Sex Hormone-binding Globulin Production Research Articles

Recent Advances on Sex Hormone-Binding Globulin Regulation by Nutritional Factors: Clinical Implications.

Sex hormone-binding globulin (SHBG) is a homodimeric glycoprotein produced by the human liver and secreted into the systemic circulation where it binds with high affinity sex steroids regulating their availability in blood and accessibility to target tissues. Plasma SHBG levels are altered in metabolic disorders such as obesity, anorexia, and insulin resistance. Several reports have shown that diets in terms of total calories or fat, fiber, or protein content can alter plasma SHBG levels. However, there are many components in a diet that can affect SHBG gene expression in the liver. In order to unravel the molecular mechanisms by which diets regulate SHBG production, it would be necessary to analyze single diet components and/or nutritional factors. This review summarizes the recent advances in identifying different nutritional factors regulating SHBG production and the related molecular mechanism, as well as the clinical implications.

PS-B11-11: IMPLICATIONS OF OBESITY ON MALE FERTILITY HORMONES

Background: The prevalence of obesity is alarming, with prevalence reported from 24 to 36% in developed worlds and a global estimate of adult obesity at over 11%. The relationship between obesity and infertility in men has been emphasized in multiple studies. However, there is a paucity of studies on the disparity between obese and overweight men fertility profiles. Therefore, this study aims to investigate the sex hormones distribution in overweight and obese men. Method: A retrospective case-control study on reproductive hormones in obese and overweight participants was conducted on 789 NHANES 2015–2016 survey data. Of the 789 participants, 229 were control, 270 were overweight, and 290 were obese between 18–80 years of age. We compared the mean plasma level of testosterone, estradiol, and Sex Hormone Binding Globulin (SHBG) among the groups using one-way ANOVA and mean differences using Tamhane post hoc tests. Results: There was a significant increase in the mean testosterone, and SHBG levels in the control group compared with overweight and obese subjects. However, a significant increase in mean estradiol was observed in the obese compared with overweight and control groups. Interestingly, there was no significant difference in the estradiol level between the control and overweight groups. There was a significant increase in BMI in the obese group compared with overweight, and control groups. Conclusion: Obesity has negative feedback effects on testosterone and SHBG production. However, an unknown mechanism contributes to the lower estradiol level in overweight relative to obese men. Therefore, there is a need to research the molecular basis of fertility hormone metabolism in obese and overweight men.

Transforming growth factor-beta 1: A new factor reducing hepatic SHBG production in liver fibrosis.

Low plasma sex hormone-binding globulin (SHBG) levels are present in fatty liver disease, which represents a spectrum of diseases ranging from hepatocellular steatosis through steatohepatitis to fibrosis and irreversible cirrhosis. We have previously determined that fat accumulation reduces SHBG production in different nonalcoholic fatty liver disease mouse models. In the present work, we are interested in elucidating the molecular mechanisms reducing SHBG plasma levels in liver fibrosis. For this purpose, in vivo studies were performed using the human SHBG transgenic mice developing liver fibrosis induced by carbon tetrachloride (CCl4 ). Our results clearly showed that CCl4 induced liver fibrosis and reduced SHBG production by reducing hepatocyte nuclear factor 4 alpha (HNF-4α). The SHBG reduction could be influenced by the increase in transforming growth factor-beta 1 (TGF-β1), which was increased in mice developing liver fibrosis. Therefore, we decided to evaluate the role of TGF-β1 in regulating hepatic SHBG production. Results obtained in both HepG2 cells and human SHBG transgenic mice showed that TGF-β1 reduced significantly SHBGmessenger RNA and protein levels. Mechanistically TGF-β1 downregulated P1-HNF-4α isoforms and increased P2-HNF-4α isoforms via Smad3 and Stat3 pathways through TGF-β1 receptor I, resulting in transcriptional repression of the SHBG gene. Takentogether, we found for the first time that TGF-β1 is a new factor regulating hepatic SHBG production in liver fibrosis. Further research is needed to determine the role of this reduction in hepatic SHBG production in the progression of nonalcoholic steatohepatitis.

Transforming growth factor beta 1: a new factor reducing hepatic sex hormone binding globulin production during liver fibrosis development

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Polycystic ovary syndrome and non-alcoholic fatty liver disease: Matched pair or sporadic coexistence?

