Gene Therapy Laboratory, Liver Unit, School of Medicine, Austral University, Buenos Aires, Argentina.
Am J Physiol Gastrointest Liver Physiol. 2011 May;300(5):G739-48. doi: 10.1152/ajpgi.00316.2010. Epub 2011 Feb 10.
Liver fibrosis is an active process that involves changes in cell-cell and cell-extracellular matrix (ECM) interaction. Secreted protein, acidic and rich in cysteine (SPARC) is an ECM protein with many biological functions that is overexpressed in cirrhotic livers and upregulated in activated hepatic stellate cells (aHSCs). We have recently shown that SPARC downregulation ameliorates liver fibrosis in vivo. To uncover the cellular mechanisms involved, we have specifically knocked down SPARC in two aHSC lines [the CFSC-2G (rat) and the LX-2 (human)] and in primary cultured rat aHSCs. Transient downregulation of SPARC in hepatic stellate cells (HSCs) did not affect their proliferation and had only minor effects on apoptosis. However, SPARC knockdown increased HSC adhesion to fibronectin and significantly decreased their migration toward PDFG-BB and TGF-β(1). Interestingly, TGF-β(1) secretion by HSCs was reduced following SPARC small interfering RNA (siRNA) treatment, and preincubation with TGF-β(1) restored the migratory capacity of SPARC siRNA-treated cells through mechanisms partially independent from TGF-β(1)-mediated induction of SPARC expression; thus SPARC knockdown seems to exert its effects on HSCs partially through modulation of TGF-β(1) expression levels. Importantly, collagen-I mRNA expression was reduced in SPARC siRNA-transfected HSCs. Consistent with previous results, SPARC knockdown in aHSCs was associated with altered F-actin expression patterns and deregulation of key ECM and cell adhesion molecules, i.e., downregulation of N-cadherin and upregulation of E-cadherin. Our data together suggest that the upregulation of SPARC previously reported for aHSCs partially mediates profibrogenic activities of TGF-β(1) and PDGF-BB and identify SPARC as a potential therapeutic target for liver fibrosis.
肝纤维化是一个活跃的过程，涉及细胞-细胞和细胞-细胞外基质（ECM）相互作用的改变。富含半胱氨酸的酸性分泌蛋白（SPARC）是一种 ECM 蛋白，具有许多生物学功能，在肝硬化肝脏中过度表达，并在上皮细胞激活的肝星状细胞（aHSCs）中上调。我们最近表明，下调 SPARC 可改善体内肝纤维化。为了揭示涉及的细胞机制，我们专门在两条 aHSC 系[CFSC-2G（大鼠）和 LX-2（人）]和原代培养的大鼠 aHSCs 中敲低了 SPARC。短暂下调肝星状细胞（HSCs）中的 SPARC 不会影响其增殖，仅对细胞凋亡有较小影响。然而，SPARC 敲低增加了 HSC 对纤维连接蛋白的黏附，并显著降低了它们向 PDFG-BB 和 TGF-β（1）的迁移。有趣的是，HSCs 分泌的 TGF-β（1）在 SPARC 小干扰 RNA（siRNA）处理后减少，并且 TGF-β（1）预孵育通过部分独立于 TGF-β（1）介导的 SPARC 表达诱导的机制恢复了 SPARC siRNA 处理细胞的迁移能力；因此，SPARC 敲低似乎通过调节 TGF-β（1）表达水平对 HSCs 发挥其作用。重要的是，SPARC siRNA 转染的 HSCs 中胶原-I mRNA 表达减少。与先前的结果一致，aHSCs 中的 SPARC 敲低与 F-肌动蛋白表达模式的改变和关键 ECM 和细胞黏附分子的失调有关，即 N-钙黏蛋白下调和 E-钙黏蛋白上调。我们的数据表明，先前报道的 aHSCs 中 SPARC 的上调部分介导了 TGF-β（1）和 PDGF-BB 的促纤维化活性，并将 SPARC 鉴定为肝纤维化的潜在治疗靶点。
