Lipoapoptosis: its mechanism and its diseases

Mechanisms and clinical implications of hepatocyte lipoapoptosis

Nonalcoholic fatty liver disease (NAFLD) is characterized by insulin resistance, elevated serum levels of free fatty acids (FFAs) and fatty infiltration of the liver. Accumulation of triglycerides in the hepatocyte results from the uptake and esterification of circulating FFAs by the liver. Contrary to current theory, hepatic steatosis appears to be a detoxification process, as FFAs are directly cytotoxic for the hepatocyte and inhibition of triglyceride formation enhances FFAs toxicity. Hepatocyte apoptosis is a key feature of NAFLD and correlates with disease severity. Since FFA-induced toxicity, or lipoapoptosis, represents a mechanism for the pathogenesis of NAFLD, this article will highlight the cellular pathways contributing to hepatocyte lipoapoptosis. To date, there is no proven effective therapy for patients with NAFLD and insights into the molecular mediators of lipoapoptosis should help promote effective therapeutic strategies for this disease.

The TGL2 gene of Saccharomyces cerevisiae encodes an active acylglycerol lipase located in the mitochondria

The Saccharomyces cerevisiae Tgl2 protein shows sequence homology to Pseudomonas triacylglycerol (TAG) lipases, but its role in the yeast lipid metabolism is not known. Using hemagglutinin-tagged Tgl2p purified from yeast, we report that this protein carries a significant lipolytic activity toward long-chain TAG. Importantly, mutant hemagglutinin-Tgl2p(S144A), which contains alanine 144 in place of serine 144 in the lipase consensus sequence (G/A)XSXG exhibits no such activity. Although cellular TAG hydrolysis is reduced in the tgl2 deletion mutant, overproduction of Tgl2p in this mutant leads to an increase in TAG degradation in the presence of fatty acid synthesis inhibitor cerulenin, but that of Tgl2p(S144A) does not. This result demonstrates the lipolytic function of Tgl2p in yeast. Although other yeast TAG lipases are localized to lipid particles, Tgl2p is enriched in the mitochondria. The mitochondrial fraction purified from the TGL2-overexpressing yeast shows a strong lipolytic activity, which was absent in the tgl2 deletion mutant. Therefore, we conclude that Tgl2p is a functional lipase of the yeast mitochondria. By analyzing phenotypic effects of TGL2-deficient yeast, we also find that lipolysis-competent Tgl2p is required for the viability of cells treated with antimitotic drug. The addition of oleic acid, the product of Tgl2p-catalyzed lipolysis, fully complements the antimitotic drug sensitivity of the tgl2 null mutation. Thus, we propose that the mitochondrial Tgl2p-dependent lipolysis is crucial for the survival of cells under antimitotic drug treatment.

Dietary soy protein reduces cardiac lipid accumulation and the ceramide concentration in high-fat diet-fed rats and ob/ob mice

Obesity is an epidemic condition strongly associated with cardiovascular morbidity and mortality. Heart disease secondary to obesity is associated with myocardial steatosis, leading to ceramide synthesis and cell dysfunction in a process known as lipotoxicity. Soy protein has been demonstrated to reduce lipotoxicity in the liver and pancreas in different rodent models of obesity. Thus, our purpose in the present work was to assess the effect of dietary soy protein on cardiac lipid accumulation and ceramide formation during obesity and to evaluate its effect in the following 2 rodent models of obesity: 1) a diet-induced obesity model in Sprague-Dawley rats was produced by feeding rats a control or a high-fat casein or soy protein diet for 180 d; and 2) wild-type and ob/ob mice were fed a casein or soy protein diet for 90 d. Soy protein intake led to lower cholesterol and triglyceride concentrations in the hearts of rats and ob/ob mice in association with a greater PPARalpha mRNA concentration and a lower level of sterol regulatory element binding protein-1 mRNA than those fed casein. The ceramide concentration was also lower in hearts of rats and ob/ob mice that were fed soy protein in association with lower serine palmitoyl transferase (SPT)-1 and tumor necrosis factor-alpha mRNA concentrations. These results indicate that dietary soy protein can reduce the heart ceramide concentration by reducing the expression of SPT-1, a key enzyme in the formation of this sphingolipid in the heart of obese rodents, and by reducing lipid accumulation. Thus, soy protein consumption may be considered as a dietary therapeutic approach for lipotoxic cardiomyopathy prevention.

Weight loss and proteinuria: systematic review of clinical trials and comparative cohorts

BACKGROUND

Obesity is a risk factor for the progression of chronic kidney disease (CKD). The impact of weight loss on proteinuria and renal function is less clear. We aimed to determine the effect of intentional weight loss on proteinuria and kidney function.

METHODS

Three bibliographic databases including Medline, Cochrane and SCUPOS as well as reference list of articles were searched. We included randomized and non-randomized controlled trials as well as single-arm trials published in English through May 2009 which examined urinary protein among obese or overweight adults before and after weight loss interventions including dietary restriction, exercise, anti-obesity medications and bariatric surgery. Study characteristics and methodological quality of trials were assessed.

RESULTS

Five hundred twenty-two subjects from five controlled and eight uncontrolled trials were included. Weight loss interventions were associated with decreased proteinuria and microalbuminuria by 1.7 g [95% confidence interval (95% CI), 0.7 to 2.6 g] and 14 mg (95% CI, 11 to 17 mg), respectively (P < 0.05). Meta-regression showed that, independent of decline in mean arterial pressure, each 1 kg weight loss was associated with 110 mg (95% CI, 60 to 160 mg, P < 0.001) decrease in proteinuria and 1.1 mg (95% CI, 0.5 to 2.4 mg, P = 0.011) decrease in microalbuminuria, respectively. The decrease was observed across different designs and methods of weight loss. Only bariatric surgery resulted in a significant decrease in creatinine clearance.

CONCLUSIONS

Weight loss is associated with decreased proteinuria and microalbuminuria. There were no data evaluating the durability of this decrease or the effect of weight loss on CKD progression.

Good fat, essential cellular requirements for triacylglycerol synthesis to maintain membrane homeostasis in yeast

Storage triacylglycerols (TAG) and membrane phospholipids share common precursors, i.e. phosphatidic acid and diacylglycerol, in the endoplasmic reticulum. In addition to providing a biophysically rather inert storage pool for fatty acids, TAG synthesis plays an important role to buffer excess fatty acids (FA). The inability to incorporate exogenous oleic acid into TAG in a yeast mutant lacking the acyltransferases Lro1p, Dga1p, Are1p, and Are2p contributing to TAG synthesis results in dysregulation of lipid synthesis, massive proliferation of intracellular membranes, and ultimately cell death. Carboxypeptidase Y trafficking from the endoplasmic reticulum to the vacuole is severely impaired, but the unfolded protein response is only moderately up-regulated, and dispensable for membrane proliferation, upon exposure to oleic acid. FA-induced toxicity is specific to oleic acid and much less pronounced with palmitoleic acid and is not detectable with the saturated fatty acids, palmitic and stearic acid. Palmitic acid supplementation partially suppresses oleic acid-induced lipotoxicity and restores carboxypeptidase Y trafficking to the vacuole. These data show the following: (i) FA uptake is not regulated by the cellular lipid requirements; (ii) TAG synthesis functions as a crucial intracellular buffer for detoxifying excess unsaturated fatty acids; (iii) membrane lipid synthesis and proliferation are responsive to and controlled by a balanced fatty acid composition.

