Eicosanoids participate in the regulation of cardiac glucose transport by contribution to a rearrangement of actin cytoskeletal elements

Microvascular insulin resistance associates with enhanced muscle glucose disposal in CD36 deficiency

Dysfunction of endothelial insulin delivery to muscle associates with insulin resistance. CD36, a fatty acid transporter and modulator of insulin signaling is abundant in endothelial cells, especially in capillaries. Humans with inherited 50% reduction in CD36 expression have endothelial dysfunction but whether it is associated with insulin resistance is unclear. Using hyperinsulinemic/euglycemic clamps in Cd36-/- and wildtype mice, and in 50% CD36 deficient humans and matched controls we found that Cd36-/- mice have enhanced systemic glucose disposal despite unaltered transendothelial insulin transfer and reductions in microvascular perfusion and blood vessel compliance. Partially CD36 deficient humans also have better glucose disposal than controls with no capillary recruitment by insulin. CD36 knockdown in primary human-derived microvascular cells impairs insulin action on AKT, endothelial nitric oxide synthase, and nitric oxide release. Thus, insulin resistance of microvascular function in CD36 deficiency paradoxically associates with increased glucose utilization, likely through a remodeling of muscle gene expression.

Extracellular Matrix Stiffness: New Areas Affecting Cell Metabolism

In recent years, in-depth studies have shown that extracellular matrix stiffness plays an important role in cell growth, proliferation, migration, immunity, malignant transformation, and apoptosis. Most of these processes entail metabolic reprogramming of cells. However, the exact mechanism through which extracellular matrix stiffness leads to metabolic reprogramming remains unclear. Insights regarding the relationship between extracellular matrix stiffness and metabolism could help unravel novel therapeutic targets and guide development of clinical approaches against a myriad of diseases. This review provides an overview of different pathways of extracellular matrix stiffness involved in regulating glucose, lipid and amino acid metabolism.

Molecular pathobiology of scleritis and its therapeutic implications

Scleritis and other autoimmune diseases are characterized by an imbalance in the levels of pro-inflammatory and anti-inflammatory molecules with the balance tilted more towards the former due to the failure of recognition of self. The triggering of inflammatory process could be ascribed to the presence of cytoplasmic DNA/chromatin that leads to activation of cytosolic DNA-sensing cGAS-STING (cyclic GMP-AMP synthase linked to stimulator of interferon genes) pathway and enhanced expression of NF-κB that results in an increase in the production of pro-inflammatory bioactive lipids. Bioactive lipids gamma-linolenic acid (GLA), dihomo-GLA (DGLA), prostaglandin E1 (PGE1), prostacyclin (PGI2) and lipoxin A4, resolvins, protectins and maresins have anti-inflammatory actions, bind to DNA to render it non-antigenic and are decreased in autoimmune diseases. These results suggest that efforts designed to enhance the production of anti-inflammatory bioactive lipids may form a new approach to autoimmune diseases. Local injection or infusion of lipoxins, resolvins, protectins and maresins or their precursors such as arachidonic acid may be exploited in the prevention and management of autoimmune diseases including scleritis, uveitis and lupus/rheumatoid arthritis.

Electrical and mechanical stimulation of cardiac cells and tissue constructs

The field of cardiac tissue engineering has made significant strides over the last few decades, highlighted by the development of human cell derived constructs that have shown increasing functional maturity over time, particularly using bioreactor systems to stimulate the constructs. However, the functionality of these tissues is still unable to match that of native cardiac tissue and many of the stem-cell derived cardiomyocytes display an immature, fetal like phenotype. In this review, we seek to elucidate the biological underpinnings of both mechanical and electrical signaling, as identified via studies related to cardiac development and those related to an evaluation of cardiac disease progression. Next, we review the different types of bioreactors developed to individually deliver electrical and mechanical stimulation to cardiomyocytes in vitro in both two and three-dimensional tissue platforms. Reactors and culture conditions that promote functional cardiomyogenesis in vitro are also highlighted. We then cover the more recent work in the development of bioreactors that combine electrical and mechanical stimulation in order to mimic the complex signaling environment present in vivo. We conclude by offering our impressions on the important next steps for physiologically relevant mechanical and electrical stimulation of cardiac cells and engineered tissue in vitro.

