We thank Daniel Mondrag&#243;n, Antonio Prado, Fernando L&#243;pez-Barrera, Mart&#237;n Garc&#237;a-Serv&#237;n, Alejandra Castilla, and Mar&#237;a Antonieta Carbajo for their technical assistance, and Jessica Gonzalez Norris for critically editing the manuscript. This protocol was supported by Consejo Nacional de Ciencia y Tecnolog&#237;a de M&#233;xico (CONACYT), Fondo Sectorial de Investigacio&#769;n para la Educacio&#769;n&#160;Grant 284771 (to Y.M.).

All rodent experiments were approved by the Bioethics Committee of the Institute of Neurobiology of the UNAM, protocol number 075.
1. Isolation of mouse adipocyte precursor cells
<ol>
	<li>Euthanize 8-10-week-old male C57BL/6 mice (e.g., by CO2&#160;inhalation and subsequent cervical dislocation) (four animals per isolation). Disinfect the mice by rubbing with 70% ethanol and obtain the adipose tissue immediately after sacrifice. 
	NOTE: After the euthanasia ...

<ol>
	<li>Elmus, G. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insulin+signaling+and+insulin+resistance.">Insulin signaling and insulin resistance.</a> Journal of Investigative Medicine. 61 (1), 11-14 (2013).</li><li>Kasuga, M., Zick, Y., Blithe, D. L., Crettaz, M., Kahn, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insulin+stimulates+tyrosine+phosphorylation+of+the+insulin+receptor+in+a+cell-free+system.">Insulin stimulates tyrosine phosphorylation of the insulin receptor in a cell-free system.</a> Nature. 298 (5875), 667-669 (1982).</li><li>Kasuga, M., Karlsson, F. A., Kahn, C. 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E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Why+does+obesity+cause+diabetes.">Why does obesity cause diabetes.</a> Cell Metabolism. 34 (1), 11-20 (2022).</li><li>Lo, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+in+vitro+insulin-resistance+models+and+their+physiological+relevance+to+in+vivo+diet-induced+adipose+insulin+resistance.">Analysis of in vitro insulin-resistance models and their physiological relevance to in vivo diet-induced adipose insulin resistance.</a> Cell Reports. 5 (1), 259-270 (2013).</li><li>Asterholm, I. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adipocyte+inflammation+is+essential+for+healthy+adipose+tissue+expansion+and+remodeling.">Adipocyte inflammation is essential for healthy adipose tissue expansion and remodeling.</a> Cell Metabolism. 20 (1), 103-118 (2014).</li><li>Hotamisligil, G. S., Murray, D. L., Choy, L. N., Spiegelman, B. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumor+necrosis+factor+alpha+inhibits+signaling+from+the+insulin+receptor.">Tumor necrosis factor alpha inhibits signaling from the insulin receptor.</a> Proceedings of the National Academy of Sciences. 91 (11), 4854-4858 (1994).</li><li>Ruan, H., Hacohen, N., Golub, T. R., Parijs, L. V., Lodish, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumor+necrosis+factor-&#945;+suppresses+adipocyte-specific+genes+and+activates+expression+of+preadipocyte+genes+in+3T3-L1+adipocytes.+Nuclear+factor-&#954;B+activation+by+TNF-&#945;+is+obligatory.">Tumor necrosis factor-&#945; suppresses adipocyte-specific genes and activates expression of preadipocyte genes in 3T3-L1 adipocytes. Nuclear factor-&#954;B activation by TNF-&#945; is obligatory.</a> Diabetes. 51 (5), 1319-1336 (2002).</li><li>Boucher, J., Kleinridders, A., Kahn, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insulin+receptor+signaling+in+normal+and+insulin-resistant+states.">Insulin receptor signaling in normal and insulin-resistant states.</a> Cold Spring Harbor Perspectives in Biology. 6 (1), 009191 (2014).</li><li>Hotamisligil, G. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=IRS-1-mediated+inhibition+of+insulin+receptor+tyrosine+kinase+activity+in+TNF-alpha-+and+obesity-induced+insulin+resistance.">IRS-1-mediated inhibition of insulin receptor tyrosine kinase activity in TNF-alpha- and obesity-induced insulin resistance.</a> Science. 271 (5249), 665-668 (1996).</li><li>Copps, K. D., White, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+insulin+sensitivity+by+serine/threonine+phosphorylation+of+insulin+receptor+substrate+proteins+IRS1+and+IRS2.">Regulation of insulin sensitivity by serine/threonine phosphorylation of insulin receptor substrate proteins IRS1 and IRS2.</a> Diabetologia. 55 (10), 2565-2582 (2012).