Regulators of adipocyte precursor cells

Folic acid perfusion administration reduced abdominal fat deposition in starter Arbor Acres broilers

With intensive selection for meat production in broilers, excessive fat accumulation is also accompanied and causes economic concerns. Folic acid was reported to be involved in lipid metabolism. The present study was conducted to investigate the role of folic acid in reducing abdominal fat deposition. A total of 105 one-day-old healthy Arbor Acres broilers were randomly distributed into 3 treatments, including the control (Con), saline-perfusion group (NS), and folic acid perfusion group (FA). The growth performance, biochemical characteristics in serum, and lipid metabolism in the liver and abdominal fat tissues were evaluated. Results have shown that folic acid significantly reduced abdominal fat percentage (P < 0.05) and had no effects on BW, ADFI, ADG, and FCR (P > 0.05). Serum triglycerides (TG), total cholesterol (TC), and alanine aminotransferase (ALT) levels were lower in FA group but albumin concentration was higher (P < 0.05). Hepatic ACC, SCD, ELOVL6, PI3K, LDLR, HMGCR, and ABCA1 mRNA abundance were all down-regulated in FA group (P < 0.05) when compared with the Con and NS groups, while CPT1 and PPARα were not affected. In addition, MTTP mRNA abundance was higher in the liver of birds subjected to folic acid (P < 0.05). There was no difference about TG deposition in the liver among all groups based on hematoxylin−eosin (HE) and Oil Red O staining. On the other hand, ELOVL6, PPARγ, IGF1, and TGFβ2 expression were notably decreased in the abdominal fat in FA group (P < 0.05). In conclusion, our data demonstrated that folic acid has reduced abdominal fat percentage by decreasing hepatic lipogenesis and suppressing adipocytes proliferation and differentiation. And the inhibiting effect of adipocytes might be mediated by IGF1 and TGFβ2 down-regulation.

Genomic Insights Into the Multiple Factors Controlling Abdominal Fat Deposition in a Chicken Model

Genetic selection for an increased growth rate in meat-type chickens has been accompanied by excessive fat accumulation particularly in abdominal cavity. These progressed to indirect and often unhealthy effects on meat quality properties and increased feed cost. Advances in genomics technology over recent years have led to the surprising discoveries that the genome is more complex than previously thought. Studies have identified multiple-genetic factors associated with abdominal fat deposition. Meanwhile, the obesity epidemic has focused attention on adipose tissue and the development of adipocytes. The aim of this review is to summarize the current understanding of genetic/epigenetic factors associated with abdominal fat deposition, or as it relates to the proliferation and differentiation of preadipocytes in chicken. The results discussed here have been identified by different genomic approaches, such as QTL-based studies, the candidate gene approach, epistatic interaction, copy number variation, single-nucleotide polymorphism screening, selection signature analysis, genome-wide association studies, RNA sequencing, and bisulfite sequencing. The studies mentioned in this review have described multiple-genetic factors involved in an abdominal fat deposition. Therefore, it is inevitable to further study the multiple-genetic factors in-depth to develop novel molecular markers or potential targets, which will provide promising applications for reducing abdominal fat deposition in meat-type chicken.

Dehydroepiandrosterone reduced lipid droplet accumulation via inhibiting cell proliferation and improving mitochondrial function in primary chicken hepatocytes

Dehydroepiandrosterone (DHEA) possesses fat-reducing effect, while little information is available on whether DHEA regulates cell proliferation and mitochondrial function, which would, in turn, affect lipid droplet accumulation in the broiler. In the present study, the lipid droplet accumulation, cell proliferation, cell cycle and mitochondrial membrane potential were analysis in primary chicken hepatocytes after DHEA treated. The results showed that total area and counts of lipid droplets were significantly decreased in hepatocytes treated with DHEA. The cell viability was significantly increased, while cell proliferation was significantly inhibited in a dose dependent manner in primary chicken hepatocytes after DHEA treated. DHEA treatment significantly increased the cell population in S phase and decreased the population in G2/M in primary chicken hepatocytes. Meanwhile, the cyclin A and cyclin-dependent kinases 2 (CDK2) mRNA abundance were significantly decreased in hepatocytes after DHEA treated. No significant differences were observed in the number of mitochondria, while the mitochondrial membrane permeability and succinate dehydrogenase (SDH) activity were significantly increased in hepatocytes after DHEA treated. In conclusion, our results demonstrated that DHEA reduced lipid droplet accumulation by inhibiting hepatocytes proliferation and enhancing mitochondrial function in primary chicken hepatocytes.

