Microarray analysis of differentiation-specific gene expression during 3T3-L1 adipogenesis

A keratinocyte-adipocyte signaling loop is reprogrammed by loss of BTG3 to augment skin carcinogenesis

Obesity is endemic to many developed countries. Overweight or obesity is associated with an increased risk of developing cancer. Dysfunctional adipose tissue alters cancer cell proliferation and migration; however, whether and how neoplastic epithelial cells communicate with adipose tissue and the underlying mechanism are less clear. BTG3 is a member of the anti-proliferative BTG/Tob family and functions as a tumor suppressor. Here, we demonstrated that BTG3 levels are downregulated in basal cell carcinoma and squamous cell carcinoma compared to normal skin tissue, and Btg3 knockout in mice augmented the development of papilloma in a mouse model of DMBA/TPA-induced skin carcinogenesis. Mechanistically, BTG3-knockout keratinocytes promoted adipocyte differentiation mainly through the release of IL1α, IL10, and CCL4, as a result of elevated NF-κB activity. These adipocytes produced CCL20 and FGF7 in a feedback loop to promote keratinocyte migration. Thus, our findings showcased the role of BTG3 in guarding the interplay between keratinocytes and adjacent adipocytes, and identified the underlying neoplastic molecular mediators that may serve as possible targets in the treatment of skin cancer.

Temporal correlation of morphological and biochemical changes with the recruitment of different mechanisms of reactive oxygen species formation during human SW872 cell adipogenic differentiation

Human SW872 preadipocyte conversion to mature adipocytes is associated with time-dependent changes in differentiation markers' expression and with morphological changes accompanied by the accumulation of lipid droplets (LDs) as well as by increased mitochondriogenesis and mitochondrial membrane potential. Under identical conditions, the formation of reactive oxygen species (ROS) revealed with a general probe was significant at days 3 and 10 of differentiation and bearly detectable at day 6. NADPH oxidase (NOX)-2 activity determined with an immunocytochemical approach followed a very similar pattern. There was no evidence of mitochondrial ROS (mROS), as detected with a selective fluorescence probe, at days 3 and 6, possibly due to the triggering of the Nrf-2 antioxidant response. mROS were instead clearly detected at day 10, concomitantly with the accumulation of very large LDs, oxidation of both cardiolipin and thioredoxin 2, and decreased mitochondrial glutathione. In conclusion, the morphological and biochemical changes of differentiating SW872 cells are accompanied by the discontinuous formation of ROS derived from NOX-2, increasingly implicated in adipogenesis and adipose tissue dysfunction. In addition, mROS formation was significant only in the late phase of differentiation and was associated with mitochondrial dysfunction.

Striatal transcriptome changes linked to drug-induced repetitive behaviors

Disruptive or excessive repetitive motor patterns (stereotypies) are cardinal symptoms in numerous neuropsychiatric disorders. Stereotypies are also evoked by psychomotor stimulants such as amphetamine. The acquisition of motor sequences is paralleled by changes in activity patterns in the striatum, and stereotypies have been linked to abnormal plasticity in these reinforcement-related circuits. Here, we designed experiments in mice to identify transcriptomic changes that underlie striatal plasticity occurring alongside the development of drug-induced stereotypic behavior. We identified three schedules of amphetamine treatment inducing different degrees of stereotypy and used bulk RNAseq to compare striatal gene expression changes among groups of mice treated with the different drug-dose schedules and vehicle-treated, cage-mate controls. Mice were identified as naïve, sensitized, or tolerant to drug-induced stereotypy. All drug-treated groups exhibited expression changes in genes that encode members of the extracellular signal-regulated kinase (ERK) cascades known to regulate psychomotor stimulant responses. In the sensitized group with the most prolonged stereotypy, we found dysregulation of 20 genes that were not changed in other groups. Gene set enrichment analysis indicated highly significant overlap with genes regulated by neuregulin 1 (Nrg1). Nrg1 is known to be a schizophrenia and autism susceptibility gene that encodes a ligand for Erb-B receptors, which are involved in neuronal migration, myelination, and cell survival, including that of dopamine-containing neurons. Stimulant abuse is a risk factor for schizophrenia onset, and these two disorders share behavioral stereotypy phenotypes. Our results raise the possibility that drug-induced sensitization of the Nrg1 signaling pathway might underlie these links.

T-Cell Death Associated Gene 51 Is a Novel Negative Regulator of PPARγ That Inhibits PPARγ-RXRα Heterodimer Formation in Adipogenesis

The nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) is the master transcriptional regulator in adipogenesis. PPARγ forms a heterodimer with another nuclear receptor, retinoid X receptor (RXR), to form an active transcriptional complex, and their transcriptional activity is tightly regulated by the association with either coactivators or corepressors. In this study, we identified T-cell death-associated gene 51 (TDAG51) as a novel corepressor of PPARγ-mediated transcriptional regulation. We showed that TDAG51 expression is abundantly maintained in the early stage of adipogenic differentiation. Forced expression of TDAG51 inhibited adipocyte differentiation in 3T3-L1 cells. We found that TDAG51 physically interacts with PPARγ in a ligand-independent manner. In deletion mutant analyses, large portions of the TDAG51 domains, including the pleckstrin homology-like, glutamine repeat and proline-glutamine repeat domains but not the proline-histidine repeat domain, are involved in the interaction with the region between residues 140 and 506, including the DNA binding domain, hinge, ligand binding domain and activation function-2 domain, in PPARγ. The heterodimer formation of PPARγ-RXRα was competitively inhibited in a ligand-independent manner by TDAG51 binding to PPARγ. Thus, our data suggest that TDAG51, which could determine adipogenic cell fate, acts as a novel negative regulator of PPARγ by blocking RXRα recruitment to the PPARγ-RXRα heterodimer complex in adipogenesis.

Whole transcriptome analysis and validation of metabolic pathways in subcutaneous adipose tissues during FGF21-induced weight loss in non-human primates

Fibroblast growth factor 21 (FGF21) induces weight loss in mouse, monkey, and human studies. In mice, FGF21 is thought to cause weight loss by stimulating thermogenesis, but whether FGF21 increases energy expenditure (EE) in primates is unclear. Here, we explore the transcriptional response and gene networks active in adipose tissue of rhesus macaques following FGF21-induced weight loss. Genes related to thermogenesis responded inconsistently to FGF21 treatment and weight loss. However, expression of gene modules involved in triglyceride (TG) synthesis and adipogenesis decreased, and this was associated with greater weight loss. Conversely, expression of innate immune cell markers was increased post-treatment and was associated with greater weight loss. A lipogenesis gene module associated with weight loss was evaluated by testing the function of member genes in mice. Overexpression of NRG4 reduced weight gain in diet-induced obese mice, while overexpression of ANGPTL8 resulted in elevated TG levels in lean mice. These observations provide evidence for a shifting balance of lipid storage and metabolism due to FGF21-induced weight loss in the non-human primate model, and do not fully recapitulate increased EE seen in rodent and in vitro studies. These discrepancies may reflect inter-species differences or complex interplay of FGF21 activity and counter-regulatory mechanisms.

Gene expression profiling of chondrogenic differentiation by dexamethasone-conjugated polyethyleneimine with SOX trio genes in stem cells

Background

During differentiation of stem cells, it is recognized that molecular mechanisms of transcription factors manage stem cells towards the intended lineage. In this study, using microarray-based technology, gene expression profiling was examined during the process of chondrogenic differentiation of human mesenchymal stem cells (hMSCs). To induce chondrogenic differentiation of hMSCs, the cationic polymer polyethyleneimine (PEI) was coupled with the synthetic glucocorticoid dexamethasone (DEX). DEX/PEI could be polyplexed with anionic plasmid DNAs (pDNAs) harboring the chondrogenesis-inducing factors SOX5, SOX6, and SOX9. These are named differentiation-inducing nanoparticles (DI-NPs).

