Ethic Permission.
This study was approved by the Cleveland Clinic's Institutional Review Board (IRB) (Ethical Approval 19–908).
Animals.
Wild-type (WT) mice (C57Bl6 background) were maintained under pathogen-free conditions in the animal facility of Lerner Research Institute, Cleveland Clinic, Cleveland OH. All animal handling and associated procedures were approved by the Institutional Animal Care and Use Committee of Cleveland Clinic, and all were done in accordance with the Uunited States Department of Health and Human Services Guide for the Care and Use of Laboratory Animals and institutional guidelines.
Induction and Assessment of Disease Severity of Colitis.
Dextran sulfate sodium (DSS)-induced colitis has been widely used as an experimental model to study pathogenic mechanisms underlying IBD, and disease severity was assessed by assigning clinical scores by following previously published protocols.(32–34) In brief, on day 0, 3% DSS (MW 40 kDa; Sigma-Aldrich, St. Louis, MO) was added to the drinking water. Mice were weighed daily and inspected visually for any sign of sickness. The presence of blood in the stool was tested by Hemoccult II Sensa Fecal Occult Blood Test (Beckman Coulter, Brea, CA) every other day. Previously published literature described that the mice would develop disease on days 3 to 5 (clinical score = 1, scoring charts listed below). (32, 34) The delivery of MSCs, EVs or normal saline (PBS control) was performed on day 4. DSS was continued. Four days after MSC, EV or placebo injection (8 days from initiation of DSS), the mice were sacrificed by carbon dioxide followed by cervical dislocation, and their colons were collected for histological analysis. Differences in serum and intestinal levels of inflammatory factors between PBS control and MSC or EV treated mice were compared. The serum collected from the mice after sacrifice was diluted and the measurement levels of total systemic cytokines calculated by using commercial kits (BioLegend, San Diego, CA) following manufacturer-provided protocols
Evaluation of Colitis severity.
To grade the clinical severity of DSS-induced colitis, mice were assessed for body weight (daily), stool consistency (daily), and hematochezia by fecal occult blood test (every other day) with clinical scores as described in Table 1.
Table 1
Clinical Score
|
Weight loss (%)
|
Stool Consistency
|
Hematochezia
|
0
|
None
|
Normal
|
None
|
1
|
1–10%
|
Soft stool
|
Hemaoccult positive
|
2
|
10–20%
|
Diarrhea
|
Gross blood
|
3
|
20%
|
Diarrhea
|
n/a
|
Isolation of Adipose-Derived Mesenchymal Stem Cells.
Following institutional review board approval (IRB) and patient consent, abdominal subcutaneous adipose-derived MSCs were isolated following the protocol described in the previous study with minor modifications.(35–37) Briefly, healthy human adult subcutaneous adipose tissue was obtained during open ventral hernia repairs of healthy patients defined as no history of malignancy or IBD. The subcutaneous adipose pearls were micro-dissected, washed in phosphate buffer saline (PBS) to remove erythrocytes, minced, and digested with 0.25% type I collagenase type II (Gibco Life Technologies, Waltman, MA) at 37 °C for 60 minutes under constant shaking. Cells were pelleted, supernatant was removed, and cells were resuspended and cultured in xeno-free, serum-free MSC NutriStem® XF Medium (Biological Industries USA, Cromwell, CT, cat# 05-200-1A-KT) under standard cell culture conditions of 37 °C/5% CO2. The cultured MSCs were grown to 85–90% confluency in T75 tissue culture flasks before passaging. MSCs were finally harvested at passage 3 to 4.
To demonstrate the colonic distribution of the injected MSCs, MSCs labeled with CFSE Cell-Labeling Solution (Life Technologies, Carlsbad, CA) were injected into the peritoneal cavity of the mouse. After sacrifice, the colon tissues were harvested to make cryosections for examination under a fluorescence microscope (Leica Microsystems, Buffalo Grove, IL).
Extracellular Vesicle isolation.
