Function of pref-1 as an inhibitor of adipocyte differentiation

During conversion of preadipocytes to adipocytes, growth arrest and subsequent activation of adipocyte genes by the transcription factors, C/EBPalpha and PPARgamma, lead to adipogenesis. During differentiation, these cells not only start expressing those genes necessary for adipocyte function, but also undergo changes in morphology to become rounded lipid filled adipocytes. Various factors in cell-cell communication or cell-matrix interaction may govern whether preadipocytes are kept in an undifferentiated state or undergo differentiation. In an attempt to identify molecules that play critical roles in the conversion of preadipocytes to adipocytes, we cloned by differential screening several regulatory molecules, including pref-1. Pref-1 is an inhibitor of adipocyte differentiation and is synthesized as a plasma membrane protein containing 6 EGF-repeats in the extracellular domain. Pref-1 is highly expressed in 3T3-L1 preadipocytes, but is not detectable in mature fat cells. Dexamethasone, a component of standard differentiation agents, inhibits pref-1 transcription and thereby promotes adipogenesis. Downregulation of pref-1 is required for adipose conversion and constitutive expression of pref-1 inhibits adipogenesis. Conversely, decreasing pref-1 levels by antisense pref-1 transfection greatly enhances adipogenesis. The ectodomain of pref-1 is cleaved to generate a biologically active 50kDa soluble form. There are four major forms of membrane pref-1 resulting from alternate splicing. Two of these forms which have a deletion that includes the putative processing site proximal to the membrane do not produce a biologically active soluble form. This indicates that alternate splicing may determine the range of action, juxtacrine or paracrine, of pref-1.

The role of lipoprotein lipase in adipose tissue development and metabolism

Lipoprotein lipase (LPL) is essential for the hydrolysis and distribution of triglyceride-rich lipoprotein-associated fatty acids among extrahepatic tissues. Additionally, the enzyme facilitates several non-lipolysis associated functions including the cellular uptake of whole lipoprotein particles and lipophilic vitamins. The tissue-specific variations of LPL expression have been implicated in the pathogenesis of various lipid disorders, obesity and atherosclerosis. Transgenic technology provided the means to study the physiological response to the overexpression or absence of the enzyme in adipose tissue, muscle and macrophages. The effects of varying LPL expression in adipose tissue and muscle are summarized in this article.

Regulation of adipogenesis and energy balance by PPARgamma and PGC-1

There has been a great deal of recent progress in our understanding of the transcriptional control of adipogenesis. Current data suggest that fat cell differentiation involves an interplay between the C/EBP family of transcription factors and PPARgamma. The thermogenic program of brown fat cells may also include a contribution from a new coactivator, PGC-1. Recent data suggests that this coactivator is responsible for activation of thermogenesis and oxidative metabolism in both brown fat and muscle. The PGC-1 dependent program includes both mitochondrial biogenesis and tissue-specific expression of uncoupling proteins.

Angiotensinogen, angiotensin II and adipose tissue development

Adipose tissue is an important source of angiotensinogen (AGT). Recent evidence shows that a local renin-angiotensinogen system (RAS) is present in human adipose tissue and may act as a distinct system from plasma RAS. In obese patients, the involvement of angiotensin II (angII) as a consequence of increased plasma AGT secreted from adipose tissue has been proposed in the development of hypertension. Another role of AGT via angII in the development of adipose tissue is supported by the following: (i) in vitro, angII stimulates the production and release of prostacyclin from adipocytes, which in turn promotes the differentiation of precursor cells into adipocytes; (ii) ex vivo and in vivo, both angII and (carba)prostacyclin promote the formation of new fat cells; and (iii) AGT -/- mice exhibit a slowing down of adipose tissue development, as compared to wild-type mice. Altogether the data are consistent with an autocrine/paracrine mechanism implicating AGT, angII and prostacyclin in adipose tissue development.

Adipose cell apoptosis: death in the energy depot

Apoptosis is critical for mammalian tissue homeostasis, and its disruption has been linked to a wide variety of disorders, including cancer, neurodegenerative disease, autoimmune disease and diabetes. This review will focus on recent investigations that have begun to address the potential role of apoptosis in adipose tissue growth. Evidence for apoptosis occurring in mature adipocytes has been obtained through the use of in vitro cell culture models as well as in vivo studies in rodents and humans. Preadipocytes, fibroblast-like adipocyte precursor cells, can also undergo apoptotic cell death. As they differentiate, preadipocytes acquire a relative resistance to apoptosis. The levels of the cell survival proteins Bcl-2 and neuronal apoptosis inhibitory protein (NAIP) have been observed to increase during adipogenesis. Further research on the effect of apoptosis on adipose tissue cellularity should clarify its influence on adipose tissue mass and distribution.

