Cloning of comparative gene identification-58 gene in avian species and investigation of its developmental and nutritional regulation in chicken adipose tissue

Adipose triglyceride lipase (ATGL) is the rate-limiting enzyme of lipolysis in chicken adipose tissue. Its regulation is not fully understood. Recent studies suggest ATGL may be regulated by physical protein-protein interactions. Comparative gene identification 58 (CGI-58) has been identified as an activator of ATGL in mice. The purpose of the current study was to clone and sequence the CGI-58 gene in avian species and to investigate its regulation during development, fasting, and refeeding. Here, we report the cloning and sequencing of the complete coding sequence of CGI-58 and the deduced AA sequences for the domestic chicken, turkey, and Coturnix quail. The CGI-58 protein is a 343-AA protein in the chicken and quail, and a 344-AA protein in the turkey. Sequence comparisons with the human and mouse show that the CGI-58 gene is highly conserved among avian and mammalian species, with complete identities at the predicted lipid-binding site. Cell fractionation of chicken fat cells and stromal-vascular cells revealed that CGI-58 is expressed primarily in mature adipocytes (P < 0.01). When compared in multiple organs and tissues, avian CGI-58 is expressed predominantly in the adipose tissue (P < 0.001), similar to ATGL. To understand CGI-58 expression during adipose tissue development, its mRNA expression was measured along with ATGL and stearoyl CoA desaturase (SCD-1) mRNA, an adipogenic marker, in embryos and adults. Messenger RNA expression of CGI-58 increased (P < 0.05) immediately after hatching, concurrent with peak ATGL expression. It is interesting that CGI-58 remained somewhat increased at posthatch d 11 and 33 as SCD-1 mRNA expression increased (P < 0.05). To evaluate the response of CGI-58 to nutritional status, chickens and quail were fasted for 24 h and subsequently refed. After the fasting period, CGI-58 mRNA was induced (P < 0.05) for both chickens and quail and was returned to control levels upon refeeding. The ATGL mRNA responded similarly, increasing dramatically after fasting and quickly decreasing with refeeding. The direct relationship between CGI-58 and ATGL mRNA expression indicates a role for CGI-58 in activating ATGL-mediated lipolysis in avian species.     

Porcine adipose triglyceride lipase complementary deoxyribonucleic acid clone, expression pattern, and regulation by resveratrol

Adipose triglyceride lipase (ATGL) was recently identified and described as a major novel triglyceride lipase in animals. In this study, we aimed to study the tissue-specific and developmental expression pattern of porcine ATGL (pATGL) and the effect of resveratrol (RES) on expression of pATGL in vitro. The full-length cDNA sequence of pATGL was 1,958 bp (accession no. EF583921), with a 1,458-bp open reading frame encoding a 486-AA protein (the predicted molecular mass of 53.2 kDa, accession no. ABS58651). Comparison of the deduced AA sequence with the bovine, mouse, rat, dog, and human adipose triglyceride lipase showed 87, 84, 83, 81, and 80% similarity, respectively. Furthermore, the pATGL was highly expressed in porcine adipose tissue, to a lesser degree in kidney, heart, and muscle, and least but detectable in brain. In s.c. adipose tissue, pATGL mRNA was low at birth (1 kg of BW) and then increased, reaching a maximal value at 20 kg of BW (approximately 8 wk old; P < 0.01). In peritoneal and omental adipose tissue, the greatest expression of pATGL was observed at 40 kg of BW (approximately 12 wk old). In vitro, exposure of cultured adipocytes to 40 and 80 muM RES for 24 h increased the mRNA levels of pATGL by 95.3% (P < 0.05) and 146.8% (P < 0.01), respectively. Accordingly, lipid accumulation was decreased by 25.7% (P < 0.05) and 60.8% (P < 0.01), respectively. When treated with RES for 48 h, the mRNA levels of pATGL were increased by 104.1% (P < 0.05) and 163.1% (P < 0.01), respectively. As expected, lipid accumulation was decreased by 9.7% (P > 0.05) and 29.0% (P < 0.05), respectively. These results add to our understanding of the role of pATGL in adipose tissue development and as a potential target for regulating fat deposition and meat quality.     

