Cloning of avian G(0)/G(1) switch gene 2 genes and developmental and nutritional regulation of G(0)/G(1) switch gene 2 in chicken adipose tissue

Genomic insights into metabolic flux in hummingbirds

Hummingbirds are very well adapted to sustain efficient and rapid metabolic shifts. They oxidize ingested nectar to directly fuel flight when foraging but have to switch to oxidizing stored lipids derived from ingested sugars during the night or long-distance migratory flights. Understanding how this organism moderates energy turnover is hampered by a lack of information regarding how relevant enzymes differ in sequence, expression, and regulation. To explore these questions, we generated a chromosome-scale genome assembly of the ruby-throated hummingbird (A. colubris) using a combination of long- and short-read sequencing, scaffolding it using existing assemblies. We then used hybrid long- and short-read RNA sequencing of liver and muscle tissue in fasted and fed metabolic states for a comprehensive transcriptome assembly and annotation. Our genomic and transcriptomic data found positive selection of key metabolic genes in nectivorous avian species and deletion of critical genes (SLC2A4, GCK) involved in glucostasis in other vertebrates. We found expression of a fructose-specific version of SLC2A5 putatively in place of insulin-sensitive SLC2A5, with predicted protein models suggesting affinity for both fructose and glucose. Alternative isoforms may even act to sequester fructose to preclude limitations from transport in metabolism. Finally, we identified differentially expressed genes from fasted and fed hummingbirds, suggesting key pathways for the rapid metabolic switch hummingbirds undergo.

G0S2 Gene Polymorphism and Its Relationship with Carcass Traits in Chicken

Gene single nucleotide polymorphisms can be used as auxiliary markers in molecular breeding and are an effective method to improve production performance. G0S2 is a key gene involved in regulating fat metabolism, but little research has been conducted on this gene regarding its role in poultry. In this study, the specialized commercial partridge chicken strain G0S2 gene was cloned and sequenced, and the relationship between the SNP sites on G0S2 and the carcass traits of chickens was investigated. The results showed that a total of seven SNPs were detected on G0S2 (g.102G > A, g.255G > A, g.349C > T, g.384A > G, g.386G > A, g.444G > A, g.556G > A). Two sites are located in the coding region and five sites are located in the 3′-UTR. SNPs located in the coding region are synonymous mutations. g.444G > A has a significant correlation with abdominal fat weight. The chickens with AG and GG genotypes have the highest abdominal fat weight, while the AA genotype is lower. The g.102G > A genotype has a significant correlation with live and abdominal fat weight. The live weight and abdominal fat weight of the chickens with AA and AG genotypes are at a higher level and have a larger gap than the GG genotype. Chickens with the AA genotype in g.556G > A had the lowest fat weight. The results of present study can provide practical information for molecular marker-assisted breeding of chicken carcass traits.

Transcriptomic signature of fasting in human adipose tissue

Little is known about gene regulation by fasting in human adipose tissue. Accordingly, the objective of this study was to investigate the effects of fasting on adipose tissue gene expression in humans. To that end, subcutaneous adipose tissue biopsies were collected from 11 volunteers 2 and 26 h after consumption of a standardized meal. For comparison, epididymal adipose tissue was collected from C57Bl/6J mice in the ab libitum-fed state and after a 16 h fast. The timing of sampling adipose tissue roughly corresponds with the near depletion of liver glycogen. Transcriptome analysis was carried out using Affymetrix microarrays. We found that, 1) fasting downregulated numerous metabolic pathways in human adipose tissue, including triglyceride and fatty acid synthesis, glycolysis and glycogen synthesis, TCA cycle, oxidative phosphorylation, mitochondrial translation, and insulin signaling; 2) fasting downregulated genes involved in proteasomal degradation in human adipose tissue; 3) fasting had much less pronounced effects on the adipose tissue transcriptome in humans than mice; 4) although major overlap in fasting-induced gene regulation was observed between human and mouse adipose tissue, many genes were differentially regulated in the two species, including genes involved in insulin signaling (PRKAG2, PFKFB3), PPAR signaling (PPARG, ACSL1, HMGCS2, SLC22A5, ACOT1), glycogen metabolism (PCK1, PYGB), and lipid droplets (PLIN1, PNPLA2, CIDEA, CIDEC). In conclusion, although numerous genes and pathways are regulated similarly by fasting in human and mouse adipose tissue, many genes show very distinct responses to fasting in humans and mice. Our data provide a useful resource to study adipose tissue function during fasting.

