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A. J. Hutchinson, S. C. Coons, D. F. Woodward, W. D. Stamer, J. W. Regan; Novel Signaling Pathways Regulated by Prostanoid Receptors in Human Ciliary Smooth Muscle Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2619. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Prostaglandin analogs are widely used for the treatment of glaucoma due to their ability to reduce intraocular pressure by promoting uveoscleral outflow of aqueous humor. Animal studies show that these drugs act on E and F prostanoid receptors (EP1, EP2, EP3, EP4 and FP) in ciliary muscle, where they initiate tissue remodeling processes believed to facilitate aqueous outflow. We aim to address questions regarding the intracellular mechanisms that link the prostanoid receptors to tissue remodeling.
To investigate the activity of prostanoid receptors in ciliary muscle, we established cultures of human ciliary smooth muscle (HCSM) cells from fetal eye tissue explants. These cultures were characterized by their immunoreactivity for alpha-smooth muscle-actin. We further tested these cells for prostaglandin-dependent activation of second messengers, signaling effectors, and reporter gene constructs.
Treatment of HCSM cells with prostaglandin E2 (PGE2) causes a dose-dependent formation of cyclic AMP (EC50=133 nM), the major second messenger associated with the activation of the EP2 and EP4 receptors. Likewise, stimulation of the FP receptor in these cultures with prostaglandin F2α (PGF2α) leads to a dose-dependent accumulation of inositol phosphates (EC50 = 79 nM). PGF2α stimulation of HCSM cells also up regulates the transcription factors hypoxia-inducible factor-1α (HIF-1α), nuclear factor/erythroid-derived 2 related factor-2 (Nrf2) and early growth response factor-1 (EGR-1). Additionally, PGF2α stimulates luciferase activity in cells transfected with plasmids containing either the hypoxia response element (HRE, controlled by HIF-1α) or the antioxidant response element (ARE, controlled by Nrf2).
These signaling effectors, particularly HIF-1α and EGR-1, are known to regulate tissue remodeling in other physiological settings and are potentially involved in the remodeling observed in the ciliary muscle. Activation of the Nrf2/ARE pathway is also interesting for its potential to regulate the expression of cell adhesion molecules, which is also potentially important in remodeling processes. Our findings indicate that cultured HCSM cells express functional prostanoid receptors that are coupled to signaling mechanisms that may contribute to the therapeutic benefit of antiglaucoma drugs.
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