Thyroid hormone inhibits vascular remodeling through suppression of cAMP response element binding protein activity

The Role of Thyroid Disorders, Obesity, Diabetes Mellitus and Estrogen Exposure as Potential Modifiers for Pulmonary Hypertension

Pulmonary hypertension (PH) is a progressive disorder characterized by a chronic in-crease in pulmonary arterial pressure, frequently resulting in right-sided heart failure and potentially death. Co-existing medical conditions are important factors in PH, since they not only result in the genesis of the disorder, but may also contribute to its progression. Various studies have assessed the impact of thyroid disorders and other endocrine conditions (namely estrogen exposure, obesity, and diabetes mellitus) on the progression of PH. The complex interactions that hormones may have with the cardiovascular system and pulmonary vascular bed can create several pathogenetic routes that could explain the effects of endocrine disorders on PH development and evolution. The aim of this review is to summarize current knowledge on the role of concomitant thyroid disorders, obesity, diabetes mellitus, and estrogen exposure as potential modifiers for PH, and especially for pulmonary arterial hypertension, and to discuss possible pathogenetic routes linking them with PH. This information could be valuable for practicing clinicians so as to better evaluate and/or treat concomitant endocrine conditions in the PH population.

Assessment of causal direction between thyroid function and cardiometabolic health: a Mendelian randomization study

BACKGROUND

Growing evidence have demonstrated that thyroid hormones have been involved in the processes of cardiovascular metabolism. However, the causal relationship of thyroid function and cardiometabolic health remains partly unknown.

METHODS

The Mendelian randomization (MR) was used to test genetic, potentially causal relationships between instrumental variables and cardiometabolic traits. Genetic variants of free thyroxine (FT4) and thyrotropin (TSH) levels within the reference range were used as instrumental variables. Data for genetic associations with cardiometabolic diseases were acquired from the genome-wide association studies of the FinnGen, CARDIoGRAM and CARDIoGRAMplusC4D, CHARGE, and MEGASTROKE. This study was conducted using summary statistic data from large, previously described cohorts. Association between thyroid function and essential hypertension (EHTN), secondary hypertension (SHTN), hyperlipidemia (HPL), type 2 diabetes mellitus (T2DM), ischemic heart disease (IHD), myocardial infarction (MI), heart failure (HF), pulmonary heart disease (PHD), stroke, and non-rheumatic valve disease (NRVD) were examined.

RESULTS

Genetically predicted FT4 levels were associated with SHTN (odds ratio = 0.48; 95% CI = 0.04−0.82,P = 0.027), HPL (odds ratio = 0.67; 95% CI = 0.18−0.88,P = 0.023), T2DM (odds ratio = 0.80; 95% CI = 0.42−0.86,P = 0.005), IHD (odds ratio = 0.85; 95% CI = 0.49−0.98,P = 0.039), NRVD (odds ratio = 0.75; 95% CI = 0.27−0.97,P = 0.039). Additionally, genetically predicted TSH levels were associated with HF (odds ratio = 0.82; 95% CI = 0.68−0.99,P = 0.042), PHD (odds ratio = 0.75; 95% CI = 0.32−0.82,P = 0.006), stroke (odds ratio = 0.95; 95% CI = 0.81−0.97,P = 0.007). However, genetically predicted thyroid function traits were not associated with EHTN and MI.

CONCLUSIONS

Our study suggests FT4 and TSH are associated with cardiometabolic diseases, underscoring the importance of the pituitary-thyroid-cardiac axis in cardiometabolic health susceptibility.

Thyroid hormone receptor alpha sumoylation modulates white adipose tissue stores

Thyroid hormone (TH) and thyroid hormone receptor (THR) regulate stem cell proliferation and differentiation during development, as well as during tissue renewal and repair in the adult. THR undergoes posttranslational modification by small ubiquitin-like modifier (SUMO). We generated the THRA (K283Q/K288R)^−/− mouse model for in vivo studies and used human primary preadipocytes expressing the THRA sumoylation mutant (K283R/K288R) and isolated preadipocytes from mutant mice for in vitro studies. THRA mutant mice had reduced white adipose stores and reduced adipocyte cell diameter on a chow diet, compared to wild-type, and these differences were further enhanced after a high fat diet. Reduced preadipocyte proliferation in mutant mice, compared to wt, was shown after in vivo labeling of preadipocytes with EdU and in preadipocytes isolated from mice fat stores and studied in vitro. Mice with the desumoylated THRA had disruptions in cell cycle G₁/S transition and this was associated with a reduction in the availability of cyclin D2 and cyclin-dependent kinase 2. The genes coding for cyclin D1, cyclin D2, cyclin-dependent kinase 2 and Culin3 are stimulated by cAMP Response Element Binding Protein (CREB) and contain CREB Response Elements (CREs) in their regulatory regions. We demonstrate, by Chromatin Immunoprecipitation (ChIP) assay, that in mice with the THRA K283Q/K288R mutant there was reduced CREB binding to the CRE. Mice with a THRA sumoylation mutant had reduced fat stores on chow and high fat diets and reduced adipocyte diameter.