Adiponectin stimulates Rho-mediated actin cytoskeleton remodeling and glucose uptake via APPL1 in primary cardiomyocytes

OBJECTIVE

Adiponectin is known to confer its cardioprotective effects in obesity and type 2 diabetes, mainly by regulating glucose and fatty acid metabolism in cardiomyocytes. Dynamic actin cytoskeleton remodeling is involved in regulation of multiple biological functions, including glucose uptake. Here we investigated in neonatal cardiomyocytes whether adiponectin induced actin cytoskeleton remodeling and if this played a role in adiponectin-stimulated glucose uptake.

MATERIALS/METHODS

Primary cardiomyocytes were treated with full-length and globular adiponectin (fAd and gAd, respectively).

RESULTS

Both fAd and gAd increased RhoA activity, phosphorylation of the Rho/ROCK signaling target cofilin and actin polymerization to form filamentous actin as determined by rhodamine-phallodin immunofluorescence and quantitative analysis of filamentous to globular actin ratio. Scanning electron microscopy also demonstrated structural remodeling. Adiponectin stimulated glucose uptake, was significantly abrogated in the presence of inhibitors of actin cytoskeleton remodeling (cytochalasin D) and Rho/ROCK signaling (C3 transferase, Y27632). We showed that adiponectin increased colocalization of actin and APPL1 and that actin remodeling, phosphorylation of AMPK, p38MAPK and cofilin, glucose uptake and oxidation were all attenuated after siRNA-mediated knockdown of APPL1.

CONCLUSION

We show that adiponectin mediates Rho/ROCK-dependent actin cytoskeleton remodeling to increase glucose uptake and metabolism via APPL1 signaling.

Involvement of protein kinase C and RhoA in protease-activated receptor 1-mediated F-actin reorganization and cell growth in rat cardiomyocytes

Protease-activated receptor 1 (PAR1) that can be activated by serine proteinases such as thrombin has been demonstrated to contribute to the development of cardiac remodeling and hypertrophy after myocardial injury. Here, we investigated the mechanisms by which PAR1 leads to hypertrophic cardiomyocyte growth using cultured rat neonatal ventricular myocytes. PAR1 stimulation with thrombin (1 U/ml) or a synthetic agonist peptide (TFLLR-NH(2), 50 µM) for 48 h induced an increase in cell size and myofibril formation associated with BNP (brain natriuretic peptide) production. This actin reorganization assessed by fluorescein isothiocyanate (FITC)-conjugated phalloidin staining appeared at 1 h after PAR1 stimulation, and this response was reduced by a protein kinase C (PKC) inhibitor, chelerythrine, inhibitors of Rho (simvastatin) and Rho-associated kinase (ROCK) (Y-27632), but not by pertussis toxin (PTX). By Western blot analysis, translocation of PKCα or PKCε from the cytosol to membrane fractions was observed in cells stimulated with thrombin or TFLLR-NH(2) for 2 - 5 min. In addition, PAR1 stimulation for 3 - 5 min increased the level of active RhoA. Furthermore, inhibitors of PKC and ROCK and Rho abrogated PAR1-mediated increase in cell size. Depletion of PKCα or PKCε by specific small interfering RNA also suppressed both actin reorganization and cell growth. These results suggest that PAR1 stimulation of cardiomyocytes induces cell hypertrophy with actin cytoskeletal reorganization through activation of PKCα and PKCε isoforms and RhoA via PTX-insensitive G proteins.

Role of caveolin-3 and glucose transporter-4 in isoflurane-induced delayed cardiac protection

BACKGROUND

Caveolae are small, flask-like invaginations of the plasma membrane. Caveolins are structural proteins found in caveolae that have scaffolding properties to allow organization of signaling. The authors tested the hypothesis that delayed cardiac protection induced by volatile anesthetics is caveolae or caveolin dependent.