Research Note: Association of temporal expression of myostatin with hypertrophic muscle growth in different Japanese quail lines

Myostatin (MSTN) negatively regulates in muscle growth and development. Among alternative splicing isoforms of avian MSTN, MSTN-A has antimyogenic activities and MSTN-B functions as a promyogenic factor. In this study, different lines of Japanese quail were used: a random bred control (RBC) and a heavy weight (HW) quail line with muscle hypertrophy. The objectives of the current study are to compare temporal expression of the MSTN isoforms in pectoralis major muscle (PM) between 2 quail lines and to relate MSTN expression with temporal changes in muscle growth and total amounts of DNA in PM. Gains of body weight (BW) and PM weight were greater until posthatch day (D) 28 (P < 0.001), and the fold increases in total DNA contents of PM were greater in the HW line compared with the RBC line during D7 to D28 (P < 0.05). PCR analysis showed that MSTN-A expression was greater at 14 D (E14) of embryonic age (P < 0.01), D7 (P = 0.052), and D14 (P < 0.01) in the RBC line compared with the HW line. At D28 and D75, expression of MSTN-A was greater in the HW line compared with the RBC line (P < 0.05). MSTN-B expression was barely detectable from E14 to D14 and measurable from D28 to D75 in the muscle of both lines. Ratios of the MSTN-B/-A form ranging from 0.15 to 0.29 indicate a minor expression of the B form. Taken together, the lesser expression levels of MSTN-A at E14, D7, and D14 are associated with the fast growth of PM, and greater MSTN-A expression at D28 and D75 are associated with a slowdown of PM growth in the HW line. These data indicate a negative association of MSTN expression with PM growth and provide a scientific basis for potential usage of MSTN expression as a selection marker for greater muscle growth in poultry.

Adipose-Specific Expression, Developmental and Nutritional Regulation of the Gene-Encoding Retinol-Binding Protein 7 in Pigs

Modulation of expression of adipose tissue-specific transcripts has been known to regulate adipogenesis and lipid metabolism. Recently, adipose-specific expression patterns and developmental regulation of the gene-encoding retinol-binding protein 7 (RBP7) was identified. However, its expression in adipose tissue of the porcine species has yet to be explored. In this study, adipose tissue-specific expression of porcine RBP7 was identified and conservation of the fatty acid-binding domains and evolutionary relationship of the RBP7 gene were verified comparatively across mammalian species. Our in vitro and in vivo analysis of gene expression revealed that RBP7 expression was significantly high in fat cell fraction compared to stromal vascular cells (p < 0.05) and increased during development (p < 0.05). The level of RBP7 expression was upregulated during a 24-h short-term fasting intervention and restored 6 h after refeeding (p < 0.05). Taken together, these studies provide insights into the role of RBP7 in adipose tissue of pigs during development and nutritional intervention and pave the way for future studies on the regulation of retinol homeostasis in porcine adipose tissue.

Adipose KLF15 Controls Lipid Handling to Adapt to Nutrient Availability

Adipose tissue stores energy in the form of triglycerides. The ability to regulate triglyceride synthesis and breakdown based on nutrient status (e.g., fed versus fasted) is critical for physiological homeostasis and dysregulation of this process can contribute to metabolic disease. Whereas much is known about hormonal control of this cycle, transcriptional regulation is not well understood. Here, we show that the transcription factor Kruppel-like factor 15 (KLF15) is critical for the control of adipocyte lipid turnover. Mice lacking Klf15 in adipose tissue (AK15KO) display decreased adiposity and are protected from diet-induced obesity. Mechanistic studies suggest that adipose KLF15 regulates key genes of triglyceride synthesis and inhibits lipolytic action, thereby promoting lipid storage in an insulin-dependent manner. Finally, AK15KO mice demonstrate accelerated lipolysis and altered systemic energetics (e.g., locomotion, ketogenesis) during fasting conditions. Our study identifies adipose KLF15 as an essential regulator of adipocyte lipid metabolism and systemic energy balance.

