Investigation of the function of the ER/mitochondria contact sites in cell physiology and disease

Mitochondria are highly dynamic organelles essential for the survival of the cell. Mitochondrial dynamics has been linked to different physiological functions, and contacts with other organelles are required for specific metabolic activity and mitochondrial behaviour. Indeed, endoplasmic reticulum and mitochondria work together and their closed juxtaposition is considered as a signalling platform for metabolite flux. Alteration of these contacts has been associated with defects in cellular homeostasis and with human disease. The goal of our group is to characterise the architecture and understand the associated functions of these inter-organelle contacts. Using biochemical, molecular and cell biological approaches, we want to investigate the function of the mitochondria/endoplasmic reticulum contact sites in different cell physiology processes including cell death, lipid and calcium fluxes and cell migration. This work will lead us to obtaining new insights into the importance of mitochondria and mitochondria/ER contacts in cellular signalling pathways, and to better understanding the pathomechanisms underpinning human diseases associated with defects in their regulation and dynamics.

Mitochondria are complex organelles that provide essentially all of the energy, mainly through ATP synthesis, required for normal physiological function in nearly all cells of the body. They also play a central role in a number of cell signaling pathways, including cell death and regulation of the intracellular calcium homeostasis. Mitochondria are highly dynamic organelles that can adapt their network in response to specific cellular needs. Indeed, they are able to constantly fuse and divide, and these events are intimately related to their metabolic functions and cellular stress signals. Impairment of mitochondrial physiology is linked to human diseases including neurodegenerative and metabolic disorders such as Parkinson’s disease and diabetes, and also in the progression of certain forms of cancer. It has become clear recently that mitochondria do not function in isolation, but establish direct contact and communication with other cellular organelles to exchange metabolites and signals converging on, or streaming from, mitochondria. For instance, mitochondria are physically coupled to the endoplasmic reticulum through contact sites that act as a signaling platform. These are called mitochondria-associated membranes (MAM), and are essential for a number of processes, including intracellular calcium homeostasis, lipid exchange, mitochondrial dynamics and motility, ROS production and apoptosis. Studies performed in the last decade have identified several proteins which directly tether the two organelles in MAMs and proteins enriched in these contact sites that play highly specialised homeostatic or execution roles. However, the biogenesis, regulation and precise molecular mechanisms associated with these signaling platforms are still poorly understood. The goal of our lab is to understand the physiological importance of these inter-organelle contacts in specific cellular contexts, including metabolite flux during steady state, and in response to specific triggers, particularly during cell death or cell migration. Using molecular biological and biochemical approaches we will focus on the characterisation of proteins localised at the interface of the mito/ER contacts sites, their potential role in the stability of the MAM structures, and their functions in lipid and calcium fluxes during the execution of the cell death programme. We will couple these techniques with the state-of-the-art advanced microscopic analysis, including spinning disc and scanning confocal systems, super-resolution microscopy, and electron microscopy. To unravel the function of mito/ER contacts sites on cell physiology, live cell imaging will be performed to study organelle movements during cell migration. The precise localisation of target proteins will be studied by the emergent super-resolution microscopy techniques. Finally, we are also interested in understanding the relevance of mitochondrial dynamics and MAMs in the context of mitochondrial disease. We will study the mitochondrial biology, in different cellular models derived from patients, to characterize how mitochondrial morphology and inter-organelle contacts are affected by different gene mutations, and how this contributes to disease progression.