Adipose Gene Expression Patterns of Weight Gain Suggest Counteracting Steroid Hormone Synthesis

Prenylcysteine Oxidase 1 Is a Key Regulator of Adipogenesis

The process of adipogenesis involves the differentiation of preadipocytes into mature adipocytes. Excessive adipogenesis promotes obesity, a condition that increasingly threatens global health and contributes to the rapid rise of obesity-related diseases. We have recently shown that prenylcysteine oxidase 1 (PCYOX1) is a regulator of atherosclerosis-disease mechanisms, which acts through mechanisms not exclusively related to its pro-oxidant activity. To address the role of PCYOX1 in the adipogenic process, we extended our previous observations confirming that Pcyox1−/−/Apoe−/− mice fed a high-fat diet for 8 or 12 weeks showed significantly lower body weight, when compared to Pcyox1+/+/Apoe−/− mice, due to an evident reduction in visceral adipose content. We herein assessed the role of PCYOX1 in adipogenesis. Here, we found that PCYOX1 is expressed in adipose tissue, and, independently from its pro-oxidant enzymatic activity, is critical for adipogenesis. Pcyox1 gene silencing completely prevented the differentiation of 3T3-L1 preadipocytes, by acting as an upstream regulator of several key players, such as FABP4, PPARγ, C/EBPα. Proteomic analysis, performed by quantitative label-free mass spectrometry, further strengthened the role of PCYOX1 in adipogenesis by expanding the list of its downstream targets. Finally, the absence of Pcyox1 reduces the inflammatory markers in adipose tissue. These findings render PCYOX1 a novel adipogenic factor with possible pathophysiological or therapeutic potential.

Endothelial dysfunction in small arteries and early signs of atherosclerosis in ApoE knockout rats

Endothelial dysfunction is recognized as a major contributor to atherosclerosis and has been suggested to be evident far before plaque formation. Endothelial dysfunction in small resistance arteries has been suggested to initiate long before changes in conduit arteries. In this study, we address early changes in endothelial function of atherosclerosis prone rats. Male ApoE knockout (KO) rats (11- to 13-weeks-old) were subjected to either a Western or standard diet. The diet intervention continued for a period of 20–24 weeks. Endothelial function of pulmonary and mesenteric arteries was examined in vitro using an isometric myograph. We found that Western diet decreased the contribution of cyclooxygenase (COX) to control the vascular tone of both pulmonary and mesenteric arteries. These changes were associated with early stage atherosclerosis and elevated level of plasma total cholesterol, LDL and triglyceride in ApoE KO rats. Chondroid-transformed smooth muscle cells, calcifications, macrophages accumulation and foam cells were also observed in the aortic arch from ApoE KO rats fed Western diet. The ApoE KO rats are a new model to study endothelial dysfunction during the earlier stages of atherosclerosis and could help us improve preclinical drug development.

Direct and Long-Term Metabolic Consequences of Lowly vs. Highly-Digestible Starch in the Early Post-Weaning Diet of Mice

Starches of low and high digestibility have different metabolic effects. Here, we examined whether this gives differential metabolic programming when fed in the immediate post-weaning period. Chow-fed mice were time-mated, and their nests were standardized and cross-fostered at postnatal days 1⁻2. After postnatal week (PW) 3, individually housed female and male offspring were switched to a lowly-digestible (LDD) or highly-digestible starch diet (HDD) for three weeks. All of the mice received the same high-fat diet (HFD) for nine weeks thereafter. Energy and substrate metabolism and carbohydrate fermentation were studied at the end of the HDD/LDD and HFD periods by extended indirect calorimetry. Glucose tolerance (PW 11) and metabolic flexibility (PW14) were analyzed. Directly in response to the LDD versus the HDD, females showed smaller adipocytes with less crown-like structures in gonadal white adipose tissue, while males had a lower fat mass and higher whole body fat oxidation levels. Both LDD-fed females and males showed an enlarged intestinal tract. Although most of the phenotypical differences disappeared in adulthood in both sexes, females exposed to LDD versus HDD in the early post-weaning period showed improved metabolic flexibility in adulthood. Cumulatively, these results suggest that the type of starch introduced after weaning could, at least in females, program later-life health.