Methods

A DI-NP system for inducing chondrogenic differentiation was designed and characterized by dynamic light scattering and scanning electron microscopy (SEM). Chondrogenic induction of hMSCs was evaluated using various tools such as reverse-transcription polymerase chain reaction (RT-PCR), Western blotting, confocal fluorescent microscopy, and immunohistochemistry analysis. The gene expression profiling of DI-NP-treated hMSCs was performed by microarray analysis.

Results

The hMSCs were more efficiently transfected with pDNAs using DI-NPs than using PEI. Moreover, microarray analysis demonstrated the gene expression profiling of hMSCs transfected with DI-NPs. Chondrogenic factors including SOX9, collagen type II (COLII), Aggrecan, and cartilage oligometric matrix protein (COMP) were upregulated while osteogenic factors including collagen type I (COLI) was downregulated. Chondrogenesis-induced hMSCs were better differentiated as assessed by RT-PCR, Western blotting analyses, and immunohistochemistry.

Conclusion

DI-NPs are good gene delivery carriers and induce chondrogenic differentiation of hMSCs. Additionally, comprehensive examination of the gene expression was attempted to identify specific genes related to differentiation by microarray analysis.

Graphical abstract

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0998-7) contains supplementary material, which is available to authorized users.

Targeting nuclear receptor NR4A1-dependent adipocyte progenitor quiescence promotes metabolic adaptation to obesity

Adipocyte turnover in adulthood is low, suggesting that the cellular source of new adipocytes, the adipocyte progenitor (AP), resides in a state of relative quiescence. Yet the core transcriptional regulatory circuitry (CRC) responsible for establishing a quiescent state and the physiological significance of AP quiescence are incompletely understood. Here, we integrate transcriptomic data with maps of accessible chromatin in primary APs, implicating the orphan nuclear receptor NR4A1 in AP cell-state regulation. NR4A1 gain and loss of function in APs ex vivo decreased and enhanced adipogenesis, respectively. Adipose tissue of Nr4a1-/- mice demonstrated higher proliferative and adipogenic capacity compared with that of WT mice. Transplantation of Nr4a1-/- APs into the subcutaneous adipose tissue of WT obese recipients improved metrics of glucose homeostasis relative to administration of WT APs. Collectively, these data identify NR4A1 as a previously unrecognized constitutive regulator of AP quiescence and suggest that augmentation of adipose tissue plasticity may attenuate negative metabolic sequelae of obesity.

Combined deficiency of the Cnr1 and Cnr2 receptors protects against age-related bone loss by osteoclast inhibition

The endocannabinoid system plays a role in regulating bone mass and bone cell activity and inactivation of the type 1 (Cnr1) or type 2 (Cnr2) cannabinoid receptors influences peak bone mass and age‐related bone loss. As the Cnr1 and Cnr2 receptors have limited homology and are activated by different ligands, we have evaluated the effects of combined deficiency of Cnr1 and 2 receptors (Cnr1/2^−/−) on bone development from birth to old age and studied ovariectomy induced bone loss in female mice. The Cnr1/2^−/− mice had accelerated bone accrual at birth when compared with wild type littermates, and by 3 months of age, they had higher trabecular bone mass. They were also significantly protected against ovariectomy‐induced bone loss due to a reduction in osteoclast number. The Cnr1/2^−/− mice had reduced age‐related bone loss when compared with wild‐type due to a reduction in osteoclast number. Although bone formation was reduced and bone marrow adiposity increased in Cnr1/2^−/− mice, the osteoclast defect outweighed the reduction in bone formation causing preservation of bone mass with aging. This contrasts with the situation previously reported in mice with inactivation of the Cnr1 or Cnr2 receptors individually where aged‐related bone loss was greater than in wild‐type. We conclude that the Cnr1 and Cnr2 receptors have overlapping but nonredundant roles in regulating osteoclast and osteoblast activities. These observations indicate that combined inhibition of Cnr1 and Cnr2 receptors may be beneficial in preventing age‐related bone loss, whereas blockade of individual receptors may be detrimental.

Hierarchical role for transcription factors and chromatin structure in genome organization along adipogenesis

The three dimensional folding of mammalian genomes is cell type specific and difficult to alter suggesting that it is an important component of gene regulation. However, given the multitude of chromatin-associating factors, the mechanisms driving the colocalization of active chromosomal domains and the role of this organization in regulating the transcription program in adipocytes are not clear. Analysis of genome-wide chromosomal associations revealed cell type-specific spatial clustering of adipogenic genes in 3T3-L1 cells. Time course analysis demonstrated that the adipogenic 'hub', sampled by PPARγ and Lpin1, undergoes orchestrated reorganization during adipogenesis. Coupling the dynamics of genome architecture with multiple chromatin datasets indicated that among all the transcription factors (TFs) tested, RXR is central to genome reorganization at the beginning of adipogenesis. Interestingly, at the end of differentiation, the adipogenic hub was shifted to an H3K27me3-repressive environment in conjunction with attenuation of gene transcription. We propose a stage-specific hierarchy for the activity of TFs contributing to the establishment of an adipogenic genome architecture that brings together the adipogenic genetic program. In addition, the repositioning of this network in a H3K27me3-rich environment at the end of differentiation may contribute to the stabilization of gene transcription levels and reduce the developmental plasticity of these specialized cells.

DATABASE

All sequence data reported in this paper have been deposited at GEO (http://www.ncbi.nlm.nih.gov/geo/) (GSE92475).

Echinomycin inhibits adipogenesis in 3T3-L1 cells in a HIF-independent manner

Obesity is a risk factor for many diseases including diabetes, cancer, cardiovascular disease, and chronic kidney disease. Obesity is characterized by the expansion of white adipose tissue (WAT). Hypertrophy and hyperplasia of adipocytes cause tissue hypoxia followed by inflammation and fibrosis. Its trigger, preadipocyte differentiation into mature adipocytes, is finely regulated by transcription factors, signal molecules, and cofactors. We found that echinomycin, a potent HIF-1 inhibitor, completely inhibited adipogenesis in 3T3-L1 WAT preadipocytes by affecting the early phase of mitotic clonal expansion. The dose required to exert the effect was surprisingly low and the time was short. Interestingly, its inhibitory effect was independent of HIF-1 pathways. Time-course DNA microarray analysis of drug-treated and untreated preadipocytes extracted a major transcription factor, CCAAT/enhancer-protein β, as a key target of echinomycin. Echinomycin also inhibited adipogenesis and body weight gain in high fat diet mice. These findings highlight a novel role of echinomycin in suppressing adipocyte differentiation and offer a new therapeutic strategy against obesity and diabetes.

The Alkamide trans-Pellitorine Targets PPARγ via TRPV1 and TRPA1 to Reduce Lipid Accumulation in Developing 3T3-L1 Adipocytes

Adipose tissue is an important endocrine organ in the human body. However, pathological overgrowth is associated with chronic illness. Regulation of adipogenesis and maturation of adipocytes via bioactive compounds in our daily diet has been in focus of research in the past years and showed promising results for agonists of the ion channels transient receptor potential channel (TRP) V1 and A1. Here, we investigated the anti-adipogenic potential and underlying mechanisms of the alkamide trans-pellitorine present in Piper nigrum via TRPV1 and TRPA1 in 3T3-L1 cells. trans-pellitorine was found to suppress mean lipid accumulation, when applied during differentiation and maturation, but also during maturation phase solely of 3T3-L1 cells in a concentration range between 1 nM and 1 μM by up to 8.84 ± 4.97 or 7.49 ± 5.08%, respectively. Blockage of TRPV1 using the specific inhibitor trans-tert-butyl-cyclohexanol demonstrated that the anti-adipogenic activity of trans-pellitorine depends on TRPV1. In addition, blockage of the TRPA1 channel using the antagonist AP-18 showed a TRPA1-dependent signaling in the early to intermediate stages of adipogenesis. On a mechanistic level, treatment with trans-pellitorine during adipogenesis led to reduced PPARγ expression on gene and protein level via activation of TRPV1 and TRPA1, and increased expression of the microRNA mmu-let-7b, which has been associated with reduced PPARγ levels. In addition, cells treated with trans-pellitorine showed decreased expression of the gene encoding for fatty acid synthase, increased expression of microRNA-103 and a decreased short-term fatty acid uptake on the functional level. In summary, these data point to an involvement of the TRPV1 and TRPA1 cation channels in the anti-adipogenic activity of trans-pellitorine via microRNA-let7b and PPARγ. Since trans-pellitorine does not directly activate TRPV1 or TRPA1, an indirect modulation of the channel activity is assumed and warrants further investigation.

