Preadipocyte and adipose tissue differentiation in meat animals: influence of species and anatomical location

Early in porcine adipose tissue development, the stromal-vascular (SV) elements control and dictate the extent of adipogenesis in a depot-dependent manner. The vasculature and collagen matrix differentiate before overt adipocyte differentiation. In the fetal pig, subcutaneous (SQ) layer development is predictive of adipocyte development, as the outer, middle, and inner layers of dorsal SQ adipose tissue develop and maintain layered morphology throughout postnatal growth of SQ adipose tissue. Bovine and ovine fetuses contain brown adipose tissue but SQ white adipose tissue is poorly developed structurally. Fetal adipose tissue differentiation is associated with the precocious expression of several genes encoding secreted factors and key transcription factors like peroxisome proliferator activated receptor (PPAR)γ and CCAAT/-enhancer-binding protein. Identification of adipocyte-associated genes differentially expressed by age, depot, and species in vivo and in vitro has been achieved using single-gene analysis, microarrays, suppressive subtraction hybridization, and next-generation sequencing applications. Gene polymorphisms in PPARγ, cathepsins, and uncoupling protein 3 have been associated with back fat accumulation. Genome scans have mapped several quantitative trait loci (QTL) predictive of adipose tissue-deposition phenotypes in cattle and pigs.

Association of adenovirus 36 infection with adiposity and inflammatory-related markers in children

CONTEXT

Although animal studies suggest that adenovirus 36 (Ad36) infection is linked to obesity and systemic inflammation, human data are scant and equivocal.

OBJECTIVE

Associations of Ad36 infection with total body adiposity and inflammatory-related markers were determined in 291 children aged 9-13 years (50% female, 49% black).

DESIGN

Fasting blood samples were measured for presence of Ad36-specific antibodies and TNF-α, IL-6, vascular endothelial growth factor (VEGF), and monocyte chemoattractant protein-1 (MCP-1). Fat mass and fat-free soft tissue mass were measured by dual-energy X-ray absorptiometry.

RESULTS

The overall prevalence of Ad36 seropositivity [Ad36(+)] was 42%. There was a higher percentage of Ad36(+) children in the highest tertiles of TNF-α and IL-6 compared with their respective middle and lowest tertiles (both P < .03). There was also a trend toward a higher prevalence of Ad36(+) children in the highest tertile of VEGF compared with tertiles 1 and 2 (P = .05). Multinomial logistic regression, adjusting for age, race, sex, and fat-free soft tissue mass, revealed that compared with children with the lowest TNF-α, IL-6, and VEGF levels (tertile 1), the adjusted odds ratios for Ad36(+) were 2.2 [95% confidence interval (CI) 1.2-4.0], 2.4 (95% CI 1.4-4.0), and 1.8 (95% CI 1.0-3.3), respectively, for those in the highest TNF-α, IL-6, and VEGF levels (tertile 3). No association was observed between Ad36(+) and greater levels of fat mass or MCP-1 (all P > .05).

CONCLUSIONS

In children, our data suggest that Ad36(+) may be associated with biomarkers implicated in inflammation but not with greater levels of fat mass.

A randomized trial of vitamin D₃ supplementation in children: dose-response effects on vitamin D metabolites and calcium absorption

CONTEXT

Changes in serum vitamin D metabolites and calcium absorption with varying doses of oral vitamin D₃ in healthy children are unknown.

OBJECTIVE

Our objective was to examine the dose-response effects of supplemental vitamin D₃ on serum vitamin D metabolites and calcium absorption in children living at two U.S. latitudes.

DESIGN

Black and white children (n = 323) participated in a multisite (U.S. latitudes 34° N and 40° N), triple-masked trial. Children were randomized to receive oral vitamin D₃ (0, 400, 1000, 2000, and 4000 IU/d) and were sampled over 12 weeks in winter. Serum 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D (1,25(OH)₂D) were measured using RIA and intact PTH (iPTH) by immunoradiometric assay. Fractional calcium absorption was determined from an oral stable isotope ⁴⁴Ca (5 mg) in a 150-mg calcium meal. Nonlinear and linear regression models were fit for vitamin D metabolites, iPTH, and calcium absorption.

RESULTS

The mean baseline 25(OH)D value for the entire sample was 70.0 nmol/L. Increases in 25(OH)D depended on dose with 12-week changes ranging from -10 nmol/L for placebo to 76 nmol/L for 4000 IU. Larger 25(OH)D gains were observed for whites vs blacks at the highest dose (P < .01). Gains for 1,25(OH)₂D were not significant (P = .07), and decreases in iPTH were not dose-dependent. There was no dose effect of vitamin D on fractional calcium absorption when adjusted for pill compliance, race, sex, or baseline 25(OH)D.

CONCLUSION

Large increases in serum 25(OH)D with vitamin D₃ supplementation did not increase calcium absorption in healthy children living at 2 different latitudes. Supplementation with 400 IU/d was sufficient to maintain wintertime 25(OH)D concentrations in healthy black, but not white, children.

Racial differences in cortical bone and their relationship to biochemical variables in Black and White children in the early stages of puberty

Osteoporotic fracture rates differ according to race with Blacks having up to half the rate of Whites. The current study demonstrates that racial divergence in cortical bone properties develops in early childhood despite lower serum 25-hydroxyvitamin D in Blacks.

INTRODUCTION

Racial differences in bone structure likely have roots in childhood as bone size develops predominantly during growth. This study aimed to compare cortical bone health within the tibial diaphysis of Black and White children in the early stages of puberty and explore the contributions of biochemical variables in explaining racial variation in cortical bone properties.

METHODS

A cross-sectional study was performed comparing peripheral quantitative computed tomography-derived cortical bone measures of the tibial diaphysis and biochemical variables in 314 participants (n = 155 males; n = 164 Blacks) in the early stages of puberty.

RESULTS

Blacks had greater cortical volumetric bone mineral density, mass, and size compared to Whites (all p < 0.01), contributing to Blacks having 17.0 % greater tibial strength (polar strength-strain index (SSIP)) (p < 0.001). Turnover markers indicated that Blacks had higher bone formation (osteocalcin (OC) and bone-specific alkaline phosphatase) and lower bone resorption (N-terminal telopeptide) than Whites (all p < 0.01). Blacks also had lower 25-hydroxyvitamin D (25(OH)D) and higher 1,25-dihydroxyvitamin D (1,25(OH)2D) and parathyroid hormone (PTH) (all p < 0.05). There were no correlations between tibial bone properties and 25(OH)D and PTH in Whites (all p ≥ 0.10); however, SSIP was negatively and positively correlated with 25(OH)D and PTH in Blacks, respectively (all p ≤ 0.02). Variation in bone cross-sectional area and SSIP attributable to race was partially explained by tibial length, 25(OH)D/PTH, and OC.

CONCLUSIONS

Divergence in tibial cortical bone properties between Blacks and Whites is established by the early stages of puberty with the enhanced cortical bone properties in Black children possibly being explained by higher PTH and OC.

Endocrine Regulation of Fetal Adipose Tissue Metabolism in the Pig: Role of Hydrocortisone

Glucocorticoids have been shown to be essential for the excessive fat deposition and development of obesity in several animal models. This study was performed to characterize the role of glucocorticoids in the developmental regulation of adipose tissue metabolism. On day 70 of gestation, pig fetuses were hypophysectomized by micro-cauterization. Hypophysectomized fetuses were implanted subcutaneously with hydrocortisone pellets or received no hormone replacement. Fetuses were removed by laparotomy on day 90 of gestation. Additional fetuses were hypophysectomized on day 70, implanted with hydrocortisone pellets on day 90 and removed on day 105 of gestation. Several intact fetuses were also implanted subcutaneously with hydrocortisone pellets during this later gestational period. Serum cortisol concentrations were reduced in hypophysectomized pigs at both fetal ages and were restored to intact levels by hydrocortisone treatment. Hydrocortisone supplementation enhanced lipolytic response to isoproterenol in intact fetuses but failed to restore lipolytic response to isoproterenol in hypophysectomized animals at either fetal age. Hydrocortisone induced a slight increase in lipogenesis in hypophysectomized fetuses when administered from 70 to 90 days of gestation and a more dramatic increase when administered from days 90 to 105 of gestation. However, hydrocortisone had no effect on basal or insulin stimulated lipogenesis in intact fetuses when administered from days 90 to 105 of gestation. These results indicate that hydrocortisone may have a primary influence on adipose tissue metabolism during late fetal development only in the absence of inhibition from counterregulatory hormones of pituitary origin.

Life events and personality predicting loneliness among centenarians: findings from the Georgia Centenarian Study

Regarding the purpose of this study, the researchers analyzed the roles that both life events (life-time positive events and life-time negative events) and personality (Neuroticism, Extraversion, Trust, Competence, and Ideas) played in participants of the Georgia Centenarian Study. The researchers analyzed these variables to determine whether they predicted loneliness. Analyses indicated that life-time negative events significantly predicted loneliness. In essence, the higher was the number of life-time negative life events, the higher was the loneliness score. Moreover, Neuroticism, Competence, and Ideas were all significant predictors of loneliness. The higher was the level of Neuroticism and intellectual curiosity, the higher was the level of loneliness, whereas the lower was the level of Competence, the higher was the level of loneliness. In addition, both life-time positive and life-time negative life events were significant predictors of Neuroticism. The higher was the number of life-time positive events, the lower was the level of Neuroticism, and the higher was the number of life-time negative events, the greater was the level of Neuroticism. These results indicated that life-time negative events indirectly affect loneliness via Neuroticism. Last, our results indicated that the Competence facet mediated the relationship between lifetime negative life events and loneliness. Life-time negative life events significantly affected centenarians' perceived competence, and Competence in turn significantly affected the centenarians' loneliness. These results as a whole not only add to our understanding of the link between personality and loneliness, but also provide new insight into how life events predict loneliness.

