Analysis of α-synuclein species enriched from cerebral cortex of humans with sporadic dementia with Lewy bodies

Abstract

Since researchers identified α-synuclein as the principal component of Lewy bodies and Lewy neurites, studies have suggested that it plays a causative role in the pathogenesis of dementia with Lewy bodies and other ‘synucleinopathies’. While α-synuclein dyshomeostasis likely contributes to the neurodegeneration associated with the synucleinopathies, few direct biochemical analyses of α-synuclein from diseased human brain tissue currently exist. In this study, we analysed sequential protein extracts from a substantial number of patients with neuropathological diagnoses of dementia with Lewy bodies and corresponding controls, detecting a shift of cytosolic and membrane-bound physiological α-synuclein to highly aggregated forms. We then fractionated aqueous extracts (cytosol) from cerebral cortex using non-denaturing methods to search for soluble, disease-associated high molecular weight species potentially associated with toxicity. We applied these fractions and corresponding insoluble fractions containing Lewy-type aggregates to several reporter assays to determine their bioactivity and cytotoxicity. Ultimately, high molecular weight cytosolic fractions enhances phospholipid membrane permeability, while insoluble, Lewy-associated fractions induced morphological changes in the neurites of human stem cell-derived neurons. While the concentrations of soluble, high molecular weight α-synuclein were only slightly elevated in brains of dementia with Lewy bodies patients compared to healthy, age-matched controls, these observations suggest that a small subset of soluble α-synuclein aggregates in the brain may drive early pathogenic effects, while Lewy body-associated α-synuclein can drive neurotoxicity.

A toxic subset of soluble α-synuclein species in dementia with Lewy body

“…The work from Sanderson et al (2020 ) broadens previous work from others and provides evidence for the presence of soluble neurotoxic αSyn aggregates in DLB brain tissue. As previously shown, αSyn species can be detected using specific tools designed to recognize these unstable intermediates.…”

“…In this issue, Sanderson et al (2020 ) took a step towards unveiling dysfunctional αSyn contributing to the sporadic DLB pathology, by providing compelling evidence of the existence of neurotoxic soluble αSyn species in the human brain. This small protein (140 amino acids), which is abundant in presynaptic terminals in a healthy brain, is the main component of Lewy body deposits and Lewy neurites in synucleinopathies.…”

“…A key challenge in the field that we need to overcome on the road to develop effective therapeutics is to develop a more thorough picture of which oligomeric forms of αSyn are toxic and how they confer this toxicity. Sanderson et al (2020 ) have helped address this challenge by examining αSyn oligomers isolated from human disease tissue and their toxic effects in human induced pluripotent stem cell-derived neurons.…”

“…Following a different approach, Sanderson et al (2020 ) developed a method to investigate αSyn species in a cohort of patients with a neuropathological diagnosis of DLB and also control brains, by using a sequence of non-denaturing biochemical fractionation followed by enzyme-linked immunosorbent assay (ELISA) analysis. They measured absolute αSyn by ELISA and found enriched αSyn species in the cytosolic fraction of the DLB cortex, which was lower in the membrane-associated fraction.…”

Microglia modulate neurodegeneration in Alzheimer’s and Parkinson’s diseases

“…Familial synucleinopathies can be tied to the expression levels of total neuronal αSyn (54). However, in sporadic PD, neurodegeneration strongly correlates with certain bioactive forms of αSyn rather than total levels of αSyn (55). Furthermore, three "synucleinopathies"-PD, Dementia with Lewy Bodies (DLB) and Multiple System Atrophy (MSA)-are all characterized by amyloid αSyn burden but interestingly show distinct brain regionspecific patterns of amyloid accumulation and neuronal dysfunction (56).…”