Beijing Institute of Basic Medical Sciences, Beijing 100850, China.
Chinese Institute for Brain Research, Beijing 102206, China.
Theranostics. 2022 Feb 14;12(5):2248-2265. doi: 10.7150/thno.65916. eCollection 2022.
Fulminant hepatitis (FH) is a life-threatening disease with partially understood pathogenesis. It has been demonstrated that myeloid-derived suppressor cells (MDSCs) are recruited into the liver during this process, and their augmented accumulation by various strategies protects against liver injury. However, the underlying mechanism(s) remain elusive. Receptor for activated C kinase 1 (RACK1), a multi-functional scaffold protein, is highly expressed in normal liver and has been implicated in liver physiology and diseases, but the role of hepatic RACK1 in FH remains unknown. Survival curves and liver damage were monitored to investigate the role of hepatic RACK1 in FH. The liver microenvironment was explored by microarray-based transcriptome analysis, flow cytometry, immunoblotting, and immunohistochemistry. MDSCs were identified with phenotypic and functional characteristics. Functional antibodies were used to target MDSCs. Co-culture techniques were used to study the underlying mechanism(s) of protection. The interaction of RACK1 with histone deacetylase 1 (HDAC1) and the consequent effects on HDAC1 ubiquitination were analyzed. Ectopic expression of HDAC1 with recombinant adeno-associated virus serotype 8 was conducted to confirm the role of HDAC1 in the protective effects of hepatic RACK1 deficiency against FH. Post-translational modifications of RACK1 were also investigated during the induction of FH. Liver-specific RACK1 deficiency rendered mice resistant to FH. RACK1-deficient livers exhibited high basal levels of chemokine (C-X-C motif) ligand 1 (CXCL1) and S100 calcium-binding protein A9 (S100A9), associated with MDSC accumulation under steady-state conditions. Targeting MDSCs with an antibody against either Gr1 or DR5 abrogated the protective effects of liver-specific RACK1 deficiency. Accumulated MDSCs inhibited inflammatory cytokine production from macrophages and enhanced IκB kinase (IKK)/NF-κB pathway activation in hepatocytes. Further investigation revealed that RACK1 maintained HDAC1 protein level in hepatocytes by direct binding, thereby controlling histone H3K9 and H3K27 acetylation at the and promoters. Ectopic expression of HDAC1 in livers with RACK1 deficiency partially reversed the augmented → MDSCs → IKK/NF-κB axis. During FH induction, RACK1 was phosphorylated at serine 110, enhancing its binding to ubiquitin-conjugating enzyme E2T and promoting its ubiquitination and degradation. Liver-specific RACK1 deficiency protects against FH through accelerated HDAC1 degradation and the consequent CXCL1/S100A9 upregulation and MDSC accumulation.
暴发性肝炎（FH）是一种具有部分不明发病机制的危及生命的疾病。已经证明，髓源性抑制细胞（MDSCs）在这个过程中被招募到肝脏中，并且通过各种策略增加其积累可以防止肝损伤。然而，潜在的机制仍然难以捉摸。激活蛋白激酶 C 受体 1（RACK1）是一种多功能支架蛋白，在正常肝脏中高度表达，并与肝脏生理学和疾病有关，但肝 RACK1 在 FH 中的作用仍不清楚。通过监测生存曲线和肝损伤来研究肝 RACK1 在 FH 中的作用。通过基于微阵列的转录组分析、流式细胞术、免疫印迹和免疫组织化学来探索肝微环境。通过表型和功能特征鉴定 MDSCs。使用功能性抗体靶向 MDSCs。使用共培养技术研究潜在的保护机制。分析了 RACK1 与组蛋白去乙酰化酶 1（HDAC1）的相互作用及其对 HDAC1 泛素化的影响。用重组腺相关病毒血清型 8 进行 HDAC1 的异位表达，以证实 HDAC1 在肝 RACK1 缺乏对 FH 的保护作用中的作用。还在 FH 诱导过程中研究了 RACK1 的翻译后修饰。肝特异性 RACK1 缺乏使小鼠对 FH 具有抗性。RACK1 缺陷型肝脏在稳态条件下表现出高水平的趋化因子（C-X-C 基序）配体 1（CXCL1）和 S100 钙结合蛋白 A9（S100A9），与 MDSC 积累有关。用针对 Gr1 或 DR5 的抗体靶向 MDSC 会消除肝特异性 RACK1 缺乏的保护作用。积累的 MDSC 抑制巨噬细胞中炎性细胞因子的产生，并增强肝细胞中 IκB 激酶（IKK）/NF-κB 途径的激活。进一步的研究表明，RACK1 通过直接结合维持肝细胞中 HDAC1 的蛋白水平，从而控制组蛋白 H3K9 和 H3K27 在 和 启动子上的乙酰化。在 RACK1 缺陷型肝脏中异位表达 HDAC1 部分逆转了增强的 → MDSC → IKK/NF-κB 轴。在 FH 诱导过程中，RACK1 在丝氨酸 110 处磷酸化，增强其与泛素连接酶 E2T 的结合，并促进其泛素化和降解。肝特异性 RACK1 缺乏通过加速 HDAC1 降解以及随后的 CXCL1/S100A9 上调和 MDSC 积累来防止 FH。