25-hydroxyvitamin D, insulin-like growth factor-I, and bone mineral accrual during growth

CONTEXT

The extent to which 25-hydroxyvitamin D [25(OH)D] and IGF-I influence bone mineral content (BMC) accrual from early to mid-puberty is unclear. OBJECTIVE, SETTING, AND PARTICIPANTS: This study sought to determine relationships among 25(OH)D, IGF-I, and BMC in community-dwelling prepubertal females (n = 76; aged 4-8 yr at baseline) over a period of up to 9 yr.

DESIGN

The hypothesis that changes in IGF-I vs. 25(OH)D are more strongly associated with BMC accrual was formulated after data collection. 25(OH)D and IGF-I were log-transformed and further adjusted using two-way ANOVA for differences in season and race. Linear mixed modeling (including a random subject-specific intercept and a random subject-specific slope on age) was employed to analyze the proportion of variance the transformed 25(OH)D and IGF-I variables explained for the bone outcomes.

RESULTS

IGF-I was more strongly associated with BMC accrual than 25(OH)D at the total body (R(2) = 0.874 vs. 0.809), proximal femur (R(2) = 0.847 vs. 0.771), radius (R(2) = 0.812 vs. 0.759), and lumbar spine (R(2) = 0.759 vs. 0.698). The rate of BMC accrual was positively associated with changes in IGF-I but negatively associated with 25(OH)D. When IGF-I and 25(OH)D were included in the same regression equation, 25(OH)D did not have a significant predictive effect on BMC accrual above and beyond that of IGF-I.

CONCLUSIONS

These prospective data in early adolescent females indicate that both 25(OH)D and IGF-I have a significant impact on bone mineral accrual; however, the positive association of IGF-I and BMC accrual is greater than the negative association of 25(OH)D and BMC accrual.

Cognitive performance in centenarians and the oldest old: norms from the Georgia Centenarian Study

We present normative data from a large population-based sample of centenarians for several brief, global neurocognitive tasks amenable for frail elders. Comparative data from octogenarians are included. A total of 244 centenarians and 80 octogenarians from Phase III of the Georgia Centenarian Study were administered the Mini-Mental Status Examination, Severe Impairment Battery, and Behavioral Dyscontrol Scale. Centenarians (age 98-107) were stratified into three age cohorts (98-99, 100-101, 102-107), octogenarians into two 5- year cohorts (80-84, 85-89). Highly significant differences were observed between groups on all measures, with greater variation and dispersion in performance among centenarians, as well as stronger associations between age and performance. Descriptive statistics and normative ranges (unweighted and population-weighted) are provided by age cohort. Additional statistics are provided by education level. While most previous centenarian studies have used convenience samples, ours is population-based and likely more valid for comparison in applied settings. Results suggest centenarians look different than do even the oldest age range of most normative aging datasets (e.g., 85-90). Results support using global measures of neurocognition to describe cognitive status in the oldest old, and we provide normative comparisons to do so.

Predicting happiness among centenarians

BACKGROUND

Happiness is believed to evolve from the comparison of current circumstances relative to past achievement. However, gerontological literature on happiness in extreme old age has been limited.

OBJECTIVE

The purpose of this study was to determine how perceptions of health, social provisions, and economics link past satisfaction with life to current feelings of happiness among persons living to 100 years of age and beyond.

METHODS

A total of 158 centenarians from the Georgia Centenarian Study were included to conduct the investigation. Items reflecting congruence and happiness from the Life Satisfaction Index were used to evaluate a model of happiness. Pathways between congruence, perceived economic security, subjective health, perceived social provisions, and happiness were analyzed using structural equation modeling.

RESULTS

Congruence emerged as a key predictor of happiness. Furthermore, congruence predicted perceived economic security and subjective health, whereas perceived economic security had a strong influence on subjective health status.

CONCLUSION

It appears that past satisfaction with life influences how centenarians frame subjective evaluations of health status and economic security. Furthermore, past satisfaction with life is directly associated with present happiness. This presents implications relative to understanding how perception of resources may enhance quality of life among persons who live exceptionally long lives.

Family history and adaptation among centenarians and octogenarians

BACKGROUND

The purpose of this study was to analyze various 'family history' variables (i.e. childhood health, financial situation while growing up, living with grandparents before age 17, and number of children) among participants of the Georgia Centenarian Study.

OBJECTIVE

To determine whether family history variables predict critical outcome areas such as cognitive functioning, activities of daily living, mental health, and economic dependence.

METHODS

A total of 318 older adults (236 centenarians and 82 octogenarians) were assessed with regard to their mental status, ADL (activities of daily living) functioning, depression, family history, loneliness, and perceived economic status.

RESULTS

Analyses indicated that the number of children significantly predicted the ability to engage in activities of daily living and loneliness. In essence, the more children, the higher the activities of the daily living score and the lower the loneliness scores. In addition, childhood health significantly predicted loneliness. The poorer one's health in childhood, the higher the loneliness scores.

CONCLUSION

The results of this study confirm the importance of distal family history variables on present-day functioning.

Depression among centenarians and the oldest old: contributions of cognition and personality

BACKGROUND

An estimated 20% of adults over the age of 55 experience clinical mental disorders such as depression and anxiety. For older adults, mental health concerns are often undetected, concomitant with physical challenges, and ultimately go untreated. These realities have significant implications for older adults' day-to-day functioning, particularly among the oldest old.

OBJECTIVE

The present study examined the ability of cognition and personality in explaining depression within a sample of octogenarians and centenarians.

METHODS

Participants were assessed during the most recent cross-sectional data collection of the Georgia Centenarian Study. The final eligible sample included 76 octogenarians (mean: 84.25 years, SD: 2.82; range: 81-90) and 158 centenarians and near centenarians (mean: 99.82 years, SD: 1.72; range: 98-109).

RESULTS

Hierarchical regression analyses were conducted to examine the relation between key variables and depressive symptoms in the two age groups. Blocks entered into the analyses included: demographics (i.e. age group, residential status, sex, and ethnicity) and functioning, memory and problem-solving ability, and personality (i.e. extraversion and neuroticism). Models differed for octogenarians and centenarians. Decreased problem-solving ability was related to greater depressive symptoms among octogenarians. For centenarians, institutional residence and increased neurotic tendencies were related to greater depressive symptoms.

CONCLUSION

Study findings demonstrate the need to examine a variety of factors which influence mental health in later life and to consider the unique contexts and differential experiences of octogenarians and centenarians.

Distal and proximal resource influences on economic dependency among the oldest old

BACKGROUND

As exceptional survivors, centenarians may have characteristics that reduce their dependency on family and community support systems despite the expectation that their extreme age creates a burden on those systems. The Georgia Centenarian Study obtained information about assistance for income, medical care, and caregiving of all types for a sample of centenarians and octogenarians. Previous studies have not established which characteristics may contribute to economic dependency among the oldest old.

OBJECTIVE

To identify distal and proximal resource influences on economic dependency, considering past lifestyle, proximal health, economic resources, personality, and coping behavior.

METHODS

Analysis sample sizes ranged from 109 to 138 octogenarians and centenarians. Blockwise multiple regressions predicted whether they received income assistance, number of medical care events, number of caregiving types, and total caregiving hours.

RESULTS

Past life style, gender, ethnicity, socioeconomic status, functional health, and coping were not related to economic dependency. With the exception of the number of types of care, centenarians were not more dependent than octogenarians. Cognitive ability had the strongest effects for medical care and caregiving services. 'Extraversion', 'ideas', 'neuroticism', and 'competence' personality factors had significant effects for caregiving types and total hours of care received.

CONCLUSION

Monitoring and intervention to maintain cognitive ability are critical practices for autonomy and reduced economic dependency among the oldest old. Psychological resources are more important influences on social support than functional health and other proximal economic resources.

Social resources and longevity: findings from the Georgia centenarian study

BACKGROUND

As the proportion of adults aged 85 and older increases, investigations of resources essential for adapting to the challenges of aging are required.

OBJECTIVE

To comprehensively investigate the social resources of cognitively intact centenarians participating in the Georgia Centenarian Study and the association between these resources and residence status.

METHODS

Two widely used measures of social resources were investigated among participants living in private homes, personal care facilities, and nursing homes. Logistic regression was used to determine significant predictors of nursing home residence.

RESULTS

Differences in levels of social resources were found between centenarians and octogenarians, and among centenarians in different living situations. Analyses revealed differential findings between self- and proxy reports. Controlling for education, activities of daily living, and financial ability to meet needs, only one of the two social resources measures significantly reduced the odds of nursing home residence.

CONCLUSION

The findings of this study add to the existing literature on one of the basic adaptive resources (social resources) for centenarians. Whether a more specific assessment of network contact is employed, or a more global assessment is used, differences in these constructs exist between centenarians and octogenarians, among centenarians in differing living conditions, and across types of informants. Researchers examining the different resources that may contribute to extraordinary longevity and positive adaptation may find it essential to differentiate between the oldest old and centenarians, and to account for differences based upon measure, reporter type, and centenarian residence status.

