Effects of cell size and animal age on glucose metabolism in pig adipose tissue

Fattening chips: hypertrophy, feeding, and fasting of human white adipocytes in vitro

Adipose is a distributed organ that performs vital endocrine and energy homeostatic functions. Hypertrophy of white adipocytes is a primary mode of both adaptive and maladaptive weight gain in animals and predicts metabolic syndrome independent of obesity. Due to the failure of conventional culture to recapitulate adipocyte hypertrophy, technology for production of adult-size adipocytes would enable applications such as in vitro testing of weight loss therapeutics. To model adaptive adipocyte hypertrophy in vitro, we designed and built fat-on-a-chip using fiber networks inspired by extracellular matrix in adipose tissue. Fiber networks extended the lifespan of differentiated adipocytes, enabling growth to adult sizes. By micropatterning preadipocytes in a native cytoarchitecture and by adjusting cell-to-cell spacing, rates of hypertrophy were controlled independent of culture time or differentiation efficiency. In vitro hypertrophy followed a nonlinear, nonexponential growth model similar to human development and elicited transcriptomic changes that increased overall similarity with primary tissue. Cells on the chip responded to simulated meals and starvation, which potentiated some adipocyte endocrine and metabolic functions. To test the utility of the platform for therapeutic development, transcriptional network analysis was performed, and retinoic acid receptors were identified as candidate drug targets. Regulation by retinoid signaling was suggested further by pharmacological modulation, where activation accelerated and inhibition slowed hypertrophy. Altogether, this work presents technology for mature adipocyte engineering, addresses the regulation of cell growth, and informs broader applications for synthetic adipose in pharmaceutical development, regenerative medicine, and cellular agriculture.

Longitudinal investigation of the swine gut microbiome from birth to market reveals stage and growth performance associated bacteria

BACKGROUND

Despite recent advances in the understanding of the swine gut microbiome at different growth stages, a comprehensive longitudinal study of the lifetime (birth to market) dynamics of the swine gut microbiome is lacking.

RESULTS

To fill in this gap of knowledge, we repeatedly collected a total of 273 rectal swabs from 18 pigs during lactation (day (d) 0, 11, 20), nursery (d 27, 33, 41, 50, 61), growing (d 76, 90, 104, 116), and finishing (d 130, 146, 159, 174) stages. DNA was extracted and subjected to sequencing with an Illumina Miseq sequencer targeting the V4 region of the 16S rRNA gene. Sequences were analyzed with the Deblur algorithm in the QIIME2 package. A total of 19 phyla were detected in the lifetime pig gut microbiome with Firmicutes and Bacteroidetes being the most abundant. Alpha diversity including community richness (e.g., number of observed features) and diversity (e.g., Shannon index) showed an overall increasing trend. Distinct shifts in microbiome structure along different growth stages were observed. LEfSe analysis revealed 91 bacterial features that are stage-specific. To validate these discoveries, we performed fecal microbiota transplantation (FMT) by inoculating weanling pigs with mature fecal microbiota from a growing stage pig. Similar stage-specific patterns in microbiome diversity and structures were also observed in both the FMT pigs and their littermates. Although FMT remarkably increased growth performance, it did not change the overall swine gut microbiome. Only a few taxa including those associated with Streptococcus and Clostridiaceae were enriched in the FMT pigs. These data, together with several other lines of evidence, indicate potential roles these taxa play in promoting animal growth performance. Diet, especially crude fiber from corn, was a major factor shaping the swine gut microbiome. The priority effect, i.e., the order and timing of species arrival, was more evident in the solid feed stages.

CONCLUSIONS

The distinct stage-associated swine gut microbiome may be determined by the differences in diet and/or gut physiology at different growth stages. Our study provides insight into mechanisms governing gut microbiome succession and also underscores the importance of optimizing stage-specific probiotics aimed at improving animal health and production.

