Adipocyte STAT5 (signal transducer and activator of transcription 5) is not required for glucocorticoid-induced metabolic dysfunction.

Excess glucocorticoid (GC) signaling in adipose tissue is a key driver of insulin resistance and hepatic steatosis, but underlying mechanisms have not been fully elucidated. Signal transducer and activator of transcription 5 (STAT5) signaling in adipocytes has also been implicated in the progression of similar metabolic disturbances. Although STAT5 has been shown to interact with the glucocorticoid receptor (GR) in many cell types including adipocytes, the relevance of the STAT5/GR complex has not been investigated in adipocytes. Adult male and female adipocyte-specific STAT5 knockout (STAT5AKO) and floxed mice were given corticosterone (CORT) or vehicle in their drinking water for 1 wk and examined for differences in their metabolic responses to GC excess. CORT-induced lipolysis, insulin resistance, and changes in body composition were comparable between genotypes and in both sexes. Adipocyte STAT5 is not necessary for GC-mediated progression of metabolic disease.NEW & NOTEWORTHY Both STAT5 and glucocorticoid receptor contribute to metabolic processes and type 2 diabetes, in large part, due to their functions in adipocytes. These two transcription factors can form a complex and function together. Our novel studies determined the role of adipocyte STAT5 in glucocorticoid-induced diabetes. We observed that STAT5 in adipocytes is not needed for glucocorticoid-induced diabetes.

Loss of Adipocyte STAT5 Confers Increased Depot-Specific Adiposity in Male and Female Mice That Is Not Associated With Altered Adipose Tissue Lipolysis.

STATs (Signal Transducers and Activators of Transcription) 5A and 5B are induced during adipocyte differentiation and are primarily activated by growth hormone (GH) and prolactin in fat cells. Previous studies in mice lacking adipocyte GH receptor or STAT5 support their roles in lipolysis-mediated reduction of adipose tissue mass. Male and female mice harboring adipocyte-specific deletion of both STAT5 genes (STAT5AKO) exhibit increased subcutaneous or inguinal adipose tissue mass, but no changes in visceral or gonadal fat mass. Both depots display substantial increases in adipocyte size with no changes in lipolysis in adipose tissue explants. RNA sequencing analysis of subcutaneous adipose tissue and indirect calorimetry experiments reveal sex-dependent differences in adipose gene expression and whole-body energy expenditure, respectively, resulting from the loss of adipocyte STAT5.

Adaptive Fat Oxidation Is Coupled with Increased Lipid Storage in Adipose Tissue of Female Mice Fed High Dietary Fat and Sucrose.

Western diets high in fat and sucrose are associated with metabolic syndrome (MetS). Although the prevalence of MetS in women is comparable to that in men, metabolic adaptations in females to Western diet have not been reported in preclinical studies. This study investigates the effects of Western diet on risk factors for MetS in female mice. Based on our earlier studies in male mice, we hypothesized that dietary supplementation with extracts of Artemisia dracunculus L. (PMI5011) and Momordica charantia (bitter melon) could affect MetS risk factors in females. Eight-week-old female mice were fed a 10% kcal fat, 17% kcal sucrose diet (LFD); high-fat, high-sucrose diet (HFS; 45% kcal fat, 30% kcal sucrose); or HFS diet with PMI5011 or bitter melon for three months. Body weight and adiposity in all HFS groups were greater than the LFD. Total cholesterol level was elevated with the HFS diets along with LDL cholesterol, but triglycerides and free fatty acids were unchanged from the LFD. Over the three month period, female mice responded to the HFS diet by adaptive increases in fat oxidation energy in muscle and liver. This was coupled with increased fat storage in white and brown adipose tissue depots. These responses were enhanced with botanical supplementation and confer protection from ectopic lipid accumulation associated with MetS in female mice fed an HFS diet.

Hepatic IKKε expression is dispensable for high-fat feeding-induced increases in liver lipid content and alterations in glucose tolerance.

