Differential regulation of the myosin heavy chain genes alpha and beta in rat atria and ventricles: role of antisense RNA

The Timing Sequence and Mechanism of Aging in Endocrine Organs

The world is increasingly aging, and there is an urgent need to find a safe and effective way to delay the aging of the body. It is well known that the endocrine glands are one of the most important organs in the context of aging. Failure of the endocrine glands lead to an abnormal hormonal environment, which in turn leads to many age-related diseases. The aging of endocrine glands is closely linked to oxidative stress, cellular autophagy, genetic damage, and hormone secretion. The first endocrine organ to undergo aging is the pineal gland, at around 6 years old. This is followed in order by the hypothalamus, pituitary gland, adrenal glands, gonads, pancreatic islets, and thyroid gland. This paper summarises the endocrine gland aging-related genes and pathways by bioinformatics analysis. In addition, it systematically summarises the changes in the structure and function of aging endocrine glands as well as the mechanisms of aging. This study will advance research in the field of aging and help in the intervention of age-related diseases.

T3 Critically Affects the Mhrt/Brg1 Axis to Regulate the Cardiac MHC Switch: Role of an Epigenetic Cross-Talk

The LncRNA my-heart (Mhrt) and the chromatin remodeler Brg1 inhibit each other to respectively prevent or favor the maladaptive α-myosin-heavy-chain (Myh6) to β-myosin-heavy-chain (Myh7) switch, so their balance crucially guides the outcome of cardiac remodeling under stress conditions. Even though triiodothyronine (T3) has long been recognized as a critical regulator of the cardiac Myh isoform composition, its role as a modulator of the Mhrt/Brg1 axis is still unexplored. Here the effect of T3 on the Mhrt/Brg1 regulatory circuit has been analyzed in relation with chromatin remodeling and previously identified T3-dependent miRNAs. The expression levels of Mhrt, Brg1 and Myh6/Myh7 have been assessed in rat models of hyperthyroidism or acute myocardial ischemia/reperfusion (IR) treated with T3 replacement therapy. To gain mechanistic insights, in silico analyses and site-directed mutagenesis have been adopted in combination with gene reporter assays and loss or gain of function strategies in cultured cardiomyocytes. Our results indicate a pivotal role of Mhrt over-expression in the T3-dependent regulation of Myh switch. Mechanistically, T3 activates the Mhrt promoter at two putative thyroid hormone responsive elements (TRE) located in a crucial region that is necessary for both Mhrt activation and Brg1-dependent Mhrt repression. This newly identified T3 mode of action requires DNA chromatinization and is critically involved in mitigating the repressive function of the Brg1 protein on Mhrt promoter. In addition, T3 is also able to prevent the Brg1 over-expression observed in the post-IR setting through a pathway that might entail the T3-mediated up-regulation of miR-208a. Taken together, our data evidence a novel T3-responsive network of cross-talking epigenetic factors that dictates the cardiac Myh composition and could be of great translational relevance.

Characterization of biventricular alterations in myocardial (reverse) remodelling in aortic banding-induced chronic pressure overload

Aortic Stenosis (AS) is the most frequent valvulopathy in the western world. Traditionally aortic valve replacement (AVR) has been recommended immediately after the onset of heart failure (HF) symptoms. However, recent evidence suggests that AVR outcome can be improved if performed earlier. After AVR, the process of left ventricle (LV) reverse remodelling (RR) is variable and frequently incomplete. In this study, we aimed at detecting mechanism underlying the process of LV RR regarding myocardial structural, functional and molecular changes before the onset of HF symptoms. Wistar-Han rats were subjected to 7-weeks of ascending aortic-banding followed by a 2-week period of debanding to resemble AS-induced LV remodelling and the early events of AVR-induced RR, respectively. This resulted in 3 groups: Sham (n = 10), Banding (Ba, n = 15) and Debanding (Deb, n = 10). Concentric hypertrophy and diastolic dysfunction (DD) were patent in the Ba group. Aortic-debanding induced RR, which promoted LV functional recovery, while cardiac structure did not normalise. Cardiac parameters of RV dysfunction, assessed by echocardiography and at the cardiomyocyte level prevailed altered after debanding. After debanding, these alterations were accompanied by persistent changes in pathways associated to myocardial hypertrophy, fibrosis and LV inflammation. Aortic banding induced pulmonary arterial wall thickness to increase and correlates negatively with effort intolerance and positively with E/e′ and left atrial area. We described dysregulated pathways in LV and RV remodelling and RR after AVR. Importantly we showed important RV-side effects of aortic constriction, highlighting the impact that LV-reverse remodelling has on both ventricles.

