Cardiac hypertrophy that affects hyperthyroidism occurs independently of the NLRP3 inflammasome

Cardiac hypertrophy (CH) is an adaptive response to maintain cardiac function; however, persistent stress responses lead to contractile dysfunction and heart failure. Although inflammation is involved in these processes, the mechanisms that control cardiac inflammation and hypertrophy still need to be clarified. The NLRP3 inflammasome is a cytosolic multiprotein complex that mediates IL-1β production. The priming step of NLRP3 is essential for increasing the expression of its components and occurs following NF-κB activation. Hyperthyroidism triggers CH, which can progress to maladaptive CH and even heart failure. We have shown in a previous study that thyroid hormone (TH)-induced CH is linked to the upregulation of S100A8, leading to NF-κB activation. Therefore, we aimed to investigate whether the NLRP3 inflammasome is involved in TH-induced CH and its potential role in CH pathophysiology. Hyperthyroidism was induced in NLRP3 knockout (NLRP3-KO), Caspase-1-KO and Wild Type (WT) male mice of the C57Bl/6J strain, aged 8-12 weeks, by triiodothyronine (7 μg/100 g BW, i.p.) administered daily for 14 days. Morphological and cardiac functional analysis besides molecular assays showed, for the first time, that TH-induced CH is accompanied by reduced NLRP3 expression in the heart and that it occurs independently of the NLRP3 inflammasome and caspase 1-related pathways. However, NLRP3 is important for the maintenance of basal cardiac function since NLRP3-KO mice had impaired diastolic function and reduced heart rate, ejection fraction, and fractional shortening compared with WT mice.

Beta-arrestin 2 mediates cardiac hypertrophy induced by thyroid hormones via AT1R

We have previously reported that angiotensin II receptor type 1 (AT1R) contributes to the hypertrophic effects of thyroid hormones (TH) in cardiac cells. Even though evidence indicates crosstalks between TH and AT1R, the underlying mechanisms are poorly understood. Beta-arrestin (ARRB) signaling has been described as noncanonical signal transduction pathway that exerts important effects in the cardiovascular system through G-protein-coupled receptors, as AT1R. Herein, we investigated the contribution of ARRB signaling in TH-induced cardiomyocyte hypertrophy. Primary cardiomyocyte cultures were treated with Triiodothyronine (T3) to induce cell hypertrophy. T3 rapidly activates extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, which was partially inhibited by AT1R blockade. Also, ERK1/2 inhibition attenuated the hypertrophic effects of T3. ARRB2 was upregulated by T3, and small interfering RNA assays revealed the role of ARRB2-but not ARRB1-on ERK1/2 activation and cardiomyocyte hypertrophy. Corroborating these findings, the ARRB2-overexpressed cells showed increased expression of hypertrophic markers, which were attenuated by ERK1/2 inhibition. Immunocytochemistry and immunoprecipitation assays revealed the increased expression of nuclear AT1R after T3 stimulation and the increased interaction of AT1R/ARRB2. The inhibition of endocytosis also attenuated the T3 effects on cardiac cells. Our results evidence the contribution of ARRB2 on ERK1/2 activation and cardiomyocyte hypertrophy induced by T3 via AT1R.

Impact of hyperthyroidism on cardiac hypertrophy

The cardiac growth process (hypertrophy) is a crucial phenomenon conserved across a wide array of species and it is critically involved in maintenance of cardiac homeostasis. This process enables organism adaptation to changes of systemic demand and occurs due to a plethora of responses, depending on the type of signal or stimuli received. The growth of cardiac muscle cells in response to environmental conditions depends on the type, strength and duration of stimuli, and results in adaptive physiologic response or non-adaptive pathologic response. Thyroid hormones (TH) have a direct effect on the heart and induce a cardiac hypertrophy phenotype, which may evolve to heart failure. In this review, we summarize the literature on TH function in heart presenting results from experimental studies. We discuss the mechanistic aspects of TH associated with cardiac myocyte hypertrophy, increased cardiac myocyte contractility and electrical remodeling as well as the signaling pathways associated. In addition to classical crosstalk with the Sympathetic Nervous System (SNS), emerging work points to the new endocrine interaction between TH and Renin-Angiotensin System (RAS) is also explored. Given the inflammatory potential of the angiotensin II peptide, this new interaction may open the door for new therapeutic approaches that target key mechanisms responsible for TH-induced cardiac hypertrophy.

