Downregulation in GATA4 and Downstream Structural and Contractile Genes in the db/db Mouse Heart

Mesenchymal Stem Cell Transplantation Has a Regenerative Effect in Ischemic Myocardium: An Experimental Rat Model Evaluated by SPECT-CT Assessment

Translational perspective: Ischemic heart disease remains a major medical problem with high mortality rates. Beside the great efforts devoted to research worldwide and the use of numerous experimental models, an absolute understanding of myocardial infarction and tissue loss has not yet been achieved. Furthermore, the regeneration of myocardial tissue and the improvement of myocardial activity after ischemia is one of the major areas of interest in the medical (and especially cardiovascular) community. In a novel experimental rat model, the beneficial effect of mesenchymal stem cell transplantation (MSCT) in a surgically induced ischemic myocardium was documented. From a clinical perspective, this work supports the surgical administration of MSCT in the infarcted area during coronary artery bypass surgery.

AIMS

The regeneration of myocardial tissue and the improvement of myocardial activity after ischemia is one of the major areas of interest in cardiovascular research. We developed a novel experimental rat model and used it to examine the effect of mesenchymal stem cell transplantation (MSCT) on myocardial ischemia evaluated by SPECT-CT and immunohistochemistry.

METHODS AND RESULTS

An open thoracotomy took place for forty adult female Wistar rats with (n = 30) or without (n = 10) surgical ligation of the left anterior descending coronary artery (LAD) in order to cause myocardial ischemia. Myocardial viability was evaluated via SPECT/CT 7 days before surgery, as well as at 7 and 14 days post-surgery. At day 0, 15 animals received homologous stem cells injected at the ischemic myocardium area. A SPECT/CT evaluation showed decreased activity of the myocardial cells in the left ventricle one week post-infarction. Regeneration of the ischemic myocardium fifteen days post-infarction was recorded only in animals subjected to stem cell transplantation. These findings were also confirmed by histology and immunohistochemical analysis, with the significantly higher expression of GATA4 and Nkx2.5.

CONCLUSIONS

The positive effect of mesenchymal stem cell transplantation in the ischemic myocardium was recorded. The application of SPECT-CT allowed a clear evaluation of both the quality and quantity of the living myocardium post-infarction, leading to a new approach in the research of cardiovascular diseases. From a clinical perspective, MSCT may be beneficial when accompanied by myocardial revascularization procedures.

Cytokine receptor gp130 promotes postnatal proliferation of cardiomyocytes required for the normal functional development of the heart

Mammalian ventricular cardiomyocytes are premature at birth and exhibit substantial phenotypic changes before weaning. Mouse ventricular myocytes undergo cell division several times after birth; however, the regulatory mechanisms and roles of cardiomyocyte division in postnatal heart development remain unclear. Here, we investigated the physiological role of gp130, the main subunit of multifunctional receptors for the IL-6 family of cytokines, in postnatal cardiomyocyte proliferation. Pharmacological inhibition of gp130 within the first month after birth induced significant systolic dysfunction of the left ventricle in mice. Consistently, mice with postnatal cardiomyocyte-specific gp130 depletion exhibited impaired left ventricular contractility compared to control mice. In these mice, cardiomyocytes exhibited a moderately decreased size and dramatically inhibited proliferation in the left ventricle but not in the right ventricle. Stereological analysis revealed that this change significantly decreased the number of cardiomyocytes in the left ventricle. Furthermore, IL-6 was mainly responsible for promoting ventricular cardiomyocyte proliferation by activating the JAK/STAT3 pathway. Taken together, the IL-6/gp130/JAK/STAT3 axis plays a crucial role in the physiological postnatal proliferation and hypertrophy of left ventricular cardiomyocytes to ensure normal cardiac functional development.

