We thank Danielle Berger, Marilyn Woodruff, Simone Correa, and Retha Geiss for assistance with study coordination. SEM was performed by University of Michigan Microscopy &#38; Image Analysis Laboratory Biomedical Research Core Facility. This project was supported by NIH grants R01DK097449 (RWO), R01DK115190 (RWO, CNL), R01DK090262 (CNL), Veterans Affairs Merit Grant I01CX001811 (RWO), Pilot and Feasibility Grant from the Michigan Diabetes Research Center (NIH Grant P30-DK020572) (RWO), Veterans Administration VISN 10 SPARK Pilot Grant (RWO). Scanning electron microscopy performed by the University of Michigan Microscopy &#38; Image Analysis Laboratory Biomedical Research Core Facility. Figure 4 of this manuscript was originally published in Baker et al., J Clin Endo Metab 2017; Mar 1;102 (3), 1032-1043. doi: 10.1210/jc.2016-2915, and has been reproduced by permission of Oxford University Press [https://academic.oup.com/jcem/article/102/3/1032/2836329]. For permission to reuse this material, please visit http://global.oup.com/academic/rights.

Adipose tissues are procured from human subjects undergoing elective bariatric surgery under institutional review board approval.
1. Preadipocyte isolation and culture reagent preparation
<ol>
	<li>Prepare 2% bovine serum albumin (BSA) in 1x phosphate buffered saline solution (PBS). Filter sterilize, and store at 4 &#176;C.</li>
	<li>Prepare Type II collagenase: 2 mg/mL in 2% BSA in 1x PBS. Prepare immediately before use.</li>
	<li>Prepare Red Blood Cell (RBC) Lysing Solution: 1.5 M NH4...

<ol>
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The ECM-adipocyte culture model provides a valuable tool for dissecting the individual roles of ECM and cells in dictating ultimate tissue phenotype. The ECM isolation protocol is quite reproducible, but variability in the decellularization process may be observed. The Day 3 delipidation step is a critical point in the protocol. At the completion of the overnight extraction, delipidation of the matrix should be evidenced by the Polar Solvent Solution turning yellow, while the matrix should transition from a yellow-orange...

