Regulation of angiopoietin-like protein 4/fasting-induced adipose factor (Angptl4/FIAF) expression in mouse white adipose tissue and 3T3-L1 adipocytes

Knockdown of ANGPTL4 inhibits adipogenesis of preadipocyte via autophagy

It has been demonstrated that angiopoietin-like protein 4 (ANGPTL4) plays an important regulatory role in lipid metabolism and backfat deposition appears to vary in different pig breeds. However, the correlation between ANGPTL4 and backfat deposition have not been well characterized and the role of ANGPTL4 in regulating adipogenesis remains unclear. Therefore, this study aimed to investigate correlation between ANGPTL4 and backfat deposition and to explore the effects of ANGPTL4 on preadipocyte differentiation and the underlying mechanism. Our results showed that the backfat thickness and the ANGPTL4 gene expression of Laiwu pigs were significantly higher than those in DLY pigs and the ANGPTL4 gene expression was positively correlated with backfat thickness both in DLY pigs and Laiwu pigs. Moreover, an increase in ANGPTL4 expression and activation of autophagy were observed during the differentiation of stromal vascular fraction cells. In addition, knockdown of ANGPTL4 inhibited the differentiation of 3T3-L1 cells with decreased expression of LC3-II and ATG5 and increased expression of SQSTM1, suggesting the involvement of autophagy in ANGPTL4-mediated adipogenesis. In conclusion, these results suggested that ANGPTL4 is positively correlated with backfat deposition in pigs and knockdown of ANGPTL4 inhibits adipogenesis of preadipocyte via autophagy, providing new insights into the regulation of fat deposition and to improve the carcass quality and meat quality of porcine.

The role of the gut microbiota in health and cardiovascular diseases

The gut microbiota is critical to human health, such as digesting nutrients, forming the intestinal epithelial barrier, regulating immune function, producing vitamins and hormones, and producing metabolites to interact with the host. Meanwhile, increasing evidence indicates that the gut microbiota has a strong correlation with the occurrence, progression and treatment of cardiovascular diseases (CVDs). In patients with CVDs and corresponding risk factors, the composition and ratio of gut microbiota have significant differences compared with their healthy counterparts. Therefore, gut microbiota dysbiosis, gut microbiota-generated metabolites, and the related signaling pathway may serve as explanations for some of the mechanisms about the occurrence and development of CVDs. Several studies have also demonstrated that many traditional and latest therapeutic treatments of CVDs are associated with the gut microbiota and its generated metabolites and related signaling pathways. Given that information, we summarized the latest advances in the current research regarding the effect of gut microbiota on health, the main cardiovascular risk factors, and CVDs, highlighted the roles and mechanisms of several metabolites, and introduced corresponding promising treatments for CVDs regarding the gut microbiota. Therefore, this review mainly focuses on exploring the role of gut microbiota related metabolites and their therapeutic potential in CVDs, which may eventually provide better solutions in the development of therapeutic treatment as well as the prevention of CVDs.

Hepatic PTEN Signaling Regulates Systemic Metabolic Homeostasis through Hepatokines-Mediated Liver-to-Peripheral Organs Crosstalk

Liver-derived circulating factors deeply affect the metabolism of distal organs. Herein, we took advantage of the hepatocyte-specific PTEN knockout mice (LPTENKO), a model of hepatic steatosis associated with increased muscle insulin sensitivity and decreased adiposity, to identify potential secreted hepatic factors improving metabolic homeostasis. Our results indicated that protein factors, rather than specific metabolites, released by PTEN-deficient hepatocytes trigger an improved muscle insulin sensitivity and a decreased adiposity in LPTENKO. In this regard, a proteomic analysis of conditioned media from PTEN-deficient primary hepatocytes identified seven hepatokines whose expression/secretion was deregulated. Distinct expression patterns of these hepatokines were observed in hepatic tissues from human/mouse with NAFLD. The expression of specific factors was regulated by the PTEN/PI3K, PPAR or AMPK signaling pathways and/or modulated by classical antidiabetic drugs. Finally, loss-of-function studies identified FGF21 and the triad AHSG, ANGPTL4 and LECT2 as key regulators of insulin sensitivity in muscle cells and in adipocytes biogenesis, respectively. These data indicate that hepatic PTEN deficiency and steatosis alter the expression/secretion of hepatokines regulating insulin sensitivity in muscles and the lipid metabolism in adipose tissue. These hepatokines could represent potential therapeutic targets to treat obesity and insulin resistance.

Impact of oral lipid and glucose tolerance tests on the postprandial concentrations of angiopoietin-like proteins (Angptl) 3 and 4

Background

The postprandial regulation of angiopoietin-like proteins (Angptls) and their expression in adipocytes is poorly characterized.

Objective

Circulating Angptl3 and 4 were analyzed in healthy individuals undergoing either an oral lipid tolerance test (OLTT; n = 98) or an oral glucose tolerance test (OGTT; n = 99). Venous blood was drawn after 0, 2, 4, and 6 h during OLTT and after 0, 1, and 2 h during OGTT. Anthropometric and laboratory parameters were assessed and concentrations of Angptls were quantified by enzyme-linked immunosorbent assay. Angptl gene expression in 3T3-L1 adipocytes and in murine adipose tissues and cellular fractions was analyzed by quantitative real-time PCR.

Results

Angptl3 concentrations significantly decreased while Angptl4 levels continuously increased during OLTT. Both proteins remained unaffected during OGTT. Angptl3 and Angptl4 were expressed in murine subcutaneous and visceral AT with higher mRNA levels in mature adipocytes when compared to the stroma-vascular cell fraction. Both proteins were strongly induced during 3T3-L1 adipocyte differentiation and they were unresponsive to glucose in mature fat cells. Adipocyte Angptl3 (but not Angptl4) mRNA expression was inhibited by the polyunsaturated fatty acids arachidonic acid and docosahexaenoic acid, whereas nine types of dietary fatty acids remained without any effect.

Conclusions

There is evidence of short-time regulation of Angptl3/4 levels upon metabolic stress. Angptl4 expression is high and Angptl3 expression is low in AT and restricted mainly to mature adipocytes without any differences concerning fat compartments. Whereas dietary fatty acids and glucose are without any effect, omega-3/-6-polyunsaturated fatty acids inhibited Anptl3 expression in adipocytes.

Skeletal Muscle Angiopoietin-Like Protein 4 and Glucose Metabolism in Older Adults after Exercise and Weight Loss

Angiopoietin-like protein 4 (ANGPTL4) is an adipokine that plays an important role in energy homoeostasis and lipid and lipoprotein metabolism. This study was designed to determine the effect of an exercise plus weight loss intervention on ANGPTL4 expression and its relationship with metabolic health. Thirty-five obese sedentary men (n = 18) and postmenopausal women (n = 17), (X ± SEM, age: 61 ± 1 years, BMI: 31.3 ± 0.7 kg/m², VO₂max: 21.7 ± 0.9 L/kg/min) completed a 6 month program of 3×/week aerobic exercise and 1×/week dietary instruction to induce weight loss (AEX + WL). Participants underwent vastus lateralis muscle biopsies, a hyperinsulinemic–euglycemic clamp, oral glucose tolerance tests and body composition testing. Basal skeletal muscle ANGPTL4 mRNA was lower in men than women (p < 0.01). Peroxisome proliferator-activated receptor (PPAR) alpha (PPARα) mRNA expression was higher in men than women (p < 0.05). There were no significance changes in serum or skeletal muscle ANGPTL4 (basal or insulin-stimulated) or muscle PPARα mRNA expression after AEX + WL. Muscle mRNA ANGPTL4 is correlated with serum ANGPTL4 (r = 0.41, p < 0.05), body fat (r = 0.64, p < 0.0001), and glucose utilization (r = 0.38, p < 0.05). AEX + WL does not change basal or insulin-stimulated skeletal muscle ANGPTL4 mRNA expression, suggesting other factors contribute to improved insulin sensitivity after the loss of body fat and improved fitness.