Age and Sex Differences in Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is a multi-organ disorder that represents about 50% of total heart failure (HF) cases and is the most common form of HF in the elderly. Because of its increasing prevalence caused by the aging population, high mortality and morbidity, and very limited therapeutic options, HFpEF is considered as one of the greatest unmet medical needs in cardiovascular medicine. Despite its complex pathophysiology, numerous preclinical models have been established in rodents and in large animals to study HFpEF pathophysiology. Although age and sex differences are well described in HFpEF population, there are knowledge gaps in sex- and age-specific differences in established preclinical models. In this review, we summarize various strategies that have been used to develop HFpEF models and discuss the knowledge gaps in sex and age differences in HFpEF.

Heart failure with preserved ejection fraction in humans and mice: embracing clinical complexity in mouse models

Heart failure (HF) with preserved ejection fraction (HFpEF) is a multifactorial disease accounting for a large and increasing proportion of all clinical HF presentations. As a clinical syndrome, HFpEF is characterized by typical signs and symptoms of HF, a distinct cardiac phenotype and raised natriuretic peptides. Non-cardiac comorbidities frequently co-exist and contribute to the pathophysiology of HFpEF. To date, no therapy has proven to improve outcomes in HFpEF, with drug development hampered, at least partly, by lack of consensus on appropriate standards for pre-clinical HFpEF models. Recently, two clinical algorithms (HFA-PEFF and H₂FPEF scores) have been developed to improve and standardize the diagnosis of HFpEF. In this review, we evaluate the translational utility of HFpEF mouse models in the context of these HFpEF scores. We systematically recorded evidence of symptoms and signs of HF or clinical HFpEF features and included several cardiac and extra-cardiac parameters as well as age and sex for each HFpEF mouse model. We found that most of the pre-clinical HFpEF models do not meet the HFpEF clinical criteria, although some multifactorial models resemble human HFpEF to a reasonable extent. We therefore conclude that to optimize the translational value of mouse models to human HFpEF, a novel approach for the development of pre-clinical HFpEF models is needed, taking into account the complex HFpEF pathophysiology in humans.

Ambient air PM2.5 exposure induces heart injury and cardiac hypertrophy in rats through regulation of miR-208a/b, α/β-MHC, and GATA4

Ambient air fine particulate matter (PM2.5) may increase cardiovascular disease risks. In this study, we investigated the miR-208/GATA4/myosin heavy chain (MHC) regulation mechanisms on cardiac injury in rats after PM2.5 exposure via an animal inhalation device. The results showed that PM2.5 exposure for 2 months caused pathological heart injury, reduced nucleus-cytoplasm ratio, and increased the levels of CK-MB and cTnI, showing cardiac hypertrophy. Oxidative stress and inflammatory responses were also observed in rats' hearts exposed to PM2.5. Of note, PM2.5 exposure for 2-month significantly elevated GATA4 and β-MHC mRNA and protein expression compared with the corresponding controls, along with the high-expression of miR-208b. The ratios of β-MHC/α-MHC expression induced by PM2.5 were remarkably raised in comparison to their controls. It suggested that the up-regulation of miR-208b/β-MHC and GATA4 and the conversion from α-MHC to β-MHC may be the important causes of cardiac hypertrophy in rats incurred by PM2.5.

The transcriptional factor GATA-4 negatively regulates Hsp70 transcription in Crassostrea hongkongensis

To better explore the application potential of heat shock protein Hsp70s in diverse areas including biomonitoring, a further investigation of the details of the regulatory mechanism governing Hsp70 transcription is required. A transcriptional factor ChGATA-4 that displayed affinity to the ChHsp70 promoter of Crassostrea hongkongensis was isolated and identified by DNA affinity purification as well as mass spectrometry analysis. The ChGATA-4 cDNA is 2162 bp in length and the open reading frame encodes a polypeptide containing 482 amino acids with a conserved zinc finger domain. The over-expression of ChGATA-4 significantly inhibited the expression of ChHsp70 promoter in heterologous HEK293T cells. However, the depletion of ChGATA-4 mRNA by RNAi technique resulted in significant increase of ChHsp70 transcription in oyster hemocytes. The RT-PCR results demonstrated that the transcription of both ChHsp70 and ChGATA-4 were induced by heat, Cd, or NP (Nonyl phenol) stress. This suggested a potential correlation between ChHsp70 and ChGATA-4 in the stress-mediated genetic regulatory cascade. This study demonstrated that ChGATA-4 acts in a negative manner in controlling ChHsp70 transcription in C. hongkongensis and promotes to further understand the mechanisms leading Hsp70 transcription.

