Hesperetin Inhibit Adipocyte Differentiation and Enhance Bax‐ and p21‐Mediated Adipolysis in Human Mesenchymal Stem Cell Adipogenesis

We aimed to explore the antiadipogenic and adipolysis effect of hesperetin in human mesenchymal stem cells (hMSCs)–induced adipogenesis. IC₅₀ value of hesperetin was higher for hMSCs such as 149.2 ± 13.2 μmol for 24 h and 89.4 ± 11.4 μmol in 48 h, whereas in preadipocytes was 87.6 ± 9.5 μmol and 72.4 ± 5.6 μmol in 24 h and 48 h, respectively. Hesperetin treatment (5, 10, and 20 μmol) to adipogenesis‐induced hMSCs (Group 1) and preadipocytes (Group 2) resulted in a significantly (p < 0.05) increased lipolysis. The treatment with hesperetin decreased the expression of resistin, adiponectin, aP₂, LPL, PPAR‐γ, and TNF‐α in Groups 1 and 2, whereas a significant increase was observed in Bcl, Bax, and p21 expression in Group 2 compared to untreated preadipocytes. hMSCs cultured in adipogenic medium along with hesperetin significantly inhibited adipocyte differentiation and increased the proapoptotic gene expression levels in preadipocyte. Our result indicates the antiadipogenic and adipolysis effects of hesperetin.     

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.     

An Evi1-C/EBPβ complex controls peroxisome proliferator-activated receptor γ2 gene expression to initiate white fat cell differentiation

Fibroblastic preadipocyte cells are recruited to differentiate into new adipocytes during the formation and hyperplastic growth of white adipose tissue. Peroxisome proliferator-activated receptor γ (PPARγ), the master regulator of adipogenesis, is expressed at low levels in preadipocytes, and its levels increase dramatically and rapidly during the differentiation process. However, the mechanisms controlling the dynamic and selective expression of PPARγ in the adipocyte lineage remain largely unknown. We show here that the zinc finger protein Evi1 increases in preadipocytes at the onset of differentiation prior to increases in PPARγ levels. Evi1 expression converts nonadipogenic cells into adipocytes via an increase in the predifferentiation levels of PPARγ2, the adipose-selective isoform of PPARγ. Conversely, loss of Evi1 in preadipocytes blocks the induction of PPARγ2 and suppresses adipocyte differentiation. Evi1 binds with C/EBPβ to regulatory sites in the Pparγ locus at early stages of adipocyte differentiation, coincident with the induction of Pparγ2 expression. These results indicate that Evi1 is a key regulator of adipogenic competency.     

Inhibition of preadipocyte differentiation by myostatin treatment in 3T3-L1 cultures

Myostatin, a new TGF-beta family member, is known as a muscle growth inhibitor, but its role in adipocyte development has not been studied. To test the role of Myostatin in 3T3-L1 preadipocyte differentiation, we treated cultured 3T3-L1 preadipocytes with Myostatin dissolved in 0.1% trifluoroacetic acid (TFA) during differentiation after they had become confluent. Myostatin treatment significantly decreased glycerol-3-phosphate dehydrogenase (GPDH) activity and oil Red-O staining compared to controls that did not receive Myostatin. Western blot analysis showed that the expression levels of CCAAT/enhancer binding protein alpha (C/EBP alpha) and peroxisome proliferator-activated receptor gamma (PPAR gamma) were significantly decreased by Myostatin treatment (P < 0.05). However, the expression of C/EBP beta was not significantly changed by the treatment (P > 0.05). From RT-PCR result, the relative level of leptin mRNA in Myostatin-treated cells was not significantly different (P > 0.1) from the level in cells without Myostatin treatment. Our data show that Myostatin, a secreted protein from muscle, inhibits preadipocyte differentiation in 3T3-L1 cells, which is mediated, in part, by altered regulation of C/EBP alpha and PPAR gamma.     

Licochalcone E has an antidiabetic effect

Licochalcone E (lico E) is a retrochalcone isolated from the root of Glycyrrhiza inflata. Retrochalcone compounds evidence a variety of pharmacological profiles, including anticancer, antiparasitic, antibacterial, antioxidative and superoxide-scavenging properties. In this study, we evaluated the biological effects of lico E on adipocyte differentiation in vitro and obesity-related diabetes in vivo. We employed 3T3-L1 preadipocyte and C3H10T1/2 stem cells for in vitro adipocyte differentiation study and diet-induced diabetic mice for in vivo study. The presence of lico E during adipogenesis induced adipocyte differentiation to a significant degree, particularly at the early induction stage. Licochalcone E evidenced weak, but significant, peroxisome proliferator-activated receptor gamma (PPARγ) ligand-binding activity. Two weeks of lico E treatment lowered blood glucose levels and serum triglyceride levels in the diabetic mice. Additionally, treatment with lico E resulted in marked reductions in adipocyte size and increases in the mRNA expression levels of PPARγ in white adipose tissue (WAT). Licochalcone E was also shown to significantly stimulate Akt signaling in epididymal WAT. In conclusion, lico E increases the levels of PPARγ expression, at least in part, via the stimulation of Akt signals and functions as a PPARγ partial agonist, and this increased PPARγ expression enhances adipocyte differentiation and increases the population of small adipocytes, resulting in improvements in hyperglycemia and hyperlipidemia under diabetic conditions.     

