Androgen regulation and site specificity of angiotensinogen gene expression and secretion in rat adipocytes

Periarterial fat from two human vascular beds is not a source of aldosterone to promote vasoconstriction

Mouse adipocytes have been reported to release aldosterone and reduce endothelium-dependent relaxation. It is unknown whether perivascular adipose tissue (PVAT) releases aldosterone in humans. The present experiments were designed to test the hypothesis that human PVAT releases aldosterone and induces endothelial dysfunction. Vascular reactivity was assessed in human internal mammary and renal segmental arteries obtained at surgery. The arteries were prepared with/without PVAT, and changes in isometric tension were measured in response to the vasoconstrictor thromboxane prostanoid receptor agonist U46619 and the endothelium-dependent vasodilator acetylcholine. The effects of exogenous aldosterone and of mineralocorticoid receptor (MR) antagonist eplerenone were determined. Aldosterone concentrations were measured by ELISA in conditioned media incubated with human adipose tissue with/without angiotensin II stimulation. Presence of aldosterone synthase and MR mRNA was examined in perirenal, abdominal, and mammary PVAT by PCR. U46619 -induced tension and acetylcholine-induced relaxation were unaffected by exogenous and endogenous aldosterone (addition of aldosterone and MR blocker) in mammary and renal segmental arteries, both in the presence and absence of PVAT. Aldosterone release from incubated perivascular fat was not detectable. Aldosterone synthase expression was not consistently observed in human adipose tissues in contrast to that of MR. Thus, exogenous aldosterone does not affect vascular reactivity and endothelial function in ex vivo human arterial segments, and the tested human adipose tissues have no capacity to synthesize/release aldosterone. In perspective, physiologically relevant effects of aldosterone on vascular function in humans are caused by systemic aldosterone originating from the adrenal gland.

Adipocytes do not significantly contribute to plasma angiotensinogen

Recently, it has been reported that 25% of plasma angiotensinogen (Agt) is derived from fat. Meanwhile, liver-specific Agt knockout (KO) mice have markedly low plasma Agt, which may be due to reduced fat mass. To study the contribution of the fat to plasma Agt, we tested whether increasing fat mass can elevate plasma Agt and blood pressure in liver-Agt KO mice. Epididymal fat mass in liver-Agt KO mice fed a high-fat diet (HFD) was 4.1-fold larger than that in liver-Agt KO mice on a normal-fat diet (NFD). The liver-Agt KO mice on NFD were hypotensive with low levels of plasma Agt (on average, 0.11 vs 2.38 μg/ml). HFD slightly increased plasma Agt (0.17 μg/ml) without increase in blood pressure. To further increase fat mass, liver-Agt KO mice were fed HFD and simultaneously supplemented with low-dose angiotensin II and compared with control mice. Fat mass was comparable between the two groups. However, liver-Agt KO mice had uniformly low plasma Agt (0.09 vs 2.07 μg/ml) and systolic blood pressure (78±12 vs 111±6 mm Hg). In conclusion, adipocyte-derived Agt has essentially no contribution to the plasma concentration and no impact on blood pressure compared to liver-derived Agt.

Regulation and Functions of the Renin-Angiotensin System in White and Brown Adipose Tissue

The renin angiotensin system (RAS) is a major regulator of blood pressure, fluid, and electrolyte homeostasis. RAS precursor angiotensinogen (Agt) is cleaved into angiotensin I (Ang I) and II (Ang II) by renin and angiotensin converting enzyme (ACE), respectively. Major effects of Ang II, the main bioactive peptide of this system, is mediated by G protein coupled receptors, Angiotensin Type 1 (AGTR1, AT1R) and Type 2 (AGTR2, AT2R) receptors. Further, the discovery of additional RAS peptides such as Ang 1-7 generated by the action of another enzyme ACE2 identified novel functions of this complex system. In addition to the systemic RAS, several local RAS exist in organs such as the brain, kidney, pancreas, and adipose tissue. The expression and regulation of various components of RAS in adipose tissue prompted extensive research into the role of adipose RAS in metabolic diseases. Indeed, animal studies have shown that adipose-derived Agt contributes to circulating RAS, kidney, and blood pressure regulation. Further, mice overexpressing Agt have high blood pressure and increased adiposity characterized by inflammation, adipocyte hypertrophy, and insulin resistance, which can be reversed at least in part by RAS inhibition. These findings highlight the importance of this system in energy homeostasis, especially in the context of obesity. This overview article discusses the depot-specific functions of adipose RAS, genetic and pharmacological manipulations of RAS, and its applications to adipogenesis, thermogenesis, and overall energy homeostasis. © 2017 American Physiological Society. Compr Physiol 7:1137-1150, 2017.

