REGULATION OF HEPATIC FIBROGENEISS BY TANGO1

摘要 肝硬变是终末期肝病的主要原因。肝硬变的一个特征是纤维化：分泌物 以及肝星状细胞(HSCs)沉积过量的细胞外基质(ECM)蛋白。突出 分泌的细胞外基质蛋白中有I型胶原。尽管I型胶原在肝硬变中的沉积作用很好 众所周知，目前还缺乏旨在破坏纤维化形成的治疗方法。这在一定程度上是由于我们对 I型前胶原通过分泌途径运输。转化生长因子β等纤维化信号驱动血管内皮生长因子的表达 I型胶原前体I型前胶原，随后共翻译成内质网 (呃)。I型前胶原纤维在内质网内寡聚，形成一个太大(~300 nm)的复合体，无法包装 典型的内质网输出小泡(60-90 nm)。因此，额外的，未知的细胞机械是必要的 贩卖I型前胶原蛋白。如果这一机制被破坏，前胶原纤维将保留在内质网和铅中 内质网应激，未折叠蛋白反应(UPR)的激活，以及可能的细胞凋亡。最近的优雅 在非肝细胞中进行的研究表明，TANGO1对前胶原的运输至关重要。 TANGO1是否促进内质网输出和HSCs分泌I型胶原，这是纤维化形成的关键步骤 未知。我们假设，TANGO1驱动内质网输出的I型前胶原，需要UPR 介导这一效应的信号，以及TANGO1和UPR共同在体内纤维化形成中起关键作用。 这一假说是基于初步数据显示：(A)TANGO1基因敲除可破坏I型前胶原ER 导出，导致UPR信号和HSC凋亡，(B)TANGO1的表达至少部分地通过 UPR激活的转录因子XBP1和(C)TANGO1/-小鼠对肝硬变的保护作用 发展。研究TANGO1在I型前胶原蛋白运输中的作用及其相关性的新颖性和相关性 调控有两个方面：1)我们可以确定新的靶点，在纤维化形成过程中干扰I型胶原的分泌；2) I型前胶原滞留导致的内质网应激不能被化解，可能导致HSC的凋亡。后一种机制 有利于肝纤维化的消退。我们的长期目标是阐明I型前胶原蛋白运输的机制 并找出治疗肝硬变的新靶点。这里提出的研究将 利用严谨的体内外方法揭示TANGO1介导的I型前胶原的作用机制 HSC的贩运、在HSC激活期间TANGO1与普遍定期审议之间的管制关系；以及 最后探讨了TANGO1和UPR在纤维化形成和纤维化消退中的作用。

Abstract Liver cirrhosis is the leading cause of end-stage liver disease. A hallmark of cirrhosis is fibrogenesis: secretion and deposition of excess extracellular matrix (ECM) proteins by hepatic stellate cells (HSCs). Prominent among secreted ECM proteins is collagen I. Although the role of collagen I deposition in cirrhosis is well known, therapies aimed at disrupting fibrogenesis are lacking. This is due in part to our poor understanding of procollagen I trafficking through the secretory pathway. Fibrogenic signals such as TGFβ drive expression of the collagen I precursor procollagen I, which is subsequently cotranslationed into the endoplasmic reticulum (ER). Procollagen I fibrils oligomerize within the ER, forming a complex too large (~300nm) to package into canonical ER export vesicles (60-90nm). Thus, additional, unknown cellular machinery is necessary for procollagen I trafficking. If this machinery is disrupted, procollagen fibrils would be retained in the ER and lead to ER stress, activation of the unfolded protein response (UPR), and possibly apoptosis. Recent elegant studies performed in non-liver cells suggested that TANGO1 is critical for the transport of procollagens. Whether TANGO1 facilitates ER export and secretion of collagen I from HSCs, a critical step in fibrogenesis, is unknown. We hypothesize that TANGO1 drives procollagen I export from the ER, requires UPR signaling to mediate this effect, and together TANGO1 and the UPR are critical for fibrogenesis in vivo. This hypothesis is based on preliminary data showing (a) TANGO1 knockdown disrupts procollagen I ER export, leading to UPR signaling and HSC apoptosis, (b) TANGO1 expression is mediated, at least in part, by the UPR-activated transcription factor XBP1, and (c) TANGO1+/- mice are protected from cirrhosis development. The novelty and relevance of studying the role of TANGO1 in procollagen I trafficking and its regulation are two-fold: 1) we can identify new targets to disrupt collagen I secretion in fibrogenesis, and 2) failure to resolve ER stress driven by procollagen I retention may lead to HSC apoptosis. The latter mechanism is favorable for fibrosis resolution. Our long-term goal is to elucidate mechanisms of procollagen I trafficking within HSCs and identify novel therapeutic targets to treat liver cirrhosis. The research proposed here will utilize rigorous in vitro and in vivo approaches to unveil the mechanisms of TANGO1-mediated procollagen I trafficking in HSCs, the regulatory relationship between TANGO1 and the UPR during HSC activation, and finally the role of TANGO1 and the UPR in fibrogenesis and fibrosis regression.