Set7 Deletion Prevents Glucose Intolerance and Improves the Recovery of Cardiac Function After Ischemia and Reperfusion in Obese Female Mice.

BACKGROUND/AIMS: An obesogenic diet (high fat and sugar, low fiber) is associated with an increased risk for metabolic and cardiovascular disorders. Previous studies have demonstrated that epigenetic changes can modify gene transcription and protein function, playing a key role in the development of several diseases. The methyltransferase Set7 methylates histone and non-histone proteins, influencing diverse biological and pathological processes. However, the functional role of Set7 in obesity-associated metabolic and cardiovascular complications is unknown. METHODS: Wild type and Set7 knockout female mice were fed a normal diet or an obesogenic diet for 12 weeks. Body weight gain and glucose tolerance were measured. The 3T3-L1 cells were used to determine the role of Set7 in white adipogenic differentiation. Cardiac morphology and function were evaluated by histology and echocardiography. An ex vivo Langendorff perfusion system was used to model cardiac ischemia/reperfusion (I/R). RESULTS: Here, we report that Set7 protein levels were enhanced in the heart and perigonadal adipose tissue (PAT) of female mice fed an obesogenic diet. Significantly, loss of Set7 prevented obesogenic diet-induced glucose intolerance in female mice although it did not affect the obesogenic diet-induced increase in body weight gain and adiposity in these animals, nor did Set7 inhibition change white adipogenic differentiation in vitro. In addition, loss of Set7 prevented the compromised cardiac functional recovery following ischemia and reperfusion (I/R) injury in obesogenic diet-fed female mice; however, deletion of Set7 did not influence obesogenic diet-induced cardiac hypertrophy nor the hemodynamic and echocardiographic parameters. CONCLUSION: These data indicate that Set7 plays a key role in obesogenic diet-induced glucose intolerance and compromised myocardial functional recovery after I/R in obese female mice.

Set7 deletion attenuates isoproterenol-induced cardiac fibrosis and delays cardiac dysfunction.

Cardiovascular diseases are the main cause of death worldwide. Recent studies have revealed the influence of histone-modifying enzymes in cardiac remodeling and heart dysfunction. The Set7 methyltransferase regulates the expression of several genes through the methylation of histones and modulates the activity of non-histone proteins. However, the role of Set7 in cardiac remodeling and heart dysfunction remains unknown. To address this question, wild-type (WT) and Set7 knockout (KO) male mice were injected with isoproterenol or saline. WT mice injected with isoproterenol displayed a decrease in Set7 activity in the heart. In addition, WT and Set7 KO mice injected with isoproterenol exhibited cardiac hypertrophy. Interestingly, Set7 deletion exacerbated cardiac hypertrophy in response to isoproterenol but attenuated myocardial fibrosis. Echocardiograms revealed that WT mice injected with isoproterenol had lowered ejection fractions and fractional shortening, and increased E'-wave deceleration time and E/A ratio compared with their controls. Conversely, Set7 KO mice did not show alteration in these parameters in response to isoproterenol. However, prolonged exposure to isoproterenol induced cardiac dysfunction both in WT and Set7 KO mice. Both isoproterenol and Set7 deletion changed the transcriptional profile of the heart. Moreover, Set7 deletion increased the expression of Pgc1α and mitochondrial DNA content in the heart, and reduced the expression of cellular senescence and inflammation markers in response to isoproterenol. Taken together, our data suggest that Set7 deletion attenuates isoproterenol-induced myocardial fibrosis and delays heart dysfunction, suggesting that Set7 plays an important role in cardiac remodeling and dysfunction in response to stress.

The miRNA-143-3p-Sox6-Myh7 pathway is altered in obesogenic diet-induced cardiac hypertrophy.