Therapeutic Efficacy of Antioxidants in Ameliorating Obesity Phenotype and Associated Comorbidities

Obesity has been a worldwide epidemic for decades. Despite the abundant increase in knowledge regarding the etiology and pathogenesis of obesity, the prevalence continues to rise with estimates predicting considerably higher numbers by the year 2030. Obesity is characterized by an abnormal lipid accumulation, however, the physiological consequences of obesity are far more concerning. The development of the obesity phenotype constitutes dramatic alterations in adipocytes, along with several other cellular mechanisms which causes substantial increase in systemic oxidative stress mediated by reactive oxygen species (ROS). These alterations promote a chronic state of inflammation in the body caused by the redox imbalance. Together, the systemic oxidative stress and chronic inflammation plays a vital role in maintaining the obese state and exacerbating onset of cardiovascular complications, Type II diabetes mellitus, dyslipidemia, non-alcoholic steatohepatitis, and other conditions where obesity has been linked as a significant risk factor. Because of the apparent role of oxidative stress in the pathogenesis of obesity, there has been a growing interest in attenuating the pro-oxidant state in obesity. Hence, this review aims to highlight the therapeutic role of antioxidants, agents that negate pro-oxidant state of cells, in ameliorating obesity and associated comorbidities. More specifically, this review will explore how various antioxidants target unique and diverse pathways to exhibit an antioxidant defense mechanism.

Research Progress on the Involvement of ANGPTL4 and Loss-of-Function Variants in Lipid Metabolism and Coronary Heart Disease: Is the "Prime Time" of ANGPTL4-Targeted Therapy for Coronary Heart Disease Approaching?

BACKGROUND

Multiple genetic studies have confirmed the definitive link among the loss-of-function variants of angiogenin-like protein 4 (ANGPTL4), significantly decreased plasma triglyceride (TG) levels, and reduced risk of coronary heart disease (CHD). The potential therapeutic effect of ANGPTL4 on dyslipidemia and CHD has been widely studied.

OBJECTIVE

This review provides a detailed introduction to the research progress on the involvement of ANGPTL4 in lipid metabolism and atherosclerosis and evaluates the efficacy and safety of ANGPTL4 as a therapeutic target for CHD.

RELEVANT FINDINGS

By inhibiting lipoprotein lipase (LPL) activity, ANGPTL4 plays a vital role in the regulation of lipid metabolism and energy balance. However, the role of ANGPTL4 in regulating lipid metabolism is tissue-specific. ANGPTL4 acts as a locally released LPL inhibitor in the heart, skeletal muscle and small intestine, while ANGPTL4 derived from liver and adipose tissue mainly acts as an endocrine factor that regulates systemic lipid metabolism. As a multifunctional protein, ANGPTL4 also inhibits the formation of foam cells in macrophages, exerting an anti-atherogenic role. The function of ANGPTL4 in endothelial cells is still uncertain. The safety of ANGPTL4 monoclonal antibodies requires further evaluation due to their potential adverse effects.

CONCLUSION

The biological characteristics of ANGPTL4 are much more complex than those demonstrated by genetic studies. Future studies must elucidate how to effectively reduce the risk of CHD while avoiding potential atherogenic effects and other complications before the "prime time" of ANGPTL4-targeted therapy arrives.

Growth hormone upregulates ANGPTL4 mRNA and suppresses lipoprotein lipase via fatty acids: Randomized experiments in human individuals

OBJECTIVES

Lipoprotein lipase (LPL) catalyzes the hydrolysis of circulating triglycerides into free fatty acids (FFA) and thereby promotes FFA uptake in peripheral tissues. LPL is negatively regulated by angiopoietin-like protein 4 (ANGPTL4) presumably by an FFA-dependent mechanism. Growth hormone (GH) suppresses LPL activity, but it is unknown whether this is mediated by FFA and ANGPTL4. Therefore, we investigated the concerted effect of GH on ANGPTL4 and LPL in the presence and absence of lipolysis in two in vivo studies in human subjects.

METHODS

In a randomized, placebo-controlled, cross-over study, nine obese men were examined after injection of 1) a GH bolus, and 2) a GH-receptor antagonist followed by four adipose tissue biopsies obtained over a 5-h period. In a second study, nine hypopituitary men were examined in a 2 × 2 factorial design including GH and acipimox (an anti-lipolytic agent), with biopsies from adipose tissue and skeletal muscle obtained during a basal period and a subsequent hyperinsulinemic-euglycemic clamp. The mRNA expression of ANGPTL4 and LPL as well as LPL activity were analyzed in the biopsies.

RESULTS

In both studies, GH increased serum FFA levels, upregulated ANGPTL4 mRNA expression and suppressed LPL activity. In study 2, acipimox completely suppressed FFA levels and antagonized the effects of GH on ANGPTL4 and LPL.

CONCLUSIONS

These human in vivo studies demonstrate that GH upregulates ANGPTL4 mRNA and suppresses LPL activity via an FFA-dependent mechanism.

A review of the multifunctionality of angiopoietin-like 4 in eye disease

Angiopoietin-like protein 4 (ANGPTL4) is a multifunctional cytokine regulating vascular permeability, angiogenesis, and inflammation. Dysregulations in these responses contribute to the pathogenesis of ischemic retinopathies such as diabetic retinopathy (DR), age-related macular degeneration (AMD), retinal vein occlusion, and sickle cell retinopathy (SCR). However, the role of ANGPTL4 in these diseases remains controversial. Here, we summarize the functional mechanisms of ANGPTL4 in several diseases. We highlight original studies that provide detailed data about the mechanisms of action for ANGPTL4, its applications as a diagnostic or prognostic biomarker, and its use as a potential therapeutic target. Taken together, the discussions in this review will help us gain a better understanding of the molecular mechanisms by which ANGPTL4 functions in eye disease and will provide directions for future research.

