Role of NF-κB and p38 MAPK activation in mediating angiotensin II and endothelin-1-induced stimulation in leptin production and cardiomyocyte hypertrophy

Molecular and Cellular Mechanisms Underlying the Cardiac Hypertrophic and Pro-Remodelling Effects of Leptin

Since its initial discovery in 1994, the adipokine leptin has received extensive interest as an important satiety factor and regulator of energy expenditure. Although produced primarily by white adipocytes, leptin can be synthesized by numerous tissues including those comprising the cardiovascular system. Cardiovascular function can thus be affected by locally produced leptin via an autocrine or paracrine manner but also by circulating leptin. Leptin exerts its effects by binding to and activating specific receptors, termed ObRs or LepRs, belonging to the Class I cytokine family of receptors of which six isoforms have been identified. Although all ObRs have identical intracellular domains, they differ substantially in length in terms of their extracellular domains, which determine their ability to activate cell signalling pathways. The most important of these receptors in terms of biological effects of leptin is the so-called long form (ObRb), which possesses the complete intracellular domain linked to full cell signalling processes. The heart has been shown to express ObRb as well as to produce leptin. Leptin exerts numerous cardiac effects including the development of hypertrophy likely through a number of cell signaling processes as well as mitochondrial dynamics, thus demonstrating substantial complex underlying mechanisms. Here, we discuss mechanisms that potentially mediate leptin-induced cardiac pathological hypertrophy, which may contribute to the development of heart failure.

An Updated Insight Into Molecular Mechanism of Hydrogen Sulfide in Cardiomyopathy and Myocardial Ischemia/Reperfusion Injury Under Diabetes

Cardiovascular diseases are the most common complications of diabetes, and diabetic cardiomyopathy is a major cause of people death in diabetes. Molecular, transcriptional, animal, and clinical studies have discovered numerous therapeutic targets or drugs for diabetic cardiomyopathy. Within this, hydrogen sulfide (H₂S), an endogenous gasotransmitter alongside with nitric oxide (NO) and carbon monoxide (CO), is found to play a critical role in diabetic cardiomyopathy. Recently, the protective roles of H₂S in diabetic cardiomyopathy have attracted enormous attention. In addition, H₂S donors confer favorable effects in myocardial infarction, ischaemia-reperfusion injury, and heart failure under diabetic conditions. Further studies have disclosed that multiplex molecular mechanisms are responsible for the protective effects of H₂S against diabetes-elicited cardiac injury, such as anti-oxidative, anti-apoptotic, anti-inflammatory, and anti-necrotic properties. In this review, we will summarize the current findings on H₂S biology and pharmacology, especially focusing on the novel mechanisms of H₂S-based protection against diabetic cardiomyopathy. Also, the potential roles of H₂S in diabetes-aggravated ischaemia-reperfusion injury are discussed.

Effect of Leptin on Chronic Inflammatory Disorders: Insights to Therapeutic Target to Prevent Further Cardiovascular Complication

In response to obesity-associated chronic inflammatory disorders, adipose tissue releases a biologically active peptide known as leptin. Leptin activates the secretion of chemical mediators, which contribute to the pathogenesis of chronic inflammatory disorders, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and psoriasis. Conversely, adiposity and obesity are the major aggravating risk factors in the pathogenesis of metabolic syndrome (MetS), including type II diabetes mellitus and obesity-associated hypertension. Elevated level of leptin in obesity-associated hypertension causes an increase in the production of aldosterone, which also results in elevation of arterial blood pressure. Hyperleptinemia is associated with the progress of the atherosclerosis through secretion of pro-inflammatory cytokines, like interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), IL-17, and other cytokines to promote inflammation. The release of those cytokines leads to chronic inflammatory disorders and obesity-associated MetS. Thus, the aberrant leptin level in both MetS and chronic inflammatory disorders also leads to the complication of cardiovascular diseases (CVD). Therapeutic target of leptin regarding its pro-inflammatory effect and dysregulated sympathetic nervous system activity may prevent further cardiovascular complication. This review mainly assesses the mechanism of leptin on the pathogenesis and further cardiovascular risk complication of chronic inflammatory disorders.

The endocrinological component and signaling pathways associated to cardiac hypertrophy

Although myocardial growth corresponds to an adaptive response to maintain cardiac contractile function, the cardiac hypertrophy is a condition that occurs in many cardiovascular diseases and typically precedes the onset of heart failure. Different endocrine factors such as thyroid hormones, insulin, insulin-like growth factor 1 (IGF-1), angiotensin II (Ang II), endothelin (ET-1), catecholamines, estrogen, among others represent important stimuli to cardiomyocyte hypertrophy. Thus, numerous endocrine disorders manifested as changes in the local environment or multiple organ systems are especially important in the context of progression from cardiac hypertrophy to heart failure. Based on that information, this review summarizes experimental findings regarding the influence of such hormones upon signalling pathways associated with cardiac hypertrophy. Understanding mechanisms through which hormones differentially regulate cardiac hypertrophy could open ways to obtain therapeutic approaches that contribute to prevent or delay the onset of heart failure related to endocrine diseases.

Endothelial Leptin Receptor Deletion Promotes Cardiac Autophagy and Angiogenesis Following Pressure Overload by Suppressing Akt/mTOR Signaling

BACKGROUND

Cardiac remodeling is modulated by overnutrition or starvation. The adipokine leptin mediates energy balance between adipose tissue and brain. Leptin and its receptors are expressed in the heart.

METHODS AND RESULTS

To examine the importance of endothelial leptin signaling in cardiac hypertrophy, transverse aortic constriction was used in mice with inducible endothelium-specific deletion of leptin receptors (End.LepR-KO) or littermate controls (End.LepR-WT). End.LepR-KO was associated with improved left ventricular function (fractional shortening, 28.4% versus 18.8%; P=0.0114), reduced left ventricular dilation (end-systolic inner left ventricular diameter, 3.59 versus 4.08 mm; P=0.0188) and lower heart weight (133 versus 173 mg; P<0.0001) 20 weeks after transverse aortic constriction. Histology and quantitative polymerase chain reaction analysis confirmed reduced cardiomyocyte hypertrophy. STAT3 (signal transducer and activator of transcription) activation was reduced, and Akt (protein kinase B) and mTOR (mammalian target of rapamycin) phosphorylation after transverse aortic constriction were blunted in End.LepR-KO hearts. Elevated LC3 (microtubule associated protein 1 light chain 3)-I/-II conversion ( P=0.0041) and increased (LC3II-positive) endothelial cells ( P=0.0042) in banded hearts of End.LepR-KO mice suggested improved cardiac angiogenesis because of activated autophagy. Microscopy confirmed autophagosome accumulation after genetic or small interfering RNA-mediated LepR downregulation. Enhanced sprouting angiogenesis was observed in endothelial cells ( P<0.0001) and aortic rings ( P=0.0060) from End.LepR-KO mice, and murine and human endothelial sprouting angiogenesis was reduced after mTOR inhibition using rapamycin or autophagy inhibition using 3-methyladenine. Banded End.LepR-KO mouse hearts exhibited less apoptosis ( P=0.0218), inflammation ( P=0.0251), and fibrosis ( P=0.0256). Reduced endothelial autophagy was also observed in myocardial biopsies of heart failure patients with cardiac fibrosis.

CONCLUSIONS

Our findings suggest that endothelial leptin signaling contributes to cardiac fibrosis and functional deterioration by suppressing endothelial autophagy and promoting endothelial dysfunction in a chronic pressure overload model.