Molecular and metabolic profiles suggest that increased lipid catabolism in adipose tissue contributes to leanness in domestic chickens

Domestic broiler chickens rapidly accumulate fat and are naturally hyperglycemic and insulin resistant, making them an attractive model for studies of human obesity. We previously demonstrated that short-term (5 h) fasting rapidly upregulates pathways of fatty acid oxidation in broiler chickens and proposed that activation of these pathways may promote leanness. The objective of the current study was to characterize adipose tissue from relatively lean and fatty lines of chickens and determine if heritable leanness in chickens is associated with activation of some of the same pathways induced by fasting. We compared adipose gene expression and metabolite profiles in white adipose tissue of lean Leghorn and Fayoumi breeds to those of fattier commercial broiler chickens. Both lipolysis and expression of genes involved in fatty acid oxidation were upregulated in lean chickens compared with broilers. Although there were strong similarities between the lean lines compared with broilers, distinct expression signatures were also found between Fayoumi and Leghorn, including differences in adipogenic genes. Similarities between genetically lean and fasted chickens suggest that fatty acid oxidation in white adipose tissue is adaptively coupled to lipolysis and plays a role in heritable differences in fatness. Unique signatures of leanness in Fayoumi and Leghorn lines highlight distinct pathways that may provide insight into the basis for leanness in humans. Collectively, our results provide a number of future directions through which to fully exploit chickens as unique models for the study of human obesity and adipose metabolism.

Expression of Potential Regulatory Genes in Abdominal Adipose Tissue of Broiler Chickens during Early Development

The identities of genes that underlie population variation in adipose tissue development in farm animals are poorly understood. Previous studies in our laboratory have suggested that increased fat tissue involves the expression modulation of an array of genes in broiler chickens. Of special interest are eight genes, FGFR3, EPHB2, IGFBP2, GREM1, TNC, COL3A1, ACBD7, and SCD. To understand their expression regulation and response to dietary manipulation, we investigated their mRNA levels after dietary manipulation during early development. Chickens were fed either a recommended standard or a high caloric diet from hatch to eight weeks of age (WOA). The high caloric diet markedly affected bodyweight of the broiler birds. mRNA levels of the eight genes in the abdominal adipose tissue were assayed at 2, 4, 6, and 8 WOA using RT-qPCR. Results indicate that (1) FGFR3 mRNA level was affected significantly by diet, age, and diet:age interaction; (2) COL3A mRNA level was repressed by high caloric diet; (3) mRNA levels of EPHB2, ACBD7, and SCD were affected by age; (4) mRNA level of TNC was modulated by age:diet interaction; (5) changes in GREM1 and IGFBP2 mRNA levels were not statistically different.

Glypican-4 enhances insulin signaling via interaction with the insulin receptor and serves as a novel adipokine

Obesity, especially visceral obesity, is associated with insulin resistance and metabolic syndrome. We previously identified the cell surface proteoglycan glypican-4 as differentially expressed in subcutaneous versus visceral white fat depots. Here we show that glypican-4 is released from cells and adipose tissue explants of mice, and that circulating glypican-4 levels correlate with BMI and insulin sensitivity in humans. Furthermore, glypican-4 interacts with the insulin receptor, enhances insulin receptor signaling, and enhances adipocyte differentiation. Conversely, depletion of glypican-4 results in reduced activation of the insulin receptor and prevents adipocyte differentiation in vitro by inhibiting insulin-mediated C/EBPβ phosphorylation. These functions of glypican-4 are independent of its glycosylphosphatidylinositol membrane anchorage, as a nonmembrane-bound mutant of glypican-4 phenocopies the effects of native glypican-4 overexpression. In summary, glypican-4 is a novel circulating insulin sensitizing adipose-derived factor that, unlike other insulin sensitizers, acts directly on the insulin receptor to enhance signaling.