There are endocrine and immunological changes that occur during onset and progression of the overweight and obese states. The inhibitor of nuclear factor-κB kinase-ε (IKKε) was originally described as an inducible protein kinase; whole body gene deletion or systemic pharmaceutical targeting of this kinase improved insulin sensitivity and glucose tolerance in mice. To investigate the primary sites of action associated with IKKε during weight gain, we describe the first mouse line with conditional elimination of IKKε in the liver (IKKεAlb-/-). IKKεAlb-/- mice and littermate controls gain weight, show similar changes in body composition, and do not display any improvements in insulin sensitivity or whole body glucose tolerance. These studies were conducted using breeder chow diets and matched low- vs. high-fat diets. While glycogen accumulation in the liver is reduced in IKKεAlb-/- mice, lipid storage in liver is similar in IKKεAlb-/- mice and littermate controls. Our results using IKKεAlb-/- mice suggest that the primary action of this kinase to impact insulin sensitivity during weight gain lies predominantly within extrahepatic tissues.

Correction to: Siah2 modulates sex-dependent metabolic and inflammatory responses in adipose tissue to a high-fat diet challenge.

Following publication of the original article [1], the authors reported that additional file 1 was incorrect. The corrected additional file 1 is given below.

Extensive metabolic remodeling after limiting mitochondrial lipid burden is consistent with an improved metabolic health profile.

Mitochondrial lipid overload in skeletal muscle contributes to insulin resistance, and strategies limiting this lipid pressure improve glucose homeostasis; however, comprehensive cellular adaptations that occur in response to such an intervention have not been reported. Herein, mice with skeletal muscle-specific deletion of carnitine palmitoyltransferase 1b (Cpt1bM-/-), which limits mitochondrial lipid entry, were fed a moderate fat (25%) diet, and samples were subjected to a multimodal analysis merging transcriptomics, proteomics, and nontargeted metabolomics to characterize the coordinated multilevel cellular responses that occur when mitochondrial lipid burden is mitigated. Limiting mitochondrial fat entry predictably improves glucose homeostasis; however, remodeling of glucose metabolism pathways pales compared with adaptations in amino acid and lipid metabolism pathways, shifts in nucleotide metabolites, and biogenesis of mitochondria and peroxisomes. Despite impaired fat utilization, Cpt1bM-/- mice have increased acetyl-CoA (14-fold) and NADH (2-fold), indicating metabolic shifts yield sufficient precursors to meet energy demand; however, this does not translate to enhance energy status as Cpt1bM-/- mice have low ATP and high AMP levels, signifying energy deficit. Comparative analysis of transcriptomic data with disease-associated gene-sets not only predicted reduced risk of glucose metabolism disorders but was also consistent with lower risk for hepatic steatosis, cardiac hypertrophy, and premature death. Collectively, these results suggest induction of metabolic inefficiency under conditions of energy surfeit likely contributes to improvements in metabolic health when mitochondrial lipid burden is mitigated. Moreover, the breadth of disease states to which mechanisms induced by muscle-specific Cpt1b inhibition may mediate health benefits could be more extensive than previously predicted.

Siah2 modulates sex-dependent metabolic and inflammatory responses in adipose tissue to a high-fat diet challenge.

BACKGROUND: The obesity-related risk of developing metabolic syndrome is higher in males than in females of reproductive age, likely due to estrogen-mediated reduced adipose tissue inflammation and fibrosis with hypertrophied adipocytes. Depletion of the ubiquitin ligase Siah2 reduced white adipose tissue inflammation and improved glucose metabolism in obese male mice. Siah2 is a transcriptional target of estrogen, but data is lacking about the effect of Siah2 on adipose tissue of females. We therefore evaluated the impact of Siah2 deficiency on white and brown adipose tissue in females of reproductive age. METHODS: Body composition, adipose tissue morphology, brown adipose tissue gene, and protein expression and adipocyte sizing were evaluated in wild-type and Siah2KO female and male mice fed a low-fat or high-fat diet. Glucose and insulin tolerance, fasting glucose, insulin, fatty acids and triglycerides, and gene expression of inflammation markers in perigonadal fat were evaluated in wild-type and Siah2KO female mice. Microarray analysis of brown fat gene expression was carried out in both sexes. Statistical analysis was assessed by unpaired two-tailed t test and repeated measures ANOVA. RESULTS: Siah2 deficiency improves glucose and insulin tolerance in the presence of hypertrophied white adipocytes in high-fat-fed female mice with percent fat comparable to male mice. While previous studies showed Siah2KO reduces the white adipose tissue inflammatory response in male mice, the response in females is biased toward the upregulation of M2-like markers in white adipose tissue. In contrast, loss of Siah2 leads to increased whitening of brown fat in males, but not in females. This corresponded to increased expression of markers of inflammation (F4/80, Ccl2) and thermogenic genes (Pgc1alpha, Dio2, Ucp-1) and proteins (PGC-1α, UCP-1) in females. Contrary to expectations, increased expression of thermogenic markers in females was coupled with a downregulation of ERalpha and ERRgamma protein levels. CONCLUSIONS: The most striking sex-related effect of Siah2 deficiency is reduced whitening of brown fat in high-fat-fed females. Protection from accumulating unilocular adipocytes in the brown fat corresponds to increased expression of thermogenic genes and proteins in female, but not in male mice. These results raise the possibility that Siah2 contributes to the estrogen-related effects on brown fat function in males and females.

