PPARα deficiency augments a ketogenic diet-induced circadian PAI-1 expression possibly through PPARγ activation in the liver

Adult Inception of Ketogenic Diet Therapy Increases Sleep during the Dark Cycle in C57BL/6J Wild Type and Fragile X Mice

Sleep problems are a significant phenotype in children with fragile X syndrome. Our prior work assessed sleep-wake cycles in Fmr1KO male mice and wild type (WT) littermate controls in response to ketogenic diet therapy where mice were treated from weaning (postnatal day 18) through study completion (5-6 months of age). A potentially confounding issue with commencing treatment during an active period of growth is the significant reduction in weight gain in response to the ketogenic diet. The aim here was to employ sleep electroencephalography (EEG) to assess sleep-wake cycles in mice in response to the Fmr1 genotype and a ketogenic diet, with treatment starting at postnatal day 95. EEG results were compared with prior sleep outcomes to determine if the later intervention was efficacious, as well as with published rest-activity patterns to determine if actigraphy is a viable surrogate for sleep EEG. The data replicated findings that Fmr1KO mice exhibit sleep-wake patterns similar to wild type littermates during the dark cycle when maintained on a control purified-ingredient diet but revealed a genotype-specific difference during hours 4-6 of the light cycle of the increased wake (decreased sleep and NREM) state in Fmr1KO mice. Treatment with a high-fat, low-carbohydrate ketogenic diet increased the percentage of NREM sleep in both wild type and Fmr1KO mice during the dark cycle. Differences in sleep microstructure (length of wake bouts) supported the altered sleep states in response to ketogenic diet. Commencing ketogenic diet treatment in adulthood resulted in a 15% (WT) and 8.6% (Fmr1KO) decrease in body weight after 28 days of treatment, but not the severe reduction in body weight associated with starting treatment at weaning. We conclude that the lack of evidence for improved sleep during the light cycle (mouse sleep time) in Fmr1KO mice in response to ketogenic diet therapy in two studies suggests that ketogenic diet may not be beneficial in treating sleep problems associated with fragile X and that actigraphy is not a reliable surrogate for sleep EEG in mice.

Ketogenic Diet Affects Sleep Architecture in C57BL/6J Wild Type and Fragile X Mice

Nearly half of children with fragile X syndrome experience sleep problems including trouble falling asleep and frequent nighttime awakenings. The goals here were to assess sleep-wake cycles in mice in response to Fmr1 genotype and a dietary intervention that reduces hyperactivity. Electroencephalography (EEG) results were compared with published rest-activity patterns to determine if actigraphy is a viable surrogate for sleep EEG. Specifically, sleep-wake patterns in adult wild type and Fmr1KO littermate mice were recorded after EEG electrode implantation and the recordings manually scored for vigilance states. The data indicated that Fmr1KO mice exhibited sleep-wake patterns similar to wild type littermates when maintained on a control purified ingredient diet. Treatment with a high-fat, low-carbohydrate ketogenic diet increased the percentage of non-rapid eye movement (NREM) sleep in both wild type and Fmr1KO mice during the dark cycle, which corresponded to decreased activity levels. Treatment with a ketogenic diet flattened diurnal sleep periodicity in both wild type and Fmr1KO mice. Differences in several sleep microstructure outcomes (number and length of sleep and wake bouts) supported the altered sleep states in response to a ketogenic diet and were correlated with altered rest-activity cycles. While actigraphy may be a less expensive, reduced labor surrogate for sleep EEG during the dark cycle, daytime resting in mice did not correlate with EEG sleep states.

Association of plasminogen activator inhibitor-1 and fibroblastic growth factor 21 in 3 groups of type 2 diabetes: Without overweight/obesity, free of insulin resistance, and without hepatosteatosis

