Ufbp1, a Key Player of Ufm1 Conjugation System, Protects Against Ketosis-Induced Liver Injury via Suppressing Smad3 Activation.
Ufbp1, a Key Player of Ufm1 Conjugation System, Protects Against Ketosis-Induced Liver Injury via Suppressing Smad3 Activation.
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DOI：
10.3389/fcell.2021.676789
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发表时间：
2021
影响因子：
5.5
通讯作者：
Cai Y
中科院分区：
文献类型：
--
作者：
Chen F;Sheng L;Xu C;Li J;Ali I;Li H;Cai Y
奶牛在酮症发病过程中出现严重的肝功能障碍。Ufm1偶联系统对肝脏发育和体内平衡至关重要。Ufm1结合蛋白（Ufbp1）是公认的Ufm1靶点和不可或缺的组成部分，但其在酮症诱导的肝损伤中的作用目前尚不清楚。本研究的目的是在体内和体外探讨Ufbp1在酮症引起的肝纤维化中的关键作用。在体内收集酮症奶牛和Ufbp1条件敲除（CKO）小鼠的肝脏组织。然而，使用Ufbp1 - / -小鼠胚胎成纤维细胞和Hela细胞进行体外验证。随后，进行了各种分析以揭示Ufbp1保护作用的潜在分子机制。本研究发现，酮症奶牛肝脏出现肝纤维化、内质网应激和细胞凋亡，纤维化标志物（α -平滑肌肌动蛋白、Collagen1）和内质网应激标志物（葡萄糖调节蛋白78、CEBP同源蛋白）显著上调，凋亡相关基因（Bcl2、Bax）表达符合预期。有趣的是，在酮症奶牛的肝脏中，Ufbp1的表达几乎消失，Smad2/Smad3蛋白在很大程度上被磷酸化，但Ufbp1缺失导致Smad3而不是Smad2明显磷酸化，并且在CKO小鼠模型中观察到内质网应激升高。在细胞水平上，Ufbp1缺失导致严重的纤维化和内质网应激反应，Smad3被磷酸化显著激活，然后被转运到细胞核中，而p-Smad2在胚胎成纤维细胞中基本不受影响。在Hela细胞中，Ufbp1过表达明显抑制Smad3磷酸化。内源性免疫沉淀法发现Ufbp1与Smad3完全结合。综上所述，我们的研究结果表明，下调或消融Ufbp1会导致Smad3激活、内质网应激升高和肝细胞凋亡，进而导致肝纤维化。Ufbp1在酮症诱导的肝损伤中起保护作用。
The dairy cattle suffer from severe liver dysfunction during the pathogenesis of ketosis. The Ufm1 conjugation system is crucial for liver development and homeostasis. Ufm1 binding protein (Ufbp1) is a putative Ufm1 target and an integral component, but its role in ketosis-induced liver injury is unclear so far. The purpose of this study is to explore the key role of Ufbp1 in liver fibrosis caused by ketosis in vivo and in vitro. Liver tissues were collected from ketotic cows and Ufbp1 conditional knockout (CKO) mice in vivo. However, Ufbp1–/– mouse embryonic fibroblast cells and Hela cells were used for in vitro validation. Subsequently, various assays were performed to reveal the underlying molecular mechanisms of the Ufbp1 protective effect. In this study, hepatic fibrosis, endoplasmic reticulum (ER) stress, and apoptosis were reported in the liver of ketotic cows, fibrotic markers (alpha-smooth muscle actin, Collagen1) and ER stress markers (glucose-regulated protein 78, CEBP homologous protein) were upregulated remarkably, and the apoptosis-related genes (Bcl2, Bax) were in line with expectations. Interestingly, Ufbp1 expression was almost disappeared, and Smad2/Smad3 protein was largely phosphorylated in the liver of ketotic cows, but Ufbp1 deletion caused Smad3 phosphorylation apparently, rather than Smad2, and elevated ER stress was observed in the CKO mice model. At the cellular level, Ufbp1 deficiency led to serious fibrotic and ER stress response, Smad3 was activated by phosphorylation significantly and then was translocated into the nucleus, whereas p-Smad2 was largely unaffected in embryonic fibroblast cells. Ufbp1 overexpression obviously suppressed Smad3 phosphorylation in Hela cells. Ufbp1 was found to be in full combination with Smad3 using endogenous immunoprecipitation. Taken together, our findings suggest that downregulation or ablation of Ufbp1 leads to Smad3 activation, elevated ER stress, and hepatocyte apoptosis, which in turn causes liver fibrosis. Ufbp1 plays a protective role in ketosis-induced liver injury.