Transcriptomic and metabolomic profiling of chicken adipose tissue in response to insulin neutralization and fasting

BACKGROUND

Domestic broiler chickens rapidly accumulate adipose tissue due to intensive genetic selection for rapid growth and are naturally hyperglycemic and insulin resistant, making them an attractive addition to the suite of rodent models used for studies of obesity and type 2 diabetes in humans. Furthermore, chicken adipose tissue is considered as poorly sensitive to insulin and lipolysis is under glucagon control. Excessive fat accumulation is also an economic and environmental concern for the broiler industry due to the loss of feed efficiency and excessive nitrogen wasting, as well as a negative trait for consumers who are increasingly conscious of dietary fat intake. Understanding the control of avian adipose tissue metabolism would both enhance the utility of chicken as a model organism for human obesity and insulin resistance and highlight new approaches to reduce fat deposition in commercial chickens.

RESULTS

We combined transcriptomics and metabolomics to characterize the response of chicken adipose tissue to two energy manipulations, fasting and insulin deprivation in the fed state. Sixteen to 17 day-old commercial broiler chickens (ISA915) were fed ad libitum, fasted for five hours, or fed but deprived of insulin by injections of anti-insulin serum. Pair-wise contrasts of expression data identified a total of 2016 genes that were differentially expressed after correction for multiple testing, with the vast majority of differences due to fasting (1780 genes). Gene Ontology and KEGG pathway analyses indicated that a short term fast impacted expression of genes in a broad selection of pathways related to metabolism, signaling and adipogenesis. The effects of insulin neutralization largely overlapped with the response to fasting, but with more modest effects on adipose tissue metabolism. Tissue metabolomics indicated unique effects of insulin on amino acid metabolism.

CONCLUSIONS

Collectively, these data provide a foundation for further study into the molecular basis for adipose expansion in commercial poultry and identify potential pathways through which fat accretion may be attenuated in the future through genetic selection or management practices. They also highlight chicken as a useful model organism in which to study the dynamic relationship between food intake, metabolism, and adipose tissue biology.

Native human adipose stromal cells: localization, morphology and phenotype

Objectives:

Beside having roles in energy homeostasis and endocrine modulation, adipose tissue (AT) is now considered a promising source of mesenchymal stromal cells (adipose-derived stromal cells or ASCs) for regenerative medicine. Despite numerous studies on cultured ASCs, native human ASCs are rarely investigated. Indeed, the phenotype of ASCs in their native state, their localization within AT and comparison with bone marrow-derived mesenchymal stromal cells (BM-MSCs) has been poorly investigated.

Design:

To address these issues, the stroma vascular fraction (SVF) of human AT was extracted and native cell subtypes were isolated by immunoselection to study their clonogenic potential in culture. Immunohistology on samples of human AT in combination with reconstruction of confocal sections were performed in order to localize ASCs.

Results:

Compared with BM-MNCs, all native ASCs were found in the CD34⁺ cell fraction of the AT-SVF. Native ASCs expressed classical mesenchymal markers described for BM-MSCs. Interestingly, CD34 expression decreased during ASC cell culture and was negatively correlated with cell proliferation rate. Immunohistological analysis revealed that native ASCs exhibited specific morphological features with protrusions. They were found scattered in AT stroma and did not express in vivo pericytic markers such as NG2, CD140b or alpha-smooth muscle actin, which appeared during the culture process. Finally, ASCs spontaneous commitment to adipocytic lineage was enhanced in AT from obese humans.

