Circadian clock disruption attenuated growth hormone(GH)-mediated signalling

Augmented Cardiac Growth Hormone Signaling Contributes to Cardiomyopathy Following Genetic Disruption of the Cardiomyocyte Circadian Clock

Circadian clocks regulate numerous biological processes, at whole body, organ, and cellular levels. This includes both hormone secretion and target tissue sensitivity. Although growth hormone (GH) secretion is time-of-day-dependent (increased pulse amplitude during the sleep period), little is known regarding whether circadian clocks modulate GH sensitivity in target tissues. GH acts in part through induction of insulin-like growth factor 1 (IGF1), and excess GH/IGF1 signaling has been linked to pathologies such as insulin resistance, acromegaly, and cardiomyopathy. Interestingly, genetic disruption of the cardiomyocyte circadian clock leads to cardiac adverse remodeling, contractile dysfunction, and reduced lifespan. These observations led to the hypothesis that the cardiomyopathy observed following cardiomyocyte circadian clock disruption may be secondary to chronic activation of cardiac GH/IGF1 signaling. Here, we report that cardiomyocyte-specific BMAL1 knockout (CBK) mice exhibit increased cardiac GH sensitivity, as evidenced by augmented GH-induced STAT5 phosphorylation (relative to littermate controls) in the heart (but not in the liver). Moreover, Igf1 mRNA levels are approximately 2-fold higher in CBK hearts (but not in livers), associated with markers of GH/IGF1 signaling activation (e.g., p-ERK, p-mTOR, and p-4EBP1) and adverse remodeling (e.g., cardiomyocyte hypertrophy and interstitial fibrosis). Genetic deletion of one allele of the GH receptor (GHR) normalized cardiac Igf1 levels in CBK hearts, associated with a partial normalization of adverse remodeling. This included attenuated progression of cardiomyopathy in CBK mice. Collectively, these observations suggest that excessive cardiac GH/IGF1 signaling contributes toward cardiomyopathy following genetic disruption of the cardiomyocyte circadian clock.

Protective Effects of Melatonin against Obesity-Induced by Leptin Resistance

Consumption of an exceedingly high-fat diet with irregular eating and sleeping habits is typical in the current sedentary lifestyle, leading to chronic diseases like obesity and diabetes mellitus. Leptin is a primary appetite-regulating hormone that binds to its receptors in the hypothalamic cell membrane and regulates downstream appetite-regulating neurons NPY/AgRp and POMC in the hypothalamus. Based on the fat content of the adipose tissue, leptin is secreted, and excess accumulation of fat in adipose tissue stimulates the abnormal secretion of leptin. The secreted leptin circulating in the bloodstream uses its transporters to cross the blood-brain barrier (BBB) and reach the CSF. There is a saturation limit for leptin bound to its transporters to cross the BBB, and increased leptin secretion in adipose tissue has a defect in its transport across the BBB. Leptin resistance is due to excess leptin, a saturation of its transporters, and deficiency in either the receptor level or signalling in the hypothalamus. Leptin resistance leads to obesity due to excess food intake and less energy expenditure. Normal leptin secretion follows a rhythm, and alteration in the lifestyle leads to hormonal imbalances and increases ROS generation leading to oxidative stress. The sleep disturbance causes obesity with increased lipid accumulation in adipose tissue. Melatonin is the master regulator of the sleep-wake cycle secreted by the pineal gland during the night. It is a potent antioxidant with anti-inflammatory properties. Melatonin is secreted in a pattern called the circadian rhythm in humans as well. Research indicates that melatonin plays a vital role in hormonal regulation and energy metabolism, including leptin signalling and secretion. Studying the role of melatonin in leptin regulation will help us combat the pathologies of obesity caused by leptin resistance.

The nuclear-localized GHR is involved in the cell proliferation of gastric cancer, and pegvisomant may be an important potential drug to inhibit the proliferation of gastric cancer cells

Under normal physiological conditions, growth hormones (GH) play an important role in body growth and metabolism. A recent study showed that GH has important biological effects on gastric cancer (GC) both in vitro and in vivo. However, the biological properties of GH/GHR (GHR, growth hormone receptor) in GC cells have not been fully elucidated. To this end, we systemically studied the biological properties of GH in GC cells and found that GH/GHR was transported into the nuclei of GC cells. Furthermore, we investigated the functions of nuclear GHR and its potential mechanisms of action. We found that nuclear-localized GHR was closely related to the proliferation of GC cells. In addition, we systematically studied the effect of a GHR inhibitor (pegvisomant) on GC in vivo and in vitro, and the results showed that pegvisomant can not only inhibit the proliferation of GC cells but also inhibit the nuclear localization of GHR, suggesting that pegvisomant may be a dual-effect antagonist. Current research indicates that GHR may be a potential target for the treatment of GC.