Lactate-upregulation of lactate oxidation complex-related genes is blunted in left ventricle of myocardial infarcted rats

Lactate modulates the expression of lactate oxidation complex (LOC)-related genes and cardiac blood flow under physiological conditions, but its modulatory role remains to be elucidated regarding pathological cardiac stress. The present study evaluated the effect of lactate on LOC-related genes expression and hemodynamics of hearts submitted to myocardial infarction (MI). Four weeks after MI or sham operation, isolated hearts of male Wistar rats were perfused for 60 min with Na⁺-lactate (20 mM). As expected, MI reduced cardiac contractility and relaxation with no changes in perfusion. The impaired cardiac hemodynamics were associated with increased reactive oxygen species (ROS) levels (Sham: 19.3±0.5 vs MI: 23.8±0.3 µM), NADPH oxidase (NOX) activity (Sham: 42.2±1.3 vs MI: 60.5±1.5 nmol·h⁻¹·mg⁻¹) and monocarboxylate transporter 1 (mct1) mRNA levels (Sham: 1.0±0.06 vs MI: 1.7±0.2 a.u.), but no changes in superoxide dismutase (SOD), catalase, NADH oxidase (NADox), and xanthine oxidase activities. Lactate perfusion in MI hearts had no additional effect on ROS levels, NADox, and NOX activity, however, it partially reduced mct1 mRNA expression (MI-Lactate 1.3±0.08 a.u.). Interestingly, lactate significantly decreased SOD (MI-Lactate: 54.5±4.2 µmol·mg⁻¹·min⁻¹) and catalase (MI: 1.1±0.1 nmol·mg⁻¹·min⁻¹) activities in MI. Collectively, our data suggest that under pathological stress, lactate lacks its ability to modulate the expression of cardiac LOC-related genes and the perfused pressure in hearts submitted to chronic MI. Together, these data contribute to elucidate the mechanisms involved in the pathogenesis of heart failure induced by MI.

Cardiac microRNA-133 is down-regulated in thyroid hormone-mediated cardiac hypertrophy partially via Type 1 Angiotensin II receptor

Elevated thyroid hormone (TH) levels induce cardiac hypertrophy partially via type 1 Angiotensin II receptor (AT1R). MicroRNAs (miRNAs) are key regulators of cardiac homeostasis, and miR-133 has been shown to be involved in cardiac hypertrophy. However, the potential role of miR-133 in cardiac growth induced by TH is unknown. Thus, we aimed to investigate the miR-133 expression, as well as its potential role in cardiac hypertrophy in response to TH. Wistar rats were subjected to hyperthyroidism combined or not with the AT1R blocker. T3 serum levels were assessed to confirm the hyperthyroid status. TH induced cardiac hypertrophy, as evidenced by higher cardiac weight/tibia length ratio and α-actin mRNA levels, which was prevented by AT1R blocker. miR-133 expression was decreased in TH-induced cardiac hypertrophy in part through the AT1R. Additionally, the cardiac mRNA levels of miR-133 targets, SERCA2a and calcineurin were increased in hyperthyroidism partially via AT1R, as evaluated by real-time RT-PCR. Interestingly, miR-133 levels were unchanged in T3-induced cardiomyocyte hypertrophy in vitro. However, a gain-of-function study revealed that miR-133 mimic blunted the T3-induced cardiomyocyte hypertrophy in vitro. Together, our data indicate that miR-133 expression is reduced in TH-induced cardiac hypertrophy partially by the AT1R and that miR-133 mimic prevents the cardiomyocyte hypertrophy in response to T3 in vitro. These findings provide new insights regarding the mechanisms involved in the cardiac growth mediated by TH, suggesting that miR-133 plays a key role in TH-induced cardiomyocyte hypertrophy.

