Glucocorticoid receptor gene expression in adipose tissue and associated metabolic risk in black and white South African women

Glucocorticoids associate with cardiometabolic risk factors in black South Africans

Circulating glucocorticoids are associated with metabolic syndrome and related cardiometabolic risk factors in non-Africans. This study investigated these associations in Africans, whose metabolic phenotype reportedly differs from Europeans. Adiposity, blood pressure, glycaemia, insulin resistance, and lipid profile, were measured in 316 African men and 788 African women living in Soweto, Johannesburg. The 2009 harmonized criteria were used to define metabolic syndrome. Serum glucocorticoids were measured using liquid chromatography-mass spectrometry. Cortisol was associated with greater odds presenting with metabolic syndrome (odds ratio (95% CI) =1.50 (1.04, 2.17) and higher systolic (beta coefficient, β (95% CI) =0.04 (0.01, 0.08)) and diastolic (0.05 (0.02, 0.09)) blood pressure, but higher HDL (0.10 (0.02, 0.19)) and lower LDL (-0.14 (-0.24, -0.03)) cholesterol concentrations, in the combined sample of men and women. In contrast, corticosterone was only associated with higher insulin sensitivity (Matsuda index; 0.22 (0.03, 0.41)), but this was not independent of BMI. Sex-specific associations were observed, such that both cortisol and corticosterone were associated with higher fasting glucose (standardized β (95% CI): 0.24 (0.12, 0.36) for cortisol and 0.12 (0.01, 0.23) for corticosterone) and HbA1c (0.13 (0.01, 0.25) for cortisol and 0.12 (0.01, 0.24) for corticosterone) in men only, but lower HbA1c (0.10 (-0.20, -0.01) for cortisol and -0.09 (-0.18, -0.03) for corticosterone) in women only. Our study reports for the first time that associations between circulating glucocorticoid concentrations and key cardiometabolic risk factors exhibit both glucocorticoid- and sex-specificity in Africans.

The Impact of Macronutrient Intake on Non-alcoholic Fatty Liver Disease (NAFLD): Too Much Fat, Too Much Carbohydrate, or Just Too Many Calories?

Non-alcoholic fatty liver disease (NAFLD) is a growing epidemic, in parallel with the obesity crisis, rapidly becoming one of the commonest causes of chronic liver disease worldwide. Diet and physical activity are important determinants of liver fat accumulation related to insulin resistance, dysfunctional adipose tissue, and secondary impaired lipid storage and/or increased lipolysis. While it is evident that a hypercaloric diet (an overconsumption of calories) promotes liver fat accumulation, it is also clear that the macronutrient composition can modulate this risk. A number of other baseline factors modify the overfeeding response, which may be genetic or environmental. Although it is difficult to disentangle the effects of excess calories vs. specifically the individual effects of excessive carbohydrates and/or fats, isocaloric, and hypercaloric dietary intervention studies have been implemented to provide insight into the effects of different macronutrients, sub-types and their relative balance, on the regulation of liver fat. What has emerged is that different types of fat and carbohydrates differentially influence liver fat accumulation, even when diets are isocaloric. Furthermore, distinct molecular and metabolic pathways mediate the effects of carbohydrates and fat intake on hepatic steatosis. Fat accumulation appears to act through impairments in lipid storage and/or increased lipolysis, whereas carbohydrate consumption has been shown to promote liver fat accumulation through de novo lipogenesis. Effects differ dependent upon carbohydrate and fat type. Saturated fat and fructose induce the greatest increase in intrahepatic triglycerides (IHTG), insulin resistance, and harmful ceramides compared with unsaturated fats, which have been found to be protective. Decreased intake of saturated fats and avoidance of added sugars are therefore the two most important dietary interventions that can lead to a reduction in IHTG and potentially the associated risk of developing type 2 diabetes. A healthy and balanced diet and regular physical activity must remain the cornerstones of effective lifestyle intervention to prevent the development and progression of NAFLD. Considering the sub-type of each macronutrient, in addition to the quantity, are critical determinants of liver health.

DNA methylation of FKBP5 in South African women: associations with obesity and insulin resistance

BACKGROUND

Disruption of the hypothalamic-pituitary-adrenal (HPA) axis, a neuroendocrine system associated with the stress response, has been hypothesized to contribute to obesity development. This may be mediated through epigenetic modulation of HPA axis-regulatory genes in response to metabolic stressors. The aim of this study was to investigate adipose tissue depot-specific DNA methylation differences in the glucocorticoid receptor (GR) and its co-chaperone, FK506-binding protein 51 kDa (FKBP5), both key modulators of the HPA axis.

METHODS

Abdominal subcutaneous adipose tissue (ASAT) and gluteal subcutaneous adipose tissue (GSAT) biopsies were obtained from a sample of 27 obese and 27 normal weight urban-dwelling South African women. DNA methylation and gene expression were measured by pyrosequencing and quantitative real-time PCR, respectively. Spearman's correlation coefficients, orthogonal partial least-squares discriminant analysis and multivariable linear regression were performed to evaluate the associations between DNA methylation, messenger RNA (mRNA) expression and key indices of obesity and metabolic dysfunction.

