Nanobody-mediated detection and modulation of the molecular machinery generating Alzheimer’s disease-linked amyloid β peptides

Gamma-secretases (GSECs) are membrane-embedded protein complexes exerting proteolytic activity on numerous type 1 membrane proteins, including amyloid precursor protein (APP), Notch, ErbB4, neuregulin and N-cadherin. GSEC activity thus regulates several physiological processes, such as cell adhesion, embryonic development and axon guidance. The GSEC-mediated cleavage of APP generates amyloid β (Aβ) peptides of different length. Notably, GSECs and APP are mutated in the familial form of Alzheimer’s disease (AD). AD-pathogenic mutations destabilize the fragile GSEC-APP (Enzyme-Substrate) complexes during the sequential proteolysis, and thereby promote the release of partially digested, longer Aβ peptides. These longer fragments are proposed to trigger toxic molecular cascades eventually leading to neurodegeneration and AD. We propose the stabilization of GSEC-APP complexes as an original strategy to shift the production of Aβ towards the generation of shorter Aβ peptides. To this end, we will generate conformation specific nanobodies that selectively bind to GSEC and/or APP and efficiently secure the GSEC-APP interactions. Nanobodies are revolutionary single domain antigen binding molecules, derived from camelid heavy chain only antibodies. Due to their small size and the preference for conformational epitopes, they have a unique ability to reach and bind pockets inaccessible for conventional antibodies. Importantly, nanobodies can be easily engineered for their application in affinity purification, (in vitro and in vivo) immunodetection as well as labelling of the target interactome. The generated anti-GSEC and/or anti-GSEC-APP nanobodies will be used to investigate the biology of GSECs, by the immunodetection of the complexes and the immunomodulation of Aβ production (as stabilizers) in vitro and in vivo. We anticipate that these studies will provide new insights into the GSEC-APP interactions and may pave the way for the development rationale-based drugs targeting safely GSECs in AD therapy.