Stem Cell Therapy for Liver Diseases

細胞移植 (cell transplantation) 可以取代器官移植 (organ transplantation) 成為器官衰竭病人的第一治療選擇。不管在動物實驗或臨床上肝細胞移植 (hepatocyte transplantation) 已被證明可用來治療多種不同的肝臟疾病。然而肝細胞移植的發展仍需克服肝細胞來源短缺以及異體排斥的問題。幹細胞移植近年來被應用在許多疾病上並且具有治療的可行性。因此，幹細胞療法 (stem cell therapy) 有可能成為協助治療肝臟疾病的新選擇。目前幹細胞被應用於動物實驗與臨床試驗做為修補和組織再生之用途。本論文利用誘導性全能幹細胞 (induce pluripotent stem cells, iPSCs) 的分化潛能獲得具有功能性的肝細胞以及網膜脂肪幹細胞 (adipose stem cells, ASCs) 做為細胞移植的細胞來源，並分別移植到不同類型的肝臟疾病-第九凝血因子(clotting factor IX, FIX) 剔除之B型血友病 (hemophilia B, HB) 的基因缺陷的疾病模式與乙醯胺酚 (acetaminophen, APAP) 引起的急性肝臟衰竭 (acute liver failure, ALF) 的動物模式分別探討其治療潛能性。誘導性全能幹細胞具有與胚胎幹細胞 (embryonic stem cells, ESCs) 相同特質，並且具有可分化成特定細胞的能力。在體外誘導條件下將誘導性全能幹細胞分化成具有功能性的肝細胞並進一步去探討其細胞對於基因缺陷肝臟疾病的治療效果。結果顯示來自誘導性全能幹細胞分化而成的肝細胞具有肝臟的主要功能，包含合成血清白蛋白 (albumin) 與尿素 (uric acid)、代謝功能並儲存肝醣 (glycogen) 能力。將此細胞移植到第九凝血因子剔除之B型血友病小鼠後可在宿主的血清中偵測到第九凝血因子活性並改善凝血能力且可嵌入 (engraftment) 宿主的肝臟組織中。因此，來自於誘導性全能幹細胞所分化的肝細胞可提供做為細胞移植的細胞來源並做為基因缺陷肝臟疾病的新治療選擇。再者，從網膜脂肪組織去提取脂肪幹細胞並探討其細胞對於急性肝衰竭的治療潛力。網膜脂肪幹細胞做為細胞移植的來源可以明顯改善急性肝衰竭動物的死亡率並且抑制細胞色素P450 (cytochrome P450) 表現，進而減少硝基酪氨酸 (nitrotyrosine)的堆積並同時提高NF-E2-related factor 2 (Nrf2)的表現進而減低乙醯胺酚的毒性傷害達到保護肝臟。綜合上述實驗結果顯示幹細胞療法提供肝臟疾病治療的新契機。Cell transplantation are expected to replace the whole organ transplantation as the first therapeutic choice for patients with organ failure. Hepatocyte transplantation has been proved with the ability of treating a wide variety of liver disease in both animal experiments and clinical studies. However, the hepatocytes shortage and allograft rejection remained unsolved during the development of hepatocyte transplantation. On the other hand, stem cell therapy has been shown to have the therapeutic potential in many kinds of diseases, and the autograft of stem cell is suggested as the key of organ shortage and allograft rejection. Therefore, the stem cell transplantation is gathering the attention with the potential of being the next therapeutic strategy for liver diseases. For the reason, various cell types have been tried, whether in animal models or in clinical trials, to repair or regenerate the damage tissue. In this dissertation, we allowed hepatocyte-like cell derived from induce pluripotent stem cells (iPSCs) and adipose stem cells (ASCs) generated from omentum adipose tissue as the candidates, and addressed their therapeutic potential in inherited diseases-hemophilia B and acute liver failure (ALF) induced by acetaminophen (APAP), respectively. iPSCs, shared some characteristics with the ESCs, have been demonstrated with the capability of differentiating into different somatic cells. However, whether hepatocytes differentiated from iPSCs is functioning with the therapeutic efficiency of genetic liver disease, the hemophilia B disease (factor IX knockout mice model), has never been proved. Our data showed that iPSCs derived hepatocytes shared many characteristics with hepatocytes, including albumin synthesis, metabolic capacity, glycogen storage, and ureagenesis. In fact, iPSCs-derived hepatocytes transplantation led to increased coagulation factor IX activity, improved thrombus generation, and better hemostasis parameters, moreover, the transferred cells were localized in the liver in recipient HB mice. As a result, hepatocyte-like cells derived from iPSCs is suggested to be a potential cell source for cell-based therapy in the treatment of HB. Another study is about the therapeutic potential of omentum derived adipose stem cells in APAP-induced ALF. We successfully acquired the ASCs from omentum adipose tissue, and proved the antioxidant activity of the candidate. Our data showed that ASCs transplantation significantly improved the survival rate of mice with ALF, and attenuated the severity of APAP-induced liver damage by suppressing cytochrome P450 activity. Following the activity, the cell reduced the accumulation of toxic nitrotyrosine and the upregulation of NF-E2-related factor 2 (Nrf2) expression, and in sequential resulted in the increase of antioxidant activity. Taken together, our results suggested the stem cell therapy is an opportunity to open up entirely new perspectives for treatment of severe liver diseases