Mice
Female mice (6–8 weeks) of the C57BL/6 strain were purchased from the Royan Institute (Tehran, Iran) and were housed and manipulated in accordance with the ethical committee’s guidelines of Shahid Beheshti University of Medical Sciences (66001030). Three to 5 mice were used in each experimental group.
AMSCs isolation and culture from adipose tissue
Liposuction aspirates were obtained from abdomen of five different donors (healthy adult aged 25–40 years) with written informed consent. All procedures were performed in accordance with the ethical committee guidelines of Shahid Beheshti University of Medical Sciences (66001030). A previously described collagenase digestion method was used to AMSCs isolation [18]. In brief, 0.075% type I collagenase (Gibco, Grand Island, NY) was used for adipose tissue dissociation at 37°C for 20 min. After collagenase neutralization by FBS, the samples were centrifuged and the pellet was cultured at 37°C in DMEM/F12 (Dulbecco modified Eagle medium) plus 10% Fetal Bovine Serum (FBS) (Gibco, Rockville, MD) and 100 U/ml streptomycin/penicillin in a 5% CO2 humidified incubator. Next day nonadherent cells were removed and medium was changed. The half of media was changed every 3 days and adherent cells were grown to 80% confluency. The cells were used at passage 3 for the following experiments.
AMSCs characterization
The AMSCs at passage 3 were characterized by phenotyping of surface markers using FACSCalibur analyzer (Becton Dickinson, San Jose, CA, USA). In short, cells were detached and washed with Phosphate-Buffered Saline (PBS). Then Phycoerythrin (PE)-labeled antibodies against CD90, CD34, CD105, CD14, CD73, and CD45 (all from eBioscience, San Diego, CA) were used for surface antigens labeling. Flowjo (Tree Star, Inc., Ashland, OR) was used for data analysis.
Besides, the AMSCs were also identified by the induction of mesenchymal lineages differentiation via osteogenic and adipogenic differentiation media as described previously [18].
Exosomes purification from AMSCs conditioned media
To exosomes isolation, first, AMSCs were adapted to serum-free medium [19]. AMSCs were cultured in descending concentration of FBS in presences of 1% insulin/transferrin/selenium (Invitrogen, Carlsbad, CA, USA). After reaching 0% FBS, conditioned media was collected every 3 days, and exosomes were isolated using an isolation kit from Cibbiotech (Tehran, Iran) according to the instructions provided with the kit. In short, supernatants were filtered by a 0.22 µm filter and centrifuged for 20 min at 3000g to remove cell debris. Supernatants were then incubated with exosome precipitation buffer (5:1 ratio) overnight at 4°C to precipitate exosomes. The samples were centrifuged at 4°C for 40 min at 3000g and pellets were resuspended in 200µL PBS and stored at -70°C. The protein content of isolated exosomes was calculated using a bicinchoninic acid protein assay kit (Parstous, Mashad, Iran).
Scanning electron microscopy examination
The shape and size of the purified exosomes were examined with Scanning Electron Microscopy (SEM). To do this, Specimens were prepared by fixing 10µL exosomes with 2.5% glutaraldehyde (Sigma–Aldrich, St. Louis, MO). After dehydration in increasing concentrations of ethanol, they were left to dry at room temperature. Finally, the samples were evaluated under SEM (MIRA3 TESCAN, Brno, Czech Republic) at 30 kV following gold-palladium sputtering.
Transmission electron microscopy examination
For morphology analysis of purified exosomes from AMSCs, after fixing with 2.5% glutaraldehyde and dehydration in ascending sequence of ethanol, the samples were further proceed for epoxy resin (PolySciences, Warrington, PA, USA) embedding in accordance with the manufacturer's instruction. Ultrathin sections (a thickness of maximum 70 nm) were loaded onto formvar coated copper grids, contrasted with uranyl acetate, and visualized by Zeiss-EM10C (Germany) transmission electron microscope (TEM).
Exosomes size distribution analysis
Dynamic light scattering (DLS) measured the size distribution and average size of small particles. Exosomes obtained from the supernatants of AMSCs were diluted 1:10 in PBS and examined by Malvern Zetasizer (Worcestershire, UK).
Exosomes Immunophenotyping
To further characterization, exosomes immunophenotyping was performed using antibodies against CD63 and CD81 (important markers of exosomes). The data were collected via flow cytometry. The relative fluorescence was calculated by Flowjo (Tree Star, Inc., Ashland, OR).
miR-29b1-3p mimic loading into exosomes
In order to loading of exosomes with miR-29b1-3p mimic, 100 µg of purified exosomes were gently diluted with EDTA (1 mM) containing electroporation buffer (1:1 v/v). 100 pm of miR-29b1-3p mimic (Exiqon, Vedbaek, Denmark) was added to the electroporation sample, mixed thoroughly, and transferred into 4 mm cuvettes (All procedures were performed on ice) and electroporated by Eppendorf Multiporator (Eppendorf AG, Hamburg, Germany). The electric conditions were double pulses of 400 V and 100 µs. The unincorporated free miR-29b was removed by 5 µg/ml RNase A (Sigma-Aldrich, St. Louis, MO) and exosomes re-isolation by isolation kit (Cibbiotech, Tehran, Iran).
