Primary culture of human adipocyte precursor cells: expansion and differentiation

Lesson on obesity and anatomy of adipose tissue: new models of study in the era of clinical and translational research

Obesity is a serious global illness that is frequently associated with metabolic syndrome. Adipocytes are the typical cells of adipose organ, which is composed of at least two different tissues, white and brown adipose tissue. They functionally cooperate, interconverting each other under physiological conditions, but differ in their anatomy, physiology, and endocrine functions. Different cellular models have been proposed to study adipose tissue in vitro. They are also useful for elucidating the mechanisms that are responsible for a pathological condition, such as obesity, and for testing therapeutic strategies. Each cell model has its own characteristics, culture conditions, advantages and disadvantages. The choice of one model rather than another depends on the specific study the researcher is conducting. In recent decades, three-dimensional cultures, such as adipose spheroids, have become very attractive because they more closely resemble the phenotype of freshly isolated cells. The use of such models has developed in parallel with the evolution of translational research, an interdisciplinary branch of the biomedical field, which aims to learn a scientific translational approach to improve human health and longevity. The focus of the present review is on the growing body of data linking the use of new cell models and the spread of translational research. Also, we discuss the possibility, for the future, to employ new three-dimensional adipose tissue cell models to promote the transition from benchside to bedsite and vice versa, allowing translational research to become routine, with the final goal of obtaining clinical benefits in the prevention and treatment of obesity and related disorders.

Discovering cellular programs of intrinsic and extrinsic drivers of metabolic traits using LipocyteProfiler

A primary obstacle in translating genetic associations with disease into therapeutic strategies is elucidating the cellular programs affected by genetic risk variants and effector genes. Here, we introduce LipocyteProfiler, a cardiometabolic-disease-oriented high-content image-based profiling tool that enables evaluation of thousands of morphological and cellular profiles that can be systematically linked to genes and genetic variants relevant to cardiometabolic disease. We show that LipocyteProfiler allows surveillance of diverse cellular programs by generating rich context- and process-specific cellular profiles across hepatocyte and adipocyte cell-state transitions. We use LipocyteProfiler to identify known and novel cellular mechanisms altered by polygenic risk of metabolic disease, including insulin resistance, fat distribution, and the polygenic contribution to lipodystrophy. LipocyteProfiler paves the way for large-scale forward and reverse deep phenotypic profiling in lipocytes and provides a framework for the unbiased identification of causal relationships between genetic variants and cellular programs relevant to human disease.

Pleiotropic and multi-systemic actions of physical exercise on PGC-1α signaling during the aging process

Physical training is a potent therapeutic approach for improving mitochondrial health through peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) signaling pathways. However, comprehensive information regarding the physical training impact on PGC-1α in the different physiological systems with advancing age is not fully understood. This review sheds light on the frontier-of-knowledge data regarding the chronic effects of exercise on the PGC-1α signaling pathways in rodents and humans. We address the molecular mechanisms involved in the different tissues, clarifying the precise biological action of PGC-1α, restricted to the aged cell type. Distinct exercise protocols (short and long-term) and modalities (aerobic and resistance exercise) increase the transcriptional and translational PGC-1α levels in adipose tissue, brain, heart, liver, and skeletal muscle in animal models, suggesting that this versatile molecule induces pleiotropic responses. However, PGC-1α function in some human tissues (adipose tissue, heart, and brain) remains challenging for further investigations. PGC-1α is not a simple transcriptional coactivator but supports a biochemical environment of mitochondrial dynamics, controlling physiological processes (primary metabolism, tissue remodeling, autophagy, inflammation, and redox balance). Acting as an adaptive mechanism, the long-term effects of PGC-1α following exercise may reflect the energy demand to coordinate multiple organs and contribute to cellular longevity.

