Congratulations Allison Steele, PhD

On November 22, 2017 Allison Steele successfully defended her dissertation and earned her doctoral degree.

New Insights into Post-Sepsis Muscle Weakness Elucidated using a Novel Animal Model

Doctoral Committee

Dr. Hiroshi Saito, Department of Physiology
Dr. Francisco H. Andrade, Department of Physiology
Dr. Karin Westlund High, Department of Physiology
Dr. Subbarao Bondada, Department of Microbiology, Immunology & Molecular Genetics
Dr. Samir P. Patel, Department of Physiology
Dr. Marlene E. Starr, Department of Surgery
Dr. Tadahide Izumi, Outside Examiner, Department of Toxicology and Cancer Biology

Abstract

Sepsis is a severe life-threatening critical illness that damages multiple physiological systems.  After hospital discharge, more than 70% of severe sepsis survivors report profound weakness which significantly impacts quality of life.  Such weakness gives rise to new limitations of daily living, which ultimately leads to loss of independence in many patients.  Despite wide recognition of this serious issue by clinicians and researchers alike, the mechanisms contributing to chronic skeletal muscle dysfunction after sepsis are not well understood.  Lack of progress in this field is largely due to the absence of an appropriate animal model; current models are either too mild to induce muscle weakness or too severe and cause death within a few days.  As such, this dissertation work first focused on establishing a clinically-relevant animal model of sepsis which yields surviving mice with chronic skeletal muscle weakness (Aim 1).  This aim involved refining the cecal slurry injection model of polymicrobial sepsis in young adult animals, as well as optimizing the timing, duration, and dose of multiple therapeutic agents.  The resulting resuscitation protocol was adapted for use in late-middle-aged animals, and muscle strength was evaluated using an ex vivo system which confirmed significant muscle weakness in sepsis survivors, long after sepsis was resolved.  Next, using this novel model, we sought to characterize sepsis-induced long-term muscle dysfunction at the molecular level (Aim 2).  The first set of experiments under this aim was designed to identify the primary global mechanism(s) (i.e. atrophy, polyneuropathy, and/or myopathy) responsible for muscle weakness in sepsis survivors. Analysis of the force-frequency curves and specific force measurements led to the conclusion that myopathy is the primary cause.  Electron micrograph observation, functional assays, and protein analysis then showed that sepsis survivors’ skeletal muscles are characterized by profound mitochondrial abnormalities and oxidative damage.  Collectively, these studies show that long-term muscle weakness is apparent in sepsis-surviving animals, and the functional decline is associated with unresolved mitochondrial damage and dysfunction.  This work suggests that medical treatments beyond targeting muscle wasting alone could allow sepsis survivors to regain function and return to productive lives.

Acknowledgments

It is with sincere gratitude that I thank my mentor, Dr. Hiroshi Saito, who has instilled in me a strong sense of scientific curiosity and perseverance while I have been fortunate enough to be his graduate student.  Your mentorship has also translated to my personal growth, for which I am equally thankful.  
Next, I thank committee member Dr. Marlene Starr, who was a post-doctoral fellow in the laboratory when I first joined.  Your daily support has been a key driver in getting me to this point today.  Thank you for being my teacher, my mentor, and for leading by example. 
I am highly appreciative of my co-mentor, Dr. Francisco Andrade; thank you for challenging me to think critically, and for your help in framing my data into a story.  I would like to express my thanks to members of my advisory committee, Drs. Karin High, Subbarao Bondada, Samir Patel, and former member Dr. Karyn Esser.  Your guidance has helped me develop critical thinking, taught me to prioritize, and how to focus my attention; thank you for your dedication and involvement in my training. 
A great thank-you to the Department of Physiology for providing an education and sense of community for which I am extremely fortunate and grateful.  I would like to specifically thank our Director of Graduate Studies, Dr. Ken Campbell, for your dedication to us PGY students collectively and individually.  Additionally, I’d like to thank the Center for Muscle Biology, and its director and co-sponsor of my fellowship, Dr. Charlotte Peterson; thank you for expanding my knowledge of muscle biology and providing resources to learn and perform crucial techniques for this project.  Further, thank you to the Department of Surgery, Markey Cancer Center, and CCTS at the University of Kentucky, and the Harvard Medical School Electron Microscopy Facility, which have all largely contributed to my project.
My educational endeavor, however, would likely be unexplored or unfinished without the support of my family.  I would like to thank my “step” mother, Laurie, for having confidence in my abilities when I did not, and encouraging me to enroll in honors classes in high school, which honestly was the spark of this entire journey.  Thank you to my father, Frank, not only for your daily support but also for learning about my project which has meant the world to me.  Thank you to my mother for always being willing to give me what I needed even though it was often beyond her personal interest. 
A special thank-you to Michael, my better half; you have brought joy and inspiration to my life at a time when I needed it the most.  Your support and patience have been limitless, and I hate to say that even your cheesy jokes never failed to make me smile and keep me going when I was otherwise overwhelmed. 
Thank you to my “twin” Kendra; you have been with me every step of this winding path of graduate school (and life), and I cannot thank you enough.  Thank you, Brittany, for finding ways to support and encourage me, even from a distance.  You have been my friend, sister, but also role model and I am so thankful to have you in my life.  Also, thank you Beverly not only for your help in lab but also always bringing a positive energy.
Finally, I’d like to thank my undergraduate research mentors, Drs. Sarah Mordan-McCombs and Edward Chikwana, for sparking the research bug in me, seeing my potential, and starting me on this journey.  My life has been changed through your confidence and guidance, and I hope that I can ‘pay it forward’ one day.