Mechanistic and therapeutic advances in non-alcoholic fatty liver disease by targeting the gut microbiota

Non-alcoholic fatty liver disease (NAFLD) is one of the most common metabolic diseases currently in the context of obesity worldwide, which contains a spectrum of chronic liver diseases, including hepatic steatosis, non-alcoholic steatohepatitis and hepatic carcinoma. In addition to the classical "Two-hit" theory, NAFLD has been recognized as a typical gut microbiota-related disease because of the intricate role of gut microbiota in maintaining human health and disease formation. Moreover, gut microbiota is even regarded as a "metabolic organ" that play complementary roles to that of liver in many aspects. The mechanisms underlying gut microbiota-mediated development of NAFLD include modulation of host energy metabolism, insulin sensitivity, and bile acid and choline metabolism. As a result, gut microbiota have been emerging as a novel therapeutic target for NAFLD by manipulating it in various ways, including probiotics, prebiotics, synbiotics, antibiotics, fecal microbiota transplantation, and herbal components. In this review, we summarized the most recent advances in gut microbiota-mediated mechanisms, as well as gut microbiota-targeted therapies on NAFLD.

Transcriptome analysis of adipose tissues from two fat-tailed sheep breeds reveals key genes involved in fat deposition

BACKGROUND

The level of fat deposition in carcass is a crucial factor influencing meat quality. Guangling Large-Tailed (GLT) and Small-Tailed Han (STH) sheep are important local Chinese fat-tailed breeds that show distinct patterns of fat depots. To gain a better understanding of fat deposition, transcriptome profiles were determined by RNA-sequencing of perirenal, subcutaneous, and tail fat tissues from both the sheep breeds. The common highly expressed genes (co-genes) in all the six tissues, and the genes that were differentially expressed (DE genes) between these two breeds in the corresponding tissues were analyzed.

RESULTS

Approximately 47 million clean reads were obtained for each sample, and a total of 17,267 genes were annotated. Of the 47 highly expressed co-genes, FABP4, ADIPOQ, FABP5, and CD36 were the four most highly transcribed genes among all the known genes related to adipose deposition. FHC, FHC-pseudogene, and ZC3H10 were also highly expressed genes and could, thus, have roles in fat deposition. A total of 2091, 4233, and 4131 DE genes were identified in the perirenal, subcutaneous, and tail fat tissues between the GLT and STH breeds, respectively. Gene Ontology (GO) analysis showed that some DE genes were associated with adipose metabolism. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that PPAR signaling pathway and ECM-receptor interaction were specifically enriched. Four genes, namely LOC101102230, PLTP, C1QTNF7, and OLR1 were up-regulated and two genes, SCD and UCP-1, were down-regulated in all the tested tissues of STH. Among the genes involved in ECM-receptor interaction, the genes encoding collagens, laminins, and integrins were quite different depending on the depots or the breeds. In STH, genes such as LAMB3, RELN, TNXB, and ITGA8, were identified to be up regulated and LAMB4 was observed to be down regulated.

CONCLUSIONS

This study unravels the complex transcriptome profiles in sheep fat tissues, highlighting the candidate genes involved in fat deposition. Further studies are needed to investigate the roles of the candidate genes in fat deposition and in determining the meat quality of sheep.

Angiopoietin-like protein 3 and 4 in obesity, type 2 diabetes mellitus, and malnutrition: the effect of weight reduction and realimentation

Background

Angiopoietin-like proteins (ANGPTLs) 3 and 4 are circulating factors that participate in the regulation of lipid and glucose metabolism.

Subjects and methods

We measured serum ANGPTL3 and 4 levels in 23 patients with obesity, 40 patients with obesity and type 2 diabetes mellitus (T2DM), 22 patients with anorexia nervosa (AN), 15 subjects undergoing 72-h fasting, and 12 patients with short bowel syndrome (SBS), and their changes after very-low-calorie diet (VLCD), bariatric surgery, partial realimentation, acute fasting, and parenteral nutrition in order to assess their possible role in metabolic regulations.

Results

Serum ANGPTL4 levels were higher in obese subjects without/with T2DM (94.50 ± 9.51 and 134.19 ± 7.69 vs. 50.34 ± 4.22 ng/ml, p < 0.001) and lower in subjects with AN relative to healthy control subjects (38.22 ± 4.48 vs. 65.80 ± 7.98 ng/ml, p = 0.002), while serum ANGPTL3 levels demonstrated inverse tendency. Nutritional status had no effect on ANGPTL3 and 4 mRNA expression in adipose tissue. Fasting decreased ANGPTL3 and increased ANGPTL4 levels, while VLCD reduced only ANGPTL3. Bariatric surgery and realimentation of AN or SBS patients had no effect on either ANGPTL. Multiple regression analysis identified BMI as an independent predictor of ANGPTL3; and BMI and HbA_1c as independent predictors of ANGPTL4, respectively.

Conclusions

Taken together, our data suggest that serum ANGPTL3 and 4 levels are influenced by nutritional status and fasting and could be involved in the metabolic disturbances present in obesity and AN.

Adipose tissue lipolysis and remodeling during the transition period of dairy cows

Elevated concentrations of plasma fatty acids in transition dairy cows are significantly associated with increased disease susceptibility and poor lactation performance. The main source of plasma fatty acids throughout the transition period is lipolysis from adipose tissue depots. During this time, plasma fatty acids serve as a source of calories mitigating the negative energy balance prompted by copious milk synthesis and limited dry matter intake. Past research has demonstrated that lipolysis in the adipose organ is a complex process that includes not only the activation of lipolytic pathways in response to neural, hormonal, or paracrine stimuli, but also important changes in the structure and cellular distribution of the tissue in a process known as adipose tissue remodeling. This process involves an inflammatory response with immune cell migration, proliferation of the cellular components of the stromal vascular fraction, and changes in the extracellular matrix. This review summarizes current knowledge on lipolysis in dairy cattle, expands on the new field of adipose tissue remodeling, and discusses how these biological processes affect transition cow health and productivity.

Gut Microbiota Modulation and Its Relationship with Obesity Using Prebiotic Fibers and Probiotics: A Review

In the present world scenario, obesity has almost attained the level of a pandemic and is progressing at a rapid rate. This disease is the mother of all other metabolic disorders, which apart from placing an added financial burden on the concerned patient also has a negative impact on his/her well-being and health in the society. Among the various plausible factors for the development of obesity, the role of gut microbiota is very crucial. In general, the gut of an individual is inhabited by trillions of microbes that play a significant role in host energy homeostasis by their symbiotic interactions. Dysbiosis in gut microbiota causes disequilibrium in energy homeostasis that ultimately leads to obesity. Numerous mechanisms have been reported by which gut microbiota induces obesity in experimental models. However, which microbial community is directly linked to obesity is still unknown due to the complex nature of gut microbiota. Prebiotics and probiotics are the safer and effective dietary substances available, which can therapeutically alter the gut microbiota of the host. In this review, an effort was made to discuss the current mechanisms through which gut microbiota interacts with host energy metabolism in the context of obesity. Further, the therapeutic approaches (prebiotics/probiotics) that helped in positively altering the gut microbiota were discussed by taking experimental evidence from animal and human studies. In the closing statement, the challenges and future tasks within the field were discussed.