Hypertrophied human adipocyte spheroids as in vitro model of weight gain and adipose tissue dysfunction

KEY POINTS

Adipocyte enlargement is a key feature of obesity and associated with insulin resistance and metabolic disease The cause and consequences of adipocyte enlargement have remained hard to study in vitro due to a lack of human cell models with representative morphology This paper provides an easily set up spheroid culture method, HUVAS (human unilocular vascularized adipocyte spheroids), for the differentiation and culturing of human adipocytes with a more unilocular morphology We show that providing adipocyte progenitors with a vascular differentiation niche is key for achieving in vitro differentiated adipocytes with large lipid droplets Lipid treatment of the HUVAS spheroids can further adipocyte enlargement and induce cellular dysfunction, mimicking the in vivo effects of weight gain The model will allow a wider research community to perform mechanistic studies of the factors impacting human adipocyte differentiation and growth, increasing our understanding of how obesity develops and why it has such detrimental consequences on whole body metabolism ABSTRACT: The rise in obesity prevalence has created an urgent need for new and improved methods to study human adipocytes and the pathogenic effects of weight gain in vitro. Despite the proven advantage of culturing adipocyte progenitors as 3D structures, the majority of studies continue using traditional 2D cultures which result in small, multilocular adipocytes with poor representability. We hypothesized that providing differentiating pre-adipocytes with a vascular growth niche would mimic in vivo adipogenesis and improve the differentiation into unilocular adipocytes. Here we present HUVAS (human unilocular vascularized adipocyte spheroids), a simple, easily applicable culture protocol that allows for the differentiation of human adipocytes with a more unilocular morphology and larger lipid droplets than previous protocols. Moreover, we offer a protocol for inducing adipocyte enlargement in vitro, resulting in larger lipid droplets and development of several key features of adipocyte dysfunction, including altered adipokine secretion, impaired lipolysis and insulin resistance. Taken together, our HUVAS model offers an improved culture system for studying the cellular and molecular mechanisms causing metabolic dysfunction and inflammation in human adipose tissue during weight gain. This article is protected by copyright. All rights reserved.

Effects of Pioglitazone on Glucose-Dependent Insulinotropic Polypeptide-Mediated Insulin Secretion and Adipocyte Receptor Expression in Patients With Type 2 Diabetes

Incretin hormone dysregulation contributes to reduced insulin secretion and hyperglycemia in patients with type 2 diabetes mellitus (T2DM). Resistance to glucose-dependent insulinotropic polypeptide (GIP) action may occur through desensitization or downregulation of β-cell GIP receptors (GIP-R). Studies in rodents and cell lines show GIP-R expression can be regulated through peroxisome proliferator-activated receptor γ (PPARγ) response elements (PPREs). Whether this occurs in humans is unknown. To test this, we conducted a randomized, double-blind, placebo-controlled trial of pioglitazone therapy on GIP-mediated insulin secretion and adipocyte GIP-R expression in subjects with well-controlled T2DM. Insulin sensitivity improved, but the insulinotropic effect of infused GIP was unchanged following 12 weeks of pioglitazone treatment. In parallel, we observed increased GIP-R mRNA expression in subcutaneous abdominal adipocytes from subjects treated with pioglitazone. Treatment of cultured human adipocytes with troglitazone increased PPARγ binding to GIP-R PPREs. These results show PPARγ agonists regulate GIP-R expression through PPREs in human adipocytes, but suggest this mechanism is not important for regulation of the insulinotropic effect of GIP in subjects with T2DM. Because GIP has antilipolytic and lipogenic effects in adipocytes, the increased GIP-R expression may mediate accretion of fat in patients with T2DM treated with PPARγ agonists.

Adipose Organ Development and Remodeling

During the last decades, research on adipose tissues has spread in parallel with the extension of obesity. Several observations converged on the idea that adipose tissues are organized in a large organ with endocrine and plastic properties. Two parenchymal components: white (WATs) and brown adipose tissues (BATs) are contained in subcutaneous and visceral compartments. Although both have endocrine properties, their function differs: WAT store lipids to allow intervals between meals, BAT burns lipids for thermogenesis. In spite of these opposite functions, they share the ability for reciprocal reversible transdifferentiation to tackle special physiologic needs. Thus, chronic need for thermogenesis induces browning and chronic positive energy balance induce whitening. Lineage tracing and data from explant studies strongly suggest other remodeling properties of this organ. During pregnancy and lactation breast WAT transdifferentiates into milk-secreting glands, composed by cells with abundant cytoplasmic lipids (pink adipocytes) and in the postlactation period pink adipocytes transdifferentiate back into WAT and BAT. The plastic properties of mature adipocytes are supported also by a liposecretion process in vitro where adult cell in culture transdifferentiate to differentiated fibroblast-like elements able to give rise to different phenotypes (rainbow adipocytes). In addition, the inflammasome system is activated in stressed adipocytes from obese adipose tissue. These adipocytes die and debris are reabsorbed by macrophages inducing a chronic low-grade inflammation, potentially contributing to insulin resistance and T2 diabetes. Thus, the plastic properties of this organ could open new therapeutic perspectives in the obesity-related metabolic disease and in breast pathologies. © 2018 American Physiological Society. Compr Physiol 8:1357-1431, 2018.