Conclusions:

The use of complementary methodological approaches to study native human ASCs revealed their immunophenotype, their specific morphology, their location within AT and their stemness. Furthermore, our data strongly suggest that human ASCs participate in adipogenesis during AT development.

Fatty acids but not dexamethasone are essential inducers for chick adipocyte differentiation in vitro

The present study was carried out to clarify the direct effect of fatty acids (FAs) on chick (Gallus gallus) adipocyte differentiation in the absence of dexmethasone (DEX), a commonly used as strong inducer for adipocyte differentiation. Adipocyte differentiation was initiated by maintaining confluent cell in serum-free medium supplemented with FAs. Upon exposure to FAs, glycerol-3-phosphate dehydrogenase activity (GPDH) as adipocyte differentiation marker rapidly increased, and was significantly higher in chick adipocyte than in control cell. The morphology of the FAs-treated cell changed from fibroblast-like to polygon, and the cells accumulated many cytoplasmic lipid droplets as estimated by Oil red O staining. Neither insulin nor bovine serum albumin, as substitutes for serum, had an effect on chick adipocyte differentiation. The FAs-treated cell had a higher protein and mRNA expression levels for peroxisome proliferator-activated receptor-gamma (PPARgamma), a master regulator of differentiation, compared with untreated cell. In FAs-treated cell, the mRNA expression levels of adipocyte-specific genes, such as CCAAT/enhancer binding protein-alpha (C/EBP alpha) and adipocyte fatty acid-binding protein (aP2) were higher than in control cell. These results indicated that FAs, but not DEX, are essential inducers for chick adipocyte differentiation by elevating PPARgamma expression.

Poly(ethylene glycol) hydrogel system supports preadipocyte viability, adhesion, and proliferation

The ultimate goal of this research is to develop an injectable cell-scaffold system capable of permitting adipogenesis to abrogate soft tissue deficiencies resulting from trauma, tumor resection, and congenital abnormalities. The present work compares the efficacy of photopolymerizable poly(ethylene glycol) and specific derivatives as a scaffold for preadipocyte (adipocyte precursor cell) viability, adhesion, and proliferation. Four variations of a poly(ethylene glycol) scaffold are prepared and examined. The first scaffold consists of poly(ethylene glycol) diacrylate, which is not susceptible to hydrolysis or enzymatic degradation. Preadipocyte death is observed over 1 week in this hydrogel configuration. Adhesion sites, specifically the laminin-binding peptide sequence YIGSR, were incorporated into the second scaffold to promote cellular adhesion as a prerequisite for preadipocyte proliferation. Preadipocytes remain viable in this scaffold system, but do not proliferate in this nondegradable hydrogel. The third scaffold system studied consists of poly(ethylene glycol) modified with the peptide sequence LGPA to permit polymer degradation by cell-secreted collagenase. No adhesion peptide is incorporated into this scaffold system. Cellular proliferation is initially observed, followed by cell death. The previous three scaffold configurations do not permit preadipocyte adhesion and proliferation. In contrast, the fourth system studied, poly(ethylene glycol) modified to incorporate both LGPA and YIGSR, permits preadipocyte adherence and proliferation subsequent to polymer degradation. Our results indicate that a scaffold system containing specific degradation sites and cell adhesion ligands permits cells to adhere and proliferate, thus providing a potential cell-scaffold system for adipogenesis.

