Fenoxycarb promotes adipogenesis in 3T3‐L1 preadipocytes

Lipophilic insect hormones and their analogs affect mammalian physiology by regulating the expression of metabolic genes. Therefore, we determined the effect of fenoxycarb, a juvenile hormone analog, on lipid metabolism in adipocytes. Here, we demonstrated that fenoxycarb dose‐dependently promoted lipid accumulation in 3T3‐L1 adipocytes during adipocyte differentiation and that its lipogenic effect was comparable to that of rosiglitazone, a well‐known ligand for peroxisome proliferator‐activated receptor gamma (PPARγ). Furthermore, fenoxycarb stimulated PPARγ activity without affecting other nuclear receptors, such as liver X receptor (LXR), farnesoid X‐activated receptor (FXR) and Nur77. In addition, fenoxycarb treatment increased the expression of PPARγ and fatty acid transporter protein 1 (FATP1) in 3T3‐L1 adipocytes, suggesting that fenoxycarb may facilitate adipocyte differentiation by enhancing PPARγ signaling, the master regulator of adipogenesis. Together, our results suggest that fenoxycarb promoted lipid accumulation in adipocytes, in part, by stimulating PPARγ.     

MicroRNA-302a inhibits adipogenesis by suppressing peroxisome proliferator-activated receptor γ expression

The present study explored the involvement of miR-302a in adipocyte differentiation via interaction with 3′-untranslated region of peroxisome proliferator-activated receptor gamma (PPARγ) mRNA. In differentiating 3T3-L1 adipocytes, expression of miR-302a was negatively correlated with that of the adipogenic gene aP2 and PPARγ. Overexpression of miR-302a inhibited adipogenic differentiation with lipid accumulation, and inversely anti-miR-302a increased the differentiation. In silico analysis revealed a complementary region of miR-302a seed sequence in 3′-UTR of PPARγ mRNA. Luciferase assay showed the direct interaction of miR-302a with PPARγ at the cellular level. The miR-302a inhibition of adipocyte differentiation was reversed by PPARγ overexpression. These findings suggest that miR-302a might be a negative regulator of adipocyte differentiation and that the dysregulation of miR-302a should lead to metabolic disorders.     

Asiatic Acid Inhibits Adipogenic Differentiation of Bone Marrow Stromal Cells

Bone marrow mesenchymal stromal cells (BMSCs) are the common precursors for both osteoblasts and adipocytes. With aging, BMSC osteoblast differentiation decreases whereas BMSC differentiation into adipocytes increases, resulting in increased adipogenesis and bone loss. In the present study, we investigated the effect of asiatic acid (AA) on adipocytic differentiation of BMSCs. AA inhibited the adipogenic induction of lipid accumulation, activity of glycerol-3-phosphate dehydrogenase, and expression of marker genes in adipogenesis: peroxisome proliferation-activated receptor (PPAR)γ, adipocyte fatty acid-binding protein (ap) 2, and adipsin. Further, we found that AA did not alter clonal expansion rate and expression of C/EBPβ, upstream key regulator of PPARγ, and binding activity of C/EBPβ to PPARγ promoter was not affected by AA as well. These findings suggest that AA may modulate differentiation of BMSCs to cause a lineage shift away from the adipocytes, and inhibition of PPARγ by AA is through C/EBPβ-independent mechanisms. Thus, AA could be a potential candidate for a novel drug against osteoporosis.     

Activation of peroxisome proliferator-activated receptor-α enhances fatty acid oxidation in human adipocytes

Peroxisome proliferator-activated receptor-α (PPARα) is a key regulator for maintaining whole-body energy balance. However, the physiological functions of PPARα in adipocytes have been unclarified. We examined the functions of PPARα using human multipotent adipose tissue-derived stem cells as a human adipocyte model. Activation of PPARα by GW7647, a potent PPARα agonist, increased the mRNA expression levels of adipocyte differentiation marker genes such as PPARγ, adipocyte-specific fatty acid-binding protein, and lipoprotein lipase and increased both GPDH activity and insulin-dependent glucose uptake level. The findings indicate that PPARα activation stimulates adipocyte differentiation. However, lipid accumulation was not changed, which is usually observed when PPARγ is activated. On the other hand, PPARα activation by GW7647 treatment induced the mRNA expression of fatty acid oxidation-related genes such as CPT-1B and AOX in a PPARα-dependent manner. Moreover, PPARα activation increased the production of CO₂ and acid soluble metabolites, which are products of fatty acid oxidation, and increased oxygen consumption rate in human adipocytes. The data indicate that activation of PPARα stimulates both adipocyte differentiation and fatty acid oxidation in human adipocytes, suggesting that PPARα agonists could improve insulin resistance without lipid accumulation in adipocytes. The expected effects of PPARα activation are very valuable for managing diabetic conditions accompanied by obesity, because PPARγ agonists, usually used as antidiabetic drugs, induce excessive lipid accumulation in adipocytes in addition to improvement of insulin resistance.     

