Sequential or Simultaneous Injection of Preformed Fibrils and AAV Overexpression of Alpha-Synuclein Are Equipotent in Producing Relevant Pathology and Behavioral Deficits

Abstract

Background: Preclinical rodent models for Parkinson’s disease (PD) based on viral human alpha-synuclein (h-αSyn) overexpression recapitulate some of the pathological hallmarks as it presents in humans, such as progressive cell loss and additional synucleinopathy in cortical and subcortical structures. Recent studies have combined viral vector-based overexpression of human wild-type αSyn with the sequential or simultaneous inoculation of preformed fibrils (PFFs) derived from human αSyn. Objective: The goal of the study was to investigate whether sequential or combined delivery of the AAV vector and the PFFs are equipotent in inducing stable neurodegeneration and behavioral deficits. Methods: Here we compare between four experimental paradigms (PFFs only, AAV-h-αSyn only, AAV-h-αSyn with simultaneous PFFs, and AAV-h-αSyn with sequential PFFs) and their respective GFP control groups. Results: We observed reduction of TH expression and loss of neurons in the midbrain in all AAV (h-αSyn or GFP) injected groups, with or without additional PFFs inoculation. The overexpression of either h-αSyn or GFP alone induced motor deficits and dysfunctional dopamine release/reuptake in electrochemical recordings in the ipsilateral striatum. However, we observed a substantial formation of insoluble h-αSyn aggregates and inflammatory response only when h-αSyn and PFFs were combined. Moreover, the presence of h-αSyn induced higher axonal pathology compared to control groups. Conclusion: Simultaneous AAV and PFF injections are equipotent in the presented experimental setup in inducing histopathological and behavioral changes. This model provides new and interesting possibilities for characterizing PD pathology in preclinical models and means to assess future therapeutic interventions.

A Combined α-Synuclein/Fibril (SynFib) Model of Parkinson-Like Synucleinopathy Targeting the Nigrostriatal Dopamine System

“…Studies performed in rats [11,13,18] confirm that this is the case also in nigral DA neurons in vivo. Thus, the use of this combined approach makes it possible to speed up the pathogenetic process and induce more prominent DA neuron loss and motor impairments, accompanied by extensive ␣-syn pathology and a prominent inflammatory response akin to what is observed in patients [13,18,19]. In this combined AAV-␣-syn/fibril (SynFib) model, the AAV-␣-syn vector and the PFFs are injected unilaterally into the SN at doses that have only moderate impact when each component is administered individually.…”

“…4A-F), as well as in distorted axons and terminals distributed along the nigrostriatal pathway and within striatum (Fig. 4G-J; see Supplementary 3D movie S1 of axonal pathology in the striatum, panel J) [13,18,19]. The p-syn+pathology seen in the SynFib model is much more prominent, develops earlier, and involves larger numbers of nigral neurons than is the case in either the AAV only or PFF only models.…”

“…4 C) and downregulation of TH in most, but not all, p-syn+nigral neurons (arrows in Fig. 4D) [13,18]. The activated Iba1 + microglia are confined to areas of As shown in Fig.…”

“…The idea of combining the two approaches¾AAV mediated ␣-syn delivery with the addition of PFF seeds¾is based on the finding that the generation, magnitude, and speed of progression of toxic ␣-syn aggregates is limited by the level of endogenous ␣-syn available in the cell, and that the aggregation process is amplified in the presence of elevated levels of monomeric ␣-syn [15][16][17]. Studies performed in rats [11,13,18] confirm that this is the case also in nigral DA neurons in vivo. Thus, the use of this combined approach makes it possible to speed up the pathogenetic process and induce more prominent DA neuron loss and motor impairments, accompanied by extensive ␣-syn pathology and a prominent inflammatory response akin to what is observed in patients [13,18,19].…”

“…Scale bars in A-C: 1 mm. Data compiled from refs [13] and [18]. tributed in the cytoplasm and often combined with a 367 prominent localization to the nucleus [13].…”