Insulin Resistance In Cardiomyocytes Research Articles

Studying the role of random translocation of GLUT4 in cardiomyocytes on calcium oscillations

Defective excitation-contraction coupling (ECC) is one of the causes of contractile dysfunction linked to diabetic cardiomyopathy (DCM). This defect in ECC is mainly caused by the dysregulation of the calcium homeostasis in normal cardiomyocytes due to prolonged elevated blood glucose levels. Different types of channels inside the cardiomyocytes help maintain calcium homeostasis in the cell. Free cytosolic calcium concentration changes are one of several variables that affect complicated physiological cardiac processes and significantly impact proper heart functioning. Glucose concentration in the cardiac cell also plays a vital role in altering the calcium homeostasis in the DCM condition. In the current study, we develop a mathematical model that explicitly represents many of the known signalling components mediating translocation of the insulin-responsive glucose transporter type 4 (GLUT4) to gain insight into the complexities of metabolic insulin signalling pathways in cardiac cells. We examined the effect of the random movement of GLUT4 responsible for the entry of glucose in the cardiomyocytes. In non-paced cardiac cells calcium remains in the steady state in the absence of external pacing and avoid oscillation for healthy cardiomyocyte functioning. Intracellular calcium transients were observed during action potential. We investigated the circumstances under which the system transits from a stable state to an oscillatory state. We studied the effect of random translocation of GLUT4 on calcium oscillation. By altering system parameters, we induced insulin resistance in cardiomyocytes to mimic diabetic conditions and proposed some potential restoration strategies to restore normal calcium dynamics. Early bifurcation was observed with the introduction of randomness in the system.

Investigating the Contribution of Subcellular Redox Imbalance to Lipid-Induced Insulin Resistance in Cardiomyocytes

Investigating the Contribution of Subcellular Redox Imbalance to Lipid-Induced Insulin Resistance in Cardiomyocytes

Acetylation of α-tubulin on Lys40, a new way to modulate cardiac glucose transport

Cardiovascular disease remains the leading cause of death in the diabetic population. Diabetic patients develop a specific heart condition called diabetic cardiomyopathy that can evolve to heart failure and that is characterized by altered metabolism in the early stages of the disease. Our group previously demonstrated that overfueling the heart with branched-chain amino acids, ketone bodies or fatty acids, substrates that are upregulated in diabetes, inhibits glucose entry in cardiomyocytes through a global rise in protein acetylation that interferes with glucose transporter 4 (GLUT4) translocation to the plasma membrane. However, the acetylated proteins involved in this process were not yet identified. We investigated the role of α-tubulin, an important cytoskeleton element responsible for GLUT4 translocation, that is known to be acetylable on Lys40 (K40). Acetylation level of α-tubulin on K40 was evaluated in a mouse model of diabetes (high-fat diet, 4 months) and in primary cultured adult rat cardiomyocytes. Its acetylation level was modulated by using a pharmacological inhibitor of its deacetylase (tubacin 10 μM, 5 hrs) and by overexpressing a non-acetylable form of α-tubulin (mCherry α-tubulin K40A). GLUT4 translocation was assessed by fluorescent immunostaining in cells expressing the fusion protein HA-GLUT4-GFP. Glucose transport was measured by following the detritiation rate of 2-3H-glucose in insulin-sensitive and insulin-resistant cardiomyocytes. Acetylation of α-tubulin on K40 was significantly enhanced in the heart of diet-induced diabetic mice. Experimentally increasing its acetylation level in cardiomyocytes with tubacin impaired GLUT4 translocation to the plasma membrane and reduced both basal and insulin-dependent glucose uptake. On the other hand, decreasing α-tubulin K40 acetylation via the overexpression of the K40A form of α-tubulin stimulated glucose transport. Interestingly, reducing α-tubulin K40 acetylation similarly promoted glucose entry in insulin-resistant conditions. Cardiac glucose transport can be regulated by modulation of α-tubulin K40 acetylation, which may lead to new therapeutic strategies preventing the metabolic changes occurring during the development of diabetic cardiomyopathy.

α-Tubulin acetylation on lysine 40 controls cardiac glucose uptake.

