Defect in peroxisome proliferator-activated receptor alpha-inducible fatty acid oxidation determines the severity of hepatic steatosis in response to fasting

Oleuropein mitigates non-alcoholic fatty liver disease (NAFLD) and modulates liver metabolites in high-fat diet-induced obese mice via activating PPARα

BACKGROUND

This study aimed to elucidate the mechanism of oleuropein (OLE) ameliorates non-alcoholic fatty liver disease (NAFLD) and its underlying mechanisms.

RESULTS

Male C57BL/6J mice were fed either a low-fat diet (LFD), a high-fat diet (HFD), or a HFD supplemented with 0.03% (w/w) OLE for 16 weeks. OLE supplementation decreased body weight and liver weight, improved serum lipid profiles, and ameliorated HFD-induced hepatic dysfunction. Liver metabolomics analysis revealed that OLE increased the levels of nicotinamide, tauroursodeoxycholic acid, taurine, and docosahexaenoic acid, which were beneficial for lipid homeostasis and inflammation regulation. OLE exerted its protective effects by activating peroxisome proliferator-activated receptor alpha (PPARα), a key transcription factor that regulates fibroblast growth factor 21 (FGF21) expression and modulates lipid oxidation, lipogenesis and inflammation pathways. Importantly, OLE supplementation did not significantly affect body weight or liver weight in PPARα knockout (PPARα KO) mice, indicating that PPARα is essential for OLE-mediated NAFLD prevention.

CONCLUSION

Our results suggest that OLE alleviates NAFLD in mice by activating PPARα and modulating liver metabolites. © 2024 Society of Chemical Industry.

Endoplasmic reticulum stress induces hepatic steatosis through interaction between PPARα and FoxO6 in vivo and in vitro

Endoplasmic reticulum (ER) stress is a major cause of hepatic steatosis through increasing de novo lipogenesis. Forkhead box O6 (FoxO6) is a transcription factor mediating insulin signaling to glucose and lipid metabolism. Therefore, dysregulated FoxO6 is involved in hepatic lipogenesis. This study elucidated the role of FoxO6 in ER stress-induced hepatic steatosis in vivo and in vitro. Hepatic ER stress responses and β-oxidation were monitored in mice overexpressed with constitutively active FoxO6 allele and FoxO6-null mice. For the in vitro study, liver cells overexpressing constitutively active FoxO6 and FoxO6-siRNA were treated with high glucose, and lipid metabolism alterations were measured. ER stress-induced FoxO6 activation suppressed hepatic β-oxidation in vivo. The expression and transcriptional activity of peroxisome proliferator-activated receptor α (PPARα) were significantly decreased in the constitutively active FoxO6 allele. Otherwise, inhibiting β-oxidation genes were reduced in the FoxO6-siRNA and FoxO6-KO mice. Our data showed that the FoxO6-induced hepatic lipid accumulation was negatively regulated by insulin signaling. High glucose treatment as a hyperglycemia condition caused the expression of ER stress-inducible genes, which was deteriorated by FoxO6 activation in liver cells. However, high glucose-mediated ER stress suppressed β-oxidation gene expression through interactions between PPARα and FoxO6 corresponding to findings in the in vivo study-lipid catabolism is also regulated by FoxO6. Furthermore, insulin resistance suppressed b-oxidation through the interaction between FoxO6 and PPARα promotes hepatic steatosis, which, due to hyperglycemia-induced ER stress, impairs insulin signaling. KEY MESSAGES: Our original aims were to delineate the interrelation between the regulation of PPARα and the transcription factor FoxO6 pathway in relation to lipid metabolism at molecular levels. Evidence on high glucose promoted FoxO6 activation induced lipid accumulation in liver cells. The effect of PPARα activation of the insulin signaling. FoxO6 plays a pivotal role in hepatic lipid accumulation through inactivation of PPARα in FoxO6-overexpression mice.

COL6A6 Peptide Vaccine Alleviates Atherosclerosis through Inducing Immune Response and Regulating Lipid Metabolism in Apoe-/- Mice

Atherosclerosis is an autoimmune disease characterized by lipid imbalances and chronic inflammation within blood vessels, with limited preventive and treatment options currently available. In this study, a vaccine prepared with COL6A6 peptide (named the Pep_A6 vaccine) was administered to immunize Apoe-/- mice, and the immune mechanism of the Pep_A6 vaccine against atherosclerosis was first investigated. The results of arterial oil red O staining demonstrated that the Pep_A6 vaccine significantly reduced the atherosclerotic plaque area in Apoe-/- mice fed with a high-fat diet for 20 weeks. A flow cytometry analysis revealed that the Pep_A6 vaccine inhibited Th1 cell differentiation and increased the proportion of Treg cells. Furthermore, there was a significant increase in Ly6Clow monocytes observed in the vaccinated group. The ELISA results showed that the Pep_A6 vaccine induced a significant expression of Pep_A6-specific antibody IgG and IgG1 in mouse serum. Additionally, we found that the Pep_A6 vaccine significantly decreased serum LDL-C content and regulated the expression of genes related to liver lipid metabolism. Together, our findings suggest that the Pep_A6 vaccine alleviates atherosclerosis by inducing a positive immune response and regulating lipid metabolism, providing new insights into potential prevention strategies for atherosclerosis as an innovative vaccine.

Daily Orange Consumption Reduces Hepatic Steatosis Prevalence in Patients with Metabolic Dysfunction-Associated Steatotic Liver Disease: Exploratory Outcomes of a Randomized Clinical Trial

Background: Consumption of flavonoid-rich orange juice has been shown to reduce adiposity and liver steatosis in murine models of diet-induced obesity. However, little is known about the effects of whole orange intake, independent of body weight changes, on liver function and steatosis in individuals with metabolic dysfunction-associated steatotic liver disease (MASLD). The goal is to understand the direct impact of orange consumption on metabolic health. Methods: Sixty-two men and women aged 30-65 with MASLD (Controlled Attenuation Parameter, (CAP) > 275 dB/m) were randomly assigned to consume either 400 g of whole oranges or non-citrus fruits daily for 4 weeks. Baseline evaluations included medical assessments, blood tests, and body composition. Liver health was assessed using transient elastography (FibroScan®) for steatosis and fibrosis, conducted by blinded personnel. This clinical trial was registered at ClinicalTrials.gov (NCT05558592). Results: After 4 weeks of orange supplementation, liver steatosis decreased in the treatment group, with 70.9% showing steatosis compared to 100% in controls (p < 0.004), indicating a 30% reduction in liver disease prevalence. There were no significant changes in fibrosis or plasma liver enzymes, though plasma gamma glutaril transferase (GGT) levels decreased significantly. Body weight, waist circumference, body composition, lipid profile, fasting glucose, insulin, and C-reactive protein levels remained unchanged. Dietary analysis revealed no change in caloric intake, but vitamins C, A, thiamine, and riboflavin increased in the orange group. Conclusions: Our findings suggest that phytochemical-rich foods, especially whole fruits like oranges, may enhance liver function as an adjunct treatment for MASLD. The notable reduction in liver steatosis prevalence occurred independently of body weight changes. Further studies are needed to investigate the long-term effects of orange supplementation on steatosis and fibrosis progression and to identify the specific bioactive compounds and mechanisms involved.

Maladaptive regeneration and metabolic dysfunction associated steatotic liver disease: Common mechanisms and potential therapeutic targets

The normal liver has an extraordinary capacity of regeneration. However, this capacity is significantly impaired in steatotic livers. Emerging evidence indicates that metabolic dysfunction associated steatotic liver disease (MASLD) and liver regeneration share several key mechanisms. Some classical liver regeneration pathways, such as HGF/c-Met, EGFR, Wnt/β-catenin and Hippo/YAP-TAZ are affected in MASLD. Some recently established therapeutic targets for MASH such as the Thyroid Hormone (TH) receptors, Glucagon-like protein 1 (GLP1), Farnesoid X receptor (FXR), Peroxisome Proliferator-Activated Receptors (PPARs) as well as Fibroblast Growth Factor 21 (FGF21) are also reported to affect hepatocyte proliferation. With this review we aim to provide insight into common molecular pathways, that may ultimately enable therapeutic strategies that synergistically ameliorate steatohepatitis and improve the regenerating capacity of steatotic livers. With the recent rise of prolonged ex-vivo normothermic liver perfusion prior to organ transplantation such treatment is no longer restricted to patients undergoing major liver resection or transplantation, but may eventually include perfused (steatotic) donor livers or even liver segments, opening hitherto unexplored therapeutic avenues.

