Tissue-specific overexpression of lipoprotein lipase causes tissue-specific insulin resistance

Exploring the Role of Skeletal Muscle in Insulin Resistance: Lessons from Cultured Cells to Animal Models

Skeletal muscle is essential to maintain vital functions such as movement, breathing, and thermogenesis, and it is now recognized as an endocrine organ. Muscles release factors named myokines, which can regulate several physiological processes. Moreover, skeletal muscle is particularly important in maintaining body homeostasis, since it is responsible for more than 75% of all insulin-mediated glucose disposal. Alterations of skeletal muscle differentiation and function, with subsequent dysfunctional expression and secretion of myokines, play a key role in the pathogenesis of obesity, type 2 diabetes, and other metabolic diseases, finally leading to cardiometabolic complications. Hence, a deeper understanding of the molecular mechanisms regulating skeletal muscle function related to energy metabolism is critical for novel strategies to treat and prevent insulin resistance and its cardiometabolic complications. This review will be focused on both cellular and animal models currently available for exploring skeletal muscle metabolism and endocrine function.

Distinct Roles of Perilipins in the Intramuscular Deposition of Lipids in Glutamine-Supplemented, Low-, and Normal-Birth-Weight Piglets

Piglets with low birth weight (LBW) usually have reduced muscle mass and increased lipid deposition compared with their normal-birth-weight (NBW) littermates. Supplementation of piglets with amino acids during the first days of life may improve muscle growth and simultaneously alter the intramuscular lipid deposition. The aim of the current study was to investigate the influence of glutamine (Gln) supplementation during the early suckling period on lipid deposition in the longissimus muscle (MLD) and the role of different perilipin (PLIN) family members in this process. Four groups were generated consisting of 72 male LBW piglets and 72 NBW littermates. Piglets were supplemented with either 1 g Gln/kg body weight or an isonitrogenous amount of alanine (Ala) between days post natum (dpn) 1 and 12. Twelve piglets per group were slaughtered at 5, 12, and 26 dpn, and muscle tissue was collected. Perilipins were localized by immunohistochemistry in muscle sections. The mRNA and protein abundances of PLIN family members and related lipases were quantified by quantitative RT-PCR (qPCR) and western blots, respectively. While PLIN1 was localized around lipid droplets in mature and developing adipocytes, PLIN2 was localized at intramyocellular lipid droplets, PLIN3 and 4 at cell membranes of muscle fibers and adipocytes, and PLIN5 in the cytoplasm of undefined cells. The western blot results indicated higher protein abundances of PLIN2, 3, 4, and 5 in LBW piglets (p < 0.05) at 5 dpn compared with their NBW littermates independent of supplementation, while not directly reflecting the mRNA expression levels. The mRNA abundance of PLIN2 was lower while PLIN4 was higher in piglets at 26 dpn in comparison with piglets at 5 dpn (p < 0.01). Relative mRNA expression of LPL and CGI-58 was lowest in piglets at 5 dpn (p < 0.001). However, ATGL mRNA was not influenced by birth weight or supplementation, but the Spearman correlation coefficient analysis revealed close correlations with PLIN2, 4, and 5 mRNA at 5 and 26 dpn (r > 0.5, p < 0.001). The results indicated the importance of birth weight and age for intramuscular lipid deposition and different roles of PLIN family members in this process, but no clear modulating effect of Gln supplementation.

Analysis of anti-obesity and anti-diabetic effects of acacia bark-derived proanthocyanidins in type 2 diabetes model KKAy mice

The acacia bark extract derived from Acacia mearnsii De Wild is rich in proanthocyanidins, whose constituent units are robinetinidol, fisetinidol, catechin, and gallocatechin. In this study, we examined the effect of proanthocyanidins on obesity and diabetes using KKAy mice, a type 2 diabetes model. KKAy mice were fed either a low-fat diet, a high-fat diet, or a high-fat diet mixed with an acacia bark extract, a proanthocyanidins fraction, and other fraction for 7 weeks. Monitoring the changes in the body weight revealed that acacia bark extract and proanthocyanidins fraction could prevent excessive weight gain resulting from a high-fat diet. In addition, increases in the fasting blood glucose level due to high-fat diet intake were found to be suppressed by acacia bark extract and proanthocyanidins fraction. Furthermore, proanthocyanidins derived from acacia bark were found to increase the expression of adiponectin in white adipose tissue, which enhances the action of insulin. In addition, acacia bark-derived proanthocyanidins suppressed gluconeogenesis and fatty acid synthesis in the liver, as well as suppressing the decrease in energy production under pathological conditions in skeletal muscle. In addition, acacia bark-derived proanthocyanidins showed AMPK activation and DPP-4 inhibitory action. Therefore, it was suggested that acacia bark-derived proanthocyanidins lowered fasting blood glucose levels through the above mechanism. These results suggest that proanthocyanidins derived from acacia bark are the active ingredients of the anti-obesity and anti-diabetic effects of acacia bark extract.

1H NMR Metabolomics and Full-Length RNA-Seq Reveal Effects of Acylated and Nonacylated Anthocyanins on Hepatic Metabolites and Gene Expression in Zucker Diabetic Fatty Rats

Anthocyanins have been reported to possess antidiabetic effects. Recent studies indicate acylated anthocyanins have better stability and antioxidative activity compared to their nonacylated counterparts. This study compared the effects of nonacylated and acylated anthocyanins on hepatic gene expression and metabolic profile in diabetic rats, using full-length transcriptomics and ¹H NMR metabolomics. Zucker diabetic fatty (ZDF) rats were fed with nonacylated anthocyanin extract from bilberries (NAAB) or acylated anthocyanin extract from purple potatoes (AAPP) at daily doses of 25 and 50 mg/kg body weight for 8 weeks. Both anthocyanin extracts restored the levels of multiple metabolites (glucose, lactate, alanine, and pyruvate) and expression of genes (G6pac, Pck1, Pklr, and Gck) involved in glycolysis and gluconeogenesis. AAPP decreased the hepatic glutamine level. NAAB regulated the expression of Mgat4a, Gstm6, and Lpl, whereas AAPP modified the expression of Mgat4a, Jun, Fos, and Egr1. This study indicated different effects of AAPP and NAAB on the hepatic transcriptomic and metabolic profiles of diabetic rats.

Lipoprotein Lipase Overexpression in Skeletal Muscle Attenuates Weight Regain by Potentiating Energy Expenditure

Moderate weight loss improves numerous risk factors for cardiometabolic disease; however, long-term weight loss maintenance (WLM) is often thwarted by metabolic adaptations that suppress energy expenditure and facilitate weight regain. Skeletal muscle has a prominent role in energy homeostasis; therefore, we investigated the effect of WLM and weight regain on skeletal muscle in rodents. In skeletal muscle of obesity-prone rats, WLM reduced fat oxidative capacity and downregulated genes involved in fat metabolism. Interestingly, even after weight was regained, genes involved in fat metabolism were also reduced. We then subjected mice with skeletal muscle lipoprotein lipase overexpression (mCK-hLPL), which augments fat metabolism, to WLM and weight regain and found that mCK-hLPL attenuates weight regain by potentiating energy expenditure. Irrespective of genotype, weight regain suppressed dietary fat oxidation and downregulated genes involved in fat metabolism in skeletal muscle. However, mCK-hLPL mice oxidized more fat throughout weight regain and had greater expression of genes involved in fat metabolism and lower expression of genes involved in carbohydrate metabolism during WLM and regain. In summary, these results suggest that skeletal muscle fat oxidation is reduced during WLM and regain, and therapies that improve skeletal muscle fat metabolism may attenuate rapid weight regain.

Oxidative stress and Liver X Receptor agonist induce hepatocellular carcinoma in Non-alcoholic steatohepatitis model

BACKGROUND AND AIM

The incidence of non-alcoholic steatohepatitis (NASH)-related hepatocellular carcinoma (HCC) is progressively increasing. However, the pathophysiology and etiology of NASH progression to HCC are unknown. We hypothesized that steatosis was the key factor in NASH-related hepatocarcinogenesis and aimed to evaluate the effects of long-term liver X receptor (LXR) agonist stimulation on hepatic steatosis induced by a high-fat diet and oxidative stress.

