EP2576770A1 - Method for culturing adipocytes - Google Patents

Abstract

The present invention relates to a method for culturing adipocytes, in which a homogeneous population of mature adipocytes isolated from adipose tissue is cultured on a three-dimensional culture substrate.

Description

 PROCESS FOR CULTIVATION OF ADIPOCYTES

Field of the invention

 The invention relates to a method of culturing adipocytes, a culture of adipocytes, and its use for the screening of compounds modulating adipocyte metabolism.

Technical background

The prevalence of obesity, associated with hypertrophy of white adipose tissue, is steadily increasing in the general population. Thus, the proportion of overweight or obese people increased from 36.7% to 41.6% between 1997 and 2003 in France, in addition, the prevalence of obesity (defined by a higher body mass index (BMI) 30 kg / m ² ) is 14.5% in 2009. In addition, obesity is a risk factor for many pathological disorders, including cardiovascular events, making it all the more urgent for its therapeutic management. .

 If the main axes of fight against this epidemic remain the improvement of the food and the increase of the physical expenditure of the obese individuals, other approaches, in particular surgical and medicinal ones are also explored.

 The current drug approaches are mainly aimed at reducing energy intake, for example by limiting the intestinal absorption of lipids (orlistat), or by decreasing the appetite, either by promoting the feeling of satiety (sibutramine), or by decreasing the pleasure associated with food intake (rimonabant).

However, the limited effectiveness of these methods or their side effects - it has been reported that rimonabant could cause severe depressive disorders - have notably led to the withdrawal of sibutramine and rimonabant from the market, leaving very limited therapeutic options and making it necessary to explore other ways, for example to modulate the metabolism of adipocyte cells to limit the storage of lipids or otherwise promote their use. The latter pathway, however, is made difficult to approach by the absence of in vitro models or animal studies of adipocyte metabolism truly representative of the in vivo situation in humans.

 Indeed, in the case of in vitro models, mature adipocyte cells, in particular characterized by the presence of a single lipid vacuole, which form the white adipose tissue, are particularly fragile and, in fact, these cells generally lose in less than 48 h their metabolic and secretory properties in culture.

 Several cropping systems have been proposed to overcome these difficulties. However, these cultures include additional cell types in addition to adipocytes, such as pre-adipocytes or endothelial cells (Sonda et al., (2008) Endocrinology 149: 4794-4798), or generally using adipocytes. differentiated in vitro from stem cells (Choi et al, (2010) Tissue Engineering: Part C, Kang et al (2007) Biomaterials 28: 450-458) or pre-adipocytes (Daya et al (2007) Differentiation 75: 360-370, WO 2007/113591, Stacey et al (2009) Tissue Engineering: Part A 15: 3389-3399), whose phenotype is relatively remote from that of mature adipocytes isolated from adipose tissue (see FIGS. 1 to 3).

 Thus, these systems do not appear to be specifically and directly representative of the metabolism of mature adipocytes isolated from adipose tissue.

 It is therefore an object of the present invention to provide such a culture system, close to physiology, especially human.

Summary of the invention

 The present invention results from the unexpected finding by the inventors that mature adipocytes isolated from adipose tissue could be cultured, in the absence of other cell types, using a three-dimensional culture support and that the adipocytes thus cultured retain for at least 48 hours a phenotype similar to that of freshly isolated mature adipocytes.

The present invention thus relates to a method of culturing adipocytes, wherein a homogeneous population of mature adipocytes isolated from adipose tissue is cultured on a three-dimensional culture support. The present invention also relates to an adipocyte culture, comprising a monoculture of mature adipocytes isolated from adipose tissue in contact with a three-dimensional culture support.

 The invention also relates to the use of an adipocyte culture according to the invention, for the screening of compounds modulating adipocyte metabolism.

 The invention also relates to a method for screening compounds that modulate adipocyte metabolism, in which:

 a compound to be screened is contacted with a culture of adipocytes according to the invention;

 it is determined whether at least one representative parameter of the adipocyte metabolism of the adipocyte culture is modified with respect to a culture of adipocytes according to the invention which has not been brought into contact with the compound to be screened;

 the compound is selected if it modifies at least one representative parameter of the adipocyte metabolism.