The extracellular matrix (ECM) not only provides a mechanical scaffold for tissues, but also engages in complex crosstalk with cells that reside within it, regulating diverse processes necessary for tissue homeostasis, including cell proliferation, differentiation, signaling, and metabolism1. While healthy ECM plays an essential role the maintenance of normal tissue function, dysfunctional ECM has been implicated in multiple diseases2.
Adipose tissue plays an important role in the pathogenesis of metabolic disease. Obesity is associated with excessive adipocyte hypertrophy and cellular hypoxia, defects in adipocyte cellular metabolism, and adipose tissue endoplasmic reticulum and oxidative stress and inflammation. While poorly understood, these complex processes conspire to impair adipose tissue nutrient buffering capacity, leading to nutrient overflow from adipose tissue, toxicity in multiple tissues, and systemic metabolic disease3,4,5.The sequence of events and specific mechanisms that underlie adipose tissue failure are poorly understood, but alterations in adipose tissue ECM have been implicated. The ECM composition is altered within adipose tissue in human and murine obesity, with increased deposition of ECM protein along with qualitative biochemical and structural differences in the adipose tissue ECM associated with human metabolic disease, including type 2 diabetes and hyperlipidemia6,7,8,9,10,11.
Despite these observations, the role of adipose tissue ECM in mediating adipose tissue dysfunction is not well-defined. This is in part due to a lack of tractable experimental models that permit dissection of the specific roles of ECM and adipocytes in regulating ultimate adipose tissue function. ECM-adipocyte culture better simulates the in vivo environment of native adipose tissue in at least two respects. Firstly, ECM culture provides a molecular environment similar to native adipose tissue, including native collagens, elastins, and other matrix proteins absent in standard 2D culture. Secondly, culture on 2D plastic has been shown to alter adipocyte metabolism via mechanical effects due to decreased elasticity of plastic substrate12, which ECM-culture eliminates.
Methods to engineer biological scaffolds by isolation of ECM from decellularized adipose and other tissues have been studied in the context of regenerative and reconstructive medicine and tissue engineering13,14,15,16,17,18. We have previously published methodology in which we adapted these methods to develop an in vitro 3D model of human ECM-adipocyte culture, using ECM and adipocyte stem cells (preadipocytes) derived from human visceral adipose tissues11. In the present article, we describe these methods in detail. The decellularization procedure for human adipose tissue is a four-day process that involves mechanical and enzymatic treatments to remove cells and lipid, leaving a biological scaffold that maintains characteristics of the tissue from which it is derived. Decellularized ECM supports adipogenic differentiation of human preadipocytes, and when reconstituted with adipocytes, maintains microarchitecture and biochemical and disease-specific characteristics of intact adipose tissue and engages in metabolic functions characteristic of native adipose tissue. This matrix can be studied alone or reseeded with cells, permitting study of interactions and crosstalk between the cellular and extra-cellular components of adipose tissue.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.25% trypsin-EDTA</td>
			<td>Gibco, ThermoFisher Scientific Inc., Waltham, MA, USA</td>
			<td>Cat#25200056</td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 mL cryovial tube</td>
			<td>Fisher Scientific, ThermoFisher Scientific Inc., Waltham, MA USA</td>
			<td>Cat#02-682-557</td>
			<td></td>
		</tr>
		<tr>
			<td>10% Neutral Buffered Formalin</td>
			<td>VWR International LLC., Radnor, PA, USA</td>
			<td>Cat#89370-094</td>
			<td></td>
		</tr>
		<tr>
			<td>100 &#181;m nylon mesh filter</td>
			<td>Corning Inc., Corning, NY, USA</td>
			<td>Cat#352360</td>
			<td></td>
		</tr>
		<tr>
			<td>2-Deoxy-D-glucose</td>
			<td>Sigma-Aldrich, Inc., St Louis, MO, USA</td>
			<td>Cat#D8375</td>
			<td></td>
		</tr>
		<tr>
			<td>2 nM 3,3&#8217;-5,Triiodo,L-thyronine sodium salt (T3)</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#T6397</td>
			<td></td>
		</tr>
		<tr>
			<td>24-well tissue culture plates</td>
			<td>VWR International LLC., Radnor, PA, USA</td>
			<td>Cat#10861-700</td>
			<td></td>
		</tr>
		<tr>
			<td>3-Isobutyl-1-methylxanthine (IBMX)</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#I5879</td>
			<td></td>
		</tr>
		<tr>
			<td>96-well tissue culture plates</td>
			<td>VWR International LLC., Radnor, PA, USA</td>
			<td>Cat#10861-666</td>
			<td></td>
		</tr>
		<tr>
			<td>Antibiotic-Antimycotic Solution (ABAM)</td>
			<td>Gibco, ThermoFisher Scientific Inc., Waltham, MA, USA</td>
			<td>Cat#15240062</td>
			<td></td>
		</tr>
		<tr>
			<td>Biotin</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#B4639</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin (BSA)</td>
			<td>Sigma-Aldrich, Inc., St Louis, MO, USA</td>
			<td>Cat#A8806</td>
			<td></td>
		</tr>
		<tr>
			<td>Buffer RLT</td>
			<td>Qiagen, Hilden, Germany</td>
			<td>Cat#79216</td>
			<td></td>
		</tr>
		<tr>
			<td>Ciglitizone</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#C3974</td>
			<td></td>
		</tr>
		<tr>
			<td>Deoxy-D-glucose, 2-[1,2-3H (N)]-</td>
			<td>PerkinElmer Inc., Waltham, MA, USA</td>
			<td>Cat#NET328A250UC</td>
			<td></td>
		</tr>
		<tr>
			<td>Deoxyribonuclease I from bovine pancreas, type II-S</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#D4513</td>
			<td></td>