</li><li>Gassmann, M., Grenacher, B., Rohde, B., Vogel, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantifying+western+blots:+pitfalls+of+densitometry.">Quantifying western blots: pitfalls of densitometry.</a> Electrophoresis. 30 (11), 1845-1855 (2009).</li><li>Skurk, T., Hauner, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primary+culture+of+human+adipocyte+precursor+cells:+expansion+and+differentiation.">Primary culture of human adipocyte precursor cells: expansion and differentiation.</a> Methods in Molecular Biology. 806, 215-226 (2012).</li><li>Hausman, D. 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M., Tchkonia, T., Pirtskhalava, T., Han, J., Karagiannides, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adipogenesis+and+aging:+does+aging+make+fat+go+MAD.">Adipogenesis and aging: does aging make fat go MAD.</a> Experimental Geronotology. 37 (6), 757-767 (2002).</li><li>Guo, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aging+results+in+paradoxical+susceptibility+of+fat+cell+progenitors+to+lipotoxicity.">Aging results in paradoxical susceptibility of fat cell progenitors to lipotoxicity.</a> American Journal of Physiology. Endocrinology and Metabolism. 292 (4), 1041-1051 (2007).</li><li>Ruan, H., Hacohen, N., Golub, T. R., Van Parijs, L., Lodish, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=F.Tumor+necrosis+factor-a+suppresses+adipocyte-specific+genes+and+activatesexpression+of+preadipocyte+genes+in+3T3-L1+adipocytes:+nuclear+factor-kappaB+activation+by+TNF-a+is+obligatory.">F.Tumor necrosis factor-a suppresses adipocyte-specific genes and activatesexpression of preadipocyte genes in 3T3-L1 adipocytes: nuclear factor-kappaB activation by TNF-a is obligatory.</a> Diabetes. 51 (5), 1319-1336 (2002).</li><li>Jager, J., Gre &#769;meaux, T., Cormont, M., Le Marchand-Brustel, Y., Tanti, J. 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This paper provides a method for studying insulin resistance that uses primary adipocytes in culture treated with TNF-&#945;. This model has the advantage that primary adipocytes can be cultured under defined conditions for long periods of time with a tight control of cellular environmental factors26. The assay duration is 15-20 days, although variations in the percentage of differentiated adipocytes can occur between experiments. Primary adipocytes have advantages over cell lines since they have ...

Insulin is an anabolic hormone produced by pancreatic islet &#946;-cells and the key regulator of glucose and lipid metabolism. Among its many functions, insulin regulates glucose uptake, glycogen synthesis, gluconeogenesis, protein synthesis, lipogenesis, and lipolysis1. The initial molecular signal after insulin interaction with its receptor (IR) is the activation of the intrinsic tyrosine protein kinase activity of IR2, resulting in its autophosphorylation3&#160;and the subsequent activation of a family of proteins known as insulin receptor substrates (IRS), which binds to adaptor proteins leading to activation of a cascade of protein kinases4. Insulin activates two main signaling pathways: phosphatidylinositol 3-kinase (PI3K)-protein kinase B (AKT)&#160;and Ras-mitogen-activated protein kinase (MAPK). The former constitutes a major branch point or node4,5&#160;for the activation of numerous downstream effectors involved in diverse physiological functions, including the regulation of fuel homeostasis, whereas the latter regulates cell growth and differentiation4,6. Insulin actions ultimately depend on the cell type and physiological context7.
One of the main insulin-responsive metabolic tissues is the adipose tissue. White adipose tissue is the most abundant type of fat in humans and rodents, distributed within subcutaneous fat (between the skin and muscles) and visceral fat (around the organs in the abdominal cavity). Given their large volume, adipocytes or fat cells are the most abundant cell type in adipose tissue. These fat cells can be brown/beige (thermogenic), pink (in the mammary gland), and white8,9. White adipocytes keep the main energy reserves in the body in the form of triglycerides, an insulin-dependent process. Insulin promotes glucose transport and lipogenesis, while it inhibits lipolysis or lipid breakdown7,10. It also facilitates the differentiation of preadipocytes into adipocytes&#160;&#8212; the mature fat-storing cells11.