Impact of fliD and virulence plasmid pSEV on response of chicken embryo fibroblasts to Salmonella Enteritidis

Salmonella Enteritidis is the main serovar of poultry origin in humans, but its complex interaction with certain avian cells is still not fully understood. Previously we identified several genes significantly induced in chicken embryo fibroblasts (CEFs) by the wild-type strain S. Enteritidis 11 (SE 11). In the present study, we raised the question whether virulence-attenuated mutants of this strain would induce altered expression of the newly identified fibroblast genes associated with immune and non-immune functions of CEFs. Gene expression was evaluated by real-time PCR following challenge by the parental strain SE 11 and its virulence attenuated mutants lacking flagellin gene fliD only or fliD and the serovar-specific virulence plasmid pSEV. As a result, deletion mutants induced a lower expression of all immune genes, but an increased expression of the non-immune genes G0S2 and ENO2 relative to the parental strain. Our data indicate the importance of flagella and pSEV in modulation of virulence and host response in this model. We demonstrated, for the first time ever, an increased induction of survival genes G0S2 and ENO2 by virulence-attenuated mutants of S. Enteritidis.

G0S2a1 (G0/G1 switch gene 2a1) is downregulated by TNF-α in grass carp (Ctenopharyngodon idellus) hepatocytes through PPARα inhibition

G0/G1 switch gene 2 plays an important role in the regulation of lipolysis in mammals, but little is known about its gene (G0S2) structure and function in fish. In the present study, two genes, G0S2a and G0S2b were isolated and characterized from grass carp Ctenopharyngodon idella, which encode peptides of 111 and 84 amino acids, respectively. Moreover, alternative multiple exon usage resulted in a significant variation in the 5'-region of G0S2a transcripts yielding two isoforms (G0S2a1 and G0S2a2). Phylogenetic and synteny analyses indicated that G0S2a and G0S2b could have originated from the teleost-specific genome duplication event. Analysis of the exon-intron structures clarified that G0S2a contained an extra intron compared with G0S2b. G0S2a1, G0S2a2 and G0S2b mRNAs were highly expressed in adipose tissue and liver. G0S2a was localized to the cytoplasm and nucleus, while G0S2b was mainly localized in cytoplasm, suggesting that G0S2a and G0S2b may have different functions in grass carp. PPARα agonist caused an increase in G0S2a1 and G0S2b expression, revealing that they are subject to transcriptional control by PPARα-mediated signals. TNF-α treatment decreased G0S2a1 and G0S2a2 transcripts that paralleled TNF-α downregulation of PPARα; however, only the effects of TNF-α on G0S2a1 were attenuated by treatment with PPARα agonist. Our findings identify G0S2a, not G0S2b, as a target gene for TNF-α and reveal that TNF-α suppresses G0S2a1 gene expression through a PPARα-dependent pathway in grass carp hepatocytes.

G0S2: A small giant controller of lipolysis and adipose-liver fatty acid flux

The discovery of adipose triglyceride lipase (ATGL) and its coactivator comparative gene identification-58 (CGI-58) provided a major paradigm shift in the understanding of intracellular lipolysis in both adipocytes and nonadipocyte cells. The subsequent discovery of G0/G1 switch gene 2 (G0S2) as a potent endogenous inhibitor of ATGL revealed a unique mechanism governing lipolysis and fatty acid (FA) availability. G0S2 is highly conserved in vertebrates, and exhibits cyclical expression pattern between adipose tissue and liver that is critical to lipid flux and energy homeostasis in these two tissues. Biochemical and cell biological studies have demonstrated that a direct interaction with ATGL mediates G0S2's inhibitory effects on lipolysis and lipid droplet degradation. In this review we examine evidence obtained from recent in vitro and in vivo studies that lends support to the proof-of-principle concept that G0S2 functions as a master regulator of tissue-specific balance of TG storage vs. mobilization, partitioning of metabolic fuels between adipose and liver, and the whole-body adaptive energy response. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.

