Lipogenesis and stearoyl-CoA desaturase gene expression and enzyme activity in adipose tissue of short- and long-fed Angus and Wagyu steers fed corn- or hay-based diets

Angus and Wagyu steers consuming high-roughage diets exhibit large differences in adipose tissue fatty acid composition, but there are no differences in terminal measures of stearoyl-CoA desaturase (SCD) activity or gene expression. Also, adipose tissue lipids of cattle fed corn-based diets have greater MUFA:SFA ratios than cattle fed hay-based diets. We hypothesized that any changes in SCD gene expression and activity would precede similar changes in adipose tissue lipogenesis between short- and long-fed endpoints. Furthermore, changes in SCD activity and gene expression between production endpoints would differ between corn- and hay-fed steers and between Wagyu and Angus steers. Angus (n = 8) and Wagyu (n = 8) steers were fed a corn-based diet for 8 mo (short-fed; 16 mo of age) or 16 mo (long-fed; 24 mo of age), whereas another group of Angus (n = 8) and Wagyu (n = 8) steers was fed a hay-based diet for 12 mo (short-fed; 20 mo of age) or 20 mo (long-fed; 28 mo of age) to match the end point BW of the corn-fed steers. Acetate incorporation into lipids in vitro was greater (P < 0.01) in corn-fed steers than in hay-fed steers and tended (P = 0.06) to be greater in Wagyu than in Angus s.c. adipose tissue because the rate in Wagyu was twice that of Angus adipose tissue in the corn-fed, short-fed steers. There were diet x end point interactions for lipogenesis in i.m. and s.c. adipose tissues (both P < 0.01) because lipogenesis was 60 to 90% lower in the long-fed cattle than in short-fed cattle fed the corn-based diet. The greatest SCD enzyme activity in Angus s.c. adipose tissue was observed at 24 mo of age (corn-based diet), but activity in Wagyu adipose tissue was greatest at 28 mo of age (hay-based diet; breed x diet x end point interaction, P = 0.08). For short- vs. long-fed endpoints in Angus, s.c. adipose tissue SCD activity was less (hay diet) or the same (corn diet). Conversely, SCD gene expression was greatest in long-fed Wagyu steers fed the hay- or corn-based diets (breed x end point interaction; P < 0.01). Contrary to our hypotheses, SCD activity increased over time, whereas lipogenesis from acetate decreased. However, the developmental pattern of SCD gene expression and activity differed markedly between hay-fed Angus and Wagyu adipose tissues, which may explain the differences in the MUFA:SFA ratios observed in adipose tissues from these cattle.     

Subcutaneous and intramuscular adipose tissue stearoyl-coenzyme A desaturase gene expression and fatty acid composition in calf- and yearling-fed Angus steers

We proposed that stearoyl-CoA desaturase (SCD) activity dictates fatty acid composition of adipose tissue and muscle in beef cattle, regardless of ruminal or hepatic fatty acid hydrogenation or desaturation. Twelve Angus steers were assigned to a calf-fed (CF) group and slaughtered at weaning (8 mo of age; n=4), 12 mo of age (n=4), or 16 mo of age (n=4). Twelve steers were assigned to a yearling-fed (YF) group and slaughtered at 12 mo of age (n=4), 16 mo of age (n=4), and 17.5 mo of age (n=4; 525 kg, market weight). Data were analyzed based on time on the corn-based finishing diet, with terminal age as a covariate, and orthogonal polynomial contrasts were tested on the main effects of treatment group and time on the finishing diet. Fatty acids from duodenal digesta, plasma, liver, LM, and subcutaneous and intramuscular adipose tissue were measured, and SCD gene expression was measured in intramuscular and subcutaneous adipose tissues. In duodenal digesta, palmitic and linoleic acids increased by 100% over the sampling period, α-linolenic acid decreased over the sampling period, and trans-vaccenic acid was greater in YF than in CF steers (all P < 0.01). The proportion of α-linolenic acid decreased over time in all tissues, including liver. The SCD index (ratio of SCD fatty acid products to SCD fatty acid substrates) increased over time in LM and in intramuscular and subcutaneous adipose tissues. The SCD:glyceraldehyde 3-phosphate dehydrogenase mRNA ratio was virtually undetectable at the initial sampling periods in subcutaneous adipose tissue of YF and CF steers, and it increased over time (P < 0.01). The SCD index and SCD:glyceraldehyde 3-phosphate dehydrogenase ratio were greater in intramuscular adipose tissue of CF steers than in that of YF steers. The SCD index did not change over time in liver and decreased over time in duodenal digesta. We conclude that, unlike essential fatty acids, the SFA and MUFA composition of adipose tissue is regulated by adipose tissue fatty acid desaturation, with little contribution from hepatic or duodenal fatty acids.     