PPAR-α Insufficiency Enhances Doxorubicin-Induced Nephropathy in PPAR-α Knockout Mice and a Murine Podocyte Cell Line

Peroxisome proliferator-activated receptor-alpha (PPAR-α) and its exogenous activators (fibrates) promote autophagy. However, whether the deleterious effects of PPAR-α deficiency on doxorubicin (DOX)-induced podocytopathy are associated with reduced autophagy remains to be clarified. We investigated the mechanisms of PPAR-α in DOX-induced podocytopathy and tubular injury in PPAR-α knockout (PAKO) mice and in a murine podocyte cell line. DOX-treated PAKO mice showed higher serum levels of triglycerides and non-esterified fatty acids and more severe podocytopathy than DOX-treated wild-type mice, as evidenced by higher urinary levels of proteins and podocalyxin at 3 days to 2 weeks and higher blood urea nitrogen and serum creatinine levels at 4 weeks. Additionally, there was an increased accumulation of p62, a negative autophagy marker, in the glomerular and tubular regions in DOX-treated PAKO mice at Day 9. Moreover, DOX-treated PAKO mice showed more severe glomerulosclerosis and tubular damage and lower podocalyxin expression in the kidneys than DOX-treated control mice at 4 weeks. Furthermore, DOX treatment increased p-p53, an apoptosis marker, and cleaved the caspase-3 levels and induced apoptosis, which was ameliorated by fenofibrate, a PPAR-α activator. Fenofibrate further enhanced AMPK activation and autophagy under fed and fasting conditions. Conclusively, PPAR-α deficiency enhances DOX-induced podocytopathy, glomerulosclerosis, and tubular injury, possibly by reducing autophagic activity in mouse kidneys.

Long-term exposure to polychlorinated biphenyl 126 induces liver fibrosis and upregulates miR-155 and miR-34a in C57BL/6 mice

Environmental pollutants, including polychlorinated biphenyls (PCBs), act as endocrine disruptors and impair various physiological processes. PCB 126 is associated with steatohepatitis, fibrosis, cirrhosis, and other hepatic injuries. These disorders can be regulated by microRNAs (miRNAs). Therefore, this study aimed to investigate the role of miRNAs in non-alcoholic fatty liver disease associated with exposure to PCB 126. Adult male C57BL/6 mice were exposed to PCB 126 (5 μmol/kg of body weight) for 10 weeks. The PCB group showed lipid accumulation in the liver in the presence of macro- and microvesicular steatosis and fibrosis with increased inflammatory and profibrotic gene expression, consistent with non-alcoholic steatohepatitis (NASH). PCB exposure also upregulated miR-155 and miR-34a, which induce the expression of proinflammatory cytokines and inflammation in the liver and reduce the expression of peroxisome proliferator-activated receptor α, which, in turn, impairs lipid oxidation and hepatic steatosis. Therefore, the present study showed that PCB 126 induced NASH via potential mechanisms involving miR-155 and miR-34a, which may contribute to the development of new diagnostic markers and therapeutic strategies.

HSDL2 links nutritional cues to bile acid and cholesterol homeostasis

In response to energy and nutrient shortage, the liver triggers several catabolic processes to promote survival. Despite recent progress, the precise molecular mechanisms regulating the hepatic adaptation to fasting remain incompletely characterized. Here, we report the identification of hydroxysteroid dehydrogenase-like 2 (HSDL2) as a mitochondrial protein highly induced by fasting. We show that the activation of PGC1α-PPARα and the inhibition of the PI3K-mTORC1 axis stimulate HSDL2 expression in hepatocytes. We found that HSDL2 depletion decreases cholesterol conversion to bile acids (BAs) and impairs FXR activity. HSDL2 knockdown also reduces mitochondrial respiration, fatty acid oxidation, and TCA cycle activity. Bioinformatics analyses revealed that hepatic Hsdl2 expression positively associates with the postprandial excursion of various BA species in mice. We show that liver-specific HSDL2 depletion affects BA metabolism and decreases circulating cholesterol levels upon refeeding. Overall, our report identifies HSDL2 as a fasting-induced mitochondrial protein that links nutritional signals to BAs and cholesterol homeostasis.

Tyrosol regulates hepatic lipid metabolism in high-fat diet-induced NAFLD mice

This study aimed to elucidate the effect of tyrosol (TYR) on the amelioration of nonalcoholic fatty liver disease (NAFLD). Male C57BL/6J mice were fed a low-fat diet (LFD), a high-fat diet (HFD), or a HFD supplemented with 0.025% (w/w) TYR (TYR) for 16 weeks. Following a 16-week intervention, the TYR cohort exhibited diminished final body weight and hepatic lipid accumulation, compared to HFD fed mice. Liver metabolomics analysis revealed that TYR increased the hepatic levels of spermidine, taurine, linoleic acid, malic acid and eicosapentaenoic acid (EPA), indicating the beneficial effect of TYR on lipid homeostasis. Using molecular docking analysis and the luciferase assay, we found that TYR acts as a ligand and binds with peroxisome proliferator-activated receptor-α (PPARα), which plays a pivotal role in the modulation of hepatic lipid metabolism, thereby activating the transcription of downstream genes. Our results suggest that TYR alleviates NAFLD in HFD-fed mice probably by the modulation of the PPARα signaling pathway.

Sodium butyrate alleviates free fatty acid-induced steatosis in primary chicken hepatocytes via the AMPK/PPARα pathway

Fatty liver hemorrhagic syndrome (FLHS) is a prevalent metabolic disorder observed in egg-laying hens, characterized by fatty deposits and cellular steatosis in the liver. Our preliminary investigations have revealed a marked decrease in the concentration of butyric acid in the FLHS strain of laying hens. It has been established that sodium butyrate (NaB) protects against metabolic disorders. However, the underlying mechanism by which butyrate modulates hepato-lipid metabolism to a great extent remains unexplored. In this study, we constructed an isolated in vitro model of chicken primary hepatocytes to induce hepatic steatosis by free fatty acids (FFA). Our results demonstrate that treatment with NaB effectively mitigated FFA-induced hepatic steatosis in chicken hepatocytes by inhibiting lipid accumulation, downregulating the mRNA expression of lipo-synthesis-related genes (sterol regulatory element binding transcription factor 1 (SREBF1), acetyl-CoA carboxylase 1(ACC1), fatty acid synthase (FASN), stearoyl-CoA desaturase 1 (SCD1), liver X receptor α (LXRα), 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR)) (P < 0.05), and upregulating the mRNA and protein expression of AMP-activated protein kinase α1 (AMPKα1), peroxisome proliferator-activated receptor α (PPARα), and carnitine palmitoyl-transferase 1A (CPT1A) (P < 0.05). Moreover, AMPK and PPARα inhibitors (Compound C (Comp C) and GW6471, respectively) reversed the protective effects of NaB against FFA-induced hepatic steatosis by blocking the AMPK/PPARα pathway, leading to lipid droplet accumulation and triglyceride (TG) contents in chicken primary hepatocytes. With these findings, NaB can alleviate hepatocyte lipoatrophy injury by activating the AMPK/PPARα pathway, promoting fatty acid oxidation, and reducing lipid synthesis in chicken hepatocytes, potentially being able to provide new ideas for the treatment of FLHS.

Blood-brain barrier disruption and edema formation due to prolonged starvation in wild-type mice

INTRODUCTION

Different types of diseases have been treated by restricted caloric intake or fasting. Although during this long time, fasting protective measures, for example, supplements, are given to the patients to protect vital organs such as the liver and kidney, little attention is given to the brain. The current research aims to investigate hypoglycemia due to prolonged fasting disrupts blood-brain barrier (BBB) in mice.

MATERIALS AND METHODS

Immunohistochemistry (IHC) and in situ hybridization (ISH) techniques were used to examine the expression of different genes. Evans blue extravasation and wet-dry technique were performed to evaluate the integrity of BBB and the formation of brain edema, respectively.

RESULTS

We confirmed that hypoglycemia affected mice fasting brain by examining the increased expression of glucose transporter protein 1 and hyperphosphorylation of tau protein. We subsequently found downregulated expression of some genes, which are involved in maintaining BBB such as vascular endothelial growth factor (VEGF) in astrocytes and claudin-5 (a vital component of BBB) and VEGF receptor (VEGFR1) in endothelial cells by ISH. We also found that prolonged fasting caused the brain endothelial cells to express lipocalin-2, an inflammatory marker of brain endothelial cells. We performed Evans blue extravasation to show more dye was retained in the brain of fasted mice than in control mice as a result of BBB disruption. Finally, wet-dry method showed that the brain of prolonged fasted mice contained significantly higher amount of water confirming the formation of brain edema. Therefore, special attention should be given to the brain during treatment with prolonged fasting for various diseases.

CONCLUSIONS

Our results demonstrated that hypoglycemia due to prolonged fasting disrupts BBB and produces brain edema in wild-type mice, highlighting the importance of brain health during treatment with prolonged fasting.

