SorLA Complement-type Repeat Domains Protect the Amyloid Precursor Protein against Processing

Arnela Mehmedbasic,Sofie K Christensen,Jonas Nilsson,Ulla Rüetschi,Camilla Gustafsen,Annemarie Svane Aavild Poulsen,Rikke W Rasmussen,Anja N Fjorback,Göran Larson,Olav M Andersen

doi:10.1074/jbc.m114.619940

Arnela Mehmedbasic, Sofie K Christensen + Show 8 more

Open Access

https://doi.org/10.1074/jbc.m114.619940

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Abstract

SorLA is a neuronal sorting receptor that is genetically associated with Alzheimer disease. SorLA interacts directly with the amyloid precursor protein (APP) and affects the processing of the precursor, leading to a decreased generation of the amyloid-β peptide. The SorLA complement-type repeat (CR) domains associate in vitro with APP, but the precise molecular determinants of SorLA·APP complex formation and the mechanisms responsible for the effect of binding on APP processing have not yet been elucidated. Here, we have generated protein expression constructs for SorLA devoid of the 11 CR-domains and for two SorLA mutants harboring substitutions of the fingerprint residues in the central CR-domains. We generated SH-SY5Y cell lines that stably express these SorLA variants to study the binding and processing of APP using co-immunoprecipitation and Western blotting/ELISAs, respectively. We found that the SorLA CR-cluster is essential for interaction with APP and that deletion of the CR-cluster abolishes the protection against APP processing. Mutation of identified fingerprint residues in the SorLA CR-domains leads to changes in the O-linked glycosylation of APP when expressed in SH-SY5Y cells. Our results provide novel information on the mechanisms behind the influence of SorLA activity on APP metabolism by controlling post-translational glycosylation in the Golgi, suggesting new strategies against amyloidogenesis in Alzheimer disease.

Highlights

SorLA binds amyloid precursor protein (APP) and decreases the production of A␤; the molecular mechanisms controlling these processes are poorly understood
We found that the SorLA complement-type repeat (CR)-cluster is essential for interaction with APP and that deletion of the CR-cluster abolishes the protection against APP processing
Binding Site Characterization—In this study, we investigated the binding between APP and SorLA, focusing on the role of the CR-domains

Summary

Background

SorLA binds APP and decreases the production of A␤; the molecular mechanisms controlling these processes are poorly understood. SorLA binds directly to APP and slows down its cellular transport out of the Golgi; less of the precursor protein enters secretase-containing compartments, decreasing the processing of APP to both nonamyloidogenic (sAPP␣) and amyloidogenic (A␤) products [10, 11, 21,22,23]. This function is dependent on receptor localization to the Golgi, establishing a direct link to the trafficking pathway from endosomes to the trans-Golgi network/Golgi, a pathway suspected to be altered in sporadic AD [2, 24, 25]. This study provides novel insight into the mechanisms that determine APP trafficking and maturation, factors that strongly regulate the generation of A␤ and are risk factors for AD

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION