Hyperglycemia activates JAK2 signaling pathway in human failing myocytes via angiotensin II-mediated oxidative stress

Oxidative stress as a culprit in diabetic kidney disease

Diabetic kidney disease (DKD) has become the leading cause of end-stage renal disease (ESRD), and the prevalence of DKD has increased worldwide during recent years. DKD is associated with poor therapeutic outcomes in most patients, but there is limited understanding of its pathogenesis. This review suggests that oxidative stress interacts with many other factors in causing DKD. Highly active mitochondria and NAD(P)H oxidase are major sources of oxidants, and they significantly affect the risk for DKD. Oxidative stress and inflammation may be considered reciprocal causes of DKD, in that each is a cause and an effect of DKD. Reactive oxygen species (ROS) can act as second messengers in various signaling pathways and as regulators of metabolism, activation, proliferation, differentiation, and apoptosis of immune cells. Epigenetic modifications, such as DNA methylation, histone modifications, and non-coding RNAs can modulate oxidative stress. The development of new technologies and identification of new epigenetic mechanisms may provide novel opportunities for the diagnosis and treatment of DKD. Clinical trials demonstrated that novel therapies which reduce oxidative stress can slow the progression of DKD. These therapies include the NRF2 activator bardoxolone methyl, new blood glucose-lowering drugs such as sodium-glucose cotransporter 2 inhibitors, and glucagon-like peptide-1 receptor agonists. Future studies should focus on improving early diagnosis and the development of more effective combination treatments for this multifactorial disease.

Immune responses in diabetic nephropathy: Pathogenic mechanisms and therapeutic target

Diabetic nephropathy (DN) is a chronic, inflammatory disease affecting millions of diabetic patients worldwide. DN is associated with proteinuria and progressive slowing of glomerular filtration, which often leads to end-stage kidney diseases. Due to the complexity of this metabolic disorder and lack of clarity about its pathogenesis, it is often more difficult to diagnose and treat than other kidney diseases. Recent studies have highlighted that the immune system can inadvertently contribute to DN pathogenesis. Cells involved in innate and adaptive immune responses can target the kidney due to increased expression of immune-related localization factors. Immune cells then activate a pro-inflammatory response involving the release of autocrine and paracrine factors, which further amplify inflammation and damage the kidney. Consequently, strategies to treat DN by targeting the immune responses are currently under study. In light of the steady rise in DN incidence, this timely review summarizes the latest findings about the role of the immune system in the pathogenesis of DN and discusses promising preclinical and clinical therapies.

The Role of Oxidative Stress in the Aging Heart

Medical advances and the availability of diagnostic tools have considerably increased life expectancy and, consequently, the elderly segment of the world population. As age is a major risk factor in cardiovascular disease (CVD), it is critical to understand the changes in cardiac structure and function during the aging process. The phenotypes and molecular mechanisms of cardiac aging include several factors. An increase in oxidative stress is a major player in cardiac aging. Reactive oxygen species (ROS) production is an important mechanism for maintaining physiological processes; its generation is regulated by a system of antioxidant enzymes. Oxidative stress occurs from an imbalance between ROS production and antioxidant defenses resulting in the accumulation of free radicals. In the heart, ROS activate signaling pathways involved in myocyte hypertrophy, interstitial fibrosis, contractile dysfunction, and inflammation thereby affecting cell structure and function, and contributing to cardiac damage and remodeling. In this manuscript, we review recent published research on cardiac aging. We summarize the aging heart biology, highlighting key molecular pathways and cellular processes that underlie the redox signaling changes during aging. Main ROS sources, antioxidant defenses, and the role of dysfunctional mitochondria in the aging heart are addressed. As metabolism changes contribute to cardiac aging, we also comment on the most prevalent metabolic alterations. This review will help us to understand the mechanisms involved in the heart aging process and will provide a background for attractive molecular targets to prevent age-driven pathology of the heart. A greater understanding of the processes involved in cardiac aging may facilitate our ability to mitigate the escalating burden of CVD in older individuals and promote healthy cardiac aging.

Protective effect of cinnamon on diabetic cardiomyopathy in nicotinamide-streptozotocin induced diabetic rat model

There is an increase in the incidence and prevalence of type-2 diabetes and obesity which leads to the structural and functional changes in myocardium leading to a lethal complication called diabetic cardiomyopathy (DCM). In the present study, we investigated the preventive effect of cinnamon (3% of Cinnamomum zeylanicum bark powder in AIN-93 diet for 3 months) feeding on DCM and the concerned mechanisms in a rodent model. Experimental diabetes was induced by a single intraperitoneal injection of 40 mg/kg b.w streptozotocin (STZ), 15 min after the ip administration of 60 mg/kg b.w of nicotinamide (NA) in Wistar-NIN (WNIN) male rats. The oxidative stress parameters were investigated by assessing superoxide dismutase (SOD), glutathione-s-transferase (GST) enzyme activity, protein carbonyls and malondialdehyde (MDA) levels. The histopathology of myocardium was analyzed by H&E and Masson's trichrome staining, and scanning electron microscopy. The changes in diabetic rat heart involved the altered left ventricular parietal pericardium, structural changes in myocardial cells, enhanced oxidative stress. Masson's trichrome and H&E staining have shown increased fibrosis, and perinuclear vacuolization in NA-STZ induced diabetic rat myocardium. Cinnamon feeding prevented the oxidative stress and myocardial alterations in the heart of diabetic rats. Taken together, these results suggest that cinnamon can effectively prevent the metabolic and structural changes in NA-STZ induced diabetic cardiomyopathy.

Long non-coding RNA Linc00092 inhibits cardiac fibroblast activation by altering glycolysis in an ERK-dependent manner

AIMS

Cardiac fibroblast (CF) activation is the key event for cardiac fibrosis. The role of glycolysis and the glycolysis-related lncRNAs in CF activation are unknown. Thus, we aimed to investigate the role of glycolysis in CF activation and to identify the glycolysis-related lncRNAs involved.

MAIN METHODS

Glycolysis-related lncRNAs were searched and their expression profiles were validated in activated human CF (HCF) and human failing heart tissues. Expression of the target lncRNA was manipulated to determine its effects on HCF activation and glycolysis. The underlying mechanisms of lncRNA-dependent glycolysis regulation were also addressed.

KEY FINDINGS

HCF activation induced by transforming growth factor-β1 was accompanied by an enhanced glycolysis, and 2-Deoxy-d-glucose, a specific glycolysis inhibitor, dramatically attenuated HCF activation. Twenty-eight glycolysis-related lncRNAs were identified and Linc00092 expression was changed mostly upon HCF activation. In human heart tissue, Linc00092 is primarily expressed in cardiac fibroblasts. Linc00092 knockdown activated HCFs with enhanced glycolysis, while its overexpression rescued the activated phenotype of HCFs and down-regulated glycolysis. Restoration of glycolysis abolished the anti-fibrotic effects conferred by Linc00092. Linc00092 inhibited ERK activation in activated HCFs, and ERK inhibition counteracted the fibrotic phenotype in Linc00092 knockdown HCFs.

SIGNIFICANCE

These results revealed that Linc00092 could attenuate HCF activation by suppressing glycolysis. The inhibition of ERK by Linc00092 may play an important role in this process. Together, this provides a better understanding of the mechanism of CF activation and may serve as a novel target for cardiac fibrosis treatment.

Protective effect of Berberine on reproductive function and spermatogenesis in diabetic rats via inhibition of ROS/JAK2/NFκB pathway

BACKGROUND

Diabetes mellitus (DM) induces impairment of male reproductive system and is considered as a key factor that could partially provide an explanation for male infertility. Thus, understanding the mechanism underlying DM-induced infertility will aid in the identification of novel therapeutic stratagems.

OBJECTIVES

To delineate the role of ROS/JAK2/NFκB pathway in DM-induced low reproductive function and impaired spermatogenesis. Additionally, to investigate the protective effect of monomeric Berberine (BB) that inhibits ROS/JAK2/NFκB pathway, in the pathogenesis of DM-induced infertility.