Gene expression profile during proliferation and differentiation of rainbow trout adipocyte precursor cells

BACKGROUND

Excessive accumulation of adipose tissue in cultured fish is an outstanding problem in aquaculture. To understand the development of adiposity, it is crucial to identify the genes which expression is associated with adipogenic differentiation. Therefore, the transcriptomic profile at different time points (days 3, 8, 15 and 21) along primary culture development of rainbow trout preadipocytes has been investigated using an Agilent trout oligo microarray.

RESULTS

Our analysis identified 4026 genes differentially expressed (fold-change >3) that were divided into two major clusters corresponding to the main phases observed during the preadipocyte culture: proliferation and differentiation. Proliferation cluster comprised 1028 genes up-regulated from days 3 to 8 of culture meanwhile the differentiation cluster was characterized by 2140 induced genes from days 15 to 21. Proliferation was characterized by enrichment in genes involved in basic cellular and metabolic processes (transcription, ribosome biogenesis, translation and protein folding), cellular remodelling and autophagy. In addition, the implication of the eicosanoid signalling pathway was highlighted during this phase. On the other hand, the terminal differentiation phase was enriched with genes involved in energy production, lipid and carbohydrate metabolism. Moreover, during this phase an enrichment in genes involved in the formation of the lipid droplets was evidenced as well as the activation of the thyroid-receptor/retinoic X receptor (TR/RXR) and the peroxisome proliferator activated receptors (PPARs) signalling pathways. The whole adipogenic process was driven by a coordinated activation of transcription factors and epigenetic modulators.

CONCLUSIONS

Overall, our study demonstrates the coordinated expression of functionally related genes during proliferation and differentiation of rainbow trout adipocyte cells. Furthermore, the information generated will allow future investigations of specific genes involved in particular stages of fish adipogenesis.

WNK4 is an Adipogenic Factor and Its Deletion Reduces Diet-Induced Obesity in Mice

The with-no-lysine kinase (WNK) 4 gene is a causative gene in pseudohypoaldosteronism type II. Although WNKs are widely expressed in the body, neither their metabolic functions nor their extrarenal role is clear. In this study, we found that WNK4 was expressed in mouse adipose tissue and 3T3-L1 adipocytes. In mouse primary preadipocytes and in 3T3-L1 adipocytes, WNK4 was markedly induced in the early phase of adipocyte differentiation. WNK4 expression preceded the expression of key transcriptional factors PPARγ and C/EBPα. WNK4-siRNA-transfected 3T3-L1 cells and human mesenchymal stem cells showed reduced expression of PPARγ and C/EBPα and lipid accumulation. WNK4 protein affected the DNA-binding ability of C/EBPβ and thereby reduced PPARγ expression. In the WNK4^−/− mice, PPARγ and C/EBPα expression were decreased in adipose tissues, and the mice exhibited partial resistance to high-fat diet-induced adiposity. These data suggest that WNK4 may be a proadipogenic factor, and offer insights into the relationship between WNKs and energy metabolism.

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WNK4 regulates adipocyte differentiation in mouse and human preadipocytes.

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WNK4^−/− mice exhibit reduced adiposity and increased insulin sensitivity.

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WNK4 may be a drug target for diet-induced obesity and salt-sensitive hypertension.

The with-no-lysine kinase (WNK) 4 gene is a causative gene in pseudohypoaldosteronism type II, a hereditary hypertensive disease. Although WNKs are widely expressed in the body and are involved in the pathogenesis of hypertension, neither their metabolic functions nor their extrarenal role is clear. This study demonstrated a contribution of WNK4 to the regulation of core transcriptional factors for adipogenesis and that its depletion indicates some beneficial effects for obesity by a high-fat diet. This study suggests a role of hypertension-causing WNK4 as a proadipogenic factor and offers insights into the relationship between WNKs and energy metabolism.

The Multifaceted Haptoglobin in the Context of Adipose Tissue and Metabolism

Obesity is a low chronic inflammatory state because several inflammatory factors are increased in obese subjects, this having important implications for the onset of obesity-associated complications. The source of most of these inflammatory molecules is white adipose tissue (WAT), which upon excessive weight gain, becomes infiltrated with macrophages and lymphocytes and undergoes important changes in its gene expression. Haptoglobin (Hp), a typical marker of inflammation in clinical practice, main carrier of free hemoglobin, and long known to be part of the hepatic acute phase response, perfectly sits in the intersection between obesity and inflammation: it is expressed by adipocytes and its abundance in WAT and in plasma positively relates to the degree of adiposity. In the present review, we will analyze causes and consequences of Hp expression and regulation in WAT and how these relate to the obesity/inflammation paradigm and comorbidities.

Metallomics approach to changes in element concentration during differentiation from fibroblasts into adipocytes by element array analysis

We aimed to establish an element array analysis that involves the simultaneous detection of all elements in cells and the display of changes in element concentration before and after a cellular event. In this study, we demonstrated changes in element concentration during the differentiation of 3T3-L1 mouse fibroblasts into adipocytes. This metallomics approach yielded unique information of cellular response to physiological and toxicological events.

Steroid biosynthesis in adipose tissue

Tissue-specific expression of steroidogenic enzymes allows the modulation of active steroid levels in a local manner. Thus, the measurement of local steroid concentrations, rather than the circulating levels, has been recognized as a more accurate indicator of the steroid action within a specific tissue. Adipose tissue, one of the largest endocrine tissues in the human body, has been established as an important site for steroid storage and metabolism. Locally produced steroids, through the enzymatic conversion from steroid precursors delivered to adipose tissue, have been proven to either functionally regulate adipose tissue metabolism, or quantitatively contribute to the whole body's steroid levels. Most recently, it has been suggested that adipose tissue may contain the steroidogenic machinery necessary for the initiation of steroid biosynthesis de novo from cholesterol. This review summarizes the evidence indicating the presence of the entire steroidogenic apparatus in adipose tissue and discusses the potential roles of local steroid products in modulating adipose tissue activity and other metabolic parameters.

Glucose starvation and hypoxia, but not the saturated fatty acid palmitic acid or cholesterol, activate the unfolded protein response in 3T3-F442A and 3T3-L1 adipocytes

Obesity is associated with endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) in adipose tissue. In this study we identify physiological triggers of ER stress and of the UPR in adipocytes in vitro. We show that two markers of adipose tissue remodelling in obesity, glucose starvation and hypoxia, cause ER stress in 3T3-F442A and 3T3-L1 adipocytes. Both conditions induced molecular markers of the IRE1α and PERK branches of the UPR, such as splicing of XBP1 mRNA and CHOP, as well as transcription of the ER stress responsive gene BiP. Hypoxia also induced an increase in phosphorylation of the PERK substrate eIF2α. By contrast, physiological triggers of ER stress in many other cell types, such as the saturated fatty acid palmitic acid, cholesterol, or several inflammatory cytokines including TNF-α, IL-1β, and IL-6, do not cause ER stress in 3T3-F442A and 3T3-L1 adipocytes. Our data suggest that physiological changes associated with remodelling of adipose tissue in obesity, such as hypoxia and glucose starvation, are more likely physiological ER stressors of adipocytes than the lipid overload or hyperinsulinemia associated with obesity.