Thyroid hormone receptor β sumoylation is required for thyrotropin regulation and thyroid hormone production

Thyroid hormone receptor β (THRB) is posttranslationally modified by small ubiquitin-like modifier (SUMO). We generated a mouse model with a mutation that disrupted sumoylation at lysine 146 (K146Q) and resulted in desumoylated THRB as the predominant form in tissues. The THRB K146Q mutant mice had normal serum thyroxine (T4), markedly elevated serum thyrotropin-stimulating hormone (TSH; 81-fold above control), and enlargement of both the pituitary and the thyroid gland. The marked elevation in TSH, despite a normal serum T4, indicated blunted feedback regulation of TSH. The THRB K146Q mutation altered the recruitment of transcription factors to the TSHβ gene promoter, compared with WT, in hyperthyroidism and hypothyroidism. Thyroid hormone content (T4, T3, and rT3) in the thyroid gland of the THRB K146Q mice was 10-fold lower (per gram tissue) than control, despite normal TSH bioactivity. The expression of thyroglobulin and dual oxidase 2 genes in the thyroid was reduced and associated with modifications of cAMP response element-binding protein DNA binding and cofactor interactions in the presence of the desumoylated THRB. Therefore, thyroid hormone production had both TSH-dependent and TSH-independent components. We conclude that THRB sumoylation at K146 was required for normal TSH feedback regulation and TH synthesis in the thyroid gland, by a TSH-independent pathway.

PDGF-BB-mediated activation of CREB in vascular smooth muscle cells alters cell cycling via Rb, FoxO1 and p27kip1

INTRODUCTION & AIM

The vascular response to injury leads to the secretion of several factors, including platelet-derived growth factor (PDGF-BB). PDGF-BB stimulates smooth muscle cell (SMC) conversion to the synthetic phenotype, thereby enhancing proliferation and migration, and contributing to neointimal hyperplasia. Likewise, the cAMP response element binding protein (CREB) transcription factor has been shown to mediate SMC proliferation in response to various mitogens. We therefore investigated the contribution of CREB to PDGF-BB-dependent proliferation of SMCs with the intention of identifying signaling pathways involved both up and downstream of CREB activation.

METHODS & RESULTS

Treatments were performed on vascular SMCs from a porcine coronary artery explant model. The role of CREB was examined via adenoviral expression of a dominant-negative CREB mutant (kCREB) as well as inhibition of CREB binding protein (CBP). Involvement of the p27^kip1 pathway was determined using a constitutively expressing p27^kip1 adenoviral vector. PDGF-BB stimulated transient CREB phosphorylation on Ser-133 via ERK1/2-, PI3-kinase- and Src-dependent pathways. Expression of kCREB decreased PDGF-BB-dependent cell proliferation. PCNA expression and Rb phosphorylation were also inhibited by kCREB. These cell cycle proteins are controlled via p27^kip1 expression in response to CREB-dependent post-translational modification of FoxO1. kCREB had no effect on Cyclin D1 expression, but did prevent PDGF-BB-induced Cyclin D1 nuclear translocation. An interaction inhibitor of CBP confirmed that Cyclin D1 is downstream of PDGF-BB and CREB.

CONCLUSION

CREB phosphorylation is required for SMC proliferation in response to PDGF-BB. This phenotypic change requires CBP and is mediated by Cyclin D1 and p27^kip as a result of changes in FoxO1 activity.

Prognostic Value of Free Triiodothyronine Level in Patients With Hypertrophic Obstructive Cardiomyopathy

CONTEXT

Thyroid hormone acts as a fundamental regulator in cardiovascular homeostasis in pathophysiological conditions.

OBJECTIVE

This study aims to determine whether thyroid hormone could be an independent predictor of adverse events in patients with hypertrophic obstructive cardiomyopathy (HOCM).

DESIGN, PATIENTS, AND OUTCOME MEASURES

The original cohort consisted of 965 consecutive patients with HOCM who were admitted to Fuwai Hospital from October 2009 to December 2014, and 756 patients completed thyroid function evaluations. Patients were divided into three groups according to free triiodothyronine (FT3) levels: tertile 1 (<2.81 pg/mL, n = 247), tertile 2 (2.81 to 3.11 pg/mL, n = 250), tertile 3 (3.12 to 4.09 pg/mL, n = 259).

RESULTS

In correlation analysis, FT3 showed significantly positive correlation with left ventricular ejection fraction (r = 0.109, P = 0.003). After a median follow-up of 44 months, a total of 45 (6.0%) endpoints (all-cause mortality or cardiac transplantation) occurred with rates of 13.4%, 3.6%, and 1.2% in tertiles 1, 2, and 3, respectively. Univariate Cox analysis established FT3 as a predictor of endpoint [hazard ratio (HR), 0.111; 95% confidence interval (CI), 0.065, 0.189; P < 0.001]. After adjustment for traditional risk factors, the prognostic value of FT3 level was still significant (HR, 0.216; 95% CI, 0.083, 0.559; P = 0.002). Compared with patients in tertile 3, those in tertile 1 were at a much higher risk of endpoint (HR, 4.918; 95% CI, 1.076, 22.485; P = 0.040).

