RESUMEN
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.
Asunto(s)
Cardiomegalia/inducido químicamente , Miocitos Cardíacos/efectos de los fármacos , Receptor de Angiotensina Tipo 1/metabolismo , Triyodotironina/toxicidad , Arrestina beta 2/metabolismo , Animales , Animales Recién Nacidos , Cardiomegalia/metabolismo , Cardiomegalia/patología , Células Cultivadas , Endocitosis/efectos de los fármacos , Activación Enzimática , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Miocitos Cardíacos/metabolismo , Miocitos Cardíacos/patología , Fosforilación , Ratas Wistar , Transducción de Señal , Arrestina beta 2/genéticaRESUMEN
Background: Thyrotoxicosis increases bone turnover, resulting in net bone loss. Sympathetic nervous system (SNS) activation, via ß2-adrenoceptor (ß2-AR) signaling, also has osteopenic effects. Because thyroid hormones (TH) interact with the SNS to regulate several physiological processes, we hypothesized that this interaction also occurs to regulate bone mass. Previous studies support this hypothesis, as α2-AR knockout (KO) mice are less susceptible to thyrotoxicosis-induced osteopenia. Here, we evaluated whether TH-SNS interactions in bone involve ß2-AR signaling. Methods: Thyrotoxicosis was induced in 120-day-old female and male mice with ß2-AR gene inactivation (ß2-AR-/-) by daily treatment with supraphysiological doses of triiodothyronine (T3) for 12 weeks. The impact of thyrotoxicosis on femoral bone microarchitecture, remodeling, fracture risk, and gene expression of the receptor activator of nuclear factor-kappa-B (RANK)-RANK ligand (RANKL)-osteoprotegerin (OPG) pathway was evaluated. In addition, the effect of the ß2-AR-specific agonist clenbuterol (CL) on cAMP accumulation was determined in osteoblastic (MC3T3-E1) cells treated with T3 and/or 17ß-estradiol (E2). Results: Thyrotoxicosis negatively affected trabecular bone microarchitecture in wild-type (WT) females, but this effect was milder or nonexistent in ß2-AR-/- animals, whereas the opposite was seen in males. T3 treatment increased the femoral RANKL/OPG mRNA ratio and the endosteal perimeter and medullary area of the diaphysis in WT females and males, but not in ß2-AR-/- mice, suggesting that T3 promotes endosteal resorption in cortical bone, in a mechanism that involves ß2-AR signaling. T3 treatment increased endocortical mineral apposition rate only in WT females but not in ß2-AR-/- mice, suggesting that TH also induce bone formation in a ß2-AR signaling-dependent mechanism. T3 treatment decreased femoral resistance to fracture only in WT females, but not in KO mice. E2 and CL similarly increased cAMP accumulation in MC3T3-E1 cells; whereas T3 alone had no effect, but it completely blocked E2-stimulated cAMP accumulation, suggesting that some T3 effects on bone may involve E2/cAMP signaling in osteoblasts. Conclusions: These findings sustain the hypothesis that T3 interacts with the SNS to regulate bone morphophysiology in a ß2-AR signaling-dependent mechanism. The data also reveal sex as an important modifier of skeletal manifestations of thyrotoxicosis, as well as a modifier of the TH-SNS interactions to control bone microarchitecture, remodeling, and resistance to fracture.
