Stearoyl-CoA desaturase (SCD) is a central lipogenic enzyme catalyzing the synthesis of monounsaturated fatty acids, mainly oleate (C18:1) and palmitoleate (C16:1), which are components of membrane phospholipids, triglycerides, wax esters, and cholesterol esters. Several SCD isoforms (SCD1-3) exist in the mouse. Here we show that mice with a targeted disruption of the SCD1 isoform have reduced body adiposity, increased insulin sensitivity, and are resistant to diet-induced weight gain. The protection from obesity involves increased energy expenditure and increased oxygen consumption. Compared with the wild-type mice the SCD1؊͞؊ mice have increased levels of plasma ketone bodies but reduced levels of plasma insulin and leptin. In the SCD1؊͞؊ mice, the expression of several genes of lipid oxidation are up-regulated, whereas lipid synthesis genes are down-regulated. These observations suggest that a consequence of SCD1 deficiency is an activation of lipid oxidation in addition to reduced triglyceride synthesis and storage.S tearoyl-CoA desaturase (SCD) is the rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids. It catalyzes the introduction of the cis double bond in the ⌬9 position of fatty acyl-CoA substrates. The preferred desaturation substrates are palmitoyl-CoA and stearoyl-CoA, which are converted to palmitoleoyl-CoA (16:1) and oleoyl-CoA (18:1), respectively (1-4). These fatty acids are requisite components of membrane phospholipids, triglycerides, cholesterol esters, and wax esters (5-7). Effects on composition of phospholipids ultimately determine membrane fluidity, and the effects on the composition of cholesterol esters and triglycerides can affect lipoprotein metabolism and adiposity. SCD expression is sensitive to dietary factors including polyunsaturated fatty acids, cholesterol and vitamin A, hormonal changes (i.e., insulin and glucagon), developmental processes, temperature changes, thiazolinediones, metals, alcohol, peroxisomal proliferators, and phenolic compounds (3). High SCD activity has been implicated in a wide range of disorders including diabetes, atherosclerosis, cancer, obesity, and viral infection (3,(8)(9)(10)(11)(12)(13).The existence of multiple SCD isoforms in mice (6, 14-18) and rats makes it difficult to determine the role of each isoform in lipid metabolism. New insights into the physiological role of the SCD1 gene and its endogenous products came from recent studies of the asebia mouse strains (ab j and ab 2j ) that have naturally occurring mutations in SCD1 (17-19) as well as a laboratory mouse model with a targeted disruption (SCD1Ϫ͞Ϫ) (6). We used these animal models to show that SCD1Ϫ͞Ϫ mice are deficient in hepatic triglycerides and cholesterol esters (7,20). The levels of palmitoleate (16:1) and oleate (18:1) are reduced, whereas palmitate and stearate are increased in the lipid fractions of SCD1Ϫ͞Ϫ mice. On a high carbohydrate diet supplemented with triolein, the cholesterol ester levels are corrected but the triglyceride levels are not reversed to the ...

DNA microarrays provide for unprecedented large-scale views of gene expression and, as a result, have emerged as a fundamental measurement tool in the study of diverse biological systems. Statistical questions abound, but many traditional data analytic approaches do not apply, in large part because thousands of individual genes are measured with relatively little replication. Empirical Bayes methods provide a natural approach to microarray data analysis because they can significantly reduce the dimensionality of an inference problem while compensating for relatively few replicates by using information across the array. We propose a general empirical Bayes modelling approach which allows for replicate expression profiles in multiple conditions. The hierarchical mixture model accounts for differences among genes in their average expression levels, differential expression for a given gene among cell types, and measurement fluctuations. Two distinct parameterizations are considered: a model based on Gamma distributed measurements and one based on log-normally distributed measurements. False discovery rate and related operating characteristics of the methodology are assessed in a simulation study. We also show how the posterior odds of differential expression in one version of the model is related to the ratio of the arithmetic mean to the geometric mean of the two sample means. The methodology is used in a study of mammary cancer in the rat, where four distinct patterns of expression are possible.

