Knockdown of KLF9 promotes the differentiation of both intramuscular and subcutaneous preadipocytes in goat

ABSTRACT

KLF9 is reported to promote adipocyte differentiation in 3T3-L1 cells and pigs. However, the roles of KLF9 in adipocytes differentiation of goat remain unknown. In this study, the expression profiles of KLF9 were different between subcutaneous and intramuscular preadipocytes of goat during differentiation process. After silencing KLF9 gene, the lipid droplets were increased in both two types of adipocytes. In subcutaneous preadipocyte with silencing KLF9, the expressions of C/EBPβ, PPARγ, LPL, KLF1-2, KLF5, and KLF17 genes were up-regulated, while KLF12, KLF4, and KLF13 genes were down-regulated in expression level. In intramuscular preadipocyte, aP2, C/EBPα, KLF2-3, KLF5, and KLF7 gene were up-regulated, and Pref-1 gene was down-regulated. In addition, the binding sites of KLF9 existed in the promoters of aP2, C/EBPα, C/EBPβ, LPL and Pref-1. Taken together, KLF9 play a negative role in the differentiation of both intramuscular and subcutaneous preadipocytes in goats, but the functional mechanism may be different.     

<Emphasis Type="Italic">NYGGF4</Emphasis> homologous gene expression in 3T3-L1 adipocytes: regulation by FFA and adipokines

NYGGF4 is a novel gene that is abundantly expressed in the adipose tissue of obese subjects and is involved in insulin resistance. In the present study, the mRNA expression of NYGGF4 homologous genes was examined in the 3T3-L1 cell line. The NYGGF4 mRNAs were expressed at low levels in the 3T3-L1 preadipocytes. During the conversion of 3T3-L1 preadipocytes to adipocytes, the expression of NYGGF4 mRNA was upregulated. On the 8th day after induction of differentiation, the NYGGF4 mRNA levels peaked and remained high. Free fatty acids (FFA) and tumor necrosis factor-α (TNFα) could upregulate NYGGF4 mRNA expression in 3T3-L1 adipocytes, while interleukin-6 (IL-6), leptin, and resistin exerted an inhibitory effect. The results suggest that the expression of NYGGF4 mRNA is affected by a variety of factors that are related to insulin sensitivity. It is likely that NYGGF4 may be an important mediator in the development of obesity-related insulin resistance.     

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.

     

视黄酸X受体α促进猪前体脂肪细胞分化

采用细胞转染、油红O染色、油红O染色提取法、GPDH活性测定、semi-qRT-PCR等方法研究了视黄酸X受体α (retinoic acid X receptor α, RXRα)在猪原代前体脂肪细胞分化中的作用及其机理.结果表明,转染pRXRα-EGFP促进了猪前体脂肪细胞RXRα 的表达,脂肪细胞分化能力随之增强, 脂肪细胞GPDH活性、分化转录因子PPARγ和C/EBPαmRNA表达水平均显著升高(P<0.05). 结果提示,RXRα可能通过调控过氧化物酶体增殖物激活受体γ(peroxisome proliferators-activated receptor-γ, PPARγ)和CAAT/增强子结合蛋白家族（CCAAT/enhancer binding proteins, C/EBP）C/EBPα 基因表达变化促进猪前体脂肪细胞分化.     

The effect of the HIV protease inhibitor ritonavir on proliferation, differentiation, lipogenesis, gene expression and apoptosis of human preadipocytes and adipocytes.

HIV patients in highly active antiretroviral therapy (HAART) develop lipodystrophy and insulin resistance. Protease inhibitors have been shown to alter adipocyte metabolism in murine cell lines. In this study, biological effects of the HIV protease inhibitor, ritonavir, were investigated on human SGBS preadipocytes and adipocytes. Ritonavir dose-dependently impaired preadipocyte proliferation and adipogenic differentiation. Gene expression analysis measured by real-time PCR, showed no effect of ritonavir (up to 20 microM) on expression of mRNA of PPARgamma2 and SREBP1c, but suppressed adiponectin mRNA while increasing IL-6 mRNA expression. In human adipocytes, ritonavir at therapeutic concentrations inhibited insulin-stimulated lipogenesis, reduced GLUT4 mRNA, fatty acid synthase and adiponectin expression, while increasing IL-6 mRNA expression. Finally, long-term treatment (72 and 120 h) of SGBS adipocytes but not preadipocytes with ritonavir induced apoptosis in up to 15% of the cells. All together, these data show effects of ritonavir on human preadipocytes and adipocytes aiming at reducing adipose tissue mass and increasing insulin resistance. These in vitro findings may partly explain the clinical findings in patients under HAART. Furthermore, SGBS cells may serve as a useful tool in further investigation of the mechanism of protease inhibitor action in human adipocytes.     