Adiponectin‐impaired adipocyte differentiation negatively regulates fat deposition in chicken

Adiponectin is a protein hormone secreted exclusively by adipocytes that plays an important role in the modulation of glucose and lipid metabolism. To investigate the effect of adiponectin on lipid metabolism in chicken, rosiglitazone (agonist of adiponectin) and dexamethasone (inhibitor of adiponectin) were used to treat 23‐day‐old broilers in vivo. To verify the functionality of adiponectin on fat deposition, chicken pre‐adipocytes were cultured in the medium containing 10 μg/ml adiponectin. Serum adiponectin and lipids and fat distribution were analysed. Oil Red O staining was used to determine lipid deposition in adipocytes. The expression levels of adiponectin, adiponectin receptors (AdipoR) and lipid metabolism–related genes in different tissues and pre‐adipocytes were measured using real‐time PCR, and the abundance of lipid metabolism–related proteins was measured by Western blot. Rosiglitazone increased serum adiponectin concentration and the expression levels of adiponectin and adiponectin receptor 1 (AdipoR1) in tissues and significantly decreased levels of serum lipids and fat deposition. Rosiglitazone significantly increased the expression levels of adipose triglyceride lipase (ATGL) and AdipoR1 and decreased the expression levels of fatty acid synthase (FAS). Dexamethasone had the converse effects compared with rosiglitazone. Oil red O staining results showed a marked decrease in fat deposition in cells treated with adiponectin. In adipocytes, adiponectin could decrease the expression levels of CCAAT/enhancer‐binding protein α (C/EBPα) and FAS and increased the expression levels of ATGL and AdipoR1. These results indicate that adiponectin has a remarkable effect on impairment of adipocyte differentiation, which contributes to the negative regulation of fat deposition in chicken.     

猪ATGL基因5′调控区的SNPs检测及生物信息学分析

脂肪甘油三酯水解酶(ATGL)是脂肪组织脂肪动员过程中的水解限速酶,主要催化甘油三酯水解为甘油二酯。研究对金华猪、岔路黑猪、杜洛克、大约克和皮特兰5个猪种ATGL基因其5′调控区1.2 kb的片段进行SNPs检测和生物信息学分析。结果表明:ATGI基因5'调控区存在第-845位G→C和第-854位T→C的连锁突变。序列分析显示该区域可能存在启动子区,且2个突变都会导致其部分潜在转录因子结合位点的产生或消失。采用PCR-RFLP方法检测g-845G→C座位在金华猪、岔路黑猪、杜洛克、大约克和皮特兰中的分布情况,卡方分析结果显示,3种基因型在5个猪种中的分布存在极显著差异(P<0.01),提示不同猪种间脂肪性状的差异可能与ATGL基因5'调控区的基因突变有关。     

Adiposity of calf- and yearling-fed Brangus steers raised to constant-age and constant-body weight endpoints