Carbonic anhydrase III (Car3) is not required for fatty acid synthesis and does not protect against high-fat diet induced obesity in mice

Carbonic anhydrases are a family of enzymes that catalyze the reversible condensation of water and carbon dioxide to carbonic acid, which spontaneously dissociates to bicarbonate. Carbonic anhydrase III (Car3) is nutritionally regulated at both the mRNA and protein level. It is highly enriched in tissues that synthesize and/or store fat: liver, white adipose tissue, brown adipose tissue, and skeletal muscle. Previous characterization of Car3 knockout mice focused on mice fed standard diets, not high-fat diets that significantly alter the tissues that highly express Car3. We observed lower protein levels of Car3 in high-fat diet fed mice treated with niclosamide, a drug published to improve fatty liver symptoms in mice. However, it is unknown if Car3 is simply a biomarker reflecting lipid accumulation or whether it has a functional role in regulating lipid metabolism. We focused our in vitro studies toward metabolic pathways that require bicarbonate. To further determine the role of Car3 in metabolism, we measured de novo fatty acid synthesis with in vitro radiolabeled experiments and examined metabolic biomarkers in Car3 knockout and wild type mice fed high-fat diet. Specifically, we analyzed body weight, body composition, metabolic rate, insulin resistance, serum and tissue triglycerides. Our results indicate that Car3 is not required for de novo lipogenesis, and Car3 knockout mice fed high-fat diet do not have significant differences in responses to various diets to wild type mice.

Metabolic Response of Visceral White Adipose Tissue of Obese Mice Exposed for 5 Days to Human Room Temperature Compared to Mouse Thermoneutrality

Housing of laboratory mice at room temperature (22°C) might be considered a constant cold stress, which induces a thermogenic program in brown adipose tissue (BAT). However, the early adaptive response of white adipose tissue (WAT), the fat storage organ of the body, to a change from thermoneutrality to room temperature is not known. This was investigated here for various WAT depots, focusing on epididymal WAT (eWAT), widely used as reference depot. Male adult diet-induced obese (DIO) C57BL/6JOlaHsd mice housed at thermoneutrality (29°C), were for 5 days either switched to room temperature (22°C) or remained at thermoneutrality. Energy metabolism was continuously measured using indirect calorimetry. At the end of the study, serum metabolomics and WAT transcriptomics were performed. We confirmed activation of the thermogenic program in 22°C housed mice. Body weight and total fat mass were reduced. Whole body energy expenditure (EE) was increased, with a higher fatty acid to carbohydrate oxidation ratio and increased serum acylcarnitine levels, while energy intake was not significantly different between the two groups. Transcriptome analysis of eWAT identified tissue remodeling and inflammation as the most affected processes. Expression of pro-inflammatory M1 macrophage-related genes, and M1 over M2 macrophage ratio were decreased, which might be linked to an increased insulin sensitivity. Markers of thermogenesis were not altered in eWAT. Decreased expression of tryptophan hydroxylase 2 (Tph2) and cholecystokinin (Cck) might represent altered neuroendocrine signaling. eWAT itself does not show increased fatty acid oxidation. The three measured WATs, epididymal, mesenteric, and retroperitoneal, showed mainly similar responses; reduced inflammation (s100a8), decreased carbohydrate oxidation, and no or small differences in fatty acid oxidation. However, Ucp1 was only expressed and increased in rWAT in 22°C housed mice. Cck expression was decreased in the three WATs, significantly in eWAT and rWAT, in contrast to Tph2, which was decreased in eWAT while not expressed in mWAT and rWAT. Our data show that tissue remodeling, inflammation and neuroendocrine signaling are early responses in WAT to a moderate decrease in environmental temperature.

Steroid biosynthesis in adipose tissue

Tissue-specific expression of steroidogenic enzymes allows the modulation of active steroid levels in a local manner. Thus, the measurement of local steroid concentrations, rather than the circulating levels, has been recognized as a more accurate indicator of the steroid action within a specific tissue. Adipose tissue, one of the largest endocrine tissues in the human body, has been established as an important site for steroid storage and metabolism. Locally produced steroids, through the enzymatic conversion from steroid precursors delivered to adipose tissue, have been proven to either functionally regulate adipose tissue metabolism, or quantitatively contribute to the whole body's steroid levels. Most recently, it has been suggested that adipose tissue may contain the steroidogenic machinery necessary for the initiation of steroid biosynthesis de novo from cholesterol. This review summarizes the evidence indicating the presence of the entire steroidogenic apparatus in adipose tissue and discusses the potential roles of local steroid products in modulating adipose tissue activity and other metabolic parameters.

