ER-mitochondria contact sites in neurodegeneration: genetic screening approaches to investigate novel disease mechanisms

Emma Louise Wilson,Emmanouil Metzakopian

doi:10.1038/s41418-020-00705-8

Abstract

Mitochondria-ER contact sites (MERCS) are known to underpin many important cellular homoeostatic functions, including mitochondrial quality control, lipid metabolism, calcium homoeostasis, the unfolded protein response and ER stress. These functions are known to be dysregulated in neurodegenerative diseases, including Parkinson’s disease (PD), Alzheimer’s disease (AD) and amyloid lateral sclerosis (ALS), and the number of disease-related proteins and genes being associated with MERCS is increasing. However, many details regarding MERCS and their role in neurodegenerative diseases remain unknown. In this review, we aim to summarise the current knowledge regarding the structure and function of MERCS, and to update the field on current research in PD, AD and ALS. Furthermore, we will evaluate high-throughput screening techniques, including RNAi vs CRISPR/Cas9, pooled vs arrayed formats and how these could be combined with current techniques to visualise MERCS. We will consider the advantages and disadvantages of each technique and how it can be utilised to uncover novel protein pathways involved in MERCS dysfunction in neurodegenerative diseases.

Highlights

For many years, the textbook view of organelles has been that they function independently and in isolation from each other, forming separate contained entities within a cell
This review aims to update the field on the molecular composition and functions of mitochondria-ER contact site (MERCS), with specific focus on its impact in Alzheimer’s disease (AD), Parkinson’s disease (PD) and amyloid lateral sclerosis (ALS)
MERCS has been implicated in a range of neurodegenerative diseases, but many questions still remain unanswered

Summary

Introduction

The textbook view of organelles has been that they function independently and in isolation from each other, forming separate contained entities within a cell. Further studies have revealed that the mitophagy machinery uncouples the mitochondria from the ER via destruction of MFN2, which is an early target of PINK1/Parkin-mediated phosphoubiquitination, facilitating mitophagy [46] This demonstrates that uncoupling and coupling of ER and mitochondria membranes are both required for efficient mitophagy, and that MERCS has a key role in maintaining efficient MQC mechanisms and mitochondrial health. The addition of rapamycin allows maximal energy transfer between FRET pairs, enabling quantitative measurements of contact distance; equimolar concentrations of the FRET pairs are required as FRET is affected by the relative amount of each florophore [125] This was skilfully overcome by transfection of one plasmid containing both acceptor and donor constructs separated by TAV2a sequence (which self-cleaves), achieving equal expression of both FRET pairs, and has been used in conjunction with rapamycin to investigate potential MERCS proteins, including MFN2 and Parkin [11, 74]. GECIs have the potential to be used as a tool in HTS of MERCS, in pooled CRISPR screening due to their ease of use with flow cytometry [133, 134]

Conclusions

Findings

Compliance with ethical standards