PubMed Health⌕ Search

Biomedical subjects

Evan D Rosen

Publications and source records attributed to Evan D Rosen.

17 recordsLinked to original sources
PubMed2025

The extracellular vesicle transcriptome provides tissue-specific functional genomic annotation relevant to disease susceptibility in obesity.

We characterized circulating extracellular vesicles (EVs) in obese and lean humans, identifying transcriptional cargo differentially expressed in obesity (277 unique genes; false discovery rate < 10%). Since circulating EVs may have broad origin, we compared this obesity EV transcriptome with expression from human visceral-adipose-tissue-derived EVs from freshly collected and cultured biopsies from the same obese individuals, observing high concordance. Using a comprehensive set of adipose-specific epigenomic and chromatin conformation assays, we found that the differentially expressed transcripts from the EVs were those regulated in adipose by body mass index-associated SNPs (p < 5 &#xd7; 10-8) from a large-scale genome-wide association study (GWAS). Using a phenome-wide association study of the regulatory SNPs for the EV-derived transcripts, we identified a substantial enrichment for inflammatory phenotypes, including type 2 diabetes. Collectively, these findings represent the convergence of the GWAS (genetics), epigenomics (transcript regulation), and EV (liquid biopsy) fields, enabling powerful future genomic studies of complex diseases.

Humans↗
PubMed2007

FSTL3 deletion reveals roles for TGF-beta family ligands in glucose and fat homeostasis in adults.

Activin and myostatin are related members of the TGF-beta growth factor superfamily. FSTL3 (Follistatin-like 3) is an activin and myostatin antagonist whose physiological role in adults remains to be determined. We found that homozygous FSTL3 knockout adults developed a distinct group of metabolic phenotypes, including increased pancreatic islet number and size, beta cell hyperplasia, decreased visceral fat mass, improved glucose tolerance, and enhanced insulin sensitivity, changes that might benefit obese, insulin-resistant patients. The mice also developed hepatic steatosis and mild hypertension but exhibited no alteration of muscle or body weight. This combination of phenotypes appears to arise from increased activin and myostatin bioactivity in specific tissues resulting from the absence of the FSTL3 antagonist. Thus, the enlarged islets and beta cell number likely result from increased activin action. Reduced visceral fat is consistent with a role for increased myostatin action in regulating fat deposition, which, in turn, may be partly responsible for the enhanced glucose tolerance and insulin sensitivity. Our results demonstrate that FSTL3 regulation of activin and myostatin is critical for normal adult metabolic homeostasis, suggesting that pharmacological manipulation of FSTL3 activity might simultaneously reduce visceral adiposity, increase beta cell mass, and improve insulin sensitivity.

Animals↗
PubMed2006

Adipocytes as regulators of energy balance and glucose homeostasis.

Adipocytes have been studied with increasing intensity as a result of the emergence of obesity as a serious public health problem and the realization that adipose tissue serves as an integrator of various physiological pathways. In particular, their role in calorie storage makes adipocytes well suited to the regulation of energy balance. Adipose tissue also serves as a crucial integrator of glucose homeostasis. Knowledge of adipocyte biology is therefore crucial for understanding the pathophysiological basis of obesity and metabolic diseases such as type 2 diabetes. Furthermore, the rational manipulation of adipose physiology is a promising avenue for therapy of these conditions.

Adipocytes↗
PubMed2006

Critical role for Ebf1 and Ebf2 in the adipogenic transcriptional cascade.

The Ebf (O/E) family of helix-loop-helix transcription factors plays a significant role in B lymphocyte and neuronal development. The three primary members of this family, Ebf1, 2, and 3, are all expressed in adipocytes, and Ebf1 promotes adipogenesis when overexpressed in NIH 3T3 fibroblasts. Here we report that these three proteins have adipogenic potential in multiple cellular models and that peroxisome proliferator-activated receptor gamma (PPARgamma) is required for this effect, at least in part due to direct activation of the PPARgamma1 promoter by Ebf1. Ebf1 also directly binds to and activates the C/EBPalpha promoter, which exerts positive feedback on C/EBPdelta expression. Despite this, C/EBPalpha is dispensable for the adipogenic action of Ebf proteins. Ebf1 itself is induced by C/EBPbeta and delta, which bind and activate its promoter. Reduction of Ebf1 and Ebf2 proteins by specific short hairpin RNA blocks differentiation of 3T3-L1 cells, suggesting a critical role for these factors and the absence of functional redundancy between members of this family. Altogether, these data place Ebf1 within the known transcriptional cascade of adipogenesis and suggest critical roles for Ebf1 and Ebf2.

