Search

Nowadays, a lot of food ingredients are marketed as dietary supplements for health. Because the effectiveness and mechanisms of these compounds have not been fully characterized, they might have unknown functions. Therefore, we investigated the effect of several food ingredients (Bergamottin, Chrysin, L-Citrulline and β-Carotene) known as health foods on adipocyte differentiation by using 3T3-L1 preadipocytes. In this study, we found that Bergamottin, a furanocoumarin isolated from grapefruit juice, promotes adipocyte differentiation. In addition, Bergamottin increases the expression of adiponectin, an anti-inflammatory adipokine, and peroxisome proliferator activated receptor γ (PPARγ), a nuclear receptor regulating adipocyte differentiation. Furthermore, the anti-inflammatory activity of Bergamottin was demonstrated by its inhibition of the activation of nuclear factor-κB (NF-κB), an inflammatory transcription factor. Stimulation of mature 3T3-L1 adipocytes by tumor necrosis factor-α (TNF-α) decreased the expression of the endogeneous NF-κB inhibitor, IκBα. Treatment with Bergamottin further decreased the TNF-α-induced change in IκBα expression, suggesting that Bergamottin mediated the inhibition of NF-κB activation. In addition, Bergamottin decreased the TNF-α-induced increase in the mRNA levels of pro-inflammatory adipokines, monocyte chemoattractant protein-1 and interleukin-6. Taken together, our results show that Bergamottin treatment could inhibit inflammatory activity through promoting adipocyte differentiation, which in turn suggests that Bergamottin has the potential to minimize the risk factors of metabolic syndrome.

Cells have developed ingenious defense mechanisms in response to oxidative stress. Here, we evaluated changes in anti-oxidative capacity during differentiation of 3T3-L1 preadipocytes into adipocytes. When 3T3-L1 preadipocytes were treated with H 2 O 2 (0.10-2.0 mM) for 21 h, cell viability decreased in response to H 2 O 2 concentration, with an LD 50 of approximately 0.35 mM H 2 O 2 . In the cells undergoing differentiation at 2 and 6 d, LD 50 increased to 1.0 and >2.0 mM H 2 O 2 , respectively. These results indicate that resistance to oxidative stress dramatically increased with progression of differentiation of preadipocytes into adipocytes. Catalase activity and GSH content increased in the differentiated cells at 6 d, whereas superoxide dismutase and glutathione peroxidase activities were slightly lower in adipocytes than in preadipocytes. Moreover, knockdown of catalase or depletion of intracellular GSH enhanced the sensitivity to H 2 O 2 . When GSH was added to the cells depleted of intracellular GSH, the antioxidant capacity recovered. Autophagy was increased in differentiated adipocytes but was not affected by H 2 O 2 treatment. Therefore, these results suggest that the increase in intracellular catalase activity and GSH content played a role in the increased anti-oxidative capacity of differentiated 3T3-L1 adipocytes.

Obesity is a major risk factor for diabetes, hypertension, hyperlipidemia, and arteriosclerosis. Although the middle and late stages of adipocyte differentiation are well characterized, the earliest step in the differentiation process has remained largely unknown. We isolated 102 genes expressed at the beginning of the differentiation of a mouse preadipocyte cell line, 3T3-L1 cells. Because approximately half of these genes were unknown, we named them factor for adipocyte differentiation (fad) genes. I first show how these genes regulate the early stage of adipocyte differentiation. We next generated fad104-deficient mice, and demonstrated that fad104-deficient mice died due to cyanosis-associated lung dysplasia with atelectasis. We also found that fad104 positively regulated adipocyte differentiation and negatively regulated osteoblast differentiation. We then demonstrated that fad24-knockdown inhibited mitotic clonal expansion (MCE) and that FAD24 contributed to the regulation of DNA replication by recruiting histone acetyltransferase binding to ORC1 (HBO1) to DNA replication origins. In vitro culture experiments revealed that fad24-null embryos developed normally to the morula stage, but acquired growth defects in subsequent stages. These results strongly suggest that fad24 is essential for pre-implantation in embryonic development, particularly for progression to the blastocyst stage. These findings together indicate that both fad104 and fad24 contribute not only to adipogenesis but also to other physiological events. The multi-functional roles of these genes are discussed.