Can betaine partially replace or enhance the effect of methionine by improving broiler growth and carcase characteristics?

1. Growth rates and carcase characteristics were measured in male broiler chickens fed on a control diet deficient in methionine (c. 2.8 g/kg methionine) or a series of diets containing graded levels of betaine or DL-methionine or both additives. 2. We aimed to answer 2 main questions. First, can betaine replace part of the methionine in a broiler ration? Secondly is there a synergism between methionine and betaine? 3. Birds given the control diet or that supplemented only with betaine ate less, grew more slowly, had higher food convension ratio (FCR) and varied more in mass at 42 d than birds fed diets with DL-methionine. Adding 1.2 g/kg DL-methionine to the control ration produced the heaviest birds at 42 d (2500 g) with the 2nd heaviest breast muscle (366 g). 4. After correcting for treatment differences in body mass (analysis of convariance), birds fed on the control diet and the diet supplemented with betaine only, had relatively lighter breast muscles but relatively heavier abdominal fat pads than those of birds given diets supplemented with DL-methionine. However, adding betaine to diets containing added methionine further improved the relative breast muscle yield. 5. After correcting for differences in body mass between treatments, birds fed on diets containing most methionine had lighter viscera than birds fed diets deficient in methionine. This demonstrated gut plasticity, suggesting that the viscera enlarged to sequester methionine from low-methionine diets. 6. Our data refute the hypothesis that betaine can substitute for methionine in broilers fed diets that are marginally deficient in methionine plus cystine. However, betaine may improve carcase composition, especially breast meat yield.

Interaction of genetic and environmental programming of the leptin system and of obesity disposition

Possible adverse interactions between an usually inconspicuous genetic trait and early environmental factors favoring the development of obesity were investigated in rats heterozygous for the leptin receptor defect "fatty" (fa). Pups were exposed to early postnatal overfeeding by reducing litter size from normally 10-12 to only 4. Rearing +/+ and +/fa pups from day 3 to 21 in small litters increased fat-free dry mass and body fat, but only in the latter did a significant interaction with genotype occur. Pronounced differences in the responsiveness of +/+ and +/fa pups to "prophylactic" leptin treatment (from day 1 to 21) were observed, with +/fa females from small litters being nearly as fat and unresponsive as previously reported for normally reared fa/fa pups. Clear heterozygous differences in total hypothalamic leptin binding, but no litter size effect, paralleling the differences in leptin responsiveness, were observed. By early postnatal overfeeding an usually inconspicuous genetic trait may thus become etiologic for the development of obesity via physiological changes other than the decreased leptin binding characterizing the genetic defect.

Combined analyses of data from quantitative trait loci mapping studies. Chromosome 4 effects on porcine growth and fatness

For many species several similar QTL mapping populations have been produced and analyzed independently. Joint analysis of such data could be used to increase power to detect QTL and evaluate population differences. In this study, data were collated on almost 3000 pigs from seven different F(2) crosses between Western commercial breeds and either the European wild boar or the Chinese Meishan breed. Genotypes were available for 31 markers on chromosome 4 (on average 8.3 markers per population). Data from three traits common to all populations (birth weight, mean backfat depth at slaughter or end of test, and growth rate from birth to slaughter or end of test) were analyzed for individual populations and jointly. A QTL influencing birth weight was detected in one individual population and in the combined data, with no significant interaction of the QTL effect with population. A QTL affecting backfat that had a significantly greater effect in wild boar than in Meishan crosses was detected. Some evidence for a QTL affecting growth rate was detected in all populations, with no significant differences between populations. This study is the largest F(2) QTL analysis achieved in a livestock species and demonstrates the potential of joint analysis.

