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

Increased macrophages contribute to thyroid hormone-induced cardiac alterations in mice

AIMS

The heart is one of the main targets of thyroid hormone. Patients with hyperthyroidism, a disease with high incidence in the population, have increased arrhythmia risk and cardiac hypertrophy, which is an independent predictor of adverse cardiovascular outcomes. Recent research has revealed the essential roles of leukocytes in cardiac homeostasis and stress-induced responses. Here, we aimed to evaluate the role of immune cells in cardiac changes induced by elevated triiodothyronine (T3) levels.

METHODS

The hyperthyroid condition in mice was mimicked by daily injections (i.p.) of T3 (14 μg/100 g BW) for 7 or 14 days.

RESULTS

Increased heart rate and cardiac mass observed after 7 days of T3 treatment was associated with enhanced myocardial population of neutrophils, dendritic cells, and inflammatory phenotypes of monocytes and macrophages, without circulating changes in these cells, as evaluated by flow cytometry. In vitro experiments demonstrated bias toward pro-inflammatory polarization in isolated bone marrow-derived macrophages (BMDM) in response to T3. Interestingly, depletion of macrophages in mice prevented hypertrophic heart growth, tachycardia, and increased gene expression of the pro-inflammatory cytokine interleukin-(IL)-6 caused by hyperthyroid condition.

CONCLUSION

Together, these new findings indicate the involvement of macrophages in the cardiac changes promoted by higher T3 levels. Considering that sustained cardiac growth and tachycardia can potentially lead to heart failure, our results suggest that targeting macrophages might be a novel therapeutic approach for attenuating cardiac disorders caused by hyperthyroidism.

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.

Cardioprotection by Hypothyroidism Is Not Mediated by Favorable Hemodynamics-Role of Canonical Thyroid Hormone Receptor Alpha Signaling

Hypothyroidism has been shown to reduce infarct size in rats, but the underlying mechanisms are unclear. We used isolated pressure-constant perfused hearts of control, hypothyroid and hyperthyroid mice and measured infarct size, functional parameters and phosphorylation of key molecules in cardioprotective signaling with matched heart rate. Compared with controls, hypothyroidism was cardioprotective, while hyperthyroidism was detrimental with enlarged infarct size. Next, we asked how thyroid hormone receptor α (TRα) affects ischemia/reperfusion (IR) injury. Thus, canonical and noncanonical TRα signaling was investigated in the hearts of (i) mice lacking TRα (TRα0), (ii) with a mutation in TRα DNA-binding domain (TRαGS) and (iii) in hyperthyroid TRα0 (TRα0hyper) and TRαGS mice (TRαGShyper). TRα0 mouse hearts were protected against IR injury. Furthermore, infarct size was reduced in the hearts of TRαGS mice that lack canonical TRα signaling but maintain noncanonical TRα action. Hyperthyroidism did not increase infarct size in TRα0 and TRαGS mouse hearts. These cardioprotective effects were not associated with increased phosphorylation of key proteins of RISK, SAFE and eNOS pathways. In summary, chronic hypothyroidism and the lack of canonical TRα signaling are cardioprotective in IR injury and protection is not due to favorable changes in hemodynamics.

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.

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.

Octreotide (somatostatin analog) attenuates cardiac ischemia/reperfusion injury via activating nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling pathway in rat model of hyperthyroidism

Background

Hyperthyroidism is known to increase the risk of ischemic heart diseases. Octreotide has been reported to attenuate ischemia/reperfusion (I/R) injury. Whether it is useful when ischemic heart disease is accompanied with co-morbidities like hyperthyroidism needs more clarifying. So, this study aimed to explore the effect of octreotide on cardiac I/R injury in hyperthyroid rats and to clarify if Nrf2 activation is involved in this effect. Forty adult female Wistar rats were subdivided into control (euthyroid) (n = 10) and hyperthyroid (n = 30) groups. Rats in hyperthyroid group received l-thyroxine (12 mg/L) in drinking water for 35 days, then were randomly divided into three equal subgroups (n = 10): hyperthyroid control positive group, hyperthyroid octreotide treated group, and hyperthyroid octreotide + Nrf2 inhibitor (brusatol) treated group. Isolated hearts were submitted to I/R and evaluated for cardiac hemodynamics and infarct size. Serum T3 and T4, coronary efflux lactate dehydrogenase (LDH) and creatine kinase-myoglobin binding (CK-MB) and cardiac tissue malondialdehyde (MDA) were estimated. Nrf2- regulated gene expressions of HO-1, SOD, GPx, and catalase were assessed.