Pronounced expression of the lipolytic inhibitor G0/G1 Switch Gene 2 (G0S2) in adipose tissue from brown bears (Ursus arctos) prior to hibernation

Prior to hibernation, the brown bear (Ursus arctos) exhibits unparalleled weight gain. Unlike humans, weight gain in bears is associated with lower levels of circulating free fatty acids (FFA) and increased insulin sensitivity. Understanding how free‐ranging brown bears suppress lipolysis when gaining weight may therefore provide novel insight toward the development of human therapies. Blood and subcutaneous adipose tissue were collected from immobilized free‐ranging brown bears (fitted with GPS‐collars) during hibernation in winter and from the same bears during the active period in summer in Dalarna, Sweden. The expression of lipid droplet‐associated proteins in adipose tissue was examined under the hypothesis that bears suppress lipolysis during summer while gaining weight by increased expression of negative regulators of lipolysis. Adipose triglyceride lipase (ATGL) expression did not differ between seasons, but in contrast, the expression of ATGL coactivator Comparative gene identification‐58 (CGI‐58) was lower in summer. In addition, the expression of the negative regulators of lipolysis, G0S2 and cell‐death inducing DNA fragmentation factor‐a‐like effector (CIDE)C markedly increased during summer. Free‐ranging brown bears display potent upregulation of inhibitors of lipolysis in adipose tissue during summer. This is a potential mechanism for increased insulin sensitivity during weight gain and G0S2 may serve as a target to modulate insulin sensitivity.

Overexpression of G0/G1 Switch Gene 2 in Adipose Tissue of Transgenic Quail Inhibits Lipolysis Associated with Egg Laying

In avians, yolk synthesis is regulated by incorporation of portomicrons from the diet, transport of lipoproteins from the liver, and release of lipids from adipose tissue; however, the extent to which lipolysis in adipose tissue contributes to yolk synthesis and egg production has yet to be elucidated. G0/G1 switch gene 2 (G0S2) is known to bind and inhibit adipose triglyceride lipase (ATGL), the rate-limiting enzyme in lipolysis. The objective of this study was to determine whether overexpression of the G0S2 gene in adipose tissue could successfully inhibit endogenous ATGL activity associated with egg laying. Two independent lines of transgenic quail overexpressing G0S2 had delayed onset of egg production and reduced number of eggs over a six-week period compared to non-transgenic quail. Although no differences in measured parameters were observed at the pre-laying stage (5 weeks of age), G0S2 transgenic quail had significantly larger interclavicular fat pad weights and adipocyte sizes and lower NEFA concentrations in the serum at early (1 week after laying first egg) and active laying (5 weeks after laying first egg) stages. Overexpression of G0S2 inhibited lipolysis during early and active laying, which drastically shifted the balance towards a net accumulation of triacylglycerols and increased adipose tissue mass. Thereby, egg production was negatively affected as less triacylglycerols were catabolized to produce lipids for the yolk.

Regulation of G0/G1 switch gene 2 (G0S2) expression in human adipose tissue

The G0/G1 switch gene 2 (G0S2) protein attenuated adipose triglyceride lipase (ATGL) activity and decreased lipolysis in rodent and human adipocytes. We hypothesized that G0S2 mRNA expression in human adipose tissue is influenced by depot, adipocyte size, body weight and caloric intake. Adipose tissue samples were obtained during abdominal surgery and by needle biopsy before and 3 h after an extended glucose load in lean subjects. G0S2 mRNA was 7× higher expressed in mature human adipocytes compared to the stromavascular fraction. Cell size inversely correlated with G0S2 mRNA expression in both, subcutaneous and omental adipose depots. G0S2 mRNA expression was 75% higher in subcutaneous compared to omental adipose tissue. Obesity was associated with lower G0S2 mRNA expression in subcutaneous adipose tissue. Acute glucose ingestion after an overnight fast did not significantly increase G0S2 expression in subcutaneous adipose tissue. In conclusion, differences in G0S2 expression may explain depot-specific and obesity-associated differences in lipolysis on the molecular level.

Identification of the avian RBP7 gene as a new adipose-specific gene and RBP7 promoter-driven GFP expression in adipose tissue of transgenic quail

The discovery of an increasing number of new adipose-specific genes has significantly contributed to our understanding of adipose tissue biology and the etiology of obesity and its related diseases. In the present study, comparison of gene expression profiles among various tissues was performed by analysis of chicken microarray data, leading to identification of RBP7 as a novel adipose-specific gene in chicken. Adipose-specific expression of RBP7 in the avian species was further confirmed at the protein and mRNA levels. Examination of the transcription factor binding sites within the chicken RBP7 promoter by Matinspector software revealed potential binding sites for adipogenic transcription factors. This led to the hypothesis that the RBP7 promoter can be utilized to overexpress a transgene in adipose tissue in order to further investigate the function of a transgene in adipose tissue. Several lines of transgenic quail containing a green fluorescent protein (GFP) gene under the control of the RBP7 promoter were generated using lentivirus-mediated gene transfer. The GFP expression in transgenic quail was specific to adipose tissue and increased after adipocyte differentiation. This expression pattern was consistent with endogenous RBP7 expression, suggesting the RBP7 promoter is sufficient to overexpress a gene of interest in adipose tissue at later developmental stages. These findings will lead to the establishment of a novel RBP7 promoter cassette which can be utilized for overexpressing genes of interest in adipose tissue in vivo to study the function of genes in adipose tissue development and lipid metabolism.

