Unit:
Library of the School of Health SciencesFaculty of Medicine
Author:
Mavroeidi Panagiota
Dissertation committee:
Στεφανής Λεωνίδας, Καθηγητής, Τμήμα Ιατρικής, ΕΚΠΑ
Καραγωγέως Δόμνα, Καθηγήτρια, Τμήμα Ιατρικής, Πανεπιστήμιο Κρήτης
Ευθυμιόπουλος Σπύρος, Καθηγητής, Τμήμα Βιολογίας, ΕΚΠΑ
Ρουμπελάκη Μαρία, Αναπληρώτρια Καθηγήτρια, Τμήμα Ιατρικής, ΕΚΠΑ
Jensen Poul Henning, Καθηγητής, Τμήμα Βιοιατρικής, Πανεπιστήμιο Aarhus, Δανία
Ξυλούρη Μαρία, Ερευνήτρια Γ΄, Κέντρο Κλινικής, Πειραματικής Χειρουργικής & Μεταφραστικής Έρευνας, ΙΙΒΕΑΑ
Πολίτης Παναγιώτης, Ερευνητής Β', Κέντρο Βασικής Έρευνας, ΙΙΒΕΑΑ
Original Title:
Διερεύνηση του ρόλου της πρωτεΐνης α-συνουκλεΐνης στην παθογένεια της Ατροφίας Πολλαπλών Συστημάτων
Translated title:
Investigation of the role of the protein alpha synuclein on Multiple System Atrophy Pathogenesis
Summary:
Multiple System Atrophy is a rare debilitating disease characterized by the presence of
distinct glial cytoplasmic inclusions within oligodendrocytes. These inclusions are mainly
composed of the neuronal protein alpha-synuclein and the oligodendroglia-specific phosphoprotein TPPP/p25α. The precise role of oligodendroglial alpha-synuclein and p25α in the formation of glial cytoplasmic inclusions and the subsequent neuronal death, as well as the proteolytic mechanisms involved in their turnover in health and disease remains hitherto unclear. To address these questions, we have utilized three immortalized oligodendroglial cell lines originated from rat brain glial cultures: wild-type oligodendrocytes (OLN-93) expressing low to non-detectable levels of the endogenous alpha-synuclein and p25α and cells stably overexpressing human alpha-synuclein
(OLN-AS7) or human p25α (OLN-p25α). In parallel, we have used primary cultures of
differentiated oligodendroglial cells deriving from wild-type (WT-aSyn) mice or transgenic mice lacking the endogenous alpha-synuclein expression (KO-aSyn) or overexpressing human alphasynuclein selectively in oligodendrocytes (PLP-haSyn). Both cell lines and primary oligodendrocytes were incubated with human alpha synuclein pre-formed fibrils as a model of alpha-synucleinopathy. Initially, we verified that alpha-synuclein fibrils are readily taken up by oligodendroglial cells and can recruit minute amounts of endogenous alpha-synuclein into the formation of insoluble, highly aggregated, pathological assemblies. The overexpression of human alpha-synuclein or p25α accelerates the recruitment of the endogenous protein and the generation of such aberrant species. In fibril-treated primary oligodendrocytes, the microtubule and myelin networks are disrupted, thus recapitulating a pathological hallmark of Multiple System Atrophy, in
a manner totally dependent upon the presence of endogenous alpha-synuclein.
Furthermore, utilizing oligodendroglial and cortical cultures, we demonstrated that the
pathology-related phosphorylation of alpha-synuclein at Serine 129 depends on alpha-synuclein and p25α protein load and may involve different alpha-synuclein “strains” present in oligodendroglial and neuronal synucleinopathies. Importantly, this hypothesis was further supported by data obtained from human post-mortem brain material derived from patients with Multiple System Atrophy and dementia with Lewy bodies, where alpha-synuclein accumulates in neurons. Importantly, delivery of alpha-synuclein fibrils into the mouse striatum led to the formation of aberrant alpha-synuclein
forms within oligodendroglia, incorporating the endogenous protein, and evoked myelin
decompaction in WT-aSyn mice, but not in KO-aSyn mice.
In order to elucidate the degradation mechanisms responsible for the removal of both
endogenous oligodendroglial alpha-synuclein and p25α, we pharmacologically and molecularly modulated the autophagy-lysosome pathway and performed pharmacological inhibition of the proteasome. According to our results, both the endogenous oligodendroglial alpha-synuclein and p25α are degraded mainly by the autophagy-lysosome pathway in oligodendroglial cell lines and murine primary oligodendrocytes under basal conditions. We have also identified a KFERQ-like
motif in p25α sequence that enables its effective degradation via chaperone-mediated autophagy in an in vitro system of isolated rat brain lysosomes. Utilizing pre-formed alpha-synuclein fibrils as seeds of pathology, we thoroughly characterized the contribution of autophagy-lysosome pathway in the removal of the exogenously added and the seeded oligodendroglial alpha-synuclein pathological assemblies. We have also showed that inoculation with alpha-synuclein fibrils impairs autophagic flux in oligodendrocytes and that p25α exerts an inhibitory effect on macroautophagy,
while at the same time chaperone-mediated autophagy is upregulated, probably as a compensatory mechanism, to remove the pathological alpha-synuclein species formed within oligodendrocytes.
Collectively, this line of research highlights the role of endogenous alpha-synuclein and
p25α in the formation of pathological aSyn assemblies in experimental models of Multiple System Atrophy. In addition, this study pinpoints the contribution of chaperone-mediated autophagy and macroautophagy in the regulation of oligodendroglial alpha-synuclein and p25α levels, in physiological and pathological conditions and highlights their targeting as a potential therapeutic strategy against Multiple System Atrophy.
Main subject category:
Health Sciences
Keywords:
α-Synuclein, Oligodndrocytes, Autophagy, Myelin Basic Protein
Number of references:
652