CONCLUSIONS

FT3 correlated with cardiac function and could serve as an independent predictor of all-cause mortality and cardiac transplantation in patients with HOCM. These results suggest that monitoring thyroid function in HOCM patients is necessary.

Pulmonary hypertension in thyroid diseases

The influence of thyroid hormones on cardiovascular system is well established. Thyroid diseases can effectively enhance the alteration on cardiovascular system by influencing chronotropic and inotropic actions of the heart; altering the strength and the speed of contraction, the speed of relaxation, the duration of the potential of action, and the duration of the refractory period and atrio-ventricular conduction time; modulating circulation and peripheral vascular beds. One of the more intriguing insights in the connection between thyroid diseases and cardiovascular alterations is related to the evaluation of the influence of thyroid hormones on pulmonary vascular beds. Literature reported several studies regarding the association between both hypothyroidism and hyperthyroidism and the occurrence of increased vascular pulmonary arterial pressure. Nevertheless, the pathogenetic mechanisms able to explain such relationship are not fully understood. Many doubts still persist in the comprehension of the mechanisms of pulmonary hypertension in thyroid diseases. The aim of this review was to provide possible explanation about the possible interaction between pulmonary vascular beds and thyroid function in order to evaluate the possibility of novel perspectives in the general management of patients suffering from thyroid and cardiovascular diseases.

Association of low baseline free thyroxin levels with progression of coronary artery calcification over 4 years in euthyroid subjects: the Kangbuk Samsung Health Study

OBJECTIVE

Overt and subclinical hypothyroidism are risk factors for atherosclerosis and cardiovascular diseases. It is unclear whether thyroid hormone levels within the normal range are also associated with atherosclerosis measured by coronary artery calcium (CAC).

CONTEXT

This study aimed to examine the relationship between normal variations in thyroid function and changes in CAC.

MEASUREMENTS

We conducted a 4-year retrospective study of 2173 apparently healthy men and women with normal thyroid hormone levels. Their free thyroxin (FT4), free triiodothyronin (FT3) and thyroid-stimulating hormone (TSH) levels were measured by electrochemiluminescent immunoassay. The CAC score (CACS) of each subject was measured by multidetector computed tomography in both 2010 and 2014. Progression of CAC was defined as a CACS change over 4 years > 0.

RESULTS

The mean CACS changes over 4 years by quartiles of baseline FT4 level (lowest to highest) were 12·9, 8·43, 7·82 and 7·81 (P = 0·028). CAC progression was not significantly associated with either the baseline FT3 or TSH levels. The odds ratios (OR) for CAC progression over 4 years (highest vs lowest quartile for baseline FT4) were 0·647 (95% confidence interval (CI) 0·472-0·886) after adjustment for confounding factor, which were attenuated with further adjustment for lipid profiles, homoeostasis model assessment of insulin resistance, high-sensitivity C-reactive protein and hypertension [0·747 (95% CI 0·537-1·038)]. Quartiles of baseline FT3 or TSH level did not show any increased OR for CAC progression after adjustment for confounding factors.

CONCLUSIONS

In this cohort of euthyroid men and women, a low baseline FT4 level was associated with a high risk of CACS progression over 4 years.

Raised HIF1α during normoxia in high altitude pulmonary edema susceptible non-mountaineers

High altitude pulmonary edema (HAPE) susceptibility is associated with EGLN1 polymorphisms, we hypothesized that HAPE-susceptible (HAPE-S, had HAPE episode in past) subjects may exhibit abnormal HIF1α levels in normoxic conditions. We measured HIF1α levels in HAPE-S and HAPE resistant (HAPE-R, no HAPE episode) individuals with similar pulmonary functions. Hemodynamic responses were also measured before and after normobaric hypoxia (Fi02 = 0.12 for 30 min duration at sea level) in both groups. . HIF1α was higher in HAPE-S (320.3 ± 267.5 vs 58.75 ± 33.88 pg/ml, P < 0.05) than HAPE-R, at baseline, despite no significant difference in baseline oxygen saturations (97.7 ± 1.7% and 98.8 ± 0.7). As expected, HAPE-S showed an exaggerated increase in pulmonary artery pressure (27.9 ± 6 vs 19.3 ± 3.7 mm Hg, P < 0.05) and a fall in peripheral oxygen saturation (66.9 ± 11.7 vs 78.7 ± 3.8%, P < 0.05), when exposed to hypoxia. HIF1α levels at baseline could accurately classify members of the two groups (AUC = 0.87). In a subset of the groups where hemoglobin fractions were additionally measured to understand the cause of elevated hypoxic response at baseline, two of four HAPE-S subjects showed reduced HbA. In conclusion, HIF 1 α levels during normoxia may represent an important marker for determination of HAPE susceptibility.

