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A mitochondrial ROS signal activates mitochondrial turnover and represses TOR during stress Ashwin Sriram Thesis submitted to the Newcastle University in candidature for the degree of Doctor of Philosophy Newcastle University Faculty of Medical Sciences Institute of Cellular and Molecular Biosciences 1 DECLARATION I certify that this thesis is my own work and I have correctly acknowledged the work of collaborators. I also declare that this thesis has not been previously submitted for a degree or any other qualification at this or any other university. Ashwin Sriram July 2016 2 3 ACKNOWLEDGEMENTS This research work was carried out at the Institute for Cell and Molecular Biosciences and the Institute for Ageing, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, United Kingdom under the supervision of Dr. Alberto Sanz. I owe my deepest of gratitude to my supervisor Dr. Alberto Sanz for giving me an opportunity to carry out this research project in his lab under his esteemed guidance. I am deeply indebted to him especially for the confidence that he always placed in me, his encouragement and support throughout the work. He has contributed a lot to my development as a scientist. A special thanks for all the conversations regarding how science “works”. I would also like to thank him for teaching me most of the techniques that have been implemented in this thesis. I am very grateful to Dr. Filippo Scialo for all his support and help with many experiments that are a part of this thesis. I thank him for all the long discussions in the office and during coffee breaks. It was an absolute pleasure working with him. I would also like to thank the Sanz lab members; Dr. Rhoda Stefanatos, Charlotte Graham and Elise Bennett for the lab environment they provided, especially during scientific discussions, the parties and dinners and the everyday coffee breaks. I am immensely grateful to Dr. Gabriele Saretzki and Dr. Elizabeth Veal from the Newcastle University for kindly reviewing my progress and for the number of constructive comments. I am also very thankful to Dr. Eric Dufour and Prof. Seppo Parkkila from the University of Tampere, Finland for my first year progress review and their advice and guidance. I would like to thank Essi Kiviranta for her laboratory and technical support during this work. I would also like to thank Prof. Reinald Pamplona and Prof. Reinald Pamplona’s lab members for the collaborative work involving analysis of oxidative damage markers by mass spectrometry. 4 5 It is my great pleasure to express my sincere and heartfelt thanks to my wife, Nalini, for the encouragement, support and love that she showed me. A special mention for her patience and understanding while I have been completing my thesis. To all my friends, I am very thankful for just being who they are. I am eternally grateful to my parents Chitra and Sriram and my brother Dhiraj at this time for their endless love and always believing in me. Last but not the least, to those who have indirectly contributed to this research, your kindness means a lot to me. Thank you, one and all. Ashwin Sriram 6 7 ABSTRACT Ageing and age-related diseases are multidimensional processes characterised by the accumulation of damaged mitochondria and a reduced capacity to respond to stress. While mitochondria play a central role in cellular signalling and stress adaptation, how damaged mitochondria accumulate and whether this affects healthy lifespan and onset of age-related diseases is unclear. In the following chapters, I demonstrate how mitochondrial turnover is involved in the process of stress adaptation, mediated by mitochondrial reactive oxygen species (mtROS), using the power of Drosophila genetics. I focus on the role of mitochondria, specifically on how Reactive oxygen species (ROS) are involved in the process of temperature adaptation. Additionally, I establish that ROS acts as a signalling molecule in communicating with different downstream processes. Combining different approaches to measure ROS, I have dissected the nature of this signal. I show that an increase in mtROS associated with thermal stress is produced as a consequence of over-reduction of the electron transport chain and identify the molecular intermediate as H2O2. Moreover, I study in detail the downstream targets and demonstrate that the levels of mtROS regulate levels of Pink1. Furthermore, I provide evidence that mitochondrial H2O2 (mtH2O2) act as a mitochondrial signal to activate mitophagy, and to repress Target of rapamycin (TOR). When this signal is supressed, mitochondrial respiration is markedly diminished, canonical Pink1-Parkin mediated mitophagy is obstructed and TOR signalling is hyper-activated. This in turn causes the