METHODS

12-week-old male Sprague-Dawley rats were divided into four groups: control group, DM group, control plus BB group, and DM plus BB group. Streptozotocin was used to induce DM. After treating the rats with BB for 4 weeks, fertility tests were conducted to investigate the reproductive function, and testis weight along with sperm motility was assessed through microscope. Oxidative stress was evaluated by DHE staining. TUNEL staining was utilized to detect the state of apoptosis. Cell experiments were carried out to define the role of BB in vitro. Immunohistochemistry, immunofluorescence, and Western blotting were employed to measure the protein expression.

RESULTS

Our results indicate that the reproductive function of DM rats was low, accompanied by decreased testis weight and sperm motility in addition to the impairment of the seminiferous tubules. However, there was a significant improvement in the reproductive function parameters in the BB-treated DM rats. Subsequently, our data revealed that DM rats produce an increased level of ROS in the testis, which activates JAK2 further activating the NFκB pathway, leading to increased apoptosis and impaired cells in the testicles. However, BB could attenuate the ROS production and abrogate activation of JAK2/NFκB pathway, thus inhibiting the apoptosis in the testicular cells of DM rats.

CONCLUSION

ROS/JAK2/NFκB pathway is involved in the DM-induced low reproductive function and impaired spermatogenesis. BB can play a protective role in preserving the reproductive function and spermatogenesis in DM by inhibiting ROS/JAK2/NFκB pathway.

Inflammatory Targets in Diabetic Nephropathy

One of the most frequent complications in patients with diabetes mellitus is diabetic nephropathy (DN). At present, it constitutes the first cause of end stage renal disease, and the main cause of cardiovascular morbidity and mortality in these patients. Therefore, it is clear that new strategies are required to delay the development and the progression of this pathology. This new approach should look beyond the control of traditional risk factors such as hyperglycemia and hypertension. Currently, inflammation has been recognized as one of the underlying processes involved in the development and progression of kidney disease in the diabetic population. Understanding the cascade of signals and mechanisms that trigger this maladaptive immune response, which eventually leads to the development of DN, is crucial. This knowledge will allow the identification of new targets and facilitate the design of innovative therapeutic strategies. In this review, we focus on the pathogenesis of proinflammatory molecules and mechanisms related to the development and progression of DN, and discuss the potential utility of new strategies based on agents that target inflammation.

A high-fat diet rich in corn oil induces cardiac fibrosis in rats by activating JAK2/STAT3 and subsequent activation of ANG II/TGF-1β/Smad3 pathway: The role of ROS and IL-6 trans-signaling

This study compared the effect of low-fat diet (LFD) and high-fat diet rich in corn oil (HFD-CO) on left ventricular (LV) fibrosis in rats and examined their effect of angiotensin II (ANG II), JAK/STAT, and TGF-1β/smad3 pathways. As compared to LFD which didn't affect any of the measured parameters, HFD-CO-induced type 2 diabetes phenotype and increased LV collagen synthesis. Mechanistically, it increased LV levels of ROS, ANG II, ACE, IL-6, s-IL-6Rα, TGF-β1, Smad-3, and activities of JAK1/2 and STAT1/3. AG490, a JAK2 inhibitor, partially ameliorated these effect while Losartan, an AT1 inhibitor completely abolished collagen synthesis. However, with both treatments, levels of ANG II, IL-6, and s-IL-6Rα, and activity of JAK1/STAT3 remained high, all of which were normalized by co-administration of NAC or IL-6 neutralizing antibody. In conclusion: HFD-CO enhances LV collage synthesis by activation of JAK1/STAT3/ANG II/TGF-1β/smad3 pathway. PRACTICAL APPLICATIONS: We report that chronic consumption of a high-fat diet rich in corn oil (HFD-CO) induces diabetes mellitus phenotype 2 associated with left ventricular (LV) cardiac fibrosis in rats. The findings of this study show that HFD-CO, and through the increasing generation of ROS and IL-6 levels and shedding, could activate LV JAK1/2-STAT1/3  and  renin-angiotensin system (RAS) signaling pathways, thus creating a positive feedback between the two which ultimately leads to activation of TGF-1β/Smad3 fibrotic pathway. Herein, we also report a beneficial effect of the antioxidant, NAC, or IL-6 neutralizing antibody in preventing such adverse effects of such HFD-CO. However, this presents a warning message to the current sudden increase in idiopathic cardiac disorders, especially with the big shift in our diets toward n-6 PUFA.

A comprehensive overview on osteoporosis and its risk factors

Osteoporosis is a bone disorder with remarkable changes in bone biologic material and consequent bone structural distraction, affecting millions of people around the world from different ethnic groups. Bone fragility is the worse outcome of the disease, which needs long term therapy and medical management, especially in the elderly. Many involved genes including environmental factors have been introduced as the disease risk factors so far, of which genes should be considered as effective early diagnosis biomarkers, especially for the individuals from high-risk families. In this review, a number of important criteria involved in osteoporosis are addressed and discussed.

L-Carnitine: An Antioxidant Remedy for the Survival of Cardiomyocytes under Hyperglycemic Condition

BACKGROUND

Metabolic alterations as hyperglycemia and inflammation induce myocardial molecular events enhancing oxidative stress and mitochondrial dysfunction. Those alterations are responsible for a progressive loss of cardiomyocytes, cardiac stem cells, and consequent cardiovascular complications. Currently, there are no effective pharmacological measures to protect the heart from these metabolic modifications, and the development of new therapeutic approaches, focused on improvement of the oxidative stress condition, is pivotal. The protective effects of levocarnitine (LC) in patients with ischemic heart disease are related to the attenuation of oxidative stress, but LC mechanisms have yet to be fully understood.

OBJECTIVE

The aim of this work was to investigate LC's role in oxidative stress condition, on ROS production and mitochondrial detoxifying function in H9c2 rat cardiomyocytes during hyperglycemia.

METHODS

H9c2 cells in the hyperglycemic state (25 mmol/L glucose) were exposed to 0.5 or 5 mM LC for 48 and 72 h: LC effects on signaling pathways involved in oxidative stress condition were studied by Western blot and immunofluorescence analysis. To evaluate ROS production, H9c2 cells were exposed to H₂O₂ after LC pretreatment.

RESULTS

Our in vitro study indicates how LC supplementation might protect cardiomyocytes from oxidative stress-related damage, preventing ROS formation and activating antioxidant signaling pathways in hyperglycemic conditions. In particular, LC promotes STAT3 activation and significantly increases the expression of antioxidant protein SOD2. Hyperglycemic cardiac cells are characterized by impairment in mitochondrial dysfunction and the CaMKII signal: LC promotes CaMKII expression and activation and enhancement of AMPK protein synthesis. Our results suggest that LC might ameliorate metabolic aspects of hyperglycemic cardiac cells. Finally, LC doses herein used did not modify H9c2 growth rate and viability.

CONCLUSIONS

Our novel study demonstrates that LC improves the microenvironment damaged by oxidative stress (induced by hyperglycemia), thus proposing this nutraceutical compound as an adjuvant in diabetic cardiac regenerative medicine.

A Brief Introduction into the Renin-Angiotensin-Aldosterone System: New and Old Techniques

The renin-angiotensin-aldosterone system (RAAS) is a complex system of enzymes, receptors, and peptides that help to control blood pressure and fluid homeostasis. Techniques in studying the RAAS can be difficult due to such factors as peptide/enzyme stability and receptor localization. This paper gives a brief account of the different components of the RAAS and current methods in measuring each component. There is also a discussion of different methods in measuring stem and immune cells by flow cytometry, hypertension, atherosclerosis, oxidative stress, energy balance, and other RAAS-activated phenotypes. While studies on the RAAS have been performed for over 100 years, new techniques have allowed scientists to come up with new insights into this system. These techniques are detailed in this Methods in Molecular Biology Series and give students new to studying the RAAS the proper controls and technical details needed to perform each procedure.