Relationship between adipose maturity and fatty acid composition in various adipose tissues of Japanese Black,Holstein and Crossbred (F1) steers

The amount of monounsaturated fatty acid (MUFA) is intimately related to adipose softness, melting point (MP) and flavor in beef. Stearoyl‐CoA desaturase (SCD) is a main gene involved in MUFA synthesis. Mature adipose tends to be highly saturated, whereas immature or maturing adipose is highly unsaturated when chronologically based, so the degree of non‐saturation can be an index of adipose maturity. In this study, three different adipose tissues (coelomic (CL), perirenal (PR), and subcutaneous (SC)) from three beef breeds with differing slaughter ages (Japanese Black (29.5 months), Holstein (20.1 month), and F1 crossbreed (25.6 months)) were examined to: (i) determine adipose maturity level as indexed by MUFA %; and (ii) determine SCD and other lipogenic gene messenger RNA (mRNA) expression levels in relation to unsaturated fatty acid content. Fatty acid composition was significantly different between adipose tissues (P < 0.05). MUFA amount was high in the following order: SC > CL > PR. This pattern corresponded to SCD mRNA expression profile showing higher expression in SC than CL and PR. However, Japanese black cattle are an exception with CL adipose containing similar UFA % as SC adipose, yet having the lowest SCD mRNA expression level among all adipose tissues tested. Therefore, SCD mRNA expression and MUFA % appear to be directly related; however, differences in SCD mRNA expression among three adipose tissues may reflect differences in the fat development characteristics affected by chronological age of the cattle breeds.     

Effect of SCD and SREBP genotypes on fatty acid composition in adipose tissue of Japanese Black cattle herds

Fatty acid composition of beef adipose tissue is one of important traits because high proportions of monounsaturated fatty acid are related to favorable beef flavor and tenderness. In this study, we investigated effects of genetic factors such as stearoyl-CoA desaturase (SCD) and sterol regulatory element binding protein (SREBP) on beef carcass traits including fatty acid composition using two cattle populations. Sire effect was significantly related to almost all traits except BMS, suggesting that the trait examined in this study is highly controlled by genetic factors. The effect of SCD genotype on fatty acid composition was detected remarkably in both cattle groups, especially on stearic and oleic acids. This result was consistent with our previous studies and suggests that SCD is associated with fatty acid composition. Unlike SCD genotyping, the effect of SREBP genotype was not identified in this study. Our results suggested that SCD genotype would contribute to improving beef quality in field populations. Further studies about the relationship among these factors will bring an insight into the molecular mechanism of fatty acid metabolism in cattle.     

Epistatic effects between pairs of the growth hormone secretagogue receptor 1a,growth hormone,growth hormone receptor,non‐SMC condensin I complex,subunit G and stearoyl‐CoA desaturase genes on carcass,price‐related and fatty acid composition traits in Japanese Black cattle

Growth hormone secretagogue receptor 1a (GHSR1a), growth hormone (GH), growth hormone receptor (GHR), non‐SMC condensin I complex, subunit G (NCAPG) and stearoyl‐CoA desaturase (SCD), are known to play important roles in growth and lipid metabolisms. Single and epistatic effects of the five genes on carcass, price‐related and fatty acid (FA) composition traits were analyzed in a commercial Japanese Black cattle population of Ibaraki Prefecture. A total of 650 steers and 116 heifers for carcass and price‐related traits, and 158 steers for FA composition traits were used in this study. Epistatic effects between pairs of the five genes were found in several traits. Alleles showing strain‐specific differences in the five genes had significant single and epistatic effects in some traits. The data suggest that a TG‐repeat polymorphism of the GHSR1a.5′UTR‐(TG)_n locus plays a central role in gene–gene epistatic interaction of FA composition traits in the adipose tissue of Japanese Black cattle.     

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.     

