In the present study, we determined phenotypic alterations of the normal and hypertrophic scar fibroblasts after bFGF treatment. It was found that the growth of the hypertrophic scar fibroblasts increased slower than normal fibroblasts after exposure to bFGF. The hypertrophic scar fibroblasts were also more sensitive to bFGF-induced cell death. Furthermore, the hypertrophic scar fibroblasts produced more type Ⅰ collagen than that of the normal fibroblasts in absence of bFGF, whereas type Ⅰ collagen in hypertrophic scar fibroblasts was significantly inhibited by bFGF treatment in comparison to the normal fibroblasts. And bFGF increased fibronectin expression in the normal fibroblasts, but not so prominently in the hypertrophic scar fibroblasts. In addition, normal fibroblasts treated with bFGF (10 or 100 μg/L) showed no significant changes in the mitochondrial membrane potential. And the ATP level significantly increased in the normal fibroblasts after bFGF treatment. It is interesting to note that the mitochondrial membrane potential tended to depolarization, although no statistical difference, in hypertrophic scar fibroblasts treated with bFGF, which might explain why no changes of cellular ATP production in hypertrophic scar fibroblasts with bFGF treatment. The results indicated the different role of bFGF in the normal and hypertrophic scar fibroblasts for the regulation of wound healing. Future studies will be able to determine the different molecular mechanisms between the normal and hypertrophic scar fibroblasts.
As we know, excessive production and deposition of type Ⅰ collagen, the most abundant component of the extracellular matrix, plays an important role in hypertrophic scar formation[20]. A recent study showed that treatment with bFGF on scar tissue of a rat palate for six weeks dramatically suppressed formation of collagen type Ⅰ[21]. The inhibition occurred at the transcriptional level with down-regulation of the type Ⅰ collagen gene expression[8,22]. Our current data also support the inhibition and showed that bFGF significantly reduced the typeⅠ collagen expression in the hypertrophic scar fibroblasts compared to that of the normal fibroblasts. Furthermore, it shows that type Ⅲ collagen synthesis is increased only in the early period of wound healing[23]. However, our current study showed this collagen might not be involved in bFGF-mediated wound healing. In addition, fibronectin participates in a provisional matrix and promotes fibroblast migration in the early phase of wound healing[24]. Excess deposition of fibronectin, at least in part, due to the regulatory mechanisms that function at the transcriptional levels, has been demonstrated in the formation of hypertrophic scars and keloids[25]. Our data demonstrated that bFGF increased fibronectin production in normal fibroblasts, but had less effect on the hypertrophic scar fibroblasts, suggesting that bFGF-mediated modulation of fibroblast growth, extracellular matrix production and gene expression is cell phenotype-dependent, although the underlying mechanism remains unclear.
Mitochondria are membrane-enclosed organelles found in most eukaryotic cells. They are usually termed to be the “power plants” in the cells. Mitochondria are also involved in a range of other cellular processes, such as cell signaling, differentiation, death, as well as the control of the cell cycle and cell growth. During wound repair, a number of events become active, such as secretion of growth factors, cell migration, proliferation, and the production of the extracellular matrix, which are partly controlled by the energy production. It is evident that the extracellular matrix quantity and quality influence cellular growth, differentiation, morphology, survival, and mobility. Mitochondria can sense changes in extracellular matrix composition, and alterations in mitochondrial function also modify the extracellular matrix[26]. As a result, the different response of fibroblast mitochondria to bFGF between the normal and hypertrophic scar fibroblasts is important in determining bFGF regulating the scarless wound repair process. To date, such a study has not been documented in literature. In the present study, bFGF had no effect on the mitochondrial membrane potential in the normal skin fibroblasts, but tended to depolarized mitochondria in hypertrophic scar fibroblasts. Maintaining mitochondrial membrane potential was found to be a prominent mechanism in producing cellular ATP by means of the mitochondria[27-28]. Consistent with this mechanism, our results showed that bFGF, which induced an increment of relative ATP levels in the normal fibroblasts, had no effect on the cellular ATP in the hypertrophic scar fibroblasts. And growth of the normal fibroblasts increased faster than hypertrophic scar fibroblasts after exposure to bFGF. These findings suggest that the effect of bFGF on skin fibroblasts may occur with the involvement of the mitochondria. The proposal is of limited information that exists primarily as a potential and direct interaction of regulatory growth factor, such as bFGF, with the mitochondria during wound healing.
Taken together, our data demonstrated that in vitro exposure of fibroblasts to bFGF had different effects on fibroblast growth and extracellular matrix production between the normal and hypertrophic scar fibroblasts. Moreover, the effect of bFGF on these fibroblasts may be associated with the mitochondria for normal wound healing and hypertrophic scar formation. Thus, further investigation is needed to better understand the interaction of bFGF with the mitochondria during wound healing.
