Understanding how regulation of membrane contacts coordinates lipid channelling at the peroxisome-ER metabolic hub

Conceptually, the human cell can be divided into numerous separate compartments (organelles) which form part of wider networks or production lines. Each organelle has its own specific role but also interacts and coordinates with other organelles. Metabolites such as lipids can be partially processed in one organelle before being passed onto another for further processing. Cells also have to produce new, complex lipids which are used in cell membranes throughout the body and play important roles in controlling how particular membranes function. Two organelles which are critical to produce and process lipids are the endoplasmic reticulum (ER) and the peroxisome. The ER is the key lipid-producing organelle in the cell whilst peroxisomes are associated with processing of particular lipids and detoxification of toxic by-products but also play a crucial role, in collaboration with the ER, in producing lipids (called plasmalogens and polyunsaturated fatty acids). Those are critically important in the membranes of nerve cells, where the balance of membrane lipids is important in regulating neuronal firing, the transfer of signals from one nerve cell to another. Defects in these processes, caused by abnormal peroxisomes, or by the inability of the ER and peroxisomes to work together to produce the required lipids, results in severe disorders with developmental and neurological defects. We recently discovered the protein components which mediate peroxisome-ER interaction in human cells. A protein on the membrane of peroxisomes, ACBD5, binds to a protein on the ER membrane, VAPB, and this binding event brings the two organelles into close proximity, allowing exchange of lipids between the two. Removal of ACBD5 or VAPB reduces the interaction between the ER and peroxisomes, preventing correct lipid exchange and causing cellular lipid balance to be disrupted. We also recently identified patients with mutations in the ACBD5 gene who have a severe, progressive neurological disorder.
We now seek to build on our previous work to further understand how peroxisome-ER interactions are regulated and how they influence lipid metabolism. We will use mammalian cells to answer questions such as how is ACBD5 and VAPB binding achieved, under what conditions is binding switched on and off and what are the systems which control how and when this happens? Understanding this will allow us to look for strategies which will enable us to modulate these interactions, potentially leading to future therapeutic approaches to restore organelle cooperation and lipid balance in pathological conditions, where organelle contacts are disrupted.
This is an extremely exciting area of biology which promises to not only deliver fundamental insights into how individual organelle interaction events in cells happen but also how failure of organelles to communicate is linked to disease, including age-related disorders.

Peroxisomes (PO) are multifunctional organelles with an important role in the metabolism of cellular lipids and are essential for human health and development. Peroxisomal lipid metabolism requires cooperation with the endoplasmic reticulum (ER), which is mediated via membrane contacts. How PO-ER contacts form and function is still poorly understood, but disruption of organelle contacts has been implicated in altered lipid metabolism and neurodegeneration. In a recent study we identified the first proteins, peroxisomal ACBD4/5 and ER-resident VAPA/B, mediating PO-ER interactions but how contacts are regulated and function in lipid metabolism is unknown. This new project will uncover mechanisms that regulate membrane contact site formation, inter-organelle cooperation and lipid metabolism between PO and the ER. We aim to elucidate how regulation of PO-ER contacts is mediated at the mechanistic, structural and physiological level, establishing the ACBD-VAP contact site as a lipid exchange hub to coordinate lipid flux.
We have uncovered a role for phosphorylation and will (1) assess how it regulates PO-ER interaction, and identify and characterise regulatory factors using a combination of phospho-proteomics, mutational studies in mammalian cells, a BioID screen to identify potential kinases/phosphatases and in vitro phosphorylation assays. We will (2) determine the structural basis for modulation of ACBD-VAP interaction by combining peptide affinity measurements with structural analyses. Furthermore, we will (3) investigate the role of the PO-ER hub in lipid metabolism, and identify mechanisms to modulate ACBD5 expression and PO-ER interplay to improve fatty acid metabolism.
This inter-disciplinary project applies molecular cell biology, biochemical/metabolic, proteomic, and structural approaches, as well as cutting edge imaging techniques to improve our understanding of organelle cooperation and its impact on healthy ageing and common, degenerative disorders.

The research outcomes of this study will have ongoing national and international i) academic, ii) medical, iii) political, iv) economic and v) social impacts by building knowledge about the link between organelle contact formation, their metabolic interplay, (dys)regulation (I-iv) and their impact on lipid homeostasis, metabolic and age-related disorders (i, ii, iv, v). The research will create new cellular models and tools for investigating organelle interplay. Disruption of organelle contacts has been linked to disease. Understanding how organelle interactions are controlled promises to help the identification of novel targets for drug development (of benefit to the UK, EU pharmaceutical & health sectors) and therapeutic approaches to restore organelle cooperation in pathological conditions (public health sector).
Engagement, communication and dissemination of our research and its outcomes with beneficiaries will take place through (i) high-impact publications in international journals (ii) presentations at inter/national conferences (iii) the organisation of sessions linked to forthcoming science conferences, e.g. SSIEM meetings attracting > 2500 internat. delegates (incl. academics, clinicians, charities, business partners) with strong interest in the diagnosis and treatment of metabolic disorders. We plan to host a workshop (impact activity) to disseminate our research findings to key beneficiaries. It will target research groups interested in organelle-related disorders, metabolism and ageing, research funders, charities and others engaged with health promotion. It will also inform the development of more applied follow-on studies that will inform and develop future interventions and policies. We will also (iv) participate in events of the local Neuroscience Network, GW4 consortium, SW Peninsula Ageing Networks and include established networks (EU Marie Curie ITN PERICO) to promote our research and to discuss medical implications. In addition, we will exploit established national and international links (MPI for Biology of Ageing, GER; University Hospitals Leuven, BE; UoE Medical School) to cooperate, discuss, and disseminate any findings with potential clinical implications. During interactions with specific audiences 'Key Findings' leaflets (Impact activity) and online publications will be produced and disseminated to facilitate lasting impact and awareness of the research. To provide impact from the outset in the form of initial publicity and beyond the lifespan of the project, we will continue with the development of (v) a professional "Organelle Biology & Disease website" (impact activity) with general and specialist information including research progress, methods, teaching resources and information for patients and caretakers. We are in discussion with leading research teams to build a larger online organelle knowledge base providing useful national and international links for academics, clinicians and non-specialists. (vi) Tools and proteomics/structural data will be made available on public webpages (e.g. PRIDE, PBD) and the project website. As part of raising project awareness with society we plan to (vii) - visit local schools and offer work placement experiences; - edit a "special research topic" and submit articles to popular science magazines (e.g. Frontiers), - engage with the interested wider public (e.g. Exeter's Science Café), - provide up to date news stories on research findings through the University press office and organisations (Scientia, SciTech), - integrate the research in teaching approaches such as hot topic courses and modules on cell biology of disease. We will work closely with the Communications Offices of our Universities to explore all resources that exist (e.g. newsletters, press releases, websites) to translate our most significant and relevant results to the public.