Forkhead class O transcription factor 3a activation and Sirtuin1 overexpression in the hypertrophied myocardium of the diabetic Goto-Kakizaki rat

Identification of HDAC9 and ARRDC4 as potential biomarkers and targets for treatment of type 2 diabetes

We aimed to identify the key potential insulin resistance (IR)-related genes and investigate their correlation with immune cell infiltration in type 2 diabetes (T2D). The GSE78721 dataset (68 diabetic patients and 62 controls) was downloaded from the Gene Expression Omnibus database and utilized for single-sample gene set enrichment analysis. IR-related genes were obtained from the Comparative Toxicology Genetics Database, and the final IR-differentially expressed genes (DEGs) were screened by intersecting with the DEGs obtained from the GSE78721 datasets. Functional enrichment analysis was performed, and the networks of the target gene with microRNA, transcription factor, and drug were constructed. Hub genes were identified based on a protein-protein interaction network. Least absolute shrinkage and selection operator regression and Random Forest and Boruta analysis were combined to screen diagnostic biomarkers in T2D, which were validated using the GSE76894 (19 diabetic patients and 84 controls) and GSE9006 (12 diabetic patients and 24 controls) datasets. Quantitative real-time polymerase chain reaction was performed to validate the biomarker expression in IR mice and control mice. In addition, infiltration of immune cells in T2D and their correlation with the identified markers were computed using CIBERSORT. We identified differential immune gene set regulatory T-cells in the GSE78721 dataset, and T2D samples were assigned into three clusters based on immune infiltration. A total of 2094 IR-DEGs were primarily enriched in response to endoplasmic reticulum stress. Importantly, HDAC9 and ARRDC4 were identified as markers of T2D and associated with different levels of immune cell infiltration. HDAC9 mRNA level were higher in the IR mice than in control mice, while ARRDC4 showed the opposite trend. In summary, we discovered potential vital biomarkers that contribute to immune cell infiltration associated with IR, which offers a new sight of immunotherapy for T2D.

SIRT1: a promising therapeutic target in type 2 diabetes mellitus

A significant increase in the worldwide incidence and prevalence of type 2 diabetic mellitus (T2DM) has elevated the need for studies on novel and effective therapeutic strategies. Sirtuin 1 (SIRT1) is an NAD + dependent protein deacetylase with a critical function in the regulation of glucose/lipid metabolism, insulin resistance, inflammation, oxidative stress, and mitochondrial function. SIRT1 is also involved in the regulation of insulin secretion from pancreatic β-cells and protecting these cells from inflammation and oxidative stress-mediated tissue damages. In this regard, major SIRT1 activators have been demonstrated to exert a beneficial impact in reversing T2DM-related complications including cardiomyopathy, nephropathy, retinopathy, and neuropathy, hence treating T2DM. Therefore, an accumulating number of recent studies have investigated the efficacy of targeting SIRT1 as a therapeutic strategy in T2DM. In this review we aimed to discuss the current understanding of the physiological and biological roles of SIRT1, then its implication in the pathogenesis of T2DM, and the therapeutic potential of SIRT1 in combating T2DM.

Activation of the sirtuin silent information regulator 1 pathway inhibits pathological myocardial remodeling

Myocardial remodeling refers to structural and functional disorders of the heart caused by molecular biological changes in the cardiac myocytes in response to neurological and humoral factors. A variety of heart diseases, such as hypertension, coronary artery disease, arrhythmia, and valvular heart disease, can cause myocardial remodeling and eventually lead to heart failure. Therefore, counteracting myocardial remodeling is essential for the prevention and treatment of heart failure. Sirt1 is a nicotinamide adenine dinucleotide⁺-dependent deacetylase that plays a wide range of roles in transcriptional regulation, energy metabolism regulation, cell survival, DNA repair, inflammation, and circadian regulation. It positively or negatively regulates myocardial remodeling by participating in oxidative stress, apoptosis, autophagy, inflammation, and other processes. Taking into account the close relationship between myocardial remodeling and heart failure and the involvement of SIRT1 in the development of the former, the role of SIRT1 in the prevention of heart failure via inhibition of myocardial remodeling has received considerable attention. Recently, multiple studies have been conducted to provide a better understanding of how SIRT1 regulates these phenomena. This review presents the progress of research involving SIRT1 pathway involvement in the pathophysiological mechanisms of myocardial remodeling and heart failure.

Klotho and SIRT1 changes from pre-diabetes to diabetes and pre-hypertension to hypertension

BACKGROUND

Hypertension and diabetes are among the most important risk factors of cardiovascular diseases. Klotho and SIRT1 are known as anti-aging factors with beneficial effects on cardiovascular system. In this study we investigated the serum Klotho and SIRT1 levels in pre-diabetic and pre-hypertensive individuals and then in diabetic and hypertensive patients to see their relationship with these diseases.

METHOD

229 individuals divided into six groups with similar gender and age distribution 1-Control (normal BP and FBS) 2-pre-diabetic (FBS between 100 and 125 mg/dl) 3-diabetic (FBS ≥ 126 mg/dl), 4-pre-hypertensive (SBP 120-139 or DBP 80-89 mm Hg) 5-hypertensive (SBP ≥ 140 or DBP ≥ 90 mm Hg), and 6-patients with combined hypertension/diabetes. Serum levels of Klotho and SIRT1 were measured by ELISA method.

RESULTS

Serum Klotho and STRT1 levels decreased in pre-diabetes and returned to normal in diabetic patients. Their concentration increased in pre-hypertension and recovered to normal in hypertension. In the physiologic range of FBS there is a negative correlation between Klotho and SIRT1 with FBS. When pathologic ranges of FBS added to analysis, the negative correlation abolished/U shaped. Also an inverse U shape correlation observed between Klotho and SIRT1 with MAP in the range of normal to hypertensive BP levels. There was an overall positive relationship between the serum levels of Klotho and SIRT1 themselves.

CONCLUSION

The serum levels of the anti-aging proteins Klotho and SIRT1 increases or reduces at the onset of the disease, as a compensatory mechanism, but as the disease progresses their level recovers.

Sirt1 Activity in PBMCs as a Biomarker of Different Heart Failure Phenotypes

Heart Failure (HF) is a syndrome, which implies the existence of different phenotypes. The new categorization includes patients with preserved ejection fraction (HFpEF), mid-range EF (HFmrEF), and reduced EF (HFrEF) but the molecular mechanisms involved in these HF phenotypes have not yet been exhaustively investigated. Sirt1 plays a crucial role in biological processes strongly related to HF. This study aimed to evaluate whether Sirt1 activity was correlated with EF and other parameters in HFpEF, HFmrEF, and HFrEF. Seventy patients, HFpEF (n = 23), HFmrEF (n = 23) and HFrEF (n = 24), were enrolled at the Cardiology Unit of the University Hospital of Salerno. Sirt1 activity was measured in peripheral blood mononuclear cells (PBMCs). Angiotensin-Converting Enzyme 2 (ACE2) activity, Tumor Necrosis Factor-alpha (TNF-α) and Brain Natriuretic Peptide (BNP) levels were quantified in plasma. HFpEF showed lower Sirt1 and ACE2 activities than both HFmrEF and HFrEF (p < 0.0001), without difference compared to No HF controls. In HFmrEF and HFrEF a very strong correlation was found between Sirt1 activity and EF (r² = 0.899 and r² = 0.909, respectively), and between ACE2 activity and Sirt1 (r² = 0.801 and r² = 0.802, respectively). HFrEF showed the highest TNF-α levels without reaching statistical significance. Significant differences in BNP were found among the groups, with the highest levels in the HFrEF. Determining Sirt1 activity in PBMCs is useful to distinguish the HF patients’ phenotypes from each other, especially HFmrEF/HFrEF from HFpEF.