METHODS

An in vivo mouse model of ischemia-reperfusion injury with delayed anesthetic preconditioning (APC) was tested in wild-type, caveolin-1 knockout, and caveolin-3 knockout mice. Mice were exposed to 30 min of oxygen or isoflurane and allowed to recover for 24 h. After 24 h recovery, mice underwent 30-min coronary artery occlusion followed by 2 h of reperfusion at which time infarct size was determined. Biochemical assays were also performed in excised hearts.

RESULTS

Infarct size as a percent of the area at risk was reduced by isoflurane in wild-type (24.0 +/- 8.8% vs. 45.1 +/- 10.1%) and caveolin-1 knockout mice (27.2 +/- 12.5%). Caveolin-3 knockout mice did not show delayed APC (41.5 +/- 5.0%). Microscopically distinct caveolae were observed in wild-type and caveolin-1 knockout mice but not in caveolin-3 knockout mice. Delayed APC increased the amount of caveolin-3 protein but not caveolin-1 protein in discontinuous sucrose-gradient buoyant fractions. In addition, glucose transporter-4 was increased in buoyant fractions, and caveolin-3/glucose transporter-4 colocalization was observed in wild-type and caveolin-1 knockout mice after APC.

CONCLUSIONS

These results show that delayed APC involves translocation of caveolin-3 and glucose transporter-4 to caveolae, resulting in delayed protection in the myocardium.

Short-term fatty acid effects on adipocyte glucose uptake: mechanistic insights

The modulation of insulin sensitivity in visceral fat tissue could be important in the treatment of Type 2 diabetes mellitus. Selected fatty acids may impact on insulin-stimulated and basal glucose uptake in adipocytes, thus isolated rat epididymal adipocytes were exposed to 100 microM oleic, arachidonic, eicosapentaenoic, docosahexaenoic or stearic acids and insulin (15 nM) or vehicle for 30 min. Glucose uptake was quantified by measuring uptake of 3H-deoxyglucose/mg adipocyte protein/min. Where appropriate, inhibitors were included to elucidate the mechanisms involved. In this model, insulin stimulated glucose uptake with 62+/-7%. All fatty acids tested, except for stearic acid, depressed insulin-stimulated glucose uptake by an average of 33+/-4.2%. On the other hand, all fatty acids tested except stearic and arachidonic acids, stimulated basal glucose uptake with an average of 34+/-8.1%. Inhibitor studies showed the involvement of prostaglandins, lipoxins, protein kinase C and tyrosine kinase in these processes.

Eicosanoid signalling pathways in the heart

Myocardial phospholipids serve as primary reservoirs of arachidonic acid (AA), which is liberated through the rate-determining hydrolytic action of cardiac phospholipases A2 (PLA2s). A predominant PLA2 in myocardium is calcium-independent phospholipase A2beta (iPLA2beta), which, through its calmodulin (CaM) and ATP-binding domains, is regulated by alterations in local cellular Ca2+ concentrations and cardiac bioenergetic status, respectively. Importantly, iPLA2beta has been demonstrated to be activated by ischaemia through elevation of the concentration of myocardial fatty acyl-CoA, which abrogates Ca2+/CaM-mediated inhibition of iPLA2beta. AA released by PLA2-catalysed hydrolysis of phospholipids serves as a precursor for eicosanoids generated by pathways dependent on cyclooxygenases (COX), lipoxygenases (LOX), and cytochromes P450 (CYP). Eicosanoids initiate and propagate diverse signalling cascades, primarily through their interaction with cellular receptors and ion channels. However, during pathologic states such as ischaemia or congestive heart failure, eicosanoids contribute to multiple maladaptive changes including inflammation, alterations of cellular growth programmes, and activation of multiple transcriptional events leading to the deleterious sequelae of these pathologic states. This review summarizes the central roles of myocardial PLA(2)s in eicosanoid signalling in the heart, the major COX, LOX, and CYP pathways of eicosanoid generation in the myocardium, and the effects of important eicosanoids on receptor-, ion channel-, and transcription-mediated processes that facilitate cardiac hypertrophy, mediate ischaemic preconditioning, and precipitate arrhythmogenesis in response to pathologic stimuli.