		</tr>
		<tr>
			<td>Dexamethasone</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#D4902</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl Sulfoxide</td>
			<td>Fisher Scientific, ThermoFisher Scientific Inc., Waltham, MA USA</td>
			<td>Cat#BP231</td>
			<td>Flammable, caustic</td>
		</tr>
		<tr>
			<td>Disodium EDTA</td>
			<td>Fisher Scientific, ThermoFisher Scientific Inc., Waltham, MA USA</td>
			<td>Cat#BP118</td>
			<td></td>
		</tr>
		<tr>
			<td>D-pantothenic acid hemicalcium salt</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#21210</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#8217;s Modified Eagle Medium: Nutrient Mixture F-12 (DMEM/F12</td>
			<td>Gibco, ThermoFisher Scientific Inc., Waltham, MA USA</td>
			<td>Cat#11320033</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Decon Labs, Inc., King of Prussia, PA, USA</td>
			<td>Cat#DSP-MD.43</td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>EVE Cell Counting Slides, NanoEnTek</td>
			<td>VWR International LLC., Radnor, PA, USA</td>
			<td>Cat#10027-446</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum (FBS)</td>
			<td>Gibco, ThermoFisher Scientific Inc., Waltham, MA, USA</td>
			<td>Cat#10437028</td>
			<td></td>
		</tr>
		<tr>
			<td>Glutaraldehyde</td>
			<td>Sigma-Aldrich, Inc., St Louis, MO, USA</td>
			<td>Cat#G5882</td>
			<td>Caustic</td>
		</tr>
		<tr>
			<td>Hexamethyldisalizane</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#440191</td>
			<td>Flammable, caustic</td>
		</tr>
		<tr>
			<td>Human insulin solution</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#I9278</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Fisher Scientific, ThermoFisher Scientific Inc., Waltham, MA USA</td>
			<td>Cat#A415</td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>Isoproterenol</td>
			<td>Sigma-Aldrich, Inc., St Louis, MO, USA</td>
			<td>Cat#I5627</td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#S25484</td>
			<td></td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#P5655</td>
			<td></td>
		</tr>
		<tr>
			<td>Lipase from porcine pancreas, type VI-S</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#L0382</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4*7H2O</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#230391</td>
			<td></td>
		</tr>
		<tr>
			<td>Na2HPO4</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#S5136</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#S3014</td>
			<td></td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Fisher Scientific, ThermoFisher Scientific Inc., Waltham, MA USA</td>
			<td>Cat#S233</td>
			<td></td>
		</tr>
		<tr>
			<td>NH4Cl</td>
			<td>Fisher Scientific, ThermoFisher Scientific Inc., Waltham, MA USA</td>
			<td>Cat#A661</td>
			<td></td>
		</tr>
		<tr>
			<td>Optimal cutting temperature (OCT) compound</td>
			<td>Agar Scientific, Ltd., Stansted, Essex, UK</td>
			<td>Cat# AGR1180</td>
			<td></td>
		</tr>
		<tr>
			<td>Oil Red-O Solution (ORO)</td>
			<td>Sigma-Aldrich, Inc., St Louis, MO, USA</td>
			<td>Cat#O1391</td>
			<td></td>
		</tr>
		<tr>
			<td>Oil Red-O Stain Kit</td>
			<td>American Master Tech Scientific Inc., Lodi, CA, USA</td>
			<td>Cat#KTORO-G</td>
			<td></td>
		</tr>
		<tr>
			<td>Osmium tetroxide</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#201030</td>
			<td>Caustic</td>
		</tr>
		<tr>
			<td>Phenylmethylsulfonyl fluoride (PMSF)</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#93482</td>
			<td>Caustic</td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline Solution (PBS)</td>
			<td>Fisher Scientific, ThermoFisher Scientific Inc., Waltham, MA USA</td>
			<td>Cat#SH3025601</td>
			<td></td>
		</tr>
		<tr>
			<td>Ribonuclease A from bovine pancreas, type III-A</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#R5125</td>
			<td></td>
		</tr>
		<tr>
			<td>RNAEasy Fibrous Tissue MiniKit</td>
			<td>Qiagen, Hilden, Germany</td>
			<td>Cat#74704</td>
			<td></td>
		</tr>
		<tr>
			<td>Scintillation Fluid</td>
			<td>Fisher Scientific, ThermoFisher Scientific Inc., Waltham, MA USA</td>
			<td>Cat#SX18</td>
			<td></td>
		</tr>
		<tr>
			<td>Scintillation Counter</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Scissors, forceps, sterile</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sorensen&#39;s phosphate buffer</td>
			<td>Thomas Scientific, Inc., Swedesboro, NJ</td>
			<td>CAS #: 10049-21-5</td>
			<td></td>
		</tr>
		<tr>
			<td>T-150 culture flask</td>
			<td>VWR International LLC., Radnor, PA, USA</td>
			<td>Cat#10062-864</td>
			<td></td>
		</tr>
		<tr>
			<td>TaqMan Gene Expression Master Mix</td>
			<td>ThermoFisher Scientific Inc., Waltham, MA USA</td>
			<td>Cat#4369016</td>
			<td></td>
		</tr>
		<tr>
			<td>Temperature-controlled orbital shaker</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue Homogenizer, BeadBug Microtube Homogenizer</td>
			<td>Benchmark Scientific</td>
			<td>Cat#D1030</td>
			<td></td>
		</tr>
		<tr>
			<td>Transferrin</td>
			<td>Sigma-Aldrich, Inc. St Louis, MO, USA</td>
			<td>Cat#T3309</td>
			<td></td>
		</tr>
		<tr>
			<td>Triglyceride Determination Kit</td>
			<td>Sigma-Aldrich, Inc., St Louis, MO, USA</td>
			<td>Cat#TR0100</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypan blue stain, 0.4%</td>
			<td>VWR International LLC., Radnor, PA, USA</td>
			<td>Cat#10027-446</td>
			<td></td>
		</tr>
		<tr>
			<td>Type II collagenase</td>
			<td>Gibco, ThermoFisher Scientific Inc., Waltham, MA, USA</td>
			<td>Cat#17101015</td>
			<td></td>
		</tr>
		<tr>
			<td>Whatman Reeve Angel filter paper, Grade 201, 150mm</td>
			<td>Sigma-Aldrich, Inc., St Louis, MO, USA</td>
			<td>Cat#WHA5201150</td>
			<td></td>
		</tr>
	</tbody>
</table>