We tested the hypothesis that fatty acid biosynthesis and adipocyte diameter and volume would be greater in s.c. and i.m. adipose tissues of calf-fed steers than in yearling-fed steers at a constant BW, due to the greater time on feed for the calf-fed steers. Conversely, we predicted that the capacity for s.c. and i.m. preadipocytes to divide, as estimated by 3H-thymidine incorporation into DNA, would be greater in the less mature adipose tissues of calf-fed steers and in yearling-fed steers at 16 mo of age than in yearling-fed steers fed to 18 mo of age. Brangus steers were fed a corn-based finishing diet as calves (calf-fed; n = 9) or yearlings (n = 4) to 16 mo of age (CA yearling-fed); another group of yearlings (n = 5) was fed to a constant-BW end point of 530 kg (CW yearling-fed). Both groups of yearling-fed steers had free access to native pasture until 12 mo of age. At slaughter, the fifth to eighth thoracic rib section of the LM was removed, and fresh s.c. and i.m. adipose tissues were removed for in vitro incubations. There were no differences in the number of s.c. adipocytes/g or mean peak volumes of adipocytes across production groups (P > or = 0.14). However, s.c. adipose tissue of CA yearling-fed steers contained greater proportions of smaller adipocytes (<1,500 pL) than calffed or CW yearling-fed steers, and similar results were observed for i.m. adipose tissue. Acetate incorporation into total lipids was greater (P = 0.02) in s.c. adipose tissue of CA yearling-fed steers than in calf-fed or CW yearling-fed steers, and tended to be different (P = 0.10) across production groups in i.m. adipose tissue. The production system x cell fraction interaction was significant (P = 0.03) for s.c. adipose tissue DNA synthesis, which was greatest in adipocytes from CA yearling-fed steers, whereas there were no differences across production system in stromal vascular (SV) DNA synthesis. For i.m. adipose tissue, DNA synthesis was greatest in adipocytes and SV cells from CA yearling-fed calves, and was greater in SV cells than in adipocytes (both P = 0.01). Therefore, stage of adipose tissue development more strongly influenced fatty acid synthesis, adipocyte volume, and DNA synthesis than age at sampling, final BW, or time on the finishing diet.     

Characterisation of glucose transporter (GLUT) gene expression in broiler chickens

1. Glucose transporter (GLUT) proteins, one of which is the major insulin-responsive transporter GLUT4, play a crucial role in cellular glucose uptake and glucose homeostasis in mammals. The aim of this study was to identify the extent of mRNA expression of GLUT1, GLUT2, GLUT3 and GLUT8 in chickens intrinsically lacking GLUT4. 2. GLUT1 mRNA was detected in most tissues of 3-week-old broiler chickens, with the highest expression measured in brain and adipose tissue. GLUT2 was expressed only in the liver and kidney. GLUT3 was highly expressed in the brain. GLUT8 was expressed ubiquitously, with expression in kidney and adipose tissue relatively higher than that of other tissues. 3. Expression levels of GLUT isoforms 1, 3 and 8 in skeletal muscle tissue were very low compared to the other tissues tested. 4. [3H]Cytochalasin B binding assays on tissue from 3-week-old chickens showed that the number of cytochalasin B binding sites in skeletal muscle plasma membranes was higher than in liver plasma membranes. These results suggest that GLUT proteins and/or GLUT-like proteins that bind cytochalasin B are expressed in chicken skeletal muscles. 5. It is proposed that GLUT expression and glucose transport in chicken tissues are regulated in a manner different from that in mammals.     

Postnatal development of stearoyl coenzyme A desaturase gene expression and adiposity in bovine subcutaneous adipose tissue

This investigation addressed the hypothesis that stearoyl coenzyme A desaturase (SCD) gene expression would serve as a postnatal marker of adipocyte differentiation in bovine s.c. adipose tissue. Samples of tailhead s.c. adipose tissue were obtained by biopsy from preweaning steer calves 2.5 wk, 5 mo, and 7.5 mo of age and from yearling steers 12 mo of age. Samples also were obtained at slaughter when the steers were 18 mo of age. The steers sampled as yearlings were fed native pasture from weaning until 12 mo of age, and the steers sampled at slaughter were fed a high-concentrate diet from 12 to 18 mo of age. Major peak adipocyte volumes for the 2.5-wk-, 5-mo-, and 7.5-mo-old steers were 14, 270, and 700 pL, respectively (P < .001). The steers did not gain weight during pasture feeding, and at 12 mo of age peak adipocyte volume had decreased (P = .009) to 270 pL. At this time, a second, smaller population of adipocytes had appeared with a peak volume of 115 pL. At slaughter, adjusted fat thickness of the steers was 1.60 +/- .13 cm, the USDA yield grade of the carcasses was 3.51 +/- .31, and peak adipocyte volume had increased (P = .01) to over 2,500 pL. The number of adipocytes per 100 mg of adipose tissue doubled (P = .006) between 2.5 wk and 5 mo of age, concurrent with the nearly 20-fold increase in peak adipocyte volume, indicating that this was a period of apparent adipocyte hyperplasia. Uncoupling protein mRNA was undetectable at all stages of postnatal growth, indicating that differentiating tailhead s.c. adipocytes do not acquire brown adipocyte characteristics postnatally. Lipogenesis expressed on a cellular basis was low in all preweaning samples and increased significantly above preweaning values only in the 18-mo-old steers. Stearoyl coenzyme A desaturase mRNA concentration also was low in all preweaning samples, but it peaked (P = .07) at 12 mo of age. Because the peak in SCD mRNA concentration preceded a significant rise in lipogenesis and lipid filling, we conclude that the level SCD gene expression may be indicative of the extent of terminal differentiation in bovine tailhead s.c. adipose tissue.     