Novel Insight Into the Epigenetic and Post-transcriptional Control of Cardiac Gene Expression by Thyroid Hormone

Thyroid hormone (TH) signaling is critically involved in the regulation of cardiovascular physiology. Even mild reductions of myocardial TH levels, as occur in hypothyroidism or low T3 state conditions, are thought to play a role in the progression of cardiac disorders. Due to recent advances in molecular mechanisms underlying TH action, it is now accepted that TH-dependent modulation of gene expression is achieved at multiple transcriptional and post-transcriptional levels and involves the cooperation of many processes. Among them, the epigenetic remodeling of chromatin structure and the interplay with non-coding RNA have emerged as novel TH-dependent pathways that add further degrees of complexity and broaden the network of genes controlled by TH signaling. Increasing experimental and clinical findings indicate that aberrant function of these regulatory mechanisms promotes the evolution of cardiac disorders such as post-ischemic injury, pathological hypertrophy, and heart failure, which may be reversed by the correction of the underlying TH dyshomeostasis. To encourage the clinical implementation of a TH replacement strategy in cardiac disease, here we discuss the crucial effect of epigenetic modifications and control of non-coding RNA in TH-dependent regulation of biological processes relevant for cardiac disease evolution.

Thyroid hormones and cardiac remodeling

Thyroid hormones have many cardioprotective actions expressed mainly through the action of T3 on thyroid receptors α1 and β1. They are procontractile anti-apoptotic, anti-inflammatory, and anti-fibrotic, promote angiogenesis and regeneration, and have beneficial effects on microRNA profiles. They have proven to be anti-remodeling in numerous animal studies, mostly in rodents; a specific action on the border zone has been described. Studies in humans with DIPTA have been in conclusion. Remodeling can be defined as an increase of ≥20 % of the end-diastolic or end-systolic volume, together with a return to the fetal phenotype. An overview of animal and clinical studies is given.

Perinatal exposure to glyphosate-based herbicide alters the thyrotrophic axis and causes thyroid hormone homeostasis imbalance in male rats

Glyphosate-based herbicides (GBHs) are widely used in agriculture. Recently, several animal and epidemiological studies have been conducted to understand the effects of these chemicals as an endocrine disruptor for the gonadal system. The aim of the present study was to determine whether GBHs could also disrupt the hypothalamic-pituitary-thyroid (HPT) axis. Female pregnant Wistar rats were exposed to a solution containing GBH Roundup®Transorb (Monsanto). The animals were divided into three groups (control, 5mg/kg/day or 50mg/kg/day) and exposed from gestation day 18 (GD18) to post-natal day 5 (PND5). Male offspring were euthanized at PND 90, and blood and tissues samples from the hypothalamus, pituitary, liver and heart were collected for hormonal evaluation (TSH-Thyroid stimulating hormone, T3-triiodothyronine and T4-thyroxine), metabolomic and mRNA analyses of genes related to thyroid hormone metabolism and function. The hormonal profiles showed decreased concentrations of TSH in the exposed groups, with no variation in the levels of the thyroid hormones (THs) T3 and T4 between the groups. Hypothalamus gene expression analysis of the exposed groups revealed a reduction in the expression of genes encoding deiodinases 2 (Dio2) and 3 (Dio3) and TH transporters Slco1c1 (former Oatp1c1) and Slc16a2 (former Mct8). In the pituitary, Dio2, thyroid hormone receptor genes (Thra1 and Thrb1), and Slc16a2 showed higher expression levels in the exposed groups than in the control group. Interestingly, Tshb gene expression did not show any difference in expression profile between the control and exposed groups. Liver Thra1 and Thrb1 showed increased mRNA expression in both GBH-exposed groups, and in the heart, Dio2, Mb, Myh6 (former Mhca) and Slc2a4 (former Glut4) showed higher mRNA expression in the exposed groups. Additionally, correlation analysis between gene expression and metabolomic data showed similar alterations as detected in hypothyroid rats. Perinatal exposure to GBH in male rats modified the HPT set point, with lower levels of TSH likely reflecting post-translational events. Several genes regulated by TH or involved in TH metabolism and transport presented varying degrees of gene expression alteration that were probably programmed during intrauterine exposure to GBHs and reflects in peripheral metabolism. In conclusion, the role of GBH exposure in HPT axis disruption should be considered in populations exposed to this herbicide.