a human 3d extracellular matrix-adipocyte culture model for studying matrix-cell metabolic crosstalk

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of cellular function. The ECM plays a particularly important role in adipose tissue function in obesity, and alterations in adipose tissue ECM deposition and composition are associated with metabolic disease in mice and humans. Tractable in vitro models that permit dissection of the roles of the ECM and cells in contributing to global tissue phenotype are sparse. We describe a novel 3D in vitro model of human ECM-adipocyte culture that permits study of the specific roles of the ECM and adipocytes in regulating adipose tissue metabolic phenotype. Human adipose tissue is decellularized to isolate ECM, which is subsequently repopulated with preadipocytes that are then differentiated within the ECM into mature adipocytes. This method creates ECM-adipocyte constructs that are metabolically active and retain characteristics of the tissues and patients from which they are derived. We have used this system to demonstrate disease-specific ECM-adipocyte crosstalk in human adipose tissue. This culture model provides a tool for dissecting the roles of the ECM and adipocytes in contributing to global adipose tissue metabolic phenotype and permits study of the role of the ECM in regulating adipose tissue homeostasis.

Preparation of adipose tissue ECM, seeding with preadipocytes, and in vitro differentiation into mature adipocytes result in clear sequential morphologic changes in tissue that permits visual assessment of progress throughout the protocol (Figure 1). Preadipocytes used to seed the ECM are isolated using collagenase digestion from separate VAT samples (Figure 2). Scanning electron microscopy of ECM-adipocyte constructs at each sta...

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A Human 3D Extracellular Matrix-Adipocyte Culture Model for Studying Matrix-Cell Metabolic Crosstalk

We describe a 3D human extracellular matrix-adipocyte in vitro culture system that permits dissection of the roles of the matrix and adipocytes in contributing to adipose tissue metabolic phenotype.

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of ...

Our protocol demonstrates that the ECM may promote adipogenic differentiation in the absence of classic adipogenic mediators and is the first to demonstrate disease-specific regulation of cellular metabolism by the ECM. Our technique provides a tool for dissecting the roles of the ECM and adipocytes in adipose tissue metabolism and permit study of the role of the ECM in regulating adipose tissue homeostasis. Compared with standard 2D cell culture, our 3D model allows for more robust examination and dissection of cross-talk between adipocytes and adipose tissue ECM in the context of type 2 diabetes.We recommend beginning with smaller samples to gauge how well it is cellularized. Keep in mind there is interpatient variability in how well the cells grow and how well the tissue decellularizes. It is important to observe the tissue before and after each step to ensure the tissue is becoming decellularized and to understand potential differences between samples.After obtaining visceral adipose tissue or VAT from surgery, prepare it for storage by adding 5-10 grams of the tissue to 15-25 milliliters of freezing buffer solution in a 50 milliliter conical tube. Completely immerse the sample and store it at minus 80 degrees Celsius until decellularization. For preadipocyte isolation, place two grams of a fresh sample of intact VAT in 20 milliliters of collagenase type II solution, then insert sterile scissors into the tube and thoroughly mince the tissue.Once minced to a fine slurry, incubate it in the collagenase solution at 37 degrees Celsius on an orbital shaker for 60 minutes. After the incubation, filter the resultant digested through a 100 micrometer nylon mesh into a fresh 50 milliliter conical tube. The digested should be a yellow-orange liquid with moderate viscosity and a small amount of residual strands of undigested tissue.Centrifuge the sample at 270 times g for 10 minutes, remove the supernatant and resuspend the cell pellet in two milliliters of 1X RBC lysing solution with a pipette. Incubate the solution for one minute at 25 degrees Celsius, then add 10 milliliters of 15%FBS DMEM F12 and centrifuge it at 270 times g for 10 minutes. To prepare the ECM, freeze/thaw the previously frozen VAT sample to 37 degrees Celsius by incubating it in a pre-heated water bath for 20 minutes with periodic gentle manual agitation.Once thawed, transfer the tissue back to minus 80 degrees Celsius for 20 minutes and repeat the freeze/thaw process three times ending with the thawing. Use sterile forceps to transfer the VAT sample to a fresh 50 milliliter conical tube containing 15-25 milliliters of enzymatic solution 1 making sure that the sample is fully immersed. Then incubate it overnight at 37 degrees Celsius while shaking at 130 RPM.On the next day, wash the sample three times with 15-25 milliliters of rinsing buffer solution, pouring off the solution after each wash. Transfer the sample to a fresh 50 milliliter tube with 15-25 milliliters of enzymatic solution 2 and incubate it overnight. Repeat the washes with the rinsing buffer solution and transfer the sample to a fresh tube containing 15-25 milliliters of polar solvent extraction solution.Incubate the sample overnight while shaking. After incubation with the polar solvent solution, it is important to examine the sample for lipid removal. If most of the lipid is not removed, it may be necessary to repeat this step.Shorter incubation time may be used. After the incubation, transfer the sample to a fresh tube containing 15-25 milliliters of rinsing buffer solution and wash the sample three times on the shaker. Then wash the sample three times with 70%ethanol solution, pouring off the ethanol after each wash.Wash the sample once with storage solution, then use sterile forceps to transfer to a fresh tube containing 15-25 milliliters of storage solution making sure to fully immerse it. The sample can then be stored at four degrees Celsius for up to one month. The isopropanol and ethanol are flammable and must be at room temperature and disposed of in flammable waste.Any human waste must be disposed of separately from the usual biohazard waste. Transfer the stored ECM fragments to individual wells of a 24-well plate with sterile forceps adding as many fragments as required for the planned downstream assays. Wash them three times with 500 microliters of 70%ethanol on an orbital shaker, then rehydrate them by washing three times with PBS.Use sterile scissors to cut the ECM into 100 milligram fragments. Place each fragment into one well of a 24-well plate and incubate the plate at 25 degrees Celsius for 15 minutes to allow excess PBS to extrude from the fragments. Then carefully remove any leftover PBS from the wells with a pipette.Seed each fragment with 20 microliters of preadipocyte cell suspension by pipetting the cells directly into the ECM. Place the pipette tip in the ECM and gently expel it into the center of the matrix making sure that the cell suspension does not overflow and end up at the bottom of the well. If the cell suspension overflows from the ECM, remove the pipette tip from that location and insert it elsewhere in the ECM.After cell seeding, incubate the ECM for 40 minutes at 37 degrees Celsius. Fill each well with 500 microliters of growth media to cover the seeded ECM fragments. Culture the cells at 37 degrees Celsius and 5%carbon dioxide for 72 hours.After 72 hours, carefully aspirate the growth media without disturbing the ECM fragment. Add 500 microliters of differentiation media and culture the cells for 14 days changing the media every two to three days. Check for differentiation using light microscopy.Cells will accumulate lipids, turn brown-yellow in color and become more spherical as they differentiate. Preparation of adipose tissue ECM, seeding with preadipocytes, and in vitro differentiation into mature adipocytes was monitored with scanning electron microscopy which revealed decellularization of ECM and subsequent recapitulation of lipid containing adipocytes upon reseeding and differentiation. Collagen 1 specific immunohistochemistry of decellularized ECM showed maintenance of collagen micro architecture while Oil Red-O staining of live and fixed 3D ECM-adipocyte constructs showed lipid containing adipocytes.The adipocytes differentiated in ECM were screened for adipogenic genes using quantitative real-time PCR which demonstrated that these genes are upregulated in the differentiated cells relative to undifferentiated preadipocytes cultured in ECM. The full difference in transcript levels is shown. Four combinations of ECM and adipocytes from diabetic and nondiabetic subjects were subjected to metabolic phenotyping.Impaired glucose uptake in lipolytic function was discovered in constructs from diabetic tissues. Importantly, it was found that nondiabetic ECM rescues insulin-stimulated glucose uptake and lipolytic capacity in diabetic adipocytes. Contamination of the isolated preadipocytes, the decellularized tissue, and the reseeded ECM is not uncommon.Sterility must be diligently maintained throughout the protocol.

