Downloaded from Sequence Read Archive
Total Page：16
File Type：pdf, Size：1020Kb
UCSF UC San Francisco Electronic Theses and Dissertations Title BCL6 maintains thermogenic capacity of brown adipose tissue during dormancy Permalink https://escholarship.org/uc/item/6d28473c Author Kutyavin, Vassily Igor Publication Date 2019 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California BCL6 maintains thermogenic capacity of brown adipose tissue during dormancy by Vassily Kutyavin DISSERTATION Submitted in partial satisfaction of the requirements for degree of DOCTOR OF PHILOSOPHY in Biomedical Sciences in the GRADUATE DIVISION of the UNIVERSITY OF CALIFORNIA, SAN FRANCISCO Approved: ______________________________________________________________________________Eric Verdin Chair ______________________________________________________________________________Ajay Chawla ______________________________________________________________________________Ethan Weiss ______________________________________________________________________________ ______________________________________________________________________________ Committee Members Copyright 2019 by Vassily Kutyavin ii Dedicated to everyone who has supported me during my scientific education iii Acknowledgements I'm very grateful to my thesis adviser, Ajay Chawla, for his mentorship and support during my dissertation work over the past five years. Throughout my time in his lab, I was always able to rely on his guidance, and his enthusiasm for science was a great source of motivation. Even when he was traveling, he could easily be reached for advice by phone or e- mail. I am particularly grateful for his help with writing the manuscript, which was probably the most challenging aspect of graduate school for me. I am also very grateful to him for helping me find a postdoctoral fellowship position. Ajay's inquisitive and fearless approach to science have been a great inspiration to me. In contrast to the majority of scientists who focus narrowly on a specific topic, Ajay pursued fundamental questions across a broad range of topics and was able to make tremendous contributions. My experience in his lab instilled in me a deep appreciation for thinking about the entire organism from an evolutionary perspective and focusing on the key questions that escape the attention of the larger scientific community. As I move forward in my scientific career, there is no doubt that I will rely on him as a role model. I am very grateful to the other members of Ajay's lab who supported me during my thesis work. I am especially grateful to José Barreto Campello Carvalheira who worked directly with me during my first few months in the lab and helped to make the transition a smooth one. I am also grateful to Yifu Qiu, Min Woo Lee, and Yoshitaka Sogawa for teaching me many of the experimental approaches that proved to be very useful during my thesis work. I am also grateful to Xiaojin Cui for taking care of the lab, ordering all of the reagents that I needed, and helping to assemble the mouse lines that I used during my thesis work. I am grateful to fellow graduate students Yixuan Wu and Nyasha Chagwedera for their camaraderie and support. iv I also would like to thank my thesis committee members, Eric Verdin and Ethan Weiss, for their excellent advice and support. In particular I appreciate Eric's willingness to continue his role on the committee even when he relocated to the Buck Institute halfway through my thesis and consequently had to drive a long distance to attend the committee meetings. I also want to thank De'Broski Herbert, Emin Maltepe, Jayanta Debnath, and Jeffrey Cox for serving on my qualifying exam committee. In addition, I am grateful to Art Weiss and Jason Cyster for granting me the opportunity to work in their labs as a rotation student. They were fantastic mentors and role models during my first year of graduate school. I would also like to thank Judy Shigenega, the manager of the Molecular Core Facility at San Francisco VA Medical Center who provided invaluable assistance with next generation sequencing. In addition, I would like to thank Reena Zalpuri from the UC Berkeley Electron Microscope Lab for her assistance with electron microscopy. Finally, I would like to thank my family for their great support during the past five years. Contributions to the presented work Chapter 2 is adapted from a manuscript (in preparation) with the following citation: Kutyavin, V., Chawla, A. (2019). BCL6 regulates thermogenic capacity and survival of brown adipocytes during dormancy. Proc Natl Acad Sci U S A. Manuscript in preparation. Vassily Kutyavin designed, performed, and analyzed all experiments. Vassily Kutyavin and Ajay Chawla wrote and edited the manuscript. Ajay Chawla supervised the study. Vassily Kutyavin’s contributions to the work in Chapter 2 were equivalent in scope to the corresponding section of a standard doctoral thesis. v BCL6 maintains thermogenic capacity of brown adipose tissue during dormancy by Vassily Kutyavin Abstract During exposure to environmental cold, brown adipocytes protect against hypothermia by generating heat (thermogenesis). In warm environments, brown adipocytes become inactive or dormant, but still maintain their identity and thermogenic capacity, allowing rapid reactivation of thermogenesis upon subsequent cold exposure. Our understanding of the dormant state and its regulation is very limited. Here, we show that the transcription factor B cell leukemia/lymphoma 6 (BCL6) is specifically required for maintenance of thermogenic capacity during dormancy in mouse brown adipocytes. By a combination of both direct and indirect transcriptional mechanisms, BCL6 promotes uncoupled respiration, fatty acid oxidation, and survival in dormant brown adipocytes. In part, BCL6 achieves this by remodeling the epigenome of brown adipocytes to enforce brown and oppose white adipocyte cellular identity. Thus, unlike other transcription factors that regulate cold-induced thermogenesis, BCL6 is specifically required for maintenance of thermogenic fitness during adaptation to environmental warmth. vi TABLE OF CONTENTS Chapter 1: Introduction ............................................................................................................... 1 The importance of temperature for living organisms .................................................................. 2 Diverse strategies of thermoregulation in the animal kingdom .................................................. 2 Ectotherms ............................................................................................................................... 3 Endotherms .............................................................................................................................. 4 The thermoregulatory circuit in mammals .................................................................................. 6 Physiological mechanisms that increase body temperature in response to cold ..................... 6 Behavioral mechanisms that increase body temperature in response to cold .......................... 8 Physiological mechanisms that decrease body temperature in response to heat ..................... 8 Behavioral mechanisms that decrease body temperature in response to heat ......................... 9 Roles of adipocytes in energy homeostasis and thermoregulation ........................................... 10 UCP1-dependent thermogenesis in brown and beige adipocytes .......................................... 10 Alternative, UCP1-independent pathways of thermogenesis in brown and beige adipocytes ............................................................................................................................................... 13 Short- and long-term adaptation of brown and beige adipocytes to environmental temperature ............................................................................................................................ 13 The role of thermogenic adipocytes in diet-induced thermogenesis ..................................... 15 Brown adipose tissue in humans ............................................................................................... 16 Transcriptional regulation of brown adipocyte thermogenesis ................................................. 17 vii Transcriptional mechanisms governing brown adipocyte differentiation ............................. 18 Transcriptional mechanisms controlling acute activation of thermogenesis in response to cold ........................................................................................................................................ 19 Thyroid hormone receptors ................................................................................................... 20 Estrogen-related receptors ..................................................................................................... 21 B cell leukemia/lymphoma 6 (BCL6) ...................................................................................... 21 Molecular mechanisms of transcriptional regulation by BCL6 ............................................. 22 Transcriptional regulation of Bcl6 ......................................................................................... 23 Post-translational regulation of BCL6 ................................................................................... 23 Functions of BCL6 in germinal center B cells ...................................................................... 24 BCL6 as an oncogene ...........................................................................................................