Effects of dietary copper on the expression of lipogenic genes and metabolic hormones in steers

An experiment was conducted to determine the effects of Cu supplementation on performance, subcutaneous adipose tissue mRNA expression of acetyl CoA carboxylase (ACC), stearoyl CoA desaturase (SCD), uncoupling protein 2 (UCP2), and leptin in growing and finishing steers. Forty-eight purebred Angus steers were allotted to one of five treatments: 1) control (no supplemental Cu); 2) 10 mg Cu/kg DM from CuSO4; 3) 10 mg Cu/kg DM from a Cu amino acid complex (Availa Cu); 4) 20 mg Cu/kg DM from CuSO4; 5) 20 mg Cu/kg DM from Availa Cu. Steers were fed an alfalfa hay corn-based diet for 56 d (basal diet contained 7.1 mg Cu/kg DM) and switched to a high-concentrate diet for 144 d (basal diet contained 6.1 mg Cu/kg DM). Blood samples were obtained every 28 d throughout the entire experiment. On d 112 of the finishing period, subcutaneous adipose tissue biopsies were obtained from the tailhead of three animals per treatment and analyzed for ACC, SCD, UCP2, and leptin mRNA expression. Animal performance was not affected by Cu supplementation during the growing phase. Steers receiving 10 mg Cu/kg DM from Availa Cu had higher (P < 0.05) ending body weights and tended (P < 0.10) to have higher ADG than steers receiving 10 mg Cu/kg DM from CuSO4 during the finishing phase. Serum concentrations of nonesterified fatty acid and insulin were not affected by Cu supplementation. Steers receiving supplemental Cu tended (P < 0.11) to have less backfat relative to controls. However, dietary Cu did not influence the level of subcutaneous adipose tissue ACC and SCD mRNA. Neither UCP2 nor leptin gene expression was affected by Cu supplementation. These results indicate that dietary Cu supplementation (10 to 20 mg Cu/kg DM diet) may alter lipid metabolism of subcutaneous adipose tissue; however, it does not seem to affect expression of certain lipogenic genes.     

Effect of dietary energy source on in vitro substrate utilization and insulin sensitivity of muscle and adipose tissues of Angus and Wagyu steers

Angus (n = 8; 210 kg of BW) and 7/8 Wagyu (n = 8; 174 kg of BW) steers were used to evaluate the effects of dietary energy source on muscle and adipose tissue metabolism and insulin sensitivity. Steers were assigned to either a grain-based (corn) or hay-based (hay) diet and fed to similar final BW. At slaughter, LM and s.c. and i.m. adipose tissue samples were collected. Portions of the LM and adipose tissues were placed immediately in liquid N for later measurement of glycolytic intermediates. Fresh LM and s.c. and i.m. adipose tissues were incubated with [U-(14)C]glucose to assess glucose metabolism in vitro. All in vitro measures were in the presence of 0 or 500 ng/mL of insulin. Also, s.c. and i.m. adipose tissues were incubated with [1-(14)C]acetate to quantify lipid synthesis in vitro. Glucose-6-phosphate and fructose-6-phosphate concentrations were 12.6- and 2.4-fold greater in muscle than in s.c. and i.m. adipose tissues, respectively. Diet did not affect acetate incorporation into fatty acids (P = 0.86). Insulin did not increase conversion of glucose to CO(2), lactate, or total lipid in steers fed hay but caused an increase (per cell) of 97 to 110% in glucose conversion to CO(2), 46 to 54% in glucose conversion to lactate, and 65 to 160% in glucose conversion to total lipid content in adipose tissue from steers fed corn. On a per-cell basis, s.c. adipose tissue had 37% greater glucose oxidation than i.m. adipose (P = 0.04) and 290% greater acetate incorporation into fatty acids than i.m. adipose (P = 0.04). Insulin addition to s.c. adipose tissue from corn-fed steers failed to stimulate glucose incorporation into fatty acids, but exposing i.m. adipose tissue from corn-fed steers to insulin resulted in a 165% increase in glucose incorporation into fatty acids. These results suggest that feeding hay limited both glucose supply and tissue capacity to increase glucose utilization in response to insulin without altering acetate conversion to fatty acids. Because s.c. adipose tissue consistently utilized more acetate and oxidized more glucose than did i.m. adipose, these results suggest that hay-based diets may alter i.m. adipose tissue metabolism with less effect on s.c. adipose tissue.     

