PGC1A regulates the IRS1:IRS2 ratio during fasting to influence hepatic metabolism downstream of insulin

Hydroxymethylglutaryl-CoA reductase activity is essential for mitochondrial β-oxidation of fatty acids to prevent lethal accumulation of long-chain acylcarnitines in the mouse liver

BACKGROUND AND PURPOSE

Statins are competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMGCR), and exert adverse effects on mitochondrial function, although the mechanisms underlying these effects remain unclear. We used a tamoxifen-induced Hmgcr-knockout (KO) mouse model, a multi-omics approach and mitochondrial function assessments to investigate whether decreased HMGCR activity impacts key liver energy metabolism pathways.

EXPERIMENTAL APPROACH

We established a new mouse strain using the Cre/loxP system, which enabled whole-body deletion of Hmgcr expression. These mice were crossed with Rosa26Cre mice and treated with tamoxifen to delete Hmgcr in all cells. We performed transcriptomic and metabolomic analyses and thus evaluated time-dependent changes in metabolic functions to identify the pathways leading to cell death in Hmgcr-KO mice.

KEY RESULTS

Lack of Hmgcr expression resulted in lethality, due to acute liver damage caused by rapid disruption of mitochondrial fatty acid β-oxidation and very high accumulation of long-chain (LC) acylcarnitines in both male and female mice. Gene expression and KO-related phenotype changes were not observed in other tissues. The progression to liver failure was driven by diminished peroxisome formation, which resulted in impaired mitochondrial and peroxisomal fatty acid metabolism, enhanced glucose utilization and whole-body hypoglycaemia.

CONCLUSION AND IMPLICATIONS

Our findings suggest that HMGCR is crucial for maintaining energy metabolism balance, and its activity is necessary for functional mitochondrial β-oxidation. Moreover, statin-induced adverse reactions might be rescued by the prevention of LC acylcarnitine accumulation.

Calorie restriction and life-extending mutation downregulate miR-34a to facilitate lipid metabolism in the liver

Ames dwarf mice (df/df) display delayed aging relative to their normal (N) siblings, living approximately 40-60 % longer. As such, investigating the mechanisms that enable these organisms to have extended lifespan is useful for the development of interventions to slow aging and deter age-related disease. Nonalcoholic fatty liver disease (NAFLD) is a condition that is characterized by the accumulation of excess adipose tissue in the liver. Previous studies highlight the potential of calorie restriction (CR) in promoting longevity, but little is known about its effects on the biomolecular processes that govern NAFLD. In this study, we examined the role of 6-month CR on genes regulating lipid metabolism in the livers of long-living df/df mice and their N littermates. Importantly, our findings showed significant downregulation of miR-34a-5p in N-CR mice and df/df mice regardless of dietary regimen. Alongside, our RT-PCR results indicated that downregulation of miR-34a-5p is correlated with the expression of metabolism-associated mRNAs involved in modulating the processes of de novo lipogenesis (DNL), fatty acid oxidation (FAO), very-low density lipoprotein transport (VLDL-T), and reverse cholesterol transport (RCT). To further verify the role of miR-34a-5p in regulating metabolic processes, we transfected the human liver cancer (HepG2) cell line with miR-34a mimic, and studied its effect on direct targets Sirt1, Ampk, and Ppara as well as downstream lipid transport regulating genes. Our findings suggest that CR and df/df life extending mutation are robust drivers of the miR-34a-5p signaling pathway and prevent the pathogenesis of age-related diseases by improving overall lipid homeostasis.

IFNγ-IL12 axis regulates intercellular crosstalk in metabolic dysfunction-associated steatotic liver disease

Obesity is a major cause of metabolic dysfunction-associated steatohepatitis (MASH) and is characterized by inflammation and insulin resistance. Interferon-γ (IFNγ) is a pro-inflammatory cytokine elevated in obesity and modulating macrophage functions. Here, we show that male mice with loss of IFNγ signaling in myeloid cells (Lyz-IFNγR2-/-) are protected from diet-induced insulin resistance despite fatty liver. Obesity-mediated liver inflammation is also attenuated with reduced interleukin (IL)-12, a cytokine primarily released by macrophages, and IL-12 treatment in vivo causes insulin resistance by impairing hepatic insulin signaling. Following MASH diets, Lyz-IFNγR2-/- mice are rescued from developing liver fibrosis, which is associated with reduced fibroblast growth factor (FGF) 21 levels. These results indicate critical roles for IFNγ signaling in macrophages and their release of IL-12 in modulating obesity-mediated insulin resistance and fatty liver progression to MASH. In this work, we identify the IFNγ-IL12 axis in regulating intercellular crosstalk in the liver and as potential therapeutic targets to treat MASH.

Adaptive Effects of Endocrine Hormones on Metabolism of Macronutrients during Fasting and Starvation: A Scoping Review

Food deprivation can occur for different reasons. Fasting (<24 h duration) occurs to meet religious or well-being goals. Starvation (>1-day duration) occurs when there is intentional (hunger strike or treatment of a medical condition) or unintentional (anorexia nervosa, drought, epidemic famine, war, or natural disaster) food deprivation. A scoping review was undertaken using the PubMed database to explore 1805 abstracts and review 88 eligible full-text articles to explore the adaptive relationships that emerge between cortisol, insulin, glucagon, and thyroid hormones on the metabolic pathways of macronutrients in humans during fasting and starvation. The collected data indicate that fasting and starvation prime the human body to increase cortisol levels and decrease the insulin/glucagon ratio and triiodothyronine (T3) levels. During fasting, increased levels of cortisol and a decreased insulin/glucagon ratio enhance glycogenolysis and reduce the peripheral uptake of glucose and glycogenesis, whereas decreased T3 levels potentially reduce glycogenolysis. During starvation, increased levels of cortisol and a decreased insulin/glucagon ratio enhance lipolysis, proteolysis, fatty acid and amino acid oxidation, ketogenesis, and ureagenesis, and decreased T3 levels reduce thermogenesis. We present a potential crosstalk between T3 and the above hormones, including between T3 and leptin, to extend their adaptive roles in the metabolism of endogenous macronutrients during food deprivation.

Chrysanthemum morifolium Ramat extract and probiotics combination ameliorates metabolic disorders through regulating gut microbiota and PPARα subcellular localization

BACKGROUND

Chrysanthemum morifolium Ramat, a traditional Chinese medicine, has the effects on liver clearing, vision improving, and anti-inflammation. C. morifolium and probiotics have been individually studied for their beneficial effects on metabolic diseases. However, the underlying molecular mechanisms were not completely elucidated. This study aims to elucidate the potential molecular mechanisms of C. morifolium and probiotics combination (CP) on alleviating nonalcoholic fatty liver disease (NAFLD) and the dysregulation of glucose metabolism in high-fat diet (HFD)-fed mice.

METHODS

The therapeutic effect of CP on metabolism was evaluated by liver histology and serum biochemical analysis, as well as glucose tolerance test. The impact of CP on gut microbiota was analyzed by 16S rRNA sequencing and fecal microbiota transplantation. Hepatic transcriptomic analysis was performed with the key genes and proteins validated by RT-qPCR and western blotting. In addition, whole body Pparα knockout (Pparα-/-) mice were used to confirm the CP-mediated pathway.

RESULTS

CP supplementation ameliorated metabolic disorders by reducing body weight and hepatic steatosis, and improving glucose intolerance and insulin resistance in HFD fed mice. CP intervention mitigated the HFD-induced gut microbiota dysbiosis, which contributed at least in part, to the beneficial effect of improving glucose metabolism. In addition, hepatic transcriptomic analysis showed that CP modulated the expression of genes associated with lipid metabolism. CP downregulated the mRNA level of lipid droplet-binding proteins, such as Cidea and Cidec in the liver, leading to more substrates for fatty acid oxidation (FAO). Meanwhile, the expression of CPT1α, the rate-limiting enzyme of FAO, was significantly increased upon CP treatment. Mechanistically, though CP didn't affect the total PPARα level, it promoted the nuclear localization of PPARα, which contributed to the reduced expression of Cidea and Cidec, and increased expression of CPT1α, leading to activated FAO. Moreover, whole body PPARα deficiency abolished the anti-NAFLD effect of CP, suggesting the importance of PPARα in CP-mediated beneficial effect.

CONCLUSION

This study revealed the hypoglycemic and hepatoprotective effect of CP by regulating gut microbiota composition and PPARα subcellular localization, highlighting its potential for therapeutic candidate for metabolic disorders.

