Effect of lipoproteins on the differentiation of 3T3-L1 and human preadipocytes in cell culture

Research Note: Adipogenic differentiation of embryonic fibroblasts of chicken, turkey, duck, and quail in vitro by medium containing chicken serum alone

The study of adipogenesis is one of the most important areas for not only regulating meat quality, but production efficiency associated with fat accretion in the poultry species. Current in vitro models for avian adipogenesis require adipogenic inducers including dexamethasone, 3-isobutyl-1-methylxanthine (IBMX), fatty acids, or insulin. However, problems still remain in these models for testing/screening potential nutritional, hormonal, and pharmaceutical factors because of interfering/overriding effects of the inducing factors. Therefore, the purpose of this study was to develop a simple in vitro method for avian adipogenesis. In this study, chicken serum (CS) and fetal bovine serum (FBS) were compared for adipogenic potential using chicken embryonic fibroblasts (CEF). Oil-red O staining at 4 d in culture of CEF under CS revealed that lipid droplet formation was increased by CS in a dose-dependent manner (0 to 10%). On the contrary, all concentrations of FBS (0 to 10%) alone did not show lipid droplet formation. In accordance with the morphological data of CEF, mRNA expression of genes involved in adipocyte differentiation/determination, fatty acid uptake, and triacylglycerol (TAG) synthesis, were most significantly up-regulated by 10% CS at d 4 compared to 1 or 5% CS. In addition, embryonic cells isolated from quail (QEF) at E5, duck (DEF) at E6, and turkey (TEF) at E6, were tested for adipogenic differentiation by media containing the same concentrations of CS. Similar to the morphological data from CEF, quantitative data of the Oil-red O staining showed that lipid droplet formation in QEF, DEF, and TEF was increased by CS in a dose-dependent manner (0 to 10%). The current study demonstrates that CS alone can induce adipogenesis on embryonic fibroblasts of various poultry species. By providing a new simple in vitro method of avian adipogenesis, diverse nutritional, hormonal, and pharmaceutical factors can be broadly and easily tested for scientific and industrial purposes.

Higher plane of nutrition pre-weaning enhances Holstein calf mammary gland development through alterations in the parenchyma and fat pad transcriptome

Background

To reduce costs of rearing replacement heifers, researchers have focused on decreasing age at breeding and first calving. To increase returns upon initiation of lactation the focus has been on increasing mammary development prior to onset of first lactation. Enhanced plane of nutrition pre-weaning may benefit the entire replacement heifer operation by promoting mammary gland development and greater future production.

Methods

Twelve Holstein heifer calves (< 1 week old) were reared on 1 of 2 dietary treatments (n = 6/group) for 8 weeks: a control group fed a restricted milk replacer at 0.45 kg/d (R, 20% crude protein, 20% fat), or an accelerated group fed an enhanced milk replacer at 1.13 kg/d (EH, 28% crude protein, 25% fat). At weaning (8 weeks), calves were euthanized and sub-samples of mammary parenchyma (PAR) and mammary fat pad (MFP) were harvested upon removal from the body. Total RNA from both tissues was extracted and sequenced using the Illumina HiSeq2500 platform. The Dynamic Impact Approach (DIA) and Ingenuity Pathway Analysis (IPA) were used for pathway analysis and functions, gene networks, and cross-talk analyses of the two tissues.

Results

When comparing EH vs R 1561 genes (895 upregulated, 666 downregulated) and 970 genes (506 upregulated, 464 downregulated) were differentially expressed in PAR and MFP, respectively. DIA and IPA results highlight a greater proliferation and differentiation activity in both PAR and MFP, supported by an increased metabolic activity. When calves were fed EH, the PAR displayed transcriptional signs of greater overall organ development, with higher ductal growth and branching, together with a supportive blood vessel and nerve network. These activities were mediated by intracellular cascades, such as AKT, SHH, MAPK, and Wnt, probably activated by hormones, growth factors, and endogenous molecules. The analysis also revealed strong communication between MFP and PAR.

Conclusion

The transcriptomics and bioinformatics approach highlighted key mechanisms that mediate the mammary gland response to a higher plane of nutrition in the pre-weaning period.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5303-8) contains supplementary material, which is available to authorized users.

Knocking down Stard3 decreases adipogenesis with decreased mitochondrial ROS in 3T3-L1 cells

Start domain-containing protein 3 (Stard3) plays roles in intracellular cholesterol distribution, however, the role of Stard3 in the adipogenesis of 3T3-L1 preadipocytes remains unclear. We demonstrated that Stard3 expression was significantly increased during the adipogenesis of 3T3-L1 preadipocytes, accompanied by an increase of mitochondrial Reactive oxygen species (ROS). Stard3 knocking-down inhibited 3T3-L1 preadipocyte adipogenesis with decreased mitochondrial ROS levels, while ROS inducer rescued the stard3 silencing 3T3 cells with increased ROS. Moreover, Stard3 silencing reduced the expression of peroxisome proliferator-activated receptor-γ (PPARγ) and CCAAT/enhancer binding protein (C/EBP)α in 3T3- L1 cells. In conclusion, Stard3 enhanced the adipogenesis of preadipocytes by enhancement of cholesterol redistribution to the mitochondrial, increasing mitochondrial ROS production. These results suggest that Stard3 is an essential factor for the 3T3-L1 cells' differentiation.