METHODS

We used an LXR agonist (T0901317) and CCl4 to induce hepatic steatosis and oxidative stress, respectively. C57BL/6 mice fed with a high-fat diet were treated with either T0901317 + CCl4 (T09 + CCl4 group) or CCl4 alone (CCl4 group). T0901317 (2.5 mg/kg) and CCl4 (0.1 mL/kg) were intraperitoneally administered twice weekly for 24 weeks.

RESULTS

The liver-to-body weight ratio was significantly higher in the T09 + CCl4 group than in the CCl4 group. Mice in the T09 + CCl4 group exhibited abnormal lipid metabolism and NASH-like histopathological features. Additionally, all mice in the T09 + CCl4 group developed liver tumors diagnosed as well-differentiated HCC. The genes identified via microarray analysis were related to NASH and HCC development.

CONCLUSIONS

By combining long-term LXR agonist stimulation with oxidative stress and a high-fat diet, we successfully reproduced liver conditions in mice similar to those in humans with NASH and progression to HCC. Our results provide new insight into NASH-related HCC progression and therapy.

Divergent trajectories of cellular bioenergetics, intermediary metabolism and systemic redox status in survivors and non-survivors of critical illness

Background

Numerous pathologies result in multiple-organ failure, which is thought to be a direct consequence of compromised cellular bioenergetic status. Neither the nature of this phenotype nor its relevance to survival are well understood, limiting the efficacy of modern life-support.

Methods

To explore the hypothesis that survival from critical illness relates to changes in cellular bioenergetics, we combined assessment of mitochondrial respiration with metabolomic, lipidomic and redox profiling in skeletal muscle and blood, at multiple timepoints, in 21 critically ill patients and 12 reference patients.

Results

We demonstrate an end-organ cellular phenotype in critical illness, characterized by preserved total energetic capacity, greater coupling efficiency and selectively lower capacity for complex I and fatty acid oxidation (FAO)-supported respiration in skeletal muscle, compared to health. In survivors, complex I capacity at 48 h was 27% lower than in non-survivors (p = 0.01), but tended to increase by day 7, with no such recovery observed in non-survivors. By day 7, survivors’ FAO enzyme activity was double that of non-survivors (p = 0.048), in whom plasma triacylglycerol accumulated. Increases in both cellular oxidative stress and reductive drive were evident in early critical illness compared to health. Initially, non-survivors demonstrated greater plasma total antioxidant capacity but ultimately higher lipid peroxidation compared to survivors. These alterations were mirrored by greater levels of circulating total free thiol and nitrosated species, consistent with greater reductive stress and vascular inflammation, in non-survivors compared to survivors. In contrast, no clear differences in systemic inflammatory markers were observed between the two groups.

Conclusion

Critical illness is associated with rapid, specific and coordinated alterations in the cellular respiratory machinery, intermediary metabolism and redox response, with different trajectories in survivors and non-survivors. Unravelling the cellular and molecular foundation of human resilience may enable the development of more effective life-support strategies.

Virtual metabolic human dynamic model for pathological analysis and therapy design for diabetes

A virtual metabolic human model is a valuable complement to experimental biology and clinical studies, because in vivo research involves serious ethical and technical problems. I have proposed a multi-organ and multi-scale kinetic model that formulates the reactions of enzymes and transporters with the regulation of hormonal actions at postprandial and postabsorptive states. The computational model consists of 202 ordinary differential equations for metabolites with 217 reaction rates and 1,140 kinetic parameter constants. It is the most comprehensive, largest, and highly predictive model of the whole-body metabolism. Use of the model revealed the mechanisms by which individual disorders, such as steatosis, β cell dysfunction, and insulin resistance, were combined to cause diabetes. The model predicted a glycerol kinase inhibitor to be an effective medicine for type 2 diabetes, which not only decreased hepatic triglyceride but also reduced plasma glucose. The model also enabled us to rationally design combination therapy.

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A standard of virtual metabolic human dynamic models is proposed

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It integrates the three scales of molecules, organs, and whole body

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It gets insight into pathological mechanisms of type 1 and type 2 diabetes

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It enables the computer-aided design of medication treatment for diabetes

Dietary sodium restriction alters muscle lipidomics that relates to insulin resistance in mice

A low-sodium (LS) diet has been shown to reduce blood pressure (BP) and the incidence of cardiovascular diseases. However, severe dietary sodium restriction promotes insulin resistance (IR) and dyslipidemia in animal models and humans. Thus, further clarification of the long-term consequences of LS is needed. Here, we investigated the effects of chronic LS on gastrocnemius gene and protein expression and lipidomics and its association with IR and plasma lipids in LDL receptor knockout mice. Three-month-old male mice were fed a normal sodium diet (NS; 0.5% Na; n = 12-19) or LS (0.06% Na; n = 14-20) over 90 days. Body mass (BM), BP, plasma total cholesterol, triacylglycerol (TG), glucose, hematocrit, and IR were evaluated. LS increased BM (9%), plasma TG (51%), blood glucose (19%), and IR (46%) when compared with the NS. RT-qPCR analysis revealed that genes involved in lipid uptake and oxidation were increased by the LS: Fabp3 (106%), Prkaa1 (46%), and Cpt1 (74%). Genes and proteins (assessed by Western blotting) involved in insulin signaling were not changed by the LS. Similarly, lipid species classically involved in muscle IR, such as diacylglycerols and ceramides detected by ultra-high-performance liquid chromatography coupled to mass spectrometry, were also unchanged by LS. Species of phosphatidylcholines (68%), phosphatidylinositol (90%), and free fatty acids (59%) increased while cardiolipins (41%) and acylcarnitines (9%) decreased in gastrocnemius in response to LS and were associated with glucose disposal rate. Together these results suggest that chronic LS alters glycerophospholipid and fatty acids species in gastrocnemius that may contribute to glucose and lipid homeostasis derangements in mice.

Effect of maternal nutrient restriction on expression of glucose transporters (SLC2A4 and SLC2A1) and insulin signaling in skeletal muscle of SGA and Non-SGA sheep fetuses

Maternal nutrient restriction (NR) causes small for gestational age (SGA) offspring, which are at higher risk for accelerated postnatal growth and developing insulin resistance in adulthood. Skeletal muscle is essential for whole-body glucose metabolism, as 80% of insulin-mediated glucose uptake occurs in this tissue. Maternal NR can alter fetal skeletal muscle mass, expression of glucose transporters, insulin signaling, and myofiber type composition. It also leads to accumulation of intramuscular triglycerides (IMTG), which correlates to insulin resistance. Using a 50% NR treatment from gestational day (GD) 35 to GD 135 in sheep, we routinely observe a spectral phenotype of fetal weights within the NR group. Thus, we classified those fetuses into NR(Non-SGA; n = 11) and NR(SGA; n = 11). The control group (n = 12) received 100% of nutrient requirements throughout pregnancy. At GD 135, fetal plasma and gastrocnemius and soleus muscles were collected. In fetal plasma, total insulin was lower in NR(SGA) fetuses compared NR(Non-SGA) and control fetuses (P < 0.01), whereas total IGF-1 was lower in NR(SGA) fetuses compared with control fetuses (P < 0.05). Within gastrocnemius, protein expression of insulin receptor (INSRB; P < 0.05) and the glucose transporters, solute carrier family 2 member 1 and solute carrier family 2 member 4, was higher (P < 0.05) in NR(SGA) fetuses compared with NR(Non-SGA) fetuses; IGF-1 receptor protein was increased (P < 0.01) in NR(SGA) fetuses compared with control fetuses, and a lower (P < 0.01) proportion of type I myofibers (insulin sensitive and oxidative) was observed in SGA fetuses. For gastrocnemius muscle, the expression of lipoprotein lipase (LPL) messenger RNA (mRNA) was upregulated (P < 0.05) in both NR(SGA) and NR(Non-SGA) fetuses compared with control fetuses, whereas carnitine palmitoyltransferase 1B (CPT1B) mRNA was higher (P < 0.05) in NR(Non-SGA) fetuses compared with control fetuses, but there were no differences (P > 0.05) for protein levels of LPL or CPT1B. Within soleus, there were no differences (P > 0.05) for any characteristic except for the proportion of type I myofibers, which was lower (P < 0.05) in NR(SGA) fetuses compared with control fetuses. Accumulation of IMTG did not differ (P > 0.05) in gastrocnemius or soleus muscles. Collectively, the results indicate molecular differences between SGA and Non-SGA fetuses for most characteristics, suggesting that maternal NR induces a spectral phenotype for the metabolic programming of those fetuses.