Comparative Proteome Analysis Reveals Lipid Metabolism-Related Protein Networks in Response to Rump Fat Mobilization

Altay is a typical fat-tailed sheep breed displaying the unique ability to rapidly mobilize fat, which is vital for maintaining a normal metabolism that facilitates its survival in lengthy winter conditions. However, the physiological, biochemical, and molecular mechanisms underlying fat mobilization remain to be elucidated. In this study, the monitoring of rump fat adipocyte sizes disclosed a positive correlation between cell size and fat deposition ability. In addition, we subjected sheep to persistent starvation to imitate the conditions that trigger rump fat mobilization and screened 112 differentially expressed proteins using the isobaric peptide labeling approach. Notably, increased secretion of leptin and adiponectin activated the key fat mobilization signaling pathways under persistent starvation conditions. Furthermore, the upregulation of resistin (RETN), heat-shock protein 72 (HSP72), and complement factor D (CFD) promoted lipolysis, whereas the downregulation of cell death-inducing DFFA-like effector C (CIDEC) inhibited lipid droplet fusion, and the increase in HSP72 and apolipoprotein AI (Apo-AI) levels activated the body’s stress mechanisms. The synergistic actions of the above hormones, genes, and signaling pathways form a molecular network that functions in improving the adaptability of Altay sheep to extreme environments. Our findings provide a reference for elucidating the complex molecular mechanisms underlying rump fat mobilization.

The role for adipose tissue in weight regain after weight loss

Weight regain after weight loss is a substantial challenge in obesity therapeutics. Dieting leads to significant adaptations in the homeostatic system that controls body weight, which promotes overeating and the relapse to obesity. In this review, we focus specifically on the adaptations in white adipose tissues that contribute to the biological drive to regain weight after weight loss. Weight loss leads to a reduction in size of adipocytes and this decline in size alters their metabolic and inflammatory characteristics in a manner that facilitates the clearance and storage of ingested energy. We present the hypothesis whereby the long-term signals reflecting stored energy and short-term signals reflecting nutrient availability are derived from the cellularity characteristics of adipose tissues. These signals are received and integrated in the hypothalamus and hindbrain and an energy gap between appetite and metabolic requirements emerges and promotes a positive energy imbalance and weight regain. In this paradigm, the cellularity and metabolic characteristics of adipose tissues after energy-restricted weight loss could explain the persistence of a biological drive to regain weight during both weight maintenance and the dynamic period of weight regain.

1,3-Dichloro-2-propanol induced hyperlipidemia in C57BL/6J mice via AMPK signaling pathway

1,3-Dichloro-2-propanol (1,3-DCP) is a well-known contaminant that has been detected in a wide range of foods. Dietary intake represents the greatest source of exposure to 1,3-DCP. In the study, we first found 1,3-DCP could induce hyperlipidemia in C57BL/6J mice below 1 mg/kg/day. We investigated serum lipid profile, liver total cholesterol (TC) and triglyceride (TG), histopathology of Liver and adipose tissue. The results showed 1,3-DCP dose dependently increased serum TG, TC and low-density lipoprotein cholesterol (LDL-C), decreased serum high-density lipoprotein cholesterol (HDL-C), increased relative liver weight, liver TG and TC, relative adipose tissue weight and enlarged the size of adipose cells. Because AMPK signal pathway is important in the process of lipid metabolism, we further investigated the effects of 1,3-DCP on AMPK signaling pathway in murine models. The results showed that 1,3-DCP (0.1-1 mg/kg/day) decreased p-AMPK/tAMPK ratio, p-ACC/tACC ratio, PPARα expression, but increased FAT, SREBP1, HMGCR and FAS expression. These observations indicated that 1,3-DCP induced hyperlipidemia in C57BL/6J mice at least partially through regulating AMPK signaling pathway.

