Gene-Expression Profiles in IRS Knockout Brown Preadipocytes
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ABSTRACT: Insulin and IGF-1 promote adipocyte differentiation via complex and overlapping signalling networks. Here we used microarray analysis of brown preadipocytes derived from wild-type and insulin receptor substrate (IRS) knockout (KO) animals, which exhibited progressively impaired differentiation, to define the set of genes that predict adipogenic potential in these cells. 374 genes/ESTs were identified whose expression in preadipocytes correlated with their ultimate ability to differentiate. Many of these genes were related to early adipogenic events, including genes involved in extracellular matrix, cytoskeletal organization, growth arrest, post-mitotic clonal expansion, and inhibitors of adipogenesis, including preadipocyte factor-1 and multiple members of the Wnt-signalling pathway. Reconstitution of IRS-1 KO cells with IRS-1 reversed these changes and restored the ability to differentiate. Several of these genes showed concordant changes in brown adipose tissue in vivo. Necdin was markedly increased in IRS-1 KO cells that could not differentiate, and knockdown of necdin restored brown adipogenesis with down-regulation of Pref-1 and Wnt10a expression. We demonstrated a necdin-E2F4 interaction repressing PPARg transcription. IRS proteins regulated necdin via a CREB dependent pathway, defining a signalling network involved in brown preadipocyte determination. Keywords = brown fat Keywords = preadipocyte Keywords = adipogenesis Keywords = mouse Keywords: parallel sample
Project description:Insulin and IGF-1 promote adipocyte differentiation via complex and overlapping signalling networks. Here we used microarray analysis of brown preadipocytes derived from wild-type and insulin receptor substrate (IRS) knockout (KO) animals, which exhibited progressively impaired differentiation, to define the set of genes that predict adipogenic potential in these cells. 374 genes/ESTs were identified whose expression in preadipocytes correlated with their ultimate ability to differentiate. Many of these genes were related to early adipogenic events, including genes involved in extracellular matrix, cytoskeletal organization, growth arrest, post-mitotic clonal expansion, and inhibitors of adipogenesis, including preadipocyte factor-1 and multiple members of the Wnt-signalling pathway. Reconstitution of IRS-1 KO cells with IRS-1 reversed these changes and restored the ability to differentiate. Several of these genes showed concordant changes in brown adipose tissue in vivo. Necdin was markedly increased in IRS-1 KO cells that could not differentiate, and knockdown of necdin restored brown adipogenesis with down-regulation of Pref-1 and Wnt10a expression. We demonstrated a necdin-E2F4 interaction repressing PPARg transcription. IRS proteins regulated necdin via a CREB dependent pathway, defining a signalling network involved in brown preadipocyte determination.
Project description:Attainment of a brown adipocyte cell phenotype in white adipocytes, with their abundant mitochondria and increased energy expenditure potential, is a legitimate strategy for combating obesity. The unique transcriptional regulators of the primary brown adipocyte phenotype are unknown, limiting our ability to promote brown adipogenesis over white. In the present work, we used microarray analysis strategies to study primary preadipocytes, and we made the striking discovery that brown preadipocytes demonstrate a myogenic transcriptional signature, whereas both brown and white primary preadipocytes demonstrate signatures distinct from those found in immortalized adipogenic models. We found a plausible SIRT1-related transcriptional signature during brown adipocyte differentiation that may contribute to silencing the myogenic signature. In contrast to brown preadipocytes or skeletal muscle cells, white preadipocytes express Tcf21, a transcription factor that has been shown to suppress myogenesis and nuclear receptor activity. In addition, we identified a number of developmental genes that are differentially expressed between brown and white preadipocytes and that have recently been implicated in human obesity. The interlinkage between the myocyte and the brown preadipocyte confirms the distinct origin for brown versus white adipose tissue and also represents a plausible explanation as to why brown adipocytes ultimately specialize in lipid catabolism rather than storage, much like oxidative skeletal muscle tissue. Keywords: In vitro differentiation
Project description:Inherent depot- and age-dependent preadipocyte characteristics may contribute to age-related fat redistribution. Both aging and depot origin affect preadipocyte replication and adipogenesis. To define responsible mechanisms, we analyzed genome-wide expression profiles in epididymal (E) and perirenal (P) preadipocytes cultured from young (3 month) and old (30m) rats. Differences between depots were distinct from and more dramatic than those that occur with aging. Experiment Overall Design: Preadipocytes were isolated from perirenal and epididymal fat depots of 3 young (3 month) and 3 old (30 month) Brown Norway rats for a total of 12 samples from 6 different animals.