Clinical relevance of lipid panel and aminotransferases in the context of hepatic steatosis and fibrosis as measured by transient elastography (FibroScan®)

Background

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of chronic liver disease and is associated with various co-morbidities. Transient elastography (FibroScan®) is a non-invasive method to detect NAFLD using the controlled attenuation parameter (CAP). We aimed to evaluate the association of the lipid panel and aminotransferases concentrations with the presence or absence of steatosis and fibrosis.

Methods

One hundred and five patients with NAFLD were included. Hepatic steatosis was quantified by CAP (dB/m) and liver stiffness by Kilopascals (kPa), these values were then analyzed against patient lipid panel and serum concentrations of the liver enzymes aspartate aminotransferase (AST) and alanine aminotransferase (ALT). A correlation and multiple regression were used. Mann-Whitney U test was used as non-parametric analysis.

Results

We observed an association between hepatic steatosis and total cholesterol (B = 0.021, p = 0.038, Exp (B) = 1.021, I.C = 1.001-1.041) as well as serum triglycerides (B = 0.017, p = 0.006, Exp (B) = 1.018 and I.C = 1.005-1.030). Similarly, we found an association between significant hepatic fibrosis and lower concentrations of total cholesterol (B = -0.019, p = 0.005, Exp (B) = 0.982 I.C = 0.969-0.995) and elevated AST (B = 0.042, p = 3.25 × 10^-4, Exp (B) = 1.043 I.C = 1.019-1.068) independent of age, gender and BMI.

Conclusions

Our results suggest that, total cholesterol and triglyceride concentrations positively correlate with hepatic steatosis while significant hepatic fibrosis is associated with lower total cholesterol and higher AST concentrations.

Prediction of preeclampsia risk in first time pregnant women: Metabolite biomarkers for a clinical test

Preeclampsia remains a leading cause of maternal and perinatal morbidity and mortality. Accurate prediction of preeclampsia risk would enable more effective, risk-based prenatal care pathways. Current risk assessment algorithms depend on clinical risk factors largely unavailable for first-time pregnant women. Delivering accurate preeclampsia risk assessment to this cohort of women, therefore requires for novel biomarkers. Here, we evaluated the relevance of metabolite biomarker candidates for their selection into a prototype rapid, quantitative Liquid Chromatography-tandem Mass Spectrometry (LC-MS/MS) based clinical screening assay. First, a library of targeted LC-MS/MS assays for metabolite biomarker candidates was developed, using a medium-throughput translational metabolomics workflow, to verify biomarker potential in the Screening-for-Pregnancy-Endpoints (SCOPE, European branch) study. A variable pre-selection step was followed by the development of multivariable prediction models for pre-defined clinical use cases, i.e., prediction of preterm preeclampsia risk and of any preeclampsia risk. Within a large set of metabolite biomarker candidates, we confirmed the potential of dilinoleoyl-glycerol and heptadecanoyl-2-hydroxy-sn-glycero-3-phosphocholine to effectively complement Placental Growth Factor, an established preeclampsia biomarker, for the prediction of preeclampsia risk in first-time pregnancies without overt risk factors. These metabolites will be considered for integration in a prototype rapid, quantitative LC-MS/MS assay, and subsequent validation in an independent cohort.

The NLRP3 inflammasome regulates adipose tissue metabolism

Adipose tissue regulates metabolic homeostasis by participating in endocrine and immune responses in addition to storing and releasing lipids from adipocytes. Obesity skews adipose tissue adipokine responses and degrades the coordination of adipocyte lipogenesis and lipolysis. These defects in adipose tissue metabolism can promote ectopic lipid deposition and inflammation in insulin-sensitive tissues such as skeletal muscle and liver. Sustained caloric excess can expand white adipose tissue to a point of maladaptation exacerbating both local and systemic inflammation. Multiple sources, instigators and propagators of adipose tissue inflammation occur during obesity. Cross-talk between professional immune cells (i.e. macrophages) and metabolic cells (i.e. adipocytes) promote adipose tissue inflammation during metabolic stress (i.e. metaflammation). Metabolic stress and endogenous danger signals can engage pathogen recognition receptors (PRRs) of the innate immune system thereby activating pro-inflammatory and stress pathways in adipose tissue. The Nod-like receptor protein 3 (NLRP3) inflammasome can act as a metabolic danger sensor to a wide range of pathogen- and damage-associated molecular patterns (PAMPs and DAMPs). Activation of the NLRP3 inflammasome facilitates caspase-1 dependent production of the pro-inflammatory cytokines IL-1β and IL-18. Activation of the NLRP3 inflammasome can promote inflammation and pyroptotic cell death, but caspase-1 is also involved in adipogenesis. This review discusses the role of the NLRP3 inflammasome in adipose tissue immunometabolism responses relevant to metabolic disease. Understanding the potential sources of NLRP3 activation and consequences of NLRP3 effectors may reveal therapeutic opportunities to break or fine-tune the connection between metabolism and inflammation in adipose tissue during obesity.

Antisense Oligonucleotides as Potential Therapeutics for Type 2 Diabetes

Type 2 diabetes (T2D) is a chronic metabolic disorder characterized by persistent hyperglycemia resulting from inefficient signaling and insufficient production of insulin. Conventional management of T2D has largely relied on small molecule-based oral hypoglycemic medicines, which do not halt the progression of the disease due to limited efficacy and induce adverse effects as well. To this end, antisense oligonucleotide has attracted immense attention in developing antidiabetic agents because of their ability to downregulate the expression of disease-causing genes at the RNA and protein level. To date, seven antisense agents have been approved by the United States Food and Drug Administration for therapies of a variety of human maladies, including genetic disorders. Herein, we provide a comprehensive review of antisense molecules developed for suppressing the causative genes believed to be responsible for insulin resistance and hyperglycemia toward preventing and treating T2D.

The Role of Ceramides in Diabetes and Cardiovascular Disease Regulation of Ceramides by Adipokines

Metabolic dysfunction is intertwined with the pathophysiology of both diabetes and cardiovascular disease. Recently, one particular lipid class has been shown to influence the development and sustainment of these diseases: ceramides. As a subtype of sphingolipids, these species are particularly central to many sphingolipid pathways. Increased levels of ceramides are known to correlate with impaired cardiovascular and metabolic health. Furthermore, the interaction between ceramides and adipokines, most notably adiponectin and leptin, appears to play a role in the pathophysiology of these conditions. Adiponectin appears to counteract the detrimental effects of elevated ceramides, largely through activation of the ceramidase activity of its receptors. Elevated ceramides appear to worsen leptin resistance, which is an important phenomenon in the pathophysiology of obesity and metabolic syndrome.

Acetic acid stimulates G-protein-coupled receptor GPR43 and induces intracellular calcium influx in L6 myotube cells

Short chain fatty acids (SCFAs) produced endogenously in the gut by bacterial fermentation of dietary fiber have been studied as nutrients that act as signaling molecules to activate G-protein coupled receptors (GPCRs) such as GPR41 and GPR43. GPR43 functioning involves the suppression of lipid accumulation and maintaining body energy homeostasis, and is activated by acetic acid or propionic acid. Previously, we reported that the orally administered acetic acid improves lipid metabolism in liver and skeletal muscles and suppresses obesity, thus improving glucose tolerance. Acetic acid stimulates AMP-activated protein kinase (AMPK) through its metabolic pathway in skeletal muscle cells. We hypothesized that acetic acid would stimulate GPR43 in skeletal muscle cells and has function in modulating gene expression related to muscle characteristics through its signal pathway. The objective of the current study was to clarify this effect of acetic acid. The GPR43 expression, observed in the differentiated myotube cells, was increased upon acetic acid treatment. Acetic acid induced the intracellular calcium influx in the cells and this induction was significantly inhibited by the GPR43-specific siRNA treatment. The calcineurin molecule is activated by calcium/calmodulin and is associated with proliferation of slow-twitch fibers. Calcineurin was activated by acetic acid treatment and inhibited by the concomitant treatment with GPR43-siRNA. Acetic acid induced nuclear localization of myocyte enhancer factor 2A (MEF2A), peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), and nuclear factor of activated t cells c1 (NFATc1). However, these localizations were abolished by the treatment with GPR43-siRNA. It was concluded that acetic acid plays a role in the activation of GPR43 and involves the proliferation of slow-twitch fibers in L6 skeletal muscles through the calcium-signaling pathway caused by induction of intracellular calcium influx.

