The prostanoid FP receptor and uveoscleral outflow : A study of FP receptor expression and functions in the eye

Sammanfattning: Prostaglandin F2α is a prostanoid FP receptor agonist which acts as an intraocular pressure-lowering agent by increasing the uveoscleral outflow of aqueous humour through the ciliary muscle. The aim of this, thesis was to investigate possible mechanisms of the increased uveoscleral outflow induced by prostaglandin F2α and its analogue latanoprost acid.A cell line, suitable for biochemical isolation of the FP receptor, was established. Cat iris sphincter muscle cells were immortalised using SV-40 virus. The selected cell line was characterised morphologically, biochemically and pharmacologically.During the study, others reported the primary amino acid sequence deduced from cDNA cloning of ratcorpus luteum FP receptor. This FP receptor sequence was used to generate reagents that allowed studies of the distribution of the FP receptor in various rat organs and in the cynomolgus monkey eye by immunohistochemistry and in situ hybridisation. The FP receptor messenger RNA and protein were detected in several organs and tissue types of the rat, with the strongest expression in muscle and epithelial tissues. The FP receptor was also detected in the monkey eye, with the strongest expression in the ciliary muscle and epithelia.The effects of prostaglandin F2α and latanoprost acid on the extracellular matrix of the ciliary muscle were investigated in cultures of ciliary smooth muscle cells. Immunocytochemistry on the cells suggested that both prostaglandins reduced the deposition of extracellular matrix components such as collagens, fibronectin, laminin and hyaluronan. Furthermore, both prostaglandins increased cellular expression of matrix metalloproteinase types 2 and 3, as revealed by immunofluorescence and zymography, and stimulated the generation of plasmin. Immunohistochemistry on tissue sections of monkey eyes, obtained after in vivo treatment with latanoprost also suggested that the expression of collagens were reduced. Thus our results indicate that the extracellular matrix is remodelled by these prostaglandins, possibly by inducing matrix metalloproteinases.The adhesive interactions between cells and their extracellular matrix were also investigated. Cultured ciliary muscle cells were treated with latanoprost acid and then stained specifically for actin and vinculin which is present in focal adhesions. Effects on intracellular Ca2+ mobilization were studied fluorimetrically in cells loaded with the Ca2+ indicator fluo-3. Latanoprost acid induced transient rearrangements of actin filaments in the cell periphery, stimulated translocation of focal adhesions and increased intracellular Ca2+. Altogether, the data suggest that latanoprost induces a motility response in ciliary muscle cells. Such a motility response may be important for tissue compaction and thereby indirectly for the increased aqueous humour flow through the muscle. In summary, the results suggest that prostaglandin F2α and latanoprost increase uveoscleral outflow of aqueous humour by affecting the composition of the extracellular matrix and the cellular interaction with these components in the ciliary muscle. The FP receptor was abundantly expressed in the ciliary muscle. Since latanoprost is a selective FP receptor agonist, the effect is very likely mediated by the prostanoid FP receptor.