Cardiac SNARE Expression in Health and Disease

SNARE proteins are integral to intracellular vesicular trafficking, which in turn is the process underlying the regulated expression of substrate transporters such as the glucose transporter GLUT4 at the cell surface of insulin target tissues. Impaired insulin stimulated GLUT4 trafficking is associated with reduced cardiac function in many disease states, most notably diabetes. Despite this, our understanding of the expression and regulation of SNARE proteins in cardiac tissue and how these may change in diabetes is limited. Here we characterize the array of SNARE proteins expressed in cardiac tissue, and quantify the levels of expression of VAMP2, SNAP23, and Syntaxin4-key proteins involved in insulin-stimulated GLUT4 translocation. We examined SNARE protein levels in cardiac tissue from two rodent models of insulin resistance, db/db mice and high-fat fed mice, and show alterations in patterns of expression are evident. Such changes may have implications for cardiac function.

Dendropanax morbifera Prevents Cardiomyocyte Hypertrophy by Inhibiting the Sp1/GATA4 Pathway

An extract of Dendropanax morbifera branch exerts antioxidant, anti-inflammatory, antithrombotic, and anticancer activities. The purpose of this study was to investigate the effect of the extract in isoproterenol-induced cardiac hypertrophy. Phalloidin staining showed that treatment with the extract dramatically prevents isoproterenol-induced H9c2 cell enlargement and the expression of cardiac hypertrophic marker genes, including atrial natriuretic peptide (ANP) and B-type brain natriuretic peptide (BNP). Further, pretreatment with the extract decreased isoproterenol-induced GATA4 and Sp1 expression in H9c2 cells. Overexpression of Sp1 induced the expression of GATA4. The forced expression of Sp1 or its downstream target GATA4, as well as the co-transfection of Sp1 and GATA4 increased the expression of ANP, which was decreased by treatment with the extract. To further elucidate the regulation of the Sp1/GATA4-mediated expression of ANP, knockdown experiments were performed. Transfection with small interfering RNAs (siRNAs) for Sp1 or GATA4 decreased ANP expression. The extract did not further inhibit the expression of ANP reduced by the transfection of GATA4 siRNA. Sp1 knockdown did not affect the expression of ANP that was induced by the overexpression of GATA4; however, GATA4 knockdown abolished the expression of ANP that had been induced by Sp1 overexpression. The extract treatment also attenuated the isoproterenol-induced activation of p38 MAPK, ERK1/2, and JNK1. Hesperidin, catechin, 2,5-dihydroxybenzoic acid, and salicylic acid are the main phenolic compounds present in the extract as observed by high performance liquid chromatography. Hesperidin and 2,5-dihydroxybenzoic acid attenuated isoproterenol-induced cardiac hypertrophy. These findings suggest that the D. morbifera branch extract prevents cardiac hypertrophy by downregulating the activation of Sp1/GATA4 and MAPK signaling pathways.