Lipotoxicity in the heart

Obesity and insulin resistance are associated with ectopic lipid deposition in multiple tissues, including the heart. Excess lipid may be stored as triglycerides, but are also shunted into non-oxidative pathways that disrupt normal cellular signaling leading to organ dysfunction and in some cases apoptosis, a process termed lipotoxicity. Various pathophysiological mechanisms have been proposed to lead to lipotoxic tissue injury, which might vary by cell type. Specific mechanisms by which lipotoxicity alter cardiac structure and function are incompletely understood, but are beginning to be elucidated. This review will focus on mechanisms that have been proposed to lead to lipotoxic injury in the heart and will review the state of knowledge regarding potential causes and correlates of increased myocardial lipid content in animal models and humans. We will seek to highlight those areas where additional research is warranted.

Lipid oversupply, selective insulin resistance, and lipotoxicity: molecular mechanisms

The accumulation of fat in tissues not suited for lipid storage has deleterious consequences on organ function, leading to cellular damage that underlies diabetes, heart disease, and hypertension. To combat these lipotoxic events, several therapeutics improve insulin sensitivity and/or ameliorate features of metabolic disease by limiting the inappropriate deposition of fat in peripheral tissues (i.e. thiazolidinediones, metformin, and statins). Recent advances in genomics and lipidomics have accelerated progress towards understanding the pathogenic events associated with the excessive production, underutilization, or inefficient storage of fat. Herein we review studies applying pharmacological or genetic strategies to manipulate the expression or activity of enzymes controlling lipid deposition, in order to gain a clearer understanding of the molecular mechanisms by which fatty acids contribute to metabolic disease.

Do muscle mass, muscle density, strength, and physical function similarly influence risk of hospitalization in older adults?

OBJECTIVES

To examine the association between strength, function, lean mass, muscle density, and risk of hospitalization.

DESIGN

Prospective cohort study.

SETTING

Two U.S. clinical centers.

PARTICIPANTS

Adults aged 70 to 80 (N=3,011) from the Health, Aging and Body Composition Study.

MEASUREMENTS

Measurements were of grip strength, knee extension strength, lean mass, walking speed, and chair stand pace. Thigh computed tomography scans assessed muscle area and density (a proxy for muscle fat infiltration). Hospitalizations were confirmed by local review of medical records. Negative binomial regression models estimated incident rate ratios (IRRs) of hospitalization for race- and sex-specific quartiles of each muscle and function parameter separately. Multivariate models adjusted for age, body mass index, health status, and coexisting medical conditions.

RESULTS

During an average 4.7 years of follow-up, 1,678 (55.7%) participants experienced one or more hospitalizations. Participants in the lowest quartile of muscle density were more likely to be subsequently hospitalized (multivariate IRR=1.47, 95% confidence interval (CI)=1.24-1.73) than those in the highest quartile. Similarly, participants with the weakest grip strength were at greater risk of hospitalization (multivariate IRR=1.52, 95% CI=1.30-1.78, Q1 vs. Q4). Comparable results were seen for knee strength, walking pace, and chair stands pace. Lean mass and muscle area were not associated with risk of hospitalization.

CONCLUSION

Weak strength, poor function, and low muscle density, but not muscle size or lean mass, were associated with greater risk of hospitalization. Interventions to reduce the disease burden associated with sarcopenia should focus on increasing muscle strength and improving physical function rather than simply increasing lean mass.

N-Myristoylation targets dihydroceramide Delta4-desaturase 1 to mitochondria: partial involvement in the apoptotic effect of myristic acid

This study was designed to analyze the effect of myristic acid on ceramide synthesis and its related lipoapoptosis pathway. It was previously observed that myristic acid binds dihydroceramide Delta4-desaturase 1 (DES1) through N-myristoylation and activates this enzyme involved in the final de novo ceramide biosynthesis step. In the present study, we show first by immunofluorescence microscopy and subcellular fractionation that DES1 myristoylation targets part of the recombinant protein to the mitochondria in COS-7 cells. In addition, native dihydroceramide Delta4-desaturase activity was found in both the endoplasmic reticulum and mitochondria in rat hepatocytes. Dihydroceramide conversion to ceramide was increased in COS-7 cells expressing DES1 and incubated with myristic acid. The expression of the wild-type myristoylable DES1-Gly alone, but not the expression of the unmyristoylable mutant DES1-Ala, induced apoptosis of COS-7 cells. Finally, myristic acid alone also increased the production of cellular ceramide and had an apoptotic effect. This effect was potentiated on caspase activity when the myristoylable form of DES1 was expressed. Therefore, these results suggest that the myristoylation of DES1 can target the enzyme to the mitochondria leading to an increase in ceramide levels which in turn contributes to partially explain the apoptosis effect of myristic acid in COS-7 cells.

JNK1-dependent PUMA expression contributes to hepatocyte lipoapoptosis

Free fatty acids (FFA) induce hepatocyte lipoapoptosis by a c-Jun N-terminal kinase (JNK)-dependent mechanism. However, the cellular processes by which JNK engages the core apoptotic machinery during lipotoxicity, especially activation of BH3-only proteins, remain incompletely understood. Thus, our aim was to determine whether JNK mediates induction of BH3-only proteins during hepatocyte lipoapoptosis. The saturated FFA palmitate, but not the monounsaturated FFA oleate, induces an increase in PUMA mRNA and protein levels. Palmitate induction of PUMA was JNK1-dependent in primary murine hepatocytes. Palmitate-mediated PUMA expression was inhibited by a dominant negative c-Jun, and direct binding of a phosphorylated c-Jun containing the activator protein 1 complex to the PUMA promoter was identified by electrophoretic mobility shift assay and a chromatin immunoprecipitation assay. Short hairpin RNA-targeted knockdown of PUMA attenuated Bax activation, caspase 3/7 activity, and cell death. Similarly, the genetic deficiency of Puma rendered murine hepatocytes resistant to lipoapoptosis. PUMA expression was also increased in liver biopsy specimens from patients with non-alcoholic steatohepatitis as compared with patients with simple steatosis or controls. Collectively, the data implicate JNK1-dependent PUMA expression as a mechanism contributing to hepatocyte lipoapoptosis.

Mechanisms of hypertension in the cardiometabolic syndrome

Arterial hypertension is often part of a constellation of anthropometric and metabolic abnormalities that occur simultaneously to a higher degree than would be expected by chance alone, supporting the existence of a discrete disorder, the so-called metabolic syndrome. It is the result of interactions among a large number of interconnected mechanisms, which eventually lead to both an increase in cardiovascular and renal risk, and the development of diabetes. Mechanisms involved in the metabolic syndrome are obesity, insulin resistance, and a constellation of independent factors, which include molecules of hepatic, vascular, and immunologic origin with pro-inflammatory properties. At each of these key points are interactions of demographics, lifestyle, genetic factors, and environmental fetal programming. Superimposing upon these are infections or chronic exposure or both to certain drugs that can also make their contribution. Skeletal muscle and the liver, not adipose tissue, are the two key insulin-response tissues involved in maintaining glucose balance, although abnormal insulin action in the adipocytes also plays a role in development of the syndrome. Factors commonly associated with and partly dependent on obesity, insulin resistance, such as overactivity of the sympathetic, stimulation of the renin-angiotensin-aldosterone systems, abnormal renal sodium handling, endothelial dysfunction, and large vessels' alterations, may play a key role in the blood pressure elevation of the syndrome.

Abdominal obesity is associated with microalbuminuria and an elevated cardiovascular risk profile in patients with hypertension

Background

Overweight and obesity are frequently associated with preventable death and have emerged as a major challenge to public health. There is an ongoing debate on the role of abdominal obesity and its value in predicting cardiovascular and renal outcomes. The present analysis evaluates the prevalence of microalbuminuria (MAU) and conventional cardiovascular risk factors in relation to measures of general and abdominal obesity.

Methods

In this multinational, observational study, 20828 hypertensive out-patients from 26 countries including Europe, North and Latin America, Middle East, and Asia were analyzed. Urinary dipstick screening for MAU was performed as well as data on patient demographics, anthropometric measures, cardiovascular risk factors, comorbid conditions, and cardiovascular drug therapy collected. MAU prevalence was determined by a stepwise logistic regression analysis with cardiovascular risk factors as univariate.

