Disruption of Thyroid Hormone Activation in Type 2 Deiodinase Knockout Mice Causes Obesity With Glucose Intolerance and Liver Steatosis Only at Thermoneutrality

Objective: Thyroid hormone accelerates energy expenditure; thus, hypothyroidism is intuitively associated with obesity. However, studies failed to establish such a connection. In brown adipose tissue (BAT), thyroid hormone activation via type 2 deiodinase (D2) is necessary for adaptive thermogenesis, such that mice lacking D2 (D2KO) exhibit an impaired thermogenic response to cold. Here we investigate whether the impaired thermogenesis of D2KO mice increases their susceptibility to obesity when placed on a high-fat diet. Research Design and Methods: To test this, D2KO mice were admitted to a comprehensive monitoring system acclimatized to room temperature (22$^\circ$C) or thermoneutrality (30$^\circ$C) and kept either on chow or high-fat diet for 60 days. Results: At 22$^\circ$C, D2KO mice preferentially oxidize fat, have a similar sensitivity to diet-induced obesity, and are supertolerant to glucose. However, when thermal stress is eliminated at thermoneutrality (30$^\circ$C), an opposite phenotype is encountered, one that includes obesity, glucose intolerance, and exacerbated hepatic steatosis. We suggest that a compensatory increase in BAT sympathetic activation of the D2KO mice masks metabolic repercussions that they would otherwise exhibit. Conclusions: Thus, upon minimization of thermal stress, high-fat feeding reveals the defective capacity of D2KO mice for diet-induced thermogenesis, provoking a paradigm shift in the understanding of the role of the thyroid hormone in metabolism

Absence of Myocardial Thyroid Hormone Inactivating Deiodinase Results in Restrictive Cardiomyopathy in Mice

Cardiac injury induces myocardial expression of the thyroid hormone inactivating type 3 deiodinase (D3), which in turn dampens local thyroid hormone signaling. Here, we show that the D3 gene (Dio3) is a tissue-specific imprinted gene in the heart, and thus, heterozygous D3 knockout (HtzD3KO) mice constitute a model of cardiac D3 inactivation in an otherwise systemically euthyroid animal. HtzD3KO newborns have normal hearts but later develop restrictive cardiomyopathy due to cardiac-specific increase in thyroid hormone signaling, including myocardial fibrosis, impaired myocardial contractility, and diastolic dysfunction. In wild-type littermates, treatment with isoproterenol-induced myocardial D3 activity and an increase in the left ventricular volumes, typical of cardiac remodeling and dilatation. Remarkably, isoproterenol-treated HtzD3KO mice experienced a further decrease in left ventricular volumes with worsening of the diastolic dysfunction and the restrictive cardiomyopathy, resulting in congestive heart failure and increased mortality. These findings reveal crucial roles for Dio3 in heart function and remodeling, which may have pathophysiologic implications for human restrictive cardiomyopathy

Role of adrenergic receptor b1 e b2 in facultative thermogenesis.