Dynamic and distinct histone modifications of osteogenic genes during osteogenic differentiation

Many skeletal diseases have common pathological phenotype of defective osteogenesis of bone marrow stromal cells (BMSCs), in which histone modifications play an important role. However, few studies have examined the dynamics of distinct histone modifications during osteogenesis. In this study, we examined the dynamics of H3K9/K14 and H4K12 acetylation; H3K4 mono-, di- and tri-methylation; H3K9 di-methylation and H3K27 tri-methylation in osteogenic genes, runt-related transcription factor 2 (Runx2), osterix (Osx), alkaline phosphatase, bone sialoprotein and osteocalcin, during C3H10T1/2 osteogenesis. H3 and H4 acetylation and H3K4 di-methylation were elevated, and H3K9 di-methylation and H3K27 tri-methylation were reduced in osteogenic genes during C3H10T1/2 osteogenesis. C3H10T1/2 osteogenesis could be modulated by altering the patterns of H3 and H4 acetylation and H3K27 tri-methylation. In a glucocorticoid-induced osteoporosis mouse model, we observed the attenuation of osteogenic potential of osteoporotic BMSCs in parallel with H3 and H4 hypo-acetylation and H3K27 hyper-tri-methylation in Runx2 and Osx genes. When H3 and H4 acetylation was elevated, and H3K27 tri-methylation was reduced, the attenuated osteogenic potential of osteoporotic BMSCs was rescued effectively. These observations provide a deeper insight into the mechanisms of osteogenic differentiation and the pathophysiology of osteoporosis and can be used to design new drugs and develop new therapeutic methods to treat skeletal diseases.

Growth without growth hormone: can growth and differentiation factor 5 be the mediator?

Growth without growth hormone (GH) is often observed in the setup of obesity; however, the missing link between adipocytes and linear growth was until now not identified. 3T3L1 cells were induced to differentiate into adipocytes and their conditioned medium (CM) (adipocytes CM, CMA) was added to metatarsals bone culture and compared to CM derived from undifferentiated cells. CMA significantly increased metatarsals bone elongation. Adipogenic differentiation increased the expression of growth and differentiation factor (GDF)-5, also found to be secreted into the CMA. GDF-5 significantly increased metatarsal length in culture; treatment of the CMA with anti-GDF-5 antibody significantly reduced the stimulatory effect on bone length. The presence of GDF-5 receptor (bone morphogenetic protein receptor; BMPR1) in metatarsal bone was confirmed by immunohistochemistry. Animal studies in rodents subjected to food restriction followed by re-feeding showed an increase in GDF-5 serum levels concomitant with nutritional induced catch up growth. These results show that adipocytes may stimulate bone growth and suggest an additional explanation to the growth without GH phenomenon.

ISL1 regulates peroxisome proliferator-activated receptor γ activation and early adipogenesis via bone morphogenetic protein 4-dependent and -independent mechanisms

While adipogenesis is controlled by a cascade of transcription factors, the global gene expression profiles in the early phase of adipogenesis are not well defined. Using microarray analysis of gene expression in 3T3-L1 cells, we have identified evidence for the activity of 2,568 genes during the early phase of adipocyte differentiation. One of these, the ISL1 gene, was of interest since its expression was markedly upregulated 1 h after initiation of differentiation, with a subsequent rapid decline. Overexpression of ISL1 at early times during adipocyte differentiation but not at later times was found to profoundly inhibit differentiation. This was accompanied by moderate downregulation of peroxisome proliferator-activated receptor γ (PPARγ) levels, substantial downregulation of PPARγ downstream genes, and downregulation of bone morphogenetic protein 4 (BMP4) levels in preadipocytes. Readdition of BMP4 overcame the inhibitory effect of ISL1 on the expression of PPARγ but not aP2, a gene downstream of PPARγ, and BMP4 also partially rescued ISL1 inhibition of adipogenesis, an effect which is additive with rosiglitazone. These results suggest that ISL1 is intimately involved in early regulation of adipogenesis, modulating PPARγ expression and activity via BMP4-dependent and -independent mechanisms. Our time course gene expression survey sets the stage for further studies to explore other early and immediate regulators.

Antiangiogenic activity of trabectedin in myxoid liposarcoma: involvement of host TIMP-1 and TIMP-2 and tumor thrombospondin-1

Trabectedin is a marine natural product, approved in Europe for the treatment of soft tissue sarcoma and relapsed ovarian cancer. Clinical and experimental evidence indicates that trabectedin is particularly effective against myxoid liposarcomas where response is associated to regression of capillary networks. Here, we investigated the mechanism of the antiangiogenic activity of trabectedin in myxoid liposarcomas. Trabectedin directly targeted endothelial cells, impairing functions relying on extracellular matrix remodeling (invasion and branching morphogenesis) through the upregulation of the inhibitors of matrix metalloproteinases TIMP-1 and TIMP-2. Increased TIMPs synthesis by the tumor microenvironment following trabectedin treatment was confirmed in xenograft models of myxoid liposarcoma. In addition, trabectedin upregulated tumor cell expression of the endogenous inhibitor thrombospondin-1 (TSP-1, a key regulator of angiogenesis-dependent dormancy in sarcoma), in in vivo models of myxoid liposarcomas, in vitro cell lines and primary cell cultures from patients' myxoid liposarcomas. Chromatin Immunoprecipitation analysis showed that trabectedin displaced the master regulator of adipogenesis C/EBPβ from the TSP-1 promoter, indicating an association between the up-regulation of TSP-1 and induction of adipocytic differentiation program by trabectedin. We conclude that trabectedin inhibits angiogenesis through multiple mechanisms, including directly affecting endothelial cells in the tumor microenvironment--with a potentially widespread activity--and targeting tumor cells' angiogenic activity, linked to a tumor-specific molecular alteration.

Adipogenic transcriptome profiling using high throughput technologies

The recent technological innovations in the area of functional genomics, gene expression/transcriptomic profiling can provide new insights to understand the molecular basis of adipogenesis. The focus of this review is to highlight the recent advances in our understanding of the complex interplay of gene expression events and the regulatory mechanisms of adipogenesis in mouse cell lines, humans and farm animals. All these studies have employed the availability of constantly evolving high throughput 'omics' technologies including microarrays, RNA-Seq, chromatin immunoprecipitation, next generation sequencing, RNAi, miRNA profiling and quantitative PCR arrays.

Effect of retinoic acid on gene expression profiles of bovine intramuscular preadipocytes during adipogenesis

To investigate genes involved in intramuscular adipogenesis in ruminants, 16 genes with dramatic variable expression were selected. These were selected from the differentiation- and proliferation-phase libraries of our previous serial analysis of gene expression (SAGE) studies of a clonal bovine intramuscular preadipocyte (BIP) cell line. We harvested the BIP cells over 12 days after adipogenic stimulation with all-trans retinoic acid (ATRA). Quantitative real-time PCR confirmed the earlier SAGE study results of the expression patterns of 15 of the genes. On day 6, TG accumulation increased significantly in the BIP cells but was completely inhibited in the 3T3-L1 cells (the monogastric reference). ATRA enhanced expression levels of six genes whereas it suppressed expression of eight genes on day 3 of adipogenesis in the BIP cells. Forty-eight hours after transfection, the messenger RNA expression level of the adipose differentiation-related protein (ADFP), encoded by one of the upregulated genes, in the ADFP small interference RNA (siRNA)-transfected cells was 3.5% of that in negative control-transfected cells. Also, 6 days after induction the TG level in the ADFP siRNA-transfected cells was 21.8% lower than that in negative control-transfected cells. This analysis of gene expression profiles after ATRA treatment will contribute to our understanding of the molecular mechanisms involved in bovine intramuscular adipogenesis.