Relationship between hepatic and systemic angiopoietin-like 3, hepatic Vitamin D receptor expression and NAFLD in obesity

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide and an independent risk factor for cardiovascular mortality. Angiopoietin-like proteins (ANGPTLs) are targets for vitamin D receptor (VDR)-mediated gene transcription and this axis may promote NAFLD. ANGPTL3 is a hepatokine which inhibits lipoprotein lipase and its experimentally induced inactivation reduces hepatosteatosis. Little is known on ANGPTL3 in human NAFLD and no data exist on its relationship with hepatic VDR/VD-related genes. The aim of this research was to investigate hepatic ANGPTLs and VDR/VD-related gene expression in human obesity in relation to NAFLD.

METHODS

We conducted a cross-sectional investigation on forty obese subjects with/without NAFLD. We evaluated hepatic ANGPTL3, ANGPTL4, ANGPTL8, LPL, VDR, CYP27A1 and CYP2R1 mRNA expression in liver biopsies by RT-PCR; VDR expression was further investigated by immunohistochemistry; circulating ANGPTL3 was measured by Milliplex assay.

RESULTS

Compared to non-NAFLD, NAFLD individuals had significantly higher hepatic VDR, ANGPTL3 and LPL expression. ANGPTL3 correlated with steatosis grade, LPL, VDR, CYP27A1 and CYP2R1 expression. Plasma ANGPTL3 concentrations were positively associated with clinical/histological markers of NAFLD/NASH and with hepatic ANGPTL3 expression. Greater hepatic VDR expression was the main determinant of hepatic ANGPTL3 after adjusting for multiple confounders.

CONCLUSIONS

Hepatic ANGPTL3 expression correlates with greater VDR expression, presence and severity of NAFLD and translates in increased circulating ANGPTL3, likely as a result of its modulation by up-regulated hepatic VDR in NAFLD. This study provides novel insights to potential mechanisms underlying ANGPTLs-mediated ectopic fat accumulation and NAFLD development in obesity.

Aging and plasma triglyceride metabolism

The risk for metabolic disease, including metabolic syndrome, insulin resistance, and diabetes, increases with age. Altered plasma TG metabolism and changes in fatty acid partitioning are also major contributors to metabolic disease. Plasma TG metabolism itself is altered by age in humans and rodents. As discussed in this review, the age-induced changes in human TG metabolism include increased plasma TG levels, reduced postprandial plasma TG clearance rates, reduced postheparin LPL activity, decreased adipose tissue lipolysis, and elevated ectopic fat deposition, all of which could potentially contribute to age-associated metabolic diseases. Similar observations have been made in aged rats. We highlight the limitations of currently available data and propose that mechanistic studies are needed to understand the extent to which age-induced alterations in TG metabolism contribute to metabolic disease. Such mechanistic insights could aid in therapeutic strategies for preventing or managing metabolic disease in older individuals.

Integrin β3 Deficiency Results in Hypertriglyceridemia via Disrupting LPL (Lipoprotein Lipase) Secretion

OBJECTIVE

Integrin β3 is implicated in numerous biological processes such as its relevance to blood triglyceride, yet whether β3 deficiency affects this metabolic process remains unknown. Approach and Results: We showed that the Chinese patients with β3-deficient Glanzmann thrombasthenia had a 2-fold higher serum triglyceride level together with a lower serum LPL (lipoprotein lipase) level than those with an αIIb deficiency or healthy subjects. The β3 knockout mice recapitulated these phenotypic features. The elevated plasma triglyceride level was due to impaired LPL-mediated triglyceride clearance caused by a disrupted LPL secretion. Further analysis revealed that β3 directly bound LPL via a juxtamembrane TIH (threonine isoleucine histidine)^720-722 motif in its cytoplasmic domain and functioned as an adaptor protein by interacting with LPL and PKD (protein kinase D) to form the PKD/β3/LPL complex that is required for β3-mediated LPL secretion. Furthermore, the impaired triglyceride clearance in β3 knockout mice could be corrected by adeno-associated virus serotype 9 (AAV9)-mediated delivery of wild-type but not TIH^720-722-mutated β3 genes.

CONCLUSIONS

This study reveals a hypertriglyceridemia in both β3-deficient Chinese patients and mice and provides novel insights into the molecular mechanisms of the significant roles of β3 in LPL secretion and triglyceride metabolism, drawing attention to the metabolic consequences in patients with β3-deficient Glanzmann thrombasthenia.

Antihyperlipidaemic effect of microencapsulated Lactobacillus plantarum LIP-1 on hyperlipidaemic rats

BACKGROUND

Previous studies have shown that Lactobacillus plantarum LIP-1 (hereafter LIP-1) has an obvious hypolipidemic effect, and microencapsulated probiotics can ensure the strains live through the gastrointestinal tract. Although there has been much research on both preparation and assessment methods for probiotics microcapsules, most assessments were made in vitro and few were validated in vivo. In this study, the protective effect of microencapsulation and the possible hypolipidemic mechanisms of probiotic LIP-1 were evaluated in rats. Treatments included rats fed on a normal diet, a high-fat diet, and a high-fat diet with an intragastric supplement of either non-microencapsulated LIP-1 cells (NME LIP-1) or microencapsulated LIP-1 (ME LIP-1). Lipid metabolism indicators were measured during the experiment and following euthanasia.

RESULTS

Microencapsulation increased survival and colonization of LIP-1 in the colon. ME LIP-1 was superior to NME LIP-1 in reducing cholesterol. The mechanisms behind the hypolipidemic effect exerted by LIP-1 are possibly due to promoting the excretion of cholesterol, improving antioxygenic potentials, enhancing recovery from the injury in the liver, cardiovascular intima and intestinal mucosa, promoting the generation of short-chain fatty acids, and improving lipid metabolism.

CONCLUSIONS

This study confirms that microencapsulation provides effective protection of LIP-1 in the digestive system and the role of LIP-1 in the prevention and cure of hyperlipidaemia, providing theoretical support for probiotics to enter clinical applications. © 2019 Society of Chemical Industry.

The expression signatures in liver and adipose tissue from obese Göttingen Minipigs reveal a predisposition for healthy fat accumulation

BACKGROUND

Model animals are valuable resources for dissecting basic aspects of the regulation of obesity and metabolism. The translatability of results relies on understanding comparative aspects of molecular pathophysiology. Several studies have shown that despite the presence of overt obesity and dyslipidemia in the pig key human pathological hepatic findings such as hepatocellular ballooning and abundant steatosis are lacking in the model.

OBJECTIVES

The aim of this study was to elucidate why these histopathological characteristics did not occur in a high fat, fructose and cholesterol (FFC) diet-induced obese Göttingen Minipig model.

METHODS

High-throughput expression profiling of more than 90 metabolically relevant genes was performed in liver, subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) of male minipigs diet fed: standard chow (SD, n = 7); FFC diet (n = 14); FFC diet in streptozotocin-induced diabetic pigs (FFCDIA, n = 8). Moreover, histopathological assessment of SAT and VAT was performed.

RESULTS

12, 4 and 1 genes were highly significantly differentially expressed in liver, SAT and VAT when comparing the FFC and SD groups whereas the corresponding numbers were 15, 2, and 1 when comparing the FFCDIA and SD groups. Although the minipigs in both FFC groups developed sever obesity and dyslipidemia, the insulin-signaling pathways were not affected. Notably, four genes involved in lipid acquisition and removal, were highly deregulated in the liver: PPARG, LPL, CD36 and FABP4. These genes have been reported to play a major role in promoting hepatic steatosis in rodents and humans. Since very little macrophage-associated pro-inflammatory response was detected in the adipose tissues the expansion appears to have no adverse impact on adipose tissue metabolism.