Paternal starvation affects metabolic gene expression during zebrafish offspring development and lifelong fitness

Dietary restriction in the form of fasting is a putative key to a healthier and longer life, but these benefits may come at a trade-off with reproductive fitness and may affect the following generation(s). The potential inter- and transgenerational effects of long-term fasting and starvation are particularly poorly understood in vertebrates when they originate from the paternal line. We utilised the externally fertilising zebrafish amenable to a split-egg clutch design to explore the male-specific effects of fasting/starvation on fertility and fitness of offspring independently of maternal contribution. Eighteen days of fasting resulted in reduced fertility in exposed males. While average offspring survival was not affected, we detected increased larval growth rate in F1 offspring from starved males and more malformed embryos at 24 h post-fertilisation in F2 offspring produced by F1 offspring from starved males. Comparing the transcriptomes of F1 embryos sired by starved and fed fathers revealed robust and reproducible increased expression of muscle composition genes but lower expression of lipid metabolism and lysosome genes in embryos from starved fathers. A large proportion of these genes showed enrichment in the yolk syncytial layer suggesting gene regulatory responses associated with metabolism of nutrients through paternal effects on extra-embryonic tissues which are loaded with maternal factors. We compared the embryo transcriptomes to published adult transcriptome datasets and found comparable repressive effects of starvation on metabolism-associated genes. These similarities suggest a physiologically relevant, directed and potentially adaptive response transmitted by the father, independently from the offspring's nutritional state, which was defined by the mother.

Mechanisms of hepatic fatty acid oxidation and ketogenesis during fasting

Fasting is part of many weight management and health-boosting regimens. Fasting causes substantial metabolic adaptations in the liver that include the stimulation of fatty acid oxidation and ketogenesis. The induction of fatty acid oxidation and ketogenesis during fasting is mainly driven by interrelated changes in plasma levels of various hormones and an increase in plasma nonesterified fatty acid (NEFA) levels and is mediated transcriptionally by the peroxisome proliferator-activated receptor (PPAR)α, supported by CREB3L3 (cyclic AMP-responsive element-binding protein 3 like 3). Compared with men, women exhibit higher ketone levels during fasting, likely due to higher NEFA availability, suggesting that the metabolic response to fasting shows sexual dimorphism. Here, we synthesize the current molecular knowledge on the impact of fasting on hepatic fatty acid oxidation and ketogenesis.

Linoleic and Arachidonic Fatty Acids and their Potential Relationship with Inflammation, Pregnancy, and Fetal Development

A healthy maternal diet must consider an appropriate supply of long-chain polyunsaturated fatty acids (LCPUFAs) precursors to ensure adequate growth and development of the fetus. In this regard, n-6 PUFAs, predominantly linoleic (C18:2 n-6, LA) and arachidonic acid (C20:4 n-6), have a central role in the development of the central nervous system because they are part of the membrane structure and participate in the metabolism and signal transduction of cells. Nevertheless, they can also be transformed into inflammatory metabolites promoting the pathogenesis of cardiovascular diseases, cancer, and autoimmune or inflammatory conditions. In modern westernized societies, there is a high dietary consumption of foods rich in n-6 PUFAs which could have detrimental consequences for the fetus and neonate due to excessive exposure to these fatty acids (FAs).

OBJECTIVE

To summarize the evidence of maternal, placental, and fetal alterations that an excessive intake of n-6 polyunsaturated FAs (PUFAs), LA, and AA, could produce during pregnancy.

METHODS

A thorough review of the literature regarding the effects of n-6 PUFAs during pregnancy and lactation including in vivo and in vitro models, was carried out using the PubMed database from the National Library of Medicine-National Institutes of Health.

RESULTS

An elevated intake of n-6 PUFA, specifically LA, during pregnancy influences children's motor, cognitive, and verbal development during infancy and early childhood. Similarly, they could harm the placenta and the development of other fetal organs such as the fat tissue, liver, and cardiovascular system.

CONCLUSION

Maternal diet, specifically LA intake, could have significant repercussions on fetal development and long-term consequences in the offspring, including the possibility of future metabolic and mental diseases. It would be necessary to focus on the prevention of these alterations through timely dietary interventions in the target population.

Time-restricted feeding regulates lipid metabolism under metabolic challenges

Dysregulation of lipid metabolism is a commonly observed feature associated with metabolic syndrome and leads to the development of negative health outcomes such as obesity, diabetes mellitus, non-alcoholic fatty liver disease, or atherosclerosis. Time-restricted feeding/eating (TRF/TRE), an emerging dietary intervention, has been shown to promote pleiotropic health benefits including the alteration of diurnal expression of genes associated with lipid metabolism, as well as levels of lipid species. Although TRF likely induces a response in multiple organs leading to the modulation of lipid metabolism, a majority of the studies related to TRF effects on lipids have focused only on individual tissues, and furthermore there is a lack of insight into potential underlying mechanisms. In this review, we summarize the current insights regarding TRF effects on lipid metabolism and the potential mechanisms in adipose tissue, liver, skeletal muscle, and heart, and conclude by outlining possible avenues for future exploration.

Prenatal caloric restriction adjusts the energy homeostasis and behavior in response to acute and chronic variations in food availability in adulthood

Fetal metabolic programming produced by unfavorable prenatal nutritional conditions leads to the development of a disorder called "thrifty phenotype", which is associated with pathologies such as diabetes and obesity in adulthood. However, from an ecophysiological approach, few studies have addressed the development of thrifty phenotypes in terms of energy. This might represent an adaptive advantage against caloric deficiency conditions extending into adulthood. The objective of this study is to investigate the potential adaptive value of the thrifty phenotype expression through prenatal programming in a rodent model experiencing varying dietary conditions in different temporal contexts. To fill this gap, adult males of Mus musculus (BALB/C) from two maternal pregnancy groups were analyzed: control (ad libitum feeding) and caloric restriction from day 10 of gestation (70% restriction). Adult offspring of these groups were split further for two experiments: acute food deprivation and chronic caloric restriction at 60%. The acute food deprivation was performed for 24, 48 or 72 h while the caloric restriction regime was sustained for 20 days. For each experiment, morphological variables, such as body and organ mass, and gene expression related to lipid and carbohydrate metabolism from the liver and brain, were evaluated. In chronic caloric restriction, behavioral tests (open-field test and home-cage behavior) were performed. Our results indicate that under acute deprivation, the liver mass and triglyceride content remained unchanged in individuals subjected to prenatal restriction, in contrast to the reduction experienced by the control group. The latter is associated with the expression of the key genes involved in energy homeostasis (Pepck, Pparα/Pparγ), indicating a differential use of nutritional resources. In addition, thrifty animals, subjected to chronic caloric restriction, showed a severe reduction in locomotor and gluconeogenic activity, which is consistent with the regulatory role of Sirt1 and its downstream targets Mao and Pepck. Our results reveal that prenatal caloric restriction translates into a sparing metabolism in response to acute and chronic lack of food in adulthood.

The proteasome regulates body weight and systemic nutrient metabolism during fasting

The ubiquitin-proteasome system (UPS) and the autophagy-lysosome pathway are the primary means of degradation in mammalian tissues. We sought to determine the individual contribution of the UPS and autophagy to tissue catabolism during fasting. Mice were overnight fasted for 15 h before regaining food access ("Fed" group, n = 6) or continuing to fast ("Fast" group, n = 7) for 3 h. In addition, to investigate the effects of autophagy on systemic metabolism and tissue degradation, one group of mice was fasted for 18 h and treated with chloroquine ("Fast + CLQ" group, n = 7) and a fourth group of mice was treated with bortezomib ("Fast + Bort" group, n = 7) to assess the contribution of the UPS. Body weight, tissue weight, circulating hormones and metabolites, intracellular signaling pathways, and protein synthesis were investigated. Fasting induced the loss of body weight, liver mass, and white adipose tissue in the Fast and the Fast + CLQ group, whereas the Fast + Bort group maintained tissue and body weight. Fasting reduced glucose and increased β hydroxybutyrate in the circulation of all mice. Both changes were most profound in the Fast + Bort group compared with the other fasting conditions. Molecular signaling indicated a successful inhibition of hepatic UPS with bortezomib and an upregulation of the PI3K/AKT/mTOR pathway. The latter was further supported by an increase in hepatic protein synthesis with bortezomib. Inhibition of the UPS through bortezomib blocks body weight loss and tissue catabolism during an acute overnight fast in mice. The effects were likely mediated through a combined effect of the drug on biomolecule degradation and synthesis.NEW & NOTEWORTHY Bortezomib treatment prevents tissue and body weight loss during fasting. The loss of proteasome activity with bortezomib exacerbates fasting-induced ketogenesis. During fasting, bortezomib increases AMPK and PI3K/AKT signaling in the liver, which promotes protein synthesis.