Adipocytes↗
PubMed2006

Reactive oxygen species have a causal role in multiple forms of insulin resistance.

Insulin resistance is a cardinal feature of type 2 diabetes and is characteristic of a wide range of other clinical and experimental settings. Little is known about why insulin resistance occurs in so many contexts. Do the various insults that trigger insulin resistance act through a common mechanism? Or, as has been suggested, do they use distinct cellular pathways? Here we report a genomic analysis of two cellular models of insulin resistance, one induced by treatment with the cytokine tumour-necrosis factor-alpha and the other with the glucocorticoid dexamethasone. Gene expression analysis suggests that reactive oxygen species (ROS) levels are increased in both models, and we confirmed this through measures of cellular redox state. ROS have previously been proposed to be involved in insulin resistance, although evidence for a causal role has been scant. We tested this hypothesis in cell culture using six treatments designed to alter ROS levels, including two small molecules and four transgenes; all ameliorated insulin resistance to varying degrees. One of these treatments was tested in obese, insulin-resistant mice and was shown to improve insulin sensitivity and glucose homeostasis. Together, our findings suggest that increased ROS levels are an important trigger for insulin resistance in numerous settings.

3T3-L1 Cells↗
PubMed2006

New drugs from fat bugs?

Signal transduction cascades, such as Hedgehog (Hh) signaling, are potentially important targets for new drugs. A new study in this issue of Cell Metabolism identifies hedgehog signaling in the formation of the Drosophila fly body and in mammalian adipogenesis.

Adipogenesis↗
PubMed2006

Adipocyte differentiation from the inside out.

Improved knowledge of all aspects of adipose biology will be required to counter the burgeoning epidemic of obesity. Interest in adipogenesis has increased markedly over the past few years with emphasis on the intersection between extracellular signals and the transcriptional cascade that regulates adipocyte differentiation. Many different events contribute to the commitment of a mesenchymal stem cell to the adipocyte lineage including the coordination of a complex network of transcription factors, cofactors and signalling intermediates from numerous pathways.

Adipocytes↗
PubMed2005

The transcriptional basis of adipocyte development.

Adipogenesis is the developmental process by which a multipotent mesenchymal stem cell differentiates into a mature adipocyte. This process involves a highly regulated and coordinated cascade of transcription factors that together lead to the establishment of the differentiated state. In the presence of the correct hormonal cues, committed pre-adipocytes express the bZIP factors C/EBPb and C/EBPd. These factors in turn induce the expression of C/EBPa and peroxisome proliferator-activated receptor g (PPARg). C/EBPa and PPARg together promote differentiation by activating adipose-specific gene expression and by maintaining each others expression at high levels. We have investigated the relative contributions of PPARg and C/EBPa to adipogenesis by selectively ablating these genes in mouse embryonic fibroblasts (MEFs). MEFs that lack C/EBPa are able to undergo adipogenesis, but only when PPARg is ectopically expressed. Interestingly, these cells are not sensitive to the metabolic actions of insulin. By way of contrast, cells that lack PPARg are utterly incapable of adipogenic conversion, even when supplemented with high levels of C/EBPa. Our current investigations are centered on the identification of novel adipogenic transcription factors, utilizing a variety of techniques, ranging from BAC transgenics to computational approaches. These approaches will be discussed, along with the roles of some new transcriptional players in adipogenesis, including the O/E family of proteins.

Adipocytes↗
PubMed2005

Mutational analysis of PPARG as a candidate tumour suppressor gene in enteropancreatic endocrine tumours.

OBJECTIVES: Loss of heterozygosity (LOH) or deletion of chromosome 3p is a frequent finding in enteropancreatic endocrine tumours (EPETs), suggesting the pathogenetic involvement of one or more tumour suppressor genes on 3p. PPARG, the gene encoding the gamma isoform of the peroxisome proliferator-activated receptor (PPARgamma), is highly expressed in normal human pancreatic islet cells, is located at 3p25, and has been reported to sustain loss-of-function mutations in human colorectal carcinomas. Additionally, the development of islet cell hyperplasia in an islet cell-specific pparg knockout mouse has further emphasized the attractiveness of PPARG as a candidate gene important in the pathogenesis of EPETs. Therefore, we sought to examine PPARG for intragenic inactivating mutations, the evidence needed to rigorously establish it as a tumour suppressor in EPETs. PATIENTS AND DESIGN: Twenty-three EPETs from 20 patients were examined for coding region mutations in PPARG and for LOH on 3p at microsatellite markers flanking PPARG. RESULTS: LOH on 3p was detected in tumours from six patients (30%), but no intragenic mutations were detected in PPARG, whether or not LOH was present. CONCLUSION: These findings strongly suggest that PPARG does not commonly function as a classical tumour suppressor gene in the pathogenesis of EPETs.