Updated survey of the steroid-converting enzymes in human adipose tissues

Over the past decade, adipose tissues have been increasingly known for their endocrine properties, that is, their ability to secrete a number of adipocytokines that may exert local and/or systemic effects. In addition, adipose tissues have long been recognized as significant sites for steroid hormone transformation and action. We hereby provide an updated survey of the many steroid-converting enzymes that may be detected in human adipose tissues, their activities and potential roles. In addition to the now well-established role of aromatase and 11β-hydroxysteroid dehydrogenase (HSD) type 1, many enzymes have been reported in adipocyte cell lines, isolated mature cells and/or preadipocytes. These include 11β-HSD type 2, 17β-HSDs, 3β-HSD, 5α-reductases, sulfatases and glucuronosyltransferases. Some of these enzymes are postulated to bear relevance for adipose tissue physiology and perhaps for the pathophysiology of obesity. This elaborate set of steroid-converting enzymes in the cell types of adipose tissue deserves further scientific attention. Our work on 20α-HSD (AKR1C1), 3α-HSD type 3 (AKR1C2) and 17β-HSD type 5 (AKR1C3) allowed us to clarify the relevance of these enzymes for some aspects of adipose tissue function. For example, down-regulation of AKR1C2 expression in preadipocytes seems to potentiate the inhibitory action of dihydrotestosterone on adipogenesis in this model. Many additional studies are warranted to assess the impact of intra-adipose steroid hormone conversions on adipose tissue functions and chronic conditions such as obesity, diabetes and cancer.

Oxygen restriction as challenge test reveals early high-fat-diet-induced changes in glucose and lipid metabolism

Challenge tests stress homeostasis and may reveal deviations in health that remain masked under unchallenged conditions. Ideally, challenge tests are non-invasive and applicable in an early phase of an animal experiment. Oxygen restriction (OxR; based on ambient, mild normobaric hypoxia) is a non-invasive challenge test that measures the flexibility to adapt metabolism. Metabolic inflexibility is one of the hallmarks of the metabolic syndrome. To test whether OxR can be used to reveal early diet-induced health effects, we exposed mice to a low-fat (LF) or high-fat (HF) diet for only 5 days. The response to OxR was assessed by calorimetric measurements, followed by analysis of gene expression in liver and epididymal white adipose tissue (eWAT) and serum markers for e.g. protein glycation and oxidation. Although HF feeding increased body weight, HF and LF mice did not differ in indirect calorimetric values under normoxic conditions and in a fasting state. Exposure to OxR; however, increased oxygen consumption and lipid oxidation in HF mice versus LF mice. Furthermore, OxR induced gluconeogenesis and an antioxidant response in the liver of HF mice, whereas it induced de novo lipogenesis and an antioxidant response in eWAT of LF mice, indicating that HF and LF mice differed in their adaptation to OxR. OxR also increased serum markers of protein glycation and oxidation in HF mice, whereas these changes were absent in LF mice. Cumulatively, OxR is a promising new method to test food products on potential beneficial effects for human health.

Adipose tissue metabolism and inflammation are differently affected by weight loss in obese mice due to either a high-fat diet restriction or change to a low-fat diet

Restriction of a high-fat diet (HFD) and a change to a low-fat diet (LFD) are two interventions that were shown to promote weight loss and improve parameters of metabolic health in obesity. Examination of the biochemical and molecular responses of white adipose tissue (WAT) to these interventions has not been performed so far. Here, male C57BL/6JOlaHsd mice, harboring an intact nicotinamide nucleotide transhydrogenase gene, were fed a purified 40 energy% HFD for 14 weeks to induce obesity. Afterward, mice were divided into three dietary groups: HFD (maintained on HFD), LFD (changed to LFD with identical ingredients), and HFD-CR (restricted to 70 % of the HFD). The effects of the interventions were examined after 5 weeks. Beneficial effects were seen for both HFD-CR and LFD (compared to HFD) regarding physiological parameters (body weight and fat mass) and metabolic parameters, including circulating insulin and leptin levels. Macrophage infiltration in WAT was reduced by both interventions, although more effectively by HFD-CR. Strikingly, molecular parameters in WAT differed between HFD-CR and LFD, with increased activation of mitochondrial carbohydrate and fat metabolism in HFD-CR mice. Our results confirm that restriction of the amount of dietary intake and reduction in the dietary energy content are both effective in inducing weight loss. The larger decrease in WAT inflammation and increase in mitochondrial carbohydrate metabolism may be due to a larger degree of energy restriction in HFD-CR, but could also be due to superior effectiveness of dietary restriction in weight loss strategies.

Thermoneutrality results in prominent diet-induced body weight differences in C57BL/6J mice, not paralleled by diet-induced metabolic differences

SCOPE

Mice are usually housed at 20-24 °C. At thermoneutrality (28 °C) larger diet-induced differences in obesity are seen. We tested whether this leads to large differences in metabolic health parameters.