LMO4 modulates proliferation and differentiation of 3T3-L1 preadipocytes

Previous microarray analyses revealed that LMO4 is expressed in 3T3-L1 preadipocytes, however, its roles in adipogenesis are unknown. In the present study, using RT-PCR sequencing and quantitative real-time RT-PCR, we confirmed that LMO4 gene is expressed in 3T3-L1 preadipocytes and its expression peaks at the early stage of 3T3-L1 preadipocyte differentiation. Further analyses showed that LMO4 knockdown decreased the proliferation of 3T3-L1 preadipocytes, and attenuated the differentiation of 3T3-L1 preadipocytes, as evidenced by reduced lipid accumulation and down-regulation of PPARγ gene expression. Collectively, our findings indicate that LMO4 is a novel modulator of adipogenesis.

Proteomic analysis of the inhibitory effect of epigallocatechin gallate on lipid accumulation in human HepG2 cells

Background

(−)-Epigallocatechin-3-gallate (EGCG), the most abundant catechin found in green tea, effectively reduces body weight and tissue and blood lipid accumulation. To explore the mechanism by which EGCG inhibits cellular lipid accumulation in free fatty acid (FFA) induced HepG2 cell culture, we investigated the proteome change of FFA-induced HepG2 cells exposed to EGCG using two-dimensional gel electrophoresis and mass spectrometry.

Results

In this study, 36 protein spots showed a significant change in intensity by more than 1.5-fold from the control group to the FFA group and from the FFA group to the FFA + EGCG group. Among them, 24 spots were excised from gels and identified by LC-MS/MS. In total, 18 proteins were successfully identified. All identified proteins were involved in lipid metabolism, glycometabolism, antioxidant defense, respiration, cytoskeleton organization, signal transduction, DNA repair, mRNA processing, iron storage, or were chaperone proteins. This indicated that these physiological processes may play roles in the mechanism of inhibition of lipid accumulation by EGCG in FFA-induced HepG2 cells. Western blotting analysis was used to verify the expression levels of differentially expressed proteins, which agree with the proteomic results.

Conclusions

From the proteomic analysis, we hypothesized that EGCG reduced cellular lipid accumulation in FFA-induced HepG2 cells through the activation of AMP-activated protein kinase (AMPK) resulting from the generation of reactive oxygen species (ROS). The induction of ROS may be a result of EGCG regulation of the antioxidant defense system. Activation of AMPK shifted some FFA toward oxidation, away from lipid and triglyceride storage, and suppressed hepatic gluconeogenesis. The findings of this study improve our understanding of the molecular mechanisms of inhibition of lipid accumulation by EGCG in HepG2 cells.

Changes in mouse cognition and hippocampal gene expression observed in a mild physical- and blast-traumatic brain injury

Warfare has long been associated with traumatic brain injury (TBI) in militarized zones. Common forms of TBI can be caused by a physical insult to the head-brain or by the effects of a high velocity blast shock wave generated by the detonation of an explosive device. While both forms of trauma are distinctly different regarding the mechanism of trauma induction, there are striking similarities in the cognitive and emotional status of survivors. Presently, proven effective therapeutics for the treatment of either form of TBI are unavailable. To be able to develop efficacious therapies, studies involving animal models of physical- and blast-TBI are required to identify possible novel or existing medicines that may be of value in the management of clinical events. We examined indices of cognition and anxiety-like behavior and the hippocampal gene transcriptome of mice subjected to both forms of TBI. We identified common behavioral deficits and gene expression regulations, in addition to unique injury-specific forms of gene regulation. Molecular pathways presented a pattern similar to that seen in gene expression. Interestingly, pathways connected to Alzheimer's disease displayed a markedly different form of regulation depending on the type of TBI. While these data highlight similarities in behavioral outcomes after trauma, the divergence in hippocampal transcriptome observed between models suggests that, at the molecular level, the TBIs are quite different. These models may provide tools to help define therapeutic approaches for the treatment of physical- and blast-TBIs. Based upon observations of increasing numbers of personnel displaying TBI related emotional and behavioral changes in militarized zones, the development of efficacious therapies will become a national if not a global priority.

Metabolic reprogramming by class I and II histone deacetylases

Accumulating evidence suggests that protein acetylation plays a major regulatory role in many facets of transcriptional control of metabolism. The enzymes that catalyze the addition and removal of acetyl moieties are the histone acetyl transferases (HATs) and histone deacetylases (HDACs), respectively. Several recent studies have uncovered novel mechanisms and contexts in which different HDACs play crucial roles in metabolic control. Understanding the role of class I and II HDACs in different metabolic programs during development, as well as in the physiology and pathology of the adult organism, will lead to novel therapeutics for metabolic disease. Here, we review the current understanding of how class I and class II HDACs contribute to metabolic control.

Loss of TDAG51 results in mature-onset obesity, hepatic steatosis, and insulin resistance by regulating lipogenesis

Regulation of energy metabolism is critical for the prevention of obesity, diabetes, and hepatic steatosis. Here, we report an important role for the pleckstrin homology-related domain family member, T-cell death-associated gene 51 (TDAG51), in the regulation of energy metabolism. TDAG51 expression was examined during adipocyte differentiation. Adipogenic potential of preadipocytes with knockdown or absence of TDAG51 was assessed. Weight gain, insulin sensitivity, metabolic rate, and liver lipid content were also compared between TDAG51-deficient (TDAG51(-/-)) and wild-type mice. In addition to its relatively high expression in liver, TDAG51 was also present in white adipose tissue (WAT). TDAG51 was downregulated during adipogenesis, and TDAG51(-/-) preadipocytes exhibited greater lipogenic potential. TDAG51(-/-) mice fed a chow diet exhibited greater body and WAT mass, had reduced energy expenditure, displayed mature-onset insulin resistance (IR), and were predisposed to hepatic steatosis. TDAG51(-/-) mice had increased hepatic triglycerides and SREBP-1 target gene expression. Furthermore, TDAG51 expression was inversely correlated with fatty liver in multiple mouse models of hepatic steatosis. Taken together, our findings suggest that TDAG51 is involved in energy homeostasis at least in part by regulating lipogenesis in liver and WAT, and hence, may constitute a novel therapeutic target for the treatment of obesity and IR.

Dynamic and distinct histone modifications modulate the expression of key adipogenesis regulatory genes

Histone modifications and their modifying enzymes are fundamentally involved in the epigenetic regulation of adipogenesis. This study aimed to define the roles of various histone modifications and their "division of labor" in fat cell differentiation. To achieve these goals, we examined the distribution patterns of eight core histone modifications at five key adipogenic regulatory genes, Pref-1, C/EBPβ, C/EBPα, PPARγ2 and aP2, during the adipogenesis of C3H 10T1/2 mouse mesenchymal stem cells (MSCs) and 3T3-L1 preadipocytes. We found that the examined histone modifications are globally stable throughout adipogenesis but show distinct and highly dynamic distribution patterns at specific genes. For example, the Pref-1 gene has lower levels of active chromatin markers and significantly higher H3 K27 tri-methylation in MSCs compared with committed preadipocytes; the C/EBPβ gene is enriched in active chromatin markers at its 3'-UTR; the C/EBPα gene is predominantly marked by H3 K27 tri-methylation in adipogenic precursor cells, and this repressive marker decreases dramatically upon induction; the PPARγ2 and aP2 genes show increased histone acetylation on both H3 and H4 tails during adipogenesis. Further functional studies revealed that the decreased level of H3 K27 tri-methylation leads to de-repression of Pref-1 gene, while the increased level of histone acetylation activates the transcription of PPARγ2 and aP2 genes. Moreover, the active histone modification-marked 3'-UTR of C/EBPβ gene was demonstrated as a strong enhancer element by luciferase assay. Our results indicate that histone modifications are gene-specific at adipogenic regulator genes, and they play distinct roles in regulating the transcriptional network during adipogenesis.