High BMI and waist circumference are associated with a high prevalence of comorbidities in older Americans Act programs in Georgia senior centers

OBJECTIVE

This study characterized the relationship of body mass index (BMI) and high waist circumference (WC) with the prevalence of selected comorbidities among older adults receiving nutrition and wellness services from Georgia's Older Americans Act programs at senior centers.

METHODS

Participants were a convenience sample (N = 759, mean age = 75 years, 81% female, 63% white, 36% black). Correction factors were applied to measured WC and to measured and self-reported height and weight.

RESULTS

The prevalence of several comorbidities showed striking relationships with WC and BMI, independent of age, gender, and race.

CONCLUSION

The health burden of overweight/obesity is very high in these older adults creating an urgent need for evidence-based nutrition, physical activity programs, and therapeutic lifestyle counseling to prevent and manage weight-related comorbidities.

Age, race and season predict vitamin D status in African American and white octogenarians and centenarians

OBJECTIVE

Poor vitamin D status has been associated with osteoporosis, falls, cardiovascular diseases, cancer, autoimmune diseases, pain, nursing home placement, and other age-related conditions, but little is known about the prevalence and predictors of vitamin D status in those aged 80 and older. Thus, this study tested the hypothesis that vitamin D status would be 1) poorer in a population-based multi-ethnic sample of centenarians as compared with octogenarians and 2) predicted by specific dietary, demographic or environmental factors.

DESIGN

Cross-sectional population-based analyses.

SETTING

Northern Georgia in the United States.

PARTICIPANTS

Men and women aged 80 to 89 (octogenarians, n=80) and 98 and older (centenarians, n=237).

MEASUREMENTS

Regression analyses were used to examine the associations of serum 25-hydroxyvitamin D [25(OH)D] with age, gender, race, living arrangements, dairy food intake, supplement intake, and season.

RESULTS

The prevalence of vitamin D insufficiency [25(OH)D<50 nmol/L] was higher in centenarians than in octogenarians (p<0.02). In logistic regression analyses, the risk of being vitamin D insufficient was significantly increased by being a centenarian vs. octogenarian (p<0.005) and by being African American vs. white (p<0.001) and decreased by taking a supplement with vitamin D (p<0.001) or by having vitamin D status measured in the summer or fall (each p<0.05), compared with spring.

CONCLUSIONS

Centenarians and octogenarians are at high risk for vitamin D insufficiency for many of the same reasons identified in younger populations. Given the numerous potential adverse consequences of poor vitamin D status, efforts are needed to ensure vitamin D adequacy in these older adults.

What are subcutaneous adipocytes really good for?

Our acute awareness of the cosmetic, psychosocial and sexual importance of subcutaneous adipose tissue contrasts dramatically with how poorly we have understood the biology of this massive, enigmatic, often ignored and much-abused skin compartment. Therefore, it is timely to recall the exciting, steadily growing, yet underappreciated body of evidence that subcutaneous adipocytes are so much more than just 'fat guys', hanging around passively to conspire, at most, against your desperate attempts to maintain ideal weight. Although the subcutis, quantitatively, tends to represent the dominant architectural component of human skin, conventional wisdom confines its biological key functions to those of energy storage, physical buffer, thermoregulation and thermoinsulation. However, already the distribution of human superficial adipose tissue, by itself, questions how justified the popular belief is that 'skin fat' (which actually may be more diverse than often assumed) serves primarily thermoinsulatory purposes. And although the metabolic complications of obesity are well appreciated, our understanding of how exactly subcutaneous adipocytes contribute to extracutaneous disease - and even influence important immune and brain functions! - is far from complete. The increasing insights recently won into subcutaneous adipose tissue as a cytokine depot that regulates innate immunity and cell growth exemplarily serve to illustrate the vast open research expanses that remain to be fully explored in the subcutis. The following public debate carries you from the evolutionary origins and the key functional purposes of adipose tissue, via adipose-derived stem cells and adipokines straight to the neuroendocrine, immunomodulatory and central nervous effects of signals that originate in the subcutis - perhaps, the most underestimated tissue of the human body. The editors are confident that, at the end, you shall agree: No basic scientist and no doctor with a serious interest in skin, and hardly anyone else in the life sciences, can afford to ignore the subcutaneous adipocyte - beyond its ample impact on beauty, benessence and body mass.

Adipose tissue cellularity and apoptosis after intracerebroventricular injections of leptin and 21 days of recovery in rats

OBJECTIVE

To determine the effect of leptin and post-treatment recovery on adipose tissue cellularity and apoptosis. In addition, to investigate whether Bcl-2 and/or Bax is involved in the mechanism of leptin-induced adipose tissue apoptosis.

DESIGN

A total of 24 adult male Sprague-Dawley rats were injected i.c.v. with either 10 microg mouse leptin or 10 microl vehicle once per day for 4 days. At 24 h after the last injection, one group was killed while the other was monitored for 21 days.

MEASUREMENTS

DNA fragmentation and Bcl-2 and Bax protein levels were determined in inguinal (ING), epididymal (EPI) and retroperitoneal (RP) white adipose tissues and the interscapular brown adipose tissue (BAT). Cellularity was determined in ING and EPI.

RESULTS

Leptin significantly reduced the masses of all white fat pads [RPINGEPI] but not BAT. Cell volume was significantly reduced in EPI and ING. Only ING had a significantly reduced cell number from leptin treatment plus exhibited apoptosis by increased DNA fragmentation and DNA laddering, and upregulation of pro-apoptosis Bax protein. The other fat pads exhibited a general trend to increase the Bcl-2/Bax ratio. Recovery allowed for normalization of white fat pad mass, cell number and cell volume; however, BAT mass increased 42% over control. After recovery, apoptosis was not detected, Bcl-2 protein had increased in ING, and the Bcl-2/Bax ratio had risen overall.

CONCLUSIONS

Central administration of mouse leptin in the rat targets white fat depots individually to reduce mass by a reduction in cell volume plus adipocyte deletion in, at least, the ING fat pad by Bax-mediated apoptosis. Even after a dramatic loss in adipose tissue mass and change in cellularity, the rat demonstrates a resilient return to control levels together with an increase in factors that prevent adipocyte loss.

The biology of white adipocyte proliferation

Expanded adipose tissue mass increases the risk for many clinical conditions including diabetes, hypertension, coronary atherosclerotic heart disease, and some forms of cancer. Therefore, it is imperative that we understand the mechanisms by which fat pads expand. The enlargement of fat cells during the development of obesity has been previously hypothesized to be a triggering factor for the proliferation of new fat cells. There is now a preponderance of evidence that adipose tissue is a source of growth factors such as IGF-I, IGF binding proteins, TNF alpha, angiotensin II, and MCSF that are capable of stimulating proliferation. The relative importance of these autocrine/paracrine factors in the normal control of preadipocyte proliferation is unknown. In addition, the proliferative response of preadipocytes to the paracrine milieu is undoubtedly modulated by neural inputs to fat tissue and/or serum factors. Together, these multiple regulatory controls orchestrate overall and region-specific adipose tissue cellularity responses associated with the development of hyperplastic obesity. Both in vivo and in vitro studies are needed to understand the complex, interacting physiological mechanisms by which growth of this important organ is regulated.

Pre- and postnatal dietary conjugated linoleic acid alters adipose development, body weight gain and body composition in Sprague-Dawley rats

Sprague-Dawley rats were fed either a control diet (7 g/100 g soybean oil) or a conjugated linoleic acid (CLA) diet (6.5 g/100 g soybean oil and 0.5 g/100 g CLA) beginning on d 7 of gestation to determine whether pre- and postnatal CLA affects short- and long-term growth and adiposity. At weaning (d 21), progeny were assigned control or CLA diet and fed until 11 wk of age. At birth, litter size and weight were not different between treatments. There were age- and sex-dependent changes in inguinal adipose fatty acid composition at birth and weaning, whereas there were no differences in lipid accretion or adipocyte proliferation. At weaning, CLA did not alter inguinal adipocyte proliferation but increased (P < 0.01) CCAAT/enhancer binding protein alpha expression in inguinal adipose tissue from females, whereas there was no difference in expression in males. Significant differences in size distribution of inguinal adipocytes at weaning and retroperitoneal adipocytes at 11 wk of age were observed. In general, CLA increased the proportion of smaller cells and decreased the proportion of larger cells. The main long-term effect of the dams' diet was the significantly heavier gastrocnemius and soleus muscles, and significantly longer tail lengths, an indication of skeletal growth, of male pups whose dams were fed CLA. Postweaning diet reduced fat pad weights in female but not male pups fed CLA. This response was due to differences in cell size rather than number. Response to CLA treatment may depend on the sex and age of the animal as well as duration of feeding.

The expression of cyclin D1 during adipogenesis in pig primary stromal-vascular cultures

OBJECTIVE

Our objective in this study was to measure the expression of cyclin D1 in pig primary stromal-vascular (S-V) cells as they differentiate into adipose cells and to identify which factors may alter cyclin D1 expression.

