Cell culture and transfection
Human dermal microvascular endothelial cells (HDMECs, ScienCell Research Laboratories, catalog number #2000) were cultured according to the manufacturer’s protocol. Briefly, HDMECs were cultured in Endothelial Cell Medium (ECM, ScienCell Research Laboratories, catalog number #1001) supplemented with 5% fetal bovine serum (FBS, ScienCell Research Laboratories), 4 mmol/l L-glutamine, 100 U/ml penicillin-G, 100 g/ml streptomycin, and 1% endothelial cell growth supplement (v/v; ScienCell Research Laboratories). HDMECs were used from the passage 4 to the passage 5.
Adenoviruses that over-express DARC (Ad-DARC, experimental group) and empty vector of adenovirus without target gene (Ad-eGFP, control group) were made by the Cyagen Biotechnology Co., Ltd. All the adenoviruses were labeled with green fluorescent tags. HDMECs were infected with Ad-DARC or Ad-eGFP at 1 × 106 PFU, in a minimal volume of serum-free medium, and the infection efficiency of HDMECs was confirmed to be above 80% by preliminary experiments.
Cell proliferation and viability assay
Cells were grown on glass coverslips and cultured with anti- bromodeoxyuridine (BrdU) antibody (1:500, ThermoFisher #B35128) at 4℃ through the night. After the coverslips were washed with phosphate buffer saline (PBS, Gibco, catalog number 20012027), the cells were fixed with 4% paraformaldehyde for 15 minutes at room temperature. Then the coverslips were placed in 2N HCl for 30 minutes and washed with PBS. After that, the cells were incubated with antibodies against BrdU (Abcam, ab6326), and Cy3-conjugated secondary antibodies, and then unspecific bindings were blocked with PBS containing 5% goat serum. Finally, the cells were stained with 4’,6-diamidino-2-phenylindole (DAPI) for 10 minutes, and then examined by fluorescence microscopy.
CellTiter-Glo Luminescent Cell Viability Assay Kit (Cat# G7570, Promega) was used according to the manufacturer’s protocol. Briefly, cells were cultured in 96-well plates and infected with Ad-DARC as well as Ad-eGFP in the following day. Equal volumes of medium and CellTiter-Glo Reagent were added at 1st day, 3rd day, and 5th day respectively, and the results were analyzed. Luminescence was detected by a multiwell scanning spectrophotometer.
Cell migration assay
Oris™ Cell Migration Assay Kit (PLATYPUS Technologies, Product No: CMA1.101) was used for cell migration detection according to the manufacturer’s protocol. Briefly, cells were infected with Ad-DARC as well as Ad-eGFP and then seeded in each test well through one of the side ports of the Oris™ Cell Seeding Stopper. When cells had grown to be a confluent monolayer, we removed all the stoppers. Cells were imaged kinetically for up to 24 hours in a CytationTM3(BioTek Instruments, Inc.) microplate imager with incubation at 37℃ and a gas control module set to 5% CO2 using the settings outlined. Then photos were taken at 6-hour intervals with 3 random locations to examine the extent of wound closure. The gap area was calculated with Image-Pro Plus version 6.0 (Media Cybernetics, Inc., Warrendale, PA). The analysis relied on the determination of the area of the detection zone of post-migration wells in comparison with pre-migration wells in which no migration occurred to calculate post-migration percent closure using imaging data.
Tube formation assay
Matrigel (BD Biosciences) was added to 96-well plates with a volume of 50 µl per well, and HDMECs (2 × 104 cells/100 µl) were cultured after the matrigel had solidified at 37℃. To observe tube formation, photographs were taken 24 hours later with the fluorescence microscope, and the degree of tube formation was quantified by measuring the branch points with the use of Image J software.
Cytoskeleton staining
Cells were grown on glass coverslips and fixed with 4% paraformaldehyde for 15 minutes at room temperature. Then they were incubated with 10 µg/ml phalloidine for 30 minutes. After that, the cells were washed with PBS and stained with DAPI for 10 minutes. Finally, the cells were observed under the Olympus IX71 fluorescent microscope.
Immunofluorescence staining
Cells on glass coverslips were fixed with 4% paraformaldehyde for 15 minutes at room temperature and then permeabilized using 0.1% Triton X-100 for 5 minutes. After blocking in 5% goat serum for 60 minutes, the samples were immunostained with primary antibodies against connexin 43(1:5000, ab11369, Abcam,), RhoA(10 µg/ml, ab86297, Abcam), followed by incubation with the goat anti-mouse IgG Alexa Fluor-cy3-conjugated and the goat anti-rabbit IgG Alexa Fluor-488-conjugated secondary antibodies(1:200, Invitrogen). A confocal laser scanning microscopy with an Olympus FV 1000 device was used to observe cellular fluorescence associated with the cell connection.
Western blot analysis
After being washed twice with PBS, the cells were lysed for 30 minutes in ice-cold lysis buffer containing 50 mM Tris, pH 7.5, 150 mM NaCl, 1% NP-40, 0.5% sodium deoxycholate, 0.1% sodium dodecyl sulfate, 1 mM sodium orthovanadate, 5 mM sodium fluoride, 1 mM ethylene diamine tetraacetic acid (EDTA), and the Protease Inhibitors Cocktail (Sigma). Then the samples were boiled at 100℃ for 10 minutes and were placed in ice immediately. Cell lysates were subjected to western blot analysis using rabbit antibodies against RhoA (1 µg/ml, ab86297, Abcam) and mouse antibodies against GAPDH (1 µg/ml, ab9484, Abcam) as the primary antibodies. The significance of the protein expression differences was calculated at last.
In vivo matrigel angiogenesis model
Eight-week-old nude mice were purchased from the Animal Center of the Air Forth Medical University. All animal procedures were performed in accordance with the Animal Care and Use Committee at the University of Air Forth Medical. Matrigel (BD Bioscience, catalog number 354248) was diluted with serum-free Dulbecco’s modified Eagle’s medium(DMEM, Gibco, catalog number 11965092) to 10 mg/ml. All the nude mice were weighed and anesthetized by 60 µl/20 g bodyweight injection of 1% sodium pentobarbital. The dorsal skin was disinfected with 70% ethanol, then tissue engineering chambers were filled with matrigel and then implanted subcutaneously into the dorsal of athymic nude mice. Sixteen nude mice were implanted with matrigel and randomly divided into four groups: the positive control group (n = 4), tissue engineering chambers that were filled with matrigel containing angiogenic factors (heparin and vascular endothelial growth factor); the negative control group (n = 4), tissue engineering chambers that were filled with matrigel without angiogenic factors; the DARC group (n = 4), tissue engineering chambers that were filled with matrigel containing angiogenic factors and Ad-DARC adenovirus; the control group (n = 4), tissue engineering chambers that were filled with matrigel containing angiogenic factors and Ad-eGFP adenovirus. The tissue engineering chambers were removed 6 days after implanted and Dextran was injected into nude mice via the tail vein before removed to mark the blood vessels. New blood capillaries in the matrigel were observed by fluorescence microscopy. To quantify the neovascularization in vivo, the cells were recovered from the matrigel by dispase (Corning, Cat. No. 354235) digestion and cell recovery solution (Corning, Cat. No. 354253). Then the recovered cells were stained with FITC-lectin for statistical analysis .