The experiment was completed at the Medical Research Center, the First Affiliated Hospital of Xinjiang Medical University from June 2011 to January 2012.
Animals: Two healthy male Sprague Dawley rats, specific pathogen-free grade, weighing 160-180 g, were provided by the Experimental Animal Center, the First Affiliated Hospital of Xinjiang Medical University. All animal procedures were in accordance with animal ethics standards[10].
Main reagents and instruments for isolation, culture and identification of adipose-derived stem cells are as follows.
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Methods
In vitro isolation, culture and passage of adipose-derived stem cells
Sprague Dawley rats were anesthetized by intraperitoneal injection of 10% chloral hydrate
(3 mL/kg) under sterile conditions, to extract the inguinal adipose tissue. After removing soft tissue and small blood vessels, the tissues were washed with PBS three times. Then, according to the method of Zuk
et al [2], the tissues were cut into pieces by a microsurgery scissor, digested with 0.075% type Ⅰ collagenase at 37 ℃ for 40 minutes and centrifuged at 1 000 r/min (centrifugal radius, 150 mm) for 10 minutes. After the removal of supernatant and PBS resuspension, the samples were filtered using 400-mesh filter and then centrifuged at 1 000 r/min (centrifugal radius, 150mm) for 5 minutes to harvest sediment. The sediment was even mixed with low-glucose DMEM medium containing 10% fetal bovine serum, and cultured in a 37 ℃, 5% CO2 incubator. After 24 hours, the medium was changed for the first time, and then it was changed every 3 days. When the cells reached over 90% confluence, the cells were digested with 0.25% trypsin/ethylene diamine tetraacetie acid and then passaged at a ratio of 1:2.
MTT determination of growth curve of adipose-derived stem cells
The third generation of adipose-derived stem cells were digested with trypsin to prepare single cell suspension, and then seeded in 96-well plates at a concentration of 5 × 103 per well. After cultured 1-8 days, 20 μL of 5 g/L MTT solution was added for continuous culture in the dark for 4 hours. After liquid removal, 150 μL dimethyl sulfoxide solution was added per well, and the samples were placed on the micro-oscillator at room temperature for 10 minutes. Absorbance value at 490 nm was detected using the microplate reader, and cell growth curve was drawn.
Identification of stem cell surface markers
The third generation of cells were seeded on 6-well plates with sterilized coverslip. The sample was placed in 60 mm petri dish, rinsed with PBS three times, fixed in cold acetone for 8 minutes, washed with PBS
5 minutes×3, fixed with 3% H2O2 for 10 minutes, washed with PBS 5 minutes×3. The diluted rabbit anti-rat CD44 antibody was added to the sample overnight at 4 ℃ wet box. After washed with PBS
5 minutes×3, the diluted FITC-labeled rabbit anti-rat IgG was added to the sample at room temperature for 1 hour. Then, the sample was washed with PBS
(pH 7.4) 5 minutes×3, and cemented with 4,6-diamino-2-phenyl indole. Fluorescence microscope (Olympus) was used to take photos in the darkroom.
Adipogenic differentiation of adipose-derived stem cells and identification using oil red "O" staining
The third generation of adipose-derived stem cells were divided into experimental and control groups, three wells per group. After digestion, the cells were collected and counted. Cells were seeded into 6-well plates with sterilized coverslip at a density of 5×104 cells per well, and then cultured in adipogenic induction medium: DMEM/F12 medium containing 10% fetal bovine serum, 1 μmol/L dexamethasone, and
10 μmol/L insulin (experimental group), or DMEM/F12 medium containing 10% fetal bovine serum (control group). The culture medium was exchanged every 3 days. After 14 days of induction, the culture slide was rinsed with distilled water, and incubated and sealed with oil red O dilutions in the dark for 10-15 minutes. Before usage, 6 mL stock solution was taken, 4 mL distilled water was added for standing 5-10 minutes, and then, the sample was filtered twice and used within 2 hours. The sample was differentiated after addition of 60% ethanol under microscopy till the gap was clear, and then washed with water. Mayer’s hematoxylin nuclear staining was done for 1 minute followed by washing. The sample was mounted with glycerogelatin glue, and observed under the phase contrast microscope. Digital camera was used to take photos. In the control group, the same procedures were done.
Neuronal differentiation of adipose-derived stem cells and identification
After centrifugation, the third generation of cells were resuspended using neural stem cell culture medium and seeded into 6-well plates for neuronal differentiation. After 6 days of directional induction, the cell culture slide was placed in 60 mm petri dish, rinsed with PBS (pH 7.4) three times, fixed in cold acetone for 8 minutes, washed with PBS (pH 7.4) 5 minutes×3, fixed with 3% H2O2 for 10 minutes, washed with PBS (pH 7.4) 5 minutes×3. The diluted first antibody was added to the sample overnight at 4 ℃ wet box. After washed with PBS (pH 7.4) 5 minutes×3, 50-100 μL horseradish peroxidase anti-mouse/anti-rabbit polymer was added to the sample at room temperature for 10 minutes. Then, the culture slide was washed with PBS (pH 7.4) 5 minutes×3. After removal of PBS, 100 μL fresh 3,3'-diaminobenzidine was added to the culture slide for coloration under microscope. After rinsing with tap water, the culture slide was couterstained with hematoxylin, and treated with 0.1% HCl for differentiation. After rinsing with tap water, the culture slide was dehydrated, transparent, mounted with neutral balsam, and observed under phase contrast microscope. Digital camera was used to take photos.
Main outcome measures
(1) In vitro morphology of adipose-derived stem cells and growth curve reflecting the proliferative capacity; (2) CD44 expression in adipose-derived stem cells; (3) identification results of adipogenic and neuronal differentiation of adipose-derived stem cells.