RESEARCH METHODS AND PROCEDURES

Western blot analysis was performed on cultured S-V cells using 8% sodium dodecyl sulfate-polyacrylamide gels, mouse monoclonal cyclin D1 antibody, and anti-mouse IgG secondary labeled with horseradish peroxidase. For immunocytochemistry, cultures were fixed with 4% paraformaldehyde and incubated with anti-CCAAT/enhancer binding protein (C/EBP alpha) and anti-cyclin D1 together. Cyclin D1 expression was evaluated in 105-day fetal dorsal subcutaneous tissues using paraffin sections.

RESULTS

Our results with Western blot analysis showed that cyclin D1 was found in freshly isolated S-V cells and continued to be expressed during the first 3 days of adipose cell development with a significant increase in late development at day 9. Elevated cyclin D1 levels were colocalized with C/EBP alpha beginning at day 3 and remained colocalized with C/EBP alpha through day 9. Removing insulin from cultures resulted in a reduction in differentially elevated levels of cyclin D1.

DISCUSSION

The elevated level of cyclin D1 expression colocalized with C/EBP alpha expression is unexpected because differentiated adipocytes would be expected to have reduced proliferative potential. The elevated levels of cyclin D1 expression we observed in mature adipocytes depend on insulin. In addition, cyclin D1 is absent from lipid-filled fetal adipose cells in vivo, where insulin levels are very low. The activity of cyclin D1 in differentiated adipocytes may be directed toward proteins outside of the cell cycle.

TNFalpha induces and insulin inhibits caspase 3-dependent adipocyte apoptosis

Regulation of fat cell number by apoptosis is proposed to be part of a normal physiological cycle in adipose growth and development. To investigate this process, cultured rat adipocytes were treated with various concentrations of tumor necrosis factor alpha (TNFalpha) and/or insulin to determine the roles of these factors in adipocyte apoptosis. The cells were analyzed by flow cytometry using a TUNEL assay. TNFalpha increased adipocyte apoptosis in a dose-dependent fashion. TNFalpha-mediated apoptosis was detectable within 6 h of treatment and continued to increase with time. Decreasing media insulin concentration from 8.5 to 0.85 nM resulted in increased adipocyte apoptosis, whereas high doses of insulin protected adipocytes from TNFalpha-induced apoptosis. TNFalpha-activated apoptosis was accompanied by an increase in caspase 3 activity and could be inhibited by a caspase 3-specific inhibitor. These data suggest that adipose tissue cell number is regulated, in part, by an apoptotic signaling pathway that involves TNFalpha, insulin, and caspase 3.

Dietary conjugated linoleic acid reduces adiposity in lean but not obese Zucker rats

Recent studies have demonstrated a reduction in body fat in growing animals fed conjugated linoleic acid (CLA). Two experiments were conducted to extend these observations to obese rats so that the mechanism of the actions of CLA might be more easily elucidated. In experiment 1, male lean and obese Zucker rats were fed diets containing either 0 or 0.5% CLA for 5 wk. There was no effect of diet on growth rate or food intake. Dietary CLA reduced retroperitoneal and inguinal fat pad weights in the lean rats but increased fat pad weights in the obese genotype (diet x genotype interaction; P < 0.05). Determination of fat pad cellularity indicated that these changes in fat pad weight were due to a reduction or increase in average fat cell size for the lean and obese Zucker rats, respectively. In experiment 2, we sought to reproduce these effects on fat pad size, as well as to determine the effect of dietary CLA on the catabolic response to bacterial endotoxin injection in obese Zucker rats. Growing female lean and obese Zucker rats were fed diets containing 0 or 0.5% CLA for 8 wk. On d 28, each rat was injected intraperitoneally with lipopolysaccharide from Escherichia coli serotype 055:B5 (1 mg/kg body weight) and body weight was determined over the next 96 h. There was a diet x genotype interaction (P < 0.05) for the body weight response to lipopolysaccharide 24 h postinjection. Lean rats fed CLA lost less weight than did lean controls, but obese rats fed CLA lost more weight than did obese controls. As in the first experiment, there was a diet x genotype (P < 0.05) for the effect of treatment on retroperitoneal fat pad weights determined at the end of the experiment. Lean rats fed CLA had smaller RP fat pads than did lean controls, but obese rats fed CLA once again had heavier RP fat pads than did obese controls. These results indicate that CLA reduces body fat and catabolic response to endotoxin injection in lean Zucker rats but not in the obese genotype. The observed interaction between diet and genotype warrants additional investigation into the specific mechanism(s) of the biological activities of CLA.

Tumor necrosis factor-alpha binding in porcine primary stromal-vascular cell cultures

The binding characteristics of tumor necrosis factor-alpha receptors (TNFRs) in primary stromal-vascular cultures from fat tissue of 7-d-old pigs were analyzed. Cells were plated and maintained in 10% fetal bovine serum from day 0 to day 3 and then switched to serum-free medium from day 3 to day 6 to induce lipid filling. On days 3 and 6 of culture, some of the cells were lysed for ligand and immunoblotting and the remainder subjected to competitive and inhibitory-binding assays. Media from day 6 of culture were subjected to ligand and immunoblotting. Competitive binding analysis showed one-site bindings, with IC50s in the nanomolar and Kds in the picomolar ranges, that were not significantly different at both time-points of measurement. However, the Bmax decreased significantly with differentiation. Preincubation with antibody against TNF receptor type 1 (TNFR1) or TNF receptor type 2 reduced the specific binding by 95 and 15%, respectively, suggesting a dominating role of TNFR1 in 125I-labeled TNFalpha (125I-TNFalpha) binding. This was further supported by ligand blotting of cell lysates. Ligand and immunoblotting of cell lysates indicated that TNFalpha utilizes both types of surface receptors and their isoforms which were not modified during differentiation. Ligand blotting of media revealed soluble receptors with high Mr implying the formation of multimers. Immunoblotting suggested the presence of both types of TNFRs, but a greater abundance of soluble TNFR1. Also, it indicated the additional formation of smaller oligomers from both types of soluble receptors suggesting higher affinity of larger multimers for 125I-TNFalpha.

Inhibition of preadipocyte differentiation by myostatin treatment in 3T3-L1 cultures

Myostatin, a new TGF-beta family member, is known as a muscle growth inhibitor, but its role in adipocyte development has not been studied. To test the role of Myostatin in 3T3-L1 preadipocyte differentiation, we treated cultured 3T3-L1 preadipocytes with Myostatin dissolved in 0.1% trifluoroacetic acid (TFA) during differentiation after they had become confluent. Myostatin treatment significantly decreased glycerol-3-phosphate dehydrogenase (GPDH) activity and oil Red-O staining compared to controls that did not receive Myostatin. Western blot analysis showed that the expression levels of CCAAT/enhancer binding protein alpha (C/EBP alpha) and peroxisome proliferator-activated receptor gamma (PPAR gamma) were significantly decreased by Myostatin treatment (P < 0.05). However, the expression of C/EBP beta was not significantly changed by the treatment (P > 0.05). From RT-PCR result, the relative level of leptin mRNA in Myostatin-treated cells was not significantly different (P > 0.1) from the level in cells without Myostatin treatment. Our data show that Myostatin, a secreted protein from muscle, inhibits preadipocyte differentiation in 3T3-L1 cells, which is mediated, in part, by altered regulation of C/EBP alpha and PPAR gamma.

Enhancing effect of troglitazone on porcine adipocyte differentiation in primary culture: a comparison with dexamethasone

OBJECTIVE

This study compares the effects of the thiazolidinedione, troglitazone (TGZ), dexamethasone (DEX), and DEX plus TGZ on preadipocyte differentiation and the expression of CCAAT/enhancer-binding protein-alpha (C/ EBPalpha) and peroxisome proliferator-activated receptor-gamma (PPARgamma).

RESEARCH METHODS AND PROCEDURES

Adipose tissue was obtained from postnatal pigs to isolate stromal-vascular cells. First, we applied 1, 5, or 10 microM TGZ and 10% fetal bovine serum for 3 days and counted the number of recruited preadipocytes. Next, we used either 10 microM TGZ, 80 nM DEX, or DEX plus TGZ with 10% fetal bovine serum for 3 days and then switched to serum-free medium with insulin for 6 days. On day 3 of culture, we counted preadipocytes, and on days 3 and 6 of culture, we performed immunostaining and Western blot analysis to determine the expression of C/EBPalpha and PPARgamma proteins. On day 9 of culture, we stained for lipids with oil red-O and measured the activity of glycerol phosphate dehydrogenase.

RESULTS

DEX and TGZ equally enhanced recruitment of preadipocytes and late differentiation, but these effects were not additive with DEX plus TGZ treatment. However, TGZ and DEX had a differential effect on morphogenesis; DEX-treated adipocytes were larger and organized in loose clusters, whereas TGZ-treated cells were smaller and formed compact clusters. Both agents increased C/EBPalpha expression but in a temporally distinct manner. DEX was a better inducer than TGZ, and its effect was early and temporary. However, treatment with either TGZ or DEX did not change PPARgamma protein expression as evaluated by a Western blotting, but immunocytochemistry showed a tendency for increased numbers of PPARgamma positive cells.

DISCUSSION

TGZ and DEX equally enhance early and late adipocyte differentiation, possibly by using some common pathways for preadipocyte recruitment. The differential effect on morphogenesis implies a potential differential effect on the expression of extracellular matrix components. C/EBPalpha may be the critical transcription factor involved in TGZ- and DEX-induced adipogenesis.