Enhancement of Inflammatory Protein Expression and Nuclear Factor Κb (NF-Κb) Activity by Trichostatin A (TSA) in OP9 Preadipocytes

The production of inflammatory proteins such as interleukin-6 (IL-6) by preadipocytes and mature adipocytes is closely associated with the impairment of systemic glucose homeostasis. However, precisely how the production is regulated and the roles of histone deacetylases (HDACs) remain largely unknown. The aim of this study was to establish whether HDAC inhibitors affect the expression of inflammatory proteins in pre/mature adipocytes, and, if so, to determine the mechanism involved. Trichostatin A (TSA), an HDAC inhibitor, enhanced lipopolysaccharide (LPS)-induced production of IL-6 in OP9 preadipocytes but not the mature adipocytes. Moreover, TSA also enhanced palmitic acid-induced IL-6 production and the expression of inflammatory genes induced by LPS in preadipocytes. Although TSA did not affect TLR4 mRNA expression or the activation of MAPKs, a reporter gene assay revealed that the LPS-induced increase in nuclear factor κB (NF-κB) activity was enhanced by TSA. Moreover, TSA increased the level of NF-κB p65 acetylation at lysine 310 and duration of its translocation into the nucleus, which leads to enhancement of NF-κB activity and subsequently expression of inflammatory genes. These findings shed new light on the regulatory roles of HDACs in preadipocytes in the production of inflammatory proteins.     

Differential DNA Methylation Status Between Human Preadipocytes and Mature Adipocytes

Obesity is a multifactorial disease resulting from interactions between susceptibility genes, psychosocial, and environmental factors. However, it is becoming evident that interindividual differences in obesity susceptibility depend also on epigenetic factors, although the mechanisms have not been fully elucidated. We have undertaken a genome-wide analysis of DNA methylation of human preadipocytes and mature adipocytes to examine the differences in methylation between them. We found hypomethylation occurring in 2,701 genes and hypermethylation in 1,070 genes after differentiation. Meanwhile, Gene Ontology analysis and Ingenuity Pathway Analysis showed many significant gene functions and pathways with altered methylation status after adipocyte differentiation. In addition, Signal-Net analysis showed that tumor necrosis factor-α, mitogen-activated protein kinase, and interleukin-8 were important to the formation of this network. Our results suggest that DNA methylation mechanisms may be involved in regulating the differentiation process of human preadipocytes.     

Reciprocal regulation of tissue-type and urokinase-type plasminogen activators in the differentiation of murine preadipocyte line 3T3-L1 and the hormonal regulation of fibrinolytic factors in the mature adipocytes

Adipose tissue expresses a variety of genes including tumor necrosis factor alpha and type-1 plasminogen activator inhibitor (PAI-1); and these factors, produced by adipocytes, may be associated with the risk of coronary events in obesity. In this study, we characterized the production of fibrinolytic factors including tissue-type plasminogen activator (tPA), urokinase-type PA (uPA), and PAI-1 in the differentiation of preadipocytes, and examined the hormonal regulation of these fibrinolytic factors in mature adipocytes. Mouse 3T3-L1 preadipocytes were employed as a model of adipocytes. Adipocyte differentiation was induced by insulin, dexamethasone, and 3-isobutyl-1-methyl xanthine (IBMX). alpha-Glycerophosphate dehydrogenase (GPDH) activity and glucose transporter 4 (GLUT4) mRNA, indices for adipocyte maturation, were induced on Day 4, and gradually increased. GPDH activity reached its maximum level on Day 14. The level of tPA, a major PA in preadipocytes, dramatically decreased with differentiation. On the other hand, that of uPA reciprocally increased. PAI-1 production was also dramatically induced concomitant with differentiation. In mature adipocytes, uPA production was dominant (25 microg/ml/24 h vs. 0.8 microg/ml/24 h for tPA). Total PA activity in the mature adipocytes was reduced by insulin or dexamethasone, but not by glucagon. Insulin, IBMX, and dexamethasone significantly decreased both uPA and tPA production, and increased PAI-1 production. Glucagon had no effect on the production of these fibrinolytic factors. Our results reveal that uPA is one of the markers for the differentiation of 3T3-L1 cells and that insulin, IBMX, and dexamethasone are potent regulators of the fibrinolytic activity in differentiated 3T3-L1 cells, reciprocally affecting PA and PAI-1 levels in them.     