Triiodothyronine Attenuates Prostate Cancer Progression Mediated by β-Adrenergic Stimulation

Prostate cancer cells are responsive to adrenergic and thyroid stimuli. It is well established that β-adrenergic activation (protein kinase A [PKA]/cAMP response element binding protein [CREB]) promotes cancer progression, but the role of thyroid hormones is poorly understood. We analyzed the effects of β-adrenergic stimulation (isoproterenol [ISO]) and/or thyroid hormone on neuroendocrine (NE) differentiation and cell invasion, using in vivo (LNCaP tumor) and in vitro models (LNCaP and DU145 human cells). Nude mice were inoculated with LNCaP cells and were treated for 6 wks with ISO (200 μg/d), triiodothyronine (T3, 2.5 μg/d) or both. ISO alone reduced tumor growth but increased tumor expression of cAMP response element (CRE)-dependent genes (real-time polymerase chain reaction, chromogranin A, neuron-specific enolase, survivin, vascular endothelial growth factor [VEGF], urokinase plasmin activator [uPA] and metalloproteinase-9 [MMP-9]) and some proteins related to NE differentiation and/or invasiveness (synaptophysin, VEGF, pCREB). T3 reduced tumor growth and prevented the overexpression of ISO-stimulated factors through a pCREB-independent mechanism. In low invasive LNCaP cells, 50 μmol/L ISO or 100 nmol/L thyroxine (T4) induced the acquisition of NE-like morphology (phase-contrast microscopy), increased VEGF secretion (ELISA) and invasive capacity (Transwell assay), but no synergistic effects were observed after the coadministration of ISO + T4. In contrast, 10 nmol/L T3 alone had no effect, but it prevented the NE-like morphology and invasiveness stimulated by ISO. None of these treatments had any effect on highly invasive DU145 cells. In summary, this study showed that ISO and T4 increase cancer progression, and T3 attenuates ISO-stimulated progression. Further studies are required to determine if changes in the ratio of T4/T3 could be relevant for prostate cancer progression.

Prevention of vascular smooth muscle cell proliferation and injury-induced neointimal hyperplasia by CREB-mediated p21 induction: An insight from a plant polyphenol

Cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP response element (CRE)-binding protein (CREB) signaling cascade negatively regulates platelet-derived growth factor BB (PDGF-BB)-induced smooth muscle cell (SMC) proliferation, which is a critical event in the initiation and development of restenosis and atherosclerotic lesions. Salvianolic acid A (SAA) is one of the most abundant polyphenols extracted from salvia. The aim of this study is to investigate whether SAA exerts an action on PDGF-BB-induced proliferation via cAMP/PKA/CREB mechanism. SAA blunts PDGF-BB-induced human umbilical artery smooth muscle cell (hUASMC) proliferation via p21 induction, as evidenced by its increased mRNA and protein expression levels. The SAA-induced upregulation of p21 involves the cAMP/PKA signaling pathway; a cAMP analog mimicked the effects of SAA and a specific cAMP/PKA inhibitor opposed these effects. SAA also activated CREB, including phosphorylation at Ser133, and induced its nuclear translocation. Deletion and mutational analysis of p21 promoters, co-immunoprecipitation, and western blot analysis showed that CRE is essential for SAA-induced p21 protein expression. Transfection of dominant-negative CREB (mutated Ser133) plasmids into hUASMCs attenuated SAA-stimulated p21 expression. SAA upregulated p21 expression and activated CREB in the neointima of balloon-injured arteries in vivo. Our results indicate that SAA promotes p21 expression in SMCs through the cAMP/PKA/CREB signaling cascade in vitro and prevents injury-induced neointimal hyperplasia.

Thyroid Hormone and Vascular Remodeling

Both hyperthyroidism and hypothyroidism affect the cardiovascular system. Hypothyroidism is known to be associated with enhanced atherosclerosis and ischemic heart diseases. The accelerated atherosclerosis in the hypothyroid state has been traditionally ascribed to atherogenic lipid profile, diastolic hypertension, and impaired endothelial function. However, recent studies indicate that thyroid hormone has direct anti-atherosclerotic effects, such as production of nitric oxide and suppression of smooth muscle cell proliferation. These data suggest that thyroid hormone inhibits atherogenesis through direct effects on the vasculature as well as modification of risk factors for atherosclerosis. This review summarizes the basic and clinical studies on the role of thyroid hormone in vascular remodeling. The possible application of thyroid hormone mimetics to the therapy of hypercholesterolemia and atherosclerosis is also discussed.

Thyroid hormone in the frontier of cell protection, survival and functional recovery

Thyroid hormone (TH) exerts important actions on cellular energy metabolism, accelerating O2consumption with consequent reactive oxygen species (ROS) generation and redox signalling affording cell protection, a response that is contributed by redox-independent mechanisms. These processes underlie genomic and non-genomic pathways, which are integrated and exhibit hierarchical organisation. ROS production led to the activation of the redox-sensitive transcription factors nuclear factor-κB, signal transducer and activator of transcription 3, activating protein 1 and nuclear factor erythroid 2-related factor 2, promoting cell protection and survival by TH. These features involve enhancement in the homeostatic potential including antioxidant, antiapoptotic, antiinflammatory and cell proliferation responses, besides higher detoxification capabilities and energy supply through AMP-activated protein kinase upregulation. The above aspects constitute the molecular basis for TH-induced preconditioning of the liver that exerts protection against ischemia-reperfusion injury, a strategy also observed in extrahepatic organs of experimental animals and with other types of injury, which awaits application in the clinical setting. Noteworthy, re-adjusting TH to normal levels results in several beneficial effects; for example, it lengthens the cold storage time of organs for transplantation from brain-dead donors; allows a superior neurological outcome in infants of <28 weeks of gestation; reduces the cognitive side-effects of lithium and improves electroconvulsive therapy in patients with bipolar disorders.