Subacute cadmium exposure changes different metabolic functions, leading to type 1 and 2 diabetes mellitus features in female rats

Cadmium (Cd) is a heavy metal that acts as endocrine disrupting chemical (EDC). Few studies have investigated the effects of Cd exposure on metabolic dysfunctions, such as type 1 and 2 diabetes mellitus (T1DM and T2DM). Thus, we assessed whether subacute Cd exposure at occupational levels causes abnormalities in white adipose tissue (WAT), liver, pancreas, and skeletal muscle. We administered cadmium chloride (CdCl2) (100 ppm in drinking water for 30 days) to female rats and evaluated Cd levels in serum and metabolic organs, morphophysiology, inflammation, oxidative stress, fibrosis, and gene expression. High Cd levels were found in serum, WAT, liver, pancreas, and skeletal muscle. Cd-exposed rats showed low adiposity, dyslipidemia, insulin resistance, systemic inflammation, and oxidative stress compared to controls. Cd exposure reduced adipocyte size, hyperleptinemia, increased cholesterol levels, inflammation, apoptosis and fibrosis in WAT. Cd-exposed rats had increased liver cholesterol levels, insulin receptor beta (IRβ) and peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC1α) expression, karyomegaly, inflammation, and fibrosis. Cd exposure reduced insulin levels and pancreatic islet size and increased inflammation and fibrosis. Cd exposure reduced skeletal muscle fiber diameter and increased IR expression and inflammation. Finally, strong positive correlations were observed between serum, tissue Cd levels, abnormal morphology, tissue inflammation and fibrosis. Thus, these data suggest that subacute Cd exposure impairs WAT, liver, pancreas and skeletal muscle function, leading to T1DM and T2DM features and other complications in female rats.

High-fat diet induced obesity promotes inflammation, oxidative stress, and hepatotoxicity in female FVB/N mice

Although obesity and subsequent liver injury are increasingly prevalent in women, female mouse models have generally shown resistance to high-fat diet (HFD)-induced obesity. We evaluated control and HFD-fed male and female FVB/N mice, a strain well-suited to transgenic analyses, for phenotypic, histological, and molecular markers related to control of glucose, lipids, and inflammation in serum, liver, and perigonadal white adipose tissues. Unlike many mouse models, HFD-fed FVB/N females gained more perigonadal and mesenteric fat mass and overall body weight than their male counterparts, with increased hepatic expression of lipogenic PPARγ target genes (Cd36, Fsp27, and Fsp27β), oxidative stress genes and protein (Nqo1 and CYP2E1), inflammatory gene (Mip-2), and the pro-fibrotic gene Pai-1, along with increases in malondialdehyde and serum ALT levels. Further, inherent to females (independently of HFD), hepatic antioxidant heme oxygenase-1 (HMOX1, HO-1) protein levels were reduced compared to their male counterparts. In contrast, males may have been relatively protected from HFD-induced oxidative stress and liver injury by elevated mRNA and protein levels of hepatic antioxidants BHMT and Gpx2, increased fatty acid oxidation genes in liver and adipocytes (Pparδ), despite disorganized and inflamed adipocytes. Thus, female FVB/N mice offer a valuable preclinical, genetically malleable model that recapitulates many of the features of diet-induced obesity and liver damage observed in human females.

High Glucose Levels Promote Switch to Synthetic Vascular Smooth Muscle Cells via Lactate/GPR81

Hyperglycemia, lipotoxicity, and insulin resistance are known to increase the secretion of extracellular matrix from cardiac fibroblasts as well as the activation of paracrine signaling from cardiomyocytes, immune cells, and vascular cells, which release fibroblast-activating mediators. However, their influences on vascular smooth muscle cells (vSMCs) have not been well examined. This study aimed to investigate whether contractile vascular vSMCs could develop a more synthetic phenotype in response to hyperglycemia. The results showed that contractile and synthetic vSMCs consumed high glucose in different ways. Lactate/GPR81 promotes the synthetic phenotype in vSMCs in response to high glucose levels. The stimulation of high glucose was associated with a significant increase in fibroblast-like features: synthetic vSMC marker expression, collagen 1 production, proliferation, and migration. GPR81 expression is higher in blood vessels in diabetic patients and in the high-glucose, high-lipid diet mouse. The results demonstrate that vSMCs assume a more synthetic phenotype when cultured in the presence of high glucose and, consequently, that the high glucose could trigger a vSMC-dependent cardiovascular disease mechanism in diabetes via lactate/GPR81.

The analysis of fatty acids and their derivatives in the liver of C57BL/6 mice with long-term caloric restrictions

Caloric restriction (CR) is a dietetic intervention based on the reduction of daily calorie intake by 10-30 %. When subjected to CR, the organism adjusts its metabolism to the changing availability of key nutrients. However, fatty acids' content in organisms subjected to long-term CR has not been evaluated. The aim of the research was to analyze the influence of long-term CR on the contents of medium- and long-chain fatty acids, as well as on the contents of fatty acid derivatives in liver. The study was performed on C57BL female (n = 12) and male (n = 12) mice subjected to lifelong 30 % calorie restriction. Fatty acids were analyzed using gas chromatography, while fatty acid derivatives were analyzed with liquid chromatography. The dynamics of change of the lipid profile of the labeled fatty acids observed in the liver tissue confirms that lipolysis actively takes place in this organ when hungry. Moreover, it is highly possible that de novo synthesis of acids takes place, with the aim to ensure energy substrates to the body. Moreover, an increase of concentration was observed for fatty acid derivatives, those with anti-inflammatory properties (resolvin, LTX A4). However, there was no increase in the concentration of pro-inflammatory eicosanoids. The results suggest that it is important to take into consideration the introduction of appropriate supplements when using CR.

A low-carbohydrate diet with different fatty acids' sources in the treatment of obesity: Impact on insulin resistance and adipogenesis

BACKGROUND

The search for nutritional intervention strategies against obesity has grown, highlighting the low-carbohydrate diet model. However, little is known about the impact of the quality of fatty acids consumed in this diet. Thus, we aim to investigate the influence of fatty acid quality on dietary strategy on obesity.

METHODS

Male Swiss mice were diet-induced to obesity. Afterward, mice consume a low-carb diet with different types of fat: saturated, polyunsaturated ω-3, ω-6, and monounsaturated ω-9 fatty acids. Weight gain and food consumption were monitored weekly. An oral glucose tolerance test was performed and blood and tissue samples were collected for analysis of insulin resistance markers. Protein expression of insulin signaling pathway molecules, lipid metabolism, mitochondrial function, macrophage polarization, and cytokine production were analyzed.

RESULTS

The high-fat diet was able to induce obesity and glucose intolerance. The switch to a low-carbohydrate dietary pattern reversed the glucose intolerance, with better results in the ω-3 and ω-9 groups. After the low-carbohydrate diet, groups ω-3 and ω-9 presented improved fasting serum glucose, insulin, and HOMA indexes. The low-carbohydrate diet also increased the activity of insulin pathway proteins such as IR, IRS1, and AKT. Furthermore, the ω-3 diet group showed greater activity of mitochondrial complexes and AMPK signaling pathway proteins. The ω-6 and ω-9 -rich diet induced M2-type macrophage polarization, as well as cytokine production modulation by the low-carbohydrate diet in the ω-3 and ω-9 groups.

CONCLUSIONS

Consuming a low-carbohydrate diet pattern promotes weight loss and improves glucose intolerance in obesity. Also, the quality of lipids has a direct influence, demonstrating that the consumption of ω-3 polyunsaturated and ω-9 monounsaturated lipids can lead to more favorable outcomes for the improvement of glucose intolerance, lipid metabolism, and anti-inflammatory effects.

Molecular mechanisms involved in fetal programming and disease origin in adulthood

Fetal programming occurs during the gestational age when exposure to environmental stimuli can cause long-term changes in the fetus, predisposing it to develop chronic non-communicable diseases (CNCD) in adulthood. Herein, we summarized the role of low-calorie or high-fat diets during pregnancy as fetal programming agents that induce intrauterine growth restriction (IUGR), amplified de novo lipogenesis, and increased amino acid transport to the placenta, which favor the CNCD onset in the offspring. We also outlined how maternal obesity and gestational diabetes act as fetal programming stimuli by reducing iron absorption and oxygen transport to the fetus, stimulating inflammatory pathways that boost neurological disorders and CNCD in the progeny. Moreover, we reviewed the mechanisms through which fetal hypoxia elevates the offspring's risk of developing hypertension and chronic kidney disease in adult life by unbalancing the renin-angiotensin system and promoting kidney cell apoptosis. Finally, we examined how inadequate vitamin B12 and folic acid consumption during pregnancy programs the fetus to greater adiposity, insulin resistance, and glucose intolerance in adulthood. A better understanding of the fetal programming mechanisms may help us reduce the onset of insulin resistance, glucose intolerance, dyslipidemia, obesity, hypertension, diabetes mellitus, and other CNCD in the offspring during adulthood.