A metabolome atlas of mouse brain on the global metabolic signature dynamics following short-term fasting

Calorie restriction (CR) or a fasting regimen is considered one of the most potent non-pharmacological interventions to prevent chronic metabolic disorders, ameliorate autoimmune diseases, and attenuate aging. Despite efforts, the mechanisms by which CR improves health, particularly brain health, are still not fully understood. Metabolic homeostasis is vital for brain function, and a detailed metabolome atlas of the brain is essential for understanding the networks connecting different brain regions. Herein, we applied gas chromatography-mass spectrometry-based metabolomics and lipidomics, covering 797 structurally annotated metabolites, to investigate the metabolome of seven brain regions in fasted (3, 6, 12, and 24 h) and ad libitum fed mice. Using multivariate and univariate statistical techniques, we generated a metabolome atlas of mouse brain on the global metabolic signature dynamics across multiple brain regions following short-term fasting (STF). Significant metabolic differences across brain regions along with STF-triggered region-dependent metabolic remodeling were identified. We found that STF elicited triacylglycerol degradation and lipolysis to compensate for energy demand under fasting conditions. Besides, changes in amino acid profiles were observed, which may play crucial roles in the regulation of energy metabolism, neurotransmitter signaling, and anti-inflammatory and antioxidant in response to STF. Additionally, this study reported, for the first time, that STF triggers a significant elevation of N-acylethanolamines, a class of neuroprotective lipids, in the brain and liver. These findings provide novel insights into the molecular basis and mechanisms of CR and offer a comprehensive resource for further investigation.

Metabolic intervention by low carbohydrate diet suppresses the onset and progression of neuroendocrine tumors

Insulin signaling often plays a role in the regulation of cancer, including tumor initiation, progression, and response to treatment. In addition, the insulin-regulated PI3K-Akt-mTOR pathway plays an important role in the regulation of islet cell proliferation, and this pathway is hyperactivated in human non-functional pancreatic neuroendocrine tumors (PanNETs). We, therefore, investigated the effect of a very low carbohydrate diet (ketogenic diet) on a mouse model that develops non-functional PanNETs to ask how reduced PI3K-Akt-mTOR signaling might affect the development and progression of non-functional PanNET. We found that this dietary intervention resulted in lower PI3K-Akt-mTOR signaling in islet cells and a significant reduction in PanNET formation and progression. We also found that this treatment had a significant effect on the suppression of pituitary NET development. Furthermore, we found that non-functional PanNET patients with lower blood glucose levels tend to have a better prognosis than patients with higher blood glucose levels. This preclinical study shows that a dietary intervention that results in lower serum insulin levels leads to lower insulin signals within the neuroendocrine cells and has a striking suppressive effect on the development and progression of both pancreatic and pituitary NETs.

p21-activated kinase 4 suppresses fatty acid β-oxidation and ketogenesis by phosphorylating NCoR1

PPARα corepressor NCoR1 is a key regulator of fatty acid β-oxidation and ketogenesis. However, its regulatory mechanism is largely unknown. Here, we report that oncoprotein p21-activated kinase 4 (PAK4) is an NCoR1 kinase. Specifically, PAK4 phosphorylates NCoR1 at T1619/T2124, resulting in an increase in its nuclear localization and interaction with PPARα, thereby repressing the transcriptional activity of PPARα. We observe impaired ketogenesis and increases in PAK4 protein and NCoR1 phosphorylation levels in liver tissues of high fat diet-fed mice, NAFLD patients, and hepatocellular carcinoma patients. Forced overexpression of PAK4 in mice represses ketogenesis and thereby increases hepatic fat accumulation, whereas genetic ablation or pharmacological inhibition of PAK4 exhibites an opposite phenotype. Interestingly, PAK4 protein levels are significantly suppressed by fasting, largely through either cAMP/PKA- or Sirt1-mediated ubiquitination and proteasome degradation. In this way, our findings provide evidence for a PAK4-NCoR1/PPARα signaling pathway that regulates fatty acid β-oxidation and ketogenesis.

Hepatocyte-specific loss of LAP2α protects against diet-induced hepatic steatosis, steatohepatitis, and fibrosis in male mice

There is increasing evidence for the importance of the nuclear envelope in lipid metabolism, nonalcoholic fatty liver disease (NAFLD), and nonalcoholic steatohepatitis (NASH). Human mutations in LMNA, encoding A-type nuclear lamins, cause early-onset insulin resistance and NASH, while hepatocyte-specific deletion of Lmna predisposes to NASH with fibrosis in male mice. Given that variants in the gene encoding LAP2α, a nuclear protein that regulates lamin A/C, were previously identified in patients with NAFLD, we sought to determine the role of LAP2α in NAFLD using a mouse genetic model. Hepatocyte-specific Lap2α-knockout (Lap2α(ΔHep)) mice and littermate controls were fed normal chow or high-fat diet (HFD) for 8 wk or 6 mo. Unexpectedly, male Lap2α(ΔHep) mice showed no increase in hepatic steatosis or NASH compared with controls. Rather, Lap2α(ΔHep) mice demonstrated reduced hepatic steatosis, with decreased NASH and fibrosis after long-term HFD. Accordingly, pro-steatotic genes including Cidea, Mogat1, and Cd36 were downregulated in Lap2α(ΔHep) mice, along with concomitant decreases in expression of pro-inflammatory and pro-fibrotic genes. These data indicate that hepatocyte-specific Lap2α deletion protects against hepatic steatosis and NASH in mice and raise the possibility that LAP2α could become a potential therapeutic target in human NASH.NEW & NOTEWORTHY The nuclear envelope and lamina regulate lipid metabolism and susceptibility to nonalcoholic steatohepatitis (NASH), but the role of the nuclear lamin-binding protein LAP2α in NASH has not been explored. Our data demonstrate that hepatocyte-specific loss of LAP2α protects against diet-induced hepatic steatosis, NASH, and fibrosis in male mice, with downregulation of pro-steatotic, pro-inflammatory, and pro-fibrotic lamin-regulated genes. These findings suggest that targeting LAP2α could have future potential as a novel therapeutic avenue in NASH.

Insulin resistance and adipose tissue interactions as the cornerstone of metabolic (dysfunction)-associated fatty liver disease pathogenesis

The relationship between metabolic derangements and fatty liver development are undeniable, since more than 75% of patients with type 2 diabetes mellitus present with fatty liver. There is also significant epidemiological association between insulin resistance (IR) and metabolic (dysfunction)-associated fatty liver disease (MAFLD). For little more than 2 years, the nomenclature of fatty liver of non-alcoholic origin has been intended to change to MAFLD by multiple groups. While a myriad of reasons for which MAFLD is thought to be of metabolic origin could be exposed, the bottom line relies on the role of IR as an initiator and perpetuator of this disease. There is a reciprocal role in MAFLD development and IR as well as serum glucose concentrations, where increased circulating glucose and insulin result in increased de novo lipogenesis by sterol regulatory element-binding protein-1c induced lipogenic enzyme stimulation; therefore, increased endogenous production of triglycerides. The same effect is achieved through impaired suppression of adipose tissue (AT) lipolysis in insulin-resistant states, increasing fatty acid influx into the liver. The complementary reciprocal situation occurs when liver steatosis alters hepatokine secretion, modifying fatty acid metabolism as well as IR in a variety of tissues, including skeletal muscle, AT, and the liver. The aim of this review is to discuss the importance of IR and AT interactions in metabolic altered states as perhaps the most important factor in MAFLD pathogenesis.

Rhein for treating diabetes mellitus: A pharmacological and mechanistic overview

With the extension of life expectancy and changes in lifestyle, the prevalence of diabetes mellitus is increasing worldwide. Rheum palmatum L. a natural botanical medicine, has been used for thousands of years to prevent and treat diabetes mellitus in Eastern countries. Rhein, the main active component of rhubarb, is a 1, 8-dihydroxy anthraquinone derivative. Previous studies have extensively explored the clinical application of rhein. However, a comprehensive review of the antidiabetic effects of rhein has not been conducted. This review summarizes studies published over the past decade on the antidiabetic effects of rhein, covering the biological characteristics of Rheum palmatum L. and the pharmacological effects and pharmacokinetic characteristics of rhein. The review demonstrates that rhein can prevent and treat diabetes mellitus by ameliorating insulin resistance, possess anti-inflammatory and anti-oxidative stress properties, and protect islet cells, thus providing a theoretical basis for the application of rhein as an antidiabetic agent.

Brain histone beta-hydroxybutyrylation couples metabolism with gene expression

Little is known about the impact of metabolic stimuli on brain tissue at a molecular level. The ketone body beta-hydroxybutyrate (BHB) can be a signaling molecule regulating gene transcription. Thus, we assessed lysine beta-hydroxybutyrylation (K-bhb) levels in proteins extracted from the cerebral cortex of mice undergoing a ketogenic metabolic challenge (48 h fasting). We found that fasting enhanced K-bhb in a variety of proteins including histone H3. ChIP-seq experiments showed that K9 beta-hydroxybutyrylation of H3 (H3K9-bhb) was significantly enriched by fasting on more than 8000 DNA loci. Transcriptomic analysis showed that H3K9-bhb on enhancers and promoters correlated with active gene expression. One of the most enriched functional annotations both at the epigenetic and transcriptional level was "circadian rhythms''. Indeed, we found that the diurnal oscillation of specific transcripts was modulated by fasting at distinct zeitgeber times both in the cortex and suprachiasmatic nucleus. Moreover, specific changes in locomotor activity daily features were observed during re-feeding after 48-h fasting. Thus, our results suggest that fasting remarkably impinges on the cerebral cortex transcriptional and epigenetic landscape, and BHB acts as a powerful epigenetic molecule in the brain through direct and specific histone marks remodeling in neural tissue cells.