Association of thyroid-stimulating hormone and cardiovascular risk factors

Thyroid hormone plays an important role in regulating the lipid and glucose metabolism. Previously, much attention has been drawn to define the pathophysiological relationship between thyroid dysfunction and the incidence of cardiovascular diseases (CVDs). While the conditions of overt hypothyroidism and subclinical hypothyroidism were both emphasized, the association between CVD risks and the deregulated circulating thyroid-stimulating hormone (TSH) level remains to be elucidated. Nevertheless, multiple TSH-mediated physiological adaptations, including alteration of the serum lipids, body mass index, blood pressure and insulin sensitivity, have led to the difficulty of clearly examining the association between the TSH level and CVD prevalence. The current review aims to 1) summarize the evidence for the role of thyroid dysfunction and TSH abnormality in CVD pathogenesis and 2) explore the possible underlying molecular mechanisms of TSH-mediated cardiovascular pathology in hopes of providing better therapeutic strategies for the patients with deregulated TSH.

Thyroid hormones and coronary artery calcification in euthyroid men and women

OBJECTIVE

Overt and subclinical hypothyroidism are risk factors for atherosclerosis. It is unclear whether thyroid hormone levels within the normal range are also associated with atherosclerosis measured by coronary artery calcium (CAC).

APPROACH AND RESULTS

We conducted a cross-sectional study of 41 403 apparently healthy young and middle-aged men and women with normal thyroid hormone levels. Free thyroxin, free triiodothyronine, and thyroid-stimulating hormone levels were measured by electrochemiluminescent immunoassay. CAC score was measured by multidetector computed tomography. The multivariable adjusted CAC ratios comparing the highest versus the lowest quartile of thyroid hormones were 0.74 (95% confidence interval, 0.60-0.91; P for trend <0.001) for free thyroxin, 0.81 (0.66-1.00; P for trend=0.05) for free triiodothyronine, and 0.78 (0.64-0.95; P for trend=0.01) for thyroid-stimulating hormone. Similarly, the odds ratios for detectable CAC (CAC >0) comparing the highest versus the lowest quartiles of thyroid hormones were 0.87 (0.79-0.96; P for linear trend <0.001) for free thyroxin, 0.90 (0.82-0.99; P for linear trend=0.02) for free triiodothyronine, and 0.91 (0.83-1.00; P for linear trend=0.03) for thyroid-stimulating hormone.

CONCLUSIONS

In a large cohort of apparently healthy young and middle-aged euthyroid men and women, low-normal free thyroxin and thyroid-stimulating hormone were associated with a higher prevalence of subclinical coronary artery disease and with a greater degree of coronary calcification.

Free triiodothyronine concentrations are inversely associated with microalbuminuria

Thyroid function and microalbuminuria are both associated with vascular disease and endothelial damage. However, whether thyroid function is associated with microalbuminuria is not well established. The objective was to explore the relationship between thyroid hormones and microalbuminuria in Chinese population. A community-based cross-sectional study was performed among 3,346 Chinese adults (aged ≥ 40 years). Serum free triiodothyronine (FT3), free thyroxine (FT4), and TSH (thyroid stimulating hormone) were determined by chemiluminescent microparticle immunoassay. A single-void first morning urine sample was obtained for urinary albumin-creatinine ratio measurement. The prevalence of microalbuminuria decreased according to FT3 quartiles (13.2, 9.5, 8.6, and 8.2%, P for trend = 0.0005). A fully adjusted logistic regression analysis showed that high FT3 levels were associated with low prevalent microalbuminuria. The adjusted odds ratios for microalbuminuria were 0.61 (95% CI, 0.43-0.87, P = 0.007) when comparing the highest with the lowest quartile of FT3. The exclusion of participants with abnormal FT3 did not appreciably change the results (OR = 0.69, 95% CI, 0.49-0.98, P = 0.02). We concluded that serum FT3 levels, even within the normal range, were inversely associated with microalbuminuria in middle-aged and elderly Chinese adults. FT3 concentrations might play a role in the pathogenesis of microalbuminuria.

The transcription factor Foxf1 binds to serum response factor and myocardin to regulate gene transcription in visceral smooth muscle cells

Smooth muscle cells (SMCs) modulate their phenotype from a quiescent contractile state to a dedifferentiated, proliferative and migratory state during the pathogenesis of many diseases, including intestinal pseudoobstruction. Understanding how smooth muscle gene expression is regulated in these different phenotypic states is critical for unraveling the pathogenesis of these diseases. In the current study we examined the specific roles of Foxf1 in visceral SMC differentiation. Data show that Foxf1 is specifically required for expression of several contractile and regulatory proteins such as telokin, smooth muscle γ-actin, and Cav1.2b in visceral SMCs. Mechanistically, Foxf1 directly binds to and activates the telokin promoter. Foxf1 also directly binds to serum response factor (SRF) and myocardin-related transcription factors (MRTFs). Unlike Foxo4 and Foxq1, which bind to MRTFs and block their interaction with SRF, Foxf1 acts synergistically with these proteins to regulate telokin expression. Knock-out of Foxf1 specifically in SMCs results in neonatal lethality, with mice exhibiting GI tract abnormalities. Mice heterozygous for Foxf1 in SMC exhibited impaired colonic contractility and decreased expression of contractile proteins. These studies together with previous studies, suggest that different forkhead proteins can regulate gene expression in SMCs through modulating the activity of the SRF-myocardin axis to either promote or inhibit differentiation and proliferation thereby altering gastrointestinal contractility and development.