Hormonal regulation of leptin and leptin receptor expression in porcine subcutaneous adipose tissue

The current study was performed to examine the response of the leptin gene to hormonal stimuli in porcine adipose tissue from finishing pigs. Yorkshire gilts (approximately 150 kg BW) were used in this study. Tissue from four to six pigs was used per experiment. Dorsal subcutaneous adipose tissue samples were acquired, and adipose tissue explants (approximately 100 mg) were prepared using sterile technique. Tissue slices were transferred to 12-well tissue culture plates containing 1 mL of Media 199 with 25 mM HEPES, 0.5% BSA, pH 7.4, and various hormone supplements. Triplicate tissue slices were incubated with either basal medium or hormone-supplemented media in a tissue culture incubator at 37 degrees C with 95% air:5% CO2. Hormones included insulin (100 nM), dexamethasone (1 microM), porcine GH, 100 ng/mL), triiodothyronine (T3, 10 nM), porcine leptin (100 ng/mL), or IGF-I (250 ng/mL). Following incubation for 24 h, tissue samples from the incubations were blotted and transferred to microfuge tubes, frozen in liquid N, and stored at -80 degrees C before analysis for gene mRNA abundance by reverse-transcription PCR and subsequent quantification of transcripts by capillary electrophoresis with laser-induced fluorescence detection. Media from the incubations were collected in microfuge vials and stored at -20 degrees C before analysis for leptin content by RIA. Insulin was required to maintain tissue and mRNA integrity; therefore, insulin was included in all incubations. The combination of insulin and dexamethasone stimulated leptin secretion into the medium by 60% (P < 0.05; n = 6). Porcine GH inhibited insulin induced leptin secretion by 25% (P < 0.05; n = 6). Dexamethasone in combination with insulin produced a 22% increase in leptin mRNA abundance relative to insulin (P < 0.05; n = 4), and T3 stimulated a 28% increase in insulin-induced leptin mRNA abundance (P < 0.05; n = 4). Leptin receptor mRNA abundance was decreased by 25% with the combination of insulin and dexamethasone, relative to insulin-treated adipose tissue slices (P < 0.05; n = 4). Porcine GH decreased leptin receptor mRNA abundance by 17% (P < 0.05; n = 6). These data suggest that leptin secretion is a regulated phenomenon and that posttranslational processing may be significant. Alternatively, transport and exocytosis of leptin containing vesicles in the pig adipocyte may be quite complicated, which could account for the differences in observed mRNA abundance and protein secretion.

Lipid metabolism and secretory function of porcine intramuscular adipocytes compared with subcutaneous and perirenal adipocytes

The function of adipocytes interspersed between myofiber fasciculi in skeletal muscle physiology and physiopathology is poorly documented. Because regional differences in adipocyte features have been reported in various species, we hypothesized that lipid metabolism and secretory function of intramuscular (IM) adipocytes differ from that of nonmuscular adipocytes. In the present study, adipocytes isolated from trapezius muscle were compared with subcutaneous and perirenal adipocytes in growing pigs. Between 80 and 210 days of age, gene expressions and/or activities of enzymes involved in lipogenesis or lipolysis were much lower (P < 0.05) in adipocytes isolated from muscle than in those from other locations. Insulin-induced lipogenesis and lipolytic efficiency after catecholamine addition were also the lowest (P < 0.05) in IM adipocytes. In these cells, the age-related increase (+300%) in the ratio of mRNA levels of fatty acid synthase to hormone-sensitive lipase paralleled the enlargement of adipocyte diameters (+70%, P < 0.05) and the increase in lipid content in muscle (+135%, P < 0.05) during growth. Expressions of genes coding for leptin, adiponectin, and IGF-I, as well as for various hormonal receptors, were lower (P < 0.05) in IM adipocytes than in other adipocytes, whereas levels of TNF-alpha mRNA did not differ between sites. Interestingly, IGF-II mRNA levels were higher (P < 0.05) in IM adipocytes than in other adipocytes. These data support the view that IM fat is not just an ectopic extension of other fat locations but displays specific biological features during growth.

