PROJECT SUMMARY Robust daily biological rhythms over the 24-hour (h) day-night cycles are key hallmarks of animal healthspan and are strongly regulated by circadian clocks. Circadian clocks are cell-autonomous, endogenous molecular timers present in the brain and peripheral organs that enable animals to adapt to daily changes in their environment. Clock-controlled outputs are all-encompassing and clock disruption is associated with a wide range of pathologies and chronic diseases. While the brain clock is synchronized to external environment via photic cues from light-dark cycles, peripheral clocks in major organs are entrained and synchronized by metabolic signals mediated primarily via food intake that are regulated by the brain clock. This coupled brain and peripheral clock system promotes internal synchrony, maintaining balance between metabolism and energy use. Given the importance of metabolic signals in regulating body clocks, it is critical to understand mechanisms underlying metabolic regulation of daily biological rhythms. The overall goal of this project is to investigate post-translational mechanisms that mediate metabolic regulation of time-of-day protein functions to orchestrate daily rhythms. Efforts to understand the underpinnings of circadian clocks and their control over daily rhythms have long focused on regulation at the transcriptional level. However, recent studies have demonstrably confirmed the importance of post-translational modifications (PTMs) in shaping robust daily rhythms, often bypassing regulation at the gene expression level. We recently established that metabolic signals from feeding-fasting cycles drive robust daily rhythms of global O-GlcNAcylation in Drosophila and in mouse peripheral tissues. O-GlcNAcylation is a nutrient-sensitive PTM that interacts extensively with phosphorylation to regulate protein structure and function as both PTMs modify serine and threonine residues. We will test the hypothesis that rhythmic O-GlcNAcylation and phosphorylation work in conjunction to regulate daily rhythms of protein activities. We further test the hypothesis that altering timing of metabolic input by mistimed feeding will remodel the O-GlcNAcome, phosphoproteome, and their interactions, resulting in potential disruption of peripheral clock functions. To date, there have only been a handful of studies investigating rhythmic O-GlcNAcylation and the consequences of its disruption. This project is designed to address this significant knowledge gap. In Aim 1, we will identify proteins that are rhythmically modified by O-GlcNAcylation and phosphorylation in key mammalian organs and investigate whether and to what extent rhythmic PTM profiles are sensitive to timing of metabolic input. In Aim 2, we will incorporate proteomics data generated from this project into O-GlcNAc Atlas, a searchable database with a web interface constructed by our collaborator Dr. Junfeng Ma, to enable user-friendly data discovery. This R21 project...