Blockade of extracellular high-mobility group box 1 attenuates inflammation-mediated damage and haze grade in mice with corneal wounds.

PURPOSE

To investigate the expression of extracellular high mobility group box 1 (HMGB1) and the effect of its inhibitor glycyrrhizin (GL) in corneal wound healing.

METHODS

We treated C57BL/6J mice with GL or PBS before and after establishing a corneal injury model. Fluorescein staining, Ki-67 expression, haze grade, and haematoxylin/eosin (H&E) staining were used to assess treatment efficacy. The expression of HMGB1, NF-κB-p65, the NLRP3 inflammasome, IL-1β, CCL2, CXCL2, TGF-β1, α-SMA, fibronectin, and collagen III and neutrophil influx were examined by immunohistochemical staining, western blot, and RT-qPCR at various time points after corneal injury.

RESULTS

After corneal injury, HMGB1 transferred from the nucleus to the cytoplasm and was passively released or actively secreted into the corneal stroma from epithelial cells and inflammatory cells; however, this increase was attenuated by GL treatment. Furthermore, GL indirectly attenuated the expression of IL-1β by directly inhibiting extracellular HMGB1 functions, which activated the NF-κB-p65/NLRP3/IL-1β signalling pathway. Moreover, application of GL alleviated the neutrophil infiltration that delays wound healing, accompanied by the downregulation of expression of the chemokines CCL2 and CXCL2. More interestingly, application of GL reduced the degree of haze grade through inactivating extracellular HMGB1 functions that induced TGF-β1 release and myofibroblast differentiation. In addition, fluorescein and H&E staining and Ki-67 levels suggest that GL promotes regeneration of corneal epithelium.

CONCLUSIONS

After corneal injury, extracellular HMGB1 can be an essential driver to trigger a neutrophil- and cytokine-mediated inflammatory injury amplification loop. The application of GL promotes the cornea to restore transparency and integrity, which may be related to the attenuation of extracellular HMGB1 levels and function.