Role of Corticosterone in Lipid Metabolism in Broiler Chick White Adipose Tissue

Excessive accumulation of body fat in broiler chickens has become a serious problem in the poultry industry. However, the molecular mechanism of triglyceride accumulation in chicken white adipose tissue (WAT) has not been elucidated. In the present study, we investigated the physiological importance of the catabolic hormone corticosterone, the major glucocorticoid in chickens, in the regulation of chicken WAT lipid metabolism. We first examined the effects of fasting on the mRNA levels of lipid metabolism-related genes associated with WAT, plasma corticosterone, and non-esterified fatty acid (NEFA). We then examined the effects of corticosterone on the expression of these genes in vivo and in vitro. In 10-day-old chicks, 3 h of fasting significantly decreased mRNA levels of lipoprotein lipase (LPL) in WAT and significantly elevated plasma concentrations of NEFA. Six hours of fasting significantly increased mRNA levels of adipose triglyceride lipase (ATGL) in WAT and significantly elevated plasma concentrations of corticosterone. On the other hand, fasting significantly reduced mRNA levels of LPL in WAT and elevated plasma concentrations of NEFA in 29-day-old chicks without affecting mRNA levels of ATGL in WAT or plasma corticosterone concentrations. Oral administration of corticosterone significantly reduced mRNA levels of LPL and significantly increased the mRNA levels of ATGL in WAT in 29-day-old chicks without affecting plasma NEFA concentrations. The addition of corticosterone to primary chicken adipocytes significantly increased mRNA levels of ATGL, whereas mRNA levels of LPL tended to decrease. NEFA concentrations in the culture medium were not influenced by corticosterone levels. These results suggest that plasma corticosterone partly regulates the gene expression of lipid metabolism-related genes in chicken WAT and this regulation is different from the acute elevation of plasma NEFA due to short-term fasting.     

Cellular and enzyme-histochemical aspects of adipose tissue development in obese (Ossabaw) and lean (crossbred) pig fetuses: an ontogeny study

The cellular and enzyme-histochemical differentiation of subcutaneous adipose tissue was studied in lean and obese pig fetuses at several ages. Positive reactions for a variety of cytosolic and organellar enzyme markers indicate metabolic competence of fetal adipocytes despite their small size (12 to 15 microns). Reactions for several enzymes decreased with fetal age and may be associated with a qualitative change in activity of adipocyte organelles. Age-associated increases in two lipogenic enzymes were observed in obese adipocytes. Observations on developing cells around hair follicles in the younger fetuses indicated significant temporal lags between the appearance of detectable enzyme activities in adipocytes. Enzyme activities in order of appearance were: dehydrogenases (cytosolic and mitochondrial), lipoprotein lipase and esterase. Esterase activity and several other enzymes were never observed in lipid positive cells that were not spherical. A proportion of hair follicle associated adipocytes in 110-d-old lean fetuses were histochemically and morphologically similar to brown adipocytes in the young rat. There was no evidence for brown adipocyte like cells in obese fetuses. Finally, comparison of the enzyme-histochemical differentiation of lean and obese fetal adipocytes indicates that fetal adipocytes become sensitive to external stimuli between 70 and 90 d of gestation.     