O peso corporal dos animais tende a ser relativamente estável durante longos períodos de tempo. Situações de restrição calórica ou aumento na ingestão de calorias levam a alterações fisiológicas compensatórias que resistem aos efeitos destas perturbações. De fato, o gasto energético aumenta em animais submetidos à dieta hipercalórica, a chamada termogênese facultativa, de modo a manter os estoques energéticos constantes. É possível que defeitos na termogênese facultativa estejam envolvidos no desenvolvimento da obesidade. O BAT, o principal sítio de termogênese facultativa, é ativado pela liberação de NE pelo Sistema Nervoso Simpático, que se liga aos receptores adrenérgicos b1, b2 e b3 expressos nos adipócitos marrons. Diversos estudos demonstram que os receptores b são importantes na proteção contra a obesidade, mas ainda não é claro qual o papel de cada isoforma neste processo. Assim sendo, o objetivo do nosso trabalho foi avaliar o papel das isoformas b1 e b2 na mediação da termogênese facultativa induzida pela dieta. Para tanto, nós tratamos camundongos com nocaute para o receptor adrenérgico b1 (KOb1) e camundongos com nocaute para o receptor b2 (KOb2) com dieta hipercalórica por 22 semanas. O peso corporal foi medido diariamente e o consumo de oxigênio foi determinado usando-se um sistema de respirometria aberto ao final do experimento. A composição corporal foi determinada pela análise da carcaça. Animais foram expostos ao frio de 4ºC por 4h e sua temperatura corporal foi medida em vários tempos e a resposta térmica do iBAT foi determinada pela infusão de NE ou agonista b adrenérgico. Além disso, foram determinados os níveis de RNAm das isoformas de receptores adrenérgicos b nos animais nocaute. Os resultados obtidos em nosso estudo mostram que os animais KOb1 e KOb2 tratados com dieta hipercalórica não desenvolvem obesidade mais severa do que os animais selvagens mas não são capazes de aumentar o consumo de oxigênio induzido pela dieta, sugerindo que estes receptores não são relevantes na termogênese induzida pela dieta. Por outro lado, nossos dados indicam que a presença do receptor b1 é exigida para termogênese induzida pelo frio, uma vez que os camundongos KOb1 são sensíveis ao frio e a capacidade termogênica do BAT destes animais em reposta à NE é bastante reduzida quando comparados com animais selvagens. A ausência do receptor b2 não piora a resposta dos animais ao frio sugerindo que esta isoforma não esteja envolvida na termogênese induzida pela dieta ou pelo frio. Os nossos achados indicam que a isoforma do receptor adrenérgico b1 é fundamental na termogênese induzida pelo frio, mas não pela dieta. Além disso, é provável que a termogênese induzida pela dieta seja regulada por mecanismos distintos da termogênese induzida pelo frio.The body weight of animals tends to be relatively stable over long periods of time. Situations of caloric restriction or increase in intake of calories lead to compensatory physiological changes that resist the effects of these disorders. In fact, the energy expenditure increases in animals treated with diet hypercaloric called facultative thermogenesis, in order to keep to energy stock constant. Defects in this facultative thermogenesis may be related to the development of obesity. Brown adipose tissue is the main site of facultative thermogenesis and is activated by signaling of b1, b2 e b3 adrenergic receptors by Norepinephrine released by Sympathetic Nervous System. Several studies showed that the isoforms b of adrenergic receptors are important in mechanisms involved in obesity and also in promoting cold tolerance. Nonetheless, it is unclear the role of each isoform in these process. Therefore, the purpose of our study was to evaluate the role of isoforms b1 and b2 in mediate the facultative thermogenesis. For that, we fed nocaute mice for the adrenergic receptor b1 (KOb1) and nocaute mice for the adrenergic receptor b2 (KOb2) with high fat diet for 22 weeks. During treatment body weight was determined daily. By the end of the experiment oxygen consumption was measured using a system of open respirometry and body composition was determined by analysis of the carcass. We also exposed KOb1 and KOb2 animals to cold (4C). The thermogenic response of iBAT was evaluated through i.v NE infusion. The results obtained in our study showed that the animals KOb1 and KOb2 treated with high fat diet did not gain more fat when compared to wild type animals, but are unable to increase the oxygen consumption, suggesting that these receptors are not relevant in development of obesity. Furthermore, our data indicate that the presence of the b1 receptor is required for cold-induced thermogenesis, since the KOb1 mice are sensitive to cold and BAT thermogenic response is significantly impaired when compared with animals wild type. The absence of b2 receptor does not worsen the response of animals to cold suggesting that this isoform is not involved in the diet- or cold- induced thermogenesis. In conclusion, our findings indicate that the b1 isoform of the adrenergic receptor is critical in the cold-induced thermogenesis, but not in diet induced thermogenesis. Moreover, it is likely that the diet-induced thermogenesis and cold-induced thermogenesis are regulated by different mechanisms

