Reorganization of extracellular matrix by hepatic stellate cells (Ito cells) : Possible amelioration of liver fibrosis

以细胞外基质(ECM)为基质的肝星状细胞(HSCs)在形态上发生了显著变化，通过间质胶原凝胶的培养，HSCs被改变以延长许多细胞过程，如在体内所见。这项研究的结果表明，细胞表面整合素与细胞外基质成分结合，随后是各种细胞内信号转导，最后是细胞骨架，特别是微管组装，导致了过程的延长。正如Senoo等人以前报道的那样，HSC不仅在形态上发生了变化，而且在增殖和胶原合成/分泌方面也发生了变化。明胶酶谱结果进一步证明，HSC在I型胶原胶上培养的条件培养液中含有基质金属蛋白酶(MMP2)-2的激活形式，而在I型胶原胶上培养的HSC培养上清液中没有发现MMP2的激活形式，但逆转录-聚合酶链式反应(RT-PCR)检测到HSC培养上清液中也有基质金属蛋白酶组织抑制因子(TIMP)-2的表达，提示MMP2的激活形式受到抑制。荧光免疫染色和原位酶谱进一步表明，在I型胶原胶上培养的细胞中存在基质金属蛋白酶-1蛋白及其活性。综上所述，这些结果表明，在转录水平或翻译/翻译后阶段，ECM成分的重组存在复杂的调控机制，如含有IV型胶原的基底膜或包括I型胶原的间质基质成分。因此，使用不同ECM组分的HSC培养体系有助于研究ECM在肝组织中重组的机制，并进一步探索通过控制包括胶原在内的ECM组分的合成和分泌以及基质金属蛋白酶的表达来减轻肝纤维化的可能性。

Hepatic stellate cells (HSCs) exhibited a marked change in morphology depending on the extracellular matrix (ECM) component as a substratum, and HSCs were altered to elongate many cellular processes, as seen in vivo, by the culturing using interstirial collagen gel. The results from this study revealed that the process elongation was induced by cell surface integrin binding to ECM components, followed by various intracellular signaling and finally cytoskeleton, particularly, microtubule assembly. As previously reported by Senoo et al., HSCs displayed an alteration not only in morphology, but also in proliferation and collagen synthesis/secretion. The results from gelatin zymography in this study further demonstrated that the conditioned medium from HSC culture on type I collagen gel but not on polystyrene surface and on Matrigel contained an activated form of matrix metalloproteinase (MMP)-2, However, the culture on type I collagen gel also indicated the expression of tissue inhibitor of matrix metalloprotease (TIMP)-2, as detected by reverse transcriptase-polymerase chain reaction (RT-PCR), suggesting the suppression of the activated form of MMP-2. Fluorescence immunostaining and in situ zymography further indicated the presence of MMP- 1 proteins and their activities in the culture on type I collagen gel. Taken together, these results suggest a complicated regulatory mechanism at transcriptional level or at translational/posttranslational stages for reorganization of ECM components such as the basement membrane containing type IV collagen or interstitial matrix components including type I collagen. HSC culture system using various ECM components is, therefore, useful to investigate the mechanism of reorganization of ECM in the liver tissue, and further to explore the possibility to ameliorate liver fibrosis by the control of synthesis and secretion of ECM components including collagen and of MMP expression.