Our group previously demonstrated that an excess of nutrients, as observed in diabetes, provokes an increase in cardiac protein acetylation responsible for a reduced insulin-stimulated translocation of the glucose transporter GLUT4 to the plasma membrane. The acetylated proteins involved in this event have yet not been identified. α-Tubulin is a promising candidate as a major cytoskeleton component involved, among other things, in the translocation of GLUT4-containing vesicles from their intracellular pools toward the plasma membrane. Moreover, α-tubulin is known to be acetylated, Lys40 (K40) being its best characterized acetylated residue. The present work sought to evaluate the impact of α-tubulin K40 acetylation on cardiac glucose entry, with a particular interest in GLUT4 translocation. First, we observed that a mouse model of high-fat diet-induced obesity presented an increase in cardiac α-tubulin K40 acetylation level. We next showed that treatment of insulin-sensitive primary cultured adult rat cardiomyocytes with tubacin, a specific tubulin acetylation inducer, reduced insulin-stimulated glucose uptake and GLUT4 translocation. Conversely, decreasing α-tubulin K40 acetylation by expressing a nonacetylable dominant form of α-tubulin (mCherry α-tubulin K40A mutant) remarkably intensified insulin-induced glucose transport. Finally, mCherry α-tubulin K40A expression similarly improved glucose transport in insulin-resistant cardiomyocytes or after AMP-activated protein kinase activation. Taken together, our study demonstrates that modulation of α-tubulin K40 acetylation level affects glucose transport in cardiomyocytes, offering new putative therapeutic insights regarding modulation of glucose metabolism in insulin-resistant and diabetic hearts.NEW & NOTEWORTHY Acetylation level of α-tubulin on K40 is increased in the heart of a diet-induced mouse model of type 2 diabetes. Pharmacological stimulation of α-tubulin K40 acetylation lowers insulin-mediated GLUT4 vesicles translocation to the plasma membrane, reducing glucose transport. Expressing a nonacetylable dominant form of α-tubulin boosts glucose uptake in both insulin-sensitive and insulin-resistant cardiomyocytes.

Silencing TXNIP ameliorates high uric acid-induced insulin resistance via the IRS2/AKT and Nrf2/HO-1 pathways in macrophages

Insulin resistance (IR) promotes atherosclerosis and increases the risk of diabetes and cardiovascular diseases. Our previous studies have demonstrated that high uric acid (HUA) increased oxidative stress, leading to IR in cardiomyocytes and pancreatic β cells. However, whether HUA can induce IR in monocytes/macrophages, which play critical roles in all stages of atherosclerosis, is unclear. Recent findings revealed that thioredoxin-interacting protein (TXNIP) negatively regulates insulin signaling; however, the roles and mechanisms of TXNIP in HUA-induced IR remain unclear. Therefore, in this study, we investigated the function of TXNIP in macrophages treated with UA. Transcriptomic profiling revealed TXNIP as one of the most upregulated genes, and subsequent RT-PCR and Western blot analyses confirmed that TXNIP was upregulated by HUA. HUA treatment significantly increased mitochondrial reactive oxygen species (MtROS) levels and decreased insulin-stimulated glucose uptake. Silencing TXNIP by RNA interference significantly diminished HUA-induced oxidative stress and IR. Mechanistically, silencing TXNIP reversed the inhibition of the phosphorylation of insulin receptor substrate 2 (IRS2)/protein kinase B (AKT) pathway induced by HUA. Additional study revealed that HUA induced the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase 1 (HO-1) signaling pathway, but silencing TXNIP abolished it. Moreover, Nrf2 inhibitor (ML385) ameliorated HUA-induced IR independent of IRS2/AKT signaling. Probenecid, a well-known UA-lowering drug, significantly suppressed the activation of TXNIP and Nrf2/HO-1 signaling. Furthermore, RNA-seq revealed that activation of the TXNIP-related redox pathway may be a key regulator in patients with asymptomatic hyperuricemia. These data suggest that silencing TXNIP could ameliorate HUA-induced IR via the IRS2/AKT and Nrf2/HO-1 pathways in macrophages. Additionally, TXNIP might be a promising therapeutic target for preventing and treating oxidative stress and IR induced by HUA.

Metformin protects against insulin resistance induced by high uric acid in cardiomyocytes via AMPK signalling pathways in vitro and in vivo.