Potential adverse effects of botanical supplementation in high-fat-fed female mice.

BACKGROUND: Insulin resistance underlies metabolic syndrome and is associated with excess adiposity and visceral fat accumulation, which is more frequently observed in males than females. However, in young females, the prevalence of metabolic syndrome is rising, mainly driven by accumulation of abdominal visceral fat. The degree to which sex-related differences could influence the development of insulin resistance remains unclear, and studies of potential therapeutic strategies to combat metabolic syndrome using rodent models have focused predominantly on males. We therefore evaluated the effects of two nutritional supplements derived from botanical sources, an extract of Artemisia dracunculus L. (termed PMI5011) and Momordica charantia (commonly known as bitter melon), on female mice challenged with a high-fat diet in order to determine if dietary intake of these supplements could ameliorate obesity-induced insulin resistance and metabolic inflexibility in skeletal muscle. METHODS: Body composition, physical activity and energy expenditure, fatty acid oxidation, insulin signaling, and gene and protein expression of factors controlling lipid metabolism and ectopic lipid accumulation were evaluated in female mice fed a high-fat diet supplemented with either PMI5011 or bitter melon. Statistical significance was assessed by unpaired two-tailed t test and repeated measures ANOVA. RESULTS: PMI5011 supplementation resulted in increased body weight and adiposity, while bitter melon did not induce changes in these parameters. Pyruvate tolerance testing indicated that both supplements increased hepatic glucose production. Both supplements induced a significant suppression in fatty acid oxidation in skeletal muscle homogenates treated with pyruvate, indicating enhanced metabolic flexibility. PMI5011 reduced lipid accumulation in skeletal muscle, while bitter melon induced a downward trend in lipid accumulation in the skeletal muscle and liver. This was accompanied by transcriptional regulation of autophagic genes by bitter melon in the liver. CONCLUSIONS: Data from the current study indicates that dietary supplementation with PMI5011 and bitter melon evokes a divergent, and generally less favorable, set of metabolic responses in female mice compared to effects previously observed in males. Our findings underscore the importance of considering sex-related variations in responses to dietary supplementation aimed at combating metabolic syndrome.

Pancreatic deletion of the interleukin-1 receptor disrupts whole body glucose homeostasis and promotes islet ß-cell de-differentiation.

OBJECTIVE: Pancreatic tissue, and islets in particular, are enriched in expression of the interleukin-1 receptor type I (IL-1R). Because of this enrichment, islet ß-cells are exquisitely sensitive to the IL-1R ligands IL-1α and IL-1ß, suggesting that signaling through this pathway regulates health and function of islet ß-cells. METHODS: Herein, we report a targeted deletion of IL-1R in pancreatic tissue (IL-1RPdx1-/-) in C57BL/6J mice and in db/db mice on the C57 genetic background. Islet morphology, ß-cell transcription factor abundance, and expression of the de-differentiation marker Aldh1a3 were analyzed by immunofluorescent staining. Glucose and insulin tolerance tests were used to examine metabolic status of these genetic manipulations. Glucose-stimulated insulin secretion was evaluated in vivo and in isolated islets ex vivo by perifusion. RESULTS: Pancreatic deletion of IL-1R leads to impaired glucose tolerance, a phenotype that is exacerbated by age. Crossing the IL-1RPdx1-/- with db/db mice worsened glucose tolerance without altering body weight. There were no detectable alterations in insulin tolerance between IL-1RPdx1-/- mice and littermate controls. However, glucose-stimulated insulin secretion was reduced in islets isolated from IL-1RPdx1-/- relative to control islets. Insulin output in vivo after a glucose challenge was also markedly reduced in IL-1RPdx1-/- mice when compared with littermate controls. Pancreatic islets from IL-1RPdx1-/- mice displayed elevations in Aldh1a3, a marker of de-differentiation, and reduction in nuclear abundance of the ß-cell transcription factor MafA. Nkx6.1 abundance was unaltered. CONCLUSIONS: There is an important physiological role for pancreatic IL-1R to promote glucose homeostasis by suppressing expression of Aldh1a3, sustaining MafA abundance, and supporting glucose-stimulated insulin secretion in vivo.