Circulating extracellular vesicles from patients with valvular heart disease induce neutrophil chemotaxis via FOXO3a and the inhibiting role of dexmedetomidine

We previously demonstrated that circulating extracellular vesicles (EVs) from patients with valvular heart disease (VHD; vEVs) contain inflammatory components and inhibit endothelium-dependent vasodilation. Neutrophil chemotaxis plays a key role in renal dysfunction, and dexmedetomidine (DEX) can reduce renal dysfunction in cardiac surgery. However, the roles of vEVs in neutrophil chemotaxis and effects of DEX on vEVs are unknown. Here, we investigated the impact of vEVs on neutrophil chemotaxis in kidneys and the influence of DEX on vEVs. Circulating EVs were isolated from healthy subjects and patients with VHD. The effects of EVs on chemokine generation, forkhead box protein O3a (FOXO3a) pathway activation and neutrophil chemotaxis on cultured human umbilical vein endothelial cells (HUVECs) and kidneys in mice and the influence of DEX on EVs were detected. vEVs increased FOXO3a expression, decreased phosphorylation of Akt and FOXO3a, promoted FOXO3a nuclear translocation, and activated the FOXO3a signaling pathway in vitro. DEX pretreatment reduced vEV-induced CXCL4 and CCL5 expression and neutrophil chemotaxis in cultured HUVECs via the FOXO3a signaling pathway. vEVs were also found to suppress Akt phosphorylation and activate FOXO3a signaling to increase plasma levels of CXCL4 and CCL5 and neutrophil accumulation in kidney. The overall mechanism was inhibited in vivo with DEX pretreatment. Our data demonstrated that vEVs induced CXCL4-CCL5 to stimulate neutrophil infiltration in kidney, which can be inhibited by DEX via the FOXO3a signaling. Our findings reveal a unique mechanism involving vEVs in inducing neutrophils chemotaxis and may provide a novel basis for using DEX in reducing renal dysfunction in valvular heart surgery.

SIRT1 Activation by Equisetum Arvense L. (Horsetail) Modulates Insulin Sensitivity in Streptozotocin Induced Diabetic Rats

BACKGROUND: Equisetum arvense L., commonly known as field horsetail is a perennial fern of which extracts are rich sources of phenolic compounds, flavonoids, and phenolic acids. Activation of SIRT1 that was shown to be involved in well-known signal pathways of diabetic cardiomyopathy has a protective effect against oxidative stress, inflammatory processes, and apoptosis that are the basis of diseases such as obesity, diabetes mellitus, or cardiovascular diseases. The aim of our study was to evaluate the antidiabetic and cardioprotective effects of horsetail extract in streptozotocin induced diabetic rats. METHODS: Diabetes was induced by a single intraperitoneal injection of 45 mg/kg streptozotocin. In the control groups (healthy and diabetic), rats were administered with vehicle, whilst in the treated groups, animals were administered with 50, 100, or 200 mg/kg horsetail extract, respectively, for six weeks. Blood glucose levels, glucose tolerance, and insulin sensitivity were determined, and SIRT1 levels were measured from the cardiac muscle. RESULTS: The horsetail extract showed moderate beneficial changes in blood glucose levels and exhibited a tendency to elevate SIRT1 levels in cardiomyocytes, furthermore a 100 mg/kg dose also improved insulin sensitivity. CONCLUSIONS: Altogether our results suggest that horsetail extract might have potential in ameliorating manifested cardiomyopathy acting on SIRT1.

The Role of Myocardial Mitochondrial Quality Control in Heart Failure

At present, the treatment of heart failure has entered the plateau phase, and it is necessary to thoroughly study the pathogenesis of heart failure and find out the corresponding treatment methods. Myocardial mitochondria is the main site of cardiac energy metabolism, whose dysfunction is an important factor leading to cardiac dysfunction and heart failure. Mitochondria are highly dynamic organelles. Continuous biogenesis, fusion, fission and mitophagy, contribute to the balance of mitochondria's morphology, quantity, and quality, which is called mitochondrial quality control. Mitochondrial quality control is the cornerstone of normal mitochondrial function and is found to play an important role in the pathological process of heart failure. Here, we provide an overview of the mechanisms of mitochondrial quality control and recent studies on mitochondrial quality control in heart failure, hoping to provide new ideas for drug development in heart failure.

Brain GLP-1/IGF-1 Signaling and Autophagy Mediate Exendin-4 Protection Against Apoptosis in Type 2 Diabetic Rats

Type 2 diabetes (T2D) is a modern socioeconomic burden, mostly due to its long-term complications affecting nearly all tissues. One of them is the brain, whose dysfunctional intracellular quality control mechanisms (namely autophagy) may upregulate apoptosis, leading to cognitive dysfunction and Alzheimer disease (AD). Since impaired brain insulin signaling may constitute the crosslink between T2D and AD, its restoration may be potentially therapeutic herein. Accordingly, the insulinotropic anti-T2D drugs from glucagon-like peptide-1 (GLP-1) mimetics, namely, exendin-4 (Ex-4), could be a promising therapy. In line with this, we hypothesized that peripherally administered Ex-4 rescues brain intracellular signaling pathways, promoting autophagy and ultimately protecting against chronic T2D-induced apoptosis. Thus, we aimed to explore the effects of chronic, continuous, subcutaneous (s.c.) exposure to Ex-4 in brain cortical GLP-1/insulin/insulin-like growth factor-1 (IGF-1) signaling, and in autophagic and cell death mechanisms in middle-aged (8 months old), male T2D Goto-Kakizaki (GK) rats. We used brain cortical homogenates obtained from middle-aged (8 months old) male Wistar (control) and T2D GK rats. Ex-4 was continuously administered for 28 days, via s.c. implanted micro-osmotic pumps (5 μg/kg/day; infusion rate 2.5 μL/h). Peripheral characterization of the animal models was given by the standard biochemical analyses of blood or plasma, the intraperitoneal glucose tolerance test, and the heart rate. GLP-1, insulin, and IGF-1, their downstream signaling and autophagic markers were evaluated by specific ELISA kits and Western blotting. Caspase-like activities and other apoptotic markers were given by colorimetric methods and Western blotting. Chronic Ex-4 treatment attenuated peripheral features of T2D in GK rats, including hyperglycemia and insulin resistance. Furthermore, s.c. Ex-4 enhanced their brain cortical GLP-1 and IGF-1 levels, and subsequent signaling pathways. Specifically, Ex-4 stimulated protein kinase A (PKA) and phosphoinositide 3-kinase (PI3K)/Akt signaling, increasing cGMP and AMPK levels, and decreasing GSK3β and JNK activation in T2D rat brains. Moreover, Ex-4 regulated several markers for autophagy in GK rat brains (as mTOR, PI3K class III, LC3 II, Atg7, p62, LAMP-1, and Parkin), ultimately protecting against apoptosis (by decreasing several caspase-like activities and mitochondrial cytochrome c, and increasing Bcl2 levels upon T2D). Altogether, this study demonstrates that peripheral Ex-4 administration may constitute a promising therapy against the chronic complications of T2D affecting the brain.