Effect of feeding level and thyroxine on adipose tissue development and growth in postnatal lambs

We investigated the influence of exogenous thyroxine (T4) administration in conjunction with level of feeding on adipose tissue and liver growth in postnatal lambs. Pairs of lambs were fed either 100 g (i.e. low fed) or 200 g (i.e. high fed) of milk powder per litre of reconstituted milk replacer over the first month of life. Half of the pairs of lambs were fed a bolus dose of T4 (15 mg (kg body weight)-1) daily until 8 days of age. Perirenal adipose tissue and hepatic tissue were sampled at either 8 or 35 days of age. High fed lambs grew faster, possessed more adipose tissue and had larger livers than low fed lambs at 8 and 35 days of age. T4 administration resulted in a lower thermogenic activity (i.e. GDP binding) in adipose tissue at 8 days of age in low, but not high fed lambs. There was no difference between groups in colonic temperature or oxygen consumption. Between 17 and 35 days of age high fed lambs previously treated with T4 had lower daily milk consumption than untreated siblings, but still attained the same growth rate. Plasma insulin-like growth factor-I concentrations were greater in high than low fed lambs, a relationship that was not influenced by T4 treatment. In adipose tissue, iodothyronine 5' deiodinase activity was not influenced by T4 administration and was greater in high than low fed lambs. Hepatic iodothyronine 5' deiodinase activity was not influenced by T4 administration in low fed lambs, but was reduced by T4 in high fed lambs. In conclusion, T4 administration over the first 8 days of life can accelerate the rate of decline in thermogenic activity of uncoupling protein-1. This effect is not observed when the level of feeding is increased. Following withdrawal of T4 treatment, high fed T4-treated lambs were able to maintain the same growth rate as untreated lambs despite having a lower food intake.

The adipose conversion process: regulation by extracellular and intracellular factors

White adipose tissue regulates lipid metabolism and acts as a secretory organ. Because of its importance for human health and animal production, many studies have attempted to better understand its development at the cellular and molecular levels by culturing preadipose cells in vitro. This synthesis article describes our current knowledge, acquired by this approach, concerning the regulation of the different steps of the adipocyte differentiation program by extracellular (hormones, cytokines, growth factors, retinoids and fatty acids) and intracellular agents (second messengers and transcription factors). The discrepant effects that have been observed for some of these factors are also discussed. This information is very important in the perspective of a better control of fat deposits in human and breeding species.

Effects of green tea on growth, food utilization and lipid metabolism in mice

To find whether green tea has anti-obesity effects in mice, female ICR mice were fed on diets containing 1, 2 and 4% green tea powder for 16 weeks and the body weight and food intake were weighed. After the administration of green tea, the ovaries, kidneys, adrenals, liver, spleen, brain, pituitary and intraperitoneal adipose tissues in the mice were weighed and lipid levels in the serum and in the liver and serum leptin levels were measured. It was found that body weight increase and intraperitoneal adipose tissues were remarkably suppressed by the administration of diets containing 2 and 4% green tea powder. Food intake was suppressed by feeding the 4% green tea diet. Concentrations of total cholesterol in the liver, triglycerides in serum and liver and nonestrified fatty acids in serum from mice which were administered green tea diet were lower than those in the controls. Leptin levels in serum showed a decrease with green tea treatments. These results indicated that lipid metabolism in mice was suppressed by the administration of green tea powder and thereby the fatty accumulation and body weight increase was suppressed.

Characterisation of gene expression in bovine adipose tissue before and after fattening

It has been reported that fattening causes bovine adipose tissue development associated with an enlargement in adipocyte cell size. As a first study to elucidate mechanisms of bovine adipose tissue development during fattening, our experiment was designed to characterise gene expression in bovine adipose tissue before and after fattening. We randomly isolated a large number of cDNA clones derived from bovine adipose tissue before and after fattening. Sequence analysis of the isolated clones showed that 3 and 10 clones from before and after fattening, respectively, correspond to genes related to adipocyte development and/or function in the adipose tissue. In addition, we isolated cDNA clones that possess negative signal by hybridising the cDNA population from the adipose tissue after fattening with that before fattening as a probe. As a result, we identified five types of transcripts observed in the adipose tissue after fattening but not before fattening. Two of the five are likely to encode bovine orthologs of phospholipase A2 and RNA helicase p68, while the other three represent unknown genes. Further functional investigation of the identified genes might lead to elucidation of mechanisms of bovine adipose tissue development during fattening.

