Circadian clock regulation of the glycogen synthase ( gsn ) gene by WCC is critical for rhythmic glycogen metabolism in Neurospora crassa

Abstract

Circadian clocks generate rhythms in cellular functions, including metabolism, to align biological processes with the 24-hour environment. Disruption of this alignment by shift work alters glucose homeostasis. Glucose homeostasis depends on signaling and allosteric control; however, the molecular mechanisms linking the clock to glucose homeostasis remain largely unknown. We investigated the molecular links between the clock and glycogen metabolism, a conserved glucose homeostatic process, in Neurospora crassa. We find that glycogen synthase (gsn) mRNA, glycogen phosphorylase (gpn) mRNA, and glycogen levels, accumulate with a daily rhythm controlled by the circadian clock. Because the synthase and phosphorylase are critical to homeostasis, their roles in generating glycogen rhythms were investigated. We demonstrate that while gsn was necessary for glycogen production, constitutive gsn expression resulted in high and arrhythmic glycogen levels, and deletion of gpn abolished gsn mRNA rhythms and rhythmic glycogen accumulation. Furthermore, we show that gsn promoter activity is rhythmic and is directly controlled by core clock component white collar complex (WCC). We also discovered that WCC-regulated transcription factors, VOS-1 and CSP-1, modulate the phase and amplitude of rhythmic gsn mRNA, and these changes are similarly reflected in glycogen oscillations. Together, these data indicate the importance of clock-regulated gsn transcription over signaling or allosteric control of glycogen rhythms, a mechanism that is potentially conserved in mammals and critical to metabolic homeostasis.

Muscle Glycogen Phosphorylase and Its Functional Partners in Health and Disease

“…The metabolism, including glucose homeostasis, is linked to the circadian clock. The glycogen synthase (GS), glycogen phosphorylase, and glycogen level itself undergo regular changes in 24-h manner [ 6 , 7 , 8 ]. Despite that the GS and GP has an opposite functions, namely synthesis and sequestering of glycogen, their mRNA level is rising simultaneously at the morning phase in Neurospora crassa .…”

“…The GP is activated by phosphorylation, whereas phosphorylated GS is inactivated. This may result in the “switch like” system, in which one enzyme is active while the second is inactive [ 8 ]. The crucial role of clock-controlled glucose homeostasis and energy balance among mammals indicates that this mechanism may be evolutionarily conserved [ 6 , 7 , 9 ].…”

The nutrient-sensing GCN2 signaling pathway is essential for circadian clock function by regulating histone acetylation under amino acid starvation

“…Circadian clock has been shown to control metabolic processes and rhythmic transcription of metabolic genes (Baek et al, 2019; Hurley et al, 2014). To determine the role of the GCN2 pathway in controlling gene expression under amino acid starvation, we performed RNA-seq experiments to analyze the genome-wide mRNA levels in the WT and cpc-1 KO strains in the presence of 3-AT (12 mM).…”

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

“…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). For the mammalian clock, it will be critical to define “physiologically relevant” nutrient levels, which could vary by organ or even cell type.…”