Alterations in fetal adipose tissue leptin expression correlate with the development of adipose tissue

Control pig fetuses and fetuses hypophysectomized (hypox) at 70 days of gestation were treated with hormones on day 90. At 105 days of gestation, subcutaneous adipose tissue was prepared for morphological studies, leptin Northern blot and Western blot analysis. Fetal ontogeny studies showed that leptin mRNA in adipose tissue increased with morphological development, and the highest level of leptin mRNA was observed in 105-day fetal pigs. In hypox fetuses, levels of leptin mRNA were similar to those in controls. Treatment with either hydrocortisone (HC) or thyroxine (T(4)) resulted in a slight increase in leptin mRNA levels in hypox fetuses but not in intact fetuses. Supplementation with both HC and T(4) markedly stimulated leptin mRNA expression in both hypox and intact fetuses. Morphological data showed that hypox slightly enhanced lipid accretion and treatment of hypox fetuses with HC and T(4) increased lipid accretion to a greater degree than did either HC or T(4) alone. However, serum leptin levels were not influenced by age, hypox or hormone treatment. Leptin protein expression was not detected in adipose tissue of hypox or intact fetuses regardless of hormone treatment. Leptin protein was detected in adipose tissue of 7-day-old pigs and placenta. As compared to 7-day postnatal adipose tissue, placenta showed a higher level of leptin protein expression. Leptin mRNA expression in fetal adipose tissue was not correlated with body weight and organ weight. The expression of long-form leptin receptor mRNA was detected in fetal adipose tissue. Our results indicate that adipose tissue leptin may not be the main source of serum leptin in the fetus and may not be involved in general prenatal growth and development. But adipose tissue leptin may act as an autocrine or paracrine factor in the development of fetal adipose tissue.

Dietary conjugated linoleic acid reduces rat adipose tissue cell size rather than cell number

We investigated the basis for the reduction in fat pad size in rats fed conjugated linoleic acid (CLA). In the first study, growing female Sprague-Dawley rats (initial weight150 g) were fed diets containing 0, 0.25 and 0.5 g/100 g diet of a purified (97% CLA) and 0.5% of a feed-grade (55% CLA) source of CLA for 5 wk to determine the effects on growth performance and fat mass. There was no effect of CLA on growth rate or food intake. Dietary CLA reduced retroperitoneal fat pad weight 13, 25 and 32% in rats fed 0.25 and 0. 5% of the pure CLA and 0.5% of the feed-grade CLA, respectively (P < 0.05). Similar effects were observed in the parametrial fat pad. The reduced pad size was due to smaller adipocyte size rather than a reduced cell number. Relative to the control group, mean cell volume was 15, 28 and 29% lower in tissue from rats fed 0.25 and 0.5% of the pure CLA and 0.5% of the feed-grade CLA, respectively (P < 0.01). In the second study, rats were fed CLA (0 vs. 0.5%) for 7 or 49 d. Reductions in fat pad weight were observed within 7 d. In addition, the effects of CLA on energy metabolism were studied in the chronically fed rats. There were no significant effects of CLA on oxygen consumption, CO(2) or heat production. During wk 4 of feeding, but not at other times, there was a 5% lower respiratory quotient in CLA-fed rats (P < 0.05). There was a time-dependent accumulation of CLA in adipose tissue and a decrease in monounsaturated fatty acids. These results suggest that the reduction in fat mass in rats fed CLA can be accounted for by a reduction in cell size rather than a change in cell number.

Somatotropin and adipose tissue metabolism: substrate and temporal effects

The purpose of these studies was to determine the time course for changes in feed intake, blood metabolites, and lipogenic activity in adipose tissue in response to the initiation of porcine somatotropin (pST) treatment and following withdrawal from treatment in barrows. An initial study was conducted to determine the impact of chronic pST treatment (4 wk of daily injection; 0 vs 4 mg/d) on adipose tissue lipid metabolism in barrows (initial weight 67 kg). Feed efficiency was improved 27%, backfat thickness was decreased 43%, and glucose and lactate oxidation and incorporation into lipid in adipose tissue was reduced 70 to 86% in pST-treated pigs. Palmitate esterification was decreased 44%, whereas palmitate oxidation was unaffected. In vitro metabolism of lactate, glucose, and palmitate in liver slices was not affected by pST treatment. The time-course for changes in intake and adipose tissue metabolism in response to 7 d of pST (0 vs 4 mg/d) treatment and 7 d of withdrawal was examined in subsequent studies in barrows (initial weight 75 kg). Feed intake during pST treatment was significantly (P < .05) less than in control pigs within 24 h of the initiation of treatment and remained low through 3 d after withdrawal. Adipose tissue biopsies were obtained on d 0, 1, 2, 4, and 7 of the treatment phase and on d 2, 4, and 7 after withdrawal from 7 d of treatment. Maximal inhibition of lipogenesis by pST treatment in adipose tissue in vitro was observed on d 4 (-68%) and d 7 (-69%). Similarly, fatty acid synthase activity declined during the treatment period, with the greatest change noted on d 7 (-26%). After withdrawal from treatment, lipogenesis gradually increased, returning to control values 7 d after withdrawal. Levels of IGF-I began to increase from d 1 to d 7 of treatment, continually decreased during withdrawal, and were normalized by the end of the withdrawal period. Plasma urea nitrogen concentrations decreased during treatment, increased during the withdrawal phase, and were normalized 4 d after the last pST treatment. Overall results indicate that most of the metabolic changes in response to pST occur within 1 wk of treatment and return to pretreatment values after 7 d of withdrawal from treatment.

Induction of apoptosis by all-trans-retinoic acid and C2-ceramide treatment in rat stromal-vascular cultures

Apoptosis of preadipocytes and adipocytes contributes to the balance of adipose tissue mass by reducing adipocyte number. To address this phenomenon, we treated cultured rat S-V cells with all-trans-retinoic acid (RA) (10 microM) or C2-ceramide (50 microM) during adipogenesis. Gel electrophoresis of DNA from treated cells cultured in serum-free medium showed that 10 microM RA or 50 microM ceramide induced a distinct laddering pattern of DNA fragments. Cellular caspase 3 activity, another marker of apoptosis, was increased by RA (10 microM) (P < 0.05), but not by 50 microm C2-ceramide. RT-PCR results showed that RA (10 microM) decreased the expression of Bcl-2 mRNA. These results suggest that fat cell loss by apoptosis can be regulated, in part, by RA (10 microM) which increases caspase 3 activity and decreases Bcl-2 expression in rat S-V cells. C2-ceramide apparently works through a different cellular mechanism to induce apoptosis.

Insulin-like growth factor I mediates high-fat diet-induced adipogenesis in Osborne-Mendel rats

To determine if high-fat (HF) diet-induced changes in adipose tissue cellularity are associated with the presence of paracrine growth factor(s) that alter preadipocyte proliferation, Osborne-Mendel rats were fed either a HF (76% energy) or a low-fat (LF, 12% energy) diet for 85 days. HF-fed rats had greater (P < 0.05) fat pad size, total fat cell number, number of small (30-70 microm) and large (80-140 microm) adipocytes, and percentage of 100- to 140-microm adipocytes compared with LF-fed rats. Preadipocytes in primary cell culture treated with inguinal adipose tissue conditioned medium (ATCM) prepared from HF-fed rats had greater (P < 0.05) proliferation compared with cultures treated with ATCM from LF-fed rats. Proliferative capacity of ATCM prepared from HF-fed rats was attenuated after the stripping of the medium of insulin-like growth factor I using an immunomagnetic bead separation system. These data are consistent with the concept that insulin-like growth factor I is involved in the paracrine regulation of adipogenesis.

Tumor necrosis factor-alpha stimulates cell proliferation in adipose tissue-derived stromal-vascular cell culture: promotion of adipose tissue expansion by paracrine growth factors

OBJECTIVE

Elevated levels of tumor necrosis factor-alpha (TNF-alpha) protein and mRNA have been reported in adipose tissue from obese humans and rodents. However, TNF-alpha has catabolic and antiadipogenic effects on adipocytes. Addressing this paradox, we tested the hypothesis that paracrine levels of TNF-alpha, alone or together with insulin-like growth factor-I (IGF-I), support preadipocyte development.

RESEARCH METHODS AND PROCEDURES

Cultured stromal-vascular cells from rat inguinal fat depots were exposed to serum-free media containing insulin and 0.2 nM TNF-alpha, 2.0 nM TNF-alpha, or 0.2 nM TNF-alpha + 1.0 nM IGF-I at different times during 7 days of culture.

RESULTS

TNF-alpha inhibited adipocyte differentiation as indicated by a reduction in both immunocytochemical reactivity for the preadipocyte-specific antigen (AD3; early differentiation marker) and glycerol-3-phosphate dehydrogenase activity (late differentiation marker). Early exposure (Days 1 through 3 of culture) to 0.2 nM TNF-alpha did not have a long term effect on inhibiting differentiation. Continuous exposure to 0.2 nM TNF-alpha from Days 1 through 7 of culture resulted in a 75% increase in cell number from control. There was a synergistic effect of 0.2 nM TNF-alpha + 1 nM IGF-I on increasing cell number by Day 7 of culture to levels greater than those observed with either treatment applied alone.

