Obesity affects 30% of people worldwide and is the leading cause for Type 2 Diabetes. In recent years, a paradigm shift has occurred: Instead of being considered a lifestyle problem, obesity is seen as disease of the brain, determined by an interplay of genetic and environmental factors. Homeostatic networks of the central nervous system (CNS) controlling metabolism have moved into the focus of research. The adipokine leptin is one of the key hormones activating CNS signaling pathways to reduce food intake and increase energy expenditure. In obesity, people are resistant to leptin action. To develop effective and safe pharmacological weight loss agents, better understanding of the molecular events underlying leptin signaling and leptin resistance are indispensable.
The application of proteomic workflows in neuroscience has been limited so far by the tremendous cellular heterogeneity of the CNS and the resulting scarcity of neuronal subpopulations across brain regions thereby limiting available material input. However, in recent years, groundbreaking technological advances have now opened the field to investigate neuronal signaling by proteomics. We aim to interrogate cellular mechanisms of body weight control in the CNS by proteomics. Our data will have the potential to provide prospective targets for future analyses in humans and will inspire novel therapeutic strategies built upon leptin re-sensitization.
Identification of Regulators of Leptin Signaling via Proteomics
This project will combine cutting-edge phosphoproteomic workflows optimized for minute sample amounts with organelle proteomics to dissect phosphorylation events underlying leptin signaling in a spatial-temporal resolved manner and test for perturbations of leptin signaling in obesity. To gain a comprehensive picture of leptin induced cellular processes, we will then use systematic interaction proteomics and recently developed proximity-labeling strategies to investigate leptin induced protein interaction networks. By combining phosphoproteomics, organelle proteomics and interaction proteomics, this project will yield considerable new insights into which proteins are phosphorylated by leptin signaling and how this affects protein interactions and localizations.
The second part of this project will focus on the feedback-regulation of leptin signaling by phosphorylation. We have recently discovered that phosphorylation of the Leptinreceptor at specific sites leads to the termination of the signaling. We now aim to investigate the role of these phosphorylations in in vivo mouse models and to identify the kinases that regulate the leptin receptor activity by a kinase inhibitor screen.
Krahmer N, Najafi B, Schueder F, Quagliarini F, Steger M, Seitz S, Kasper R, Salinas F, Cox J, Uhlenhaut NH, Walther TC, Jungmann R, Zeigerer A, Borner GHH, Mann M. Organellar Proteomics and Phospho-Proteomics Reveal Subcellular Reorganization in Diet-Induced Hepatic Steatosis. Dev Cell. 2018;47(2):205-221 e207.
Sacco F, Seelig A, Humphrey SJ, Krahmer N, Volta F, Reggio A, Marchetti P, Gerdes J, Mann M. Phosphoproteomics Reveals the GSK3-PDX1 Axis as a Key Pathogenic Signaling Node in Diabetic Islets. Cell Metab. 2019;29(6):1422-1432 e1423.