Inhibition of lipolysis in the novel transgenic quail model overexpressing G0/G1 switch gene 2 in the adipose tissue during feed restriction

In addition to the issue of obesity in humans, the production of low-fat meat from domestic animals is important in the agricultural industry to satisfy consumer demand. Understanding the regulation of lipolysis in adipose tissue could advance our knowledge to potentially solve both issues. Although the G₀/G₁ switch gene 2 (G0S2) was recently identified as an inhibitor of adipose triglyceride lipase (ATGL) in vitro, its role in vivo has not been fully clarified. This study was conducted to investigate the role of G0S2 gene in vivo by using two independent transgenic quail lines during different energy conditions. Unexpectedly, G0S2 overexpression had a negligible effect on plasma NEFA concentration, fat cell size and fat pad weight under ad libitum feeding condition when adipose lipolytic activity is minimal. A two-week feed restriction in non-transgenic quail expectedly caused increased plasma NEFA concentration and dramatically reduced fat cell size and fat pad weight. Contrary, G0S2 overexpression under a feed restriction resulted in a significantly less elevation of plasma NEFA concentration and smaller reductions in fat pad weights and fat cell size compared to non-transgenic quail, demonstrating inhibition of lipolysis and resistance to loss of fat by G0S2. Excessive G0S2 inhibits lipolysis in vivo during active lipolytic conditions, such as food restriction and fasting, suggesting G0S2 as a potential target for treatment of obesity. In addition, transgenic quail are novel models for studying lipid metabolism and mechanisms of obesity.

Dissecting adipose tissue lipolysis: molecular regulation and implications for metabolic disease

Lipolysis is the process by which triglycerides (TGs) are hydrolyzed to free fatty acids (FFAs) and glycerol. In adipocytes, this is achieved by sequential action of adipose TG lipase (ATGL), hormone-sensitive lipase (HSL), and monoglyceride lipase. The activity in the lipolytic pathway is tightly regulated by hormonal and nutritional factors. Under conditions of negative energy balance such as fasting and exercise, stimulation of lipolysis results in a profound increase in FFA release from adipose tissue (AT). This response is crucial in order to provide the organism with a sufficient supply of substrate for oxidative metabolism. However, failure to efficiently suppress lipolysis when FFA demands are low can have serious metabolic consequences and is believed to be a key mechanism in the development of type 2 diabetes in obesity. As the discovery of ATGL in 2004, substantial progress has been made in the delineation of the remarkable complexity of the regulatory network controlling adipocyte lipolysis. Notably, regulatory mechanisms have been identified on multiple levels of the lipolytic pathway, including gene transcription and translation, post-translational modifications, intracellular localization, protein-protein interactions, and protein stability/degradation. Here, we provide an overview of the recent advances in the field of AT lipolysis with particular focus on the molecular regulation of the two main lipases, ATGL and HSL, and the intracellular and extracellular signals affecting their activity.

Tissue expression pattern and polymorphism of G0S2 gene in porcine

Adipose triglyceride lipase (ATGL), catalyzing the initial step of hydrolysis of triacylglycerol (TAG) in adipocytes, has been known to be inhibited by G0/G1 switch protein 2 (G0S2). In this study, we determined tissue expression pattern and polymorphism of G0S2 gene in porcine. The results showed that the G0S2 transcript levels were very high in the liver and, to a lesser degree, in adipose tissues of greater omentum and suet fat; and low G0S2 transcript levels were observed in other tissues. A comparative study on the transcript levels between ATGL and G0S2 genes showed that ATGL transcript levels were high in all six adipose tissues, but negligible in the liver. Higher transcript levels were obtained for sows in adipose tissues of the inner layer of subcutaneous fat and suet fat, but higher expression values were found for boars in the liver, spleen, and stomach. 19 single nucleotide polymorphisms (SNPs), including 4 nonsynonymous SNPs (g.-307A>T, g.-394C>G, g.-565G>A, and g.-566T>C), were found in porcine G0S2 genomic DNA. Association analyses showed that the g.-565G>A and g.-742T>A SNPs were associated with back fat thickness (BFT). In conclusion, G0S2 mRNAs are abundantly expressed in porcine liver and adipose tissues of greater omentum and suet fat, and sex affects porcine G0S2 tissue transcript levels; meanwhile, the genetic diversity of porcine G0S2 gene is abundant and 2 SNPs are a genetic factor affecting BFT.

