Transcription factor EGR2 alleviates autoimmune uveitis via activation of GDF15 to modulate the retinal microglial phenotype

Uveitis is a vision-threatening disease primarily driven by a dysregulated immune response, with retinal microglia playing a pivotal role in its progression. Although the transcription factor EGR2 is known to be closely associated with uveitis, including Vogt-Koyanagi-Harada disease and Behcet's disease, and is essential for maintaining the dynamic homeostasis of autoimmunity, its exact role in uveitis remains unclear. In this study, diminished EGR2 expression was observed in both retinal microglia from experimental autoimmune uveitis (EAU) mice and inflammation-induced human microglia cell line (HMC3). We constructed a mice model with conditional knockout of EGR2 in microglia and found that EGR2 deficiency resulted in increased intraocular inflammation. Meanwhile, EGR2 overexpression downregulated the expression of inflammatory cytokines as well as cell migration and proliferation in HMC3 cells. Next, RNA-seq and ChIP-PCR results indicated that EGR2 directly bound to its downstream target GDF15 and further regulated GDF15 transcription. Furthermore, intravitreal injection of GDF15 recombinant protein was shown to ameliorate EAU progression in vivo. Meanwhile, knockdown of GDF15 reversed the phenotype of EGR2 overexpression induced microglial inflammation in vitro. In summary, this study highlighted the protective role of the transcription factor EGR2 in autoimmune uveitis by modulating the microglial phenotype. GFD15 was identified as a downstream target of EGR2, providing a novel target for uveitis treatment.

葡萄膜炎（Uveitis）是一类以免疫应答失调为核心致病机制的致盲性眼部疾病，视网膜小胶质细胞（retinal microglia）在其病程进展中发挥关键性作用。尽管已知转录因子EGR2与多种葡萄膜炎亚型密切相关，包括伏格特-小柳-原田病（Vogt-Koyanagi-Harada disease）与贝赫切特病（Behcet's disease），且其对维持自身免疫动态稳态至关重要，但该转录因子在葡萄膜炎中的确切功能仍未明确。本研究在实验性自身免疫性葡萄膜炎（EAU）小鼠的视网膜小胶质细胞，以及炎症诱导的人类小胶质细胞系（HMC3）中，均检测到EGR2表达水平显著下调。我们构建了小胶质细胞特异性条件性敲除EGR2的小鼠模型，实验发现EGR2缺失会加重眼内炎症反应。同时，在HMC3细胞中过表达EGR2可下调炎性细胞因子的表达，并抑制细胞迁移与增殖能力。后续通过RNA测序（RNA-seq）与染色质免疫沉淀PCR（ChIP-PCR）实验证实，EGR2可直接结合下游靶基因GDF15并调控其转录。进一步功能实验显示，玻璃体内注射GDF15重组蛋白可在体内缓解EAU的病程进展；而在体外实验中，敲低GDF15可逆转EGR2过表达所减轻的小胶质细胞炎症表型。综上，本研究阐明了转录因子EGR2通过调控小胶质细胞表型，在自身免疫性葡萄膜炎中发挥保护性作用；并鉴定出GDF15作为EGR2的下游靶基因，为葡萄膜炎的临床治疗提供了全新靶点。