The E46K mutation modulates α-synuclein prion replication in transgenic mice

Abstract

In multiple system atrophy (MSA), the α-synuclein protein misfolds into a self-templating prion conformation that spreads throughout the brain, leading to progressive neurodegeneration. While the E46K mutation in α-synuclein causes familial Parkinson’s disease (PD), we previously discovered that this mutation blocks in vitro propagation of MSA prions. Recent studies by others indicate that α-synuclein adopts a misfolded conformation in MSA in which a Greek key motif is stabilized by an intramolecular salt bridge between residues E46 and K80. Hypothesizing that the E46K mutation impedes salt bridge formation and, therefore, exerts a selective pressure that can modulate α-synuclein strain propagation, we asked whether three distinct α-synuclein prion strains could propagate in TgM47+/- mice, which express human α-synuclein with the E46K mutation. Following intracranial injection of these strains, TgM47+/- mice were resistant to MSA prion transmission, whereas recombinant E46K preformed fibrils (PFFs) transmitted neurological disease to mice and induced the formation of phosphorylated α-synuclein neuropathology. In contrast, heterotypic seeding following wild-type (WT) PFF–inoculation resulted in preclinical α-synuclein prion propagation. Moreover, when we inoculated TgM20+/- mice, which express WT human α-synuclein, with E46K PFFs, we observed delayed transmission kinetics with an incomplete attack rate. These findings suggest that the E46K mutation constrains the number of α-synuclein prion conformations that can propagate in TgM47+/- mice, expanding our understanding of the selective pressures that impact α-synuclein prion replication.

The role of α-synuclein prion strains in Parkinson’s disease and multiple system atrophy

“…Additional differences include the presence of a salt bridge between residues E35 and K80 in the PD structure, whereas the stabilizing salt bridge is between residues E46 and K80 in the MSA structure. Recent findings have shown that this structural difference is responsible for distinct biological properties between the PD and MSA strain in both in vitro and in vivo models [ 16 , 17 ]. Finally, differences in N-terminal contributions are also likely to alter fibril kinetics and stability.…”

“…Finally, cell culture models have also been used to investigate differences in α-synuclein strain biology, with the notable ability to predict in vivo outcomes [ 17 , 28 , 30 , 31 ]. For example, PD patient samples do not transmit disease to TgM83 +/− mice, nor do they infect HEK293T cells expressing YFP-tagged α-synuclein.…”

“…Additionally, as noted previously, MSA prions are stabilized by a salt bridge between residues E46 and K80. Cell-based studies showed that the presence of the PD-causing E46K mutation inhibits replication of MSA prions in vitro [ 16 ], which was subsequently confirmed by in vivo experiments finding transgenic mice expressing the E46K mutation are protected from MSA transmission [ 17 ].…”

“…Moreover, TgM83 +/− mice also develop neurological disease following intramuscular (tongue or hind leg), intraperitoneal, or intravenous exposure [19,29], though transmission efficiency was low for intralingual injections. Finally, cell culture models have also been used to investigate differences in α-synuclein strain biology, with the notable ability to predict in vivo outcomes [17,28,30,31]. For example, PD patient samples do not transmit disease to TgM83 +/− mice, nor do they infect HEK293T cells expressing YFP-tagged α-synuclein.…”

Air pollution nanoparticle and alpha-synuclein fibrils synergistically decrease glutamate receptor A1, depending upon nPM batch activity

“…Experimental evidence is needed to show how air pollution may influence the progression of α-syn pathology. We used a mouse model of progressive α-syn neuropathology [ [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] ] to evaluate the effects of ambient nPM exposure on (i) levels and spread of α-syn aggregates from the OB to interconnected brain regions, (ii) microglial activation and (iii) expression of glutamate receptor A1 (GluA1, encoded by Gria1 ), which is involved in learning and memory [ 37 ] and odor/olfaction memory process [ 38 ], which are relevant to PD symptoms of dementia and hyposmia. The nPM batches were collected at the same site in downtown Los Angeles, and were later shown to vary widely in activities as evaluated by induction of NF-κB in vitro and neurotoxic responses in vivo [ 28 ].…”