Myocardial Hypertrophic Remodeling and Impaired Left Ventricular Function in Mice with a Cardiac-Specific Deletion of Janus Kinase 2

The Janus kinase (JAK) system is involved in numerous cell signaling processes and is highly expressed in cardiac tissue. The JAK isoform JAK2 is activated by numerous factors known to influence cardiac function and pathologic conditions. However, although abundant, the role of JAK2 in the regulation or maintenance of cardiac homeostasis remains poorly understood. Using the Cre-loxP system, we generated a cardiac-specific deletion of Jak2 in the mouse to assess the effect on cardiac function with animals followed up for a 4-month period after birth. These animals had marked mortality during this period, although at 4 months mortality in male mice (47%) was substantially higher compared with female mice (30%). Both male and female cardiac Jak2-deleted mice had hypertrophy, dilated cardiomyopathy, and severe left ventricular dysfunction, including a marked reduction in ejection fractions as assessed by serial echocardiography, although the responses in females were somewhat less severe. Defective cardiac function was associated with altered protein levels of sarcoplasmic reticulum calcium-regulatory proteins particularly in hearts from male mice that had depressed levels of SERCA2 and phosphorylated phospholamban. In contrast, SERCA2 was unchanged in hearts of female mice, whereas phosphorylated phospholamban was increased. Our findings suggest that cardiac JAK2 is critical for maintaining normal heart function, and its ablation produces a severe pathologic phenotype composed of myocardial remodeling, heart failure, and pronounced mortality.

Curcumin Protects Neonatal Rat Cardiomyocytes against High Glucose-Induced Apoptosis via PI3K/Akt Signalling Pathway

The function of curcumin on NADPH oxidase-related ROS production and cardiac apoptosis, together with the modulation of protein signalling pathways, was investigated in cardiomyocytes. Primary cultures of neonatal rat cardiomyocytes were exposed to 30 mmol/L high glucose with or without curcumin. Cell viability, apoptosis, superoxide formation, the expression of NADPH oxidase subunits, and potential regulatory molecules, Akt and GSK-3β, were assessed in cardiomyocytes. Cardiomyocytes exposure to high glucose led to an increase in both cell apoptosis and intracellular ROS levels, which were strongly prevented by curcumin treatment (10 μM). In addition, treatment with curcumin remarkably suppressed the increased activity of Rac1, as well as the enhanced expression of gp91(phox) and p47(phox) induced by high glucose. Lipid peroxidation and SOD were reversed in the presence of curcumin. Furthermore, curcumin treatment markedly inhibited the reduced Bcl-2/Bax ratio elicited by high glucose exposure. Moreover, curcumin significantly increased Akt and GSK-3β phosphorylation in cardiomyocytes treated with high glucose. In addition, LY294002 blocked the effects of curcumin on cardiomyocytes exposure to high glucose. In conclusion, these results demonstrated that curcumin attenuated high glucose-induced cardiomyocyte apoptosis by inhibiting NADPH-mediated oxidative stress and this protective effect is most likely mediated by PI3K/Akt-related signalling pathway.

Astragalus polysaccharides repress myocardial lipotoxicity in a PPARalpha-dependent manner in vitro and in vivo in mice

BACKGROUND

The role of peroxisome proliferator-activated receptor alpha (PPARα) in the development of myocardial lipotoxicity is widely observed in diabetic disorders. Thus, we investigated if treatment of Astragalus polysaccharides modulates lipotoxic cardiomyopathy both in vivo and in vitro through PPARα mechanisms.

METHODOLOGY/PRINCIPAL FINDINGS

The effects of Astragalus polysaccharides (APS) on PPARα target gene expression and protein levels were tested in vitro and in vivo, including in mice with PPARα cardiac-restricted overexpression [myosin heavy chain (MHC)-PPARα] and in H9c2 embryonic rat cardiomyocytes with or without PPARα agonist. Echocardiographic studies, analyses of myocardial triglyceride and cardiac fuel utilization analyses were also performed in MHC-PPARα mice. Treatment with APS prevented myocardial triglyceride accumulation and cardiac dysfunction in the MHC-PPARα mice, with the normalization of energy metabolic derangements in hearts including reduced free fatty acids utilization and increased glucose uptake. Consistently, both in the MHC-PPARα hearts and H9c2 cardiomyocytes with PPARα agonist, the activation of PPARα gene regulatory pathway involved in FFA-oxidation was down-regulated by APS treatment, while the suppression of PPARα target genes involved in glucose uptake and oxidation was normalized by APS administration.

CONCLUSIONS

Therapy with APS could prevent the development of lipotoxic cardiomyopathy through a mechanism mainly dependent on the cardiac PPARα-mediated regulatory pathways.

Mitochondria-targeted antioxidant prevents cardiac dysfunction induced by tafazzin gene knockdown in cardiac myocytes

Tafazzin, a mitochondrial acyltransferase, plays an important role in cardiolipin side chain remodeling. Previous studies have shown that dysfunction of tafazzin reduces cardiolipin content, impairs mitochondrial function, and causes dilated cardiomyopathy in Barth syndrome. Reactive oxygen species (ROS) have been implicated in the development of cardiomyopathy and are also the obligated byproducts of mitochondria. We hypothesized that tafazzin knockdown increases ROS production from mitochondria, and a mitochondria-targeted antioxidant prevents tafazzin knockdown induced mitochondrial and cardiac dysfunction. We employed cardiac myocytes transduced with an adenovirus containing tafazzin shRNA as a model to investigate the effects of the mitochondrial antioxidant, mito-Tempo. Knocking down tafazzin decreased steady state levels of cardiolipin and increased mitochondrial ROS. Treatment of cardiac myocytes with mito-Tempo normalized tafazzin knockdown enhanced mitochondrial ROS production and cellular ATP decline. Mito-Tempo also significantly abrogated tafazzin knockdown induced cardiac hypertrophy, contractile dysfunction, and cell death. We conclude that mitochondria-targeted antioxidant prevents cardiac dysfunction induced by tafazzin gene knockdown in cardiac myocytes and suggest mito-Tempo as a potential therapeutic for Barth syndrome and other dilated cardiomyopathies resulting from mitochondrial oxidative stress.

Hyperglycemia and angiotensin II cooperate to enhance collagen I deposition by cardiac fibroblasts through a ROS-STAT3-dependent mechanism

Cardiac fibroblasts significantly contribute to diabetes-induced structural and functional changes in the myocardium. The objective of the present study was to determine the effects of high glucose (alone or supplemented with angiotensin II) in the activation of the JAK2/STAT3 pathway and its involvement in collagen I production by cardiac fibroblasts. We observed that the diabetic environment 1) enhanced tyrosine phosphorylation of JAK2 and STAT3; 2) induced nuclear localization of tyrosine phosphorylated STAT3 through a reactive oxygen species-mediated mechanism, with angiotensin II stimulation further enhancing STAT3 nuclear accumulation; and 3) stimulated collagen I production. The effects were inhibited by depletion of reactive oxygen species or silencing of STAT3 in high glucose alone or supplemented with exogenous angiotensin II. Combined, our data demonstrate that increased collagen I deposition in the setting of high glucose occurred through a reactive oxygen species- and STAT3-dependent mechanism. Our results reveal a novel role for STAT3 as a key signaling molecule of collagen I production in cardiac fibroblasts exposed to a diabetic environment.

Role of Nodal-PITX2C signaling pathway in glucose-induced cardiomyocyte hypertrophy

Pathological cardiac hypertrophy is a major cause of morbidity and mortality in cardiovascular disease. Recent studies have shown that cardiomyocytes, in response to high glucose (HG) stimuli, undergo hypertrophic growth. While much work still needs to be done to elucidate this important mechanism of hypertrophy, previous works have showed that some pathways or genes play important roles in hypertrophy. In this study, we showed that sublethal concentrations of glucose (25 mmol/L) could induce cardiomyocyte hypertrophy with an increase in the cellular surface area and the upregulation of the atrial natriuretic peptide (ANP) gene, a hypertrophic marker. High glucose (HG) treatments resulted in the upregulation of the Nodal gene, which is under-expressed in cardiomyocytes. We also determined that the knockdown of the Nodal gene resisted HG-induced cardiomyocyte hypertrophy. The overexpression of Nodal was able to induce hypertrophy in cardiomyocytes, which was associated with the upregulation of the PITX2C gene. We also showed that increases in the PITX2C expression, in response to Nodal, were mediated by the Smad4 signaling pathway. This study is highly relevant to the understanding of the effects of the Nodal-PITX2C pathway on HG-induced cardiomyocyte hypertrophy, as well as the related molecular mechanisms.

