Expression of endogenous transforming growth factor-beta and its type I and type II receptors in rat burn wounds

Transforming growth factor-beta is a potent regulator of numerous processes in wound healing. These biological activities require the interaction of the growth factor with two classes of cell surface receptors, namely the type I and type II receptors. To understand the role of transforming growth factor-beta in burn wound healing, we undertook a study to localize this growth factor and its cell surface receptors within dermal burn wounds. Partial-thickness burn injuries were made on the backs of Wistar rats. At 1, 3, 5, 7, 10, 15, and 20 days after burning, samples of wounded and control skin were removed for the isolation of total RNA and immunohistochemistry. Thermal injury induced the expression of mRNA for transforming growth factor-beta and both type I and type II receptors. The expression of transforming growth factor-beta peaked 5 to 7 days after injury, then gradually declined. Of note, the expression of the transforming growth factor-beta receptors returned to normal before the expression of the growth factor. Immunohistochemical analysis showed that transforming growth factor-beta protein levels paralleled mRNA expression, and the protein was primarily localized to the migrating epidermal cells and dermal fibroblasts. The differences between the expression of transforming growth factor-beta and its receptors in the later stages of healing thermal injuries suggests the presence of a well-controlled mechanism to limit the effect of the growth factor on repair cells.