Ultrasonographic Characterization of the db/db Mouse: An Animal Model of Metabolic Abnormalities

The availability of an animal model able to reliably mirror organ damage occurring in metabolic diseases is an urgent need. These models, mostly rodents, have not been fully characterized in terms of cardiovascular, renal, and hepatic ultrasound parameters, and only sparse values can be found in literature. Aim of this paper is to provide a detailed, noninvasive description of the heart, vessels, liver, and kidneys of the db/db mouse by ultrasound imaging. Sixteen wild type and thirty-four db/db male mice (11-week-old) were studied. State-of-the-art ultrasound technology was used to acquire images of cardiovascular, renal, and hepatic districts. A set of parameters describing function of the selected organs was evaluated. db/db mice are characterized by systolic and diastolic dysfunction, confirmed by strain analysis. Abdominal aortic and carotid stiffness do not seem to be increased in diabetic rodents; furthermore, they are characterized by a smaller mean diameter for both vessels. Renal microcirculation is significantly compromised, while liver steatosis is only slightly higher in db/db mice than in controls. We offer here for the first time an in vivo detailed ultrasonographic characterization of the db/db mouse, providing a useful tool for a thoughtful choice of the right rodent model for any experimental design.

Murine Models of Heart Failure with Preserved Ejection Fraction: a "Fishing Expedition"

Heart failure with preserved ejection fraction (HFpEF) is characterized by signs and symptoms of HF in the presence of a normal left ventricular (LV) ejection fraction (EF). Despite accounting for up to 50% of all clinical presentations of HF, the mechanisms implicated in HFpEF are poorly understood, thus precluding effective therapy. The pathophysiological heterogeneity in the HFpEF phenotype also contributes to this disease and likely to the absence of evidence-based therapies. Limited access to human samples and imperfect animal models that completely recapitulate the human HFpEF phenotype have impeded our understanding of the mechanistic underpinnings that exist in this disease. Aging and comorbidities such as atrial fibrillation, hypertension, diabetes and obesity, pulmonary hypertension and renal dysfunction are highly associated with HFpEF. Yet, the relationship and contribution between them remains ill-defined. This review discusses some of the distinctive clinical features of HFpEF in association with these comorbidities and highlights the advantages and disadvantage of commonly used murine models, used to study the HFpEF phenotype.

GATA4 protects against hyperglycemia‑induced endothelial dysfunction by regulating NOX4 transcription

Endothelial dysfunction is one of the most common complications associated with diabetes and may lead to atherosclerosis. Conflicting reports indicate that NADPH oxidase 4 (NOX4) induces hydrogen peroxide production and cytotoxicity, but also has a protective effect on endothelial dysfunction. The present study aimed to identify the transcription factor responsible for NOX4 expression using a transcription factor activation profiling plate array and chromatin immunoprecipitation. Data from these analyses indicated that GATA-binding protein 4 (GATA4) was able to mediate NOX4 transcription and is downregulated in human umbilical vein endothelial cells (HUVECs) that were exposed to hyperglycemic conditions as well as in the endothelial cells of a mouse diabetes model. Overexpression of GATA4 was demonstrated to lead to increased expression of NOX4 mRNA and protein. Furthermore, GATA4 overexpression resulted in increased nitric oxide (NO) production through the upregulation of endothelial NO synthase phosphorylation. Treatment with simvastatin, a drug known to preserve endothelial function through an unknown mechanism, improved endothelial cell function by upregulating GATA4 expression in HUVECs exposed to hyperglycemia. Results from these experiments demonstrated that GATA4 may inhibit diabetes-induced endothelial dysfunction by acting as a transcription factor for NOX4 expression and increasing NO production. Thus, the present study revealed a novel molecular mechanism underlying endothelial dysfunction in diabetes and identified GATA4 as a potential therapeutic target.

ENOblock, a unique small molecule inhibitor of the non-glycolytic functions of enolase, alleviates the symptoms of type 2 diabetes