DISCUSSION

These data suggest that paracrine levels (0.2 nM) of TNF-alpha alone or in combination with IGF-I may support adipose tissue development by increasing the total number of stromal-vascular and/or uncommitted cells within the tissue. These cells may then be recruited to become preadipocytes or may alternatively serve as infrastructure to support adipose tissue growth.

The expression of peroxisome proliferator-activated receptor gamma in pig fetal tissue and primary stromal-vascular cultures

OBJECTIVE

This study was designed to determine when peroxisome proliferator-activated receptor gamma (PPARgamma) is expressed in developing fetal adipose tissue and stromal-vascular adipose precursor cells derived from adipose tissue. In addition we examined developing tissue for CCAAT/enhancer-binding protein beta (C/EBPbeta) expression to see if it was correlated with PPARgamma expression. Pituitary function and hormones involved with differentiation (dexamethasone and retinoic acid) were also tested for their effects on PPARgamma expression to determine if hormones known to affect differentiation also effect PPARgamma expression in vivo and in cell culture.

RESEARCH METHODS AND PROCEDURES

Developing subcutaneous adipose tissues from the dorsal region of the fetal pig were collected at different gestation times and assayed using Western blot analysis to determine levels of PPARgamma and C/EBPbeta. Hypophysectomy was performed on 75-day pig fetuses and tissue samples were then taken at 105 days for Western blot analysis. Adipose tissue was also taken from postnatal pigs to isolate stromal-vascular (S-V) cells. These adipose precursor cells were grown in culture and samples were taken for Western blot analysis to determine expression levels of PPARgamma.

RESULTS

Our results indicate that PPARgamma is expressed as early as 50 days of fetal development in adipose tissue and continues through 105 days. Expression of PPARgamma was found to be significantly enhanced in adipose tissue from hypophysectomized fetuses at 105 days of fetal development (p<0.05). C/EBPbeta was not found in 50- or 75-day fetal tissues and was found only at low levels in 105-day tissues. C/EBPbeta was not found in hypophysectomized (hypoxed) 105-day tissue where PPARgamma was elevated. S-V cells freshly isolated from adipose tissue of 5- to 7-day postnatal pigs showed the expression of PPARgamma1. When S-V cells were cultured, both PPARgamma1 and 2 were expressed after the first day and continued as cells differentiated. High concentrations of retinoic acid decreased PPARgamma expression in early S-V cultures (p<0.05).

DISCUSSION

Our data indicate that PPARgamma is expressed in fetal adipose tissue very early before distinct fat cells are observed and can be expressed without the expression of C/EBPbeta. The increase in PPARgamma expression after hypophysectomy may explain the increase in fat cell size under these conditions. Adipose precursor cells (S-V cells) from 5- to 7-day postnatal pigs also express PPARgamma in the tissue before being induced to differentiate in culture. Thus S-V cells from newborn pig adipose tissue are probably more advanced in development than the 3T3-L1 cell model. S-V cells may be in a state where PPARgamma and C/EBPalpha are expressed but new signals or vascularization are needed before cells are fully committed and lipid filling begins.

Adipocyte development is dependent upon stem cell recruitment and proliferation of preadipocytes

OBJECTIVES

The ability to acquire fat cells persists over the life spans of animals. It is unknown whether adipocyte acquisition is the result of preadipocyte proliferation or stem cell recruitment to become adipocytes. The purposes of these studies were 1) to characterize early differentiation of stromal vascular (S-V) cells to preadipocytes as it is influenced by insulin, dexamethasone (DEX), and insulin-like growth factor-I (IGF-I); and 2) to determine whether new fat cells arise from stem cell recruitment or preadipocyte proliferation.

RESEARCH METHODS AND PROCEDURES

Freshly isolated S-V cells from rat inguinal adipose tissues were plated for 24 hours then exposed to serum-free medium.

RESULTS

Approximately 15% of freshly plated S-V cells were preadipocytes as determined by a preadipocyte specific marker, AD3. Total cell number and proportion of preadipocytes were significantly greater with 100 nM insulin treatment than with 0, 0.1, or 1.0 nM, but IGF-I treatment at 10 nM resulted in preadipocyte development similar to that with 100 nM insulin treatment. The addition of 5 nM DEX to the 100 nM insulin treatment resulted in a 20% increase in preadipocyte number by day 2 when compared to either treatment alone. 5-Bromo-2'-deoxy-uridine treatment suppressed the increased proportion of preadipocytes from days 0-2 in non-insulin treated cells and prevented the increase typically observed with insulin. A mitosis inhibitor also significantly reduced the proportion of preadipocytes.

DISCUSSION

These results show for the first time that S-V cells are recruited as preadipocytes and that proliferation of these preadipocytes and early differentiation occur simultaneously.

Expression of CCAAT/enhancer binding protein C/EBPalpha, beta and delta in rat adipose stromal-vascular cells in vitro

Stromal-vascular (S-V) cells from rat inguinal fat depots were isolated and cultured in medium containing fetal bovine serum (FBS) and differentiated in defined medium until lipid accumulation was apparent. C/EBPalpha, beta and delta levels were evaluated for different growth conditions and at different times using Western blots. Immediately after isolation C/EBPalpha, beta and delta could not be detected in S-V cells. After seeding for 24 h in Dulbecco's modified Eagle's medium (DMEM) with FBS, C/EBPalpha, beta and delta could all be detected. Cells at day 1 of culture in insulin, transferrin, triiodothyronine and selenium (ITTS) had increased levels of C/EBPalpha and continued steady high levels to day 6 of culture. Cultures grown in DMEM alone, with no ITTS, showed C/EBPalpha levels similar to ITTS cultures at day 1 and day 3; however, levels diminished after day 3. DMEM cultures also showed lipid accumulation at day 6; however, the number of cells and the amount of lipid cell were reduced from levels observed in ITTS cultures. C/EBPbeta was expressed uniformly throughout the culture period in either DMEM or ITTS cultures while C/EBPdelta expression was higher with DMEM treatment than with ITTS. Treatment of 2 day DMEM cultures with FBS increased levels of C/EBPbeta and delta but significantly reduced levels of C/EBPalpha. Immunocytochemical analysis of S-V cells at day 1 of culture showed a similar percentage of cells stained in DMEM cultures and ITTS cultures. However, by day 6 of culture the percentage of cells staining positively for C/EBPalpha in DMEM had been reduced by one half while in ITTS the percent positive cells remained about the same. Our results indicate that ITTS is not necessary for the induction of C/EBPalpha and accumulation of lipid in S-V cells. However, ITTS is responsible for maintaining C/EBPalpha and enhanced lipid accumulation. Because C/EBPalpha, beta and delta expression occurs very early in cell culture and C/EBPalpha and delta expression continues to increase in DMEM without any apparent inducing agents, our results suggest that these factors may be expressed by the same cells in vivo before being placed in culture. Thus, a large fraction of S-V cells may be further along in the differentiation program than 3T3 cells are when they begin differentiation.

Endocrine regulation of fetal adipose tissue metabolism in the pig: interaction of porcine growth hormone and thyroxine

OBJECTIVE

This study tested the hypothesis that combined treatment of thyroxine (T4) and growth hormone (GH) could normalize cellular and metabolic aspects of adipose tissue development of hypophysectomized fetal pigs.

RESEARCH METHODS AND PROCEDURES

On day 70 of gestation, pig fetuses were hypophysectomized by microcauterization or remained intact. Hypophysectomized fetuses remained untreated or were treated from day 90 to day 105 of gestation with T4, GH, or a combination of both hormones.

RESULTS

Body weights were unaffected by hypophysectomy or hormone treatment. De novo lipogenesis in subcutaneous adipose tissue was increased 10-fold by hypophysectomy, consistent with our previous results. This increase was abolished by GH treatment in the hypophysectomized fetuses. In contrast, T4 treatment of the hypophysectomized fetuses resulted in a 12-fold further increase in adipose tissue lipogenesis, an effect that was negated by concomitant administration of GH. Lipolytic response to isoproterenol was decreased by hypophysectomy, unaffected by GH treatment, and restored to intact values by T4 or by T4+GH treatment in the hypophysectomized fetuses.

DISCUSSION

In contrast to T4, GH does not influence serum insulin-like growth factor-I or adipose tissue lipolysis, but decreases lipogenesis in the fetal pig. However, replacing both T4 and GH normalized hypophysectomized fetuses to a greater extent than either GH or T4 alone. Thus, any influence of thyroid hormones on stimulating adipose tissue lipogenesis in the developing fetal pig may be normally counterregulated by pituitary-derived growth hormone.

Regulation of adipose cell development in utero

The condition of obesity is impacted by increases in fat cell number, fat cell size, or a combination of the two. It is generally believed that fat cell number is dependent on the age of onset and the degree of obesity. This review provides an update on intrauterine growth of fetal adipose tissue, the earliest period of proliferation onset, and the factors that interact to enhance or suppress development. Fetal adipose tissue development is regulated by the complex interaction of maternal, endocrine, and paracrine influences that initiate specific changes in angiogenesis, adipogenesis, and metabolism. Developmental stages and metabolic processes influenced by specific hormones and paracrine factors have been identified through examination of the offspring of obese and diabetic pregnancies, hormonal manipulation during late pregnancy in animal models, and the use of cell culture. Collectively, the results of the studies cited herein delineate the basis for imprinting or conditioning of fetal preadipocytes at the paracrine/autocrine level and a role of thyroxine, glucocorticoids, and other hormones in fetal adipose tissue development and metabolism.

