Valproate decreases transgenerationally blood pressure by affecting thyrotropin-releasing hormone promoter DNA methylation and gene expression in spontaneously hypertensive rat.

Central TRH, a neuropeptide, is involved in cardiovascular regulation. We demonstrated that the overexpression of diencephalic TRH (dTRH) in SHR rats can be prevented by antisense treatment, normalizing blood pressure (BP). Valproate (VPA) is an inhibitor of histone deacetylases (HDAC) which modulates gene expression through epigenetic modifications such as DNA methylation. AIMS: Study the role of HDAC inhibition in the regulation of dTRH gene expression and its effect on the pathogenesis of hypertension. MAIN METHODS: We treated 7-weeks-old male and female SHR and WKY rats with VPA for 10 weeks and evaluated BP, dTRH mRNA and methylation gene status. KEY FINDINGS: VPA attenuated the elevated BP and dTRH mRNA expression characteristic of SHR. Indeed, we found a significant 62% reduction in dTRH mRNA expression in the SHR + VPA group compared to control SHR. The decrease TRH mRNA expression induced by VPA was confirmed "in vitro" in a primary neuron culture using trichostatin A. With methylation specific PCR we demonstrated a significant increase in TRH promoter DNA methylation level in SHR + VPA group compared to control SHR. After 2 weeks of treatment interruption, rats were mated. Although they did not receive any treatment, the offspring born from VPA-treated SHR parents showed similar changes in BP, dTRH expression and methylation status, implying a transgenerational inheritance. Our findings suggest that dTRH modulation by epigenetics mechanism affects BP and could be inherited by the next generation in SHR rats.

Cardiac Thyrotropin-releasing Hormone Inhibition Improves Ventricular Function and Reduces Hypertrophy and Fibrosis After Myocardial Infarction in Rats.

BACKGROUND: Cardiac thyrotropin-releasing hormone (TRH) is a tripeptide with still unknown functions. We demonstrated that the left ventricle (LV) TRH system is hyperactivated in spontaneously hypertensive rats and its inhibition prevented cardiac hypertrophy and fibrosis. Therefore, we evaluated whether in vivo cardiac TRH inhibition could improve myocardial function and attenuate ventricular remodeling in a rat model of myocardial infarction (MI). METHODS AND RESULTS: In Wistar rats, MI was induced by a permanent left anterior descending coronary artery ligation. A coronary injection of a specific small interfering RNA against TRH was applied simultaneously. The control group received a scrambled small interfering RNA. Cardiac remodeling variables were evaluated one week later. In MI rats, TRH inhibition decreased LV end-diastolic (1.049 ± 0.102 mL vs 1.339 ± 0.102 mL, P < .05), and end-systolic volumes (0.282 ± 0.043 mL vs 0.515 ± 0.037 mL, P < .001), and increased LV ejection fraction (71.89 ± 2.80% vs 65.69 ± 2.85%, P < .05). Although both MI groups presented similar infarct size, small interfering RNA against TRH treatment attenuated the cardiac hypertrophy index and myocardial interstitial collagen deposition in the peri-infarct myocardium. These effects were accompanied by attenuation in the rise of transforming growth factor-ß, collagen I, and collagen III, as well as the fetal genes (atrial natriuretic peptide, B-type natriuretic peptide, and beta myosin heavy chain) expression in the peri-infarct region. In addition, the expression of Hif1α and vascular endothelial growth factor significantly increased compared with all groups. CONCLUSIONS: Cardiac TRH inhibition improves LV systolic function and attenuates ventricular remodeling after MI. These novel findings support the idea that TRH inhibition may serve as a new therapeutic strategy against the progression of heart failure.

Cardiovascular and body weight regulation changes in transgenic mice overexpressing thyrotropin-releasing hormone (TRH).

