Differential influence of TGFbeta1 and TGFbeta3 isoforms on cell cycle kinetics and postirradiation recovery of normal and malignant colorectal epithelial cells

TGF-β3 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-β) family are key players in the fibrotic response. While TGF-β1 is known to be pro-fibrotic, TGF-β3 has mainly been considered anti-fibrotic. Moreover, TGF-β3 has been shown to act protective against acute toxicities after radio- and chemotherapy. In the present study, we investigated the effect of TGF-β3 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-β3 group received local fractionated H&N RT with 66 Gy over five days, combined with TGF-β3-injections at 24-hour intervals. Animals in the RT reference group received identical RT without TGF-β3 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-β3 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-β3 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-β3 treatment did not impact saliva production.

CONCLUSIONS

When repeatedly administered during fractionated RT at the current dose, TGF-β3 treatment increased acute H&N radiation toxicities and increased mortality. Furthermore, TGF-β3 treatment may increase the severity of radiation-induced salivary gland fibrosis.

The Role of TGF-β3 in Radiation Response

Transforming growth factor-beta 3 (TGF-β3) 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-β3. Furthermore, the cell cycle regulating and anti-fibrotic effects of TGF-β3 have identified it as a potential mitigator of radiation- and chemotherapy-induced toxicity in healthy tissue. This review discusses the radiobiology of TGF-β3, its induction in tissue by ionizing radiation, and its potential radioprotective and anti-fibrotic effects.

Cell kinetic studies in the murine ventral tongue epithelium: the effects of repeated exposure to keratinocyte growth factor

Keratinocyte growth factor (KGF) stimulates proliferation and differentiation in various epithelial systems. Three daily subcutaneous injections of 125 microg of this protein into mice induce dramatic changes in the histology and histometric measurements of the ventral tongue epithelium. The thickness of the epithelium is increased two-fold and the number of cells beneath a 1-mm length of the surface is increased 1.6-fold. KGF also induces a four-fold increase in the number of S phase cells labelled with tritiated thymidine in the basal layer on the third day after KGF administration. The increase in thickness and cellularity persist for at least 4 days after the end of the KGF injections. However, there is a dramatic fall in the number of S phase cells detected by 3HTdR pulse labelling 2 days after the end of the KGF treatment. There are indications that by 7 days after the 3-day regimen of KGF treatment, both thickness and cellularity have fallen back to near control levels. Continued exposure to KGF over a period of 7 days does not result in any further increases in thickness, cellularity or proliferation. In fact, the proliferation decreases on the fifth, sixth and seventh days of KGF injection to control values on day 7. These changes in the epithelium following KGF treatment suggest that the thicker and more cellular epithelium may be more able to cope with an exposure to a cytotoxic agent and hence be protected in comparison with normal or vehicle-treated epithelium.

Transforming growth factor-B3 protects murine small intestinal crypt stem cells and animal survival after irradiation, possibly by reducing stem-cell cycling

Damage to the normal replacing tissues of the body, specifically the gastro-intestinal tract, limits the treatment and hence, cure rate of cancer patients. Here, we investigate the possibility that the sensitivity of the gastro-intestinal tract can be manipulated by transforming growth factor beta3 (TGF-beta3), making it more resistant to radiation in a murine model. The effects of TGF-beta3 were assessed using the crypt microcolony assay, a test of crypt stem-cell functional competence, in animal survival studies examining diarrhoea severity, labelling index and crypt size. Prior treatment with TGF-beta3 can result in a 3- to 4-fold increase (protection factor, PF) in surviving crypts, whilst longer exposure can raise the PF to almost 12. Protection of intestinal clonogenic stem cells results in marked protection of survival with a corresponding reduction in the duration and level of diarrhoea and ultimate restoration of normal histology in surviving mice. Inhibition of proliferation can be demonstrated when sufficient TGF-beta3 exposure is studied. Crypt size is also reduced. In conclusion, TGF-beta3 protects small intestinal clonogenic stem cells from radiation damage, reducing diarrhoea and animal mortality. The mode of action is believed to be specific inhibition of stem-cell proliferation.