Redox regulation of Janus kinase: The elephant in the room

The redox regulation of Janus kinases (JAKs) is a complex subject. Due to other redox-sensitive kinases in the kinome, redox-sensitive phosphatases, and cellular antioxidant systems and reactive oxygen species (ROS) production systems, the net biological outcomes of oxidative stress on JAK-dependent signal transduction vary according to the specific biological system examined. This review begins with a discussion of the biochemical evidence for a cysteine-based redox switch in the catalytic domain of JAKs, proceeds to consider direct and indirect regulatory mechanisms involved in biological experiments, and ends with a discussion of the role(s) of redox regulation of JAKs in various diseases.

Biomolecular basis of the role of diabetes mellitus in osteoporosis and bone fractures

Osteoporosis has become a serious health problem throughout the world which is associated with an increased risk of bone fractures and mortality among the people of middle to old ages. Diabetes is also a major health problem among the people of all age ranges and the sufferers due to this abnormality increasing day by day. The aim of this review is to summarize the possible mechanisms through which diabetes may induce osteoporosis. Diabetes mellitus generally exerts its effect on different parts of the body including bone cells specially the osteoblast and osteoclast, muscles, retina of the eyes, adipose tissue, endocrine system specially parathyroid hormone (PTH) and estrogen, cytokines, nervous system and digestive system. Diabetes negatively regulates osteoblast differentiation and function while positively regulates osteoclast differentiation and function through the regulation of different intermediate factors and thereby decreases bone formation while increases bone resorption. Some factors such as diabetic neuropathy, reactive oxygen species, Vitamin D, PTH have their effects on muscle cells. Diabetes decreases the muscle strength through regulating these factors in various ways and ultimately increases the risk of fall that may cause bone fractures.

Multiple antioxidants improve cardiac complications and inhibit cardiac cell death in streptozotocin-induced diabetic rats

Diabetic cardiomyopathy, a disorder of the heart muscle in diabetic patients, is one of the major causes of heart failure. Since diabetic cardiomyopathy is now known to have a high prevalence in the asymptomatic diabetic patient, prevention at the earliest stage of development by existing molecules would be appropriate in order to prevent the progression of heart failure. In this study, we investigated the protective role of multiple antioxidants (MA), on cardiac dysfunction and cardiac cell apoptosis in streptozotocin (STZ)-induced diabetic rat. Diabetic cardiomyopathy in STZ-treated animals was characterized by declined systolic, diastolic myocardial performance, oxidative stress and apoptosis in cardiac cells. Diabetic rats on supplementation with MA showed decreased oxidative stress evaluated by the content of reduced levels of lipid per-oxidation and decreased activity of catalase with down-regulation of heme-oxygenase-1 mRNA. Supplementation with MA also resulted in a normalized lipid profile and decreased levels of pro-inflammatory transcription factor NF-kappaB as well as cytokines such as TNF-α, IFN-γ, TGF-β, and IL-10. MA was found to decrease the expression of ROS-generating enzymes like xanthine oxidase, monoamine oxidase-A along with 5-Lipoxygenase mRNA and/or protein expression. Further, left ventricular function, measured by a microtip pressure transducer, was re-established as evidenced by increase in ±dp/dtmax, heart rate, decreased blood pressure, systolic and diastolic pressure as well as decrease in the TUNEL positive cardiac cells with increased Bcl-2/Bax ratio. In addition, MA supplementation decreased cell death and activation of NF-kappaB in cardiac H9c2 cells. Based on our results, we conclude that MA supplementation significantly attenuated cardiac dysfunction in diabetic rats; hence MA supplementation may have important clinical implications in terms of prevention and management of diabetic cardiomyopathy.

Glucose regulation of load-induced mTOR signaling and ER stress in mammalian heart

BACKGROUND

Changes in energy substrate metabolism are first responders to hemodynamic stress in the heart. We have previously shown that hexose-6-phosphate levels regulate mammalian target of rapamycin (mTOR) activation in response to insulin. We now tested the hypothesis that inotropic stimulation and increased afterload also regulate mTOR activation via glucose 6-phosphate (G6P) accumulation.

METHODS AND RESULTS

We subjected the working rat heart ex vivo to a high workload in the presence of different energy-providing substrates including glucose, glucose analogues, and noncarbohydrate substrates. We observed an association between G6P accumulation, mTOR activation, endoplasmic reticulum (ER) stress, and impaired contractile function, all of which were prevented by pretreating animals with rapamycin (mTOR inhibition) or metformin (AMPK activation). The histone deacetylase inhibitor 4-phenylbutyrate, which relieves ER stress, also improved contractile function. In contrast, adding the glucose analogue 2-deoxy-d-glucose, which is phosphorylated but not further metabolized, to the perfusate resulted in mTOR activation and contractile dysfunction. Next we tested our hypothesis in vivo by transverse aortic constriction in mice. Using a micro-PET system, we observed enhanced glucose tracer analog uptake and contractile dysfunction preceding dilatation of the left ventricle. In contrast, in hearts overexpressing SERCA2a, ER stress was reduced and contractile function was preserved with hypertrophy. Finally, we examined failing human hearts and found that mechanical unloading decreased G6P levels and ER stress markers.

CONCLUSIONS

We propose that glucose metabolic changes precede and regulate functional (and possibly also structural) remodeling of the heart. We implicate a critical role for G6P in load-induced mTOR activation and ER stress.

Effects of angiotensin II type 1 receptor antagonist and temperature on prolonged cardioplegic arrest in neonatal rat myocytes

Cardioplegic arrest is a model of ischemia/reperfusion injury and results in the death of irreplaceable cardiac myocytes by a programmed cell death or apoptosis. Signal transducers and activators of transcription (STAT) signaling pathways play an important role in the modulation of apoptosis after ischemia and reperfusion. Angiotensin II type 1 (AT1) receptor antagonist added to cardioplegia could represent an additional modality for enhancing myocardial protection during cardioplegic arrest. To test that hypothesis, we studied the effect of AT1 receptor antagonism and cardioplegia temperature perfusion on STATs modulation during cardioplegic arrest in neonatal rat hearts. Isolated, nonworking hearts (n = 4 per group) from neonatal rats were perfused aerobically in the Langendorff mode according to the following scheme: Dulbecco's Modified Eagle's Medium solution (Group 1); cold (4°C) modified St. Thomas' Hospital no. 2 (MSTH2) cardioplegic solution (Group 2); cold (4°C) MSTH2 cardioplegic solution plus AT1 antagonist (Valsartan) (Group 3); and warm (34°C) MSTH2 cardioplegic solution (Group 4). Thus, myocytes were isolated by enzymatic digestion, and STAT1, STAT2, STAT3, and STAT5 were investigated in Western blot studies. Times to arrest after cardioplegia were 6-10 s for all groups with the exception of Group 1 (spontaneous arrest after 12-16 s). Total cardioplegia delivery volume was about 300 mL in 15 min. Perfusion with cold MSTH2 supplemented with AT1 receptor antagonist (Group 3) induced a significant reduction in STAT1, STAT2, and STAT5 tyrosine phosphorylation versus other groups (P < 0.05). The decreased activation of STAT1, STAT2, and STAT5 observed in Group 3 was accompanied by reduction of interleukin-1β (P < 0.05). On the other hand, STAT3 activation was significantly reduced in Groups 1 and 4 (P < 0.05). Only perfusion with AT1 receptor antagonist supplemented with cold MSTH2 significantly decreases the inflammatory response of the neonatal rat cardiomyocytes without affecting antiapoptotic influence provided by activation of STAT3. Therefore, AT1 receptor antagonist could play a pivotal role in cytoprotective effect and cardiac recovery in neonates and infants.