Asunto(s)
Enfermedades Óseas Metabólicas/metabolismo , Fémur/metabolismo , Receptores Adrenérgicos beta 2/metabolismo , Tirotoxicosis/metabolismo , Agonistas de Receptores Adrenérgicos beta 2/farmacología , Animales , Fenómenos Biomecánicos , Enfermedades Óseas Metabólicas/etiología , Enfermedades Óseas Metabólicas/patología , Enfermedades Óseas Metabólicas/fisiopatología , Remodelación Ósea , Línea Celular , Clenbuterol/farmacología , AMP Cíclico/metabolismo , Estradiol/farmacología , Estrógenos/farmacología , Femenino , Fémur/diagnóstico por imagen , Fémur/patología , Fémur/fisiopatología , Expresión Génica , Masculino , Ratones , Ratones Noqueados , Osteoblastos/efectos de los fármacos , Osteoblastos/metabolismo , Osteoprotegerina/genética , Osteoprotegerina/metabolismo , Ligando RANK/genética , Ligando RANK/metabolismo , Receptor Activador del Factor Nuclear kappa-B/genética , Receptor Activador del Factor Nuclear kappa-B/metabolismo , Receptores Adrenérgicos beta 2/genética , Transducción de Señal , Sistema Nervioso Simpático/metabolismo , Tirotoxicosis/inducido químicamente , Tirotoxicosis/complicaciones , Triyodotironina/farmacología , Triyodotironina/toxicidad , Microtomografía por Rayos XRESUMEN
This study was designed to determine the genotoxicity of a supraphysiological dose of triiodothyronine (T3) in both obese and calorie-restricted obese animals. Fifty male Wistar rats were randomly assigned to one of the two following groups: control (C; nâ=â10) and obese (OB; nâ=â40). The C group received standard food, whereas the OB group was fed a hypercaloric diet for 20 weeks. After this period, half of the OB animals (nâ=â20) were subjected to a 25%-calorie restriction of standard diet for 8 weeks forming thus a new group (OR), whereas the remaining OB animals were kept on the initial hypercaloric diet. During the following two weeks, 10 OR animals continued on the calorie restriction diet, whereas the remaining 10 rats of this group formed a new group (ORS) given a supraphysiological dose of T3 (25 µg/100 g body weight) along with the calorie restriction diet. Similarly, the remaining OB animals were divided into two groups, one that continued on the hypercaloric diet (OB, nâ=â10), and one that received the supraphysiological dose of T3 (25 µg/100 g body weight) along with the hypercaloric diet (OS, nâ=â10) for two weeks. The OB group showed weight gain, increased adiposity, insulin resistance, increased leptin levels and genotoxicity; T3 administration in OS animals led to an increase in genotoxicity and oxidative stress when compared with the OB group. The OR group showed weight loss and normalized levels of adiposity, insulin resistance, serum leptin and genotoxicity, thus having features similar to those of the C group. On the other hand, the ORS group, compared to OR animals, showed higher genotoxicity. Our results indicate that regardless of diet, a supraphysiological dose of T3 causes genotoxicity and potentiates oxidative stress.
Asunto(s)
Restricción Calórica , Hipertiroidismo/complicaciones , Obesidad/etiología , Triyodotironina/toxicidad , Tejido Adiposo , Animales , Composición Corporal , Peso Corporal , Ensayo Cometa , Ingestión de Energía , Resistencia a la Insulina , Leptina/sangre , Masculino , Malondialdehído/metabolismo , Ratas , Triyodotironina/administración & dosificación , Triyodotironina/sangreRESUMEN
Parameters related to hepatic oxidative stress, cell injury, phagocytic activity, and liver histology were studied in control rats and in animals subjected to L-3,3',5-triiodothyronine (T3) and/or lindane administration. Hyperthyroidism elicited a calorigenic response and increased rates of hepatic O2 uptake, which were not modified by lindane treatment. T3 diminished serum lindane levels as well as those in the liver and adipose tissue, whereas lindane enhanced serum T3 levels in animals given T3. Compared with control rats, lindane significantly increased the rate of formation of thiobarbituric acid reactants (TBARS) by the liver, with no changes in either the reduced glutathione (GSH) content, the TBARS/GSH ratio as indicator of oxidative stress, or in the fractional rates of lactate dehydrogenase (LDH) and GSH efflux from perfused livers as integrity parameters. Hyperthyroidism induced GSH depletion in the liver, with a significant enhancement in the TBARS formation, the TBARS/GSH ratio, and in the fractional LDH and GSH efflux. These parameters were increased further by joint T3 and lindane administration in a magnitude exceeding the sum of the effects produced by the separate treatments. In addition, hyperthyroidism led to Kupffer cell hyperplasia and significant increases in serum glutamate oxalacetate transaminase (GOT) and in hepatic zymosan-induced chemiluminescence, while liver myeloperoxidase (MPO) activity was found unchanged, compared with controls. Rats treated with lindane presented normal liver histology, with no changes in biochemical parameters related to cell injury. The joint administration of T3 and lindane, however, elicited a marked elevation in serum GOT and glutamate pyruvate transaminase (GPT), concomitantly with extensive liver necrosis and the presence of granulomas containing lymphocytes, Kupffer cells and polymorphonuclear leukocytes (PMN). In this condition, hepatic zymosan-induced light emission and MPO activity were enhanced over control values. It is concluded that hyperthyroidism increases the susceptibility of the liver to the toxic effects of lindane, which seems to be accomplished by potentiation of the hepatic oxidative stress status. The latter effect may be conditioned by an enhanced phagocytic respiratory burst activity due to the observed Kupffer cell hyperplasia and PMN infiltration, in addition to the increased production of reactive oxygen species in parenchymal cells.