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of liver disease in developed countries. This condition includes benign non-alcoholic fatty liver disease and non-alcoholic steatohepatitis with possible fibrosis leading to cirrhosis and hepatocellular carcinoma. Association of NAFLD and polycystic ovary syndrome (PCOS) has been widely discussed. Women with PCOS are prone to develop NAFLD more often. PCOS is one of the most common endocrine disorders among reproductive-age women, characterized by an excess of androgens, anovulation, and polycystic ovary on ultrasound. Obesity, dyslipidemia and insulin resistance (IR) are frequently observed in women with PCOS, being also important factors predisposing to the development of NAFLD. IR may stimulate theca cells to excessive production of androgens, inhibits the production of sex hormone-binding globulin in the liver, which contributes to the increase of the bioactive form of testosterone. Hyperandrogenemia also plays an important role in NAFLD pathogenesis and progression. Androgen excess promotes visceral fat accumulation, development of dyslipidemia, IR, and contributes to low-grade inflammation. The pathophysiological associations between PCOS and NAFLD are not fully understood although it seems reasonable to screen PCOS women for the presence of NAFLD.

Caffeine Upregulates Hepatic Sex Hormone-Binding Globulin Production by Increasing Adiponectin Through AKT/FOXO1 Pathway in White Adipose Tissue.

Epidemiological studies have shown that caffeine increases serum sex hormone-binding globulin (SHBG) levels. The relationship between caffeine and SHBG production has never been studied before at molecular level. The aim of this study is to examine whether caffeine regulates SHBG production and to determine the associated molecular mechanisms. Two different studies are performed; in vitro studies using human HepG2 cells treated with caffeine (100 and 500 µm) and in vivo studies using a humanized SHBG transgenic mice drinking caffeine in the water (0.1 mg mL-1 ) for 12 days. The results show that caffeine does not change SHBG production in HepG2 cells. By contrast, caffeine treatment increases significantly hepatic SHBG production in human SHBG transgenic mice when compared with control mice. Caffeine increases adiponectin levels in epididymal adipose tissue of human SHBG transgenic mice. Moreover, caffeine increases adiponectin production by reducing protein kinase B (AKT) phosphorylation which increases forkhead box protein O1 (FOXO1) protein levels in 3T3-L1 mature adipocytes and human SHBG transgenic mice. Finally, caffeine-induced increase in adiponectin in turn upregulates hepatic hepatocyte nuclear receptor 4-alpha (HNF-4α) levels in human SHBG transgenic mice. The results show that caffeine upregulates hepatic SHBG expression by increasing adiponectin production through AKT/FOXO1 pathway in the adipose tissue.

Molecular mechanisms regulating hepatic sex hormone-binding globulin production: clinical implications in human diseases

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

In vitro and in vivo androgen regulation of Dendropanax morbiferus leaf extract on late-onset hypogonadism

Late-onset hypogonadism (LOH) is associated with advancing age and is caused by a deficiency in serum testosterone levels. The aim of this study was to examine the effect of a Dendropanax morbiferus H.Lév. leaf extract (DME) on LOH using TM3 cells and aging male rats as in vitro and in vivo models, respectively. The in vitro effects of DME on testosterone levels and 3β-hydroxysteroid dehydrogenase (3β-HSD) protein expression in TM3 cells were analyzed. In the in vivo experiments, DME was orally administered to rats at three doses (50, 100, and 200 mg/kg/day) for 4 weeks. DME significantly increased the testosterone levels and 3β-HSD protein expression in TM3 cells. The DME groups showed significantly increased levels of androgenic hormones such as testosterone and dehydroepiandrosterone sulfate. The sex hormone-binding globulin production was significantly lower in the DME groups than that in the control group, while the neurohormone levels in the hypothalamic-pituitary-gonadal axis markedly increased. No significant differences were observed in the glutamic pyruvic transaminase, glutamic oxaloacetic transaminase, and prostate-specific antigen levels among the DME and control groups. The triglyceride and low-density lipoprotein cholesterol levels were significantly lower, while the high-density lipoprotein cholesterol levels were significantly higher in the DME groups than those in the control group. The latency time in the rotarod, treadmill, and swimming tests increased with the DME treatment. Furthermore, the sperm counts in the epididymis markedly increased. These results suggest that DME can be effectively used to alleviate the symptoms of LOH.