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Research

JoVE Journal

Bioengineering

A Simple Hanging Drop Cell Culture Protocol for Generation of 3D Spheroids

Studies of cell-cell cohesion and cell-substratum adhesion have historically been performed on monolayer cultures adherent to rigid substrates. Cells within a tissue, however, are typically encased within a closely packed tissue mass in which cells establish intimate connections with many near-neighbors and with extracellular matrix components. Accordingly, the chemical milieu and physical forces experienced by cells within a 3D tissue are fundamentally different than those experienced by cells grown in monolayer culture. This has been shown to markedly impact cellular morphology and signaling. Several methods have been devised to generate 3D cell cultures including encapsulation of cells in collagen gels1or in biomaterial scaffolds2. Such methods, while useful, do not recapitulate the intimate direct cell-cell adhesion architecture found in normal tissues. Rather, they more closely approximate culture systems in which single cells are loosely dispersed within a 3D meshwork of ECM products. Here, we describe a simple method in which cells are placed in hanging drop culture and incubated under physiological conditions until they form true 3D spheroids in which cells are in direct contact with each other and with extracellular matrix components. The method requires no specialized equipment and can be adapted to include addition of any biological agent in very small quantities that may be of interest in elucidating effects on cell-cell or cell-ECM interaction. The method can also be used to co-culture two (or more) different cell populations so as to elucidate the role of cell-cell or cell-ECM interactions in specifying spatial relationships between cells. Cell-cell cohesion and cell-ECM adhesion are the cornerstones of studies of embryonic development, tumor-stromal cell interaction in malignant invasion, wound healing, and for applications to tissue engineering. This simple method will provide a means of generating tissue-like cellular aggregates for measurement of biomechanical properties or for molecular and biochemical analysis in a physiologically relevant model.

We describe a simple, rapid method of generating 3D tissue-like spheroids and their potential application to quantify differences in cell-cell interactions.

Studies of cell-cell cohesion and cell-substratum adhesion have historically been performed on monolayer cultures adherent to rigid substrates. Cells ...

Rotating Cell Culture Systems for Human Cell Culture: Human Trophoblast Cells as a Model

