ER-associated degradation regulates Alzheimer\u2019s amyloid pathology and memory function by modulating \u03b3-secretase activity

Bing Zhu,Eliezer Masliah,Yingjun Zhao,Xiaoguang Li,Huaxi Xu,Yongwang Zhong,Alexandre Campos,Tongfei Liu,Timothy Huang,Lulin Jiang,Dongxian Zhang,Kenneth Pomeroy

doi:10.1038/s41467-017-01799-4

Abstract

Endoplasmic-reticulum-associated degradation (ERAD) is an important protein quality control system which maintains protein homeostasis. Constituents of the ERAD complex and its role in neurodegeneration are not yet fully understood. Here, using proteomic and FRET analyses, we demonstrate that the ER protein membralin is an ERAD component, which mediates degradation of ER luminal and membrane substrates. Interestingly, we identify nicastrin, a key component of the γ-secretase complex, as a membralin binding protein and membralin-associated ERAD substrate. We demonstrate a reduction of membralin mRNA and protein levels in Alzheimer’s disease (AD) brain, the latter of which inversely correlates with nicastrin abundance. Furthermore, membralin deficiency enhances γ-secretase activity and neuronal degeneration. In a mouse AD model, downregulating membralin results in β-amyloid pathology, neuronal death, and exacerbates synaptic/memory deficits. Our results identify membralin as an ERAD component and demonstrate a critical role for ERAD in AD pathogenesis.

Highlights

Endoplasmic-reticulum-associated degradation (ERAD) is an important protein quality control system which maintains protein homeostasis
A recent genome-wide association (GWAS) study has shown that the membralin gene is located within 500 bp of a single nucleotide polymorphism (SNP) locus tightly associated with late-onset AD24, and an additional study demonstrated that membralin transcript splicing is significantly altered in AD25
In order to elucidate a potential role for membralin in the endoplasmic reticulum (ER), we searched for membralin-interacting proteins by immunoprecipitating Myc-tagged mouse membralin complexes from HEK293T cells and characterizing bound components by affinitypurification mass spectrometry (AP-MS)[14]

Summary

Introduction

Endoplasmic-reticulum-associated degradation (ERAD) is an important protein quality control system which maintains protein homeostasis. Using proteomic and FRET analyses, we demonstrate that the ER protein membralin is an ERAD component, which mediates degradation of ER luminal and membrane substrates. We identify nicastrin, a key component of the γ-secretase complex, as a membralin binding protein and membralin-associated ERAD substrate. We demonstrate a reduction of membralin mRNA and protein levels in Alzheimer’s disease (AD) brain, the latter of which inversely correlates with nicastrin abundance. Membralin deficiency enhances γ-secretase activity and neuronal degeneration. Our results identify membralin as an ERAD component and demonstrate a critical role for ERAD in AD pathogenesis. We identify and confirm that membralin is a component of the ERAD network to maintain homeostatic degradation of both luminal and membrane substrates, and pathophysiological substrates such as nicastrin. AMFR AUP1 EMC3 EMC4 EMC7 EMC8 FAM8A1 HERPUD1 Nicastrin Os9 RNF170 RNF5 SEL1L UBAC2 UBL4A (Nicastrin)

Methods

Results

Conclusion