NEW FINDINGS: What is the central question of this study? What is the effect of an obesogenic diet on the expression of microRNAs (miRNAs) involved in cardiac hypertrophy in female mice? What is the main finding and its importance? Female mice fed an obesogenic diet exhibited cardiac hypertrophy associated with increased levels of miRNA-143-3p, decreased mRNA levels of Sox6 and increased mRNA levels of Myh7. Inhibition of miRNA-143-3p increased Sox6 mRNA levels and reduced Myh7 expression in cardiomyocytes, and prevented angiotensin II-induced cardiomyocyte hypertrophy. The results indicate that the miRNA-143-3p-Sox6-Myh7 pathway may play a key role in obesity-induced cardiac hypertrophy. ABSTRACT: Obesity induces cardiometabolic disorders associated with a high risk of mortality. We have previously shown that the microRNA (miRNA) expression profile is changed in obesity-induced cardiac hypertrophy in male mice. Here, we investigated the effect of an obesogenic diet on the expression of miRNAs involved in cardiac hypertrophy in female mice. Female mice fed an obesogenic diet displayed an increased body weight gain, glucose intolerance, insulin resistance and dyslipidaemia. In addition, obese female mice exhibited cardiac hypertrophy associated with increased levels of several miRNAs, including miR-143-3p. Bioinformatic analysis identified Sox6, regulator of Myh7 gene transcription, as a predicted target of miR-143-3p. Female mice fed an obesogenic diet exhibited decreased mRNA levels of Sox6 and increased expression of Myh7 in the heart. Loss-of-function studies in cardiomyocytes revealed that inhibition of miR-143-3p increased Sox6 mRNA levels and reduced Myh7 expression. Collectively, our results indicate that obesity-associated cardiac hypertrophy in female mice is accompanied by alterations in diverse miRNAs, and suggest that the miR-143-3p-Sox6-Myh7 pathway may play a key role in obesity-induced cardiac hypertrophy.

SOCS3 Ablation in Leptin Receptor-Expressing Cells Causes Autonomic and Cardiac Dysfunctions in Middle-Aged Mice despite Improving Energy and Glucose Metabolism.

Leptin resistance is a hallmark of obesity. Treatments aiming to improve leptin sensitivity are considered a promising therapeutical approach against obesity. However, leptin receptor (LepR) signaling also modulates several neurovegetative aspects, such as the cardiovascular system and hepatic gluconeogenesis. Thus, we investigated the long-term consequences of increased leptin sensitivity, considering the potential beneficial and deleterious effects. To generate a mouse model with increased leptin sensitivity, the suppressor of cytokine signaling 3 (SOCS3) was ablated in LepR-expressing cells (LepR∆SOCS3 mice). LepR∆SOCS3 mice displayed reduced food intake, body adiposity and weight gain, as well as improved glucose tolerance and insulin sensitivity, and were protected against aging-induced leptin resistance. Surprisingly, a very high mortality rate was observed in aging LepR∆SOCS3 mice. LepR∆SOCS3 mice showed cardiomyocyte hypertrophy, increased myocardial fibrosis and reduced cardiovascular capacity. LepR∆SOCS3 mice exhibited impaired post-ischemic cardiac functional recovery and middle-aged LepR∆SOCS3 mice showed substantial arhythmic events during the post-ischemic reperfusion period. Finally, LepR∆SOCS3 mice exhibited fasting-induced hypoglycemia and impaired counterregulatory response to glucopenia associated with reduced gluconeogenesis. In conclusion, although increased sensitivity to leptin improved the energy and glucose homeostasis of aging LepR∆SOCS3 mice, major autonomic/neurovegetative dysfunctions compromised the health and longevity of these animals. Consequently, these potentially negative aspects need to be considered in the therapies that increase leptin sensitivity chronically.

Angiotensin-(1-7) prevents T3-induced cardiomyocyte hypertrophy by upregulating FOXO3/SOD1/catalase and downregulating NF-ĸB.

Clinical studies have shown a correlation between thyroid disorders and cardiac diseases. High levels of triiodothyronine (T3) induce cardiac hypertrophy, a risk factor for cardiac complications and heart failure. Previous results have demonstrated that angiotensin-(1-7) is able to block T3-induced cardiac hypertrophy; however, the molecular mechanisms involved in this event have not been fully elucidated. Here, we evidenced the contribution of FOXO3 signaling to angiotensin-(1-7) effects. Angiotensin-(1-7) treatment increased nuclear FOXO3 levels and reduced p-FOXO3 levels (inactive form) in isolated cardiomyocytes. Knockdown of FOXO3 by RNA silencing abrogated the antihypertrophic effect of angiotensin-(1-7). Increased expression of antioxidant enzymes superoxide dismutase 1 (SOD1 and catalase) and lower levels of reactive oxygen species and nuclear factor-κB (NF-κB) were observed after angiotensin-(1-7) treatment in vitro. Consistent with these results, transgenic rats overexpressing angiotensin-(1-7) displayed increased nuclear FOXO3 and SOD1 levels and reduced NF-κB levels in the heart. These results provide a new molecular mechanism responsible for the antihypertrophic effect of angiotensin-(1-7), which may contribute to future therapeutic targets.

