Purpose: To determine the expression and precise cellular and subcellular localization of the EP prostanoid receptor subtypes EP(1) through EP(4) and the FP receptor in normal human ocular tissues on the protein and mRNA levels.
Methods: Expression of EP and FP receptor proteins was examined by immunohistochemistry on the light microscopic level, using subtype-specific antibodies on frozen and paraffin-embedded tissue sections of 10 normal human donor eyes. The subcellular distribution of the receptor proteins was studied by electron microscopic immunogold labeling. mRNA expression in various ocular tissues was analyzed by reverse transcription-polymerase chain reaction, using subtype-specific primers.
Results: The highest expression of the EP(1) receptor protein was found in the epithelia of the cornea, conjunctiva, lens, and the ciliary body; trabecular cells; iris vessels; and retinal ganglion cells. EP(2) receptor labeling was most prominent in the corneal epithelium and choriocapillaries. EP(3) and EP(4) receptor labeling was primarily observed in the corneal endothelium and keratocytes, trabecular cells, ciliary epithelium, and conjunctival and iridal stroma cells, and EP(3) was found, in addition, in retinal Müller cells. The highest expression of FP receptor protein was found in the corneal epithelium, ciliary epithelium, the circular portion of ciliary muscle, and iris stromal and smooth muscle cells. Immunoelectron microscopy showed a subcellular distribution of all prostanoid receptors along plasma membranes and the nuclear envelope. EP and FP receptor mRNA expression largely paralleled the proteins' expression patterns.
Conclusions: The findings demonstrate a wide distribution but differential expression of FP and EP prostanoid receptor subtypes in human ocular tissues. EP(1) through EP(4) receptor subtype expression in human outflow pathways could be significant for future pharmacologic management strategies for the glaucomas.