Preparation of a nano emodin transfersome and study on its anti-obesity mechanism in adipose tissue of diet-induced obese rats

Objective

To describe the preparation of nano emodin transfersome (NET) and investigate its effect on mRNA expression of adipose triglyceride lipase (ATGL) and G0/G1 switch gene 2 (G0S2) in adipose tissue of diet-induced obese rats.

Methods

NET was prepared by film-ultrasonic dispersion method. The effects of emodin components at different ratios on encapsulation efficiency were investigated.The NET envelopment rate was determined by ultraviolet spectrophotometry. The particle size and Zeta potential of NET were evaluated by Zetasizer analyzer. Sixty male SD rats were assigned to groups randomly. After 8-week treatment, body weight, wet weight of visceral fat and the percentage of body fat (PBF) were measured. Fasting blood glucose and serum lipid levels were determined. The adipose tissue section was HE stained, and the cellular diameter and quantity of adipocytes were evaluated by light microscopy. The mRNA expression of ATGL and G0S2 from the peri-renal fat tissue was assayed by RT-PCR.

Results

The appropriate formulation was deoxycholic acid sodium salt vs. phospholipids 1:8, cholesterol vs. phospholipids 1:3, vitamin Evs. phospholipids 1:20, and emodin vs. phospholipid 1:6. Zeta potential was −15.11 mV, and the particle size was 292.2 nm. The mean encapsulation efficiency was (69.35 ± 0.25)%. Compared with the obese model group, body weight, wet weight of visceral fat, PBF and mRNA expression of G0S2 from peri-renal fat tissue were decreased significantly after NET treatment (all P < 0.05), while high-density lipoprotein cholesterol (HDL-C), the diameter of adipocytes and mRNA expression of ATGL from peri-renal fat tissue were increased significantly (all P < 0.05).

Conclusion

The preparation method is simple and reasonable. NET with negative electricity was small and uniform in particle size, with high encapsulation efficiency and stability. NET could reduce body weight and adipocyte size, and this effect was associated with the up-regulation of ATGL, down-regulation of G0S2 expression in the adipose tissue, and improved insulin sensitivity.

Targeted disruption of G0/G1 switch gene 2 enhances adipose lipolysis, alters hepatic energy balance, and alleviates high-fat diet-induced liver steatosis

Recent biochemical and cell-based studies identified G0/G1 switch gene 2 (G0S2) as an inhibitor of adipose triglyceride lipase (ATGL), a key mediator of intracellular triacylglycerol (TG) mobilization. Here, we show that upon fasting, G0S2 protein expression exhibits an increase in liver and a decrease in adipose tissue. Global knockout of G0S2 in mice enhanced adipose lipolysis and attenuated gain of body weight and adiposity. More strikingly, G0S2 knockout mice displayed a drastic decrease in hepatic TG content and were resistant to high-fat diet (HFD)-induced liver steatosis, both of which were reproduced by liver-specific G0S2 knockdown. Mice with hepatic G0S2 knockdown also showed increased ketogenesis, accelerated gluconeogenesis, and decelerated glycogenolysis. Conversely, overexpression of G0S2 inhibited fatty acid oxidation in mouse primary hepatocytes and caused sustained steatosis in liver accompanied by deficient TG clearance during the fasting-refeeding transition. In response to HFD, there was a profound increase in hepatic G0S2 expression in the fed state. Global and hepatic ablation of G0S2 both led to improved insulin sensitivity in HFD-fed mice. Our findings implicate a physiological role for G0S2 in the control of adaptive energy response to fasting and as a contributor to obesity-associated liver steatosis.

