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

肝星状细胞（hsc）表现出明显的形态学变化，这取决于细胞外基质（ECM）成分作为基质，并且hsc被改变为延长许多细胞过程，通过使用间质胶原凝胶培养在体内观察到。本研究的结果表明，细胞表面整合素与ECM成分结合，然后是各种细胞内信号传导，最后是细胞骨架，特别是微管组装，诱导了细胞延伸过程。正如Senoo等人先前报道的那样，造血干细胞不仅在形态上表现出改变，而且在增殖和胶原合成/分泌方面也表现出改变。本研究明胶酶谱分析结果进一步表明，在I型胶原凝胶上培养HSC，而不是在聚苯乙烯表面和Matrigel上培养HSC的条件培养基中含有活化形式的基质金属蛋白酶(MMP)-2，而在I型胶原凝胶上培养的HSC，通过逆转录-聚合酶链反应（RT-PCR）检测，也表达了基质金属蛋白酶(TIMP)-2的组织抑制剂。这表明MMP-2的活化形式受到抑制。荧光免疫染色和原位酶谱分析进一步证实了MMP- 1蛋白的存在及其在I型胶原凝胶培养中的活性。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（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）的重组存在复杂的调控机制。因此，使用多种ECM成分的HSC培养系统有助于研究肝组织中ECM重组的机制，并进一步探索通过控制包括胶原在内的ECM成分的合成和分泌以及MMP的表达来改善肝纤维化的可能性。

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.