间充质干细胞跨越分化肝细胞及其参与肝脏损伤修复的探索研究

发布时间：2019-02-27 06:38

【摘要】：间充质干细胞(Mesenchymal stem cells,MSCs)来源于中胚层,能够分化为成骨、软骨和脂肪,为原始造血干/祖细胞在骨髓微环境中的生长和分化提供支持。近年来研究发现MSCs的分化潜能远超过最初的预期,甚至可以跨越分化为其他胚层来源的细胞,MSCs也因此迅速成为干细胞领域的一个热点。本研究重点研究了小鼠骨髓MSCs向肝细胞的跨越分化能力,以及在体内情况下能否参与肝脏损伤修复。研究的第一部分,我们首先建立了三套条件培养液诱导体系,成功将小鼠骨髓来源MSCs诱导分化为肝样细胞。诱导体系包括肝损伤条件培养液、肝细胞条件培养液和胎肝条件培养液。诱导得到的细胞具备典型的肝细胞形态,表达肝系细胞特异性基因,具备肝细胞的正常功能,如ICG吞噬、白蛋白合成和糖原储存等。随后的研究发现HGF、FGF-4和OSM是条件培养液诱导体系中发挥作用的关键因子,组合上述三种细胞因子即可将小鼠骨髓MSCs诱导成典型的肝样细胞,但诱导效率较低。此外,本研究发现使用丙戊酸钠(VPA)预处理MSCs,可以显著提高MSCs向肝细胞的分化效率。实验发现MSCs在VPA处理过程中伴随着细胞周期阻滞、组蛋白乙酰化程度增加、染色质结构疏松。表观遗传修饰导致的FGF受体和HGF受体基因表达上调可能是肝细胞分化效率提高的关键因素。研究的第二部分,我们从肝脏损伤小鼠中分离得到了外周血间充质干细胞,发现该细胞与骨髓来源的MSCs具备类似的细胞表面标记,可以向成骨、脂肪和软骨诱导分化,但是增殖能力较弱,易衰老。本研究还通过活体动物分子成像等技术对骨髓腔移植的eGFP~+MSCs进行追踪,证明MSCs在特定状态下可以从骨髓迁移到外周血继而迁移到损伤肝脏中,提示病理状态下分离得到的外周血间充质干细胞可能来源于骨髓。此外,通过免疫荧光染色等检测方法,发现迁移到损伤肝脏的MSCs可以通过多种方式参与组织修复,包括直接分化为多种细胞类型,包括AFP阳性、ALB阳性的肝系细胞、CK19阳性的胆管类细胞、CD146阳性的血管内皮类细胞等,同时MSCs还能通过分泌细胞因子调控星形细胞的活性来改善肝脏胶原沉积和纤维化。综上所述,本研究证明小鼠骨髓MSCs不仅在体外可以跨越分化为肝实质细胞,而且体内状态能够在肝脏损伤条件下,自发的迁移出骨髓,并通过血液循环向肝脏迁移,通过跨越分化和细胞因子分泌等方式参与肝脏的损伤修复。
[Abstract]:Mesenchymal stem cells (Mesenchymal stem cells,MSCs), derived from mesoderm, can differentiate into osteogenesis, cartilage and fat, which can support the growth and differentiation of primitive hematopoietic stem / progenitor cells in bone marrow microenvironment. In recent years, it has been found that the differentiation potential of MSCs is much higher than originally expected, and it can even differentiate into cells derived from other germ layers. Therefore, MSCs has become a hot spot in stem cell field. This study focused on the ability of mouse bone marrow MSCs to differentiate into hepatocytes and whether it can participate in the repair of liver injury in vivo. In the first part of the study, we first established three sets of conditioned medium induction system, and successfully induced mouse bone marrow-derived MSCs to differentiate into hepatocyte-like cells. The induction system includes liver injury conditioned medium, hepatocyte conditioned medium and fetal liver conditioned medium. The induced cells possess typical hepatocyte morphology, express liver cell-specific genes, and possess normal functions of hepatocytes, such as ICG phagocytosis, albumin synthesis and glycogen storage. Subsequently, it was found that HGF,FGF-4 and OSM were the key factors in the conditioned medium induction system. The combination of these three cytokines could induce mouse bone marrow MSCs into typical hepatocyte-like cells, but the induction efficiency was low. In addition, we found that pretreatment of MSCs, with sodium valproate (VPA) could significantly improve the differentiation efficiency of MSCs into hepatocytes. It was found that MSCs was accompanied by cell cycle arrest, histone acetylation increased and chromatin structure loose during VPA treatment. The up-regulation of FGF receptor and HGF receptor gene expression induced by epigenetic modification may be the key factor to improve the differentiation efficiency of hepatocytes. In the second part of the study, we isolated mesenchymal stem cells from liver-injured mice and found that these cells have similar cell surface markers to bone marrow-derived MSCs and can differentiate into osteogenesis, adipose tissue and cartilage. However, the ability of proliferation is weak, easy to aging. In this study, we also tracked the eGFP~ MSCs of bone marrow transplantation by living animal molecular imaging and other techniques, which showed that MSCs can migrate from bone marrow to peripheral blood and then to injured liver under certain conditions. These results suggest that the mesenchymal stem cells isolated from peripheral blood may come from bone marrow. In addition, by immunofluorescence staining and other methods, it was found that MSCs migrated to injured liver can participate in tissue repair in a variety of ways, including direct differentiation into a variety of cell types, including AFP-positive and ALB-positive liver cell lines. CK19-positive bile duct cells, CD146-positive vascular endothelial cells, and so on. At the same time, MSCs can also improve hepatic collagen deposition and fibrosis by secreting cytokines to regulate the activity of astrocytes. In conclusion, this study demonstrated that mouse bone marrow MSCs can not only differentiate into liver parenchyma cells in vitro, but also migrate spontaneously out of bone marrow and migrate to the liver through blood circulation under the condition of liver injury in vivo. Cross-differentiation and cytokine secretion are involved in the repair of liver injury.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2009
【分类号】：R329

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