Synergistic effects of cAMP–dependent protein kinase A and AMP-activated protein kinase on lipolysis in kinsenoside-treated C3H10T1/2 adipocytes

Abstract

BackgroundWe previously showed that 3-O‐β‐D‐glucopyranosyl‐(3R)‐hydroxybutanolide (kinsenoside), a major compound of Anoectochilus formosanus, increased lipolysis through an AMP–activated protein kinase (AMPK)–dependent pathway. PurposeTo extend our previous finding, we investigated the in vivo and in vitro effects of kinsenoside on lipolysis and the involvement of cyclic AMP (cAMP)–dependent protein kinase A (PKA) and AMPK in kinsenoside-mediated lipolysis. Study design/methodsMice were fed a high-fat diet for six weeks to induce lipid deposition and then treated with 50 and 100 mg/kg kinsenoside for two weeks. The coordination of PKA and AMPK activation in lipolysis in C3H10T1/2 adipocytes was evaluated in vitro by using PKA and AMPK's corresponding inhibitors, oil-red O staining, a glycerol production assay, and Western blot analysis. ResultsKinsenoside reduced body weight, fat pad mass, and hepatic lipid accumulation in obese mice, and concurrently increased the induction and activation of hormone-sensitive lipase (HSL), perilipin, adipose triglyceride lipase (ATGL), and carnitine palmitoyltransferase I (CPT1). Kinsenoside concentration-dependently increased PKA activation by increasing the phosphorylation of Ser/Thr-PKA substrates in vitro. These increases were accompanied by a reduction in fat accumulation. Using H89 and Rp-8-Br-cAMPs to inhibit PKA reduced the release of glycerol but did not alter the activation of peroxisome proliferator–activated receptor alpha or the expression of CPT1 or ATGL. By contrast, compound C, an AMPK inhibitor, inhibited CPT1 and ATGL expression in kinsenoside-treated C3H10T1/2 adipocytes. In addition, H89 caused the reactivation of AMPK downstream targets by increasing the levels of the active form of pAMPK-Thr172, suggesting that PKA negatively modulates AMPK activity. ConclusionKinsenoside increased HSL activation through PKA-mediated phosphorylation at Ser660/563 and concomitantly increased perilipin activation in lipolysis. These lipolytic effects of kinsenoside were validated using 6-Bnz-cAMPs, a PKA agonist. In this study, we demonstrated that in addition to AMPK, PKA also plays a crucial role in kinsenoside-mediated lipolysis.