Detailed description of the invention

As used herein, the term "mature adipocytes" represents differentiated adipocytes. The mature adipocytes can be easily identified by those skilled in the art. In particular, a mature adipocyte according to the invention usually has a single lipid vacuole, a lipolytic activity, in particular inducible by β-adrenergic agents, such as adrenaline and norepinephrine, as well as an insulin sensitivity, in particular particular defined by insulin-inducible transport, from the extracellular medium to the intracellular medium, glucose and fatty acids, which transport is particularly related to the insulin-dependent translocation, within the plasma membrane of mature adipocytes, GLUT-4 and CD36 carriers respectively. The mature adipocytes according to the invention are distinguished in particular from pre-adipocytes, in particular in that the expression of the specific marker of the pre-adipocytes DelK1 / Prefl, well known to those skilled in the art, which can be measured by PCR in time. real, is essentially absent in mature adipocytes according to the invention. The mature adipocytes according to the invention are isolated from adipose tissue. Thus, mature adipocytes according to the invention are especially such that they do not come from the in vitro differentiation of adipocyte precursors, such as pre-adipocytes or stem cells, totipotent, multipotent, or pluripotent.

 As regards the adipose tissue according to the invention, it can come from any animal species. However, it is preferred that the adipose tissue according to the invention has been removed from one or more human individuals.

 The mature adipocytes can be isolated from adipose tissue by many methods well known to those skilled in the art, taking particular advantage of the low density of mature adipocytes. In particular, the adipose tissue can be treated with collagenase, then after digestion, be filtered on woven cotton gauze; the filtrate is left to decant in an aqueous medium and a homogeneous population of mature adipocytes according to the invention can be recovered by harvesting the floating cells.

As used herein, "a homogeneous population of mature adipocytes" is especially such ^that it is substantially free ^of other cell types, including endothelial cells, or preadipocytes. In particular, a homogeneous population of mature adipocytes according to the invention comprises less than 10%, more particularly less than 5% of cells other than mature adipocytes, in particular pre-adipocytes. The amount of pre-adipocytes in a homogenous population of mature adipocytes can be determined by quantifying the number of cells expressing a specific preadipocyte marker, such as DelK1 / Prefl for example.

 As used herein, a "mature adipocyte monoculture" is a culture of a homogeneous population of mature adipocytes.

A homogeneous population of mature adipocytes is said to be "cultured" or "cultured" when it is incubated, that is to say preserved in vitro, under conditions allowing the survival of the cells constituting the population. Such conditions as well as suitable culture media are well known to those skilled in the art. These culture media are such that they contain all the elements, in particular nutrients, capable of ensuring the survival of the cells constituting the population for at least 12 hours, preferably at least 24 hours, more preferably at least 48 h. For example, the population can be incubated in a DMEM / F12 medium, 1% Penicillin-Streptomycin, 50 nM Insulin, with stirring, at 37 ° C. and in an atmosphere at 5% C0 ₂ , the medium being regularly renewed. . Advantageously, the mature adipocyte culture media according to the invention may comprise compounds intended to modulate the metabolic activity of mature adipocytes, such as forskinin and dexamethasone, for example. Moreover, the culture of the mature adipocyte population is preferably carried out for at least 3 h, 6 h, 12 h, 24 h, or 48 h.

 According to the invention, the mature adipocytes are "cultured on a three-dimensional culture support" when the adipocytes are in contact with the support, ie they rest on the support or they adhere to the support.

 In a particular embodiment, the method for culturing adipocytes according to the invention comprises the following steps:

 contacting a homogeneous population of adipocytes with a three-dimensional culture support;

 incubate the mature adipocytes in contact with the culture medium, in particular under conditions allowing the survival of the cells, in particular for at least 48 hours.

 A "three-dimensional culture support" according to the invention consists of a material, in particular biocompatible, adapted to obtain a three-dimensional cell culture; in other words, the three-dimensional culture support is adapted, in particular, to obtaining several layers of superposed cells. Thus, a culture support allowing only the culture of a two-dimensional cellular mat, namely a monolayer of cells, is not a three-dimensional culture support according to the invention.