Results

In the univariate analysis, MAU prevalence systematically increased with body mass index (BMI) from 54.4% (1st tertial) to 62.1% (3rd tertial) (p < 0.0001), an increase which was also observed for waist circumference (WC). At any level of BMI, MAU increased with WC from 53.5%, 54.8%, and 55.0% (1st tertial of WC in all three BMI tertials) to 61.4%, 62.1%, and 64.0% (3rd tertial of WC in all BMI tertials) (p < 0.0001). In the multivariate analysis, WC, but not BMI was independently associated with MAU. Furthermore, overweight/obesity were associated with the presence of modifiable and nonmodifiable risk factors.

Conclusion

An abnormal WC, but not BMI appears to be independently associated with MAU, an early marker of cardiovascular and renal risk. Increasing WC confers an incremental risk for MAU at any level of BMI, underlining the prognostic importance of abdominal fat accumulation beyond general obesity.

The genetics of neutral lipid biosynthesis: an evolutionary perspective

The storage of fatty acids and fatty alcohols in the form of neutral lipids such as triacylglycerol (TAG), cholesteryl ester (CE), and wax ester (WE) serves to provide reservoirs for membrane formation and maintenance, lipoprotein trafficking, lipid detoxification, evaporation barriers, and fuel in times of stress or nutrient deprivation. This ancient process likely originated in actinomycetes and has persisted in eukaryotes, albeit by different molecular mechanisms. A surfeit of neutral lipids is strongly, perhaps causally, related to several human diseases such as diabetes mellitus, obesity, atherosclerosis and nonalcoholic fatty liver disease. Therefore, understanding the metabolic pathways of neutral lipid synthesis and the roles of the enzymes involved may facilitate the development of new therapeutic interventions for these syndromes.

Fenofibrate and PBA prevent fatty acid-induced loss of adiponectin receptor and pAMPK in human hepatoma cells and in hepatitis C virus-induced steatosis

Adiponectin receptors play a key role in steatosis and inflammation; however, very little is known about regulation of adiponectin receptors in liver. Here, we examined the effects of palmitate loading, endoplasmic reticulum (ER) stress, and the hypolipidemic agent fenofibrate on adiponectin receptor R2 (AdipoR2) levels and AMP-activated protein kinase (AMPK) in human hepatoma Huh7 cells and in Huh.8 cells, a model of hepatitis C-induced steatosis. Palmitate treatment reduced AdipoR2 protein and basal AMPK phosphorylation in Huh7 cells. Fenofibrate treatment preserved AdipoR2 and phosphorylated AMPK (pAMPK) levels in palmitate-treated cells accompanied by reduced triglyceride (TG) accumulation and less activation of ER stress markers CCAAT/enhancer binding (C/EBPbeta) and eukaryotic translation initiation factor 2 alpha. ER stress agents thapsigargin and tunicamycin suppressed AdipoR2 and pAMPK levels in Huh7 cells, while fenofibrate and the chemical chaperone 4-phenylbutyrate (PBA) prevented these changes. AdipoR2 levels were lower in Huh.8 cells and fenofibrate treatment increased AdipoR2 while reducing activation of c-Jun N-terminal kinase and C/EBPbeta expression without changing TG levels. Taken together, these results suggest that fatty acids and ER stress reduce AdipoR2 protein and pAMPK levels, while fenofibrate and PBA might be important therapeutic agents to correct lipid- and ER stress-mediated loss of AdipoR2 and pAMPK associated with nonalcoholic steatohepatitis.

Reduced endoplasmic reticulum luminal calcium links saturated fatty acid-mediated endoplasmic reticulum stress and cell death in liver cells

Chronic exposure to elevated free fatty acids, in particular long chain saturated fatty acids, provokes endoplasmic reticulum (ER) stress and cell death in a number of cell types. The perturbations to the ER that instigate ER stress and activation of the unfolded protein in response to fatty acids in hepatocytes have not been identified. The present study employed H4IIE liver cells and primary rat hepatocytes to examine the hypothesis that saturated fatty acids induce ER stress via effects on ER luminal calcium stores. Exposure of H4IIE liver cells and primary hepatocytes to palmitate and stearate reduced thapsigargin-sensitive calcium stores and increased biochemical markers of ER stress over similar time courses (6 h). These changes preceded cell death, which was only observed at later time points (16 h). Co-incubation with oleate prevented the reduction in calcium stores, induction of ER stress markers and cell death observed in response to palmitate. Inclusion of calcium chelators, BAPTA-AM or EGTA, reduced palmitate- and stearate-mediated enrichment of cytochrome c in post-mitochondrial supernatant fractions and cell death. These data suggest that redistribution of ER luminal calcium contributes to long chain saturated fatty acid-mediated ER stress and cell death.

Myocardial metabolism of triacylglycerol-rich lipoproteins in type 2 diabetes

Cardiac utilisation of very-low-density lipoprotein (VLDL) and chylomicrons (CM) was investigated in the ZDF rat model of type 2 diabetes, in order to define the role of triacylglycerol (TAG) metabolism in the development of contractile dysfunction. Hearts from obese diabetic and lean littermate control rats were perfused with VLDL and CM from diabetic and control rats. Metabolic fate of the lipoprotein TAG and contractile function were examined. Myocardial utilisation of both VLDL- and CM-TAG was increased in the diabetic state. Diabetic hearts oxidised diabetic lipoprotein-TAG to a greater extent than control lipoproteins; glucose oxidation was decreased. There was no difference in lipoprotein-TAG assimilation into diabetic heart lipids; diabetic lipoproteins were, however, a poor substrate for control heart tissue lipid accumulation. Although the proportion of exogenous lipid incorporated into tissue TAG was increased in diabetic hearts perfused with control lipoproteins, this effect was not seen in diabetic hearts perfused with diabetic lipoproteins. Myocardial heparin-releasable lipoprotein lipase (LPL) activity was moderately increased in the diabetic state, and diabetic lipoproteins increased tissue-residual LPL activity. Cardiac hydraulic work was decreased only in diabetic hearts perfused with diabetic CM. Compositional analysis of diabetic variant lipoproteins indicated changes in size and apoprotein content. Alterations in cardiac TAG-rich lipoprotein metabolism in type 2 diabetes are due to changes in both the diabetic myocardium and the diabetic lipoprotein particle; decreased contractile function is not related to cardiac lipid accumulation from TAG-rich lipoproteins but may be associated with changes in TAG-fatty acid oxidation.

Differential effect of oleic and palmitic acid on lipid accumulation and apoptosis in cultured hepatocytes

BACKGROUND AND AIM

Studies have shown monounsaturated oleic acid to be less toxic than palmitic acid and to prevent/attenuate palmitic acid hepatocites toxicity in steatosis models in vitro. However, to what degree these effects are mediated by steatosis extent is unknown.

METHODS

We evaluated whether steatosis per se is associated with hepatocytes apoptosis and determined the role of oleic and palmitic acid, the most abundant fatty acids in western diets, on triglyceride accumulation and apoptosis in an in vitro model of steatosis induced in three hepatocytic cell lines (HepG2, HuH7, WRL68). The impact of incubation for 24 h with oleic (0.66 and 1.32 mM) and palmitic acid (0.33 and 0.66 mM), alone or combined (molar ratio 2 : 1) on steatosis, apoptosis, and insulin signalling, was evaluated.

RESULTS

Concurrent with PPARgamma and SREBP-1 gene activation, steatosis extent was larger when cells were treated with oleic than with palmitic acid; the latter fatty acid was associated with increased PPARalpha expression. Cell apoptosis was inversely proportional to steatosis deposition. Moreover, palmitic, but not oleic acid, impaired insulin signalling. Despite the higher amount of fat resulting from incubation of the two fatty acids combined, the apoptosis rate and impaired insulin signalling were lower than in cells treated with palmitic acid alone, indicating a protective effect of oleic acid.