Thyrotropin-releasing hormone (TRH) plays several roles as a hormone/neuropeptide. Diencephalic TRH (dTRH) participates in the regulation of blood pressure in diverse animal models, independently of the thyroid status. The present study aimed to evaluate whether chronic overexpression of TRH in mice affects cardiovascular and metabolic variables. We developed a transgenic (TG) mouse model that overexpresses dTrh. Despite having higher food consumption and water intake, TG mice showed significantly lower body weight respect to controls. Also, TG mice presented higher blood pressure, heart rate, and locomotor activity independently of thyroid hormone levels. These results and the higher urine noradrenaline excretion observed in TG mice suggest a higher metabolic rate mediated by sympathetic overflow. Cardiovascular changes were impeded by siRNA inhibition of the diencephalic Trh overexpression. Also, the silencing of dTRH in the TG mice normalized urine noradrenaline excretion, supporting the view that the cardiovascular effects of TRH involve the sympathetic system. Overall, we show that congenital dTrh overexpression leads to an increase in blood pressure accompanied by changes in body weight and food consumption mediated by a higher sympathetic overflow. These results provide new evidence confirming the participation of TRH in cardiovascular and body weight regulation.

Short-term doxorubicin cardiotoxic effects: involvement of cardiac Thyrotropin Releasing Hormone system.

Doxorubicin is an antineoplastic in the anthracycline class widely used for the treatment of several solid tumors and blood cancers. Cardiotoxicity is the major dose-limiting adverse effect of the drug. Chronic and accumulated doxorubicin administration cause myocyte damage and myocardial fibrosis. Doxorubicin-associated cardiotoxicity can be also observed after a short-course drug treatment even without clinical evidence of cardiac disease. Nevertheless, acute underlying mechanisms involved in the initiation of drug-induced cardiotoxicity remain poorly explored despite their similarities with pathophysiological conditions where cardiac TRH (cTRH) plays a central role. We showed that cTRH mediates myocardial injury induced by hypertension, and angiotensin II. Further, cTRH overexpression induces cardiac apoptosis, hypertrophy and fibrosis. AIM: To demonstrate that cTRH could mediate acute doxorubicin cardiotoxicity. MAIN METHOD: A single injection of doxorubicin (10 mg kg/day i.p.) was used to evaluate acute cardiac damage in a short-term experimental model of doxorubicin-induced cardiotoxicity. While inhibiting cTRH by small interfering RNA (siRNA), we evaluated the progression of cardiotoxicity. KEY FINDINGS: We found a doxorubicin-induced TRH overexpression in the LV, which was associated with apoptosis, hypertrophy and fibrosis. siRNA-mediated cTRH suppression prevented the doxorubicin-associated cardiac histological lesions. SIGNIFICANCES: doxorubicin requires an active cardiac TRH system to promote heart injury.

Angiotensin II requires an intact cardiac thyrotropin-releasing hormone (TRH) system to induce cardiac hypertrophy in mouse.

Cardiac tyhrotropin-releasing hormone (TRH) is overexpressed in the hypertrophied left ventricle (LV) of spontaneously hypertensive rats (SHR) and its inhibition prevents both hypertrophy and fibrosis. In a normal heart, the TRH increase induces fibrosis and hypertrophy opening the question of whether TRH could be a common mediator of left ventricular hypertrophy (LVH). We used angiotensin II (AngII) as an inductor of LVH to evaluate if the blockade of LV-TRH prevents hypertrophy and fibrosis in mice. We challenged C57BL/6 adult male mice with an infusion of AngII (osmotic pumps; 2 mg/kg.day) to induce LVH. Groups of mice were injected with an intracardiac siRNA-TRH or scrambled siRNA (siRNA-Con). Body weight, water intake and systolic arterial blood pressure (SABP) were measured daily. AngII significantly increased water intake and SABP (p < .05). Cardiac hypertrophy (heart weight/body weight) was evident in the group with the normal cardiac TRH system. In fact, it was found an AngII-induced increase of TRH precursor mRNA (p < .05) in conjunction with elevated TRH levels measured by immunohistochemistry and western blot. These changes were not observed in the AngII + siRNA-TRH group. Furthermore, AngII increased significantly (p < .05) BNP (hypertrophic marker), collagens I and III and TGF-ß (fibrosis markers) expression in the group with the native cardiac TRH system. These increases were attenuated in the groups with the TRH system blocked despite the high blood pressure. Similar and stronger results were observed "in vitro" with NIH3T3 and H9C2 cell culture models, where, when the TRH system is blocked, AngII stimulus was not able to induce the markers of its fibrotic and hypertrophic effects, so we believe that these effects are independent of any other physiological modifications. Our results point out that cardiac TRH is required for AngII-induced hypertrophic and fibrotic effects.