Differential RNA Expression Profile of Skeletal Muscle Induced by Experimental Autoimmune Myasthenia Gravis in Rats

The differential susceptibility of skeletal muscle by myasthenia gravis (MG) is not well understood. We utilized RNA expression profiling of extraocular muscle (EOM), diaphragm (DIA), and extensor digitorum (EDL) of rats with experimental autoimmune MG (EAMG) to evaluate the hypothesis that muscles respond differentially to injury produced by EAMG. EAMG was induced in female Lewis rats by immunization with acetylcholine receptor purified from the electric organ of the Torpedo. Six weeks later after rats had developed weakness and serum antibodies directed against the AChR, animals underwent euthanasia and RNA profiling performed on DIA, EDL, and EOM. Profiling results were validated by qPCR. Across the three muscles between the experiment and control groups, 359 probes (1.16%) with greater than 2-fold changes in expression in 7 of 9 series pairwise comparisons from 31,090 probes were identified with approximately two-thirds being increased. The three muscles shared 16 genes with increased expression and 6 reduced expression. Functional annotation demonstrated that these common expression changes fell predominantly into categories of metabolism, stress response, and signaling. Evaluation of specific gene function indicated that EAMG led to a change to oxidative metabolism. Genes related to muscle regeneration and suppression of immune response were activated. Evidence of a differential immune response among muscles was not evident. Each muscle had a distinct RNA profile but with commonality in gene categories expressed that are focused on muscle repair, moderation of inflammation, and oxidative metabolism.

Gut microbiome and metabolic syndrome

The gut microbiome contributes approximately 2kg of the whole body weight, and recent studies suggest that gut microbiota has a profound effect on human metabolism, potentially contributing to several features of the metabolic syndrome. Metabolic syndrome is defined by a clustering of metabolic disorders that include central adiposity with visceral fat accumulation, dyslipidemia, insulin resistance, dysglycemia and non-optimal blood pressure levels. Metabolic syndrome is associated with an increased risk of cardiovascular diseases and type 2 diabetes. It is estimated that around 20-25 percent of the world's adult population has metabolic syndrome. In this manuscript, we have reviewed the existing data linking gut microbiome with metabolic syndrome. Existing evidence from studies both in animals and humans support a link between gut microbiome and various components of metabolic syndrome. Possible pathways include involvement with energy homeostasis and metabolic processes, modulation of inflammatory signaling pathways, interferences with the immune system, and interference with the renin-angiotensin system. Modification of gut microbiota via prebiotics, probiotics or other dietary interventions has provided evidence to support a possible beneficial effect of interventions targeting gut microbiota modulation to treat components or complications of metabolic syndrome.

Influence of intestinal microbiota on body weight gain: a narrative review of the literature

In recent decades, experimental and clinical studies have associated the development of obesity with the composition of the gut microbiota. Mechanisms potentially involved in the contribution of gut microbiota to body weight gain include changes in energy extraction from the diet and the modulation of lipid metabolism, endocrine functions, and the immune system. The host's specific genetic heritage, the type and amount of food intake, chronic inflammation, reduced body energy expenditure, and exposure to obesogenic pollutants are also potential contributing factors. The pathophysiological processes involved in the relationship between gut microbiota and obesity are not fully understood, and further studies are needed to establish whether differences in gut bacterial diversity between obese and normal body weight individuals are the cause or a consequence of obesity.

Cancer as a Proinflammatory Environment: Metastasis and Cachexia

The development of the syndrome of cancer cachexia and that of metastasis are related with a poor prognostic for cancer patients. They are considered multifactorial processes associated with a proinflammatory environment, to which tumour microenvironment and other tissues from the tumour bearing individuals contribute. The aim of the present review is to address the role of ghrelin, myostatin, leptin, HIF, IL-6, TNF-α, and ANGPTL-4 in the regulation of energy balance, tumour development, and tumoural cell invasion. Hypoxia induced factor plays a prominent role in tumour macro- and microenvironment, by modulating the release of proinflammatory cytokines.

mRNA Expression of Ovine Angiopoietin-like Protein 4 Gene in Adipose Tissues

Angiopoietin-like protein 4 (ANGPTL4) is involved in a variety of functions, including lipoprotein metabolism and angiogenesis. To reveal the role of ANGPTL4 in fat metabolism of sheep, ovine ANGPTL4 mRNA expression was analyzed in seven adipose tissues from two breeds with distinct tail types. Forty-eight animals with the gender ratio of 1:1 for both Guangling Large Tailed (GLT) and Small Tailed Han (STH) sheep were slaughtered at 2, 4, 6, 8, 10, and 12 months of age, respectively. Adipose tissues were collected from greater and lesser omental, subcutaneous, retroperitoneal, perirenal, mesenteric, and tail fats. Ontogenetic mRNA expression of ANGPTL4 in these adipose tissues from GTL and STH was studied by quantitative real time polymerase chain reaction. The results showed that ANGPTL4 mRNA expressed in all adipose tissues studied with the highest in subcutaneous and the lowest in mesenteric fat depots. Months of age, tissue and breed are the main factors that significantly influence the mRNA expression. These results provide new insights into ovine ANGPTL4 gene expression and clues for its function mechanism.

Differential modulation by Akkermansia muciniphila and Faecalibacterium prausnitzii of host peripheral lipid metabolism and histone acetylation in mouse gut organoids

The gut microbiota is essential for numerous aspects of human health. However, the underlying mechanisms of many host-microbiota interactions remain unclear. The aim of this study was to characterize effects of the microbiota on host epithelium using a novel ex vivo model based on mouse ileal organoids. We have explored the transcriptional response of organoids upon exposure to short-chain fatty acids (SCFAs) and products generated by two abundant microbiota constituents, Akkermansia muciniphila and Faecalibacterium prausnitzii. We observed that A. muciniphila metabolites affect various transcription factors and genes involved in cellular lipid metabolism and growth, supporting previous in vivo findings. Contrastingly, F. prausnitzii products exerted only weak effects on host transcription. Additionally, A. muciniphila and its metabolite propionate modulated expression of Fiaf, Gpr43, histone deacetylases (HDACs), and peroxisome proliferator-activated receptor gamma (Pparγ), important regulators of transcription factor regulation, cell cycle control, lipolysis, and satiety. This work illustrates that specific bacteria and their metabolites differentially modulate epithelial transcription in mouse organoids. We demonstrate that intestinal organoids provide a novel and powerful ex vivo model for host-microbiome interaction studies.

We investigated the influence of the gut microbiota and microbially produced short-chain fatty acids (SCFAs) on gut functioning. Many commensal bacteria in the gut produce SCFAs, particularly butyrate, acetate, and propionate, which have been demonstrated to reduce the risk of gastrointestinal disorders. Organoids—small crypt-villus structures grown from ileal intestinal stem cells—were exposed to SCFAs and two specific gut bacteria. Akkermansia muciniphila, found in the intestinal mucus, was recently shown to have a favorable effect on the disrupted metabolism associated with obesity. Faecalibacterium prausnitzii is a commensal gut bacterium, the absence of which may be associated with Crohn’s disease. We showed that in our model, A. muciniphila induces stronger effects on the host than F. prausnitzii. We observed that A. muciniphila and propionate affect the expression of genes involved in host lipid metabolism and epigenetic activation or silencing of gene expression. We demonstrated that organoids provide a powerful tool for host-microbe interaction studies.