Identification and utilization of genes associated with beef qualities

The fatty acid composition of adipose tissue in beef has been recognized as an important trait because of its relationship with beef quality, including favorable beef flavor and tenderness. Over the last decade, we have tried to identify the genes responsible for the fatty acid composition in cattle, and have found the following. (i) Genetic polymorphism of stearoyl‐CoA desaturase (SCD) is one of the responsible genes associated with fatty acid composition. The average effects of gene substitution of the SCD type A gene on the monounsaturated fatty acid (MUFA) percentage and the melting point of intramuscular fat were approximately +1.0% and ?1.0°C, respectively. (ii) Intron polymorphism of sterol regulatory element binding protein–1 (SREBP‐1) also affected MUFA. (iii) No effect of SCD or SREBP‐1 genotypes on any representative carcass traits of Japanese Black in the field population was observed. (iv) Additional genetic markers adipocytes fatty acid binding protein 4 (FABP4) and liver X receptor α also affected the fatty acid composition. (v) SCD and FABP4 significantly affected fatty acid composition in Holstein steers. These findings will bring new insight into the fat‐related carcass traits of beef cattle and will thus contribute to the beef industry.     

Breed differences in macrophage infiltration and senescence state in adipose tissues of Wagyu and Holsteins

Obesity stimulates the macrophage infiltration and senescence state in adipose tissues of humans and rodents. The adipogenesis capacity of Japanese Black cattle (Wagyu) is higher than that of Holsteins. We hypothesized that breed differences between Wagyu and Holsteins may affect the level of macrophage infiltration and senescence state in adipose tissues. The macrophage infiltration, senescence marker gene expression and activity of senescence‐associated β‐galactosidase (SA‐βgal) in visceral and intramuscular adipose tissue of Wagyu were higher than those of Holsteins. In contrast, there were no differences in macrophage infiltration, senescence marker gene expression and activity of SA‐βgal in subcutaneous adipose tissue between the breeds. Expression of p53 gene, the master regulator of macrophage infiltration and senescence state, in visceral and intramuscular adipose tissue of Wagyu was higher than that of Holsteins. In contrast, there was no difference in the expression of p53 gene in subcutaneous adipose tissue between the breeds. These results suggest that breed differences in macrophage infiltration and senescence state in adipose tissues of Wagyu and Holsteins are affected by p53 expression.     

Fat depot‐specific effects of body fat distribution and adipocyte size on intramuscular fat accumulation in Wagyu cattle

Ectopic fats have been recognized as a new risk factor for metabolic syndrome. In obese humans, ectopic fat accumulations are affected by body fat distribution. Intramuscular adipose tissue is categorized as one of the ectopic fats. Japanese black cattle (Wagyu) are characterized by the ability to accumulate high amounts of intramuscular adipose tissue. In Japan, the marbling level is indicated by the beef marbling standard number (BMS No.), which reflects the intramuscular fat content of longissimus muscle. We hypothesized that the intramuscular fat accumulation is affected by the body fat distribution in Wagyu cattle. In this study, we showed that the BMS No. was not correlated with the subcutaneous and visceral adipocyte diameter. In contrast, the BMS No. was positively correlated with intramuscular adipocyte diameter. These results indicate that the intramuscular adipocyte diameter of Wagyu is hypertrophied with an increase in the intramuscular fat accumulation. In addition, we showed that the BMS No. was positively correlated with the subcutaneous fat percentage. In contrast, the BMS No. was negatively correlated with the visceral fat percentage. These results indicate that highly marbled Wagyu cattle have a higher percentage of subcutaneous fat and a lower percentage of visceral fat.     

Effect of breed on fatty acid composition and stearoyl-CoA desaturase protein expression in the Semimembranosus muscle and subcutaneous adipose tissue of cattle

