Objective
Studies suggest that assembling endothelial cell into blood vessel shape, prior to implantation may be the key to generating functional blood vessels in vivo. Our goal is to develop a new strategy to form perfused blood vessels in vitro at a large enough scale to be able to use them in transplantation studies in combination with beta-cells in animal models of type 1 diabetes. These studies will provide the proof-of-concept required before further scaling up small caliber blood vessel generation in vitro to support clinical trials in humans for their effectiveness.
Background Rationale
Type 1 diabetes is a disease where the lack of insulin-secreting beta-cells leads to that increase in blood glucose levels. Although type 1 diabetes is not a death sentence anymore due to the discovery of insulin 100 years ago and its use as an injectable drug, a cure for diabetes still does not exist. While native beta-cells sense and deliver insulin into the bloodstream every second as required, 1 or 2 daily injections of insulin do not offer the same precision in controlling blood glucose. In the long run, the poor control of blood glucose by exogenous insulin affects the blood vessels and the heart leading to increase in limb amputations, blindness, and heart attacks - to name a few.
The transplantation of insulin-secreting cells is a promising strategy to cure diabetes. However, cell death post transplantation is a major issue that limits the use of insulin-secreting cells in the clinic. This is due to the lack of oxygen and nutrients for the transplanted cells because of the lack of blood vessels in the grafts. Therefore, it stands to reason that in order to generate an effective strategy to cure diabetes by transplanting beta cells, we need to improve the survival of the insulin-secreting cells post-transplantation.
Previous attempts at creating blood vessels to support the survival of different cell types in vivo demonstrated that simply transplanting dissociated endothelial cells is not enough to generate functional blood vessels. Instead, our studies using small blood vessels harvested from fat and brains suggest that blood vessel shape may be key for obtaining functional vessels. The proposed work builds on these findings to generate functional blood vessels to support beta-cell transplantation therapy.
Description of Project
Transplantation of insulin-secreting cells is a promising strategy to cure diabetes. However, cell death post transplantation is a major issue that limits the use of insulin-secreting cells in the clinic. This is due to the lack of oxygen and nutrients for the transplanted cells because of the lack of blood vessels in the grafts. Previous attempts at using endothelial cells – the building blocks of blood vessels - differentiated from human stem cells to support cell transplantation were not successful as these cells also died and were not able to form blood vessels in vivo. Here, we propose to investigate different ways of generating blood vessels in the lab prior to transplantation to support the application of insulin-secreting cells in diabetes reversal.
We will explore if pre-assembling small caliber blood vessels in the lab from endothelial cells differentiated from human stem cells enables the formation of functional blood vessels in vivo upon implantation and if this is sufficient to support the survival of insulin-secreting cells in models of diabetes. Work in small size apparatus have shown that endothelial cells will assemble themselves into blood vessels under liquid flow. Thus, in Aim 01, we will use liquid flow to generate perfused blood vessels in vitro by using engineering approaches to develop a device to do so in larger scale that can generate enough vessels for use in vivo. We will also make blood vessels without flow by growing endothelial cells in conditions where they form tube-like vessels. These consist of endothelial cells in vessel shape but that lack the hollow channel inside where blood flows through.
By transplanting a combination of insulin secreting cells obtained from stem cells with either 1) dissociated endothelial cells, 2) tube-like vessels or 3) vessels formed under liquid flow, we will be able to understand if changes in vessels architecture allows for the formation of functional blood vessels in vivo and if they, in turn, will promote the survival of insulin secreting cells. This would provide a means to cure diabetes in mouse models and could be explored for use in cell transplantation in humans.
Anticipated Outcome
We anticipate that scaling up the device size will enable the generation of perfused blood vessels in large enough numbers to be used in animal studies. We expect that the transplantation of blood vessels generated in the lab with endothelial cells obtained from human stem cells in combination with insulin secreting cells (also obtained from stem cells) will enable the survival of the insulin secreting cells in vivo. We expect that lab generated blood vessels will connect with the host blood vessels and carry blood to the grafts and that this will promote the survival of a large enough number of insulin secreting cells. This will enable beta cells to sense blood glucose levels and to secrete insulin, as needed, reversing diabetes.
Relevance to T1D
Type 1 diabetes is a disease where the lack of insulin-secreting beta-cells leads to that increase in blood glucose levels. Although type 1 diabetes is not a death sentence anymore due to the discovery of insulin 100 years ago and it’s use as an injectable drug, there still is not cure for diabetes. While native beta-cells sense and deliver insulin into the bloodstream as required every second, 1 or 2 daily injections of insulin do not offer the same precision in controlling blood glucose. In the long run, the poor control of blood glucose by drugs affects the blood vessels and the heart leading to increase in limb amputations, blindness, and heart attacks - to name a few. Therefore, it is imperative to find a way to restore glucose sensing and insulin secretion by the body.
The field of stem cells has provided a potential solution for type 1 diabetes: the implantation of beta-cells differentiated from stem cells. These cells could secrete insulin and normalize blood glucose levels. However, the rapid death of implanted cells is a major bottleneck for these therapies. These cells die upon implantation due to the lack of a vasculature to enable the delivery of oxygen and nutrients needed for cell survival. Moreover, diabetes is known to affect the ability of blood vessels to grow, making it even more important to find strategies that will enable vessel formation for application in people with diabetes. In this proposal, we will pursue a new strategy for the generation of blood vessels in the lab to be used to support the transplantation of insulin secreting cells and to reverse type 1 diabetes. This is imperative to enable cell-based therapies for type 1 diabetes.