Poon - Apoptotic cell disassembly and clearance

In humans, billions of cells will die daily as part of normal turnover in various organs. It is vital that dying cells are rapidly removed as their accumulation has been linked to inflammation, autoimmunity, cancer and infection. To aid efficient removal of dead cells, dying cells often disassemble into smaller fragments for neighboring cells to engulf. Furthermore, certain cellular components can be packaged selectively into these fragments to regulate tissue repair and immunity.

We aim to understand the machinery that control how dying cells can disassemble into smaller pieces, the importance of cell disassembly in disease settings (e.g. influenza A infection and atherosclerosis), and identify new drugs to control this process.

Research areas

Molecular mechanism of apoptotic cell disassembly

Apoptosis (programmed cell death) occurs in essentially all tissues as part of development, homeostasis, and pathogenic processes including infection and cardiovascular disorders. Apoptotic cells often disassemble into smaller membrane-bound extracellular vesicles called apoptotic bodies.

Recently, we demonstrated that the formation of apoptotic bodies is a highly regulated process in T lymphocytes and monocytes. In particular, we discovered a new type of membrane protrusion (coined "apoptopodia") that facilitates the separation of membrane blebs during apoptosis to generate individual apoptotic bodies. However, the molecular machinery that controls the formation of apoptopodia is undefined. In this project, we aim to determine the molecular machineries that are required for the formation of apoptopodia.

Function of apoptotic bodies in pathophysiological settings

Extracellular vesicles including apoptotic bodies have been implicated to regulate physiological and pathological processes via the molecules they carry inside or exposed on their surface. However, the importance of generating apoptotic bodies during apoptosis in pathophysiological settings is poorly understood.

In this project, the role of apoptotic cell disassembly will be examined in the context of influenza A infection in collaboration with Prof Weisan Chen (La Trobe University). During viral infection, infected cells often undergo apoptosis to shutdown cellular machinery as a defence mechanism to limit viral replication. However, phagocytic removal of infected apoptotic cells/fragments may also facilitate the spread of infection, whereby the phagocyte could become infected following the engulfment of apoptotic cells/fragments containing viral particles. Although viral proteins have been suggested to accumulate in apoptotic bodies during apoptosis, the role of apoptotic cell disassembly in the context of viral infection is underexplored. To address this fundamental problem, the importance of apoptotic body formation in influenza A infection will be investigated.

Discovery of novel pharmacological compounds to modulate the apoptotic cell disassembly process

Although apoptotic body formation is a key cellular process for efficient removal of apoptotic debris and intercellular communication in certain disease settings, there is currently a lack of pharmacological compounds available to target this process. Identifying drugs that could modulate apoptotic cell disassembly is likely to provide new research directions that are clinically relevant.

Using a novel flow cytometry-based drug screen approach, we have recently identified a number of drugs that can inhibit or enhance the formation of apoptotic bodies without having an impact on the level of apoptosis. Importantly, some of these drugs are FDA approved and currently being used clinically.

In this project, we aim to characterise these novel inhibitors and enhancers of apoptotic cell disassembly in detail, in particular how these compounds could modulate the morphological steps of apoptotic body formation as well as the activities of known molecular regulators of apoptotic cell disassembly (e.g. ROCK1 kinase and pannexin 1 channel). Furthermore, whether these drugs can be used to control the apoptotic cell disassembly process in disease settings will also be examined.

Development of new methodologies to monitor the progression of cell death and disassembly of dying cells by flow cytometry

The use of annexin V and 7-aminoactinomycin D/propidium iodide stains to quantify cell death by flow cytometry has been considered the gold standard by most laboratories. However, this widely used method often makes the assumption that there are only three types of particles in a sample, that is viable, apoptotic and necrotic (membrane permeabilized) cells.

In order to study the progression of cell death in greater detail, in particular how apoptotic cells undergo fragmentation to generate apoptotic bodies, we aim to establish new flow cytometry-based methods to accurately measure the cell death process.

Meet the team

Group members

Group LeaderPoon lab

Dr Ivan Poon

Research Fellows

Dr Amy Baxter (NHMRC Peter Doherty Biomedical Fellow)
Dr Kha Phan
Dr Georgia Atkin-Smith
Dr Rochelle Tixeira

Research Officer

Gemma Ryan

PhD students

Sarah Caruso
Amy Hodge
Bo Shi
Lanzhou Jiang
Jascinta Santavanond

Honours student

Dilara Ozkocak

Patents

Novel forms of plant defensins: WO 2013/056308

Treatment of proliferative diseases: AU 2011/269726

Treatment of proliferative diseases: WO 2011/160174  A1

Publications

See a full list of publications on Google Scholar [external link] or view Dr Ivan Poon's profile.