Effects of glucagon-like peptide-1 on advanced glycation endproduct-induced aortic endothelial dysfunction in streptozotocin-induced diabetic rats: possible roles of Rho kinase- and AMP kinase-mediated nuclear factor κB signaling pathways

Interaction between advanced glycation endproducts (AGEs) and receptor for AGEs (RAGE) as well as downstream pathways leads to vascular endothelial dysfunction in diabetes. Glucagon-like peptide-1 (GLP-1) has been reported to attenuate endothelial dysfunction in the models of atherosclerosis. However, whether GLP-1 exerts protective effects on aortic endothelium in diabetic animal model and the underlying mechanisms are still not well defined. Experimental diabetes was induced through administration with combination of high-fat diet and intraperitoneal injection of streptozotocin. Rats were randomly divided into four groups, including controls, diabetes, diabetes + sitagliptin (30 mg/kg/day), diabetes + exenatide (3 μg/kg/12 h). Eventually, endothelial damage, markers of inflammation and oxidative stress, were measured. After 12 weeks administration, diabetic rats received sitagliptin and exenatide showed significant elevation of serum NO level and reduction of ET-1 as well as inflammatory cytokines levels. Moreover, sitagliptin and exenatide significantly inhibited aortic oxidative stress level and improved aortic endothelial function in diabetic rats. Importantly, these drugs inhibited the protein expression level in AGE/RAGE-induced RhoA/ROCK/NF-κB/IκBα signaling pathways and activated AMPK in diabetic aorta. Finally, the target proteins of p-eNOS, iNOS, and ET-1, which reflect endothelial function, were also changed by these drugs. Our present study indicates that sitagliptin and exenatide administrations can improve endothelial function in diabetic aorta. Of note, RAGE/RhoA/ROCK and AMPK mediated NF-κB signaling pathways may be the intervention targets of these drugs to protect aortic endothelium.

Physiological and pathological cardiac hypertrophy

The heart must continuously pump blood to supply the body with oxygen and nutrients. To maintain the high energy consumption required by this role, the heart is equipped with multiple complex biological systems that allow adaptation to changes of systemic demand. The processes of growth (hypertrophy), angiogenesis, and metabolic plasticity are critically involved in maintenance of cardiac homeostasis. Cardiac hypertrophy is classified as physiological when it is associated with normal cardiac function or as pathological when associated with cardiac dysfunction. Physiological hypertrophy of the heart occurs in response to normal growth of children or during pregnancy, as well as in athletes. In contrast, pathological hypertrophy is induced by factors such as prolonged and abnormal hemodynamic stress, due to hypertension, myocardial infarction etc. Pathological hypertrophy is associated with fibrosis, capillary rarefaction, increased production of pro-inflammatory cytokines, and cellular dysfunction (impairment of signaling, suppression of autophagy, and abnormal cardiomyocyte/non-cardiomyocyte interactions), as well as undesirable epigenetic changes, with these complex responses leading to maladaptive cardiac remodeling and heart failure. This review describes the key molecules and cellular responses involved in physiological/pathological cardiac hypertrophy.

Angiotensin-converting enzyme 2 (ACE2) activator diminazene aceturate ameliorates endotoxin-induced uveitis in mice

PURPOSE

Uveitis is a common cause of vision loss. The renin angiotensin system (RAS), which plays a vital role in cardiovascular system, is a potent mediator of inflammation and has been implicated in the pathogenesis of uveitis. A newly identified axis of RAS, ACE2/Ang-(1-7)/Mas, has emerged as a novel target because it counteracts the deleterious effect of angiotensin II. The purpose of this study was to investigate the effect of endogenous ACE2 activation in preventing endotoxin-induced uveitis (EIU) in mice.

METHODS

ACE2 activator diminazene aceturate (DIZE) was administered both systemically and locally. For systemic administration, female BALB/c mice received intraperitoneal injection of DIZE (60 mg/kg body weight [BW]) for 2 days prior to lipopolysaccharide (LPS) intravitreal injection (125 ng) to induce uveitis. For local study, DIZE was given at 0.5, 0.1, and 0 mg/mL as eyedrops six times per day for 2 days before LPS injection. The anterior segment of the mice was examined at 12, 24, 48, and 72 hours after LPS injection, and clinical scores were determined at the same time. Morphology and infiltrating inflammatory cells were evaluated after 24 hours. The mRNA levels of inflammatory cytokines were analyzed by real-time RT-PCR. ACE2 activity was determined using a self-quenching fluorescent substrate.

