Tracking the Elusive Fibrocytes and Detecting Serum Biomarkers in Radiation Skin Fibrosis in a Murine Model

Radiation-induced skin fibrosis is a major complication in patients receiving head and neck irradiation for head and neck cancers and in patients who receive breast and anterior chest wall irradiation for breast cancer. In both human and animal model systems, acute skin ulcer and late organizing skin and subcutaneous tissue fibrosis are directly dependent upon total irradiation dose, fraction size, and volume irradiated. The radiation-induced skin and subcutaneous tissue alteration could be considered as a “complex wound”. How to develop methods of tissue rehabilitation and to improve the quality of life of patients is a challenge encountered in plastic surgery. Optimum rehabilitation and restoration of injuried tissue encompasses a complex process that requires the integration of the biological and molecular events including cell migration and proliferation as well as extracellular matrix (ECM) deposition, angiogenesis, and remodeling. Fibrocytes are a unique population of circulating cells reported to exhibit characteristics of both hematopoietic and mesenchymal cells. Converging evidence from several studies suggests that fibrocytes contribute directly to a new population of fibroblast- and myofibroblast-like cells in wounds and the secretion of inflammatory cytokines, chemokines, and extracellular matrix (ECM) proteins. In addition, fibrocytes have been implicated in influencing human disorders in bronchial asthma, idiopathic pulmonary fibrosis, nephrogenic systemic fibrosis, scleroderma, post-burn hypertrophic scar, atherosclerosis, and tumor biology in recent studies. The role of fibrocytes and its mechanism of action in radiation induced skin fibrosis is still unclear because putative fibrocytes have been found to lose expression of hematopoietic surface markers such as CD45 during differentiation, making it difficult to track these cells in vivo. In the prior studies, most of proposed mechanistic processes in the genesis of radiation induced skin ulceration and subcutaneous fibrosis focus in the critical role of the transforming growth factor P (TGF-P) and pro-inflammatory cytokines, and propose the factor as a major target for antifibrotic agents. The nuclear factor NF-kB pathway has long been considered a proptotypical proinflammatory signaling pathway, largely based on the role of NF-kB in the expression of proinflammatory genes including cytokines, chemokines, and adhesion molecules. The related markers include interleukin family, tissue necrosis factors, cyclins, and antigen receptors. Celastrol, with the potential of anti-cancer and anti-inflammatory activities, was shown to act as an effective inhibitor of the transcription factor NF-kB potentiating the apoptosis induced by TNF-a and chemotherapeutic agents and inhibiting invasion. In radiation induced skin fibrosis, the associated serum biomarkers and their correlation with the severity of fibrosis are still unknown. In our preliminary results, we found that FVB mice with radiation-induced skin fibrosis have a higher number of fibrocytes when compared to the control group. The mRNA expression of inflammatory markers in the radiated group is also higher than the control group. In addition, tail-vein injected fibrocytes could migrate to the radiated skin within 3 days. We hypothesized that fibrocyte may play an important role in radiation induced skin fibrosis because cytokines and related inflammatory markers attract fibrocytes to the injuried area. The purposes of this 3-year proposal are as followed: (1) (1st year) to determine whether cells from whole bone marrow, or from a clonal bone marrow stromal cell line derived from a green fluorescent protein (GFP)+ transgenic mouse, contributed to the histopathologic lesions in areas of radiation-induced skin fibrosis in the irradiated GFP-mouse skin. (2) (2nd year) to detect and to determine the related serum inflammatory markers in radiation-induced skin fibrosis by using FVB mice and diabetes mice model as well as to explore the relationship between the biomarkers and severity of fibrosis. (3) (3rd year) to test the therapeutic potential of celastrol in radiation-induced skin fibrosis and to explore the mechanism of action.

Project ID:PC10601-0398
External Project ID:MOST104-2314-B182-063-MY3