Adipocyte metabolism and cellularity are related to differences in adipose tissue maturity between Holstein and Charolais or Blond d'Aquitaine fetuses

This paper reports the metabolic and morphological characteristics of bovine adipose tissue (AT) at end of fetal life and its variability with breed and anatomical site of AT. Our hypothesis was that, in cattle, end-of-fetal-life differences in adipocyte number, size, and histology may account for differences in AT maturity. To address this question, perirenal and intermuscular AT were sampled from Charolais, Blond d'Aquitaine, and Holstein fetuses at 260 d postconception. Holstein fetuses showed greater leptin mRNA abundance, which is consistent with the greater perirenal AT weight (P = 0.03) than Blond d'Aquitaine fetuses. Compared with Blond d'Aquitaine or Charolais fetuses, Holstein fetuses had larger (P < 0.001) adipocytes, greater (P < 0.05) activities of enzymes involved in de novo fatty acid (FA) synthesis (FA synthase, glucose-6-phosphate dehydrogenase, malic enzyme) and FA esterification (glycerol-3-phosphate dehydrogenase), and greater (P = 0.06, P = 0.10, P < 0.001) mRNA abundance for lipolytic enzymes (hormone-sensitive lipase and adipose triglyceride lipase) and uncoupling protein 1 in both perirenal and intermuscular AT. This indicates increased FA turnover in Holstein adipocytes through FA storage, mobilization, and oxidation pathways. Whatever the breed, adipocytes were smaller in perirenal AT than intermuscular AT. Whatever the breed or anatomical site, bovine AT at 260 d postconception contained predominantly unilocular adipocytes believed to be white adipocytes together with a few multilocular brown adipocytes. We conclude that the greater metabolic and morphologic maturity of adipocytes from Holstein than Blond d'Aquitaine and Charolais fetuses may contribute to the greater thermogenic aptitude of Holstein newborns. Moreover, the presence of both white and brown adipocytes at the end of fetal life highlights the complexity of AT structure and may indicate that the cellular and functional heterogeneity of AT repeatedly observed postnatally has a developmental origin.     

Ovine adipose tissue monounsaturated fat content is correlated to depot-specific expression of the stearoyl-CoA desaturase gene

The basis for the variation in fatty acid composition in different ovine adipose tissue depots was investigated. The proportion of stearic (C18:0) and oleic (C18:1) acids vary in a site-specific fashion; abdominal depots (omental and perirenal) contain relatively more C18:0 than C18:1, and carcass depots, especially sternum, have a markedly higher proportion of C18:1. Additionally, expression of a number of lipogenic enzyme genes (stearoyl-CoA desaturase [SCD], acetyl-CoA carboxylase-alpha [ACC-alpha], lipoprotein lipase [LPL]) and the cytoskeletal protein gene alpha-tubulin vary among depots, although the pattern of variation differs for each mRNA. When these expression data were related to the mean cell volume of adipocytes pooled from all depots, a significant pattern emerged: expression of the ACC-alpha, LPL, and alpha-tubulin genes was highly correlated with the size of adipocytes. In contrast, when the expression of SCD mRNA was assessed as a function of mean cell volume, two populations of adipocytes emerged: no significant correlation was found between the expression of SCD mRNA per adipocyte and mean cell volume for the abdominal depots, although a highly significant correlation was observed between SCD gene expression and mean cell volume for the carcass and epicardial depots. Similarly, a highly significant correlation was found for the amount of C18:1 per adipocyte and the abundance of SCD mRNA per adipocyte for the carcass and epicardial depots, whereas no significant correlation was observed for these traits for the omental and perirenal depots. Thus, the SCD gene seems to be regulated in a depot-specific fashion and in a manner distinct from that of the ACC and LPL genes.     