Preferably, the three-dimensional culture support according to the invention is a hydrogel. More preferably, the three-dimensional culture support according to the invention is a hydrogel formed from the non-covalent association of peptides comprising from 10 to 30 residues, such as peptides comprising a repetition of the RADA sequence, and in particular a RADARADARADARA-DA sequence. (SEQ ID NO: 11). The peptides forming the hydrogel can be modified, for example by the addition of acetyl groups on the N-terminus of the peptides and by the addition of a group -N¾ at the C-terminus of the peptides. Thus, the peptides can be represented by the sequence: Ac-RADA-RADARADARADA-CONH ₂ . More preferably, the three-dimensional culture carrier according to the invention is ^the hydrogel PuraMatrix ™ (3DM, Inc.).

The compounds which can be screened according to the invention can be of any type. In particular, they may be compounds from chemical libraries. Moreover, the culture of adipocytes according to ^the invention can be used to screen compounds activating lipolysis, or compounds activating PPARy2 transcription factor; or compounds that modulate insulin sensitivity.

 As used herein, lipolysis (or lipolytic activity), insulin sensitivity, or activity of the PPARγ2 transcription factor, are representative parameters of adipocyte metabolism.

 The determination of lipolysis can be carried out by many methods well known to those skilled in the art. In particular, lipolytic activity can be determined by measuring the amount of glycerol and free fatty acids released by an adipocyte culture according to the invention, in particular by spectrophotometry as described in Lacasa et al. (1991) Endocrinology 128: 747-753. The insulin sensitivity of adipocytes can be evaluated from the measurement of glucose transport in the adipocyte as described in Wood et al. (2007) B toc hem. Biophys. Res. Common. 361: 468-473. The activity of the transcription factor PPARy2 can be measured by determining the amount of mRNA encoding it in a cell, for example by RT-PCR or by direct measurement of the binding activity at its specific DNA sites, such as is described in particular in Keophiphath et al. (2009) J. Nutr. 139: 2055-2060.

Description of figures

Figures 1, 2 and 3

Figures 1 to 3 respectively represent the level of relative expression (ordinate axis, arbitrary units) measured by real-time PCR of three specific markers of mature adipocytes, namely PPARy2, FABP4 (a fatty acid transporter whose gene is a target of PPARy2), and an adipokine, adiponectin, in mature adipocytes freshly isolated from adipose tissue on the one hand (black bars) and in adipocytes obtained by in vitro differentiation of pre-adipocytes as described in Lacasa et al. Endocrinology 148: 868-877, on the other hand ( white bars).

Figure 4

4 shows a cell lysates immunoelectrophoresis gel prepared from ^mature adipocytes maintained in culture on the three-dimensional support for 48 hours (3D) and freshly isolated mature adipocytes (J0) then labeled using an antibody directed against the adipocyte marker aP2 / FABP4 and an antibody directed against a positive control (actin).

Figures 5 and 6

Figures 5 and 6 show levels of lipolytic activity (y-axis in arbitrary units) basal and stimulated by forskolin (FK) ^of mature adipocytes grown (i) in the three-dimensional culture substrate (3D) in the absence (white bars) and in the presence of dexamethasone (Dex) (black bars), and (ii) in monolayers (2D) (shaded bars), depending on the culture time (x axis, in days). The experiment presented is representative of a set of three replicated experiments.

Figures 7 and 8

 Figures 7 and 8 respectively represent the secreted amounts of leptin and adiponectin (y-axis, in μg / ml / 24h) by mature adipocytes cultured in the three-dimensional culture support (3D) in the absence (white bars) and in the presence of dexamethasone (Dex) (black bars). The experiment presented is representative of a set of three replicated experiments.

Figure 9

FIG. 9 represents the relative gene expression of adipocyte markers (ordinate axes, arbitrary units) measured by real-time PCR from extracts of freshly isolated mature adipocytes (black bars) and mature adipocytes. maintained for 48 hours in culture in the three-dimensional culture support (white bars).

Figure 10

Figure 10 shows a cell lysates immunoelectrophoresis gel prepared from mature adipocytes maintained in culture on the three-dimensional support for 48 hours (3D) and freshly isolated mature adipocytes (2D) incubated in the presence ^of insulin (1 nM) at the indicated times then labeled with an antibody directed against the phosphorylated form of Akt and an antibody directed against a positive control (actin).

Examples

A. Materials and Methods

1. Materials

 The BDTM Puramatrix ™ peptide hydrogel is obtained from BD Biosciences (Two Oak Park, Bedford, MA, USA).