In a microarray experiment, messenger RNA samples are oftentimes pooled across subjects out of necessity, or in an effort to reduce the effect of biological variation. A basic problem in such experiments is to estimate the nominal expression levels of a large number of genes. Pooling samples will affect expression estimation, but the exact effects are not yet known as the approach has not been systematically studied in this context. We consider how mRNA pooling affects expression estimates by assessing the finite-sample performance of different estimators for designs with and without pooling. Conditions under which it is advantageous to pool mRNA are defined; and general properties of estimates from both pooled and non-pooled designs are derived under these conditions. A formula is given for the total number of subjects and arrays required in a pooled experiment to obtain gene expression estimates and confidence intervals comparable to those obtained from the no-pooling case. The formula demonstrates that by pooling a perhaps increased number of subjects, one can decrease the number of arrays required in an experiment without a loss of precision. The assumptions that facilitate derivation of this formula are considered using data from a quantitative real-time PCR experiment. The calculations are not specific to one particular method of quantifying gene expression as they assume only that a single, normalized, estimate of expression is obtained for each gene. As such, the results should be generally applicable to a number of technologies provided sufficient pre-processing and normalization methods are available and applied.

We previously mapped the type 2 diabetes mellitus-2 locus (T2dm2), which affects fasting insulin levels, to distal chromosome 19 in a leptin-deficient obese F2 intercross derived from C57BL/6 (B6) and BTBR T+ tf/J (BTBR) mice. Introgression of a 7-Mb segment of the B6 chromosome 19 into the BTBR background (strain 1339A) replicated the reduced insulin linked to T2dm2. The 1339A mice have markedly impaired insulin secretion in vivo and disrupted islet morphology. We used subcongenic strains derived from 1339A to localize the T2dm2 quantitative trait locus (QTL) to a 242-kb segment comprising the promoter, first exon and most of the first intron of the Sorcs1 gene. This was the only gene in the 1339A strain for which we detected amino acid substitutions and expression level differences between mice carrying B6 and BTBR alleles of this insert, thereby identifying variation within the Sorcs1 gene as underlying the phenotype associated with the T2dm2 locus. SorCS1 binds platelet-derived growth factor, a growth factor crucial for pericyte recruitment to the microvasculature, and may thus have a role in expanding or maintaining the islet vasculature. Our identification of the Sorcs1 gene provides insight into the pathway underlying the pathophysiology of obesity-induced type 2 diabetes mellitus.

Cardiac injury in neonatal 1-day-old mice stimulates a regenerative response characterized by reactive cardiomyocyte proliferation, which is distinguished from the fibrotic repair process in adults. Acute inflammation occurs immediately after heart injury and has generally been believed to exert a negative effect on heart regeneration by promoting scar formation in adults; however, little is known about the role of acute inflammation in the cardiac regenerative response in neonatal mice. Here, we show that acute inflammation induced cardiomyocyte proliferation after apical intramyocardial microinjection of immunogenic zymosan A particles into the neonatal mouse heart. We also found that cardiac injury-induced regenerative response was suspended after immunosuppression in neonatal mice, and that cardiomyocytes could not be reactivated to proliferate after neonatal heart injury in the absence of interleukin-6 (IL-6). Furthermore, cardiomyocyte-specific deletion of signal transducer and activator of transcription 3 (STAT3), the major downstream effector of IL-6 signaling, decreased reactive cardiomyocyte proliferation after apical resection. Our results indicate that acute inflammation stimulates the regenerative response in neonatal mouse heart, and suggest that modulation of inflammatory signals might have important implications in cardiac regenerative medicine.