The present study investigated (i) the effect of breed on the expression of stearoyl-CoA desaturase (SCD) protein and fatty acid composition in Semimembranosus muscle and subcutaneous adipose tissue of beef cattle and (ii) the relationship between SCD expression, cis-9, trans-11 conjugated linoleic acid (CLA) content, and monounsaturated fatty acid (MUFA) level. The study was conducted on the following breeds: Longhorn (L), Charolais cross with Holstein–Friesian (CX), Hereford (H), Belted Galloway (BG) and Beef Shorthorn (BS). Significant breed differences in the total fatty acid content, saturated fatty acid (SFA) level, MUFA and n−3 PUFA content were observed in subcutaneous adipose tissue but not in muscle. In the case of CLA, the breed differences were observed in both muscle and subcutaneous adipose tissue, with the highest level in L and the lowest level in H. In the case of subcutaneous adipose tissue, the breed with the highest CLA content (L) also had the highest SCD protein expression. The breed-specific pattern of SCD expression in subcutaneous adipose tissue was similar to the breed-specific pattern of one of the products of an SCD-catalysed reaction, C16:1 (BS < BG < H < CX < L). It has been concluded that (i) the mechanisms regulating SCD protein expression and CLA level in beef cattle are tissue-specific; (ii) breed-specific variations in SCD expression might contribute to breed variations in MUFA and CLA content in subcutaneous adipose tissue but not in Semimembranosus muscle.     

Copper and lipid metabolism in beef cattle: a review

Results from experiments investigating Cu metabolism in ruminants indicate that Cu is involved in lipid metabolism. Copper supplementation ranging from 10 to 40 mg of Cu/kg of DM to high-concentrate finishing diets decreased subcutaneous adipose tissue deposition and decreased cholesterol concentrations but increased unsaturated fatty acid composition of LM. Serum norepinephrine tended to be greater in Cu-supplemented steers after a 24-h feed withdrawal and at 2 h postfeed consumption, potentially explaining the reduction in subcutaneous adipose tissue deposition. However, when exogenous norepinephrine was administrated, serum NEFA concentrations were less in Cu-supplemented steers, possibly due to the nonsupplemented control steers having a greater subcutaneous adipose tissue depth at slaughter relative to Cu-supplemented steers. Furthermore, in vitro basal and epinephrine-stimulated lipolytic rates of subcutaneous adipose tissue were greater in Cu-supplemented steers relative to controls. These data indicate that that Cu may influence lipogenic or lipolytic function in subcutaneous adipose tissue. In an attempt to further investigate the effect of Cu on lipid metabolism, lipogenic, lipolytic, and homeostatic mechanisms related to Cu are currently being studied. Recent data indicate that genes involved in bovine liver Cu homeostasis are correlated with Cu transporter protein gene expression in the bovine liver. Therefore, the overall intent of this review is to discuss possible mechanisms whereby Cu may affect lipid metabolism in ruminants.     

Growth,carcass characteristics,muscle conjugated linoleic acid (CLA) content,and response to intravenous glucose challenge in high percentage Wagyu,Wagyu x Limousin,and Limousin steers fed sunflower oil-containing diet

The effect of breed and diet on insulin response to glucose challenge and its relation to intramuscular fat deposition was determined in 36 steers with 12 each of greater than 87% Wagyu (referred to as Wagyu), Wagyu x Limousin, and Limousin breeds. Weaned steers were blocked by weight into heavy, medium, and light calves and placed in six pens with two pens per weight type and with two steers of each breed per pen. Three pens with steers from each weightclass were fed backgrounding and finishing diets for 259 d, while the other three pens were fed the same diets where 6% of the barley grain was replaced with sunflower oil. Prior to initiation of the finishing phase of the study the intravenous glucose tolerance test (VGTIT) was conducted in all steers. Once steers were judged as carrying adequate 12th-rib fat, based on weight and days on feed, they were harvested and graded and samples of the longissimus muscle were procured for determination of fat content and fatty acid composition. Dietary oil improved (P = 0.011; 0.06) ADG and feed conversion efficiency of steers during the latter part of backgrounding and only ADG during early part ofthe finishing period. Generally percent kidney, pelvic, and heart fat was the only adiposity assessment increased (P = 0.003) by dietary oil. The IVGTT results indicated that insulin response to intravenous glucose was lower in Limousin steers than in Wagyu steers. Dietary oil decreased (P = 0.052) fasting plasma insulin concentration in Wagyu steers compared with Limousin steers. The correlation coefficients among the IVGTT measures and intramuscular fat content or marbling score were less than 0.4, and only a negative trend existed between fasting insulin and USDA marbling scores. However, the carcasses of the Wagyu steers graded US Choice, and 66% of the Wagyu carcasses graded US Prime, which were substantially better than the quality grades obtained for the carcasses from the other breed types. Dietary oil did not affect muscle fat content but increased (P = 0.01) conjugated linoleic acid (CLA) concentrations by 339%. Results indicated that IVGTT measures were not appropriate indices of marbling potential in cattle and that dietary oil can enhance CLA content of beef.     

