Rolle der ER-Mitochondrien-Kontaktstellen in der Pathogenese der Alzheimer-Erkrankung
Molekulare Biologie und Physiologie von Nerven- und Gliazellen
Zusammenfassung der Projektergebnisse
n a recent study, the host laboratory had shown that ER-mitochondria contact sites, consisting of specialized regions of the ER membrane (mitochondria-associated ER membranes, MAM) and regions of the outer mitochondrial membrane (OMM), are present in neurons and that specific MAM-associated proteins are upregulated in human AD brain and an AD mouse model entailing an increased connectivity between ER and mitochondria including for example an increased flux of calcium from ER to mitochondria. Mitochondrial calcium overload triggers apoptosis explaining how the dysregulation of MAM could contribute to synapse loss and neurodegeneration in AD. The proposed study was designed to investigate the structure and function of ER- mitochondria contact sites in neuronal cells and brain tissue with the aim to elucidate the role of ER-mitochondria contact site dysfunction in neuronal cell death that is underlying the pathogenesis of Alzheimer’s disease (AD). Biochemical, cell biological, immunological and imaging techniques were used in order to determine intracellular production sites of disease-associated amyloid βpeptide (Aβ), to identify components of ER-mitochondria contact sites, to analyse the structure of the contact sites in brain tissue of an AD mouse model and to study the effects of Aβ, electron transfer chain deficiency and drugs “boosting” mitochondrial performance on the ER-mitochondrial contact site integrity. Importantly, we found that highest intracellular Aβ production takes place at ER- mitochondria contact sites where Aβ-producing enzymes are residing in MAM, at the ER-site of the contact. We demonstrated that structural modulation of ER-mitochondria contact sites by siRNA-induced knockdown of Mfn2 led to a downregulation of intracellular and secreted Aβ levels. Furthermore, we confirmed the presence of TOM20 and TOM70, both receptor components of the translocase of the outer mitochondria membrane (TOM), at ER- mitochondria contact sites and moreover, co-precipitation of these TOM components with the known MAM marker protein IP3R3 that constitutes an ER-to-mitochondria calcium bridge together with VDAC1 in the (OMM). Taking into account our finding that a considerable amount of Aβ is produced in the fraction containing ER-mitochondria contact sites, the subpopulation of TOM residing at ER-mitochondria contact sites could function as import channel for MAM- produced Aβ. Several of our approaches confronted us with the same issue: the high dynamic of the structure of mammalian ER-mitochondria contact sites over time. Whereas ER-mitochondria contact sites of S. cerevisiae seem rather static structures, it becomes more and more evident that mammalian contact sites are highly dynamic entities that change both, their structure and function, in response to changing cellular needs. Taken together, our observations support a role of ER-mitochondria contact sites in the pathogenesis of AD as intracellular production site of the disease-related Aβ peptide. Further studies have to elucidate the feasibility of ER-mitochondria contact modulation as new treatment approach to halt progressive neurodegeneration in AD.
Projektbezogene Publikationen (Auswahl)
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(2015). Amyloid-beta Peptides are Generated in Mitochondria- Associated Endoplasmic Reticulum Membranes. Journal of Alzheimer's disease : JAD 43: 369-374
Schreiner, B., Hedskog, L., Wiehager, B., Ankarcrona, M.
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Mitofusin-2 knockdown increases ER-mitochondria contact and decreases amyloid β-peptide production. Journal of Cellular and Molecular Medicine; Vol 20 Issue 9, September 2016, Pages 1686-1695
Nuno Leal, Bernadette Schreiner, Catarina Moreira Pinho, Riccardo Filadi, Birgitta Wiehager, Helena Karlström, Paola Pizzo and Maria Ankarcrona
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Isolation of mitochondria-associated membranes (MAM) from mouse brain tissue. In: Mokranjac D., Perocchi F. (eds) Mitochondria. Methods in Molecular Biology, vol 1567. Humana Press, New York, NY, 2017. Chapter; pp 53-68
Bernadette Schreiner and Maria Ankarcrona