An Extract of Russian Tarragon Prevents Obesity-Related Ectopic Lipid Accumulation.

SCOPE: The primary disorder underlying metabolic syndrome is insulin resistance due to excess body weight and abdominal visceral fat accumulation. In this study, it is asked if dietary intake of an ethanolic extract from Russian tarragon (Artemisia dracunculus L., termed PMI5011), shown to improve glucose utilization by enhancing insulin signaling in skeletal muscle, could prevent obesity-induced insulin resistance, skeletal muscle metabolic inflexibility, and ectopic lipid accumulation in the skeletal muscle and liver. METHODS AND RESULTS: Male wild-type mice are fed a high-fat diet alone or supplemented with PMI5011 (1% w/w) over 3 months. Dietary intake of PMI5011 improved fatty acid oxidation and metabolic flexibility in the skeletal muscle, reduced insulin levels, and enhanced insulin signaling in the skeletal muscle and liver independent of robust changes in expression of factors that control fatty acid oxidation. This corresponds with significantly reduced lipid accumulation in the skeletal muscle and liver, although body weight gain is comparable to a high-fat diet alone. CONCLUSION: Previous studies showed that PMI5011 enhances insulin sensitivity in the setting of established obesity-induced insulin resistance. The current study demonstrates that dietary intake of PMI5011 prevents high-fat diet-induced insulin resistance, metabolic dysfunction, and ectopic lipid accumulation in the skeletal muscle and liver without reducing body weight.

Mitochondrial fat oxidation is essential for lipid-induced inflammation in skeletal muscle in mice.

Inflammation, lipotoxicity and mitochondrial dysfunction have been implicated in the pathogenesis of obesity-induced insulin resistance and type 2 diabetes. However, how these factors are intertwined in the development of obesity/insulin resistance remains unclear. Here, we examine the role of mitochondrial fat oxidation on lipid-induced inflammation in skeletal muscle. We used skeletal muscle-specific Cpt1b knockout mouse model where the inhibition of mitochondrial fatty acid oxidation results in accumulation of lipid metabolites in muscle and elevated circulating free fatty acids. Gene expression of pro-inflammatory cytokines, chemokines, and cytokine- and members of TLR-signalling pathways were decreased in Cpt1bm-/- muscle. Inflammatory signalling pathways were not activated when evaluated by multiplex and immunoblot analysis. In addition, the inflammatory response to fatty acids was reduced in primary muscle cells derived from Cpt1bm-/- mice. Gene expression of Cd11c, the M1 macrophage marker, was decreased; while Cd206, the M2 macrophage marker, was increased in skeletal muscle of Cpt1bm-/- mice. Finally, expression of pro-inflammatory markers was decreased in white adipose tissue of Cpt1bm-/- mice. We show that the inflammatory response elicited by elevated intracellular lipids in skeletal muscle is repressed in Cpt1bm-/- mice, strongly supporting the hypothesis that mitochondrial processing of fatty acids is essential for the lipid-induction of inflammation in muscle.

Impaired Mitochondrial Fat Oxidation Induces FGF21 in Muscle.