High uric acid (HUA) is associated with insulin resistance (IR) in cardiomyocytes. We investigated whether metformin protects against HUA‐induced IR in cardiomyocytes. We exposed primary cardiomyocytes to HUA, and cellular glucose uptake was quantified by measuring the uptake of 2‐NBDG, a fluorescent glucose analog. Western blot was used to examine the levels of signalling protein. Membrane of glucose transporter type 4 (GLUT4) was analysed by immunofluorescence. We monitored the impact of metformin on HUA‐induced IR and in myocardial tissue of an acute hyperuricaemia mouse model established by potassium oxonate treatment. Treatment with metformin protected against HUA‐reduced glucose uptake induced by insulin in cardiomyocytes. HUA directly inhibited the phosphorylation of Akt and the translocation of GLUT4 induced by insulin, which was blocked by metformin. Metformin promoted phosphorylation of AMP‐activated protein kinase (AMPK) and restored the insulin‐stimulated glucose uptake in HUA‐induced IR cardiomyocytes. As a result of these effects, in a mouse model of acute hyperuricaemia, metformin improved insulin tolerance and glucose tolerance, accompanied by increased AMPK phosphorylation, Akt phosphorylation and translocation of GLUT4 in myocardial tissues. As expected, AICAR, another AMPK activator, had similar effects to metformin, demonstrating the important role of AMPK activation in protecting against IR induced by HUA in cardiomyocytes. Metformin protects against IR induced by HUA in cardiomyocytes and improves insulin tolerance and glucose tolerance in an acute hyperuricaemic mouse model, along with the activation of AMPK. Consequently, metformin may be an important potential new treatment strategy for hyperuricaemia‐related cardiovascular disease.

PXDN reduces autophagic flux in insulin-resistant cardiomyocytes via modulating FoxO1

Autophagy, a well-observed intracellular lysosomal degradation process, is particularly important to the cell viability in diabetic cardiomyopathy (DCM). Peroxidasin (PXDN) is a heme-containing peroxidase that augments oxidative stress and plays an essential role in cardiovascular diseases, while whether PXDN contributes to the pathogenesis of DCM remains unknown. Here we reported the suppression of cell viability and autophagic flux, as shown by autophagosomes accumulation and increased expression level of LC3-II and p62 in cultured H9C2 and human AC16 cells that treated with 400 μM palmitate acid (PA) for 24 h. Simultaneously, PXDN protein level increased. Moreover, cell death, autophagosomes accumulation as well as increased p62 expression were suppressed by PXDN silence. In addition, knockdown of PXDN reversed PA-induced downregulated forkhead box-1 (FoxO1) and reduced FoxO1 phosphorylation, whereas did not affect AKT phosphorylation. Not consistent with the effects of si-PXDN, double-silence of PXDN and FoxO1 significantly increased cell death, suppressed autophagic flux and declined the level of FoxO1 and PXDN, while the expression of LC3-II was unchanged under PA stimulation. Furthermore, inhibition of FoxO1 in PA-untreated cells induced cell death, inhibited autophagic flux, and inhibited FoxO1 and PXDN expression. Thus, we come to conclusion that PXDN plays a key role in PA-induced cell death by impairing autophagic flux through inhibiting FoxO1, and FoxO1 may also affect the expression of PXDN. These findings may develop better understanding of potential mechanisms regarding autophagy in insulin-resistant cardiomyocytes.

Irisin improves insulin resistance by inhibiting autophagy through the PI3K/Akt pathway in H9c2 cells.

As an important complication of diabetes mellitus, diabetic cardiomyopathy (DCM) is thought to arise as a result of insulin resistance (IR) in cardiomyocytes. Improving IR in cardiomyocytes may therefore be a way to treat DCM. A recently discovered myokine, irisin, has been shown to be significantly associated with increased insulin sensitivity both in clinical and pre-clinical studies of diabetes mellitus. Based on previously research, we hypothesized that irisin may be a potential candidate for increasing the insulin sensitivity of cardiomyocytes. The aim of the present study was to examine the ability of irisin to affect IR induced by treatment of rat cardiomyocyte H9c2 cells with palmitic acid (PA) and to explore its underlying mechanism. Differentiated H9c2 cells were treated with 500μM PA, 200ng/mL irisin, and 500μM PA+200ng/mL irisin with or without 100nM rapamycin (RAP) for 24h. We found that coincubation with 200ng/mL irisin for 24h significantly increased insulin-stimulated glucose consumption compared to the 500μM PA group alone. Additionally, coincubation with irisin significantly alleviated the degree of autophagy compared to the 500μM PA group alone as evidenced by monodansylcadaverine (MDC) fluorescence, the LC3II/LC3I protein levels ratio, and the protein levels of Atg5 and Atg7. Coincubation with irisin increased the levels of PI3Kp110α, pAkt and Akt compared to the 500μM PA group alone. All these effects of irisin were reversed by RAP. Our results indicate that irisin improves IR in H9c2 cells, possibly in part by inhibiting autophagy through activating the PI3K/Akt pathway.

MiR-150 regulates glucose utilization through targeting GLUT4 in insulin-resistant cardiomyocytes.