New insights into mechanisms of cardioprotection mediated by thyroid hormones

Heart failure represents the final common outcome in cardiovascular diseases. Despite significant therapeutic advances, morbidity and mortality of heart failure remain unacceptably high. Heart failure is preceded and sustained by a process of structural remodeling of the entire cardiac tissue architecture. Prevention or limitation of cardiac remodeling in the early stages of the process is a crucial step in order to ameliorate patient prognosis. Acquisition of novel pathophysiological mechanisms of cardiac remodeling is therefore required to develop more efficacious therapeutic strategies. Among all neuroendocrine systems, thyroid hormone seems to play a major homeostatic role in cardiovascular system. In these years, accumulating evidence shows that the “low triiodothyronine” syndrome is a strong prognostic, independent predictor of death in patients affected by both acute and chronic heart disease. In experimental models of cardiac hypertrophy or myocardial infarction, alterations in the thyroid hormone signaling, concerning cardiac mitochondrion, cardiac interstitium, and vasculature, have been suggested to be related to heart dysfunction. The aim of this brief paper is to highlight new developments in understanding the cardioprotective role of thyroid hormone in reverting regulatory networks involved in adverse cardiac remodeling. Furthermore, new recent advances on the role of specific miRNAs in thyroid hormone regulation at mitochondrion and interstitial level are also discussed.

Thyroid hormone and tissue repair: new tricks for an old hormone?

Although the role of thyroid hormone during embryonic development has long been recognized, its role later in adult life remains largely unknown. However, several lines of evidence show that thyroid hormone is crucial to the response to stress and to poststress recovery and repair. Along this line, TH administration in almost every tissue resulted in tissue repair after various injuries including ischemia, chemical insults, induction of inflammation, or exposure to radiation. This novel action may be of therapeutic relevance, and thyroid hormone may constitute a paradigm for pharmacologic-induced tissue repair/regeneration.

Association between low serum free thyroxine concentrations and coronary artery calcification in healthy euthyroid subjects

BACKGROUND

Considerable evidence suggests that hypothyroidism could promote atherosclerotic vascular changes. We planned this study to investigate whether serum free thyroxine (FT4) or thyroid-stimulating hormone (TSH) levels are associated with coronary artery calcification measured in healthy euthyroid subjects.

METHODS

A cross-sectional analysis was performed among subjects who visited our hospital for a health checkup. Among 1849 subjects, 669 (mean age 55.3±8.8 years; 392 men) with FT4 and TSH in the normal ranges were included after excluding those with diabetes, a history of current smoking and cardiovascular disease (CVD), or the use of drugs for hypertension, antithyroid drugs, or thyroid hormone preparations. Coronary artery calcium scores (CACS) were measured by multi-detector computed tomography.

RESULTS

Subjects with a CACS >100 had lower FT4 levels than those with a lower CACS (p=0.017), whereas no difference was observed in the TSH levels among CACS categories. FT4 levels had an odds ratio of 0.06 for high CACS (95% confidence interval=0.01-0.74; p=0.028) after the adjustment for CVD risk factors. In multivariate regression analysis, CACS was negatively correlated with FT4 levels (β=-0.823, p=0.032), and the inverse association between FT4 and CACS remained significant only in men (p=0.011).

CONCLUSION

FT4 levels were inversely associated with coronary artery calcification in euthyroid healthy subjects, especially in men independent of conventional CVD risk factors. Further studies are needed to validate whether subjects with decreased FT4 levels within the normal reference range are at a high CVD risk and have poor cardiovascular outcomes.

Relative hypoadiponectinemia, insulin resistance, and increased visceral fat in euthyroid prepubertal girls with low-normal serum free thyroxine

A lower activity of the thyroid axis within the clinical reference range is related to a dysmetabolic phenotype in adult populations. We posited that such an association is already present as early as in prepubertal childhood. Serum thyroid stimulating hormone (TSH) and free T4, body fat (bioelectric impedance), insulin resistance (homeostasis model assessment of insulin resistance (HOMA(IR))), total and high molecular weight (HMW)-adiponectin and serum lipids were assessed in 234 euthyroid prepubertal children (113 boys and 121 girls) attending primary care clinics. Visceral fat (abdominal ultrasound) was measured in a subset of these subjects (n = 147; 74 boys and 73 girls). Explants of visceral adipose tissue from an additional six prepubertal children (three boys and three girls) were used to study the regulation of total and HMW-adiponectin by thyroid hormone. Serum free T4 was in girls independently associated with HMW-adiponectin, HOMA(IR) and visceral fat, so that circulating HMW-adiponectin decreased by 30% (β = 0.305 P < 0.005, R(2) = 0.13) and HOMA(IR) and visceral fat increased, respectively, by 90% (β = -0.255 P < 0.01, R(2) = 0.05) and 30% (β = -0.369, P < 0.005, R(2) = 0.12) from the highest to the lowest tertile of serum free T4. Nonsignificant differences in these parameters were found in boys. Treatment of visceral fat explants with thyroid hormone increased total and HMW-adiponectin by 70% and 53%, respectively, above control values (P < 0.01). In conclusion, a dysmetabolic phenotype, consisting of relative hypoadiponectinemia, insulin resistance and increased visceral fat, is associated with low-normal serum free thyroxine in euthyroid prepubertal girls. These associations may be partly explained by a positive regulation of HMW-adiponectin secretion by thyroid hormone.