猪甘油三酯水解酶和激素敏感脂酶基因表达规律的研究

利用半定量RT-PCR法分析比较了甘油三酯水解酶(Triacylglycerol hydrolase,TGH)和激素敏感脂酶(Hormone-sensitive lipase,HSL)基因在不同猪种、不同发育阶段及不同部位脂肪组织中转录表达的差异,探讨其在猪脂肪组织的表达规律。结果显示,脂肪型个体TGHmRNA表达丰度显著低于瘦肉型和杂交型个体,成年猪较初生仔猪低,皮下、腹膜和内脏脂肪组织中TGH表达量依次递增;其变化规律与HSL相同。此外,对分离培养的原代前体脂肪细胞通过诱导分化和油红O染色区分分化状态,分析TGHmRNA表达的时序变化,发现TGH在前脂肪细胞中不转录表达,诱导分化后开始表达,且在诱导分化第4天表达量最高,分化第10天表达量下降,达到峰值的时间较HSL早。结果表明,TGH的表达与个体肥胖程度、年龄、脂肪组织部位以及脂肪细胞分化程度相关,同时,在脂肪细胞分化过程中,TGH表达峰值早于HSL,提示TGH在脂肪细胞发育过程中可能较早承担基础脂解作用。     

Adipogenic differentiation state-specific gene expression as related to bovine carcass adiposity

Genetic regulation of the site of fat deposition is not well defined. The objective of this study was to investigate adipogenic differentiation state-specific gene expression in feedlot cattle (>75% Angus; <25% Simmental parentage) of varying adipose accretion patterns. Four groups of 4 steers were selected via ultrasound for the following adipose tissue characteristics: low subcutaneous-low intramuscular (LSQ-LIM), low subcutaneous-high intramuscular (LSQ-HIM), high subcutaneous-low intramuscular (HSQ-LIM), and high subcutaneous-high intramuscular (HSQ-HIM). Adipose tissue from the subcutaneous (SQ) and intramuscular (IM) depots was collected at slaughter. The relative expression of adipogenic genes was evaluated using quantitative PCR. Data were analyzed using the mixed model of SAS, and gene expression data were analyzed using covariate analysis with ribosomal protein L19 as the covariate. No interactions (P > 0.10) were observed between IM and SQ adipose tissue depots for any of the variables measured. Therefore, only the main effects of high and low accretion within a depot and the effects of depot are reported. Steers with LIM had smaller mean diameter IM adipocytes (P < 0.001) than HIM steers. Steers with HSQ had larger mean diameter SQ adipocytes (P < 0.001) than LSQ. However, there were no differences (P > 0.10) in any of the genes measured due to high or low adipose accretion. Preadipogenic delta-like kinase1 mRNA was greater in the IM than the SQ adipose tissue; conversely, differentiating and adipogenic genes, lipoprotein lipase, PPARγ, fatty acid synthetase, and fatty acid binding protein 4 were greater (P < 0.001) in the SQ than the IM depot. Intramuscular adipocytes were smaller than SQ adipocytes and had greater expression of the preadipogenic gene, indicating that more hyperplasia was occurring. Meanwhile, SQ adipose tissue contained much larger (P < 0.001) adipocytes that had a greater expression (P < 0.001) of differentiating and adipogenic genes than did the IM adipose tissue, indicating more cells were undergoing differentiation and hypertrophy. Adipogenic differentiation state-specific gene expression was not different in cattle with various phenotypes, but adipogenesis in the SQ and IM adipose tissues seems to occur independently.     