Effects of obesity on the relationship of leptin mRNA expression and adipocyte size in anatomically distinct fat depots in mice

In support of leptin's physiological role as humoral signal of fat mass, we have shown that adipocyte volume is a predominant determinant of leptin mRNA levels in anatomically distinct fat depots in lean young mice in the postabsorptive state. In this report, we investigated how obesity may affect the relationship between leptin mRNA levels and adipocyte volume in anatomically distinct fat depots in mice with genetic ( Lepob/ Lepoband Ay/+), diet-induced, and aging-related obesity. In all of the obese mice examined, tissue leptin mRNA levels relative to the average adipocyte volume were lower in the perigonadal and/or retroperitoneal than in the inguinal fat depots and were lower than those of the lean young mice in the perigonadal fat depot. A close, positive correlation between leptin mRNA level and adipocyte volume was present from small to hypertrophic adipocytes within each perigonadal and inguinal fat pad in the obese mice, but the slopes of the regression lines relating leptin mRNA level to adipocyte volume were significantly lower in the perigonadal than in the inguinal fat pads of the same mice. These results suggest that obesity per se is associated with a decreased leptin gene expression per unit of fat mass in mice and that the positive correlation between leptin mRNA level and adipocyte volume is an intrinsic property of adipocytes that is not disrupted by adipocyte hypertrophy in obese mice.

Adipose tissue selective insulin receptor knockout protects against obesity and obesity-related glucose intolerance

Insulin signaling in adipose tissue plays an important role in lipid storage and regulation of glucose homeostasis. Using the Cre-loxP system, we created mice with fat-specific disruption of the insulin receptor gene (FIRKO mice). These mice have low fat mass, loss of the normal relationship between plasma leptin and body weight, and are protected against age-related and hypothalamic lesion-induced obesity, and obesity-related glucose intolerance. FIRKO mice also exhibit polarization of adipocytes into populations of large and small cells, which differ in expression of fatty acid synthase, C/EBP alpha, and SREBP-1. Thus, insulin signaling in adipocytes is critical for development of obesity and its associated metabolic abnormalities, and abrogation of insulin signaling in fat unmasks a heterogeneity in adipocyte response in terms of gene expression and triglyceride storage.

Determinants of leptin gene expression in fat depots of lean mice

The relationship of leptin gene expression to adipocyte volume was investigated in lean 10-wk-old male C57BL/6J mice. mRNA levels for leptin, insulin receptor, glucocorticoid receptor, and tumor necrosis factor (TNF)-alpha in inguinal, epididymal, and retroperitoneal adipose tissues were quantified and related to adipocyte volume. Leptin mRNA levels were highly correlated with adipocyte volume within each fat depot. Multiple regression analysis of pooled data from the three depots showed that leptin mRNA levels were strongly correlated with adipocyte volumes (beta = 0.84, P < 0.001) and, to a smaller degree, with glucocorticoid receptor mRNA levels (beta = 0.36, P < 0.001). Depot of origin had no effect (P > 0.9). Rates of leptin secretion in vitro were strongly correlated with leptin mRNA levels (r = 0.89, P < 0.001). mRNA levels for TNF-alpha, insulin receptor, and glucocorticoid receptor showed no significant correlation with adipocyte volume. These results demonstrate that depot-specific differences in leptin gene expression are mainly related to the volumes of the constituent adipocytes. The strong correlation between leptin gene expression and adipocyte volume supports leptin's physiological role as a humoral signal of fat mass.

The acylation stimulating protein pathway: clinical implications

OBJECTIVES

The present review will focus particularly on acylation stimulating protein (ASP) and its role in adipose tissue. Two issues will be addressed (1) in vitro biochemical characterization of ASP in cell culture studies, and (2) in vivo clinical relevance for normal physiology and in pathological conditions.

CONCLUSIONS

Fat is In! There can be no question that in recent years fat tissue has become recognized as more than just a passive storage site. It is a metabolically active tissue that, under normal conditions, allows the efficient clearance of triglyceride and glucose for storage as energy. Under abnormal conditions, adipose tissue dysfunction is associated with obesity, diabetes and coronary heart disease. Adipose tissue function may be controlled by many factors.

