The role of the osmosensitive transcription factor NFAT5 in corneal edema resorption after injury

The osmosensitive transcription factor nuclear factor of activated T cells 5 (NFAT5; or tonicity-responsive enhancer binding protein; TonEBP) plays a key role in macrophage-driven regulation of cutaneous salt and water balance. In the immune-privileged and transparent cornea, disturbances in fluid balance and pathological edema result in corneal transparency loss, which is one of the main causes of blindness worldwide. The role of NFAT5 in the cornea has not yet been investigated. We analyzed the expression and function of NFAT5 in naive corneas and in an established mouse model of perforating corneal injury (PCI), which causes acute corneal edema and transparency loss. In uninjured corneas, NFAT5 was mainly expressed in corneal fibroblasts. In contrast, after PCI, NFAT5 expression was highly upregulated in recruited corneal macrophages. NFAT5 deficiency did not alter corneal thickness in steady state; however, loss of NFAT5 led to accelerated resorption of corneal edema after PCI. Mechanistically, we found that myeloid cell-derived NFAT5 is crucial for controlling corneal edema, as edema resorption after PCI was significantly enhanced in mice with conditional loss of NFAT5 in the myeloid cell lineage, presumably due to increased pinocytosis of corneal macrophages. Collectively, we uncovered a suppressive role for NFAT5 in corneal edema resorption, thereby identifying a novel therapeutic target to combat edema-induced corneal blindness. Vision: Potential therapeutic target for corneal blindness A protein called nuclear factor of activated T cells 5 (NFAT5) plays a significant role in maintaining fluid balance in the cornea, the anterior part of the eye. Disturbances in corneal fluid balance and pathological swelling known as edema potentially lead to loss of corneal transparency and blindness. Deniz Hos and colleagues at the University of Cologne, Germany, studied the functional role of NFAT5 in a mouse model of corneal injury. They found that corneal injury induced significantly increased NFAT5 activity. Furthermore, NFAT5 in macrophages was crucial for controlling corneal fluid balance and the extent of and recovery from corneal edema. These results suggest that drugs able to modify NFAT5 activity could offer a novel way to combat edema-induced corneal blindness.