Fatty acids are the primary fuel source for skeletal muscle during most of our daily activities, and impaired fatty acid oxidation (FAO) is associated with insulin resistance. We have developed a mouse model of impaired FAO by deleting carnitine palmitoyltransferase-1b specifically in skeletal muscle (Cpt1b(m-/-)). Cpt1b(m-/-) mice have increased glucose utilization and are resistant to diet-induced obesity. Here, we show that inhibition of mitochondrial FAO induces FGF21 expression specifically in skeletal muscle. The induction of FGF21 in Cpt1b-deficient muscle is dependent on AMPK and Akt1 signaling but independent of the stress signaling pathways. FGF21 appears to act in a paracrine manner to increase glucose uptake under low insulin conditions, but it does not contribute to the resistance to diet-induced obesity.

Lactation undernutrition leads to multigenerational molecular programming of hypothalamic gene networks controlling reproduction.

BACKGROUND: Reproductive success is dependent on development of hypothalamic circuits involving many hormonal systems working in concert to regulate gonadal function and sexual behavior. The timing of pubertal initiation and progression in mammals is likely influenced by the nutritional and metabolic state, leading us to the hypothesis that transient malnutrition experienced at critical times during development may perturb pubertal progression through successive generations. To test this hypothesis we have utilized a mouse model of undernutrition during suckling by exposing lactating mothers to undernutrition. RESULTS: Using a combination of transcriptomic and biological approaches, we demonstrate that molecular programming of hypothalamus may perturb gender specific phenotypes across generations that are dependent on the nutritional environment of the lactation period. Lactation undernutrition in first (F1) generation offspring affected body composition, reproductive performance parameters and influenced the expression of genes responsible for hypothalamic neural circuits controlling reproductive function of both sexes. Strikingly, F2 offspring showed phenotypes similar to F1 progeny; however, they were sex and parental nutritional history specific. Here, we showed that deregulated expression of genes involved in kisspeptin signaling within the hypothalamus is strongly associated with a delay in the attainment of puberty in F1 and F2 male and female offspring. CONCLUSION: The early developmental plasticity of hypothalamus when challenged with undernutrition during postnatal development not only leads to altered expression of genes controlling hypothalamic neural circuits, altered body composition, delayed puberty and disturbed reproductive performance in F1 progeny, but also affects F2 offspring, depending on parental malnutrition history and in sexually dimorphic manner.

An adenovirus-derived protein: A novel candidate for anti-diabetic drug development.

AIMS: Exposure to human adenovirus Ad36 is causatively and correlatively linked with better glycemic control in animals and humans, respectively. Although the anti-hyperglycemic property of Ad36 may offer some therapeutic potential, it is impractical to use an infectious agent for therapeutic benefit. Cell-based studies identified that Ad36 enhances cellular glucose disposal via its E4orf1 protein. Ability to improve glycemic control in vivo is a critical prerequisite for further investigating the therapeutic potential of E4orf1. Therefore, the aim of this study was to determine the ability of E4orf1 to improve glycemic control independent of insulin despite high fat diet. MATERIALS & METHODS: 8-9wk old male C57BL/6J mice fed a high-fat diet (60% kcal) were injected with a retrovirus plasmid expressing E4orf1, or a null vector (Control). Glycemic control was determined by glucose and insulin tolerance test. Islet cell size, amount of insulin and glucagon were determined in formalin-fixed pancreas. Rat insulinoma cell line (832/13) was infected with E4orf1 or control to determine changes in glucose stimulated insulin secretion. Protein from flash frozen adipose tissue depots, liver and muscle was used to determine molecular signaling by western blotting. RESULTS: In multiple experiments, retrovirus-mediated E4orf1 expression in C57BL/6J mice significantly and reproducibly improved glucose excursion following a glucose load despite a high fat diet (60% energy). Importantly, E4orf1 improved glucose clearance without increasing insulin sensitivity, production or secretion, underscoring its insulin-independent effect. E4orf1 modulated molecular signaling in mice tissue, which included greater protein abundance of adiponectin, p-AKT and Glucose transporter Glu4. CONCLUSIONS: This study provides the proof of concept for translational development of E4orf1 as a potential anti-diabetic agent. High fat intake and impaired insulin signaling are often associated with obesity, diabetes and insulin resistance. Hence, the ability of E4orf1 to improve glycemic control despite high fat diet and independent of insulin, is particularly attractive.

UCP1 is an essential mediator of the effects of methionine restriction on energy balance but not insulin sensitivity.