METHODS AND RESULTS

We performed a 14-wk dietary intervention in C57BL/6J mice at 28 °C and assessed adiposity and metabolic health parameters for a semipurified low fat (10 energy%) diet and a moderate high fat (30 energy%) diet. A large and significant diet-induced differential increase in body weight, adipose tissue mass, adipocyte size, serum leptin level, and, to some extent, cholesterol level was observed. No adipose tissue inflammation was seen. No differential effect of the diets on serum glucose, free fatty acids, triacylglycerides, insulin, adiponectin, resistin, PAI-1, MMP-9, sVCAM-1, sICAM-1, sE-selectin, IL-6, ApoE, fibrinogen levels, or HOMA index was observed. Also in muscle no differential effect on mitochondrial density, mitochondrial respiratory control ratio, or mRNA expression of metabolic genes was found. Finally, in liver no differential effect on weight, triacylglycerides level, aconitase/citrate synthase activity ratio was seen.

CONCLUSION

Low fat diet and moderate high fat diet induce prominent body weight differences at thermoneutrality, which is not paralleled by metabolic differences. Our data rather suggest that thermoneutrality alters metabolic homeostasis.

Age-related modulation of the effects of obesity on gene expression profiles of mouse bone marrow and epididymal adipocytes

This study aimed to characterize and compare the effects of obesity on gene expression profiles in two distinct adipose depots, epididymal and bone marrow, at two different ages in mice. Alterations in gene expression were analyzed in adipocytes isolated from diet-induced obese (DIO) C57BL/6J male mice at 6 and 14 months of age and from leptin deficient mice (ob/ob) at 6 months of age using microarrays. DIO affected gene expression in both depots at 6 and 14 months, but more genes were altered in epididymal than bone marrow adipocytes at each age and younger mice displayed more changes than older animals. In epididymal adipocytes a total of 2789 (9.6%) genes were differentially expressed at 6-months with DIO, whereas 952 (3.3%) were affected at 14-months. In bone marrow adipocytes, 347 (1.2%) genes were differentially expressed at 6-months with DIO, whereas only 189 (0.66%) were changed at 14-months. 133 genes were altered by DIO in both fat depots at 6-months, and 37 genes at 14-months. Only four genes were altered in both depots at both ages with DIO. Bone marrow adipocytes are less responsive to DIO than epididymal adipocytes and the response of both depots to DIO declines with age. This loss of responsiveness with age is likely due to age-associated changes in expression of genes related to adipogenesis, inflammation and mitochondrial function that are similar to and obscure the changes commonly associated with DIO. Patterns of gene expression were generally similar in epididymal adipocytes from ob/ob and DIO mice; however, several genes were differentially expressed in bone marrow adipocytes from ob/ob and DIO mice, perhaps reflecting the importance of leptin signaling for bone metabolism. In conclusion, obesity affects age-associated alterations in gene expression in both epididymal and bone marrow adipocytes regardless of diet or genetic background.

Short-term, high fat feeding-induced changes in white adipose tissue gene expression are highly predictive for long-term changes

SCOPE

We aimed to evaluate the predictability of short-term (5 days) changes in epididymal white adipose tissue (eWAT) gene expression for long-term (12 weeks) changes induced by high-fat diet (HFD) feeding.

METHODS AND RESULTS

Mice were fed semisynthetic diets containing 10 (low-fat diet) or 40 (HFD) energy% of fat. Global gene expression in eWAT was analyzed using microarrays and confirmed by quantitative PCR. As expected, HFD feeding resulted in increased body fat accumulation and reduced glucose tolerance after 12 weeks. A total of 4678 transcripts were significantly changed by HFD after 12 weeks and 973 after 5 days, with an overlap of 764 transcripts encoding 549 genes. Of these, 79% were downregulated and 21% were upregulated by HFD, all in the same direction and highly correlated (r(2) = 0.90) between the time points. Pathway analysis showed downregulation of the main identified processes: lipid metabolism, carbohydrate metabolism, and oxidative phosphorylation. Mest (mesoderm-specific transcript) was highly upregulated, confirming its role as an early marker of fat cell expansion.

CONCLUSION

The high predictive value of short-term gene expression changes for long-term effects of high fat feeding is a promising step to establish robust early biomarkers that could shorten animal trials to assess health-promoting food compounds.

BIOCLAIMS standard diet (BIOsd): a reference diet for nutritional physiology

Experimental replication is fundamental for practicing science. To reduce variability, it is essential to control sources of variation as much as possible. Diet is an important factor that can influence many processes and functional outcomes in studies performed with rodent models. This is especially true for, but not limited to, nutritional studies. To compare functional effects of different nutrients, it is important to use standardized, semi-purified diets. Here, we propose and describe a standard reference diet, the BIOCLAIMS standard diet. The diet is AIN-93 based, but further defined with dietary and experimental requirements taken into account that allow for experiments with bioactive food components and natural (non-expensive) labeling. This diet will be implemented by two European research consortia, Mitofood and BIOCLAIMS, to ensure inter-laboratory comparability.

