Inefficient physiological transitions are known to cause metabolic disorders. Therefore, investigating mechanisms that constitute molecular switches in a central metabolic organ like the liver becomes crucial. Specifically, upstream mechanisms that control temporal engagement of transcription factors, which are essential to mediate physiological fed–fast–refed transitions are less understood. SIRT1, a NAD+-dependent deacetylase, is pivotal in regulating hepatic gene expression and has emerged as a key therapeutic target. Despite this, if/how nutrient inputs regulate SIRT1 interactions, stability, and therefore downstream functions are still unknown. Here, we establish nutrient-dependent O-GlcNAcylation of SIRT1, within its N-terminal domain, as a crucial determinant of hepatic functions. Our findings demonstrate that during a fasted-to-refed transition, glycosylation of SIRT1 modulates its interactions with various transcription factors and a nodal cytosolic kinase involved in insulin signaling. Moreover, sustained glycosylation in the fed state causes nuclear exclusion and cytosolic ubiquitin-mediated degradation of SIRT1. This mechanism exerts spatiotemporal control over SIRT1 functions by constituting a previously unknown molecular relay. Of note, loss of SIRT1 glycosylation discomposed these interactions resulting in aberrant gene expression, mitochondrial dysfunctions, and enhanced hepatic gluconeogenesis. Expression of nonglycosylatable SIRT1 in the liver abrogated metabolic flexibility, resulting in systemic insulin resistance, hyperglycemia, and hepatic inflammation, highlighting the physiological costs associated with its overactivation. Conversely, our study also reveals that hyperglycosylation of SIRT1 is associated with aging and high-fat–induced obesity. Thus, we establish that nutrient-dependent glycosylation of SIRT1 is essential to gate its functions and maintain physiological fitness.

Inefficient fasted-to-refed transitions are known to cause metabolic diseases. Thus, identifying mechanisms that may constitute molecular switches during such physiological transitions become crucial. Specifically, whether nutrients program a relay of interactions in master regulators, such as SIRT1, and affect their stability is underexplored. Here, we elucidate nutrientdependent O-GlcNAcylation of SIRT1, within its N-terminal domain, as a key determinant of hepatic glucose-and fat-metabolism, and insulin signaling. SIRT1 glycosylation dictates interactions with PPARα/FOXO1/PGC1α/SREBP1, to exert a temporal control over transcription of genes during fasted-to-refed transitions. Interestingly, glycosylation-dependent cytosolic export of SIRT1 promotes a transient interaction with AKT and subsequent proteasomal degradation. Loss of glycosylation discomposes these interactions and enhances stability of SIRT1 even upon refeeding, which causes insulin resistance, hyperglycemia and hepatic-inflammation. Aberrant glycosylation of SIRT1 is associated with aging and/or metabolic diseases. Thus, nutrient-dependent glycosylation constrains spatio-temporal dynamics of SIRT1 and gates its functions to maintain metabolic homeostasis.