NR4A1 Alleviates Subretinal Fibrosis by Inhibiting Macrophage to Myofibroblast Transition

Subretinal fibrosis (SF) secondary to neovascular age-related macular degeneration (nAMD) is the most predominant cause of central visual impairment in all patients with AMD. NR4A1 is a member of the nuclear orphan receptor superfamily, and has shown inhibitory effects on fibrosis in tissues such as the dermis, intestines, and heart. Cytosporone B (Csn-B) is a natural agonist of NR4A1. This study aims to explore whether NR4A1 plays a role in SF associated with nAMD.

Mice RPE-choroid-sclera flat mounts were prepared for serial observation of changes in macrophage infiltration, as well as macrophage to myofibroblast transformation (MMT). The morphology of MMT cells and differences in extracellular matrix (ECM) expression were further observed in TGF-β1-induced THP-1 cells. The role of NR4A1 in MMT was confirmed by small interfering RNA (siRNA) after changes in NR4A1 were observed. To determine whether NR4A1 could be a target for SF treatment, we intervened with the Csn-B and observed the MMT and SF changes.

Macrophages were rapidly recruited in the early stage and gradually decreased after the second week. MMT was observed in the lesions and the maximum number of MMT cells was observed at the third week. NR4A1 was transiently upregulated with induction, followed by a gradual decrease and a continuous phosphorylation. The knockdown of NR4A1 promoted MMT and ECM expression, whereas treatment with Csn-B had an inhibitory effect. P-NR4A1 expression was significantly suppressed in Csn-B-treated MMT cells. Finally, MK-2206 was found to inhibit sustained TGF-β1-induced NR4A1 phosphorylation and also ECM expression.

NR4A1 inhibits MMT and reduces ECM deposition in SF. Its agonist Csn-B inhibits MMT by inhibiting AKT-induced NR4A1 phosphorylation, which then attenuates SF.