Insulin resistance occurs when a normal insulin level produces an attenuated biological response, resulting in compensatory hyperinsulinemia12. Insulin resistance is a condition associated with overweight and obesity5, that when combined leads to type 2 diabetes (T2D) and other metabolic diseases13. Hyperinsulinemia compensates insulin resistance in peripheral tissues to maintain normal blood glucose levels14. However, eventual &#946;-cell loss or exhaustion, together with exacerbated insulin resistance, leads to elevated blood glucose levels consistent with T2D5. Therefore, insulin resistance and hyperinsulinemia can contribute to the development of obesity-derived metabolic diseases15. Furthermore, obesity may cause chronic low-grade local inflammation promoting insulin resistance in adipose tissue15,16,17. In addition, obesity-derived alterations in adipose tissue, such as fibrosis, inflammation, and reduced angiogenesis and adipogenesis, lead to lower adiponectin serum levels (an insulin sensitizer) and increased secretion of factors such as plasminogen activator inhibitor 1 (PAI-1), free fatty acids, and exosomes into the bloodstream, exacerbating insulin resistance17.
Many aspects underlying insulin resistance remain unknown. In vitro and in vivo models have been developed to study the mechanisms mediating insulin resistance in major target tissues, including adipose tissue. The advantage of in vitro models is that researchers have more control of the environmental conditions and can evaluate insulin resistance in specific cell types. Particularly, adipocyte precursor cells (APCs) have the individual phenotype of the donor tissue, which might reflect physiology better than adipocyte cell lines. A main factor inducing insulin resistance in vitro is tumor necrosis factor-&#945; (TNF-&#945;). TNF-&#945; is a proinflammatory cytokine secreted by adipocytes and macrophages in adipose tissue18. While it is required for proper adipose tissue remodeling and expansion19, long-term exposure to TNF-&#945; induces insulin resistance in adipose tissue in vivo and in adipocytes in vitro20. Chronic TNF-&#945; treatment of several cell types leads to increased serine phosphorylation of both IR and IRS-1, thereby promoting decreased tyrosine phosphorylation21. Increased phosphorylation of IRS-1 on serine residues inhibits the IR tyrosine kinase activity and may be one of the key mechanisms by which chronic TNF-&#945; treatment impairs insulin action22,23. TNF-&#945; activates pathways involving the serine/threonine kinase inhibitor of nuclear factor &#312;B kinase &#946; (IKK&#946;) and c-Jun N terminal kinase (JNK)24. JNK induces a complex proinflammatory transcriptional program but also directly phosphorylates IRS-16.
Understanding the pathogenesis of insulin resistance has become increasingly important to guide the development of future therapies against T2D. APCs have proven to be an excellent model for the study of fat cell biology, including the sensitivity and resistance to insulin, and for identifying the intrinsic properties of adipocytes independent of the systemic environment. APCs can be easily obtained from different adipose depots, and under the appropriate conditions, differentiated into mature adipocytes. With this method, direct effects on insulin resistance/sensitivity can be evaluated in adipocytes.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1. Isolation mouse adipocyte precursor cells</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ACK lysing buffer&#160;</td>
			<td>LONZA</td>
			<td>10-548E</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Biotin Microbeads&#160;</td>
			<td>Miltenyi</td>