CONCLUSIONS

Oleic acid is more steatogenic but less apoptotic than palmitic acid in hepatocityc cell cultures. These data may provide a biological basis for clinical findings on dietary patterns and pathogenetic models of nonalcoholic fatty liver disease.

The farnesoid X receptor (FXR) as a new target in non-alcoholic steatohepatitis

The farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily that is mainly expressed in liver, intestine, kidney and adipose tissue. On activation by bile acids, FXR regulates a wide variety of target genes that are critically involved in the control of bile acid, lipid and glucose homeostasis. Thus, FXR appears to be a promising target for the treatment of non-alcoholic steatohepatitis (NASH). Notably, FXR activation inhibits hepatic de novo lipogenesis, increases insulin sensitivity and protects hepatocytes against bile acid-induced cytotoxicity. More recent data also indicate a critical role of FXR in liver regeneration and hepatocarcinogenesis. For this reason, the development of FXR agonists and/or modulators (SBARMs) may prove to be clinically useful for treating NASH. While preclinical studies in rodents support this hypothesis, clinical studies are still warranted in humans.

Reducing glycosphingolipid content in adipose tissue of obese mice restores insulin sensitivity, adipogenesis and reduces inflammation

Adipose tissue is a critical mediator in obesity-induced insulin resistance. Previously we have demonstrated that pharmacological lowering of glycosphingolipids and subsequently GM3 by using the iminosugar AMP-DNM, strikingly improves glycemic control. Here we studied the effects of AMP-DNM on adipose tissue function and inflammation in detail to provide an explanation for the observed improved glucose homeostasis. Leptin-deficient obese (Lep^Ob) mice were fed AMP-DNM and its effects on insulin signalling, adipogenesis and inflammation were monitored in fat tissue. We show that reduction of glycosphingolipid biosynthesis in adipose tissue of Lep^Ob mice restores insulin signalling in isolated ex vivo insulin-stimulated adipocytes. We observed improved adipogenesis as the number of larger adipocytes was reduced and expression of genes like peroxisome proliferator-activated receptor (PPAR) γ, insulin responsive glucose transporter (GLUT)-4 and adipsin increased. In addition, we found that adiponectin gene expression and protein were increased by AMP-DNM. As a consequence of this improved function of fat tissue we observed less inflammation, which was characterized by reduced numbers of adipose tissue macrophages (crown-like structures) and reduced levels of the macrophage chemo attractants monocyte-chemoattractant protein-1 (Mcp-1/Ccl2) and osteopontin (OPN). In conclusion, pharmacological lowering of glycosphingolipids by inhibition of glucosylceramide biosynthesis improves adipocyte function and as a consequence reduces inflammation in adipose tissue of obese animals.

Saturated with fat: new perspectives on lipotoxicity

PURPOSE OF REVIEW

To present current perspectives on the mediators and mechanisms of cyto-lipotoxic events and their relevance to human health.

RECENT FINDINGS

The relatively recent isolation of lipid acyltransferase genes from yeast to mice and humans has resulted in a paradigm shift that now establishes all fatty acids as toxic, albeit in tissue specific patterns and by different mechanisms. Furthermore, the dysregulation of glucose homeostasis in combination with excess fatty acids provides a synergistic effect leading to glucolipotoxicity and cell death. These findings are relevant to the development of disease states associated with the pathogenesis of the metabolic syndrome.

SUMMARY

In an era when an astounding number of people are diagnosed with metabolic disorders, it is imperative that we understand the consequences of a chronic metabolic surplus. Excessive fat, saturated or otherwise, has to be accommodated. Multiple aspects of this homeostasis are emerging, some of which are described here.

A human apoB100 transgenic mouse expresses human apoB100 in the RPE and develops features of early AMD

apoB100 lipoprotein particles have been found to accumulate in Bruch membrane prior to the development of age-related macular degeneration (AMD). This work was performed to determine whether mice that overexpress apoB100 in the RPE/choroid and liver develop landmarks of early AMD over time. Mice transgenic for a human genomic fragment encoding the full length human apoB ("apoB100" mice) and litter-mate control mice were given a normal chow or high-fat diet for 12 months. Mice were evaluated for human apoB mRNA expression in the RPE/choroid and liver by RT-qPCR. Phenotypic changes associated with early AMD were evaluated by ultrastructural analysis using transmission electron microscopy. Changes were semi-quantified using linear regression analysis. Both the RPE/choroid and liver of apoB100 mice expressed both human and mouse apoB mRNA. Transmission electron microscopy showed ultrastructural changes consistent with early human AMD including loss of basal infoldings and accumulation of cytoplasmic vacuoles in the RPE, and basal laminar deposits containing long-spacing collagen and heterogeneous debris in Bruch membrane of apoB100 mice. In apoB100 mice given a high-fat diet, basal linear-like deposits were identified in 12-month-old mice. Linear regression analysis showed that the genotype (human apoB transgene) was a stronger influencing factor than high-fat diet in producing AMD-like lesions used in this study. Human apoB100 transgenic mice overexpress apoB in RPE and, with time, develop validated phenotypic changes that are seen in early human AMD. The phenotypic changes were aggravated by feeding a high-fat diet. The apoB100 mouse model could be valuable in determining the role of apoB-containing lipoproteins in triggering the onset of early AMD.

Effect of ceramide on mesenchymal stem cell differentiation toward adipocytes

Proinflammatory cytokines such as tumor necrosis factor (TNF) alpha are well known to inhibit adipocyte differentiation. TNF-alpha triggers ceramide synthesis through binding of TNF-alpha to its p55 receptor. Therefore, ceramide is implicated in many of the multiple signaling pathways initiated by TNF-alpha. In breast tissue engineering, it is important to know how to modulate adipocyte differentiation of the stem cells with exogenous additives like ceramide in vitro. We hypothesized that stem cell adipogenesis could be retained in TNF-alpha-treated preadipocytes in which ceramide synthesis was blocked and that exogenous ceramide could inhibit adipocyte differentiation. We first studied the effect of ceramide synthase inhibitor, Fumonisin B2, on the adipogenesis of murine mesenchymal stem cells (D1 cells), treated with TNF-alpha. We then studied the effect of specific exogenous C6-ceramide on D1 cell viability and differentiation. It was found that 1 ng/ml of TNF-alpha significantly inhibited D1 cell adipogenesis. Cells treated with 5 microM of Fumonisin B2 were able to undergo adipogenesis, even when treated with TNF-alpha. High concentrations of exogenous C6-ceramide (>50 microM) had an inhibitory effect, not only on the pre-confluent proliferation of the D1 cells but also on the post-confluent cell viability. High concentrations of C6-ceramide (>50 microM) also inhibited mitotic clonal expansion when D1 cell differentiation was induced by the addition of an adipogenic hormonal cocktail. C6-ceramide at low concentrations (10-25 microM) inhibited lipid production in D1 cells, demonstrated by decreased levels of both total triglyceride content and specific fatty acid composition percentages. Genetic expression of peroxisome proliferator-activated receptor (PPAR) gamma and aP2 in D1 cells was reduced by C6-ceramide treatment. CCAAT/enhancer-binding protein (C/EBP) beta levels in D1 cells were reduced by C6-ceramide treatment during early differentiation; PPARgamma and aP2 protein levels were reduced at terminal differentiation. C6-ceramide at lower concentrations also decreased lipid accumulation of differentiating D1 cells. Our results suggest that ceramide synthase inhibitor retains the adipogenic potential of TNF-alpha-treated mesenchymal stem cells, while exogenous ceramide at lower concentrations inhibit the adipogenesis of mesenchymal stem cells. Ceramide, therefore, could be a modulator candidate in breast tissue engineering strategies.