The physiological effects of fibroblast growth factor 21 (FGF21), leading to beneficial metabolic outcomes, have been extensively revealed in recent decades. Significantly elevated serum levels of FGF21 in obesity and type 2 diabetes mellitus (T2DM) are referred to as FGF21 resistance. However, Asian population tend to develop metabolic disorders at a lesser degree of obesity than those of Western. This study aimed to explore factors potentially related to serum FGF21 according to the severity of metabolic disorders in patients with T2DM. This cross-sectional study included 176 T2DM patients. The patients were categorized according to whether they had hepatic steatosis (fatty liver index [FLI] ≥ 60), insulin resistance (homeostasis model assessment of insulin resistance [HOMA-R] ≥ median), and/or overweight/obesity (body mass index [BMI] ≥ 25.0 kg/m2). Independent predictors of serum FGF21 were determined using multiple linear regression analysis in these 3 groups of T2DM patients. Circulating FGF21 levels were correlated positively with BMI, abdominal fat areas, leptin, and plasminogen activator inhibitor-1 (PAI-1). After adjustment for potential confounders, multiple linear regression analysis identified leptin as a factor strongly associated with serum FGF21 levels in all patients. Moreover, PAI-1 was a significant predictor of FGF21 in those with FLI < 60, BMI < 25.0 kg/m2, and HOMA-R < median, while leptin was the only independent factor in each of their counterparts. The factors related to serum FGF21 differ according to the severity of metabolic disorders. FGF21 appears to be independently associated with PAI-1 in T2DM patients: without overweight/obesity, those free of insulin resistance, and those without hepatic steatosis.

The Effect of Diet on the Cardiac Circadian Clock in Mice: A Systematic Review

Circadian rhythms play important roles in regulating physiological and behavioral processes. These are adjusted by environmental cues, such as diet, which acts by synchronizing or attenuating the circadian rhythms of peripheral clocks, such as the liver, intestine, pancreas, white and brown adipose tissue, lungs, kidneys, as well as the heart. Some studies point to the influence of diet composition, feeding timing, and dietary restriction on metabolic homeostasis and circadian rhythms at various levels. Therefore, this systematic review aimed to discuss studies addressing the effect of diet on the heart clock in animal models and, additionally, the chronodisruption of the clock and its relation to the development of cardiovascular disorders in the last 15 years. A search was conducted in the PubMed, Scopus, and Embase databases. The PRISMA guide was used to construct the article. Nineteen studies met all inclusion and exclusion criteria. In summary, these studies have linked the circadian clock to cardiovascular health and suggested that maintaining a robust circadian system may reduce the risks of cardiometabolic and cardiovascular diseases. The effect of time-of-day-dependent eating on the modulation of circadian rhythms of the cardiac clock and energy homeostasis is notable, among its deleterious effects predominantly in the sleep (light) phase and/or at the end of the active phase.

Review article: vascular effects of PPARs in the context of NASH

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors known to regulate glucose and fatty acid metabolism, inflammation, endothelial function and fibrosis. PPAR isoforms have been extensively studied in metabolic diseases, including type 2 diabetes and cardiovascular diseases. Recent data extend the key role of PPARs to liver diseases coursing with vascular dysfunction, including nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH).

AIM

This review summarises and discusses the pathobiological role of PPARs in cardiovascular diseases with a special focus on their impact and therapeutic potential in NAFLD and NASH.

RESULTS AND CONCLUSIONS

PPARs may be attractive for the treatment of NASH due to their liver-specific effects but also because of their efficacy in improving cardiovascular outcomes, which may later impact liver disease. Assessment of cardiovascular disease in the context of NASH trials is, therefore, of the utmost importance, both from a safety and efficacy perspective.

Identification of IQ motif-containing GTPase-activating protein 1 as a regulator of long-term ketosis

IQ motif-containing GTPase-activating protein 1 (IQGAP1) is a ubiquitously expressed scaffolding protein that integrates multiple cellular processes, including motility, adhesion, and proliferation, but its role in metabolism is unknown. Here, we show that IQGAP1 is induced upon fasting and regulates β-oxidation of fatty acids and synthesis of ketone bodies in the liver. IQGAP1-null (Iqgap1-/-) mice exhibit reduced hepatic PPARα transcriptional activity, as evidenced during fasting, after ketogenic diet, and upon pharmacological activation. Conversely, we found that the activity of fed-state sensor mTORC1 is enhanced in Iqgap1-/- livers, but acute inhibition of mTOR in Iqgap1-/- mice was unable to rescue the defect in ketone body synthesis. However, reexpressing IQGAP1 in the livers of Iqgap1-/- mice was sufficient to promote ketone body synthesis, increase PPARα signaling, and suppress mTORC1 activity. Taken together, we uncover what we believe to be a previously unidentified role for IQGAP1 in regulating PPARα activity and ketogenesis.