			<td>130-090-485</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-CD31</td>
			<td>eBioscience</td>
			<td>13-0311-85</td>
			<td></td>
		</tr>
		<tr>
			<td>AutoMACS Pro Separator</td>
			<td>Miltenyi</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Basement membrane matrix (matrigel)</td>
			<td>Corning</td>
			<td>354234</td>
			<td></td>
		</tr>
		<tr>
			<td>bFGF</td>
			<td>Sigma</td>
			<td>F0291</td>
			<td>Growth factor</td>
		</tr>
		<tr>
			<td>BSA</td>
			<td>Equitech-Bio, Inc.</td>
			<td>BAC63-1000</td>
			<td></td>
		</tr>
		<tr>
			<td>CD45 Monoclonal Antibody (30-F11) - Biotin&#160;</td>
			<td>eBioscience</td>
			<td>13-0451-85</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase, Type 1</td>
			<td>Worthington Biochem</td>
			<td>LS004197</td>
			<td></td>
		</tr>
		<tr>
			<td>Dexamethasone</td>
			<td>Sigma</td>
			<td>D1756</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>GIBCO</td>
			<td>12800017</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM low glucose</td>
			<td>GIBCO</td>
			<td>31600-034</td>
			<td></td>
		</tr>
		<tr>
			<td>EGF</td>
			<td>Peprotech</td>
			<td>315-09</td>
			<td>Growth factor</td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>GIBCO</td>
			<td>26140-079</td>
			<td></td>
		</tr>
		<tr>
			<td>ITS mix</td>
			<td>Sigma</td>
			<td>I3146</td>
			<td></td>
		</tr>
		<tr>
			<td>L-ascorbic acid 2-phosphate</td>
			<td>Sigma</td>
			<td>A8960</td>
			<td></td>
		</tr>
		<tr>
			<td>LIF</td>
			<td>Millipore</td>
			<td>ESG1107</td>
			<td>Growth factor</td>
		</tr>
		<tr>
			<td>Linoleic acid-albumin</td>
			<td>Sigma</td>
			<td>L9530</td>
			<td></td>
		</tr>
		<tr>
			<td>MCDB 201 medium</td>
			<td>Sigma</td>
			<td>M6770</td>
			<td></td>
		</tr>
		<tr>
			<td>Normocin</td>
			<td>InvivoGen</td>
			<td>ant-nr-2</td>
			<td></td>
		</tr>
		<tr>
			<td>PDGF-BB&#160;</td>
			<td>Peprotech</td>
			<td>315-18</td>
			<td>Growth factor</td>
		</tr>
		<tr>
			<td>Peniciline-Streptomycine</td>
			<td>BioWest</td>
			<td>L0022-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Pre-Separation Filters (70 &#181;m)</td>
			<td>Miltenyi</td>
			<td>130-095-823</td>
			<td></td>
		</tr>
		<tr>
			<td>Purified Rat Anti-Mouse CD16 / CD32&#160;</td>
			<td>BD Pharmingen</td>
			<td>553142</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA&#160;</td>
			<td>GIBCO</td>
			<td>25300062</td>
			<td></td>
		</tr>
		<tr>
			<td>2. Adipocyte differentiation and insulin resistance induction</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>3-Isobutyl-1-methylxanthine [IBMX]</td>
			<td>Sigma</td>
			<td>I5879</td>
			<td>Differentiation cocktail</td>
		</tr>
		<tr>
			<td>BMP4</td>
			<td>R&#38;D Systems</td>
			<td>5020-BP-010</td>
			<td>Differentiation cocktail</td>
		</tr>
		<tr>
			<td>Dexamethasone</td>
			<td>Sigma</td>
			<td>D1756</td>
			<td>Differentiation cocktail</td>
		</tr>
		<tr>
			<td>Insulin</td>
			<td>Sigma</td>
			<td>I9278</td>
			<td></td>
		</tr>
		<tr>
			<td>Rosiglitazone</td>
			<td>Cayman</td>
			<td>71742</td>
			<td>Differentiation cocktail</td>
		</tr>
		<tr>
			<td>TNF&#945;</td>
			<td>R&#38;D Systems</td>
			<td>210-TA-005&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>3. Evaluation of insulin signaling pathway by western blot</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-beta tubulin antibody</td>
			<td>Abcam</td>
			<td>ab6046</td>
			<td></td>
		</tr>
		<tr>
			<td>Bromophenol blue</td>
			<td>BioRad</td>
			<td>161-0404</td>
			<td>Laemmli buffer</td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Sigma</td>
			<td>E5134</td>
			<td>RIPA buffer</td>
		</tr>
		<tr>
			<td>EGTA</td>
			<td>Sigma</td>