Physiological regulation of lipoprotein lipase

The enzyme lipoprotein lipase (LPL), originally identified as the clearing factor lipase, hydrolyzes triglycerides present in the triglyceride-rich lipoproteins VLDL and chylomicrons. LPL is primarily expressed in tissues that oxidize or store fatty acids in large quantities such as the heart, skeletal muscle, brown adipose tissue and white adipose tissue. Upon production by the underlying parenchymal cells, LPL is transported and attached to the capillary endothelium by the protein GPIHBP1. Because LPL is rate limiting for plasma triglyceride clearance and tissue uptake of fatty acids, the activity of LPL is carefully controlled to adjust fatty acid uptake to the requirements of the underlying tissue via multiple mechanisms at the transcriptional and post-translational level. Although various stimuli influence LPL gene transcription, it is now evident that most of the physiological variation in LPL activity, such as during fasting and exercise, appears to be driven via post-translational mechanisms by extracellular proteins. These proteins can be divided into two main groups: the liver-derived apolipoproteins APOC1, APOC2, APOC3, APOA5, and APOE, and the angiopoietin-like proteins ANGPTL3, ANGPTL4 and ANGPTL8, which have a broader expression profile. This review will summarize the available literature on the regulation of LPL activity in various tissues, with an emphasis on the response to diverse physiological stimuli.

Regulation of lipoprotein lipase by Angptl4

Triglyceride (TG)-rich chylomicrons and very low density lipoproteins (VLDL) distribute fatty acids (FA) to various tissues by interacting with the enzyme lipoprotein lipase (LPL). The protein angiopoietin-like 4 (Angptl4) is under sensitive transcriptional control by FA and the FA-activated peroxisome proliferator activated receptors (PPARs), and its tissue expression largely overlaps with that of LPL. Growing evidence indicates that Angptl4 mediates the physiological fluctuations in LPL activity, including the decrease in adipose tissue LPL activity during fasting. This review focuses on the major ambiguities concerning the mechanism of LPL inhibition by Angptl4, as well as on the physiological role of Angptl4 in lipid metabolism, highlighting its function in a variety of tissues, and uses this information to make suggestions for further research.

Repression of glucocorticoid-stimulated angiopoietin-like 4 gene transcription by insulin

Angiopoietin-like 4 (Angptl4) is a glucocorticoid receptor (GR) primary target gene in hepatocytes and adipocytes. It encodes a secreted protein that inhibits extracellular LPL and promotes adipocyte lipolysis. In Angptl4 null mice, glucocorticoid-induced adipocyte lipolysis and hepatic steatosis are compromised. Markedly, insulin suppressed glucocorticoid-induced Angptl4 transcription. To unravel the mechanism, we utilized small molecules to inhibit insulin signaling components and found that phosphatidylinositol 3-kinase and Akt were vital for the suppression in H4IIE cells. A forkhead box transcription factor response element (FRE) was found near the 15 bp Angptl4 glucocorticoid response element (GRE). Mutating the Angptl4 FRE significantly reduced glucocorticoid-induced reporter gene expression in cells. Moreover, chromatin immunoprecipitation revealed that GR and FoxO1 were recruited to Angptl4 GRE and FRE in a glucocorticoid-dependent manner, and cotreatment with insulin abolished both recruitments. Furthermore, in 24 h fasted mice, significant occupancy of GR and FoxO1 at the Angptl4 GRE and FRE was found in the liver. In contrast, both occupancies were diminished after 24 h refeeding. Finally, overexpression of dominant negative FoxO1 mutant abolished glucocorticoid-induced Angptl4 expression, mimicking the insulin suppression. Overall, we demonstrate that both GR and FoxO1 are required for Angptl4 transcription activation, and that FoxO1 negatively mediates the suppressive effect of insulin.

Characterization of the myometrial transcriptome in women with an arrest of dilatation during labor

OBJECTIVE

The molecular basis of failure to progress in labor is poorly understood. This study was undertaken to characterize the myometrial transcriptome of patients with an arrest of dilatation (AODIL).

STUDY DESIGN

Human myometrium was prospectively collected from women in the following groups: (1) spontaneous term labor (TL; n=29) and (2) arrest of dilatation (AODIL; n=14). Gene expression was characterized using Illumina® HumanHT-12 microarrays. A moderated Student's t-test and false discovery rate adjustment were used for analysis. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) of selected genes was performed in an independent sample set. Pathway analysis was performed on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database using Pathway Analysis with Down-weighting of Overlapping Genes (PADOG). The MetaCore knowledge base was also searched for pathway analysis.

RESULTS

(1) Forty-two differentially expressed genes were identified in women with an AODIL; (2) gene ontology analysis indicated enrichment of biological processes, which included regulation of angiogenesis, response to hypoxia, inflammatory response, and chemokine-mediated signaling pathway. Enriched molecular functions included transcription repressor activity, heat shock protein (Hsp) 90 binding, and nitric oxide synthase (NOS) activity; (3) MetaCore analysis identified immune response chemokine (C-C motif) ligand 2 (CCL2) signaling, muscle contraction regulation of endothelial nitric oxide synthase (eNOS) activity in endothelial cells, and triiodothyronine and thyroxine signaling as significantly overrepresented (false discovery rate <0.05); (4) qRT-PCR confirmed the overexpression of Nitric oxide synthase 3 (NOS3); hypoxic ischemic factor 1A (HIF1A); Chemokine (C-C motif) ligand 2 (CCL2); angiopoietin-like 4 (ANGPTL4); ADAM metallopeptidase with thrombospondin type 1, motif 9 (ADAMTS9); G protein-coupled receptor 4 (GPR4); metallothionein 1A (MT1A); MT2A; and selectin E (SELE) in an AODIL.

CONCLUSION

The myometrium of women with AODIL has a stereotypic transcriptome profile. This disorder has been associated with a pattern of gene expression involved in muscle contraction, an inflammatory response, and hypoxia. This is the first comprehensive and unbiased examination of the molecular basis of an AODIL.

Angiopoietin-like protein 4 (ANGPTL4) is induced by high glucose in retinal pigment epithelial cells and exhibits potent angiogenic activity on retinal endothelial cells

PURPOSE

Hyperglycaemia has been identified as major risk factor for diabetic retinopathy (DR). It is widely accepted that the progression of DR is mainly due to a local imbalance of pro- versus anti-angiogenic factors in the retina. In this study, we investigated whether retinal pigment epithelial (RPE) cells produced pro-angiogenic factors under high glucose (HG) conditions in vitro.

METHODS

Cultured human retinal endothelial (RE) cells were exposed to conditioned medium from retinal pigment epithelium cells (ARPE-19) grown in HG medium and assessed for tube formation. Based on the expression profiles of ARPE-19, we investigated whether ANGPTL4 was a major angiogenic factor released from ARPE-19 under HG conditions using cultured human RE cells as the test system for experiments with recombinant protein, conditioned medium from ARPE-19 and RNA interference (RNAi).

RESULTS

The conditioned medium from ARPE-19 cultured under HG conditions promoted tube formation of cultured human RE cells. GeneChip analysis showed that ANGPTL4 was one of the highest upregulated genes under HG conditions. In addition, recombinant ANGPTL4 promoted all of the elements of angiogenesis in human RE cells in vitro. The results of experiments using conditioned medium from ARPE-19 combined with RNAi demonstrated that ANGPTL4 was a major angiogenic factor released from ARPE-19 under HG conditions.