Fat-specific protein 27, a novel lipid droplet protein that enhances triglyceride storage

Fat-specific protein (FSP)27/Cidec is most highly expressed in white and brown adipose tissues and increases in abundance by over 50-fold during adipogenesis. However, its function in adipocytes has remained elusive since its discovery over 15 years ago. Here we demonstrate that FSP27/Cidec localizes to lipid droplets in cultured adipocytes and functions to promote lipid accumulation. Ectopically expressed FSP27-GFP surrounds lipid droplets in 3T3-L1 adipocytes and colocalizes with the known lipid droplet protein perilipin. Immunostaining of endogenous FSP27 in 3T3-L1 adipocytes also confirmed its presence on lipid droplets. FSP27-GFP expression also markedly increases lipid droplet size and enhances accumulation of total neutral lipids in 3T3-L1 preadipocytes as well as other cell types such as COS cells. Conversely, RNA interference-based FSP27/Cidec depletion in mature adipocytes significantly stimulates lipolysis and reduces the size of lipid droplets. These data reveal FSP27/Cidec as a novel adipocyte lipid droplet protein that negatively regulates lipolysis and promotes triglyceride accumulation.     

Activation of peroxisome proliferator-activated receptor-alpha stimulates both differentiation and fatty acid oxidation in adipocytes

Peroxisome proliferator-activated receptor-α (PPARα) is a dietary lipid sensor, whose activation results in hypolipidemic effects. In this study, we investigated whether PPARα activation affects energy metabolism in white adipose tissue (WAT). Activation of PPARα by its agonist (bezafibrate) markedly reduced adiposity in KK mice fed a high-fat diet. In 3T3-L1 adipocytes, addition of GW7647, a highly specific PPARα agonist, during adipocyte differentiation enhanced glycerol-3-phosphate dehydrogenase activity, insulin-stimulated glucose uptake, and adipogenic gene expression. However, triglyceride accumulation was not increased by PPARα activation. PPARα activation induced expression of target genes involved in FA oxidation and stimulated FA oxidation. In WAT of KK mice treated with bezafibrate, both adipogenic and FA oxidation-related genes were significantly upregulated. These changes in mRNA expression were not observed in PPARα-deficient mice. Bezafibrate treatment enhanced FA oxidation in isolated adipocytes, suppressing adipocyte hypertrophy. Chromatin immunoprecipitation (ChIP) assay revealed that PPARα was recruited to promoter regions of both adipogenic and FA oxidation-related genes in the presence of GW7647 in 3T3-L1 adipocytes. These findings indicate that the activation of PPARα affects energy metabolism in adipocytes, and PPARα activation in WAT may contribute to the clinical effects of fibrate drugs.     

Lycopene attenuates body weight gain through induction of browning via regulation of peroxisome proliferator-activated receptor γ in high-fat diet-induced obese mice

Lycopene (LYC), one of the major carotenoids in tomatoes, has been preclinically and clinically used to obesity and type 2 diabetes management. However, whether its ability of countering body weight gain is related to induction of brown-like adipocyte phenotype in white adipose tissues (WAT) remains largely unknown. Activation of peroxisome proliferator-activated receptor γ (PPARγ) serves the brown-like phenotype conversion and energy expenditure. Here, we show that LYC treatment promotes glucose consumption and improves insulin sensitivity, as well as fosters white adipocytes browning through up-regulating mRNA and protein expression levels of PPARγ, uncoupling protein 1, PPARγ coactivator-1α and PR domain-containing 16 in the differentiated 3T3-L1 adipocytes and primary adipocytes, as well as in the WAT of HFD-exposed obese mice. In addition, LYC treatment attenuates body weight gain and improves serum lipid profiles as well as promotes brown adipose tissue activation in obese mice. Moreover, PPARγ is induced with LYC intervention in mitochondria respiration and browning in white adipocytes and tissues. Taken together, these results suggest that LYC counteracts obesity and improves glucose and lipid metabolism through induction of the browning via up-regulation of PPARγ, which offers a new perspective of this compound to combat obesity and obesity-related disorders.