Common genetic variants in the sex hormone-binding globulin (SHBG) gene in idiopathic recurrent pregnancy loss: a case control study

BackgroundA role for sex hormone-binding globulin (SHBG) in determining the pregnancy outcome was evidenced by the rise in SHBG levels during pregnancy linked with favorable pregnancy, while reduction in SHBG levels and hyperandrogenemia were linked with poor pregnancy outcome. Since SHBG production is genetically determined, this study investigated the association of SHBG polymorphisms with the susceptibility to recurrent pregnancy loss (RPL).MethodsRetrospective case-control study, involving 308 women with RPL, and 310 control women RPL, defined as ≥3 consecutive miscarriages, and with the same partner, was the main outcome measure. SHBG genotyping was done by allelic exclusion method (real-time PCR).ResultsOf the seven tested SHBG SNP, lower MAF of rs6257 was seen in RPL cases than in control women, which was linked with lower risk of RPL, after controlling for key covariates. At the genotype level, significantly higher frequencies of heterozygous rs858521 and rs6259, and homozygous rs858521 genotype carriers, and reduced frequency of heterozygous rs6257 and homozygous rs6257 and rs6259 genotype carriers were seen in RPL cases vs. control women, respectively. Univariate regression analysis confirmed the positive association of rs858521 and rs6259 with RPL. Multivariate regression analysis confirmed the positive association of rs858521 heterozygote and homozygote genotypes with RPL; only heterozygous rs6259 remained associated with RPL. Haploview analysis demonstrated marked linkage disequilibrium among 6 of the 7 tested SHBG SNP. Of the possible 6-locus haplotypes, 12 were common, and were included in subsequent analysis. Within these haplotypes, only increased frequency of CCGTGA haplotypes was seen in RPL cases, thus conferring RPL susceptibility.ConclusionsSpecific SHBG variants, and SHBG haplotypes are associated with altered risk of RPL, suggesting role for SHBG as RPL candidate gene.

Are the estrogenic hormonal effects of environmental toxins affecting small intestinal bacterial and microfilaria overgrowth?

The important role of microfilaria (worms) in human and animal disease remains an area of key disagreement between the naturopathic and allopathic physicians. While microfilaria infections are rampart in undeveloped countries, they rarely rise to identification as a cause of disease in Western countries. New research studies in the diagnosis and treatment of SIBO (Small Intestinal Bacterial Overgrowth) and (IBD) Inflammatory Bowel Diseases of ulcerative colitis, Crohn’s Disease and microcytic colitis may make both sides equally correct. A study of rifaximin failures in SIBO positive individuals finds biomarkers of decreased Free Androgen Index (FAI), high incidence of autoimmune disease and elevated Sex Hormone Binding Globulin (SHBG). The author hypothesizes that the underlying pathophysiology is increased exposure to Endocrine Disrupting Chemicals (EDCs) which hormonally act as xeno-estrogens. These xeno-estrogens increase the host production of SHBG, reduce pituitary stimulation of androgen product and result in a shift to estrogen dominance. Estrogen dominance is associated with autoimmune diseases and catabolic states. Treatment with a mixture of anabolic steroids that raises the FAI and lowers SHBG results in dramatic improvement in the signs and symptoms and recovery of the vast percentage of severe SIBO sufferers the author has treated. Similar results have been seen in severe pre-surgical cases of IBD whom fail all pharmaceutical interventions. Based on the recent recognition of the biological importance of Wolbachia in the occurrence of major diseases in the underdeveloped countries such as onchocerciasis, and the sexual nature of Wolbachia’s role in helminths reproduction, the author hypothesizes that the EDCs are shifting the host’s hormonal milieu in a more estrogenic direction and increasing reproduction of helminths changing the gastrointestinal microbiota. Present allopathic treatment of onchocerciasis utilizes albendazole and avermectin as therapy against the microfilaria larvae and doxycycline as bactericidal for Wolbachia. The allopathic treatments are unacceptable for pregnancy and children. Both naturopathic and allopathic treatments share a common focus on the suppression of the underlying bacterium Wolbachia infestation. The author hypothesizes that treatment of these two very different gastrointestinal diseases involves first establishing a normal, anabolic hormonal milieu and concurrently controlling an underlying yet unrecognized microfilaria overgrowth through naturopathic and allopathic treatments prescribed to the host. A case report of one such critically ill individual is noted. A thorough case controlled observation of symptoms matched with biological culture colony count and concentration of microfilaria in disease before and after the aforementioned anabolic treatment may answer the hypothesis.