Effects of quercetin on hepatic fibroblast growth factor-21 (FGF-21) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) levels in rats fed with high fructose

BACKGROUND

Available studies show that quercetin reduces Metabolic Syndrome (MetS) and its complications, increases insulin sensitivity and improves glucose levels. It has been reported that the increase in hepatic gene expressions of fibroblast growth factor-21 (FGF-21), an important metabolic regulator of insulin sensitivity, glucose and energy homeostasis, and peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), which plays a central role in the regulation of cellular energy metabolism, eliminate the negative effects of fructose in fructose-fed rats. The main purpose of our study is to examine the effects of quercetin on hepatic FGF-21 and PGC-1α expressions and levels, as well as its protective and therapeutic role on MetS components in rats fed with fructose.

METHODS AND RESULTS

In our study, 24 Sprague Dawley male rats were divided into 4 groups: control, fructose, quercetin, fructose+quercetin (n = 6). During the 10-week experiment, quercetin was administered at a daily dose of 15 mg/kg body weight and fructose at a rate of 20%. Blood pressure and weights of all groups were measured and recorded. At the end of week 10, blood and liver tissue samples were taken. Serum insulin, glucose and triglyceride, total, HDL and VLDL cholesterol levels were determined from the samples. Insulin resistance was calculated using the HOMA-IR formula. Hepatic PGC-1α and FGF-21 protein levels and their mRNA expressions were determined. Criteria for metabolic syndrome were successfully established with fructose. It was observed that the administration of quercetin alone and in combination with fructose exerted positive effects and improved MetS criteria. It was determined that the administration of quercetin increased hepatic FGF-21 and PGC-1α protein levels and Messenger RNA (mRNA) expressions of them, which were decreased by fructose application.

CONCLUSIONS

The results of our study showed that 10-week administration of quercetin at 15 mg/kg exerted beneficial effects on lipid and carbohydrate metabolism in the fructose-mediated MetS model; therefore, quercetin may have great potential in the prevention and treatment of metabolic disorders.

Pleiotropic and multi-systemic actions of physical exercise on PGC-1α signaling during the aging process

Physical training is a potent therapeutic approach for improving mitochondrial health through peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) signaling pathways. However, comprehensive information regarding the physical training impact on PGC-1α in the different physiological systems with advancing age is not fully understood. This review sheds light on the frontier-of-knowledge data regarding the chronic effects of exercise on the PGC-1α signaling pathways in rodents and humans. We address the molecular mechanisms involved in the different tissues, clarifying the precise biological action of PGC-1α, restricted to the aged cell type. Distinct exercise protocols (short and long-term) and modalities (aerobic and resistance exercise) increase the transcriptional and translational PGC-1α levels in adipose tissue, brain, heart, liver, and skeletal muscle in animal models, suggesting that this versatile molecule induces pleiotropic responses. However, PGC-1α function in some human tissues (adipose tissue, heart, and brain) remains challenging for further investigations. PGC-1α is not a simple transcriptional coactivator but supports a biochemical environment of mitochondrial dynamics, controlling physiological processes (primary metabolism, tissue remodeling, autophagy, inflammation, and redox balance). Acting as an adaptive mechanism, the long-term effects of PGC-1α following exercise may reflect the energy demand to coordinate multiple organs and contribute to cellular longevity.

Dietary Methionine Restriction Improves Gastrocnemius Muscle Glucose Metabolism through Improved Insulin Secretion and H19/IRS-1/Akt Pathway in Middle-Aged Mice

Methionine restriction (MR) improves glucose metabolism. In skeletal muscle, H19 is a key regulator of insulin sensitivity and glucose metabolism. Therefore, this study aims to reveal the underlying mechanism of H19 upon MR on glucose metabolism in skeletal muscle. Middle-aged mice were fed MR diet for 25 weeks. Mouse islets β cell line β-TC6 cells and mouse myoblast cell line C2C12 cells were used to establish the apoptosis or insulin resistance model. Our findings showed that MR increased B-cell lymphoma-2 (Bcl-2) expression, deceased Bcl-2 associated X protein (Bax), cleaved cysteinyl aspartate-specific proteinase-3 (Caspase-3) expression in pancreas, and promoted insulin secretion of β-TC6 cells. Meanwhile, MR increased H19 expression, insulin Receptor Substrate-1/insulin Receptor Substrate-2 (IRS-1/IRS-2) value, protein Kinase B (Akt) phosphorylation, glycogen synthase kinase-3β (GSK3β) phosphorylation, and hexokinase 2 (HK2) expression in gastrocnemius muscle and promoted glucose uptake in C2C12 cells. But these results were reversed after H19 knockdown in C2C12 cells. In conclusion, MR alleviates pancreatic apoptosis and promotes insulin secretion. And MR enhances gastrocnemius muscle insulin-dependent glucose uptake and utilization via the H19/IRS-1/Akt pathway, thereby ameliorating blood glucose disorders and insulin resistance in high-fat-diet (HFD) middle-aged mice.

Low Protein Programming Causes Increased Mitochondrial Fusion and Decreased Oxygen Consumption in the Hepatocytes of Female Rats

The liver is one of the major organs involved in the regulation of glucose and lipid homeostasis. The effectiveness of metabolic activity in hepatocytes is determined by the quality and quantity of its mitochondria. Mitochondrial function is complex, and they act via various dynamic networks, which rapidly adapt to changes in the cellular milieu. Our present study aims to investigate the effects of low protein programming on the structure and function of mitochondria in the hepatocytes of adult females. Pregnant rats were fed with a control or isocaloric low-protein diet from gestational day 4 until delivery. A normal laboratory chow was given to all dams after delivery and to pups after weaning. The rats were euthanized at 4 months of age and the livers were collected from female offspring for investigating the mitochondrial structure, mtDNA copy number, mRNA, and proteins expression of genes associated with mitochondrial function. Primary hepatocytes were isolated and used for the analysis of the mitochondrial bioenergetics profiles. The mitochondrial ultrastructure showed that the in utero low-protein diet exposure led to increased mitochondrial fusion. Accordingly, there was an increase in the mRNA and protein levels of the mitochondrial fusion gene Opa1 and mitochondrial biogenesis genes Pgc1a and Essra, but Fis1, a fission gene, was downregulated. Low protein programming also impaired the mitochondrial function of the hepatocytes with a decrease in basal respiration ATP-linked respiration and proton leak. In summary, the present study suggests that the hepatic mitochondrial dysfunction induced by an in utero low protein diet might be a potential mechanism linking glucose intolerance and insulin resistance in adult offspring.

Fasting: From Physiology to Pathology

Overnutrition is a risk factor for various human diseases, including neurodegenerative diseases, metabolic disorders, and cancers. Therefore, targeting overnutrition represents a simple but attractive strategy for the treatment of these increasing public health threats. Fasting as a dietary intervention for combating overnutrition has been extensively studied. Fasting has been practiced for millennia, but only recently have its roles in the molecular clock, gut microbiome, and tissue homeostasis and function emerged. Fasting can slow aging in most species and protect against various human diseases, including neurodegenerative diseases, metabolic disorders, and cancers. These centuried and unfading adventures and explorations suggest that fasting has the potential to delay aging and help prevent and treat diseases while minimizing side effects caused by chronic dietary interventions. In this review, recent animal and human studies concerning the role and underlying mechanism of fasting in physiology and pathology are summarized, the therapeutic potential of fasting is highlighted, and the combination of pharmacological intervention and fasting is discussed as a new treatment regimen for human diseases.

Differential Roles of CD36 in Regulating Muscle Insulin Response Depend on Palmitic Acid Load

The possible role of fatty acid translocase (CD36) in the treatment of obesity has gained increasing research interest since researchers recognized its coordinated function in fatty acid uptake and oxidation. However, the effect of CD36 deficiency on intracellular insulin signaling is complex and its impact may depend on different nutritional stresses. Therefore, we investigated the various effects of CD36 deletion on insulin signaling in C2C12 myotubes with or without palmitic acid (PA) overload. In the present work, we reported the upregulated expression levels of CD36 in the skeletal muscle tissues of obese humans and mice as well as in C2C12 myotubes with PA stimulation. CD36 knockdown using RNA interference showed that insulin signaling was impaired in CD36-deficient C2C12 cells in the absence of PA loading, suggesting that CD36 is essential for the maintenance of insulin action, possibly resulting from increased mitochondrial dysfunction and endoplasmic reticulum (ER) stress; however, CD36 deletion improved insulin signaling in the presence of PA overload due to a reduction in lipid overaccumulation. In conclusion, we identified differential roles of CD36 in regulating muscle insulin response under conditions with and without PA overload, which provides supportive evidence for further research into therapeutic approaches to diabetes.