Impaired JAK2-induced activation of STAT3 in failing human myocytes

Although angiotensin (Ang)II-induced Janus-activated kinase (JAK)2 phosphorylation was reported to be enhanced in failing human cardiomyocytes, the downstream balance between cardio-protective (signal transducer and activator of transcription-STAT3) and the pro-inflammatory (STAT2 and STAT5) response remains unexplored. Therefore STATs phosphorylation and putative genes overexpression following JAK2 activation were investigated in isolated cardiomyocytes obtained from failing human hearts (n = 16), and from non-failing(NF) hearts of humans (putative donors, n = 6) or adult rats. In NF myocytes Ang II-induced JAK2 activation was followed by STAT3 phosphorylation (186 ± 45% at 30 min), with no STAT2 or STAT5 response. The associated B cell lymphoma (Bcl)-xL overexpression (1.05 ± 0.39 fold) was abolished by both JAK2 and extracellular signal-regulated kinase (ERK)1/2 inhibitors (AG490, 10 μM, and PD98059, 30 μM, respectively), whereas Fas ligand (Fas-L) response (0.91 ± 0.21 fold) was inhibited only by p38MAPK antagonism (SB203580, 10 μM). In failing myocytes Ang II-induced JAK2 activation was followed by STAT2 (237 ± 38%) and STAT5 (222 ± 31%) phosphorylation, with no STAT3 response. No changes in Bcl-xL expression were observed, and the associated Fas-L gene overexpression (1.14 ± 0.27 fold) being abolished by p38 mitogen-activated protein kinase (MAPK) antagonism. The altered JAK2 induced STATs response in human failing cardiomyocytes may be of relevance for the progression of cardiac dysfunction in heart failure.

Angiotensin II-induced JNK activation is mediated by NAD(P)H oxidase in isolated rat pancreatic islets

Angiotensin II (AII), the active component of the renin angiotensin system (RAS), plays a vital role in the regulation of physiological processes of the cardiovascular system, but also has autocrine and paracrine actions in various tissues and organs. Many studies have shown the existence of RAS in the pancreas of humans and rodents. The aim of this study was to evaluate potential signaling pathways mediated by AII in isolated pancreatic islets of rats. Phosphorylation of MAPKs (ERK1/2, JNK and p38MAPK), and the interaction between proteins JAK/STAT were evaluated. AII increased JAK2/STAT1 (42%) and JAK2/STAT3 (100%) interaction without altering the total content of JAK2. Analyzing the activation of MAPKs (ERK1/2, JNK and p38MAPK) in isolated pancreatic islets from rats we observed that AII rapidly (3 min) promoted a significant increase in the phosphorylation degree of these proteins after incubation with the hormone. Curiously JNK protein phosphorylation was inhibited by DPI, suggesting the involvement of NAD(P)H oxidase in the activation of protein.

Prevention of hyperglycemia-induced myocardial apoptosis by gene silencing of Toll-like receptor-4

Background

Apoptosis is an early event involved in cardiomyopathy associated with diabetes mellitus. Toll-like receptor (TLR) signaling triggers cell apoptosis through multiple mechanisms. Up-regulation of TLR4 expression has been shown in diabetic mice. This study aimed to delineate the role of TLR4 in myocardial apoptosis, and to block this process through gene silencing of TLR4 in the myocardia of diabetic mice.

Methods

Diabetes was induced in C57/BL6 mice by the injection of streptozotocin. Diabetic mice were treated with 50 μg of TLR4 siRNA or scrambled siRNA as control. Myocardial apoptosis was determined by TUNEL assay.

Results

After 7 days of hyperglycemia, the level of TLR4 mRNA in myocardial tissue was significantly elevated. Treatment of TLR4 siRNA knocked down gene expression as well as diminished its elevation in diabetic mice. Apoptosis was evident in cardiac tissues of diabetic mice as detected by a TUNEL assay. In contrast, treatment with TLR4 siRNA minimized apoptosis in myocardial tissues. Mechanistically, caspase-3 activation was significantly inhibited in mice that were treated with TLR4 siRNA, but not in mice treated with control siRNA. Additionally, gene silencing of TLR4 resulted in suppression of apoptotic cascades, such as Fas and caspase-3 gene expression. TLR4 deficiency resulted in inhibition of reactive oxygen species (ROS) production and NADPH oxidase activity, suggesting suppression of hyperglycemia-induced apoptosis by TLR4 is associated with attenuation of oxidative stress to the cardiomyocytes.

Conclusions

In summary, we present novel evidence that TLR4 plays a critical role in cardiac apoptosis. This is the first demonstration of the prevention of cardiac apoptosis in diabetic mice through silencing of the TLR4 gene.

Diabetic Cardiomyopathy: Mechanisms and Therapeutic Targets

The incidence and prevalence of diabetes mellitus are each increasing rapidly in our society. The majority of patients with diabetes succumb ultimately to heart disease, much of which stems from atherosclerotic disease and hypertension. However, cardiomyopathy can develop independent of elevated blood pressure or coronary artery disease, a process termed diabetic cardiomyopathy. This disorder is a complex diabetes-associated process characterized by significant changes in the physiology, structure, and mechanical function of the heart. Here, we review recently derived insights into mechanisms and molecular events involved in the pathogenesis of diabetic cardiomyopathy.

Rac1 is required for cardiomyocyte apoptosis during hyperglycemia

OBJECTIVE

Hyperglycemia induces reactive oxygen species (ROS) and apoptosis in cardiomyocytes, which contributes to diabetic cardiomyopathy. The present study was to investigate the role of Rac1 in ROS production and cardiomyocyte apoptosis during hyperglycemia.

RESEARCH DESIGN AND METHODS

Mice with cardiomyocyte-specific Rac1 knockout (Rac1-ko) were generated. Hyperglycemia was induced in Rac1-ko mice and their wild-type littermates by injection of streptozotocin (STZ). In cultured adult rat cardiomyocytes, apoptosis was induced by high glucose.

RESULTS

The results showed a mouse model of STZ-induced diabetes, 7 days of hyperglycemia-upregulated Rac1 and NADPH oxidase activation, elevated ROS production, and induced apoptosis in the heart. These effects of hyperglycemia were significantly decreased in Rac1-ko mice or wild-type mice treated with apocynin. Interestingly, deficiency of Rac1 or apocynin treatment significantly reduced hyperglycemia-induced mitochondrial ROS production in the heart. Deficiency of Rac1 also attenuated myocardial dysfunction after 2 months of STZ injection. In cultured cardiomyocytes, high glucose upregulated Rac1 and NADPH oxidase activity and induced apoptotic cell death, which were blocked by overexpression of a dominant negative mutant of Rac1, knockdown of gp91(phox) or p47(phox), or NADPH oxidase inhibitor. In type 2 diabetic db/db mice, administration of Rac1 inhibitor, NSC23766, significantly inhibited NADPH oxidase activity and apoptosis and slightly improved myocardial function.

CONCLUSIONS

Rac1 is pivotal in hyperglycemia-induced apoptosis in cardiomyocytes. The role of Rac1 is mediated through NADPH oxidase activation and associated with mitochondrial ROS generation. Our study suggests that Rac1 may serve as a potential therapeutic target for cardiac complications of diabetes.

Histamine induces human beta-defensin-3 production in human keratinocytes

BACKGROUND

The antimicrobial peptide human beta-defensin-3 (hBD-3) is produced by epidermal keratinocytes, and promotes cutaneous antimicrobial defense, inflammation, and wound repair. hBD-3 induces histamine release from mast cells. We previously showed that histamine enhanced transcriptional activity of activator protein-1 (AP-1) in human keratinocytes by inducing the expression of AP-1 component c-Fos via the activation of extracellular signal-regulated kinase (ERK) through H1 receptors.

OBJECTIVE

To examine in vitro effects of histamine on hBD-3 production in normal human keratinocytes.

METHODS

The hBD-3 production was examined by enzyme-linked immunosorbent assays and reverse transcription-polymerase chain reaction. The transcriptional activities were analyzed by dual luciferase assays. The phosphorylation of proteins was examined by Western blotting.

RESULTS

Histamine enhanced hBD-3 secretion and mRNA expression in keratinocytes. The histamine-induced hBD-3 production was suppressed by H1 antagonist pyrilamine and antisense oligonucleotides against signal transducer and activator of transcription 3 (STAT3) and AP-1 components c-Jun and c-Fos. Histamine enhanced STAT3 transcriptional activity and induced tyrosine and serine phosphorylation of STAT3. The former was suppressed by Janus kinase 2 (JAK2) inhibitor AG490, while the latter was suppressed by mitogen-activated protein kinase kinase (MEK) inhibitor PD98059; both were suppressed by pyrilamine. AG490 and PD98059 suppressed histamine-induced hBD-3 production and STAT3 activity. Histamine induced tyrosine phosphorylation of JAK2, and pyrilamine suppressed the phosphorylation.