AMPK signaling pathway is rapidly activated by T3 and regulates the cardiomyocyte growth

Previous studies have indicated that AMP-activated protein kinase (AMPK) plays a critical role in the control of cardiac hypertrophy mediated by different stimuli such as thyroid hormone (TH). Although the classical effects of TH mediating cardiac hypertrophy occur by transcriptional mechanisms, recent studies have identified other responses to TH, which are more rapid and take place in seconds or minutes evidencing that TH rapidly modulates distinct signaling pathway, which might contribute to the regulation of cardiomyocyte growth. Here, we evaluated the rapid effects of TH on AMPK signaling pathway in cultured cardiomyocytes and determined the involvement of AMPK in T3-induced cardiomyocyte growth. We found for the first time that T3 rapidly activated AMPK signaling pathway. The use of small interfering RNA against AMPK resulted in increased cardiomyocyte hypertrophy while the pharmacological stimulation of AMPK attenuated this process, demonstrating that AMPK contributes to regulation of T3-induced cardiomyocyte growth.

MiRNA-208a and miRNA-208b are triggered in thyroid hormone-induced cardiac hypertrophy - role of type 1 Angiotensin II receptor (AT1R) on miRNA-208a/α-MHC modulation

Hyperthyroidism promotes cardiac hypertrophy and the Angiotensin type 1 receptor (AT1R) has been demonstrated to mediate part of this response. Recent studies have uncovered a potentially important role for the microRNAs (miRNAs) in the control of diverse aspects of cardiac function. Then, the objective of the present study was to investigate the action promoted by hyperthyroidism on β-MHC/miR-208b expression and on α-MHC/miR-208a expression, as well as the possible contribution of the AT1R in this event. The findings of this study confirmed that AT1R is a key mediator of the cardiac hypertrophy induced by hyperthyroidism. Additionally, we demonstrated that like β-MHC, miR-208b was down-regulated in the hyperthyroid group. Similarly, like the expression of its host gene, α-MHC, miR-208a expression was up-regulated in response to hyperthyroidism. Finally, our data suggest for the first time that AT1R mediates the hyperthyroidism-induced increase on cardiac miRNA-208a/α-MHC levels, while does not influence on the reduction of miRNA-208b/β-MHC levels.

New insight into the mechanisms associated with the rapid effect of T₃ on AT1R expression

The angiotensin II type 1 receptor (AT1R) is involved in the development of cardiac hypertrophy promoted by thyroid hormone. Recently, we demonstrated that triiodothyronine (T₃) rapidly increases AT1R mRNA and protein levels in cardiomyocyte cultures. However, the molecular mechanisms responsible for these rapid events are not yet known. In this study, we investigated the T₃ effect on AT1R mRNA polyadenylation in cultured cardiomyocytes as well as on the expression of microRNA-350 (miR-350), which targets AT1R mRNA. The transcriptional and translational actions mediated by T₃ on AT1R levels were also assessed. The total content of ubiquitinated proteins in cardiomyocytes treated with T₃ was investigated. Our data confirmed that T₃ rapidly raised AT1R mRNA and protein levels, as assessed by real-time PCR and western blotting respectively. The use of inhibitors of mRNA and protein synthesis prevented the rapid increase in AT1R protein levels mediated by T₃. In addition, T₃ rapidly increased the poly-A tail length of the AT1R mRNA, as determined by rapid amplification of cDNA ends poly-A test, and decreased the content of ubiquitinated proteins in cardiomyocytes. On the other hand, T₃ treatment increased miR-350 expression. In parallel with its transcriptional and translational effects on the AT1R, T₃ exerted a rapid posttranscriptional action on AT1R mRNA polyadenylation, which might be contributing to increase transcript stability, as well as on translational efficiency, resulting to the rapid increase in AT1R mRNA expression and protein levels. Finally, these results show, for the first time, that T₃ rapidly triggers distinct mechanisms, which might contribute to the regulation of AT1R levels in cardiomyocytes.

