Identification and characterization of modulators affecting Amyloid precursor protein (APP) family members synaptogenic activity
Molecular Biology and Physiology of Neurons and Glial Cells
Final Report Abstract
The amyloid precursor protein (APP) plays a central role in the pathology of Alzheimer`s disease and has a central function at the synapse. We and others could show that APP and its homologues APLP1 and APLP2 can trans-dimerize and that this trans-cellular interaction contributes to formation and/or stabilization of synapses. In course of this project we focused on the question, how APP/APLPs trans-directed dimerization can be regulated. For this purpose, an in vitro bead aggregation assay (BAA) with APP/APLP-coated beads was established. Using the BAA in combination with isothermal titration calorimetry (ITC) we could demonstrate that zinc ions can bind with high affinity to the E1 domain of APP and promote its dimerization. Interestingly, copper and zinc ions bind to distinct sites of APP/APLPs extracellular domain and affect its trans-dimerization properties in different fashions, likely by changing the structural features of the extracellular domain. Originally, we indented to screen only for proteins affecting APP/APLPs dimerization. However, the identification of zinc as a modulator of trans-dimerization is very interesting, as zinc ions get released upon neuronal activity at certain synapses. However, future experiments addressing the role of zinc in regulation of APP/APLPs synaptogenic function will be required to clarify the role of zinc in modulation of APP/APLPs function. Moreover, the BAA was used in combination with mass spectrometric analisis to identify proteins modulating APP trans-dimerization. Here, we succeeded to identify thrombospondin-1 (TSP 1) from astrocyte-conditioned medium (ACM) as a putative factor promoting APP transdimerization. Notably, a knockdown of TSP-1 in astrocytes abolished the APP dimerizing activity of ACM, suggesting that TSP-1 is the major factor secreted by astrocytes that promotes APP trans-dimerization. Further studies will be necessary to decipher the functional interaction of APP and TSP-1 in more detail. In summary, this study clearly showed that trans-directed dimerization of APP/APLPs can be regulated by different factors, including zinc ions and TSP-1, both known as important modulators of synaptic activity and/or synaptic development. In future work we intend to clarify the in vivo function of these modulators in regard to APP/APLPs synaptogenic function.
Publications
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Dimerization leads to changes in APP (amyloid precursor protein) trafficking mediated by LRP1 and SorLA. Cell Mol Life Sci. 2018 Jan;75(2):301- 322
Eggert S, Gonzalez AC, Thomas C, Schilling S, Schwarz SM, Tischer C, Adam V, Strecker P, Schmidt V, Willnow TE, Hermey G, Pietrzik CU, Koo EH, Kins S
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Copper and zinc ions govern the trans-directed dimerization of APP family members in multiple ways. J Neurochem. 2019 Dec;151(5):626-641
August A, Schmidt N, Klingler J, Baumkötter F, Lechner M, Klement J, Eggert S, Vargas C, Wild K, Keller S, Kins S
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The Rab5 activator RME-6 is required for amyloid precursor protein endocytosis depending on the YTSI motif. Cell Mol Life Sci. 2020 Dec;77(24):5223-5242
Eggert S, Gruebl T, Rajender R, Rupp C, Sander B, Heesch A, Zimmermann M, Hoepfner S, Zentgraf H, Kins S