Time-Restricted Feeding Restored Insulin-Growth Hormone Balance and Improved Substrate and Energy Metabolism in MC4RKO Obese Mice

BACKGROUND

Dysregulation of metabolic regulatory hormones often occurs during the progress of obesity. Key regulatory hormone insulin-growth hormone (GH) balance has recently been proposed to maintain metabolism profiles. Time-restricted feeding (TRF) is an effective strategy against obesity without detailed research on pulsatile GH releasing patterns.

METHODS

TRF was performed in an over-eating melanocortin 4 receptor-knockout (MC4RKO) obese mouse model using normal food. Body weight and food intake were measured. Series of blood samples were collected for 6-h pulsatile GH profile, glucose tolerance test, and insulin tolerance test at 5, 8, and 9 weeks of TRF, respectively. Indirect calorimetric recordings were performed by the Phenomaster system at 6 weeks for 1 week, and body composition was measured by nuclear magnetic resonance spectroscopy (NMR). Substrate- and energy metabolism-related gene expressions were measured in terminal liver and subcutaneous white adipose tissues.

RESULTS

TRF increased pulsatile GH secretion in dark phase and suppressed hyperinsulinemia in MC4RKO obese mice to reach a reduced insulin/GH ratio. This was accompanied by the improvement in insulin sensitivity, metabolic flexibility, glucose tolerance, and decreased glucose fluctuation, together with appropriate modification of gene expression involved in substrate metabolism and adipose tissue browning. NMR measurement showed that TRF decreased fat mass but increased lean mass. Indirect calorimeter recording indicated that TRF decreased the respiratory exchange ratio (RER) reflecting consumption of more fatty acid in energy production in light phase and increased the oxygen consumption during activities in dark phase.

CONCLUSIONS

TRF effectively decreases hyperinsulinemia and restores pulsatile GH secretion in the overeating obese mice with significant improvement in substrate and energy metabolism and body composition without reducing total caloric intake.

The effect of circadian rhythm on prolactin/PRLR-mediated intracellular signaling profiles in vivo and in vitro

The circadian molecular Clock is an internal time-keeping system, which regulates various physiological processes. The circadian Clock may be involved in all biological processes. The circadian Clock is closely related to prolactin's activities. However, until now, the effect of circadian Clock dysregulation on PRL's bioactivities remains unclear. Clock protein is an essential component in circadian Clock and necessary for Clock function. Therefore, Clock gene knockout mice (CLOCK -/- mice) was used to explore the effect of circadian Clock dysfunction on PRL's activities. The in vitro and in vivo experimental results showed that PRLR-mediated signaling was significantly down-regulated. PRL-induced JAK2-STAT5 signaling in Clock-/- mice was significantly decreased compared to control mice in vivo. In vitro, PRL/PRLR-mediated signaling in mammary epithelial cell that Clock was knocked down by siRNA was significantly down-regulated compared to control cells. Mechanistically, the expression levels of negative regulatory molecule (the suppressor of cytokine signaling (SOCS) was upregulated in vitro and in vivo, which may be one of the factors that causes the PRL-signaling downregulation. Taken together, the current work indicates that the circadian Clock affects the PRL's activities. This finding lays the foundation for studying the relationship between the circadian Clock and PRL's biological activities.

The GH-IGF-1 Axis in Circadian Rhythm

Organisms have developed common behavioral and physiological adaptations to the influence of the day/night cycle. The CLOCK system forms an internal circadian rhythm in the suprachiasmatic nucleus (SCN) during light/dark input. The SCN may synchronize the growth hormone (GH) secretion rhythm with the dimming cycle through somatostatin neurons, and the change of the clock system may be related to the pulsatile release of GH. The GH-insulin-like growth factor 1 (IGF-1) axis and clock system may interact further on the metabolism through regulatory pathways in peripheral organs. We have summarized the current clinical and animal evidence on the interaction of clock systems with the GH-IGF-1 axis and discussed their effects on metabolism.