Glycemic index differences of high-fat diets modulate primarily lipid metabolism in murine adipose tissue

A low vs. high glycemic index of a high-fat (HF) diet (LGI and HGI, respectively) significantly retarded adverse health effects in adult male C57BL/6J mice, as shown recently (Van Schothorst EM, Bunschoten A, Schrauwen P, Mensink RP, Keijer J. FASEB J 23: 1092–1101, 2009). The LGI diet enhanced whole body insulin sensitivity and repressed HF diet-induced body and white adipose tissue (WAT) weight gain, resulting in significantly reduced serum leptin and resistin levels and increased adiponectin levels. We questioned how WAT is modulated and characterized the molecular mechanisms underlying the glycemic index-mediated effects using whole genome microarrays. This showed that the LGI diet mainly exerts its beneficial effects via substrate metabolism, especially fatty acid metabolism. In addition, cell adhesion and cytoskeleton remodeling showed reduced expression, in line with lower WAT mass. An important transcription factor showing enhanced expression is PPAR-γ. Furthermore, serum levels of triglycerides, total cholesterol, and HDL- and LDL-cholesterol were all significantly reduced by LGI diet, and simultaneously muscle insulin sensitivity was significantly increased as analyzed by protein kinase B/Akt phosphorylation. Cumulatively, even though these mice were fed an HF diet, the LGI diet induced significantly favorable changes in metabolism in WAT. These effects suggest a partial overlap with pharmacological approaches by thiazolidinediones to treat insulin resistance and statins for hypercholesterolemia. It is therefore tempting to speculate that such a dietary approach might beneficially support pharmacological treatment of insulin resistance or hypercholesterolemia in humans.

Dietary restriction of mice on a high-fat diet induces substrate efficiency and improves metabolic health

High energy intake and, specifically, high dietary fat intake challenge the mammalian metabolism and correlate with many metabolic disorders such as obesity and diabetes. However, dietary restriction (DR) is known to prevent the development of metabolic disorders. The current western diets are highly enriched in fat, and it is as yet unclear whether DR on a certain high-fat (HF) diet elicits similar beneficial effects on health. In this research, we report that HF-DR improves metabolic health of mice compared with mice receiving the same diet on an ad libitum basis (HF-AL). Already after five weeks of restriction, the serum levels of cholesterol and leptin were significantly decreased in HF-DR mice, whereas their glucose sensitivity and serum adiponectin levels were increased. The body weight and measured serum parameters remained stable in the following 7 weeks of restriction, implying metabolic adaptation. To understand the molecular events associated with this adaptation, we analyzed gene expression in white adipose tissue (WAT) with whole genome microarrays. HF-DR strongly influenced gene expression in WAT; in total, 8643 genes were differentially expressed between both groups of mice, with a major role for genes involved in lipid metabolism and mitochondrial functioning. This was confirmed by quantitative real-time reverse transcription-PCR and substantiated by increase in mitochondrial density in WAT of HF-DR mice. These results provide new insights in the metabolic flexibility of dietary restricted animals and suggest the development of substrate efficiency.

DNA microarrays to define and search for genes associated with obesity

One of the major goals of this review was to identify obesity-specific gene profiles in animal models to help comprehend the pathogenic mechanisms and the prediction of the phenotypic outcomes of obesity and its associated metabolic diseases. The genomic examination of insulin-sensitive tissues, such as the adipose and hepatic tissues, has provided a wealth of information about the changes in gene expression in obesity and its associated metabolic diseases. The overexpression of genes related to inflammation, immune response, adhesion molecules, and lipid metabolism is a major characteristic of white adipose tissue, while the overexpression of the genes related to lipid metabolism, adipocyte differentiation, defense, and stress responses is noticeable in the non-alcoholic fatty liver of obese rodents. The hepatic-gene expression profiles led us to hypothesize that in obese rodents, the livers are supplied with large amounts of free fatty acids under conditions associated with obesity either through increased fatty acid biosynthesis or through decreased fatty acid oxidation, which may lead to increased mitochondrial respiratory activity. The wide list of genes that were identified in previous studies could be a source of potential therapeutic targets because most of these genes are involved in the key mechanisms of obesity development, from adipocyte differentiation to the disturbance of metabolism.