Conjugated linoleic acid depresses the delta9 desaturase index and stearoyl coenzyme A desaturase enzyme activity in porcine subcutaneous adipose tissue

Conjugated linoleic acid (CLA) has been shown to have an effect on subcutaneous fatty acid composition and has been reported to decrease stearoyl coenzyme A desaturase (SCD) activity by decreasing mRNA expression and(or) catalytic activity in rodents and rodent cell lines. This investigation was designed to study the effects of CLA, corn oil, or beef tallow supplementation on s.c. adipose tissue fatty acid composition, adiposity, SCD enzyme activity, and the delta9 desaturase index in piglets. Eighteen crossbred barrows 16 to 18 d of age were adapted to diet for 1 wk and then assigned randomly to one of three treatments: 1.5% added CLA, 1.5% added corn oil, or 1.5% added beef tallow. Barrows were penned individually and fed the supplemental oils for 35 d (to 25.6 +/- 0.6 kg BW). Subcutaneous adipose tissue samples were obtained after slaughter. Fatty acid composition of the s.c. adipose tissue differed for each fatty acid measured due to diet with the exception of 18:3. The concentrations of CLA trans-10, cis-12 and cis-9, trans-11 were elevated from nondetectable to 1.62 and 2.52 g/100 g lipid, respectively (P < 0.001 for both isomers). Conjugated linoleic acid decreased the delta9 desaturase index (P < 0.01) and SCD enzyme activity, expressed as nanomoles of palmitate converted to palmitoleate/(7 min x g of tissue) (P = 0.075) and nanomoles of palmitate converted to palmitoleate/(7 min 105 cells) (P= 0.056). Tallow-fed pigs had a greater proportion of large adipocytes (> 700 pL) and the greatest SCD activity. These data provide the first direct evidence that dietary CLA depresses SCD enzyme activity in porcine adipose tissue, which may in part be responsible for the depression of adiposity by CLA observed by others in market weight pigs.     

Differing effects of forage and concentrate diets on the oleic acid and conjugated linoleic acid content of sheep tissues: the role of stearoyl-CoA desaturase

Feeding sheep concentrate-based diets increases the oleic acid content of their tissues, whereas the cis-9, trans-11 conjugated linoleic acid (CLA) content is increased by feeding forage diets. Both these metabolic transformations could be attributable to increased activity of stearoyl-CoA desaturase (SCD). Therefore, the effect of forage or concentrate feeding regimens on the fatty acid composition of sheep tissues were investigated to determine whether any changes are related to an alteration of SCD mRNA levels. Twenty-four ewe lambs were randomly allotted to one of three dietary treatment groups: 1) dehydrated grass pellets, 2) concentrate diet fed to achieve a growth rate similar to that of the dehydrated grass pellets, and 3) the same concentrate diet approaching ad libitum intake. As expected, animals fed ad libitum concentrates grew at a greater (P = 0.001) rate (280 g/d) than those fed either of the other two diets (180 g/d), which were similar. In samples of liver and the three adipose tissue depots studied, the concentration of oleic acid from sheep fed either level of the concentrate diet was greater (P < 0.001) than from animals fed forage. This was associated with an increase (P < 0.05) in the ratio of SCD to acetyl-CoA carboxylase mRNA in adipose tissue and liver. Compared with concentrate-fed, the forage-fed lambs had increased (P < 0.05) levels of the cis-9, trans-11 isomer of CLA and C18:1, trans-11 in all their tissues, although the levels of SCD mRNA were lower. It therefore seems that the increased oleic acid content of sheep tissues in response to concentrate-rich diets is associated with an increase in SCD gene expression. By contrast, the increased concentration of CLA in animals fed forage-based diets is associated with an increase in substrate (C18:1 trans-11) availability.     

