Research Report 2010 - MDC

Dr. Pablo Porras-MillanDr. Ellen Ramminger*Dr. Tamás RaskóDr. Sean-Patrick Riechers*Dr. Michael Schmidt*Dr. Martin StrödickeDr. Bernhard Suter*Dr. Thomas WiglendaAffiliated ScientistsDr. Matthias Futschik* (HU Berlin)Graduate and UndergraduateStudentsAnup ArumughanYacine Bounab*Gautam Chaurasia* (HU Berlin)Anja Fritzsche*Antje Haug*Manuela JacobNancy Keil*Matthias KönnShuang Li*Annekathrin MöllerMonique Rothe*Jenny Russ*Maliha Shah*Anne WagnerKatja WelschHeike Wobst*Systematic investigation of predicteddysregulated huntingtin interactionpartners in a HD Drosophila model. (A)Dysregulated huntingtin PPI networkpredicted by bioinformatic analysis ofPPI and gene expression data fromhuman tissues and clinical case-controlstudies. (B) Expression of the proteinsCRMP1, CRMP, PACSIN1, Profilin2 andChic reduce mutant huntingtin-mediatedphotoreceptor degeneration in aHD model, whereas expression of theprotein PRPF40a has the oppositeeffect.Identification and characterization of small moleculesthat modulate protein misfolding pathwaysIn previous studies, we have identified the natural compound(-)-epigallocatechin gallate (EGCG) as a modulatorof polyQ-mediated huntingtin aggregation(Ehrnhoefer et al., 2006). We continued these studieswith the disease proteins causative of PD and AD. α-synuclein and amyloid-β amyloidogenesis was investigatedusing biochemical, biophysical and cell biologicalmethods. We found that EGCG efficiently prevents fibrilformation of both polypeptides in cell-free model systems,supporting the previous results with the huntingtinprotein and hinting at a generic mechanism.Further studies subsequently revealed that EGCG isable to redirect the amyloid fibril formation pathway. Itbinds to α-synuclein and amyloid-β monomers andstimulates the assembly of off-pathway, highly stableoligomers, which are non-toxic for mammalian cells.These investigations suggest that EGCG functions as achemical chaperone that recognizes natively unfoldedpolypeptides and influences their ability to spontaneouslymisfold and self-assemble into amyloidogenicprotein aggregates (Ehrnhoefer and Bieschke, 2008).Most recently, we studied whether EGCG disassemblespreformed amyloid fibrils. Our data indicate that EGCGhas the ability to convert preformed, mature α-synucleinand amyloid-β fibrils into smaller, amorphous proteinaggregates that are non-toxic for mammaliancells. These findings suggest that EGCG is a potentremodelling agent of mature amyloid fibrils and supportour hypothesis that the compound has chemicalchaperone function.Several lines of experimental evidence indicate thatsoluble, pre-fibrillar assemblies of the amyloid-βpolypeptide rather than mature, end-stage amyloid fibrilscause neuronal dysfunction and memory impairmentin Alzheimer’s disease. This suggests that accelerationof fibrillogenesis might reduce the levels of toxicaggregation intermediates. To address this question,we searched for chemical compounds that promotespontaneous amyloid-β formation. Using a filter assay,the natural dye orcein and related substances wereidentified which directly bind to small transient amyloidoligomers and stimulate their assembly intomature amyloid fibrils. These structures have alteredsurface properties and are non-toxic for mammaliancells. Our results suggest that conversion of smallFunction and Dysfunction of the Nervous System 183