The eye is equipped with a distinct ability to restrain inflammatory activity. This unusual property of the eye is mediated, in art, by the ability of cell surface corneal derived Fas ligand (FasL) to induce apoptosis by engaging Fas on influxing inflammatory cells. Establishment of ocular inflammation, therefore, likely involves surmounting the immune regulatory effects of corneal-derived FasL. Thus, we hypothesize that alterations in the expression or function of corneal derived FasL regulates, in part, the inflammatory state of the eye. The understanding of the factors which regulate Fas dependent killing in the cornea has been limited by the lack of an adequate in vitro system which allows for the systematic analyses of this phenomenon, and y a lack of information regarding the genetic mechanisms which restrict FasL expression to the cornea. In this regard, we have established a FasL expressing corneal cell culture system in which corneal cells specifically kill T cells but not B cell Fas+ immune cell targets. Because release of the inactive soluble FasL is likely to be a key site in the regulation of Fas killing, we have also developed an ELISA assay which allows for the specific measurement of the released, cleaved soluble form in cell culture medium. Moreover, we have isolated the mouse FasL promoter so that the key DNA elements and transcription factors controlling FasL expression can be identified. Consistent with its proinflammatory actions in eye tissue, we found that the cytokine IL-1beta markedly depresses the ability of corneal cells to induce apoptosis in Fas+ targets. Furthermore, our deletion analyses and gel shift studies indicate that transcription factors which bind to a promoter segment located between -332 and -228 FasL expression in corneal cells. In this grant, we will further examine the ability of specific inflammatory mediators, including IL-I, to regulate corneal cell mediated apoptosis; mechanisms responsible for modulating FasL activity will be identified. The role of adhesion molecules in the differential capacity of primary and immortalized corneal cells to kill particular T and B cell targets will be investigated. We will also further characterize the genetic basis for FasL expression in the cornea. We believe these studies should provide novel insight into a key mechanism which normally serves to restrain ocular inflammation but may be suppressed in conditions such as corneal transplant rejection and anterior uveitis.
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| Zhang, J; Ma, B; Marshak-Rothstein, A et al. (1999) Characterization of a novel cis-element that regulates Fas ligand expression in corneal endothelial cells. J Biol Chem 274:26537-42 |