Levantamento da parasitofauna de duas espécies de peixes do Rio Mogi Guaçu, Região Sudeste do Brasil

A bacia do Rio Mogi Guaçu tem uma das ictiofaunas mais bem estudadas do Brasil. Seus peixes representam importante fonte de alimento para os habitantes da região. Os objetivos deste trabalho foram analisar a parasitofauna encontrada neste rio. Foram coletados 229 espécimes de Prochilodus lineatus, conhecido como curimbatá, e 130 espécimes de Pimelodus maculatus, conhecido como mandi-amarelo durante o ano de 2012, em Cachoeira de Emas, município de Pirassununga, São Paulo. Foram analisados os órgãos para coleta e retirada os parasitos intestinais para análise. O total de 2.437 de parasitos foi coletado de Prochilodus lineatus, sendo a maior ocorrência de monogenéticos em brânquias (n=1.425). Pimelodus maculatus apresentou um total de 4.742 parasitos coletados, com fauna parasitológica semelhante à de outros rios estudados, com 99,2% dos indivíduos parasitados, por pelo menos uma espécie. Também nesta espécie de peixe os parasitos mais prevalentes foram os monogenéticos (n = 3.870), que ocorreram em quase todos os indivíduos coletados. A parasitofauna encontrada apresentou relação com de outros rios já estudado

Targeted deletion of one or two copies of the G protein β subunit Gβ5 gene has distinct effects on body weight and behavior in mice

We investigated the physiological role of Gβ5, a unique G protein β subunit that dimerizes with regulators of G protein signaling (RGS) proteins of the R7 family instead of Gγ. Gβ5 is essential for stability of these complexes, so that its knockout (KO)causes degradation of the entire Gβ5-R7 family. We report that the Gβ5-KO mice remain leaner than the wild type (WT) throughout their lifetime and are resistant to a high-fat diet. They have a 5-fold increase in locomotor activity, increased thermogenesis, and lower serum insulin, all of which correlate with a higher level of secreted epinephrine. Heterozygous (HET) mice are 2-fold more active than WT mice. Surprisingly, with respect to body weight, the HET mice display a phenotype opposite to that of the KO mice: by the age of 6 mo, they are ≥15% heavier than the WT and have increased adiposity, insulin resistance, and liver steatosis. These changes occur in HET mice fed a normal diet and without apparent hyperphagia, mimicking basic characteristics of human metabolic syndrome. We conclude that even a partial reduction in Gβ5-R7 level can perturb normal animal metabolism and behavior. Our data on Gβ5 haploinsufficient mice may explain earlier observations of genetic linkage between R7 family mutations and obesity in humans.—Wang, Q., Levay, K., Chanturiya, T., Dvoriantchikova, G., Anderson, K. L., Bianco, S. D. C., Ueta, C. B., Molano, R. D., Pileggi, A., Gurevich, E. V., Gavrilova, O., and Slepak, V. Z. Targeted deletion of one or two copies of the G protein β subunit Gβ5 gene has distinct effects on body weight and behavior in mice

Coordination of hypothalamic and pituitary T3 production regulates TSH expression

Type II deiodinase (D2) activates thyroid hormone by converting thyroxine (T4) to 3,5,3'-triiodothyronine (T3). This allows plasma T4 to signal a negative feedback loop that inhibits production of thyrotropin-releasing hormone (TRH) in the mediobasal hypothalamus (MBH) and thyroid-stimulating hormone (TSH) in the pituitary. To determine the relative contributions of these D2 pathways in the feedback loop, we developed 2 mouse strains with pituitary- and astrocyte-specific D2 knockdown (pit-D2 KO and astro-D2 KO mice, respectively). The pit-D2 KO mice had normal serum T3 and were systemically euthyroid, but exhibited an approximately 3-fold elevation in serum TSH levels and a 40% reduction in biological activity. This was the result of elevated serum T4 that increased D2-mediated T3 production in the MBH, thus decreasing Trh mRNA. That tanycytes, not astrocytes, are the cells within the MBH that mediate T4-to-T3 conversion was defined by studies using the astro-D2 KO mice. Despite near-complete loss of brain D2, tanycyte D2 was preserved in astro-D2 KO mice at levels that were sufficient to maintain both the T4-dependent negative feedback loop and thyroid economy. Taken together, these data demonstrated that the hypothalamic-thyroid axis is wired to maintain normal plasma T3 levels, which is achieved through coordination of T4-to-T3 conversion between thyrotrophs and tanycytes