Effect of insulin and isoproterenol on lipid metabolism in porcine adipose tissue from different depots

Significant differences were found in the rates of lipogenesis, glucose oxidation and lipolysis in porcine adipose tissue from four depots; outer subcutaneous (OSC), middle subcutaneous (MSC), perirenal (PR) and omental (OM). Lipogenesis was stimulated by insulin in all depots in the order PR > OM > MSC > OSC. Lipolysis was stimulated by isoproterenol in all depots in the order PR > OM > MSC > OSC. Differences in lipid metabolism by the different depots may have an important impact on lipid accretion in vivo.

Is the lipolytic response in porcine adipose tissue slices equivalent to the lipolytic response in isolated adipocytes?

1. In most cases, when isolated adipocytes and adipose tissue slices from the same animal were stimulated with various lipolytic agents (adrenergic agonists, theophylline, adenosine deaminase), the qualitative response was similar. 2. There were, however, numerous exceptions; e.g. quinterenol did not affect isolated adipocytes whereas it was a partial agonist for adipose slices from the same animal. 3. The adipocytes present in slices were larger than those isolated from slices by collagenase digestion. 4. Isolated adipocytes were not more sensitive than tissue slices to stimulation by lipolytic agents.

Oxygen consumption in collagenase-liberated rat adipocytes in relation to cell size and age

Oxygen consumption of collagenase-liberated rat adipocytes was measured by two different techniques: a microspectrophotometric method using hemoglobin as indicator of respiration and a technique using the oxygen electrode. These two completely different techniques gave similar values for oxygen consumption. With the spectrophotometric method, the oxygen consumption of single fat cells was determined. A close positive correlation (r = greater than 0.90) between oxygen consumption and fat cell size was observed in each tissue examined. With the oxygen electrode technique, oxygen consumption of adipocyte suspensions from young (40 days, 180 g) and old (90 days, 480 g) rats was examined. Fat cells of the suspensions were separated into classes of different size by a flotation technique. A significant positive correlation between fat cell size and oxygen consumption was observed in both young (r = 0.88) and old (r = 0.95) rats. However, the slope was much steeper in young rats. At a cell weight of 0.1 microgram the oxygen consumption was 0.364 and 0.086 microL O2/10(6) cells/min-1 in young and old rats, respectively. In the literature, a number of separate metabolic pathways have been found to be related positively to fat cell size and negatively to age. We conclude that these scattered metabolic observations are in agreement with integrated data on energy expenditure as evaluated from oxygen consumption. Estimations of the energy expenditure of adipose tissue indicates that this tissue is responsible for about 1% and 0.5% of the total energy expenditure in young and old rats, respectively.

Effects of cell volume on insulin binding, internalization and degradation in rat adipocytes

Adipocytes from old rats (greater than 450 g) were separated into 2 populations with mean cell volumes of 201 +/- 14 and 813 +/- 41 pl (mean +/- SEM, 20 observations) by filtering through nylon mesh (64 microns diameter) and compared with adipocytes from young rats (less than 150 g) with a mean adipocyte volume of 154 +/- 20 pl (14 observations). Large adipocytes had more insulin receptors per cell but less per unit of surface area. They internalized greater amounts of insulin than small cells in the presence or absence of bacitracin and chloroquine, although the proportion of bound hormone which was internalized was similar in all 3 groups. Down-regulation of the insulin receptor was evident in large and small adipocytes after incubation in the presence of 10(-7)M insulin. Large cells degraded insulin (extracellularly and intracellularly) at significantly greater rates than small cells whether expressed per cell or per unit of surface area. Small cells from old rats had essentially identical properties to small cells from young rats in all parameters examined. The results suggest that the decreased surface density of insulin receptors observed in large adipocytes from old rats is due to size rather than age and that the decreased insulin sensitivity of large adipocytes is not due to an inability to internalize insulin or down-regulate its receptors but may be due to increased rates of insulin degradation.

