Publicação
Evaluating alterations in adenosine metabolism and function responsible for brown adipose tissue deregulation: Implications in obesity and type 2 diabetes
| Resumo: | In the last decades, there has been a huge increase in the prevalence of metabolic disorders, like obesity and Type 2 diabetes (T2D). Brown adipose tissue (BAT) has been described as a potential target to control and treat these disorders, since is involved in body thermogenesis, which is regulated by UCP1, and in energy expenditure. Moreover, BAT activity is inversed correlated with obesity and insulin resistance. However, there is not enough knowledge about its function and how this tissue is affected in these disorders. It is consensual that higher BAT activity is associated with a better metabolic profile, meaning that higher BAT activity is associated with body weight reduction and improved glucose homeostasis. Brown adipocytes phenotype is quite different from the white adipocytes exhibiting higher mitochondrial content. BAT is activated by the sympathetic nervous system (SNS), which is involved in thermogenesis regulation and when active, BAT is capable of producing several bioactive substances, like adenosine. Adenosine is a purine nucleoside that has been shown to be involved in glucose homeostasis. It is involved in the regulation of lipolysis and inflammation, being expressed in adipose tissue. Recently adenosine has been shown to be involved in BAT activation through SNS via A2A adenosine receptor. However, the role of adenosine in BAT regulation is not yet well defined and clear, with a lot of controversial data in literature. Herein, we hypothesize that the adenosine metabolic pathway is essential to maintain BAT function and that adenosinergic system is impaired in metabolic pathologies as obesity and T2D, being a likely therapeutic target for metabolic diseases. Therefore, the general aim of the present study was to investigate if alterations in adenosine metabolism and function in BAT can contribute to metabolic dysfunction in obesity and T2D. The experiments were performed in male Wistar rats of 8 weeks old. Two groups of animals were used: 1) the high-fat high-sucrose animal model (HFHSu), obtained by submitting the animals to a 60% lipid-rich diet (5.1Kcal/g) and 35% sucrose in drinking water for 25 weeks, and 2) an age-matched control group, fed with standard chow (2.56Kcal/g). Fasting glucose and insulinemia were monitored during diet-induced T2D. Glucose tolerance was evaluated by an oral glucose tolerance test and insulin sensitivity by an insulin tolerance test. At a terminal experiment, animals were anesthetized with pentobarbital (60 mg/kg, i.p) and BAT and white adipose tissue (WAT) around BAT was collected and weighted. Glucose uptake was evaluated in BAT through the uptake of 2-deoxy-D-1,2-3H-glucose (2-DG) in the presence and/or absence of adenosine receptors agonists in animal fed with standard diet. The effect of the HFHSu diet in BAT morphology was evaluated by H&E staining. Also, the effect of the diet on BAT dysfunction and inflammation was evaluated through the quantification of mitochondrial markers, hypoxic signaling molecules and inflammatory markers. To evaluate alterations in adenosine metabolism and function in BAT, the expression of adenosine receptors and proteins involved in adenosine metabolism were also assessed, as well as the adenosine content and release in BAT. In this study it was observed an increase in weight gain and caloric intake as consequence of the HFHSu diet, these animals also exhibited decreased insulin sensitivity and glucose tolerance. Moreover, the hypercaloric diet promoted an increase in BAT and WAT around BAT, and a morphologic dysfunction in the tissue demonstrated by a change in BAT color and an increase in adipocytes size in the H&E staining. Beside was also observed a decrease in the expression of mitochondrial markers as PGC-1α and UCP1, alterations in the expression of hypoxia markers as VEGF, HIF-1α and HIF-2α and an increase in inflammatory markers expression as IL1R and IL6R. Moreover, it was shown that adenosine controls glucose uptake in BAT mainly via A1 receptors, since we observed an increase in glucose uptake under incubation with an A1 receptor agonist and decreased glucose uptake with A2A and A2B adenosine receptors agonists. Furthermore, it was demonstrated that HFHSu diet lead to dysregulation of adenosine receptors expression, with overexpression of A2A and downregulation of A2B. Regarding alterations in adenosine metabolism it was observed that adenosine content and release is decreased in the disease model and incubation with EHNA reestablish adenosine levels to values similar to control values, Furthermore it was observed an overexpression of CD73 and ENT1 in the HFHSu diet in BAT, proteins involved on adenosine metabolism. To conclude, this study demonstrate that the targeting of adenosine might contribute to improve metabolic function in obesity and T2D and the modulation of adenosine receptor expression or adenosine levels in BAT could be a therapeutic tool to treat metabolic dysfunction related disorders. |
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| Autores principais: | Martins, Inês Isabel Baltazar Belo |