Emerging Roles for SIRT5 in Metabolism and Cancer

SIGNIFICANCE

Developing evidence in the literature suggests that sirtuin 5 (SIRT5) may be involved in metabolic reprogramming, an emerging hallmark of cancer by which neoplastic cells reconfigure their metabolism to support the anabolic demands of rapid cell division. SIRT5 is one of the seven members of the nicotinamide adenine dinucleotide-dependent sirtuin family of lysine deacetylases. It removes succinyl, malonyl, and glutaryl groups from protein targets within the mitochondrial matrix and other subcellular compartments. SIRT5 substrates include a number of proteins integral to metabolism. Recent Advances: New work has begun to elucidate the roles of SIRT5 in glycolysis, tricarboxylic acid cycle, fatty acid oxidation, nitrogen metabolism, pentose phosphate pathway, antioxidant defense, and apoptosis.

CRITICAL ISSUES

In this study, we summarize biological functions of SIRT5 reported in normal tissues and in cancer and discuss potential mechanisms whereby SIRT5 may impact tumorigenesis, particularly focusing on its reported roles in metabolic reprogramming. Finally, we review current efforts to target SIRT5 pharmacologically.

FUTURE DIRECTIONS

The biological significance of SIRT5 has been elucidated in the context of only an extremely small fraction of its targets and interactors. There is no doubt that further studies in this area will provide a wealth of insights into functions of SIRT5 and its targets in normal and neoplastic cells. Antioxid. Redox Signal. 28, 677-690.

Regulation on SIRT1-PGC-1α/Nrf2 pathway together with selective inhibition of aldose reductase makes compound hr5F a potential agent for the treatment of diabetic complications

(R,E)-N-(3-(2-acetamido-3-(benzyloxy) propanamido)propyl)-2-cyano-3-(4-hydroxy phenyl)acrylamide (hr5F) was design-synthesized based on bioactivity focus strategy as a potential agent to treat diabetic complicates. With in vitro enzyme assay, it is confirmed that hr5F is an effective ALR2 inhibitor with IC₅₀ value of 2.60 ± 0.15 nM, and selectivity index of 86.0 over ALR1, which is a little bit better than the reference Epalrestat (Epa). hr5F inhibits the increase of ALR2 enzyme activity and expression in human lens epithelial cells (HLECs) induced by high glucose. By applying western blot, it was found that hr5F alleviates the high glucose-induced superoxide overproduction insults by regulating SIRT1-PGC-1α/Nrf2 pathway, together with regulating NRF-1, mtTFA, Bax/Bcl-2 to ameliorate cell apoptosis. The in vivo effects of hr5F on short term streptozocin (STZ)-induced diabetic mice confirm the same functions disclosed in vitro. All the evidences support that hr5F may serve as a promising agent in the treatment of diabetic complications with close efficacy and broader indication than the reference Epa.

The role of SIRT1 in diabetic cardiomyopathy

The prevalence of diabetes mellitus (DM) has been increasing worldwide. Diabetic cardiomyopathy (DCP) is the major risk for diabetes associated morbidity and mortality. Hyperglycemia and hyperinsulinemia play an indispensable role in underlying mechanisms of DCP. They increase advanced glycation end products (AGEs) following a series of events leading to myocardial damage and cardiomyopathy which include oxidative stress, increased inflammation, fibrosis, hypertrophy and apoptosis. SIRT1 is a nicotinamide adenosine dinucleotide (NAD)-dependent deacetylase that removes acetyl groups from proteins which can be implicated in DCP. SIRT1 modulate different proteins related to hyperglycemia. SIRT1 inhibits transcriptional factors, such as p300, NF-κB, P38MAPK, Histone 3, MMP-9, FOXO3a and p53. On the other hand, it increases SERCA2a, ERK1/2/Homer1, eNOS, PGC-1α and AMPK. Therefore, SIRT1 attenuate cardiac dysfunction and improve DCP. This review focus on the role of SIRT1 in diabetic cardiomyopathy.

Global comparison of phosphoproteins in human and rodent hearts: implications for translational studies of myosin light chain and troponin phosphorylations

Cardiac remodeling and failure are regulated by a myriad of cardiac protein phosphorylations. In the present study, cardiac phosphoprotein patterns were examined in rodent and human hearts Left ventricular tissue samples were obtained from human systolic failing (n = 5) and control (n = 5) hearts and from two rat models of hypertensive heart failure, i.e., spontaneously hypertensive heart failure and Dahl salt-sensitive rats and corresponding controls. Phosphoproteins were separated by 2D-DIGE with Cydye staining, phosphoprotein patterns were analyzed using pixel intensity in rectified images. Specific phosphoproteins which were different in human versus rodent hearts were identified by MALDI-TOF/TOF Mass Spectrometry. Targeted pair-wise analyses showed differences (p < 0.05) in 26 % of the pixels, which included pixels containing phosphorylated troponin T, myosin light chain, peroxiredoxin, and haptoglobin. These results show differences in rodent versus human cardiac remodeling which will influence the translation rodent studies to humans in this area.

FOXOs in the impaired heart: New therapeutic targets for cardiac diseases

Cardiac diseases have a high morbidity and mortality and affect the global population. Based on recent accumulating evidence, Forkhead box O (FOXOs) play important roles in cardiac diseases. Therefore, a summary of the current literature on the molecular mechanisms and roles of FOXOs in the heart will provide valuable information. In this review, we first briefly introduce the molecular features of FOXOs. Then, we discuss the regulation and cardiac actions of the FOXO pathways. Based on this background, we expand our discussion to the roles of FOXOs in several major cardiac diseases, such as ischemic cardiac diseases, diabetic cardiomyopathy and myocardial hypertrophy. Then, we describe some methodological problems associated with the FOXO gene-modified animal models. Finally, we discuss potential future directions. The information reviewed here may be significant for the design of future studies and may increase the potential of FOXOs as therapeutic targets.

Regulation of podoplanin expression by microRNA-29b associates with its antiapoptotic effect in angiotensin II-induced injury of human podocytes

BACKGROUND

Angiotensin (Ang)II is involved in induction of proteinuria, renal injury, and apoptosis and thus a major contributor to the development of chronic kidney disease. Podocytes are of major importance for the pathogenesis of several kidney diseases. Decrease of podoplanin (PDPN) in podocytes and podocyte loss has been associated with the development of proteinuria. Little is known about the regulation and biological function of PDPN in podocytes and its role in AngII-mediated kidney damage. Here, we determined the influence of AngII on the expression of PDPN, microRNA (miRNA)-29b and miRNA-497 in human podocytes. Further, we analyzed the impact of small interfering RNA-mediated downregulation of PDPN on AngII-induced apoptosis and viability. Moreover, we characterized the role of miRNA-29b and miRNA-497 in expression regulation of PDPN.

METHODS

Cell viability and apoptosis were determined by functional assays. Expression analyses were done via Real-Time PCR and western blot analyses. Dual luciferase assay was performed to characterize miRNA-mediated expression control.

RESULTS

AngII increased the expression of miRNA-29b and reduced PDPN. Small interfering RNA-mediated downregulation of PDPN increased proapoptotic caspase-3 activation and cytochrome C translocation, whereas cell viability and Akt phosphorylation were reduced in AngII-stimulated podocytes. In contrast to miRNA-497, transfection of cells with miRNA-29b mimics significantly decreased PDPN. Cotransfection of cells with miRNA-29b and a dual luciferase reporter vector decreased the luciferase activity compared with controls.

CONCLUSION

These data demonstrate the posttranscriptional control of PDPN expression by miRNA-29b and support a role of PDPN as an antiapoptotic prosurvival factor in AngII-induced injury of human podocytes.