Adipose tissue renin-angiotensin-aldosterone system (RAAS) and progression of insulin resistance

This review focuses on the expression of the key components of the renin-angiotensin-aldosterone axis in fat tissue. At the center of this report is the role of RAAS in normal and excessive fat mass enlargement, the leading etiology of insulin resistance. Understanding the expression and regulation of RAAS components in various fat depots allows insight not only into the processes by which these complex patterns are modified by the enlargement of adipose tissue, but also into their impact on local and systemic response to insulin.

The adipose tissue renin-angiotensin system and metabolic disorders: a review of molecular mechanisms

The renin-angiotensin system (RAS) is classically known for its role in regulation of blood pressure, fluid and electrolyte balance. In this system, angiotensinogen (Agt), the obligate precursor of all bioactive angiotensin peptides, undergoes two enzymatic cleavages by renin and angiotensin converting enzyme (ACE) to produce angiotensin I (Ang I) and angiotensin II (Ang II), respectively. The contemporary view of RAS has become more complex with the discovery of additional angiotensin degradation pathways such as ACE2. All components of the RAS are expressed in and have independent regulation of adipose tissue. This local adipose RAS exerts important auto/paracrine functions in modulating lipogenesis, lipolysis, adipogenesis as well as systemic and adipose tissue inflammation. Mice with adipose-specific Agt overproduction have a 30% increase in plasma Agt levels and develop hypertension and insulin resistance, while mice with adipose-specific Agt knockout have a 25% reduction in Agt plasma levels, demonstrating endocrine actions of adipose RAS. Emerging evidence also points towards a role of RAS in regulation of energy balance. Because adipose RAS is overactivated in many obesity conditions, it is considered a potential candidate linking obesity to hypertension, insulin resistance and other metabolic derangements.

The renin-angiotensin system: a link between obesity, inflammation and insulin resistance

The renin-angiotensin system (RAS) is classically known for its role in regulation of blood pressure, fluid and electrolyte balance. Recently, several local RASs in organs such as brain, heart, pancreas and adipose tissue have also been identified. Evidence from clinical trials suggests that in addition to anti-hypertensive effects, pharmacological inhibition of RAS also provides protection against the development of type-2 diabetes. Moreover, animal models with targeted inactivation of RAS genes exhibit improved insulin sensitivity and are protected from high-fat diet-induced obesity and insulin resistance. Because there is evidence for RAS overactivation in obesity, it is possible that RAS is a link between obesity and insulin resistance. This review summarizes the evidence and mechanistic insights on the associations between RAS, obesity and insulin resistance, with special emphasis on the role of adipose tissue RAS in the pathogenesis of metabolic derangements in obesity.

The adipose renin-angiotensin system: role in cardiovascular disease

Several reviews have highlighted the importance of local tissue production of components of the renin-angiotensin system (RAS) [Bader, M., Ganten, D., 2008. Update on tissue renin-angiotensin systems. J. Mol. Med. 86, 615-621; Krop, M., Danser, A.H., 2008. Circulating versus tissue renin-angiotensin system: on the origin of (pro)renin. Curr. Hypertens. Rep. 10, 112-118; Paul, M., Poyan Mehr, A., Kreutz, R., 2006. Physiology of local renin-angiotensin systems. Physiol. Rev. 86, 747-803]. While the concept of tissue RAS is gaining more widespread acceptance, the concept of local angiotensin II (AngII) production, acting in coordinate or independently of the endocrine RAS, continues to be debated. The primary reasons that local AngII production has been studied by many investigators are that components of the RAS are expressed by multiple cell types, and that the endocrine RAS cannot fully explain all effects of AngII. Moreover, through the development and study of genetically altered models for over-expression or knockdown of individual RAS components within specific cell types, it is becoming increasingly more evident that local RAS contribute to effects of AngII in normal physiology and disease. The purpose of this review is to define the presence and physiological significance of a local RAS in adipose tissue in relation to cardiovascular disease.

