Translational control underlies nutrition and metabolism in health and disease - PROJECT ABSTRACT / SUMMARY: Fatty acids (FAs) are essential signaling molecules that induce cellular metabolic reprogramming in addition to their conventional roles as energy fuel. Elevated FA during fasting is the primary fuel for the body and an essential substrate to generate an alternative energy source, ketone bodies. However, excessive plasma FA levels in obese or diabetic patients are associated with inflammation, insulin resistance, and cardiovascular diseases. Consequently, understanding the functional role of FAs in cells will uncover novel physiological mechanisms in the health and pathogenesis of metabolic diseases, leading to new therapeutic approaches for disease prevention and treatment. Our compelling preliminary data reveal a novel signaling role for FAs in regulating a specific translation network to induce the synthesis of proteins that are important for ketogenesis upon fasting and inflammation in hyperlipidemia. Fasting can lead to wide-ranging health benefits, including weight loss, improved insulin sensitivity, enhanced brain function, and even offer protection against cancer. Fasting triggers the body to switch its source of energy from glucose to ketone bodies (KBs). KBs are an alternative energy source that is mainly generated in the liver from fatty acids stored as fat. Despite decades of work, how fasting signals elicit changes in gene expression at the level of the proteome to establish metabolic programs that underlie lipid catabolism and production of ketone bodies remain unknown. Our findings remarkably show that while global translation is downregulated during fasting, hepatocytes selectively remodel the translatome to sustain lipid metabolism and ketogenesis. We uncovered a new signaling pathway, induced by FAs directly binding to the AMP-activated protein kinase (AMPK), that upregulates the translation of hundreds of mRNAs, that are under pervasive translational regulation that was missed by conventional transcriptomics analysis. In this pathway, we found the rate limiting enzyme of ketogenesis, Hmgcs2 and the master regulator of lipid metabolism and ketogenesis in the liver, peroxisome proliferator-activated receptor alpha PPARa to be under translational control. We mechanistically uncovered that the phosphorylation of the major cap binding protein, eukaryotic translation initiation factor (P-eIF4E) is induced during fasting and is essential for regulating ketogenesis and ketone body production. Interestingly, our published and unpublished findings have further also demonstrated that P-eIF4E is activated during high fat diet and is critical for lipid accumulation and inflammation upon a high fat diet. Thereby P-eIF4E is a node of convergence downstream of changes to fatty acids both in nutrient deprivation such as fasting as well as nutrient overload. In this grant, we will investigate three outstanding questions: 1) What are the molecular mechanisms that establish a specific tailor-made translation program underlying fasting? 2) What is the signaling pathway responsible for fatty acid-induced activation of eIF4E during fasting, and the molecular mechanism underlying FA induced AMPK activation? 3) We will leverage our expertise in polysome sequencing and genome wide translation control to characterize the metabolic programs that are regulated at the translation level downstream of P-eIF4E during the development of fatty liver (NAFLD) and nonalcoholic steatohepatitis (NASH). The results from these experiments in combination with our ability to pharmacologically target P-eIF4E will provide new therapeutic interventions for metabolic dysfunctions.