Myostatin regulates preadipocyte differentiation and lipid metabolism of adipocyte via ERK1/2

Myostatin is known as an inhibitor of muscle development, but its role in adipogenesis and lipid metabolism is still unclear, especially the underlying mechanisms. Here, we demonstrated that myostatin inhibited 3T3-L1 preadipocyte differentiation into adipocyte by suppressing C/EBPα (CCAAT/enhancer-binding protein α) and PPARγ (peroxisome-proliferator-activated receptor γ), also activated ERK1/2 (extracellular-signal-regulated kinase 1/2). Furthermore, myostatin enhanced the phosphorylation of HSL (hormone-sensitive lipase) and ACC (acetyl-CoA carboxylase) in fully differentiated adipocytes, as well as ERK1/2. Besides, we noted that myostatin markedly raised the levels of leptin and adiponectin release and mRNA expression during preadipocyte differentiation, but the levels were inhibited by myostatin treatments in fully differentiated adipocytes. These results suggested that myostatin suppressed 3T3-L1 preadipocyte differentiation and regulated lipid metabolism of mature adipocyte, in part, via activation of ERK1/2 signalling pathway.     

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.     

The adipokine Chemerin induces lipolysis and adipogenesis in bovine intramuscular adipocytes

The adipokine Chemerin is reported to regulate adipogenesis and glucose homeostasis in vivo and in 3T3-L1 cells. Our team is focused on the role of Chemerin in metabolism and intramuscular adipocyte differentiation because intramuscular fat is the basic material for the formation of marbling in livestock and poultry meat. In this study, bovine intramuscular mature adipocytes were cultured in medium with Chemerin, and the process of lipolysis of mature adipocytes and the adipogenesis of de-differentiated preadipocytes were investigated. The results showed that Chemerin induced significant lipolytic metabolism in intramuscular mature adipocytes, indicated by increased levels of glycerol, FFA, and up-regulated expression of the lipolysis critical factors HSL, LPL, and leptin. Meanwhile, the expressions of adipogenic key factors PPARγ, C/EBPα, and A-FABP were decreased by Chemerin during lipolysis or dedifferentiation in mature adipocytes. The de-differentiated preadipocytes could re-differentiate into mature adipocytes. Intriguingly, the formation of cells’ lipid droplets was promoted by Chemerin during preadipocyte differentiation. In addition, mRNA and protein expressions of PPARγ, C/EBPα, and A-FABP were up-regulated by Chemerin during preadipocytes differentiation. These results suggest that Chemerin promotes lipolysis in mature adipocytes and induces adipogenesis during preadipocyte re-differentiation, further indicating a dual role for Chemerin in the deposition of intramuscular fat in ruminant animals.

     

EMF acts on rat bone marrow mesenchymal stem cells to promote differentiation to osteoblasts and to inhibit differentiation to adipocytes

The use of electromagnetic fields (EMFs) to treat nonunion fractures developed from observations in the mid‐1900s. Whether EMF directly regulates the bone marrow mesenchymal stem cells (MSCs), differentiating into osteoblasts or adipocytes, remains unknown. In the present study, we investigated the roles of sinusoidal EMF of 15 Hz, 1 mT in differentiation along these separate lineages using rat bone marrow MSCs. Our results showed that EMF promoted osteogenic differentiation of the stem cells and concurrently inhibited adipocyte formation. EMF increased alkaline phosphatase (ALP) activity and mineralized nodule formation, and stimulated osteoblast‐specific mRNA expression of RUNX2, ALP, BMP2, DLX5, and BSP. In contrast, EMF decreased adipogenesis and inhibited adipocyte‐specific mRNA expression of adipsin, AP‐2, and PPARγ2, and also inhibited protein expression of PPARγ2. These observations suggest that commitment of MSCs into osteogenic or adipogenic lineages is influenced by EMF. Bioelectromagnetics 31:277–285, 2010. © 2009 Wiley‐Liss, Inc.     

Cystathionine γ lyase–hydrogen sulfide increases peroxisome proliferator-activated receptor γ activity by sulfhydration at C139 site thereby promoting glucose uptake and lipid storage in adipocytes

Adipocytes express the cystathionine γ lyase (CSE)–hydrogen sulfide (H₂S) system. CSE–H₂S promotes adipogenesis but ameliorates adipocyte insulin resistance. We investigated the mechanism of how CSE–H₂S induces these paradoxical effects. First, we confirmed that an H₂S donor or CSE overexpression promoted adipocyte differentiation. Second, we found that H₂S donor inhibited but CSE inhibition increased phosphodiesterase (PDE) activity. H₂S replacing isobutylmethylxanthine in the differentiation program induced adipocyte differentiation in part. Inhibiting PDE activity by H₂S induced peroxisome proliferator activated receptor γ (PPARγ) protein and mRNA expression. Of note, H₂S directly sulfhydrated PPARγ protein. Sulfhydrated PPARγ increased its nuclear accumulation, DNA binding activity and adipogenesis gene expression, thereby increasing glucose uptake and lipid storage, which were blocked by the desulfhydration reagent DTT. H₂S induced PPARγ sulfhydration, which was blocked by mutation of the C139 site of PPARγ. In mice fed a high-fat diet (HFD) for 4 weeks, the CSE inhibitor decreased but H₂S donor increased adipocyte numbers. In obese mice fed an HFD for 13 weeks, H₂S treatment increased PPARγ sulfhydration in adipose tissues and attenuated insulin resistance but did not increase obesity. In conclusion, CSE–H₂S increased PPARγ activity by direct sulfhydration at the C139 site, thereby changing glucose into triglyceride storage in adipocytes. CSE–H₂S-mediated PPARγ activation might be a new therapeutic target for diabetes associated with obesity.