Whole grains-derived functional ingredients against hyperglycemia: targeting hepatic glucose metabolism

Type 2 diabetes mellitus (T2DM) is characterized by the dysregulation of glucose homeostasis, resulting in hyperglycemia. However, concerns have been raised about the safety and efficacy of current hypoglycemic drugs due to undesirable side effects. Increasing studies have shown that whole grains (WG) consumption is inversely associated with the risk of T2DM and its subsequent complications. Thus, dietary strategies involving functional components from the WG provide an intriguing approach to restoring and maintaining glucose homeostasis. This review provides a comprehensive understanding of the major functional components derived from WG and their positive effects on glucose homeostasis, demonstrates the underlying molecular mechanisms targeting hepatic glucose metabolism, and discusses the unclear aspects according to the latest viewpoints and current research. Improved glycemic response and insulin resistance were observed after consumption of WG-derived bioactive ingredients, which are involved in the integrated, multi-factorial, multi-targeted regulation of hepatic glucose metabolism. Promotion of glucose uptake, glycolysis, and glycogen synthesis pathways, while inhibition of gluconeogenesis, contributes to amelioration of abnormal hepatic glucose metabolism and insulin resistance by bioactive components. Hence, the development of WG-based functional food ingredients with potent hypoglycemic properties is necessary to manage insulin resistance and T2DM.

Pre-Diabetes-Linked miRNA miR-193b-3p Targets PPARGC1A, Disrupts Metabolic Gene Expression Profile and Increases Lipid Accumulation in Hepatocytes: Relevance for MAFLD

Distinct plasma microRNA profiles associate with different disease features and could be used to personalize diagnostics. Elevated plasma microRNA hsa-miR-193b-3p has been reported in patients with pre-diabetes where early asymptomatic liver dysmetabolism plays a crucial role. In this study, we propose the hypothesis that elevated plasma hsa-miR-193b-3p conditions hepatocyte metabolic functions contributing to fatty liver disease. We show that hsa-miR-193b-3p specifically targets the mRNA of its predicted target PPARGC1A/PGC1α and consistently reduces its expression in both normal and hyperglycemic conditions. PPARGC1A/PGC1α is a central co-activator of transcriptional cascades that regulate several interconnected pathways, including mitochondrial function together with glucose and lipid metabolism. Profiling gene expression of a metabolic panel in response to overexpression of microRNA hsa-miR-193b-3p revealed significant changes in the cellular metabolic gene expression profile, including lower expression of MTTP, MLXIPL/ChREBP, CD36, YWHAZ and GPT, and higher expression of LDLR, ACOX1, TRIB1 and PC. Overexpression of hsa-miR-193b-3p under hyperglycemia also resulted in excess accumulation of intracellular lipid droplets in HepG2 cells. This study supports further research into potential use of microRNA hsa-miR-193b-3p as a possible clinically relevant plasma biomarker for metabolic-associated fatty liver disease (MAFLD) in dysglycemic context.

Regulation of Liver Glucose and Lipid Metabolism by Transcriptional Factors and Coactivators

The prevalence of nonalcoholic fatty liver disease (NAFLD) worldwide is on the rise and NAFLD is becoming the most common cause of chronic liver disease. In the USA, NAFLD affects over 30% of the population, with similar occurrence rates reported from Europe and Asia. This is due to the global increase in obesity and type 2 diabetes mellitus (T2DM) because patients with obesity and T2DM commonly have NAFLD, and patients with NAFLD are often obese and have T2DM with insulin resistance and dyslipidemia as well as hypertriglyceridemia. Excessive accumulation of triglycerides is a hallmark of NAFLD and NAFLD is now recognized as the liver disease component of metabolic syndrome. Liver glucose and lipid metabolisms are intertwined and carbon flux can be used to generate glucose or lipids; therefore, in this review we discuss the important transcription factors and coactivators that regulate glucose and lipid metabolism.

Comprehensive Analysis of the lncRNA-miRNA-mRNA Regulatory Network for Intramuscular Fat in Pigs

Intramuscular fat (IMF) is an essential trait closely related to meat quality. The IMF trait is a complex quantitative trait that is regulated by multiple genes. In order to better understand the process of IMF and explore the key factors affecting IMF deposition, we identified differentially expressed mRNA, miRNA, and lncRNA in the longissimus dorsi muscle (LD) between Songliao Black (SL) pigs and Landrace pigs. We obtained 606 differentially expressed genes (DEGs), 55 differentially expressed miRNAs (DEMs), and 30 differentially expressed lncRNAs (DELs) between the SL pig and Landrace pig. Enrichment results from GO and KEGG indicate that DEGs are involved in fatty acid metabolism and some pathways related to glycogen synthesis. We constructed an lncRNA-miRNA-mRNA interaction network with 18 DELs, 11 DEMs, and 42 DEGs. Finally, the research suggests that ARID5B, CPT1B, ACSL1, LPIN1, HSP90AA1, IRS1, IRS2, PIK3CA, PIK3CB, and PLIN2 may be the key genes affecting IMF deposition. The LncRNAs MSTRG.19948.1, MSTRG.13120.1, MSTRG.20210.1, and MSTRG.10023.1, and the miRNAs ssc-miRNA-429 and ssc-miRNA-7-1, may play a regulatory role in IMF deposition through their respective target genes. Our research provides a reference for further understanding the regulatory mechanism of IMF.

TSC22D4 interacts with Akt1 to regulate glucose metabolism

Maladaptive insulin signaling is a key feature in the pathogenesis of severe metabolic disorders, including obesity and diabetes. Enhancing insulin sensitivity represents a major goal in the treatment of patients affected by diabetes. Here, we identify transforming growth factor-β1 stimulated clone 22 D4 (TSC22D4) as a novel interaction partner for protein kinase B/Akt1, a critical mediator of insulin/phosphatidylinositol 3-kinase signaling pathway. While energy deprivation and oxidative stress promote the TSC22D4-Akt1 interaction, refeeding mice or exposing cells to glucose and insulin impairs this interaction, which relies on an intrinsically disordered region (D2 domain) within TSC22D4. Functionally, the interaction with TSC22D4 reduces basal phosphorylation of Akt and its downstream targets during starvation, thereby promoting insulin sensitivity. Genetic, liver-specific reconstitution experiments in mice demonstrate that the interaction between TSC22D4 and Akt1 improves glucose handling and insulin sensitivity. Overall, our findings postulate a model whereby TSC22D4 acts as an environmental sensor and interacts with Akt1 to regulate insulin signaling and glucose metabolism.

Hepatic mTORC2 Signaling Facilitates Acute Glucagon Receptor Enhancement of Insulin-Stimulated Glucose Homeostasis in Mice

Long-term glucagon receptor (GCGR) agonism is associated with hyperglycemia and glucose intolerance, while acute GCGR agonism enhances whole-body insulin sensitivity and hepatic AKTSer473 phosphorylation. These divergent effects establish a critical gap in knowledge surrounding GCGR action. mTOR complex 2 (mTORC2) is composed of seven proteins, including RICTOR, which dictates substrate binding and allows for targeting of AKTSer473. We used a liver-specific Rictor knockout mouse (RictorΔLiver) to investigate whether mTORC2 is necessary for insulin receptor (INSR) and GCGR cross talk. RictorΔLiver mice were characterized by impaired AKT signaling and glucose intolerance. Intriguingly, RictorΔLiver mice were also resistant to GCGR-stimulated hyperglycemia. Consistent with our prior report, GCGR agonism increased glucose infusion rate and suppressed hepatic glucose production during hyperinsulinemic-euglycemic clamp of control animals. However, these benefits to insulin sensitivity were ablated in RictorΔLiver mice. We observed diminished AKTSer473 and GSK3α/βSer21/9 phosphorylation in RictorΔLiver mice, whereas phosphorylation of AKTThr308 was unaltered in livers from clamped mice. These signaling effects were replicated in primary hepatocytes isolated from RictorΔLiver and littermate control mice, confirming cell-autonomous cross talk between GCGR and INSR pathways. In summary, our study reveals the necessity of RICTOR, and thus mTORC2, in GCGR-mediated enhancement of liver and whole-body insulin action.

