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Insulin elevates leptin secretion and mRNA levels via cyclic AMP in 3T3-L1 adipocytes deprived of glucose

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ABSTRACT

Aims: Leptin plays an important role in the pathogenesis of obesity and diabetes, yet the regulatory mechanisms of this hormone have not been fully elucidated. In this study, we aimed to clarify the roles of insulin and glucose in leptin secretion and mRNA production using inhibitors of insulin signal transduction in adipocytes cultured under glucose-free or normal conditions.

Methods: Differentiated 3T3-L1 adipocytes were stimulated with insulin in combination with inhibitors for phosphoinositide 3-kinase (PI3K), Akt, and phosphodiesterase 3B (PDE3B), as well as epinephrine and a cyclic AMP (cAMP) analog under glucose-free or normal conditions. After 8 h of stimulation, leptin protein levels in the media and leptin mRNA expression levels in the adipocytes were measured.

Results: Insulin significantly increased the secretion and mRNA levels of leptin under the depletion of glucose. Glucose augmented basal leptin secretion without insulin, while glucose ified insulin-induced leptin mRNA upregulation. The PI3K inhibitor BEZ-235, the Akt inhibitor MK-2206, and the PDE3B inhibitor cilostazol attenuated the insulin stimulation of leptin secretion, but did not suppress the insulin-induced leptin mRNA upregulation with glucose depletion. In contrast to the glucose-free condition, insulin failed to upregulate leptin mRNA in the presence of glucose. The cAMP analog dibutyryl cAMP and epinephrine decreased both leptin secretion and mRNA regardless of glucose supplementation.

Conclusion: Insulin alone stimulates leptin secretion and elevates leptin mRNA levels via cAMP under the lack of glucose metabolism, while glucose is a significant and ambivalent effector on the insulin effects of leptin.

No MeSH data available.


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Effects of the PDE3B inhibitor cilostazol (A and B) or a cyclic AMP analog (C and D) on insulin-induced leptin secretion and mRNA levels in 3T3-L1 adipocytes under glucose-free conditions. 3T3-L1 adipocytes were incubated for 8 h in glucose-free DMEM with each substance at the indicated concentrations. *p < 0.05, ***p < 0.001. n.s., not significant. Data are expressed as means ± SE.
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fig0015: Effects of the PDE3B inhibitor cilostazol (A and B) or a cyclic AMP analog (C and D) on insulin-induced leptin secretion and mRNA levels in 3T3-L1 adipocytes under glucose-free conditions. 3T3-L1 adipocytes were incubated for 8 h in glucose-free DMEM with each substance at the indicated concentrations. *p < 0.05, ***p < 0.001. n.s., not significant. Data are expressed as means ± SE.

Mentions: PDE3B, an enzyme catalyzing the conversion of cAMP to AMP, is expressed in adipocytes [7] and located downstream of Akt signaling. The PDE3B inhibitor cilostazol suppressed insulin stimulated leptin secretion in a dose-dependent manner, while it showed no effect on leptin mRNA levels under the lack of glucose (Fig. 3A and B). These effects were similar to those of the PI3K inhibitor and the Akt inhibitor. A cAMP analog, dibutyryl cAMP, also decreased leptin secretion (Fig. 3C). In contrast to cilostazol, the insulin upregulation of leptin mRNA was abrogated by dibutyryl cAMP (Fig. 3D).


Insulin elevates leptin secretion and mRNA levels via cyclic AMP in 3T3-L1 adipocytes deprived of glucose
Effects of the PDE3B inhibitor cilostazol (A and B) or a cyclic AMP analog (C and D) on insulin-induced leptin secretion and mRNA levels in 3T3-L1 adipocytes under glucose-free conditions. 3T3-L1 adipocytes were incubated for 8 h in glucose-free DMEM with each substance at the indicated concentrations. *p < 0.05, ***p < 0.001. n.s., not significant. Data are expressed as means ± SE.
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5121139&req=5

fig0015: Effects of the PDE3B inhibitor cilostazol (A and B) or a cyclic AMP analog (C and D) on insulin-induced leptin secretion and mRNA levels in 3T3-L1 adipocytes under glucose-free conditions. 3T3-L1 adipocytes were incubated for 8 h in glucose-free DMEM with each substance at the indicated concentrations. *p < 0.05, ***p < 0.001. n.s., not significant. Data are expressed as means ± SE.
Mentions: PDE3B, an enzyme catalyzing the conversion of cAMP to AMP, is expressed in adipocytes [7] and located downstream of Akt signaling. The PDE3B inhibitor cilostazol suppressed insulin stimulated leptin secretion in a dose-dependent manner, while it showed no effect on leptin mRNA levels under the lack of glucose (Fig. 3A and B). These effects were similar to those of the PI3K inhibitor and the Akt inhibitor. A cAMP analog, dibutyryl cAMP, also decreased leptin secretion (Fig. 3C). In contrast to cilostazol, the insulin upregulation of leptin mRNA was abrogated by dibutyryl cAMP (Fig. 3D).

View Article: PubMed Central - PubMed

ABSTRACT

Aims: Leptin plays an important role in the pathogenesis of obesity and diabetes, yet the regulatory mechanisms of this hormone have not been fully elucidated. In this study, we aimed to clarify the roles of insulin and glucose in leptin secretion and mRNA production using inhibitors of insulin signal transduction in adipocytes cultured under glucose-free or normal conditions.

Methods: Differentiated 3T3-L1 adipocytes were stimulated with insulin in combination with inhibitors for phosphoinositide 3-kinase (PI3K), Akt, and phosphodiesterase 3B (PDE3B), as well as epinephrine and a cyclic AMP (cAMP) analog under glucose-free or normal conditions. After 8 h of stimulation, leptin protein levels in the media and leptin mRNA expression levels in the adipocytes were measured.

Results: Insulin significantly increased the secretion and mRNA levels of leptin under the depletion of glucose. Glucose augmented basal leptin secretion without insulin, while glucose ified insulin-induced leptin mRNA upregulation. The PI3K inhibitor BEZ-235, the Akt inhibitor MK-2206, and the PDE3B inhibitor cilostazol attenuated the insulin stimulation of leptin secretion, but did not suppress the insulin-induced leptin mRNA upregulation with glucose depletion. In contrast to the glucose-free condition, insulin failed to upregulate leptin mRNA in the presence of glucose. The cAMP analog dibutyryl cAMP and epinephrine decreased both leptin secretion and mRNA regardless of glucose supplementation.

Conclusion: Insulin alone stimulates leptin secretion and elevates leptin mRNA levels via cAMP under the lack of glucose metabolism, while glucose is a significant and ambivalent effector on the insulin effects of leptin.

No MeSH data available.


Related in: MedlinePlus