Recent studies estimate ~40% of the U.S. population is obese, constituting ~$200 billion in annual medical costs. Obesity is a major risk factor for cardiovascular disease, type 2 diabetes mellitus (T2DM), and non-alcoholic fatty liver disease (NAFLD), all of which have dysregulated glucose and lipid homeostasis. Liver Receptor Homolog-1 (LRH-1) is a nuclear hormone receptor that regulates diverse cellular processes including hepatic glucose, cholesterol, and bile acid homeostasis. Despite identification of LRH-1 as a validated drug target for the treatment of T2DM and NAFLD, previous drug development efforts have been unsuccessful. Further, recent studies have shown ~30% of LRH- 1 is modified through SUMOylation of its dynamic hinge region. Ablation of this SUMOylation in a knock-in mouse model showed this modification was necessary for proper cholesterol and lipid homeostasis as the transgenic mice developed worse NAFLD compared to their wildtype littermates. Although the physiological relevance of LRH-1 SUMOylation has been well validated, how SUMOylation affects LRH-1 structure remains unknown.
In Aim 1, we propose to determine the effects of SUMOylation on the LRH-1 ligand-binding domain through structural and functional assays. Structural effects will be determined through using NMR to determine which amino acids are altered due to this modification, while functional effects will be determined through coactivator recruitment binding assays and gene expression assays.
In Aim 2, we propose to determine how SUMOylation affects the multi-domain architecture of LRH-1 using a combination of small angle X-ray scattering and electron paramagnetic resonance distance measurements to develop computational models of unmodified and SUMOylated LRH-1. These models will be validated genetically through a combination of in vitro and in vivo functional assays. Together, these aims seek to determine how SUMOylation of an unstructured hinge region affect the structure and function of LRH-1. This study will address a clear gap in literature and may provide crucial structural information necessary to effectively drug LRH-1 for the treatment of T2MD and NAFLD.
Diabetes and nonalcoholic fatty liver disease (NAFLD) are rapidly growing metabolic disorders in the United States and the developed world. LRH-1 is a validated drug target for the treatment of these obesity related diseases, yet no drug design efforts have been successful. This proposed research study will provide structural details of how LRH-1 is inactivated through a reversible-modification, details of which may be crucial for successful design of an LRH-1 targeted therapy for diabetes and NAFLD.
