Division of Gastroenterology, Hepatology & Nutrition, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH.
Cincinnati VA Medical Center, Cincinnati, OH.
Hepatology. 2020 Nov;72(5):1800-1818. doi: 10.1002/hep.31188. Epub 2020 Oct 22.
During liver injury, quiescent hepatic stellate cells (qHSCs) transdifferentiate into proliferative and fibrogenic activated myofibroblastic phenotype (activated hepatic stellate cell; aHSCs) expressing smooth muscle α-actin (αSMA) and platelet-derived growth factor beta receptor (PDGFβR). Their interactions with gut-derived bacterial lipopolysaccharide (LPS) are implicated in hepatic fibrogenesis. However, LPS can also attenuate fibrogenic characteristics of aHSCs.
We examined molecular mechanisms of antifibrogenic effects of LPS on aHSCs in vitro and in vivo. Culture-activated rat HSCs were exposed to 0-100 ng/mL of LPS or its active component, diphosphoryl-lipid A (DPLA), and parameters of fibrosis and inflammatory cytokines/chemokines were determined by qRT-PCR, western, and immunohistochemical analyses. In vivo, HSCs were activated by repeated CCl administration to rats every 3 days for 3 or 8 weeks, then challenged with LPS (5 mg/kg; IP). HSCs were isolated 24 hours later, and fibrogenic/inflammatory parameters were analyzed. LPS induced phenotypic changes in aHSCs (rounding, size reduction) and loss of proliferation. LPS down-regulated expression of αSMA, PDGFβR, transforming growth factor beta receptor 1 (TGFβR1), collagen 1α1 (Col1α1), and fibronectin while up-regulating tumor necrosis factor alpha, interleukin-6, and C-X-C motif chemokine ligand 1 expression. LPS did not increase peroxisome proliferation-activated receptor gamma expression or lipid accumulation typical of qHSCs. DPLA elicited the same effects as LPS on aHSCs, indicating specificity, and monophosphoryl lipid A down-regulated fibrogenic markers, but elicited very weak inflammatory response. LPS down-regulated the expression of cMyb, a transcription factor for αSMA, and up-regulated small mother against decapentaplegic (SMAD)7 and CCAAT/enhancer-binding protein (C/EBP)δ, the transcriptional inhibitors of Col1α1 expression. In vivo LPS treatment of aHSCs inhibited their proliferation, down-regulated PDGFβR, αSMA, TGFβR1, Col1α1, and cMyb expression, and increased expression of SMAD7, C/EBPα, and C/EBPδ.
In conclusion, LPS induces a unique phenotype in aHSCs associated with down-regulation of key fibrogenic mechanisms and thus may have an important role in limiting fibrosis.
在肝损伤过程中，静止的肝星状细胞（qHSCs）转分化为增殖和纤维化的激活肌成纤维细胞表型（激活的肝星状细胞；aHSCs），表达平滑肌α-肌动蛋白（αSMA）和血小板衍生生长因子β受体（PDGFβR）。它们与肠道来源的细菌脂多糖（LPS）的相互作用与肝纤维化有关。然而，LPS 也可以减弱 aHSCs 的纤维化特征。
我们在体外和体内研究了 LPS 对 aHSCs 的抗纤维化作用的分子机制。培养激活的大鼠 HSCs 暴露于 0-100ng/mL LPS 或其活性成分二磷酸脂 A（DPLA），通过 qRT-PCR、western blot 和免疫组织化学分析测定纤维化和炎症细胞因子/趋化因子的参数。在体内，用 CCl 重复处理大鼠，每 3 天一次，共 3 或 8 周，然后用 LPS（5mg/kg；IP）处理。24 小时后分离 HSCs，分析纤维化/炎症参数。LPS 诱导 aHSCs 的表型变化（圆化、大小减小）和增殖丧失。LPS 下调 αSMA、PDGFβR、转化生长因子β受体 1（TGFβR1）、胶原 1α1（Col1α1）和纤维连接蛋白的表达，同时上调肿瘤坏死因子-α、白细胞介素-6 和 C-X-C 基序趋化因子配体 1 的表达。LPS 没有增加过氧化物酶体增殖物激活受体γ的表达或 qHSCs 中典型的脂质堆积。DPLA 对 aHSCs 产生与 LPS 相同的作用，表明其特异性，单磷酰脂质 A 下调纤维化标志物，但引起的炎症反应非常弱。LPS 下调转录因子 αSMA 的 cMyb 表达，上调小母 against decapentaplegic（SMAD）7 和 CCAAT/增强子结合蛋白（C/EBP）δ的表达，这是 Col1α1 表达的转录抑制剂。体内 LPS 处理 aHSCs 抑制其增殖，下调 PDGFβR、αSMA、TGFβR1、Col1α1 和 cMyb 的表达，增加 SMAD7、C/EBPα 和 C/EBPδ 的表达。
总之，LPS 在 aHSCs 中诱导出一种独特的表型，与关键纤维化机制的下调有关，因此可能在限制纤维化中具有重要作用。
