Flavia Fonseca Bloise

Female mice target deleted for the neuromedin B receptor have partial resistance to diet‐induced obesity

Previous studies have proposed a role for neuromedin B (NB), a bombesin‐like peptide, in the control of body weight homeostasis. However, the nature of this role is unclear. The actions of NB are mediated preferentially by NB‐preferring receptors (NBRs). Here we examined the consequences of targeted deletion of NBRs in female mice on body weight homeostasis in mice fed a normolipid diet (ND) or a high‐fat diet (HFD) for 13 weeks. Body weight and food ingestion of neuromedin B receptor knockout (NBR‐KO) mice fed a normolipid diet showed no difference in relation to wild‐type (WT). However, the high‐fat diet induced an 8.9‐ and 4.8‐fold increase in body weight of WT and NBR‐KO, respectively, compared to their controls maintained with a normolipid diet, even though the mice ingested the same amount of calories, regardless of genotype. Comparing mice fed the high‐fat diet, NBR‐KO mice accumulated approximately 45% less fat depot mass than WT, exhibited a lower percentage of fat in their carcasses (19.2 vs. 31.3%), and their adipocytes were less hypertrophied. Serum leptin and leptin mRNA in inguinal and perigonadal fat were lower in HFD NBR‐KO than HFD WT, and serum adiponectin was similar among HFD groups and unaltered in comparison to ND‐fed mice. HFD‐fed WT mice developed glucose intolerance but not the HFD‐fed NBR‐KO mice, although they had similar glycaemia and insulinaemia. NBR‐KO and WT mice on the normolipid diet showed no differences in any parameters, except for a trend to lower insulin levels. Therefore, disruption of the neuromedin B receptor pathway did not change body weight homeostasis in female mice fed a normolipid diet; however, it did result in partial resistance to diet‐induced obesity.

Ouabain inhibits p38 activation in thymocytes

The MAPK p38 is phosphorylated by multiple stimuli and regulates a number of transcription factors. It is reported that activation of p38 leading to the regulation of NFAT may result from an alternative MKK‐independent mechanism. This alternative pathway involves the protein Dlgh1 as an essential scaffold that assembles a module for the activation of p38. Ouabain, a specific inhibitor of the Na+/K+‐ATPase, is capable of inducing the activation of various signal transduction cascades. In the present work, P‐p38 levels of ConA‐activated thymocytes treated with ouabain (1, 10 and 100 nM) were measured as also the effect of ouabain on NFATc1 expression. p38 phosphorylation and NFATc1 levels were analyzed by flow cytometry. The results indicated that ouabain inhibited both ConA‐dependent increase in P‐p38 and NFATc1 levels, which suggests an effect of ouabain on the p38 alternative pathway.

Thyroid hormone regulation of Sirtuin 1 expression and implications to integrated responses in fasted mice

Sirtuin 1 (SIRT1), a NAD(+)-dependent deacetylase, has been connected to beneficial effects elicited by calorie restriction. Physiological adaptation to starvation requires higher activity of SIRT1 and also the suppression of thyroid hormone (TH) action to achieve energy conservation. Here, we tested the hypothesis that those two events are correlated and that TH may be a regulator of SIRT1 expression. Forty-eight-hour fasting mice exhibited reduced serum TH and increased SIRT1 protein content in liver and brown adipose tissue (BAT), and physiological thyroxine replacement prevented or attenuated the increment of SIRT1 in liver and BAT of fasted mice. Hypothyroid mice exhibited increased liver SIRT1 protein, while hyperthyroid ones showed decreased SIRT1 in liver and BAT. In the liver, decreased protein is accompanied by reduced SIRT1 activity and no alteration in its mRNA. Hyperthyroid and hypothyroid mice exhibited increases and decreases in food intake and body weight gain respectively. Food-restricted hyperthyroid animals (pair-fed to euthyroid group) exhibited liver and BAT SIRT1 protein levels intermediary between euthyroid and hyperthyroid mice fed ad libitum. Mice with TH resistance at the liver presented increased hepatic SIRT1 protein and activity, with no alteration in Sirt1 mRNA. These results suggest that TH decreases SIRT1 protein, directly and indirectly, via food ingestion control and, in the liver, this reduction involves TRβ. The SIRT1 reduction induced by TH has important implication to integrated metabolic responses to fasting, as the increase in SIRT1 protein requires the fasting-associated suppression of TH serum levels.