Expression of Potential Regulatory Genes in Abdominal Adipose Tissue of Broiler Chickens during Early Development

The identities of genes that underlie population variation in adipose tissue development in farm animals are poorly understood. Previous studies in our laboratory have suggested that increased fat tissue involves the expression modulation of an array of genes in broiler chickens. Of special interest are eight genes, FGFR3, EPHB2, IGFBP2, GREM1, TNC, COL3A1, ACBD7, and SCD. To understand their expression regulation and response to dietary manipulation, we investigated their mRNA levels after dietary manipulation during early development. Chickens were fed either a recommended standard or a high caloric diet from hatch to eight weeks of age (WOA). The high caloric diet markedly affected bodyweight of the broiler birds. mRNA levels of the eight genes in the abdominal adipose tissue were assayed at 2, 4, 6, and 8 WOA using RT-qPCR. Results indicate that (1) FGFR3 mRNA level was affected significantly by diet, age, and diet:age interaction; (2) COL3A mRNA level was repressed by high caloric diet; (3) mRNA levels of EPHB2, ACBD7, and SCD were affected by age; (4) mRNA level of TNC was modulated by age:diet interaction; (5) changes in GREM1 and IGFBP2 mRNA levels were not statistically different.

Autocrine function of aldehyde dehydrogenase 1 as a determinant of diet- and sex-specific differences in visceral adiposity

Mechanisms for sex- and depot-specific fat formation are unclear. We investigated the role of retinoic acid (RA) production by aldehyde dehydrogenase 1 (Aldh1a1, -a2, and -a3), the major RA-producing enzymes, on sex-specific fat depot formation. Female Aldh1a1(-/-) mice, but not males, were resistant to high-fat (HF) diet-induced visceral adipose formation, whereas subcutaneous fat was reduced similarly in both groups. Sexual dimorphism in visceral fat (VF) was attributable to elevated adipose triglyceride lipase (Atgl) protein expression localized in clusters of multilocular uncoupling protein 1 (Ucp1)-positive cells in female Aldh1a1(-/-) mice compared with males. Estrogen decreased Aldh1a3 expression, limiting conversion of retinaldehyde (Rald) to RA. Rald effectively induced Atgl levels via nongenomic mechanisms, demonstrating indirect regulation by estrogen. Experiments in transgenic mice expressing an RA receptor response element (RARE-lacZ) revealed HF diet-induced RARE activation in VF of females but not males. In humans, stromal cells isolated from VF of obese subjects also expressed higher levels of Aldh1 enzymes compared with lean subjects. Our data suggest that an HF diet mediates VF formation through a sex-specific autocrine Aldh1 switch, in which Rald-mediated lipolysis in Ucp1-positive visceral adipocytes is replaced by RA-mediated lipid accumulation. Our data suggest that Aldh1 is a potential target for sex-specific antiobesity therapy.

The G0/G1 switch gene 2 (G0S2): regulating metabolism and beyond

The G0/G1 switch gene 2 (G0S2) was originally identified in blood mononuclear cells following induced cell cycle progression. Translation of G0S2 results in a small basic protein of 103 amino acids in size. It was initially believed that G0S2 mediates re-entry of cells from the G0 to G1 phase of the cell cycle. Recent studies have begun to reveal the functional aspects of G0S2 and its protein product in various cellular settings. To date the best-known function of G0S2 is its direct inhibitory capacity on the rate-limiting lipolytic enzyme adipose triglyceride lipase (ATGL). Other studies have illustrated key features of G0S2 including sub-cellular localization, expression profiles and regulation, and possible functions in cellular proliferation and differentiation. In this review we present the current knowledge base regarding all facets of G0S2, and pose a variety of questions and hypotheses pertaining to future research directions.

G0/G1 switch gene-2 regulates human adipocyte lipolysis by affecting activity and localization of adipose triglyceride lipase

The hydrolysis of triglycerides in adipocytes, termed lipolysis, provides free fatty acids as energy fuel. Murine lipolysis largely depends on the activity of adipose triglyceride lipase (ATGL), which is regulated by two proteins annotated as comparative gene identification-58 (CGI-58) and G0/G1 switch gene-2 (G0S2). CGI-58 activates and G0S2 inhibits ATGL activity. In contrast to mice, the functional role of G0S2 in human adipocyte lipolysis is poorly characterized. Here we show that overexpression or silencing of G0S2 in human SGBS adipocytes decreases and increases lipolysis, respectively. Human G0S2 is upregulated during adipocyte differentiation and inhibits ATGL activity in a dose-dependent manner. Interestingly, C-terminally truncated ATGL mutants, which fail to localize to lipid droplets, translocate to the lipid droplet upon coexpression with G0S2, suggesting that G0S2 anchors ATGL to lipid droplets independent of ATGL's C-terminal lipid binding domain. Taken together, our results indicate that G0S2 also regulates human lipolysis by affecting enzyme activity and intracellular localization of ATGL. Increased lipolysis is known to contribute to the pathogenesis of insulin resistance, and G0S2 expression has been shown to be reduced in poorly controlled type 2 diabetic patients. Our data indicate that downregulation of G0S2 in adipose tissue could represent one of the underlying causes leading to increased lipolysis in the insulin-resistant state.

