Department of Biochemistry & Molecular Biology, Medical School, Nantong University, Qi xiou Road 19, Nantong 226001, Jiangsu, China.
Department of Pathology and Laboratory Medicine, Schulich School of Medicine & Dentistry, Western University, 1151 Richmond Street, London, Ontario N6A 3K7, Canada.
Biochim Biophys Acta Mol Cell Res. 2023 Dec;1870(8):119569. doi: 10.1016/j.bbamcr.2023.119569. Epub 2023 Aug 18.
Liver fibrosis is characterized by the excessive deposition of extracellular matrix in liver. Chronic liver injury induces the activation of hepatic stellate cell (HSCs), a key step in liver fibrogenesis. The activated HSC is the primary source of ECM and contributes significantly to liver fibrosis. TGFβ1 is the most potent pro-fibrotic cytokine. Bromodomain protein 4 (BrD4), an epigenetic reader of histone acetylation marks, was crucial for profibrotic gene expression in HSCs. The present study aimed to investigate the roles of BRD4 in TGFβ1-dependent HSC activation and liver fibrosis, focusing on TGFβ1-induced alterations of the levels of the fibrotic-related important proteins in HSCs by employing the heterozygous TGFβ1 knockout mice and BrD4 knockdown in vivo and in vitro. Results revealed that BrD4 protein level was significantly upregulated by TGFβ1 and BrD4 knockdown reduced TGFβ1-induced HSC activation and liver fibrosis. BrD4 was required for the influences of TGFβ1 on PDGFβ receptor and on the pathways of Smad3, Stat3, and Akt. BrD4 also mediated TGFβ1-induced increases in histone acetyltransferase p300, the pivotal pro-inflammatory NFkB p65, and tissue inhibitor of metalloproteinase 1 whereas BrD4 reduced Caspase-3 protein levels in HSCs during liver injury, independent of TGFβ1. Further experiments indicated the interaction between TGFβ1-induced BrD4 and NFkB p65 in HSCs and in liver of TAA-induced liver injury. Human cirrhotic livers were demonstrated a parallel increase in the protein levels of BrD4 and NFkB p65 in HSCs. This study revealed that BrD4 was a key molecular driver of TGFβ1-induced HSC activation and liver fibrosis.
肝纤维化的特征是肝脏细胞外基质的过度沉积。慢性肝损伤诱导肝星状细胞（HSCs）的激活，这是肝纤维化发生的关键步骤。激活的 HSC 是 ECM 的主要来源，并对肝纤维化有重要贡献。TGFβ1 是最有效的促纤维化细胞因子。溴结构域蛋白 4（BrD4）是组蛋白乙酰化标记的表观遗传读取器，对 HSCs 中的促纤维化基因表达至关重要。本研究旨在研究 BRD4 在 TGFβ1 依赖性 HSC 激活和肝纤维化中的作用，重点研究 TGFβ1 诱导的 HSCs 中纤维化相关重要蛋白水平的变化，采用杂合 TGFβ1 敲除小鼠和 BrD4 体内和体外敲低。结果表明，TGFβ1 显著上调 BrD4 蛋白水平，BrD4 敲低减少了 TGFβ1 诱导的 HSC 激活和肝纤维化。BrD4 是 TGFβ1 对 PDGFβ 受体和 Smad3、Stat3 和 Akt 途径影响所必需的。BrD4 还介导了 TGFβ1 诱导的组蛋白乙酰转移酶 p300、关键促炎 NFkB p65 和组织金属蛋白酶抑制剂 1 的增加，而 BrD4 降低了 Caspase-3 蛋白水平在肝损伤期间的 HSCs 中，独立于 TGFβ1。进一步的实验表明，TGFβ1 诱导的 BrD4 和 NFkB p65 在 HSCs 中的相互作用以及在 TAA 诱导的肝损伤中的肝中。人类肝硬化肝脏中 HSCs 中 BrD4 和 NFkB p65 的蛋白水平呈平行增加。本研究表明，BrD4 是 TGFβ1 诱导的 HSC 激活和肝纤维化的关键分子驱动因素。