Human metabolomics reveal daily variations under nutritional challenges specific to serum and skeletal muscle

Objective

Advances in the field of metabolomics and the concomitant development of bioinformatics tools constitute a promising avenue towards the development of precision medicine and personalized profiling for numerous disease states. Studies in animal models have strengthened this concept, but the application in human subjects is scarce.

Methods

Utilizing high-throughput metabolomics, we have analyzed the metabolome levels of human serum and skeletal muscle in the morning and evening in response to divergent nutritional challenges in order to identify unique signatures present in serum and muscle.

Results

We reveal dynamic daily variation of human metabolome unique to serum and muscle. The overall effect of nutritional challenges on the serum and muscle metabolome results in a profound rewiring of morning-evening metabolic profiles in human participants in response to the timing and type of dietary challenge.

Conclusion

We highlight time-of-day and meal-composition dependence of reprogramming of human metabolome by nutritional challenges.

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Human metabolome identifies the daily variation of metabolite levels.

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Divergent nutritional challenges reprogram the daily variation of human serum/muscle metabolome.

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Metabolomics delineates parallels between human serum and skeletal muscle.

Circadian Clocks in the Hematologic System

The hematologic system performs a number of essential functions, including oxygen transport, the execution of the immune response against tumor cells and invading pathogens, and hemostasis (blood clotting). These roles are performed by erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets), respectively. Critically, circadian rhythms are evident in the function of all 3 cell types. In this review, we describe these oscillations, explore their mechanistic bases, and highlight their key implications. Since erythrocytes are anucleate, circadian rhythms in these cells testify to the existence of a nontranscriptional circadian clock. From a clinical perspective, leukocyte rhythms could underlie daily variation in the severity of allergic reactions, the symptoms of chronic inflammatory diseases, and the body’s response to infection, while the rhythmic properties of thrombocytes may explain daily fluctuations in the incidence of heart attack and stroke. Consequently, the efficacy of treatments for these conditions is likely to depend on the timing of their administration. Last, we outline preliminary evidence that circadian disruption in the hematologic system could contribute to the deleterious effects of poor diet, shift work, and alcohol abuse on human health.

MicroRNA-101 overexpression by IL-6 and TNF-α inhibits cholesterol efflux by suppressing ATP-binding cassette transporter A1 expression

BACKGROUND

MicroRNAs play key roles in regulating cholesterol homeostasis. Here, we investigated the role of microRNA-101 (miR-101) in regulating ATP-binding cassette transporter A1 (ABCA1) expression and cholesterol efflux under non-inflammatory and inflammatory conditions in human THP-1-derived macrophages and HepG2 hepatoblastoma cells.

METHODS

The cell lines were transfected with one of four lentiviral vectors: miR-101, miR-101 control, anti-miR-101, or anti-miR-101 control. A luciferase reporter assay was used to examine miR-101 binding to the 3' untranslated region (UTR) of ABCA1. Western blotting was conducted to assess ABCA1 protein expression. Cells were loaded with BODIPY-cholesterol and stained with oil red O to assess cholesterol efflux.

RESULTS

The luciferase activity assay revealed that wild-type miR-101 binding at site 2 significantly repressed ABCA1 3' UTR activity, suggesting that miR-101 directly targets the ABCA1 mRNA at site 2. In both cell lines, Western blotting revealed that miR-101 expression negatively regulates ABCA1 protein expression and significantly suppresses cholesterol efflux to ApoA1 under both low-density lipoprotein (LDL) and non-LDL conditions, which was confirmed by pronounced lipid inclusions visible by oil red O staining. In HepG2 cells, both IL-6 and TNF-α treatments produced significant miR-101 overexpression; however, in THP-1-derived macrophages, only IL-6 treatment produced significant miR-101 overexpression. Anti-mir-101 transfection under both IL-6 and TNF-α treatment conditions led to ABCA1 upregulation, indicating that miR-101 expression represses ABCA1 expression under inflammatory conditions.

CONCLUSIONS

miR-101 promotes intracellular cholesterol retention under inflammatory conditions through suppressing ABCA1 expression and suggests that the miR-101-ABCA1 axis may play an intermediary role in the development of NAFLD and vascular atherosclerosis.