Identification of Potential miRNA-mRNA Regulatory Network Contributing to Parkinson’s Disease

Parkinson's disease (PD) is a common neurodegenerative disease, and the mechanism underlying PD pathogenesis is not completely understood. Increasing evidence indicates that microRNAs (miRNAs) play a critical regulatory role in the pathogenesis of PD. This study aimed to explore the miRNA-mRNA regulatory network for PD. The differentially expressed miRNAs (DEmis) and genes (DEGs) between PD patients and healthy donors were screened from the miRNA dataset GSE16658 and mRNA dataset GSE100054 downloaded from the Gene Expression Omnibus (GEO) database. Target genes of the DEmis were selected when they were predicted by three or four online databases and overlapped with DEGs from GSE100054. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were then conducted by Database for Annotation, Visualization and Integrated Discovery (DAVID) and Metascape analytic tools. The correlation between the screened genes and PD was evaluated with the online tool Comparative Toxicogenomics Database (CTD), and protein-protein interaction (PPI) networks were built by the STRING platform. We further investigated the expression of genes in the miRNA-mRNA regulatory network in blood samples collected from PD patients and healthy donors via qRT-PCR. We identified 1505 upregulated and 1302 downregulated DEGs, and 77 upregulated and 112 downregulated DEmis were preliminarily screened from the GEO database. Further functional enrichment analysis identified 10 PD-related hub genes, including RAC1, IRS2, LEPR, PPARGC1A, CAMKK2, RAB10, RAB13, RAB27B, RAB11A, and JAK2, which were mainly involved in Rab protein signaling transduction, AMPK signaling pathway, and signaling by Leptin. A miRNA-mRNA regulatory network was then constructed with 10 hub genes, and their interacting miRNAs overlapped with DEmis, including miR-30e-5p, miR-142-3p, miR-101-3p, miR-32-3p, miR-508-5p, miR-642a-5p, miR-19a-3p, and miR-21-5p. Analysis of clinical samples verified significant upregulation of LEPR and downregulation of miR-101-3p and miR-30e-5p in PD patients as compared with healthy donors. Thus, the miRNA-mRNA regulatory network was initially constructed and has the potential to provide novel insights into the pathogenesis and treatment of PD.

Cross Talk Between Insulin and Glucagon Receptor Signaling in the Hepatocyte

While the consumption of external energy (i.e., feeding) is essential to life, this action induces a temporary disturbance of homeostasis in an animal. A primary example of this effect is found in the regulation of glycemia. In the fasted state, stored energy is released to maintain physiological glycemic levels. Liver glycogen is liberated to glucose, glycerol and (glucogenic) amino acids are used to build new glucose molecules (i.e., gluconeogenesis), and fatty acids are oxidized to fuel long-term energetic demands. This regulation is driven primarily by the counterregulatory hormones epinephrine, growth hormone, cortisol, and glucagon. Conversely, feeding induces a rapid influx of diverse nutrients, including glucose, that disrupt homeostasis. Consistently, a host of hormonal and neural systems under the coordination of insulin are engaged in the transition from fasting to prandial states to reduce this disruption. The ultimate action of these systems is to appropriately store the newly acquired energy and to return to the homeostatic norm. Thus, at first glance it is tempting to assume that glucagon is solely antagonistic regarding the anabolic effects of insulin. We have been intrigued by the role of glucagon in the prandial transition and have attempted to delineate its role as beneficial or inhibitory to glycemic control. The following review highlights this long-known yet poorly understood hormone.

Differential regulatory roles of microRNAs during intramuscular adipogenesis in Chinese Guizhou Congjiang Xiang pigs

Intramuscular fat development is regulated by a series of complicated processes, with non-coding RNA (ncRNA) such as microRNA (miRNA) having a critical role during intramuscular preadipocyte proliferation and differentiation in pigs. In the present study, the miRNA expression profiles of intramuscular preadipocytes from the longissimus dorsi muscle of Chinese Guizhou Congjiang Xiang pigs were detected by RNA-seq during various differentiation stages, namely, day 0 (D0), day 4 (D4), and day 8 (D8). A total of 67, 95, and 16 differentially expressed (DE) miRNAs were detected between D4 and D0, D8 and D0, and D8 and D4, respectively. According to gene ontology and Kyoto Encyclopedia of Genes analysis, target genes of DE miRNAs were enriched in categories and pathways related to lipid metabolic process, lipid biosynthetic process, as well as the PI3K-Akt, AMPK, and MAPK signalling pathways. Notably, miR-148a-3p was differentially expressed, with highest expressed abundance in D0, D4, and D8. Overexpression of miR-148a-3p in intramuscular preadipocytes increased cell proliferation and differentiation, and decreased apoptosis, in comparison to the knockdown of miR-148a-3p in intramuscular preadipocytes. Luciferase activity assays, quantitative polymerase-chain reaction, and western blot analysis confirmed that miR-148a-3p regulated adipogenesis by repressing PPARGC1A expression. Accordingly, the effect of miR-148a-3p mimic was attenuated by overexpression of PPARGC1A intramuscular preadipocytes. Furthermore, miR-148a-3p promoted intramuscular preadipocyte differentiation by inhibiting the AMPK/ACC/CPT1C signalling pathway. Taken together, we identified expression profiles of miRNAs in intramuscular preadipocytes and determined that miR-148a-3p acted as a promoter of adipogenesis.

Reduced insulin signaling and high glucagon in early insulin resistance impaired fast-fed regulation of renal gluconeogenesis via insulin receptor substrate

Gluconeogenesis is one of the key processes through which the kidney contributes to glucose homeostasis. Urinary exosomes (uE) have been used to study renal gene regulation noninvasively in humans and rodents. Recently, we demonstrated fast-fed regulation of phosphoenolpyruvate carboxykinase (PEPCK), the rate-limiting enzyme for gluconeogenesis, in human uE. The regulation was impaired in subjects with early insulin resistance. Here, we studied primary human proximal tubule cells (hPT) and human uE to elucidate a potential link between insulin resistance and fast-fed regulation of renal PEPCK. We demonstrate that fasted hPTs had higher PEPCK and insulin receptor substrate-2 (IRS2) mRNA and protein levels, relative to fed cells. The fast-fed regulation was, however, attenuated in insulin receptor knockdown (IRKO) hPTs. The IRKO was confirmed by the blunted insulin-induced response on PEPCK, PGC1α, p-IR, and p-AKT expression in IRKO cells. Exosomes secreted by the wild-type or IRKO hPT showed similar regulation to the respective hPT. Similarly, in human uE, the relative abundance of IRS-2 mRNA (to IRS1) was higher in the fasted state relative to the fed condition. However, the fast-fed difference was absent in subjects with early insulin resistance. These subjects had higher circulating glucagon levels relative to subjects with optimal insulin sensitivity. Furthermore, in hPT cells, glucagon significantly induced PEPCK and IRS2 gene, and gluconeogenesis. IR knockdown in hPT cells further increased the gene expression levels. Together the data suggest that reduced insulin sensitivity and high glucagon in early insulin resistance may impair renal gluconeogenesis via IRS2 regulation.

MicroRNA-7 regulates insulin signaling pathway by targeting IRS1, IRS2, and RAF1 genes in gestational diabetes mellitus

BACKGROUND

Small non-coding micro RNAs (miRNAs) are indicated in various metabolic processes and play a critical role in disease pathology, including gestational diabetes mellitus (GDM).

OBJECTIVE

The purpose of this study was to examine the altered expression of miRNAs and their target genes in placental tissue (PL), cord blood (CB), and maternal blood (MB) of matched non-glucose tolerant (NGT) and GDM mother.

METHODS

In a case-control study, micro-RNA was quantified from forty-five serum (MB n = 15, CB n = 15, and PL n = 15) and matched placental tissue using stem-loop RT-qPCR followed by target prediction, network construction and functional and pathways enrichment analysis. Further, target genes were verified in-vitro through transfection and RT-qPCR.

RESULTS

Five miRNAs, namely hsa-let 7a-5P, hsa-miR7-5P, hsa-miR9-5P, hsa-miR18a-5P, and hsa-miR23a-3P were significantly over-expressed (p < 0.05) in all three samples namely PL, CB, and MB of GDM patients. However, the sample-wise comparison reveals higher expression of miRNA 7 in MB while lowest in CB than control. Furthermore, a comparison of fold change expression of target genes discloses a lower expression of IRS1, IRS2, and RAF1 in MB while comparatively higher expression of NRAS in MB and CB. In-vitro validation reveals lower expression of IRS1/2 and RAF1 in response to overexpression of miR-7 and vice-versa. Thus it is evident that increased miRNA7 expression causes down-regulation of its target genes IRS1, IRS2, and RAF1 in GDM mother compared to control. Further, target prediction, pathway enrichment, and hormone analysis (significantly higher FSH & LH in MB of GDM compared to NGT) revealed the insulin signaling, inflammatory and GnRH signaling as major pathways regulated by miRNA7.

CONCLUSIONS

Thus, an elevated level of miRNA7 may be associated with the progression of GDM by altering the multiple pathways like insulin, GnRH, and inflammatory signaling pathways via targeting IRS1, IRS2, and RAF1, implicating a new therapeutic target for GDM.

