Inhibitory Effects of A-769662, a Novel Activator of AMP-Activated Protein Kinase, on 3T3-L1 Adipogenesis

Abstract

Obesity is a chronic metabolic disorder caused by an imbalance between energy intake and expenditure. It is a major known risk factor for many chronic diseases such as type 2 diabetes, hypertension and atherosclerosis.1) Therefore, it has become a major obstacle of improving human health and life quality. Obesity is characterized by a pathologic growth of adipose tissues, which is intrinsically a consequence of adipocyte hypertrophy and differentiation. 2)Studies on several established immortal preadipocyte cell lines such as 3T3-L1 and 3T3-F442A have greatly facilitated our understanding of adipocyte differentiation, which is a tightly controlled and highly orchestrated event accompanied by expression of multiple transcription factors and adipogenic markers, including the CCAAT/enhancer binding proteins (C/EBPs), the peroxisome proliferator-activated receptors (PPARs), fatty acid synthase (FAS) and the adipocyte-specific fatty acid binding protein (aP2).3,4) Briefly, growth-arrested preadipocytes reenter the cell cycle and undergo one or two rounds of division known as mitotic clonal expansion (MCE), during which an immediate and transient induction of C/EBPb and C/EBPd occurs and is followed by up-regulation of PPARg and C/EBPa, two master transcription factors of adipogenesis. PPARg and C/EBPa further trigger expression of multiple adipogenic genes that synergistically lead to adipocyte phenotype. 4) Tang et al. reported that MCE was a prerequisite for adipogenesis and C/EBPb was required for MCE, 5,6) suggesting the importance of C/EBPb in the initial stage of adipocyte differentiation.AMP-activated protein kinase (AMPK), a serine/threonine kinase consisting of a catalytic subunit a and two regulatory subunits b and g, plays a key role in regulation of fatty acid and glucose homeostasis.7) AMPK activation requires phosphorylation at Thr172 of AMPKa subunit by upstream AMPK kinase. Once activated, AMPK blocks ATP-consuming pathways and stimulates ATP-generating pathways. AMPK acts via phosphorylation of downstream metabolic enzymes and transcription factors.8) Acetyl-CoA carboxylase (ACC), a critical enzyme for lipid biosynthesis, can be phosphorylated and inactivated by AMPK. 9) Inactivation of ACC leads to a decreased production of malonyl CoA, which in turn de-represses carnitine palmitoyl-CoA transferase (CPT1) to increase fatty acid oxidation.10) Previous studies have demonstrated the involvement of AMPK activation in the anti-adipogenic effects of several compounds. 11,12) On the other hand, low-level activation of AMPK is likely to play a role in the development of obesity and diabetes.13) Hence, the function of AMPK activation in adipogenesis needs further investigation.A-769662 is a novel activator of AMPK which activates AMPK directly in vivo and in vitro. 14,15) Previous research demonstrated that A-769662 reduced body weight gain and decreased liver and plasma triglyceride levels via increasing fatty acid oxidation and reducing fatty acid synthesis in vivo.14) However, the effect of A-769662 on ad...

Caffeic Acid Phenethyl Ester Suppresses the Production of Adipocytokines, Leptin, Tumor Necrosis Factor -Alpha and Resistin, during Differentiation to Adipocytes in 3T3-L1 Cells

“…[15][16][17] In a previous report, we observed that CAPE treatment dose-dependently suppressed oil droplet accumulation, reduced the size of droplets and could significantly inhibit triglyceride deposition in 3T3-L1 cells. These results indicate that CAPE administration may be effective for adipocytes differentiation.…”

Chronic AMP-kinase activation with AICAR reduces adiposity by remodeling adipocyte metabolism and increasing leptin sensitivity

“…These effects were characterized by increased mitochondrial density and by the presence of mitochondria with more defi ned cristae in the WAT of AICAR-treated animals. This was also accompanied by time-dependent upregulation of FA oxidation in ING and RP but not in EPI been demonstrated in 3T3-L1 adipocytes that the content and/or activity of ACC are decreased in cells treated with various AMPK agonists, along with other adipogenic markers required for differentiation of preadipocytes into mature fat cells ( 4,5 ). In our study, animals begin AICAR treatment at ‫ف‬ 6 to 7 weeks in age, which may have affected adipogenesis in preadipocytes present in the WAT.…”

“…AMPK has also been shown to block adipocyte differentiation in the early stages by inhibiting clonal expansion, which is a critical step for adipogenesis to occur ( 4,5 ). Additionally, treatment of preadipocytes with pharmacological agents to activate AMPK prevents the expression of late adipogenic markers, fatty acid synthase, acetyl-CoA carboxylase (ACC), and transcription factors peroxisome proliferator-activated receptor (PPAR) ␥ 1/2 and CCAAT-enhancer-binding protein (C/EBP) ␣ which are required for the synthesis and storage of lipids in mature adipocytes ( 4,5 ). AMPK also phosphorylates and activates PPAR-␥ coactivator-1 ␣ (PGC-1 ␣ ) and promotes mitochondrial biogenesis in skeletal muscle ( 6 ).…”

LKB1 signalling attenuates early events of adipogenesis and responds to adipogenic cues

“…In this way, AMPK functions as an energy sensor, restoring energy levels by phosphorylating a wide array of substrates (Carling 2004, Carling et al 2008. Several reports have demonstrated that some activators of AMPK, including AICAR and A-769662, inhibit adipogenesis (Giri et al 2006, Zhou et al 2009, Lee et al 2011. Both PKA and PKB, which are activated during the differentiation of adipocytes, have been suggested to inhibit the activity of AMPK by phosphorylating S485 on the catalytic subunit (Hurley et al 2006).…”