Project Summary Sepsis is a leading cause of death in critical care units. The long-term goal of my research is to understand the mechanisms of sepsis-induced multi-organ failure and to identify potential new therapeutic opportunities for this devastating clinical condition. Studies proposed in this application are designed to elucidate novel pathological functions of a mitochondrial metabolism regulatory kinase, pyruvate dehydrogenase kinase 4 (PDK4), in sepsis-induced cardiomyopathy using preclinical models. Previous studies showed that energy deficiency due to metabolic inflexibility is tightly associated with adverse outcomes in sepsis. Ongoing investigation in my lab obtained exciting preliminary evidence suggesting that overstimulation of PDK4 is a key causative factor for myocardial metabolic inflexibility in sepsis, and the underlying mechanism may involve causing impairments at mitochondria-associated membranes (MAMs), a previously unknown signal of PDK4. We also found that cardiac specific ablation of PDK4 is cardiac protective, suggesting that PDK4 is a promising therapeutic target for sepsis. This exploratory project is to test the hypothesis that, during sepsis, PDK4 triggers metabolic inflexibility via pathological injuries at MAMs, leading to an insufficient, maladaptive autophagy and overwhelming inflammation in the heart. Using both gain-of- function and loss-of-function approaches in vitro and in vivo, we will examine whether PDK4 induces functional deficiency and structural damage in MAMs, which in turn produce dysfunctional mitochondria and initiate metabolic inflexibility in septic hearts (aim 1). Further, we will address the roles of PDK4 in cardiac autophagy and inflammation in sepsis by interrogating its regulation in the inhibition of autophagy, production of cytokines, activation of inflammatory factors, and infiltration of immune cells in myocardium (aim 2). Together, this investigation is expected not only to advance the fundamental understanding of sepsis pathology but also to evaluate whether blockage of PDK4 improves cardiac outcomes in sepsis, laying a scientific foundation for future development of novel therapies.