The Symbiotic Effect of a New Nutraceutical with Yeast β-Glucan, Prebiotics, Minerals, and Silybum marianum (Silymarin) for Recovering Metabolic Homeostasis via Pgc-1α, Il-6, and Il-10 Gene Expression in a Type-2 Diabetes Obesity Model

The use of natural products and derivatives for the prevention and control of non-communicable chronic diseases, such as type-2 diabetes (T2D), obesity, and hepatic steatosis is a way to achieve homeostasis through different metabolic pathways. Thus, male C57BL/6 mice were divided into the following groups: high-fat diet (HFD) vehicle, HFD + Supplemented, HFD + Supplemented_S, and isolated compounds. The vehicle and experimental formulations were administered orally by gavage once a day over the four weeks of the diet (28 consecutive days). We evaluated the energy homeostasis, cytokines, and mitochondrial gene expression in these groups of mice. After four weeks of supplementation, only the new nutraceutical group (HFD + Supplemented) experienced reduced fasting glycemia, insulin, HOMA index, HOMA-β, dyslipidemia, ectopic fat deposition, and hepatic fibrosis levels. Additionally, the PPARγ coactivator 1 α (Pgc-1α), interleukin-6 (Il-6), and interleukin-10 (Il-10) gene expression were augmented, while hepatic steatosis decreased and liver parenchyma was recovered. The glutathione-S-transferase activity status was found to be modulated by the supplement. We discovered that the new nutraceutical was able to improve insulin resistance and hepatic steatosis mainly by regulating IL-6, IL-10, and Pgc-1α gene expression.

Effects of Training Status and Exercise Mode on Global Gene Expression in Skeletal Muscle

The aim of this study was to investigate differences in skeletal muscle gene expression of highly trained endurance and strength athletes in comparison to untrained individuals at rest and in response to either an acute bout of endurance or strength exercise. Endurance (ET, n = 8, VO₂max 67 ± 9 mL/kg/min) and strength athletes (ST, n = 8, 5.8 ± 3.0 training years) as well as untrained controls (E-UT and S-UT, each n = 8) performed an acute endurance or strength exercise test. One day before testing (Pre), 30 min (30'Post) and 3 h (180'Post) afterwards, a skeletal muscle biopsy was obtained from the m. vastus lateralis. Skeletal muscle mRNA was isolated and analyzed by Affymetrix-microarray technology. Pathway analyses were performed to evaluate the effects of training status (trained vs. untrained) and exercise mode-specific (ET vs. ST) transcriptional responses. Differences in global skeletal muscle gene expression between trained and untrained were smaller compared to differences in exercise mode. Maximum differences between ET and ST were found between Pre and 180'Post. Pathway analyses showed increased expression of exercise-related genes, such as nuclear transcription factors (NR4A family), metabolism and vascularization (PGC1-α and VEGF-A), and muscle growth/structure (myostatin, IRS1/2 and HIF1-α. The most upregulated genes in response to acute endurance or strength exercise were the NR4A genes (NR4A1, NR4A2, NR4A3). The mode of acute exercise had a significant effect on transcriptional regulation Pre vs. 180'Post. In contrast, the effect of training status on human skeletal muscle gene expression profiles was negligible compared to strength or endurance specialization. The highest variability in gene expression, especially for the NR4A-family, was observed in trained individuals at 180'Post. Assessment of these receptors might be suitable to obtain a deeper understanding of skeletal muscle adaptive processes to develop optimized training strategies.

LRG1 is an adipokine that mediates obesity-induced hepatosteatosis and insulin resistance

Dysregulation in adipokine biosynthesis and function contributes to obesity-induced metabolic diseases. However, the identities and functions of many of the obesity-induced secretory molecules remain unknown. Here, we report the identification of leucine-rich alpha-2-glycoprotein 1 (LRG1) as an obesity-associated adipokine that exacerbates high fat diet-induced hepatosteatosis and insulin resistance. Serum levels of LRG1 were markedly elevated in obese humans and mice compared to their respective controls. LRG1 deficiency in mice greatly alleviated diet-induced hepatosteatosis, obesity, and insulin resistance. Mechanistically, LRG1 bound with high selectivity to the liver and promoted hepatosteatosis by increasing de novo lipogenesis and suppressing fatty acid β-oxidation. LRG1 also inhibited hepatic insulin signaling by down-regulating insulin receptor substrates 1 and 2. Our study identified LRG1 as a key molecule that mediates the crosstalk between adipocytes and hepatocytes in diet-induced hepatosteatosis and insulin resistance. Suppressing LRG1 expression and function may be a promising strategy for the treatment of obesity-related metabolic diseases.

Identification of novel key molecular signatures in the pathogenesis of experimental diabetic retinopathy

Deep mining of the molecular mechanisms underlying diabetic retinopathy (DR) is critical for the development of novel therapeutic targets. This study aimed to identify key molecular signatures involved in experimental DR on the basis of integrated bioinformatics analysis. Four datasets consisting of 37 retinal samples were downloaded from the National Center of Biotechnology Information Gene Expression Omnibus. After batch-effect adjustment, bioinformatics tools such as Networkanalyst, Enrichr, STRING, and Metascape were used to evaluate the differentially expressed genes (DEGs), perform enrichment analysis, and construct protein-protein interaction networks. The hub genes were identified using Cytoscape software. The DEGs of interest from the meta-analysis were confirmed by quantitative reverse transcription-polymerase chain reaction in diabetic rats and a high-glucose-treated retinal cell model, respectively. A total of 743 DEGs related to lens differentiation, insulin resistance, and high-density lipoprotein (HDL) cholesterol metabolism were obtained using the meta-analysis. Alterations of dynamic gene expression in the chloride ion channel, retinol metabolism, and fatty acid metabolism were involved in the course of DR in rats. Importantly, H3K27m3 modifications regulated the expression of most DEGs at the early stage of DR. Using an integrated bioinformatics approach, novel molecular signatures were obtained for different stages of DR progression, and the findings may represent distinct therapeutic strategies for DR patients.

A novel supplement with yeast β-glucan, prebiotic, minerals and Silybum marianum synergistically modulates metabolic and inflammatory pathways and improves steatosis in obese mice

OBJECTIVE

To evaluate the synergic effects of a novel oral supplement formulation, containing prebiotics, yeast β-glucans, minerals and silymarin (Silybum marianum), on lipid and glycidic metabolism, inflammatory and mitochondrial proteins of the liver, in control and high-fat diet-induced obese mice.

METHODS

After an acclimation period, 32 male C57BL/6 mice were divided into the following groups: nonfat diet (NFD) vehicle, NFD supplemented, high-fat diet (HFD) vehicle and HFD supplemented. The vehicle and experimental formulation were administered orally by gavage once a day during the last four weeks of the diet (28 consecutive days). We then evaluated energy homeostasis, inflammation, and mitochondrial protein expression in these groups of mice.

RESULTS

After four weeks of supplementation, study groups experienced reduced glycemia, dyslipidemia, fat, and hepatic fibrosis levels. Additionally, proliferator-activated receptor-α, AMP-activated protein kinase-1α, peroxisome proliferator-activated receptor γ co-activator-1α, and mitochondrial transcription factor A expression levels were augmented; however, levels of inhibitor of nuclear factor-κB kinase subunit α and p65 nuclear factor-κB expression, and oxidative markers were reduced. Notably, the cortisol/C-reactive protein ratio, a well-characterized marker of the hypothalamic-pituitary-adrenal axis immune interface status, was found to be modulated by the supplement.

CONCLUSION

We discovered that the novel supplement was able to modify different antioxidant, metabolic and inflammatory pathways, improving the energy homeostasis and inflammatory status, and consequently alleviated hepatic steatosis.

PARPs in lipid metabolism and related diseases

PARPs and tankyrases (TNKS) represent a family of 17 proteins. PARPs and tankyrases were originally identified as DNA repair factors, nevertheless, recent advances have shed light on their role in lipid metabolism. To date, PARP1, PARP2, PARP3, tankyrases, PARP9, PARP10, PARP14 were reported to have multi-pronged connections to lipid metabolism. The activity of PARP enzymes is fine-tuned by a set of cholesterol-based compounds as oxidized cholesterol derivatives, steroid hormones or bile acids. In turn, PARPs modulate several key processes of lipid homeostasis (lipotoxicity, fatty acid and steroid biosynthesis, lipoprotein homeostasis, fatty acid oxidation, etc.). PARPs are also cofactors of lipid-responsive nuclear receptors and transcription factors through which PARPs regulate lipid metabolism and lipid homeostasis. PARP activation often represents a disruptive signal to (lipid) metabolism, and PARP-dependent changes to lipid metabolism have pathophysiological role in the development of hyperlipidemia, obesity, alcoholic and non-alcoholic fatty liver disease, type II diabetes and its complications, atherosclerosis, cardiovascular aging and skin pathologies, just to name a few. In this synopsis we will review the evidence supporting the beneficial effects of pharmacological PARP inhibitors in these diseases/pathologies and propose repurposing PARP inhibitors already available for the treatment of various malignancies.