CONCLUSIONS

ANGPTL4 was induced by high glucose in RPE cells and exhibited potent angiogenic activity on RE cells. Our results are unique and may potentially add a new candidate to the long list of molecules involved in diabetic retinopathy.

Probiotics, prebiotics, energy balance, and obesity: mechanistic insights and therapeutic implications

Obesity-related disorders derive from a combination of genetic susceptibility and environmental factors. Recent evidence supports the role of gut microbiota in the pathogenesis of obesity, type 2 diabetes mellitus, and insulin resistance by increasing energy harvest from diet and by inducing chronic, low-grade inflammation. Several studies describe characteristic differences between composition and activity of gut microbiota of lean individuals and those with obesity. Despite this evidence, some pathophysiological mechanisms remain to be clarified. This article discusses mechanisms connecting gut microbiota to obesity and fat storage and the potential therapeutic role of probiotics and prebiotics.

Adipose tissue angiopoietin-like protein 4 messenger RNA changes with altered energy balance in lactating Holstein cows

Negative energy balance at the onset of lactation is unfavorably associated with fitness traits in high-producing dairy cows. Angiopoietin-like protein 4 (ANGPTL4) is an adipokine that has been associated with the regulation of lipid metabolism through the inhibition of lipoprotein lipase activity and regulation of lipolysis. Expression of ANGPTL4 messenger RNA (mRNA) increases during early lactation, but its regulation with changing energy status is currently unknown. Accordingly, the objective of this study was to determine whether ANGPTL4 mRNA abundance is responsive to declining energy balance induced by the transition from pregnancy to lactation, feed restriction, and GH administration in lactating dairy cows. The mRNA abundance of leptin, adiponectin, and adiponectin receptor 2 were also measured to compare adipokine mRNA profiles during changes in energy metabolism. Repeated adipose tissue biopsies were taken from different cows during transition from late pregnancy to lactation (n = 26), feed restriction (n = 19), and GH administration (n = 20). As expected, milk yield increased with the onset of lactation and GH administration (P < 0.01) but declined during feed restriction. Energy balance declined in each experiment, resulting in negative energy balance at the onset of lactation and after feed restriction. Abundance of ANGPTL4 mRNA expression increased 2- to 6-fold with declining energy balance in each experiment. Leptin mRNA declined with feed restriction, and adiponectin mRNA decreased with the onset of lactation. The consistency and magnitude of the increase in ANGPTL4 mRNA across multiple models of altered energy balance identifies it as an adipokine that is uniquely responsive to changes in energy balance in the lactating dairy cow.

Grape skin extract reduces adipogenesis- and lipogenesis-related gene expression in 3T3-L1 adipocytes through the peroxisome proliferator-activated receptor-γ signaling pathway

We previously reported that grape skin ethanol extract (GSE) decreases adipogenic transcription factor gene expression, inhibiting triglyceride accumulation in 3T3-L1 adipocytes. In this study, we hypothesized that GSE may induce differential expression profiles in adipocytes, thus providing protection against obesity. Thirty-five genes involved in the peroxisome proliferator-activated receptor-γ (PPARγ) signaling pathway, lipid metabolism, or adipogenesis were identified through microarray analysis of adipocytes treated with GSE. Expression of the genes involved in PPARγ signaling, Adipoq, Scd1, Nr1h3, Fabp5, Scd2, and Pparg decreased with GSE treatment, whereas expression of Ppargc1a increased. Lipid metabolism-associated genes Mlxp1, Stat5a, Hsl, Plin1, and Vdr were down-regulated. Interestingly, GSE also affected expression of genes related to the mitogen-activated protein kinases pathway. GSE extract treatment decreased expression of aP2, Fas, and Tnfa, known markers of adipogenesis, as measured by real-time polymerase reaction. These findings demonstrate the antiadipogenic effects of GSE on 3T3-L1 adipocytes at the genetic level, primarily on the PPARγ signaling pathway.

Angiopoietin-like protein 4: health effects, modulating agents and structure-function relationships

Angiopoietin-like protein 4 (ANGPTL4) has been identified as a multifunctional signal protein. It is produced by a variety of tissues, and is secreted into the bloodstream in glycosylated, oligomerized, native and cleaved isoforms to modulate physiological events such as angiogenesis, cell differentiation and the crosstalk between liver, brain, adipose and muscle tissue in lipid and glucose metabolism. In addition, the expression and isoform appearance of ANGPTL4 are modified by the intestinal microbiota. With an eye on an effective strategy to improve health using ANGPTL4, we will focus on: health issues associated with ANGPTL4 expression, including obesity, Type 2 diabetes, cardiovascular diseases and cancer; several modulators of ANGPTL4 of chemical, microbiological, food and host origin; and the correlation of the specific ANGPTL4 isoforms with these modulators and their health effects.

Fatty acids bind tightly to the N-terminal domain of angiopoietin-like protein 4 and modulate its interaction with lipoprotein lipase

Angiopoietin-like protein 4 (Angptl4), a potent regulator of plasma triglyceride metabolism, binds to lipoprotein lipase (LPL) through its N-terminal coiled-coil domain (ccd-Angptl4) inducing dissociation of the dimeric enzyme to inactive monomers. In this study, we demonstrate that fatty acids reduce the inactivation of LPL by Angptl4. This was the case both with ccd-Angptl4 and full-length Angptl4, and the effect was seen in human plasma or in the presence of albumin. The effect decreased in the sequence oleic acid > palmitic acid > myristic acid > linoleic acid > linolenic acid. Surface plasmon resonance, isothermal titration calorimetry, fluorescence, and chromatography measurements revealed that fatty acids bind with high affinity to ccd-Angptl4. The interactions were characterized by fast association and slow dissociation rates, indicating formation of stable complexes. The highest affinity for ccd-Angptl4 was detected for oleic acid with a subnanomolar equilibrium dissociation constant (K(d)). The K(d) values for palmitic and myristic acid were in the nanomolar range. Linoleic and linolenic acid bound with much lower affinity. On binding of fatty acids, ccd-Angptl4 underwent conformational changes resulting in a decreased helical content, weakened structural stability, dissociation of oligomers, and altered fluorescence properties of the Trp-38 residue that is located close to the putative LPL-binding region. Based on these results, we propose that fatty acids play an important role in modulating the effects of Angptl4.

Angiopoietin-like 4: a decade of research

The past decade has seen a rapid development and increasing recognition of ANGPTL4 (angiopoietin-like 4) as a remarkably multifaceted protein that is involved in many metabolic and non-metabolic conditions. ANGPTL4 has been recognised as a central player in various aspects of energy homoeostasis, at least in part, via the inhibitory interaction between the coiled-coil domain of ANGPTL4 and LPL (lipoprotein lipase). The fibrinogen-like domain of ANGPTL4 interacts and activates specific integrins to facilitate wound healing, modulates vascular permeability, and regulates ROS (reactive oxygen species) level to promote tumorigenesis. The present review summarizes these landmark findings about ANGPTL4 and highlights several important implications for future clinical practice. Importantly, these implications have also raised many questions that are in urgent need of further investigations, particularly the transcription regulation of ANGPTL4 expression, and the post-translation cleavage and modifications of ANGPTL4. The research findings over the past decade have laid the foundation for a better mechanistic understanding of the new scientific discoveries on the diverse roles of ANGPTL4.

