α-Synuclein is readily released in human and mouse brain parenchyma, even though the normal function of the secreted protein has not been yet elucidated. Under pathological conditions, such as in ...Parkinson's disease, pathologically relevant species of α-synuclein have been shown to propagate between neurons in a prion-like manner, although the mechanism by which α-synuclein transfer induces degeneration remains to be identified. Due to this evidence extracellular α-synuclein is now considered a critical target to hinder disease progression in Parkinson's disease. Given the importance of extracellular α-synuclein levels, we have now investigated the molecular pathway of α-synuclein secretion in mouse brain. To this end, we have identified a novel synaptic network that regulates α-synuclein release in mouse striatum. In this brain area, the majority of α-synuclein is localized in corticostriatal glutamatergic terminals. Absence of α-synuclein from the lumen of brain-isolated synaptic vesicles suggested that they are unlikely to mediate its release. To dissect the mechanism of α-synuclein release, we have used reverse microdialysis to locally administer reagents that locally target specific cellular pathways. Using this approach, we show that α-synuclein secretion in vivo is a calcium-regulated process that depends on the activation of sulfonylurea receptor 1-sensitive ATP-regulated potassium channels. Sulfonylurea receptor 1 is distributed in the cytoplasm of GABAergic neurons from where the ATP-dependent channel regulates GABA release. Using a combination of specific agonists and antagonists, we were able to show that, in the striatum, modulation of GABA release through the sulfonylurea receptor 1-regulated ATP-dependent potassium channels located on GABAergic neurons controls α-synuclein release from the glutamatergic terminals through activation of the presynaptic GABAB receptors. Considering that sulfonylurea receptors can be selectively targeted, our study highlights the potential use of the key molecules in the α-synuclein secretory pathway to aid the discovery of novel therapeutic interventions for Parkinson's disease.
Parkinson's disease is biochemically characterized by the deposition of aberrant aggregated α‐synuclein in the affected neurons. The aggregation properties of α‐synuclein greatly depend on its ...affinity to bind cellular membranes via a dynamic interaction with specific lipid moieties. In particular, α‐synuclein can interact with arachidonic acid (AA), a polyunsaturated fatty acid, in a manner that promotes the formation of α‐helix enriched assemblies. In a cellular context, AA is released from membrane phospholipids by phospholipase A2 (PLA2). To investigate the impact of PLA2 activity on α‐synuclein aggregation, we have applied selective PLA2 inhibitors to a SH‐SY5Y cellular model where the expression of human wild‐type α‐synuclein is correlated with a gradual accumulation of soluble oligomers and subsequent cell death. We have found that pharmacological and genetic inhibition of GIVA cPLA2 resulted in a dramatic decrease of intracellular oligomeric and monomeric α‐synuclein significantly promoting cell survival. Our data suggest that alterations in the levels of free fatty acids, and especially AA and adrenic acid, promote the formation of α‐synuclein conformers which are more susceptible to proteasomal degradation. This mechanism is active only in living cells and is generic since it does not depend on the absolute quantity of α‐synuclein, the presence of disease‐linked point mutations, the expression system or the type of cells. Our findings indicate that the α‐synuclein‐fatty acid interaction can be a critical determinant of the conformation and fate of α‐synuclein in the cell interior and, as such, cPLA2 inhibitors could serve to alleviate the intracellular, potentially pathological, α‐synuclein burden.
Synucleinopathies are disorders characterized by the abnormal accumulation of α-synuclein (aSyn). Synaptic compromise is observed in synucleinopathies parallel to aSyn aggregation and is accompanied ...by transcript deregulation.
We sought to identify microRNAs associated with synaptic processes that may contribute to synaptic dysfunction and degeneration in synucleinopathies.
We performed small RNA-sequencing of midbrain from 6-month-old transgenic mice expressing A30P mutant aSyn, followed by comparative expression analysis. We then used real-time quantitative polymerase chain reaction (qPCR) for validation. Functional analysis was performed in primary neurons by biochemical assays and imaging.
We found several deregulated biological processes linked to the synapse. miR-101a-3p was validated as a synaptic miRNA upregulated in aSyn Tg mice and in the cortex of dementia with Lewy bodies patients. Mice and primary cultured neurons overexpressing miR-101a-3p showed downregulation of postsynaptic proteins GABA Ab2 and SAPAP3 and altered dendritic morphology resembling synaptic plasticity impairments and/or synaptic damage. Interestingly, primary cultured neuron exposure to recombinant wild-type aSyn species efficiently increased miR-101a-3p levels. Finally, a dynamic role of miR-101a-3p in synapse plasticity was shown by identifying downregulation of miR-101a-3p in a condition of enhanced synaptic plasticity modelled in Wt animals housed in enriched environment.
To conclude, we correlated pathologic aSyn with high levels of miR-101a-3p and a novel dynamic role of the miRNA in synaptic plasticity.
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