Activation of the NFAT-Calcium Signaling Pathway in Human Lamina Cribrosa Cells in Glaucoma

Optic nerve cupping in glaucoma is characterized by remodeling of the extracellular matrix (ECM) and fibrosis in the lamina cribrosa (LC). We have previously shown that glaucoma LC cells express raised levels of ECM genes and have elevated intracellular calcium ([Ca2+]i). Raised [Ca2+]i is known to promote proliferation, activation, and contractility in fibroblasts via the calcineurin-NFAT (nuclear factor of activated T-cells) signaling pathway. In this study, we examine NFAT expression in normal and glaucoma LC cells, and investigate the effect of cyclosporin A (CsA, a known inhibitor of NFAT activity) on [Ca2+]i and ECM gene expression in normal and glaucoma LC cells.

[Ca2+]i was measured with dual-wavelength Ca2+ imaging and confocal microscopy using Fura-2-AM and Fluo-4 under physiological isotonic and hypotonic cell stretch treatment. Human donor LC cells were cultured under normal physiological conditions or using a glaucoma-related stimulus, oxidative stress (H2O2, 100 μM), for 6 hours with or without CsA. NFATc3 protein levels were examined using Western blot analysis. Profibrotic ECM gene transcription (including transforming growth factor-β1 [TGFβ1], collagen 1A1 [Col1A1], and periostin) was analyzed using quantitative real time RT-PCR.

Basal and hypotonic cell membrane stretch-induced [Ca2+]i were significantly (P < 0.05) elevated in glaucoma LC cells compared to normal controls. There was a significant delay in [Ca2+]i reuptake into internal stores in the glaucoma LC cells. NFATc3 protein levels were increased in glaucoma LC cells. CsA (10 μM) significantly inhibited the H2O2-induced expression of NFATc3 in normal and glaucoma LC cells. CsA also reduced the H2O2-induced NFATc3 dephosphorylation (and nuclear translocation), and also suppressed the H2O2-induced elevation in profibrotic ECM genes (TGFβ1, Col1A1, and periostin), both in normal and in glaucoma LC cells.

Intracellular Ca2+ and NFATc3 expression were significantly increased in glaucoma LC cells. CsA reduced the H2O2-induced enhancement in NFATc3 protein expression and nuclear translocation and the profibrotic gene expression both in normal and in glaucoma LC cells. Therefore, targeting the calcineurin-NFATc3 signaling pathway may represent a potential avenue for treating glaucoma-associated LC fibrosis.