Molecular mechanisms of estrogen receptors' suppression of lipogenesis in pancreatic β-cells - PubMed (original) (raw)
Molecular mechanisms of estrogen receptors' suppression of lipogenesis in pancreatic β-cells
Joseph P Tiano et al. Endocrinology. 2012 Jul.
Abstract
The gonadal steroid, 17β-estradiol (E2), suppresses pancreatic islet fatty acid and glycerolipid synthesis and prevents β-cell failure in rodent models of type 2 diabetes. β-Cell estrogen receptors (ER) mediate these actions by suppressing the expression and enzymatic activity of fatty acid synthase (FAS). Here, we explored the mechanism of FAS suppression. We show that E2, and pharmacological agonists for ERα, ERβ, and the G protein-coupled ER, suppress mRNA and protein expression of the transcriptional regulators of FAS, namely, sterol regulatory element-binding protein 1c (SREBP1c) and carbohydrate response element binding protein (ChREBP) in insulin-secreting INS-1 cells. ER suppress SREBP1c and ChREBP mRNA and protein expression via an extranuclear localization. Using two mouse lines with pancreas-specific null deletion of either ERα or the signal transducer and activator of transcription 3 (STAT3), we show that ERα activation in vivo reduces SREBP1c and ChREBP mRNA expression via a direct islet action involving STAT3 activation. The master regulators of lipogenesis, liver X receptor (LXR) α and β, transcriptionally up-regulate SREBP1c and ChREBP. We find that activation of ERα, ERβ, and G protein-coupled ER suppresses LXR's mRNA expression in INS-1 cells. We also observe that activation of ERα in mouse islets in vivo suppresses LXR mRNA in a STAT3-dependent manner. Finally, we show that E2 also activates and uses AMP-activated protein kinase in INS-1 cells to suppress SREBP1c protein expression. This study identifies extranuclear ER pathways involving STAT3 and AMP-activated protein kinase in the genetic control of lipogenesis with therapeutic implications to protect β-cells in type 2 diabetes.
Figures
Fig. 1.
ER activation suppresses SREBP1c and ChREBP protein expression in β-cells. Effects of E2 (10−8
m
), PPT (10−8
m
), G1 (10−7
m
), and DPN (10−8
m
) treatments (4 h) on (A) SREBP1c and (B) ChREBP protein expression in INS-1 cells cultured under lipogenic conditions (16 m
m
glucose without FFA). Results represent the mean ±
se
of at least three experiments. *, **, or ***, vs. 16 m
m
glucose. *, P < 0.05; **, P < 0.01; ***, P < 0.001.
Fig. 2.
Activation of islet ER in vivo suppresses SREBP1c and ChREBP mRNA expression. A, Gene expression of lipogenic genes normalized to β-actin in islets of male control (ERαlox/lox) and PERαKO−/− mice treated with PPT (200 μg/d for 2 d) (n = 8–24 mice). Results represent the mean ±
se.
*, **, ***, vs. control vehicle. *, P < 0.05; **, P < 0.01; ***, P < 0.001.
Fig. 3.
Extranuclear ER suppress SREBP1c and ChREBP mRNA and protein expression in β-cells. A, Effects of E2 (10−8
m
) and EDC (10−8
m
) treatments (4 h) on lipogenic gene expression normalized to β-actin in INS-1 cells cultured under lipogenic conditions (11 m
m
glucose without FFA). B and C, Effects of E2 (10−8
m
) and EDC (10−8
m
) treatments (4 h) on (B) SREBP1c and (C) ChREBP protein expression in INS-1 cells cultured under lipogenic conditions (16 m
m
glucose without FFA). Results represent the mean ±
se
of at least three experiments. *, **, or ***, vs. 11 m
m
or 16 m
m
glucose. *, P < 0.05; **, P < 0.01; ***, P < 0.001.
Fig. 4.
