Role of the BHB shunt in energy balance

About This Grant

Abstract. Beta-hydroxybutyrate (BHB) is an abundant metabolite and a major ketone body whose levels rise in response to low carbohydrate availability. Despite decades of research, only two biochemical pathways – ketogenesis and ketone oxidation – were thought to fully encompass the metabolism of BHB. We have recently identified a previously unknown third metabolic pathway for BHB: the “BHB shunt” (Moya-Garzon, Cell 2025). This third pathway involves enzymatic derivatization of BHB to generate a family of orphan ketone metabolites, the BHB-amino acids. We have used gain- and loss-of-function studies establish a critical role of the BHB shunt in ketosis-associated weight loss. The discovery of this BHB shunt is therefore exciting and important because it upends our textbook understanding of BHB biochemistry and uncovers an underappreciated role for anorexigenic ketone metabolites in ketosis-associated weight loss. Because of these fundamentally new insights, here in this proposal we focus entirely on additional biochemical and physiologic studies of this BHB shunt. We will test the central hypothesis that the BHB shunt constitutes a third branch of BHB metabolism linked to energy balance. In Aim 1, we will determine the cell type-specific contribution of the BHB shunt to the generation of ketone metabolites and to energy balance. This goal is enabled by the generation of a unique collection of conditional knockout mice in which the BHB shunt is specifically ablated in liver, macrophages, or the gut. In Aim 2, we turn to the molecular mechanism by which the downstream BHB-amino acid products regulate feeding and energy balance. We have identified a body weight-associated ion channel that can be directly liganded by the most abundant BHB-amino acid, BHB-Phe. We will determine how BHB-Phe modulates the activity of this ion channel, and whether related BHB-amino acids also exhibit similar effects or not. Using knockout mice, we will critically determine the requirement of this ion channel as a downstream mediator of ketone metabolites on energy balance. Lastly in Aim 3, we turn to additional downstream metabolites from the BHB shunt. In preliminary studies, we have now used in vitro biochemistry to determine an oxidative pathway of BHB-amino acid metabolism. We will test the role of known oxidoreductases in catalyzing this transformation. We will determine the endogenous levels and dynamics of the downstream AcAc-amino acid products. Successful completion of this proposal will provide a detailed and molecular understanding of biochemistry and physiology of a newly discovered ketone metabolic pathway, thereby establishing a scientific foundation for developing new therapeutics that target ketosis for obesity and associated metabolic diseases.