Association of fat cell size and paracrine growth factors in development of hyperplastic obesity

Inguinal, epididymal, and retroperitoneal adipose tissue from lean and obese Zucker rats, 3-15 wk of age, was used to determine the association among adipocyte size distribution, the presence of paracrine growth factors in adipose tissue, and subsequent changes in adipocyte number. For each specific depot and time point, obese rats had a greater percentage of large adipocytes than did lean rats. A positive correlation (P < 0.02) was found in obese rats between the percentage of inguinal and epididymal adipocytes in the 140- to 180-micrometer size range and the ability of conditioned medium prepared from these depots to stimulate cellular proliferation in a bioassay system utilizing preadipocytes from inguinal fat pads of normal rats. Proliferative activity of the conditioned medium from all depots in obese rats was positively correlated (P < 0.01) to subsequent changes in fat cell number. The data presented here for the inguinal and epididymal depot of obese Zucker rats are consistent with the hypothesis that enlarged adipocytes secrete growth factors that induce preadipocyte proliferation.

Dietary fat type and level influence adiposity development in obese but not lean Zucker rats

The development of obesity is influenced by a variety of factors including genetics and dietary fat type and level. To examine the interaction between these factors, male lean and obese Zucker rats (5 weeks initial age) were fed either a low-fat (15% calories) or one of two high-fat diets (65% calories; predominant fat source of either soybean oil or palm olein) for 8 weeks. Body weight, food intake, indirect calorimetry, and body composition determinations were performed. As expected, food intake, body weight, feed efficiency, oxygen consumption, heat production and carcass lipid were all significantly higher in obese compared to lean rats. Dietary fat level and/or type influenced body weight gain, oxygen consumption, heat production, energy balance, and carcass weight and lipid content in the obese but not in the lean Zucker rats. Oxygen consumption and carcass weight were increased approximately 25% and 10% respectively in obese rats fed either of the two high-fat diets as compared to those fed the low-fat diet. The type of fat fed in the high-fat diets also influenced body weight gain, heat production, energy balance, and carcass lipid content of the obese rats. Body weight gain and carcass lipid content were increased (16%-17%; P < 0.005) in obese rats fed the high-fat palm olein diet as compared to those fed the low-fat diet. These parameters were not increased in obese rats fed the high-fat soybean oil diet. In contrast, indirect calorimetry measurements indicated a moderate increase in heat production (Kcal/effective body mass/day; 14.5%) and decrease in energy balance (44.8%) in the obese rats fed the high-fat soybean oil diet as compared to those fed the low-fat diet. Energy expenditure and lipid accumulation were negligibly influenced by dietary fat level or type in the lean Zucker rats. The differential response of the lean and obese Zucker rats to this short-term dietary manipulation demonstrate that genetic background can influence an individual's response to dietary fat type and level. The genetically obese Zucker rat appears to be a good model for further studies of high-fat diet-induced obesity.

Hormonal regulation of leptin mRNA expression and preadipocyte recruitment and differentiation in porcine primary cultures of S-V cells

The hormonal regulation of leptin mRNA expression and the association between leptin expression and adipocyte differentiation were examined in primary cultures of porcine S-V cells with Northern blot and immunocytochemical analysis. Seeding for 3 days with fetal bovine serum (FBS) with varying levels of dexamethasone (Dex) increased levels of leptin mRNA in a dose-dependent manner in parallel with increases in the proportion of preadipocytes (AD-3 positive cells; AD-3, a preadipocyte marker). Six-day treatment with 10 or 850 nM insulin after FBS+Dex treatment resulted in a similar increase in leptin mRNA expression and morphological differentiation. However, significantly lower levels of leptin mRNA and smaller fat cells were observed in cultures treated with 1 nM insulin or 10 nM insulin-like growth factor-I (IGF-I). Dex-induced increases in leptin mRNA levels and AD-3 cell numbers were blocked completely by the addition of transforming growth factor-beta (TGF-beta) to FBS+Dex-treated cultures. However TGF-beta significantly increased fat cell size and leptin mRNA expression when added to ITS (insulin, 850 nM; transferrin, 5 microg/ml; and selenium, 5 microg/mL) treated cultures during the lipid-filling stage. When added with FBS+DEX for the first 3 days, growth hormone (GH) did not influence the Dex-induced increase in AD-3 cells and leptin mRNA expression, but GH reduced leptin mRNA levels when added with insulin for 6 days after FBS+Dex. These results demonstrated that regulation of leptin mRNA expression by Dex, insulin, IGF-I, TGF-beta, and GH may be associated with changes in preadipocyte number and fat cell size.

Differentiation-dependent expression of obese (ob) gene by preadipocytes and adipocytes in primary cultures of porcine stromal-vascular cells

The relationship between obese (ob) gene expression and preadipocyte differentiation was examined in primary cultures of porcine stromal-vascular (S-V) cells by Northern-blot analysis using a pig ob cDNA probe. Isolated adipocytes expressed high levels of ob gene, but S-V cells did not express the ob gene. Cultures were seeded with fetal bovine serum (FBS) plus dexamethasone (Dex) for 3 days followed by ITS (insulin 5 microg/ml, transferrin 5 microg/ml, and selenium 5 ng/ml) treatment for 6 days. Detectable levels of ob mRNA first appeared at day 1 with very low activity of glycerol phosphate dehydrogenase (GPDH). Levels of ob mRNA increased in parallel with preadipocyte number or GPDH activity at the later times in cultures. The depletion of preadipocytes by complement-mediated cytotoxicity at day 3 of culture resulted in markedly decreased ob mRNA expression. Immunocytochemical analysis showed that ob protein was localized in the cytosol of preadipocytes and adipocytes. These data indicated that the ob gene is expressed by preadipocytes and ob gene expression may be correlated with preadipocyte recruitment as well as fat cell size.

Adipose tissue expansion and the development of obesity: influence of dietary fat type

Recent studies indicate that the prevalence of obesity in adults has increased by 30% or more in the past decade, with increases in both genders and in all ethnic and racial populations and age groups. Obesity is associated with many chronic diseases and alterations in physiologic function including cardiovascular disease, hypertension, diabetes mellitus, gallbladder disease and certain types of cancer. Much attention regarding dietary influences on obesity development or prevention has focused on high fat diets. Many studies have confirmed that high fat feeding leads to an expansion of adipose tissue mass through an increase in fat cell size and/or number and to the subsequent development of obesity. However, there is little definitive information on the effect of type of dietary fat, especially palm oil, on adipose tissue cellularity and the development of obesity. These studies were designed to determine whether dietary fat of different sources vary in their ability to produce obesity and to begin to elucidate the mechanism by which such divergence occurs. Male Osborne-Mendel rats were fed either a low fat (15% calories) or one of three high fat diets (65% calories) for 12 weeks. The predominant fat source in the high fat diets was either soybean oil, tallow, or palm-olein (a fraction of palm oil). Final body weight was not influenced by fat level or type; however, percent carcass lipid and fat pad weight were higher in soybean oil and tallow fed rats than in low fat and palm-olein fed rats. Fat pad specific increases in cell size and cell number were observed for tallow and soybean oil fed compared to low fat and palm-olein fed rats. Serum triglycerides were higher in the tallow and palm-olein fed rats compared to low fat fed rats; no significant effects of dietary fat type on serum cholesterol were observed. These results indicate that palm-olein, unlike tallow and soybean oil, were comparable to a low fat diet concerning fat pad weight, body composition and adipose tissue cellularity when fed for twelve weeks as 65% of energy intake. The lower fat storage in the palm-olein fed rats is perhaps associated with a slower rate of triglyceride uptake and/ or a reduced fat cell proliferative capacity. The influence of dietary fat type on the proliferative capacity of the pre-adipocytes and on the production of a local or systemic adipogenic factor is being determined in subsequent studies.

Endocrine regulation of fetal adipose tissue metabolism in the pig: ontogeny of thyroxine influence

Our previous studies indicated that thyroxine (T4) markedly enhanced adipose tissue development and metabolism when administered to hypophysectomized fetal pigs from days 70 to 90 of gestation. In this study, hypophysectomized (day 70) fetal pigs were implanted with T4 pellets, and blood and adipose tissue samples were obtained upon removal on days 73, 75, 80, or 85 of gestation to examine the time course of T4 response. T4 treatment in hypophysectomized fetuses resulted in an elevation in serum T4 levels by day 73 of gestation, with no further increase on day 80 or 85. Quantitative analysis of subcutaneous adipose tissue indicated that hypophysectomy per se had no influence on lipid deposition, whereas the extent of T4-stimulated lipid deposition increased with fetal age beginning on day 75. Glucose oxidation and lipogenesis in subcutaneous adipose tissue slices was increased by T4 treatment in hypophysectomized fetuses by day 73 of gestation and further increased with additional time of treatment. Hypophysectomy per se induced a slight increase in lipogenesis only on days 80 and 85 of gestation. Basal lipolysis was unaffected by age, hypophysectomy, or T4 treatment. The responsiveness for a variety of lipolytic stimuli was both accelerated and enhanced by T4 treatment in hypophysectomized fetuses. The results indicate that the T4 influence on adipose tissue development (1) is already apparent following only 3 days of hormone treatment in the hypophysectomized fetuses, (2) clearly precedes hypophysectomy-induced alterations in cellular and metabolic development of adipose tissue, and (3) is not mediated exclusively by serum concentrations of the hormone.

