Hexosamine biosynthetic pathway and O-GlcNAc-processing enzymes regulate daily rhythms in protein O-GlcNAcylation

Abstract

The integration of circadian and metabolic signals is essential for maintaining robust circadian rhythms and ensuring efficient metabolism and energy use. Using Drosophila as an animal model, we show that cellular protein O-GlcNAcylation exhibits robust 24-hour rhythm and represents a key post-translational mechanism that regulates circadian physiology. We observe strong correlation between protein O-GlcNAcylation rhythms and clock-controlled feeding-fasting cycles, suggesting that O-GlcNAcylation rhythms are primarily driven by nutrient input. Interestingly, daily O-GlcNAcylation rhythms are severely dampened when we subject flies to time-restricted feeding at unnatural feeding time. This suggests the presence of clock-regulated buffering mechanisms that prevent excessive O-GlcNAcylation at non-optimal times of the day-night cycle. We show that this buffering mechanism is mediated by the expression and activity of GFAT, OGT, and OGA, which are regulated through integration of circadian and metabolic signals. Finally, we generate a mathematical model to describe the key factors that regulate daily O-GlcNAcylation rhythm.

A nexus of lipid and O-Glcnac metabolism in physiology and disease

“…Nevertheless, ectopic overexpression of either protein is sufficient to rescue loss of the other ( 47 ), suggesting that the nutrient access and/or responsivity of gfat1 and gfat2 expressing cells may be meaningfully distinct. Indeed, a recent study in WT flies confirms that of the two genes, only gfat2 expression is correlated with circadian eating patterns ( 64 ). By contrast, gfat1 may be more sensitive to lipid-induced stress, which is consistent with its proposed role in mediating the depressive effects of hyperlipidemia on neural O -GlcNAcylation.…”

“…However, it also potentiating OGT activity through tyrosine phosphorylation ( 323 ) and directs its translocation to cell membranes, particularly lipid rafts ( 92 ) that play a significant role in protein complex assembly and signal transduction [for review ( 324 )]. In a detailed characterization of feeding-related O -GlcNAc regulatory patterns in the fly body, Liu et al demonstrate how both eating and circadian rhythmicity drive transient elevations in pre-prandial Ogt and fasting Oga ( 64 ). These cycles guide global O -GlcNAcylation levels to rise and fall in tandem with eating ( 64 ), evidencing the important role of this modification in the ingestion and post-prandial response to food.…”

“…In a detailed characterization of feeding-related O -GlcNAc regulatory patterns in the fly body, Liu et al demonstrate how both eating and circadian rhythmicity drive transient elevations in pre-prandial Ogt and fasting Oga ( 64 ). These cycles guide global O -GlcNAcylation levels to rise and fall in tandem with eating ( 64 ), evidencing the important role of this modification in the ingestion and post-prandial response to food.…”

Characterization of Gfat1 (zeppelin) and Gfat2, Essential Paralogous Genes Which Encode the Enzymes That Catalyze the Rate-Limiting Step in the Hexosamine Biosynthetic Pathway in Drosophila melanogaster

“…In contrast with Gfat1, the expression of Gfat2 is also moderately high in adult males and females. Interestingly, a very recent study of links between nutrient availability, protein O-GlcNAcylation, and diurnal rhythm in adult flies also found much higher levels of Gfat2 mRNA versus very low levels of Gfat1 mRNA [46]. Indeed, based on these and other data, these authors contend that Gfat2 is the primary functional paralogue in adults.…”

A role for gene expression and mRNA stability in nutritional compensation of the circadian clock

“…Thus, deleterious SNPs in Nutritional Compensation-relevant genes could exacerbate disease outcomes when cellular clocks encounter nutrients outside of the physiological range. In addition to Nutritional Compensation, there is a large body of quality literature describing the set of metabolites and metabolic enzymes that can directly feed back and affect circadian function, including adenosine monophosphate (AMP) and AMP kinase, nicotinamide adenine dinucleotide (NAD+) and SIRT1 activity, acetylglucosamine (O-GlcNAc) (Liu et al, 2021), and mTOR activity (Ramanathan et al, 2018) (reviewed in: Bass and Takahashi, 2010; Sancar and Brunner, 2014; Asher and Sassone-Corsi, 2015; Dibner and Schibler, 2015). In Neurospora , extensive metabolic rhythms are also present (Hurley et al, 2018; Baek et al, 2019), and rhythmic metabolic reaction fluxes likely function similarly to the mammalian clock (Krishnaiah et al, 2017; Thurley et al, 2017; Collins et al, 2021).…”