Factors associated with early adiposity rebound. ALSPAC Study Team

OBJECTIVE

The age at which body mass index (BMI) increases after its nadir in childhood, adiposity rebound (AR), is a critical period for the development of obesity. Children with early AR are at substantially increased risk of adult obesity. Few studies have examined the factors that influence the timing of the AR. The aims of this study were to test for influences on the timing of the AR, and to test the hypothesis that early AR is promoted by high-protein intake.

DESIGN AND PARTICIPANTS

Longitudinal cohort study of 889 children representative of the United Kingdom, followed from birth to 5 years.

MAIN OUTCOME MEASURES

We tested for differences in dietary intake, parental BMI, socioeconomic status, and childhood BMI between 3 groups of children characterized by the following: very early AR (at or before 43 months), early AR (from 49 but before 61 months), and later AR (after 61 months).

RESULTS

There was no evidence of associations between dietary protein intake, or any other dietary variable, and timing of the AR. Children with very early AR and early AR had parents with significantly higher BMI, and were significantly more likely to have at least 1 obese parent.

CONCLUSION

This study does not support the hypothesis that early AR is promoted by high-protein intake. None of the dietary variables tested were significantly associated with timing of the AR, and timing of AR was not associated with socioeconomic status. Parental obesity was associated with an earlier AR.

Lipid metabolism in the fetus and the newborn

During late gestation, although maternal adipose tissue lipolytic activity becomes enhanced, lipolytic products cross the placenta with difficulty. Under fasting conditions, free fatty acids (FFA) are used for ketogenesis by the mother, and ketone bodies are used as fuels and lipogenic substrates by the fetus. Maternal glycerol is preferentially used for glucose synthesis, saving other gluconeogenic substrates, like amino acids, for fetal growth. Placental transfer of triglycerides is null, but essential fatty acids derived from maternal diet, which are transported as triglycerides in lipoproteins, become available to the fetus owing to the presence of both lipoprotein receptors and lipase activities in the placenta. Diabetes in pregnancy promotes lipid transfer to the fetus by increasing the maternal-fetal gradient, which may contribute to an increase in body fat mass in newborns of diabetic women. Deposition of fat stores in the fetus is very low in the rat but high in humans, where body fat accretion occurs essentially during the last trimester of intra-uterine life. This is sustained by the intense placental transfer of glucose and by its use as a lipogenic substrate, as well as by the placental transfer of fatty acids and to their low oxidation activity. During the perinatal period an active ketonemia develops, which is maintained in the suckling newborn by several factors: (i) the high-fat and low-carbohydrate content in milk, (ii) the enhanced lipolytic activity occurring during the first few hours of life, and (iii) both the uptake of circulating triglycerides by the liver due to the induction of lipoprotein lipase (LPL) activity in this organ, and the presence of ketogenic activity in the intestinal mucose. Changes in LPL activity, lipogenesis and lipolysis contribute to the sequential steps of adipocyte hyperplasia and hypertrophia occurring during the extra-uterine white adipose tissue development in rat, and this may be used as a model to extrapolate the intra-uterine adipose tissue development in other species, including humans.

Modulation of lipogenic enzymes, fatty acid synthase and delta9-desaturase, in relation to migration in the western sandpiper (Calidris mauri)

Long-distance migration in birds is characterized physiologically by periods of rapid fattening and lipogenesis, and increased desaturation of fatty acids stored in adipose tissue. We investigated seasonal, age- and sex-related differences in activities of two lipogenic enzymes, fatty acid synthase and delta9-desaturase, in relation to migration in the small, Arctic-nesting western sandpiper (Calidris mauri). Migration, and associated lipogenesis and fattening, involved marked upregulation of these enzymes in this species. However, this increase in enzyme activity was only seen in actively migrating birds during spring migration, when fatty acid synthase and delta9-desaturase levels increased by 53% and 113%, respectively, compared to non-migrating birds. There was no change in fatty acid synthase enzyme activity during the premigration period, even though body mass of adult birds increased significantly during this period. Similarly, there was no increase in delta9-desaturase activity during premigration, despite the fact that birds increase the proportion of monounsaturated fatty acids in their fat stores at this time. We suggest that upregulation of lipogenic enzymes is required to support high rates of mass gain (0.4 g day(-1)) during short (1-4 day) periods at stop-over sites. However, slower rates of mass gain (0.09 g day(-1)) over several weeks prior to migration can be achieved without any increase in tissue-specific enzyme activity.

