madman
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Testosterone metabolites differentially regulate obesogenesis and fat distribution
Zachary L. Sebo, Matthew S. Rodeheffer
Abstract
Objective: Low testosterone in men (hypogonadism) is associated with obesity and type II diabetes. Testosterone replacement therapy has been shown to reverse these effects. However, the mechanisms by which testosterone regulates total fat mass, fat distribution, and metabolic health are unclear. In this study, we clarify the impact of hypogonadism on these parameters, as well as parse the role of testosterone from its downstream metabolites, dihydrotestosterone (DHT) and estradiol, in the regulation of depot-specific adipose tissue mass.
Methods: To do this, we utilized mouse models of male hypogonadism coupled with hormone replacement therapy, magnetic resonance imaging (MRI), glucose tolerance tests (GTTs), flow cytometry, and immunohistochemical techniques.
Results: We find that castrated mice develop increased fat mass, reduced muscle mass, and impaired glucose metabolism compared to gonadally intact males. Interestingly, obesity is further accelerated in castrated mice fed a high-fat diet, suggesting hypogonadism increases susceptibility to obesogenesis when dietary consumption of fat is elevated. By performing hormone replacement therapy in castrated mice, we show that testosterone impedes visceral and subcutaneous fat mass expansion. Whereas testosterone-derived estradiol selectively blocks visceral fat growth and DHT selectively blocks the growth of subcutaneous fat. These effects are mediated by depot-specific alterations in adipocyte size. In addition, we show that high-fat diet-induced adipogenesis is elevated in castrated mice and that this can be rescued by androgen treatment. Obesogenic adipogenesis is also elevated in mice where androgen receptor activity is inhibited.
Conclusion: These data indicate hypogonadism impairs glucose metabolism and increases obesogenic fat mass expansion through adipocyte hypertrophy and adipogenesis. In addition, our findings highlight distinct roles for testosterone, DHT, and estradiol in the regulation of total fat mass and fat distribution and reveal that androgen signaling blocks obesogenic adipogenesis in vivo.
1. Introduction
Low testosterone in men, known as hypogonadism, is associated with reduced muscle mass [1, 2] and an increased incidence of obesity and diabetes [3-6]. While the role of testosterone in maintaining muscle mass in males is well established [7-9] how testosterone exerts its anti-obesogenic effects is less clear. It is known that testosterone acts as an agonist of the androgen receptor (AR) and as a pro-hormone capable of being converted to the more potent androgen, dihydrotestosterone (DHT), or estradiol by 5a-reductase and aromatase, respectively. DHT cannot be aromatized to estradiol like testosterone and exerts its biological effects through AR, whereas estradiol does so through the estrogen receptors (ERs) and GPR30 [10, 11]. Both androgens and estrogens are thought to mediate anti-obesogenic processes. For example, testosterone and DHT have been shown to inhibit adipogenesis in vitro [12-14] and testosterone replacement therapy reduces adiposity in hypogonadal men and mice [15, 16]. However, data involving the role of DHT in fat mass regulation in vivo are conflicting. DHT treatment of hypogonadal males has been shown to decrease fat mass [17], have little to no effect on adiposity [15, 16] and even promote fat mass expansion [18].
In contrast to DHT, estradiol has consistently been observed to negatively regulate fat mass. For example, treating gonadally intact male mice with estradiol impedes excessive fat mass expansion when animals are fed a high-fat diet (HFD) [19] and ERα knockout male mice develop obesity [20]. Aromatase knockout mice, which fail to convert testosterone to estradiol, also develop obesity [21, 22] and a deleterious mutation in the aromatase gene of a man resulted in excessive adipose tissue and metabolic complications [23]. Therefore, the conversion of testosterone to estradiol by aromatase is likely important for impeding fat mass expansion in males. However, the role of estradiol in the regulation of male fat distribution is less clear.
