757 A possible role for M2 macrophages in preservation of dermal collagen during UVB exposure

Abstract

We previously reported that giving anti-TNFα antibodies (etanercept) to mice blocks UVB recruitment of neutrophils and macrophages into the dermis, but paradoxically, etanercept accelerates UVB-induced loss of dermal collagen. To examine an unsuspected role for neutrophils or macrophages in dermal collagen preservation during UVB exposure, we performed neutrophil depletion and quantification of macrophage subtypes. Of note, M2 macrophages are involved in tissue remodeling in other circumstances and produce TGFβ, an inducer of procollagen. C57BL/6J mice were treated with either murine etanercept (4mg/kg/d) or an anti-Ly6G-specific monoclonal antibody (400μg/d to deplete neutrophils) for 7 days i.p, beginning 2 days before UVB exposure. Mice were irradiated with UVB (100 mJ/cm2/d for 5 d) or sham-irradiated. Skin was stained for neutrophils, M2 macrophages, TGFβ by IHC, and collagen fibers using picrosirius red. Under circular polarized light, picrosirius red differentiates collagen fibers as red or yellow (mature thick type I fibers) versus green (thin type III fibers). Our data show that in UVB-irradiated mice red fibers were decreased compared with sham-irradiated controls. In UVB+etanercept-treated mice, red fibers were markedly decreased compared to UVB without etanercept (p=0.001). Neutrophil-depleted UVB-treated mice showed more red fibers relative to UVB+etanercept-treated mice (p=0.01) and were similar to that seen with sham-irradiated mice. We show that blocking TNFα significantly inhibited M2 macrophage recruitment and TGFβ accumulation in UVB-irradiated mice (p=0.01). Neutrophil depletion in UVB-treated mice did not inhibit M2 macrophage recruitment or TGFβ staining relative to UVB alone. In conclusion etanercept inhibits recruitment of M2 macrophages into skin, as well as TGFβ production, coinciding with decreased mature collagen in the dermis of UVB+etanercept–treated mice relative to neutrophil-depleted UVB-treated mice. Future studies will examine the effects of macrophage depletion on mature collagen in UV-irradiated murine models.