Type 2 diabetes mellitus (T2DM) significantly impacts on human health and patient numbers are predicted to rise. Discovering novel drugs and targets for treating T2DM is a research priority. In this study, we investigated targeting of the glycolysis enzyme, enolase, using the small molecule ENOblock, which binds enolase and modulates its non-glycolytic ‘moonlighting’ functions. In insulin-responsive cells ENOblock induced enolase nuclear translocation, where this enzyme acts as a transcriptional repressor. In a mammalian model of T2DM, ENOblock treatment reduced hyperglycemia and hyperlipidemia. Liver and kidney tissue of ENOblock-treated mice showed down-regulation of known enolase target genes and reduced enolase enzyme activity. Indicators of secondary diabetic complications, such as tissue apoptosis, inflammatory markers and fibrosis were inhibited by ENOblock treatment. Compared to the well-characterized anti-diabetes drug, rosiglitazone, ENOblock produced greater beneficial effects on lipid homeostasis, fibrosis, inflammatory markers, nephrotoxicity and cardiac hypertrophy. ENOblock treatment was associated with the down-regulation of phosphoenolpyruvate carboxykinase and sterol regulatory element-binding protein-1, which are known to produce anti-diabetic effects. In summary, these findings indicate that ENOblock has potential for therapeutic development to treat T2DM. Previously considered as a ‘boring’ housekeeping gene, these results also implicate enolase as a novel drug target for T2DM.

The effects of exercise training and caloric restriction on the cardiac oxytocin natriuretic peptide system in the diabetic mouse

BACKGROUND

Regular exercise training (ET) and caloric restriction (CR) are the frontline strategies in the treatment of type 2 diabetes mellitus with the aim at reducing cardiometabolic risk. ET and CR improve body weight and glycemic control, and experimental studies indicate that these paradigms afford cardioprotection. In this study, the effects of combined ET and CR on the cardioprotective oxytocin (OT)-natriuretic peptide (NP) system were determined in the db/db mouse, a model of type 2 diabetes associated with insulin resistance, hyperglycemia, and obesity.

METHODS

Five-week-old male db/db mice were assigned to the following groups: sedentary, ET, and ET + CR. Nonobese heterozygote littermates served as controls. ET was performed on a treadmill at moderate intensity, and CR was induced by reducing food intake by 30% of that consumed by sedentary db/db mice for a period of 8 weeks.

RESULTS

After 8 weeks, only ET + CR, but not ET, slightly improved body weight compared to sedentary db/db mice. Regardless of the treatment, db/db mice remained hyperglycemic. Hearts from db/db mice demonstrated reduced expression of genes linked to the cardiac OT-NP system. In fact, compared to control mice, mRNA expression of GATA binding protein 4 (GATA4), OT receptor, OT, brain NP, NP receptor type C, and endothelial nitric oxide synthase (eNOS) was decreased in hearts from sedentary db/db mice. Both ET alone and ET + CR increased the mRNA expression of GATA4 compared to sedentary db/db mice. Only ET combined with CR produced increased eNOS mRNA and protein expression.

CONCLUSION

Our data indicate that enhancement of eNOS by combined ET and CR may improve coronary endothelial vasodilator dysfunction in type 2 diabetes but did not prevent the downregulation of cardiac expression in the OT-NP system, possibly resulting from the sustained hyperglycemia and obesity in diabetic mice.

Oxytocin and cardioprotection in diabetes and obesity

Oxytocin (OT) emerges as a drug for the treatment of diabetes and obesity. The entire OT system is synthesized in the rat and human heart. The direct myocardial infusion with OT into an ischemic or failing heart has the potential to elicit a variety of cardioprotective effects. OT treatment attenuates cardiomyocyte (CMs) death induced by ischemia-reperfusion by activating pro-survival pathways within injured CMs in vivo and in isolated cells. OT treatment reduces cardiac apoptosis, fibrosis, and hypertrophy. The OT/OT receptor (OTR) system is downregulated in the db/db mouse model of type 2 diabetes which develops genetic diabetic cardiomyopathy (DC) similar to human disease. We have shown that chronic OT treatment prevents the development of DC in the db/db mouse. In addition, OT stimulates glucose uptake in both cardiac stem cells and CMs, and increases cell resistance to diabetic conditions. OT may help replace lost CMs by stimulating the in situ differentiation of cardiac stem cells into functional mature CMs. Lastly, adult stem cells amenable for transplantation such as MSCs could be preconditioned with OT ex vivo and implanted into the injured heart to aid in tissue regeneration through direct differentiation, secretion of protective and cardiomyogenic factors and/or their fusion with injured CMs.