RESULTS

At 24 hours, the clinical score of mice treated with DIZE systemically was significantly lower (mean, ∼1.75) than the saline vehicle group (mean, ∼4) (P < 0.001). Histological examination showed 63.4% reduction of infiltrating inflammatory cells in the anterior segment and 57.4% reduction in the posterior segment of DIZE-treated eyes. The number of CD45(+) inflammatory cells in the vitreous of the DIZE-treated group was decreased (43.3%) compared to the vehicle group (P < 0.01). The mRNA levels of inflammatory cytokines were significantly reduced in the DIZE-treated group (P < 0.01, P < 0.001). The number of infiltrating inflammatory cells was also significantly reduced in eyes that received topical administration of DIZE: 73.8% reduction in the 0.5 mg/mL group and 51.7% reduction in the 0.1mg/mL group compared to the control group. DIZE treatment resulted in significantly increased ACE2 activity in the retina (P < 0.001).

CONCLUSIONS

Endogenous ACE2 activation by DIZE has a preventive effect on LPS-induced ocular inflammation in the EIU mouse model. These results support the notions that RAS plays a role in modulating ocular immune response and that enhancing ACE2 provides a novel therapeutic strategy for uveitis.

Glucagon-like peptide-1 receptor agonist liraglutide inhibits endothelin-1 in endothelial cell by repressing nuclear factor-kappa B activation

PURPOSE

The increase in endothelin-1 (ET-1) and the decrease in endothelial nitric oxide synthase (eNOS) both induce vasoconstriction and lead to molecular changes associated with diabetes mellitus and atherosclerosis. Glucagon-like peptide-1 (GLP-1) activation stimulates insulin secretion and may prevent atherosclerosis by increasing eNOS synthesis. However, there is paucity of information on the effect of GLP-1 activation on ET-1 expression. This study was conducted to address this issue.

METHODS AND RESULTS

Human umbilical vein endothelial cells (HUVECs) were incubated with different concentrations of liraglutide, a GLP-1 agonist, and the expression of ET-1 and eNOS and activity of NF-κB were measured. Liraglutide, in a concentration-dependent manner, was observed to promote eNOS expression and to inhibit ET-1 expression both at mRNA and protein levels. Liraglutide also inhibited NF-κB phosphorylation and its translocation from cytoplasm to the nucleus. To ascertain the role of NF-κB activation in the altered expression of ET-1 and eNOS, we treated HUVECs with phorbol 12-myristate 13-acetate (PMA). PMA activated NF-κB and reversed the effects of liraglutide on eNOS and ET-1 expression. The effects of PMA on eNOS and ET-1 expression were reproduced in experiments wherein cells were treated with TNF-α. Further, we measured the generation of IL-6, apowerful pro-inflammatory molecule released by endothelial cells, as a measure of cellular function. PMA increased IL-6 generation, and this effect was blocked by liraglutide.

CONCLUSIONS

Our observations suggest liraglutide suppresses ET-1 expression by inhibiting the phosphorylation of NF-κB. This mechanism may underlie the potential anti-atherosclerotic effects of GLP-1 agonists. Of note, these effects of liraglutide were seen in an in vitro setting wherein cellular glucose concentrations were elevated.

Exogenous hydrogen sulfide alleviates high glucose-induced cardiotoxicity via inhibition of leptin signaling in H9c2 cells