Dietary methionine restriction (MR) by 80% increases energy expenditure (EE), reduces adiposity, and improves insulin sensitivity. We propose that the MR-induced increase in EE limits fat deposition by increasing sympathetic nervous system-dependent remodeling of white adipose tissue and increasing uncoupling protein 1 (UCP1) expression in both white and brown adipose tissue. In independent assessments of the role of UCP1 as a mediator of MR's effects on EE and insulin sensitivity, EE did not differ between wild-type (WT) and Ucp1(-/-) mice on the control diet, but MR increased EE by 31% and reduced adiposity by 25% in WT mice. In contrast, MR failed to increase EE or reduce adiposity in Ucp1(-/-) mice. However, MR was able to increase overall insulin sensitivity by 2.2-fold in both genotypes. Housing temperatures used to minimize (28°C) or increase (23°C) sympathetic nervous system activity revealed temperature-independent effects of the diet on EE. Metabolomics analysis showed that genotypic and dietary effects on white adipose tissue remodeling resulted in profound increases in fatty acid metabolism within this tissue. These findings establish that UCP1 is required for the MR-induced increase in EE but not insulin sensitivity and suggest that diet-induced improvements in insulin sensitivity are not strictly derived from dietary effects on energy balance.

Inherent plasticity of brown adipogenesis in white fat of mice allows for recovery from effects of post-natal malnutrition.

Interscapular brown adipose tissue (iBAT) is formed during fetal development and stable for the life span of the mouse. In addition, brown adipocytes also appear in white fat depots (wBAT) between 10 and 21 days of age in mice maintained at a room temperature of 23 °C. However, this expression is transient. By 60 days of age the brown adipocytes have disappeared, but they can re-emerge if the adult mouse is exposed to the cold (5 °C) or treated with ß3-adrenergic agonists. Since the number of brown adipocytes that can be induced in white fat influences the capacity of the mouse to resist the obese state, we determined the effects of the nutritional conditions on post-natal development (birth to 21 days) of wBAT and its long-term effects on diet-induced obesity (DIO). Under-nutrition caused essentially complete suppression of wBAT in inguinal fat at 21 days of age, as indicated by expression of Ucp1 and genes of mitochondrial structure and function based upon microarray and qRT-PCR analysis, whereas over-nutrition had no discernible effects on wBAT induction. Surprisingly, the suppression of wBAT at 21 days of age did not affect DIO in adult mice maintained at 23 °C, nor did it affect the reduction in obesity or cold tolerance when DIO mice were exposed to the cold at 5 °C for one week. Gene expression analysis indicated that mice raised under conditions that suppressed wBAT at 21 days of age were able to normally induce wBAT as adults. Therefore, neither severe hypoleptinemia nor hypoinsulinemia during suckling permanently impaired brown adipogenesis in white fat. In addition, energy balance studies of DIO mice exposed to cold indicates that mice with reduced adipose stores preferentially increased food intake, whereas those with larger adipose tissue depots preferred to utilize energy from their adipose stores.

The early nutritional environment of mice determines the capacity for adipose tissue expansion by modulating genes of caveolae structure.

While the phenomenon linking the early nutritional environment to disease susceptibility exists in many mammalian species, the underlying mechanisms are unknown. We hypothesized that nutritional programming is a variable quantitative state of gene expression, fixed by the state of energy balance in the neonate, that waxes and wanes in the adult animal in response to changes in energy balance. We tested this hypothesis with an experiment, based upon global gene expression, to identify networks of genes in which expression patterns in inguinal fat of mice have been altered by the nutritional environment during early post-natal development. The effects of over- and under-nutrition on adiposity and gene expression phenotypes were assessed at 5, 10, 21 days of age and in adult C57Bl/6J mice fed chow followed by high fat diet for 8 weeks. Under-nutrition severely suppressed plasma insulin and leptin during lactation and diet-induced obesity in adult mice, whereas over-nourished mice were phenotypically indistinguishable from those on a control diet. Food intake was not affected by under- or over-nutrition. Microarray gene expression data revealed a major class of genes encoding proteins of the caveolae and cytoskeleton, including Cav1, Cav2, Ptrf (Cavin1), Ldlr, Vldlr and Mest, that were highly associated with adipose tissue expansion in 10 day-old mice during the dynamic phase of inguinal fat development and in adult animals exposed to an obesogenic environment. In conclusion gene expression profiles, fat mass and adipocyte size in 10 day old mice predicted similar phenotypes in adult mice with variable diet-induced obesity. These results are supported by phenotypes of KO mice and suggest that when an animal enters a state of positive energy balance adipose tissue expansion is initiated by coordinate changes in mRNA levels for proteins required for modulating the structure of the caveolae to maximize the capacity of the adipocyte for lipid storage.

