Transgenic M83 mice, which overexpress human SNCA A53T under the murine prion protein promoter, serve as a robust platform for investigating the mechanisms of α-synucleinopathy in the context of Parkinson’s disease (PD). To enhance the translational relevance of this model, we established a “second hit” approach by performing unilateral injections of α-synuclein (α-syn) pre-formed fibrils (PFFs) into two anatomically relevant sites, the somatosensory cortex and the dorsal striatum, following the protocol described by Luk et al. (2012).
The injection of PFFs in M83 mice triggered a robust spreading of pathology that was not only limited to the injection site. Analysis of pFTAA––a marker for fibrillar protein aggregates––and pSer129α-syn revealed a heavy pathological signal in the ipsilateral hemisphere, particularly in the caudate putamen (CPu) and substantia nigra (SN) (Figure 1). Interestingly, these signals were also detected in the contralateral hemisphere, including the cortex, CPu, SN, and brainstem, consistent with α‑syn‑mediated seeding and propagation between interconnected regions (Figure 2).
Additionally, neuroinflammation was assessed using Iba1 to label microglia. In M83 PFF-injected mice, there was a significant increase in Iba1 immunoreactivity within the targeted ipsilateral CPu compared to sham-injected animals.
Figure 1: Immunofluorescent labeling of terminal brain tissue. Representative images of pentameric formyl thiophene acetic acid (pFTAA), ionized calcium-binding adapter molecule 1 (Iba1), tyrosine hydroxylase (TH) and α-syn phosphorylated at serine 129 (pSer129 α-Syn) in sagittal brain sections from M83 PFF injected animals. Panels show contralateral and ipsilateral hemispheres from both groups: contralateral M83 PFF SPR-326 (A) and ipsilateral M83 PFF SPR-326 (B). Nuclei were counterstained with DAPI. Single-channel magnifications show labeling in the caudate putamen (CPu) and substantia nigra (SN), corresponding to the regions indicated by the rectangles.
Figure 2: Contralateral α-synuclein pathology after PFF injection. Representative immunofluorescent images of brain compartments––cortex, CPu, SN and brainstem––of the contralateral hemisphere of M83 mice after sham or SNCA-A53T PFF injection. Images show a merge of DAPI staining in blue, pFTAA labelling in green and pSer129 α-syn immunoreactivity in red. Partial colocalization between pFTAA and pSer129 α-syn suggests a mixed population of α-syn aggregates, with some showing both fibrillar (pFTAA-positive) and phosphorylated pathology (pSer129 α-syn-positive) [indicated by arrow heads] and others only being positive for pFTAA [indicated by stars] or pSer129 α-syn [indicated by arrows]. Scale bar 50 µm.
Based on these results, PFF-injected M83 mice can be used to test drugs for their efficacy to prevent or decrease disease progression as well as reduce already existing α-syn pathology.
Reference:
Luk KC, Kehm VM, Zhang B, O’Brien P, Trojanowski JQ, Lee VMY. Intracerebral inoculation of pathological α‑synuclein initiates a neurodegenerative cascade that propagates in a prion‑like manner. J Exp Med. 2012;209(5):957–967.
