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R Lang, B Harten, H Kalden, FJ Legat, PI Song, NW Bunnett, CA Armstrong, JC Ansel; Human Corneal Epithelial Cells Express Functional PAR-1 and PAR-2 Receptors . Invest. Ophthalmol. Vis. Sci. 2002;43(13):40.
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Purpose: Proteinase-activated receptors (PARs) are a recently described, novel family of G-protein-coupled receptors, which are activated by the cleavage of their N-terminal domain by serine proteases. These receptors are activated by serine proteases such as trypsin and thrombin released after tissue inflammation and injury. In this study we determined if human corneal cells express functional PAR-1 and PAR-2 receptors and examined the effects of receptor activation on corneal proinflammatory cytokine production. Methods: Human primary corneal epithelial cells (HCEC) and the human corneal epithelial cell line HCE-T were cultured to 80% confluence and then exposed to 10 nM thrombin, 100 M human PAR-1 peptide agonist TFLLRN-NH2, 10 nM trypsin, and 100 M murine PAR-2 peptide agonist SLIGRL-NH2 for 3, 6 and 24 hours. Cells treated with PMA (50ng/ml) and TNF-α-treated (10ng/ml) cells served as positive controls for these studies. PAR-1 and PAR-2 mRNA levels were determined by RT-PCR and functionality of the receptors was assessed by intracellular Ca2+ responses. HCE-T cytokine expression (IL-8, IL-6, IL-1-α and TNF-α) in response to PAR-1 and PAR-2 activation was measured by quantitative RT-PCR and ELISA. Localization of PAR-1 and PAR-2 in normal human cornea was determined by immunofluorescence using PAR-1 and PAR-2 antibodies. Results: Our results demonstrated functional PAR-1 and PAR-2 expression in both HCEC and HCE-T. Activation of PAR-1 and PAR-2 led to upregulation of the proinflammatory cytokines IL-8, IL-6, IL-1-α and TNF-α in HCE-T. In human corneal sections PAR-1 and PAR-2 were expressed in the outer epithelial layer of the cornea. Conclusions: These results show for the first time expression of functional receptors for PAR-1 and PAR-2 in human cornea. Activation of these receptors results in the production of various proinflammatory cytokines. These data suggest that PAR-1 and PAR-2 receptors may be important mediators of corneal inflammation.
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