Left ventricular pressure-volume measurements and myocardial gene expression profile in type 2 diabetic Goto-Kakizaki rats

The Goto-Kakizaki (GK) rat, a non-obese model of type 2 diabetes mellitus (T2DM), was generated by the selective inbreeding of glucose-intolerant Wistar rats. This is a convenient model for studying diabetes-induced cardiomyopathy independently from the effects of the metabolic syndrome. We investigated the myocardial functional and structural changes and underlying molecular pathomechanisms of short-term and mild T2DM. The presence of DM was confirmed by an impaired oral glucose tolerance in the GK rats compared with the age-matched nondiabetic Wistar rats. Data from cardiac catheterization showed that in GK rats, although the systolic indexes were not altered, the diastolic stiffness was increased compared with nondiabetics (end-diastolic-pressure-volume-relationship: 0.12 ± 0.04 vs. 0.05 ± 0.01 mmHg/μl, P < 0.05). Additionally, DM was associated with left-ventricular hypertrophy and histological evidence of increased myocardial fibrosis. The plasma pro-B-type natriuretic peptide, the cardiac troponin-T, glucose, and the urinary glucose concentrations were significantly higher in GK rats. Among the 125 genes surveyed using PCR arrays, DM significantly altered the expression of five genes [upregulation of natriuretic peptide precursor-A and connective tissue growth factor, downregulation of c-reactive protein, interleukin-1β, and tumor necrosis factor (TNF)-α mRNA-level]. Of the altered genes, which were evaluated by Western blot, only TNF-α protein expression was significantly decreased. The ECG recordings revealed no significant differences. In conclusion, while systolic dysfunction, myocardial inflammation, and abnormal electrical conduction remain absent, short-term and mild T2DM induce the alteration of cardiac TNF-α at both the mRNA and protein levels. Further assessments are required to reveal if TNF-α plays a role in the early stage of diabetic cardiomyopathy development.

Diabetic cardiomyopathy: role of the E3 ubiquitin ligase

Diabetic cardiomyopathy (DCM) is the leading cause of mortality in diabetes. As the number of cases of diabetes continues to rise, it is urgent to develop new strategies to protect against DCM, which is characterized by cardiac hypertrophy, increased apoptosis, fibrosis, and altered insulin metabolism. The E3 ubiquitin ligases (E3s), one component of the ubiquitin-proteasome system, play vital roles in all of the features of DCM listed above. They also modulate the activity of several transcription factors involved in the pathogenesis of DCM. In addition, the E3s degrade both insulin receptor and insulin receptor substrates and also regulate insulin gene transcription, leading to insulin resistance and insulin deficiency. Therefore, the E3s may be a driving force for DCM. This review summarizes currently available studies to analyze the roles of the E3s in DCM, enriches our knowledge of how DCM develops, and provides a novel strategy to protect heart from diabetes.

Metformin and Resveratrol Inhibited High Glucose-Induced Metabolic Memory of Endothelial Senescence through SIRT1/p300/p53/p21 Pathway

Endothelial senescence plays crucial roles in diabetic vascular complication. Recent evidence indicated that transient hyperglycaemia could potentiate persistent diabetic vascular complications, a phenomenon known as "metabolic memory." Although SIRT1 has been demonstrated to mediate high glucose-induced endothelial senescence, whether and how "metabolic memory" would affect endothelial senescence through SIRT1 signaling remains largely unknown. In this study, we investigated the involvement of SIRT1 axis as well as the protective effects of resveratrol (RSV) and metformin (MET), two potent SIRT1 activators, during the occurrence of "metabolic memory" of cellular senescence (senescent "memory"). Human umbilical vascular endothelial cells (HUVECs) were cultured in either normal glucose (NG)/high glucose (HG) media for 6 days, or 3 days of HG followed by 3 days of NG (HN), with or without RSV or MET treatment. It was shown that HN incubation triggered persistent downregulation of deacetylase SIRT1 and upregulation of acetyltransferase p300, leading to sustained hyperacetylation (at K382) and activation of p53, and subsequent p53/p21-mediated senescent "memory." In contrast, senescent "memory" was abrogated by overexpression of SIRT1 or knockdown of p300. Interestingly, we found that SIRT1 and p300 could regulate each other in response to HN stimulation, suggesting that a delicate balance between acetyltransferases and deacetylases may be particularly important for sustained acetylation and activation of non-histone proteins (such as p53), and eventually the occurrence of "metabolic memory." Furthermore, we found that RSV or MET treatment prevented senescent "memory" by modulating SIRT1/p300/p53/p21 pathway. Notably, early and continuous treatment of MET, but not RSV, was particularly important for preventing senescent "memory." In conclusion, short-term high glucose stimulation could induce sustained endothelial senescence via SIRT1/p300/p53/p21 pathway. RVS or MET treatment could enhance SIRT1-mediated signaling and thus protect against senescent "memory" independent of their glucose lowering mechanisms. Therefore, they may serve as promising therapeutic drugs against the development of "metabolic memory."

Asiatic acid inhibits left ventricular remodeling and improves cardiac function in a rat model of myocardial infarction

Left ventricular remodeling results in cardiac dysfunction and accounts for the majority of the morbidity and mortality following myocardial infarction (MI). The aim of the present study was to investigate the effect of asiatic acid (AA) on cardiac function and left ventricular remodeling in a rat model of MI and explore the underlying mechanisms. Rats were subjected to coronary artery ligation to model MI and orally treated with AA. After 4 weeks, cardiac function was assessed by echocardiography. Cardiomyocyte cross-sectional area was recorded, and the expression levels of a number of inflammatory cytokines were detected using ELISA. The degree of interstitial fibrosis was determined by evaluating the mRNA expression levels of collagen II and III. Western blot analysis was performed to detect the expression levels of total and phosphorylated p38 MAPK and ERK1/2, to investigate whether they are involved in the mechanism underlying the effect of AA on the heart. Rats subjected to MI displayed significantly impaired cardiac function compared with those subjected to a sham procedure, while this change was reversed by treatment with AA. Furthermore, AA markedly inhibited cardiac hypertrophy, reduced the mRNA expression levels of inflammatory cytokines and decreased interstitial fibrosis in the infarct border zone of MI model rats compared with those in vehicle-treated MI model rats. Furthermore, the phosphorylation of p38 MAPK and ERK1/2 was blocked by AA in the MI rats but not in the sham rats. In summary, AA treatment preserved cardiac function and inhibited left ventricular remodeling, potentially by blocking the phosphorylation of p38 MAPK and ERK1/2 in the infarct border zone of the ischemic myocardium, indicating that AA may be a novel candidate for development as a therapy for MI.

Reduced silent information regulator 1 signaling exacerbates myocardial ischemia-reperfusion injury in type 2 diabetic rats and the protective effect of melatonin

Diabetes mellitus (DM) increases myocardial oxidative stress and endoplasmic reticulum (ER) stress. Melatonin confers cardioprotective effect by suppressing oxidative damage. However, the effect and mechanism of melatonin on myocardial ischemia-reperfusion (MI/R) injury in type 2 diabetic state are still unknown. In this study, we developed high-fat diet-fed streptozotocin (HFD-STZ) rat, a well-known type 2 diabetic model, to evaluate the effect of melatonin on MI/R injury with a focus on silent information regulator 1 (SIRT1) signaling, oxidative stress, and PERK/eIF2α/ATF4-mediated ER stress. HFD-STZ treated rats were exposed to melatonin treatment in the presence or the absence of sirtinol (a SIRT1 inhibitor) and subjected to MI/R surgery. Compared with nondiabetic animals, type 2 diabetic rats exhibited significantly decreased myocardial SIRT1 signaling, increased apoptosis, enhanced oxidative stress, and ER stress. Additionally, further reduced SIRT1 signaling, aggravated oxidative damage, and ER stress were found in diabetic animals subjected to MI/R surgery. Melatonin markedly reduced MI/R injury by improving cardiac functional recovery and decreasing myocardial apoptosis in type 2 diabetic animals. Melatonin treatment up-regulated SIRT1 expression, reduced oxidative damage, and suppressed PERK/eIF2α/ATF4 signaling. However, these effects were all attenuated by SIRT1 inhibition. Melatonin also protected high glucose/high fat cultured H9C2 cardiomyocytes against simulated ischemia-reperfusion injury-induced ER stress by activating SIRT1 signaling while SIRT1 siRNA blunted this action. Taken together, our study demonstrates that reduced cardiac SIRT1 signaling in type 2 diabetic state aggravates MI/R injury. Melatonin ameliorates reperfusion-induced oxidative stress and ER stress via activation of SIRT1 signaling, thus reducing MI/R damage and improving cardiac function.

