The SOD3 synthesis in dermal fibroblasts and in smooth muscle cells is not regulated directly by oxidative stress but rather via inflammatory cytokines and growth factors

The stroma of the human cornea has a slow tissue turnover rate and absorbs a large part of the ultraviolet light entering the eye. Also, the high demands of the eye’s optical system call for a very exact tissue organization in the corneal stroma. As a consequence, the cornea is potentially vulnerable to oxidative stress. The cytosolic copper-zinc superoxide dismutase (SOD1) [1] and the extracellular-superoxide dismutase (SOD3) [2] are approximately equally abundant in the human cornea [3]. The substrate of the SOD isoenzymes, the superoxide anion, penetrates membranes poorly. The SOD isoenzymes therefore exert their actions in their respective compartments SOD1 within the cells and SOD3 in the extracellular space. Since the extracellular space comprises a large proportion of the cornea and in particular the corneal stroma [4], SOD3 is likely to be the major superoxide scavenger in this tissue [3]. Oxidative stress is thought to contribute to the pathogenesis of the non-inflammatory ectatic corneal degeneration keratoconus (KC) [5-9]. Although the SOD3 mRNA levels in keratoconus are unaltered [8], the corneal levels of SOD3 enzyme are halved [10], which is likely to increase the risk of oxidative damage in the corneal stroma in KC. In the present study, our aim was to elucidate the mechanisms regulating corneal stromal SOD3 synthesis in KC utilizing a model based on cultured stromal cells from patients with KC. As controls, we used stromal cells from normal corneas and from corneas with bullous keratopathy (BKP). BKP is a commonly occurring corneal disease with corneal edema caused by insufficient corneal endothelial pump function [11]. We have previously shown that the overall SOD3 levels in the cornea are unaltered in BKP after correction for the tissue edema [10]. We chose to use corneas from another corneal disease as an additional control in the present investigation since these corneas can be handled exactly like the KC corneas, while some post mortem time is inevitable with the normal control corneas. In addition, deviations in the SOD3 synthesis response occurring in the KC cultures, but not in the BKP or normal controls, are more likely to be specific for KC rather than an unspecific finding seen in any corneal disease. The SOD3 synthesis in dermal fibroblasts and in smooth muscle cells is not regulated directly by oxidative stress but rather via inflammatory cytokines and growth factors [12-14]. Therefore, we chose to quantify the SOD3 synthesis in the presence of various cytokines and growth factors. The cytokines and growth factors investigated here have been shown earlier to regulate SOD3 synthesis in other cell types [12-14] and also have a putative relevance to corneal disease processes [15-18].