Reactive oxygen and nitrogen species balance in the determination of thyroid hormones-induced cardiac hypertrophy mediated by renin-angiotensin system

Role of reactive oxygen species (ROS)/nitric oxide (NO) balance and renin-angiotensin system in mediating cardiac hypertrophy in hyperthyroidism was evaluated in an in vivo and in vitro experimental model. Male Wistar rats were divided into four groups: control, thyroid hormone, vitamin E (or Trolox, its hydrosoluble analogue), thyroid hormone+vitamin E. Angiotensin II receptor (AT1/AT2) gene expression, immunocontent of AT1/AT2 receptors, angiotensinogen, NADPH oxidase (Nox2), and nitric oxide synthase isoforms, as well as ROS concentration (hydrogen peroxide and superoxide anion) were quantified in myocardium. Thyroid hormone increased ROS and NO metabolites, iNOS, nNOS and eNOS isoforms and it was accompanied by cardiac hypertrophy. AT1/AT2 expression and the immunocontent of angiotensinogen and Nox2 were enhanced by thyroid hormone. Antioxidants reduced ROS levels, Nox2, AT1/AT2, NOS isoforms and cardiac hypertrophy. In conclusion, ROS/NO balance may play a role in the control of thyroid hormone-induced cardiac hypertrophy mediated by renin-angiotensin system.

Involvement of the AT1 receptor in the venoconstriction induced by angiotensin II in both the inferior vena cava and femoral vein

Although angiotensin II-induced venoconstriction has been demonstrated in the rat vena cava and femoral vein, the angiotensin II receptor subtypes (AT(1) or AT(2)) that mediate this phenomenon have not been precisely characterized. Therefore, the present study aimed to characterize the pharmacological receptors involved in the angiotensin II-induced constriction of rat venae cavae and femoral veins, as well as the opposing effects exerted by locally produced prostanoids and NO upon induction of these vasomotor responses. The obtained results suggest that both AT(1) and AT(2) angiotensin II receptors are expressed in both veins. Angiotensin II concentration-response curves were shifted toward the right by losartan but not by PD 123319 in both the vena cava and femoral vein. Moreover, it was observed that both 10(-5)M indomethacin and 10(-4)M L-NAME improve the angiotensin II responses in the vena cava and femoral vein. In conclusion, in the rat vena cava and femoral vein, angiotensin II stimulates AT(1) but not AT(2) to induce venoconstriction, which is blunted by vasodilator prostanoids and NO.

Thyroid Hormone Increases TGF-beta1 in Cardiomyocytes Cultures Independently of Angiotensin II Type 1 and Type 2 Receptors

TH-induced cardiac hypertrophy in vivo is accompanied by increased cardiac Transforming Growth Factor-beta1 (TGF-beta1) levels, which is mediated by Angiotensin II type 1 receptors (AT1R) and type 2 receptors (AT2R). However, the possible involvement of this factor in TH-induced cardiac hypertrophy is unknown. In this study we evaluated whether TH is able to modulate TGF-beta1 in isolated cardiac, as well as the possible contribution of AT1R and AT2R in this response. The cardiac fibroblasts treated with T(3) did not show alteration on TGF-beta1 expression. However, cardiomyocytes treated with T(3) presented an increase in TGF-beta1 expression, as well as an increase in protein synthesis. The AT1R blockade prevented the T(3)-induced cardiomyocyte hypertrophy, while the AT2R blockage attenuated this response. The T(3)-induced increase on TGF-beta1 expression in cardiomyocytes was not changed by the use of AT1R and AT2R blockers. These results indicate that Angiotensin II receptors are not implicated in T(3)-induced increase on TGF-beta expression and suggest that the trophic effects exerted by T(3) on cardiomyocytes are not dependent on the higher TGF-beta1 levels, since the AT1R and AT2R blockers were able to attenuate the T(3)-induced cardiomyocyte hypertrophy but were not able to attenuate the increase on TGF-beta1 levels promoted by T(3).

Angiotensin type 1 receptor mediates thyroid hormone-induced cardiomyocyte hypertrophy through the Akt/GSK-3beta/mTOR signaling pathway