 The primary anti-caveolin-1 (N-20, SC-894) and antiCD36 (1.BB.3414, CS-70642) antibodies used are from Santa Cruz Biotcchnology (Santa Cruz, CA, USA). The corresponding Cy3-coupled antibodies are obtained from GE Healthcare (Little Chalfont, UK).

2. Preparation of isolated mature adipocytes

 The mature adipocytes are isolated by collagenase treatment of human adipose tissue. The subcutaneous human adipose tissue of young (<45 years old) and non-obese (BMI <30) women is cut out of digestion media (DMEM, 2% low fatty acid albumin (A6003, Sigma St Louis, MI, USA). ), 1 mg / ml collagenase A (Roche Diagnostics, Mannheim, Germany) in the proportion of 1 g of tissue per 2 ml of digestion medium in polypropylene tubes The tubes are placed at 37 ° C. for 30 minutes with shaking (200 cycles / minute) After digestion, the medium is filtered on woven cotton gauze The mature adipocytes are allowed to settle by flotation for 5 minutes and then washed 3 times with 5 volumes of sucrose 10% At the end of the last washing, the sucrose is withdrawn and the mature adipocytes are ready to be incorporated into the Puramatrix ™ hydrogel.

3. Preparation of the hydrogel containing the mature adipocytes

As recommended by the manufacturer, the hydrogel is sonicated for 30 minutes to reduce its viscosity. The gel is then diluted V / V with 20% sucrose and then centrifuged for 5 minutes at 1000 g to remove the air bubbles. The washed mature adipocytes are rapidly incorporated into this mixture with homogenization by gentle suction with the pipette. The adipocytes / gel mixture is then distributed in the proportion of 100 μl · per well in 96-well culture plates. Very rapidly, the incubation medium (150 μl) (DMEM / F12, 1% Penicillin-Streptomycin, 50 nM Insulin) (DMI) is added to the wells and the plates placed in an incubator at 37 ° C. under a 5% atmosphere. of C0 ₂ . After 30 minutes, the DMI medium is renewed. The change of medium is repeated twice. The next day, the medium DMI is changed and this operation is renewed every day. In some experiments, DMI contains 100 nM dexamethasone (Sigma Aldricht, St. Louis, MO, USA) or 100 nM rosiglitazone (Merck, Nottingham, UK).

4. Measurement of lipolvetic activity

Wells containing all hydro gel / adipocytes are washed once with 150 medium μΐ _^ Krebs Ringer (115 mM NaCl, 4.7 mM KC1, 1.2 mM CaCl _2, 1, 2 m M KH ₂ P0 ₄ , 1, 2 mM MgSO ₄ , 20 m NaHCO ₃ ), 5 m M glucose, 3% albumin low in fatty acids (KRB / ALB) to balance the hydrogel. 100 μl of RB / ALB containing either 0.1% DMSO or 10 μΜ Forskolin (Sigma) are distributed in the wells. The plates are then placed in the incubator for 4 hours. The medium is removed and placed for 10 minutes at 70 ° C in order to inactivate the adipocyte enzymes that can interfere with the glycerol assay. The glycerol released is assayed spectrophotometrically (Glycerol Assay Kit, R-Biopharm) as described in Lacasa et al. (1991) Endocrinology 128: 747-753.

5. Measurement of adipokine secretion

 The DMI medium is taken 24 hours after the last change of medium.

The dosage of adipokines (leptin, adiponectin) is carried out directly on this medium (100 μl) by the ELISA technique (Duoset, R & D Systems, Minneapolis, MN USA) as described by the manufacturer.

6. Measurement of gene expression

The DMI medium is rapidly removed from the wells and the gel / adipocyte assembly is homogenized by the lysis buffer in the proportion of 1 ml of lysis buffer / lml of gel / adipocyte assembly. The RNAs are then extracted with chloroform delipidation treatment beforehand using the RNeasy extraction kit. (Qiagen, Courtaboeuf, France) as described in Lacasa et al. (2007) Endocrinology 148: 868-877. The total (1 μ ") RNAs are then transcribed into cDNA as described in Lacasa et al. (2007) Endocrinology 148: 868-877. The list of primers used is shown in Table 1. The PCR test in real time are performed with 25ng ^cDNA and forward and reverse primers using the universal PCR mixture Sybergreen (Applied Biosystems, Minneapoîis, MN USA) and measured in a detection device (Applied Biosystems). All values are normalized to RPLPO ribosomal protein expression.