Resveratrol Increases Hepatic SHBG Expression through Human Constitutive Androstane Receptor: a new Contribution to the French Paradox

Sex hormone-binding globulin (SHBG) carries sex steroids in blood regulating their bioavailability. Red wine consumption increases plasma SHBG levels, and we have discovered that resveratrol, a polyphenol enriched in red wine, acts specifically through the human constitutive androstane receptor (CAR), a drug/xenobiotic detoxification gene regulator, to increase hepatic SHBG production. Chromatin immunoprecipitation and luciferase reporter gene assays show that human CAR binds to a typical direct repeat 1 nuclear hormone receptor-binding element in the human SHBG proximal promoter. Resveratrol also increased hepatic SHBG production in humanized SHBG/CAR transgenic mice. Moreover, SHBG expression correlated significantly with CAR mRNA levels in human liver biopsies. We conclude that the beneficial effects of red wine on the metabolic syndrome and it associated co-morbidities, including cardiovascular disease and type 2 diabetes, may be mediated in part by resveratrol acting via CAR to increase plasma SHBG levels.

Sex hormone-binding globulin and antithrombin III activity in women with oral ultra-low-dose estradiol

Oral oestrogen increases the risk of venous thromboembolism (VTE) and increases production of sex hormone-binding globulin (SHBG) in a dose-dependent manner. SHBG has been suggested to be involved in venous thromboembolism. We examined the effects of oral ultra-low-dose oestradiol on circulating levels of SHBG and coagulation parameters, and we compared the effects to those of transdermal oestradiol. Twenty women received oral oestradiol (500 μg) every day (oral ultra-low-dose group) and 20 women received a transdermal patch (50 μg) as a transdermal group. In addition, the women received dydrogesterone continuously (5 mg) except for women who underwent hysterectomy. Circulating SHBG, antithrombin III (ATIII) activity, d-dimer, thrombin–antithrombin complex and plasmin–α2 plasmin inhibitor complex were measured before and 3 months after the start of treatment. SHBG was significantly increased at 3 months in the oral ultra-low-dose group, but not in the transdermal group. However, percent changes in SHBG were not significantly different between the two groups. In both groups, ATIII was significantly decreased at 3 months. In conclusion, even ultra-low-dose oestradiol orally increases circulating SHBG level. However, the magnitude of change in SHBG caused by oral ultra-low-dose oestradiol is small and is comparable to that caused by transdermal oestradiol.Impact statementOral oestrogen replacement therapy increases production of SHBG which may be related to increase in VTE risk. However, the effect of oral ultra-low-dose oestradiol on SHBG has not been clarified.Even ultra-low-dose oestradiol orally increases circulating SHBG levels, but the magnitude of change in SHBG caused by oral ultra-low-dose oestradiol is small and is comparable to that caused by transdermal oestradiol.VTE risk in women receiving oral ultra-low-dose oestradiol may be comparable to that in women receiving transdermal oestradiol.

Sex Hormone-Binding Globulin Reduction in Metabolic Disorders May Play a Role in NAFLD Development.

Low plasma sex hormone-binding globulin (SHBG) levels are a hallmark in chronic metabolic diseases, including nonalcoholic fatty liver disease (NAFLD), which represents a spectrum of disease ranging from hepatocellular steatosis through steatohepatitis to fibrosis and irreversible cirrhosis. The functional link between altered SHBG production and NAFLD development and progression remains unclear. We investigated the effects of overexpressing human SHBG in 2 mouse models of NAFLD: a genetically induced double transgenic mouse and a diet-induced model. Remarkably, SHBG overexpression in both NAFLD models significantly reduced liver fat accumulation by reducing key lipogenic enzymes. These findings were corroborated by modulating SHBG expression and by adding exogenous SHBG in HepG2 cells, suggesting the cell autonomous nature of the mechanism. Mechanistically, exogenous SHBG treatment downregulated key lipogenic enzymes by reducing PPARγ messenger RNA and protein levels through activation of extracellular signal-regulated kinase-1/2 mitogen-activated protein kinase pathway. Taking together, we found that SHBG modulates hepatic lipogenesis. This is of importance because reduction of SHBG plasma levels in obese and type 2 diabetic subjects could be directly associated with NAFLD development through an increase in hepatic lipogenesis. Our results point to SHBG as a therapeutic target for preventing or arresting NAFLD development.

Plasma steroid-binding proteins: primary gatekeepers of steroid hormone action.