The field of human trophoblast research aids in understanding the complex environment established during placentation. Due to the nature of these studies, human in vivo experimentation is impossible. A combination of primary cultures, explant cultures and trophoblast cell lines1 support our understanding of invasion of the uterine wall2 and remodeling of uterine spiral arteries3,4 by extravillous trophoblast cells (EVTs), which is required for successful establishment of pregnancy. Despite the wealth of knowledge gleaned from such models, it is accepted that in vitro cell culture models using EVT-like cell lines display altered cellular properties when compared to their in vivo counterparts5,6. Cells cultured in the rotating cell culture system (RCCS) display morphological, phenotypic, and functional properties of EVT-like cell lines that more closely mimic differentiating in utero EVTs, with increased expression of genes mediating invasion (e.g. matrix metalloproteinases (MMPs)) and trophoblast differentiation7,8,9. The Saint Georges Hospital Placental cell Line-4 (SGHPL-4) (kindly donated by Dr. Guy Whitley and Dr. Judith Cartwright) is an EVT-like cell line that was used for testing in the RCCS.
The design of the RCCS culture vessel is based on the principle that organs and tissues function in a three-dimensional (3-D) environment. Due to the dynamic culture conditions in the vessel, including conditions of physiologically relevant shear, cells grown in three dimensions form aggregates based on natural cellular affinities and differentiate into organotypic tissue-like assemblies10,11,12 . The maintenance of a fluid orbit provides a low-shear, low-turbulence environment similar to conditions found in vivo. Sedimentation of the cultured cells is countered by adjusting the rotation speed of the RCCS to ensure a constant free-fall of cells. Gas exchange occurs through a permeable hydrophobic membrane located on the back of the bioreactor. Like their parental tissue in vivo, RCCS-grown cells are able to respond to chemical and molecular gradients in three dimensions (i.e. at their apical, basal, and lateral surfaces) because they are cultured on the surface of porous microcarrier beads. When grown as two-dimensional monolayers on impermeable surfaces like plastic, cells are deprived of this important communication at their basal surface. Consequently, the spatial constraints imposed by the environment profoundly affect how cells sense and decode signals from the surrounding microenvironment, thus implying an important role for the 3-D milieu13.
We have used the RCCS to engineer biologically meaningful 3-D models of various human epithelial tissues7,14,15,16. Indeed, many previous reports have demonstrated that cells cultured in the RCCS can assume physiologically relevant phenotypes that have not been possible with other models10,17-21. In summary, culture in the RCCS represents an easy, reproducible, high-throughput platform that provides large numbers of differentiated cells that are amenable to a variety of experimental manipulations. 
In the following protocol, using EVTs as an example, we clearly describe the steps required to three-dimensionally culture adherent cells in the RCCS.

Traditional, two dimensional cell culture techniques often result in altered characteristics with respect to differentiation markers, cytokines and growth factors. Three-dimensional cell culture in the rotating cell culture system (RCCS) reestablishes expression of many of these factors as shown here with an extravillous trophoblast cell line.

The field of human trophoblast research aids in  understanding the complex environment established during placentation. Due to the  nature of these ...

Production, Characterization and Potential Uses of a 3D Tissue-engineered Human Esophageal Mucosal Model

The incidence of both esophageal adenocarcinoma and its precursor, Barrett&#8217;s Metaplasia, are rising rapidly in the western world. Furthermore esophageal adenocarcinoma generally has a poor prognosis, with little improvement in survival rates in recent years. These are difficult conditions to study and there has been a lack of suitable experimental platforms to investigate disorders of the esophageal mucosa.
A model of the human esophageal mucosa has been developed in the MacNeil laboratory which, unlike conventional 2D cell culture systems, recapitulates the cell-cell and cell-matrix interactions present in vivo and produces a mature, stratified epithelium similar to that of the normal human esophagus. Briefly, the model utilizes non-transformed normal primary human esophageal fibroblasts and epithelial cells grown within a porcine-derived acellular esophageal scaffold. Immunohistochemical characterization of this model by CK4, CK14, Ki67 and involucrin staining demonstrates appropriate recapitulation of the histology of the normal human esophageal mucosa.
This model provides a robust, biologically relevant experimental model of the human esophageal mucosa. It can easily be manipulated to investigate a number of research questions including the effectiveness of pharmacological agents and the impact of exposure to environmental factors such as alcohol, toxins, high temperature or gastro-esophageal refluxate components. The model also facilitates extended culture periods not achievable with conventional 2D cell culture, enabling, inter alia, the study of the impact of repeated exposure of a mature epithelium to the agent of interest for up to 20 days. Furthermore, a variety of cell lines, such as those derived from esophageal tumors or Barrett&#8217;s Metaplasia, can be incorporated into the model to investigate processes such as tumor invasion and drug responsiveness in a more biologically relevant environment.

This manuscript describes the production, characterization and potential uses of a tissue engineered 3D esophageal construct prepared from normal primary human esophageal fibroblast and squamous epithelial cells seeded within a de-cellularized porcine scaffold. The results demonstrate the formation of a mature stratified epithelium similar to the normal human esophagus.

The incidence of both esophageal adenocarcinoma and its precursor, Barrett&#8217;s Metaplasia, are rising rapidly in the western world. Furthermore ...

A Hormone-responsive 3D Culture Model of the Human Mammary Gland Epithelium

The process of mammary epithelial morphogenesis is influenced by hormones. The study of hormone action on the breast epithelium using 2D cultures is limited to cell proliferation and gene expression endpoints. However, in the organism, mammary morphogenesis occurs in a 3D environment. 3D culture systems help bridge the gap between monolayer cell culture (2D) and the complexity of the organism. Herein, we describe a 3D culture model of the human breast epithelium that is suitable to study hormone action. It uses the commercially available hormone-responsive human breast epithelial cell line, T47D, and rat tail collagen type 1 as a matrix. This 3D culture model responds to the main mammotropic hormones: estradiol, progestins and prolactin. The influence of these hormones on epithelial morphogenesis can be observed after 1- or 2-week treatment according to the endpoint. The 3D cultures can be harvested for analysis of epithelial morphogenesis, cell proliferation and gene expression.