Profiling Analysis Reveals the Potential Contribution of Peptides to Human Adipocyte Differentiation

PURPOSE

Peptide drugs provide promising regimes in anti-obesity treatment. In order to identify potential bioactive peptides involved in adipogenesis.

EXPERIMENTAL DESIGN

The intracellular peptides between preadipocytes and adipocytes are compared by liquid chromatography/mass spectrometry. The underlying biological function of the identified peptides are evaluated by gene ontology (GO) and pathway analysis of their precursors. To find more potential bioactive peptides, 50 peptide sequences are identified located in the functional domains with the use of the SMART and UniProt databases. Finally, the Open Targets Platform database is used to investigate the precursors related to metabolic diseases.

RESULTS

A total of 181 downregulated peptides and 89 upregulated peptides after differentiation (fold change > 1.5 and p-value < 0.05) are identified. The GO and pathway analysis indicate that these differentially expressed peptides play a role in adipogenesis. A total of 10 putative peptides 6 to 26 amino acids in length are identified that might have bioactive effects in adipogenesis and metabolic diseases.

CONCLUSIONS AND CLINICAL RELEVANCE

On one hand, present preliminary research provides a better understanding of the intracellular peptides during adipocyte differentiation. On the other hand, it lays a foundation for discovering new peptide drugs in anti-obesity treatment.

p62 is linked to mitophagy in oleic acid-induced adipogenesis in human adipose-derived stromal cells

BACKGROUND

Obesity is closely related to the abnormal differentiation of adipocytes, which are subjected to high plasma levels of free fatty acids (FFAs). As the most abundant FFA in the bloodstream, oleic acid (OA) has the ability to induce adipogenic differentiation in human adipose-derived stromal cells (hADSCs). Recently, p62, an autophagy mediator, has been shown to play a role in obesity and adipose tissue metabolism. Therefore, the aim of this study was to investigate the roles of autophagy and mitochondrial function at different stages of OA (in combination with insulin and dexamethasone)-induced adipogenesis in hADSCs.

METHODS

The hADSCs were incubated with OA, insulin, and dexamethasone after pretreatment with autophagy inhibitors or knockdown of p62 with shRNA. The adiposeness level was then analyzed by oil red O staining in the cells. The related proteins or mRNA levels were detected by western blot analysis or quantitative real-time polymerase chain reaction (PCR).

RESULTS

Treatment with 80 μM OA (substituted for isobutylmethylxantine; IBMX) for 10 days successfully induced hADSCs to adipocytes. During OA-induced adipogenesis, autophagy was induced, with an increased LC3II/I ratio on day 3 and a decreased protein level of p62 on and after day 3. Inhibition of autophagy with 3-methyladenine (3MA) at the early stage (day 0 to day 3) of differentiation, but not at the middle or late stage, significantly decreased OA-induced adipogenesis; while knockdown of p62 with shRNA significantly promoted adipogenesis in hADSCs. Moreover, the copy number of mtDNA (the ND1 gene) and the protein level of TOM20, a mitochondrial membrane protein, were increased following OA treatment, which was related to the stability of mitochondria. Interestingly, knockdown of p62 increased the mito-LC3II/I and cyto-LC3II/I ratios by 110.1% and 73.3%, respectively. The increase in the ratio of mito-LC3II/I was higher than that of cyto-LC3II/I. Furthermore, p62 knockdown-enhanced adipogenesis in hADSCs was abolished by inhibiting mitophagy with cyclosporine A.

CONCLUSIONS

These results suggested that p62 plays a protective role in adipogenesis of hADSCs through regulating mitophagy.