Baseline levels and trimestral variation of triiodothyronine and thyroxine and their association with mortality in maintenance hemodialysis patients

BACKGROUND AND OBJECTIVES

Conflicting evidence exists with regard to the association of thyroid hormones and mortality in dialysis patients. This study assesses the association between basal and trimestral variation of thyroid stimulating hormone, triiodothyronine, and thyroxine and mortality.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In 210 prevalent hemodialysis patients, serum triiodothyronine, thyroxine, thyroid stimulating hormone, and interleukin-6 were measured 3 months apart. Cardiovascular and non-cardiovascular deaths were registered during follow-up. Based on fluctuations along tertiles of distribution, four trimestral patterns were defined for each thyroid hormone: persistently low, decrease, increase, and persistently high. The association of baseline levels and trimestral variation with mortality was investigated with Kaplan-Meier curves and Cox proportional hazard models.

RESULTS

During follow-up, 103 deaths occurred. Thyroid stimulating hormone levels did not associate with mortality. Patients with relatively low basal triiodothyronine concentrations had higher hazards of dying than patients with high levels. Longitudinally, patients with persistently low levels of triiodothyronine during the 3-month period had higher mortality hazards than those having persistently high levels. These associations were mainly attributable to cardiovascular-related mortality. The association between thyroxine and mortality was not altered after adjustment for triiodothyronine.

CONCLUSIONS

Hemodialysis patients with reduced triiodothyronine or thyroxine levels bear an increased mortality risk, especially due to cardiovascular causes. This was true when considering both baseline measurements and trimestral variation patterns. Our longitudinal design adds observational evidence supporting the hypothesis that the link may underlie a causal effect.

Associations of triiodothyronine levels with carotid atherosclerosis and arterial stiffness in hemodialysis patients

BACKGROUND AND OBJECTIVES

End-stage renal disease is linked to alterations in thyroid hormone levels and/or metabolism, resulting in a high prevalence of subclinical hypothyroidism and low triiodothyronine (T3) levels. These alterations are involved in endothelial damage, cardiac abnormalities, and inflammation, but the exact mechanisms are unclear. In this study, we investigated the relationship between serum free-T3 (fT3) and carotid artery atherosclerosis, arterial stiffness, and vascular calcification in prevalent patients on conventional hemodialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

137 patients were included. Thyroid-hormone levels were determined by chemiluminescent immunoassay, carotid artery-intima media thickness (CA-IMT) by Doppler ultrasonography, carotid-femoral pulse wave velocity (c-f PWV), and augmentation index by Sphygmocor device, and coronary artery calcification (CAC) scores by multi-slice computerized tomography.

RESULTS

Mean fT3 level was 3.70 ± 1.23 pmol/L. Across decreasing fT3 tertiles, c-f PWV and CA-IMT values were incrementally higher, whereas CACs were not different. In adjusted ordinal logistic regression analysis, fT3 level (odds ratio, 0.81; 95% confidence interval, 0.68 to 0.97), age, and interdialytic weight gain were significantly associated with CA-IMT. fT3 level was associated with c-f PWV in nondiabetics but not in diabetics. In nondiabetics (n = 113), c-f PWV was positively associated with age and systolic BP but negatively with fT3 levels (odds ratio = 0.57, 95% confidence interval 0.39 to 0.83).

CONCLUSIONS

fT3 levels are inversely associated with carotid atherosclerosis but not with CAC in hemodialysis patients. Also, fT3 levels are inversely associated with surrogates of arterial stiffness in nondiabetics.

Thyroid hormone induces artery smooth muscle cell proliferation: discovery of a new TRalpha1-Nox1 pathway