DNA Mutational Analysis↗
PubMed2004

Absence of a reductase, NCB5OR, causes insulin-deficient diabetes.

NCB5OR is a highly conserved NAD(P)H reductase that contains a cytochrome b5-like domain at the N terminus and a cytochrome b5 reductase-like domain at the C terminus. The enzyme is located in the endoplasmic reticulum (ER) and is widely expressed in organs and tissues. Targeted inactivation of this gene in mice has no impact on embryonic or fetal viability. At 4 weeks of age, Ncb5or-/- mice have normal blood glucose levels but impaired glucose tolerance. Isolated Ncb5or-/- islets have markedly impaired glucose- or arginine-stimulated insulin secretion. By 7 weeks of age, these mice develop severe hyperglycemia with markedly decreased serum insulin levels and nearly normal insulin tolerance. As the animals age, there is a progressive loss of beta cells in pancreatic islets, but there is no loss of alpha, delta, or PP cells. Electron microscopy reveals degranulation of beta cells and hypertrophic and hyperplastic mitochondria, some of which contain electron dense inclusions. Four-week-old Ncb5or-/- mice have enhanced sensitivity to the diabetogenic agent streptozotocin. NCB5OR appears to play a critical role in protecting pancreatic beta cells against oxidant stress.

Animals↗
PubMed2004

Peroxisome proliferator-activated receptor-gamma-independent repression of collagenase gene expression by 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid and prostaglandin 15-deoxy-delta(12,14) J2: a role for Smad signaling.

Matrix metalloproteinases (MMPs) degrade extracellular matrix components, and overexpression of these enzymes contributes to tissue destruction in arthritis. Of particular importance are the collagenases, MMP-1 and MMP-13, which have high activity against the interstitial collagens in cartilage. In this study, we address the mechanisms of two inhibitors of collagenase gene expression, the synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and 15-deoxy-delta(12,14)-prostaglandin J2 (15-dPGJ2). Although both inhibitors are ligands for the nuclear hormone receptor peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a connection between PPAR-gamma and collagenase gene expression has yet to be established. Here, we test the hypothesis that CDDO and 15-dPGJ2 use PPAR-gamma to repress MMP gene expression. Our findings with the PPAR-gamma antagonist 2-[4-[2-[3-(2,4-difluorophenyl)-1-heptylureido]ethyl]rsqb]-phenylsulfanyl]-2-methylpropionic acid (GW9662) and mouse embryonic fibroblasts lacking PPAR-gamma demonstrate that CDDO and 15-dPGJ2 use PPAR-gamma-independent mechanisms to inhibit collagenase gene expression. To address a potential PPAR-gamma-independent mechanism leading to the repression of MMPs by CDDO, we tested the effect of CDDO on the transforming growth factor-beta (TGF-beta) signaling pathway. We found that CDDO requires Smads (transcription factors activated by TGF-beta) for the repression of MMP-1. Specifically, MMP-1 is inhibited neither by CDDO in the absence of TGF-beta receptor-activated Smad3 nor when a negative regulator, Smad7, attenuates TGF-beta signaling. We conclude that CDDO represses MMP gene expression through a novel PPAR-gamma-independent mechanism that requires Smad signaling.

Animals↗
PubMed2003

Targeted elimination of peroxisome proliferator-activated receptor gamma in beta cells leads to abnormalities in islet mass without compromising glucose homeostasis.

The nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPAR gamma) is an important regulator of lipid and glucose homeostasis and cellular differentiation. Studies of many cell types in vitro and in vivo have demonstrated that activation of PPAR gamma can reduce cellular proliferation. We show here that activation of PPAR gamma is sufficient to reduce the proliferation of cultured insulinoma cell lines. We created a model with mice in which the expression of the PPARG gene in beta cells was eliminated (beta gamma KO mice), and these mice were found to have significant islet hyperplasia on a chow diet. Interestingly, the normal expansion of beta-cell mass that occurs in control mice in response to high-fat feeding is markedly blunted in these animals. Despite this alteration in beta-cell mass, no effect on glucose homeostasis in beta gamma KO mice was noted. Additionally, while thiazolidinediones enhanced insulin secretion from cultured wild-type islets, administration of rosiglitazone to insulin-resistant control and beta gamma KO mice revealed that PPAR gamma in beta cells is not required for the antidiabetic actions of these compounds. These data demonstrate a critical physiological role for PPAR gamma function in beta-cell proliferation and also indicate that the mechanisms controlling beta-cell hyperplasia in obesity are different from those that regulate baseline cell mass in the islet.

