Elevation of IL-1β and matrix metalloproteinases (MMPs) in radiation induced mouse dermatitis and fibrosis.

3119 Interleukin-1 beta (IL-1β) is a potent pro-inflammatory cytokine, which is up-regulated by a variety factors including radiation. IL-1β also modulates the production of other inflammation related molecules, such as, MMPs and MMP inhibitors (TIMPs). Although IL-1β has been reported to enhance the production of MMPs in several cells, and the imbalanced induction of MMPs, TIMPs, and collagen synthesis is in part regulated by IL-1. The effects of elevated cutaneous IL-1β after irradiation on MMPs and/or TIMPs are unknown. Primary cultured human cutaneous keratinocyte, fibroblast and endothelial cell lines from a single donor were irradiated with 10 Gy in order to identify cytokine-producing cells responding to radiation. Then the right hind leg of C57BL/6 WT and IL-1R1(-/-) mice were given a single dose of 30Gy radiation to elucidate radiation induced cytokines in an in-vivo mouse model. Finally, the IL-1β recombinant protein (10 ng x 5 days) per mouse was intramuscularly injected into irradiated mouse leg to explore the causal relationship between IL-1β levels and cutaneous fibrosis. Our results show that: 1) mRNA of IL-1α, IL-1β and IL-1Ra, but not IL-6 were significantly induced by 10 Gy radiation in all three cell types. Keratinocyte however are the major IL-1-producing cells in the skin. 2) Radiation chronically elevated skin IL-1β mRNA including the stage of early dermatitis (14 and 19 Days), and also the stage of late fibrosis (60 and 90 day). While both the WT and IL-1R1-/- mice had elevated IL-1 at early time points, the effect was enormous in the WT animals. Only the WT animals had chronic elevations of IL-1. 3) Similarly, IL-1α mRNA in WT mice were significantly elevated compare to the IL-1R1-/- mice on 60 and 90 days after radiation. 4) Radiation induced mRNA expression for MMP-1/13, -2, -3 at early time points in both WT and IL-1R1-/- mice, only the WT mice had elevation of MMP’s at late time points. None of the TIMPs tested in skin and muscle changed after radiation in either mouse model. 5) Exogenous IL-1β robustly induced endogenous IL-1β mRNA expression, along with a brisk increase in MMP-1/13, -2, -3 in skin of WT mice, but not in IL-1R1-/- mice. 6) The type III collagen detected by immunohistochemistry was also increased in WT cutaneous fibrotic tissues compare with that of the IL-1R1-/- mice. In conclusion, IL-1β and MMPs, produced by keratinocytes in irradiated skin plays a critical role in radiation induced dermatitis and late fibrosis.