Metabolic consequences of ENPP1 overexpression in adipose tissue.

Ectonucleotide pyrophosphate phosphodiesterase (ENPP1) has been shown to negatively modulate insulin receptor and to induce cellular insulin resistance when overexpressed in various cell types. Systemic insulin resistance has also been observed when ENPP1 is overexpressed in multiple tissues of transgenic models and attributed largely to tissue insulin resistance induced in skeletal muscle and liver. Another key tissue in regulating glucose and lipid metabolism is adipose tissue (AT). Interestingly, obese patients with insulin resistance have been reported to have increased AT ENPP1 expression. However, the specific effects of ENPP1 in AT have not been studied. To better understand the specific role of AT ENPP1 on systemic metabolism, we have created a transgenic mouse model (C57/Bl6 background) with targeted overexpression of human ENPP1 in adipocytes, using aP2 promoter in the transgene construct (AdiposeENPP1-TG). Using either regular chow or pair-feeding protocol with 60% fat diet, we compared body fat content and distribution and insulin signaling in adipose, muscle, and liver tissues of AdiposeENPP1-TG and wild-type (WT) siblings. We also compared response to intraperitoneal glucose tolerance test (IPGTT) and insulin tolerance test (ITT). Our results show no changes in Adipose ENPP1-TG mice fed a regular chow diet. After high-fat diet with pair-feeding protocol, AdiposeENPP1-TG and WT mice had similar weights. However, AdiposeENPP1-TG mice developed fatty liver in association with changes in AT characterized by smaller adipocyte size and decreased phosphorylation of insulin receptor Tyr(1361) and Akt Ser(473). These changes in AT function and fat distribution were associated with systemic abnormalities of lipid and glucose metabolism, including increased plasma concentrations of fatty acid, triglyceride, plasma glucose, and insulin during IPGTT and decreased glucose suppression during ITT. Thus, our results show that, in the presence of a high-fat diet, ENPP1 overexpression in adipocytes induces fatty liver, hyperlipidemia, and dysglycemia, thus recapitulating key manifestations of the metabolic syndrome.

Endogenous endothelin-1 is required for cardiomyocyte survival in vivo.

BACKGROUND: Endothelin-1 (ET-1) has potent vasoconstrictor and hypertrophic actions. Pharmacological antagonists of endothelin receptors attenuate cardiac hypertrophy, have been approved for treatment of pulmonary hypertension, and are under investigation for treatment of heart failure. To investigate the role of ET-1 in the heart, we created mice with cardiomyocyte deletion of ET-1. METHODS AND RESULTS: Mice with cardiomyocyte-specific deletion of ET-1 are phenotypically normal when young. Remarkably, as the mice age or when young animals are subjected to aortic banding, they develop an unexpected phenotype of progressive systolic dysfunction and cardiac dilation. Echocardiography, necropsy, histology, and molecular phenotype confirm a dilated cardiomyopathy. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling analysis reveals greater abundance of apoptotic nuclei in the ET-1-deficient hearts. Transcriptional and Western analyses suggest enhanced tumor necrosis factor (TNF)-mediated apoptosis with increases in caspase-8 activity. These ET-1-deficient hearts also have diminished nuclear factor (NF)-kappaB activity, resulting in diminution of downstream inhibitors of TNF signaling. CONCLUSIONS: Local ET-1 gene expression is necessary to maintain normal cardiac function and cardiomyocyte survival in mice with both age and hemodynamic stress. This cardiac-protective effect is mediated by paracrine ET-1 modulation of TNF-related apoptosis, in part through upregulation of NF-kappaB signaling.

Effects of ultrasound-targeted microbubble destruction on cardiac gene expression.