Intestinal peroxisome proliferator-activated receptor α-fatty acid-binding protein 1 axis modulates nonalcoholic steatohepatitis

BACKGROUND AND AIMS

Peroxisome proliferator-activated receptor α (PPARα) regulates fatty acid transport and catabolism in liver. However, the role of intestinal PPARα in lipid homeostasis is largely unknown. Here, intestinal PPARα was examined for its modulation of obesity and NASH.

APPROACH AND RESULTS

Intestinal PPARα was activated and fatty acid-binding protein 1 (FABP1) up-regulated in humans with obesity and high-fat diet (HFD)-fed mice as revealed by using human intestine specimens or HFD/high-fat, high-cholesterol, and high-fructose diet (HFCFD)-fed C57BL/6N mice and PPARA -humanized, peroxisome proliferator response element-luciferase mice. Intestine-specific Ppara or Fabp1 disruption in mice fed a HFD or HFCFD decreased obesity-associated metabolic disorders and NASH. Molecular analyses by luciferase reporter assays and chromatin immunoprecipitation assays in combination with fatty acid uptake assays in primary intestinal organoids revealed that intestinal PPARα induced the expression of FABP1 that in turn mediated the effects of intestinal PPARα in modulating fatty acid uptake. The PPARα antagonist GW6471 improved obesity and NASH, dependent on intestinal PPARα or FABP1. Double-knockout ( Ppara/Fabp1ΔIE ) mice demonstrated that intestinal Ppara disruption failed to further decrease obesity and NASH in the absence of intestinal FABP1. Translationally, GW6471 reduced human PPARA-driven intestinal fatty acid uptake and improved obesity-related metabolic dysfunctions in PPARA -humanized, but not Ppara -null, mice.

CONCLUSIONS

Intestinal PPARα signaling promotes NASH progression through regulating dietary fatty acid uptake through modulation of FABP1, which provides a compelling therapeutic target for NASH treatment.

Protein Targeting to Glycogen (PTG): A Promising Player in Glucose and Lipid Metabolism

Protein phosphorylation and dephosphorylation are widely considered to be the key regulatory factors of cell function, and are often referred to as "molecular switches" in the regulation of cell metabolic processes. A large number of studies have shown that the phosphorylation/dephosphorylation of related signal molecules plays a key role in the regulation of liver glucose and lipid metabolism. As a new therapeutic strategy for metabolic diseases, the potential of using inhibitor-based therapies to fight diabetes has gained scientific momentum. PTG, a protein phosphatase, also known as glycogen targeting protein, is a member of the protein phosphatase 1 (PP1) family. It can play a role by catalyzing the dephosphorylation of phosphorylated protein molecules, especially regulating many aspects of glucose and lipid metabolism. In this review, we briefly summarize the role of PTG in glucose and lipid metabolism, and update its role in metabolic regulation, with special attention to glucose homeostasis and lipid metabolism.

Cyclosorus terminans Extract Ameliorates Insulin Resistance and Non-Alcoholic Fatty Liver Disease (NAFLD) in High-Fat Diet (HFD)-Induced Obese Rats

Interruptins A and B exhibited anti-diabetic, anti-inflammatory, and anti-oxidative effects. This study aimed to investigate the therapeutic ability of extract enriched by interruptins A and B (EEI) from an edible fern Cyclosorus terminans on insulin resistance and non-alcoholic fatty liver disease (NAFLD) in a high-fat diet (HFD)-induced obese rats and elucidate their possible mechanisms. HFD-induced obese rats were treated with EEI for 2 weeks. Real-time polymerase chain reaction (PCR) was used to examine the molecular basis. We found that EEI supplementation significantly attenuated body and liver weight gain, glucose intolerance, and insulin resistance. Concurrently, EEI increased liver and soleus muscle glycogen storage and serum high-density lipoprotein (HDL) levels. EEI also attenuated NAFLD, as indicated by improving liver function. These effects were associated with enhanced expression of insulin signaling genes (Slc2a2, Slc2a4, Irs1 and Irs2) along with diminished expression of inflammatory genes (Il6 and Tnf). Furthermore, EEI led to the suppression of lipogenesis genes, Srebf1 and Fasn, together with an increase in fatty acid oxidation genes, Ppara and Cpt2, in the liver. These findings suggest that EEI could ameliorate HFD-induced insulin resistance and NAFLD via improving insulin signaling pathways, inflammatory response, lipogenesis, and fatty acid oxidation.

Dietary Histidine Supplementation Maintained Amino Acid Homeostasis and Reduced Hepatic Lipid Accumulation of Juvenile Largemouth Bass, Micropterus Salmoides

This 56-day research aimed to evaluate the recommended histidine requirement and the influence of dietary histidine levels on the protein and lipid metabolism of juvenile largemouth bass (Mieropterus salmoides). The initial weight of the largemouth bass was 12.33 ± 0.01 g, which was fed with six graded levels of histidine. The results showed that appropriate dietary histidine had a positive effect on growth, with a higher specific growth rate, final weight, weight gain rate, protein efficiency rate, and a lower feed conversion rate and feed intake rate being observed in 1.08-1.48% dietary histidine groups. Furthermore, the mRNA levels of GH, IGF-1, TOR, and S6 showed an increasing trend first and then declined, similar to the trend of the growth and protein content of the whole body composition. Meanwhile, dietary histidine levels could be sensed by the AAR signaling pathway, representing as downregulation of core genes of AAR signaling pathway with the increased dietary histidine levels, including GCN2, eIF2α, CHOP, ATF4, and REDD1. In addition, increased dietary histidine levels decreased the lipid content of the whole body and the liver by upregulating the mRNA levels of core genes of the PPARα signaling pathways, including PPARα, CPT1, L-FABP, and PGC1α. However, increased dietary histidine levels downregulated the mRNA levels of core genes of the PPARγ signaling pathways such as PPARγ, FAS, ACC, SREBP1, and ELOVL2. These findings were also supported by the positive area ratio of hepatic oil red O staining and the TC content of plasma. According to the specific growth rate and feed conversion rate, the recommended histidine requirement of juvenile largemouth bass was 1.26% of the diet (2.68% of dietary protein) by regression lines calculated using a quadratic model. In general, histidine supplementation promoted protein synthesis and lipid decomposition and reduced lipid synthesis by activating the TOR, AAR, PPARα, and PPARγ signaling pathways, which provided a new perspective to solve the fatty liver problem of largemouth bass by nutritional means.

Circadian clock controls rhythms in ketogenesis by interfering with PPARα transcriptional network

Ketone bodies are energy-rich metabolites and signaling molecules whose production is mainly regulated by diet. Caloric restriction (CR) is a dietary intervention that improves metabolism and extends longevity across the taxa. We found that CR induced high-amplitude daily rhythms in blood ketone bodies (beta-hydroxybutyrate [βOHB]) that correlated with liver βOHB level. Time-restricted feeding, another periodic fasting-based diet, also led to rhythmic βOHB but with reduced amplitude. CR induced strong circadian rhythms in the expression of fatty acid oxidation and ketogenesis genes in the liver. The transcriptional factor peroxisome-proliferator-activated-receptor α (PPARα) and its transcriptional target hepatokine fibroblast growth factor 21 (FGF21) are primary regulators of ketogenesis. Fgf21 expression and the PPARα transcriptional network became highly rhythmic in the CR liver, which implicated the involvement of the circadian clock. Mechanistically, the circadian clock proteins CLOCK, BMAL1, and cryptochromes (CRYs) interfered with PPARα transcriptional activity. Daily rhythms in the blood βOHB level and in the expression of PPARα target genes were significantly impaired in circadian clock-deficient Cry1,2^-/- mice. These data suggest that blood βOHB level is tightly controlled and that the circadian clock is a regulator of diet-induced ketogenesis.

Noncoding RNAs Associated with PPARs in Etiology of MAFLD as a Novel Approach for Therapeutics Targets

Background. Metabolic associated fatty liver disease (MAFLD) is a complex disease that results from the accumulation of fat in the liver. MAFLD is directly associated with obesity, insulin resistance, diabetes, and metabolic syndrome. PPARγ ligands, including pioglitazone, are also used in the management of this disease. Noncoding RNAs play a critical role in various diseases such as diabetes, obesity, and liver diseases including MAFLD. However, there is no adequate knowledge about the translation of using these ncRNAs to the clinics, particularly in MAFLD conditions. The aim of this study was to identify ncRNAs in the etiology of MAFLD as a novel approach to the therapeutic targets. Methods. We collected human and mouse MAFLD gene expression datasets available in GEO. We performed pathway enrichment analysis of total mRNAs based on KEGG repository data to screen the most potential pathways in the liver of MAFLD human subjects and mice model, and analyzed pathway interconnections via ClueGO. Finally, we screened disease causality of the MAFLD ncRNAs, which were associated with PPARs, and then discussed the role of revealed ncRNAs in PPAR signaling and MAFLD. Results. We found 127 ncRNAs in MAFLD which 25 out of them were strongly validated before for regulation of PPARs. With a polypharmacology approach, we screened 51 ncRNAs which were causal to a subset of diseases related to MAFLD. Conclusion. This study revealed a subset of ncRNAs that could help in more clear and guided designation of preclinical and clinical studies to verify the therapeutic application of the revealed ncRNAs by manipulating the PPARs molecular mechanism in MAFLD.