 Table 1: Primers used

7. ^Techniques immunotluorcsccnce

After removal of the DMI medium and washing with PBS, the gel / adipocyte assembly is deposited in wells of 96-well plates and fixed with 4% paraformaldehyde (PAF) for 1 hour. After inactivation of the PAF by treatment with PBS / 0.1 M glycine buffer, the cells are permeabilized for 5 minutes at room temperature with 0.1% Triton X-100 in PBS / 3% albumin. Non-specific sites are blocked by PBS / 3% albumin buffer for 4 hours at room temperature, then primary antibodies are added and incubation is continued for 14 hours at 4 ° C. After 6 washes (1 hour), the gel / adipocyte assembly is incubated with the secondary antibodies for 4 hours at room temperature in the dark. The gel / adipocyte assembly is then washed (1 hour) and fragments of this gel are deposited in mounting medium (Fluomount, Birmingham, Alabama, USA) between blade and lamellae. The slides are examined in fluorescence after 24 hours.

8. ^Techniques immune clectrophorèsc

 After removal of the DMI medium and washing with PBS, the gel / adipocyte assembly is rapidly lysed with a volume of lysis buffer (PBS, 2% IGEPAL, 0.2% SDS, 1% sodium desoxycholate) containing a mixture of protease inhibitors and phosphatases (Complete mini and Phosphostop, Roche diagnoses). The homogenate is then kept 15 minutes at 4 ° C. and then centrifuged for 10 minutes at 5000 g. The cell lysate is then collected and diluted in Laemmli buffer and electrophoresed as described in Lacasa et al. (2007) Endocrinology 148: 868-877. After transfer of the proteins on cellulose membrane, Ponceau red staining allows to check the load and the quality of the transfer. The membranes are then incubated with the primary antibodies at 4 ° C for 14 hours. Then, after washing, the membranes are incubated with the secondary antibodies (GE Healthcare, Littlc Chai font, U). The signals are detected by chemiluminescence (ECL Detection, GE Healthcare) and quantified by densitometry.

9. Measurement of insulin sensitivity

Wells containing Phydro gel / déprivés adipocytes insulin standby times are incubated with ^incubation medium (150 (DMEM / F 12 and 10 nM Insulin). The plates are then placed in the incubator for 15 to 30 minutes. The gel / adipocytes is rapidly lysed with a volume of lysis buffer (PBS, 2% IGEPAL, 0.2% SDS, 1% sodium deoxycholate) containing a mixture of protease inhibitors and phosphatases (Complete mini and Phosphostop, Roche diagnostics) The homogenate is then kept 15 minutes at 4 ° C and then centrifuged for 10 minutes at 5000 g. The lysate is then collected and diluted in Laemmli buffer and electrophoresed as previously described. The membranes are then incubated with the primary antibodies respectively against the phosphorylated form of Akt at Ser ⁴⁷³ (ref G7441 Promega) or against actin (positive control) (MAB1501R, Millipore) at 4 ° C for 14 hours. . After washing, the membranes are incubated with the secondary antibodies (GE Healthcare, Little Chalfont, UK). The signals are detected by chemiluminescence (ECL detection, GE Healthcare) and quantified by densitometry.

B. Results

1. Homogeneity of the mature adipocyte population

 The proportion of contaminating pre-adipocytes present in the mature adipocyte population isolated from adipose tissue used for culture was determined by measuring the real-time PCR expression of the pre-adipocyte specific Del 1 / Prefl marker.

 This measurement shows that the mature adipocyte population used is essentially homogeneous, since it comprises less than 5% of preadipocytes (approximately 4%).

2. Detection of adipocyte proteins

 The mature adipocytes cultured in the three-dimensional support formed by the hydrogel do indeed exhibit a unilocular appearance after immunofluorescence labeling of the CD36 and caveolin-1 membrane proteins, which demonstrates the possibility of detecting membrane adipocyte proteins. Moreover, the adipocyte lysates can be analyzed by immunoelectrophoresis as shown by the detection of the cytosolic adipocyte protein aP2 / FABP4 and actin (FIG. 4),

3. Lipolytic activity

^The lipolytic activity is measured in terms basalcs conditions and stimulated with 10 μΜ forskolin in mature adipocytes maintained in the hydrogel for 7 days. This activity is also compared to that of the same freshly isolated cells. The results presented in Figures 5 and 6 show that the basal lipophilic activity (Figure 5) and forskolin-stimulated (Figure 6) is of the same order as that of freshly isolated adipocytes and remains constant for 5-7 days. Moreover, the presence of dexamethasone (synthetic glucocorticoid) in the culture medium does not modify the basal and stimulated activities.