Reduced body weight, adipose tissue, and leptin levels despite increased energy intake in female mice lacking acylation-stimulating protein

Acylation-stimulating protein (ASP) is a potent lipogenic protein produced by adipocytes. In vitro studies have shown that ASP increases triglyceride synthesis and glucose transport in both murine and human adipocytes. Our initial study indicated that complement C3-deficient (-/-) mice (and, therefore, ASP deficient) demonstrated altered dietary postprandial triglyceride clearance. In the present study we examined the phenotype of female mice longitudinally on different diets. Female C3(-/-) mice on both low (10% of energy) and high (40% of energy) fat diets displayed an average reduction in total body weight of 10.1+/-0.5% (P < 0.0003, by ANOVA) compared with the C3(+/+) littermates. Reductions in white adipose tissue mass accounted for most of this weight difference (59% reduction; P < 0.01 on low fat diet). Plasma leptin levels were significantly reduced in C3(-/-) mice on both high (P < 0.001) and low fat diets (P < 0.01). This reduction was significant even after adjusting for the reduced body weight and body fat (P < 0.001). Leptin reductions in the C3(-/-) were greater on the high fat diet and were associated with increased food intake (18+/-2% increase; P < 0.001). Furthermore, there was a decrease in basal glucose levels and basal insulin levels [12.8% decrease in glucose at 14 weeks (HF; P < 0.05) and 41% decrease in insulin at 26 weeks (HF; P < 0.05)]. These in vivo experiments demonstrate that female mice lacking ASP have marked alterations of body weight, adiposity, plasma leptin, and plasma insulin levels. Decreased adiposity and leptin levels occurred in the ASP-deficient animals despite increased energy intake, suggesting that energy expenditure was elevated in these animals. Thus, ASP appears to have an important role in the regulation of energy balance in mice.

Levels and patterns of PCBs and OC pesticides in harbour and grey seals from the St Lawrence Estuary, Canada

Blubber samples from harbour (Phoca vitulina) and grey seals (Halichoerus grypus) captured in the St Lawrence Estuary were analysed for PCBs and OC pesticides. Concentrations of sigma PCB, sigma DDT, sigma CHLOR and mirex were higher in harbour than in grey seals, while sigma HCH and HCB were similar in the two species. Age vs. concentration plots showed that sigma PCB, sigma DDT and sigma CHLOR concentrations increased with age in males, but plateaued at sexual maturity in females. Concentrations of sigma HCH decreased and mirex increased with age for post-weaning animals, regardless of gender. HCB did not show age-related trends. PCB congener and OC pesticide patterns varied within harbour seals (based on gender and maturity) and between harbour and grey seals. PCB and OC concentrations in harbour seals were lower than those seen in a sample of significantly older beluga whales. Both species remain in the Estuary year-round. PCB and OC pesticide concentrations were higher in resident harbour seals than in either grey or harp seals that visit the Estuary seasonally. PCB and OC pesticide concentrations in harbour seals from the Estuary were generally higher than in harbour seals from other regions of North America. They were comparable to, or higher than those from the NE Atlantic Ocean and the North Sea, and lower than those from the Wadden and Baltic Seas.

[Secular increase of adipose tissue in adolescents from Zaragoza from 1980 to 1995]

BACKGROUND

To quantify the differences between anthropometric measurements obtained nowadays in male and female adolescents and those obtained 15 years ago in a sample of similar characteristics.

SUBJECTS AND METHODS

We have studied 658 healthy individuals, 329 males and 329 females from 10.0 to 15.0 years of age, from different socioeconomic levels. Weight, height, arm circumference and left skinfold thickness (biceps, triceps, subscapular and suprailiac) have been measured. We have calculated the body mass index (BMI), density, total body fat, percentage of body fat and the body adipose muscular index (BAMI), which is the ratio between body fat (kg) and non fat mass (kg). The values obtained have been compared with those obtained fifteen years ago, in another sample of 1,465 children with similar characteristics. The research team and the material used were the same in both studies. Mean differences were compared using the unpaired t-test.

RESULTS

Weight has increased significantly (p < 0.05), except for males at 12 years and females at 13 and at 14 years. Height has increased significantly at all ages and in males and females (p < 0.05). BMI has only increased significantly at 10 and at 11 years in males, and at 10 years in females. Skinfold thicknesses have also increased significantly, except for biceps in males between ages of 12 and 14 years and biceps and subscapular in females at 14 years. Body fat mass and percentage of body fat have also increased significantly and, in consequence, the density has decreased and BAMI has increased both significantly (p < 0.05).