Antidepressant phenelzine alters differentiation of cultured human and mouse preadipocytes

Change in body weight is a frequent side effect of antidepressants and is considered to be mediated by central effects on food intake and energy expenditure. The antidepressant phenelzine (Nardil) potently inhibits both monoamine oxidase and semicarbazide-sensitive amine oxidase activities, two enzymes that are highly expressed in adipose tissue, raising the possibility that it could directly alter adipocyte biology. Treatment with this compound is rather associated with weight gain. The aim of this work was to examine the effects of phenelzine on differentiation and metabolism of cultured human and mouse preadipocytes and to characterize the mechanisms involved in these effects. In all preadipocyte models, phenelzine induced a time- and dose-dependent reduction in differentiation and triglyceride accumulation. Modulation of lipolysis or glucose transport was not involved in phenelzine action. This effect was supported by the reduced expression in the key adipogenic transcription factors peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and CCAAT/enhancer binding protein-alpha, which was observed only at the highest drug concentrations (30-100 microM). The PPAR-gamma agonists thiazolidinediones did not reverse phenelzine effects. By contrast, the reduction in both cell triglycerides and sterol regulatory element-binding protein-1c (SREBP-1c) was detectable at lower phenelzine concentrations (1-10 microM). Phenelzine effect on triglyceride content was prevented by providing free fatty acids to the cells and was partially reversed by overexpression of a dominant-positive form of SREBP-1c, showing the privileged targeting of the lipogenic pathway. When considered together, these findings demonstrate that an antidepressant directly and potently inhibits adipocyte lipid storage and differentiation, which could contribute to psychotropic drug side effects on energy homeostasis.

Androgens and body fat distribution

An important sex difference in body fat distribution is generally observed. Men are usually characterized by the android type of obesity, with accumulation of fat in the abdominal region, whereas women often display the gynoid type of obesity, with a greater proportion of their body fat in the gluteal-femoral region. Accordingly, the amount of fat located inside the abdominal cavity (intra-abdominal or visceral adipose tissue) is twice as high in men compared to women. This sex difference has been shown to explain a major portion of the differing metabolic profiles and cardiovascular disease risk in men and women. Association studies have shown that circulating androgens are negatively associated with intra-abdominal fat accumulation in men, which explains an important portion of the link between low androgens and features of the metabolic syndrome. In women, the low circulating sex hormone-binding globulin (SHBG) levels found in abdominal obesity may indirectly indicate that elevated free androgens are related to increased visceral fat accumulation. However, data on non SHBG-bound and total androgens are not unanimous and difficult to interpret for total androgens. These studies focusing on plasma levels of sex hormones indirectly suggest that androgens may alter adipose tissue mass in a depot-specific manner. This could occur through site-specific modulation of preadipocyte proliferation and/or differentiation as well as lipid synthesis and/or lipolysis in mature adipocytes. Recent results on the effects of androgens in cultured adipocytes and adipose tissue have been inconsistent, but may indicate decreased adipogenesis and increased lipolysis upon androgen treatment. Finally, adipose tissue has been shown to express several steroidogenic and steroid-inactivating enzymes. Their mere presence in fat indirectly supports the notion of a highly complex enzymatic system modulating steroid action on a local basis. Recent data obtained in both men and women suggest that enzymes from the aldoketoreductase 1C family are very active and may be important modulators of androgen action in adipose tissue.

Angiotensin II increases adipose angiotensinogen expression

In addition to the well-defined contribution of the liver, adipose tissue has been recognized as an important source of angiotensinogen (AGT). The purpose of this study was to define the angiotensin II (ANG II) receptors involved in regulation of adipose AGT and the relationship of this control to systemic AGT and/or angiotensin peptide concentrations. In LDL receptor-deficient (LDLR(-/-)) male mice, adipose mRNA abundance of AGT was 68% of that in liver, and adipose mRNA abundance of the angiotensin type 1a (AT(1a)) receptor (AT(1a)R) was 38% of that in liver, whereas mRNA abundance of the angiotensin type 2 (AT(2)) receptor (AT(2)R) was 57% greater in adipose tissue than in liver. AGT and angiotensin peptide concentrations were decreased in plasma of AT(1a)R-deficient (AT(1a)R(-/-)) mice and were paralleled by reductions in AGT expression in liver. In contrast, adipose AGT mRNA abundance was unaltered in AT(1a)R(-/-) mice. AT(2)R(-/-) mice exhibited elevated plasma angiotensin peptide concentrations and marked elevations in adipose AGT and AT(1a)R mRNA abundance. Increases in adipose AGT mRNA abundance in AT(2)R(-/-) mice were abolished by losartan. In contrast, liver AGT and AT(1a)R mRNA abundance were unaltered in AT(2)R(-/-) mice. Infusion of ANG II for 28 days into LDLR(-/-) mice markedly increased adipose AGT and AT(1a)R mRNA but did not alter liver AGT and AT(1a)R mRNA. These results demonstrate that differential mRNA abundance of AT(1a)/AT(2) receptors in adipose tissue vs. liver contributes to tissue-specific ANG II-mediated regulation of AGT. Chronic infusion of ANG II robustly stimulated AT(1a)R and AGT mRNA abundance in adipose tissue, suggesting that adipose tissue serves as a primary contributor to the activated systemic renin-angiotensin system.