Sphingolipids: players in the pathology of metabolic disease

The contribution of aberrant production of bioactive lipids to pathophysiological changes associated with obesity has risen to the forefront of lipid research. Increased diacylglycerol has been appreciated as a cause of insulin resistance, but emerging data support a role for sphingolipids in other metabolic diseases including obesity, diabetes, atherosclerosis and metabolic syndrome. Recent data demonstrate that elevation of plasma free fatty acids promotes aberrant sphingolipid production and composition in various tissues including skeletal muscle, pancreas and adipocytes. Moreover, rectifying these aberrant sphingolipid profiles often attenuates pathologies associated with their production. Although data thus far generate more questions than they answer, they indicate a major contribution of sphingolipids to pathologies associated with obesity. This review summarizes recent work in these areas.

Lipid droplet biogenesis induced by stress involves triacylglycerol synthesis that depends on group VIA phospholipase A2

This work investigates the metabolic origin of triacylglycerol (TAG) formed during lipid droplet (LD) biogenesis induced by stress. Cytotoxic inhibitors of fatty acid synthase induced TAG synthesis and LD biogenesis in CHO-K1 cells, in the absence of external sources of fatty acids. TAG synthesis was required for LD biogenesis and was sensitive to inhibition and down-regulation of the expression of group VIA phospholipase A(2) (iPLA(2)-VIA). Induction of stress with acidic pH, C(2)-ceramide, tunicamycin, or deprivation of glucose also stimulated TAG synthesis and LD formation in a manner dependent on iPLA(2)-VIA. Overexpression of the enzyme enhanced TAG synthesis from endogenous fatty acids and LD occurrence. During stress, LD biogenesis but not TAG synthesis required phosphorylation and activation of group IVA PLA(2) (cPLA(2)alpha). The results demonstrate that iPLA(2)-VIA provides fatty acids for TAG synthesis while cPLA(2)alpha allows LD biogenesis. LD biogenesis during stress may be a survival strategy, recycling structural phospholipids into energy-generating substrates.

The metabolic syndrome in hypertension: European society of hypertension position statement

The metabolic syndrome considerably increases the risk of cardiovascular and renal events in hypertension. It has been associated with a wide range of classical and new cardiovascular risk factors as well as with early signs of subclinical cardiovascular and renal damage. Obesity and insulin resistance, beside a constellation of independent factors, which include molecules of hepatic, vascular, and immunologic origin with proinflammatory properties, have been implicated in the pathogenesis. The close relationships among the different components of the syndrome and their associated disturbances make it difficult to understand what the underlying causes and consequences are. At each of these key points, insulin resistance and obesity/proinflammatory molecules, interaction of demographics, lifestyle, genetic factors, and environmental fetal programming results in the final phenotype. High prevalence of end-organ damage and poor prognosis has been demonstrated in a large number of cross-sectional and a few number of prospective studies. The objective of treatment is both to reduce the high risk of a cardiovascular or a renal event and to prevent the much greater chance that metabolic syndrome patients have to develop type 2 diabetes or hypertension. Treatment consists in the opposition to the underlying mechanisms of the metabolic syndrome, adopting lifestyle interventions that effectively reduce visceral obesity with or without the use of drugs that oppose the development of insulin resistance or body weight gain. Treatment of the individual components of the syndrome is also necessary. Concerning blood pressure control, it should be based on lifestyle changes, diet, and physical exercise, which allows for weight reduction and improves muscular blood flow. When antihypertensive drugs are necessary, angiotensin-converting enzyme inhibitors, angiotensin II-AT1 receptor blockers, or even calcium channel blockers are preferable over diuretics and classical beta-blockers in monotherapy, if no compelling indications are present for its use. If a combination of drugs is required, low-dose diuretics can be used. A combination of thiazide diuretics and beta-blockers should be avoided.

Intricacies of fat

One of the most exciting cell biology fields of study concerns the physiology and pathology of fat. The basic assumptions once held concerning the function of adipose tissue have been shown to be oversimplified or sometimes completely wrong. Fat does more than store excess energy; it is actually the largest endocrine organ in the body, and it may be one of the most active. Adipocytes release hormones and other molecules that act on nearby tissues and travel through the vasculature to distant sites, such as the brain, skeletal muscle, and liver. Under conditions of normal weight, those signals help the body to suppress hunger, utilize glucose, and decrease the risk of cardiovascular disease. However, under conditions of obesity, the hormones (or the proteins that bind the hormones) become abnormal and can result in states of chronic inflammation leading to diabetes and heart disease. In addition, excessive fat can lead to the accumulation of lipid droplets in nonfat cells, including skeletal and cardiac muscle. Although some lipid droplets are used as an immediate source of energy for cells, large numbers of stored droplets can cause cellular damage and cell death. The purposes of this article are to review the normal and deviant signals released by fat cells, to draw a link between those signals and chronic diseases such as diabetes, and to discuss the role of exercise in reversing some of the deviant signaling perpetrated by excess fat.

Glycerolipid metabolism and signaling in health and disease

Maintenance of body temperature is achieved partly by modulating lipolysis by a network of complex regulatory mechanisms. Lipolysis is an integral part of the glycerolipid/free fatty acid (GL/FFA) cycle, which is the focus of this review, and we discuss the significance of this pathway in the regulation of many physiological processes besides thermogenesis. GL/FFA cycle is referred to as a "futile" cycle because it involves continuous formation and hydrolysis of GL with the release of heat, at the expense of ATP. However, we present evidence underscoring the "vital" cellular signaling roles of the GL/FFA cycle for many biological processes. Probably because of its importance in many cellular functions, GL/FFA cycling is under stringent control and is organized as several composite short substrate/product cycles where forward and backward reactions are catalyzed by separate enzymes. We believe that the renaissance of the GL/FFA cycle is timely, considering the emerging view that many of the neutral lipids are in fact key signaling molecules whose production is closely linked to GL/FFA cycling processes. The evidence supporting the view that alterations in GL/FFA cycling are involved in the pathogenesis of "fatal" conditions such as obesity, type 2 diabetes, and cancer is discussed. We also review the different enzymatic and transport steps that encompass the GL/FFA cycle leading to the generation of several metabolic signals possibly implicated in the regulation of biological processes ranging from energy homeostasis, insulin secretion and appetite control to aging and longevity. Finally, we present a perspective of the possible therapeutic implications of targeting this cycling.

The association of pericardial fat with calcified coronary plaque

BACKGROUND

Pericardial fat has a higher secretion of inflammatory cytokines than subcutaneous fat. Cytokines released from pericardial fat around coronary arteries may act locally on the adjacent cells.

OBJECTIVE

We examined the relationship between pericardial fat and calcified coronary plaque.

METHODS AND PROCEDURES

Participants in the community-based Multi-Ethnic Study of Atherosclerosis (MESA) underwent a computed tomography (CT) scan for the assessment of calcified coronary plaque in 2000/2002. We measured the volume of pericardial fat using these scans in 159 whites and blacks without symptomatic coronary heart disease from Forsyth County, NC, aged 55-74 years.

RESULTS

Calcified coronary plaque was observed in 91 participants (57%). After adjusting for height, a 1 s.d. increment in pericardial fat was associated with an increased odds of calcified coronary plaque (odds ratio (95% confidence interval): 1.92 (1.27, 2.90)). With further adjustment of other cardiovascular factors, pericardial fat was still significantly associated with calcified coronary plaque. This relationship did not differ by gender and ethnicity. On the other hand, BMI and height-adjusted waist circumference were not associated with calcified coronary plaque.

DISCUSSION

Pericardial fat is independently associated with calcified coronary plaque.