CONCLUSIONS

Secular increase in weight and height during fifteen years has occurred. In general, BMI has not increased but skinfold thicknesses and body fat have increased significantly, this fact demonstrates that there has been increase in the body fat compartment.

G(s)alpha repression of adipogenesis via Syk

G(s)alpha regulates the differentiation of 3T3-L1 mouse embryonic fibroblasts to adipocytes, a process termed adipogenesis. Inducers of adipogenesis lead to a loss of G(s)alpha and derepress differentiation to adipocytes. The broad spectrum tyrosine kinase inhibitor genistein is shown to block induction of adipogenesis, suggesting an early role of tyrosine phosphorylation in adipogenesis. Staining of phosphotyrosine identified prominent staining of a approximately 70-kDa protein, hypothesized to be the tyrosine kinase Syk. Reverse transcription and polymerase chain reaction amplification established the expression of Syk mRNA in these embryonic fibroblasts. Immunoprecipitations with Syk-specific antibodies demonstrated the presence of Syk in fibroblasts and a rapid increase in the amount of phospho-Syk, peaking at 24 h post induction. Clones constitutively expressing G(s)alpha, which can no longer be induced to differentiate, no longer display increased phospho-Syk levels in response to inducers. The linkage between G(s)alpha and Syk was probed by immunoprecipitations revealing association of Syk with G(s)alpha in the absence of induction. Upon induction of adipogenesis, G(s)alpha levels decline and phospho-Syk levels as well as Syk kinase activity increase. Expression of wild-type Syk both potentiates the ability of inducers to act as well as induces adipogenesis itself. Expression of the kinase-deficient Syk had no such effects on adipogenesis. These data provide a new insight into the control of adipogenesis, suggesting that G(s)alpha represses adipogenesis via Syk. Treatment with the inducers promotes a decline in G(s)alpha, increases in levels of phospho-Syk, and adipogenesis.

Expression of leptin mRNA and CCAAT-enhancer binding proteins in response to insulin deprivation during preadipocyte differentiation in primary cultures of porcine stromal-vascular cells

The aim of this study was to examine the correlation between CCAAT-enhancer binding proteins (C/EBPs) and leptin gene expression in response to insulin deprivation in preadipocytes and adipocytes. Adipose tissue from 7 d-old pigs was digested enzymatically and stromal-vascular (S-V) cells were seeded and plated for 3 d in fetal bovine serum (FBS) with dexamethasone (DEX) followed by 6 d (Days 3-9) in serum-free medium with insulin (850 nM or 10 nM), transferrin, and selenium. During FBS+DEX treatment (Days 0-3) a large number of preadipocytes develop with no lipid accretion. In contrast, preadipocyte number does not change with lipid accretion during insulin treatment (Days 3-9). Total RNA and cells were harvested from S-V cultures after periods with and without insulin after FBS+DEX. Northern-blotting and Western blot analysis were used to study leptin mRNA and C/EBP protein expression in cultures, respectively. Insulin deprivation from Days 3-4 reduced leptin mRNA and C/EBP-alpha protein expression. Treatment with 850 nM or 10 nM insulin from Days 3-9 induced leptin mRNA and C/EBP-alpha expression at a similar level. In cultures treated with 10 nM insulin from Days 3-7, leptin and C/EBP-alpha expression were reduced markedly by insulin deprivation from Days 7-9, but were restored by insulin treatment for 6 hr before harvesting. The restoration of leptin expression by insulin was blocked by cycloheximide treatment. However, C/EBP-beta protein levels did not change regardless of insulin deprivation. Insulin deprivation from Days 7-9 in cultures treatedwith 850 nM insulin from Days 3-7 did not influence C/EBP-alpha or leptin mRNA expression, whereas C/EBP-alpha and leptin expression were reduced after treating these cultures with 1.5 uM okadaic acid for 45 min before harvesting on Day 9. However, cycloheximide treatment for 6 hr before harvesting did not reduce leptin mRNA expression. These results suggest that 1) leptin expression is positively correlated with C/EBP-alpha expression, and 2) the maintenance of leptin expression after insulin deprivation in 850 nM insulin-treated cultures on Day 9 may be associated with the presence of C/EBP-alpha expression and/or activation.