accumulation of damaged proteins and organelles and a drastic reduction in fly lifespan. I show that restoring mitophagy in a low mtH2O2 background restores mitochondrial respiration, TOR signalling and rescues lifespan. In the following chapters, I describe in detail a novel mitochondrial H2O2-Pink1/Parkin-TOR signalling axis that regulates cellular quality control and how it can be modulated by pharmacological and genetic interventions. My results also reveal the existence of a novel ROS signalling pathway that regulates mitochondrial density, which in turn determines the activation of TOR signalling and lifespan. i In summary, I show that (1) mtH2O2 is instrumental for the process of canonical Pink1-Parkin mediated mitophagy; (2) mtH2O2 production can be precisely regulated in vivo; (3) Mitochondrial turnover determines the activation of TOR signalling; and (4) Mitochondrial turnover is important in maintaining homeostasis of an organism. KEYWORDS: Mitochondria, Drosophila, ROS, ageing. ii AWARDS AND PUBLICATIONS Awards Newcastle University Travel Award for the Molecular Basis of Ageing and Disease conference, Suzhou, China. 2015. Travel award for Coimbra Healthy Ageing Symposium, Coimbra, Portugal. 2015. Travel award for 6th Annual Alliance for Healthy Ageing Conference, Newcastle upon Tyne, United Kingdom. 2015. Won the best oral presentation award in the Postgraduate meeting in Newcastle University, Newcastle upon Tyne, United Kingdom. 2015. Won the best poster award in Institute for Cell and Molecular Biosciences away day, Newcastle University, Newcastle upon Tyne, United Kingdom. 2015. Peer-reviewed Publications 1. Scialo, F., Sriram, A (co-first author)., Fernandez-Ayala, D., Gubina, N., Lõhmus, M., Nelson, G., Logan, A., Cooper, H.M., Navas, P., Enriquez, J.M., Murphy, M.P. and Sanz, A. Mitochondrial ROS produced via reverse electron transport extends animal lifespan. Cell Metabolism. 2016 Apr 12; 23(4):725-34. 2. Stefanatos, R., Sriram, A (co-first author)., Kiviranta, E., Mohan, A., Ayala, V., Jacobs, HT., Pamplona, R. and Sanz, A. DJ-1β Regulates Oxidative Stress, Insulin- Like Signalling, and Development in Drosophila melanogaster. Cell Cycle. 2012 Oct 15; 11(20):3876-86. 3. Scialo, F., Sriram, A (co-first author), Naudí, A., Ayala,V., Jové, M., Pamplona, R. and Sanz, A. Target of rapamycin activation predicts lifespan in fruit flies. Cell Cycle. 2015 Sep 17; 14(18):2949-58. 4. Kemppainen, K., Rinne, J., Sriram, A., Lakanmaa, M., Zeb, A., Tuomela, T., Popplestone, A., Singh, S., Sanz, A., Rustin, P. and Jacobs, HT. Expression of the Ciona intestinalis alternative oxidase in Drosophila ameliorates diverse phenotypes due to cytochrome oxidase deficiency. Human Molecular Genetics. 2014 Apr 15; 23(8):2078-93. iii 5. Mallikarjun, V., Sriram, A., Scialo, F. and Sanz, A. The interplay between mitochondrial protein and iron homeostasis and the role this plays in ageing. Experimental Gerontology. 2014 Aug; 56:123-34. 6. Syrjänen, L., Valannea, S., Kuuslahtia, M., Tuomelaa, T., Sriram, A., Sanz, A., Jacobs, HT., Rämet, M. and Parkkilaa, S. β carbonic anhydrase is required for female fertility in Drosophila melanogaster. Frontiers in Zoology. 2015 Aug 22; 12:19. iv ABBREVIATIONS LIST ADP Adenosine Diphosphate ANOVA Analysis of Variance ATP Adenosine Triphosphate BNE Blue Native Electrophoresis BSA Bovine Serum Albumin C.elegans Caenoharbditis elegans CAFE Capillary Feeding cDNA Complementary Deoxyribonucleic Acid CO2 Carbon-di-Oxide CR Caloric Restriction CYT C Cytochrome c DAH Dahomey DEPC Diethylpirocarbonate DNA Deoxyribonucleic Acid dNTP Deoxynucleotide Triphosphate EDTA Ethyldiaminetetraacetic Acid EGTA Ethyl Glycol Tetraacetic Acid ETC Electron Transport Chain FAD Flavin Adenine Dinucleotide FADH2 Reduced Flavin Adenine Dinucleotide FeS Ferrous-Sulphate cluster FMN Flavin Mononucleotide FMNH2 Reduced Flavin Mononucleotide G3P Glycerol-3-Phosphate GAPDH Glyceraldehyde 3-phosphate dehydrogenase H2O2 Hydrogen Peroxide HCl Hydrogen Chloride .OH Hydroxyl Radical HRP Horseradish Peroxidase KCl Potassium Cyanide KDa Kilo Dalton units KH2PO4 Monopotassium phosphate Mb Mega base v MDa Mega Dalton units MELAS Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes MFRTA Mitochondrial Free Radical Theory of Ageing MgCl2 Magnesium Chloride MLSP Maximum Lifespan mtDNA Mitochondrial Deoxyribonucleic Acid mtROS Mitochondrial Reactive Oxygen Species NAD+ Nicotinamide Adenine dinucleotide NADH Reduced Nicotinamide adenine dinucleotide NDi1 NADH dehydrogenase internal 1 nDNA Nuclear Deoxyribonucleic Acid OXPHOS Oxidative Phosphorylation PAGE Polyacrylamide Gel Electrophoresis PBS Phosphate Buffer Saline PBS-T Phosphate Buffer Saline-Tween PCD Programmed Cell Death PD Parkinson’s Disease PDHα Pyruvate Dehydrogenase PVDF Polyvinylidene