CONCLUSION

The study shows that morbidly obese Göttingen Minipigs are protected against many of the metabolic and hepatic abnormalities associated with obesity due to a remarkable ability to expand the adipose compartments to accommodate excess calories.

Glucolipotoxicity: A Proposed Etiology for Wooden Breast and Related Myopathies in Commercial Broiler Chickens

Wooden breast is one of several myopathies of fast-growing commercial broilers that has emerged as a consequence of intensive selection practices in the poultry breeding industry. Despite the substantial economic burden presented to broiler producers worldwide by wooden breast and related muscle disorders such as white striping, the genetic and etiological underpinnings of these diseases are still poorly understood. Here we propose a new hypothesis on the primary causes of wooden breast that implicates dysregulation of lipid and glucose metabolism. Our hypothesis addresses recent findings that have suggested etiologic similarities between wooden breast and type 2 diabetes despite their phenotypic disparities. Unlike in mammals, dysregulation of lipid and glucose metabolism is not accompanied by an increase in plasma glucose levels but generates a unique skeletal muscle phenotype, i.e., wooden breast, in chickens. We hypothesize that these phenotypic disparities result from a major difference in skeletal muscle glucose transport between birds and mammals, and that the wooden breast phenotype most closely resembles complications of diabetes in smooth and cardiac muscle of mammals. Additional basic research on wooden breast and related muscle disorders in commercial broiler chickens is necessary and can be informative for poultry breeding and production as well as for human health and disease. To inform future studies, this paper reviews the current biological knowledge of wooden breast, outlines the major steps in its proposed pathogenesis, and examines how selection for production traits may have contributed to its prevalence.

Atorvastatin promotes AMPK signaling to protect against high fat diet-induced non-alcoholic fatty liver in golden hamsters

Non-alcoholic fatty liver disease (NAFLD) is characterized by diffuse fatty acid degeneration and excess fat accumulation in the liver. Notably, the currently available medications used to treat NAFLD remain limited. The aim of the present study was to investigate the protective role of atorvastatin (Ato) against NAFLD in golden hamsters fed a high fat diet (HFD) and in HepG2 cells treated with palmitate, and identify the underlying molecular mechanism. Ato (3 mg/kg) was administered orally every day for 8 weeks to the hamsters during HFD administration. Hamsters in the model group developed hepatic steatosis with high serum levels of triglyceride, cholesterol, insulin and C-reactive protein, which were effectively reduced by treatment with Ato. Additionally, the relative liver weight of hamsters treated with Ato was markedly lower compared with that of the model group. Hematoxylin and eosin, and oil red O staining indicated that the livers of the animals in the model group exhibited large and numerous lipid droplets, which were markedly decreased after Ato treatment. Western blot analysis indicated that Ato inhibited fat accumulation in the liver through the AMP-activated protein kinase (AMPK)-dependent activation of peroxisome proliferator activated receptor α (PPARα), peroxisome proliferator-activated receptor-γ coactivator 1 α and their target genes. Furthermore, in vitro, Ato inhibited PA-induced lipid accumulation in HepG2 cells. This inhibitory effect was attenuated following Compound C treatment, indicating that AMPK may be a potential target of Ato. In conclusion, the increase in AMPK-mediated PPARα and its target genes may represent a novel molecular mechanism by which Ato prevents NAFLD.

Dynamic accumulation of fatty acids in duck (Anas platyrhynchos) breast muscle and its correlations with gene expression

Background

Fatty acid composition contributes greatly to the quality and nutritional value of meat. However, the molecular regulatory mechanisms underlying fatty acid accumulation in poultry have not yet been cleared. The aims of this study were to characterize the dynamics of fatty acid accumulation in duck breast muscle and investigate its correlations with gene expression.

Results

Here, we analyzed the fatty acid profile and transcriptome of breast muscle derived from Pekin ducks and mallards at the ages of 2 weeks, 4 weeks, 6 weeks and 8 weeks. Twenty fatty acids were detected in duck breast muscle, with palmitic acid (C16:0, 16.6%~ 21.1%), stearic acid (C18:0, 9.8%~ 17.7%), oleic acid (C18:1n-9, 15.7%~ 33.8%), linoleic acid (C18:2n-6, 10.8%~ 18.9%) and arachidonic acid (C20:4n-6, 11.7%~ 28.9%) as the major fatty acids. Our results showed that fatty acid composition was similar between the two breeds before 6 weeks, but the compositions diverged greatly after this point, mainly due to the stronger capacity for C16:0 and C18:1n-9 deposition in Pekin ducks. By comparing the multistage transcriptomes of Pekin ducks and mallards, we identified 2025 differentially expressed genes (DEGs). Cluster analysis of these DEGs revealed that the genes involved in oxidative phosphorylation, fatty acid degradation and the PPAR signaling pathway were upregulated in mallard at 8 weeks. Moreover, correlation analysis of the DEGs and fatty acid composition traits suggested that the DEGs involved in lipogenesis, lipolysis and fatty acid β-oxidation may interact to influence the deposition of fatty acids in duck breast muscle.

Conclusions

We reported the temporal progression of fatty acid accumulation and the dynamics of the transcriptome in breast muscle of Pekin ducks and mallards. Our results provide insights into the transcriptome regulation of fatty acid accumulation in duck breast muscle, and will facilitate improvements of fatty acid composition in duck breeding.

Altered Gene Expression Profiles in Peripheral Blood Mononuclear Cells in Obese Subjects

INTRODUCTION

Gene expression profiles in human peripheral blood mononuclear cells (PBMCs) may act as a useful tool to better understand obesity. We investigated gene expression levels in PMBCs for possible differences between obese and non-obese subjects (19-55 years) and evaluated correlations between gene expression in PBMCs and clinical obesity indices.

METHODS

Body weight, BMI, fat amount, fat percentage, waist/hip ratio, leptin, and adiponectin levels were determined in 30 obese and 20 non-obese subjects. Expression levels of 19 genes, which were differentially expressed by clinical obesity indices in the PBMCs of high fat-fed rats, were determined in their PBMCs using real-time PCR.

RESULTS

The expression of 9 of 19 previously selected genes was significantly correlated with one or more clinical obesity indices. Both TFEC and CCL2 expression were negatively correlated with BMI, fat amount, fat percentage, waist/hip ratio, and leptin concentration. Similarly, TNFAIP2, VCAN, ASSI, IRF1, and HK3 expression negatively correlated with some clinical obesity indices, such as TNFAIP2 for BMI, fat amount, fat percentage, and waist/hip ratio, VCAN for fat amount, fat percentage, and waist/hip ratio, ASS1 for BMI and fat amount, IRF1 for BMI, fat amount, and fat percentage, and HK3 for fat amount. In contrast, both TNF-α and LPL expression were positively correlated with waist/hip ratio.

CONCLUSION

We identified 9 of 19 genes in human PBMCs that significantly correlated with one or more clinical obesity indices. Because these genes have a mechanistic basis for the development or progression of obesity and its metabolic derangements, they may help to determine possible underlying mechanisms for obesity.

Pathogenesis of Insulin Resistance and Atherogenic Dyslipidemia in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in the developed world, with a global prevalence of around 25%. NAFLD is considered to be the hepatic manifestation of metabolic syndrome and is strongly associated with obesity, insulin resistance and dyslipidemia. Insulin resistance plays a pivotal role in the development of NAFLD-related dyslipidemia, which ultimately increases the risk of premature cardiovascular diseases, a leading cause of morbidity and mortality in patients with NAFLD. Insulin affects hepatic glucose and lipid metabolism by hepatic or extrahepatic pathways. Aside from insulin resistance, several other factors also contribute to the pathogenesis of atherogenic dyslipidemia in patients with NAFLD. These include diet composition, gut microbiota and genetic factors, to name a few. The identification of potentially modifiable risk factors of NAFLD is of importance, so as to target those who may benefit from lifestyle changes and to help develop targeted therapies that decrease the risk of cardiovascular diseases in patients with NAFLD.

Natural Alkaloids Intervening the Insulin Pathway: New Hopes for Anti-Diabetic Agents?