To prepare EVs, the previous listed medium(s) from MSC culture was ultra-centrifuged for 16 hours at 100,000x g at 4 °C in a 45Ti fixed angle rotor using polycarbonate tubes (Beckman Coulter, Brea, CA). After ultracentrifugation, the top layer medium suspension was harvested, filtered with a 0.22 µm PES filter and stored at 4 °C. The MSC derived EVs were extracted and concentrated from MSC cultured media. Briefly, during the MSC harvest procedure, the cultured media was collected and filtered through a 0.22 µm filter to remove cell debris and large vesicles, followed by ultracentrifugation at 30,000x g for 20 minutes to pellet larger microvesicles. The supernatants were then subjected to ultracentrifugation at 120,000x g for 3 hours to sediment the EVs. The resulting pellets were resuspended in PBS for injection purposes. To demonstrate the distribution of the injected EVs in the colon, EVs labeled with CFSE Cell-Labeling Solution (Life Technologies, Carlsbad, CA) were injected into the peritoneal cavity of the mouse. To fluorescently label EVs proteins, the isolated EVs were incubated in 100 nM to 10 µM CFSE (BioLegend, San Diego, CA) for 30 to 45 minutes at 37 °C in the dark. After sacrifice, the colon tissues were harvested to make cryosections for examination under a fluorescence microscope (Leica Microsystems, Buffalo Grove, IL).
Histopathological analysis.
Proximal and distal colonic sections were fixed in 4% paraformaldehyde and embedded in optimal cutting temperature (O.C.T.). The 5 mm sections were stained with haematoxylin and eosin (H&E). The microscopic colonic epithelial damage and inflammation severity(38, 39) were assigned scores as follows: 0 = normal; 1 = hyperproliferation, irregular crypts, and goblet cell loss; 2 = mild to moderate crypt loss (10%-50%); 3 = severe crypt loss.
Systemic and Local Cytokine Production.
Blood was collected from the mice of MSC, EV and control groups at the end of experiment and centrifuged for 10 minutes at 800x g at 4 °C. The sera were then frozen and stored at -80 °C until further examination. The colon tissue was mechanically homogenized in RIPA lysis buffer (Santa Cruz Biotechnology, Dallas, TX) containing a mixture of protease inhibitors (Santa Cruz Biotechnology, Dallas, TX). The homogenized tissue was incubated on ice for 30 minutes, with brief vortexing every 5 minutes. Tissue lysates were centrifuged at 13,000 rpm for 30 minutes at 4 °C, the pellets were discarded, and protein concentration of the supernatant was measured using the Pierce BCA Protein Assay kit (Waltman, MA). For the detection of cytokines levels, 96-well high binding plates were coated with 2 µg/ml anti-mouse IL-6, IL-10, TNF-α, IFN-γ, IL-17, or IL-12 (BioLegend, San Diego, CA) diluted in PBS. Protein lysates (diluted 1:20) or serum (diluted 1:50) were loaded onto the coated ELISA plate. Bound cytokines were detected using biotin anti-mouse IL-6, IL-10, TNF-α, IFN-γ, IL-17, or IL-12 (BioLegend, San Diego, CA) and subsequent avidin-HRP antibodies (BioLegend, San Diego, CA). The ELISA color reaction was initiated using tetramethylbenzidine (TMB) substrate (Thermo Scientific, Waltman, MA). 2 M H2SO4 was used to stop the TMB reaction, and absorbance at 450 nm was measured. The colon local cytokines concentrations were normalized to the starting initial protein concentration.
Western blotting and signaling determination.
The protein lysates from colonic tissue were mixed with 2x Laemmli buffer and separated according to their molecular mass on 4–20% SDS-PAGE gel and transferred to a nitrocellulose membrane (Bio-Rad, Hercules, CA). Western blot and antibody detection were performed by established protocol. Rabbit anti-STAT3 (4904), anti-JNK (9252), anti-JAK1 (3344), anti-JAK2 (3230) antibodies were purchased from Cell Signaling Technologies (Danvers, MA) and mouse Direct HRP anti-β-actin (664803) was purchased from BioLegend (San Diego, CA).
Hyperbaric Oxygen-Related Tissue Damage Analysis.
Superoxide dismutase (SOD) were employed for the hyperbaric oxygen-related tissue damage analysis. Lipid peroxidation levels were measured by SOD Assay Kit (Cayman Chemicals, Ann Arbor, MI) according to the manufacturer's instructions. Absorption was recorded at 450 nm. The SOD levels were expressed as nmol/mg protein.
Statistical Analysis.
All listed experiments were repeated at least twice with similar results. To determine whether statistically significant differences existed between groups, data were analyzed by nonparametric Kruskal-Wallis ANOVA. Further analysis by using two-way ANOVA test or, if group variances were dissimilar, Bonferroni-corrected multiple t-tests, produced outcomes similar to those of Kruskal-Wallis ANOVA. A p-value of < 0.05 was considered significant.