Evidence for functional G-coupled protein receptors 43 and 120 in subcutaneous and intramuscular adipose tissue of Angus crossbred steers

We conducted 3 independent experiments to demonstrate functional G-coupled protein receptor 43 (GPR43) and GPR120 in bovine intramuscular (i.m.) and subcutaneous (s.c.) adipose tissues. We hypothesized that media volatile fatty acids and long-chain fatty acids would affect cAMP-activated protein kinase-alpha (AMPKα) protein expression and cAMP concentrations differently in i.m. and s.c. adipose tissue. Experiment 1: oleic acid (18:1n-9) decreased phosphorylated AMPKα protein (p-AMPKα) and the p-AMPKα/AMPKα protein ratio in i.m. preadipocytes, increased the p-AMPKα/AMPKα protein ratio in bovine satellite cells, and had no effect in s.c. preadipocytes. Experment 2: ex vivo explants from the 5th to 8th longissimus thoracic rib muscle section of Angus crossbred steers were cultured 48 hr in media containing 0.25 µM ciglitizone, 5 mM glucose, and 5 mM acetate, in the absence or the presence of 100 µM oleic acid. Oleic acid increased acetate incorporation into fatty acids and GPR43 gene expression in i.m. adipose tissue (P < 0.05), but oleic acid had no effect on fatty acid synthesis or GPR43 expression in s.c. adipose tissue. Experiment 3: fresh s.c. and i.m. adipose tissue from the 5th to 8th longissimus thoracic rib muscle section of Angus crossbred steers was transferred immediately to 6-well culture plates containing 3 mL of KHB/Hepes/5 mM glucose. Samples were preincubated with 0.5 mM theophylline plus 10 μM forskolin for 30 min, after which increasing concentrations of acetate or propionate (0, 10⁻³, 10^−2.3, and 10⁻³ M) in the absence or the presence of 100 μM oleic acid or 100 µM palmitic acid (16:0) were added to the incubation media. Acetate had no effect on forskolin-stimulated cAMP production in s.c. adipose tissue but decreased cAMP in i.m. adipose tissue (P < 0.05); this indicates a functional GPR43 receptor in i.m. adipose tissue. The combination of 10⁻² M acetate and oleic acid decrease cAMP production in s.c. adipose tissue, consistent with GPR120 receptor activity, but oleic acid and palmitic acid attenuated the depression of cAMP production caused by acetate in i.m. adipose tissue. Palmitic acid depressed cAMP production in s.c. adipose tissue, and increased cAMP production in i.m. adipose tissue (P < 0.05). Propionate had no effect on cAMP production in s.c. or i.m. adipose tissue. These results provide evidence for functional GPR43 receptors in i.m. adipose tissue and GPR120 receptors in s.c. adipose tissue, both of which would suppress lipolysis.     

Adipogenic gene expression and fatty acid composition in subcutaneous adipose tissue depots of Angus steers between 9 and 16 months of age

We have demonstrated that among carcass adipose tissue depots, brisket subcutaneous adipose tissue contains the greatest concentration of MUFA and lowest concentration of SFA. Therefore, we hypothesized that brisket subcutaneous adipose tissue depots would exhibit greater adipogenic gene expression over time than other major subcutaneous adipose tissue depots. Four Angus steers, each at 9, 12, 14, and 16 mo of age, were harvested and fresh subcutaneous adipose tissue samples were collected from over the brisket, chuck, rib, loin, sirloin, round, flank, and plate. Relative gene expression for C/EBPβ, PPARγ, carnitine palmitoyltransferase-1 beta (CPT-1β), stearoyl-coenzyme A desaturase (SCD), AMP-activated protein kinase alpha (AMPKα), and G-coupled protein receptor 43 (GPR43) was analyzed by quantitative real-time PCR. Expression of C/EBPβ, PPARγ, and CPT-1β was greatest at 12 to 14 mo of age (all P < 0.0001) and declined to very low abundance by 16 mo of age in all depots. Expression of PPARγ and CPT-1β was greater (P < 0.03) in flank, rib, and sirloin subcutaneous adipose tissues than in brisket and round adipose tissues. The expression of the SCD gene did not differ among the 4 age groups (P = 0.95). The palmitoleic:stearic acid ratio (an estimate of SCD activity) was greater (P < 0.001) in the subcutaneous adipose tissues from brisket, plate, and round than in the loin, rib, and sirloin. Conversely, subcutaneous adipose tissue from the loin, rib, and sirloin had greater (P < 0.001) SCD gene expression than the brisket, plate, and round. In general, subcutaneous adipose tissues with the highest concentration of MUFA and least SFA consistently exhibited the least SCD gene expression and adipogenic gene expression. We conclude that MUFA in the brisket and other depots with large SCD indices were deposited before 9 mo of age, during a time when the subcutaneous adipocytes were highly differentiated.