Depot differences in steroid receptor expression in adipose tissue: possible role of the local steroid milieu

Sex hormones play an important role in adipose tissue metabolism by activating specific receptors that alter several steps of the lipolytic and lipogenic signal cascade in depot- and sex-dependent manners. However, studies focusing on steroid receptor status in adipose tissue are scarce. In the present study, we analyzed steroid content [testosterone (T), 17beta-estradiol (17beta-E2), and progesterone (P4)] and steroid receptor mRNA levels in different rat adipose tissue depots. As expected, T levels were higher in males than in females (P = 0.031), whereas the reverse trend was observed for P4 (P < 0.001). It is noteworthy that 17beta-E2 adipose tissue levels were higher in inguinal than in the rest of adipose tissues for both sexes, where no sex differences in 17beta-E2 tissue levels were noted (P = 0.010 for retroperitoneal, P = 0.005 for gonadal, P = 0.018 for mesenteric). Regarding steroid receptor levels, androgen (AR) and estrogen receptor (ER)alpha and ERbeta densities were more clearly dependent on adipose depot location than on sex, with visceral depots showing overall higher mRNA densities than their subcutaneous counterparts. Besides, expression of ERalpha predominated over ERbeta expression, and progesterone receptor (PR-B form and PR-A+B form) mRNAs were identically expressed regardless of anatomic depot and sex. In vitro studies in 3T3-L1 cells showed that 17beta-E2 increased ERalpha (P = 0.001) and AR expression (P = 0.001), indicating that estrogen can alter estrogenic and androgenic signaling in adipose tissue. The results highlighted in this study demonstrate important depot-dependent differences in the sensitivity of adipose tissues to sex hormones between visceral and subcutaneous depots that could be related to metabolic situations observed in response to sex hormones.

Human adipose angiotensinogen gene expression and secretion are stimulated by cyclic AMP via increased DNA cyclic AMP responsive element binding activity

Components of the adipose renin-angiotensin system (RAS) have been suggested as providing a potential path-way linking obesity to hypertension. In adipose cells, the biological responses to beta-adrenergic stimulation are mediated by an increase in intracellular cAMP. Because an association exists among body fat mass, hypertension, and increased sympathetic stimulation, we examined the influence of cAMP on angiotensinogen (ATG) expression and secretion in human adipose tissue and in parallel we studied the DNA binding activity of CRE transcriptional factors. A 24 h exposure to the cAMP analog 8Br-cAMP resulted in significant increases in ATG mRNA levels (+176+/-60%) and protein secretion (+40+/-27%). The ability of 8Br-cAMP to promote ATG gene expression was unaltered by H89, a protein kinase A inhibitor, because H89 per se was found to stimulate ATG mRNA levels and protein secretion. Moreover, 8Br-cAMP stimulated the specific CRE DNA binding activity (+115+/-14%) in human adipocyte nuclear extracts as assessed by electrophoretic mobility shift assays. These results indicate that cAMP upregulates in vitro ATG expression and secretion in human adipose tissue and that the induction in ATG mRNA levels appears to result, at least in part, from positive effects on the DNA binding activity of CRE transcription factors. Further studies are required to determine whether this regulatory pathway is activated in human obesity and to elucidate the importance of adipose ATG to the elevated blood pressure observed in this pathological state.

Direct regulation of prostate blood flow by vascular endothelial growth factor and its participation in the androgenic regulation of prostate blood flow in vivo

Previous studies on prostate blood flow regulation have indicated that androgen regulates prostate blood flow. However, the mechanism responsible for this regulation is unknown. In the present study, we focused on the effects of vascular endothelial growth factor (VEGF), a key factor responsible for angiogenesis and androgenic blood flow regulation. We examined in vivo the effect of VEGF on prostate blood flow and its participation in the androgenic regulation of this blood flow using a castrated rat model following subcapsular intraprostatic injection method. We found that VEGF is involved in blood flow regulation with an activity equal to that of dihydrotestosterone (DHT). The effect of VEGF on prostate blood flow was already seen at 30 min after the administration. The elevating effect of DHT on castrated rat prostate blood flow was abolished by coadministration of DHT with neutralizing anti-VEGF antibody. The change in VEGF-A mRNA expression in response to androgen stimulation was examined by double-fluorescent probe quantitative PCR (Taqman PCR). The results showed that androgenic regulation of VEGF gene expression occurred shortly after androgen stimulation. VEGF gene up-regulation was abolished or down-regulated by coadministration of neutralizing anti-VEGF antibody. This is the first report on the importance of VEGF in the androgenic regulation signaling pathway that affects prostate blood flow. Alternative treatment targeted toward anti-VEGF activity as a substitute for ordinary antiandrogenic therapy may be effective against prostate diseases, especially those with androgen-independent and hyperhemorrhagic status.

