This proposal is an extension of an evolving program investigating the importance of pantothenate kinase (PanK) regulation of coenzyme A (CoA) biosynthesis to the control of intermediary metabolism. The accomplished aims of the last grant period defined the regulatory properties and tissue-specific distribution of the PanK isoforms, generated a knockout mouse model that was used to reveal the critical importance of increasing CoA levels in fasting metabolism, employed a chemical biology approach to identify small molecule PanK inhibitors, and identified acyl-carnitine as a PanK activator. These results have refined our overall idea that altering the intracellular CoA concentration is essential for reprogramming metabolism. In the past, intracellular CoA has been considered to be in excess of what is needed to fully support CoA-dependent biochemistry, with acetyl-CoA exerting feedback control over PanK activity to buffer the cellular CoA content. This view is not correct. Our results show that the CoA supply is dynamically regulated and the failure to modulate CoA content directly impacts fuel utilization by the metabolic network. This unappreciated aspect of regulation is central to understanding the nutritional reprogramming of intermediary metabolism. The experiments in Aim #1 will determine the role of adjusting CoA levels in the transition of muscle from fed to fasting metabolism. The results from this part of the study will be of central importance to understanding the dependence of energy generation in muscle on CoA content. In humans, there is an association between low serum insulin levels and polymorphisms in the PANK1 gene. Prominent phenotypes of our Pank1/ knockout mouse are lower serum glucose, triglycerides and insulin levels. In Aim #2, we will use our Pank1/ mouse model to define the underlying metabolic basis for reduced insulin levels and to determine if muscle is the primary site for increased glucose tolerance in these animals. CoA and its thioesters are concentration- dependent substrates and allosteric regulators of key control points in intermediary metabolism, suggesting that the pharmacological manipulation of CoA levels via PanK inhibition could reprogram metabolism. This idea was validated by our experiments with a PanK inhibitor that lowers hepatic CoA and serum glucose in mice. In Aim #3, we will use this inhibitor to reduce total CoA content to pharmacologically reprogram hepatic metabolism to suppress gluconeogenesis in diet-induced obesity, and determine if the elevation of hepatic CoA is sufficient to increase glucose production. This original approach to reprogramming intermediary metabolism will define the role of CoA in hepatic gluconeogenesis and provide insight into the factors that give rise to human disorders of lipid and glucose homeostasis.