Functional thyrotropin receptor expression in the ventricle and the effects on ventricular BNP secretion

Elevated thyrotropin (TSH) and hypercholesterolemia commonly coexist in patients with subclinical hypothyroidism, which can cause and aggravate heart disease. However, it is unclear whether TSH has a direct effect on cardiac function. To determine the expression of the thyrotropin receptor (TSHR) and the effects of TSH on ventricular function, we analyzed the ventricular tissues and thyroid glands from normal rats and mice and the H9c2 cardiomyocyte cell line. The results revealed that TSHR was expressed at the transcriptional and protein levels by PCR, immunoblotting, immunohistochemistry and immunofluorescence. The mRNA levels of β-MHC and the expression of pCREB and HMGCR in the ventricle were significantly lower in Tshr (-/-) mice than in wild-type (WT) mice (p < 0.05), but serum NT-proBNP levels were similar between WT and Tshr (-/-) mice. After synchronization, H9c2 cells were stimulated with several concentrations of TSH for various time periods. TSH up-regulated β-MHC mRNA expression in H9c2 cells. Cyclic adenosine monophosphate (cAMP) production and downstream signaling, such as pCREB and HMGCR expression and NT-proBNP secretion, increased in dose- and time-dependent manners. The TSH-stimulated effects were suppressed by an adenylyl cyclase inhibitor, a protein kinase A (PKA) inhibitor and HMGCR inhibitors (all p < 0.05). The data indicate functional TSHR is expressed in ventricular myocytes and mediates TSH-induced BNP secretion and HMGCR up-regulation through the cAMP/PKA/pCREB signaling pathway. Our findings suggest a potentially novel pathophysiological role of TSH in heart failure-associated hypothyroidism.

Unexpected effects of voluntary exercise training on natriuretic peptide and receptor mRNA expression in the ob/ob mouse heart

Regular exercise is generally recommended for the treatment of obesity and type 2 diabetes. Exercise reduces body weight, improves glycemic control and cardiovascular (CV) function. This study was designed to determine the impact of voluntary wheel running on the cardiac oxytocin (OT)-natriuretic peptide (NP) system and plasma CV risk factors in the ob/ob mouse, a model of insulin resistance coupled with severe obesity. Five-week-old male ob/ob mice and non-obese heterozygote control littermates were assigned to either a sedentary or running group. Voluntary running was performed using a wheel system for a period of 8 weeks. Compared to non-obese mice, daily running activity expressed in kilometers, was significantly lower in ob/ob mice. In these mice, voluntary running improved body weight, but exacerbated CV markers, including plasma glucose and triglyceride levels. OT receptor gene expression was decreased in hearts of ob/ob mice compared to non-obese mice, and no improvement in the expression of this receptor was observed after voluntary running. Hearts from ob/ob mice also expressed lower BNP mRNA, whereas no differences in A- and C-type NP were observed between non-obese and ob/ob mice. After voluntary running, a downregulation in the expression of all three NPs coupled with increased apoptosis was observed in ob/ob hearts. Our results show that voluntary exercise running activity was decreased in the ob/ob mouse. Surprisingly, this was associated with a worsening of common CV plasma markers, reduced expression of peptides linked to the cardioprotective OT-NP system, and increased expression of cardiac apoptotic markers.