Effect of Hesperidin Supplementation on Liver Metabolomics and Gut Microbiota in a High-Fat Diet-Induced NAFLD Mice Model

The present study investigated the mechanism underlying the impact of hesperidin (HES) on nonalcoholic fatty liver (NAFLD). C57BL/6J male mice were administered a low-fat diet, high-fat diet (HFD), or HFD plus 0.2% (wt/wt) HES (HFD + HES) diet. After 16 weeks of intervention, the mice in the HFD+HES group showed a lower final body weight and liver weight and improved serum lipid profiles when compared with the HFD group. Alleviation of liver dysfunction induced by HFD was observed in HES-fed mice, and the expression of genes involved in lipid metabolism was also altered. Moreover, HES changed the composition of the intestinal microbiota and enriched specific genera such as Bacteroidota. Liver metabolomics analysis indicated that HES enhanced the abundance of metabolites in arginine-related as well as mitochondrial oxidation-related pathways, and these metabolites were predicted to be positively correlated with the gut genera enriched by HES. Together, these results indicate that HFD-fed mice supplemented with HES showed a markedly regulated hepatic metabolism concurrent with shifts in specific gut bacteria.

Natural PPARs agonists for the treatment of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a general term for a series of liver diseases including simple steatosis, non-alcoholic steatohepatitis, liver fibrosis, which is closely related to metabolic syndrome. The pathogenesis of NAFLD is relatively complex, which has gradually changed from the previous 'two-hit' hypothesis to the current "multiple hits" hypothesis. However, there is currently no approved treatment for NAFLD in clinic, highlighting the urgent need for drug development. Peroxisome proliferator activated receptors (PPARs) are members of the nuclear receptor superfamily, whose different subtypes have been proved to regulate different stages of NAFLD, thus becoming promising drug targets for NAFLD. As important sources of drug development, natural products have been proven to treat NAFLD through multiple pathways and multiple targets. In this paper, we outline the regulatory role of PPARs in NAFLD, and summarize some natural products that target PPARs to ameliorate NAFLD, in order to provide reference for drug development of NAFLD.

Hypothalamic-pituitary-adrenal axis activation and glucocorticoid-responsive gene expression in skeletal muscle and liver of Apc mice

BACKGROUND

Cancer patients at advanced stages experience a severe depletion of skeletal muscle compartment together with a decrease in muscle function, known as cancer cachexia. Cachexia contributes to reducing quality of life, treatment efficiency, and lifespan of cancer patients. However, the systemic nature of the syndrome is poorly documented. Here, we hypothesize that glucocorticoids would be important systemic mediators of cancer cachexia.

METHODS

To explore the role of glucocorticoids during cancer cachexia, biomolecular analyses were performed on several tissues (adrenal glands, blood, hypothalamus, liver, and skeletal muscle) collected from Apc^Min/+ male mice, a mouse model of intestine and colon cancer, aged of 13 and 23 weeks, and compared with wild type age-matched C57BL/6J littermates.

RESULTS

Twenty-three-week-old Apc mice recapitulated important features of cancer cachexia including body weight loss (-16%, P < 0.0001), muscle atrophy (gastrocnemius muscle: -53%, P < 0.0001), and weakness (-50% in tibialis anterior muscle force, P < 0.0001), increased expression of atrogens (7-fold increase in MuRF1 transcript level, P < 0.0001) and down-regulation of Akt-mTOR pathway (3.3-fold increase in 4EBP1 protein content, P < 0.0001), together with a marked transcriptional rewiring of hepatic metabolism toward an increased expression of gluconeogenic genes (Pcx: +90%, Pck1: +85%), and decreased expression of glycolytic (Slc2a2: -40%, Gk: -30%, Pklr: -60%), ketogenic (Hmgcs2: -55%, Bdh1: -80%), lipolytic/fatty oxidation (Lipe: -50%, Mgll: -60%, Cpt2: -60%, Hadh: -30%), and lipogenic (Acly: -30%, Acacb: -70%, Fasn: -45%) genes. The hypothalamic pituitary-adrenal axis was activated, as evidenced by the increase in the transcript levels of genes encoding corticotropin-releasing hormone in the hypothalamus (2-fold increase, P < 0.01), adrenocorticotropic hormone receptor (3.4-fold increase, P < 0.001), and steroid biosynthesis enzymes (Cyp21a1, P < 0.0001, and Cyp11b1, P < 0.01) in the adrenal glands, as well as by the increase in corticosterone level in the serum (+73%, P < 0.05), skeletal muscle (+17%, P < 0.001), and liver (+24%, P < 0.05) of cachectic 23-week-old Apc mice. A comparative transcriptional analysis with dexamethasone-treated C57BL/6J mice indicated that the activation of the hypothalamic-pituitary-adrenal axis in 23-week-old Apc^Min/+ mice was significantly associated with the transcription of glucocorticoid-responsive genes in skeletal muscle (P < 0.05) and liver (P < 0.001). The transcriptional regulation of glucocorticoid-responsive genes was also observed in the gastrocnemius muscle of Lewis lung carcinoma tumour-bearing mice and in KPC mice (tibialis anterior muscle and liver).

CONCLUSIONS

These findings highlight the role of the hypothalamic-pituitary-adrenal-glucocorticoid pathway in the transcriptional regulation of skeletal muscle catabolism and hepatic metabolism during cancer cachexia. They also provide the paradigm for the design of new therapeutic strategies.

An fgf21-like gene from swamp eel (Monopterus albus): Recombinant expression and its potential roles in glucose and lipid homeostasis

Fibroblast growth factor 21 (FGF21) plays important roles in the regulation of glucose and lipid metabolism and energy balance in mammals. In this study, the full-length cDNA of swamp eel fgf21 was cloned. Sequence analysis showed that swamp eel FGF21 displayed high similarity with FGF21 of other vertebrates. Subsequently, a prokaryotic expression vector for swamp eel fgf21 was constructed, and recombinant FGF21 (rFGF21) was successfully induced and purified. To investigate the potential roles of swamp eel FGF21 in glucose and lipid metabolism, we examined the effects of rFGF21 on regulation of glucose and lipid homeostasis in type 1 diabetes mellitus (T1DM) mice as well as swamp eels under glucose stress. In T1DM mice, the levels of blood glucose, serum triglyceride (TG), liver TG, serum total cholesterol (TC), and liver TC were significantly downregulated after repeated daily injection of rFGF21 for 15 days. In addition, liver pathological section analysis indicated that rFGF21 alleviated the degree of damage to liver cells in T1DM mice. Furthermore, rFGF21 significantly upregulated the mRNA expression levels of peroxisome proliferators-activated receptor alpha (Pparα), β-Klotho, fibroblast growth factor receptor 1 (Fgfr1), phosphoenolpyruvate carboxykinase (Pepck), glucose transporter 1 (Glut1), and glucose transporter 4 (Glut4) in T1DM mouse livers. Moreover, in swamp eels, rFGF21 significantly decreased blood glucose and liver TC levels under glucose stress and upregulated the mRNA expression levels of fgf21, pparα, β-klotho, and fgfr1 in liver tissue. These results suggested that FGF21 plays important roles in the regulation of glucose and lipid homeostasis in swamp eel.

Sepsis: a failing starvation response

Sepsis is involved in ~ 20% of annual global deaths. Despite decades of research, the current management of sepsis remains supportive rather than curative. Clinical trials in sepsis have mainly been focused on targeting the inflammatory pathway, but without success. Recent data indicate that metabolic dysregulation takes place in sepsis, and targeting metabolic pathways might hold much promise for the management of sepsis. Sepsis yields a strong starvation response, including the release of high-energy metabolites such as lactate and free fatty acids. However, the activity of two major transcription factors, GR and PPARα, is downregulated in hepatocytes, leading to the accumulation and toxicity of metabolites that, moreover, fail to be transformed into useful molecules such as glucose and ketones. We review the literature and suggest mechanisms and potential therapeutic targets that might prevent or revert the fatal metabolic dysregulation in sepsis.

A Network Pharmacology Study on the Active Components and Targets of the Radix Ginseng and Radix Bupleuri Herb Pair for Treating Nonalcoholic Fatty Liver Disease

OBJECTIVE

To explore the potential active components and corresponding target herb pairs of Radix Ginseng (Renshen) and Radix Bupleuri (Chaihu) in the treatment of nonalcoholic fatty liver disease (NAFLD) through network pharmacology and in vitro experiments.

