Depopulation of dense α-synuclein aggregates is associated with rescue of dopamine neuron dysfunction and death in a new Parkinson’s disease model

Abstract

Parkinson’s disease (PD) is characterized by the presence of α-synuclein aggregates known as Lewy bodies and Lewy neurites, whose formation is linked to disease development. The causal relation between α-synuclein aggregates and PD is not well understood. We generated a new transgenic mouse line (MI2) expressing human, aggregation-prone truncated 1–120 α-synuclein under the control of the tyrosine hydroxylase promoter. MI2 mice exhibit progressive aggregation of α-synuclein in dopaminergic neurons of the substantia nigra pars compacta and their striatal terminals. This is associated with a progressive reduction of striatal dopamine release, reduced striatal innervation and significant nigral dopaminergic nerve cell death starting from 6 and 12 months of age, respectively. In the MI2 mice, alterations in gait impairment can be detected by the DigiGait test from 9 months of age, while gross motor deficit was detected by rotarod test at 20 months of age when 50% of dopaminergic neurons in the substantia nigra pars compacta are lost. These changes were associated with an increase in the number and density of 20–500 nm α-synuclein species as shown by dSTORM. Treatment with the oligomer modulator anle138b, from 9 to 12 months of age, restored striatal dopamine release, prevented dopaminergic cell death and gait impairment. These effects were associated with a reduction of the inner density of large α-synuclein aggregates and an increase in dispersed small α-synuclein species as revealed by dSTORM. The MI2 mouse model recapitulates the progressive dopaminergic deficit observed in PD, showing that early synaptic dysfunction is associated to fine behavioral motor alterations, precedes dopaminergic axonal loss and neuronal death that become associated with a more consistent motor deficit upon reaching a certain threshold. Our data also provide new mechanistic insight for the effect of anle138b’s function in vivo supporting that targeting α-synuclein aggregation is a promising therapeutic approach for PD.Electronic supplementary materialThe online version of this article (10.1007/s00401-019-02023-x) contains supplementary material, which is available to authorized users.

Effects of pharmacological modulators of α-synuclein and tau aggregation and internalization

“…Using simple, yet powerful, human cell-based models, we found that anle138b reduces aSyn aggregation in a HEK293 venus BiFC cell model. Until now, anle138b was mostly tested in mouse models 18,23,47 . In cells, it was tested in melanoma and in H4 cells 24, 48 .…”

The good and bad of therapeutic strategies that directly target α‐synuclein

“…The deposition of fibrillary α‐syn is believed to start from synaptic terminals and can damage neurons via a two‐hit mechanism. This involves loss of function of α‐syn and collapse of synapses deriving from insoluble aggregates accumulation . The removal of α‐syn aggregates could thus reduce the neurotoxic effects of fibrils and also slow down prion‐like propagation of pathology.…”

“…NPT100‐18A was designed to target membrane‐bound α‐syn and to counteract oligomerization, while NPT200‐11 was optimized to bind specific regions of α‐syn thought to be responsible oligomerization into toxic forms and also to be orally bioavailable and brain penetrating . Finally, Anle138b, a small compound with high bioavailability and low toxicity, decreases α‐syn oligomerization and aggregation and reduces motor impairment and degeneration in MSA and PD mouse models . Of note, Anle138b is one of the few compounds successfully tested in vivo, since most of the molecules mentioned above have been tested on different cell lines or even in cell‐free models of α‐syn fibrillation (all the compounds mentioned are summarized in Table ).…”

“…This involves loss of function of α-syn and collapse of synapses deriving from insoluble aggregates accumulation. 17,[28][29][30] The removal of α-syn aggregates could thus reduce the neurotoxic effects of fibrils and also slow down prion-like propagation of pathology. In the last few years, a plethora of possible approaches has been proposed to reduce α-syn aggregation, ranging from small molecule inhibitors, to factors promoting α-syn compaction.…”

“…47 Finally, Anle138b, a small compound with high bioavailability and low toxicity, 48 decreases α-syn oligomerization and aggregation and reduces motor impairment and degeneration in MSA and PD mouse models. 29,49 Of note, Anle138b is one of the few compounds successfully tested in vivo, since most of the molecules mentioned above have been tested on different cell lines or even in cell-free models of α-syn fibrillation (all the compounds mentioned are summarized in Table 1). Speaking of ways to reduce the burden of α-syn aggregates, it is worth mentioning intracellular antibodies (usually referred as intrabodies) are recombinant antibody fragments that bind to target proteins expressed inside of the same living cell producing the antibodies.…”