Thyroid hormone (T3) can stimulate protein synthesis and cell growth. NOX1 is a mitogenic oxidase. The aim of this study was to test a novel hypothesis that T3 induces artery smooth muscle cell proliferation by up-regulating NOX1. Immunofluoresence confocal microscopy was used to visualize the sub-cellular localization of NOX1 and TRα1 in rat aorta smooth muscle (RASM) cells. Optical sectioning showed that TRα1 and NOX1 co-localized around the nucleus. T3 promoted RASM cell proliferation as determined by the fact that T3 significantly increased the number of cytokinesis cells, proliferating cellular nuclear antigen (PCNA) and smooth muscle α-actin (SM α-actin). T3 increased NOX1 expression at both the transcription (mRNA) and translation (protein) levels as evaluated by RT-PCR and Western blot, respectively. T3 also significantly increased the intracellular ROS production based on the oxidation of 2’,7’-dichlorodihydrofluoresein (H₂DCF) to a fluorescent 2’,7’-dichlorofluoresein (DCF). RNAi silence of TRα1 or NOX1 abolished T3-induced intracellular ROS generation and PCNA and SM α-actin expression, indicating that TRα1 and NOX1 mediated T3-induced RASM cell proliferation. Notably, RNAi silence of TRα1 blocked the T3-induced increase in NOX1 expression, whereas silence of NOX1 did not affect TRα1 expression, disclosing a new pathway, i.e. T3-TRα1-NOX1-cell proliferation. TRα1 and NOX1 co-localized around the nucleus. T3 induced RASM cell proliferation by up-regulating NOX1 in a TRα1-dependent manner.

Carotid artery intima media thickness is inversely related to serum free thyroxine in euthyroid subjects

OBJECTIVE

The effect of thyroid function on cardiovascular risk may extend to the euthyroid range. In euthyroid subjects, we determined whether carotid artery intima media thickness (IMT), a measure of subclinical atherosclerosis, is related to thyroid function.

DESIGN AND SUBJECTS

Cross-sectional study in a cohort of 78 nonsmoking, predominantly middle-aged, euthyroid subjects (44 men and 34 women, mean age 56 years, TSH between 0.5 mU/l and 4.0 mU/l and FT4 between 11.0 pmol/l and 19.5 pmol/l).

MEASUREMENTS

IMT (mean of three segments in both carotid arteries by ultrasonography), clinical factors, insulin resistance (HOMA(ir)), plasma lipids, C-reactive protein (CRP), serum FT4, TSH and thyroid autoantibodies.

RESULTS

In several multiple linear regression models, age- and sex-adjusted IMT was found to be independently related to either pulse pressure and body mass index (BMI), to high density lipoprotein (HDL) cholesterol or to FT4, but not to TSH, thyroid autoantibodies, HOMA(ir), CRP, non-HDL cholesterol and triglycerides. In a subsequent model which included age, sex, pulse pressure, body mass index (BMI), HDL cholesterol and FT4, IMT was independently and positively related to age (beta = 0.43, P < 0.001), male sex (beta = 0.34, P = 0.014), pulse pressure (beta = 0.29, P = 0.002), BMI (beta = 0.24, P = 0.007) and inversely related to FT4 (beta = -0.19, P = 0.046). IMT was also inversely related to FT4 in a model which included HDL cholesterol, non-HDL cholesterol and triglycerides.

CONCLUSIONS

In euthyroid subjects, IMT is associated with FT(4), after controlling for clinical factors, lipid levels and thyroid autoantibodies. These findings raise the possibility that, even within the euthyroid range, low normal thyroid function may adversely affect cardiovascular risk.

Review: The association of thyroid dysfunction with all-cause and circulatory mortality: is there a causal relationship?

CONTEXT

Currently there is ongoing debate on whether subclinical and overt thyroid dysfunction may exert deleterious effects on the cardiovascular system with the consequence of increased mortality in affected individuals. We systematically review studies on the relation of thyroid dysfunction with all-cause and circulatory mortality questioning whether thyroid dysfunction is a causal factor for mortality.

METHODS

Two investigators independently searched the MEDLINE database. All case-control and cohort studies published in peer-reviewed journals were selected. Studies on nonthyroidal illness or low-T3 syndrome and reports from highly selected populations were not considered. Risk estimates from studies with appropriate adjustment for confounders were metaanalyzed.

RESULTS

Four among eight studies performed to investigate the association between hyperthyroidism and mortality revealed an increased risk of either all-cause or circulatory mortality. Only the minority of studies, however, adjusted analyses for relevant confounders besides age, sex, and race. Studies after radioiodine therapy were generally biased by indication. Findings from 11 studies that investigated the relation between hypothyroidism and mortality were highly discrepant and partly even mutually exclusive. Some of these discrepancies are explained by confounding and selection.

CONCLUSIONS

The currently available evidence for a causal relation of both hyperthyroidism and hypothyroidism with mortality is weak and should particularly not be used to decide whether patients with subclinical thyroid conditions should be treated. Very old individuals might represent an exception from this rule and may benefit from mildly reduced thyroid function, but this has to be substantiated by further research.

Thyroid disease and vascular function

Altered cardiac function in thyroid disease is well recognized and has been extensively investigated, vascular function has however been less well studied in those with thyroid dysfunction. Thyroid hormones, thyroxine (T(4)) and triiodothyronine (T(3)) are important regulators of cardiac function and cardiovascular hemodynamics. The cardiovascular system responds to minimal but persistent changes in circulating thyroid hormone levels producing changes in vascular reactivity and endothelial function. The detection of endothelial dysfunction and/or arterial stiffness allows early identification of individuals at risk as these occur in both patients with risk factors for coronary artery disease and in those with established disease. This may allow treatment to be targeted at high risk individuals with the aim of slowing the progression of vascular disease. The various methods used to assess arterial function are reviewed and the changes demonstrated in human and animal models of thyroid dysfunction.