Expression of fat deposition and fat removal genes is associated with intramuscular fat content in longissimus dorsi muscle of Korean cattle steers

Intramuscular fat (IMF) in cattle is an important component of traits that influence meat quality. We measured carcass characteristics and gene expression in Korean steers to clarify the molecular mechanism(s) underlying IMF deposition in LM tissue by determining the correlation between IMF content and gene expression abundance and by developing models to predict IMF content using gene expression abundance. The deposition of IMF is determined by a balance between fat deposition and fat removal in the LM. We measured mRNA abundance of lipid metabolic genes including lipogenesis [acetyl CoA carboxylase (ACC), fatty acid synthase (FASN)], fatty lipid uptake [lipoprotein lipase (LPL), fatty acid translocase (CD36), fatty acid transport protein 1 (FATP1)], fatty acid esterification [glycerol-3-phosphate acyltransferase 1 (GPAT1), acylglycerol phosphate acyltransferase 1 (AGPAT1), diacylglycerol acyltransferase 1 (DGAT1), DGAT2], lipolysis [adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), monoglyceride lipase (MGL)], and fatty acid oxidation [carnitine palmitoyl transferase 1B, very long-chain acyl-CoA dehydrogenase (VLCAD), medium-chain acyl-CoA dehydrogenase (MCAD)] in the LM. The mRNA abundance of the GPAT1 gene showed the greatest correlation (r = 0.74; P < 0.001) with IMF content among 9 fat deposition genes. The gene expression abundance of other fat deposition genes including ACC, FASN, LPL, CD36, FATP1, AGPAT1, DGAT1, and DGAT2 also exhibited significant positive correlations (P < 0.05) with IMF content in the LM. Conversely, ATGL mRNA abundance showed the greatest negative correlation (r = -0.68; P < 0.001) with IMF content in the LM among 6 fat removal genes. The expression of other fat removal genes including MGL, VLCAD, and MCAD showed significant negative correlations (P < 0.05) with IMF content. Our findings show that the combined effects of increases in lipogenesis, fatty acid uptake, fatty acid esterification, and of decreases in lipolysis and fatty acid oxidation contribute to increasing IMF deposition in Korean steers. The multiple regression analysis revealed that the mRNA abundance of the GPAT1 gene in the LM was the first major variable predicting IMF content (54%) among 15 lipid metabolic genes. The second was mRNA abundance of ATGL (11%). In conclusion, these results suggest that GPAT1 and ATGL genes could be used as genetic markers to predict IMF deposition in the LM.     

Coordinate regulation of ovine adipose tissue gene expression by propionate

The current study examined the acute effects of intravenous propionate infusion on plasma hormones and metabolites and the expression of adipose tissue lipogenic genes. Four yearling rams were assigned to one oftwo groups (saline or propionate infusion) in a crossover design. All sheep were cannulated in both jugular veins and infused with 1.2 M propionate at a rate of 64 micromol x mix(-1) x kg BW(-1) for 30 min. Blood samples were collected at -10, 0, 5, 10, 20, 30, 60, and 120 min after initiation of infusion. Subcutaneous adipose tissue biopsies were obtained from the tailhead at 0 and 2 h after propionate infusion and analyzed for gene expressions of lipoprotein lipase, acetyl CoA carboxylase, fatty acid synthase, peroxisome proliferator-activated receptor gamma, leptin, and uncoupling protein-2 using a nonisotopic ribonuclease protection assay. The partial cDNA of the enoyl reductase region of ovine fatty acid synthase was cloned and sequenced from s.c. adipose tissue of sheep. The deduced amino acid sequence (210 amino acids) was 86% identical to human, 88% identical to rat, 88% identical to mouse, and 72% identical to chicken. Plasma glucose and insulin concentrations abruptly increased 5 min after beginning propionate infusion and further increased up until 30 min but were unaffected in saline-infused sheep (P < 0.05). Plasma concentration of NEFA decreased (P < 0.05) during propionate infusion, whereas IGF-I levels were unaltered. The amounts of lipoprotein lipase, acetyl CoA carboxylase, fatty acid synthase, peroxisome proliferator-activated receptor gamma, and leptin mRNA increased (P < 0.05) in s.c. adipose tissue of propionate-infused sheep compared with those of saline-infused sheep. However, uncoupling protein-2 mRNA decreased (P < 0.05) in propionate-infused sheep. This study demonstrates that an acute nutrient challenge, in the form of i.v. propionate, can stimulate or inhibit the expression of various adipose tissue genes involved with lipogenesis and adipose tissue metabolism.