SIRT1: role in cardiovascular biology

SIRT1 (silent information regulator two protein) is a type III protein deacetylase that regulates a variety of important metabolic and physiologic processes including stress resistance, metabolism, apoptosis and energy balance. It reverses cholesterol transport and reduces risk for development of atherosclerosis and cardiovascular disease. The following review highlights the potential role of SIRT1 on cardiovascular biology and function.

Impaired cardiac anti-oxidant activity in diabetes: human and correlative experimental studies

Increased reactive oxygen species (ROS) are traditionally viewed as arising from the metabolic flux of diabetes, although reduction in the activity of anti-oxidant systems has also been implicated. Among the latter is the major thiol reducing thioredoxin system, the activity of which may be diminished by high glucose-induced expression of its endogenous inhibitor, thioredoxin interacting protein (TxnIP). We assessed TxnIP mRNA/protein expression along with thioredoxin activity in human right atrial biopsy specimens from subjects with and without diabetes undergoing coronary artery grafting. In correlative experimental studies, we examined TxnIP expression in both type 1 and type 2 rodent models of diabetic cardiomyopathy. Finally, we used in vitro gene silencing to determine the contribution of changes in TxnIP abundance to the high glucose-induced reduction in thioredoxin activity. In human right atrial biopsies, diabetes was associated with a >30-fold increase in TxnIP gene expression and a 17 % increase in TxnIP protein expression (both p < 0.05). This was associated with a 21 % reduction in thioredoxin activity when compared to human non-diabetic cardiac biopsy samples (all p < 0.05). In correlative animal studies, both type 1 and type 2 diabetic rats demonstrated a significant increase in TxnIP mRNA and reduction in thioredoxin activity when compared to non-diabetic animals (all p < 0.05). This was associated with a significant increase in ROS (p < 0.05 when compared with control). In cultured cardiac myocytes, high glucose increased ROS and TxnIP mRNA expression, in association with a reduction in thioredoxin activity (p < 0.01). These findings were abrogated by TxnIP small interfering RNA (siRNA). Scrambled siRNA had no effect upon ROS or TxnIP expression. High glucose reduces thioredoxin activity and increases ROS via TxnIP overexpression. These findings suggest that impaired thiol reductive capacity, through altered TxnIP expression, contributes to increased ROS in the diabetic heart.

Diabetic cardiomyopathy: mechanisms and new treatment strategies targeting antioxidant signaling pathways

Cardiovascular disease is the primary cause of morbidity and mortality among the diabetic population. Both experimental and clinical evidence suggest that diabetic subjects are predisposed to a distinct cardiomyopathy, independent of concomitant macro- and microvascular disorders. 'Diabetic cardiomyopathy' is characterized by early impairments in diastolic function, accompanied by the development of cardiomyocyte hypertrophy, myocardial fibrosis and cardiomyocyte apoptosis. The pathophysiology underlying diabetes-induced cardiac damage is complex and multifactorial, with elevated oxidative stress as a key contributor. We now review the current evidence of molecular disturbances present in the diabetic heart, and their role in the development of diabetes-induced impairments in myocardial function and structure. Our focus incorporates both the contribution of increased reactive oxygen species production and reduced antioxidant defenses to diabetic cardiomyopathy, together with modulation of protein signaling pathways and the emerging role of protein O-GlcNAcylation and miRNA dysregulation in the progression of diabetic heart disease. Lastly, we discuss both conventional and novel therapeutic approaches for the treatment of left ventricular dysfunction in diabetic patients, from inhibition of the renin-angiotensin-aldosterone-system, through recent evidence favoring supplementation of endogenous antioxidants for the treatment of diabetic cardiomyopathy. Novel therapeutic strategies, such as gene therapy targeting the phosphoinositide 3-kinase PI3K(p110α) signaling pathway, and miRNA dysregulation, are also reviewed. Targeting redox stress and protective protein signaling pathways may represent a future strategy for combating the ever-increasing incidence of heart failure in the diabetic population.

Sirtuin 1 is upregulated in young obese Zucker rat cerebral arteries

Many diseases, including metabolic syndrome, are characterised by endothelial dysfunction mediated by reduced nitric oxide bioavailability and oxidative stress. Sirtuin 1 is a protein deacetylase that targets endothelial nitric oxide synthase resulting in enhanced nitric oxide bioavailability. Although it has been highlighted as a potential therapeutic target, we still have no understanding of vascular SIRT1 changes during obesity. Therefore, the aim of the present study was to measure vascular function, SIRT1 protein levels of expression and markers of oxidative stress in obese Zucker rats. Middle cerebral arteries from nondiabetic obese and lean Zucker rats were mounted in a pressure myograph to assess nitric oxide-dependent dilations. Western blotting was used to measure protein levels of SIRT1, p53, acetylated p53, eNOS, phosphorylated eNOS and markers of oxidative stress (nitrotyrosine, Nox4 and SOD2) in cerebral vascular tissue. SIRT1 expression was two-fold greater in both cerebral arteries and aorta from obese compared to lean Zucker rats. Acetylation of p53 at the SIRT1-specific lysine 379 site was markedly decreased. At the same time, there was noted cerebral vascular impairment however markers of oxidative stress were not increased. In fact, Nox4 appeared to be downregulated in obesity. Thus, SIRT1 protein levels within the vasculature are greater in obese compared to lean Zucker rats and are associated with higher SIRT1 activity and lower Nox4 expression. We propose that the increased expression and activity of SIRT1 may be a vascular adaptive mechanism in obesity, aiming to prevent oxidative stress.

Diabetic cardiomyopathy: pathophysiology and clinical features

Since diabetic cardiomyopathy was first reported four decades ago, substantial information on its pathogenesis and clinical features has accumulated. In the heart, diabetes enhances fatty acid metabolism, suppresses glucose oxidation, and modifies intracellular signaling, leading to impairments in multiple steps of excitation–contraction coupling, inefficient energy production, and increased susceptibility to ischemia/reperfusion injury. Loss of normal microvessels and remodeling of the extracellular matrix are also involved in contractile dysfunction of diabetic hearts. Use of sensitive echocardiographic techniques (tissue Doppler imaging and strain rate imaging) and magnetic resonance spectroscopy enables detection of diabetic cardiomyopathy at an early stage, and a combination of the modalities allows differentiation of this type of cardiomyopathy from other organic heart diseases. Circumstantial evidence to date indicates that diabetic cardiomyopathy is a common but frequently unrecognized pathological process in asymptomatic diabetic patients. However, a strategy for prevention or treatment of diabetic cardiomyopathy to improve its prognosis has not yet been established. Here, we review both basic and clinical studies on diabetic cardiomyopathy and summarize problems remaining to be solved for improving management of this type of cardiomyopathy.