METHODS

The active components and potential targets of the herb pair of Renshen and Chaihu were screened through a network database system, and Venn analysis was performed with the obtained NAFLD targets. The intersecting targets were analysed for gene ontology (GO) functions and Kyoto Encyclopedia of Genes and Genome (KEGG) pathways, and a protein-protein interaction (PPI) network was generated. Cytoscape software was used to construct active component-target networks of the Renshen and Chaihu herb pair. Free fatty acids were added to the HepG2 cell line to create high-fat models that were treated with different concentrations of stigmasterol. The effect of stigmasterol on the lipid metabolism in HepG2 cells and PPARγ-knockdown cells was determined by oil red O staining, Nile red staining, and TG level. PPARγ and UCP-1 mRNA, and protein expression levels were detected by qRT-PCR and Western blot analyses, respectively.

RESULTS

Twenty active components obtained from the Renshen and Chaihu herb pair were identified. The herb pair active component-target network showed that both Renshen and Chaihu contained stigmasterol and kaempferol as active components. The PPI network comprised 63 protein nodes. GO enrichment analysis and KEGG pathway enrichment analysis showed that the targets were mainly involved in lipid metabolism. Eight core targets were identified: AKT1, PPARG, MAPK3, TNF, TP53, SIRT1, STAT3, and PPARA. In vitro experiments demonstrated that stigmasterol reduced lipid accumulation and TG levels in HepG2 cells, and the mechanism may have been related to the activation of the PPARγ-UCP-1 signalling pathway.

CONCLUSION

This study preliminarily illustrated the potential components and corresponding core targets of the Renshen and Chaihu herb pair in treating NAFLD. The effect of stigmasterol on the PPARγ-UCP-1 signalling pathway in enhancing lipid metabolism may represent one of the mechanisms of the Renshen and Chaihu herb pair in the treatment of NAFLD. The results provide new evidence and research insights to reveal the roles of Renshen and Chaihu in the management of NAFLD.

Expressing the Human Cholesteryl Ester Transfer Protein Minigene Improves Diet-Induced Fatty Liver and Insulin Resistance in Female Mice

Mounting evidence has shown that CETP has important physiological roles in adapting to chronic nutrient excess, specifically, to protect against diet-induced insulin resistance. However, the underlying mechanisms for the protective roles of CETP in metabolism are not yet clear. Mice naturally lack CETP expression. We used transgenic mice with a human CETP minigene (huCETP) controlled by its natural flanking region to further understand CETP-related physiology in response to obesity. Female huCETP mice and their wild-type littermates were fed a high-fat diet for 6 months. Blood lipid profile and liver lipid metabolism were studied. Insulin sensitivity was analyzed with euglycemic-hyperinsulinemic clamp studies combined with ³H-glucose tracer techniques. While high-fat diet feeding induced obesity for huCETP mice and their wild-type littermates lacking CETP expression, insulin sensitivity was higher for female huCETP mice than for their wild-type littermates. There was no difference in insulin sensitivity for male huCETP mice vs. littermates. The increased insulin sensitivity in females was largely caused by the better insulin-mediated suppression of hepatic glucose production. In huCETP females, CETP in the circulation decreased HDL-cholesterol content and increased liver cholesterol uptake and liver cholesterol and oxysterol contents, which was associated with the upregulation of LXR target genes in long-chain polyunsaturated fatty acid biosynthesis and PPARα target genes in fatty acid β-oxidation in the liver. The upregulated fatty acid β-oxidation may account for the improved fatty liver and liver insulin action in female huCETP mice. This study provides further evidence that CETP has beneficial physiological roles in the metabolic adaptation to nutrient excess by promoting liver fatty acid oxidation and hepatic insulin sensitivity, particularly for females.

Perinatal Food Deprivation Modifies the Caloric Restriction Response in Adult Mice Through Sirt1

Variations in the availability of nutritional resources in animals can trigger reversible adjustments, which in the short term are manifested as behavioral and physiological changes. Several of these responses are mediated by Sirt1, which acts as an energy status sensor governing a global genetic program to cope with changes in nutritional status. Growing evidence suggests a key role of the response of the perinatal environment to caloric restriction in the setup of physiological responses in adulthood. The existence of adaptive predictive responses has been proposed, which suggests that early nutrition could establish metabolic capacities suitable for future food-scarce environments. We evaluated how perinatal food deprivation and maternal gestational weight gain impact the transcriptional, physiological, and behavioral responses in mice, when acclimated to caloric restriction in adulthood. Our results show a strong predictive capacity of maternal weight and gestational weight gain, in the expression of Sirt1 and its downstream targets in the brain and liver, mitochondrial enzymatic activity in skeletal muscle, and exploratory behavior in offspring. We also observed differential responses of both lactation and gestational food restriction on gene expression, thermogenesis, organ masses, and behavior, in response to adult caloric restriction. We conclude that the early nutritional state could determine the magnitude of responses to food scarcity later in adulthood, mediated by the pivotal metabolic sensor Sirt1. Our results suggest that maternal gestational weight gain could be an important life history trait and could be used to predict features that improve the invasive capacity or adjustment to seasonal food scarcity of the offspring.

Catalase deficiency facilitates the shuttling of free fatty acid to brown adipose tissue through lipolysis mediated by ROS during sustained fasting

Background

Fatty acids (FA) derived from adipose tissue and liver serve as the main fuel in thermogenesis of brown adipose tissue (BAT). Catalase, a peroxisomal enzyme, plays an important role in maintaining intracellular redox homeostasis by decomposing hydrogen peroxide to either water or oxygen that oxidize and provide fuel for cellular metabolism. Although the antioxidant enzymatic activity of catalase is well known, its role in the metabolism and maintenance of energy homeostasis has not yet been revealed. The present study investigated the role of catalase in lipid metabolism and thermogenesis during nutrient deprivation in catalase-knockout (KO) mice.

Results

We found that hepatic triglyceride accumulation in KO mice decreased during sustained fasting due to lipolysis through reactive oxygen species (ROS) generation in adipocytes. Furthermore, the free FA released from lipolysis were shuttled to BAT through the activation of CD36 and catabolized by lipoprotein lipase in KO mice during sustained fasting. Although the exact mechanism for the activation of the FA receptor enzyme, CD36 in BAT is still unclear, we found that ROS generation in adipocytes mediated the shuttling of FA to BAT.

Conclusions

Taken together, our findings uncover the novel role of catalase in lipid metabolism and thermogenesis in BAT, which may be useful in understanding metabolic dysfunction.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00710-5.

The pleiotropic peroxisome proliferator activated receptors: Regulation and therapeutics

The Peroxisome proliferator-activated receptors (PPARs) are key regulators of metabolic events in our body. Owing to their implication in maintenance of homeostasis, both PPAR agonists and antagonists assume therapeutic significance. Understanding the molecular mechanisms of each of the PPAR isotypes in the healthy body and during disease is crucial to exploiting their full therapeutic potential. This article is an attempt to present a rational analysis of the multifaceted therapeutic effects and underlying mechanisms of isotype-specific PPAR agonists, dual PPAR agonists, pan PPAR agonists as well as PPAR antagonists. A holistic understanding of the mechanistic dimensions of these key metabolic regulators will guide future efforts to identify novel molecules in the realm of metabolic, inflammatory and immunotherapeutic diseases.

Intravital Two-photon Imaging of Dynamic Alteration of Hepatic Lipid Droplets in Fasted and Refed State

Objective

The liver plays a central role in lipid metabolism. During fasting and feeding, the fatty acid trafficking between adipose tissue and liver induces accumulation and dissociation of dynamic hepatic lipid droplets (LDs). Herein, we established an intravital 2-photon imaging technique to longitudinally visualize the dynamic in vivo alteration of hepatic LD deposition during fasting and refeeding in the liver of live mouse.

Methods

Intravital 2-photon imaging of liver was performed to observe hepatic LD alteration induced by fasting for different periods of time, 12, 24, and 48 hours followed by refeeding. Hepatic LDs were fluorescently labelled in vivo by intravenous injection of Seoul-Flour 44 and visualized by custom-built intravital 2-photon microscope.

Results

Significant increases of the number and size of hepatic LDs were observed by intravital 2-photon imaging of the liver after 12 hours of fasting. The degree of hepatic LD accumulation continuously increased with fasting up to 48 hours. Remarkably, with refeeding for 24 hours, the hepatic LDs accumulated by fasting were fully dissociated and the LD occupancy in the liver was recovered to the normal state.

Conclusion

Utilizing intravital 2-photon microscope with in vivo systemic fluorescent labeling of LD in live mice, dynamic alterations of hepatic LDs such as accumulation and dissociation by fasting and refeeding were successfully visualized at a subcellular level in vivo. The established method enabling the in vivo visualization of LDs will be a useful tool to investigate the pathophysiology of various diseases associated with dysregulated lipid metabolism.