Several studies have implicated the renin angiotensin system in the cardiac hypertrophy induced by thyroid hormone. However, whether Angiotensin type 1 receptor (AT1R) is critically required to the development of T3-induced cardiomyocyte hypertrophy as well as whether the intracellular mechanisms that are triggered by AT1R are able to contribute to this hypertrophy model is unknown. To address these questions, we employed a selective small interfering RNA (siRNA, 50 nM) or an AT1R blocker (Losartan, 1 microM) to evaluate the specific role of this receptor in primary cultures of neonatal cardiomyocytes submitted to T3 (10 nM) treatment. The cardiomyocytes transfected with the AT1R siRNA presented reduced mRNA (90%, P < 0.001) and protein (70%, P < 0.001) expression of AT1R. The AT1R silencing and the AT1R blockade totally prevented the T3-induced cardiomyocyte hypertrophy, as evidenced by lower mRNA expression of atrial natriuretic factor (66%, P < 0.01) and skeletal alpha-actin (170%, P < 0.01) as well as by reduction in protein synthesis (85%, P < 0.001). The cardiomyocytes treated with T3 demonstrated a rapid activation of Akt/GSK-3beta/mTOR signaling pathway, which was completely inhibited by the use of PI3K inhibitors (LY294002, 10 microM and Wortmannin, 200 nM). In addition, we demonstrated that the AT1R mediated the T3-induced activation of Akt/GSK-3beta/mTOR signaling pathway, since the AT1R silencing and the AT1R blockade attenuated or totally prevented the activation of this signaling pathway. We also reported that local Angiotensin I/II (Ang I/II) levels (120%, P < 0.05) and the AT1R expression (180%, P < 0.05) were rapidly increased by T3 treatment. These data demonstrate for the first time that the AT1R is a critical mediator to the T3-induced cardiomyocyte hypertrophy as well as to the activation of Akt/GSK-3beta/mTOR signaling pathway. These results represent a new insight into the mechanism of T3-induced cardiomyocyte hypertrophy, indicating that the Ang I/II-AT1R-Akt/GSK-3beta/mTOR pathway corresponds to a potential mediator of the trophic effect exerted by T3 in cardiomyocytes.

Ectonucleotidase activities are altered in serum and platelets of L-NAME-treated rats

It is well known that hypertension is closely associated to the development of vascular diseases and that the inhibition of nitric oxide biosynthesis by administration of Nomega-Nitro-L-arginine methyl ester hydrochloride(L-NAME) leads to arterial hypertension. In the vascular system, extracellular purines mediate several effects;thus, ADP is the most important platelet agonist and recruiting ag ent, while adenosine, an end product of nucleotide metabolism, is a vasodilator and inhibitor of platelet activation and recruitment. Members of several families of enzymes, known as ectonucleotidases, including E-NTPDases (ecto-nucleoside triphosphate diphosphohydrolase), E-NPP (ecto-nucleotide pyrophosphatase/phosphodiesterase) and 5'-nucleotidase are able to hydrolyze extracellular nucleotides until their respective nucleosides. We investigated the ectonucleotidase activities of serum and platelets from rats made hypertensive by oral administration of L-NAME (30 mg/kg/day for 14 days or 30 mg/kg/day for 14 days plus 7 days of L-NAME washout, in the drinking water) in comparison to normotensive control rats. L-NAME promoted a significant rise in systolic blood pressure from 112 +/- 9.8 to 158 +/- 23 mmHg. The left ventricle weight index (LVWI) was increased in rats treated with L-NAME for 14 days when compared to control animals. In serum samples, ATP, ADP and AMP hydrolysis were reduced by about 27%, 36% and 27%, respectively. In platelets, the decrease in ATP, ADP and AMP hydrolysis was approximately 27%, 24% and 32%, respectively. All parameters recovered after 7 days of L-NAME washout. HPLC demonstrated a reduction in ADP, AMP and hypoxanthine levels by about 64%, 69% and 87%,respectively. In this study, we showed that ectonucleotidase activities are decreased in serum and platelets from L-NAME-treated rats, which should represent an additional risk for the development of hypertension. The modulation of ectonucleotidase activities may represent an approach to antihypertensive therapy via inhibition of spontaneous platelet activation and recruitment, as well as thrombus formation.