Hydrogen sulfide (H₂S) protects cardiomyoblasts against high glucose (HG)-induced injury by inhibiting the activation of p38 mitogen-activated protein kinase (MAPK). This study aims to determine whether the leptin-p38 MAPK pathway is involved in HG-induced injury and whether exogenous H2S prevents the HG-induced insult through inhibition of the leptin-p38 MAPK pathway in H9c2 cells. H9c2 cells were treated with 35 mM glucose (HG) for 24 h to establish a HG-induced cardiomyocyte injury model. Cell viability; mitochondrial membrane potential (ΔΨ m); apoptosis; reactive oxygen species (ROS) level; and leptin, leptin receptor, and p38 MAPK expression level were measured by the methods indicated. The results showed pretreatment of H9c2 cells with NaHS before exposure to HG led to an increase in cell viability, decrease in apoptotic cells, ROS generation, and a loss of ΔΨ m. Exposure of H9c2 cells to 35 mM glucose for 24 h significantly upregulated the expression levels of leptin and leptin receptors. The increased expression levels of leptin and leptin receptors were markedly attenuated by pretreatment with 400 μM NaHS. In addition, the HG-induced increase in phosphorylated (p) p38 MAPK expression was ameliorated by pretreatment with 50 ng/ml leptin antagonist. In conclusion, the present study has demonstrated for the first time that the leptin-p38 MAPK pathway contributes to the HG-induced injury in H9c2 cells and that exogenous H₂S protects H9c2 cells against HG-induced injury at least in part by inhibiting the activation of leptin-p38 MAPK pathway.

The potential contribution of circulating and locally produced leptin to cardiac hypertrophy and failure

Leptin is a 16 kDa peptide that was first identified in 1994 through positional cloning of the mouse obesity gene. Although the primary function of leptin is to act a satiety factor through its actions on the hypothalamus, it is now widely recognized that leptin can exert effects on many other organs through activation of its receptors, which are ubiquitously expressed. Leptin is secreted primarily by white adipocytes, but it is also produced by other tissues including the heart where it can exert effects in an autocrine or paracrine manner. One of these effects involves the induction of cardiomyocyte hypertrophy, which appears to occur via multiple cell signalling mechanisms. As adipocytes are the primary site of leptin production, plasma leptin concentrations are generally positively related with body mass index and the degree of adiposity. However, hyperleptinemia is also associated with cardiovascular disease, including heart failure, in the absence of obesity. Here we review the potential role of leptin in heart disease, particularly pertaining to its potential contribution to myocardial remodelling and heart failure, as well as the underlying mechanisms. We further discuss potential interactions between leptin and another adipokine, adiponectin, and the potential implications of this interaction in terms of fully understanding leptin’s effects.

Activation of retinoid receptor-mediated signaling ameliorates diabetes-induced cardiac dysfunction in Zucker diabetic rats

Diabetic cardiomyopathy (DCM) is a significant contributor to the morbidity and mortality associated with diabetes and metabolic syndrome. Retinoids, through activation of retinoic acid receptor (RAR) and retinoid x receptor (RXR), have been linked to control glucose and lipid homeostasis, with effects on obesity and diabetes. However, the functional role of RAR and RXR in the development of DCM remains unclear. Zucker diabetic fatty (ZDF) and lean rats were treated with Am580 (RARα agonist) or LGD1069 (RXR agonist) for 16 weeks, and cardiac function and metabolic alterations were determined. Hyperglycemia, hyperlipidemia and insulin resistance were observed in ZDF rats. Diabetic cardiomyopathy was characterized in ZDF rats by increased oxidative stress, apoptosis, fibrosis, inflammation, activation of MAP kinases and NF-κB signaling and diminished Akt phosphorylation, along with decreased glucose transport and increased cardiac lipid accumulation, and ultimately diastolic dysfunction. Am580 and LGD1069 attenuated diabetes-induced cardiac dysfunction and the pathological alterations, by improving glucose tolerance and insulin resistance; facilitating Akt activation and glucose utilization, and attenuating oxidative stress and interrelated MAP kinase and NF-κB signaling pathways. Am580 inhibited body weight gain, attenuated the increased cardiac fatty acid uptake, β-oxidation and lipid accumulation in the hearts of ZDF rats. However, LGD1069 promoted body weight gain, hyperlipidemia and cardiac lipid accumulation. In conclusion, our data suggest that activation of RAR and RXR may have therapeutic potential in the treatment of diabetic cardiomyopathy. However, further studies are necessary to clarify the role of RAR and RXR in the regulation of lipid metabolism and homeostasis.