Deletion of miRNA-22 Induces Cardiac Hypertrophy in Females but Attenuates Obesogenic Diet-Mediated Metabolic Disorders.

BACKGROUND/AIMS: Obesity is a risk factor associated with cardiometabolic complications. Recently, we reported that miRNA-22 deletion attenuated high-fat diet-induced adiposity and prevented dyslipidemia without affecting cardiac hypertrophy in male mice. In this study, we examined the impact of miRNA-22 in obesogenic diet-induced cardiovascular and metabolic disorders in females. METHODS: Wild type (WT) and miRNA-22 knockout (miRNA-22 KO) females were fed a control or an obesogenic diet. Body weight gain, adiposity, glucose tolerance, insulin tolerance, and plasma levels of total cholesterol and triglycerides were measured. Cardiac and white adipose tissue remodeling was assessed by histological analyses. Echocardiography was used to evaluate cardiac function and morphology. RNA-sequencing analysis was employed to characterize mRNA expression profiles in female hearts. RESULTS: Loss of miRNA-22 attenuated body weight gain, adiposity, and prevented obesogenic diet-induced insulin resistance and dyslipidemia in females. WT obese females developed cardiac hypertrophy. Interestingly, miRNA-22 KO females displayed cardiac hypertrophy without left ventricular dysfunction and myocardial fibrosis. Both miRNA-22 deletion and obesogenic diet changed mRNA expression profiles in female hearts. Enrichment analysis revealed that genes associated with regulation of the force of heart contraction, protein folding and fatty acid oxidation were enriched in hearts of WT obese females. In addition, genes related to thyroid hormone responses, heart growth and PI3K signaling were enriched in hearts of miRNA-22 KO females. Interestingly, miRNA-22 KO obese females exhibited reduced mRNA levels of Yap1, Egfr and Tgfbr1 compared to their respective controls. CONCLUSION: This study reveals that miRNA-22 deletion induces cardiac hypertrophy in females without affecting myocardial function. In addition, our findings suggest miRNA-22 as a potential therapeutic target to treat obesity-related metabolic disorders in females.

High fat diet reduces the expression of miRNA-29b in heart and increases susceptibility of myocardium to ischemia/reperfusion injury.

Several studies have shown the role of microRNAs (miRNAs) in myocardial dysfunction in response to ischemia/reperfusion (I/R). In this study, we investigated the impact of high fat (HF) diet in the myocardial susceptibility to I/R injury, as well as in the expression of miRNA-29b. Isolated heart experiments using the ex vivo Langendorff perfusion model were used to induce cardiac I/R injury. HF diet-induced cardiac hypertrophy and impaired cardiac functional recovery after I/R. miRNA-29b, which targets Col1, was reduced in the heart of HF diet-fed mice, whereas the cardiac expression of Col1 was increased. In addition, hypoxia-reoxygenation (H/R) reduced the expression of miRNA-29b in cardiomyoblasts cultures. However, the overexpression of miRNA-29b in cardiomyoblasts reduced p53 mRNA levels and H/R injury, suggesting that downregulation of miRNA-29b may be involved in I/R injury. Together, our findings suggest that the reduced expression of miRNA-29b may be involved in the deteriorated cardiac functional recovery following I/R in obese mice.

Angiotensin-(1-7) reduces cardiac effects of thyroid hormone by GSK3Β/NFATc3 signaling pathway.

Patients with hyperthyroidism exhibit increased risk of development and progression of cardiac diseases. The activation of the renin-angiotensin system (RAS) has been indirectly implicated in these cardiac effects observed in hyperthyroidism. Angiotensin-(1-7) (Ang-(1-7)) has previously been shown to counterbalance pathological effects of angiotensin II (Ang II). The aim of the present study was to investigate the effects of elevated circulating Ang-(1-7) levels on cardiac effects promoted by hyperthyroidism in a transgenic rat (TG) model that constitutively overexpresses an Ang-(1-7)-producing fusion protein [TGR(A1-7)3292]. TG and wild-type (WT) rats received daily injections (i.p.) of triiodothyronine (T3; 7 µg/100 g of body weight (BW)) or vehicle for 14 days. In contrast with WT rats, the TG rats did not develop cardiac hypertrophy after T3 treatment. Indeed, TG rats displayed reduced systolic blood pressure (SBP) and cardiac hyperdynamic condition induced by hyperthyroidism. Moreover, increased plasma levels of Ang II observed in hyperthyroid WT rats were prevented in TG rats. TG rats were protected from glycogen synthase kinase 3ß (GSK3ß) inactivation and nuclear factor of activated T cells (NFAT) nuclear accumulation induced by T3. In vitro studies evidenced that Ang-(1-7) prevented cardiomyocyte hypertrophy and GSK3ß inactivation induced by T3. Taken together, these data reveal an important cardioprotective action of Ang-(1-7) in experimental model of hyperthyroidism.