We describe a 3D culture model of the human breast epithelium that is suitable to study hormone action.

The process of mammary epithelial morphogenesis is influenced by hormones. The study of hormone action on the breast epithelium using 2D cultures is ...

Tunable Hydrogels from Pulmonary Extracellular Matrix for 3D Cell Culture

Here we present a method for establishing multiple component cell culture hydrogels for in vitro lung cell culture. Beginning with healthy en bloc lung tissue from porcine, rat, or mouse, the tissue is perfused and submerged in subsequent chemical detergents to remove the cellular debris. Histological comparison of the tissue before and after processing confirms removal of over 95% of double stranded DNA and alpha galactosidase staining suggests the majority of cellular debris is removed. After decellularization, the tissue is lyophilized and then cryomilled into a powder. The matrix powder is digested for 48 hr in an acidic pepsin digestion solution and then neutralized to form the pregel solution. Gelation of the pregel solution can be induced by incubation at 37 &#176;C and can be used immediately following neutralization or stored at 4 &#176;C for up to two weeks. Coatings can be formed using the pregel solution on a non-treated plate for cell attachment. Cells can be suspended in the pregel prior to self-assembly to achieve a 3D culture, plated on the surface of a formed gel from which the cells can migrate through the scaffold, or plated on the coatings. Alterations to the strategy presented can impact gelation temperature, strength, or protein fragment sizes. Beyond hydrogel formation, the hydrogel stiffness may be increased using genipin.

This is a method to create a 3-dimensional cell culture scaffold from pulmonary extracellular matrix. Intact lung is processed into hydrogels that can support the growth of cells in three-dimensions.

Here we present a method for establishing multiple component cell culture hydrogels for in vitro lung cell culture. Beginning with healthy en bloc lung ...

Construction of a Multilayered Mesenchymal Stem Cell Sheet with a 3D Dynamic Culture System

Stem cell therapy shows a promising future in regenerating injured organ and tissues, and the cell sheet technique has been developed to improve the low cell retention and poor survival within the target zone. However, during the in vitro construction process, a solution for maintaining stem cell bioactivity and increasing the cell amount within the cell sheet is urgently needed. Here, this protocol presents a method for constructing a multilayered cell sheet with favorable stem cell bioactivity and optimal operability. Decellularized porcine pericardium (DPP) is prepared by phospholipase A2 (PLA2) decellularization method as the cell sheet scaffold, and rat bone marrow mesenchymal stem cells (BMSCs) are isolated and expanded as the seeded cells. The temporary multilayered cell sheet structure is constructed by using RAD16-I peptide hydrogel. Finally, the cell sheet is cultured with a dynamic perfusion system to stabilize the three-dimensional (3D) structure, and the cell sheet could be obtained following a 48-hour culture in vitro. This protocol provides an efficient and feasible method for constructing a multilayered stem cell sheet, and the cell sheet could be developed as a favorable stem cell therapy product in the future.

This article provides an efficient and feasible method for constructing multilayered stem cell sheets with favorable stem cell property.

Stem cell therapy shows a promising future in regenerating injured organ and tissues, and the cell sheet technique has been developed to improve the low ...

In Vitro Model of Human Cutaneous Hypertrophic Scarring using Macromolecular Crowding

It has been shown that in vivo tissues are highly crowded by proteins, nucleic acids, ribonucleoproteins, polysaccharides, etc. The following protocol applies a macromolecular crowding (MMC) technique to mimic this physiological crowding through the addition of neutral polymers (crowders) to cell cultures in vitro. Previous studies using Ficoll or dextran as crowders demonstrate that the expression of collagen I and fibronectin in WI38 and WS-1 cell lines are significantly enhanced using the MMC technique. However, this technique has not been validated in primary hypertrophic scar-derived human skin fibroblasts (hHSFs). As hypertrophic scarring arises from the excessive deposition of collagen, this protocol aims to construct a collagen-rich in vitro hypertrophic scar model by applying the MMC technique with hHSFs. This optimized MMC model has been shown to possess more similarities with in vivo scar tissue compared to traditional 2-dimensional (2-D) cell culture systems. In addition, it is cost-effective, time-efficient, and ethically desirable compared to animal models. Therefore, the optimized model reported here offers an advanced &#8220;in vivo-like&#8221; model for hypertrophic scar-related studies.

This protocol describes the use of macromolecular crowding to create an in vitro human hypertrophic scar tissue model that resembles in vivo conditions. When cultivated in a crowded macromolecular environment, human skin fibroblasts exhibit phenotypes, biochemistry, physiology, and functional characteristics resembling scar tissue.

It has been shown that in vivo tissues are highly crowded by proteins, nucleic acids, ribonucleoproteins, polysaccharides, etc. The following protocol ...