Acute effects of endocannabinoid anandamide and CB1 receptor antagonist, AM251 in the regulation of thyrotropin secretion

We examined the acute effects of endocannabinoid, anandamide, and of synthetic cannabinoid receptor antagonist, AM251[N-(piperidin-1-yl)-1-(2,4-dichlorophenyl)-5-(4-chlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide], on TSH, thyroxine (T(4)), and triiodothyronine (T(3)) secretions. Euthyroid male rats showed a 42% decrease in serum TSH, 2 h after a single i.p. injection of 0.02, but not 0.2 mg/kg body weight (BW), anandamide, accompanied by a 39% reduction in serum T(4), without alteration in serum T(3). At 0.5 and 1 h, these serum hormones showed no significant change. Hypothyroid rats showed a 35% reduction in serum TSH (P<0.01), 2 h after anandamide injection, which had no effect on hyperthyroid rats. In both thyroid states, no modification of serum thyroid hormones was observed. Intraperitoneal injection of 0.17 or 1.7 mg/kg BW AM251 in euthyroid rats caused, 1.5 h later, 1.7-fold or 4.3-fold increase in serum TSH respectively, without changing thyroid hormones. Stimulatory effect of 0.17 mg/kg BW AM251 and inhibitory effect of anandamide was abolished in the group injected with AM251 followed by an anandamide injection, 30 min later. Intracerebroventricular injection of 20 ng (but not 200 ng) anandamide induced a decrease in serum TSH at 60 min after injection, which tended to disappear at 120 min. Anterior pituitary explants presented significant reduction in TSH release in the presence of 10(-7) M anandamide in incubation medium, which was blocked by 10(-7) M AM251. In conclusion, anandamide has the ability to acutely inhibit TSH release in eu- and hypothyroid rats, acting at the hypothalamus-pituitary axis. Since, in addition, the cannabinoid receptor antagonist AM251 increased TSH release, we suggest that endocannabinoid system has a role as negative regulator of TSH secretion.

Role of thyroid hormone in skeletal muscle physiology

Thyroid hormones (TH) are crucial for development, growth, differentiation, metabolism and thermogenesis. Skeletal muscle (SM) contractile function, myogenesis and bioenergetic metabolism are influenced by TH. These effects depend on the presence of the TH transporters MCT8 and MCT10 in the plasma membrane, the expression of TH receptors (THRA or THRB) and hormone availability, which is determined either by the activation of thyroxine (T4) into triiodothyronine (T3) by type 2 iodothyronine deiodinases (D2) or by the inactivation of T4 into reverse T3 by deiodinases type 3 (D3). SM relaxation and contraction rates depend on T3 regulation of myosin expression and energy supplied by substrate oxidation in the mitochondria. The balance between D2 and D3 expression determines TH intracellular levels and thus influences the proliferation and differentiation of satellite cells, indicating an important role of TH in muscle repair and myogenesis. During critical illness, changes in TH levels and in THR and deiodinase expression negatively affect SM function and repair. This review will discuss the influence of TH action on SM contraction, bioenergetics metabolism, myogenesis and repair in health and illness conditions.

Gene expression of T3-regulated genes in a mouse model of the human thyroid hormone resistance