Prebiotics to manage the microbial control of energy homeostasis

The prevalence of obesity is continuously growing and has reached epidemic proportions. It is clear that current methods to combat obesity are not effective enough to reduce the problem. Therefore, further investigation is needed to develop new strategies. Recent research pointed out a potential role of the microbial community associated to the human host in controlling and influencing the energy homeostasis. According to the concept of Gastrointestinal Resource Management, this microbiota and its metabolic potential can be steered with the aim of improving host health. This review therefore focuses on the modulation of the intestinal microbiota through prebiotics with the aim to control several aspects of metabolic homeostasis. In a first part, the importance of host-microbe cross-talk at the intestinal epithelium is discussed. Yet, energy metabolism, which includes both lipid and glucose metabolism, is also regulated by several key organs including the adipose tissue, brain, liver, muscles, pancreas and gut. Therefore, in a second part, we will discuss the microbial factors that are involved in the communication between these different tissues, and their potential management. Finally, we will give some future prospects of the use of prebiotics in an individualised treatment of metabolic disorders.

Angiopoietin-like 4 regulates epidermal differentiation

The nuclear hormone receptor PPARβ/δ is integral to efficient wound re-epithelialization and implicated in epidermal maturation. However, the mechanism underlying the latter process of epidermal differentiation remains unclear. We showed that ligand-activated PPARβ/δ indirectly stimulated keratinocyte differentiation, requiring de novo gene transcription and protein translation. Using organotypic skin cultures constructed from PPARβ/δ- and angiopoietin-like 4 (ANGPTL4)-knockdown human keratinocytes, we showed that the expression of ANGPTL4, a PPARβ/δ target gene, is essential for the receptor mediated epidermal differentiation. The pro-differentiation effect of PPARβ/δ agonist GW501516 was also abolished when keratinocytes were co-treated with PPARβ/δ antagonist GSK0660 and similarly in organotypic skin culture incubated with blocking ANGPTL4 monoclonal antibody targeted against the C-terminal fibrinogen-like domain. Our focused real-time PCR gene expression analysis comparing the skin biopsies from wildtype and ANGPTL4-knockout mice confirmed a consistent down-regulation of numerous genes involved in epidermal differentiation and proliferation in the ANGPTL4-knockout skin. We further showed that the deficiency of ANGPTL4 in human keratinocytes and mice skin have diminished expression of various protein kinase C isotypes and phosphorylated transcriptional factor activator protein-1, which are well-established for their roles in keratinocyte differentiation. Chromatin immunoprecipitation confirmed that ANGPTL4 stimulated the activation and binding of JUNB and c-JUN to the promoter region of human involucrin and transglutaminase type 1 genes, respectively. Taken together, we showed that PPARβ/δ regulates epidermal maturation via ANGPTL4-mediated signalling pathway.

Interactions between gut microbiota and host metabolism predisposing to obesity and diabetes

Novel, culture-independent, molecular and metagenomic techniques have provided new insight into the complex interactions between the mammalian host and gut microbial species. It is increasingly evident that gut microbes may shape the host metabolic and immune network activity and ultimately influence the development of obesity and diabetes. We discuss the evidence connecting gut microflora to obesity and to type 1 and type 2 diabetes, and we present recent insights into potential mechanisms underlying this relationship: increased nutrient absorption from the diet, prolonged intestinal transit time, altered bile acid entero-hepatic cycle, increased cellular uptake of circulating triglycerides, enhanced de novo lipogenesis, reduced free fatty acid oxidation, altered tissue composition of biologically active polyunsaturated fatty acid, chronic low-grade inflammation triggered by the endotoxin toll-like receptor 4 axis, and altered intestinal barrier function.

Bacterial monocultures, propionate, butyrate and H2O2 modulate the expression, secretion and structure of the fasting-induced adipose factor in gut epithelial cell lines

Previous research showed that an intestinal microbial community represses the fasting-induced adipose factor (FIAF) in the gut epithelium, thereby increasing fat storage in the host. This study was designed to investigate the overall effect of different bacterial species and metabolites on FIAF in intestinal (Caco-2, HT-29 and HCT-116) and hepatic (HepG2) cancer cell lines. First, we showed that FIAF was present in different isoforms, and secreted as N-glycosylated proteins, exclusively at the basal side of the cell monolayer. Second, co-incubation of cell lines with bacterial monocultures and metabolites altered both FIAF production and isoform appearance. Propionate and/or butyrate treatment increased FIAF expression and cleavage in all tested cell lines. In contrast, different bacteria induced cell line-specific FIAF modulation. Clostridium perfringens induced FIAF isoform changes in Caco-2 cells. Enterococcus faecalis and Bacteroides thetaiotaomicron treatment resulted in cell line-specific FIAF increases, whereas Escherichia coli significantly decreased FIAF expression in HCT-116 cells. Treatment with H(2) O(2) and peroxide-producing E. faecalis strains induced FIAF isoform changes in Caco-2 cells. Since bacteria and bacterial metabolites alter both FIAF production and isoform appearance, further investigation may reveal an important role for bacteria in FIAF-regulated physiological processes, such as cell differentiation and fat metabolism.

The transcriptomic profiles of adipose tissues are modified by feed deprivation in lactating goats

A major function of ruminant adipose tissue is to store lipids for use in productive functions. Body fat mobilization is required during periods of negative energy balance such as lactation or undernutrition. Until now, gene expression profiling of ruminant adipose tissue in response to nutritional restriction has not been performed. To gain a better understanding of the molecular mechanisms in adipose tissue in response to dietary factors, microarray analysis was used to compare the effects of two extreme nutritional conditions (control diet vs. 48-h feed deprivation) in the omental and perirenal adipose tissues of lactating goats (Capra hircus). We observed the altered expression of 456 and 199 genes in omental and perirenal adipose tissues, respectively. Similar biological processes were altered by feed deprivation in these two sites, although twice as many genes were differentially expressed in the omental than in the perirenal adipose tissue. Taken together, the transcriptional changes involved in lipid metabolism (decreased lipid synthesis and triglyceride storage capacity as well as increased fatty acid oxidation) were consistent with reduced energy deposition in goat adipose tissues in response to a 48-h fast. An inflammatory state of the adipose tissue was observed following the 48-h fast.

Sex-different hepaticglycogen content and glucose output in rats

Background

Genes involved in hepatic metabolism have a sex-different expression in rodents. To test whether male and female rat livers differ regarding lipid and carbohydrate metabolism, whole-genome transcript profiles were generated and these were complemented by measurements of hepatic lipid and glycogen content, fatty acid (FA) oxidation rates and hepatic glucose output (HGO). The latter was determined in perfusates from in situ perfusion of male and female rat livers. These perfusates were also analysed using nuclear magnetic resonance (NMR) spectroscopy to identify putative sex-differences in other liver-derived metabolites. Effects of insulin were monitored by analysis of Akt-phosphorylation, gene expression and HGO after s.c. insulin injections.