It is known that under normal conditions men accrue a proportionally greater quantity of visceral fat than women, who accrue more subcutaneous fat [24]. However, after menopause, when estradiol levels drop, women progressively develop a more masculine fat distribution [25] that can be slowed by estradiol treatment [26]. It is unclear if estradiol reduces visceral fat storage, enhances storage in subcutaneous depots, or both. On the other hand, treating hypogonadal men with testosterone has been shown to preferentially reduce either visceral [27, 28] or subcutaneous fat stores [29, 30], while a role for DHT in the fat distribution has not been reported. Thus, fat distribution in males may be influenced by the combined effects of testosterone, DHT, and estradiol. In this study, we leverage pharmacologic approaches and mouse models of male hypogonadism to clarify the role of testosterone metabolism in the regulation of body composition, fat distribution, and metabolic disease.
4. Discussion
Alterations in sex hormones have been associated with changes in body composition, fat distribution, and metabolic disease for decades. However, the cellular mechanisms and adipose depot-specific effects of testosterone and its metabolites are poorly described in vivo. In this study, we have shown that testosterone has potent anti-obesogenic effects. Notably, testosterone blocks the expansion of both visceral and subcutaneous fat (Fig. 3E, G), whereas DHT specifically impedes subcutaneous fat growth (Fig. 3E, G) without significantly impacting total fat mass (Fig. 3B). Estradiol, on the other hand, specifically prevents the expansion of visceral fat (Fig. 3E, G). Thus, the conversion of testosterone to DHT and estradiol likely contributes to the regulation of depot-specific fat mass. The observation that estradiol preferentially impedes visceral fat expansion in diet-induced obesity is particularly intriguing given that men are more likely to develop visceral obesity than women [52-54]. It is possible that comparatively reduced estrogen signaling promotes visceral fat mass expansion without significantly impacting subcutaneous fat storage, which could contribute not only to visceral obesity in men but in post-menopausal women as well. Consistent with this notion, ovariectomized mice display markedly enhanced visceral adipogenesis and are more prone to visceral obesity when fed HFD [55, 56]
Zachary L. Sebo, Matthew S. Rodeheffer
Abstract
Objective: Low testosterone in men (hypogonadism) is associated with obesity and type II diabetes. Testosterone replacement therapy has been shown to reverse these effects. However, the mechanisms by which testosterone regulates total fat mass, fat distribution, and metabolic health are unclear. In this study, we clarify the impact of hypogonadism on these parameters, as well as parse the role of testosterone from its downstream metabolites, dihydrotestosterone (DHT) and estradiol, in the regulation of depot-specific adipose tissue mass.
Methods: To do this, we utilized mouse models of male hypogonadism coupled with hormone replacement therapy, magnetic resonance imaging (MRI), glucose tolerance tests (GTTs), flow cytometry, and immunohistochemical techniques.
Results: We find that castrated mice develop increased fat mass, reduced muscle mass, and impaired glucose metabolism compared to gonadally intact males. Interestingly, obesity is further accelerated in castrated mice fed a high-fat diet, suggesting hypogonadism increases susceptibility to obesogenesis when dietary consumption of fat is elevated. By performing hormone replacement therapy in castrated mice, we show that testosterone impedes visceral and subcutaneous fat mass expansion. Whereas testosterone-derived estradiol selectively blocks visceral fat growth and DHT selectively blocks the growth of subcutaneous fat. These effects are mediated by depot-specific alterations in adipocyte size. In addition, we show that high-fat diet-induced adipogenesis is elevated in castrated mice and that this can be rescued by androgen treatment. Obesogenic adipogenesis is also elevated in mice where androgen receptor activity is inhibited.
Conclusion: These data indicate hypogonadism impairs glucose metabolism and increases obesogenic fat mass expansion through adipocyte hypertrophy and adipogenesis. In addition, our findings highlight distinct roles for testosterone, DHT, and estradiol in the regulation of total fat mass and fat distribution and reveal that androgen signaling blocks obesogenic adipogenesis in vivo.