Heterogeneous labeling of adipocytes during in vivo-in vitro incubation of epididymal fat pads of aging mice with [1-14C] palmitate

We have hypothesized that the in vivo-in vitro technique of Stein and Stein for studying free fatty acid incorporation into adipose tissue triglycerides and phospholipids may introduce artifacts due to diffusion barriers such as collagenous membranes, especially in fat pads of old animals. By using this technique in young and old mice and peeling the external cells, either physically or by collagenase treatment, we were able to show that the outer adipocytes are preferentially labeled. However, this pattern of heterogeneous labeling occurred in fat pads of both young (10-14 weeks) and old (80 weeks) mice. Fat pads are known to develop thicker, collagenous outer membranes during aging. Therefore, it seems likely to us that the marked decrease in free fatty acid esterification in fat pads of old mice, using the in vivo-in vitro method that we have described previously and confirmed here, could have been due to greater diffusion barriers in the tissues of the older mice.

Glycerolipid biosynthesis in rat adipose tissue. 10. Changes during a starvation and re-feeding cycle

Effects of starvation and re-feeding on adipocyte glycerolipid formation were investigated in young (age 48-55 days) and old rats (age 83-94 days). Adipocyte homogenates were used to assay glycerophosphate acyltransferase and Mg2+-dependent phosphatidase phosphohydrolase. Glycerophosphate acyltransferase was measured in the presence of [14C]glycerol 3-phosphate, palmitate, ATP, CoA and Mg2+. The release of inorganic phosphate from aqueous dispersed phosphatidase was taken as a measure of phosphatidate phosphohydrolase activity. Young rats starved for 48-72 h showed a 2-fold decline in the glycerophosphate acyltransferse activity. Older rats did not show any change in the glycerophosphate acyltransferase activity during 96 h starvation. Re-feeding of starved rats with chow for 48 h caused significant increases in the glycerophosphate acyltransferase activity. These changes were mainly limited to N-ethylmaleimide-sensitive glycerophosphate acyltransferase activity. These changes were mainly limited to N-ethylmaleimide-sensitive glycerophosphate acyltransferase. Phosphatidate phosphohydrolase activity decreased significantly (2-fold) during starvation in both young and old rats. Phosphatidate phosphohydrolase activity was regained completely after re-feeding of starved rats. Initial changes in the glycerophosphate acyltransferase and phosphatidate phosphohydrolase activities were very slow. Most notable increases in the glycerophosphate acyltransferase and phosphatidate phosphohydrolase activities were observed between 24 and 48 h after initiation of a re-feeding schedule. Mean adipocyte size decreased during starvation of rats for 72 h. Although considerable increases in the activities of both glycerophosphate acyltransferase and phosphatidate phosphohydrolase were apparent by re-feeding of starved rats for 48 h, mean adipocyte size did not change during this period. Thus, enzyme changes which occurred after re-feeding were independent of the adipocyte size. To separate the effects of age from the cell size on adipocyte glycerolipid formation during starvation and re-feeding periods, adipocytes from older rats were subjected to filtration through a nylon screen to obtain adipocytes of similar sizes. These studies suggest that the age of the animal significantly influences the effects of starvation and re-feeding on adipocyte glycerolipid formation.

Glycerolipid biosynthesis in rat adipose tissue: VIII. Effect of obesity and cell size on [14C]acetate incorporation into lipids

[14C]Acetate incorporation into different lipid fractions was measured as a function of adipocyte size by using the larger and smaller adipocytes derived from Sprague-Dawley rats. In both the larger and smaller adipocytes, [14C]acetate was incorporated into phospholipid, diacylglycerol, free fatty acid and triacylglycerol fractions. Although the rates of lipid formation were significantly higher in the larger adipocytes compared to the smaller ones, the proportions of the various lipids formed from [14C]acetate did not change significantly as a function of cell size. In some experiments, isolated adipocytes derived from obese Zucker rats were fractionated further to isolate an adipocyte preparation which was similar in size to those obtained from lean animals. The matching adipocytes derived from lean and obese animals did not differ significantly with respect to lipid formation from [14C]acetate. These studies suggest that the larger adipocytes are more active in lipogenesis from [14C]acetate than the smaller ones and that the increased capacity of lipogenesis in obese adipose tissue noted previously (Biochem. J., 170, 153-160, 1978) is not an intrinsic property of all the obese adipocytes, but is limited mainly to the larger adipocytes.