Hypercholesterolemia induces adipose dysfunction in conditions of obesity and nonobesity

It is well known that hypercholesterolemia can lead to atherosclerosis and coronary heart disease. Adipose tissue represents an active endocrine and metabolic site, which might be involved in the development of chronic disease. Because adipose tissue is a key site for cholesterol metabolism and the presence of hypercholesterolemia has been shown to induce adipocyte cholesterol overload, it is critical to investigate the role of hypercholesterolemia on normal adipose function. Studies in preadipocytes revealed that cholesterol accumulation can impair adipocyte differentiation and maturation by affecting multiple transcription factors. Hypercholesterolemia has been observed to cause adipocyte hypertrophy, adipose tissue inflammation, and disruption of endocrine function in animal studies. Moreover, these effects can also be observed in obesity-independent conditions as confirmed by clinical trials. In humans, hypercholesterolemia disrupts adipose hormone secretion of visfatin, leptin, and adiponectin, adipokines that play a central role in numerous metabolic pathways and regulate basic physiologic responses such as appetite and satiety. Remarkably, treatment with cholesterol-lowering drugs has been shown to restore adipose tissue endocrine function. In this review the role of hypercholesterolemia on adipose tissue differentiation and maturation, as well as on hormone secretion and physiologic outcomes, in obesity and non–obesity conditions is presented.

Cholesterol suppresses adipocytic differentiation of mouse adipose-derived stromal cells via PPARγ2 signaling

The effects of cholesterol on cell proliferation and adipocytic differentiation have been evaluated for the first time in mouse adipose-derived stromal cells (mASCs). Cholesterol loading by using cholesterol:methyl- β-cyclodextrin (Chol:MβCD) complexes promoted cellular levels of free cholesterol (FC) and cholesteryl ester (CE), induced high cell proliferation of mASCs dose-dependently. Compared with control cells, cholesterol-treated mASCs showed an impaired differentiation process in both dose- and time-dependent manners, based on reduced oil red O-stained lipid droplets, SREBP-1, PPARγ2 and aP2 expression levels. The involvement of SREBP-1-mediated PPARγ2 in the effects of cholesterol on mASC adipogenesis was elucidated. These results point to cholesterol as a modulator of adipogenesis, which separate cholesterol itself from other components of modified lipoproteins.

In vivo evidence for a role of adipose tissue SR-BI in the nutritional and hormonal regulation of adiposity and cholesterol homeostasis

OBJECTIVES

This study examines the role of insulin and angiotensin II in high-density lipoprotein (HDL) metabolism by focusing on the regulation and function of scavenger receptor type-BI (SR-BI) in adipose tissue.

METHODS AND RESULTS

Insulin or angiotensin II injection in wild-type mice induced a decrease in circulating HDL and it was associated with the translocation of SR-BI from intracellular sites to the plasma membrane of adipose tissue. Refeeding upregulated adipose HDL selective cholesteryl esters uptake and SR-BI proteins through transcriptional and posttranscriptional mechanisms. This occurred along with a decrease in serum HDL and an increase in adipose cholesterol content. Similar results were obtained with transgenic mice overexpressing locally angiotensinogen in adipose tissue. In adipose 3T3-L1 cell line, HDL induced lipogenesis by increasing liver X receptor binding activity. This mechanism was dependent of insulin and angiotensin II.

CONCLUSIONS

Our results raise the possibility that adipose tissue SR-BI translocation might be a link between adipose tissue lipid storage and HDL clearance.

Surface protein expression between human adipose tissue-derived stromal cells and mature adipocytes

Adipose tissue contains a stroma that can be easily isolated. Thus, human adipose tissue presents an source of multipotent stromal cells. In order to determine the implication of hematopoietic markers in adipocyte biology, we have defined part of the phenotype of the human adipose tissue-derived stromal cells, and compared this to fully differentiated adipocytes. Flow cytometry demonstrates that the protein expression phenotype of both cell types are similar and includes the expression of CD10, CD13, CD34, CD36, CD55, CD59 and CD65. No significant difference between subcutaneous and omental adipose tissue could be demonstrated concerning the expression of these markers. However, the expression of CD34, CD36 and CD65 is cell-dependent. While the expression of CD36 and CD65 doubled between stromal cells and mature adipocytes, the expression of CD34 decreased, despite this protein being present on the mature adipocyte. As CD34 is described as a stem cell marker and it being unlikely to be expressed on differentiated cells, this result was confirmed by immunostaining and western blot. The clear function of this protein on the adipocyte membrane remains to be determined. The characterization of new proteins on mature adipocytes could have broad implications for the comprehension of the biology of this tissue.