Mesoderm-specific transcript is associated with fat mass expansion in response to a positive energy balance.

A 50-fold variation in mRNA and protein levels of the mesoderm-specific transcript gene (Mest) in white fat of C57BL/6J (B6) mice fed an obesogenic diet is positively correlated with expansion of fat mass. MEST protein was detected only in adipocytes, in which its induction occurred with both unsaturated and saturated dietary fat. To test the hypothesis that MEST modulates fat mass expansion, its expression was compared to that of stearoyl CoA desaturase (Scd1) in B6 mice exposed to diets and environmental temperatures that generated conditions separating the effects of food intake and adiposity. Under a range of conditions, Mest expression was always associated with variations in adiposity, whereas Scd1 expression was associated with the amount of saturated fat in the diet. Mest mRNA was expressed at its highest levels during early postnatal growth at the onset of the most rapid phase of fat mass expansion. MEST is localized to the endoplasmic reticulum/Golgi apparatus where its putative enzymatic properties as a lipase or acyltransferase, predicted from sequence homology with members of the alpha/beta fold hydrolase superfamily, can enable it to function in lipid accumulation under conditions of positive energy balance. Variations in adiposity and Mest expression in genetically identical mice also provides a model of epigenetic regulation.

Changes in gene expression foreshadow diet-induced obesity in genetically identical mice.

High phenotypic variation in diet-induced obesity in male C57BL/6J inbred mice suggests a molecular model to investigate non-genetic mechanisms of obesity. Feeding mice a high-fat diet beginning at 8 wk of age resulted in a 4-fold difference in adiposity. The phenotypes of mice characteristic of high or low gainers were evident by 6 wk of age, when mice were still on a low-fat diet; they were amplified after being switched to the high-fat diet and persisted even after the obesogenic protocol was interrupted with a calorically restricted, low-fat chow diet. Accordingly, susceptibility to diet-induced obesity in genetically identical mice is a stable phenotype that can be detected in mice shortly after weaning. Chronologically, differences in adiposity preceded those of feeding efficiency and food intake, suggesting that observed difference in leptin secretion is a factor in determining phenotypes related to food intake. Gene expression analyses of adipose tissue and hypothalamus from mice with low and high weight gain, by microarray and qRT-PCR, showed major changes in the expression of genes of Wnt signaling and tissue re-modeling in adipose tissue. In particular, elevated expression of SFRP5, an inhibitor of Wnt signaling, the imprinted gene MEST and BMP3 may be causally linked to fat mass expansion, since differences in gene expression observed in biopsies of epididymal fat at 7 wk of age (before the high-fat diet) correlated with adiposity after 8 wk on a high-fat diet. We propose that C57BL/6J mice have the phenotypic characteristics suitable for a model to investigate epigenetic mechanisms within adipose tissue that underlie diet-induced obesity.

Bleomycin sensitivity of mice expressing dominant-negative p53 in the lung epithelium.

The chemotherapeutic drug bleomycin causes DNA damage and apoptosis in the lungs of mice within hours of endotracheal instillation followed by inflammation and fibrosis weeks later. The p53 tumor suppressor protein mediates cellular responses to DNA damage, including induction of apoptosis, but the effects of p53 activation in the various cell types of the lung during bleomycin-induced pulmonary fibrosis remain unclear. We show here that a transgene with a dominant-negative mutant form of human p53 expressed from the surfactant protein C promoter sensitizes mice to bleomycin-induced lung injury. The bleomycin-exposed transgenic animals display more severe lung pathology with associated collagen deposition and more pronounced lung eosinophilia than simultaneously exposed nontransgenic littermates. These observations suggest that compromising p53 function in the alveolar epithelium impairs recovery of the lung from bleomycin-induced injury.