ER suppress SREBP1c and ChREBP mRNA expression via STAT3. A, Gene expression of lipogenic genes normalized to β-actin in islets of male control (STAT3lox/lox) and PSTAT3KO−/− mice treated with E2 (6 μg/d for 2 d) (n = 11–20 mice). B, Effect of STAT3 and Src family kinase inhibition on E2 and PPT-induced suppression of SREBP1c mRNA expression. Cells were treated with E2 (10−8
m
) or PPT (10−8
m
) ± STAT3 inhibitor PpYLKTK (100 μ
m
) or SFK inhibitor SU6656 (2 μ
m
) for 4 h. *, **, or ***, vs. 11 m
m
glucose when not indicated. Results represent the mean ±
se
of at least three experiments. *, **, or ***, vs. control vehicle. *, P < 0.05; **, P < 0.01; ***, P < 0.001.
Fig. 5.
ER suppress LXR mRNA expression in β-cells. A, LXRα and -β gene expression normalized to β-actin in mouse liver, white adipose tissue (WAT), skeletal muscle, and islets (n = 12–18 mice). B, LXRα and β gene expression normalized to β-actin in INS-1 cells (n = at least 3 experiments). C, Effects of E2 (10−8
m
), PPT (10−8
m
), G1 (10−7
m
), and DPN (10−8
m
) treatments (4 h) on LXRα and -β gene expression normalized to β-actin in INS-1 cells cultured under lipogenic conditions (11 m
m
glucose without FFA) (n = at least 3 experiments). D, LXRα and -β gene expression normalized to β-actin in islets of male control and PERαKO−/− mice treated with PPT (200 μg/d for 2 d) (n = 8–24 mice). E, Effects of E2 (10−8
m
) and EDC (10−8
m
) treatments (4 h) on LXRα and -β gene expression normalized to β-actin in INS-1 cells cultured under lipogenic conditions (n = at least 3 experiments). Results represent mean ±
se.
*, **, or ***, vs. control vehicle or 11 m
m
glucose when not indicated. *, P < 0.05; **, P < 0.01; ***, P < 0.001.
Fig. 6.
ER suppress LXR mRNA expression via STAT3. A, LXRα and -β gene expression of lipogenic genes normalized to β-actin in islets of male control and PSTAT3KO−/− mice treated with E2 (6 μg/d for 2 d) (n = 11–20 mice). B, Effect of Src inhibition on E2 and PPT-induced suppression of LXRβ mRNA expression. INS-1 cells were treated with E2 (10−8
m
) or PPT (10−8
m
) ± SFK inhibitor SU6656 (2 μ
m
) for 4 h (n = at least 3 experiments). Results represent mean ±
se.
*, vs. control vehicle or 16 m
m
glucose when not indicated. *, **, or ***, P < 0.05; **, P < 0.01; ***, P < 0.001.
Fig. 7.
ER suppress SREBP1c protein expression via AMPK. A, INS-1 cells were treated with E2 (10−8
m
) for up to 2 h. Phosphorylation of AMPK was determined by Western blotting with an antibody against phosphorylated AMPK. Graph represents the quantification of at least two experiments. *, **, or ***, vs. 0 min. B, Effect of AMPK inhibition on E2 and PPT-induced suppression of SREBP1c protein expression. Cells were treated with E2 (10−8
m
) or PPT (10−8
m
) ± compound C (2 μ
m
) for 4 h (n = at least 3 experiments). *, **, or ***, vs. 16 m
m
glucose when not indicated. Results represent mean ±
se.
*, P < 0.05; **, P < 0.01; ***, P < 0.001.
Fig. 8.
Schematic representation of the proposed mechanisms of ERα suppression of lipogenic gene expression in β-cells. The ERα suppression of lipogenic genes can occurs through 1) a Src-STAT3-dependent pathway inhibiting LXRβ mRNA expression and eventually SREBP1c and ChREBP expression; and 2) an AMPK-dependent pathway directly inhibiting SREBP1c expression.
References
- Wong WP, Tiano JP, Liu S, Hewitt SC, Le May C, Dalle S, Katzenellenbogen JA, Katzenellenbogen BS, Korach KS, Mauvais-Jarvis F. 2010. Extranuclear estrogen receptor-α stimulates NeuroD1 binding to the insulin promoter and favors insulin synthesis. Proc Natl Acad Sci USA 107:13057–13062 - PMC - PubMed
Publication types
MeSH terms
Substances
LinkOut - more resources
Full Text Sources
Molecular Biology Databases
Research Materials
Miscellaneous