Insulin Directly Regulates the Circadian Clock in Adipose Tissue

Abstract

Adipose tissue (AT) is a key metabolic organ which functions are rhythmically regulated by an endogenous circadian clock. Feeding is a "zeitgeber" aligning the clock in AT with the external time, but mechanisms of this regulation remain largely unclear. We tested the hypothesis that postprandial changes of the hormone insulin directly entrain circadian clocks in AT and investigated a transcriptional-dependent mechanism of this regulation. We analyzed gene expression in subcutaneous AT (SAT) of obese subjects collected before and after the hyperinsulinemic-euglycemic clamp or control saline infusion (SC). The expressions of core clock genes PER2, PER3, and NR1D1 in SAT were differentially changed upon insulin and saline infusion, suggesting insulin-dependent clock regulation. In human stem cell-derived adipocytes, mouse 3T3-L1 cells, and AT explants from mPer2 Luc knockin mice, insulin induced a transient increase of the Per2 mRNA and protein expression, leading to the phase shift of circadian oscillations, with similar effects for Per1. Insulin effects were dependent on the region between 264 and 243 in the Per2 promoter but not on CRE and E-box elements. Our results demonstrate that insulin directly regulates circadian clocks in AT and isolated adipocytes, thus representing a primary mechanism of feeding-induced AT clock entrainment.Adipose tissue (AT) is a key energy storage strongly contributing to the regulation of carbohydrate and lipid metabolism. AT also acts as an endocrine organ, secreting adipokines and cytokines that are able to modulate systemic insulin sensitivity, systemic inflammation, and appetite regulation and therefore plays an essential role in the pathogenesis of metabolic diseases (1). Many metabolic and secretory AT functions are time of day

Nutrient timing and metabolic regulation

“…Even just a short delay in habitual meal timing can alter Per2 phase in adipose tissue, with corresponding phase shifts in systemic metabolites and hormones but without altering the temporal pattern of melatonin or cortisol (robust markers of the central clock) -all consistent with the idea that peripheral rhythms are closely matched to the absolute time of feeding each day (Schoeller et al 1997;Wehrens et al 2017;Gu et al 2020). Indeed, feeding responsive hormones such as insulin, glucagon and insulin-like growth factor 1 appear to be especially potent modulators of clock gene and/or protein expression in multiple tissues -at least in murine models, but emerging evidence is now beginning to demonstrate this in humans (Tahara et al 2010;Mukherji et al 2015;Sun et al 2015;Ikeda et al 2018;Crosby et al 2019;Tuvia et al 2021).…”

Time–restricted eating alters the 24‐hour profile of adipose tissue transcriptome in men with obesity

“…An advance occurs as transcripts positively related to PER1 are reinforced by temporal feeding, whereas genes negatively related to PER1 are reinforced by temporal fasting [ 17 ]. Insulin has recently emerged as a mediator of clocks that induces translation of PER2 and PER1 in human stem cell‐derived adipocytes, mouse 3 T3‐L1 cells, and adipose tissue explants from mPer2Luc knockin mice [ 2 , 3 ]. PER2 and PER3 transcripts were also upregulated, and NR1D2 was downregulated by insulin versus saline in human adipose tissue [ 3 ].…”

“…Rhythmic analysis was not applicable for this data set, as our adipose tissue biopsy specimens were sampled at only four time points [ 3 ]. Therefore, time‐series samples were treated independently, and a natural cubic spline regression model (NCSRM) [ 26 ] with three degrees of freedom for an experimental two‐way design with one treatment factor and time as a continuous variable was fitted to the edgeR normalized count data to identify the transcripts that followed the different 24‐hour profiles after TRE versus baseline using the R package splineTimeR [ 27 ].…”

“…Nutrient‐signaling molecules are strong regulators of clock genes in peripheral tissues. Feeding results in the activation of the insulin‐phosphorylated protein kinase B(pAKT)‐mammalian target of rapamycin (mTOR) pathway, which increases the stability and translation of PER [ 2 , 3 ], whereas fasting activates AMP‐activated protein kinase (AMPK) and nicotinamide phosphoribosyltransferase (NAMPT), reducing the stability and transcription of CRY and PER [ 4 , 5 ]. Therefore, meal timing is an entraining cue for peripheral clocks, and mistimed eating with shortened overnight fasting periods dampens peripheral clocks in mice [ 6 , 7 ].…”

Intermittent feeding and circadian rhythm in critical illness

“…At the molecular level, the circadian clock is based on the transcriptional/translational feedback loop of proteins such as Cryptochrome (CRY), Period (PER), Brain and muscle Arnt-like protein (BMAL), and Circadian Locomotor Output Cycles Kaput (CLOCK) that take $24 h to complete. However, nutrient signalling molecules directly regulate clock genes; activation of insulin-mTOR pathways increases the stability and translation of PER proteins [18,19,20 && ], whereas fasting activates AMP-activated protein kinase (AMPK) and nicotinamide phosphoribosyltransferase (NAMPT) pathways reducing the stability and transcription of CRY and PER [21][22][23]. In this way, changes in insulin and cAMP due to mistimed meals will influence hundreds of downstream 'clock-controlled' genes in peripheral tissues responsible for metabolic processes, including gastrointestinal function, glycaemic control, and muscle metabolism.…”