Effect of somatotropin and feed restriction on body composition and adipose metabolism in obese Zucker rats

The objective of the present study was to determine whether exogenous somatotropin (STH) administration in conjunction with feed restriction could alter the composition of gain in the obese rat. Five-week-old female lean and obese Zucker rats were assigned to the following treatments for 6 wk: ad libitum fed (AL), restricted (approximately 75% of AL lean), and restricted with STH (2 mg STH/day). Growth rate was decreased in restricted groups and was normalized to that of the AL lean group in restricted rats treated with STH. In lean rats, restriction decreased protein accretion. Restriction plus STH treatment decreased lipid accretion but increased protein accretion and body weight gain compared with the AL lean group. As expected, feed restriction reduced body size in obese rats, but carcass lipid was maintained at 44%, a level similar to that of the AL obese rats. Lipid accretion rate was decreased with restriction in obese rats and was further reduced, to a level similar to that of the lean group, in the obese rats that were restricted and treated with STH. Protein accretion was decreased in the restricted obese group but was normalized in those treated with STH to a level similar to that in the AL lean group. Basal rates of lipolysis in isolated adipocytes were not affected by STH. However, STH treatment normalized the responsiveness of cells from the obese rats to stimulation of lipolysis by isoproterenol. The results demonstrate that a combination of caloric restriction and STH was effective in normalizing body weight and composition of gain in the obese Zucker rat.

The cooperation of adipocytes and stromal cells in the secretion of prostaglandins by rat adipose tissue is not influenced by diet

This study examined the influence of dietary essential fatty acids on the cooperativity of isolated adipocytes and stromal-vascular cells in the biosynthesis of prostaglandins. Sprague-Dawley rats were fed either a diet rich in essential fatty acids (20% corn oil) or a diet poor in essential fatty acids (20% tallow) for 4 wk. Preparations containing primarily adipose cells (adipocytes) or stromal-vascular cells (nonfat cells) were obtained from epididymal fat pads by collagenase digestion and repeatedly washed. Prostaglandin production was evaluated in basal and epinephrine-stimulated media after incubation with either adipocytes or adipocytes+nonfat cells. Prostaglandin E2 and prostacyclin production by adipocytes+nonfat cells was dose-dependent with epinephrine stimulation in cells from rats fed both diets. Both prostaglandin E2 and glycerol release in response to epinephrine (10-100 mumol/L) stimulation from adipocytes or from adipocytes+nonfat cells were significantly higher for cells from corn oil-fed rats than for cells from tallow-fed rats. Regardless of dietary treatment, epinephrine-stimulated prostaglandin E2 and prostacyclin release from adipocytes+nonfat cells was much greater than from adipocytes. These results suggest that a diet high in essential fatty acids precipitates a higher prostaglandin E2 secretion and that nonfat cells potentiate the secretion of prostaglandin E2 and prostacyclin by adipocytes regardless of diet.

Influence of the pituitary on lipolysis and lipogenesis in fetal pig adipose tissue

This study was performed to verify and further characterize the role of neuroendocrine factors in the regulation of fetal adipose metabolism. On day 72 to 74 of gestation, pig fetuses in one uterine horn were hypophysectomized (hypoxed) by micro-cauterization, fetuses in the other horn served as sham controls. Fetuses were removed by laparotomy on day 110 of gestation. Slices of subcutaneous adipose tissue from control fetuses responded to lipolytic stimulation by norepinephrine alone (NE; 1 microgram/ml), NE plus adenosine deaminase (160 mUnits/ml) or dibutyryl cyclic AMP (5 mM). Adipose tissue from hypoxed fetuses, however, responded to lipolytic stimulation by only dibutyryl cyclic AMP, not NE. Lipogenesis in adipose tissue slices, as quantitated by 3H2O incorporation into triglyceride fatty acids, was increased 2.6 fold by hypophysectomy. These results demonstrate the necessity of a functioning pituitary in the normal regulation of fatty acid synthesis and receptor-mediated lipolytic response in developing fetal adipose tissue.

Endocrine regulation of fetal adipose tissue metabolism in the pig: role of thyroxine

This study was performed to characterize the role of thyroxine (T4) in the regulation of fetal adipose tissue metabolism. On day 70 of gestation, pig fetuses were hypophysectomized (hypoxed) by microcauterization. Both hypoxed and intact fetuses were implanted subcutaneously with T4 pellets or received no hormone replacement. Fetuses were removed by laparotomy on day 90 of gestation. Additional fetuses were hypoxed on day 70, implanted with T4 pellets on day 90 and removed on day 105 of gestation. Serum T4 levels were similar in hypox + T4 and intact + T4 fetuses and increased in both groups relative to their respective controls. T4 supplementation restored the lipolytic response to isoproterenol and enhanced the response to dibutyryl cyclic AMP at 90 days in hypoxed animals but had no effect on basal or stimulated lipolysis in intact fetuses. T4 induced a dramatic increase in lipogenesis in hypoxed fetuses when administered during either fetal period and produced a slight though significant increase in basal lipogenesis in intact fetuses when administered from days 70 to 90 of gestation. However, T4 had no effect on basal or insulin-stimulated lipogenesis in intact fetuses when administered from days 90 to 105 of gestation. These results indicate that T4 may have a primary influence on fetal adipose tissue metabolism only in the absence of inhibition from counterregulatory hormones of pituitary origin.

Biochemical and cytochemical studies of preadipocyte differentiation in serum-free culture of porcine stromal-vascular cells: interaction of dexamethasone and growth hormone

Stromal-vascular cells from adipose tissue of pigs 5-7 days of age were grown in serum for 2-3 days and switched to serum-free (insulin, transferrin and selenium) conditions +/- test hormones for 6-7 days. The interaction of dexamethasone (DEX) and human growth hormone (hGH) was evaluated since glucocorticoids augment and hGH antagonizes the effect of insulin. Low levels (1-10 nM) of DEX with insulin doubled (p less than 0.05) specific activity of glycerol phosphate dehydrogenase (GPDH) and doubled (p less than 0.05) the number of detectable fat cells relative to insulin alone. DEX with insulin enhanced the morphological differentiation of preadipocytes and markedly increased fat cell cluster numbers in the presence of hGH. Furthermore, 1-10 nM of DEX partially blocked (p greater than 0.05) the inhibitory effect of 10 nM hGH on GPDH activity, but 1-100 nM DEX had no effect (p greater than 0.05) on the ability of hGH to compromise lipid deposition. DEX alone (no insulin or hGH) induced the appearance of esterase-reactive but lipid-free cells. Cells with these characteristics were increased in number by DEX in the presence of hGH but were nearly absent in the presence of insulin and DEX. Therefore, transient exposure to GH in vivo may have no permanent effect on adipose tissue development in the continued presence of glucocorticoids.

Maternal dietary fat type influences the growth and fatty acid composition of newborn and weanling rats

To determine whether the long-term consumption of different amounts or types of fat by female rats affects the growth and development of their progeny, Wistar rats were fed from weaning either a low fat diet (4.5% by weight) or one of three high fat (32%) diets containing predominantly beef tallow (high saturated fat), corn oil (high polyunsaturated fat) or equal portions of tallow and corn oil (high mixed fat). Offspring were killed at birth or weaning. Weight of newborn pups was lower with maternal consumption of high polyunsaturated fat diets. Carcass composition of newborn pups and body weight of weanling rats was unaffected by maternal diet. The percentage of carcass lipid was greater in weanling rats from all high fat-fed dams. In both newborn pups and weanling rats, percent composition in carcass lipids of 16:0, 16:1 and 18:1 fatty acids generally decreased and 18:2 increased as the high fat maternal diet became more unsaturated. The consumption of diets high in polyunsaturated fatty acids prior to and throughout gestation thus seemed to have a transitory effect on reducing fetal growth in rats.

Metabolic development of liver and adipose tissue in pre-obese and control pig fetuses

The metabolic development of the liver and adipose tissue was examined in 75 and 110 day fetuses from genetically obese and control sows. In the liver, glucose and palmitate utilization was influenced by both age and strain. Higher rates of glucose oxidation and palmitate oxidation and esterification were observed in the 75 day compared to the 110 day fetuses. Hepatic palmitate oxidation was greater in pre-obese than in control fetuses at both fetal ages, while hepatic palmitate esterification was greater in pre-obese than in control fetuses at 75 days of gestation only. In subcutaneous adipose tissue, de novo lipogenesis increased with age and was higher in pre-obese than in control fetuses by 110 days of gestation. At 75 days of gestation, glucose oxidation and incorporation into fatty acids was similar in adipose tissue from both strains. However, by 110 days of gestation, both basal and insulin-stimulated rates of glucose metabolism were greater in pre-obese compared to control fetuses. Palmitate esterification increased with age but was similar in pre-obese and control fetuses. Basal lipolysis was not affected by strain or age. Isoproterenol had no effect on lipolysis in the 75 day fetuses while stimulating glycerol release to a comparable degree in 110 day fetuses of both strains. This study demonstrates that metabolic differences between genetically obese and control pigs are already apparent in the pre-obese state prior to birth. Such alterations in hepatic and adipose tissue carbohydrate and lipid metabolism, which promote early lipid storage by the pre-obese fetuses, may serve as useful metabolic markers for the development of obesity.