Biologically active steroids are transported in the blood by albumin, sex hormone-binding globulin (SHBG), and corticosteroid-binding globulin (CBG). These plasma proteins also regulate the non-protein-bound or ‘free’ fractions of circulating steroid hormones that are considered to be biologically active; as such, they can be viewed as the ‘primary gatekeepers of steroid action’. Albumin binds steroids with limited specificity and low affinity, but its high concentration in blood buffers major fluctuations in steroid concentrations and their free fractions. By contrast, SHBG and CBG play much more dynamic roles in controlling steroid access to target tissues and cells. They bind steroids with high (~nM) affinity and specificity, with SHBG binding androgens and estrogens and CBG binding glucocorticoids and progesterone. Both are glycoproteins that are structurally unrelated, and they function in different ways that extend beyond their transportation or buffering functions in the blood. Plasma SHBG and CBG production by the liver varies during development and different physiological or pathophysiological conditions, and abnormalities in the plasma levels of SHBG and CBG or their abilities to bind steroids are associated with a variety of pathologies. Understanding how the unique structures of SHBG and CBG determine their specialized functions, how changes in their plasma levels are controlled, and how they function outside the blood circulation provides insight into how they control the freedom of steroids to act in health and disease.

Common Variants in the Sex Hormone-Binding Globulin (SHBG) Gene Influence SHBG Levels in Women with Polycystic Ovary Syndrome

Background: Decreased sex hormone-binding globulin (SHBG) levels were associated with polycystic ovary syndrome (PCOS). SHBG polymorphisms associated with reduced SHBG production were tested for their association with PCOS, but with inconclusive results. We tested whether altered SHBG levels and SHBG variants were associated with PCOS. Methods: The study subjects included 242 women with PCOS and 238 control women. SHBG genotyping was done by real-time PCR. Results: Higher minor allele frequency of rs13894, rs858521 and rs727428 was seen in PCOS cases, and significant differences in rs858521 and rs727428 genotypes distribution were seen between PCOS cases and controls. Multivariate regression analysis confirmed the association of only rs727428 with PCOS. Though it was not statistically significant, serum SHBG levels were reduced according to rs727428 genotypes in PCOS cases than in controls. Carriage of rs727428 minor allele was associated with significant increases in free/bioactive testosterone in PCOS cases. Seven-locus (rs9898876-rs13894-rs858521-rs1799941-rs6257-rs6259-rs727428) haploview analysis showed increased frequency of GCCGTGA, GTCGTGA and GTCATGG, and reduced frequency of GTCGTGG haplotypes in PCOS cases than in controls, thus conferring disease susceptibility and protective nature to these haplotypes, respectively. Conclusion: Specific SHBG variants affecting serum SHBG levels and SHBG haplotypes are associated with PCOS, suggesting the role for SHBG as PCOS candidate gene.

Oleic acid increases hepatic sex hormone binding globulin production in men

Low circulating sex hormone-binding globulin (SHBG) is an independent risk factor for cardiovascular disease. Mediterranean diet has been associated with a decreased risk of cardiovascular disease. We aimed to test the hypothesis that the increase of circulating MUFA associated with olive oil consumption (primary fat source in Mediterranean diet) increases SHBG serum levels. A total of 315 men were included. In these patients, nutrition data and plasma samples for SHBG assessment were obtained. In vitro studies to examine the effects of oleic and linoleic acid on SHBG production using HepG2 cells were performed. We provided evidence that SHBG serum levels were significantly higher in subjects using olive oil for cooking in comparison with subjects using sunflower oil. The SHBG levels correlated positively with MUFA (p < 0.001) and negatively with saturated fatty acids (p = 0.003). In the multiple regression analysis, MUFA were independently associated with SHBG levels and accounted for the 20.4% of SHBG variance. In vitro studies revealed that oleoyl-CoA increases SHBG production by downregulating PPAR-γ levels in HepG2 cells. Olive oil consumption is associated with elevated SHBG serum levels. PPAR-γ downregulation induced by oleoyl-CoA is an important underlying mechanism of such regulation.