Animals↗
PubMed2003

Muscle-specific PPARgamma-deficient mice develop increased adiposity and insulin resistance but respond to thiazolidinediones.

Activation of peroxisome proliferator-activated receptor gamma (PPARgamma) by thiazolidinediones (TZDs) improves insulin resistance by increasing insulin-stimulated glucose disposal in skeletal muscle. It remains debatable whether the effect of TZDs on muscle is direct or indirect via adipose tissue. We therefore generated mice with muscle-specific PPARgamma knockout (MuPPARgammaKO) using Cre/loxP recombination. Interestingly, MuPPARgammaKO mice developed excess adiposity despite reduced dietary intake. Although insulin-stimulated glucose uptake in muscle was not impaired, MuPPARgammaKO mice had whole-body insulin resistance with a 36% reduction (P < 0.05) in the glucose infusion rate required to maintain euglycemia during hyperinsulinemic clamp, primarily due to dramatic impairment in hepatic insulin action. When placed on a high-fat diet, MuPPARgammaKO mice developed hyperinsulinemia and impaired glucose homeostasis identical to controls. Simultaneous treatment with TZD ameliorated these high fat-induced defects in MuPPARgammaKO mice to a degree identical to controls. There was also altered expression of several lipid metabolism genes in the muscle of MuPPARgammaKO mice. Thus, muscle PPARgamma is not required for the antidiabetic effects of TZDs, but has a hitherto unsuspected role for maintenance of normal adiposity, whole-body insulin sensitivity, and hepatic insulin action. The tissue crosstalk mediating these effects is perhaps due to altered lipid metabolism in muscle.

Adipose Tissue↗
PubMed2002

Genetic analysis of adipogenesis through peroxisome proliferator-activated receptor gamma isoforms.

Peroxisome proliferator-activated receptor (PPAR) gamma is a nuclear receptor that is a key regulator of adipogenesis and is present in two isoforms generated by alternative splicing, PPARgamma1 and PPARgamma2. Studies of the ability of each isoform to stimulate fat differentiation have yielded ambiguous results, in part because PPARgamma stimulates its own expression. We have thus undertaken a formal genetic analysis using PPARgamma-null fibroblast cell lines to assess the specific role of each individual isoform in adipogenesis. We show here that both PPARgamma1 and PPARgamma2 have the intrinsic ability to stimulate robust adipogenesis. Adipose cells stimulated by either PPARgamma1 or PPARgamma2 express a similar gene profile and show similar responses to insulin. However, in response to low ligand concentrations, PPARgamma2 shows a quantitatively greater ability to induce adipogenesis. Analyses involving coactivator binding and transcriptional assays indicate that PPARgamma2 has an enhanced ability to bind components of the DRIP/TRAP complex, coactivators required for fat differentiation.

Adipocytes↗
PubMed2002

C/EBPalpha induces adipogenesis through PPARgamma: a unified pathway.

PPARgamma and C/EBPalpha are critical transcription factors in adipogenesis, but the precise role of these proteins has been difficult to ascertain because they positively regulate each other's expression. Questions remain about whether these factors operate independently in separate, parallel pathways of differentiation, or whether a single pathway exists. PPARgamma can promote adipogenesis in C/EBPalpha-deficient cells, but the converse has not been tested. We have created an immortalized line of fibroblasts lacking PPARgamma, which we use to show that C/EBPalpha has no ability to promote adipogenesis in the absence of PPARgamma. These results indicate that C/EBPalpha and PPARgamma participate in a single pathway of fat cell development with PPARgamma being the proximal effector of adipogenesis.

Adipocytes↗
PubMed2002

The molecular control of adipogenesis, with special reference to lymphatic pathology.

Adipogenesis is the process by which mature fat cells are formed from pre-adipocytes. Adipogenesis has come under increasing scrutiny not only because the availability of reliable in vitro models makes it an attractive choice for developmental studies, but also because adipocytes are increasingly recognized as major players in a variety of physiological and pathophysiological states, such as obesity and type 2 diabetes. Adipocytes develop from mesenchymal stem cell precursors that are characterized by multipotency. Under the influence of various cues, these cells become committed to the adipocyte lineage. Further hormonal stimulation recruits these pre-adipocytes to accumulate lipid, express fat-specific markers, and become sensitive to the metabolic effects of insulin. A complex transcriptional cascade regulates this process, involving several distinct classes of transcription factor. In particular, the role of the nuclear hormone receptor PPARgamma will be discussed, along with bZip family members C/EBPalpha, C/EBPbeta, and C/EBPdelta. The relationship of adipose depots to the lymphatic system will also be discussed.

Adipocytes↗