| Assunto: | Obesity Type 2 diabetes Metabolic dysfunction Hypercaloric diet Brow adipose tissue Adenonise Teses de mestrado - 2018 |
| Ano: | 2018 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso restrito |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | In the last decades, there has been a huge increase in the prevalence of metabolic disorders, like obesity and Type 2 diabetes (T2D). Brown adipose tissue (BAT) has been described as a potential target to control and treat these disorders, since is involved in body thermogenesis, which is regulated by UCP1, and in energy expenditure. Moreover, BAT activity is inversed correlated with obesity and insulin resistance. However, there is not enough knowledge about its function and how this tissue is affected in these disorders. It is consensual that higher BAT activity is associated with a better metabolic profile, meaning that higher BAT activity is associated with body weight reduction and improved glucose homeostasis. Brown adipocytes phenotype is quite different from the white adipocytes exhibiting higher mitochondrial content. BAT is activated by the sympathetic nervous system (SNS), which is involved in thermogenesis regulation and when active, BAT is capable of producing several bioactive substances, like adenosine. Adenosine is a purine nucleoside that has been shown to be involved in glucose homeostasis. It is involved in the regulation of lipolysis and inflammation, being expressed in adipose tissue. Recently adenosine has been shown to be involved in BAT activation through SNS via A2A adenosine receptor. However, the role of adenosine in BAT regulation is not yet well defined and clear, with a lot of controversial data in literature. Herein, we hypothesize that the adenosine metabolic pathway is essential to maintain BAT function and that adenosinergic system is impaired in metabolic pathologies as obesity and T2D, being a likely therapeutic target for metabolic diseases. Therefore, the general aim of the present study was to investigate if alterations in adenosine metabolism and function in BAT can contribute to metabolic dysfunction in obesity and T2D. The experiments were performed in male Wistar rats of 8 weeks old. Two groups of animals were used: 1) the high-fat high-sucrose animal model (HFHSu), obtained by submitting the animals to a 60% lipid-rich diet (5.1Kcal/g) and 35% sucrose in drinking water for 25 weeks, and 2) an age-matched control group, fed with standard chow (2.56Kcal/g). Fasting glucose and insulinemia were monitored during diet-induced T2D. Glucose tolerance was evaluated by an oral glucose tolerance test and insulin sensitivity by an insulin tolerance test. At a terminal experiment, animals were anesthetized with pentobarbital (60 mg/kg, i.p) and BAT and white adipose tissue (WAT) around BAT was collected and weighted. Glucose uptake was evaluated in BAT through the uptake of 2-deoxy-D-1,2-3H-glucose (2-DG) in the presence and/or absence of adenosine receptors agonists in animal fed with standard diet. The effect of the HFHSu diet in BAT morphology was evaluated by H&E staining. Also, the effect of the diet on BAT dysfunction and inflammation was evaluated through the quantification of mitochondrial markers, hypoxic signaling molecules and inflammatory markers. To evaluate alterations in adenosine metabolism and function in BAT, the expression of adenosine receptors and proteins involved in adenosine metabolism were also assessed, as well as the adenosine content and release in BAT. In this study it was observed an increase in weight gain and caloric intake as consequence of the HFHSu diet, these animals also exhibited decreased insulin sensitivity and glucose tolerance. Moreover, the hypercaloric diet promoted an increase in BAT and WAT around BAT, and a morphologic dysfunction in the tissue demonstrated by a change in BAT color and an increase in adipocytes size in the H&E staining. Beside was also observed a decrease in the expression of mitochondrial markers as PGC-1α and UCP1, alterations in the expression of hypoxia markers as VEGF, HIF-1α and HIF-2α and an increase in inflammatory markers expression as IL1R and IL6R. Moreover, it was shown that adenosine controls glucose uptake in BAT mainly via A1 receptors, since we observed an increase in glucose uptake under incubation with an A1 receptor agonist and decreased glucose uptake with A2A and A2B adenosine receptors agonists. Furthermore, it was demonstrated that HFHSu diet lead to dysregulation of adenosine receptors expression, with overexpression of A2A and downregulation of A2B. Regarding alterations in adenosine metabolism it was observed that adenosine content and release is decreased in the disease model and incubation with EHNA reestablish adenosine levels to values similar to control values, Furthermore it was observed an overexpression of CD73 and ENT1 in the HFHSu diet in BAT, proteins involved on adenosine metabolism. To conclude, this study demonstrate that the targeting of adenosine might contribute to improve metabolic function in obesity and T2D and the modulation of adenosine receptor expression or adenosine levels in BAT could be a therapeutic tool to treat metabolic dysfunction related disorders. |
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