Cardiac angiotensin II type I and type II receptors are increased in rats submitted to experimental hypothyroidism

This study assessed the behaviour of angiotensin II (Ang II) receptors in an experimental hypothyroidism model in male Wistar rats. Animals were subjected to thyroidectomy and resting for 14 days. The alteration of cardiac mass was evaluated by total heart weight (HW), right ventricle weight (RVW), left ventricle weight (LVW), ratio of HW, RVW and LVW to body weight (BW) and atrial natriuretic factor (ANF) expression. Cardiac and plasma Ang II levels and serum T3 and T4 were determined. The mRNA and protein levels of Ang II receptors were investigated by RT-PCR and Western blotting, respectively. Functional analyses were performed using binding assays. T3 and T4 levels and the haemodynamic parameters confirmed the hypothyroid state. HW/BW, RVW/BW and LVW/BW ratios and the ANF expression were lower than those of control animals. No change was observed in cardiac or plasma Ang II levels. Both AT1/AT2 mRNA and protein levels were increased in the heart of hypothyroid animals due to a significant increase of these receptors in the RV. Experiments performed in cardiomyocytes showed a direct effect promoted by low thyroid hormone levels upon AT1 and AT2 receptors, discarding possible influence of haemodynamic parameters. Functional assays showed that both receptors are able to bind Ang II. Herein, we have identified, for the first time, a close and direct relation of elevated Ang II receptor levels in hypothyroidism. Whether the increase in these receptors in hypothyroidism is an alternative mechanism to compensate the atrophic state of heart or whether it may represent a potential means to the progression of heart failure remains unknown.

Angiotensin type 1 (AT1) and type 2 (AT2) receptors mediate the increase in TGF-β1 in thyroid hormone-induced cardiac hypertrophy

Increased thyroid hormone (TH) levels are known to induce cardiac hypertrophy. Some studies have provided evidence for a functional link between angiotensin II (ANG II) and transforming growth factor beta1 (TGF-beta1) in the heart, both being able to also induce cardiac hypertrophy. However, the contribution of this growth factor activated directly by TH or indirectly by ANG II in cardiac hypertrophy development remains unknown. To analyze the possible role of TGF-beta1 in cardiac hypertrophy induced by TH and also to evaluate if the TGF-beta1 effect is mediated by ANG II receptors, we employed Wistar rats separated into control, hypothyroid (hypo) and hyperthyroid (T4 - 10) groups combined or not with ANG II receptor blockers (losartan or PD123319). Serum levels of T3 and T4, systolic pressure and heart rate confirmed the thyroid state of the groups. The T4 - 10 group presented a significant increase in cardiac TGF-beta1 levels; however, TGF-beta1 levels in the hypo group did not change in relation to the control. Inhibition of the increase in cardiac TGF-beta1 levels was observed in the groups treated with T4 in association with losartan or PD123319 when compared to the T4 - 10 group. These results demonstrate for the first time the TH-modulated induction of cardiac TGF-beta1 in cardiac hypertrophy, and that this effect is mediated by ANG II receptors.

Tissue-specific modulation of angiotensin-converting enzyme (ACE) in hyperthyroidism

We have previously demonstrated the interaction between the RAS and thyroid hormones (TH). The present study was designed to determine the role of TH in the local regulation of ACE activity and expression in different tissues. Adult male Wistar rats were randomized into three groups: T4-25 and T4-100 (0.025 and 0.100mg/kg of body weight/day of l-thyroxine for 14 days, respectively) and control. Hemodynamic parameters as well as cardiac and renal hypertrophy were evaluated. ACE activity and mRNA levels were determined by Fluorimetric and Northern blot assays, respectively. Both doses increased SBP and HR, as well as inducing cardiac and renal hypertrophy. Pulmonary and serum ACE levels were comparable among the groups. Both doses promoted increased renal ACE activity and expression but surprisingly ACE was diminished in the heart in both hyperthyroid groups. This change was mediated by a tissue-specific transcription mechanism.

Genomic-independent action of thyroid hormones on NTPDase activities in Sertoli cell cultures from congenital hypothyroid rats

