Linderane Suppresses Hepatic Gluconeogenesis by Inhibiting the cAMP/PKA/CREB Pathway Through Indirect Activation of PDE 3 via ERK/STAT3.

Wei Xie,Ying Feng,Ying Leng,Yangliang Ye,Suling Huang,Jianhua Shen,Tifei Xu

doi:10.3389/fphar.2018.00476

Abstract

The role of phosphodiesterase 3 (PDE3), a cyclic AMP (cAMP)-degrading enzyme, in modulating gluconeogenesis remains unknown. Here, linderane, a natural compound, was found to inhibit gluconeogenesis by activating hepatic PDE3 in rat primary hepatocytes. The underlying molecular mechanism and its effects on whole-body glucose and lipid metabolism were investigated. The effect of linderane on gluconeogenesis, cAMP content, phosphorylation of cAMP-response element-binding protein (CREB) and PDE activity were examined in cultured primary hepatocytes and C57BL/6J mice. The precise mechanism by which linderane activates PDE3 and inhibits the cAMP pathway was explored using pharmacological inhibitors. The amelioration of metabolic disorders was observed in ob/ob mice. Linderane inhibited gluconeogenesis, reduced phosphoenolpyruvate carboxykinase (Pck1) and glucose-6-phosphatase (G6pc) gene expression, and decreased intracellular cAMP concentration and CREB phosphorylation in rat primary hepatocytes under both basal and forskolin-stimulated conditions. In rat primary hepatocytes, it also increased total PDE and PDE3 activity but not PDE4 activity. The suppressive effect of linderane on the cAMP pathway and gluconeogenesis was abolished by the non-specific PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX) and the specific PDE3 inhibitor cilostazol. Linderane indirectly activated PDE3 through extracellular regulated protein kinase 1/2 (ERK1/2) and signal transducer and activator of transcription 3 (STAT3) activation. Linderane improved glucose and lipid metabolism after chronic oral administration in ob/ob mice. Our findings revealed linderane as an indirect PDE3 activator that suppresses gluconeogenesis through cAMP pathway inhibition and has beneficial effects on metabolic syndromes in ob/ob mice. This investigation highlighted the potential for PDE3 activation in the treatment of type 2 diabetes.

Highlights

Persistent hyperglycemia, the most notable characteristic of type 2 diabetes mellitus (T2DM), contributes to a group of chronic complications and comorbidities (Saltiel, 2001)
The gluconeogenesis in rat primary hepatocytes was suppressed by linderane in a dose-dependent manner (Figure 1B), with 10 and 20 μM linderane resulting in a decrease of 39.8 and 65.6%, respectively
Linderane exerted an inhibitory effect on forskolin-stimulated gluconeogenesis, with 10 and 20 μM linderane causing a reduction by 44.1 and 71.7%, respectively, which were similar to the effect of linderane under basal conditions (Figure 1C)

Summary

Introduction

Persistent hyperglycemia, the most notable characteristic of T2DM, contributes to a group of chronic complications and comorbidities (Saltiel, 2001). The catalytic subunit of PKA phosphorylates CREB at Ser 133, and the activated CREB dephosphorylates and recruits cAMP-modulated transcriptional co-activators (CRTCs) This process upregulates the expression of rate-limited gluconeogenic genes including Pck ( known as Pepck) and G6pc ( known as G6Pase), enhances hepatic gluconeogenesis and increases the whole-body blood glucose levels (Herzig et al, 2001; Samuel and Shulman, 2016). Two alkaloids, lycoricidine and lycoricidinol, were discovered to inhibit endogenous hepatic glucose production by suppressing cAMP-regulated CREB phosphorylation (Yun et al, 2016) This evidence indicated that interfering with the cAMP/PKA/CREB signaling pathway would be an attractive strategy to correct dysregulated hepatic glucose production in T2DM (Unger and Cherrington, 2012)

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Results

Conclusion