New insights on molecular mechanisms regulating hepatic sex hormone-binding globulin production: clinical implications in obesity and type 2 diabetes

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Inverse association between serum insulin and sex hormone-binding globulin in a population survey in Sweden

ObjectivesObesity is associated with low levels of sex hormone-binding globulin (SHBG). While the reason is not fully understood, we aimed to study the association between serum insulin and levels of SHBG in a random population.Design and methodsBetween 2001 and 2005, a random sample of 2816 participants aged 30–74 years were enrolled in a cross-sectional survey in the South-west of Sweden. Fasting blood samples were collected and an oral glucose tolerance test (OGTT) was conducted in all subjects without known diabetes. Diabetes mellitus was defined according to criteria from WHO, and clinical characteristics were used to discriminate between type 1 (T1D) and type 2 diabetes (T2D). Analyses of SHBG were successful in 2782 participants (98%), who thus constituted the current study population.ResultsWe found significant inverse association between levels of SHBG and fasting serum insulin in both genders (men: β=−0.090, P=0.001; women: β=−0.197, P<0.001), which was independent of differences in age and BMI. The associations remained when also differences in fasting plasma glucose were accounted for (men: β=−0.062, P=0.022; women: β=−0.176, P≤0.001). Subjects with T1D exhibited higher levels of SHBG than both T2D (men: δ=15.9 nmol/l, P<0.001; women: δ=71.1 nmol/l, P<0.001) and non-diabetic subjects (men: δ=15.1 nmol/l, P<0.001; women: δ=72.9 nmol/l, P<0.001) independent of age, BMI and fasting glucose levels.ConclusionThese findings are consistent with high levels of SHBG in T1D, and correspondingly low levels in T2D subjects, suggesting an inhibitory effect of insulin on the SHBG production in the liver.

IL1β Down-regulation of Sex Hormone-Binding Globulin Production by Decreasing HNF-4α Via MEK-1/2 and JNK MAPK Pathways

Patients suffering from low-grade chronic inflammatory diseases, such as rheumatoid arthritis, osteoarthritis, diabetes, and obesity, have low plasma sex hormone-binding globulin (SHBG) levels. These diseases are characterized among other features by high plasma IL1β levels. The aim of the present study is to explore whether IL1β could regulate hepatic SHBG production to account for low SHBG levels in these diseases. We provide evidence that daily IL1β treatment reduces SHBG production in HepG2 cells by the down-regulation of HNF-4A via the MAPK kinase (MEK)-1/2 and c-Jun N-terminal kinase (JNK) MAPK signaling pathways through the activation c-Jun transcription factors. The human SHBG promoter sequence contains two putative activator protein 1 (AP1) binding sites recognized by c-Jun transcription factors, but they are not necessary for the IL1β-induced down-regulation of SHBG promoter activity in luciferase reporter gene assays. Daily treatment with IL1β reduces hepatic nuclear factor (HNF)-4α mRNA and protein levels via the MEK-1/2 and JNK MAPK signaling pathways. Moreover, IL1β rapidly decreased HNF-4α mRNA and protein levels while increased phospho-c-Jun protein levels after the treatment. Finally, daily IL1β treatment of human SHBG transgenic mice reduced plasma SHBG and SHBG mRNA levels. Moreover, IL1β treatment also reduced HNF-4α mRNA and protein levels while increased hepatic phospho-c-Jun protein levels. Our results show that IL1β reduces hepatic SHBG production by decreasing HNF-4α via MEK-1/2 and JNK MAPK pathways. In addition, our findings suggest that IL1β could be involved the low plasma SHBG levels reported in chronic low-grade inflammatory diseases.

Molecular Mechanism of TNFα-Induced Down-Regulation of SHBG Expression

The reason why obesity (a chronic low-grade inflammatory disease) is associated with low levels of sex hormone-binding globulin (SHBG) remains to be elucidated. The present study provides evidence that TNFα (a proinflammatory cytokine increased in obesity) reduces SHBG production by human HepG2 hepatoblastoma cells. Although the human SHBG promoter contains one nuclear factor-κB (NF-κB) binding site, the human SHBG promoter activity did not change after TNFα treatment or transfection with either small interfering RNA against p65 or a p65 expression vector in luciferase reporter gene assays. The effect of TNFα on human SHBG expression was indirect, and it was mediated by NF-κB through the down-regulation of hepatocyte nuclear factor (HNF)-4A: a key SHBG transcriptional regulator. Furthermore, the HNF-4A proximal promoter contains three putative NF-κB binding sites. The HNF-4A promoter activity was decreased by the treatment with TNFα or the transfection of a p65 expression vector, and it was increased by the treatment with small interfering RNA against NF-κB in luciferase reporter gene assays. Finally, the TNFα treatment promotes the NF-κB binding to the HNF-4A promoter in chromatin immunoprecipitation assays. We conclude that sustained exposition to elevated levels of TNFα decreases SHBG production by reducing hepatic HNF-4α levels via NF-κB activation in HepG2 cells.