Cardioprotective effect of thyroid hormone is mediated by AT2 receptor and involves nitric oxide production via Akt activation in mice.

Studies have demonstrated that thyroid hormone (T3) can precondition the heart against ischaemic injury and improve post-ischaemic recovery. This study investigated whether the AT2 receptor (AT2R) is involved in cardioprotection and the potential molecular mechanism responsible for this effect. Hyperthyroidism was induced in male wild-type (WT) and AT2R knockout (KO) mice by administering daily intraperitoneal injections of T3 (7 µg/100 g body weight) for 14 days. The mouse hearts were harvested and perfused with a Krebs-Henseleit solution at a constant flow in a Langendorff set-up. After 30 min of stabilization, the hearts were subjected to global ischaemia for 20 min and reperfused for 45 min. Baseline cardiac function was assessed by measuring four parameters: LVDP (mmHg), heart rate (bpm), + dP/dt and - dP/dt (mmHg/s). After reperfusion, the total protein from cardiac ventricles was obtained, and the Akt signalling pathway and NO production were evaluated. Post-ischaemic functional recovery was significantly greater (p < 0.05) in the T3-treated WT mice compared to the control, demonstrating the cardioprotective effect of T3. This effect was abolished in T3-treated KO mice, demonstrating the physiological relevance of AT2R to the cardioprotective phenotype induced by T3. Akt activation, iNOS expression and NO production increased in cardiac tissue after T3 treatment in the WT animals, but no difference was observed after treatment in the KO mice. This study indicates that AT2R acts as a cardioprotector in the case of hyperthyroidism. Strategies targeting AT2R agonists might improve cardiac function through NO production and suggest potential therapeutic targets for heart diseases.

MicroRNA Expression Signature Is Altered in the Cardiac Remodeling Induced by High Fat Diets.

Recent studies have revealed the involvement of microRNAs (miRNAs) in the control of cardiac hypertrophy and myocardial function. In addition, several reports have demonstrated that high fat (HF) diet induces cardiac hypertrophy and remodeling. In the current study, we investigated the effect of diets containing different percentages of fat on the cardiac miRNA expression signature. To address this question, male C57Bl/6 mice were fed with a low fat (LF) diet or two HF diets, containing 45 kcal% fat (HF45%) and 60 kcal% fat (HF60%) for 10 and 20 weeks. HF60% diet promoted an increase on body weight, fasting glycemia, insulin, leptin, total cholesterol, triglycerides, and induced glucose intolerance. HF feeding promoted cardiac remodeling, as evidenced by increased cardiomyocyte transverse diameter and interstitial fibrosis. RNA sequencing analysis demonstrated that HF feeding induced distinct miRNA expression patterns in the heart. HF45% diet for 10 and 20 weeks changed the abundance of 64 and 26 miRNAs in the heart, respectively. On the other hand, HF60% diet for 10 and 20 weeks altered the abundance of 27 and 88 miRNAs in the heart, respectively. Bioinformatics analysis indicated that insulin signaling pathway was overrepresented in response to HF diet. An inverse correlation was observed between cardiac levels of GLUT4 and miRNA-29c. Similarly, we found an inverse correlation between expression of GSK3ß and the expression of miRNA-21a-3p, miRNA-29c-3p, miRNA-144-3p, and miRNA-195a-3p. In addition, miRNA-1 overexpression prevented cardiomyocyte hypertrophy. Taken together, our results revealed differentially expressed miRNA signatures in the heart in response to different HF diets. J. Cell. Physiol. 231: 1771-1783, 2016. © 2015 Wiley Periodicals, Inc.

