Persistent neuroinflammation and progressive neuronal loss are defining features of acute brain injury including traumatic brain injury (TBI) and cerebral stroke. Microglia, the most abundant type of brain-resident immune cells, continuously surveil the environment and play a central role in shaping the inflammatory state of the central nervous system (CNS). In the study, we discovered that the protein expression of METTL3 (a m⁶A methyltransferase) was upregulated in inflammatory microglia independent of increased Mettl3 gene transcription following TBI in both human and mouse subjects. Subsequently, we identified TRIP12, a HECT-domain E3 ubiquitin ligase, as a negative regulator of METTL3 protein expression by facilitating METTL3 K48-linked polyubiquitination. Importantly, selective ablation of Mettl3 inhibited microglial pathogenic activities, diminished neutrophil infiltration, rescued neuronal loss and facilitated functional recovery post-TBI. Using MeRIP-seq and CUT&Tag sequencing, we identified that METTL3 promoted the expression of Basic Leucine Zipper Transcriptional Factor ATF-Like (BATF), which in turn directly bound to a cohort of characteristic inflammatory cytokines and chemokine genes. Enhanced activities of BATF in microglia elicited TNF-dependent neurotoxicity and can also promote neutrophil recruitment through releasing CXCL2. Pharmacological inhibition of METTL3 using a BBB-penetrating drug-loaded nano-system showed satisfactory therapeutic effects in both TBI and stroke mouse models. Collectively, our findings identified METTL3-m⁶A-BATF axis as a potential therapeutic target for terminating detrimental neuroinflammation and progressive neuronal loss following acute brain injury.

持续性神经炎症和进行性神经元丢失是急性脑损伤的定义特征，包括创伤性脑损伤 （TBI） 和脑卒中。小胶质细胞是大脑中存留免疫细胞最丰富的类型，持续监测环境，并在塑造中枢神经系统 （CNS） 的炎症状态中发挥核心作用。在这项研究中，我们发现 METTL3 （a m⁶A 甲基转移酶） 的蛋白表达在炎性小胶质细胞中上调，与人类和小鼠受试者 TBI 后 Mettl3 基因转录增加无关。随后，我们鉴定出 HECT 结构域 E3 泛素连接酶 TRIP12 通过促进 METTL3 K48 连接的多泛素化，成为 METTL3 蛋白表达的负调节因子。重要的是，Mettl3 的选择性消融抑制了小胶质细胞致病活性，减少了中性粒细胞浸润，挽救了神经元丢失并促进了 TBI 后的功能恢复。使用 MeRIP-seq 和 CUT&Tag 测序，我们发现 METTL3 促进了碱性亮氨酸拉链转录因子 ATF 样 （BATF） 的表达，而 BATF 又直接与一组特征性炎性细胞因子和趋化因子基因结合。增强 BATF 在小胶质细胞中的活性会引起 TNF 依赖性神经毒性，并且还可以通过释放 CXCL2 促进中性粒细胞募集。使用 BBB 穿透药物负载纳米系统对 METTL3 的药理学抑制在 TBI 和中风小鼠模型中均显示出令人满意的治疗效果。总的来说，我们的研究结果确定 METTL3-m⁶A-BATF 轴是终止急性脑损伤后有害神经炎症和进行性神经元丢失的潜在治疗靶点。