RESULTS

Two CpG dinucleotides within intron 7 of FKBP5 were hypermethylated in both ASAT and GSAT in obese compared to normal weight women, while no differences in GR methylation were observed. Higher percentage methylation of the two FKBP5 CpG sites correlated with adiposity (body mass index and waist circumference), insulin resistance (homeostasis model for insulin resistance, fasting insulin and plasma adipokines) and systemic inflammation (c-reactive protein) in both adipose depots. GR and FKBP5 mRNA levels were lower in GSAT, but not ASAT, of obese compared to normal weight women. Moreover, FKBP5 mRNA levels were inversely correlated with DNA methylation and positively associated with adiposity, metabolic and inflammatory parameters.

CONCLUSIONS

These findings associate dysregulated FKBP5 methylation and mRNA expression with obesity and insulin resistance in South African women. Additional studies are required to assess the longitudinal association of FKBP5 with obesity and associated co-morbidities in large population-based samples.

Pathogenesis of type 2 diabetes risk in black Africans: a South African perspective

The prevalence of type 2 diabetes (T2D) is higher in black Africans than their European counterparts. This review summarizes the research exploring the pathogenesis of T2D in populations of African ancestry compared to white Europeans and shows that the pathogenesis differs by ethnicity. Black Africans present with a phenotype of low insulin sensitivity and hyperinsulinaemia as a result of increased insulin secretion and reduced hepatic insulin clearance. Whether hyperinsulinaemia precedes insulin resistance or is merely a compensatory mechanism is yet to be determined. Black Africans have lower visceral adipose tissue and ectopic fat deposition and greater peripheral (gluteo-femoral) fat deposition than their European counterparts. This suggests that black Africans are more sensitive to the effects of ectopic fat deposition, or alternatively, that ectopic fat is not an important mediator of T2D in black Africans. Importantly, ethnic disparities in T2D risk factors may be confounded by differences in sociocultural and lifestyle factors. Future longitudinal and dietary intervention studies, in combination with genetic analyses, are needed for a better understanding of the pathophysiology of T2D in black Africans. This will be key for effective prevention and management strategies.

Hypoxia and extra-cellular matrix gene expression in adipose tissue associates with reduced insulin sensitivity in black South African women

Black South African women are more insulin resistant and have increased gluteal subcutaneous adipose tissue hypertrophy than white South African women. We tested the hypothesis that adipose tissue hypoxia and extracellular matrix gene expression in gluteal and abdominal subcutaneous adipose tissue is higher in black than white women, and associates with reduced insulin sensitivity in black women. Insulin sensitivity (frequently sampled intravenous glucose tolerance test), gluteal and abdominal subcutaneous adipose tissue mRNA levels of hypoxia- and extracellular matrix-related genes were measured in normal-weight and obese premenopausal black (n = 30) and white (n = 26) South African women at baseline, and in black women, at 5-year follow-up (n = 10). Compared to obese white women, obese black women had higher expression of hypoxia inducible factor 1, collagen Vα1 and collagen VIα1 and reduced vascular endothelial growth factor-α expression in gluteal (p < 0.05) but not abdominal subcutaneous adipose tissue depots. Independent of age and body fatness, gluteal expression of hypoxia inducible factor 1 (r = -0.55; p = 0.01), collagen Vα1 (r = -0.41; p = 0.05) and collagen VIα1 (r = -0.47; p = 0.03) correlated with reduced insulin sensitivity in black women only. Over a 5-year follow-up, changes in gluteal hypoxia inducible factor 1 (r = 0.77; p = 0.01) collagen Vα1 (r = 0.71; p = 0.02) and collagen VIα1 (r = 0.81; p < 0.01) expression correlated positively with the change in fasting insulin concentrations in black women. Compared to their white counterparts, black women expressed higher levels of genes associated with hypoxia and collagen deposition, and the associations between these genes and insulin sensitivity differed by ethnicity. We thus propose that insulin resistance in black women may be related to higher extracellular matrix and hypoxia gene expression.

The glucocorticoid receptor: cause of or cure for obesity?

Glucocorticoid hormones (GCs) are important regulators of lipid metabolism, promoting lipolysis with acute treatment but lipogenesis with chronic exposure. Conventional wisdom posits that these disparate outcomes are mediated by the classical glucocorticoid receptor GRα. There is insufficient knowledge of the GC receptors (GRα and GRβ) in metabolic conditions such as obesity and diabetes. We present acute models of GC exposure that induce lipolysis, such as exercise, as well as chronic-excess models that cause obesity and lipid accumulation in the liver, such as hepatic steatosis. Alternative mechanisms are then proposed for the lipogenic actions of GCs, including induction of GC resistance by the GRβ isoform, and promotion of lipogenesis by GC activation of the mineralocorticoid receptor (MR). Finally, the potential involvement of chaperone proteins in the regulation of adipogenesis is considered. This reevaluation may prove useful to future studies on the steroidal basis of adipogenesis and obesity.