CONCLUSION

It is suggested that histamine induces hBD-3 production in human keratinocytes through H1 receptors by activating STAT3 and AP-1 via JAK2 and MEK/ERK. Histamine may promote cutaneous antimicrobial defense, inflammation, and wound repair through hBD-3.

JAK redux: a second look at the regulation and role of JAKs in the heart

A number of type 1 receptor cytokine family members protect the heart from acute and chronic oxidative stress. This protection involves activation of two intracellular signaling cascades: the reperfusion injury salvage kinase (RISK) pathway, which entails activation of phosphatidylinositol 3-kinase (PI3-kinase) and ERK1/2, and JAK-STAT signaling, which involves activation of transcription factor signal transducer and activator of transcription 3 (STAT3). Obligatory for activation of both RISK and STAT3 by nearly all of these cytokines are the kinases JAK1 and JAK2. Yet surprisingly little is known about how JAK1 and JAK2 are regulated in the heart or how they couple to PI3-kinase activation. Although the JAKs are linked to antioxidative stress programs in the heart, we recently reported that these kinases are inhibited by oxidative stress in cardiac myocytes. In contrast, others have reported that cardiac JAK2 is activated by acute oxidative stress by an undefined process. Here we summarize recent insights into the regulation of JAK1 and JAK2. Besides oxidative stress, inhibitory regulation involves phosphorylation, nitration, and intramolecular restraints. Stimulatory regulation involves phosphorylation and adaptor proteins. The net effect of stress on JAK activity in the heart likely represents the sum of both inhibitory and stimulatory processes, along with their dynamic interaction. Thus the regulation of JAKs in the heart, once touted as the paragon of simplicity, is proving rather complicated indeed, requiring a second look. It is our contention that a better understanding of the regulation of this kinase family that is implicated in cardiac protection could translate into effective therapeutic strategies for preventing myocardial damage or repairing the injured heart.

Enhanced expression of Janus kinase-signal transducer and activator of transcription pathway members in human diabetic nephropathy

OBJECTIVE

Glomerular mesangial expansion and podocyte loss are important early features of diabetic nephropathy, whereas tubulointerstitial injury and fibrosis are critical for progression of diabetic nephropathy to kidney failure. Therefore, we analyzed the expression of genes in glomeruli and tubulointerstitium in kidney biopsies from diabetic nephropathy patients to identify pathways that may be activated in humans but not in murine models of diabetic nephropathy that fail to progress to glomerulosclerosis, tubulointerstitial fibrosis, and kidney failure.

RESEARCH DESIGN AND METHODS

Kidney biopsies were obtained from 74 patients (control subjects, early and progressive type 2 diabetic nephropathy). Glomerular and tubulointerstitial mRNAs were microarrayed, followed by bioinformatics analyses. Gene expression changes were confirmed by real-time RT-PCR and immunohistological staining. Samples from db/db C57BLKS and streptozotocin-induced DBA/2J mice, commonly studied murine models of diabetic nephropathy, were analyzed.

RESULTS

In human glomeruli and tubulointerstitial samples, the Janus kinase (Jak)-signal transducer and activator of transcription (Stat) pathway was highly and significantly regulated. Jak-1, -2, and -3 as well as Stat-1 and -3 were expressed at higher levels in patients with diabetic nephropathy than in control subjects. The estimated glomerular filtration rate significantly correlated with tubulointerstitial Jak-1, -2, and -3 and Stat-1 expression (R(2) = 0.30-0.44). Immunohistochemistry found strong Jak-2 staining in glomerular and tubulointerstitial compartments in diabetic nephropathy compared with control subjects. In contrast, there was little or no increase in expression of Jak/Stat genes in the db/db C57BLKS or diabetic DBA/2J mice.

CONCLUSIONS

These data suggest a direct relationship between tubulointerstitial Jak/Stat expression and progression of kidney failure in patients with type 2 diabetic nephropathy and distinguish progressive human diabetic nephropathy from nonprogressive murine diabetic nephropathy.

Impaired angiotensin II-extracellular signal-regulated kinase signaling in failing human ventricular myocytes

Angiotensin II was reported to induce insulin-like growth factor-I and endothelin-1 gene expression and peptide release by ventricular cardiomyocytes. However, the progression from cardiac hypertrophy to failure in humans is characterized by a reduced myocyte expression of insulin-like growth factor-I and endothelin-1, notwithstanding the enhanced cardiac generation of angiotensin II. In the present study we investigated the functional status of the signaling pathways responsible for angiotensin II-induced endothelin-1 and insulin-like growth factor-I formation in human ventricular myocytes isolated from patients with dilated (n = 19) or ischemic (n = 14) cardiomyopathy and nonfailing donor hearts (n = 6).In human nonfailing ventricular myocytes, angiotensin II (100 nmol/l) induced insulin-like growth factor-I and endothelin-1 gene expression, and peptide release was mediated by extracellular signal-regulated kinase activation and inhibited by extracellular signal-regulated kinase antagonism (PD98059, 30 micromol/l), endothelin-1 formation being partially reduced also by c-Jun N-terminal kinase inhibition (SP600125, 10 micromol/l); insulin-like growth factor-I and endothelin-1 formations were unaffected by the inhibition of p38 mitogen-activated protein kinase (SB203580, 10 micromol/l) and Janus tyrosine kinase 2 (AG490, 10 micromol/l). In failing myocytes, angiotensin II failed to induce insulin-like growth factor-I and endothelin-1 formation; angiotensin II-induced extracellular signal-regulated kinase activation was significantly impaired (-88% vs. controls) although c-Jun NH2-terminal kinase activation was preserved. The impaired extracellular signal-regulated kinase phosphorylation in failing myocytes was associated with increased myocyte levels of mitogen-activated protein kinase phosphatases.Therefore, the altered growth factor production in failing myocytes is associated with a significant derangement in intracellular signaling.

Decrease of peroxisome proliferator-activated receptor delta expression in cardiomyopathy of streptozotocin-induced diabetic rats

AIMS

The role of peroxisome proliferator-activated receptor delta (PPARdelta) in the development of cardiomyopathy, which is widely observed in diabetic disorders, is likely because cardiomyocyte-restricted PPARdelta deletion causes cardiac hypertrophy. Thus, we investigated the effect of hyperglycaemia-induced oxidative stress on the expression of cardiac PPARdelta both in vivo and in vitro.

METHODS AND RESULTS

We used male Wistar rats to examine the effect of hyperglycaemia on PPARdelta expression in streptozotocin-induced diabetic rats, primary neonatal rat cardiomyocytes, and H9c2 embryonic rat cardiomyocytes. PPARdelta mRNA (messenger ribonucleic acid) and protein levels were measured using northern and western blotting, respectively. The lipid deposition within the heart section was assessed by oil red O staining. The formation of reactive oxygen species (ROS) and changes in morphology, protein synthesis, and alpha-actinin content in hyperglycaemic cells were also examined. Inhibitors of ROS production or mitogen-activated protein kinase (MAPK) activation were employed to investigate the possible mechanisms. Cardiomyopathy induced in streptozotocin-diabetic rats was associated with a marked decrease in cardiac PPARdelta expression. Also, ROS production, cell size, and protein synthesis were increased while PPARdelta expression was reduced in cells exposed to hyperglycaemia in vitro. However, these glucose-induced changes were abolished in the presence of tiron or PD98059 (MEK/ERK inhibitor).

CONCLUSION

Our results suggest that inhibitors of ROS production or MAPK activation are involved in reduction of cardiac PPARdelta expression in response to hyperglycaemia.

