Role of Estrogen and Its Receptors in Adipose Tissue Glucose Metabolism in Pre- and Postmenopausal Women

Abstract

Context: Reduced estrogen levels in postmenopausal women predispose them to metabolic side effects, including insulin resistance and type 2 diabetes; however, the cellular mechanisms are not well understood.

Objective: This work aimed to study the expression of estrogen receptors in adipose tissue from pre- and postmenopausal women and the effects of estradiol (E2) on glucose uptake of adipocytes.

Methods: Subcutaneous (SAT) and visceral adipose tissue (VAT) obtained from pre- and postmenopausal women (19-51 and 46-75 years old, respectively) were used to measure gene expression of ESR1 and ESR2. SAT tissue was incubated with E2, and glucose uptake and estrogen receptor levels were measured. Polymorphisms in ESR1 and ESR2 were addressed in public databases to identify single nucleotide polymorphisms associated with metabolic traits.

Results: ESR2 expression was lower in pre- vs postmenopausal women, corresponding to lower ESR1:ESR2 gene expression ratio in postmenopausal women. In premenopausal women, the expression of ESR1 was higher in VAT than in SAT. In both pre- and postmenopausal women, ESR2 expression was lower in VAT than in SAT. In late, but not pre- or early postmenopausal women, E2 reduced glucose uptake and GLUT4 protein and increased expression of ESR2. ESR1 polymorphisms were associated with weight, body fat distribution, and total cholesterol, and ESR2 polymorphisms were associated with total cholesterol and triglyceride levels and with body fat percentage.

Conclusion: E2 inhibits glucose utilization in human adipocytes in late postmenopausal women. Changes in glucose utilization over time since menopause may be explained by a lower ESR1:ESR2 ratio. This can have clinical implications on the timing of estrogen treatment in postmenopausal women.

Keywords: adipose tissue; estradiol; insulin resistance; menopause; type 2 diabetes.

Figure 1.

Gene expression of estrogen receptors in adipose tissue from pre- and postmenopausal women. (A) ESR1 and ESR2 genes were measured in SAT from pre- and postmenopausal women (n = 32 and n = 40, respectively) with real-time polymerase chain reaction. (B) ESR1:ESR2 gene expression ratio in SAT from pre- and postmenopausal women (n = 32 and n = 40, respectively). Comparison of ESR1 and ESR2 gene expression in paired samples of SAT and VAT from (C) pre- (n = 11) and (D) postmenopausal women (n = 9). (E) ESR1:ESR2 gene expression ratio in SAT and VAT of pre- (n = 11) and postmenopausal women (n = 9). Data represent mean ± SE of the mean. *P < 0.05, **P < 0.01, ***P < 0.001. Abbreviations: Post, postmenopausal women; Pre, premenopausal women; SAT, subcutaneous adipose tissue. VAT, visceral adipose tissue.

Figure 2.

Effect of E2 on adipocyte glucose uptake in pre- and postmenopausal women. (A) Cell viability in adipocytes isolated from adipose tissue treated without (control) or with estradiol (E2) for 24 hours (0.001-1 nM). Subcutaneous adipose tissue was incubated with E2 (0.1 nM) or without (control) for 24 hours, and then adipocytes were isolated to measure glucose uptake in absence or presence of insulin (25 and 1000 µU/mL) in the (B) premenopausal group (n = 8), (C) early postmenopausal group (n = 7), and (D) late postmenopausal group (n = 10-12). (E) Basal and insulin-stimulated glucose uptake in adipocytes isolated from adipose tissue from late postmenopausal women incubated with E2 (0.1 nM) or E2 and PHTTP (1 µM) (n = 3). (F) Association between the age and the effect of E2 on insulin-stimulated glucose uptake (% change to control) in adipocytes in pre- (n = 7) and postmenopausal women (n = 25, P = 0.04). Data represent mean ± SE of the mean. *P < 0.05.

Figure 3.

Effect of estradiol (E2) on gene expression and protein levels of glucose transporters. Adipose tissue was incubated with or without E2 (0.1 nM) for 24 hours. (A) Gene expression of GLUT1 and GLUT4 were measured (n = 12, 4 early postmenopausal and 8 late postmenopausal). In addition, total protein was isolated and GLUT4 was measured with immunoblotting in adipose tissue from (B) early menopausal women (n = 7) or (C) late postmenopausal women (n = 10). (D) Representative Western blot with GLUT4 and glyceraldehyde-3-phosphate dehydrogenase. Data represent mean ± SE of the mean. *P < 0.05.

Figure 4.

Effect of estradiol (E2) on gene expression of estrogen receptors in SAT from postmenopausal women. Effect of 24-hour E2 treatment (0.1 nM, relative to control) on the expression of ESR1 and ESR2 genes in SAT from (A) early postmenopausal women and (B) late postmenopausal women. E2 effect on ESR1:ESR2 ratio in (C) early menopausal women and (D) late postmenopausal women. Early postmenopausal women, n = 4; late postmenopausal women, n = 7. Data represent mean ± SE of the mean. *P < 0.05.