| Summary: | 博士 === 國立臺灣大學 === 生物科技研究所 === 105 === Diabetes mellitus is a metabolic disorder resulted from insulin deficiency or insulin resistance. The primary treatment for patients with type I diabetes (or insulin-dependent diabetes mellitus) that are absolutely deficient in insulin is insulin injection. However, insulin injection as a regimen for treating diabetes is unable to long-termly control blood sugar levels. Instead, islet transplantation is the potential way to sustainably modulate glycemic status. However, the shortage of donor islets and poor islet graft survival and function limit the potential use of islet transplantation to treat patients with type 1 diabetes. The major goal of the PhD thesis is trying to overcome the barrier of application of islet transplantation.
In the first part of the thesis, we analyzed and found that an essential micronutrient, vitamin A, is an important factor in embryogenesis. All-trans retinoic acid (atRA), the active metabolite of vitamin A, plays an essential role in regulating pancreatic development. We initially investigated how maternal vitamin A deficiency may affect fetal islet development and revealed that atRA is involved in regulating vascularized islet formation via modulating vascular endothelial growth factor secretion. Based on the observation, we next evaluated whether treatment with atRA can ameliorate diabetes. We found that administration of atRA could gradually decrease the blood glucose levels of diabetic mice, increase the amount of β-cells, and restore the vascular laminin expression. Furthermore, atRA induced the expression of vascular endothelial growth factor-A from the pancreatic islets, which mediated the restoration of islet vascularity and recovery of β-cell mass. Importantly, we showed atRA treatment significantly improved grafted islet functionality and vascularity and the combination of islet transplantation and atRA administration could rescue hyperglycemia in diabetic mice. The findings suggest vitamin A derivatives can potentially be used as a supplementary treatment to improve diabetes management and glycemic control.
In the second part of the thesis, we tried to reprogram primary hepatocytes to Sox9-expressing progenitor cells in a three dimensional (3D) culture system. We found these Sox9-expressing progenitors could form spheroid on polyvinyl alcohol (PVA) substrates. In combination with overexpressing Pdx1, Ngn3 and MafA, these hepatocytes could further be reprogramed to insulin-producing clusters. Transplantation of insulin-producing clusters into diabetic mice was found to rescue hyperglycemia. In conclusion, these current works discovered that atRA treatment could improve survival and functionality of the grafted islets. Moreover, these works further developed a novel strategy to generate insulin-secreting cell clusters via hepatocyte reprogramming for transplantation.
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