Isolation of Viable Adipocytes and Stromal Vascular Fraction from Human Visceral Adipose Tissue Suitable for RNA Analysis and Macrophage Phenotyping

This protocol allows for isolation and study of viable adipocytes and stromal vascular fraction SVF cells from human visceral fat. Enzymatic digestion using collagenase ensures high yields of total RNA from mature adipocytes, including microRNAs suitable for expression analysis. Simultaneously, the method is optimized to identify macrophages by flow cytometry.

This protocol provides fundamental troubleshooting guidelines for easy and efficient isolation of viable mature adipocytes and SVF cells from human VAT biopsies in a single process. After the uterine closure and hemostasis, identify greater omentum and extend it on a wet compress. Identify an avascular zone and use Kelly forceps to drill the outer side of visceral adipose tissue, or VAT.

Use Ochsner forceps to clamp the proximal and distal side in the zone where VAT was drilled, and used Metzenbaum scissors to cut the tissue. Tie the greater omentum with black silk number one, then remove the Ochsner forceps and evaluate the hemostasis. To perform enzymatic digestion, cut four grams of VAT and use scissors to mince the tissue into small pieces in a dissection tray.

Transfer the pieces to a new sterile 50-milliliter centrifuge tube and add 25 milliliters of digestion solution. Incubate the tube at 37 degrees Celsius for 60 minutes in an orbital shaker at 125 RPM. Then filter the digested tissue through three layers of gauze into a new sterile 50-milliliter centrifuge tube.

Centrifuge the tube at 200 G for five minutes at four degrees Celsius. After centrifugation, two phases should be visible. The upper phase corresponds to mature adipocytes while SVF cells remain in the pellet.

Transfer the mature adipocytes to a tube. Lyse cells by adding 1000 microliters of acid-guanidinium-phenol-based reagent and mix thoroughly with a P1000 micropipette to homogenize. Incubate the mixture for five minutes at room temperature to boost dissociation of nucleo-protein complexes.

Centrifuge the cell lysate for five minutes at 12, 000 G to obtain three phases, an upper yellow phase corresponding to adipocyte lipids, a middle pink phase corresponding to nucleic acids, and a pellet with cellular debris. Carefully remove the lipid layer with a P200 micro pipette. Then transfer the middle phase into a new two-milliliter tube, taking care not to disturb the other phases.

After purifying the RNA and measuring the concentration with a UV visible spectrophotometer, use an RNA integrity kit to determine the RNA integrity number. Then use the small RNA kit to determine the concentration and percent of microRNAs. Place the clip into a bioanalyzer.

Dilute 10 microliters of SVF cell suspension into 90 microliters of 0.4%trypan blue solution, and apply 10 microliters to a standard hemocytometer. Count the viable cells carefully, excluding the dead cells, in four squares at the corner of the counting chamber. Transfer a total of 1 million SVF cells per milliliter to a five-milliliter round-bottom polypropylene test tube for flow cytometry and pellet the cells by centrifugation at 800 G for five minutes at four degrees Celsius.

Vortex carefully to loosen the pellet and resuspend the cells in 100 microliters of PBS. Add the pre-titrated optimal concentration of each fluorochrome-conjugated monoclonal antibody specific for a cell surface antigen and mix gently, then incubate the cells for 15 minutes in the dark. Add an excess of cold PBS.

And centrifuge the SVF at 400 G for five minutes at four degrees Celsius. Decant the supernatant, taking care to not disturb the pellet. Resuspend the pellet in five milliliters of sheath fluid.

Then filter the cells through three layers of gauze into a new five-milliliter round-bottom polypropylene test tube. Vortex each tube briefly before analysis and count a minimum of 10, 000 events for flow analysis. This RNA extraction protocol was used to obtain adequate purity and high integrity RNA and microRNAs from mature adipocytes.

The RNA integrity was assessed by an RNA quality control analyzer. Approximately 2.8 times 10 to the six nucleated cells were present per gram of visceral adipose tissue. The stromal vascular fraction cells were labeled with fluorophore-conjugated primary antibodies to identify and characterize 18 macrophages by fluorescence-activated cell-sorting analysis.

Cell aggregates were eliminated from analysis by plotting the forward scatter area versus forward scatter height. Then cellular debris was excluded by gating the cells, based on the correct size and complexity, using forward scatter area and the side scatter area. To analyze macrophages, the monocyte and macrophage lineage cells were selected using CD45 and CD14 markers.

Subsequently, the CD45-CD14 double positive cells were separated based on macrophage marker HLA-DR expression. Two subsets of macrophages were identified. In addition to identifying new cell phenotypes, this protocol makes it possible to use purified cell populations for future analyses, such as DNA methylation, post-translational modifications, and signaling pathways.