Sirtuin 1 and sirtuin 3: physiological modulators of metabolism

The sirtuins are a family of highly conserved NAD(+)-dependent deacetylases that act as cellular sensors to detect energy availability and modulate metabolic processes. Two sirtuins that are central to the control of metabolic processes are mammalian sirtuin 1 (SIRT1) and sirtuin 3 (SIRT3), which are localized to the nucleus and mitochondria, respectively. Both are activated by high NAD(+) levels, a condition caused by low cellular energy status. By deacetylating a variety of proteins that induce catabolic processes while inhibiting anabolic processes, SIRT1 and SIRT3 coordinately increase cellular energy stores and ultimately maintain cellular energy homeostasis. Defects in the pathways controlled by SIRT1 and SIRT3 are known to result in various metabolic disorders. Consequently, activation of sirtuins by genetic or pharmacological means can elicit multiple metabolic benefits that protect mice from diet-induced obesity, type 2 diabetes, and nonalcoholic fatty liver disease.

Phosphoprotein abundance changes in hypertensive cardiac remodeling

There is over-whelming evidence that protein phosphorylations regulate cardiac function and remodeling. A wide variety of protein kinases, e.g., phosphoinositide 3-kinase (PI3K), Akt, GSK-3, TGFβ, and PKA, MAPKs, PKC, Erks, and Jaks, as well as phosphatases, e.g., phosphatase I (PP1) and calcineurin, control cardiomyocyte growth and contractility. In the present work, we used global phosphoprotein profiling to identify phosphorylated proteins associated with pressure overload (PO) cardiac hypertrophy and heart failure. Phosphoproteins from hypertrophic and systolic failing hearts from male hypertensive Dahl salt-sensitive rats, trans-aortic banded (TAC), and spontaneously hypertensive heart failure (SHHF) rats were analyzed. Profiling was performed by 2-dimensional difference in gel electrophoresis (2D-DIGE) on phospho-enriched proteins. A total of 25 common phosphoproteins with differences in abundance in (1) the 3 hypertrophic and/or (2) the 2 systolic failure heart models were identified (CI>99%) by matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) and Mascot analysis. Among these were (1) myofilament proteins, including alpha-tropomyosin and myosin regulatory light chain 2, cap Z interacting protein (cap ZIP), and tubulin β5; (2) mitochondrial proteins, including pyruvate dehydrogenase α, branch chain ketoacid dehydrogenase E1, and mitochondrial creatine kinase; (3) phosphatases, including protein phosphatase 2A and protein phosphatase 1 regulatory subunit; and (4) other proteins including proteosome subunits α type 3 and β type 7, and eukaryotic translation initiation factor 1A (eIF1A). The results include previously described and novel phosphoproteins in cardiac hypertrophy and systolic failure.

Caloric restriction ameliorates angiotensin II-induced mitochondrial remodeling and cardiac hypertrophy

Angiotensin II-induced cardiac damage is associated with oxidative stress-dependent mitochondrial dysfunction. Caloric restriction (CR), a dietary regimen that increases mitochondrial activity and cellular stress resistance, could provide protection. We tested that hypothesis in double transgenic rats harboring human renin and angiotensinogen genes (dTGRs). CR (60% of energy intake for 4 weeks) decreased mortality in dTGRs. CR ameliorated angiotensin II-induced cardiomyocyte hypertrophy, vascular inflammation, cardiac damage and fibrosis, cardiomyocyte apoptosis, and cardiac atrial natriuretic peptide mRNA overexpression. The effects were blood pressure independent and were linked to increased endoplasmic reticulum stress, autophagy, serum adiponectin level, and 5' AMP-activated protein kinase phosphorylation. CR decreased cardiac p38 phosphorylation, nitrotyrosine expression, and serum insulin-like growth factor 1 levels. Mitochondria from dTGR hearts showed clustered mitochondrial patterns, decreased numbers, and volume fractions but increased trans-sectional areas. All of these effects were reduced in CR dTGRs. Mitochondrial proteomic profiling identified 43 dTGR proteins and 42 Sprague-Dawley proteins, of which 29 proteins were in common in response to CR. We identified 7 proteins in CR dTGRs that were not found in control dTGRs. In contrast, 6 mitochondrial proteins were identified from dTGRs that were not detected in any other group. Gene ontology annotations with the Panther protein classification system revealed downregulation of cytoskeletal proteins and enzyme modulators and upregulation of oxidoreductase activity in dTGRs. CR provides powerful, blood pressure-independent, protection against angiotensin II-induced mitochondrial remodeling and cardiac hypertrophy. The findings support the notion of modulating cardiac bioenergetics to ameliorate angiotensin II-induced cardiovascular complications.

Calorie restriction and resveratrol in cardiovascular health and disease

Calorie restriction is one of the most effective nutritional interventions that reproducibly protects against obesity, diabetes and cardiovascular disease. Recent evidence suggests that even when implemented over a short period, calorie restriction is a safe and effective treatment for cardiovascular disease. Herein, we review the effects of calorie restriction on the cardiovascular system as well as the biological effects of resveratrol, the most widely studied molecule that appears to mimic calorie restriction. An overview of microarray data reveals that the myocardial transcriptional effects of calorie restriction overlap with the transcriptional responses to resveratrol treatment. In addition, calorie restriction and resveratrol modulate similar pathways to improve mitochondrial function, reduce oxidative stress and increase nitric oxide production that are involved in atherosclerosis prevention, blood pressure reduction, attenuation of left-ventricular hypertrophy, resistance to myocardial ischemic injury and heart failure prevention. We also review the data that suggest that the effects of calorie restriction and resveratrol on the cardiovascular system may involve signaling through the silent information regulator of transcription (SIRT), Akt and the AMP-activated protein kinase (AMPK) pathways. While accumulating data demonstrate the health benefits of calorie restriction and resveratrol in experimental animal models, whether these interventions translate to patients with cardiovascular disease remains to be determined.

Upregulation of SIRT1 deacetylase in phenylephrine-treated cardiomyoblasts

The sirtuin SIRT1 is an ubiquitous NAD(+) dependent deacetylase that plays a role in biological processes such as longevity and stress response. In cardiac models, SIRT1 is associated to protection against many stresses. However, the link between SIRT1 and heart hypertrophy is complex and not fully understood. This study focuses specifically on the response of SIRT1 to the α-adrenergic agonist phenylephrine in H9c2 cardiac myoblasts, a cell model of cardiac hypertrophy. After 24 and 48h of phenylephrine treatment, SIRT1 expression and deacetylase activity were significantly increased. SIRT1 upregulation by phenylephrine was not associated to changes in NAD(+) levels, but was blocked by inhibitors of AMP-activated Protein Kinase (AMPK) or by AMPK knockdown by siRNA. When SIRT1 was inhibited with sirtinol or downregulated by siRNA, H9c2 cell viability was significantly decreased following phenylephrine treatment, showing that SIRT1 improves cell survival under hypertrophic stress. We so then propose that the increase in SIRT1 activity and expression in H9c2 cells treated with phenylephrine is an adaptive response to the hypertrophic stress, suggesting that adrenergic stimulation of heart cells activates hypertrophic programming and at the same time also promotes a self-protecting and self-regulating mechanism.

Emerging roles of SIRT1 deacetylase in regulating cardiomyocyte survival and hypertrophy

Calorie restriction is considered to be the best environmental intervention providing health benefits to mammals. The underlying mechanism of this intervention seems to be controlled by a group of NAD-dependent deacetylases, collectively called sirtuins. In mammals, there are seven sirtuin analogs, SIRT1-SIRT7. The founding member of this family, SIRT1, is shown to protect cardiomyocytes from apoptosis and age-dependent degeneration in a dose dependent manner-protecting cells at low doses but showing detrimental effects at high doses. Studies performed with overexpression or knockdown of SIRT1 indicated that, although it protects cells from oxidative stress and ischemia-reperfusion injury, it promotes hypertrophy of cardiomyocytes. Activation of endogenous SIRT1 by resveratrol also displayed pro-survival and pro-hypertrophic activity of SIRT1. In this article, we review recent findings documenting the role of SIRT1 in regulating cardiac myocyte growth and survival under stress, and the proposed mechanism behind its cardioprotective effects. We also briefly discuss two other sirtuin analogs which have been shown to have cardioprotective effects. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure".

