Background and purpose: Wound healing disorders and the development of fibrosis following surgery in preirradiated tissue are clinically well characterised and may even become more pronounced with increasing use of neoadjuvant radiochemotherapy. The cytokine transforming growth factor beta 1 TGFbeta1 has a key role either in the wound healing process or induction of fibrosis. Following activation of the TGFbeta receptors, intracellular signal transduction is mediated by a variety of Smad proteins. Smad-3 acts as an activator of signal transduction, whereas Smad-7 has an inhibitory effect. This study evaluated the biological effect of neutralizing TGFbeta1 antibodies, the relationship between TGFbeta1 and Smad-3/7 expression and changes of collagen synthesis, following inhibition of TGFbeta1 activity in irradiated rat tissue.
Patients and methods: A total of 45 Wistar rats (male, weight 300-450 g) were used. A free myocutaneous gracilis flap was transplanted in all rats and animals were allocated into 3 groups as follows: Group 1 (n = 15 rats) treated with surgery alone (TX); Group 2 (n = 15 rats) preoperative radiotherapy (RT) followed by TX; Group 3 (n = 15 rats) RT+TX+anti-TGFbeta1-treatment. The interval between end of radiotherapy and grafting was 10 days. For anti-TGFbeta1 treatment, 1 microg anti-TGFbeta1/500 microl PBS were locally applied s.c. intraoperatively and on day 1 to 7 after surgery. Tissue samples were collected perioperatively and on days 3, 7, 14, 28 following surgery from the transition area between the graft and the graft bed. ECM synthesis and expression of TGFbeta1, Smad-3, Smad-7, prolyl-hydroxyprolinase-beta were quantitated by immunohistochemistry (labelling indices). Changes in collagen synthesis were assessed qualitatively by polarisation microscopy of sirius red staining and collagen I immunohistochemistry. The different regulation of inhibitory Smad-7 was detected in irradiated and irradiated plus anti-TGFbeta1 treated animals by semiquantitative RT-PCR and the nucleocytoplasmic shuttling of phosphorylated Smad-3 was shown by isolation of nuclear proteins and Western blot analysis.
Results: Following anti-TGFbeta1 treatment, an attenuated expression of TGFbeta1, a reduction in EMC synthesis and fibrosis could be observed in irradiated tissue compared to the irradiated tissue without anti-TGFbeta1-treatment. While preoperative RT increases the expression of Smad-3/7 proteins, an upregulation of Smad-7 from day 3 until day 14 following surgery and a downregulation of Smad-3 on day 14 after surgery could be observed following anti-TGFbeta1-treatment. The samples which were irradiated alone displayed a reduced signal for Smad-7 mRNA and an induction of Smad-3 protein phosphorylation shown by nucleocytoplasmic shuttling. In contrast, the anti-TGFbeta1-treated samples showed an increase in Smad-7 mRNA and a downregulation of Smad-3 phosphorylation. Prolyl-hydroxyprolinase-beta expression and collagen I synthesis were reduced following anti-TGFbeta1-treatment.
Conclusions: A reduction of Smad-3 proteins in parallel with an increase of Smad-7 may contribute to the inhibitory effect and the reduction of ECM synthesis after blocking of TGFbeta1 activity by treatment with neutralizing antibodies. This may indicate a molecular mechanism in the therapeutic intervention to reduce fibrosis, hypertrophic scar formation and chronic wound healing disorders.