This method can help answer key questions in the obesity field, such as identifying the key factors and mechanisms that prevent a robust adipogenic response during adipose tissue remodeling. The main advantage of this technique is that it allows isolation of CD34+CD31+endothelial cells from human adipose tissue starting with small amounts of tissue. We first had the idea for this method when we wanted to identify cells in human adipose vasculature that respond to adipogenic stimulation.
Visual demonstration of this method is critical, as the cell isolation steps are difficult to practice due to the oftentimes limited access to fresh human adipose tissue. Collect human omental and subcutaneous adipose tissue from human subjects undergoing bariatric surgery. Immediately after tissue extraction, keep the human omental and subcutaneous adipose tissue in separate vials containing Hank's buffered salt solution with 50 micrograms per milliliter of penicillin streptomycin at room temperature.
Once the sample arrives at the lab after the tissue extraction, carefully clean and remove fibrotic and cauterized sections of the tissue by using 70%ethanol-swabbed scissors and tweezers. Weigh the adipose tissue and partition it into five gram aliquots for the collagenase digestion. Use two pairs of scissors to finely mince five grams of the adipose tissue in five milliliters of a collagenase solution in a scintillation vial at room temperature.
Add an additional 10 milliliters of collagenase solution to the minced tissue for 15 milliliters total. Digest the samples for one hour at 37 degrees Celsius in a water bath with continuous shaking. Following digestion, pour the samples into the 20 milliliter blunt end syringe.
Filter the sample through 250 micron nylon mesh into the 50 milliliter conical tube to separate adipocytes and stromal vascular cells from undigested tissue. Wash out the scintillation vial with 10 milliliters of KRBBS, and pour the wash through the filter to collect residual cells before incubating the filtered samples for five minutes at room temperature. Then, utilize a 20 milliliter syringe and a 20 gauge by six inch pipetting needle to remove stromal vascular fraction layer and transfer it to a clean 50 milliliter conical tube.
Add 10 milliliters of KRBBS and allow the samples to sit on the bench for five minutes at room temperature. Keep the stromal vascular fractions from both depots on ice for further processing. Spin the stromal vascular fractions at 500 times G for five minutes at 4 degrees Celsius.
Remove the samples from the centrifuge and carefully pour off the supernatant, keeping the pellet containing the stromal vascular fraction cells. Gently re-suspend the cell pellets in five milliliters of PBS. After spinning the samples again, remove the supernatant, re-suspend the cells in one milliliter of PBS, and count the cells.
Pellet the samples for a third time, and re-suspend the pellet in 100 microliters of CD34 isolation buffer. Add 10 microliters of CD34 cocktail and incubate the sample for 15 minutes at room temperature. Then add five microliters of magnetic beads and incubate the sample for 10 minutes at room temperature.
Next, add 2.5 milliliters of CD34 isolation buffer to each sample, and place the samples into the magnet for five minutes at room temperature. Invert the magnet for five seconds to pour off the isolation buffer. After repeating this process four times, remove the tube from the magnet and add two milliliters of CD34 isolation buffer.
Following another centrifugation, re-suspend the CD34+cell pellets in one milliliter of CD34 isolation buffer and count the cells. Pellet the cells again, and re-suspend the pellet in 250 microliters of Buffer B and 250 microliters of wash buffer. Next, thoroughly re-suspend the CD31 beads by vortexing the tube, then add 20 microliters of CD31 beads to the re-suspended cell pellet and incubate the sample with rocking for 30 minutes at room temperature.
Prior to the cell separation, add one milliliter of wash buffer to equilabrate the strainer. Then, apply the prepared mixture of re-suspended cells in CD31 beads to the strainer. Wash the strainer with five milliliters of wash buffer in a circular motion for a total volume of 20 milliliters.
Attach the connector to a sterile 50 milliliter conical tube and close the leur lock. After attaching the strainer to the connector, add one milliliter of wash buffer along the wall of the strainer, then add one milliliter of activated Buffer D along the wall of the strainer. Swirl the sample gently, and incubate it for 10 minutes at room temperature.
Next, add one milliliter of wash buffer and separate the cells from the beads by pipetting up and down 10 times. Open the leur lock and allow the detached cells to flow into the 50 milliliter conical tube. Wash the strainer 10 times with one milliliter of wash buffer each time.
Discard the connector and strainer, and centrifuge the samples at 300 times G for 10 minutes at 4 degrees Celsius. Finally, re-suspend the cell pellet in two milliliters of complete EGM2 media for culture. Grow the cells in six-well tissue culture treated plates with complete EGM2 media in a 37 degrees Celsius, 5%carbon dioxide incubator.
Replace the media every three to four days until the cells reach 80 to 90%confluence. Then, seed approximately 100 to 200 thousand cells into six-well plates, ensuring duplicate wells for each depot, and culture them in complete EGM2 media for two days. After two days, aspirate off any growth media.
Replace the media with two milliliters of DMEM/F-12 media with 5%FBS and 50 micrograms per milliliter of penicillin streptomycin for the control cells. For the treatment cells, replace the media with two milliliters of adipogenesis media. Incubate the cells at 37 degrees Celsius in a humidified 5%carbon dioxide incubator for 13 days replacing the respective media every three to four days.
Representative results showing the typical endothelial cobblestone-like morphology of the CD34+CD31+cells after two passages in culture is shown. Also demonstrated is the ability of cells to form tubules when cultured in Matrigel as expected. Uniform uptake of fluorescently labeled acetylated LDL shows the presence of a homogenous cell population with endothelial identity.
Shown here is Oil Red O staining of neutral lipid droplets in CD34+CD31+cells following 13 days of adipogenic induction. Representative responses of cells from omental and subcutaneous depots of three different human subjects are shown to illustrate the large variability in response to adipogenic induction between fat depots of the same donor and between donors. This image displays fluorescent intracellular lipid staining in CD34+C31+cells after adipogenic induction for 13 days.
The image shows cells with unilocular lipids, multilocular lipids, and no lipid accumulation. Real time PCR shows the expression of the pan adipocyte marker adiponectin and the brown beige markers CIDEA and UCP-1. These results confirm that cells following adipogenic induction express molecular markers consistent with a mixed white beige adipocyte phenotype.
Once mastered, this technique can be done in five hours if it is performed properly. While attempting this procedure, it is important to remember to use fresh human adipose tissue that was collected and not stored longer than two hours. Following this procedure, other methods like flow cytometry, immunohistochemistry, and RT-PCR can be performed to identify specific subsets of responding cells, and expression of mature adipocyte markers that can be utilized to identify a beige brown adipocyte phenotype.
After it's development, this technique paved the way for researchers in the filed of obesity to explore roles of adipose tissue, vascular cells, and adipogenesis in humans. After watching this video, you should have a good understanding of how to isolate, culture, and expand CD34+31+cells. Don't forget that working with human tissues can be extremely hazardous, and precautions, such as bio-safety regulations, should always be taken while performing this procedure.
The implications of this technique extend toward therapy of obesity associated comorbidities, such as insulin resistance, because it identifies adipogenic response of cells to a potential therapeutic intervention.
