Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel.
J Cell Mol Med. 2009 Aug;13(8B):2570-2581. doi: 10.1111/j.1582-4934.2008.00570.x. Epub 2008 Nov 3.
We showed previously that undifferentiated, proliferating human islet-derived precursor cells (hIPCs) are a type of mesenchymal stem/stromal cell (MSC) that can be induced by serum deprivation to form clusters and ultimately differentiate in vitro to endocrine cells. We also demonstrated that partially differentiated hIPC clusters, when implanted under the kidney capsules of mice, continued to differentiate in vivo into hormone-producing cells. However, we noted that not all hIPC preparations yielded insulin-secreting cells in vivo and that in some animals no hormone-expressing cells were found. This suggested that the implanted cells were not always irreversibly committed to further differentiation and may even de-differentiate to a mesenchymal phenotype. In this study, we show that human cells with a mesenchymal phenotype are indeed found in the grafts of mice implanted with hIPCs in epithelial cell clusters (ECCs), which are obtained after 4-day in vitro culture of hIPCs in serum-free medium (SFM); mesenchymal cells were predominant in some grafts. We could mimic the transition of ECCs to de-differentiated mesenchymal cells in vitro by exposure to foetal bovine serum (FBS) or mouse serums, and to a significantly lesser extent to human serum. In a complementary series of experiments, we show that mouse serum and FBS are more effective stimulants of mesenchymal hIPC migration than is human serum. We found that proliferation was not needed for the transition from ECCs to de-differentiated cells because mitomycin-treated hIPCs that could not proliferate underwent a similar transition. Lastly, we show that cells exhibiting a mesenchymal phenotype can be found in grafts of adult human islets in mice. We conclude that epithelial-to-mesenchymal transition (EMT) of cells in hIPC ECCs can occur following implantation in mice. This potential for EMT of human islets or differentiated precursor cells must be considered in strategies for cell replacement therapy for diabetes.
我们之前已经表明，未分化的、增殖的人胰岛源性前体细胞（hIPC）是一种间充质干细胞/基质细胞（MSC），可以通过血清剥夺诱导其形成细胞簇，最终在体外分化为内分泌细胞。我们还证明，当部分分化的 hIPC 细胞簇被植入小鼠肾囊下时，它们在体内继续分化为产生激素的细胞。然而，我们注意到并非所有 hIPC 制剂都能在体内产生胰岛素分泌细胞，而且在一些动物中没有发现表达激素的细胞。这表明植入的细胞并不总是不可逆地向进一步分化，甚至可能向间充质表型去分化。在这项研究中，我们表明，在植入 hIPC 形成的上皮细胞簇（ECC）的小鼠移植物中确实存在具有间充质表型的人细胞，这些细胞是在无血清培养基（SFM）中体外培养 4 天后获得的；在一些移植物中，间充质细胞占主导地位。我们可以通过暴露于胎牛血清（FBS）或鼠血清，在体外模拟 ECC 向去分化的间充质细胞的转变，而用人血清的效果则要差得多。在一系列补充实验中，我们表明鼠血清和 FBS 是比人血清更有效的间充质 hIPC 迁移刺激物。我们发现，从 ECC 到去分化细胞的转变不需要增殖，因为不能增殖的丝裂霉素处理的 hIPC 也经历了类似的转变。最后，我们表明在小鼠中可以在人胰岛移植物中发现具有间充质表型的细胞。我们得出结论，ECC 中的细胞上皮-间充质转化（EMT）可以在植入小鼠后发生。在糖尿病细胞替代治疗的策略中，必须考虑人胰岛或分化前体细胞的 EMT 潜力。
