Abstract: Objective To investigate the effects of hypoxia on the phenotype transformation of human dermal fibroblasts to myofibroblasts and the mechanism. Methods The third passage of healthy adult human dermal fibroblasts in logarithmic phase were cultured in DMEM medium containing 10% fetal bovine serum for the following five experiments. (1) In experiments 1, 2, and 3, cells were divided into normoxia group and hypoxia group according to the random number table, with 10 dishes in each group. Cells of normoxia group were cultured in incubator containing 21% oxygen, while those of hypoxia group with 1% oxygen. At post culture hour (PCH) 0 and 48, 5 dishes of cells were collected from each group, respectively. mRNA expressions of markers of myofibroblasts including alpha smooth muscle actin (α-SMA), type Ⅰ collagen, and type Ⅲ collagen of cells were determined with real time fluorescent quantitative reverse transcription polymerase chain reaction in experiment 1. Protein expressions of α-SMA, type Ⅰ collagen, and type Ⅲ collagen of cells were determined with Western blotting in experiment 2. The protein expression of nuclear factor-kappa B (NF-κB) of cells was determined with Western blotting in experiment 3. (2) In experiment 4, cells were divided into normoxia group, hypoxia group, and hypoxia+ pyrrolidine dithiocarbamate (PDTC) group according to the random number table, with 5 dishes in each group. Cells in the former two groups were treated the same as those in experiment 1. Cells in hypoxia+ PDTC group were treated the same as those in hypoxia group plus adding 4 mL PDTC with a final molarity of 10 μmol/L in the culture medium. At PCH 48, the protein expression of NF-κB of cells was determined with Western blotting. (3) In experiment 5, cells were divided into normoxia group, hypoxia group, hypoxia+ PDTC group, and normoxia+ PDTC group according to the random number table, with 5 dishes in each group. Cells in the former three groups were treated the same as those in experiment 4. Cells in normoxia+ PDTC group were treated the same as those in normoxia group plus adding 4 mL PDTC with a final molarity of 10 μmol/L in the culture medium. At PCH 48, protein expressions of α-SMA, type Ⅰ collagen, and type Ⅲ collagen of cells were determined with Western blotting. Data were processed with analysis of variance of factorial design, one-way analysis of variance, and LSD-t test. Results (1) Compared with those of normoxia group at corresponding time point, mRNA expressions and protein expressions of α-SMA, type Ⅰ collagen, and type Ⅲ collagen and the protein expression of NF-κB in fibroblasts of hypoxia group were not changed obviously at PCH 0 (with t values from -1.21 to 2.04, P values above 0.05), while mRNA expressions and protein expressions of α-SMA, type Ⅰ collagen, and type Ⅲ collagen and the protein expression of NF-κB significantly increased at PCH 48 (with t values from -12.57 to -3.44, P values below 0.01). (2) At PCH 48, the protein expression of NF-κB in fibroblasts of hypoxia group was 0.83±0.12, significantly higher than that of normoxia group (0.17±0.06, t=-16.96, P<0.001). The protein expression of NF-κB in fibroblasts of hypoxia+ PDTC group was 0.31±0.08, significantly lower than that of hypoxia group (t=12.73, P<0.001). (3) At PCH 48, protein expressions of α-SMA, type Ⅰ collagen, and type Ⅲ collagen in fibroblasts of hypoxia group were 0.73±0.09, 1.25±0.10, and 1.16±0.07, respectively, significantly higher than those of normoxia group (0.14±0.06, 0.87±0.08, and 0.77±0.13, respectively, with t values from 9.24 to 11.24, P values below 0.001). The protein expression of α-SMA in fibroblasts of normoxia+ PDTC group was 0.24±0.07, significantly higher than that of normoxia group (t=4.22, P<0.01). Protein expressions of type Ⅰ collagen and type Ⅲ collagen in fibroblasts of normoxia+ PDTC group were 0.25±0.06 and 0.32±0.11, respectively, significantly lower than those of normoxia group (with t values respectively -4.31 and -3.88, P values below 0.01). Protein expressions of α-SMA, type Ⅰ collagen, and type Ⅲ collagen in fibroblasts of hypoxia+ PDTC group were 0.09±0.08, 0.38±0.12, and 0.47±0.08, respectively, significantly lower than those of hypoxia group (with t values from 11.78 to 22.98, P values below 0.001). Conclusions Hypoxia can significantly up-regulate the expressions of α-SMA, type Ⅰ collagen, and type Ⅲ collagen in human dermal fibroblasts, which may promote the phenotype transformation of fibroblasts to myofibroblasts, and this is likely to be associated with the activation of NF-κB signal pathway.