Suppression of GATA-3 increases adipogenesis,reduces inflammation and improves insulin sensitivity in 3T3L-1 preadipocytes

Impaired adipogenesis plays an important role in the development of obesity-associated insulin resistance and type 2 diabetes. Adipose tissue inflammation is a crucial mediator of this process. GATA-3 plays important roles in adipogenesis and inflammation. The aim of this study is to investigate the impact of GATA-3 suppression on improving adipogenesis, lowering inflammation and reversing insulin resistance. GATA-3 levels were measured in subcutaneous (SC) and omental (OM) adipose tissues obtained from insulin sensitive (IS) and insulin resistant (IR) obese individuals during weight reduction surgeries. The effect of GATA-3 suppression on adipogenesis, expression of inflammatory cytokines and insulin resistance biomarkers was performed in 3T3L-1 mouse preadipocytes via transfection with GATA-3-specific DNAzyme. GATA-3 expression was higher in OM compared to SC adipose tissues and in stromal vascular fraction-derived differentiating preadipocytes from IR obese individuals compared to their IS counterparts. Suppression of GATA-3 expression in 3T3L-1 mouse preadipocytes with GATA-3 specific inhibitor reversed 4-hydroxynonenal-induced impaired adipogenesis and triggered changes in the expression of insulin signaling-related genes. GATA-3 inhibition also modulated the expression of IL-6 and IL-10 and lowered the expression of insulin resistance biomarkers (PAI-1 and resistin) and insulin resistance phosphoproteins (p-BAD, p-PTEN and p-GSK3β). Inhibiting GATA-3 improves adipocytes differentiation, modulates the secretion of inflammatory cytokines and improves insulin sensitivity in insulin resistant cells. Suppression of GATA-3 could be a promising tool to improve adipogenesis, restore insulin sensitivity and lower obesity-associated inflammation in insulin resistant individuals.     

MicroRNAome Comparison between Intramuscular and Subcutaneous Vascular Stem Cell Adipogenesis

Background

As an important factor affecting meat quality, intramuscular fat (IMF) content is a topic of worldwide concern. Emerging evidences indicate that microRNAs play important roles in adipocyte differentiation. However, miRNAome has neither been studied during porcine intramuscular preadipocyte differentiation, nor compared with subcutaneous preadipocytes. The objectives of this study were to identify porcine miRNAs involved in adipogenesis in primary preadipocytes, and to determine whether intramuscular and subcutaneous adipocytes differ in the expression and regulation of miRNAs.

Results

miRNAomes in primary intramuscular and subcutaneous adipocytes during differentiation were first sequenced using the Solexa deep sequencing method. The sequences and relative expression levels of 224 known (98.2% in miRbase 18.0) and 280 potential porcine miRNAs were identified. Fifty-four of them changed in similar pattern between intramuscular vascular stem cells (IVSC) and subcutaneous vascular stem cells (SVSC) differentiation, such as miR-210, miR-10b and miR-99a. Expression levels of 10 miRNAs were reversely up-or down-regulated between IVSC and SVSC differentiation, 19 were up-or down-regulated only during IVSC differentiation and 55 only during SVSC differentiation. Additionally, 30 miRNAs showed fat-depot specific expression pattern (24 in cells of intramuscular origin and 6 in cells of subcutaneous origin). These adipogenesis-related miRNAs mainly functioned by targeting similar pathways in adipogenesis, obesity and syndrome.

Conclusion

Comparison of miRNAomes in IVSC and SVSC during differentiation revealed that many different miRNAs are involved in adipogenesis, and they regulate SVSC and IVSC differentiation through similar pathways. These miRNAs may serve as biomarkers or targets for enhancing IMF content, and uncovering their function in IMF development will be of great value in the near future.     

The influence of preadipocyte differentiation capacity on lipolysis in human mature adipocytes.