4. Secretion of adipokines: adiponectin and leptin

 The secretion of adiponectin (FIG. 7) and leptin (FIG. 8) is measured up to 7 days of maintenance of the mature adipocytes in the hydrogel, in the presence or absence of dexamethasone (synthetic glucocorticoid). Moreover, as shown in FIG. 7, the secretion of leptin decreases during the culture in the absence of dexamethasone whereas this secretion increases in the presence of the glucocorticoid, thus demonstrating that the response to these hormones remains functional in the adipocytes in culture. . The secretion of adiponectin remains constant for 7 days (Figure 8).

5. Gene expression of adipocytes

 The expression of adipoeye genes is compared between freshly isolated mature adipocytes and the same cells maintained for 2 days in hydrogel. Figure 9 shows that the expression of adipokines (leptin and adiponectin), the major adipocyte transcription factor PPARy2 and its target genes aP2 / FABP4 and LPL remains constant.

6. Measurement of insulin sensitivity

Adipocytes are a prime target for insulin, a major anabolic hormone. In human adipocytes, insulin stimulates glucose consumption leading to increased synthesis of triglycerides and on the other hand inhibits the degradation of these lipids. The Akt enzyme transmits the metabolic effects of insulin which causes its activation by phosphorylation of the 473 seine (Ser ⁴⁷³ Akt). Thus, the phosphorylation level of Akt constitutes an index of insulin sensitivity of the cells.

Insulin (10 nM) stimulates phosphorylation of Akt in an identical manner in freshly isolated (2D) adipocytes and those maintained for 48 h in the hydrogel (3D) thus indicating a good maintenance of the insulin response. of these cells (Figure 10). conclusions

 The mature adipocytes maintained in a three-dimensional hydrogel culture medium with an incubation medium, which can be supplemented with glucocorticoids and thiazolinidinediones, exhibit lipolytic and secretion activity of adipokines (leptin and adiponectin) comparable to those of freshly isolated adipocytes. In addition, mature adipocytes maintained in the hydrogel retain for at least 7 days the ability to respond to glucocorticoids, hormones crucial for adipocyte metabolism and development (Macfarlane et al (2008) J. Endocrinol 197: 189-204). ).

 Thus, this system can be used for the screening of pharmacological compounds having lipolytic activities or adipo-specific transcription factor activation PPARγ2, for example.

Furthermore, the inventors have shown that mature adipocytes maintained in three-dimensional culture carrier ^hydrogel according Γ invention retain at least 2 days their insulin sensitivity compared to freshly isolated mature adipocytes. This confirms that the culture ^of adipocyte according Γ invention is a model representative of the mature adipocytes in vivo.

Claims

1. A method of adipocyte culture, wherein a homogeneous population ^of mature adipocytes isolated from adipose tissue is cultured on a three-dimensional culture carrier. 2. A method of culturing adipocytes according to claim 1, wherein the three-dimensional culture support is a hydro el. The method of culturing adipocytes according to claim 1 or 2, wherein the three-dimensional culture support is a hydrogel formed from the non-covalent association of peptides comprising from 10 to 30 residues. The adipocyte culture method according to claim 3, wherein the peptides comprise the sequence R-A-D-A-R-A-D-A-R-A-D-A-R-A-D-A (SEQ ID NO: 11). 5. A method of culturing adipocytes according to one of claims 1 to 4, wherein the adipose tissue has been removed from one or more human individuals. 6. Culture of adipocytes, comprising a mature adipocytes monoculture isolated from adipose tissue in contact ^with a three-dimensional culture carrier as defined in one of claims 1 to 3. The adipocyte culture of claim 6, wherein the adipose tissue has been removed from one or more human individuals. 8. Use ^of a culture ^of adipocytes as defined in claim 6 or 7 for the screening of compounds modulating adipocyte metabolism. Use of an adipocyte culture according to claim 8 for the screening of compounds activating lipolysis. Use of an adipocyte culture according to claim 8 for screening of compounds activating the PPARγ2 transcription factor.