Project description:Much of our knowledge on adipogenesis comes from cell culture models of preadipocyte differentiation. Adipogenesis is induced by treating confluent preadipocytes with the adipogenic cocktail, which activates transcription factors (TFs) glucocorticoid receptor (GR) and CREB within minutes and increases expression of TFs C/EBPb/d, KLF4 and Krox20 within hours. All of these TFs have been shown to be capable of promoting adipogenesis in culture when they are overexpressed. However, it has remained unclear whether endogenous KLF4 and Krox20 are required for adipogenesis in culture and in vivo. Using conditional knockout mice and derived white and brown preadipocytes, we show that endogenous KLF4 and Krox20 are dispensable for adipogenesis in culture and brown adipose tissue development in mice. In contrast, the master adipogenic TF PPARg is essential. These results challenge the existing model on transcriptional regulation in the early phase of adipogenesis and highlight the need of studying adipogenesis in vivo.
Project description:Attainment of a brown adipocyte cell phenotype in white adipocytes, with their abundant mitochondria and increased energy expenditure potential, is a legitimate strategy for combating obesity. The unique transcriptional regulators of the primary brown adipocyte phenotype are unknown, limiting our ability to promote brown adipogenesis over white. In the present work, we used microarray analysis strategies to study primary preadipocytes, and we made the striking discovery that brown preadipocytes demonstrate a myogenic transcriptional signature, whereas both brown and white primary preadipocytes demonstrate signatures distinct from those found in immortalized adipogenic models. We found a plausible SIRT1-related transcriptional signature during brown adipocyte differentiation that may contribute to silencing the myogenic signature. In contrast to brown preadipocytes or skeletal muscle cells, white preadipocytes express Tcf21, a transcription factor that has been shown to suppress myogenesis and nuclear receptor activity. In addition, we identified a number of developmental genes that are differentially expressed between brown and white preadipocytes and that have recently been implicated in human obesity. The interlinkage between the myocyte and the brown preadipocyte confirms the distinct origin for brown versus white adipose tissue and also represents a plausible explanation as to why brown adipocytes ultimately specialize in lipid catabolism rather than storage, much like oxidative skeletal muscle tissue. Experiment Overall Design: Comparisons of white and brown pre- and mature-adiposytes
Project description:PPARg and C/EBPa cooperate to control preadipocyte differentiation (adipogenesis). However, the factors that regulate PPARg and C/EBPa expression during adipogenesis remain largely unclear. Here we show PTIP, a protein that associates with histone H3K4 methyltransferases, regulates PPARg and C/EBPa expression in mouse embryonic fibroblasts (MEFs) and during preadipocyte differentiation. PTIP deletion in MEFs leads to marked decreases of PPARg expression and PPARg-stimulated C/EBPα expression. Further, PTIP is essential for induction of PPARg and C/EBPa expression during preadipocyte differentiation. Deletion of PTIP impairs the enrichment of H3K4 trimethylation and RNA polymerase II on PPARg and C/EBPa promoters. Accordingly, PTIP-/- MEFs and preadipocytes all show striking defects in adipogenesis. Furthermore, rescue of the adipogenesis defect in PTIP-/- MEFs requires co-expression of PPARg and C/EBPa. Finally, deletion of PTIP in brown adipose tissue significantly reduces tissue weight in mice. Thus, by regulating PPARg and C/EBPa expression, PTIP plays a critical role in adipogenesis.