Differences in hypothalamic type 2 deiodinase ubiquitination explain localized sensitivity to thyroxine

The current treatment for patients with hypothyroidism is levothyroxine (L-T4) along with normalization of serum thyroid-stimulating hormone (TSH). However, normalization of serum TSH with L-T4 monotherapy results in relatively low serum 3,5,3′-triiodothyronine (T3) and high serum thyroxine/T3 (T4/T3) ratio. In the hypothalamus-pituitary dyad as well as the rest of the brain, the majority of T3 present is generated locally by T4 deiodination via the type 2 deiodinase (D2); this pathway is self-limited by ubiquitination of D2 by the ubiquitin ligase WSB-1. Here, we determined that tissue-specific differences in D2 ubiquitination account for the high T4/T3 serum ratio in adult thyroidectomized (Tx) rats chronically implanted with subcutaneous L-T4 pellets. While L-T4 administration decreased whole-body D2-dependent T4 conversion to T3, D2 activity in the hypothalamus was only minimally affected by L-T4. In vivo studies in mice harboring an astrocyte-specific Wsb1 deletion as well as in vitro analysis of D2 ubiquitination driven by different tissue extracts indicated that D2 ubiquitination in the hypothalamus is relatively less. As a result, in contrast to other D2-expressing tissues, the hypothalamus is wired to have increased sensitivity to T4. These studies reveal that tissue-specific differences in D2 ubiquitination are an inherent property of the TRH/TSH feedback mechanism and indicate that only constant delivery of L-T4 and L-T3 fully normalizes T3-dependent metabolic markers and gene expression profiles in Tx rats

Targeted deletion of one or two copies of the G protein β subunit Gβ5 gene has distinct effects on body weight and behavior in mice

We investigated the physiological role of Gβ5, a unique G protein β subunit that dimerizes with regulators of G protein signaling (RGS) proteins of the R7 family instead of Gγ. Gβ5 is essential for stability of these complexes, so that its knockout (KO)causes degradation of the entire Gβ5-R7 family. We report that the Gβ5-KO mice remain leaner than the wild type (WT) throughout their lifetime and are resistant to a high-fat diet. They have a 5-fold increase in locomotor activity, increased thermogenesis, and lower serum insulin, all of which correlate with a higher level of secreted epinephrine. Heterozygous (HET) mice are 2-fold more active than WT mice. Surprisingly, with respect to body weight, the HET mice display a phenotype opposite to that of the KO mice: by the age of 6 mo, they are ≥15% heavier than the WT and have increased adiposity, insulin resistance, and liver steatosis. These changes occur in HET mice fed a normal diet and without apparent hyperphagia, mimicking basic characteristics of human metabolic syndrome. We conclude that even a partial reduction in Gβ5-R7 level can perturb normal animal metabolism and behavior. Our data on Gβ5 haploinsufficient mice may explain earlier observations of genetic linkage between R7 family mutations and obesity in humans.—Wang, Q., Levay, K., Chanturiya, T., Dvoriantchikova, G., Anderson, K. L., Bianco, S. D. C., Ueta, C. B., Molano, R. D., Pileggi, A., Gurevich, E. V., Gavrilova, O., and Slepak, V. Z. Targeted deletion of one or two copies of the G protein β subunit Gβ5 gene has distinct effects on body weight and behavior in mice