Angiotensin II: a hormone involved in and contributing to pro-hypertrophic cardiac networks and target of anti-hypertrophic cross-talks

Angiotensin II (Ang II) plays a major role in the progression of myocardial hypertrophy to heart failure. Inhibiting the angiotensin converting enzyme (ACE) or blockade of the corresponding Ang II receptors is used extensively in clinical practice, but there is scope for refinement of this mode of therapy. This review summarizes the current understanding of the direct effects of Ang II on cardiomyocytes and then focus particularly on interaction of components of the renin-angiotensin system with other hormones and cytokines. New findings described in approximately 400 papers identified in the PubMed database and published during the 2.5 years are discussed in the context of previous relevant literature. The cardiac action of Ang II is influenced by the activity of different isoforms of ACE leading to different amounts of Ang II by comparison with other angiotensinogen-derived peptides. The effect of Ang II is mediated by at least two different AT receptors that are differentially expressed in cardiomyocytes from neonatal, adult and failing hearts. The intracellular effects of Ang II are influenced by nitric oxide (NO)/cGMP-dependent cross talk and are mediated by the release of autocrine factors, such as transforming growth factor (TGF)-beta1 and interleukin (IL)-6. Besides interactions with cytokines, Ang II is involved in systemic networks including aldosterone, parathyroid hormone and adrenomedullin, which have their own effects on cardiomyocytes that modify, amplify or antagonize the primary effect of Ang II. Finally, hyperinsulemia and hyperglycaemia influence Ang II-dependent processes in diabetes and its cardiac sequelae.

Dietary flavonoids differentially reduce oxidized LDL-induced apoptosis in human endothelial cells: role of MAPK- and JAK/STAT-signaling

Endothelial apoptosis is a driving force in atherosclerosis development. Oxidized LDL promotes inflammatory and thrombotic processes and is highly atherogenic, as it stimulates macrophage cholesterol accumulation and foam cell formation. This study investigated multiple mitogen-activated protein kinase (MAPK)-responsive death/survival signaling pathways, through which flavonoids of (-)epigallocatechin gallate (EGCG) and hesperetin exerted antiapoptosis in endothelial cells exposed to oxidized LDL. EGCG and hesperetin substantially diminished the oxidized LDL-induced 2',7'-dichlorofluorecein staining, suggesting that these flavonoids inhibited intracellular accumulation of oxidized LDL-triggered reactive oxygen species and consequent apoptosis. The Western-blot data revealed that oxidized LDL upregulated c-Jun N-terminal kinase (JNK) phosphorylation, which was rapidly reversed by EGCG and hesperetin. They mitigated the consequent activation of the JNK downstream on p53 and c-Jun. Moreover, oxidized LDL increased luciferase activity of p53 in endothelial cells transfected with a p53 promoter construct, the increase of which was strikingly downregulated by EGCG and hesperetin. Surprisingly, hesperetin but not EGCG attenuated phosphorylation of p38MAPK and its downstream c-myc and signal transducers and activators of transcription (STAT)1 evoked by oxidized LDL. This study also attempted to explore a linkage of Janus kinase (JAK)2/STAT3 activation to MAPK signaling in oxidized LDL-induced endothelial apoptosis. Notably, we found that the JAK2 inhibitor substantially blocked the JNK activation. Our findings suggest that EGCG and hesperetin may act as antiatherogenic agents blocking oxidized LDL-induced endothelial apoptosis via differential cellular apoptotic machinery. These data provide evidence that the interplay between p38MAPK and JAK-STAT pathways is involved in dietary flavonoid protection against oxidized LDL through hampering MAPK-dependent pathways involving the activation of JAK2.

Renal mitochondrial impairment is attenuated by AT1 blockade in experimental Type I diabetes

To investigate whether ANG II type 1 (AT(1)) receptor blockade could protect kidney mitochondria in streptozotocin-induced Type 1 diabetes, we treated 8-wk-old male Sprague-Dawley rats with a single streptozotocin injection (65 mg/kg ip; STZ group), streptozotocin and drinking water containing either losartan (30 mg.kg(-1).day(-1); STZ+Los group) or amlodipine (3 mg.kg(-1).day(-1); STZ+Amlo group), or saline (intraperitoneally) and pure water (control group). Four-month-long losartan or amlodipine treatments started 30 days before streptozotocin injection to improve the antioxidant defenses. The number of renal lesions, plasma glucose and lipid levels, and proteinuria were higher and creatinine clearance was lower in STZ and STZ+Amlo compared with STZ+Los and control groups. Glycemia was higher in STZ+Los compared with control. Blood pressure, basal mitochondrial membrane potential and mitochondrial pyruvate content, and renal oxidized glutathione levels were higher and NADH/cytochrome c oxidoreductase activity was lower in STZ compared with the other groups. In STZ and STZ+Amlo groups, mitochondrial H(2)O(2) production rate was higher and uncoupling protein-2 content, cytochrome c oxidase activity, and renal glutathione level were lower than in STZ+Los and control groups. Mitochondrial nitric oxide synthase activity was higher in STZ+Amlo compared with the other groups. Mitochondrial pyruvate content and H(2)O(2) production rate negatively contributed to electron transfer capacity and positively contributed to renal lesions. Uncoupling protein-2 content negatively contributed to mitochondrial H(2)O(2) production rate and renal lesions. Renal glutathione reduction potential positively contributed to mitochondria electron transfer capacity. In conclusion, AT(1) blockade protects kidney mitochondria and kidney structure in streptozotocin-induced diabetes independently of blood pressure and glycemia.

Reduced expression of thyroid hormone receptors and beta-adrenergic receptors in human failing cardiomyocytes

An altered thyroid hormone profile has been reported in patients with congestive heart failure. However, information regarding the status of thyroid hormone receptors in human failing cardiomyocytes is lacking. Therefore the expression of thyroid hormone and beta-adrenergic receptors was investigated in human ventricular cardiomyocytes isolated from patients with end-stage heart failure (FM, n=12), or from tentative donors (C, n=4). The expression of thyroid (TRalpha1, and TRbeta1) and beta-adrenergic receptors (ARB1 and ARB2) was measured at both the gene, and at the protein level. In FM the reduced mRNA expression of ARB1 (p<0.05, -37%) and ARB2 (p<0.05, -42%) was associated with a reduction of the messenger for TRalpha1 (p<0.05, -85%) and TRalpha2 (p<0.05, -73%). These findings were confirmed at the protein level for ARB1, ARB2 and TRalpha1. These data reveal that in human heart failure the reduction of beta-adrenergic receptors is associated with reduced expression of both TRalpha1 and TRalpha2 isoforms of thyroid hormone receptors.

Inhibition of Jak/STAT signaling ameliorates mice experimental nephrotic syndrome

BACKGROUND/AIMS

This study investigated the role of JAK/STAT, an important pathway for cytokine signal transduction, in the progression of chronic glomerular diseases.

METHODS

BALB/c mice received a single intravenous injection of adriamycin (10 mg/kg) were sacrificed 2, 4 and 6 weeks later. In the second study, treatment with the selective JAK2 inhibitor AG490 (15 mg/kg, q.d., i.p.) or vehicle was started 5 days after adriamycin injection. Functional and pathologic markers, inflammatory infiltration, expression of pro-inflammatory cytokines and phosphorylation of JAK2/STATs were assessed.

RESULTS

JAK/STAT signaling was activated in adriamycin nephropathy. Phosphorylation of JAK2, STAT1 and STAT3 was significantly inhibited by AG490 (p <0.01). Compared to the vehicle-treated controls, AG490 treatment did not reduce proteinuria 2 weeks after induction of the disease, but resulted in significant decrease in proteinuria and serum creatinine at week 6 (p <0.05). Glomerulosclerosis, tubulointerstitial lesions and renal alpha-SMA expression were also significantly suppressed by AG490 treatment at week 6 (p < 0.01). In addition, AG490 inhibited the expression of MCP-1 mRNA, accompanied by reduced interstitial infiltration of macrophages and T cells (p <0.05).

CONCLUSIONS

This study suggests that activation of JAK/STAT signaling is involved in the progression of glomerular diseases with proteinuric state.

Long-term effects of increased glucose entry on mouse hearts during normal aging and ischemic stress

BACKGROUND

A shift of substrate preference toward glucose in the heart is considered a reversion to fetal metabolic profile, but its role in the pathogenesis of cardiac diseases is incompletely understood.

