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R. Prado, J. Son, J.L. Strande, Y. Lu, H. Chen, P.I. Song, C.A. Armstrong, J.C. Ansel; Expression and Function of Proteinase Activated Receptor–2 in Human Conjunctival Epithelial Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5435.
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Proteinase Activated Receptors (PARs) comprise an important, newly identified family of cell membrane proteins that are potent mediators of tissue inflammation, repair and sensation. PAR–2 is known to be activated by mast cell tryptase and cellular derived trypsin and in a number of inflammatory disorders. We have previously detected functional PARs on human corneal cells. Allergic conjunctivitis (AC) is a commonly encountered ocular disorder, affecting 20% of the population. The pathogenesis of AC involves binding of environmental allergens to mast cell IgE, causing cell degranulation and release of inflammatory mediators including histamine and tryptase. Severe and chronic cases of AC can lead to remodeling of the ocular surface. Current therapies are often unsatisfactory. To date, it is not known if functional PARs are expressed on conjunctival epithelial (CE) cells. We propose that PAR–2 may play a key role in the pathogenesis of AC, and may represent a novel potential therapeutic target for its treatment.
The expression of PAR–2 in human CE cells and conjunctival tissue was determined by RT–PCR and immunohistochemistry. PAR–2 function was assessed by measuring intracellular Ca++ responses to specific PAR–2 agonists, and also by immunostaining of NF–kB nuclear translocation after stimulation with PAR–2 agonists. CE cells inflammatory cytokine production was determined by quantitative PCR and ELISA.
Our results indicated that human CE cells constitutively expressed PAR–2. Activation with the PAR–2 agonist trypsin or a PAR–2 activating peptide (PAR–2 AP) caused rapid increase in intracellular calcium concentration, as well as NF–kB nuclear translocation, demonstrating functionality of these receptors in CE cells. Our results also indicated that CE cells expressed the PAR–2 activating protease trypsin. PAR–2 agonists induced a significant increase in IL–1a, IL–1b, IL–6, IL–8, and TNF–a mRNA expression, and increased cytokine protein secretion as demonstrated by ELISA. These specific cytokines are believed to play a significant role in the pathogenesis of AC.
These studies indicate for the first time that human CE cells express functional PAR–2 that can be activated to initiate inflammatory activities proposed to mediate the pathophysiological changes observed in AC. Modulation of CE cell PAR–2 may result in a novel target for treating this common inflammatory ocular disorder.
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