			<td>E4378</td>
			<td>RIPA buffer</td>
		</tr>
		<tr>
			<td>FluorChem E system</td>
			<td>ProteinSimple</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Sigma</td>
			<td>G6279</td>
			<td>Laemmli buffer</td>
		</tr>
		<tr>
			<td>Glycine</td>
			<td>Sigma</td>
			<td>G7126</td>
			<td>Running and Transfer buffer</td>
		</tr>
		<tr>
			<td>Igepal</td>
			<td>Sigma</td>
			<td>I3021</td>
			<td>RIPA buffer</td>
		</tr>
		<tr>
			<td>2- mercaptoethanol</td>
			<td>Sigma</td>
			<td>M3148</td>
			<td>Laemmli buffer</td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>JT Baker</td>
			<td>907007</td>
			<td>Transfer buffer</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>JT Baker</td>
			<td>3624-05</td>
			<td>TBS-T</td>
		</tr>
		<tr>
			<td>NaF</td>
			<td>Sigma</td>
			<td>77F-0379</td>
			<td>RIPA buffer</td>
		</tr>
		<tr>
			<td>NaOH&#160;</td>
			<td>JT Baker</td>
			<td>3722-19</td>
			<td></td>
		</tr>
		<tr>
			<td>Na4P2O7</td>
			<td>Sigma</td>
			<td>114F-0762</td>
			<td>RIPA buffer</td>
		</tr>
		<tr>
			<td>Na3VO4</td>
			<td>Sigma</td>
			<td>S6508</td>
			<td>RIPA buffer</td>
		</tr>
		<tr>
			<td>Nitrocellulose membrane&#160;</td>
			<td>BioRad</td>
			<td>1620112</td>
			<td></td>
		</tr>
		<tr>
			<td>Nonfat dry milk</td>
			<td>BioRad</td>
			<td>1706404</td>
			<td>Blocking solution</td>
		</tr>
		<tr>
			<td>Prestained protein standard&#160;</td>
			<td>BioRad</td>
			<td>1610395</td>
			<td></td>
		</tr>
		<tr>
			<td>Protease inhibitor cocktail&#160;</td>
			<td>Sigma</td>
			<td>P8340-5ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Peroxidase AffiniPure Donkey Anti-Rabbit IgG (H+L)&#160;</td>
			<td>Jackson ImmunoResearch</td>
			<td>711-035-132</td>
			<td></td>
		</tr>
		<tr>
			<td>Phospho- Insulin Receptor &#946;&#160;</td>
			<td>Cell signaling</td>
			<td>3024</td>
			<td></td>
		</tr>
		<tr>
			<td>Phospho-Akt (Ser473) Antibody</td>
			<td>Cell signaling</td>
			<td>9271</td>
			<td></td>
		</tr>
		<tr>
			<td>Phospho-IRS1 (Tyr608) antibody</td>
			<td>Millipore</td>
			<td>9432</td>
			<td></td>
		</tr>
		<tr>
			<td>Saccharose&#160;</td>
			<td>JT Baker</td>
			<td>407205</td>
			<td>RIPA buffer</td>
		</tr>
		<tr>
			<td>SDS</td>
			<td>BioRad</td>
			<td>1610302</td>
			<td>Running and laemmli buffer</td>
		</tr>
		<tr>
			<td>SuperSignal West Pico PLUS Chemiluminescent Substrate</td>
			<td>Thermo Scientific</td>
			<td>34577</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-base</td>
			<td>Promega</td>
			<td>H5135</td>
			<td>Running, transfer and laemmli buffer</td>
		</tr>
		<tr>
			<td>Tris-HCl</td>
			<td>JT Baker</td>
			<td>4103-02</td>
			<td>RIPA buffer - TBS</td>
		</tr>
		<tr>
			<td>Tween 20</td>
			<td>Sigma</td>
			<td>P1379</td>
			<td>TBS-T</td>
		</tr>
	</tbody>
</table>

differentiated mouse adipocytes in primary culture: a model of insulin resistance

Insulin resistance is a reduced effect of insulin on its target cells, usually derived from decreased insulin receptor signaling. Insulin resistance contributes to the development of type 2 diabetes (T2D) and other obesity-derived diseases of high prevalence worldwide. Therefore, understanding the mechanisms underlying insulin resistance is of great relevance. Several models have been used to study insulin resistance both in vivo and in vitro; primary adipocytes represent an attractive option to study the mechanisms of insulin resistance and identify molecules that counteract this condition and the molecular targets of insulin-sensitizing drugs. Here, we have established an insulin resistance model using primary adipocytes in culture treated with tumor necrosis factor-&#945; (TNF-&#945;).