BACKGROUND

Accumulating experimental data supports the capacity of natural compounds to intervene in complicated molecular pathways underlying the pathogenesis of certain human morbidities. Among them, diabetes is now a world's epidemic associated with increased risk of death; thus, the detection of novel anti-diabetic agents and/or adjuvants is of vital importance. Alkaloids represent a diverse group of natural products with a range of therapeutic properties; during the last 20 years, published research on their anti-diabetic capacity has been tremendously increased.

PURPOSE

To discuss current concepts on the anti-diabetic impact of certain alkaloids, with special reference to their molecular targets throughout the insulin-signaling pathway.

METHODOLOGY

Upon in-depth search in the SCOPUS and PUBMED databases, the literature on alkaloids with insulin secretion/sensitization properties was critically reviewed.

RESULTS

In-vitro and in-vivo evidence supports the effect of berberine, trigonelline, piperine, oxymatrine, vindoneline, evodiamine and neferine on insulin-signaling and related cascades in beta-cells, myocytes, adipocytes, hepatocytes and other cells. Associated receptors, kinases, hormones and cytokines, are affected in terms of gene transcription, protein expression, activity and/or phosphorylation. Pathophysiological processes associated with insulin resistance, beta-cell failure, oxidative stress and inflammation, as well as clinical phenotype are also influenced.

DISCUSSION

Growing evidence suggests the ability of specific alkaloids to intervene in the insulin-signal transduction pathway, reverse molecular defects resulting in insulin resistance and glucose intolerance and improve disease complications, in-vitro and in-vivo. Future indepth molecular studies are expected to elucidate their exact mechanism of action, while large clinical trials are urgently needed to assess their potential as anti-diabetic agents.

Transcription profiling in the liver of undernourished male rat offspring reveals altered lipid metabolism pathways and predisposition to hepatic steatosis

Clinical and animal studies have reported an association between low birth weight and the development of nonalcoholic fatty liver disease (NAFLD) in offspring. Using a model of prenatal maternal 70% food restriction diet (FR30) in the rat, we previously showed that maternal undernutrition predisposes offspring to altered lipid metabolism in adipose tissue, especially on a high-fat (HF) diet. Here, using microarray-based expression profiling combined with metabolic, endocrine, biochemical, histological, and lipidomic approaches, we assessed whether FR30 procedure sensitizes adult male offspring to impaired lipid metabolism in the liver. No obvious differences were noted in the concentrations of triglycerides, cholesterol, and bile acids in the liver of 4-mo-old FR30 rats whichever postweaning diet was used. However, several clues suggest that offspring's lipid metabolism and steatosis are modified by maternal undernutrition. First, lipid composition was changed (i.e., higher total saturated fatty acids and lower elaidic acid) in the liver, whereas larger triglyceride droplets were observed in hepatocytes of undernourished rats. Second, FR30 offspring exhibited long-term impact on hepatic gene expression and lipid metabolism pathways on a chow diet. Although the transcriptome profile was globally modified by maternal undernutrition, cholesterol and bile acid biosynthesis pathways appear to be key targets, indicating that FR30 animals were predisposed to impaired hepatic cholesterol metabolism. Third, the FR30 protocol markedly modifies hepatic gene transcription profiles in undernourished offspring in response to postweaning HF. Overall, FR30 offspring may exhibit impaired metabolic flexibility, which does not enable them to properly cope with postweaning nutritional challenges influencing the development of nonalcoholic fatty liver.

Insulin Resistance and Atherosclerosis: Implications for Insulin-Sensitizing Agents

Patients with type 2 diabetes mellitus (T2DM) are at high risk for macrovascular complications, which represent the major cause of mortality. Despite effective treatment of established cardiovascular (CV) risk factors (dyslipidemia, hypertension, procoagulant state), there remains a significant amount of unexplained CV risk. Insulin resistance is associated with a cluster of cardiometabolic risk factors known collectively as the insulin resistance (metabolic) syndrome (IRS). Considerable evidence, reviewed herein, suggests that insulin resistance and the IRS contribute to this unexplained CV risk in patients with T2DM. Accordingly, CV outcome trials with pioglitazone have demonstrated that this insulin-sensitizing thiazolidinedione reduces CV events in high-risk patients with T2DM. In this review the roles of insulin resistance and the IRS in the development of atherosclerotic CV disease and the impact of the insulin-sensitizing agents and of other antihyperglycemic medications on CV outcomes are discussed.

Polyphenols and IUGR Pregnancies: Effects of Maternal Hydroxytyrosol Supplementation on Postnatal Growth, Metabolism and Body Composition of the Offspring

Maternal supplementation with the polyphenol hydroxytyrosol in a swine model of intrauterine growth restriction (IUGR) improves the fetal oxidative status, decreases the appearance of low birth-weight neonates and favors growth during early postnatal stages (lactation). The current study aimed to determine whether hydroxytyrosol supplementation can also improve developmental patterns, metabolic traits, and body composition of the offspring during later postnatal stages (from weaning to adulthood). A total of 21 piglets born from control untreated sows and 20 piglets born from sows treated with hydroxytyrosol during the last two-thirds of pregnancy were selected on the basis of similar body weights at weaning, for avoiding any interfering effects occurred during lactation. The pigs in the treated group had higher average daily weight gain (ADWG) and, therefore, reached higher body weight and corpulence, greater muscle development and higher adiposity than their control counterparts. The following were not found: significant effects on metabolism and body composition except changes in the muscular fatty acid composition of the treated pigs coming from the largest litters; those more affected by IUGR processes. These findings suggest that maternal supplementation with hydroxytyrosol may improve juvenile development of offspring in at-risk pregnancies and pave the way for more specific studies aiming to elucidate effects on adiposity, metabolism, and meat organoleptic characteristics.

Insulin Sensitivity Is Associated with Lipoprotein Lipase (LPL) and Catenin Delta 2 (CTNND2) DNA Methylation in Peripheral White Blood Cells in Non-Diabetic Young Women

Hyperglycaemia and type 2 diabetes (T2D) are associated with impaired insulin secretion and/or insulin action. Since few studies have addressed the relation between DNA methylation patterns with elaborated surrogates of insulin secretion/sensitivity based on the intravenous glucose tolerance test (IVGTT), the aim of this study was to evaluate the association between DNA methylation and an insulin sensitivity index based on IVGTT (calculated insulin sensitivity index (CSi)) in peripheral white blood cells from 57 non-diabetic female volunteers. The CSi and acute insulin response (AIR) indexes, as well as the disposition index (DI = CSi × AIR), were estimated from abbreviated IVGTT in 49 apparently healthy Chilean women. Methylation levels were assessed using the Illumina Infinium Human Methylation 450k BeadChip. After a statistical probe filtering, the two top CpGs whose methylation was associated with CSi were cg04615668 and cg07263235, located in the catenin delta 2 (CTNND2) and lipoprotein lipase (LPL) genes, respectively. Both CpGs conjointly predicted insulin sensitivity status with an area under the curve of 0.90. Additionally, cg04615668 correlated with homeostasis model assessment insulin-sensitivity (HOMA-S) and AIR, whereas cg07263235 was associated with plasma creatinine and DI. These results add further insights into the epigenetic regulation of insulin sensitivity and associated complications, pointing the CTNND2 and LPL genes as potential underlying epigenetic biomarkers for future risk of insulin-related diseases.

