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Michael P. Fautsch, Cindy K. Bahler, Zachary T. Resch; Latanoprost-Mediated Calcipressin Accumulation in Human Trabecular Meshwork Cells Occurs Through Calcium Signaling Pathways. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4638.
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© ARVO (1962-2015); The Authors (2016-present)
We have previously shown that treatment of normal primary human trabecular meshwork (NTM) cells with latanoprost free-acid (LFA) induced the expression of RCAN1 (regulator of calcineurin) and its protein product calcipressin. We sought to determine the signaling mechanisms regulating LFA-mediated calcipressin accumulation and whether this is linked to intraocular pressure.
Serum-starved NTM cell lines (n=3) were treated for 30 minutes with prostaglandin F2 receptor antagonist AL-8810 (25 µM), intracellular calcium chelator BAPTA (1 µM), extracellular calcium chelator EGTA (1 mM), nuclear activator of T-cell (NFATc) antagonist VIVIT (25 µM), calcipressin mimetic and calcineurin antagonist cyclosporin A (1 µM) or vehicle controls. Following treatment, NTM cells were incubated for 4 hours with 100 nM LFA in the presence of the inhibitor. Total protein was isolated and calcipressin levels quantified by Western blot. Human anterior segments (range, 66-95 years; n=7) were perfused with cyclosporin A (0.1 µM) and the median outflow facility calculated at 24 hours post-treatment. Significance was determined by Wilcoxon signed-rank test.
LFA treatment of NTM cells increased calcipressin accumulation by 255.3±130.4% compared to vehicle. Inhibition of the prostaglandin F2 receptor decreased LFA-stimulated calcipressin accumulation by 91.8±0.3%. Chelation of intracellular free calcium using BAPTA and sequestration of extracellular calcium with EGTA decreased LFA-stimulated calcipressin by 83.3±5.0% and 95.1±1.6% respectively. Inhibition of calcineurin-dependent NFATc translocation to the nucleus by VIVIT decreased calcipressin expression by 48.8±24.5% suggesting that NFATc proteins are partly responsible for regulating LFA-mediated calcipressin accumulation. Cyclosporin A inhibited LFA-mediated calcipressin activation by 61.9±13.9%. In cultured human anterior segments, cyclosporin A significantly increased outflow facility (µl/min/mmHg) from 0.16 (quartiles 0.14, 0.21) to 0.31 (0.23, 0.42; p<0.02) while fellow vehicle-control eyes showed minimal change from 0.23 (0.13, 0.42) to 0.21 (0.14, 0.35; p=0.63).
LFA stimulates calcipressin accumulation via F2 receptor activation and utilization of intracellular and extracellular calcium stores. LFA-stimulated calcium signaling to the nucleus is mediated by NFATc activation. Physiologically, calcipressin acts as a negative feedback mediator to decrease calcium signaling. This may be one mechanism by which LFA increases outflow facility in cultured anterior segments.
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