Genes, diet and type 2 diabetes mellitus: a review

Diabetes mellitus is widely recognized as one of the leading causes of death and disability. While insulin insensitivity is an early phenomenon partly related to obesity, pancreatic beta-cell function declines gradually over time even before the onset of clinical hyperglycemia. Several mechanisms have been proposed to be responsible for insulin resistance, including increased non-esterified fatty acids, inflammatory cytokines, adipokines, and mitochondrial dysfunction, as well as glucotoxicity, lipotoxicity, and amyloid formation for beta-cell dysfunction. Moreover, the disease has a strong genetic component, although only a handful of genes have been identified so far. Diabetic management includes diet, exercise and combinations of antihyperglycemic drug treatment with lipid-lowering, antihypertensive, and antiplatelet therapy. Since many persons with type 2 diabetes are insulin resistant and overweight, nutrition therapy often begins with lifestyle strategies to reduce energy intake and increase energy expenditure through physical activity. These strategies should be implemented as soon as diabetes or impaired glucose homoeostasis (pre-diabetes) is diagnosed.

Insulin improves cardiomyocyte contractile function through enhancement of SERCA2a activity in simulated ischemia/reperfusion

AIM

Insulin exerts anti-apoptotic effects in both cardiomyocytes and coronary endothelial cells following ischemia/reperfusion (I/R) via the Akt-endothelial nitric oxide synthase survival signal pathway. This important insulin signaling might further contribute to the improvement of cardiac function after reperfusion. In this study, we tested the hypothesis that sarcoplasmic reticulum calcium-ATPase (SERCA2a) is involved in the insulin-induced improvement of cardiac contractile function following I/R.

METHODS

Ventricular myocytes were enzymatically isolated from adult SD rats. Simulated I/R was induced by perfusing cells with chemical anoxic solution for 15 min followed by reperfusion with Tyrode's solution with or without insulin for 30 min. Myocyte shortening and intracellular calcium transients were assessed and underlying mechanisms were investigated.

RESULTS

Reperfusion with insulin (10(-7) mol/L) significantly improved the recovery of contractile function (n=15-20 myocytes from 6-8 hearts, P<0.05), and increased calcium transients, as evidenced by the increased calcium [Ca2+] fluorescence ratio, shortened time to peak Ca2+ and time to 50% diastolic Ca2+, compared with those in cells reperfused with vehicle (P<0.05). In addition, Akt phosphorylation and SERCA2a activity were both increased in insulin-treated I/R cardiomyocytes, which were markedly inhibited by pretreatment of cells with a specific Akt inhibitor. Moreover, inhibition of Akt activity abolished insulin-induced positive contractile and calcium transients responses in I/R cardiomyocytes.

CONCLUSION

These data demonstrated for the first time that insulin improves the recovery of contractile function in simulated I/R cardiomyocytes in an Akt-dependent and SERCA2a-mediated fashion.

Disparate effects of 12-lipoxygenase and 12-hydroxyeicosatetraenoic acid in vascular endothelial and smooth muscle cells and in cardiomyocytes

The expression and activity of the arachidonic acid-metabolizing enzyme leukocyte-type 12-lipoxygenase (12-LO) are augmented in cultured vascular endothelial and smooth muscle cells exposed to high glucose concentrations and in blood vessels of diabetic animals. The product of this enzyme, 12-hydroxyeicosatetraenoic acid (12-HETE), evokes two types of interactions in these cells: on one hand it acts as a pro-inflammatory factor that contributes to the initiation and progression of atherosclerotic lesions. Yet on the other, it protects the same cells against deleterious effects of high levels of intracellular glucose by downregulating the glucose transport system in the cells. In addition, it has been shown that 12-LO and 12-HETE support insulin-dependent glucose transporter-4 translocation to the plasma membrane by maintaining intact actin fiber network in the cardiomyocytes. Here we focus on the disparate cellular interactions by which 12-LO and 12-HETE affect the glucose transport system in vascular endothelial and smooth muscle cells and in cardiomyocytes.