Pathways of adipose tissue androgen metabolism in women: depot differences and modulation by adipogenesis

The objective was to examine pathways of androgen metabolism in abdominal adipose tissue in women. Abdominal subcutaneous (SC) and omental (OM) adipose tissue samples were surgically obtained in women. Total RNA was isolated from whole adipose tissue samples and from primary preadipocyte cultures before and after induction of differentiation. Expression levels of several steroid-converting enzyme transcripts were examined by real-time RT-PCR. Androgen conversion rates were also measured. We found higher expression levels in SC compared with OM adipose tissue for type 1 3beta-hydroxysteroid dehydrogenase (3beta-HSD-1; P < 0.05), for aldo-keto reductase 1C3 (AKR1C3; P < 0.0001), for AKR1C2 (P < 0.0001), and for the androgen receptor (P < 0.0001). 17beta-HSD-2 mRNA levels were lower in SC adipose tissue (P < 0.05). Induction of adipocyte differentiation led to significantly increased expression levels in SC cultures for AKR1C3 (4.7-fold, P < 0.01), 11-cis-retinol dehydrogenase (6.9-fold, P < 0.02), AKR1C2 (5.6-fold, P < 0.004), P-450 aromatase (5.7-fold, P < 0.02), steroid sulfatase (3.1-fold, P < 0.02), estrogen receptor-beta (11.8-fold, P < 0.01), and the androgen receptor (4.0-fold, P < 0.0005). Generally similar but nonsignificant trends were obtained in OM cultures. DHT inactivation rates increased with differentiation, this effect being mediated by dexamethasone alone, through a glucocorticoid receptor-dependent mechanism. In conclusion, higher mRNA levels of enzymes synthesizing and inactivating androgens are found in differentiated adipocytes, consistent with higher androgen-processing rates in these cells. Glucocorticoid-induced androgen inactivation may locally modulate the exposure of adipose cells to active androgens.

Effects of a high-fat, low- versus high-glycemic index diet: retardation of insulin resistance involves adipose tissue modulation

Beneficial effects of low glycemic index (GI) diets in rodents have been studied using healthy low-fat diets, while the effects might be different on high-fat diets inducing progression of insulin resistance. We fed C57BL/6J male mice high-fat low/high-GI (LGI/HGI) diets for 13 wk. Glucose and insulin tolerance and serum substrates, including adipokines, were measured longitudinally. The LGI group showed a significantly higher glucose tolerance from wk 2 onwards, which was supported by lower serum insulin and free fatty acids levels at 8 wk, and a tendency for lower leptin levels, while resistin levels remained similar. At 11 wk, when differences in serum resistin started to increase, differences in serum insulin were diminished. Although food intake was similar throughout the study, body weights and epididymal adipose tissue mass became significantly lower in the LGI group at necropsy. Several serum substrates and adipose tissue leptin mRNA levels, as analyzed by Q-PCR, were, again, significantly lower, whereas adiponectin mRNA levels were higher. Taken together, an LGI high-fat diet maintains higher glucose tolerance and insulin sensitivity via adipose tissue modulation solely because of a difference in the type of carbohydrate, supporting a nutritional approach in the fight against insulin resistance.

Functional Genomics Approaches to Studies of the Cytochrome P450 Superfamily

Functional genomics approaches are widely implemented in current research and have found application in many areas of biology. This review will present research fields, novel findings and new tools developed in the cytochrome P450 field using the functional genomics techniques. The most widely used method is microarray technology, which has already greatly contributed to the understanding of the cytochromes P450 function and expression. Several focused CYP microarrays have been developed for genotyping, toxicogenomics and studies of CYP function of many different organisms. Our contribution to the CYP field by development of Steroltalk microarrays to study the cross-talk of cholesterol homeostasis and drug metabolism is also presented.

Assessment of diet-induced obese rats as an obesity model by comparative functional genomics

OBJECTIVE

We applied a comparative functional genomics approach to evaluate whether diet-induced obese (DIO) rats serve as an effective obesity model.

METHODS AND PROCEDURES

Gene-expression profiles of epididymal fat from DIO and lean rats were generated using microarrays and compared with the published array data of obese and non-obese human subcutaneous adipocytes.

RESULTS

Caloric intake and fuel efficiency were significantly higher in DIO rats, which resulted in increased body weight and adiposity. Circulating glucose, cholesterol, triglyceride, insulin, and leptin levels in DIO rats were significantly higher than those in the lean controls. DIO rats also exhibited impaired insulin sensitivity. A direct comparison of gene-expression profiles from DIO and lean rats and those from obese and non-obese humans revealed that global gene-expression patterns in DIO rat fat resemble those of obese human adipocytes. Differentially expressed genes between obese and non-obese subjects in both human and rat studies were identified and associated with biological pathways by mapping genes to Gene Ontology (GO) categories. Immune response-related genes and angiogenesis-related genes exhibited significant upregulation in both obese humans and DIO rats when compared with non-obese controls. However, genes in fatty acid metabolism and oxidation exhibited a broad downregulation only in obese human adipocytes but not in DIO rat epididymal fat.

