The role of the NFAT signaling pathway in retinal neovascularization

Abstract

Purpose: The purpose of the present study was to investigate the role of nuclear factor of activated T cells (NFAT), a transcription factor downstream of VEGF, in angiogenic cell behaviors of human retinal microvascular endothelial cells (HRMEC), and to assess the efficacy of NFAT signaling inhibitors in a rat model of oxygen-induced retinopathy (OIR).

Methods: Human retinal microvascular endothelial cells were treated with VEGF in the presence or absence of the NFAT inhibitor of NFAT-calcineurin association-6 (INCA-6), and NFAT translocation was evaluated using immunocytochemistry (ICC). Human retinal microvascular endothelial cells were treated with increasing doses of INCA-6, and cell proliferation and tube formation were assessed. Rats subjected to OIR were administered increasing doses of INCA-6 or the CN inhibitor FK-506, and the retinal neovascular area was measured.

Results: Nuclear factor of activated T-cells c1 was translocated to the nucleus of HRMEC treated with VEGF, and INCA-6 treatment blocked translocation. Inhibitor of NFAT-calcineurin association-6inhibited HRMEC proliferation and tube formation in a dose-dependent manner. Both INCA-6 and FK-506 treatment significantly reduced pathologic neovascularization in OIR.

Conclusions: This investigation has demonstrated that in HRMEC, NFATc1 is activated downstream of VEGF signaling and NFAT signaling plays a key role in angiogenic cell behaviors. In addition, NFAT inhibition is shown to be highly efficacious in an OIR model. These findings indicate that the NFAT signaling pathway may serve as a suitable therapeutic target for the treatment of neovascular eye disease.

Keywords: NFAT; neovascularization; oxygen-induced retinopathy; retinal microvascular endothelial cells; transcription factors.

Figure 1

Vascular endothelial growth factor stimulates NFATc1 nuclear translocation in HRMEC. Vascular endothelial growth factor treatment (25 ng/mL) resulted in nuclear translocation of NFATc1 after 30 minutes, and this was effectively inhibited by treatment with INCA-6 (1.0 μM).

Figure 2

The effect of NFAT inhibitor INCA-6 on HRMEC proliferation. Human retinal microvascular endothelial cell proliferation was stimulated with either VEGF (25 ng/mL on a 0.5% serum background) or 10% serum. Inhibitor of NFAT-calcineurin association-6 treatment significantly decreased both VEGF and serum-induced HRMEC proliferation, but did not affect baseline proliferation. Each bar represents the mean ± SEM (n = 21). ‡P < 0.001. †P < 0.01.

Figure 3

The effect of NFAT inhibitor INCA-6 on HRMEC tube formation. Human retinal microvascular endothelial cell tube formation was stimulated with 10% serum. Inhibitor of NFAT-calcineurin association-6 treatment significantly decreased tube formation. (A) Contrast enhanced representative images from treated wells. (B) Quantification of tube measurements. Each bar represents the mean ± SEM (n = 9). ‡P < 0.001.

Figure 4

The effect of inhibitors INCA-6 and FK-506 on the severity of OIR in the rat. Inhibitor of NFAT-calcineurin association-6 and FK-506 significantly inhibited the severity of OIR in a dose-dependent manner. (A) Representative quadrants from treatment groups. (B) Quantification of neovascular area, relative to the vehicle-injected control. Each bar represents the mean ± SEM (for no injection, n = 16; for vehicle n = 23; for INCA-6 2.5 μM, n = 12; for INCA-6 5.0 μM, n = 16; for INCA-6 25.0 μM, n = 11; and for FK-506 2.5, 5.0, and 25.0 μM, n = 7). *P < 0.05.