Nocturnal light exposure alters hepatic Pai-1 expression by stimulating the adrenal pathway in C3H mice

Recent studies have suggested the possibility that nocturnal light exposure affects many biological processes in rodents, especially the circadian rhythm, an endogenous oscillation of approximately 24 h. However, there is still insufficient information about the physiological effects of nocturnal light exposure. In this study, we examined the changes in gene expression and serum levels of plasminogen activator inhibitor-1 (PAI-1), a major component of the fibrinolytic system that shows typical circadian rhythmicity, in C3H/He mice. Zeitgeber time (ZT) was assessed with reference to the onset of light period (ZT0). Exposure to fluorescent light (70 lux) for 1 h in the dark period (ZT14) caused a significant increase in hepatic Pai-1 gene expression at ZT16. Serum PAI-1 levels also tended to increase, albeit not significantly. Expression levels of the typical clock genes Bmal1, Clock, and Per1 were significantly increased at ZT21, ZT16, and ZT18, respectively. Exposure to nocturnal light significantly increased plasma adrenalin levels. The effects of nocturnal light exposure on Pai-1 expression disappeared in adrenalectomized mice, although the changes in clock genes were still apparent. In conclusion, our results suggest that nocturnal light exposure, even for 1 h, alters hepatic Pai-1 gene expression by stimulating the adrenal pathway. Adrenalin secreted from the adrenal gland may be an important signaling mediator of the change in Pai-1 expression in response to nocturnal light exposure.

Sex differences in the circadian variation of cytochrome p450 genes and corresponding nuclear receptors in mouse liver

Sex differences and circadian variation are two major factors that affect the expression of drug-processing genes. This study aimed to examine sex differences in the circadian variation of hepatic cytochrome P450 (Cyp) genes and corresponding nuclear receptors. Adult mice were acclimated to environmentally controlled facilities for 2 wks, and livers were collected every 4 h during a 24-h period. Total RNA and protein were isolated and subjected to real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis. The mRNA expression of the aryl hydrocarbon receptor (AhR) and AhR-regulated Cyp1a1 and Cyp1a2 were higher in females and higher during the light phase. The mRNA expression of constitutive and rostane receptor (CAR) and CYP2B10 protein was female-predominant and higher in the dark phase. Pregnane X receptor (PXR) peaked around 18:00 h, but PXR-regulated Cyp3a11 and Cyp3a25 were higher at 10:00 h, without apparent sex dimorphism at protein levels. Peroxisome proliferator-activated receptor-α (PPARα), Cyp4a10, and Cyp4a14 were higher in females and peaked between 14:00 and 18:00 h. The mRNA levels of farnesoid X receptor (FXR), Cyp7a1, and Cyp27a1 peaked around 18:00 h and CYP7A1 protein was higher during the dark phase and higher in females. Cyp7b1(male-predominant) and Cyp2a4 (female-predominant) both showed circadian variation. Circadian variation of hepatic clock genes such as nuclear receptor Rev-erbα, cryptochrome 1 (Cry1), and brain muscle ARNT-like protein 1 (Bmal1) showed distinct patterns. Sex differences and circadian rhythmicity of Cyp genes and corresponding nuclear receptors exist in mouse liver that could impact xenobiotic metabolism and toxicity at different times of the day.

Ketogenic diet and fasting induce the expression of cold-inducible RNA-binding protein with time-dependent hypothermia in the mouse liver

Cold-inducible RNA-binding protein (CIRBP) induced by cold stress modulates the molecular circadian clock in vitro. The present study examines the effect of a ketogenic diet (KD) and fasting on Cirbp expression in the mouse liver. Chronic KD administration induced time-dependent Cirbp expression with hypothermia in mice. The circadian expression of clock genes such as Bmal1 and Clock was phase-advanced and augmented in the liver of mice fed with a KD. Transient food deprivation also induced time-dependent Cirbp expression with hypothermia in mice. These findings suggest that hypothermia is involved in the increased expression of Cirbp under ketogenic or fasting conditions.

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A ketogenic diet and fasting induce time-of-day-dependent hypothermia in mice.

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A ketogenic diet and fasting induce time-of-day-dependent Cirbp expression in mice.

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A ketogenic diet affects the expression of circadian genes in the mouse liver.