DISCUSSION

Our study based on gene-expression profiling suggested that DIO rats in general represent an appropriate obesity model. However, the discrepancies in gene-expression alterations between DIO rats and obese humans, particularly in the metabolic pathways, may explain the limitations of using DIO rodent models in obesity research and drug discovery.

Characterization of ScAP-23, a new cell line from murine subcutaneous adipose tissue, identifies genes for the molecular definition of preadipocytes

The 3T3-L1 model of in vitro adipogenesis has provided key insights into the molecular nature of this process. However, given that 3T3-L1 are of an embryonic origin, it is not clear to what extent they represent adipogenesis as it occurs in white adipose tissue (WAT). With the goal of better defining preadipocytes and adipogenesis in WAT, we have generated a new cell culture model from adipocyte precursors present in C57BL/6 mouse subcutaneous WAT. ScAP-23 preadipocytes show fibroblastic morphology, and on treatment with dexamethasone, 3-methylisobutylxanthine, insulin, and indomethacin, convert to nearly 100% adipocyte morphology. ScAP-23 adipocytes contain abundant lipid droplets and express transcripts for PPARγ, C/EBP family, and SREBP-1c transcription factors, SCD1, aFABP, ATGL, GLUT4, FAS, LDL, and GPDH, and are insulin responsive. Differential screening of 1,176 genes using nylon DNA arrays identified 10 transcripts enriched in ScAP-23 adipocytes vs. preadipocytes and 26 transcripts enriched in ScAP-23 preadipocytes vs. adipocytes. Semiquantitative or real-time PCR analyses identified a common cohort of 14 transcripts markedly downregulated in both ScAP-23 and 3T3-L1 adipogenesis. These included catenin-β1, chemokine ligand-2, serine or cysteine peptidase inhibitor f1, aurora kinase B, thrombospondin2, and solute carrier-7a5. Five of these transcripts (Ccl2, Serpinf1, Aurkb, Thbs2, and Slc7a5) demonstrated at least a twofold increase in WAT from obese ( ob/ob) mice compared with that of wild-type mice. This suggests that comparative gene expression studies of ScAP-23 and 3T3-L1 adipogenesis may be particularly fruitful in identifying preadipocyte-expressed genes that play a role in adipose tissue physiology and/or pathophysiology.

Lipodystrophy in HIV 1-infected patients: lessons for obesity research

Lipodystrophy is a common alteration in HIV 1-infected patients under anti-retroviral treatment. This syndrome is usually associated with peripheral lipoatrophy, central adiposity and, in some cases, lipomatosis, as well as systemic insulin resistance and hyperlipidemia. Research on the ethiopathogenesis of the disease revealed novel aspects of adipose tissue biology highly relevant to obesity research: the pivotal role of mitochondria in white adipose tissue function, the role that interference with master transcription factors of adipogenesis may have in human adipose tissue, the capacity of human white adipose tissue to acquire brown fat-like features, as well as the importance of apoptosis and the potential impact of viral infections in adipose tissue. The dramatic difference between subcutaneous adipose depots, prone to lipoatrophy, and the visceral adipose depots, prone to enlargement, has been further evidenced in the study of the lipodystrophy syndrome. The recognition of a local pro-inflammatory environment in lipoatrophic adipose tissue from affected patients, including macrophage infiltration and enhanced expression of chemokines and cytokines, points to events paradoxically similar to those in the hypertrophied adipose tissue in obesity. However, this also potentially provides an explanation for the existence of systemic alterations common to lipodystrophy and obese patients and reminiscent of the metabolic syndrome.

Neuropeptides induced a pronounced and statin-sensitive dysregulation of mevalonate cycle in human monocytes of patients with hypercholesterolemia

Angiotensin II (Ang II) and leptin generate statin-inhibitable superoxide anion production that accounts for only part of the entire superoxide anion production. In our recent studies, we aimed at elucidating whether Ang II and leptin, affecting the intensity of the mevalonate cycle, are able to increase endogenous cholesterol synthesis. Furthermore, we compared the superoxide anion and cholesterol production capability of monocytes of healthy control volunteers and monocytes obtained from patients with hypercholesterolemia (HC). We also studied the differences of the produced statin-inhibitable superoxide anion and cholesterol synthesis in control and HC-monocytes, depending on the applied stimulating ligands. In control and HC-monocytes--stimulated by Ang II, leptin, fenyl-Me-Leu-Phe (FMLP), phorbol-12-myristate-13-acetate (PMA) and A23187--we determined the proportion of mevalonate cycle-dependent and -independent superoxide and cholesterol production, using lovastatin (Lov), and 25-hydroxycholesterol (25-HC). According to our results; (1) superoxide anion generation in HC-monocytes was elevated after Ang II, leptin and FMLP-stimulation, whereas PMA and A23187-stimulation had lower stimulating effect in HC than in control cells. (2) Cholesterol synthesis was increased only after stimulation with Ang II and leptin. (3) The Ang II and leptin-induced total superoxide anion generation and cholesterol synthesis were more elevated in HC than in control monocytes. (4) In contrast, the increase in Lov and 25-HC sensitive cholesterol synthesis were higher in resting, but lower in stimulated HC monocytes than in control cells. Summarizing our results, we concluded that Ang II and leptin are involved in enhancement of endogenous cholesterol synthesis through a statin-sensitive pathway.