MicroRNAs (miRNAs) play an important role in cardiac function and metabolism. However, whether they regulate insulin resistance (IR) of cardiomyocytes remains unclear. The aim of the present study was to shed light on this issue with a focus on miR-150. We found here that miR-150 level was elevated in myocardium of type 2 diabetes mellitus (T2DM) rat model and in insulin-resistant cardiomyocytes induced by high glucose (25 mM) and high insulin (1 μM). Deregulation of miR-150 downregulated the protein and mRNA levels of glucose transporter 4 (GLUT4) as assessed by western blot, real-time polymerase chain reaction (qPCR), and immunofluorescence assays. Overexpression of miR-150 inhibited glucose utilization in cardiomyocytes as detected by 2-deoxyglucose transport and glucose consumption assays. In contrast, knockdown of miR-150 significantly increased glucose uptake in cardiomyocytes. Moreover, GLUT4 translocation was increased after transfection of miR-150 inhibitor (AMO-150). Collectively, miR-150 reduced glucose utilization by directly decreasing the expression and translocation of GLUT4 in the cardiomyocytes with IR and therefore might be a new therapeutic target for metabolic diseases such as T2DM.

Iron, Insulin and Coronary Heart Disease Emphasis on the Generation of Sudden Death and Occult Diabetes (And Why Donating Blood Can Reduce Cardiovascular Death)

Dysregulated glucose metabolism promote inflammation in monocytes and macrophages from patients with atherosclerotic coronary artery disease. Men with metabolic syndrome are at increased risk for sudden cardiac death, and the incident sudden death is not explained by obesity or traditional cardiovascular risk factors (Kurl, 2016), but the ingested nutritional iron. Individuals with increased abdominal adiposity exhibit an increased risk of heart failure, in spite of there are oweweigtht or not (Cavalera, 2014), because the insulin resistance contribute to increased myocardial fibrosis in the absence of hypertension (Quilliot, 2005). Iron overload, and plasma viscosity contributes to cardiovascular risk in the general population, particularly in men (Van der A, 2005; Junker, 1998). Iron influences glucose metabolism, even in the absence of significant iron overload, and its reduction may alleviate coronary heart disease and reduced or prevent their complications: High stored or free iron levels (measured by serum ferritin or catalytic iron concentrations) elevate risk for development of coronary atherosclerosis, because labile iron accelerates endothelial dysfunction and originates oxidative injury that promotes systemic and vascular inflammation, phrothrombotic conditions and insulin resistance (Williams, 2002). High serum ferritin is strongly and independently associated with acute myocardial infarction and constitutes a novel risk factor in acute sudden event (Holay, 2012). Iron plays a direct and causal role in diabetes pathogenesis mediated both by β-cell failure and insulin resistance (Simcox, 2013). In the general population, body iron stores are positively associated with the development of glucose intolerance, type 2 diabetes and gestational diabetes. In this way, blood donation significant drops in the incidence of cardiovascular events, as well as in procedures such as percutaneous transluminal coronary angioplasty and coronary artery bypass grafting (Holsworth, 2013): frequent blood donations decreased iron stores in healthy volunteers, improving insulin sensitivity and hemodynamic parameters. Iron and oxygen-derived free radicals are important in the pathogenesis of postischemic reperfusion injury and contributes substantially to endothelial dysfunction in acute coronary syndromes (Chekanov, 2002; Duffy, 2001) , and a high iron diet potentially increase ischemic damage induced by transient ischemia and early reperfusion (García-Yébenes, 2012) in animals and humans. Iron, hyperinsulinemia, and hyperglycemia act in concert to up regulate free-radical reactions (Facchini, 2000) and this metal excess accelerated the development of atherosclerosis and its accumulation may promotes illness, particularly, ischemic cardiovascular diseases. Insulin resistance in macrophages promotes formation of a necrotic core in atherosclerotic plaques by enhancing macrophage apoptosis, and exposure it to circulating blood in the event of plaque rupture can precipitate thrombosis, leading to unstable angina pectoris, myocardial infarction and sudden death (Rask.Madsen, 2012, rev). In humans phlebotomy slows progression of peripheral vascular disease and blood donation lowers significantly the risk of myocardial infarction (Salonen, 1998), particularly in insulin-resistant subjects. On the contrary, exogenous iron into healthy individuals provoked endothelial dysfunction accompanied by increased generation of superoxide radical in whole blood (Vinchi, 2014, rev). A causal relationship between pre-diabetes and cardiovascular disease exist (Ford, 2010, rev). Humans lack effective mechanisms to excrete excess iron, and excessive dietary iron uptake cause iron deposition in heart, and pancreas (Kulaksis, 2008) leading to sudden death and occult diabetes mellitus. Iron play an underappreciated role in the development of insulin resistance and insulin resistance-induced heart failure. In a chronic and acute way, Insulin resistance is an early and major factor in the development of heart failure and acute iron induced insulin resistance in cardiomyocytes (Sung, 2019). 1- Introduction 2- Catalytic Iron; Irreversible Oxidizer 3- Excess Hemoglobin and Cardiocerebrovascular Pathology 4- Free Iron as a promoter of Ischemic Heart Disease 5- Excess Ferritin and pathogenesis of Endothelial Dysfunction 6- Hyperinsulinemia as a Sudden Death Promoter. The determining role of Iron 7- Iron accumulated in excess and pathogenesis of Diabetes: High hemoglobin versus High Ferritin 8- Iron and atherosclerosis. The evidence 9- Blood Donation. Cardiovascular Pathology Protector