Splenocytes isolation and nCD4 cell purification
Spleens were removed from mice and subjected to mechanically disruption and homogenization. The homogenates were centrifuged for 5 min in 400g at 4°C. Then, erythrocytes were lysed at room temperature in ACK lysis buffer for 4 min, followed by additional centrifugation. The cell pellets were resuspended in RPMI-1640 medium (Life Technologies, Carlsbad, CA) plus 5% FBS and the count of splenocytes was measured by a Neubauer counting chamber. Splenocytes were subjected to magnetic-activated cell sorting for nCD4+ cells isolation. nCD4+ cells were purified from splenocytes by Miltenyi Biotech naive CD4+ T cell isolation kit II (Bergisch Gladbach, Germany) according to the instructions provided with the kit. First, non-CD4+ T cells were depleted from splenocytes via a cocktail of biotin-conjugated antibodies. Then, positive selection was used to isolate CD62L+ cells. The CD4+CD62L+ T cells was analyzed by flow cytometry and the purity was 86% (Fig. 3a).
Exosomes treatment
Isolated nCD4+ cells were seeded in RPMI-1640 plus 5% FBS, at the cell concentration of 1×106 per well in 24-well culture plates, and activated by anti-CD28 (10 µg/ml) and anti-CD3 (2 µg/ml) Abs (Invitrogen, Carlsbad, CA) for 4 hours. Then, the cells were co-incubated for 5 days with 200 µg/ml exosomes or miR-29b-3p loaded exosomes. RPMI-1640 with 5% FBS with or without 5 ng/ml TGF-β1 (eBioscience, San Diego, CA, USA) was used as a negative or positive control, respectively.
PKH67 labeling of exosomes
For exosome uptake examination, purified exosomes (200 µg protein) were fluorescently labeled by PKH67 (Sigma-Aldrich, St. Louis, MO). Exosomes were resuspended in 250 µL Diluent C and 2 µL of PKH67 dye was also diluted in the same amount of Diluent C and then they were mixed gently. After 5 min incubation at room temperature, the staining reaction was stopped by 250 µL of FBS and exosomes re-isolated via isolation kit to get rid of the excess dyes. Labeled exosomes were co-incubated with nCD4+ cells for 24 hours, and then the cells were washed with PBS, fixed with 2.5% glutaraldehyde, and observed using a Leica TCS SPE (Leica, Mannheim, Germany) confocal microscope. For the negative control, above labeling procedure was performed on a mixture without exosomes.
ELISA of cytokines
The ELISA assay was used to determine IL-17, IL-4, IFN-γ, and TGF-β concentrations. After 5 days of cell culture, cell-free supernatants were collected and the cytokine were quantified via R&D Systems ELISA kit (Minneapolis, MN, USA) following the manufacturer’s protocol. Cells were harvested, washed, and used for qPCR and flow cytometry analysis (see below).
Real-time PCR assay
To miR-29b and transcription factors expression analysis 5 days following nCD4+ cells co-culturing with exosomes, TRIzol Reagent (Life Technologies, Grand Island, NY) was used for total RNA isolation. The RNA concentration was determined via a NanoDrop spectrophotometer and then reverse transcribed to cDNA. RNA quantification was performed using a standard SYBR Green I reaction mix (Ampliqon, Odense, Denmark) on an ABI StepOne™ (Applied Biosciences, Foster City, CA). U47 and β-2M were used as background control [13].
Analysis of regulatory T cells frequency
The frequency of regulatory T cells was determined by staining with Miltenyi Biotech CD4/CD25/Foxp3 Treg detection kit (Germany) in accordance with the manufacturer’s instructions. Single-cell suspensions were incubated first with FITC-conjugated-CD4 Abs and APC-conjugated-CD25 Abs at 4°C in dark for 10 min. These cells were subsequently fixed and permeabilized to intracellular transcription factor staining by PE-conjugated-Foxp3 Abs. Data was acquired using FACSCalibur and analysis was performed by Flowjo.
Statistical data analysis
All data are the mean of 3 independent experiments with standard deviation (SD) in triplicate. One-way analysis of variance in GraphPad Prism 7.0 (GraphPad, San Diego, CA) was used to measure p-values and a p-value less than 0.05 was considered statistically significant.