The endocrinological component and signaling pathways associated to cardiac hypertrophy.

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

Angiotensin II type 2 receptor mediates high fat diet-induced cardiomyocyte hypertrophy and hypercholesterolemia.

Obesity is the major risk factor for several cardiovascular and metabolic disorders. Previous studies reported that deletion of Angiotensin II type 2 receptor (AT2R) protects against metabolic dysfunctions induced by high fat (HF) diet. However, the role of AT2R in obesity-induced cardiac hypertrophy remains unclear. Male AT2R knockout (AT2RKO) and wild type (AT2RWT) mice were fed with control or HF diet for 10 weeks. HF diet increased cardiac expression of AT2R in obese mice. Deletion of AT2R did not affect body weight gain, glucose intolerance and fat mass gain induced by HF feeding. However, loss of AT2R prevented HF diet-induced hypercholesterolemia and cardiac remodeling. Mechanistically, we found that pharmacological inhibition or knockdown of AT2R prevented leptin-induced cardiomyocyte hypertrophy in vitro. Collectively, our results suggest that AT2R is involved in obesity-induced cardiac hypertrophy.

AMP hydrolysis in soluble and microsomal rat cardiac cell fractions: kinetic characterization and molecular identification of 5'-nucleotidase.

The present study describes the enzymatic properties and molecular identification of 5'-nucleotidase in soluble and microsomal fractions from rat cardiac ventricles. Using AMP as a substrate, the results showed that the cation and the concentration required for maximal activity in the two fractions was magnesium at a final concentration of 1 mM. The pH optimum for both fractions was 9.5. The apparent K(m) (Michaelis constant) values calculated from the Eadie-Hofstee plot were 59.7+/-10.4 microM and 134.8+/-32.1 microM, with V(max) values of 6.7+/-0.4 and 143.8+/-23.8 nmol P(i)/min/mg of protein (means+/-S.D., n=4) from soluble and microsomal fractions respectively. Western blotting analysis of ecto-5'-nucleotidase revealed a 70 kDa protein in both fractions, with the major proportion present in the microsomal fraction. The presence of these enzymes in the heart probably has a physiological function in adenosine signalling. Furthermore, the presence of ecto-5'-nucleotidase in the microsomal fraction could have a role in the modulation of the excitation-contraction-coupling process through involvement of the Ca(2+) influx into the sarcoplasmic reticulum. The measurement of maximal enzyme activities in the two fractions highlights the potential capacity of the different pathways of purine metabolism in the heart.

The effects of angiotensin II and genetic hypertension upon extracellular nucleotide hydrolysis by rat platelet ectoenzymes.

The extracellular nucleotides, ATP and ADP, as well as adenosine have been implicated in a great number of physiological functions. ADP is one of the major platelet recruiting factors, whereas ATP is considered to be a competitive inhibitor of ADP-induced platelet aggregation and adenosine is able to induce vasodilatation and to inhibit platelet aggregation. The di- and triphosphate nucleosides can be hydrolyzed by members of several families of ectonucleotidases, including ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases) and ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPPs) that, together with an ecto-5'-nucleotidase, catalyze adenosine formation. The renin-angiotensin system is the most important regulator of renal and cardiovascular functions and angiotensin II induces, physiologically, platelet activation. The aim of this study was to clarify the effects of ANGII and genetic hypertension upon extracellular nucleotide hydrolysis by rat platelet ectoenzymes. ANGII, in all tested doses (5, 50, 500 and 5000 pmol), was able to increase ATP (21, 31, 44 and 27%, respectively), ADP (22, 28, 78 and 37%, respectively) and AMP (40, 64, 60 and 64%, respectively) hydrolysis by rat platelets. Furthermore, losartan, a specific antagonist of the AT1 angiotensin-receptor, prevented the nucleotide hydrolysis effects. Additionally, an increase in AMP (about 144%) hydrolysis and a decrease in p-Nph-5'TMP (about 27%) hydrolysis were observed in platelets from spontaneously hypertensive rats (SHR) when compared to Wistar normotensive rats. We, herein, present data to demonstrate interactions between rat platelet angiotensinergic and adenosinergic systems that could contribute to the understanding and treatment of cardiovascular diseases such as hypertension, thrombosis and arteriosclerosis.

E-NTPDase 3 (ATP diphosphohydrolase) from cardiomyocytes, activity and expression are modulated by thyroid hormone.

