Barrier disruption increases gene expression of cytokines and the 55 kD TNF receptor in murine skin

The signalling mechanisms that regulate epidermal permeability barrier homeostasis are not known. Previous Northern blot analysis showed that both acute and chronic barrier disruption increase mRNA levels of several cytokines in murine epidermis. To further characterize the epidermal response to barrier abrogation, we used more sensitive, multi-probe RNase protection assays to measure the mRNA levels of additional cytokines, as well as cytokine receptors in acute and chronic models of barrier disruption. Normal mouse epidermis expressed interleukin (IL)-l alpha, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha) and IL-6 mRNAs. Following tape-stripping, only the mRNA levels for TNF-alpha, IL-l alpha, IL-1 beta and IL-6 increased at 2.5 and 7 h, and returned toward normal levels by 18 h. No mRNAs encoding TNF-beta, IL-2, IL-3, IL-4 or IL-5, were detected in the epidermis either under basal conditions or after tape-stripping. Similarly, in a chronic model, essential fatty acid deficiency, epidermal levels of TNF-alpha, IL-1 alpha, IL-1 beta and IL-6 mRNAs, but not IFN-gamma mRNA, were elevated over controls; and again, mRNAs for the remaining probed cytokines were not detected. In contrast, in the dermis, only IL-1 beta mRNA levels increased 2.5 h after tape-stripping, and remained elevated at 18 h. mRNAs encoding the IL-1 (p60), IFN-gamma and IL-6 receptors were present in epidermis, but their levels remained unchanged following either acute or chronic barrier disruption. In contrast, epidermal TNF (p55) receptor mRNA levels were increased by 87% (P<0.01) at 2.5 h, returned to control levels at 7 h and were increased by 68% (P<0.03) at 18 h after tape-stripping. The increase at 2 h was confirmed by Northern blot analysis and was not prevented by latex occlusion performed immediately after tape-stripping. mRNAs for the IL-1 (p80) receptor and TNF (p75) receptor were not detected in epidermis. Low levels of TNF (p55) receptor mRNA were present in the dermis, and they remained unchanged after tape-stripping. The presence of specific receptor mRNAs in the epidermis and dermis suggests that these tissues are capable of responding in an autocrine and/or paracrine fashion to the cognate cytokines. These results suggest that epidermal cytokines produced after barrier disruption may initiate a cytokine cascade which could regulate cytokine and cytokine receptor production and/or inflammatory responses.