A Culture Method to Maintain Quiescent Human Hematopoietic Stem Cells

Human hematopoietic stem cells (HSCs), like other mammalian HSCs, maintain lifelong hematopoiesis in the bone marrow. HSCs remain quiescent in vivo, unlike more differentiated progenitors, and enter the cell cycle rapidly after chemotherapy or irradiation to treat bone marrow injury or in vitro culture. By mimicking the bone marrow microenvironment in the presence of abundant fatty acids, cholesterol, low concentration of cytokines, and hypoxia, human HSCs maintain quiescence in vitro. Here, a detailed protocol for maintaining functional HSCs in the quiescent state in vitro is described. This method will enable studies of the behavior of human HSCs under physiological conditions.

This protocol enables the maintenance of quiescent human hematopoietic stem cells in vitro by mimicking the bone marrow microenvironment using abundant fatty acids, cholesterol, lower concentrations of cytokines, and hypoxia.

Human hematopoietic stem cells (HSCs), like other mammalian HSCs, maintain lifelong hematopoiesis in the bone marrow. HSCs remain quiescent in vivo, ...

Developing 3D Organized Human Cardiac Tissue within a Microfluidic Platform

The leading cause of death worldwide persists as cardiovascular disease (CVD). However, modeling the physiological and biological complexity of the heart muscle, the myocardium, is notoriously difficult to accomplish in vitro. Mainly, obstacles lie in the need for human cardiomyocytes (CMs) that are either adult or exhibit adult-like phenotypes and can successfully replicate the myocardium&#39;s cellular complexity and intricate 3D architecture. Unfortunately, due to ethical concerns and lack of available primary patient-derived human cardiac tissue, combined with the minimal proliferation of CMs, the sourcing of viable human CMs has been a limiting step for cardiac tissue engineering. To this end, most research has transitioned toward cardiac differentiation of human induced pluripotent stem cells (hiPSCs) as the primary source of human CMs, resulting in the wide incorporation of hiPSC-CMs within in vitro assays for cardiac tissue modeling.
Here in this work, we demonstrate a protocol for developing a 3D mature stem cell-derived human cardiac tissue within a microfluidic device. We specifically explain and visually demonstrate the production of a 3D in vitro anisotropic cardiac tissue-on-a-chip model from hiPSC-derived CMs. We primarily describe a purification protocol to select for CMs, the co-culture of cells with a defined ratio via mixing CMs with human CFs (hCFs), and suspension of this co-culture within the collagen-based hydrogel. We further demonstrate the injection of the cell-laden hydrogel within our well-defined microfluidic device, embedded with staggered elliptical microposts that serve as surface topography to induce a high degree of alignment of the surrounding cells and the hydrogel matrix, mimicking the architecture of the native myocardium. We envision that the proposed 3D anisotropic cardiac tissue-on-chip model is suitable for fundamental biology studies, disease modeling, and, through its use as a screening tool, pharmaceutical testing.

The goal of this protocol is to explain and demonstrate the development of a three-dimensional (3D) microfluidic model of highly aligned human cardiac tissue, composed of stem cell-derived cardiomyocytes co-cultured with cardiac fibroblasts (CFs) within a biomimetic, collagen-based hydrogel, for applications in cardiac tissue engineering, drug screening, and disease modeling.

The leading cause of death worldwide persists as cardiovascular disease (CVD). However, modeling the physiological and biological complexity of the heart ...

Microgel-Extracellular Matrix Composite Support for the Embedded 3D Printing of Human Neural Constructs

The embedded 3D printing of cells inside a granular support medium has emerged in the past decade as a powerful approach for the freeform biofabrication of soft tissue constructs. However, granular gel formulations have been restricted to a limited number of biomaterials that allow for the cost-effective generation of large amounts of hydrogel microparticles. Therefore, granular gel support media have generally lacked the cell-adhesive and cell-instructive functions found in the native extracellular matrix (ECM).
To address this, a methodology has been developed for the generation of self-healing annealable particle-extracellular matrix (SHAPE) composites. SHAPE composites consist of a granular phase (microgels) and a continuous phase (viscous ECM solution) that, together, allow for both programmable high-fidelity printing and an adjustable biofunctional extracellular environment. This work describes how the developed methodology can be utilized for the precise biofabrication of human neural constructs.
First, alginate microparticles, which serve as the granular component in the SHAPE composites, are fabricated and combined with a collagen-based continuous component. Then, human neural stem cells are printed inside the support material, followed by the annealing of the support. The printed constructs can be maintained for weeks to allow the differentiation of the printed cells into neurons. Simultaneously, the collagen continuous phase allows for axonal outgrowth and the interconnection of regions. Finally, this works provides information on how to perform live-cell fluorescence imaging and immunocytochemistry to characterize the 3D-printed human neural constructs.

This work describes a protocol for the freeform embedded 3D printing of neural stem cells inside self-healing annealable particle-extracellular matrix composites. The protocol enables the programmable patterning of interconnected human neural tissue constructs with high fidelity.

The embedded 3D printing of cells inside a granular support medium has emerged in the past decade as a powerful approach for the freeform biofabrication ...