Evaluation and optimization of differentiation conditions for human primary brown adipocytes

As an effective way to improve energy expenditure, increasing the mass and activity of brown adipose tissue (BAT) has become a promising treatment for obesity and its associated disorders. Many efforts have been made to promote brown adipogenesis and increase the thermogenic capacity of brown adipose cells (BACs). The present culture schemes for human BAC differentiation are mostly derived from white adipocyte differentiation schemes. To solve this issue, we compared the adipogenic and thermogenic effects of various components on human BAC differentiation and optimized their concentrations as well as the culture time for BAC differentiation. In this study, we found that the induction factors did not show a dose-dependent promotion of brown adipogenesis or thermogenic capacity. The higher differentiation levels did not inevitably result in higher BAT-specific gene expression levels or increased β₃-receptor agonist sensitivity. As an important element of culture medium, triiodothyronine was found to be essential for differentiation and metabolic property maintenance. Furthermore, compared with other reported methods, this protocol induced a specific intrinsic differentiation program. Our study provides not only an optimized method for human BAC differentiation but also a cell model with good differentiation and thermogenic capacity for brown adipose research.

PPARγ agonist through the terminal differentiation phase is essential for adipogenic differentiation of fetal ovine preadipocytes

Background

Although the 3T3-L1 preadipocyte cell line represents an informative model for in vitro adipogenesis research, primary cultured cells are often needed to understand particular human or animal metabolic phenotypes. As demonstrated by in vitro cultured preadipocytes from large mammalian species, primary cultured cells require specific adipogenic differentiation conditions different to that of the 3T3-L1 cell line. These conditions are also species-specific and require optimization steps. However, efficient protocols to differentiate primary preadipocytes using alternative species to rodents are scarce. Sheep represent an amenable animal model for fetal biology and developmental origins of health and disease studies. In this work, we present with the first detailed procedure to efficiently differentiate primary fetal and adult ovine preadipocytes.

Methods

Fetal and adult ovine adipose and skin tissue harvest, preadipocyte and fibroblast isolation, proliferation, and standardization and optimization of a new adipogenic differentiation protocol. Use of commercial cell lines (3T3-L1 and NIH-3T3) for validation purposes. Oil red O stain and gene expression were used to validate adipogenic differentiation. ANOVA and Fisher’s exact test were used to determine statistical significance.

Results

Our optimized adipogenic differentiation method included a prolonged adipogenic cocktail exposure time from 2 to 8 days, higher insulin concentration, and supplementation with the peroxisome proliferator-activated receptor gamma (PPARγ) agonist, rosiglitazone. This protocol was optimized for both, fetal and adult preadipocytes.

Conclusions

Our protocol enables successful adipogenic differentiation of fetal and adult ovine preadipocytes. This work demonstrates that compared to the 3T3-L1 cell line, fetal ovine preadipocytes require a longer exposure to the differentiation cocktail, and the need for IMBX, dexamethasone, and/or the PPARγ agonist rosiglitazone through the terminal differentiation phase. They also require higher insulin concentration during differentiation to enhance lipid accumulation and similar to human primary preadipocytes, PPARγ agonist supplementation is also required for ovine adipogenic differentiation. This work highlights species-specific differences requirements for adipogenic differentiation and the need to develop standardized methods to investigate comparative adipocyte biology.

Differentiation and Metabolic Interrogation of Human Adipocytes

Adipocytes differentiated from preadipocytes provide a valuable model for the study of human adipocyte metabolism. We describe methods for isolation of human stromal vascular cells, expansion of preadipocytes, differentiation into mature adipocytes, and in vitro metabolic interrogation of adipocytes.

Effects of glucose and insulin on secretion of amyloid-β by human adipose tissue cells

OBJECTIVE

Obesity and type 2 diabetes mellitus are risk factors for developing Alzheimer disease. Overlapping patterns of metabolic dysfunction may be common molecular links between these complex diseases. Amyloid-β (Aβ) precursor protein and associated β- and γ-secretases are expressed in adipose tissue. Aβ precursor protein is up-regulated with obesity and correlated to insulin resistance. Aβ may be secreted by adipose tissue, its production may be regulated through metabolic pathways, and Aβ may exert effects on adipose tissue insulin receptor signaling.

METHODS

Human stromal-vascular cells and differentiated adipocytes were cultured with different combinations of glucose and insulin and then assayed for Aβ in conditioned media. Aβ was measured in vivo using adipose tissue microdialysis.

RESULTS

Aβ secretion was increased by glucose and insulin in vitro. Adipose tissue microdialysates contained Aβ. Adipocytes treated with Aβ had decreased expression of insulin receptor substrate-2 and reduced Akt-1 phosphorylation.