The Sertoli cells play an essential role in the maintenance and control of spermatogenesis. The ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase) and 5'-nucleotidase activities can modulate the extracellular adenine nucleotide levels, controlling nucleotide-mediated signaling events in Sertoli cells. Since thyroid hormones (TH) and adenine nucleotides and nucleosides play important modulatory roles in Sertoli cell proliferation and differentiation, the aim of our study was to investigate the effect of hypothyroidism upon the NTPDase and 5'-nucleotidase activities in Sertoli cell cultures, as well as to verify whether these effects may be reversed by short and long-term supplementation with TH. Congenital hypothyroidism was induced by adding 0.02% methimazole in the drinking water from day 9 of gestation and continually until 18 days of age. Hypothyroidism significantly decreased the extracellular ATP and ADP hydrolysis and this effect was significantly reversed when cell cultures were supplemented with 1 microM T3 or 0.1 microM T4 for 30 min. In contrast, AMP hydrolysis was not altered by hypothyroidism, but was increased by T4 supplementation for 24 h. The presence of the enzymes NTPDase 1, 2 and 3 was detected by RT-PCR in Sertoli cell cultures, however, hypothyroidism was not able to alter the expression of these enzymes. These findings demonstrate that TH modify NTPDase activities in hypothyroid Sertoli cells, probably via nongenomic mechanisms and, consequently, may influence the reproductive function throughout development.

Ecto-nucleotide pyrophosphatase/phosphodiesterase as part of a multiple system for nucleotide hydrolysis by platelets from rats: kinetic characterization and biochemical properties

In this study, we describe an ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP) activity in rat platelets. Using p-nitrophenyl 5'-thymidine monophosphate (p-Nph-5'-TMP) as a substrate for E-NPP, we demonstrate an enzyme activity that shares the major biochemical properties described for E-NPPs: alkaline pH dependence, divalent cation dependence and blockade of activity by metal ion chelator. K(m) and V(max) values for p-Nph-5'-TMP hydrolysis were found to be 106 +/- 18 microM and 3.44 +/- 0.18 nmol p-nitrophenol/min/mg (mean +/- SD, n = 5). We hypothesize that an E-NPP is co-localized with an ecto-nucleoside triphosphate diphosphohydrolase and an ecto-5'-nucleotidase on the platelet surface, as part of a multiple system for nucleotide hydrolysis, since they can act under distinct physiological conditions and can be differently regulated. Thus, 0.25 mM suramin inhibited p-Nph-5'-TMP, ATP and ADP hydrolysis, while 0.5 mM AMP decreased only p-Nph-5'-TMP hydrolysis. Besides, 5.0, 10 and 20 mM sodium azide just inhibited ATP and ADP hydrolysis. Angiotensin II (5.0 and 10 nM) affected only ADP hydrolysis. Gadolinium chloride (0.2 and 0.5 mM) strongly inhibited the ATP and ADP hydrolysis. The E-NPP described here represents a novel insight into the control of platelet purinergic signaling.

Early cardiac hypertrophy induced by thyroxine is accompanied by an increase in VEGF-A expression but not by an increase in capillary density

Cardiac hypertrophy in response to hyperthyroidism is well known. However, the effects on cardiac microcirculation are still controversial in this model. The present study evaluated the effects of acute administration of two different thyroxine (T4) dose levels on the angiogenic response in the myocardium. Capillary density (CD), the CD to fiber density (FD) ratio (CD/FD), and intercapillary distance (ICD) were assessed, as was ventricle weight (VW) to body weight (BW) ratio (VW/BW). Collagen I and III messenger ribonucleic acid (mRNA) expression and VEGF-A expression were also determined by reverse transcriptase polymerase chain reaction (RT-PCR). Immunohistochemical detection of proliferating cell nuclear antigen (PCNA) expression in endothelial cell nuclei was also carried out. We simulated an acute hyperthyroidism situation in male Wistar rats by daily intraperitoneal injection of T4 (0.025 or 0.1 mg kg(-1) day(-1)) for 7 days. Hemodynamic parameters showed that T4 did not alter systolic blood pressure (SBP) but significantly increased heart rate (HR). Both T4 doses significantly increased VW. Morphologically, the higher T4 dose resulted in a 33% greater myocardial mass, which was not accompanied by alterations in collagen I and III mRNA expression. The CD and CD/FD parameters were significantly lower in the hyperthyroid rats treated with the higher dose than in the control animals, and PCNA-labeling analysis indicated total absence of marked capillary growth. However, although the acute treatment with T4 did not induce any alteration in capillary number and endothelial cell proliferation, the vascular endothelial growth factor (VEGF)-A mRNA and protein expression were significantly increased with the higher T4 dose. These data indicate that the cardiac hypertrophy induced by acute treatment with thyroid hormone precedes the angiogenic process, which probably occurs later.