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G protein-coupled receptor 119 (GPR119) is expressed in pancreatic islets and intestine, and is involved in insulin and incretin hormone release. GPR119-knockout (Gpr119−/−) mice were reported to have normal islet morphology and normal size, body weight (BW), and fed/fasted glucose levels. However, the physiological function of GPR119 and its role in maintaining glucose homeostasis under metabolic stress remain unknown. Here, we report the phenotypes of an independently generated line of Gpr119−/− mice under basal and high-fat diet (HFD)-induced obesity. Under low-fat diet feeding, Gpr119−/− mice show normal plasma glucose and lipids, but have lower BWs and lower post-prandial levels of active glucagon-like peptide 1 (GLP-1). Nutrient-stimulated GLP-1 release is attenuated in Gpr119−/− mice, suggesting that GPR119 plays a role in physiological regulation of GLP-1 secretion. Under HFD-feeding, both Gpr119+/+ and Gpr119−/− mice gain weight similarly, develop hyperinsulinemia and hyperleptinemia, but not hyperglycemia or dyslipidemia. Glucose and insulin tolerance tests did not reveal a genotypic difference. These data show that GPR119 is not essential for the maintenance of glucose homeostasis. Moreover, we found that oleoylethanolamide (OEA), reported as a ligand for GPR119, was able to suppress food intake in both Gpr119+/+ and Gpr119−/− mice, indicating that GPR119 is not required for the hypophagic effect of OEA. Our results demonstrate that GPR119 is important for incretin and insulin secretion, but not for appetite suppression.

The lipogenic gene stearoyl-CoA desaturase (SCD)1 appears to be a promising new target for obesity-related diabetes, as mice deficient in this enzyme are resistant to diet-and leptin deficiency-induced obesity. The BTBR mouse strain replicates many features of insulin resistance found in humans with excess visceral adiposity. Using the hyperinsulinemic-euglycemic clamp technique, we determined that insulin sensitivity was improved in heart, soleus muscle, adipose tissue, and liver of BTBR SCD1-deficient mice. We next determined whether SCD1 deficiency could prevent diabetes in leptin-deficient BTBR mice. Loss of SCD1 in leptin ob/ob mice unexpectedly accelerated the progression to severe diabetes; 6-week fasting glucose increased ϳ70%. In response to a glucose challenge, Scd1 Ϫ/Ϫ leptin ob/ob mice had insufficient insulin secretion, resulting in glucose intolerance. A morphologically distinct class of islets isolated from the Scd1 Ϫ/Ϫ leptin ob/ob mice had reduced insulin content and increased triglycerides, free fatty acids, esterified cholesterol, and free cholesterol and also a much higher content of saturated fatty acids. We believe the accumulation of lipid is due to an upregulation of lipoprotein lipase (20-fold) and Cd36 (167-fold) and downregulation of lipid oxidation genes in this class of islets. Therefore, although loss of Scd1 has beneficial effects on adiposity, this benefit may come at the expense of ␤-cells, resulting in an increased risk of diabetes. Diabetes 56:1228-1239, 2007 S tearoyl-CoA desaturase (SCD) catalyzes the synthesis of monounsaturated fatty acids by introducing a cis double bond in the ⌬9 position of saturated 16-and 18-carbon fatty acyl-CoA substrates. The products of SCD, palmitoleoyl-CoA and oleoylCoA, are the most abundant monounsaturated fatty acids of phospholipids, triglycerides, cholesterol esters, and wax esters (1). Various diseases, including cancer, obesity, diabetes, and atherosclerosis, are associated with an imbalance in the ratio of saturated to monounsaturated fatty acids (2). Two human and four mouse isoforms of SCD have been characterized. SCD1 is the primary isoform found in lipogenic tissues.Loss of Scd1 is protective against obesity (3-5). The decreased adiposity in the Scd1 Ϫ/Ϫ mice is due to reduced lipid synthesis and increased energy expenditure through enhanced fatty acid oxidation (3). Scd1 Ϫ/Ϫ mice have an increase in insulin signaling and glucose uptake in muscle and brown adipose tissue (6,7).Leptin-deficient BTBR leptin ob/ob mice are a particularly useful animal model for studying obesity-related diabetes. Unlike the B6 leptin ob/ob mice, which develop only moderate hyperglycemia, BTBR leptin ob/ob mice become severely diabetic (8 -10). The diabetic BTBR leptin ob/ob mice have increased Scd1 expression in muscle and decreased expression in adipose tissue and liver, compared with nondiabetic B6 leptin ob/ob mice (10). Insulin resistance is often correlated with abdominal obesity. The BTBR mouse strain has excess abdominal obesity associated with ins...