Azoramide improves mitochondrial dysfunction in palmitate-induced insulin resistant H9c2 cells.

Azoramide is identified as a new compound with the dual properties for the improvement of ER-folding capacity in various cells as well as for the treatment of T2DM. Although the effect of azoramide in glucose-homeostasis in mammalians is not known very well, a limited number of experimental studies showed that it could improve the insulin sensitivity in genetically obese mice. Therefore, here, we aimed to investigate the direct effect of azoramide on insulin signaling in insulin-resistant (IR) cardiomyocytes using IR-modelled ventricular cardiomyocytes. This model was established in H9c2 cells using palmitic acid incubation (50-μM for 24-h). The development of IR in cells was verified by monitoring the cellular 2-DG6P uptake assays in these treated cells. The 2-DG6P uptake was 50% less in the IR-cells compared to the control cells, while azoramide treatment (20-μM for 48-h) could prevent fully that decrease. In addition, azoramide treatment markedly preserved the IR-induced less ATP production and high-ROS production in these IR-cells. Furthermore, this treatment prevented the functional changes in mitochondria characterized by depolarized mitochondrial membrane potential and mitochondrial fusion or fusion-related protein levels as well as cellular ATP level. Moreover, this treatment provided marked protection against IR-associated changes in the insulin signaling pathway in cells, including recovery in the phosphorylation of IRS1 and Akt as well as the protein level of GLUT4 and Akt. Our present results, for the first time, demonstrated that azoramide plays an important protective role in IR-cardiomyocytes, at most, protective action on mitochondria. Therefore, one can suggest that azoramide, as a novel regulator, can provide direct cardioprotection in the IR-heart, at most, via affecting mitochondria and can be a good candidate as a new drug for the treatment of IR-associated cardiovascular disorders in mammalians with systemic IR.

SUN-080 Diminished Akt Activation and Interaction with 14-3-3ζ is Associated with Insulin Resistance in Cardiomyocytes of Metabolic Syndrome Rats

Metabolic syndrome (MetS) is a cluster of physiological and biochemical disorders that increases the risk of cardiovascular disease, being insulin resistance (IR) a pivotal condition for its development. Alterations such as metabolic inflexibility, changes in calcium dynamics, oxidative stress and impaired insulin signaling have been reported in the state of IR in the heart. Akt kinase activation plays a central role in insulin actions, leading to glucose uptake and its use as the primary energy source in the heart. Akt activity and subcellular localization are highly regulated by phosphorylation and by the interaction with other proteins. It has been reported that 14-3-3 proteins regulate insulin response and in particular the ζ isoform exerts a positive regulation on Akt activation. Therefore, we studied the changes in Akt activation and interaction with 14-3-3ζ, in response to insulin in cardiomyocytes from a MetS rat model, induced by the consumption of 30% sucrose in the drinking water during 4 months. MetS rats developed obesity (body weight in g: MetS: 592±12 vs 415±5 in control rats (C), P<0.001; epididymal fat in g: MetS: 17.5±1 vs C: 7.3±0.4, P<0.001), hypertriglyceridemia (in mg/dL MetS: 137±10 vs C: 60±3, P<0.001), low HDL-cholesterol levels (in mg/dL MetS: 31±2 vs C: 44±2, P<0.01), and systemic insulin resistance (intraperitoneal glucose tolerance test, area under the curve: MetS: 34199±2555 vs C: 17908±1844, P<0.001), without significant modifications in fasting blood glucose levels (in mg/dL MetS: 76±6 vs C: 65±5, P=0.17). Isolated cardiomyocytes from MetS rats showed insulin resistance, characterized by the absence of glucose uptake after stimulation with this hormone (3H-2deoxyglucose uptake in fmol/mg of protein/min: MetS basal: 84±17 vs MetS+insulin: 94±20, P=0.63; C basal: 74±19 vs C+insulin: 190±47, P<0.05). Insulin-induced Akt phosphorylation (determined by Western Blot, after 10 min of stimulation with 100 nM) in the key activation residues Ser473/Thr308 was diminished by 51% and 66%, respectively. Insulin-induced Akt translocation towards the plasma membrane (determined by immunostaining/confocal microscopy) a process involved in its activation, was also decreased in MetS cardiomyocytes. On the other hand, we found a diminished insulin-induced Akt-14-3-3ζ interaction evaluated by Akt co-immunoprecipitation/Western blot and by Akt co-immunoprecipitation/label-free mass spectrometry, since 14-3-3 was exclusively found in a pool of 3 C rats cardiomyocytes samples, but not in the MetS pool; this impairment suggest a reduced activation of AS160 protein and glucose uptake. These findings unveil a key participation of Akt regulatory mechanisms in the establishment of IR in cardiomyocytes under the MetS condition. Sources of Research Support: PRODEP research grant to the Academic Group Cinvestav-CA-10 to AR and JAO-R. CONACYT scholarship 278067 to HVL-G.