Adipocyte precursor cells (APCs), isolated from collagenase-digested mouse subcutaneous adipose tissue by magnetic cell separation technology, are differentiated into primary adipocytes. Insulin resistance is then induced by treatment with TNF-&#945;, a proinflammatory cytokine that reduces the tyrosine phosphorylation/activation of members of the insulin signaling cascade. Decreased phosphorylation of insulin receptor (IR), insulin receptor substrate (IRS-1), and protein kinase B (AKT) are quantified by western blot. This method provides an excellent tool to study the mechanisms mediating insulin resistance in adipose tissue.

Over the last few years, the increased prevalence of obesity and T2D has prompted an intense search for the mechanisms mediating insulin resistance in adipose tissue. With the protocol described here, APCs can be differentiated into mature adipocytes to evaluate insulin resistance and sensitivity. Once the APCs reach confluence, it takes 10 days to complete their differentiation into mature adipocytes and their TNF-&#945;-mediated induction of insulin resistance (Figure 1).
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Differentiated Mouse Adipocytes in Primary Culture: A Model of Insulin Resistance

This protocol describes the isolation of mouse preadipocytes from subcutaneous fat, their differentiation into mature adipocytes, and the induction of insulin resistance. Insulin action is evaluated by the phosphorylation/activation of members of the insulin signaling pathway through western blot. This method allows direct determination of insulin resistance/sensitivity in primary adipocytes.

Insulin resistance is a reduced effect of insulin on its target cells, usually derived from decreased insulin receptor signaling. Insulin resistance ...

Insulin resistance can be evaluated in primary adipocytes, allowing the study of donors under different physiopathological contexts, such as lean versus obese, or cells from different fat depos. Primary adipocytes retain many of their intrinsic properties and can be cultured under defined conditions for a long period of time, with a tight control of cellular environmental factors. To start the differentiation process, cells must be at 80%confluence.If differentiation starts at a lower or higher confluence, cells will differentiate less or lose their differentiation capacity. After sacrificing the animal, disinfect the mice by rubbing with 70%ethanol. Dissect the inguinal subcutaneous adipose tissue from each mouse and collect it in a 15-milliliter conical tube, containing 15 milliliters of type one collagenase solution on ice.Cut the adipose tissue into small pieces with sterile surgical scissors and digest the samples by incubation with type one collagenase solution at 37 degrees Celsius in an orbital shaker at 150 RPM for 30 minutes. Check the digestion every 10 minutes to ensure it works, and to prevent over digestion. Filter using a 200-micrometer mesh syringe to eliminate the tissue not digested with collagenase, and pass the filter over the edge of the tube to drain as many cells as possible into the solution.Add 15 milliliters of cold DMEM 1%BSA to stop digestion, and centrifuge at 400 G for 10 minutes at four degrees Celsius. Aspirate the top layer containing mature adipocytes and most of the liquid layer. Add 20 milliliters of cold PBS 2%FBS to it and resuspend the pellet.After centrifuging again for five minutes, remove the supernatant by aspirating the upper layer to eliminate the remaining adipocytes and fat. Resuspend the pellet in one milliliter of ACK lysing buffer. Incubate on ice for five minutes.Add 10 milliliters of PBS 2%FBS and mix it. After centrifuging for five minutes and aspirating the supernatant, resuspend the pellet in 200 microliters of anti-FC solution. Incubate on ice for five minutes and transfer the cell suspension to a five-milliliter tube that fits into the pre-chilled racks of a magnetic cell separator.After centrifuging for five minutes and eliminating the supernatant, add 200 microliters of the mixture of CD 31 monoclonal antibody biotin and CD 45 monoclonal antibody biotin to it. Mix well and incubate on ice for 15 minutes. Then add 400 microliters of PBS 2%FBS and centrifuge again at 400 G for five minutes at four degrees Celsius.Aspirate the supernatant and incubate it in 100 microliters of anti-biotin microbeads for 15 minutes on ice. Add 400 microliters of PBS 2%FBS and centrifuge again at 400 G for five minutes at four degrees Celsius, as shown previously. After discarding the supernatant, resuspend the pellet in 350 microliters of PBS 2%FBS.To remove the cell aggregates, or large particles, from