METHODS AND RESULTS

We performed a 2-year follow-up study in transgenic mice with sustained high glucose uptake and utilization in the heart by cardiac-specific overexpression of the insulin-independent glucose transporter GLUT1 (GLUT1-TG). Compared with wild-type litter mates, the GLUT1-TG mice showed a normal survival rate and unaltered contractile function of the heart monitored by serial echocardiography and by pressure-volume studies in isolated perfused hearts in the 2-year period. Furthermore, when hearts were subjected to ischemia-reperfusion, cardiac function of young and old GLUT1-TG recovered to the same level (86% and 83%, respectively) and exceeded that of both young and old wild-type hearts (52% and 35%, respectively; P<0.05). Nuclear magnetic resonance spectroscopic measurements with 31P showed delayed ATP depletion, reduced acidosis during ischemia, and improved recovery of high-energy phosphate content in old GLUT1-TG hearts (P<0.05 versus old wild-type). During reperfusion, glucose oxidation was 3-fold higher and fatty acid oxidation was 45% lower in old GLUT1-TG hearts compared with old wild-type (P<0.05), which suggests that the deleterious effects of excessive fatty acid oxidation during reperfusion was prevented in old GLUT1-TG hearts.

CONCLUSIONS

We have demonstrated that a normal heart is able to adapt to long-term increases in basal glucose entry into cardiomyocytes without development of glucotoxicity. Furthermore, life-long increases in glucose uptake result in a favorable metabolic phenotype that affords protections against aging-associated increase of susceptibility to ischemic injury.

Inhibition of Jak2 phosphorylation attenuates pressure overload cardiac hypertrophy

RATIONALE

We examined the role of Jak2 kinase phosphorylation in the development of pressure overload hypertrophy in mice subjected to transverse aortic constriction (TAC) and treated with tyrphostin AG490, a pharmacological inhibitor of Jak2.

METHODS

Control mice (sham), subjected to TAC for 15 days (TAC) or to TAC and treated with 48 microg/kg/day i.p. of tyrphostin AG490 (TAC+AG490) were evaluated for morphological, physiological, and molecular changes associated with pressure overload hypertrophy.

RESULTS

Mice subjected to TAC alone developed concentric hypertrophy that accompanied activation of the components of the Jak/STAT signaling pathway manifested by an increase in phosphorylation of Jak2 and STAT3. We also observed increased phosphorylation of MAPK p44/p42, p38 MAPK and JNK in the TAC group, as well as, an increase in expression of MKP-1 phosphatase which negatively regulates MAPK kinases. Treatment of aortic constricted mice with tyrphostin AG490 failed to develop hypertrophy and showed a marked reduction in phosphorylation of Jak2 and STAT3. There was, however, in TAC and AG490 treated mice, a notable increase in the phosphorylation state of the MAPK p44/42, whereas MKP-1 phosphatase was downregulated.

CONCLUSION

These findings suggest that Jak2 kinase plays an important role in left ventricular remodeling during pressure overload hypertrophy. Pharmacological inhibition of Jak2 kinase during pressure overload blocks the development of concentric hypertrophy.

Hyperglycemia is a marker for poor outcome in the postoperative pediatric cardiac patient

OBJECTIVE

Hyperglycemia in critical care populations has been shown to be a risk factor for increased morbidity and mortality. Minimal data exist in postoperative pediatric cardiac patients. The goal of this study was to determine whether hyperglycemia in the postoperative period was associated with increased morbidity or mortality.

DESIGN

Retrospective chart review.

SETTING

Tertiary care, free-standing pediatric medical center with a dedicated cardiac intensive care unit.

PATIENTS

We included 184 patients <1 yr of age who underwent cardiac surgery requiring cardiopulmonary bypass from October 2002 to August 2004. Patients with a weight <2 kg, a preoperative diagnosis of diabetes, preoperative extracorporeal membrane oxygenation support, solid organ transplant recipients, and preoperative renal or liver insufficiency were excluded.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Age was 4.3 +/- 3.2 months and weight was 4.9 +/- 1.7 kg at surgery. Duration of hyperglycemia was significantly longer in patients with renal insufficiency (p = .029), liver insufficiency (p = .006), infection (p < .002), central nervous system event (p = .038), extracorporeal membrane oxygenation use (p < .001), and death (p < .002). Duration of hyperglycemia was also significantly associated with increased intensive care (p < .001) and hospital (p < .001) stay and longer ventilator use (p < .001). Peak glucose levels were significantly different in patients with renal insufficiency (p < .001), infection (p = .002), central nervous system event (p = .01), and mortality (p < .001).

CONCLUSIONS

Hyperglycemia in the postoperative period was associated with increased morbidity and mortality in postoperative pediatric cardiac patient. Strict glycemic control may improve outcomes in this patient population.

Energy deficiency in the failing heart: linking increased reactive oxygen species and disruption of oxidative phosphorylation rate

Heart failure is a complex syndrome of numerous dysfunctional components which converge to cause chronic progressive failure of ventricular contractile function and maintenance of cardiac output demand. The aim of this brief review is to highlight some of the mounting evidence indicating that augmented superoxide, related reactive oxygen species and other free radicals contribute to the oxidative stress evident during the progression of heart failure. While much of the source of increased reactive oxygen species is mitochondrial, there are other intracellular sources, which together are highly reactive with functional and structural cellular lipids and proteins. Bioenergetic defects limiting ATP synthesis in the failing myocardium relate not only to post-translational modification of electron transport respiratory chain proteins but also to perturbation of Krebs Cycle enzyme-dependent synthesis of NADH. Accumulation of pathological levels of lipid peroxides relate to dysfunction in the intrinsic capacity to clear and renew dysfunctional proteins. This review also features key limitations of human heart failure studies and potential clinical therapies that target the elevated oxidative stress that is a hallmark of human heart failure.

Cardiovascular oxidative stress is reduced by an ACE inhibitor in a rat model of streptozotocin-induced diabetes

Blockade of the renin-angiotensin system (RAS) reduces cardiovascular morbidity and mortality in diabetic patients. Ang II-mediated generation of reactive oxygen species (ROS) has been suggested to be involved in several diabetic complications. We investigated whether the inhibition of Ang II production with an ACE inhibitor (ACEi) reduces oxidative stress and limits structural cardiovascular remodeling in a rat model of streptozotocin (STZ)-induced diabetes. Diabetic rats were treated for 7 weeks with an ACEi (lisinopril, 5 mg/kg/d), an antioxidant (N-acetyl-l-cysteine (NAC), 0.5 g/kg/d) and their combination. At sacrifice, ROS in the myocardium and thoracic aorta, LV myocyte number and size and aorta morphology were determined by quantitative histological methods. Superoxide and hydroxyl radical content, detected by dihydroethidium (DHE) and 8-hydroxydeoxyguanosine (8-OHdG), were 6.7 and 4.5-fold, respectively, higher in diabetic myocardium than in non-diabetic controls (p<0.001). The amount of superoxide was 5-fold higher in the thoracic aorta of diabetic rats compared to controls (p<0.001). Diabetes caused a modest increase in myocyte volume (+13%, p<0.01), a reduction of LV myocyte number (-43%, p<0.001), an accumulation of collagen around coronary arterioles (1.9-fold increase, p<0.01) and a decrease in arterial elastin/collagen ratio (-63%, p<0.001) compared to controls. Treatment with the ACEi attenuated ROS formation and prevented phenotypic changes in the heart (cardiomyocyte hypertrophy, perivascular fibrosis) and in the aorta of diabetic rats to the same extent as NAC. The absence of an additive effect, suggests a common mechanism of action, through the reduction of oxidative stress.

Increased expression of NAD(P)H oxidase in islets of animal models of Type 2 diabetes and its improvement by an AT1 receptor antagonist

This study was undertaken to reveal the role of NAD(P)H oxidase in increased oxidative stress in islets of Type 2 diabetes. Immunostaining analysis showed that staining intensities of NAD(P)H oxidase components, gp91phox and p22phox, significantly increased in islets of animal models of Type 2 diabetes, OLETF rats (60 weeks of age) and db/db mice (14 weeks of age), compared with age-matched controls, respectively, correlating with increased levels of oxidative stress marker, 8-hydroxy-deoxyguanosine or 4-hydroxy-2-nonenal modified protein. In db/db mice, oral administration of angiotensin II Type 1 receptor antagonist valsartan (5 mg/kg) for 4 weeks significantly attenuated the increased expression of gp91phox and p22phox together with inhibition of oxidative stress and partially restored decreased insulin contents in islets. Angiotensin II-related increased expression of NAD(P)H oxidase may play an important role in increased oxidative stress in islets of Type 2 diabetes. This mechanism may be a novel therapeutic target for preventing beta-cell damage.