Progress in adipose tissue construct development

Although the field of tissue engineering has been the focus of a great deal of promise and study, only recently has significant attention been given to the engineering of soft tissues. The applicability of an engineered adipose construct as a basic science model and a reconstructive tool is unquestioned; yet, there have been limitations in previous work, specifically issues of construct size and maintenance over time. This article briefly overviews the pivotal factors necessary for adipocyte growth and differentiation, optimal scaffolds for the engineering of soft tissues, and a means of providing vascular support for these highly demanding cells. Clinical science and bioengineering concepts that may provide the foundation toward the successful in vivo engineering of an adipose tissue construct that maintains its complex three-dimensional shape over time are critically reviewed.

Effects of lipid-related factors on adipocyte differentiation of bovine stromal-vascular cells in primary culture

The effects of several factors related to lipids on bovine adipocyte differentiation were investigated in primary culture. Adipocyte differentiation was assessed by development of glycerol-3-phosphate dehydrogenase (GPDH) activity and morphological observation. Addition of triglyceride mixture (Intralipid), caprylic acid and very low-, low- and high-density lipoproteins (VLDL, LDL and HDL) stimulated bovine preadipocyte differentiation in serum-free condition. Especially, VLDL strongly increased both cell protein contents and GPDH activity, suggesting that it stimulated both proliferation and differentiation of bovine preadipocytes. Under Intralipid-induced condition, differentiation of preadipocytes from subcutaneous adipose tissues was more evident than those from omental adipose tissues. However, such depot difference was not observed in medium supplemented with indomethacin, which is a peroxisome proliferator-activated receptor (PPAR) gamma agonist. This suggests that the differentiation capacity of bovine preadipocytes was different between depots and such difference is dependent on the ability to utilize lipids as endogenous PPARgamma ligands. Therefore, lipid metabolites have the stimulatory effects on bovine adipocyte differentiation in vitro, and lipoproteins, especially VLDL, may play an important role in development of bovine adipose tissues in vivo.

Peroxisome proliferator activated receptor-gamma, leptin and tumor necrosis factor-alpha mRNA expression during very low calorie diet in subcutaneous adipose tissue in obese women

BACKGROUND

PPAR gamma, leptin and TNF alpha are three major factors that play a key role in influencing adipocyte differentiation and both adipose tissue function and metabolism. However, the regulation of these three genes during a dynamic period of weight loss is unknown. We therefore investigated the concomitant regulation of the mRNA expression of PPAR gamma, leptin and TNF alpha in adipose tissue during a 21-day very low calorie diet (VLCD) in 12 non-diabetic obese women.

METHODS

The mRNA levels of PPAR gamma, leptin and TNF alpha were quantified by quantitative RT-competitive PCR in abdominal subcutaneous adipose tissue before and during VLCD (940 kcal/day).

RESULTS

VLCD induced weight loss (approximately 6 kg) and improved insulin sensitivity. Simultaneously, VLCD induced the reduction in the adipose tissue mRNA abundances of PPAR gamma (-13%, p < 0.05) and of leptin (-58%, p < 0.005), whereas TNF alpha mRNA levels increased (+78%, p < 0.005). PPAR gamma and leptin mRNA levels were correlated before (r = 0.778, p < 0.01) and after VLCD (r = 0.797, p < 0.01). Serum HDL-cholesterol concentrations were positively associated with PPAR gamma (r = 0.696, p < 0.03) and leptin (r = 0.806, p < 0.01) mRNA levels.

CONCLUSIONS

The increase in TNF alpha mRNA levels suggested that a local increased expression of this cytokine in adipose tissue might play a role in the control of the fat mass during weight loss. PPAR gamma and leptin mRNA levels were positively associated both before and after VLCD, suggesting that common regulatory mechanism(s) might control their expression. More strikingly, we found strong positive correlations between circulating HDL-cholesterol and both PPAR gamma and leptin mRNA levels, suggesting the existence of physiological links between circulating lipoprotein metabolism and adipose tissue function.

The influence of plasma lipoprotein subfractions on 3T3-L1 and human preadipocyte differentiation in cell culture

3T3-L1 and human preadipocyte differentiation was significantly (P < 0.001) enhanced by HDL2, LDLII/III and LDLIV. The concentrations of lipoproteins required for maximal differentiation in human preadipocytes were not achieved over the concentration range 50-150 micrograms lipoprotein protein ml-1, whereas maximal differentiation in 3T3-L1 preadipocytes was achieved for all lipoprotein subfractions at approximately 75 micrograms lipoprotein ml-1, a level almost double that required for complete HDL and LDL fractions in 3T3-L1 cells. Despite the enhanced extent of differentiation caused by certain lipoprotein subfractions, the time needed for the conversion process was unaffected. GPDH activity development in both cell types was most pronounced in response to LDLIV, with HDL2 resulting in the lowest activity. In both cell types, the enhancement of differentiation was only evident when the cells were exposed to lipoproteins during the early stage of the program, i.e. before visible formation of lipid droplets.