Mitochondrial dysfunction and adipogenic reduction by prohibitin silencing in 3T3-L1 cells

Increase in mitochondrial biogenesis has been shown to accompany brown and white adipose cell differentiation. Prohibitins (PHBs), comprised of two evolutionarily conserved proteins, prohibitin-1 (PHB1) and prohibitin-2 (PHB2), are present in a high molecular-weight complex in the inner membrane of mitochondria. However, little is known about the effect of mitochondrial PHBs in adipogenesis. In the present study, we demonstrate that the levels of both PHB1 and PHB2 are significantly increased during adipogenesis of 3T3-L1 preadipocytes, especially in mitochondria. Knockdown of PHB1 or PHB2 by oligonucleotide siRNA significantly reduced the expression of adipogenic markers, the accumulation of lipids and the phosphorylation of extracellular signal-regulated kinases. In addition, fragmentation of mitochondrial reticulum, loss of mitochondrial cristae, reduction of mitochondrial content, impairment of mitochondrial complex I activity and excessive production of ROS were observed upon PHB-silencing in 3T3-L1 cells. Our results suggest that PHBs are critical mediators in promoting 3T3-L1 adipocyte differentiation and may be the potential targets for obesity therapies.

Pim1 kinase is required to maintain tumorigenicity in MYC-expressing prostate cancer cells

PIM1 kinase and MYC are commonly co-expressed in human prostate cancer and synergize to induce rapidly progressing prostate cancer in mouse models. Deficiency of the Pim kinase genes is well tolerated in vivo, suggesting that PIM1 inhibition might offer an attractive therapeutic modality for prostate cancer, particularly for MYC-expressing tumors. Here we examine the molecular consequences of Pim1 and MYC over-expression in the prostate as well as the effects of depleting Pim1 in prostate carcinoma cells with high levels of MYC. Over-expression of Pim1 in the mouse prostate induces several pro-tumorigenic genetic programs including cell cycle genes and Myc-regulated genes prior to the induction of any discernible pathology. Pim1 depletion by RNA interference in mouse and human prostate cancer cells decreased cellular proliferation, survival, Erk signaling, and tumorigenicity even when MYC levels were not significantly altered. These results indicate that PIM1 may be necessary to maintain tumorigenicity, and further support efforts aimed at developing PIM1 inhibitors for prostate cancer therapy.

Differential expression of adipose tissue proteins between obesity-susceptible and -resistant rats fed a high-fat diet

One of the major questions in the field of obesity is why some humans become obese (obesity prone, OP) and others resist the development of obesity (obesity resistant, OR) when exposed to a high-calorie diet, which has not been completely studied. Therefore, in the present study, in order to gain insight into the molecular mechanisms underlying this propensity, we have performed a comparative analysis of protein expression profiles in white adipose tissue (WAT) and brown adipose tissue (BAT) of rats fed a high-fat diet by 2-DE and MALDI-TOF-MS. Protein mapping of homogenates revealed significant alterations to a number of proteins; 60 and 70 proteins were differentially regulated in BAT and WAT, respectively. For careful interpretation of proteomic results, we categorized the identified proteins into two groups by analysis of both average spot density of pooled six rat adipose tissues and individual spot density of each adipose tissue of six rats as a function of body weight. One of the most striking findings of this study was that significant changes of Ehd1 and laminin receptor in BAT as well as antiquitin, DJ-1 protein, and paraoxonase 2 in WAT were found for the first time in obese rats. In addition, we confirmed the increased expression of some thermogenic enzymes and decreased lipogenic enzymes in adipose tissues of OR rats by immunoblot analysis. To our knowledge, this is the first proteomic study of profiling of protein modulation in OP and OR rats, thereby providing the first global evidence for different propensities to obesity between OP and OR rats.

Microarray evidences the role of pathologic adipose tissue in insulin resistance and their clinical implications

Clustering of insulin resistance and dysmetabolism with obesity is attributed to pathologic adipose tissue. The morphologic hallmarks of this pathology are adipocye hypertrophy and heightened inflammation. However, it's underlying molecular mechanisms remains unknown. Study of gene function in metabolically active tissues like adipose tissue, skeletal muscle and liver is a promising strategy. Microarray is a powerful technique of assessment of gene function by measuring transcription of large number of genes in an array. This technique has several potential applications in understanding pathologic adipose tissue. They are: (1) transcriptomic differences between various depots of adipose tissue, adipose tissue from obese versus lean individuals, high insulin resistant versus low insulin resistance, brown versus white adipose tissue, (2) transcriptomic profiles of various stages of adipogenesis, (3) effect of diet, cytokines, adipokines, hormones, environmental toxins and drugs on transcriptomic profiles, (4) influence of adipokines on transcriptomic profiles in skeletal muscle, hepatocyte, adipose tissue etc., and (5) genetics of gene expression. The microarray evidences of molecular basis of obesity and insulin resistance are presented here. Despite the limitations, microarray has potential clinical applications in finding new molecular targets for treatment of insulin resistance and classification of adipose tissue based on future risk of insulin resistance syndrome.

Mechanism of increased PLD1 gene expression during early adipocyte differentiation process of mouse cell line 3T3-L1

A mouse cell line 3T3-L1 is differentiated into adipocytes when treated with an inducer cocktail (IDX) (insulin, dexametahsone, and a cAMP phosphodiesterase inhibitor of isobutyl-methylxanthine (IBMX)). Here, we report that PLD1, but not PLD2, mRNA and protein increased during the early differentiation process. Our analysis shows that IDX resulted in a sequential induction of C/EBPbeta, PLD1, and C/EBPalpha which is a key transcription factor of late adipocyte differentiation. Among the three inducers, IBMX + any other inducer induced mild adipocyte differentiation, whereas insulin + dexamethasone did not. IBMX increased PLD1 but not PLD2 mRNA. Forskolin, an adenylate cyclase activator, and dbcAMP also increased PLD1 mRNA, suggesting the cellular cAMP as the inducer of both adipocyte differentiation and PLD1 transcription. We focused on the regulatory mechanism of PLD1 transcription during this differentiation process. IDX or a combination of inducers including IBMX increased PLD1 promoter activity, which is consistent with mRNA analysis. Promoter analysis identified two adjacent C/EBP motifs located between -338 and -231 bp from the first exon as the IBMX responsive elements. Furthermore, overexpression of C/EBPbeta, but not C/EBPalpha, increased PLD1 mRNA and PLD1 5' promoter activity. EMSA and chromatin immunoprecipitation assay confirmed the direct binding of C/EBPbeta, but not C/EBPalpha, to these C/EBP motifs of PLD1 5' promoter. Our results show that PLD1 is a target gene of C/EBPbeta through the increased cellular cAMP during early adipocyte differentiation of 3T3-L1 cells.

RNA interference-mediated knockdown of the mouse gene encoding potassium channel subfamily K member 10 inhibits hormone-induced differentiation of 3T3-L1 preadipocytes

Intramuscular fat (IMF) is an economically important trait of domestic meat animals; thus, it is important to identify the factors that influence the IMF content. In this study, we identified the gene associated with adipogenesis from all the positional candidate genes located in the quantitative trait loci (QTL) for IMF content on porcine chromosome 7. We analyzed the expression of the abovementioned genes during differentiation of mouse 3T3-L1 preadipocytes by using real-time polymerase chain reaction (PCR). Total cellular RNA was extracted before and 6, 12, 36, and 48 h and 4, 6, and 8d after treatment with standard hormonal inducers of differentiation-insulin, dexamethasone, and 3-isobutyl-1-methylxanthine (IBMX). Six hours after induction, potassium channel subfamily K member 10 (KCNK10) gene expression in the preadipocytes was found to be 100-fold greater than that at the baseline; this expression declined until day 4 after the induction. Moreover, knockdown of the KCNK10 gene by transfection with short-hairpin RNA (shRNA) significantly decreased triacylglycerol accumulation on day 8 after the induction. An RNA interference study revealed that KCNK10 knockdown inhibited the differentiation of 3T3-L1 cells. These results indicate that KCNK10 plays an important role in the early stages of preadipocyte differentiation.