Normal Thyroid Function and the Risk of Atrial Fibrillation: the Rotterdam Study

CONTEXT

Hyperthyroidism is an established risk factor for atrial fibrillation (AF), but information concerning the association with variations within the normal range of thyroid function and subgroups at risk is lacking.

OBJECTIVE

This study aimed to investigate the association between normal thyroid function and AF prospectively and explore potential differential risk patterns.

DESIGN, SETTING, AND PARTICIPANTS

From the Rotterdam Study we included 9166 participants ≥ 45 y with TSH and/or free T4 (FT4) measurements and AF assessment (1997-2012 median followup, 6.8 y), with 399 prevalent and 403 incident AF cases.

MAIN OUTCOME MEASURES

Outcome measures were 3-fold: 1) hazard ratios (HRs) for the risk of incident AF by Cox proportional-hazards models, 2) 10-year absolute risks taking competing risk of death into account, and 3) discrimination ability of adding FT4 to the CHARGE-AF simple model, an established prediction model for AF.

RESULTS

Higher FT4 levels were associated with higher risks of AF (HR 1.63, 95% confidence interval, 1.19-2.22), when comparing those in the highest quartile to those in lowest quartile. Absolute 10-year risks increased with higher FT4 in participants ≤ 65 y from 1-9% and from 6-12% in subjects ≥ 65 y. Discrimination of the prediction model improved when adding FT4 to the simple model (c-statistic, 0.722 vs 0.729; P = .039). TSH levels were not associated with AF.

CONCLUSIONS

There is an increased risk of AF with higher FT4 levels within the normal range, especially in younger subjects. Adding FT4 to the simple model slightly improved discrimination of risk prediction.

Thyroid Disease and the Heart

Thyroid hormones have an intimate relationship with cardiac function. Some of the most significant clinical signs and symptoms of thyroid disease are the cardiac manifestations. In both hypothyroidism and hyperthyroidism, the characteristic physiological effects of thyroid hormone can be understood from the actions at the molecular and cellular level. Here we explore topics from the metabolism and cellular effects of thyroid hormone to special considerations related to statin and amiodarone therapy for the alterations in thyroid hormone metabolism that accompany heart disease.

Effects of long-term thyroid hormone level alterations, n-3 polyunsaturated fatty acid supplementation and statin administration in rats

Thyroid hormones (THs) play multiple roles in the organism and alterations of their levels can result in many pathological changes. Currently, we use hyperthyroid and hypothyroid rats as "models of a diseased organism" and analyze whether n-3 polyunsaturated fatty acids (n-3 PUFA) administration can ameliorate TH-induced pathophysiological changes. We investigate myosin heavy chain composition, calsequestrin levels, changes in cardiac tissue remodeling and cell-to-cell communication, expression of protein kinases, mitochondrial functions, oxidative stress markers and cell death, changes in serum lipid levels, activities of key enzymes of thyroid hormone metabolism, activity of acetylcholine esterase and membrane anisotropy, as well as mobile behavior and thermal sensitivity. Additionally we also mention our pilot experiments dealing with the effect of statin administration on skeletal muscles and sensory functions. As THs and n-3 PUFA possess multiple sites of potential action, we hope that our complex research will contribute to a better understanding of their actions, which can be useful in the treatment of different pathophysiological events including cardiac insufficiency in humans.