CONCLUSIONS

Aβ was made by adipose tissue cells in vitro at concentrations similar to in vivo measurements. Regulation of Aβ production by glucose and insulin and effects of Aβ on the insulin receptor pathway suggest similar cellular mechanisms may exist between neuronal dysfunction in Alzheimer disease and adipose dysfunction in type 2 diabetes.

Coimplanted endothelial cells improve adipose tissue grafts' survival by increasing vascularization

BACKGROUND

With goal of improving fat graft survival, many studies have focused on supplementing cells in the graft fat. In these studies, enhanced vascularization is considered the most important mechanism for the improved graft survival. Endothelial cells (ECs) are essential in vessel formation of the vascularization. Therefore, in this study, we coimplanted ECs with adipose tissue to investigate whether the ECs can enhance graft survival in a cell concentration-dependent manner.

METHODS

Endothelial cells were isolated from stromal vascular fraction derived from human liposuction aspirates, and the EC characteristics were confirmed by CD31 immunofluorescence staining, measuring acetylated low-density lipoprotein uptake, and observing the formation of capillary-like tubular structures in Matrigel. During the animal experiment, the isolated ECs were labeled, then added to 0.5-mL fat grafts at different numbers (0.5 × 10(6), 1 × 10(6), 2 × 10(6), and 4 × 10(6) cells) before subcutaneous implantation in nude mice. Grafts were harvested at 1 week, 1 month, and 2 months after -transplantation, and graft survival and vascularization were evaluated based on weight measurements, histological assessment, and vascular gene expression.

RESULTS

Stromal vascular fraction-derived vascular cells exhibited typical EC characteristics. The observed differences in explanted graft weight, vessel density, vascular gene expression, and cell tracking result indicated that coimplantation with ECs accelerated vascularization that increased graft survival in a concentration-dependent manner. Over the experimental period, fat grafts implanted with 4 × 10(6) ECs showed no weight loss and the greatest increases in measures of vascularization.

CONCLUSIONS

Endothelial cells can effectively enhance vascularization in fat grafts, and higher EC concentrations (eg, 4 × 10(6) ECs/0.5 mL adipose tissue) may best support graft survival.

Optimal protocol for the differentiation and metabolic analysis of human adipose stromal cells

Obesity is reaching epidemic proportions so there is growing interest in the mechanisms that regulates adipose tissue development and function. Although murine adipose cell lines are useful for many mechanistic studies, primary human adipose stromal cells (ASCs), which can be isolated from distinct adipose depots and cultured in vitro, have clear translational relevance. We describe the methods to isolate, culture, and differentiate human ASCs to adipocytes that respond to physiologically relevant hormones, such as insulin and β-adrenergic agonists. We also describe methods for assaying hormonal effects on glucose transport and lipolysis.

Adipogenesis: new insights into brown adipose tissue differentiation

Confirmation of the presence of functional brown adipose tissue (BAT) in humans has renewed interest in investigating the potential therapeutic use of this tissue. The finding that its activity positively correlates with decreased BMI, decreased fat content, and augmented energy expenditure suggests that increasing BAT mass/activity or browning of white adipose tissue (WAT) could be a strategy to prevent or treat obesity and its associated morbidities. The challenge now is to find a safe and efficient way to develop this idea. Whereas BAT has being widely studied in murine models both in vivo and in vitro, there is an urgent need for human cellular models to investigate BAT physiology and functionality from a molecular point of view. In this review, we focus on the latest insights surrounding BAT development and activation in rodents and humans. Then, we discuss how the availability of murine models has been essential to identify BAT progenitors and trace their lineage. Finally, we address how this information can be exploited to develop human cellular models for BAT differentiation/activation. In this context, human embryonic stem and induced pluripotent stem cells-based cellular models represent a resource of great potential value, as they can provide a virtually inexhaustible supply of starting material for functional genetic studies, -omics based analysis and validation of therapeutic approaches. Moreover, these cells can be readily genetically engineered, opening the possibility of generating patient-specific cellular models, allowing the investigation of the influence of different genetic backgrounds on BAT differentiation in pathological or in physiological states.