Results

Octreotide administration to hyperthyroid rats improved baseline and post-ischemic recovery of cardiac hemodynamics, decreased the high coronary efflux LDH and CK-MB and tissue MDA, reduced infarction size, and upregulated the decreased antioxidative enzymes HO-1, SOD, GPx, and catalase mRNA expressions in the hyperthyroid I/R rat hearts. The Nrf2 inhibitor brusatol reversed the cardioprotective effect of octreotide in hyperthyroid I/R rat hearts.

Conclusion

Octreotide can reduce oxidative stress to effectively alleviate I/R injury in the hyperthyroid rat hearts through upregulation of Nrf2-dependent antioxidative signaling pathways.

Wound healing action of nitric oxide-releasing self-expandable collagen sponge

Mounting evidence showing that local nitric oxide (NO) delivery may significantly improve the wound healing process has stimulated the development of wound dressings capable of releasing NO topically. Herein, we describe the preparation of a self-expandable NO-releasing hydrolyzed collagen sponge (CS), charged with the endogenously found NO donor, S-nitrosoglutathione (GSNO). We show that cold pressed and GSNO-charged CS (CS/GSNO) undergo self-expansion to its original 3D shape upon water absorption to a swelling degree of 2,300 wt%, triggering the release of free NO. Topical application of compressed CS/GSNO on wounds in an animal model showed that exudate absorption by CS/GSNO leads to the release of higher NO doses during the inflammatory phase and progressively lower NO doses at later stages of the healing process. Moreover, treated animals showed significant increase in the mRNA expression levels of monocyte chemoattractant protein-1 (MCP-1), murine macrophage marker (F4/80), transforming growth factor beta (TGF-β), stromal cell-derived factor 1 (SDF-1), insulin-like growth factor-1 (IGF-1), nitric oxide synthase(iNOS), and matrix metalloproteinase(MMP-9). Cluster differentiation 31 (CD31), vascular endothelial growth factor (VEGF), and F4/80 were measured on Days 7 and 12 by immunohistochemistry in the cicatricial tissue. These results indicate that the topical delivery of NO enhances the migration and infiltration of leucocytes, macrophages, and keratinocytes to the wounded tissue, as well as the neovascularization and collagen deposition, which are correlated with an accelerated wound closure. Thus, self-expandable CS/GSNO may represent a novel biocompatible and active wound dress for the topical delivery of NO on wounds.

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.

Thyroid hormone protects cardiomyocytes from H2O2-induced oxidative stress via the PI3K-AKT signaling pathway

Oxidative stress plays an important role in the progression of cardiac diseases, including acute myocardial infarction, ischemia/reperfusion (I/R) injury and heart failure. Growing evidence indicates that thyroid hormone has protective properties against cardiovascular diseases. However, little is known about its effect on oxidative stress in cardiomyocytes or the underlying mechanisms. This study showed that T3 pretreatment in vivo significantly reduced cardiac dysfunction by increasing the left ventricular ejection function and ameliorating the pathological changes induced by I/R-induced injury. In an in vitro experiment, T3 inhibited apoptosis in H₂O₂-treated cardiomyocytes, as evidenced by the decreased expression of Bax, cleaved caspase 3 and 9, and increased expression of Bcl-2. In addition, oxidative stress observed in hearts of mice with I/R injury was significantly alleviated by T3 pretreatment, intracellular ROS and mitochondrial ROS overproduction were effectively inhibited, and similar results were also detected in H₂O₂-treated cardiomyocytes in vitro. T3 significantly increased antioxidant protein (Nrf2 and HO-1) expression levels, and inhibited NOX2 and NOX4 protein expression levels in H₂O₂-treated cardiomyocytes. Moreover, T3 preserved mitochondrial functions upon H₂O₂-induced oxidative stress by increasing mitochondrial membrane potential and promoting the expression of mitochondrial biogenesis genes. Notably, the PI3K/AKT signaling was significantly activated by T3 pretreatment in H₂O₂-induced cardiomyocytes. Together, these findings revealed that T3 could be served as potential therapeutic target for protection against cardiac oxidative stress injury through its antioxidant and anti-apoptosis effects, which are mediated by the activation of the PI3K/AKT signaling pathway.