Pan Gao, Germany
German Center for Neurodegenerative Diseases (DZNE) Translational Brain ResearchAuthor Of 2 Presentations
LOSS OF FRAGILE X MENTAL RETARDATION PROTEIN (FMRP) PRECEDES LEWY PATHOLOGY IN PARKINSON’S DISEASE (PD).
Abstract
Aims
Previous research implicated alterations of neuronal excitability in DA neuron cell death. Because the Fragile X Mental Retardation Protein (FMRP) has been shown to control a large number of genes related to neuronal excitability and synaptic function, we here investigated the role of FMRP in PD.
Methods
We combined biochemical, electrophysiological and imaging techniques to examine the effect of a-syn on FMRP in vitro and in vivo. In addition, we investigated the abundance of FMRP in SNc DA neurons of post-mortem human brain tissue from PD patients and from subjects that had incidental Lewy body disease (iLBD).
Results
We found FMRP to be decreased in cultured DA neurons and in the mouse brain in response to a-syn overexpression. Likewise, FMRP was lost in SNc DA neurons of PD patients and in neurons from iLBD cases. Similar to Fragile X Syndrome (FXS) neurons, a-syn-overexpressing cells had an increase in membrane N-type calcium channels, enhanced N-type-mediated calcium currents, an increased phosphorylation of the protein translation initiation machinery (p-ERK1/2, p-eIF4E and p-S6) and, as a consequence, an increased overall protein synthesis. The loss of FMRP appeared to have a protective effect in SNc DA neurons, because FMRP knockout mice were resistant to the effect of a-syn on striatal dopamine release.
Conclusions
Our results reveal a new and previously unrecognized role of FMRP in PD. Our data thus suggest the loss of FMRP to be an early pathogenic event that precedes Lewy pathology in PD and therefore support the examination of FMRP-regulated genes in PD onset and progression.
ALPHA-SYNUCLEIN DEFECTS AUTOPHAGY BY IMPAIRING SNAP29-MEDIATED AUTOPHAGOSOME-LYSOSOME FUSION
Abstract
Aims
Although the exact mechanism of neuronal aggregate formation and death remains elusive, recent research suggests a-Syn-mediated alterations in autophagy. In this study, we aim to investigate the effect of a-Syn on autophagy turnover in cultured human DA neurons and in human postmortem brain tissue.
Methods
We investigate the effect of a-Syn overexpression on autophagy using a combination of molecular biology and immunochemistry. Immunohistochemistry was used to study protein abundance in SNc DA neurons from human postmortem brain tissue.
Results
We found a-Syn overexpression to reduce autophagy turnover by compromising the fusion of autophagosomes with lysosomes, thus leading to a decrease in the formation of autophagolysosomes. In accord with a compensatory increase in the plasma membrane fusion of autophagosomes, a-Syn enhanced the number of extracellular vesicles (EV) and the abundance of autophagy-associated proteins in these EVs. Mechanistically, a-Syn interacted with and decreased the abundance of the v-SNARE protein SNAP29, a member of the SNARE complex mediating autophagolysosome fusion. In line, SNAP29 knockdown mimicked the effect of a-Syn on autophagy whereas SNAP29 co-expression reversed the a-Syn-induced changes on autophagy turnover and EV release and ameliorated DA neuronal cell death. In addition, we found a stage-dependent reduction of SNAP29 in SNc DA neurons from human postmortem brain tissue of Lewy body pathology (LBP) cases.
Conclusions
In summary, our results demonstrate a previously unknown effect of a-Syn on intracellular autophagy-associated SNARE proteins and, as a consequence, a reduced autophagolysosome fusion, and will therefore support the investigation of autophagy-associated pathological changes in PD.