Proteome differences associated with fat accumulation in bovine subcutaneous adipose tissues

Background

The fat components of red meat products have been of interest to researchers due to the health aspects of excess fat consumption by humans. We hypothesized that differences in protein expression have an impact on adipose tissue formation during beef cattle development and growth. Therefore, in this study we evaluated the differences in the discernable proteome of subcutaneous adipose tissues of 35 beef crossbred steers [Charolais × Red Angus (CHAR) (n = 13) and Hereford × Angus (HEAN) (n = 22)] with different back fat (BF) thicknesses. The goal was to identify specific protein markers that could be associated with adipose tissue formation in beef cows.

Results

Approximately 541-580 protein spots were detected and compared in each crossbred group, and 33 and 36 protein spots showed expression differences between tissues with high and low BF thicknesses from HEAN and CHAR crossbed, respectively. The annexin 1 protein was highly expressed in both crossbred steers that had a higher BF thickness (p < 0.05) and this was further validated by a western blot analysis. In 13 tissues of CHAR animals and 22 tissues of HEAN animals, the relative expression of annexin 1 was significantly different (p < 0.05) between tissues with high and low BF thicknesses.

Conclusion

The increased expression of annexin 1 protein has been found to be associated with higher BF thickness in both crossbred steers. This result lays the foundation for future studies to develop the protein marker for assessing animals with different BF thickness.

Differentially expressed genes during bovine intramuscular adipocyte differentiation profiled by serial analysis of gene expression

Beef marbling or intramuscular fat deposition is an economically important carcass trait in Japanese Black cattle. To investigate genes involved in intramuscular adipogenesis, differential gene expression during adipogenesis in a clonal bovine intramuscular preadipocyte (BIP) cell line was profiled with serial analysis of gene expression (SAGE). We sequenced 75 283 tags for the proliferation phase (day 0) and 81 878 tags for the differentiation phase (4 days after adipogenic stimulation: day 4). A comparison of the unique SAGE tag frequencies between the day 0- and day 4-libraries revealed that 878 (2.8%) of the 30 989 unique putative transcripts were expressed at significantly different levels (P < 0.05); 401 tags (1.4%) were up-regulated and 477 tags (1.2%) were down-regulated in the day 4-library relative to the day 0-library. We confirmed up-regulation of 10 tags of the genes that were up-regulated in the previous subtraction cloning studies in BIP cells [Animal Science Journal, 76 (2005) 479]. Of the 878 differentially expressed tags, 377 were identified in the bovine RefSeq library and 356 were assigned a bovine draft genomic sequence. Fifteen tags were mapped in previously detected beef marbling quantitative trait loci (QTL) regions [Mammalian Genome, 18 (2007) 125]. These genes may be involved in the adipogenic processes of beef marbling.

Downregulated expression of the secreted glycoprotein follistatin-like 1 (Fstl1) is a robust hallmark of preadipocyte to adipocyte conversion

Obesity is a public health crisis in the United States. Targeting preadipocyte to adipocyte conversion may be an effective approach to regulate adipose mass. Using differential screening we identified Fstl1, a secreted glycoprotein with roles in immunomodulation, cell growth, cardioprotection, and vascularization, as a "preadipokine". Fstl1 is highly expressed in 3T3-L1 preadipocytes and dramatically downregulated early in their differentiation to adipocytes. Northern blot analysis of murine tissues reveals white adipose tissue (WAT), lung and heart as primary sites of Fstl1 transcript expression. In WAT, Fstl1 transcript is restricted to the preadipocyte-containing stromal-vascular cell population. Time course studies in multiple adipogenesis models reveal downregulation of Fstl1 is a hallmark of white and brown adipocyte conversion. By Western blot, we show culture media of 3T3-L1 preadipocytes contains high levels of Fstl1 protein that rapidly decline in adipocyte conversion. Moreover, we observe a correlation between preadipocyte phenotype and Fstl1 expression in that TNFalpha-mediated de-differentiation of 3T3-L1 adipocytes is accompanied by re-expression of Fstl1 transcript and protein. Treatment of 3T3-L1 preadipocytes with a panel of 18 hormones and other agents revealed the demethylating agent 5-aza-cytidine decreases Fstl1 transcript and protein levels by approximately 90%. Furthermore, of 10 additional preadipocyte-expressed genes analyzed we find Pref-1, Col1A1, Sca-1/Ly6a, Lox and Thbs2, are also downregulated by 5-aza-cytidine. Using luciferase reporter constructs containing 791 or 3922 bp of the Fstl1 5' flanking region, we determine negative transcriptional regulation by Kruppel-like factor 15. Together, our data suggest downregulation of Fstl1 expression may be an important feature of preadipocyte to adipocyte conversion.

Presenilin enhancer-2 (PSENEN), a component of the gamma-secretase complex, is involved in adipocyte differentiation

This study was conducted to identify genes expressed during adipocyte differentiation of bovine intramuscular fibroblast-like cells using differential display reverse-transcriptase polymerase chain reaction. The presenilin enhancer-2 (PSENEN) gene was found to be down-regulated during adipocyte differentiation of bovine intramuscular fibroblast-like cells. The ectopic expression of bovine PSENEN in 3T3-L1 reduced adipogenesis and the inhibition of endogenous PSENEN by siRNA induced adipogenesis on d 4 of adipocyte differentiation of 3T3-L1 cells. Interestingly, the expression of gamma-secretase complex gene-related Notch signaling was decreased at d 2 and d 4 during adipocyte differentiation. In addition, expression of the Notch-signaling genes (Notch-1, Hes-1, Pref-1, adipsin) was regulated during adipocyte differentiation by regulation of PSENEN expression. These results suggest that PSENEN plays an important role in adipocyte differentiation and that Notch signaling is involved in adipogenesis.

On the reproducibility of results of pathway analysis in genome-wide expression studies of colorectal cancers

One of the major problems in genomics and medicine is the identification of gene networks and pathways deregulated in complex and polygenic diseases, like cancer. In this paper, we address the problem of assessing the variability of results of pathways analysis identified in different and independent genome wide expression studies, in which the same phenotypic conditions are assayed. To this end, we assessed the deregulation of 1891 curated gene sets in four independent gene expression data sets of subjects affected by colorectal cancer (CRC). In this comparison we used two well-founded statistical models for evaluating deregulation of gene networks. We found that the results of pathway analysis in expression studies are highly reproducible. Our study revealed 53 pathways identified by the two methods in all the four data sets analyzed with high statistical significance and strong biological relevance with the pathology examined. This set of pathways associated to single markers as well as to whole biological processes altered constitutes a signature of the disease which sheds light on the genetics bases of CRC.