1. Introduction
Low testosterone in men, known as hypogonadism, is associated with reduced muscle mass [1, 2] and an increased incidence of obesity and diabetes [3-6]. While the role of testosterone in maintaining muscle mass in males is well established [7-9] how testosterone exerts its anti-obesogenic effects is less clear. It is known that testosterone acts as an agonist of the androgen receptor (AR) and as a pro-hormone capable of being converted to the more potent androgen, dihydrotestosterone (DHT), or estradiol by 5a-reductase and aromatase, respectively. DHT cannot be aromatized to estradiol like testosterone and exerts its biological effects through AR, whereas estradiol does so through the estrogen receptors (ERs) and GPR30 [10, 11]. Both androgens and estrogens are thought to mediate anti-obesogenic processes. For example, testosterone and DHT have been shown to inhibit adipogenesis in vitro [12-14] and testosterone replacement therapy reduces adiposity in hypogonadal men and mice [15, 16]. However, data involving the role of DHT in fat mass regulation in vivo are conflicting. DHT treatment of hypogonadal males has been shown to decrease fat mass [17], have little to no effect on adiposity [15, 16] and even promote fat mass expansion [18].
In contrast to DHT, estradiol has consistently been observed to negatively regulate fat mass. For example, treating gonadally intact male mice with estradiol impedes excessive fat mass expansion when animals are fed a high-fat diet (HFD) [19] and ERα knockout male mice develop obesity [20]. Aromatase knockout mice, which fail to convert testosterone to estradiol, also develop obesity [21, 22] and a deleterious mutation in the aromatase gene of a man resulted in excessive adipose tissue and metabolic complications [23]. Therefore, the conversion of testosterone to estradiol by aromatase is likely important for impeding fat mass expansion in males. However, the role of estradiol in the regulation of male fat distribution is less clear.
It is known that under normal conditions men accrue a proportionally greater quantity of visceral fat than women, who accrue more subcutaneous fat [24]. However, after menopause, when estradiol levels drop, women progressively develop a more masculine fat distribution [25] that can be slowed by estradiol treatment [26]. It is unclear if estradiol reduces visceral fat storage, enhances storage in subcutaneous depots, or both. On the other hand, treating hypogonadal men with testosterone has been shown to preferentially reduce either visceral [27, 28] or subcutaneous fat stores [29, 30], while a role for DHT in the fat distribution has not been reported. Thus, fat distribution in males may be influenced by the combined effects of testosterone, DHT, and estradiol. In this study, we leverage pharmacologic approaches and mouse models of male hypogonadism to clarify the role of testosterone metabolism in the regulation of body composition, fat distribution, and metabolic disease.
4. Discussion
Alterations in sex hormones have been associated with changes in body composition, fat distribution, and metabolic disease for decades. However, the cellular mechanisms and adipose depot-specific effects of testosterone and its metabolites are poorly described in vivo. In this study, we have shown that testosterone has potent anti-obesogenic effects. Notably, testosterone blocks the expansion of both visceral and subcutaneous fat (Fig. 3E, G), whereas DHT specifically impedes subcutaneous fat growth (Fig. 3E, G) without significantly impacting total fat mass (Fig. 3B). Estradiol, on the other hand, specifically prevents the expansion of visceral fat (Fig. 3E, G). Thus, the conversion of testosterone to DHT and estradiol likely contributes to the regulation of depot-specific fat mass. The observation that estradiol preferentially impedes visceral fat expansion in diet-induced obesity is particularly intriguing given that men are more likely to develop visceral obesity than women [52-54]. It is possible that comparatively reduced estrogen signaling promotes visceral fat mass expansion without significantly impacting subcutaneous fat storage, which could contribute not only to visceral obesity in men but in post-menopausal women as well. Consistent with this notion, ovariectomized mice display markedly enhanced visceral adipogenesis and are more prone to visceral obesity when fed HFD [55, 56]