Iron induces insulin resistance in cardiomyocytes via regulation of oxidative stress

Iron overload is associated with various pathological changes which contribute to heart failure. Here, we examined mechanisms via which iron alters cardiomyocyte insulin sensitivity. Treatment of primary adult and neonatal cardiomyocytes as well as H9c2 cells with iron decreased insulin sensitivity determined via Western blotting or immunofluorescent detection of Akt and p70S6K phosphorylation and glucose uptake. Using CellROX deep red or DCF-DA probes we also observed that iron increased generation of reactive oxygen species (ROS), and that pretreatment with the superoxide dismutase mimetic MnTBAP reduced ROS production and attenuated iron-induced insulin resistance. SKQ1 and allopurinol but not apocynin reduced iron-induced ROS suggesting mitochondria and xanthine oxidase contribute to cellular ROS in response to iron. Western blotting for LC3-I, LC3-II and P62 levels as well as immunofluorescent co-detection of autophagosomes with Cyto-ID and lysosomal cathepsin activity indicated that iron attenuated autophagic flux without altering total expression of Atg7 or beclin-1 and phosphorylation of mTORC1 and ULK1. This conclusion was reinforced via protein accumulation detected using Click-iT HPG labelling after iron treatment. The adiponectin receptor agonist AdipoRon increased autophagic flux and improved insulin sensitivity both alone and in the presence of iron. We created an autophagy-deficient cell model by overexpressing a dominant-negative Atg5 mutant in H9c2 cells and this confirmed that reduced autophagy flux correlated with less insulin sensitivity. In conclusion, our study showed that iron promoted a cascade of ROS production, reduced autophagy and insulin resistance in cardiomyocytes.

Fatty Acids Prevent Hypoxia-Inducible Factor-1α Signaling Through Decreased Succinate in Diabetes

Hypoxia-inducible factor (HIF)-1α is essential following a myocardial infarction (MI), and diabetic patients have poorer prognosis post-MI. Could HIF-1α activation be abnormal in the diabetic heart, and could metabolism be causing this? Diabetic hearts had decreased HIF-1α protein following ischemia, and insulin-resistant cardiomyocytes had decreased HIF-1α-mediated signaling and adaptation to hypoxia. This was due to elevated fatty acid (FA) metabolism preventing HIF-1α protein stabilization. FAs exerted their effect by decreasing succinate concentrations, a HIF-1α activator that inhibits the regulatory HIF hydroxylase enzymes. Invivo and invitro pharmacological HIF hydroxylase inhibition restored HIF-1α accumulation and improved post-ischemic functional recovery in diabetes.

Pleiotropic Effects of Chronic Phorbol Ester Treatment to Improve Glucose Transport in Insulin-Resistant Cardiomyocytes.

Stimulation of glucose transport is an important determinant of myocardial susceptibility to ischemia and reperfusion. Stimulation of glucose transport is markedly impaired in cardiomyocytes exposed to free fatty acids (FFA). Deactivation of the Focal Adhesion Kinase (FAK) by FFA contributes to glucose transport impairment, and could be corrected by chronic treatment with the phorbol ester TPA. However, TPA must have effects in addition to FAK reactivation to restore stimulated glucose transport. Chronic treatment with TPA improved basal and stimulated glucose transport in FFA-exposed, but not in control cardiomyocytes. Chronic FFA exposure induced the activation of PKCδ and PKCϵ. TPA markedly downregulated the expression of PKCα, PKCδ, and PKCϵ, suggesting that PKCδ or PKCϵ activation could contribute to inhibition of glucose transport by FFA. Rottlerin, a specific PKCδ inhibitor, improved glucose transport in FFA-exposed cardiomyocytes; and PKCδ was reduced in the particulate fraction of FFA + TPA-exposed cardiomyocytes. TPA also activated Protein Kinase D 1(PKD1) in FFA-exposed cardiomyocytes, as assessed by autophosphorylation of PKD1 on Y916. Pharmaceutical inhibition of PKD1 only partially prevented the improvement of glucose transport by TPA. Chronic TPA treatment also increased basal and stimulated glycolysis and favored accumulation of lipid droplets in FFA-exposed cardiomyocytes. In conclusion, basal and stimulated glucose transport in cardiomyocytes is reduced by chronic FFA exposure, but restored by concomitant treatment with a phorbol ester. The mechanism of action of phorbol esters may involve downregulation of PKCδ, activation of PKD1 and a general switch from fatty acid to glucose metabolism. J. Cell. Biochem. 9999: 4716-4727, 2017. © 2017 Wiley Periodicals, Inc.