Obesity, which results from adipose differentiation and adipocyte hypertrophy, is a primary risk factor of these life-style-diseases. Obesity, is primary risk factor of these life-style-diseases, results from adipose differentiation and adipocyte hypertrophy. Adipose differentiation is regulated by several transcriptional factors, and we have focused here on the roles played by endothelial PAS domain protein1 (EPAS1) in adipogenesis. EPAS1 was identified as a factor responsible for hypoxia responses, such as angiogenesis, here we demonstrated that EPAS1 is highly induced during adipose differentiation in vivo and in vitro. We then analyzed EPAS1 promoter activity during adipose differentiation in 3T3-L1 cells. We showed that the sequence -478/-445 is responsible for the up-regulation of EPAS1 expression during adipose differentiation and that the activity of this region is controlled by Sp1 and Sp3. To examine whether EPAS1 exerts an influence on adipogenesis, we overexpressed dominant negative form of EPAS1 in 3T3-L1 cells. The expression of EPAS1 (1-485) allowed cells to accumulate only a minimum amount of lipid droplets. Therefore, induction of EPAS1 expression is necessary for execution of adipose differentiation program. The mechanism involves the direct transcriptional regulation of Glut1, Glut4 and IRS3 genes by EPAS1. These results also confirmed that the protein level of EPAS1 was increased by insulin stimulation in adipocytes. Taken together, this result also indicated that EPAS1 plays a role in the part of insulin action. Therefore, these results suggest that the quantitative and functional alteration of EPAS1 are involved in metabolic syndrome occurrence.

The mid- and late stages of adipocyte differentiation are known to be regulated by transcription factors such as peroxisome proliferator-activated receptor (PPAR)gamma and CCAAT-box/enhancer binder protein (C/EBP) families. However, events in the early stage of adipocyte differentiation remain largely unknown. To gain insights into the molecular mechanisms underlying the beginning of adipocyte differentiation, we have isolated 102 genes, which are induced at the beginning of the differentiation of mouse 3T3-L1 preadipocytes, using the polymerase chain reaction (PCR)-subtraction method. Of these, 46 appear to be unknown genes. Since rapid amplification of cDNA end (RACE), cDNA library screening, and a genome database search have revealed that two of these genes are novel, we have named them factor for adipocyte differentiation (fad) 24 and fad158. The database research of amino acid sequences revealed that fad24 has a basic leucine zipper motif and an NOC domain, and fad158 has four transmembrane domains and eight leucine-rich repeats. The expression of fad24 and fad158 transiently increased after the addition of adipogenic inducers [insulin, dexamethasone, 3-isobutyl-1-methylxanthine, fetal bovine serum (FBS)]. RNAi-mediated knockdown of fad24 or antisense fad158 inhibited adipogenesis of 3T3-L1 preadipocytes and decreased expressions of PPARgamma and C/EBPalpha. Furthermore, the constitutive overexpression of fad24 or fad158 in the mouse fibroblast cell line NIH-3T3 resulted in adipocyte conversion when stimulated with adipogenic inducers and PPARgamma ligand BRL49653. Moreover, it was found that FAD24 localizes in the nucleus, especially within nuclear speckles and nucleolus, and FAD158 localizes to the endoplasmic reticulum (ER). Taken together, fad24 and fad158 appear to regulate adipocyte differentiation by activating the PPARgamma pathway.

Obesity frequently promotes a variety of cardiovascular diseases including atherosclerosis, hypertension, and type 2 diabetes. In a view of both the preventive and therapeutic aspects of the abovementioned diseases, most intensive clinical interventions have been primarily directed at decreasing excessive amounts of fat tissue by a change in the balance between intake and expenditure of energy; such changes are typically effected via daily exercise and diet control. Mechanical stimuli such as stretching and rubbing of fat tissues using gymnastic exercises or massage are believed to decrease obesity; however, there is no report concerning the direct effect of the mechanical stimulation on adipocytes. Here, we demonstrated that cyclic stretch inhibited adipocyte differentiation of mouse 3T3-L1 cells, which was attributable to a reduced expression of adipogenic transcription factor peroxisome proliferator-activated receptor (PPAR)gamma(2) via the activation of an extracellular signal-regulated protein kinase (ERK) pathway. The inhibitory effect of the cyclic stretching on the differentiation of 3T3-L1 cells could be restored by troglitazone, a synthetic ligand for PPARgamma. Our results provide a molecular basis for the physiological significance of the local application of mechanical stimuli to fat tissues, which is totally independent of a mechanism for systemic energy consumption.