Degradation of adenine nucleotides by myocardial cells occurs, in part, by a cascade of surface-located enzymes converting ATP into adenosine that has important implications for the regulation of the nucleotide/nucleoside ratio modulating the cardiac functions. Thyroid hormones have profound effects on cardiovascular system, as observed in hypo- and hyperthyroidism. Combined biochemical parameters and gene expression analysis approaches were used to investigate the influence of tri-iodothyronine (T3) on ATP and ADP hydrolysis by isolated myocytes. Cultures of cardiomyocytes were submitted to increasing doses of T3 for 24h. Enzymatic activity and expression were evaluated. T3 (0.1 nM) caused an increase in ATP and ADP hydrolysis. Experiments with specific inhibitors suggest the involvement of an NTPDase, which was confirmed by an increase in NTPDase 3 messenger RNA (mRNA) levels. Since T3 promotes an increase in the contractile protein, leading to cardiac hypertrophy, it is tempting to postulate that the increase in ATP hydrolysis and the decrease in the extracellular levels signify an important factor for prevention of excessive contractility.

Activation of adenosine A(1) receptors alters behavioral and biochemical parameters in hyperthyroid rats.

Adenosine acting on A(1) receptors has been related with neuroprotective and neuromodulatory actions, protection against oxidative stress and decrease of anxiety and nociceptive signaling. Previous studies demonstrated an inhibition of the enzymes that hydrolyze ATP to adenosine in the rat central nervous system after hyperthyroidism induction. Manifestations of hyperthyroidism include increased anxiety, nervousness, high O(2) consumption and physical hyperactivity. Here, we investigated the effects of administration of a specific agonist of adenosine A(1) receptor (N(6)-cyclopentyladenosine; CPA) on nociception, anxiety, exploratory response, locomotion and brain oxidative stress of hyperthyroid rats. Hyperthyroidism was induced by daily intraperitoneal injections of l-thyroxine (T4) for 14 days. Nociception was assessed with a tail-flick apparatus and exploratory behavior, locomotion and anxiety were analyzed by open-field and plus-maze tests. We verified the total antioxidant reactivity (TAR), lipid peroxide levels by the thiobarbituric acid reactive species (TBARS) reaction and the free radicals content by the DCF test. Our results demonstrated that CPA reverted the hyperalgesia induced by hyperthyroidism and decreased the exploratory behavior, locomotion and anxiety in hyperthyroid rats. Furthermore, CPA decreased lipid peroxidation in hippocampus and cerebral cortex of control rats and in cerebral cortex of hyperthyroid rats. CPA also increased the total antioxidant reactivity in hippocampus and cerebral cortex of control and hyperthyroid rats, but the production of free radicals verified by the DCF test was changed only in cerebral cortex. These results suggest that some of the hyperthyroidism effects are subjected to regulation by adenosine A(1) receptor, demonstrating the involvement of the adenosinergic system in this pathology.

Cardiac ACE2/angiotensin 1-7/Mas receptor axis is activated in thyroid hormone-induced cardiac hypertrophy.

OBJECTIVES: Thyroid hormone (TH) promotes marked effects on the cardiovascular system, including the development of cardiac hypertrophy. Some studies have demonstrated that the renin-angiotensin system (RAS) is a key mediator of the cardiac growth in response to elevated TH levels. Although some of the main RAS components are changed in cardiac tissue on hyperthyroid state, the potential modulation of the counter regulatory components of the RAS, such as angiotensin-converting enzyme type 2 (ACE2), angiotensin 1-7 (Ang 1-7) levels and Mas receptor induced by hyperthyroidism is unknown. The aim of this study was to investigate the effect of hyperthyroidism on cardiac Ang 1-7, ACE2 and Mas receptor levels. METHODS: Hyperthyroidism was induced in Wistar rats by daily intraperitoneal injections of T4 for 14 days. RESULTS: Although plasma Ang 1-7 levels were unchanged by hyperthyroidism, cardiac Ang 1-7 levels were increased in TH-induced cardiac hypertrophy. ACE2 enzymatic activity was significantly increased in hearts from hyperthyroid animals, which may be contributing to the higher Ang 1-7 levels observed in the T4 group. Furthermore, elevated cardiac levels of Ang 1-7 levels were accompanied by increased Mas receptor protein levels. CONCLUSION: The counter-regulatory components of the RAS are activated in hyperthyroidism and may be contributing to modulate the cardiac hypertrophy in response to TH.