2-Arachidonoylglycerol ameliorates inflammatory stress-induced insulin resistance in cardiomyocytes

Several studies have linked impaired glucose uptake and insulin resistance (IR) to functional impairment of the heart. Recently, endocannabinoids have been implicated in cardiovascular disease. However, the mechanisms involving endocannabinoid signaling, glucose uptake, and IR in cardiomyocytes are understudied. Here we report that the endocannabinoid 2-arachidonoylglycerol (2-AG), via stimulation of cannabinoid type 1 (CB1) receptor and Ca2+/calmodulin-dependent protein kinase β, activates AMP-activated kinase (AMPK), leading to increased glucose uptake. Interestingly, we have observed that the mRNA expression of CB1 and CB2 receptors was decreased in diabetic mice, indicating reduced endocannabinoid signaling in the diabetic heart. We further establish that TNFα induces IR in cardiomyocytes. Treatment with 2-AG suppresses TNFα-induced proinflammatory markers and improves IR and glucose uptake. Conversely, pharmacological inhibition or knockdown of AMPK attenuates the anti-inflammatory effect and reversal of IR elicited by 2-AG. Additionally, in human embryonic stem cell-derived cardiomyocytes challenged with TNFα or FFA, we demonstrate that 2-AG improves insulin sensitivity and glucose uptake. In conclusion, 2-AG abates inflammatory responses, increases glucose uptake, and overcomes IR in an AMPK-dependent manner in cardiomyocytes.

Small heterodimer partner (SHP) contributes to insulin resistance in cardiomyocytes

Small heterodimer partner (SHP) is an atypical nuclear receptor expressed in heart that has been shown to inhibit the hypertrophic response. Here, we assessed the role of SHP in cardiac metabolism and inflammation. Mice fed a high-fat diet (HFD) displayed glucose intolerance accompanied by increased cardiac mRNA levels of Shp. In HL-1 cardiomyocytes, SHP overexpression inhibited both basal and insulin-stimulated glucose uptake and impaired the insulin signalling pathway (evidenced by reduced AKT and AS160 phosphorylation), similar to insulin resistant cells generated by high palmitate/high insulin treatment (HP/HI; 500μM/100nM). In addition, SHP overexpression increased Socs3 mRNA and reduced IRS-1 protein levels. SHP overexpression also induced Cd36 expression (~6.2 fold; p<0.001) linking to the observed intramyocellular lipid accumulation. SHP overexpressing cells further showed altered expression of genes involved in lipid metabolism, i.e., Acaca, Acadvl or Ucp3, augmented NF-κB DNA-binding activity and induced transcripts of inflammatory genes, i.e., Il6 and Tnf mRNA (~4-fold induction, p<0.01). Alterations in metabolism and inflammation found in SHP overexpressing cells were associated with changes in the mRNA levels of Ppara (79% reduction, p<0.001) and Pparg (~58-fold induction, p<0.001). Finally, co-immunoprecipitation studies showed that SHP overexpression strongly reduced the physical interaction between PPARα and the p65 subunit of NF-κB, suggesting that dissociation of these two proteins is one of the mechanisms by which SHP initiates the inflammatory response in cardiac cells. Overall, our results suggest that SHP upregulation upon high-fat feeding leads to lipid accumulation, insulin resistance and inflammation in cardiomyocytes.

High Uric Acid Induces Insulin Resistance in Cardiomyocytes In Vitro and In Vivo.