Caspase-dependent and -independent lipotoxic cell-death pathways in fission yeast

Understanding the mechanisms underlying lipid-induced cell death has significant implications in both cell biology and human diseases. Previously, we showed that fission-yeast Schizosaccharomyces pombe cells deficient in triacylglycerol synthesis display apoptotic markers upon entry into stationary phase. Here, we characterize the sequential molecular events that take place at the onset of cell death in S. pombe, including a surge of diacylglycerol, post-mitotic arrest, alterations in mitochondrial activities and in intracellular redox balance, chromatin condensation, nuclear-envelope fragmentation, and eventually plasma-membrane permeabilization. Our results demonstrated active roles of mitochondria and reactive oxygen species in cell death, and identified novel cell-death regulators--including metacaspase Pca1, BH3-domain protein Rad9, and diacylglycerol-binding proteins Pck1 and Bzz1. Most importantly, we show that, under different conditions and stimuli, failure to maintain intracellular-lipid homeostasis can lead to cell death with different phenotypic manifestations, genetic criteria and cellular mechanisms, pointing to the existence of multiple lipotoxic pathways in this organism. Our study represents the first in-depth analysis of cell-death pathways in S. pombe.

Bone and fat connection in aging bone

PURPOSE OF REVIEW

The fat and bone connection plays an important role in the pathophysiology of age-related bone loss. This review will focus on the age-induced mechanisms regulating the predominant differentiation of mesenchymal stem cells into adipocytes. Additionally, bone marrow fat will be considered as a diagnostic and therapeutic approach to osteoporosis.

RECENT FINDINGS

There are two types of bone and fat connection. The 'systemic connection', usually seen in obese patients, is hormonally regulated and associated with high bone mass and strength. The 'local connection' happens inside the bone marrow. Increasing amounts of bone marrow fat affect bone turnover through the inhibition of osteoblast function and survival and the promotion of osteoclast differentiation and activation. This interaction is regulated by paracrine secretion of fatty acids and adipokines. Additionally, bone marrow fat could be quantified using noninvasive methods and could be used as a therapeutic approach due to its capacity to transdifferentiate into bone without affecting other types of fat in the body.

SUMMARY

The bone and fat connection within the bone marrow constitutes a typical example of lipotoxicity. Additionally, bone marrow fat could be used as a new diagnostic and therapeutic approach for osteoporosis in older persons.

Transcriptome alteration in the diabetic heart by rosiglitazone: implications for cardiovascular mortality

BACKGROUND

Recently, the type 2 diabetes medication, rosiglitazone, has come under scrutiny for possibly increasing the risk of cardiac disease and death. To investigate the effects of rosiglitazone on the diabetic heart, we performed cardiac transcriptional profiling and imaging studies of a murine model of type 2 diabetes, the C57BL/KLS-lepr(db)/lepr(db) (db/db) mouse.

METHODS AND FINDINGS

We compared cardiac gene expression profiles from three groups: untreated db/db mice, db/db mice after rosiglitazone treatment, and non-diabetic db/+ mice. Prior to sacrifice, we also performed cardiac magnetic resonance (CMR) and echocardiography. As expected, overall the db/db gene expression signature was markedly different from control, but to our surprise was not significantly reversed with rosiglitazone. In particular, we have uncovered a number of rosiglitazone modulated genes and pathways that may play a role in the pathophysiology of the increase in cardiac mortality as seen in several recent meta-analyses. Specifically, the cumulative upregulation of (1) a matrix metalloproteinase gene that has previously been implicated in plaque rupture, (2) potassium channel genes involved in membrane potential maintenance and action potential generation, and (3) sphingolipid and ceramide metabolism-related genes, together give cause for concern over rosiglitazone's safety. Lastly, in vivo imaging studies revealed minimal differences between rosiglitazone-treated and untreated db/db mouse hearts, indicating that rosiglitazone's effects on gene expression in the heart do not immediately turn into detectable gross functional changes.

CONCLUSIONS

This study maps the genomic expression patterns in the hearts of the db/db murine model of diabetes and illustrates the impact of rosiglitazone on these patterns. The db/db gene expression signature was markedly different from control, and was not reversed with rosiglitazone. A smaller number of unique and interesting changes in gene expression were noted with rosiglitazone treatment. Further study of these genes and molecular pathways will provide important insights into the cardiac decompensation associated with both diabetes and rosiglitazone treatment.

The ageing male heart: myocardial triglyceride content as independent predictor of diastolic function

AIMS

In animal models of obesity and diabetes mellitus, myocardial TG accumulation is associated with decreased myocardial function. In the physiologically ageing heart, myocardial triglyceride (TG) accumulation may also occur due to reduced myocardial fatty acid oxidation. The role of myocardial TG in the ageing human heart is unknown. Therefore, the purpose of our study was to evaluate the effects of ageing on myocardial TG content, and to determine the association between myocardial TG content and heart function.

METHODS AND RESULTS

1H-magnetic resonance spectroscopy and magnetic resonance imaging of the heart were performed in 43 healthy male subjects. Mean age (range) of the subjects was 44 (20-66) years. Body mass index (BMI), blood pressure, and biochemical markers were determined. Age correlated significantly to myocardial TG content (r = 0.57, P < 0.05) independently of BMI. Furthermore, myocardial TG content correlated negatively with left ventricular diastolic function (represented by E/A ratio, r = -0.68, P < 0.05). Multivariable analysis indicated myocardial TG content as independent predictor (P < 0.05) of the age related decrease in diastolic heart function.

CONCLUSION

Myocardial TG content increases in the physiologically ageing male heart and is associated with the age-related decline in diastolic function, independent of BMI, blood pressure, and biochemical blood markers.

The role of fatty acids in the development and progression of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has emerged as a serious obesity-related disorder. NAFLD encompasses a wide spectrum of hepatic derangements ranging from a surfeit of fat in the liver (steatosis) to lipid surplus accompanied by fibrosis and cellular death (nonalcoholic steatohepatitis or NASH). The most widely accepted model to explain the progression from simple NAFLD to NASH is the "two-hit hypothesis," wherein fat over accumulation per se is not sufficient to induce the progression to statohepatitis, but renders the liver more susceptible to "second hits" that, once imposed upon the steatotic liver, cause further aberrations that culminate in the development of NASH. However, in light of recent data from our laboratory and elsewhere, we propose that an increased ratio of saturated-to-unsaturated fatty acids delivered to or stored within the liver may, in part, mediate the progression from simple steatosis to NASH. The molecular mechanisms that mediate the effect of saturated fatty acids are unclear, although proinflammatory cytokines, reactive oxygen species, and endoplasmic reticulum stress may all play a role. Collectively, these data suggest that saturated fatty acids may represent an intrinsic second hit to the liver that hastens the development of NASH.

Effects of ethanol on pancreatic beta-cell death: interaction with glucose and fatty acids

Western lifestyle plays an important role in the prevalence of type 2 diabetes by causing insulin resistance and pancreatic beta-cell dysfunction, a prerequisite for the development of diabetes. High fat diet and alcohol are major components of the western diet. The aim of the present study was to investigate the effects of ethanol and fatty acids on beta-cell survival and metabolism. We treated the rat beta-cell line RINm5F with ethanol, a mixture of palmitic and oleic acids, or both. Reactive oxygen species (ROS) were determined by (5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate) (CM-H2DCFDA) fluorescence assay, and mitochondrial activity was assessed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) reduction assay and by determining ATP production. Cell viability was assessed with a cell counter and trypan blue exclusion, and the mode of cell death by Hoechst33342 and propidium iodide staining. With both ethanol and fatty acid treatments, MTT reduction and ATP production decreased, whereas ROS production increased. Ethanol treatment had no effect on cell number, whereas fatty acid treatment reduced the cell number. Cell incubation with ethanol, fatty acids, or both increased the number of Hoechst 33342-positive nuclei. However, the majority of nuclei from fatty acid-treated cells were stained with propidium iodide, indicating a loss of plasma membrane integrity. We conclude that both ethanol and fatty acids generate cellular oxidative stress, and affect mitochondrial function in RINm5F beta-cells. However, ethanol causes beta-cell death by apoptosis, whereas fatty acids cause cell death predominantly by necrosis. It is not known whether these results are applicable to human beta-cells.

