Active Extracellular Vesicles - defining a novel, extracellular metabolic compartment and its role in the control of inflammation.

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Inflammation is a normal defence mechanism used by the immune system to help protect from infection and to repair damage caused by trauma. However, the benefits of inflammation are only realised when the response is turned off and the infected or traumatised tissue is returned to normal. This process is known as 'resolution' and relies on immune cells (that have done their protective job) being removed. To allow their removal, these unwanted cells die and, as they do so, they release small membrane bags (called extracellular vesicles: EV). We have shown that these EV are key to attracting 'undertaker' cells ('macrophages') that remove the dying cells by eating them and, crucially, they produce additional signals that drive the tissue to repair.Relatively little is known of how these EV function. We have identified a molecule that promotes recruitment of macrophages but the manner in which these EV promote 'repair' responses in macrophages remains unknown. Now, our preliminary work has shown that these EV carry a family of active enzymes which will help to produce small lipid molecules that may control inflammation and repair responses. The work proposed here will define the action of these active enzymes that are delivered from dying cells to macrophages in EV. As such, these 'active' EV represent a novel extracellular metabolically-active compartment capable of transmitting inflammation-controlling signals to surrounding cells such as macrophages.Why is this important? A failure to control inflammatory responses can lead to chronic inflammation and many of the inflammatory diseases associated with ageing. So, by understanding the mechanisms of communication between cells promoting inflammation, and those cells promoting resolution and repair, we will have a clearer insight to possible therapeutic approaches for diseases that are driven by inflammation (e.g. cardiovascular disease, cancer, neurodegeneration). Furthermore, we will study EV from a range of other cells that are known to help promote repair. For example, a type of stem cell, an 'MSC', has held great promise for regenerative medicine but recently the EV released from these cells have been proposed to be active to stimulate a 'repair environment'. Consequently, we will study in detail the inflammation-controlling metabolic activity of EV from MSC. This raises the possibility that we may be able to define the crucial factors required for EV repair activity, opening up novel stem cell-based or cell-free therapies for regenerative medicine. In order to test our core hypothesis, we will analyse, from a range of dying and viable cells, EV composition for the presence of enzymes, their substrates and their products. We will test the EVs' ability to promote repair in vitro and in vivo and we will inhibit the key enzymes to assess the essential nature of this activity. Furthermore, we will seek to 'tune' or refine cell culture conditions to maximise EV production and function.This work will, for the first time, detail an inflammation-controlling, metabolically-active extracellular compartment. It will define, at a molecular level, how dying cells communicate with other cells to ensure inflammation is controlled. This is important because ineffective control of inflammation leads to disease. Thus, exploitation of our work will target those conditions where inflammation helps drive disease and will enable novel strategies to promote self-repair.