Clinical studies have shown hyperuricemia strongly associated with insulin resistance as well as cardiovascular disease. Direct evidence of how high uric acid (HUA) affects insulin resistance in cardiomyocytes, but the pathological mechanism of HUA associated with cardiovascular disease remains to be clarified. We aimed to examine the effect of HUA on insulin sensitivity in cardiomyocytes and on insulin resistance in hyperuricemic mouse model. We exposed primary cardiomyocytes and a rat cardiomyocyte cell line, H9c2 cardiomyocytes, to HUA, then quantified glucose uptake with a fluorescent glucose analog, 2-NBDG, after insulin challenge and detected reactive oxygen species (ROS) production. Western blot analysis was used to examine the levels of insulin receptor (IR), phosphorylated insulin receptor substrate 1 (IRS1, Ser307) and phospho-Akt (Ser473). We monitored the impact of HUA on insulin resistance, insulin signaling and IR, phospho-IRS1 (Ser307) and phospho-Akt levels in myocardial tissue of an acute hyperuricemia mouse model established by potassium oxonate treatment. HUA inhibited insulin-induced glucose uptake in H9c2 and primary cardiomyocytes. It increased ROS production; pretreatment with N-acetyl-L-cysteine (NAC), a ROS scavenger, reversed HUA-inhibited glucose uptake induced by insulin. HUA exposure directly increased the phospho-IRS1 (Ser307) response to insulin and inhibited that of phospho-Akt in H9C2 cardiomyocytes, which was blocked by NAC. Furthermore, the acute hyperuricemic mice model showed impaired glucose tolerance and insulin tolerance accompanied by increased phospho-IRS1 (Ser307) and inhibited phospho-Akt response to insulin in myocardial tissues. HUA inhibited insulin signaling and induced insulin resistance in cardiomyocytes in vitro and in vivo, which is a novel potential mechanism of hyperuricemic-related cardiovascular disease.

Mineralocorticoid Receptor Blockade Improves Insulin Sensitivity in the Rat Heart and a Possible Molecular Mechanism

Background/Aims: Extensive research has explored the role of aldosterone in insulin resistance. Recent evidence suggests that the mineralocorticoid receptor (MR) mediates aldosterone-induced dysregulation of cytokines, and most of this research has focused on adjustments in fat tissue and adipocytes. However, the direct effect of MR blockade on insulin resistance in cardiomyocytes remains largely unknown. In the present study, we investigated whether MR blockade improves insulin-sensitizing factors in insulin-resistant rats and attenuates the dysregulation of the aldosterone-related transport of adiponectin and glucose in cardiomyocytes and examined the underlying mechanisms. Methods: The effects of aldosterone, MR inhibitors (e.g., eplerenone), a peroxisome proliferator-activated receptor (PPAR) α agonist, and a p38 mitogen-activated protein kinase (MAPK) inhibitor on adiponectin and glucose transport were studied at the mRNA and protein levels in vitro and in vivo. Results: Our data revealed that aldosterone reduced the expression of adiponectin and inhibited the transport of glucose in cardiomyocytes and that MR blockade reversed these affects. In vivo, MR blockade improved insulin-sensitive parameters and increased adiponectin expression in the myocardia of high-fat diet rats. Furthermore, aldosterone promoted p38MAPK expression but negatively affected PPARα expression, and the downregulation of adiponectin by aldosterone was reversed by MR blockade, a PPARα agonist, and a p38 MAPK inhibitor. Conclusion: The above results suggested that aldosterone promoted insulin resistance in the heart and that this effect could be partly reversed by MR blockade through signal transduction in the P38 MAPK pathway and PPARα.

Marine omega-3 fatty acids prevent myocardial insulin resistance and metabolic remodeling as induced experimentally by high insulin exposure.

Insulin resistance is an important risk factor for the development of several cardiac pathologies, thus advocating strategies for restoring insulin sensitivity of the heart in these conditions. Omega-3 polyunsaturated fatty acids (ω-3 PUFAs), mainly eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3), have been shown to improve insulin sensitivity in insulin-sensitive tissues, but their direct effect on insulin signaling and metabolic parameters in the myocardium has not been reported previously. The aim of this study was therefore to examine the ability of EPA and DHA to prevent insulin resistance in isolated rat cardiomyocytes. Primary rat cardiomyocytes were made insulin resistant by 48 h incubation in high insulin (HI) medium. Parallel incubations were supplemented by 200 μM EPA or DHA. Addition of EPA or DHA to the medium prevented the induction of insulin resistance in cardiomyocytes by preserving the phosphorylation state of key proteins in the insulin signaling cascade and by preventing persistent relocation of fatty acid transporter CD36 to the sarcolemma. Only cardiomyocytes incubated in the presence of EPA, however, exhibited improvements in glucose and fatty acid uptake and cell shortening. We conclude that ω-3 PUFAs protect metabolic and functional properties of cardiomyocytes subjected to insulin resistance-evoking conditions.