Pancreatic ectopic fat is characterized by adipocyte infiltration and altered lipid composition

OBJECTIVE

Sustained exposure to lipids is deleterious for pancreatic islet function. This could be mediated through increased pancreatic fat following increased dietary fat and in obesity, which has implications for the onset of type 2 diabetes. The aims of this study were to determine changes in extent and composition of pancreatic, hepatic, and visceral fat in mice fed a high-fat diet (HFD, 40% by weight) compared with a control diet (5% fat) of similar fatty acid composition, and to compare composition and extent of pancreatic fat in human type 2 diabetes.

METHODS AND PROCEDURES

Mice were fed HFD for 3 or 15 weeks. Human postmortem pancreas was examined from subjects with type 2 diabetes (n = 9) and controls (n = 7). Tissue lipid content and composition were determined by gas chromatography and pancreatic adipocyte infiltration quantified by morphometry.

RESULTS

Pancreatic triacylglycerol (TG) content was 20x greater (P < 0.05) in HFD mice and there were more pancreatic perilipin-positive adipocytes compared with controls after 15 weeks. The proportions of 18:1n -9 and 18:2n -6 in pancreatic TG and the 20:4n -6/18:2n -6 ratio in phospholipids, were higher (both P < 0.05) after HFD compared with controls. Human pancreatic TG content was correlated with the proportion of pancreatic perilipin-positive adipocytes (r = 0.64, P < 0.05) and associated with unsaturated fatty acid enrichment (P < 0.05).

DISCUSSION

Adipocyte infiltration in pancreatic exocrine tissue is associated with high-fat feeding in mice and pancreatic TG content in humans. This alters the fatty acid milieu of the islet which could contribute to islet dysfunction.

Programmed cell death in fission yeast Schizosaccharomyces pombe

Yeasts have proven to be invaluable, genetically tractable systems to study various fundamental biological processes including programmed cell death. Recent advances in the elucidation of the molecular pathways underlying apoptotic cell death in yeasts have revealed remarkable similarities to mammalian apoptosis at cellular, organelle and macromolecular levels, thus making a strong case for the relevance of yeast models of regulated cell death. Programmed cell death has been reported in fission yeast Schizosaccharomyces pombe, primarily in the contexts of perturbed intracellular lipid metabolism, defective DNA replication, improper mitotic entry, chronological and replicative aging. Here we review the current understanding of the programmed cell death in fission yeast, paying particular attention to lipid-induced cell death. We discuss our recent findings that fission yeast exhibits plasticity of apoptotic and non-apoptotic modes of cell death in response to different lipid stimuli and growth conditions, and that mitochondria, reactive oxygen species and novel cell death mediators including metacaspase Pca1, SpRad9 and Pck1 are involved in the lipotoxic cell death. We also present perspectives on how various aspects of the cell and molecular biology of this organism can be explored to shed light on the governing principles underlying lipid-mediated signaling and cell demise.

The blind men ‘see’ the elephant-the many faces of fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a group of diseases with excess fat in liver in the absence of a poorly defined limit of alcohol consumption. Most common variety, a universal public health problem, is associated with insulin resistance caused by a host of genetic and epigenetic defects modulated by life style and environmental factors. In fact the term NAFLD is loose to incorporate so many etiologies except alcoholism and few other etiologies, presenting as fat in liver. However as a sign fatty liver is very important in predicting the risk of diabetes, cardiovascular disease, stroke, cirrhosis and cancer. Abnormal fat accumulation can result from several defects in nuclear receptors associated with lipid sensing, synthesis and oxidation like LXR, FXR, SREBP, ChREBP and PPAR; defects in the lipid influx-efflux channels, insulin signaling, proteins involved in fatty acid catabolism, defects in adipose tissue development and function, inappropriate nutrition and finally defects in neural regulatory mechanisms. The progress of the disease is determined by the basic defects which results in fat accumulation, an individual’s immunological response to the accumulated fat and its derivatives and the oxidant stress response. Congregation of unrelated genetic defects under same diagnosis ‘NAFLD’ can result in inefficient patient management. Further studies are required to understand the molecular basis of fatty liver to enable a personalized management of diseases presenting as fatty liver in the absence of alcohol abuse.

Type 2 diabetes: Gaining insight into the disease process using proteomics

The incidence of diabetes mellitus is growing rapidly, with an increasing disease related morbidity and mortality. This is caused by macro- and microvascular complications, as a consequence of the often late diagnosis of type 2 diabetes (T2D), but especially by the difficulties to control glucose homeostasis due to the progressive nature of the disease. T2D is moreover a dual disease, with components of beta-cell failure and components of insulin resistance in peripheral organs, such as liver, fat, and muscle. Understanding the pathogenesis of the disease by gaining insight into the molecular pathways involved in both phenomena is one of the major assets of proteomic approaches. Moreover, proteomics and peptidomics may provide us with robust biomarkers for beta-cell failure, insulin resistance in pheripheral organs, but also for the development of diabetic complications. This review focuses on the knowledge gained by use of proteomic and peptidomic techniques in the study of the pathophysiology of T2D and in the attempts to discover new therapeutic targets.

Optimising islet engraftment is critical for successful clinical islet transplantation

Clinical islet transplantation is currently being explored as a treatment for persons with type 1 diabetes and hypoglycaemia unawareness. Although 'proof-of-principle' has been established in recent clinical studies, the procedure suffers from low efficacy. At the time of transplantation, the isolated islets are allowed to embolise the liver after injection in the portal vein, a procedure that is unique in the area of transplantation. A novel view on the engraftment of intraportally transplanted islets is presented that could explain the low efficacy of the procedure.

Adipogenesis and lipotoxicity: role of peroxisome proliferator-activated receptor gamma (PPARgamma) and PPARgammacoactivator-1 (PGC1)

Obesity is characterised by an increase in the adipose deposits, resulting from an imbalance between food intake and energy expenditure. When expansion of the adipose tissue reaches its maximum limit, as in obesity, fat accumulates in non-adipose tissues such as liver, heart, muscle and pancreas, developing a toxic response known as lipotoxicity, a condition that promotes the development of insulin resistance and other metabolic complications. Thus, the lipotoxic state may contribute to the increased risk of insulin resistance, diabetes, fatty liver and cardiovascular complications associated with obesity. We are interested in studying adipose tissue, specifically how mechanisms of adipogenesis and remodelling of adipose tissue, in terms of size and function of the adipocytes, could be considered a strategy to increase the capacity for lipid storage and prevent lipotoxicity. The peroxisome proliferator-activated receptors (PPARs) are a family of transcription factors that regulate energy balance by promoting either energy deposition or energy dissipation. Under normal physiological conditions, PPARgamma is mainly expressed in adipose tissue and regulates diverse functions such as the development of fat cells and their capacity to store lipids. The generation of PPARgamma knockout mice, either tissue specific or isoform specific, has provided new models to study PPARgamma's role in adipose tissue differentiation and function and have highlighted the essential role of PPARgamma in adipogenesis and lipogenesis.A second strategy to prevent lipotoxicity is to increase the capacity of tissues to oxidise fatty acids. PPARgammacoactivator-1alpha is a coactivator of PPARgamma that induces the expression of genes that promote the differentiation of preadipocytes to brown adipocytes. Recently, it has been implicated in increasing the oxidation of fatty acids via increasing mitochondrial capacity and function, making this co-factor a key candidate for the treatment of lipotoxicity.