In vivo administration of genistein has no effect on small intestinal epithelial proliferation and apoptosis, but a modest effect on clonogen survival

The soya metabolite genistein possesses anti-proliferative, pro-apoptotic activities in intestinal epithelial cells in vitro and may reduce epithelial cancer incidence. This could involve cell cycle arrest/apoptosis in the proliferative or clonogenic cells. We investigated the effects of genistein on the small intestinal epithelium in vivo. No effect on the number or distribution of proliferative cells in the crypts was detected. Similarly, no change in spontaneous apoptotic cell incidence or the characteristic stem cell apoptotic response following low dose irradiation was observed. Genistein afforded a modest decrease in clonogen radiosensitivity. Hence, using a range of dosing protocols, sub-cutaneous administration of genistein for periods of up to 1 week did not alter intestinal epithelial homeostasis.

Cellular sources of transforming growth factor-beta isoforms in early and chronic radiation enteropathy

The three mammalian transforming growth factor (TGF)-beta isoforms (TGF-beta1, TGF-beta2, and TGF-beta3) differ in their putative roles in radiation-induced fibrosis in intestine and other organs. Furthermore, tissue specificity of TGF-beta action may result from temporal or spatial changes in production and/or activation. The present study examined shifts in the cell types expressing TGF-beta mRNA relative to TGF-beta immunoreactivity and histopathological injury during radiation enteropathy development. A 4-cm loop of rat small intestine was locally exposed to O, 12, or 21-Gy single doses of x-irradiation. Sham-irradiated and irradiated intestine were procured 2 and 26 weeks after irradiation. Cells expressing the TGF-beta1, TGF-beta2, or TGF-beta3 transcripts were identified by in situ hybridization with digoxigenin-labeled riboprobes. Intestinal wall TGF-beta immunoreactivity was measured using computerized image analysis, and structural radiation injury was assessed by quantitative histopathology. Normal intestinal epithelium expressed transcripts for all three TGF-beta isoforms. Two weeks after irradiation, regenerating crypts, inflammatory cells, smooth muscle cells, and mesothelium exhibited increased TGF-beta1 expression and, to a lesser degree, TGF-beta2 and TGF-beta3 expression. Twenty-six weeks after irradiation, TGF-beta2 and TGF-beta3 expression had returned to normal. In contrast, TGF-beta1 expression remained elevated in smooth muscle, mesothelium, endothelium, and fibroblasts in regions of chronic fibrosis. Extracellular matrix-associated TGF-beta1 immunoreactivity was significantly increased at both observation times, whereas, TGF-beta2 and TGF-beta3 immunoreactivity exhibited minimal postradiation changes. Intestinal radiation injury is associated with overexpression of all three TGF-beta isoforms in regenerating epithelium. Radiation enteropathy was also associated with sustained shifts in the cellular sources of TGF-beta1 from epithelial cells to cells involved in the pathogenesis of chronic fibrosis. TGF-beta2 and TGF-beta3 did not exhibit consistent long-term changes. TGF-beta1 appears to be the predominant isoform in radiation enteropathy and may be more important in the mechanisms of chronicity than TGF-beta2 and TGF-beta3.

High value of the radiobiological parameter Dq correlates to expression of the transforming growth factor beta type II receptor in a panel of small cell lung cancer cell lines

Our panel of SCLC cell lines have previously been examined for their radiobiological characteristics and sensitivity to treatment with TGF beta 1. In this study we examined the possible correlations between radiobiological parameters and the expression of the TGF beta type II receptor (TGF beta-rII). We have, in other studies, shown that the presence of TGF beta-rII was mandatory for transmitting the growth inhibitory effect of TGF beta. The results showed a statistically significant difference in Dq, i.e. the shoulder width of the survival curve, between cell lines expressing TGF beta-rII and cell lines which did not express the receptor (P = 0.01). Cell lines expressing TGF beta-rII had a high Dq-value. TGF beta-rII expression did not correlate with any other radiobiological parameters. We suggest that an intact growth inhibitory pathway mediated by the TGF beta-rII may have a significant role for the repair of radiation induced DNA damage in SCLC.