The Role of TGF-ß3 in Radiation Response.

Transforming growth factor-beta 3 (TGF-ß3) is a ubiquitously expressed multifunctional cytokine involved in a range of physiological and pathological conditions, including embryogenesis, cell cycle regulation, immunoregulation, and fibrogenesis. The cytotoxic effects of ionizing radiation are employed in cancer radiotherapy, but its actions also influence cellular signaling pathways, including that of TGF-ß3. Furthermore, the cell cycle regulating and anti-fibrotic effects of TGF-ß3 have identified it as a potential mitigator of radiation- and chemotherapy-induced toxicity in healthy tissue. This review discusses the radiobiology of TGF-ß3, its induction in tissue by ionizing radiation, and its potential radioprotective and anti-fibrotic effects.

Low-Dose-Rate Radiation-Induced Secretion of TGF-ß3 Together with an Activator in Small Extracellular Vesicles Modifies Low-Dose Hyper-Radiosensitivity through ALK1 Binding.

Hyper-radiosensitivity (HRS) is the increased sensitivity to low doses of ionizing radiation observed in most cell lines. We previously demonstrated that HRS is permanently abolished in cells irradiated at a low dose rate (LDR), in a mechanism dependent on transforming growth factor ß3 (TGF-ß3). In this study, we aimed to elucidate the activation and receptor binding of TGF-ß3 in this mechanism. T-47D cells were pretreated with inhibitors of potential receptors and activators of TGF-ß3, along with addition of small extracellular vesicles (sEVs) from LDR primed cells, before their radiosensitivity was assessed by the clonogenic assay. The protein content of sEVs from LDR primed cells was analyzed with mass spectrometry. Our results show that sEVs contain TGF-ß3 regardless of priming status, but only sEVs from LDR primed cells remove HRS in reporter cells. Inhibition of the matrix metalloproteinase (MMP) family prevents removal of HRS, suggesting an MMP-dependent activation of TGF-ß3 in the LDR primed cells. We demonstrate a functional interaction between TGF-ß3 and activin receptor like kinase 1 (ALK1) by showing that TGF-ß3 removes HRS through ALK1 binding, independent of ALK5 and TGF-ßRII. These results are an important contribution to a more comprehensive understanding of the mechanism behind TGF-ß3 mediated removal of HRS.

TGF-ß3 increases the severity of radiation-induced oral mucositis and salivary gland fibrosis in a mouse model.

PURPOSE: Toxicities from head and neck (H&N) radiotherapy (RT) may affect patient quality of life and can be dose-limiting. Proteins from the transforming growth factor beta (TGF-ß) family are key players in the fibrotic response. While TGF-ß1 is known to be pro-fibrotic, TGF-ß3 has mainly been considered anti-fibrotic. Moreover, TGF-ß3 has been shown to act protective against acute toxicities after radio- and chemotherapy. In the present study, we investigated the effect of TGF-ß3 treatment during fractionated H&N RT in a mouse model. MATERIALS AND METHODS: 30 C57BL/6J mice were assigned to three treatment groups. The RT + TGF-ß3 group received local fractionated H&N RT with 66 Gy over five days, combined with TGF-ß3-injections at 24-hour intervals. Animals in the RT reference group received identical RT without TGF-ß3 treatment. The non-irradiated control group was sham-irradiated according to the same RT schedule. In the follow-up period, body weight and symptoms of oral mucositis and lip dermatitis were monitored. Saliva was sampled at five time points. The experiment was terminated 105 d after the first RT fraction. Submandibular and sublingual glands were preserved, sectioned, and stained with Masson's trichrome to visualize collagen. RESULTS: A subset of mice in the RT + TGF-ß3 group displayed increased severity of oral mucositis and increased weight loss, resulting in a significant increase in mortality. Collagen content was significantly increased in the submandibular and sublingual glands for the surviving RT + TGF-ß3 mice, compared with non-irradiated controls. In the RT reference group, collagen content was significantly increased in the submandibular gland only. Both RT groups displayed lower saliva production after treatment compared to controls. TGF-ß3 treatment did not impact saliva production. CONCLUSIONS: When repeatedly administered during fractionated RT at the current dose, TGF-ß3 treatment increased acute H&N radiation toxicities and increased mortality. Furthermore, TGF-ß3 treatment may increase the severity of radiation-induced salivary gland fibrosis.