Glucose-dependent insulinotropic polypeptide-mediated up-regulation of beta-cell antiapoptotic Bcl-2 gene expression is coordinated by cyclic AMP (cAMP) response element binding protein (CREB) and cAMP-responsive CREB coactivator 2

The cyclic AMP (cAMP)/protein kinase A (PKA) cascade plays a central role in beta-cell proliferation and apoptosis. Here, we show that the incretin hormone glucose-dependent insulinotropic polypeptide (GIP) stimulates expression of the antiapoptotic Bcl-2 gene in pancreatic beta cells through a pathway involving AMP-activated protein kinase (AMPK), cAMP-responsive CREB coactivator 2 (TORC2), and cAMP response element binding protein (CREB). Stimulation of beta-INS-1 (clone 832/13) cells with GIP resulted in increased Bcl-2 promoter activity. Analysis of the rat Bcl-2 promoter revealed two potential cAMP response elements, one of which (CRE-I [GTGACGTAC]) was shown, using mutagenesis and deletion analysis, to be functional. Subsequent studies established that GIP increased the nuclear localization of TORC2 and phosphorylation of CREB serine 133 through a pathway involving PKA activation and reduced AMPK phosphorylation. At the nuclear level, phospho-CREB and TORC2 were demonstrated to bind to CRE-I of the Bcl-2 promoter, and GIP treatment resulted in increases in their interaction. Furthermore, GIP-mediated cytoprotection was partially reversed by small interfering RNA-mediated reduction in BCL-2 or TORC2/CREB or by pharmacological activation of AMPK. The antiapoptotic effect of GIP in beta cells is therefore partially mediated through a novel mode of transcriptional regulation of Bcl-2 involving cAMP/PKA/AMPK-dependent regulation of CREB/TORC2 activity.

Ceramide induces mitochondrial abnormalities in insulin-secreting INS-1 cells: potential mechanisms underlying ceramide-mediated metabolic dysfunction of the beta cell

C2-ceramide, a cell permeable analogue of ceramide [CER] markedly reduced mitochondrial membrane potential [MMP] in insulin-secreting INS cells, which was followed by a significant accumulation of cytochrome c [Cyt c] into the cytosolic compartment. In a manner akin to CER, exposure of these cells to interleukin-1beta [IL-1beta] also resulted in reduction in MMP and cytosolic accumulation of Cyt c. Further, long-term exposure of these cells to either CER [but not its inactive analogue] or IL-1beta caused a marked reduction in their metabolic viability. However, unlike IL-1beta, which increased nitric oxide [NO] release, CER-treatment of INS cells had no effects of CER on NO release were demonstrable. Together, these findings suggest that CER-induced mitochondrial effects may not be mediated via iNOS gene expression and NO production. CER also activated an okadaic acid -sensitive protein phosphatase [CAPP] in the purified mitochondrial fraction, suggesting that CAPP might represent one of the target proteins for CER in the beta cell mitochondria. Together, our findings suggest direct detrimental effects of CER on mitochondrial function in beta cells leading to their dysfunction and demise via apoptosis. Moreover, our findings provide evidence for a potential difference in the mechanisms underlying CER- and IL-1beta-induced mitochondrial defects and apoptotic demise of the effete beta cell.

Short-term caloric restriction induces accumulation of myocardial triglycerides and decreases left ventricular diastolic function in healthy subjects

OBJECTIVE

Diabetes and obesity are associated with increased plasma nonesterified fatty acid (NEFA) levels, myocardial triglyceride accumulation, and myocardial dysfunction. Because a very low-calorie diet (VLCD) also increases plasma NEFA levels, we studied the effect of a VLCD on myocardial triglyceride content and cardiac function in healthy subjects.

RESEARCH DESIGN AND METHODS

Fourteen healthy nonobese men underwent (1)H-magnetic resonance spectroscopy (MRS) to determine myocardial and hepatic triglyceride content, (31)P-MRS to assess myocardial high-energy phosphate (HEP) metabolism (phosphocreatine/ATP), and magnetic resonance imaging of myocardial function at baseline and after a 3-day VLCD.

RESULTS

After the dietary intervention, plasma NEFA levels increased compared with those at baseline (from 0.5 +/- 0.1 to 1.1 +/- 0.1 mmol/l, P < 0.05). Concomitantly, myocardial triglyceride content increased by approximately 55% compared with that at baseline (from 0.38 +/- 0.05 to 0.59 +/- 0.06%, P < 0.05), whereas liver triglyceride content decreased by approximately 32% (from 2.2 +/- 0.5 to 1.5 +/- 0.4%, P < 0.05). The VLCD did not change myocardial phosphocreatine-to-ATP ratio (2.33 +/- 0.15 vs. 2.33 +/- 0.08, P > 0.05) or systolic function. Interestingly, deceleration of the early diastolic flow across the mitral valve decreased after the VLCD (from 3.37 +/- 0.20 to 2.91 +/- 0.16 ml/s(2) x 10(-3), P < 0.05). This decrease in diastolic function was significantly correlated with the increase in myocardial triglyceride content.

CONCLUSIONS

Short-term VLCD induces accumulation of myocardial triglycerides. In addition, VLCD decreases left ventricular diastolic function, without alterations in myocardial HEP metabolism. This study documents diet-dependent physiological variations in myocardial triglyceride content and diastolic function in healthy subjects.

Intracardiac lipid accumulation, lipoatrophy of muscle cells and expansion of myocardial infarction in type 2 diabetic patients

The overall mortality of diabetic patients after myocardial infarction is 3-4 times higher than non-diabetics. The cellular mechanisms underlying such a poor clinical prognosis remain incompletely understood. Recent reports suggest that lipotoxicity associated with impaired liporegulation is among the leading factors in the pathogenesis of type 2 diabetes. The goal of this study was to investigate whether excess lipid accumulation specifically in heart muscle cells contributes to the expansion of myocardial infarction in type 2 diabetic patients. Comparative structural analysis of cardiac tissue was performed on autopsy samples from the infracted hearts of diabetic and non-diabetic individuals with special reference to the expansion of the infarction, degenerative changes, lipoatrophy, cell death, and replacement fibrosis. We found that progressive accumulation of lipids in cardiac myocytes was accompanied by considerable loss of myofibrils and was frequently observed in the heart tissue of type 2 diabetic patients. This indicates that disassembly of the contractile apparatus in the cells infiltrated with lipids weakens their capability for functional activity. Analysis of degenerative changes in the diabetic tissue has shown that lipid-laden cardiac myocytes were more susceptible to necrotic and apoptotic cells death leading to expansion of the infarction and the development of progressive focal replacement fibrosis both in the perinecrotic zone and in the areas located far from the site of injury. Our data show that lipoatrophy and loss of muscle cells during the post-infarction period aggravate the functional impairment in the diabetic heart and limits its adaptive capacity for compensatory remodeling. This suggests that lipotoxic myocardial injury associated with defects of lipid metabolism in type 2 diabetes predisposes its evolution toward congestive heart failure and is an important factor contributing to a high mortality following infarction.

Leptin signaling and obesity: cardiovascular consequences

Leptin, among the best known hormone markers for obesity, exerts pleiotropic actions on multiple organ systems. In this review, we summarize major leptin signaling pathways, namely Janus-activated kinase/signal transducers and activators of transcription and mitogen-activated protein kinase, including possible mechanisms of leptin resistance in obesity. The effects of leptin on the cardiovascular system are discussed in detail, including its contributions to hypertension, atherosclerosis, depressed myocardial contractile function, fatty acid metabolism, hypertrophic remodeling, and reduction of ischemic/reperfusion injury. The overall goal is to summarize current understanding of how altered leptin signaling in obesity contributes to obesity-related cardiovascular disease.