Post-translational regulation of PGC-1α modulates fibrotic repair

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease associated with mitochondrial oxidative stress. Mitochondrial reactive oxygen species (mtROS) are important for cell homeostasis by regulating mitochondrial dynamics. Here, we show that IPF BAL cells exhibited increased mitochondrial biogenesis that is, in part, due to increased nuclear expression of peroxisome proliferator-activated receptor-ɣ (PPARɣ) coactivator (PGC)-1α. Increased PPARGC1A mRNA expression directly correlated with reduced pulmonary function in IPF subjects. Oxidant-mediated activation of the p38 MAPK via Akt1 regulated PGC-1α activation to increase mitochondrial biogenesis in monocyte-derived macrophages. Demonstrating the importance of PGC-1α in fibrotic repair, mice harboring a conditional deletion of Ppargc1a in monocyte-derived macrophages or mice administered a chemical inhibitor of mitochondrial division had reduced biogenesis and increased apoptosis, and the mice were protected from pulmonary fibrosis. These observations suggest that Akt1-mediated regulation of PGC-1α maintains mitochondrial homeostasis in monocyte-derived macrophages to induce apoptosis resistance, which contributes to the pathogenesis of pulmonary fibrosis.

Insulin action at a molecular level - 100 years of progress

The discovery of insulin 100 years ago and its application to the treatment of human disease in the years since have marked a major turning point in the history of medicine. The availability of purified insulin allowed for the establishment of its physiological role in the regulation of blood glucose and ketones, the determination of its amino acid sequence, and the solving of its structure. Over the last 50 years, the function of insulin has been applied into the discovery of the insulin receptor and its signaling cascade to reveal the role of impaired insulin signaling-or resistance-in the progression of type 2 diabetes. It has also become clear that insulin signaling can impact not only classical insulin-sensitive tissues, but all tissues of the body, and that in many of these tissues the insulin signaling cascade regulates unexpected physiological functions. Despite these remarkable advances, much remains to be learned about both insulin signaling and how to use this molecular knowledge to advance the treatment of type 2 diabetes and other insulin-resistant states.

Effects of intermittent fasting on liver physiology and metabolism in mice

A broad spectrum of health benefits from intermittent fasting have been reported in studies on animal models and human subjects. However, the underlying mechanisms of these beneficial effects remain largely elusive. The present study aimed to explore the effects and potential mode of action of intermittent fasting in mouse models with a focus on the liver. C57BL/6 mice were subjected to intermittent fasting or ad libitum feeding as controls. It was determined that 12 h of daily intermittent fasting for 30 days significantly reduced the cumulative food intake compared with that in mice with ad libitum feeding. Fasting resulted in a significantly reduced liver mass but only had a minimal effect on bodyweight. The effects on the liver by 30 days of fasting were not reversed by subsequent ad libitum refeeding for 30 days. Among the measured blood biochemical parameters, the levels of blood glucose were decreased, while the levels of alkaline phosphatase were increased in fasting mice. Of note, targeted metabolic profiling revealed global elevation of metabolites in the livers of fasting mice. These metabolic molecules included adenosine triphosphate, nicotinamide adenine dinucleotide phosphate (NADP), reduced NADP and succinate, which are essentially involved in the citric acid cycle and oxidative phosphorylation. Thus, it was concluded that daily 12 h of intermittent fasting for one month significantly reduced the liver weight of mice, which is associated with enhanced liver metabolism.

Glucose Metabolism in Burns-What Happens?

Severe burns represent an important challenge for patients and medical teams. They lead to profound metabolic alterations, trigger a systemic inflammatory response, crush the immune defense, impair the function of the heart, lungs, kidneys, liver, etc. The metabolism is shifted towards a hypermetabolic state, and this situation might persist for years after the burn, having deleterious consequences for the patient's health. Severely burned patients lack energy substrates and react in order to produce and maintain augmented levels of glucose, which is the fuel "ready to use" by cells. In this paper, we discuss biological substances that induce a hyperglycemic response, concur to insulin resistance, and determine cell disturbance after a severe burn. We also focus on the most effective agents that provide pharmacological modulations of the changes in glucose metabolism.

Evaluating causality of cellular senescence in non-alcoholic fatty liver disease

Cellular senescence is a state of irreversible cell cycle arrest that has important physiological functions. However, cellular senescence is also a hallmark of ageing and has been associated with several pathological conditions. A wide range of factors including genotoxic stress, mitogens and inflammatory cytokines can induce senescence. Phenotypically, senescent cells are characterised by short telomeres, an enlarged nuclear area and damaged genomic and mitochondrial DNA. Secretion of proinflammatory proteins, also known as the senescence-associated secretory phenotype, is a characteristic of senescent cells that is thought to be the main contributor to their disease-inducing properties. In the past decade, the role of cellular senescence in the development of non-alcoholic fatty liver disease (NAFLD) and its progression towards non-alcoholic steatohepatitis (NASH) has garnered significant interest. Until recently, it was suggested that hepatocyte cellular senescence is a mere consequence of the metabolic dysregulation and inflammatory phenomena in fatty liver disease. However, recent work in rodents has suggested that senescence may be a causal factor in NAFLD development. Although causality is yet to be established in humans, current evidence suggests that targeting senescent cells has therapeutic potential for NAFLD. We aim to provide insights into the quality of the evidence supporting a causal role of cellular senescence in the development of NAFLD in rodents and humans. We will elaborate on key cellular and molecular features of senescence and discuss the efficacy and safety of novel senolytic drugs for the treatment or prevention of NAFLD.

Hengshun Aromatic Vinegar Improves Glycolipid Metabolism in Type 2 Diabetes Mellitus via Regulating PGC-1α/PGC-1β Pathway

Hengshun aromatic vinegar (HSAV), produced by typical solid-state or liquid-state fermentation techniques, is consumed worldwide as a food condiment. HSAV shows multiple bioactivities, but its activity in type 2 diabetes mellitus (T2DM) and possible mechanisms have not been reported. In this study, the effects of HSAV against T2DM were evaluated in insulin-induced HepG2 cells and high-fat diet (HFD) and streptozotocin (STZ) induced T2DM rats. Then, the mechanisms of HSAV against T2DM were explored by Real-time PCR, Western blot, immunofluorescence assays, siRNA transfection and gene overexpression experiments. Results indicated that HSAV significantly improved glucose consumption and reduced triglycerides (TG) contents in metabolic disordered HepG2 cells. Meanwhile, HSAV obviously alleviated general status, liver and kidney functions of T2DM rats, and decreased hyperglycemia and hyperlipidemia, improved insulin resistance, and reduced lipid accumulation in liver. Mechanism studies indicated that HSAV markedly down-regulated the expression of proliferator-activated receptor γ coactivator-1α (PGC-1α), then regulated peroxisome proliferators-activated receptor α (PPAR-α)/protein kinase B (AKT) signal pathway mediated gluconeogenesis and glycogen synthesis. Meanwhile, HSAV significantly up-regulated proliferator-activated receptor γ coactivator-1β (PGC-1β), and subsequently decreased sterol regulatory element binding protein-1c (SREBP-1c) pathway mediated lipogenesis. In conclusion, HSAV showed potent anti-T2DM activity in ameliorating dysfunction of glycolipid metabolism through regulating PGC-1α/PGC-1β pathway, which has a certain application prospect as an effective diet supplement for T2DM therapy in the future.

Hepatic transcriptional responses to fasting and feeding

Mammals undergo regular cycles of fasting and feeding that engage dynamic transcriptional responses in metabolic tissues. Here we review advances in our understanding of the gene regulatory networks that contribute to hepatic responses to fasting and feeding. The advent of sequencing and -omics techniques have begun to facilitate a holistic understanding of the transcriptional landscape and its plasticity. We highlight transcription factors, their cofactors, and the pathways that they impact. We also discuss physiological factors that impinge on these responses, including circadian rhythms and sex differences. Finally, we review how dietary modifications modulate hepatic gene expression programs.

Insulin Resistance across the Spectrum of Nonalcoholic Fatty Liver Disease

Insulin resistance (IR) is defined as a lower-than-expected response to insulin action from target tissues, leading to the development of type 2 diabetes through the impairment of both glucose and lipid metabolism. IR is a common condition in subjects with nonalcoholic fatty liver disease (NAFLD) and is considered one of the main factors involved in the pathogenesis of nonalcoholic steatohepatitis (NASH) and in the progression of liver disease. The liver, the adipose tissue and the skeletal muscle are major contributors for the development and worsening of IR. In this review, we discuss the sites and mechanisms of insulin action and the IR-related impairment along the spectrum of NAFLD, from simple steatosis to progressive NASH and cirrhosis.