Project description:Brown preadipocytes were grown to confluence and synchronized by overnight serum starvation. Four independent RNA samples were analyzed from each IRS KO cell line and three independent clones of WT cells were separately analyzed as controls. Splitting of the samples resulted in a total 28 microarrays. 15 mg of adjusted cRNA were hybridized to Affymetrix U74A-v2 arrays.
Project description:PPARg and C/EBPa cooperate to control preadipocyte differentiation (adipogenesis). However, the factors that regulate PPARg and C/EBPa expression during adipogenesis remain largely unclear. Here we show PTIP, a protein that associates with histone H3K4 methyltransferases, regulates PPARg and C/EBPa expression in mouse embryonic fibroblasts (MEFs) and during preadipocyte differentiation. PTIP deletion in MEFs leads to marked decreases of PPARg expression and PPARg-stimulated C/EBPα expression. Further, PTIP is essential for induction of PPARg and C/EBPa expression during preadipocyte differentiation. Deletion of PTIP impairs the enrichment of H3K4 trimethylation and RNA polymerase II on PPARg and C/EBPa promoters. Accordingly, PTIP-/- MEFs and preadipocytes all show striking defects in adipogenesis. Furthermore, rescue of the adipogenesis defect in PTIP-/- MEFs requires co-expression of PPARg and C/EBPa. Finally, deletion of PTIP in brown adipose tissue significantly reduces tissue weight in mice. Thus, by regulating PPARg and C/EBPa expression, PTIP plays a critical role in adipogenesis. To identify PTIP-regulated genes, immortalized PTIP conditional knockout PTIPflox/flox MEFs were infected with retroviruses expressing either Cre recombinase or vector alone. We prepared duplicated RNAs from either vector or Cre infected cells (PTIP+/+ or PTIP-/-) for 4 affymetrix microarrays.
Project description:Inherent depot- and age-dependent preadipocyte characteristics may contribute to age-related fat redistribution. Both aging and depot origin affect preadipocyte replication and adipogenesis. To define responsible mechanisms, we analyzed genome-wide expression profiles in epididymal (E) and perirenal (P) preadipocytes cultured from young (3 month) and old (30m) rats. Differences between depots were distinct from and more dramatic than those that occur with aging. Keywords: cell type and age comparison
Project description:Insulin resistance and Type 2 Diabetes Mellitus (T2DM) are associated with increased adipocyte size, altered secretory pattern and decreased differentiation of preadipocytes. To identify the underlying molecular processes in preadipocytes of T2DM patients that are a characteristic of the development of T2DM, preadipocyte cell cultures were prepared from subcutaneous fat biopsies of T2DM patients and compared with age- and BMI matched control subjects. Gene expression profiling showed changed expression of transcription factors involved in adipogenesis and in extracellular matrix remodeling, actin cytoskeleton and integrin signaling genes, which indicated decreased capacity to differentiate. Additionally, genes involved in insulin signaling and lipid metabolism were down-regulated, and inflammation/apoptosis was up-regulated in T2DM preadipocytes. The down-regulation of genes involved in differentiation can provide a molecular basis for the reduced adipogenesis of preadipocytes of T2DM subjects, leading to reduced formation of adipocytes in subcutaneous fat depots, and ultimately leading to ectopic fat storage. 7 T2DM preadipocyte samples and 9 age- and BMI-matched control samples were hybridized using 70-mer oligonucleotide microarrays. Samples were labeled with either Cy3 or Cy5. A total of 20 arrays were used including dye swop. Per array, a T2DM sample was hybridized with a control sample of the same gender and matched based on age and BMI. To ensure hybridization of two samples with the same gender, three T2DM (5064, 5128, 5395) and one control sample (5616) were used twice and listed as technical replicates.