PPAR gamma is required for placental, cardiac, and adipose tissue development

The nuclear hormone receptor PPAR gamma promotes adipogenesis and macrophage differentiation and is a primary pharmacological target in the treatment of type II diabetes. Here, we show that PPAR gamma gene knockout results in two independent lethal phases. Initially, PPAR gamma deficiency interferes with terminal differentiation of the trophoblast and placental vascularization, leading to severe myocardial thinning and death by E10.0. Supplementing PPAR gamma null embryos with wild-type placentas via aggregation with tetraploid embryos corrects the cardiac defect, implicating a previously unrecognized dependence of the developing heart on a functional placenta. A tetraploid-rescued mutant surviving to term exhibited another lethal combination of pathologies, including lipodystrophy and multiple hemorrhages. These findings both confirm and expand the current known spectrum of physiological functions regulated by PPAR gamma.

PPAR gamma is required for the differentiation of adipose tissue in vivo and in vitro

The process of adipogenesis is known to involve the interplay of several transcription factors. Activation of one of these factors, the nuclear hormone receptor PPAR gamma, is known to promote fat cell differentiation in vitro. Whether PPAR gamma is required for this process in vivo has remained an open question because a viable loss-of-function model for PPAR gamma has been lacking. We demonstrate here that mice chimeric for wild-type and PPAR gamma null cells show little or no contribution of null cells to adipose tissue, whereas most other organs examined do not require PPAR gamma for proper development. In vitro, the differentiation of ES cells into fat is shown to be dependent on PPAR gamma gene dosage. These data provide direct evidence that PPAR gamma is essential for the formation of fat.

Influences of myogenin genotypes on birth weight, growth rate, carcass weight, backfat thickness, and lean weight of pigs

Lean weight is related to muscle fiber number. Muscle fiber formation (myogenesis) occurs only during embryonic development when it is under the control of the MyoD gene family consisting of myogenin, MyoD1, myf-5, and myf-6. Myogenin has a central position within the MyoD gene family because myogenin expression abrogates myoblast proliferation potential and regulates the differentiation of single nucleated myoblasts into multinucleated myofibers. Thus, myogenin genotype could be related to variation in the number of muscle fibers formed, leading to variation in muscle mass and, thus, lean weight. A polymorphism at the porcine myogenin locus was associated with birth weight, growth rate, lean weight at 200 d, and backfat thickness. Yorkshire pigs from two commercial lines were genotyped, and crosses between heterozygous pigs and heterozygous and homozygous pigs were made. Resulting litters were genotyped, and phenotypic data were collected. Significant differences were found between the two homozygous myogenin genotypes for birth weight, growth rate, and lean weight, but not for backfat thickness. Variation at the myogenin locus explained 4% of the total phenotypic variation in birth weight, growth rate, and carcass weight, and 5.8% of the total variation in lean weight. We conclude that myogenin genotype influences porcine growth rate and muscle mass.

Fat transfer and energetics during lactation in the hooded seal: the roles of tissue lipoprotein lipase in milk fat secretion and pup blubber deposition

Hooded seals (Cystophora cristata) lactate for 3.6 days during which females simultaneously fast and transfer large amounts of energy to their pups through fat-rich milk. Pups grow rapidly, principally due to blubber deposition. Lipoprotein lipase (LPL), the primary enzyme responsible for tissue uptake of triglyceride fatty acids, may strongly influence both maternal milk fat secretion and pup blubber deposition. We measured the energetic costs of lactation (using hydrogen isotope dilution, 3H2O), milk composition, prolactin, and LPL activity (post-heparin plasma LPL [PH LPL], blubber, mammary gland and milk; U) in six females. PH LPL and blubber LPL were measured in their pups. Females depleted 216.3 MJ.day-1 of body energy and fat accounted for 59% of maternal mass loss and 90% of postpartum body energy loss, but maternal body composition changed little. Maternal blubber LPL was negligible (0.0-0.2 U), while mammary LPL was elevated (1.8-2.5 U) and was paralleled by changes in prolactin. Estimated total mammary LPL activity was high (up to 20,000 U.animal-1) effectively favoring the mammary gland for lipid uptake. Levels of total blubber LPL in pups increased seven-fold over lactation. Pups with higher PH LPL at birth had greater relative growth rates (P = 0.025). Pups with greater blubber stores and total blubber LPL activity had elevated rates of fat deposition (P = 0.035).