Myocardial ultrastructure in cardiac hypertrophy induced by thyroid hormone?an acute study in rats

The early responses of the myocardium ultrastructure under thyroid dysfunction conditions, hemodynamic parameters, cardiac hypertrophy and ultrastructural evaluations were performed in hypothyroid and hyperthyroid rats submitted to different doses [T4-25 and T4-100; 0.025 mg and 0.1 mg kg(-1) body weight (BW).per day, respectively)]. All groups were treated for 7 days. The animals were sacrificed, the hearts were excised and weighed and the left ventricle tissue samples were processed for transmission election microscopy. Systolic blood pressure (SBP) was not altered by administration of T4. An increased heart rate and ratio of heart weight to body weight (HW/BW) were found in the hyperthyroid rats. However, the SBP and HW/BW decreased significantly in hypothyroid rats. No significant ultrastructural alterations were detected when the hypothyroid and T4-25 groups were compared with the control group. Alterations of cardiomyocytes nuclei of these groups were also not detected. Notably, disorganization of intercellular junctions was observed in many cardiomyocytes of T4-100 group. The present results indicate that in the early stages of hyperthyroidism, the cardiac hypertrophy development was mainly due to direct effects of thyroid hormone. Despite cardiac hypertrophy development, there is no ultrastructural evidence of myocardial degeneration.

Thyroxine-induced cardiac hypertrophy: influence of adrenergic nervous system versus renin-angiotensin system on myocyte remodeling

The present study assessed the possible involvement of the renin-angiotensin system (RAS) and the sympathetic nervous system (SNS) in thyroxine (T4)-induced cardiac hypertrophy. Hemodynamic parameters, heart weight (HW), ratio of HW to body weight (HW/BW), and myocyte width were evaluated in absence of thyroid hormone (hypothyroidism) and after T4 administration. Male Wistar rats were used. Some were subjected to thyroidectomies, whereas hyperthyroidism was induced in others via daily intraperitoneal injection of T4 (25 or 100 microg x 100 g BW(-1) x day(-1)) for 7 days. In some cases, T4 administration was combined with the angiotensin I-converting enzyme inhibitor enalapril (Ena), with the angiotensin type 1 (AT1) receptor blocker losartan (Los) or with the beta-adrenergic blocker propanolol (Prop). Hemodynamics and morphology were then evaluated. Systolic blood pressure (SBP) was not altered by administration of either T4 alone or T4 in combination with the specific inhibitors. However, SBP decreased significantly in hypothyroid rats. An increased heart rate was seen after administration of either T4 alone or T4 in combination with either Los or Ena. Although the higher dose of T4 significantly increased HW, HW/BW increased in both T4-treated groups. Ena and Prop inhibited the increase in HW or HW/BW in hyperthyroid rats. Morphologically, both T4 dose levels significantly increased myocyte width, an occurrence prevented by RAS or SNS blockers. There was a good correlation between changes in HW/BW and myocyte width. These results indicate that T4-induced cardiac hypertrophy is associated with both the SNS and the RAS.

Thyroid hormone upregulates ecto-5'-nucleotidase/CD73 in C6 rat glioma cells

Thyroid hormones have profound effects on the central nervous system, such as proliferation, secretion of growth factors and gene expression regulation. Ecto-NTPDases and ecto-5'-nucleotidase can control the extracellular ATP/adenosine levels, which have been described as proliferation factors. Here, we investigated the influence of T(3) on the enzyme cascade which catalyzes interconversion of purine nucleotides in rat C6 glioma cells. Exposure of C6 cells to T(3) caused a dose dependent increase of 30% in the AMP hydrolysis up to 0.25 nM, which was suppressed by actinomycin. No significant alteration was observed on ATP/ADP hydrolysis and T(4) at higher concentrations (10-1000 nM) promoted an increase in AMP hydrolysis that was not dose dependent. T(3) treatment also increased the expression of CD73 mRNA. Besides the importance of the ecto-5'-NT in the cell proliferation and differentiation, its overexpression can enhance extracellular adenosine levels, which could also be an important proliferation signal.