the single cell-suspensions with a 70-micrometer pre-separation filter, activate the filter with 100 microliters of PBS 2%FBS. Pass the cell suspension through the filter, and collect it in a clean tube. Then wash the filter with 100 microliters of PBS 2%FBS.To perform magnetic separation of cells using the negative separation strategy, place the sample in position A of the chilled rack and two empty tubes in positions B and C to recover the non-labeled and labeled cells. Then load the washing buffer and running buffer into the corresponding bottles. In the separation section, select the number of samples to be separated and select the deplete protocol.Press run and start the separation. At the end of the program, recover the unlabeled cells. Next, coat a 12-well plate with basement membrane matrix by adding 400 microliters of 2.5%basement membrane matrix to cover the entire surface of each well.Remove the excess solution and let the plate dry inside the laminar flow hood for at least one hour. After centrifuging for five minutes and discarding the supernatant, resuspend the pellet in 500 microliters of growth medium. Seed the adipocyte precursor cells, or APCs, in one well of the 12-well plate previously coated with 2.5%basement membrane matrix.Incubate at 37 degrees Celsius in a 5%carbon dioxide atmosphere, and change the medium every 48 hours until the cells reach 80%confluence. After removing the medium completely, wash the cells with 350 microliters of PBS 2%FBS. Harvest the cells with 350 microliters of 0.05%tripsin EDTA for two minutes at 37 degrees Celsius, and add two milliliters of growth medium.Collect the cells in a new 50-milliliter conical tube and centrifuge at 400 G for five minutes. Passage the APCs to 12-well plates, previously coated with 2.5%basement membrane matrix, and incubate at 37 degrees Celsius with 5%carbon dioxide. Change the medium every 48 hours until cells reach 80%confluence.At 80%confluence, aspirate off any growth medium and replace it with 500 microliters of differentiation medium, containing 3.3 nanomolar bone morphogenetic protein in each well. After 48 hours, replace the medium with 500 microliters per well differentiation medium, and the differentiation cocktail. Remove the medium 72 hours later and add 100 nanomolar of insulin in 500 microliters of fresh differentiation medium.48 hours later, induce insulin resistance with four nanograms per milliliter of tumor necrosis factor alpha, or TNF alpha. Aspirate off any differentiation medium and replace it with 500 microliters of simple medium 2%FBS with TNF alpha. After incubating for 24 hours, add four nanograms per milliliter of TNF alpha in a simple medium 0%FBS.Activate the insulin signaling pathway 24 hours later by adding 100 nanomolar insulin and incubate for 15 minutes at 37 degrees Celsius in a 5%carbon dioxide atmosphere, as shown earlier. After incubation, remove the medium and wash with 500 microliters of PBS, include a control well without the insulin treatment. Extract protein and measure the phosphorylation of insulin-signaling markers by Western blot.Subcutaneous adipocyte precursor cells at 80%confluence prior to inducing differentiation in the 12-well culture plates, and primary adipocytes after seven days of inducing differentiation are shown in this figure. The insulin resistance induced by TNF alpha in subcutaneous primary adipocytes was demonstrated by decreased insulin-induced phosphorylation of insulin receptor, insulin receptor substrate one, and protein kinase B or AKT. The membrane was probed with anti-phosphorylated insulin receptor, anti-phosphorylated insulin receptor substrate one, anti-phosphorylated AKT, and anti-beta tubulin was used as a loading control.The signal was visualized with chemiluminescence detection. The representative blots and the quantification from three independent experiments are shown here. When attempting this procedure, one thing that needs to be taken care of is that the induction of insulin resistance with TNF alpha is with 2%FBS for 24 hours and with 0%FBS for the last 24 hours.

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2.1K vues.  Universidad Nacional Autónoma de México (UNAM). La résistance à l’insuline peut être évaluée dans les adipocytes primaires, ce qui permet d’étudier des donneurs dans différents contextes physiopathologiques, tels que maigre versus obèse, ou des cellules provenant de différents dépôts graisseux. Les adipocytes primaires conservent bon nombre de leurs propriétés intrinsèques et peuvent être cultivés dans des conditions définies pendant une longue période, avec un contrôle étroit des facteurs environnementaux cellulair...