers Center for Neurosciences Research, Oregon Health and Science University, Portland, OR 97239, USA Full list of author information is available at the end of the article Introduction Age-related synucleinopathies including Parkinson disease (PD), Dementia with Lewy bodies (DLB), and Multiple Systems Atrophy (MSA) are common and debilitating neurodegenerative disorders that include both motor © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativeco mmons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Schaser et al. acta neuropathol commun (2020) 8:150 and non-motor symptoms [24, 58]. Despite their prevalence and impact on quality of life, there are currently no mechanism-based treatments that slow or halt the disease process involved in these disorders [Reviewed in 27]. Alpha-synuclein is a 140 amino acid protein localized to presynaptic terminals and other cellular structures that is thought to be normally intrinsically disordered and soluble [36], or potentially in a tetrameric conformation [6]. However in synucleinopathies, alpha-synuclein aggregates and forms insoluble intracellular inclusions, the hallmark lesions of this set of diseases [Reviewed in 23]. In neurons, aggregation results in somatic and neuritic inclusions, collectively known as Lewy pathology, but inclusions can also form in non-neuronal cells types, such as glial astrocytic inclusions [70] or Papp-Lantos bodies in oligodendrocytes [56, 74, 75]. A large and growing body of work suggests that one possible mechanism of pathological spread in synucleinopathies is cell-to-cell transfer of aggregated alphasynuclein [5, 16, 18, 20, 26, 30, 47]. This is referred to as the “prion-like” propagation hypothesis [3, 4, 13, 21] and dovetails with work done on human autopsy tissue by Braak and colleagues, which also suggests a pattern of pathological spread, specifically through neuroanatomically connected pathways [10, 28]. In support of the “prion-like” propagation hypothesis, work in model systems has shown that aggregated alpha-synuclein propagation can be induced by the exogenous application of small, in vitro-generated alpha-synuclein pre-formed fibrils (PFFs). Previous research in vivo has also shown that the application of PFFs causes aggregation of endogenous alpha-synuclein and resultant Lewy pathology, first at the site of injection and then in connected brain regions in a time-dependent manner [29, 34, 47, 54, 63]. This has been suggested to occur via several different possible transport mechanisms, including uptake and transport by circulating microglia [37, 64, 69], movement in the extracellular space [15, 39, 55], and neuronal uptake and intracellular transport [1, 17, 18]. To date, direct evidence for any of these mechanisms in vivo is limited [35, 80], primarily due to the previous inability to track the movement of aggregated alphasynuclein following PFF injection. In support of the neuronal uptake and transport model, data from cell culture experiments show that both anterograde and retrograde fibril movement within cells is possible [12, 20, 84] and that microtubule-associated axonal transport may be involved [31]. Human pathology studies suggest spread in the retrograde direction, with a pattern of pathology that appears specific to retrograde movement from distal axonal processes to the cell body [79, 80]. However, to our knowledge, direct evidence for (...truncated)