Lipoprotein Lipase Up-regulation in Hepatic Stellate Cells Exacerbates Liver Fibrosis in Nonalcoholic Steatohepatitis in Mice

Lipoprotein lipase (LPL) plays a central role in incorporating plasma lipids into tissues and regulates lipid metabolism and energy balance in the human body. Conversely, LPL expression is almost absent in normal adult livers. Therefore, its physiological role in the liver remains unknown. We aimed to elucidate the role of LPL in the pathophysiology of nonalcoholic steatohepatitis (NASH), a hepatic manifestation of obesity. Hepatic stellate cell (HSC)–specific LPL‐knockout (Lpl^HSC‐KO) mice, LPL‐floxed (Lpl^fl/fl) mice, or double‐mutant toll‐like receptor 4–deficient (Tlr4^−/−) Lpl^HSC‐KO mice were fed a high‐fat/high‐cholesterol diet for 4 weeks to establish the nonalcoholic fatty liver model or an high‐fat/high‐cholesterol diet for 24 weeks to establish the NASH model. Human samples, derived from patients with nonalcoholic fatty liver disease, were also examined. In human and mouse NASH livers, serum obesity‐related factors, such as free fatty acid, leptin, and interleukin‐6, dramatically increased the expression of LPL, specifically in HSCs through signal transducer and activator of transcription 3 signaling, as opposed to that in hepatocytes or hepatic macrophages. In the NASH mouse model, liver fibrosis was significantly reduced in Lpl^HSC‐KO mice compared with that in Lpl^fl/fl mice. Nonenzymatic LPL‐mediated cholesterol uptake from serum lipoproteins enhanced the accumulation of free cholesterol in HSCs, which amplified TLR4 signaling, resulting in the activation of HSCs and progression of hepatic fibrosis in NASH. Conclusion: The present study reveals the pathophysiological role of LPL in the liver, and furthermore, clarifies the pathophysiology in which obesity, as a background factor, exacerbates NASH. The LPL‐mediated HSC activation pathway could be a promising therapeutic target for treating liver fibrosis in NASH.

Palmitic acid causes insulin resistance in granulosa cells via activation of JNK

Obesity is a worldwide health problem with rising incidence and results in reproductive difficulties. Elevated saturated free fatty acids (FFAs) in obesity can cause insulin resistance (IR) in peripheral tissues. The high intra-follicular saturated FFAs may also account for IR in ovarian granulosa cells (GCs). In the present study, we investigated the relationship between saturated FFAs and IR in GCs by the use of palmitic acid (PA). We demonstrated that the glucose uptake in cultured GCs and lactate accumulation in the culture medium were stimulated by insulin, but the effects of insulin were attenuated by PA treatment. Besides, insulin-induced phosphorylation of Akt was reduced by PA in a dose- and time-dependent manner. Furthermore, PA increased phosphorylation of JNK and JNK blockage rescued the phosphorylation of Akt which was downregulated by PA. These findings highlighted the negative effect of PA on GCs metabolism and may partially account for the obesity-related reproductive disorders.

Resveratrol protects against hepatic insulin resistance in a rat's model of non-alcoholic fatty liver disease by down-regulation of GPAT-1 and DGAT2 expression and inhibition of PKC membranous translocation

Non-alcoholic fatty liver disease (NAFLD) is associated with hepatic insulin resistance (IR). Resveratrol (RES) a potent hypolipidemic dietary polyphenol has been identified for its ability to prevent hepatic steatosis and hepatic IR in high-fat diet (HFD)-fed murine models of NAFLD. In the present study, we have carried an in vivo animal experiment to identify a novel mechanism for RES protective action. Sub-chronic (45 days) RES pretreatment in 3 days HFD-fed adult Wistar rats prevented early hepatic IR through inhibiting PKC/JNK activation; decreasing p-IRS (Ser³⁰⁷ ) and increasing p-IRS(Tyr⁶¹² ), p-Akt(Ser⁴⁷³ ) and p-GSK3(Ser⁹ ). These effects of RES were associated with reduced expression of acyl-CoA:glycerol-sn-3-phosphate acyltransferase (GPAT-1) and diacylglycerol:acyl-CoA acyltransferase (DGAT2), two critical enzymes in the glycerol-3-phosphate pathway for de novo triglycerides synthesis. These data indicate that RES protects against NAFLD, initially, by inhibiting the early development of hepatic IR.

Mechanisms of obesity-induced metabolic and vascular dysfunctions

Obesity has reached epidemic proportions and its prevalence is climbing. Obesity is characterized by hypertrophied adipocytes with a dysregulated adipokine secretion profile, increased recruitment of inflammatory cells, and impaired metabolic homeostasis that eventually results in the development of systemic insulin resistance, a phenotype of type 2 diabetes. Nitric oxide synthase (NOS) is an enzyme that converts L-arginine to nitric oxide (NO), which functions to maintain vascular and adipocyte homeostasis. Arginase is a ureohydrolase enzyme that competes with NOS for L-arginine. Arginase activity/expression is upregulated in obesity, which results in diminished bioavailability of NO, impairing both adipocyte and vascular endothelial cell function. Given the emerging role of NO in the regulation of adipocyte physiology and metabolic capacity, this review explores the interplay between arginase and NO, and their effect on the development of metabolic disorders, cardiovascular diseases, and mitochondrial dysfunction in obesity. A comprehensive understanding of the mechanisms involved in the development of obesity-induced metabolic and vascular dysfunction is necessary for the identification of more effective and tailored therapeutic avenues for their prevention and treatment.

Increased Body Weight and Fat Mass After Subchronic GIP Receptor Antagonist, but Not GLP-2 Receptor Antagonist, Administration in Rats

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-2 (GLP-2) are hormones secreted from the enteroendocrine cells after a meal. They exert their actions through activation of G protein-coupled receptors (R), the GIPR and GLP-2R, respectively. Both have been reported to influence metabolism. The purpose of the study was to investigate the role of the hormones in the regulation of lipid and bone homeostasis by subchronic treatment with novel GIPR and GLP-2R antagonists. Rats were injected once daily with vehicle, GIPR, or GLP-2R antagonists for 3 weeks. Body weight, food intake, body composition, plasma lipoprotein lipase (LPL), adipokines, triglycerides and the marker of bone resorption carboxy-terminal collagen crosslinks (CTX), were examined. In rats, subchronic treatment with GIPR antagonist, rat GIP (3-30)NH₂, did not modify food intake and bone resorption, but significantly increased body weight, body fat mass, triglycerides, LPL, and leptin levels compared with vehicle treated rats. Subchronic (Pro3)GIP (a partial GIPR agonist), GLP-2(11-33), and GLP-2(3-33) (GLP-2R antagonists) treatment did not affect any parameter. The present results would be consistent with a role for GIP, but not GLP-2, in the maintenance of lipid homeostasis in rats, while neither GIPR nor GLP-2R antagonism appeared to influence bone resorption in rats.

Defining lipid mediators of insulin resistance: controversies and challenges

Essential elements of all cells - lipids - play important roles in energy production, signalling and as structural components. Despite these critical functions, excessive availability and intracellular accumulation of lipid is now recognised as a major factor contributing to many human diseases, including obesity and diabetes. In the context of these metabolic disorders, ectopic deposition of lipid has been proposed to have deleterious effects on insulin action. While this relationship has been recognised for some time now, there is currently no unifying mechanism to explain how lipids precipitate the development of insulin resistance. This review summarises the evidence linking specific lipid molecules to the induction of insulin resistance, describing some of the current controversies and challenges for future studies in this field.

Mechanisms of Insulin Action and Insulin Resistance

The 1921 discovery of insulin was a Big Bang from which a vast and expanding universe of research into insulin action and resistance has issued. In the intervening century, some discoveries have matured, coalescing into solid and fertile ground for clinical application; others remain incompletely investigated and scientifically controversial. Here, we attempt to synthesize this work to guide further mechanistic investigation and to inform the development of novel therapies for type 2 diabetes (T2D). The rational development of such therapies necessitates detailed knowledge of one of the key pathophysiological processes involved in T2D: insulin resistance. Understanding insulin resistance, in turn, requires knowledge of normal insulin action. In this review, both the physiology of insulin action and the pathophysiology of insulin resistance are described, focusing on three key insulin target tissues: skeletal muscle, liver, and white adipose tissue. We aim to develop an integrated physiological perspective, placing the intricate signaling effectors that carry out the cell-autonomous response to insulin in the context of the tissue-specific functions that generate the coordinated organismal response. First, in section II, the effectors and effects of direct, cell-autonomous insulin action in muscle, liver, and white adipose tissue are reviewed, beginning at the insulin receptor and working downstream. Section III considers the critical and underappreciated role of tissue crosstalk in whole body insulin action, especially the essential interaction between adipose lipolysis and hepatic gluconeogenesis. The pathophysiology of insulin resistance is then described in section IV. Special attention is given to which signaling pathways and functions become insulin resistant in the setting of chronic overnutrition, and an alternative explanation for the phenomenon of ‟selective hepatic insulin resistanceˮ is presented. Sections V, VI, and VII critically examine the evidence for and against several putative mediators of insulin resistance. Section V reviews work linking the bioactive lipids diacylglycerol, ceramide, and acylcarnitine to insulin resistance; section VI considers the impact of nutrient stresses in the endoplasmic reticulum and mitochondria on insulin resistance; and section VII discusses non-cell autonomous factors proposed to induce insulin resistance, including inflammatory mediators, branched-chain amino acids, adipokines, and hepatokines. Finally, in section VIII, we propose an integrated model of insulin resistance that links these mediators to final common pathways of metabolite-driven gluconeogenesis and ectopic lipid accumulation.