Resveratrol induces mitochondrial biogenesis and ameliorates Ang II-induced cardiac remodeling in transgenic rats harboring human renin and angiotensinogen genes

There is compelling evidence to indicate an important role for increased local renin-angiotensin system activity in the pathogenesis of cardiac hypertrophy and heart failure. Resveratrol is a natural polyphenol that activates SIRT1, a novel cardioprotective and longevity factor having NAD(+)-dependent histone deacetylase activity. We tested the hypothesis whether resveratrol could prevent from angiotensin II (Ang II)-induced cardiovascular damage. Four-week-old double transgenic rats harboring human renin and human angiotensinogen genes (dTGR) were treated for 4 weeks either with SIRT1 activator resveratrol or SIRT1 inhibitor nicotinamide. Untreated dTGR and their normotensive Sprague-Dawley control rats (SD) received vehicle. Untreated dTGR developed severe hypertension as well as cardiac hypertrophy, and showed pronounced cardiovascular mortality compared with normotensive SD rats. Resveratrol slightly but significantly decreased blood pressure, ameliorated cardiac hypertrophy and prevented completely Ang II-induced mortality, whereas nicotinamide increased blood pressure without significantly influencing cardiac hypertrophy or survival. Resveratrol decreased cardiac ANP mRNA expression and induced cardiac mRNA expressions of mitochondrial biogenesis markers peroxisome proliferator-activated receptor-gamma coactivator (PGC-1alpha), mitochondrial transcription factor (Tfam), nuclear respiratory factor 1 (NRF-1) and cytochrome c oxidase subunit 4 (cox4). Resveratrol dose-dependently increased SIRT1 activity in vitro. Our findings suggest that the beneficial effects of SIRT1 activator resveratrol on Ang II-induced cardiac remodeling are mediated by blood pressure-dependent pathways and are linked to increased mitochondrial biogenesis.

Effects of the calcium sensitizer OR-1896, a metabolite of levosimendan, on post-infarct heart failure and cardiac remodelling in diabetic Goto-Kakizaki rats

BACKGROUND AND PURPOSE

Levosimendan is a novel, short half-life calcium sensitizer used as pharmacological inotropic support in acute decompensated heart failure. After oral administration, levosimendan is metabolized to OR-1855, which, in rats, is further metabolized into OR-1896. OR-1896 is a long-lasting metabolite of levosimendan sharing the pharmacological properties of the parent compound.

EXPERIMENTAL APPROACH

Effects of oral OR-1896 treatment on post-infarct heart failure and cardiac remodelling were assessed in diabetic Goto-Kakizaki (GK) rats, an animal model of type II diabetes. Myocardial infarction (MI) was produced to GK rats by coronary ligation. Twenty-four hours after MI or sham operation, the rats were randomized into four groups: (i) MI; (ii) MI + OR-1896 treatment; (iii) sham; and (iv) sham + OR-1896. Cardiac function and markers of cardiac remodelling were assessed 1, 4 and 12 weeks after MI.

KEY RESULTS

OR-1896 increased ejection fraction and fractional shortening in GK rats with MI. OR-1896 ameliorated post-infarct cardiac hypertrophy, and prevented the MI-induced increase in cardiac mRNA for atrial natriuretic peptide, monocyte chemoattractant protein-1 and connective tissue growth factor, markers of pressure/volume overload, inflammation and fibrosis respectively. OR-1896 also suppressed mRNA for senescence-associated p16(INK4A) and p19(ARF). The beneficial effects of OR-1896 were more prominent at week 12 than at week 4. OR-1896 did not influence systolic blood pressure, blood glucose level, myocardial infarct size or cardiovascular mortality.

CONCLUSIONS AND IMPLICATIONS

Oral treatment with calcium sensitizer OR-1896 protects against post-infarct heart failure and cardiac remodelling in experimental model of type II diabetes.

Resveratrol, an activator of SIRT1, upregulates sarcoplasmic calcium ATPase and improves cardiac function in diabetic cardiomyopathy

Reduced sarcoplasmic calcium ATPase (SERCA2a) expression has been shown to play a significant role in the cardiac dysfunction in diabetic cardiomyopathy. The mechanism of SERCA2a repression is, however, not known. This study was designed to examine the effect of resveratrol (RSV), a potent activator of SIRT1, on cardiac function and SERCA2a expression in chronic type 1 diabetes. Adult male mice were injected with streptozotocin (STZ) and fed with either a regular diet or a diet enriched with RSV. STZ administration produced progressive decline in cardiac function, associated with markedly reduced SERCA2a and SIRT1 protein levels and increased collagen deposition; RSV treatment to these mice had a tremendous beneficial effect both in terms of improving SERCA2a expression and on cardiac function. In cultured cardiomyocytes, RSV restored SERCA2 promoter activity, which was otherwise highly repressed in high-glucose media. Protective effects of RSV were found to be dependent on its ability to activate Silent information regulator (SIRT) 1. In cardiomyocytes, overexpression of SIRT1 was found sufficient to activate SERCA2 promoter in a dose-dependent manner. In contrast, pretreatment of cardiomyocytes with SIRT1 antagonist, splitomycin, blocked these beneficial effects of RSV. In addition, SIRT1 knockout (+/-) mice were also found to be more sensitive to STZ-induced decline in SERCA2a mRNA. The data demonstrate that, in chronic diabetes, 1) the enzymatic activity of cardiac SIRT1 is reduced, which contributes to reduced expression of SERCA2a and 2) through activation of SIRT1, RSV enhances expression of SERCA2a and improves cardiac function.

Oral levosimendan prevents postinfarct heart failure and cardiac remodeling in diabetic Goto-Kakizaki rats

BACKGROUND

Diabetes increases the risk for fatal myocardial infarction and development of heart failure. Levosimendan, an inodilator acting both via calcium sensitization and opening of ATP-dependent potassium channels, is used intravenously for acute decompensated heart failure. The long-term effects of oral levosimendan on postinfarct heart failure are largely unknown.

OBJECTIVE

To examine whether oral treatment with levosimendan could improve cardiac functions and prevent cardiac remodeling after myocardial infarction in a rodent model of type 2 diabetes, the Goto-Kakizaki rat.

METHODS

Myocardial infarction (MI) was induced to diabetic Goto-Kakizaki and nondiabetic Wistar rats by coronary ligation. Twenty-four hours after surgery, Goto-Kakizaki and Wistar rats were randomized into four groups: MI group without treatment, MI group with levosimendan for 12 weeks (1 mg/kg per day), sham-operated group, sham-operated group with levosimendan. Blood pressure, cardiac functions as wells as markers of cardiac remodeling were determined.

