[Research and development for treating devastating corneal diseases]

Abstract

In order to develop new therapeutic modalities for corneal diseases, it is essential to combine cutting-edge translational research based upon liberal original ideas obtained from clinical experience with state-of-the-art basic science and technology. Here, I describe seven important research projects on which our group has been working. 1. Elucidation of the pathogenesis in gelatinous drop-like corneal dystrophy(GDLD). Due to loss of function of the tumor-associated calcium signal transducer 2 (TACSTD2), a responsible gene for this dystrophy, tight-junction-related proteins cease to function, resulting in severe corneal epithelial barrier impairment. As a result, various proteins contained in tear fluid continuously penetrate into the corneal stroma, promoting the development of massive amyloid deposits. 2. The development of cultivated mucosal epithelial transplantation: A landmark surgery, involving the transplantation of cultivated mucosal epithelial cells from in vitro to in vivo, now recognized as the next generation of ocular surface reconstruction. We began performing cultivated allocorneal epithelial transplantations in 1999, and cultivated auto-corneal and auto-oral mucosal epithelial transplantations in 2002. These proved to be very effective in the reconstruction of both the corneal surface and the conjunctival fornix. 3. Elucidation of the pathogenesis of Stevens-Johnson syndrome: Studies have shown that there is a close relationship between corneal epithelial stem cell loss and the associated degree of visual impairment. We discovered that a steroid pulse therapy at the acute phase aimed at minimizing stem cell loss is very effective in restoring visual acuity. This implies that inhibition of the cytokine storm is essential for the treatment of acute-phase Stevens-Johnson syndrome. The innate immunity abnormality seems to be heavily involved at the onset of this devastating disease. 4. Elucidation of the involvement of EP3 and toll like receptor 3 (TLR3) in inflammatory ocular surface reactions : We discovered that EP3, one of the prostanoid receptors expressed by ocular surface epithelium, has a dramatic inhibitory effect on ocular surface inflammation in a mouse model. Since EP3 is also expressed in human ocular surface epithelium, and since abnormality of its single nucleotide polymorphisms (SNPs) is involved in some ocular surface inflammatory diseases, we theorized that an allergic reaction may be negatively regulated by EP3 which is predominantly expressed by the ocular surface epithelium. Our findings show that this is similarly true for TLR3, which, conversely, upregulates ocular surface inflammation. 5. Functional regulation of the ocular surface epithelium: Our findings show that intracellular glutathione (GSH) content in the ocular surface epithelium regulates its intracellular redox state. For instance, the GSH content of the conjunctival epithelium decreases in dry eye diseases, yet recovers after the surgical insertion of a punctal plug. Since various amino acids are also heavily involved in the regulation of cellular functions, we investigated the profile of amino acids contained in tear fluids. Our results indicate that there is a marked difference in amino acid profiles between tear fluids and plasma. Furthermore, we found that several amino acids are up-regulated in inflamed eyes, probably due to an oxidative redox response. 6. The development of new therapeutic modalities for corneal edema: We are developing a new therapeutic modality of cultivated corneal endothelial transplantation using methods based on regenerative medicine. For instance, our findings show that cultivated corneal endothelial sheet transplantation in monkeys maintains corneal transparency for at least four years after transplantation. The supplementation of a Rho kinase (ROCK) inhibitor in the culture media produces an excellent result in culturing human corneal endothelium, maintaining a normal-looking endothelial cell morphology. The use of a ROCK inhibitor, both for cultivated endothelial cell injection into the anterior chamber and for use as a topical application, may prove to be a potential tool for the treatment of corneal endothelial dysfunction. 7. The development of a new type of tear function test : The results of our investigations show that the time-dependent changes of tear film lipid layer (TFLL) spread are compatible with the Voigt model of viscoelasticity, and that the initial velocity of the TFLL spread after a blink decreases in proportion to the decrease in tear volume. Thus, a lipid-layer analysis will become an important tear analysis tool. The above are projects representing the way we believe new treatments for severe corneal diseases are heading.