Blood and lymphatic microvessel damage in irradiated human skin: The role of TGF-β, endoglin and macrophages.

BACKGROUND AND PURPOSE: Microvascular damage is an important component of late radiation-induced morbidity. In our pre-clinical models, we demonstrated that repair of vessel injury is dependent on proper endoglin-mediated transforming growth factor-beta (TGF-β) signalling and that it can be affected by infiltrating macrophages. We now wanted to extend these findings in irradiated patients, using skin as a model system, and assess whether bisphosphonates could modulate the response.

MATERIALS AND METHODS: Paired skin biopsies from irradiated and non-irradiated sites were obtained from 48 breast cancer patients. In 8 patients, biopsies were repeated after 4months of bisphosphonate treatment. Immunohistochemistry was used to assess vascular alterations and leucocyte infiltration. Western Blot and qPCR were used to assess expression of growth factors and their receptors.

RESULTS: Decreased blood vessel numbers at early time points were followed by increased endoglin expression and restoration of vessel number. Loss of small lymphatic vessels was associated with increased TGF-β levels, whereas dilation of lymphatic vessels correlated with increased macrophage infiltration. Bisphosphonate treatment reduced leucocyte infiltration, but also prevented restoration of blood vessel numbers after irradiation.

CONCLUSION: Radiation injury of the microvasculature is mediated through TGF-β, whereas repair is modulated by the co-receptor endoglin and promoted by macrophages.