Downregulation of electron transport chain genes in visceral adipose tissue in type 2 diabetes independent of obesity and possibly involving tumor necrosis factor-alpha

Impaired oxidative phosphorylation is suggested as a factor behind insulin resistance of skeletal muscle in type 2 diabetes. The role of oxidative phosphorylation in adipose tissue was elucidated from results of Affymetrix gene profiling in subcutaneous and visceral adipose tissue of eight nonobese healthy, eight obese healthy, and eight obese type 2 diabetic women. Downregulation of several genes in the electron transport chain was the most prominent finding in visceral fat of type 2 diabetic women independent of obesity, but the gene pattern was distinct from that previously reported in skeletal muscle in type 2 diabetes. A similar but much weaker effect was observed in subcutaneous fat. Tumor necrosis factor-alpha (TNF-alpha) is a major factor behind inflammation and insulin resistance in adipose tissue. TNF-alpha treatment decreased mRNA expression of electron transport chain genes and also inhibited fatty acid oxidation when differentiated human preadipocytes were treated with the cytokine for 48 h. Thus, type 2 diabetes is associated with a tissue- and region-specific downregulation of oxidative phosphorylation genes that is independent of obesity and at least in part mediated by TNF-alpha, suggesting that impaired oxidative phosphorylation of visceral adipose tissue has pathogenic importance for development of type 2 diabetes.

Adipose gene expression response of lean and obese mice to short-term dietary restriction

Overweight and obesity lead to higher morbidity risks, which are alleviated even by mild weight loss. To gain insight in the molecular effects of weight loss in adipose tissue, we analyzed the effects of short-term dietary restriction (DR) on mice fed a low-fat diet (lean mice) or a high-fat diet (obese mice). Female C57Bl6/J mice on both diets were on DR until an average body weight loss of 20%, which was achieved in 8 to 12 days depending on body weight at the start of DR. Plasma free fatty acids and blood glucose levels decreased significantly on DR. In the (restricted) low-fat diet groups, gene expression analysis using adipose-enriched cDNA microarrays revealed only two transcripts to be significant differentially expressed by DR: up-regulation of malic enzyme (Mod1) and down-regulation of major urinary protein 1 (Mup1). Real-time polymerase chain reaction analysis confirmed these findings and showed, for the high-fat diet groups, an identical expression pattern for Mup1, whereas Mod1 showed an opposed gene expression pattern for the high-fat diet groups. In conclusion, initial weight loss induces transcriptional changes only in a very small number of adipose genes, which also depends on the (restricted) diet used.

Diferential gene expression and adiposity reduction induced by ascorbic acid supplementation in a cafeteria model of obesity

Obesity is considered as an inflammatory disease, in which free radical-induced oxidative stress and excessive intake of macronutrients exacerbate their symptoms. In this context, we assessed in rats the possible preventive effect of the supplementation with an antioxidant molecule, ascorbic acid, in order to reduce the adiposity induced by the intake of a high-fat diet. For this purpose, during 56 days, three groups of male Wistar rats were fed on: a) standard pelleted diet, b) Cafeteria diet, c) ascorbate-supplemented (750 mg/kg of body weight) Cafeteria diet. At the end of the experimental period, microarray analysis was used to identify genes transcriptionally induced or repressed by both experimental dietary models (Cafeteria diet supplemented or not with ascorbic acid) in subcutaneous adipose tissue. Dietary ascorbic acid was able to protect against high fat diet effects, reducing the increase of body weight, total body fat and enlargement of different adipose depots induced by the Cafeteria diet without affecting food intake. An association analysis accurately and differentially allowed the detection of gene expression changes related with adiposity and insulin resistance. The genes that more strongly correlated with body fat and HOMA insulin resistance index were involved in adipocyte differentiation, lipid and glucocorticoid metabolism, cell cycle regulation, as well as in several insulin-induced processes. Some other transcripts are regulated by the vitamin C-mediated reduction of adiposity, such as genes that participate in glucocorticoid metabolism, adipogenesis, pentose phosphate pathway, or tricarboxylic acid cycle. This strategy was able to link variations in adipose tissue gene expression with markers of diet-induced obesity in rats, such as insulin resistance and body fat content.