Extracellular α-Synuclein Disrupts Membrane Nanostructure and Promotes S-Nitrosylation-Induced Neuronal Cell Death

Abstract

α-Synuclein, a major constituent of proteinaceous inclusions named Lewy body, has been shown to be released and taken up by cells, which may facilitate its progressive pathological spreading and neuronal cell death in Parkinson's disease. However, the pathophysiological effect and signaling cascade initiated by extracellular α-synuclein in cellular milieu are not well understood. Herein we have investigated the perturbations induced by low molecular weight α-synuclein and different types of α-synuclein oligomers in the neuroblastoma SH-SY5Y cells. Atomic force microscopy studies have revealed formation of nanopores and enhanced roughness in the cell surface leading to membrane disruption. The damaged membrane allows altered ionic homeostasis leading to activation of nitric oxide synthase (NOS) machinery releasing burst of nitric oxide. The elevated levels of nitric oxide induces S-nitrosylation of key proteins like Actin, DJ-1, HSP70 UCHL1, Parkin, and GAPDH that alter cytoskeletal network, protein folding machinery, ubiquitin proteasome system inducing apoptosis.

Partially oxidized DJ-1 inhibits α-synuclein nucleation and remodels mature α-synuclein fibrils in vitro

“…This observation confirmed that DJ-1 Pox remodeled fibrils are shorter species. Our earlier report has demonstrated that extracellular α-synuclein also induces neurotoxicity due to increase in cellular nitric oxide level and subsequent protein S-nitrosylation 41 . Here we found that remodeled fibrils induced an almost two-fold higher nitric oxide level than mature fibrils in SH-SY5Y cells (Supplementary Fig.…”

“…The different samples from primary nucleation as well as seeded aggregation (20 μM) were aliquoted at different time points and incubated with 20 μM of ThT for 5 min as described earlier 41 . Three independent measurements were performed for each sample.…”

Glyceraldehyde-3-phosphate Dehydrogenase Is a Multifaceted Therapeutic Target

“…Together, the data on GAPDH-mediated cell death indicate that the chemical modifications and translocation of the enzyme to the nucleus cause cytotoxic cascades. Consistently, it is believed that inactivated, aggregation-prone GAPDH can enhance such pathologies as Alzheimer's disease [75], Huntington's disease [76,77], Parkinson's disease [78], diabetes [79], secondary damage after traumatic brain injury [28] and many others. Therefore, targeting specific sites on the GAPDH molecule may be useful for increasing the viability of cells subjected to proteotoxic factors, such as misfolded proteins in neurological diseases.…”

The Role of α-Synuclein Oligomers in Parkinson’s Disease

“…The uptake of α-syn oligomers by SH-SY5Y cells destruct the cell membrane and ion homeostasis, giving rise to the activation of nitric oxide synthase (NOS), S-nitrosylation of key proteins, and change of cytoskeletal network, protein folding mechanism and ubiquitin proteasome system. All these effects induce cell apoptosis [ 58 ]. Externally added α-syn fibers can bind to the cytoplasmic membrane and act as nucleation sites, promoting oligomerization and internalization of α-syn and activating intracellular and extracellular apoptotic pathways [ 59 ].…”