Maternal bisphenol a exposure impacts the fetal heart transcriptome

Conditions during fetal development influence health and disease in adulthood, especially during critical windows of organogenesis. Fetal exposure to the endocrine disrupting chemical, bisphenol A (BPA) affects the development of multiple organ systems in rodents and monkeys. However, effects of BPA exposure on cardiac development have not been assessed. With evidence that maternal BPA is transplacentally delivered to the developing fetus, it becomes imperative to examine the physiological consequences of gestational exposure during primate development. Herein, we evaluate the effects of daily, oral BPA exposure of pregnant rhesus monkeys (Macaca mulatta) on the fetal heart transcriptome. Pregnant monkeys were given daily oral doses (400 µg/kg body weight) of BPA during early (50–100±2 days post conception, dpc) or late (100±2 dpc – term), gestation. At the end of treatment, fetal heart tissues were collected and chamber specific transcriptome expression was assessed using genome-wide microarray. Quantitative real-time PCR was conducted on select genes and ventricular tissue glycogen content was quantified. Our results show that BPA exposure alters transcription of genes that are recognized for their role in cardiac pathophysiologies. Importantly, myosin heavy chain, cardiac isoform alpha (Myh6) was down-regulated in the left ventricle, and ‘A Disintegrin and Metalloprotease 12’, long isoform (Adam12-l) was up-regulated in both ventricles, and the right atrium of the heart in BPA exposed fetuses. BPA induced alteration of these genes supports the hypothesis that exposure to BPA during fetal development may impact cardiovascular fitness. Our results intensify concerns about the role of BPA in the genesis of human metabolic and cardiovascular diseases.

Thyroid hormone and the cardiovascular system

Thyroid hormone has profound effects on the heart and cardiovascular system. This article describes the cellular mechanisms by which thyroid hormone acts at the level of the cardiac myocyte and the vascular smooth muscle cell to alter phenotype and physiology. Because it is well established that thyroid hormone, specifically T(3), acts on almost every cell and organ in the body, studies on the regulation of thyroid hormone transport into cardiac and vascular tissue have added clinical significance. The characteristic changes in cardiovascular hemodynamics and metabolism that accompany thyroid disease states can then be best understood at the cellular level.

Electrophoretic mobility of cardiac myosin heavy chain isoforms revisited: application of MALDI TOF/TOF analysis

The expression of two cardiac myosin heavy chain (MyHC) isoforms in response to the thyroid status was studied in left ventricles (LVs) of Lewis rats. Major MyHC isoform in euthyroid and hyperthyroid LVs had a higher mobility on SDS-PAGE, whereas hypothyroid LVs predominantly contained a MyHC isoform with a lower mobility corresponding to that of the control soleus muscle. By comparing the MyHC profiles obtained under altered thyroid states together with the control soleus, we concluded that MyHCα was represented by the lower band with higher mobility and MyHCβ by the upper band. The identity of these two bands in SDS-PAGE gels was confirmed by western blot and mass spectrometry. Thus, in contrast to the literature data, we found that the MyHCα possessed a higher mobility rate than the MyHCβ isoform. Our data highlighted the importance of the careful identification of the MyHCα and MyHCβ isoforms analyzed by the SDS-PAGE.

Cardiac myosin heavy chain gene regulation by thyroid hormone involves altered histone modifications

The antithetical regulation of cardiac α- and β-myosin heavy chain (MHC) genes by thyroid hormone (T(3)) is not well understood but appears to involve thyroid hormone interaction with its nuclear receptor and MHC promoters as well as cis-acting noncoding regulatory RNA (ncRNA). Both of these phenomena involve epigenetic regulations. This study investigated the extent that altered thyroid state induces histone modifications in the chromatin associated with the cardiac MHC genes. We hypothesized that specific epigenetic events could be identified and linked to cardiac MHC gene switching in response to a hypothyroid or hyperthyroid state. A hypothyroid state was induced in rats by propylthiouracil treatment (PTU), whereas a hyperthyroid (T(3)) was induced by T(3) treatment. The left ventricle was analyzed after 7 days for MHC pre-mRNA expression, and the chromatin was assessed for enrichment in specific histone modifications using chromatin immunoprecipitation quantitative PCR assays. At both the α-MHC promoter and the intergenic region, the enrichment in acetyl histone H3 at K9/14 (H3K9/14ac) and trimethyl histone H3 at K4 (H3K4me3) changed in a similar fashion. They were both decreased with PTU treatment but did not change under T(3), except at a location situated 5' to the antisense intergenic transcription start site. These same marks varied differently on the β-MHC promoter. For example, H3K4me3 enrichment correlated with the β-promoter activity in PTU and T(3) groups, whereas H3K9/14ac was repressed in the T(3) group but did not change under PTU. Histone H3K9me was enriched in chromatin of both the intergenic and α-MHC promoters in the PTU group, whereas histone H4K20me1 was enriched in chromatin of β-MHC promoter in the normal control and T(3) groups. Collectively, these findings provide evidence that specific epigenetic phenomena modulate MHC gene expression in altered thyroid states.