Hypo-and hyperthyroidism affect the ATP, ADP and AMP hydrolysis in rat hippocampal and cortical slices.

The presence of severe neurological symptoms in thyroid diseases has highlighted the importance of thyroid hormones in the normal functioning of the mature brain. Since, ATP is an important excitatory neurotransmitter and adenosine acts as a neuromodulatory structure inhibiting neurotransmitters release in the central nervous system (CNS), the ectonucleotidase cascade that hydrolyzes ATP to adenosine, is also involved in the control of brain functions. Thus, we investigated the influence of hyper-and hypothyroidism on the ATP, ADP and AMP hydrolysis in hippocampal and cortical slices from adult rats. Hyperthyroidism was induced by daily injections of l-thyroxine (T4) 25 microg/100 g body weight, for 14 days. Hypothyroidism was induced by thyroidectomy and methimazole (0.05%) added to their drinking water for 14 days. Hypothyroid rats were hormonally replaced by daily injections of T4 (5 microg/100 g body weight, i.p.) for 5 days. Hyperthyroidism significantly inhibited the ATP, ADP and AMP hydrolysis in hippocampal slices. In brain cortical slices, hyperthyroidism inhibited the AMP hydrolysis. In contrast, hypothyroidism increased the ATP, ADP and AMP hydrolysis in both hippocampal and cortical slices and these effects were reverted by T4 replacement. Furthermore, hypothyroidism increased the expression of NTPDase1 and 5'-nucleotidase, whereas hyperthyroidism decreased the expression of 5'-nucleotidase in hippocampus of adult rats. These findings demonstrate that thyroid disorders may influence the enzymes involved in the complete degradation of ATP to adenosine and possibly affects the responses mediated by adenine nucleotides in the CNS of adult rats.

Hypothyroidism changes adenine nucleotide hydrolysis in synaptosomes from hippocampus and cerebral cortex of rats in different phases of development.

The influence of the thyroid hormones on the normal function of the mammalian central nervous system depends on the brain region and on the developmental stage. Adenine nucleotides and their products also affect the brain function; ATP is an excitatory neurotransmitter, and adenosine has inhibitory effects on neurotransmission. Thus, this study aimed to evaluate the effects of hypothyroidism on the hydrolysis of ATP to adenosine in hippocampal and cortical synaptosomes and blood serum of rats during different phases of development. Rats aged 60 and 420 days old were divided into three groups: control, sham-operated and hypothyroid. Hypothyroidism was induced in these rats by thyroidectomy and methimazole (0.05%) added to their drinking water for 14 days. Neonatal hypothyroidism was induced by adding 0.02% methimazole in the drinking water from day 9 of gestation, and continually until 14 days old. Hypothyroidism increased the AMP hydrolysis in both hippocampus and cerebral cortex synaptosomes of rats in all aged tested. In blood serum, thyroid hormones deficiency increased the AMP hydrolysis in 14-day-old rats and the hydrolysis of ATP, ADP and AMP in 60-day-old rats; however, no alteration was observed in 420-day-old rats. Thus, our results suggest the involvement of the 5'-nucleotidase in synaptic function control in hypothyroidism throughout brain development.

Maternal hyperthyroidism increases the susceptibility of rat adult offspring to cardiovascular disorders.

Suboptimal intrauterine conditions as changed hormone levels during critical periods of the development are considered an insult and implicate in physiological adaptations which may result in pathological outcomes in later life. This study evaluated the effect of maternal hyperthyroidism (hyper) on cardiac function in adult offspring and the possible involvement of cardiac Renin-Angiotensin System (RAS) in this process. Wistar dams received orally thyroxin (12 mg/L) from gestational day 9 (GD9) until GD18. Adult offspring at postnatal day 90 (PND90) from hyper dams presented increased SBP evaluated by plethysmography and worse recovery after ischemia-reperfusion (I/R), as evidenced by decreased LVDP, +dP/dT and -dP/dT at 25 min of reperfusion and by increased infarct size. Increased cardiac Angiotensin I/II levels and AT1R in hyper offspring were verified. Herein, we provide evidences that maternal hyperthyroidism leads to altered expression of RAS components in adult offspring, which may be correlated with worse recovery of the cardiac performance after ischemic insults and hypertension.