cAMP-positive regulation of angiotensinogen gene expression and protein secretion in rat adipose tissue

The adipose renin-angiotensin system (RAS) has been assigned to participate in the control of adipose tissue development and in the pathogenesis of obesity-related hypertension. In adipose cells, the biological responses to beta-adrenergic stimulation are mediated by an increase in intracellular cAMP. Because cAMP is known to promote adipogenesis and because an association exists between body fat mass, hypertension, and increased sympathetic stimulation, we examined the influence of cAMP on angiotensinogen (ATG) expression and secretion in rat adipose tissue. Exposure of primary cultured differentiated preadipocytes to the cAMP analog 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) or cAMP-stimulating agents (forskolin and IBMX) results in a significant increase in ATG mRNA levels. In adipose tissue fragments, 8-BrcAMP also increases ATG mRNA levels and protein secretion, but not in the presence of the protein kinase A inhibitor H89. The addition of isoproterenol, known to stimulate the synthesis of intracellular cAMP via beta-adrenoreceptors, had the same stimulatory effect on ATG expression and secretion. These results indicate that cAMP in vitro upregulates ATG expression and secretion in rat adipose tissue via the protein kinase A-dependent pathway. Further studies are required to determine whether this regulatory pathway is activated in human obesity, where increased sympathetic tone is frequently observed, and to elucidate the importance of adipose ATG to the elevated blood pressure observed in this pathological state.

Androgens decrease plasma adiponectin, an insulin-sensitizing adipocyte-derived protein

Adiponectin, an adipose-specific secretory protein, exhibits antidiabetic and antiatherogenic properties. In the present study, we examined the effects of sex hormones on the regulation of adiponectin production. Plasma adiponectin concentrations were significantly lower in 442 men (age, 52.6 +/- 11.9 years [mean +/- SD]) than in 137 women (53.2 +/- 12.0 years) but not different between pre- and postmenopausal women. In mice, ovariectomy did not alter plasma adiponectin levels. In contrast, high levels of plasma adiponectin were found in castrated mice. Testosterone treatment reduced plasma adiponectin concentration in both sham-operated and castrated mice. In 3T3-L1 adipocytes, testosterone reduced adiponectin secretion into the culture media, using pulse-chase study. Castration-induced increase in plasma adiponectin was associated with a significant improvement of insulin sensitivity. Our results indicate that androgens decrease plasma adiponectin and that androgen-induced hypoadiponectinemia may be related to the high risks of insulin resistance and atherosclerosis in men.

Steroid receptor concentration in aged rat hindlimb muscle: effect of anabolic steroid administration

Skeletal muscle is a target of anabolic steroid action; however, anabolic steroid's affect on aged skeletal muscle is not well understood. The effect of 4 wk of nandrolone decanoate (ND) administration on hindlimb muscles of 5- and 25-mo-old Fischer 344/Brown Norway rats was examined. ND (6 mg/kg body wt) was injected every 7th day for 4 wk. Controls received an oil injection. ND significantly reduced 25-mo-old rat perirenal fat pad mass by 30%. Soleus (Sol) and plantaris (Plan) muscle-to-body weight ratios were reduced in 25-mo-old rats. ND did not affect Sol or Plan muscle-to-body weight ratios at either age. Sol DNA concentration was reduced by 25% in 25-mo-old rats, and ND increased it to 12% greater than 5-mo-old rats. ND did not affect Plan DNA content. Sol androgen receptor (AR) protein in 25-mo-old rats was reduced to 35% of 5-mo-old values. ND increased AR protein by 900% in 25-mo-old rat Sol. Plan AR concentration was not affected by aging but was induced by ND in both age groups. Aging or ND treatment did not affect glucocorticoid receptor levels in either muscle. These data demonstrate that fast- and slow-twitch rat hindlimb muscles differ in their response to aging and ND therapy.