Choice of Lipid Emulsion Determines Inflammation of the Gut-Liver Axis, Incretin Profile, and Insulin Signaling in a Murine Model of Total Parenteral Nutrition

SCOPE

The aim of this study is to test whether the choice of the lipid emulsion in total parenteral nutrition (TPN), that is, n-3 fatty acid-based Omegaven versus n-6 fatty acid-based Intralipid, determines inflammation in the liver, the incretin profile, and insulin resistance.

METHODS AND RESULTS

Jugular vein catheters (JVC) are placed in C57BL/6 mice and used for TPN for 7 days. Mice are randomized into a saline group (saline infusion with oral chow), an Intralipid group (IL-TPN, no chow), an Omegaven group (OV-TPN, no chow), or a chow only group (without JVC). Both TPN elicite higher abundance of lipopolysaccharide binding protein in the liver, but only IL-TPN increases interleukin-6 and interferon-γ, while OV-TPN reduces interleukin-4, monocyte chemoattractant protein-1, and interleukin-1α. Insulin plasma concentrations are higher in both TPN, while glucagon and glucagon-like peptide-1 (GLP-1) were higher in IL-TPN. Gluconeogenesis is increased in IL-TPN and the nuclear profile of key metabolic transcription factors shows a liver-protective phenotype in OV-TPN. OV-TPN increases insulin sensitivity in the liver and skeletal muscle.

CONCLUSION

OV-TPN as opposed to IL-TPN mitigates inflammation in the liver and reduces the negative metabolic effects of hyperinsulinemia and hyperglucagonemia by "re-sensitizing" the liver and skeletal muscle to insulin.

Molecular Mechanisms of Glucocorticoid-Induced Insulin Resistance

Glucocorticoids (GCs) are steroids secreted by the adrenal cortex under the hypothalamic-pituitary-adrenal axis control, one of the major neuro-endocrine systems of the organism. These hormones are involved in tissue repair, immune stability, and metabolic processes, such as the regulation of carbohydrate, lipid, and protein metabolism. Globally, GCs are presented as ‘flight and fight’ hormones and, in that purpose, they are catabolic hormones required to mobilize storage to provide energy for the organism. If acute GC secretion allows fast metabolic adaptations to respond to danger, stress, or metabolic imbalance, long-term GC exposure arising from treatment or Cushing’s syndrome, progressively leads to insulin resistance and, in fine, cardiometabolic disorders. In this review, we briefly summarize the pharmacological actions of GC and metabolic dysregulations observed in patients exposed to an excess of GCs. Next, we describe in detail the molecular mechanisms underlying GC-induced insulin resistance in adipose tissue, liver, muscle, and to a lesser extent in gut, bone, and brain, mainly identified by numerous studies performed in animal models. Finally, we present the paradoxical effects of GCs on beta cell mass and insulin secretion by the pancreas with a specific focus on the direct and indirect (through insulin-sensitive organs) effects of GCs. Overall, a better knowledge of the specific action of GCs on several organs and their molecular targets may help foster the understanding of GCs’ side effects and design new drugs that possess therapeutic benefits without metabolic adverse effects.

Benzyl Butyl Phthalate Induced Early lncRNA H19 Regulation in C3H10T1/2 Stem Cell Line

Exposure to endocrine-disrupting chemicals used in plastic manufacturing may contribute to the current obesity and diabetes epidemic. Our previous study demonstrated that benzyl butyl phthalate (BBP) induced adipogenesis in the C3H10T1/2 stem cell line. Here we investigated if BBP deregulated long noncoding RNA H19 and its downstream pathway and whether BBP plays a role in the insulin signaling pathway during adipocyte diiferentiation. Cells treated with an 8 day BBP regimen showed that H19 expression was decreased at day 2 with 50 μM BBP exposure (p < 0.05). However, no significant changes were observed from day 4 to day 8. Expression of miRNA-103/107, H19 regulated miRNAs, was upregulated at day 2 (p < 0.05) but not from day 4 to day 8. Similarly, expression of the let-7 family members (a, b, c, d, f, and g) was also significantly increased at day 2 (p < 0.05 or p < 0.01), except for let-7e. Both let-7 and miRNA-103/107 are targets of H19 and play roles in insulin signaling. Insulin receptor substrate (IRS)-1, one of the key insulin signal transduction regulators, was significantly downregulated from day 2 to day 8 (p < 0.05). Gene expression of insulin receptor (IR) and IRS-2 were not altered by BBP exposure. The ratio of IRS1/IRS2 was significantly decreased from day 2 to day 8. On day 4, phospho-Akt protein expression was significantly decreased (p < 0.05). In conclusion, BBP exposure may lead to metabolic dysregulation by altering vital epigenetic regulators such as lncRNA H19 and its target microRNAs at an earlier stage, which further regulates insulin signaling.

Epigenetics of Hepatic Insulin Resistance

Insulin resistance (IR) is largely recognized as a unifying feature that underlies metabolic dysfunction. Both lifestyle and genetic factors contribute to IR. Work from recent years has demonstrated that the epigenome may constitute an interface where different signals may converge to promote IR gene expression programs. Here, we review the current knowledge of the role of epigenetics in hepatic IR, focusing on the roles of DNA methylation and histone post-translational modifications. We discuss the broad epigenetic changes observed in the insulin resistant liver and its associated pathophysiological states and leverage on the wealth of 'omics' studies performed to discuss efforts in pinpointing specific loci that are disrupted by these changes. We envision that future studies, with increased genomic resolution and larger cohorts, will further the identification of biomarkers of early onset hepatic IR and assist the development of targeted interventions. Furthermore, there is growing evidence to suggest that persistent epigenetic marks may be acquired over prolonged exposure to disease or deleterious exposures, highlighting the need for preventative medicine and long-term lifestyle adjustments to avoid irreversible or long-term alterations in gene expression.

Caffeic and Chlorogenic Acids Synergistically Activate Browning Program in Human Adipocytes: Implications of AMPK- and PPAR-Mediated Pathways

Caffeic acid (CA) and chlorogenic acid (CGA) are phenolic compounds claimed to be responsible for the metabolic effects of coffee and tea consumption. Along with their structural similarities, they share common mechanisms such as activation of the AMP-activated protein kinase (AMPK) signaling. The present study aimed to investigate the anti-obesity potential of CA and CGA as co-treatment in human adipocytes. The molecular interactions of CA and CGA with key adipogenic transcription factors were simulated through an in silico molecular docking approach. The expression levels of white and brown adipocyte markers, as well as genes related to lipid metabolism, were analyzed by real-time quantitative PCR and Western blot analyses. Mechanistically, the CA/CGA combination induced lipolysis, upregulated AMPK and browning gene expression and downregulated peroxisome proliferator-activated receptor γ (PPARγ) at both transcriptional and protein levels. The gene expression profiles of the CA/CGA-co-treated adipocytes strongly resembled brown-like signatures. Major pathways identified included the AMPK- and PPAR-related signaling pathways. Collectively, these findings indicated that CA/CGA co-stimulation exerted a browning-inducing potential superior to that of either compound used alone which merits implementation in obesity management. Further, the obtained data provide additional insights on how CA and CGA modify adipocyte function, differentiation and lipid metabolism.

An Integrated Analysis of miRNA and Gene Expression Changes in Response to an Obesogenic Diet to Explore the Impact of Transgenerational Supplementation with Omega 3 Fatty Acids

Insulin resistance decreases the ability of insulin to inhibit hepatic gluconeogenesis, a key step in the development of metabolic syndrome. Metabolic alterations, fat accumulation, and fibrosis in the liver are closely related and contribute to the progression of comorbidities, such as hypertension, type 2 diabetes, or cancer. Omega 3 (n-3) polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA), were identified as potent positive regulators of insulin sensitivity in vitro and in animal models. In the current study, we explored the effects of a transgenerational supplementation with EPA in mice exposed to an obesogenic diet on the regulation of microRNAs (miRNAs) and gene expression in the liver using high-throughput techniques. We implemented a comprehensive molecular systems biology approach, combining statistical tools, such as MicroRNA Master Regulator Analysis pipeline and Boolean modeling to integrate these biochemical processes. We demonstrated that EPA mediated molecular adaptations, leading to the inhibition of miR-34a-5p, a negative regulator of Irs2 as a master regulatory event leading to the inhibition of gluconeogenesis by insulin during the fasting-feeding transition. Omics data integration provided greater biological insight and a better understanding of the relationships between biological variables. Such an approach may be useful for deriving innovative data-driven hypotheses and for the discovery of molecular-biochemical mechanistic links.