A multiverse of α-synuclein: investigation of prion strain properties with carboxyl-terminal truncation specific antibodies in animal models

Synucleinopathies are a group of neurodegenerative disorders characterized by the presence of misfolded alpha-Synuclein (alpha Syn) in the brain. These conditions manifest with diverse clinical and pathophysiological characteristics. This disease diversity is hypothesized to be driven by alpha Syn strains with differing biophysical properties, potentially influencing prion-type propagation and consequentially the progression of illness. Previously, we investigated this hypothesis by injecting brain lysate (seeds) from deceased individuals with various synucleinopathies or human recombinant alpha Syn preformed fibrils (PFFs) into transgenic mice overexpressing either wild type or A53T human alpha Syn. In the studies herein, we expanded on these experiments, utilizing a panel of antibodies specific for the major carboxyl-terminally truncated forms of alpha Syn (alpha Syn Delta C). These modified forms of alpha Syn are found enriched in human disease brains to inform on potential strain-specific proteolytic patterns. With monoclonal antibodies specific for human alpha Syn cleaved at residues 103, 114, 122, 125, and 129, we demonstrate that multiple system atrophy (MSA) seeds and PFFs induce differing neuroanatomical spread of alpha Syn pathology associated with host specific profiles. Overall, alpha Syn cleaved at residue 103 was most widely present in the induced pathological inclusions. Furthermore, alpha Syn Delta C-positive inclusions were present in astrocytes, but more frequently in activated microglia, with patterns dependent on host and inoculum. These findings support the hypothesis that synucleinopathy heterogeneity might stem from alpha Syn strains with unique biochemical properties that include proteolytic processing, which could result in dominant strain properties.