Exercise and diabetes have opposite effects on the assembly and O-GlcNAc modification of the mSin3A/HDAC1/2 complex in the heart

Background

Exercise causes physiological cardiac hypertrophy and benefits the diabetic heart. Mammalian switch-independent 3A (mSin3A) and histone deacetylases (HDACs) 1 and 2 regulate hypertrophic genes through associations with the DNA binding proteins repressor element-1 silencing transcription factor (REST) and O-linked β-N-acetylglucosamine transferase (OGT). O-linked β-N-acetylglucosamine (O-GlcNAc) is a glucose derivative that is chronically elevated in diabetic hearts, and a previous study showed that exercise reduces cardiac O-GlcNAc. We hypothesized that O-GlcNAc and OGT would physically associate with mSin3A/HDAC1/2 in the heart, and that this interaction would be altered by diabetes and exercise.

Methods

8-week-old type 2 diabetic db/db (db) and non-diabetic C57 mice were randomized to treadmill exercise or sedentary groups for 1 or 4 weeks.

Results

O-GlcNAc was significantly higher in db hearts and increased with exercise. Db hearts showed lower levels of mSin3A, HDAC1, and HDAC2 protein, but higher levels of HDAC2 mRNA and HDAC1/2 deacetylase activity. Elevated HDAC activity was associated with significantly blunted expression of α-actin and brain natriuretic peptide in db hearts. In sedentary db hearts, co-immunoprecipitation assays showed that mSin3A and OGT were less associated with HDAC1 and HDAC2, respectively, compared to sedentary C57 controls; however, exercise removed these differences.

Conclusions

These data indicate that diabetes and exercise oppositely affect interactions between pro-hypertrophic transcription factors, and suggest that an increase in total cardiac O-GlcNAc is a mechanism by which exercise benefits type 2 diabetic hearts.

Natriuretic peptides and cGMP signaling control of energy homeostasis

Since the discovery of natriuretic peptides (NPs) by de Bold et al. in 1981, the cardiovascular community has been well aware that they exert potent effects on vessels, heart remodeling, kidney function, and the regulation of sodium and water balance. Who would have thought that NPs are also able to exert metabolic effects and contribute to an original cross talk between heart, adipose tissues, and skeletal muscle? The attention on the metabolic role of NPs was awakened in the year 2000 with the discovery that NPs exert potent lipolytic effects mediated by the NP receptor type A/cGMP pathway in human fat cells and that they contribute to lipid mobilization in vivo. In this review, we will discuss the biological effects of NPs on the main tissues involved in the regulation of energy metabolism (i.e., white and brown adipose tissues, skeletal muscle, liver, and pancreas). These recent results on NPs are opening a new chapter into the physiological properties and therapeutic usefulness of this family of hormones.

Expression of cardiac GATA4 and downstream genes after exercise training in the db/db mouse

GATA4 is a transcriptional factor expressed in heart that regulates the synthesis of structural and cardioprotective genes. We have demonstrated that low GATA4 expression in the db/db mouse heart is associated with reduced expression of key downstream genes, including oxytocin (OT) natriuretic peptide (A-, B-type), nitric oxide synthase (eNOS), and myosin heavy chain (α-MHC). In this study, the effect of exercise on GATA4 expression and related genes was determined in the db/db mouse, a model that represents human type 2 diabetes. Vascular endothelial growth factor (VEGF) and hypoxia-induced factor-α expression were also measured after 8 weeks of treadmill running. Compared with control littermates, db/db mice exhibited hyperglycemia and obesity, and exercise failed to improve these parameters. GATA4 expression was reduced in db/db hearts and this was associated with reduced expression of OT, OTR, ANP, BNP, eNOS, α-MHC, and ratio of α- to β-MHC, whereas mRNA expression of β-MHC and VEGF remained unchanged compared with control hearts. Exercise training increased GATA4 expression (mRNA and protein) but most genes regulated by GATA4 were not observed to increase accordingly. However, protein expression of eNOS, mRNA expression of α-MHC, ratio of α- to β-MHC, and protein expression of VEGF were increased in db/db hearts after exercise. In conclusion, while GATA4 expression is increased following exercise, not all structural and cardioprotective genes are expressed, suggesting other transcription factors may be involved in this regulation. Regardless of this effect, the positive effect of exercise training on key protective genes is evident in the db/db mouse heart.