Complementary deoxyribonucleic acid cloning of avian G0/G1 switch gene 2, and its expression and association with production traits in chicken

As a member of the G0/G1 switch genes, G0/G1 switch gene 2 (G0S2) is related to many regulatory processes in the human and mouse. For example, it interacts directly with adipose triglyceride lipase to active its triglyceride hydrolysis activities. In this study, G0S2 gene cDNA of the chicken (522 bp), zebra finch (420 bp), sparrow (417 bp), pigeon (417 bp), and Bengalese finch (416 bp) were cloned, and each of them was encoded as a protein of 99 amino acids. The expression of G0S2 mRNA was determined by real-time reverse-transcription PCR analysis in 20 tested tissues of 21- and 91-d-old chickens. The highest mRNA level was found in abdominal fat and subcutaneous fat in both stages. Considerable G0S2 mRNA was also observed in chicken heart and muscle tissues. Expression of the chicken G0S2 gene varied at different stages and sexes. The abundance of G0S2 mRNA on d 21 was far higher than that on d 91. The abundance in female chickens was higher than that in males at both stages. In the coding region, we found 4 SNP, among which only G197A led to a change in the amino acids (Arg66Gln); the rest were synonymous substitutions. Association analysis showed that both G102A and G255A were significantly associated with head width (P < 0.05) and were highly significantly associated with leg muscle color (P < 0.01). The G102A was significantly associated with shank diameter at 63 d (P < 0.05). The SNP G197A was significantly associated with shank diameter at 49 d; CP content of leg muscle; total weights of the heart, liver, gizzard, and glandular stomach; and small intestine length (P < 0.05). In conclusion, much higher G0S2 mRNA was detected in both male and female chickens at 21 d of age than at 91 d of age, and 3 SNP (G102A, G197, and G255A) were associated with chicken production traits.

Fasting, but not exercise, increases adipose triglyceride lipase (ATGL) protein and reduces G(0)/G(1) switch gene 2 (G0S2) protein and mRNA content in human adipose tissue

CONTEXT

Fasting and exercise are characterized by increased lipolysis, but the underlying mechanisms are not fully understood.

OBJECTIVE

The study was designed to test whether fasting and exercise affect mRNA and protein levels of adipose triglyceride lipase (ATGL) and G(0)/G(1) switch gene 2 (G0S2), a recently discovered ATGL inhibitor, in humans.

DESIGN AND PARTICIPANTS

We studied eight healthy men (age, 25.5 ± 4.3 yr) for 6 h (a 4-h basal and a 2-h clamp period) on three occasions in a randomized crossover design: 1) in the basal state and after; 2) 72-h fasting; and 3) 1-h exercise (65% VO(2max)). Subcutaneous abdominal adipose tissue (AT) biopsies were taken at t = 30 and 270 min.

SETTING

The study was conducted at a university hospital research unit.

RESULTS

Circulating free fatty acids and GH were increased, and C-peptide was decreased by both fasting and exercise. During fasting, insulin failed to suppress free fatty acid levels, suggesting AT insulin resistance. ATGL protein was increased 44% (P < 0.001), and G0S2 mRNA and protein were decreased 56% (P = 0.02) and 54% (P = 0.01), respectively, after fasting, but both ATGL and G0S2 were unaffected by exercise. Protein levels of hormone-sensitive lipase and comparative gene identification-58 were unaffected throughout.

CONCLUSIONS

We found increased AT content of ATGL and decreased protein and mRNA content of the ATGL inhibitor G0S2, suggesting increased ATGL activity during fasting, but not after short-term exercise. These findings are compatible with the notion that the ATGL-G0S2 complex is an important long-term regulator of lipolysis under physiological conditions such as fasting in humans.