Hormonal regulation of postnatal chicken preadipocyte differentiation in vitro

This study was designed to develop a culture system from the stromal-vascular fraction of chicken adipose tissue that can be used to characterize hormones that promote preadipocyte differentiation. Abdominal adipose tissue was excised from 2 to 4-week-old male broilers (Gallus domesticus) by sterile dissection. The stromal-vascular cell fraction from the adipose tissue was isolated by collagenase digestion, filtration, and subsequent centrifugation. These preadipocytes were seeded in six well culture plates and proliferated to confluency in 10% fetal bovine serum in DMEM/F12 (50:50) medium. At confluency, experiments were initiated to determine hormonal requirements for differentiation. Insulin (100 nM) stimulated expression of citrate lyase and sn-glycerol-3-phosphate dehydrogenase relative to lactate dehydrogenase in the presence of 2.5% chicken serum (P<0.05), but not with 10% chicken serum (P>0.05). Triiodothyronine (T(3), 1 nM) and insulin-like growth factor 1 (100 ng/ml) had no effect on differentiation. Dexamethasone (Dex, 1 microM) stimulated differentiation in 2.5 or 10% chicken serum (P<0.05). Insulin, Dex and 2.5% chicken serum stimulated enzymatic differentiation to the extent of 10% chicken serum, but heparin (10 U/ml) addition, in combination with insulin and Dex was necessary to stimulate lipid filling of adipocytes.

Tissue reaction and biodegradation of implanted cross-linked high amylose starch in rats

The biocompatibility and degradation characteristics of cross-linked high amylose starch (Contramid were investigated in rats over 4 months. Contramid pellets (3-mm diameter and thickness) obtained by direct compression, were implanted subcutaneously and intramuscularly. On sequential time points, macroscopic observations of implantation sites were performed and tissue samples were removed, fixed, and histologically evaluated. No macroscopic inflammatory reaction was observed with Contramid.. Upon histologic examination, inflammatory reaction produced by Contramid was moderate and restricted to implantation sites. The sequence of inflammatory events with Contramid was similar regardless of implantation site. Degradation of Contramid pellets was characterized by fragmentation with formation of fibrovascular septa and phagocytosis by macrophages. Finally Contramid was mostly absorbed by the end of the 4-month period and substituted by adipocytes. It has been demonstrated that Contramid is a biocompatible and absorbable material.

Glycerol-3-Phosphate dehydrogenase (E.C.1.1.1.8) is expressed in cultured chicken embryonic adipofibroblasts and upregulated by embryonic chicken serum

Chicken embryonic adipofibroblasts (CEA) accumulate intracytoplasmic lipids when cultured in medium containing chicken serum (CS), but not in medium with fetal bovine serum (FBS). To characterize this process of lipid accumulation, we evaluated the expression of the enzyme glycerol-3-phosphate dehydrogenase (E.C.1.1.1.8) (GPDH), first in chicken tissues and then in CEA cultured under diverse conditions. GPDH activity in adipose depots from 4-wk-old broiler chickens was similar or higher than that shown by liver, the main organ for fatty acid synthesis in chickens, while skeletal muscle had the lowest levels of GPDH. In vitro, GPDH activity increased in CEA cultured in the presence of CS but not in medium with FBS, paralleling the lipid accumulation by these cells. Both lipid accumulation and GPDH activity were further increased in CEA cultured in the presence of embryonic CS. Our results show that GPDH is highly expressed in avian tissues related to lipid metabolism and therefore can be a reliable marker for avian adipogenesis, and suggest that ECS is an optimum source for the purification of avian adipogenic factors.

Comparative responses of genetically lean and fat broiler chickens to dietary threonine concentration

Genetically lean (LL) or fat (FL) male broiler chicken's were fed on 5 diets containing either 3.80, 4.27, 4.75, 5.22 or 5.70 g true digestible threonine per kg. Threonine deficiency induced a more pronounced reduction in growth in the LL than in the FL but did not influence abdominal fat and breast muscle proportions in either line. Plotting weight gain or protein gain against threonine intake suggests that the requirement of both lines is very similar in terms of mg per g of gain. Thus food intake or appetite should account for differences between genotypes. Requirement for true digestible threonine was estimated as 10.70 mg per g of weight gain or 63.8 mg per g of protein gain, using a linear regression approach. The quadratic polynomial equations suggest that the requirements are 13.9 and 12.4 mg digestible threonine per g of gain for LL and FL respectively.