Ultrasound (US) contrast agents are increasingly used in diagnostic echocardiography. Recent studies have suggested unanticipated effects of microbubble destruction. This study was designed to evaluate gene regulation caused by US-mediated destruction of microbubbles in the heart. During IV infusion of Optison trade mark, triggered US was applied to rat hearts to destroy microbubbles. A control group received only saline and US. RNA was isolated from hearts 24 and 72 h after treatment. Analysis with a deeply representative murine cardiac-specific microarray was used to identify regulated genes. Real-time polymerase chain reaction (PCR) was then applied to verify regulated genes. Microarray analysis revealed only 5 regulated genes in the 24-h group and 4 in the 72-h group. Of these genes, only carbonic anhydrase was significantly upregulated in the 24-h Optison trade mark group (4.3 fold; p = 0.0005) when examined in individual animals by real-time PCR. By this very sensitive technique, the bioeffects of microbubble destruction are negligible.

Adipose tissue dysfunction in humans: a potential role for the transmembrane protein ENPP1.

CONTEXT: Adipose tissue (AT) helps to regulate body fat partitioning and systemic lipid/glucose metabolism. We have recently reported lipid/glucose metabolism abnormalities and increased liver triglyceride content in an AT-selective transgenic model overexpressing ectonucleotide pyrophosphatase/phosphodiesterase-1 (ENPP1), the AdiposeENPP1-Tg mouse. OBJECTIVE: The aim of the study was to test the translational hypothesis that AT-ENPP1 overexpression associates with AT dysfunction (changes in AT gene expression, plasma fatty acid, and adipokine levels), increased liver triglyceride deposition, and systemic insulin resistance in humans. DESIGN/SETTING/PARTICIPANTS: A total of 134 young normoglycemic men and women were subjected to body composition studies, hyperinsulinemic-euglycemic clamps, and AT needle biopsy. Twenty men also had liver/muscle nuclear magnetic resonance spectroscopy. MAIN OUTCOME MEASURES: Predetermined measures included AT expression of ENPP1 and other lipid metabolism/inflammation genes, plasma adipokines, and nonesterified fatty acid (NEFA) levels, liver/muscle triglyceride content, and the systemic glucose disposal rate. RESULTS: After statistical adjustment for body fat content, increasing AT-ENPP1 was associated with up-regulation of genes involved in NEFA metabolism and inflammation, increased postabsorptive NEFA levels, decreased plasma adiponectin, increased liver triglyceride content, and systemic insulin resistance in men. In women, there were no changes in plasma adiponectin, NEFAs, or glucose disposal rate associated with increasing AT-ENPP1, despite increased expression of lipid metabolism and inflammation genes in AT. CONCLUSIONS: Increased AT-ENPP1 is associated with AT dysfunction, increased liver triglyceride deposition, and systemic insulin resistance in young normoglycemic men. These findings are concordant with the AdiposeENPP1-Tg phenotype and identify a potential target of therapy for health complications of AT dysfunction, including type 2 diabetes and cardiovascular disease.

Gene expression profile of rat adipose tissue at the onset of high-fat-diet obesity.

Morbid obesity is the result of massive expansion of white adipose tissue (WAT) and requires recruitment of adipocyte precursor cells and their supporting infrastructure. To characterize the change in the expression profile of the preexisting WAT at the start of obesity, when adipocyte hypertrophy is present but hyperplasia is still minimal, we employed a cDNA subtraction screen for genes differentially expressed in epididymal fat pads harvested 1 wk after the start of a 60% fat diet. Ninety-six genes were upregulated by at least 50% above the WAT of control rats receiving a 4% fat diet. Of these genes, 30 had not previously been identified. Sixteen of the 96 genes, including leptin, adipocyte complement-related protein 30 kDa, and resistin, were predicted to encode a signal peptide. Ten of the 16 had been previously identified in other tissues and implicated in cell growth, proliferation, differentiation, cell cycle control, and angiogenesis. One was a novel gene. Twenty-nine novel fragments were identified. Thus, at the onset of high-fat-diet-induced obesity in rats, adipose tissue increases its expression of factors previously implicated in the expansion of nonadipocyte tissues and of several uncharacterized novel factors. The only one of these thus far characterized functionally was found to promote lipogenesis.