"The redox triangle" - communication between peroxisomes, the endoplasmic reticulum and mitochondria in health and disease.

This project aims to uncover how connections between different compartments in human cells are re-organised during cell division and the importance of this process in health and disease. The text-book picture of a eukaryotic cell traditionally shows a collection of apparently isolated compartments (organelles) which appear to function independently. My research focuses on an emerging concept, challenging this text-book view. Recent work has shown that organelles are not isolated islands but are instead physically and metabolically connected. These connections, known as membrane contact sites (MCSs), are critical to how cells function. Membrane contacts control the lifecycle, activity, and positioning of organelles, allowing exchange of critical messages and metabolites. For example, our work has shown that defects in one organelle, e.g. mitochondria, can impact on other organelles such as the endoplasmic reticulum (ER). Membrane contacts are generally formed by binding between pairs of proteins on different organelle membranes, forming molecular tethers which hold organelles together. Defective organelle tethering has been identified in a range of human disorders including neurodegenerative and other metabolic disorders which are increasingly prevalent in ageing populations. My research has identified tethering proteins which connect organelles and linked mutations in the tethering proteins to specific diseases. However, we have little knowledge on the cellular consequences of altered membrane contacts and how this links to disease symptoms. We also lack understanding of how tether proteins, which control organelle connections, are regulated. However, if we can understand tether protein regulation, then we may be able to develop therapeutic approaches to restore normal organelle communication in disease contexts. This proposal focuses on addressing this challenge, how membrane contacts are regulated and the cellular consequences when regulation is lost. During the first part of the fellowship, we studied membrane contacts between mitochondria, the ER and peroxisomes in human cells and identified new regulatory systems which control these connections. Specifically, we found an unexpected link between regulation of peroxisome-ER connections and the process of mitosis – when one cell replicates to form two daughter cells. In preliminary work we observed that connections between organelles change when cells divide and disrupting this process causes defects in mitosis, with potential disease-related consequences. In the fellowship extension we plan to use a combination of advanced molecular cell, biochemical and imaging approaches to pursue this novel and unexplored research direction. This work is technically challenging, addressing a highly complex system and requires collaboration across disciplines, but promises a step change in our insight into the process and consequences of MCS regulation. We aim to: Objective 1 - Elucidate the detailed mechanism of regulation of peroxisome-ER MCSs Objective 2 – Assess how post-translational modification of tether proteins leads to peroxisome-ER MCS regulation during mitosis. Objective 3 – Identify how dysregulation of peroxisome-ER MCSs leads to mitotic defects. Realisation of these aims will give comprehensive insight into a topic currently at the forefront of cell biology and inform our understanding of the pathophysiology of disease with potential to identify therapeutic approaches based on restoration of organelle connections. Therefore, this work will impact on different applications and fields, contributing to our understanding of fundamental processes in human cells, disease pathophysiology, and the cellular ageing process. This will influence the cell and developmental biology and biomedical research community as well as patient groups and, via outreach work, the UK public.