Changes in body composition and metabolic disease risk

As individuals gain weight, they increase the amount of fat that they accrue on their body. This causes adipocytes to enlarge and increases not only subcutaneous fat but also deposits fat in other vulnerable areas of the body. This ectopic fat is deposited in the intra-abdominal visceral fat depot, in muscle, in the liver and in the beta cells. Fat in these locations initiates a dysfunctional state in these insulin-sensitive tissues leading to insulin resistance, the appearance of the Metabolic Syndrome, and an increased risk of developing both type 2 diabetes and cardiovascular disease. A loss of weight and with it a loss of fat decreases this risk.

Differentially expressed genes in PPARγ-deficient MSCs

Peroxisome proliferator-activated receptor gamma (PPARγ) is a key regulator of adipogenesis. It is also a central player in energy metabolism, inflammation and immunity. As an important nuclear transcription factor, PPARγ can regulate the expression and function of genes or biological processes directly or indirectly via association with other factors and thus modulate their activities. To better understand the impact of PPARγ on the global gene expression profile, we evaluated the bioinformatic data, which revealed the changes that occurred in genes and their pathways in the absence of PPARγ. In brief, we performed RNA deep sequencing (RNA-Seq) analysis using RNA samples isolated from multipotent mesenchymal stromal cells (MSCs) of PPARγ knockout and wild type control mice. The RNA-Seq data sets were then subjected to bioinformatic analyses from various angles to better reveal the breadth of PPARγ function in different biological processes. Our results reveal novel genes and networks modulated by PPARγ and provides new insights into our understanding of the physiologic and pathophysiologic role this nuclear receptor plays in health and disease.

Er-Miao-Fang Extracts Inhibits Adipose Lipolysis and Reduces Hepatic Gluconeogenesis via Suppression of Inflammation

High-fat-diet (HFD) feeding induces adipose dysfunction. This study aims to explore whether the Traditional Chinese Medical prescription Er-Miao-Fang could ameliorate adipose dysfunction and prevent hepatic glucose output. Short-term HFD feeding induced adipose lipolysis accompanied with enhanced hepatic glucose output in mice. Adipose lipolysis is initiated by cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling. Oral administration Er-Miao-Fang inhibited inflammation in adipose tissue by dephosphorylation of JNK and reducing TNF-α and IL-1β production, and thus preserved phosphodiesterase 3B (PDE3B) induction, contributing to preventing cAMP accumulation. As a result, from suppression of PKA activation, Er-Miao-Fang reduced fatty acids and glycerol release from adipose tissue due to the inhibition hormone-sensitive lipase (HSL). By blocking the traffic of fatty acids and inflammatory mediators from adipose tissue to the liver, Er-Miao-Fang attenuated hepatic cAMP/PKA signaling by protecting phosphodiesterase 4B (PDE4B) induction from inflammatory insult, and thereby reduced hepatic glucose production by suppression of hepatic glucagon response in HFD-fed mice. In conclusion, Er-Miao-Fang prevented adipose lipolysis by suppression of inflammation, contributing to reducing excessive hepatic glucose output. These findings present a new view of regulating gluconeogenesis and provide the guiding significance for the regulation of multi-link targets with Traditional Chinese Medicine.

miR-122 inhibition in a human liver organoid model leads to liver inflammation, necrosis, steatofibrosis and dysregulated insulin signaling

To investigate the role of miR-122 in the development and regression of non-alcoholic fatty liver disease (NAFLD) in vitro, we used multicellular 3D human liver organoids developed in our laboratory. These organoids consist of primary human hepatocytes, Kupffer cells, quiescent stellate cells and liver sinusoidal endothelial cells. They remain viable and functional for 4 weeks expressing typical markers of liver function such as synthesis of albumin, urea, and alpha-1 p450 drug metabolism. Before mixing, hepatic cells were transduced with lentivirus to inhibit miR122 expression (ABM, CA). Immediately after the organoids were fully formed (day 4) or after 1 or 2 weeks of additional incubation (days 11 or 18), the organoids were analyzed using fluorescent live/dead staining and ATP production; total RNA was extracted for qPCR gene expression profiling. Our results show that miR-122 inhibition in liver organoids leads to inflammation, necrosis, steatosis and fibrosis. This was associated with increase in inflammatory cytokines (IL6, TNF), chemokines (CCL2, CCL3) and increase in a subset of Matrix Metaloproteinases (MMP8, MMP9). An altered expression of key genes in lipid metabolism (i.e LPL, LDLR) and insulin signaling (i.e GLUT4, IRS1) was also identified. Conclusion: Our results highlight the role of miR-122 inhibition in liver inflammation, steatofibrosis and dysregulation of insulin signaling. Patients with NAFLD are known to have altered levels of miR-122, therefore we suggest that miR-122 mimics could play a useful role in reversing liver steatofibrosis and insulin resistance seen in patients with NAFLD.

Inactivating hepatic follistatin alleviates hyperglycemia

Unsuppressed hepatic glucose production (HGP) contributes substantially to glucose intolerance and diabetes, which can be modeled by the genetic inactivation of hepatic insulin receptor substrate 1 (Irs1) and Irs2 (LDKO mice). We previously showed that glucose intolerance in LDKO mice is resolved by hepatic inactivation of the transcription factor FoxO1 (that is, LTKO mice)-even though the liver remains insensitive to insulin. Here, we report that insulin sensitivity in the white adipose tissue of LDKO mice is also impaired but is restored in LTKO mice in conjunction with normal suppression of HGP by insulin. To establish the mechanism by which white adipose tissue insulin signaling and HGP was regulated by hepatic FoxO1, we identified putative hepatokines-including excess follistatin (Fst)-that were dysregulated in LDKO mice but normalized in LTKO mice. Knockdown of hepatic Fst in the LDKO mouse liver restored glucose tolerance, white adipose tissue insulin signaling and the suppression of HGP by insulin; however, the expression of Fst in the liver of healthy LTKO mice had the opposite effect. Of potential clinical significance, knockdown of Fst also improved glucose tolerance in high-fat-fed obese mice, and the level of serum Fst was reduced in parallel with glycated hemoglobin in obese individuals with diabetes who underwent therapeutic gastric bypass surgery. We conclude that Fst is a pathological hepatokine that might be targeted for diabetes therapy during hepatic insulin resistance.

Transcriptome signatures of p,p´-DDE-induced liver damage in Mus spretus mice

The use of DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane) in some countries, although regulated, is contributing to an increased worldwide risk of exposure to this organochlorine pesticide or its derivative p,p'-DDE [1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene]. Many studies have associated p,p'-DDE exposure to type 2 diabetes, obesity and alterations of the reproductive system, but their molecular mechanisms of toxicity remain poorly understood. We have addressed this issue by using commercial microarrays based on probes for the entire Mus musculus genome to determine the hepatic transcriptional signatures of p,p'-DDE in the phylogenetically close mouse species Mus spretus. High-stringency hybridization conditions and analysis assured reliable results, which were also verified, in part, by qRT-PCR, immunoblotting and/or enzymatic activity. Our data linked 198 deregulated genes to mitochondrial dysfunction and perturbations of central signaling pathways (kinases, lipids, and retinoic acid) leading to enhanced lipogenesis and aerobic glycolysis, inflammation, cell proliferation and testosterone catabolism and excretion. Alterations of transcript levels of genes encoding enzymes involved in testosterone catabolism and excretion would explain the relationships established between p,p´-DDE exposure and reproductive disorders, obesity and diabetes. Further studies will help to fully understand the molecular basis of p,p´-DDE molecular toxicity in liver and reproductive organs, to identify effective exposure biomarkers and perhaps to design efficient p,p'-DDE exposure counteractive strategies.