Cell Culture
HConFs were obtained from ScienCell Research Laboratories (San Diego, CA, USA), where they were isolated from human conjunctiva. HConFs were characterized by their spindle morphology and immunoreactivity with antibodies to fibronectin. Cells were grown at 37 °C in a humidified incubator with 5% CO2 in fibroblast medium (ScienCell Research Laboratories) containing 2% FBS, 100 U/mL penicillin, 100 µg/mL streptomycin, and fibroblast growth supplement (undisclosed formulation).
Transfection of HConFs with siRNA
To knockdown ClC-2 expression, we obtained commercially available stealth siRNA duplex oligoribonucleotides targeting the human ClC-2 gene. The sequence was 5′-UCCUCAUGAGGAAACGCCUGCUCUU-3′, and its corresponding complementary strand was 5′-AAGAGCAGGCGUUUCCUCAUGAGGA-3′. The negative control consisted of a non-silencing scrambled sequence that did not recognize any known sequence available in the GenBank. To examine the uptake of ClC-2 siRNA by HConFs, siRNA was labeled with Alexa Fluor 488 (Invitrogen Life Technologies, Inc., Carlsbad, CA, USA) for determination of siRNA transfection efficiency. HConFs were transfected with oligonucleotides in the presence of Lipofectamine 2000 (Invitrogen Life Technologies, Inc.) in Opti-MEMI (Invitrogen Life Technologies, Inc.) for 4 h at 37 °C. After removing the transfection mixture, the cells were further incubated for 24 h before experiments under normal growth conditions. The expression of ClC-2 was detected by western blotting and RT-qPCR analysis.
Cell Proliferation Assay (CCK-8 Assay)
HConFs were plated at a density of 5,000 cells/well in a 96-well plate. After treatment, 10 µL of CCK-8 solution (BestBio, Jiangsu, China) was added to each well, followed by incubation for another 3 h at 37 °C. Absorbance at 450 nm was measured using an automated microplate reader (Model 3001 − 1387; Thermo Fisher, Waltham, MA, USA). Each group was provided with 6 duplicate holes, and the experiment was repeated 3 times.
Cell Cycle Analysis
Cell cycle status was assessed by flow cytometry using a Cell Cycle and Apoptosis Analysis Kit (Beyotime, Jiangsu, China). Briefly, cells were grown in 100-mm plates with 10% FBS for 24 h. After treating the cells with media containing different reagents for 48 h, they were collected and fixed in 75% ethanol for 24 h at 4 °C. After rinsing cells with PBS, the cells were stained with PI buffer (containing 500 µL staining buffer, 25 µL of 20 × propidium iodide, and 10 µL of 50 × RNase). The cell cycle distribution was assessed by flow cytometry (CYTOMICS FV 500, Beckman Coulter, Brea, CA, USA).
Reverse Transcription Quantitative Polymerase Chain Reaction (RT-qPCR)
Total RNA was extracted from HConFs at 60–80% confluency with RNAiso Plus (Takara Bio Inc., Shiga, Japan), and 500 ng RNAwas used to synthesize single-stranded cDNA with the RT for PCR Kit (Takara Bio Inc.). Quantitative real-time PCR was performed using methods similar to those previously described[11]. Oligonucleotide primers for the collagen III, MMP2, MMP9, TIMP1, and GAPDH genes were designed using the Primer3 program (http://frodo.wi.mit.edu/primer3/), and sequences are listed in Table 1.
Table 1
Oligonucleotide primers for genes in quantitative real-time RT-PCR
Human genes | Sequences | Product size (kb) |
collagen III | Forward: (5′–3′) TCAGGGTGTCAAGGGTGAA | 130 |
| Reverse:(5′–3′) AGGGTTTCCATCTCTTCCA | |
MMP2 | Forward: (5′–3′) TATGGCTTCTGCCCTGAGAC | 142 |
| Reverse:(5′–3′) CACACCACATCTTTCCGTCA | |
MMP9 | Forward: (5′–3′) AGTCCACCCTTGTGCTCTTC | 117 |
| Reverse:(5′–3′) ACTCTCCACGCATCTCTGC | |
TIMP1 | Forward: (5′–3′) CTGTTGTTGCTGTGGCTGAT | 130 |
| Reverse:(5′–3′) TCTGGTTGACTTCTGGTGTCC | |
GAPDH | Forward: (5′–3′) CAGGAGGCATTGCTGATGAT | 126 |
| Reverse:(5′–3′) CAGGAGGCATTGCTGATGAT | |
Western Blotting Analysis
HConFs were washed with pre-cooled PBS three times and lysed with RIPA buffer [50 mM Tris (pH 7.4), 150 mM NaCl, 1% Triton X-100, 1% sodium deoxycholate, 0.1% SDS, 1 mM PMSF]. The total protein was quantified with the Enhanced BCA Protein Assay Kit (Beyotime). Protein (20 µg per sample) was separated by SDS-PAGE and transferred to PVDF membranes, which were then blocked with blocking solution for 1 h at 37 °C. The membranes were incubated with rabbit polyclonal anti-ClC-2 (Abcam), mouse monoclonal anti-collagen I (Abcam), mouse monoclonal anti-collagen III (Abcam), rabbit polyclonal anti-MMP2 (Abcam), rabbit polyclonal anti-MMP9 (Abcam), rabbit polyclonal anti-TIMP1 (Abcam), and/or mouse monoclonal anti-β-actin (Beyotime) antibodies overnight at 4 °C. Following two washes with TBST, the membrane was incubated with horseradish peroxidase-conjugated anti-rabbit IgG secondary antibody (Beyotime) or anti-mouse IgG secondary antibody (Beyotime) for 1 h at room temperature. Final detection was accomplished with enhanced chemiluminescence western blotting reagents (Beyotime). Band density was analyzed using ImageJ (NIH, Bethesda, MD, USA).
Assay of Collagen Gel Contraction
The collagen gel contraction assay was performed according to previously described methods [9], with some modifications. HConFs were harvested by treatment with trypsin-EDTA, washed twice with serum-free MEM, and resuspended in the same medium. Briefly, collagen I (from a rat tail) stock solution (5 mg/mL) (Solarbio, Beijing, China), 0.1 M NaOH, 10 × concentrated PBS, and the cell suspension were mixed on ice at a volume ratio of 200:12:23:765 (final concentration of type I collagen, 1 mg/mL; final cell density, 2 × 105/mL). A portion (0.5 mL) of the mixture was added to each well of the 24-well culture plate and allowed to solidify by incubation at 37 °C under 5% CO2 for 20 min. The collagen gels were freed from the sides of the wells using a 10-µL tip, and serum-free MEM (0.5 mL) containing TGF-β1 (10 ng/mL) was then added to the top of each gel. The gel area was examined at 48 h using ImageJ. For normalization, the area of the collagen gel containing untreated HConFs was set to 100%, and the fold changes in the area for each treatment group were determined. Four gels were assayed for each experimental condition, and all experiments were repeated four times.
Data Analyses
Results are expressed as means ± standard error (number of observations), and differences among groups were evaluated using analysis of variance (ANOVA). Statistical significance was defined as p < 0.05. All experiments were repeated four times.