Organism-wide secretome mapping of tissue crosstalk in exercise

Exercise has long been known as an effective strategy to prevent and combat human diseases. Conversely, physical inactivity is considered to be an essential contributor to a variety of chronic diseases. Because of this, tremendous efforts have been dedicated to understanding the molecular mechanisms by which exercise conveys such profound health benefits. Identifying these molecular mechanisms will facilitate the development of exercise mimetics that serve as potential therapeutics to improve human health. It has been proposed that tissue crosstalk via soluble factors in the blood during exercise mediates the broad health benefits of exercise. Indeed, blood plasma from exercised animals and humans has been shown to contain exercise-inducible molecules that are sufficient to recapitulate some health benefits of exercise. However, the comprehensive identifications of such molecules and their origins in exercise have been poorly studied due to a lack of tools. In this dissertation, I use Mus musculus as the model system to study the fundamental principles of tissue crosstalk in physical activity. The rich genetic toolbox and diverse exercise training regimens of mice make these animals an ideal model for mapping exercise-inducible blood-borne factors and exploring the potential functions of these molecules. The recent advances in proximity labeling in the mammalian system provide a unique opportunity for biochemical labeling of secreted polypeptides in living mice and downstream proteomic identification via mass spectrometry. Collectively, the application of this conditionally expressed proximity labeling strategy in well-established mouse models enables the global identifications of blood-born polypeptides at a cell type, protein, and peptide resolution. This dissertation consists of two main parts: technology development and biological discoveries made with this technology. First, I describe the development and benchmarking of the proximity labeling-based secretome (secreted polypeptides collectively) profiling methodology in living cells in vitro and in mice (Chapter 2). This is, to the best of my knowledge, the first methodology for labeling and tracking secreted polypeptides from a specific cell type in mice. Additionally, the high temporal resolution of this approach enables the capture of dynamic secretome changes in pathophysiologically perturbed animals. Next, using this secretome profiling tool, I report the identifications of exercise-inducible cell type-protein pairs in mice after a 1-week treadmill running exercise (Chapter 3). We uncover fundamental secretome regulation principles in exercise in a cell type, protein, and peptide-specific manner. Furthermore, we identify the unexpected lactate-inducible release of CES2 proteins from the liver that have anti-obesity and anti-diabetic effects. Lastly, I discuss the remaining questions in exercise secretome, future development of the secretome profiling technology, and applications of this methodology to study other intriguing questions in mammalian physiology (Chapter 4)

Keywords: Biology.
Advisor: Long Jonathan Z.
Dixon Scott James
Jacobs-Wagner Christine
Wyss-Coray Anton