Fight against death: the role of autophagy in mitochondrial turnover in haematopoietic cells in vivo

Lead Research Organisation: University of Oxford
Department Name: Clinical Medicine

Abstract

In this project we will investigate the role of a cellular process called autophagy in the development and maintenance of the immune system. Most of the large structures of the cell such as the energy-producing mitochondria are continuously being engulfed and degraded by a process known as autophagy (self-eating). Insufficient autophagy may allow damaged structures and molecules to build up within the cell, and contribute to neurodegeneration and ageing. Autophagy is also used by the cell to adapt to new circumstances: if we fast or starve, our cells chew up much of their contents by autophagy to mobilize resources for the rest of the body. We have shown that failure to undergo autophagy in red blood cells causes cell death and as consequence anaemia in the whole animal. Similarly we have preliminary data showing that absence of autophagy in immune cells (leukocytes) causes cell death resulting in very low numbers of leukocytes. We are proposing to investigate why autophagy is needed for the survival of leukocytes and elucidate how cells die in the absence of autophagy. To carry oxygen to every part of the body within tiny capillaries, red blood cells (erythrocytes) need to reduce their size. They do this towards the end of their development by losing most of their proteins and organelles including nucleus and mitochondria. A consequence of this process is the loss of their major source of energy, which condemns them to die within a short period of time. However, over the course of their short lifespan (approximately 120 days in man and 30 days in mice). They have accumulated haemoglobin and can continuously transport large amounts of oxygen. Whereas it was known for some time that the nucleus is expelled, it is unclear how red blood cells lose their organelles. Early electron micrographs from the 1960s show that erythrocytes contain mitochondria within double-membraned vesicles called autophagosomes. We have generated mice in which blood cells (both red and white cells) are knocked out for autophagy. These mice die of anaemia as their red blood cells die early due to the accumulation of damaged mitochondria which cannot be eliminated though autophagy. Even though leukocytes do not have such a strict developmental requirement to remove their mitochondria, we hypothesize that general mitochondrial turnover is regulated through autophagy in leukocytes. On top of being the energy factory of the cell, mitochondria play a central role in pronouncing the death sentence of the cell. This is probably no coincidence since the mitochondria are the main target for many noxious stimuli, such as toxins, free radicals, excessive calcium and lack of oxygen. The mitochondria are damaged by these fatal stimuli. Damaged mitochondria initiate the process of cell death. In fact we observe cell death in all different types of leukocytes obtained from autophagy deficient mice analysed so far. We will now investigate whether cell death is caused by damaged mitochondria in leukocytes, and whether other organelles are accumulating such as ribosomes, ER and Golgi. Excessive levels of autophagy can lead to cell death, however our results indicate it plays a role as a cell survival mechanism. We will therefore elucidate in molecular detail how leukocytes die in the absence of autophagy. Very little is known about the role autophagy in leukocytes, in particular in vivo. The results of this study will add important information to the understanding of mitochondrial turnover and will benefit the scientific community interested in these fundamental cellular processes. It will give an insight into the senescence of cells and the link between cell death and autophagy. Extending our findings on red blood cells to leukocytes will help to generalize the observed phenomenon and make it more likely to establish it as a universal process in all cells.

Technical Summary

Autophagy is a catabolic process whereby cells sequester long-lived proteins and damaged organelles for their degradation. Recently the main molecular players in autophagy have been identified, including members of the Atg gene family, providing new tools to trace, quantify and manipulate autophagy. Mammalian red blood cells are enucleated and devoid of organelles. While it has been known for some time that the nucleus is expelled, the molecular mechanism responsible for the removal of organelles remained unclear. Our lab has recently demonstrated that mitochondrial autophagy (mitophagy) mediated by Atg7 is essential in the removal of mitochondria from developing erythroid cells. We show that the absence of autophagy in erythrocytes in vivo decreases their lifespan and causes cell death in vivo. Damaged mitochondria accumulate in Atg7-/- erythroid cells and mice lacking the autophagy gene Atg7 in the haematopoietic system (Haem-Atg7-/-) die of anaemia. It is known that most other cell types also undergo mitophagy to remove damaged mitochondria and failure to do can be pathogenic. Interestingly, we found that HaemAtg7-/- mice are severely leukopenic with only 20% of normal T cell levels, severely reduced B cell numbers, arrested macrophage and dendritic cell development. Indeed, in all leukocytes investigated so far, we found that the absence of autophagy leads to spontaneous cell death. Our hypothesis is therefore that autophagy is the major degradative pathway in mitochondrial turnover in leukocytes and that in its absence leukocytes accumulate damaged mitochondria and possibly other organelles, leading to leukocyte death. We are proposing to investigate organelle turnover in autophagy deficient leukocytes in vivo. We will address a major controversy in the field whether autophagy is an alternative form of cell death or necessary for survival. Moreover we will elucidate the apoptotic pathways of programmed cell death in the absence of autophagy.