The ability of catecholamines to maximally stimulate adipocyte lipolysis (lipolytic capacity) is decreased in obesity. It is not known whether the lipolytic capacity is determined by the ability of adipocytes to differentiate. The aim of the study was to investigate if lipolytic capacity is related to preadipocyte differentiation and if the latter can predict lipolysis in mature adipocytes. IN VITRO experiments were performed on differentiating preadipocytes and isolated mature adipocytes from human subcutaneous adipose tissue. In preadipocytes, noradrenaline-induced lipolysis increased significantly until terminal differentiation (day 12). However, changes in the expression of genes involved in lipolysis (hormone sensitive lipase, adipocyte triglyceride lipase, the alpha2-and beta1-adrenoceptors, perilipin, and fatty acid binding protein) reached a plateau much earlier during differentiation (day 8). A significant positive correlation between lipolysis in differentiated preadipocytes and mature adipocytes was observed for noradrenaline (r=0.5, p<0.01). The late differentiation capacity of preadipocytes measured as glycerol-3-phosphate dehydrogenase activity was positively correlated with noradrenaline-induced lipolysis in preadipocytes (r=0.51, p<0.005) and mature fat cells (r=0.35, p<0.05). In conclusion, intrinsic properties related to terminal differentiation determine the ability of catecholamines to maximally stimulate lipolysis in fat cells. The inability to undergo full differentiation might in part explain the low lipolytic capacity of fat cells among the obese.     

A Role for Bone Morphogenetic Protein-4 in Adipocyte Development

Obesity is characterized by increases in the number of mature adipocytes. Nascent adipocytes arise from mesenchymal stem cells (MSCs) by a multi-step process — MSCs are recruited to the adipocyte lineage forming determined preadipocytes, these committed progenitors proliferate, undergo growth arrest, and finally differentiate into mature adipocytes. Although the genetic mechanisms that control the differentiation of preadipocytes into mature adipocytes are understood to a large extent, the earliest events in adipogenesis — especially the commitment of MSCs into preadipocytes — are largely unknown. Recently, bone morphogenetic protein-4 (BMP-4) has been implicated in the commitment of pluripotent MSCs to the adipocyte lineage by two independent lines of investigation. First, growth-arrested 10T1/2 cells do not normally respond to a hormonal cocktail that causes various growth-arrested preadipocyte cell lines to differentiate into adipocytes, but if 10T1/2 cells are first treated with BMP-4 they will respond to these hormonal inducers by undergoing terminal adipocyte differentiation. Second, a preadipocyte cell line, A33 cells, derived from 10T1/2 cells after exposing the cells to the DNA methyltransferase inhibitor 5-azacytidine was shown to express BMP-4, and this endogenous BMP-4 expression is required for acquisition of the preadipocyte phenotype of these cells. A role for the BMP-4 signaling pathway in adipogenesis is discussed.     

Advanced oxidation protein products inhibit differentiation and activate inflammation in 3T3‐L1 preadipocytes

Accumulation of advanced oxidation protein products (AOPPs) is prevalent in metabolic syndromes, a condition with impaired preadipocytes differentiation. In the present study, we tested the hypothesis that AOPPs disturb preadipocyte differentiation. Exposure of 3T3‐L1 preadipocytes to increased levels of AOPPs inhibited accumulation of intracellular triglyceride and decreased the expression of the essential markers of matured adipocytes, such as adipocyte fatty‐acid‐binding protein (aP2), CAAT/enhancer‐binding protein (C/EBP)‐α, and peroxisome proliferator‐activated receptor (PPAR)‐γ, in response to standard adipogenic induction. Inhibitory effects of AOPPs on preadipocytes differentiation was time sensitive, which occurred at the early stage of differentiation. In the presence of AOPPs, induction of preadipocytes differentiation resulted in upregulated expression of C/EBP homologous protein (CHOP) and CUG‐Triplet repeat‐binding protein (CUGBP), two important inhibitors of preadipocytes differentiation. In addition, treatment with AOPPs increased abundance of C/EBP‐β‐liver enriched inhibitory protein (C/EBP‐β‐LIP), a truncated C/EBP‐β isoform without adipogenic activity. Moreover, AOPPs‐treated preadipocytes expressed a macrophage marker F4/80 and overexpressed tumor necrosis factor‐α and interleukin‐6 via nuclear factor‐κB (NF‐κB)‐dependent pathway. However, blocking inflammation with NF‐κB inhibitor failed to improve AOPPs‐induced inhibition of preadipocytes differentiation. These data suggest that accumulation of AOPPs may inhibit differentiation of preadipocytes and activate inflammation in these cells. This information might have implication for understanding the impairment of preadipocytes differentiation and fat inflammation seen in metabolic syndrome. J. Cell. Physiol. 225: 42–51, 2010. © 2010 Wiley‐Liss, Inc.