Results

Out of approximately 3 500 gene products being detected in liver, 11% were significantly higher in females, and 11% were higher in males. Many transcripts for the production of triglycerides (TG), cholesterol and VLDL particles were female-predominant, whereas genes for FA oxidation, gluconeogenesis and glycogen synthesis were male-predominant. Sex-differences in mRNA levels related to metabolism were more pronounced during mild starvation (12 h fasting), as compared to the postabsorptive state (4 h fasting). No sex-differences were observed regarding hepatic TG content, FA oxidation rates or blood levels of ketone bodies or glucose. However, males had higher hepatic glycogen content and higher HGO, as well as higher ratios of insulin to glucagon levels. Based on NMR spectroscopy, liver-derived lactate was also higher in males. HGO was inhibited by insulin in parallel with increased phosphorylation of Akt, without any sex-differences in insulin sensitivity. However, the degree of Thr172-phosphorylated AMP kinase (AMPK) was higher in females, indicating a higher degree of AMPK-dependent actions.

Conclusions

Taken together, males had higher ratios of insulin to glucagon levels, higher levels of glycogen, lower degree of AMPK phosphorylation, higher expression of gluconeogenic genes and higher hepatic glucose output. Possibly these sex-differences reflect a higher ability for the healthy male rat liver to respond to increased energy demands.

Tissue-specific effects of valsartan on rstn and fiaf gene expression in the ob/ob mouse

The RAS is a novel target in the study of diabetes, and clinical trials have indicated that ARBs, such as valsartan, may exert some of their clinical effects through an influence on adipose tissue. We studied the effect of valsartan on adipokine genes resistin (rstn) and fasting-induced adipose factor (fiaf) using obese and diabetic ob/ob mice. In addition to visceral and subcutaneous fat, rstn and fiaf mRNA levels were also measured in several other tissues known to express these adipokines, including the pituitary, cerebral cortex and hypothalamus. The significant findings were that (a) fiaf gene expression was elevated two- to fourfold in visceral and subcutaneous fat from ob/ob mice, compared with lean controls; (b) the increase in fiaf mRNA in subcutaneous, but not visceral, fat from ob/ob mice was returned to lean control levels following 2 weeks of valsartan treatment; (c) fiaf expression was reduced in the hypothalamus, but not in the cortex or pituitary, of ob/ob mice; (d) rstn expression was greatly reduced in visceral fat from ob/ob mice, compared with lean controls, but this was unaffected by valsartan; and (e) rstn expression was unchanged in all other tissues from ob/ob mice, with or without valsartan treatment.

Caloric restriction and exercise increase plasma ANGPTL4 levels in humans via elevated free fatty acids

OBJECTIVE

Plasma lipoprotein levels are determined by the balance between lipoprotein production and clearance. Recently, angiopoietin-like protein 4 (ANGPTL4) was uncovered as a novel endocrine factor that potently raises plasma triglyceride levels by inhibiting triglyceride clearance. However, very little is known about ANGPTL4 in human. Here we set out to identify physiological determinants of plasma ANGPTL4 levels in humans, focusing on the effect of energy restriction and plasma FFAs.

METHODS AND RESULTS

We developed an ELISA for quantitative measurement of ANGPTL4 in human plasma. Using this assay we found major variations in baseline plasma ANGPTL4 levels between individuals. Within an individual, plasma ANGPTL4 levels remain stable throughout the day but increase significantly in response to long-term fasting, chronic caloric restriction, and endurance exercise. Intralipid injection as well as treatment with a beta-adrenergic agonist, both of which lead to elevated plasma FFA levels, increased plasma ANGPTL4 levels compared to control treatment. Fatty acids markedly induced ANGPTL4 gene expression in rat hepatoma FAO cells, human primary myocytes, and mouse intestinal MSIE cells.

CONCLUSIONS

In conclusion, our results show that plasma ANGPTL4 levels are increased by fasting, caloric restriction, and exercise, which is likely mediated by elevated plasma FFAs.

Acute regulation of metabolic genes and insulin receptor substrates in the liver of mice by one single bout of treadmill exercise

Acute exercise performance represents a major metabolic challenge for the skeletal muscle, but also for the liver as the most important source of energy. However the molecular adaptation of the liver to one single bout of exercise is largely unknown. C57BL/6 mice performed a 60 min treadmill run at high aerobic intensity. Liver, soleus and white gastrocnemius muscle were removed immediately after exercise. The single bout of exercise resulted in a very rapid and pronounced induction of hepatic metabolic enzymes and regulators of metabolism or transcription: glucose-6-phosphatase (G6Pase; 3-fold), pyruvate dehydrogenase kinase-4 (PDK4; 4.8-fold), angiopoietin-like 4 (2.1-fold), insulin receptor substrate (IRS)-2 (5.1-fold), peroxisome proliferator activated receptor-gamma coactivator 1alpha (PGC-1alpha; 3-fold). In soleus and white gastrocnemius muscle the up-regulation of IRS-2 and PDK4 was less pronounced compared with the liver and no significant induction of PGC-1alpha could be detected at this early time point. Activation of AMPK was found in both liver and white gastrocnemius muscle as phosphorylation of Thr-172. The induction of endogenous insulin secretion by a glucose load directly after the exercise bout resulted in a significantly higher PKB/Akt phosphorylation in the liver of exercised mice. The markedly enhanced IRS-2 protein amount, and presumably reduced serine/threonine phosphorylation of the IRS proteins induced by the acute exercise could be responsible for this enhanced action of insulin. In conclusion, acute exercise induced a rapid and pronounced transcriptional adaptation in the liver, and regulated hepatic IRS proteins leading to improved cellular insulin signal transduction.

ANGPTL4 E40K and T266M: effects on plasma triglyceride and HDL levels, postprandial responses, and CHD risk

BACKGROUND

Angiopoietin-like 4 is a dual-function protein: an inhibitor of LPL, influencing plasma triglycerides (TGs), with angiogenic properties. We examined the association of common ANGPTL4 variants with CHD traits and risk in 5 studies (13,527 individuals).

METHODS AND RESULTS

The effects on plasma lipids of 6 tagging SNPs and the recently identified E40K were examined in a study of 2772 men. Only T266M (rs1044250, MAF=30%) and E40K (MAF=2%) were significantly associated with TG-lowering (-10.4%, P<0.004 and -20.4%, P<0.0001), respectively. T266M no longer showed significant associations when K40 carriers (K40+) were excluded (P=0.2). Combining data from 5 studies confirmed the TG-lowering effect of K40+ (weighted mean difference: -0.12 [95% CI -0.18, -0.05] mmol/L TG P=0.0001). Surprisingly, in the 3 prospective studies, the combined OR for CHD was 1.48 (1.11 to 1.96, P=0.007), independent of TG. In individuals with a paternal history of MI (n=332) T266M, but not E40K, showed effects on postprandial AUC TG and glucose (P=0.009 and P=0.017, respectively) compared to controls (n=370).

CONCLUSIONS

Although associated with an atheroprotective lipid profile, E40K was associated with increased CHD risk, suggesting Angptl4 influences parameters beyond lipid levels. T266M showed effects only under conditions of postprandial stress. The functionality of these potential "loss-of-function" variants needs validation.