Activation of the farnesoid X receptor induces hepatic expression and secretion of fibroblast growth factor 21

Previous studies have shown that starvation or consumption of a high fat, low carbohydrate (HF-LC) ketogenic diet induces hepatic fibroblast growth factor 21 (FGF21) gene expression in part by activating the peroxisome proliferator-activated receptor-α (PPARα). Using primary hepatocyte cultures to screen for endogenous signals that mediate the nutritional regulation of FGF21 expression, we identified two sources of PPARα activators (i.e. nonesterified unsaturated fatty acids and chylomicron remnants) that induced FGF21 gene expression. In addition, we discovered that natural (i.e. bile acids) and synthetic (i.e. GW4064) activators of the farnesoid X receptor (FXR) increased FGF21 gene expression and secretion. The effects of bile acids were additive with the effects of nonesterified unsaturated fatty acids in regulating FGF21 expression. FXR activation of FGF21 gene transcription was mediated by an FXR/retinoid X receptor binding site in the 5'-flanking region of the FGF21 gene. FGF19, a gut hormone whose expression and secretion is induced by intestinal bile acids, also increased hepatic FGF21 secretion. Deletion of FXR in mice suppressed the ability of an HF-LC ketogenic diet to induce hepatic FGF21 gene expression. The results of this study identify FXR as a new signaling pathway activating FGF21 expression and provide evidence that FXR activators work in combination with PPARα activators to mediate the stimulatory effect of an HF-LC ketogenic diet on FGF21 expression. We propose that the enhanced enterohepatic flux of bile acids during HF-LC consumption leads to activation of hepatic FXR and FGF19 signaling activity and an increase in FGF21 gene expression and secretion.

Thiazolidinediones are potent inducers of fibroblast growth factor 21 expression in the liver

Fibroblast growth factor 21 (FGF21) is an effective metabolic regulator of glucose and lipid homeostasis in the context of insulin resistance, glucose intolerance and dyslipidemia in diabetic rodents and monkeys, and peroxisome proliferator-activated receptor α (PPARα) directly induces FGF21 expression in the rodent liver. Recent findings suggest that the effects and regulation of FGF21 qualitatively differ between rodents and humans. Here, we examined the effects of PPARα and PPARγ agonists on FGF21 mRNA expression in the mouse liver and in cultured hepatocytes. Intraperitoneal injection of both bezafibrate and pioglitazone induced FGF21 mRNA expression in the mouse liver. Rosiglitazone and pioglitazone as well as bezafibrate significantly induced FGF21 mRNA expression in cultured mouse hepatocytes. On the other hand, both rosiglitazone and pioglitazone significantly induced, whereas bezafibrate did not affect FGF21 mRNA expression in the human liver carcinoma cell line HepG2. Bezafibrate significantly induced pyruvate dehydrogenase kinase 4 mRNA expression, suggesting that HepG2 cells are sensitive to bezafibrate like the mouse liver. Our findings suggest that PPARγ-activating antidiabetic drugs such as rosiglitazone and pioglitazone induce FGF21 expression in mouse and human hepatocytes, and that PPARγ rather than PPARα might play an important role in human FGF21 production.

Time-imposed daily restricted feeding induces rhythmic expression of Fgf21 in white adipose tissue of mice

Fibroblast growth factor 21 (FGF21) is a key metabolic regulator that is induced by fasting and starvation, and its expression is thought to be regulated by the circadian clock in the liver. To evaluate the functional role of FGF21 in the circadian regulation of physiology and behavior, we examined the temporal expression profiles of Fgf21 and circadian clock genes in addition to behavioral activity rhythms under adlibitum feeding (ALF) and time-imposed restricted feeding (RF) in mice. Four hours of daily restricted feeding during the daytime induced over an 80-fold increase in feeding-dependent rhythmic Fgf21 mRNA expression in epididymal white adipose tissue (eWAT), although the expression levels were continuously increased 10-fold in the liver of wild-type (WT) mice. Refeeding subsequent to transient fasting revealed that refeeding but not fasting remarkably induces Fgf21 expression in eWAT, although fasting-induced hepatic Fgf21 expression is completely reversed by refeeding. The free-running period of locomotor activity rhythm under ALF and the food anticipatory activity (FAA) under RF remained intact in Fgf21 knockout (KO) mice, suggesting that FGF21 is dispensable for both the central clock in the suprachiasmatic nucleus (SCN) and the food-entrainable oscillator that governs the FAA. Temporal expression profiles of circadian genes such as mPer2 and BMAL1 were essentially identical in both tissues between WT and Fgf21 KO mice under RF. The physiological role of the refeeding-induced adipose Fgf21 expression remains to be elucidated.