Regulatory effects and signaling mechanism of sodium ferulate on the proliferation and apoptosis of human skin hypertrophic scar fibroblasts

Objective To investigate the regulatory effects and signaling mechanism of sodium ferulate on the proliferation and apoptosis of human skin hypertrophic scar fibroblasts (HSFbs).

Methods The experimental research methods were used. The 4^th-6^th passage of HSFbs from human skin were used for the following experiments. HSFbs were co-cultured with sodium ferulate at final mass concentrations of 1, 1×10^-1, 1×10^-2, 1×10^-3, 1×10^-4, 1×10^-5, and 1×10^-6 mg/mL for 48 hours, and methyl thiazolyl tetrazolium method was used to determine the cell absorbance values and linear regression was used to analyze the half lethal concentration (LC50) of sodium ferulate (n=6). HSFbs were co-cultured with sodium ferulate at final mass concentrations of 0.1, 0.2, 0.3, and 0.4 mg/mL for 24, 48, 72, and 96 hours, and methyl thiazolyl tetrazolium method was used to determine the cell absorbance values and the cell proliferation inhibition rate was calculated (n=3). According to the random number table, the cells were divided into 0.300 mg/mL sodium ferulate group, 0.030 mg/mL sodium ferulate group, 0.003 mg/mL sodium ferulate group treated with sodium ferulate at corresponding final mass concentrations, and negative control group without any treatment. After 72 hours of culture, the cell absorbance values were determined by methyl thiazolyl tetrazolium method (n=5), the microscopic morphology of cells was observed by transmission electron microscope (n=3), the cell apoptosis was detected by TdT-mediated dUTP-biotin nick end labeling (TUNEL) assay and the apoptosis index was calculated (n=4), the protein expressions of B lymphocystoma-2 (Bcl-2), Bcl-2-associated X protein (Bax), and cysteine aspartic acid specific protease-3 (caspase-3) were determined by immunohistochemistry (n=4), and the protein expressions of transformed growth factor β₁ (TGF-β₁), phosphorylated Smad2/3, phosphorylated Smad4, and phosphorylated Smad7 were detected by Western blotting (n=4). Data were statistically analyzed with one-way analysis of variance and Dunnett test.

Results The LC50 of sodium ferulate was 0.307 5 mg/mL. After being cultured for 24-96 hours, the cell proliferation inhibition rates of cells treated with sodium ferulate at four different mass concentrations tended to increase at first but decrease later, which reached the highest after 72 hours of culture, so 72 hours was chosen as the processing time for the subsequent experiments. After 72 hours of culture, the cell absorbance values in 0.003 mg/mL sodium ferulate group, 0.030 mg/mL sodium ferulate group, and 0.300 mg/mL sodium ferulate group were 0.57±0.06, 0.53±0.04, 0.45±0.05, respectively, which were significantly lower than 0.69±0.06 in negative control group (P<0.01). After 72 hours of culture, compared with those in negative control group, the cells in the three groups treated with sodium ferulate showed varying degrees of nuclear pyknosis, fracture, or lysis, and chromatin loss. In the cytoplasm, mitochondria were swollen, the rough endoplasmic reticulum was expanded, and local vacuolation gradually appeared. After 72 hours of culture, compared with that in negative control group, the apoptosis indexes of cells were increased significantly in 0.003 mg/mL sodium ferulate group, 0.030 mg/mL sodium ferulate group, and 0.300 mg/mL sodium ferulate group (P<0.05 or P<0.01). After 72 hours of culture, compared with those in negative control group, the protein expressions of Bcl-2 of cells in 0.300 mg/mL sodium ferulate group was significantly decreased (P<0.01), the protein expressions of Bax of cells in 0.030 mg/mL sodium ferulate group and 0.300 mg/mL sodium ferulate group were significantly increased (P<0.05), and the protein expression of caspase-3 of cells in 0.300 mg/mL sodium ferulate group was significantly increased (P<0.01). After 72 hours of culture, compared with those in negative control group, the protein expression levels of TGF-β₁, phosphorylated Smad2/3, and phosphorylated Smad4 of cells in 0.030 mg/mL sodium ferulate group and 0.300 mg/mL sodium ferulate group were significantly decreased (P<0.05 or P<0.01), and the protein expression levels of phosphorylated Smad7 of cells in 0.003 mg/mL sodium ferulate group, 0.030 mg/mL sodium ferulate group, and 0.300 mg/mL sodium ferulate group were significantly increased (P<0.01).

Conclusions Sodium ferulate can inhibit the proliferation of HSFbs of human skin and promote the apoptosis of HSFbs of human skin by blocking the expression of key proteins on the TGF-β/Smad signaling pathway and synergistically activating the mitochon- drial apoptosis pathway.