Multiple organ system defects and transcriptional dysregulation in the Nipbl(+/-) mouse, a model of Cornelia de Lange Syndrome

Cornelia de Lange Syndrome (CdLS) is a multi-organ system birth defects disorder linked, in at least half of cases, to heterozygous mutations in the NIPBL gene. In animals and fungi, orthologs of NIPBL regulate cohesin, a complex of proteins that is essential for chromosome cohesion and is also implicated in DNA repair and transcriptional regulation. Mice heterozygous for a gene-trap mutation in Nipbl were produced and exhibited defects characteristic of CdLS, including small size, craniofacial anomalies, microbrachycephaly, heart defects, hearing abnormalities, delayed bone maturation, reduced body fat, behavioral disturbances, and high mortality (75–80%) during the first weeks of life. These phenotypes arose despite a decrease in Nipbl transcript levels of only ∼30%, implying extreme sensitivity of development to small changes in Nipbl activity. Gene expression profiling demonstrated that Nipbl deficiency leads to modest but significant transcriptional dysregulation of many genes. Expression changes at the protocadherin beta (Pcdhb) locus, as well as at other loci, support the view that NIPBL influences long-range chromosomal regulatory interactions. In addition, evidence is presented that reduced expression of genes involved in adipogenic differentiation may underlie the low amounts of body fat observed both in Nipbl+/− mice and in individuals with CdLS.

Cornelia de Lange Syndrome (CdLS) is a genetic disease marked by growth retardation, cognitive and neurological problems, and structural defects in many organ systems. The majority of CdLS cases are due to mutation of one copy of the Nipped B-like (NIPBL) gene, the product of which regulates a complex of chromosomal proteins called cohesin. How reduction of NIPBL function gives rise to pervasive developmental defects in CdLS is not understood, so a model of CdLS was developed by generating mice that carry one null allele of Nipbl. Developmental defects in these mice show remarkable similarity to those observed in individuals with CdLS, including small stature, craniofacial abnormalities, reduced body fat, behavioral disturbances, and high perinatal mortality. Molecular analysis of tissues and cells from Nipbl mutant mice provide the first evidence that the major role of Nipbl in the etiology of CdLS is to exert modest, but significant, effects on the expression of diverse sets of genes, some of which are located in characteristic arrangements along the DNA. Among affected genes is a set involved in the development of adipocytes, the cells that make and accumulate body fat, potentially explaining reductions in body fat accumulation commonly observed in individuals with CdLS.

Concurrent quantification of proteome and phosphoproteome to reveal system-wide association of protein phosphorylation and gene expression

Reversible phosphorylation of proteins is an important process modulating cellular activities from upstream, which mainly involves sequential phosphorylation of signaling molecules, to downstream where phosphorylation of transcription factors regulates gene expression. In this study, we combined quantitative labeling with multidimensional liquid chromatography-mass spectrometry to monitor the proteome and phosphoproteome changes in the initial period of adipocyte differentiation. The phosphorylation level of a specific protein may be regulated by a kinase or phosphatase without involvement of gene expression or as a phenomenon that accompanies the alteration of its gene expression. Concurrent quantification of phosphopeptides and non-phosphorylated peptides makes it possible to differentiate cellular phosphorylation changes at these two levels. Furthermore, on the system level, certain proteins were predicted as the targeted gene products regulated by identified transcription factors. Among them, several proteins showed significant expression changes along with the phosphorylation alteration of their transcription factors. This is to date the first work to concurrently quantify proteome and phosphoproteome changes during the initial period of adipocyte differentiation, providing an approach to reveal the system-wide association of protein phosphorylation and gene expression.

Green tea (−)-epigallocatechin gallate inhibits insulin stimulation of 3T3-L1 preadipocyte mitogenesis via the 67-kDa laminin receptor pathway

Insulin and (−)-epigallocatechin gallate (EGCG) have been reported to regulate fat cell mitogenesis and adipogenesis, respectively. This study investigated the pathways involved in EGCG modulation of insulin-stimulated mitogenesis in 3T3-L1 preadipocytes. EGCG inhibited insulin stimulation of preadipocyte proliferation in a dose- and time-dependent manner. EGCG also suppressed insulin-stimulated phosphorylation of the insulin receptor-β, insulin receptor (IR) substrates 1 and 2 (IRS1 and IRS2), and mitogen-activated protein kinase pathway proteins, RAF1, MEK1/2, and ERK1/2, but not JNK. Furthermore, EGCG inhibited the association of IR with the IRS1 and IRS2 proteins, but not with the IRS4 protein. These data suggest that EGCG selectively affects particular types of IRS and MAPK family members. Generally, EGCG was more effective than epicatechin, epicatechin gallate, and epigallocatechin in modulating insulin-stimulated mitogenic signaling. We identified the EGCG receptor [also known as the 67-kDa laminin receptor (67LR)] in fat cells and found that its expression was sensitive to growth phase, tissue type, and differentiation state. Pretreatment of preadipocytes with 67LR antiserum prevented the effects of EGCG on insulin-stimulated phosphorylation of IRS2, RAF1, and ERK1/2 and insulin-stimulated preadipocyte proliferation (cell number and bromodeoxyuridine incorporation). Moreover, EGCG tended to increase insulin-stimulated associations between the 67LR and IR, IRS1, IRS2, and IRS4 proteins. These data suggest that EGCG mediates anti-insulin signaling in preadipocyte mitogenesis via the 67LR pathway.

The effects of green tea (-)-epigallocatechin-3-gallate on reactive oxygen species in 3T3-L1 preadipocytes and adipocytes depend on the glutathione and 67 kDa laminin receptor pathways

Green tea (-)-epigallocatechin-3-gallate (EGCG) is known as to regulate obesity and fat cell activity. However, little information is known about the effects of EGCG on oxidative reactive oxygen species (ROS) of fat cells. Using 3T3-L1 preadipocytes and adipocytes, we found that EGCG increased ROS production in dose- and time-dependent manners. The concentration of EGCG that increased ROS levels by 180-500% was approximately 50 muM for a range of 8-16 h of treatment. In contrast, EGCG dose- and time-dependently decreased the amount of intracellular glutathione (GSH) levels. EGCG was more effective than (-)-epicatechin, (-)-epicatechin-3-gallate, and (-)-epigallocatechin in changing ROS and GSH levels. This suggests a catechin-specific effect. To further examine the relation of GSH to ROS as altered by EGCG, we observed that exposure of preadipocytes and adipocytes to N-acetyl-L-cysteine (a GSH precursor) blocked the EGCG-induced increases in ROS levels and decreases in GSH levels. These observations suggest a GSH-dependent effect of EGCG on ROS production. While EGCG was demonstrated to alter levels of ROS and GSH, its signaling was altered by an EGCG receptor (the so-called 67 kDa laminin receptor(67LR)) antiserum, but not by normal rabbit serum. These data suggest that EGCG mediates GSH and ROS levels via the 67LR pathway.

Temporal profiling of the adipocyte proteome during differentiation using a five-plex SILAC based strategy

The adipose tissue has important secretory and endocrine functions in humans. The regulation of adipocyte differentiation has been actively pursued using transcriptomic methods over the last several years. Quantitative proteomics has emerged as a promising approach to obtain temporal profiles of biological processes such as differentiation. Stable isotope labeling with amino acids in cell culture (SILAC) is a simple and robust method for labeling proteins in vivo. Here, we describe the development and application of a five-plex SILAC experiment using four different heavy stable isotopic forms of arginine to study the nuclear proteome and the secretome during the course of adipocyte differentiation. Tandem mass spectrometry analysis using a quadrupole time-of-flight instrument resulted in identification of a total 882 proteins from these two proteomes. Of these proteins, 427 were identified on the basis of one or more arginine-containing peptides that allowed quantitation. In addition to previously reported molecules that are differentially expressed during the process of adipogenesis (e.g., adiponectin and lipoprotein lipase), we identified several proteins whose differential expression during adipocyte differentiation has not been documented previously. For example, THO complex 4, a context-dependent transcriptional activator in the T-cell receptor alpha enhancer complex, showed highest expression at middle stage of adipogenesis, while SNF2 alpha, a chromatin remodeling protein, was downregulated upon initiation of adipogenesis and remained so during subsequent time points. This study using a 5-plex SILAC to investigate dynamics illustrates the power of this approach to identify differentially expressed proteins in a temporal fashion.