Aims To understand how thyroid hormone (TH) regulates tissue‐specific gene expression in patients with the syndrome of resistance to TH (RTH&bgr;), we used a mouse model that replicates the human RTH&bgr;, specifically the &Dgr;337T mutation in the thyroid hormone receptor &bgr; (THR&bgr;). Main methods We investigated the expression of key TH target genes in the pituitary and liver of TR&bgr;&Dgr;337T and wild type THR&bgr; mice by qPCR before and after a T3 suppression test consisting of the administration of increasing concentrations of T3 to hypothyroid mice. Key findings Pituitary Tshb and Cga expression decreased and Gh expression increased in TR&bgr;&Dgr;337T mice after T3 suppression. The stimulation of positively regulated TH genes was heterogeneous in the liver. Levels of liver Me1 and Thsrp were elevated in TR&bgr;&Dgr;337T mice after T3 administration. Slc16a2 and Gpd2 did not respond to T3 stimulation in the liver of TR&bgr;&Dgr;337T mice whereas Dio1 response was lower than that observed in WT mice. Moreover, although Chdh and Upd1 genes were negatively regulated in the liver, the expression of these genes was elevated after T3 suppression. We did not observe significant changes in THR&agr; expression in the liver and pituitary, while THR&bgr; levels were diminished in the pituitary and increased in the liver. Significance Using a model expressing a THR&bgr; unable to bind T3, we showed the expression pattern of liver negative and positive regulated genes by T3.

Corrigendum: Differential Regulation of Thyroid Hormone Metabolism Target Genes during Non-thyroidal Illness Syndrome Triggered by Fasting or Sepsis in Adult Mice

Fasting and sepsis induce profound changes in thyroid hormone (TH) central and peripheral metabolism. These changes affect TH action and are called the non-thyroidal illness syndrome (NTIS). To date, it is still debated whether NTIS represents an adaptive response or a real hypothyroid state at the tissue level. Moreover, even though it has been considered the same syndrome, we hypothesized that fasting and sepsis induce a distinct set of changes in thyroid hormone metabolism. Herein, we aimed to evaluate the central and peripheral expression of genes involved in the transport (MCT8/Slc16a2 and MCT10/Slc16a10), metabolism (Dio1, Dio2, and Dio3) and action (Thra and Thrb) of TH during NTIS induced by fasting or sepsis. Male mice were subjected to a 48 h period of fasting or cecal ligation and puncture (CLP)-induced sepsis. At the peripheral level, fasting led to: (1) reduced serum thyroxine (T4) and triiodothyronine (T3), expression of Dio1, Thra, Slc16a2, and MCT8 protein in liver; (2) increased hepatic Slc16a10 and Dio3 expression; and (3) decreased Slc16a2 and Slc16a10 expressions in the thyroid gland. Fasting resulted in reduction of Tshb expression in the pituitary and increased expression of Dio2 in total hypothalamus, arcuate (ARC) and paraventricular (PVN) nucleus. CLP induced sepsis resulted in reduced: (1) T4 serum levels; (2) Dio1, Slc16a2, Slc16a10, Thra, and Thrb expression in liver as well as Slc16a2 expression in the thyroid gland (3) Thrb and Tshb mRNA expression in the pituitary; (4) total leukocyte counts in the bone marrow while increased its number in peritoneal and pleural fluids. In summary, fasting- or sepsis-driven NTIS promotes changes in the set point of hypothalamus-pituitary-thyroid axis through different mechanisms. Reduced hepatic THRs expression in conjunction with reduced TH transporters expression in the thyroid gland may indicate, respectively, reduction in the peripheral action and in the secretion of TH, which may contribute to the low TH serum levels observed in both models.

Thyroid Hormones Play Role in Sarcopenia and Myopathies

Skeletal muscle maintains posture and enables movement by converting chemical energy into mechanical energy, further contributing to basal energy metabolism. Thyroid hormones (thyroxine, or T4, and triiodothyronine, or T3) participate in contractile function, metabolic processes, myogenesis and regeneration of skeletal muscle. T3 classically modulates gene expression after binding to thyroid hormone nuclear receptors. Thyroid hormone effects depend on nuclear receptor occupancy, which is directly related to intracellular T3 levels. Sarcolemmal thyroid hormone levels are regulated by their transport across the plasma membrane by specific transporters, as well as by the action of deiodinases types 2 and 3, which can activate or inactivate T4 and T3. Thyroid hormone level oscillations have been associated with the worsening of many myopathies such as myasthenia gravis, Duchenne muscular dystrophy (DMD) and rhabdomyolysis. During aging skeletal muscle show a decrease in mass and quality, known as sarcopenia. There is increasing evidence that thyroid hormones could have a role in the sarcopenic process. Therefore, in this review, we aim to discuss the main effects of thyroid hormones in skeletal muscular aging processes and myopathy-related pathologies.