Sex dimorphism and depot differences in adipose tissue function

Obesity, characterized by excessive adiposity, is a risk factor for many metabolic pathologies, such as type 2 diabetes mellitus (T2DM). Numerous studies have shown that adipose tissue distribution may be a greater predictor of metabolic health. Upper-body fat (visceral and subcutaneous abdominal) is commonly associated with the unfavorable complications of obesity, while lower-body fat (gluteal-femoral) may be protective. Current research investigations are focused on analyzing the metabolic properties of adipose tissue, in order to better understand the mechanisms that regulate fat distribution in both men and women. This review will highlight the adipose tissue depot- and sex-dependent differences in white adipose tissue function, including adipogenesis, adipose tissue developmental patterning, the storage and release of fatty acids, and secretory function. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Stress and obesity as risk factors in cardiovascular diseases: a neuroimmune perspective

Obesity is now growing at an alarming rate reaching epidemic proportions worldwide thus increasing morbidity and mortality rates for chronic disease. But although we have ample information on the complications associated with obesity, precisely what causes obesity remains poorly understood. Some evidence attributes a major role to a low-grade chronic inflammatory state (neurogenic inflammation) induced in obesity by inflammatory mediators produced and secreted within the expanded activated adipocyte pool. Adipose tissue is an endocrine organ that secretes numerous adipose tissue-specific or enriched hormones, known as adipokines, cytokine-like molecules thought to play a pathogenic role in cardiovascular diseases. The imbalance between increased inflammatory stimuli and decreased anti-inflammatory mechanisms may depend on chronic stress. Hence the positive correlation found between stress, obesity and cardiovascular diseases. The chronic inflammatory state associated with insulin resistance and endothelial dysfunction is highly deleterious for vascular function. This review focuses on the proposed neuroimmunodulatory mechanisms linking chronic (psychological) stress, obesity and cardiovascular diseases.

Macrophage-induced adipose tissue dysfunction and the preadipocyte: should I stay (and differentiate) or should I go?

Adipose tissue can be regarded as a multidepot organ responsible for metabolic homeostasis by managing sophisticated energy transactions as well as by producing bioactive molecules that regulate insulin sensitivity and immune and vascular responses. Chronic nutrient excess expands adipose tissue, and concomitant variations in its cellular and matrix remodeling can affect the extent of the metabolic dysfunction that is associated with obesity. Preadipocytes, also termed adipose progenitor cells, play a pivotal role in determining whether a dysfunctional hypertrophic state arises as opposed to a hyperplastic process in which mature adipocytes remain relatively responsive. Obesity is associated with infiltration of macrophages, and these immune cells have been shown to communicate with preadipocytes to influence how they differentiate, survive, and proliferate. Understanding macrophage-preadipocyte interactions and their effect on adipose remodeling mechanisms may identify potential therapeutic molecular targets to improve adipose tissue function, even in the face of obesity.

A modified protocol to maximize differentiation of human preadipocytes and improve metabolic phenotypes

Adipose stromal cells proliferate and differentiate into adipocytes, providing a valuable model system for studies of adipocyte biology. We compared differentiation protocols for human preadipocytes and report on their metabolic phenotypes. By simply prolonging the adipogenic induction period from the first 3 to 7 days, the proportion of cells acquiring adipocyte morphology increased from 30-70% to over 80% in human subcutaneous preadipocytes (passages 5-6). These morphological changes were accompanied by increases in the adipogenic marker expression and improved adipocyte metabolic phenotypes: enhanced responses to β-adrenergically stimulated lipolysis and to insulin-stimulated glucose metabolism into triglyceride (TG). Confirming previous studies, fetal bovine serum (FBS) dose-dependently inhibited adipogenesis. However, in subcutaneous preadipocytes that differentiate well (donor-dependant high capacity and subcultured fewer than two times), the use of 7d-induction protocols in both 3% FBS and serum-free conditions allowed >80% differentiation. Responsiveness to β-adrenergically stimulated lipolysis was lower in 3% FBS. Rates of insulin-stimulated glucose uptake were higher in adipocytes differentiated with 3% FBS, whereas the sensitivity to insulin was almost identical between the two groups. In summary, extending the length of the induction period in adipogenic cocktail improves the degree of differentiation and responses to key metabolic hormones. This protocol permits functional analysis of metabolic phenotypes in valuable primary human adipocyte cultures through multiple passages.