Publications

10 25 50
 
Description Autophagy, a cellular major degradation pathway, is essential in the maintenance of hematopoietic stem cells, the formation of the memory T cell pool and to delay immune system senescence
Exploitation Route to improve regenerative medicine, to treat haematological malignancies, to improve vaccination in the elderly
Sectors Healthcare,Pharmaceuticals and Medical Biotechnology

URL http://www.ndm.ox.ac.uk/principal-investigators/researcher/anna-katharina-katja-simon
 
Description Mostly within the scientific community - drug development is still ongoing
First Year Of Impact 2011
Sector Healthcare,Pharmaceuticals and Medical Biotechnology
 
Description Member of Deutsche Forschungsgemeinschaft committee for SFB
Geographic Reach National 
Policy Influence Type Participation in advisory committee
 
Description Andrew McMichael Fund - Postdoctoral Fellowship (Monika Mortensen)
Amount £103,000 (GBP)
Organisation University of Oxford 
Department Weatherall Institute of Molecular Medicine (WIMM)
Sector Academic/University
Country United Kingdom
Start 01/2010 
End 01/2012
 
Description Kidney Research UK - Mechanism of interstital nephritis, fibrosis and renal faliure due to Uromodulin mutations
Amount £235,920 (GBP)
Funding ID RP52/2012 
Organisation Kidney Research UK 
Sector Charity/Non Profit
Country United Kingdom
Start 01/2012 
End 01/2015
 
Description Lady Tata Consumables funding
Amount £30,000 (GBP)
Organisation Lady Tata Memorial Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 01/2012 
End 12/2014
 
Description Project Grant - Developing induced pluripotent stem cells as a model to investigate tissue specific mitochondrial disease
Amount £251,826 (GBP)
Organisation Medical Research Council (MRC) 
Sector Public
Country United Kingdom
Start 01/2012 
End 01/2015
 
Description Wellcome Trust New investigator Award
Amount £962,500 (GBP)
Organisation Wellcome Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 08/2014 
End 08/2019
 
Description Wellcome Trust Project Grant - Developing treatments for mitochondrial DNA diseases
Amount £251,826 (GBP)
Funding ID 0948685/Z/10/Z 
Organisation Wellcome Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 05/2011 
End 04/2014
 
Description Wellcome Trust Project Grant - Role of autophagy in anaemia and MDS
Amount £185,485 (GBP)
Funding ID 088098 
Organisation Wellcome Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 01/2010 
End 01/2013
 
Description NIH: Improving T Cell Response to Hepatitis C Virus via Modulation of Autophagy 
Organisation National Institutes of Health (NIH)
Department Center for Human Immunology, Autoimmunity and Inflammation
Country United States 
Sector Public 
PI Contribution We are doing the experiments, providing the tools and ideas.
Collaborator Contribution The consortium contributes technological platforms, discussion and samples.
Impact Not yet.
Start Year 2015
 
Description NIHR salary: improving human T cell responses via autophagy 
Organisation Oxford University Hospitals NHS Foundation Trust
Department NIHR Oxford Biomedical Research Centre
Country United Kingdom 
Sector Academic/University 
PI Contribution We are providing the tools, knowledge and data
Collaborator Contribution Provision of salary for junior research fellow, human samples and expertise
Impact none yet
Start Year 2017
 
Title Polyamines compounds and uses thereof 
Description Using Spermidine to boost the immune system in the elderly, to improve the efficacy of vaccinations 
IP Reference MPS/EOR/P129835GB01 
Protection Patent application published
Year Protection Granted 2014
Licensed No
Impact none as yet
 
Description Lab experience for Baccalaureat class 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact A European school arranged to have an annual visit to my lab for their first year baccalaureate students, giving them supervised hands on experience of working in a lab

Further enquiries about how to get in to a career in science
Year(s) Of Engagement Activity 2007,2008,2009,2010,2011,2012
 
Description Lecture - West Oxford Academy 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Talk given to the general about my research, which was followed by a question and answer session.

Enquiries from some of the younger members of the audience in how to get into research
Year(s) Of Engagement Activity 2008,2011
 
Description Press release for elife paper: Interview with BBC Radio Oxford 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Radio interview given.

further enquiries from the media about the paper and my research
Year(s) Of Engagement Activity 2014