RESULTS

In Goto-Kakizaki rats, MI induced systolic heart failure, pronounced cardiac hypertrophy in the remote area, and sustained cardiomyocyte apoptosis. Postinfarct cardiac remodeling was associated with increased atrial natriuretic peptide, interleukin-6 and connective tissue growth factor mRNA expressions, as well as three-fold increased cardiomyocyte senescence, measured as cardiac p16 mRNA expression. Levosimendan improved cardiac function and prevented postinfarct cardiomyocyte hypertrophy, cardiomyocyte apoptosis, and cellular senescence. Levosimendan also ameliorated MI-induced atrial natriuretic peptide, IL-6, and connective tissue growth factor overexpression as well as MI-induced disturbances in calcium-handling proteins (SERCA2, Na-Ca exchanger) without changes in diabetic status or systemic blood pressure. In nondiabetic Wistar rats, MI induced systolic heart failure; however, the postinfarct cardiac remodeling was associated with less pronounced cardiac hypertrophy, cardiomyocyte apoptosis, inflammatory reaction, and induction of cellular senescence. Levosimendan only partially prevented postinfarct heart failure and cardiac remodeling in Wistar rats.

CONCLUSION

Our findings suggest a therapeutic role for oral levosimendan in prevention of postinfarct heart failure and cardiac remodeling in type 2 diabetes and underscore the importance of sustained cardiomyocyte apoptosis and induction of cellular senescence in the pathogenesis.

Sirtuin1-p53, forkhead box O3a, p38 and post-infarct cardiac remodeling in the spontaneously diabetic Goto-Kakizaki rat

Background

Diabetes is associated with changes in myocardial stress-response pathways and is recognized as an independent risk factor for cardiac remodeling. Using spontaneously diabetic Goto Kakizaki rats as a model of type 2 DM we investigated whether post-translational modifications in the Akt - FOXO3a pathway, Sirt1 - p53 pathway and the mitogen activated protein kinase p38 regulator are involved in post-infarct cardiac remodeling

Methods

Experimental myocardial infarction (MI) was induced by left anterior descending coronary artery ligation in spontaneously diabetic Goto-Kakizaki rats and non-diabetic Wistar controls. Cardiac function was studied by echocardiography. Myocardial hypertrophy, cardiomyocyte apoptosis and cardiac fibrosis were determined histologically 12 weeks post MI or Sham operation. Western blotting was used to study Caspase-3, Bax, Sirt1, acetylation of p53 and phosphorylation of p38, Akt and FOXO3a. Electrophoretic mobility shift assay was used to assess FOXO3a activity and its nuclear localization.

Results

Post-infarct heart failure in diabetic GK rats was associated with pronounced cardiomyocyte hypertrophy, increased interstitial fibrosis and sustained cardiomyocyte apoptosis as compared with their non-diabetic Wistar controls. In the GK rat myocardium, Akt- and FOXO3a-phosphorylation was decreased and nuclear localization of FOXO3a was increased concomitantly with increased PTEN protein expression. Furthermore, increased Sirt1 protein expression was associated with decreased p53 acetylation, and phosphorylation of p38 was increased in diabetic rats with MI.

Conclusions

Post-infarct heart failure in diabetic GK rats was associated with more pronounced cardiac hypertrophy, interstitial fibrosis and sustained cardiomyocyte apoptosis as compared to their non-diabetic controls. The present study suggests important roles for Akt-FOXO3a, Sirt1 - p53 and p38 MAPK in the regulation of post-infarct cardiac remodeling in type 2 diabetes.

Local IGF-1 isoform protects cardiomyocytes from hypertrophic and oxidative stresses via SirT1 activity

Oxidative and hypertrophic stresses contribute to the pathogenesis of heart failure. Insulin-like growth factor-1 (IGF-1) is a peptide hormone with a complex post-transcriptional regulation, generating distinct isoforms. Locally acting IGF-1 isoform (mIGF-1) helps the heart to recover from toxic injury and from infarct. In the murine heart, moderate overexpression of the NAD⁺-dependent deacetylase SirT1 was reported to mitigate oxidative stress. SirT1 is known to promote lifespan extension and to protect from metabolic challenges. Circulating IGF-1 and SirT1 play antagonizing biological roles and share molecular targets in the heart, in turn affecting cardiomyocyte physiology. However, how different IGF-1 isoforms may impact SirT1 and affect cardiomyocyte function is unknown. Here we show that locally acting mIGF-1 increases SirT1 expression/activity, whereas circulating IGF-1 isoform does not affect it, in cultured HL-1 and neonatal cardiomyocytes. mIGF-1-induced SirT1 activity exerts protection against angiotensin II (Ang II)-triggered hypertrophy and against paraquat (PQ) and Ang II-induced oxidative stress. Conversely, circulating IGF-1 triggered itself oxidative stress and cardiomyocyte hypertrophy. Interestingly, potent cardio-protective genes (adiponectin, UCP-1 and MT-2) were increased specifically in mIGF-1-overexpressing cardiomyocytes, in a SirT1-dependent fashion. Thus, mIGF-1 protects cardiomyocytes from oxidative and hypertrophic stresses via SirT1 activity, and may represent a promising cardiac therapeutic.

Sirtuins--novel therapeutic targets to treat age-associated diseases

Sirtuins post-translationally modulate the function of many cellular proteins that undergo reversible acetylation-deacetylation cycles, affecting physiological responses that have implications for treating diseases of ageing. Potent small-molecule modulators of sirtuins have shown efficacy in preclinical models of metabolic, neurodegenerative and inflammatory diseases, and so hold promise for drug discovery efforts in multiple therapeutic areas. Here, we discuss current knowledge and data that strengthens sirtuins as a druggable set of enzymes for the treatment of age-associated diseases, including activation of SIRT1 in type 2 diabetes.

Broad profiling of DNA-binding transcription factor activities improves regulatory network construction in adult mouse tissues

Molecular systematics involves the description of the regulatory networks formed by the interconnections between active transcription factors and their target expressed genes. Here, we have determined the activities of 200 different transcription factors in six mouse tissues using an advanced mouse oligonucleotide array-based transcription factor assay (MOUSE OATFA). The transcription factor signatures from MOUSE OATFA were combined with public mRNA expression profiles to construct experimental transcriptional regulatory networks in each tissue. SRF-centered regulatory networks constructed for lung and skeletal muscle with OATFA data were confirmed by ChIP assays, and revealed examples of novel networks of expressed genes coregulated by sets of transcription factors. The combination of MOUSE OATFA with bioinformatics analysis of expressed genes provides a new paradigm for the comprehensive prediction of the transcriptional systems and their regulatory pathways in mouse.

Molecular regulation of cardiac hypertrophy

Heart failure is one of the leading causes of mortality in the western world and encompasses a wide spectrum of cardiac pathologies. When the heart experiences extended periods of elevated workload, it undergoes hypertrophic enlargement in response to the increased demand. Cardiovascular disease, such as that caused by myocardial infarction, obesity or drug abuse promotes cardiac myocyte hypertrophy and subsequent heart failure. A number of signalling modulators in the vasculature milieu are known to regulate heart mass including those that influence gene expression, apoptosis, cytokine release and growth factor signalling. Recent evidence using genetic and cellular models of cardiac hypertrophy suggests that pathological hypertrophy can be prevented or reversed and has promoted an enormous drive in drug discovery research aiming to identify novel and specific regulators of hypertrophy. In this review we describe the molecular characteristics of cardiac hypertrophy such as the aberrant re-expression of the fetal gene program. We discuss the various molecular pathways responsible for the co-ordinated control of the hypertrophic program including: natriuretic peptides, the adrenergic system, adhesion and cytoskeletal proteins, IL-6 cytokine family, MEK-ERK1/2 signalling, histone acetylation, calcium-mediated modulation and the exciting recent discovery of the role of microRNAs in controlling cardiac hypertrophy. Characterisation of the signalling pathways leading to cardiac hypertrophy has led to a wealth of knowledge about this condition both physiological and pathological. The challenge will be translating this knowledge into potential pharmacological therapies for the treatment of cardiac pathologies.