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

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

Effects of glucose concentration and insulin on the secretion (A) and mRNA levels (B) of leptin in 3T3-L1 adipocytes. 3T3-L1 adipocytes were incubated for 8 h in DMEM containing 0, 5.5, or 25 mM glucose in the presence or absence of 0.5 μM insulin. *p < 0.05, **p < 0.01, and ***p < 0.001. n.s., not significant. Data are expressed as means ± SE.
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fig0005: Effects of glucose concentration and insulin on the secretion (A) and mRNA levels (B) of leptin in 3T3-L1 adipocytes. 3T3-L1 adipocytes were incubated for 8 h in DMEM containing 0, 5.5, or 25 mM glucose in the presence or absence of 0.5 μM insulin. *p < 0.05, **p < 0.01, and ***p < 0.001. n.s., not significant. Data are expressed as means ± SE.

Mentions: We first examined the effects of insulin on leptin secretion and mRNA expression in the absence or presence of glucose in 3T3-L1 adipocytes. Insulin significantly increased both secretion and mRNA expression of leptin under the depletion of ambient glucose (Fig. 1A and B). Glucose augmented basal leptin secretion without insulin stimulation in a concentration-dependent manner, whereas glucose did not amplify the insulin effects on leptin secretion. Neither 5.5 mM nor 25 mM glucose increased mRNA expression of leptin, and the insulin stimulation on leptin mRNA seen in glucose-free media was cancelled in the presence of glucose (Fig. 1B).


Insulin elevates leptin secretion and mRNA levels via cyclic AMP in 3T3-L1 adipocytes deprived of glucose
Effects of glucose concentration and insulin on the secretion (A) and mRNA levels (B) of leptin in 3T3-L1 adipocytes. 3T3-L1 adipocytes were incubated for 8 h in DMEM containing 0, 5.5, or 25 mM glucose in the presence or absence of 0.5 μM insulin. *p < 0.05, **p < 0.01, and ***p < 0.001. n.s., not significant. Data are expressed as means ± SE.
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

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

fig0005: Effects of glucose concentration and insulin on the secretion (A) and mRNA levels (B) of leptin in 3T3-L1 adipocytes. 3T3-L1 adipocytes were incubated for 8 h in DMEM containing 0, 5.5, or 25 mM glucose in the presence or absence of 0.5 μM insulin. *p < 0.05, **p < 0.01, and ***p < 0.001. n.s., not significant. Data are expressed as means ± SE.
Mentions: We first examined the effects of insulin on leptin secretion and mRNA expression in the absence or presence of glucose in 3T3-L1 adipocytes. Insulin significantly increased both secretion and mRNA expression of leptin under the depletion of ambient glucose (Fig. 1A and B). Glucose augmented basal leptin secretion without insulin stimulation in a concentration-dependent manner, whereas glucose did not amplify the insulin effects on leptin secretion. Neither 5.5 mM nor 25 mM glucose increased mRNA expression of leptin, and the insulin stimulation on leptin mRNA seen in glucose-free media was cancelled in the presence of glucose (Fig. 1B).

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