BHBA regulates the expressions of lipid synthesis and oxidation genes in sheep hepatocytes through the AMPK pathway

Pregnancy toxemia (PT) is the most frequent metabolic disease of sheep during late pregnancy, which can lead to enormous economic losses in sheep farm industry. However, the underlying mechanism of PT in sheep has not been fully elucidated. High levels of β-hydroxy butyric acid (BHBA) exist in PT sheep. The AMP-activated protein kinase (AMPK) pathway plays a major role in regulating liver function. The aim of this study was to explore the effects of gradient concentrations of BHBA on lipid metabolism of sheep hepatocytes and the underlying molecular mechanism in vitro. The results showed that 0.6, 1.2 mmol/L BHBA could activate AMPKα, promoted the expressions of peroxisome proliferator-activated receptor alpha (PPARα) and its target genes, and inhibited the expressions of sterol regulatory element binding protein-1c (SREBP-1c) as well as its downstream genes. When the concentration of BHBA was beyond 1.2 mmol/L, the expressions of the above-mentioned proteins and genes were just the opposite. However, the expressions of adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) did not change significantly. The levels of very low density lipoprotein (VLDL), triglyceride (TG) and cholesterol (T-CHOL) showed a gradually increasing trend with the increase of BHBA concentration. According to the results above, it demonstrates that high levels of BHBA can inhibit the expression of the AMPK pathway and cause lipid metabolism disorders in sheep hepatocytes, which may lead to the occurrence of PT.

Perspectives on Mitochondria-ER and Mitochondria-Lipid Droplet Contact in Hepatocytes and Hepatic Lipid Metabolism

Emerging evidence suggests that mitochondrion–endoplasmic reticulum (ER) and mitochondrion–lipid droplet (LD) contact sites are critical in regulating lipid metabolism in cells. It is well established that intracellular organelles communicate with each other continuously through membrane contact sites to maintain organelle function and cellular homeostasis. The accumulation of LDs in hepatocytes is an early indicator of non-alcoholic fatty liver disease (NAFLD) and alcohol-related liver disease (ALD), which may indicate a breakdown in proper inter-organelle communication. In this review, we discuss previous findings in mitochondrion–ER and mitochondrion–LD contact, focusing on their roles in lipid metabolism in hepatocytes. We also present evidence of a unique mitochondrion–LD contact structure in hepatocytes under various physiological and pathological conditions and propose a working hypothesis to speculate about the role of these structures in regulating the functions of mitochondria and LDs and their implications in NAFLD and ALD.

Nuclear CoRepressors, NCOR1 and SMRT, are required for maintaining systemic metabolic homeostasis

Objective

The nuclear receptor corepressor 1 (NCOR1) and the silencing mediator of retinoic acid and thyroid hormone (SMRT, also known as NCOR2) play critical and specific roles in nuclear receptor action. NCOR1, both in vitro and in vivo specifically regulates thyroid hormone (TH) action in the context of individual organs such as the liver, and systemically in the context of the hypothalamic-pituitary-thyroid (HPT) axis. In contrast, selective deletion of SMRT in the liver or globally has shown that it plays very little role in TH signaling. However, both NCOR1 and SMRT have some overlapping roles in hepatic metabolism and lipogenesis. Here, we determine the roles of NCOR1 and SMRT in global physiologic function and find if SMRT could play a compensatory role in the regulation of TH action, globally.

Methods

We used a postnatal deletion strategy to disrupt both NCOR1 and SMRT together in all tissues at 8–9 weeks of age in male and female mice. This was performed using a tamoxifen-inducible Cre recombinase (UBC-Cre-ERT2) to KO (knockout) NCOR1, SMRT, or NCOR1 and SMRT together. We used the same strategy to KO HDAC3 in male and female mice of the same age. Metabolic parameters, gene expression, and thyroid function tests were analyzed.

Results

Surprisingly, adult mice that acquired NCOR1 and SMRT deletion rapidly became hypoglycemic and hypothermic and perished within ten days of deletion of both corepressors. Postnatal deletion of either NCOR1 or SMRT had no impact on mortality. NCOR1/SMRT KO mice rapidly developed hepatosteatosis and mild elevations in liver function tests. Additionally, alterations in lipogenesis, beta oxidation, along with hepatic triglyceride and glycogen levels suggested defects in hepatic metabolism. The intestinal function was intact in the NCOR1/SMRT knockout (KO) mice. The KO of HDAC3 resulted in a distinct phenotype from the NCOR1/SMRT KO mice, whereas none of the HDAC3 KO mice succumbed after tamoxifen injection.

Conclusions

The KO of NCOR1 and SMRT rapidly leads to significant metabolic abnormalities that do not survive – including hypoglycemia, hypothermia, and weight loss. Hepatosteatosis rapidly developed along with alterations in hepatic metabolism suggesting a contribution to the dramatic phenotype from liver injury. Glucose production and absorption were intact in NCOR1/SMRT KO mice, demonstrating a multifactorial process leading to their demise. HDAC3 KO mice have a distinct phenotype from the NCOR1/SMRT KO mice—which implies that NCOR1/SMRT together regulate a critical pathway that is required for survival in adulthood and is separate from HDAC3.

•

The knockout of corepressors NCoR1 and SMRT is rapidly lethal.

•

Metabolic abnormalities observed include hypoglycemia and hypothermia.

•

Hepatic glucose production and intestinal absorption is intact despite hypoglycemia.

•

The lethal action of NCoR1/SMRT deletion is independent of HDAC3.

2-Adrenergic receptor agonist induced hepatic steatosis in mice: modeling nonalcoholic fatty liver disease in hyperadrenergic states

Nonalcoholic fatty liver disease (NAFLD) is a spectrum of disorders ranging from hepatic steatosis [excessive accumulation of triglycerides (TG)] to nonalcoholic steatohepatitis, which can progress to cirrhosis and hepatocellular carcinoma. The molecular pathogenesis of steatosis and progression to more severe NAFLD remains unclear. Obesity and aging, two principal risk factors for NAFLD, are associated with a hyperadrenergic state. β-Adrenergic responsiveness in liver increases in animal models of obesity and aging, and in both is linked to increased hepatic expression of β2-adrenergic receptors (β2-ARs). We previously showed that in aging rodents intracellular signaling from elevated hepatic levels of β2-ARs may contribute to liver steatosis. In this study we demonstrate that injection of formoterol, a highly selective β2-AR agonist, to mice acutely results in hepatic TG accumulation. Further, we have sought to define the intrahepatic mechanisms underlying β2-AR mediated steatosis by investigating changes in hepatic expression and cellular localization of enzymes, transcription factors, and coactivators involved in processes of lipid accrual and disposition-and also functional aspects thereof-in livers of formoterol-treated animals. Our results suggest that β2-AR activation by formoterol leads to increased hepatic TG synthesis and de novo lipogenesis, increased but incomplete β-oxidation of fatty acids with accumulation of potentially toxic long-chain acylcarnitine intermediates, and reduced TG secretion-all previously invoked as contributors to fatty liver disease. Experiments are ongoing to determine whether sustained activation of hepatic β2-AR signaling by formoterol might be utilized to model fatty liver changes occurring in hyperadrenergic states of obesity and aging, and thereby identify novel molecular targets for the prevention or treatment of NAFLD.NEW & NOTEWORTHY Results of our study suggest that β2-adrenergic receptor (β2-AR) activation by agonist formoterol leads to increased hepatic TG synthesis and de novo lipogenesis, incomplete β-oxidation of fatty acids with accumulation of long-chain acylcarnitine intermediates, and reduced TG secretion. These findings may, for the first time, implicate a role for β2-AR responsive dysregulation of hepatic lipid metabolism in the pathogenetic processes underlying NAFLD in hyperadrenergic states such as obesity and aging.

ZBTB32 performs crosstalk with the glucocorticoid receptor and is crucial in glucocorticoid responses to starvation

The hypothalamic-pituitary-adrenal (HPA) axis forms a complex neuroendocrine system that regulates the body’s response to stress such as starvation. In contrast with the glucocorticoid receptor (GR), Zinc finger and BTB domain containing 32 (ZBTB32) is a transcription factor with poorly described functional relevance in physiology. This study shows that ZBTB32 is essential for the production of glucocorticoids (GCs) in response to starvation, since ZBTB32^−/− mice fail to increase their GC production in the absence of nutrients. In terms of mechanism, GR-mediated upregulation of adrenal Scarb1 gene expression was absent in ZBTB32^−/− mice, implicating defective cholesterol import as the cause of the poor GC synthesis. These lower GC levels are further associated with aberrations in the metabolic adaptation to starvation, which could explain the progressive weight gain of ZBTB32^−/− mice. In conclusion, ZBTB32 performs a crosstalk with the GR in the metabolic adaptation to starvation via regulation of adrenal GC production.

•

ZBTB32 is involved in the glucocorticoid production in response to starvation

•

GR-mediated upregulation of adrenal Scarb1 regulates cholesterol import

•

The weight gain of ZBTB32^−/− mice is associated with aberrant metabolic adaptations