iPSC Therapy in Diabetes
Case Study:
Generation of Insulin-secreting Islet-like Clusters
from Human Skin Fibroblasts
Tateishi, K., He, J., Taranova, O., Liang, G., Dalessio, A. C., & Zhang, Y. (2008).
Overview
A group of scholars from the Howard Hughes Medical Institute and University of North Carolina investigated the potential of using iPSC to produce insulin-secreting cells, which may be applicable to treat type 1 diabetes. This paper reports the generation of insulin-secreting cells from iPSC and human embryonic stem cells.
Background
Diabetes is characterized persistently high glucose level in blood. It leads to many complications and chronic diseases such as cardiovascular diseases, stroke, kidney diseases and pathologies in eyes. These complications may end up causing early or acute death. In 2015, diabetes was the 7th leading cause of death in the U.S. 252,806 deaths were resulted from diabetes and its complications, while 25.2% of American seniors aged 65 or above was diagnosed of diabetes.
What is diabetes?
Figure 1: Insulin function
There are two types of diabetes. Type I diabetes is caused by the loss of β-cells from the islets in pancreas. β-cells produce insulin, a hormone that controls blood glucose level by signaling tissue and organs to take in glucose, which in return reduces blood glucose level. Figure illustrates the production of insulin from β-cells and how insulin signals muscle cells to absorb glucose from blood. In type I diabetes, the immune system attacks the islets in the pancreas, which impairs β-cells’ function to generate insulin, leading to insulin deficiency and high glucose level. On the other hand, type II diabetes is caused by insulin resistance. That is, the insulin receptors stop working so that the body does not respond to insulin. Here, we will focus on the use of iPSCs to treat type I diabetes.
Current Solutions
The most common treatment to type I diabetes is insulin injection. By supplying the body with insulin a fews time a day, blood glucose level can be regulated. However, no matter how regulated the injections are, there will be periods of extremely high blood glucose level and extremely low blood glucose level in the body, which is still detrimental in the long run. Moreover, such treatment only slows the the progression of the disease, but does not prevent the development of complications such as cardiovascular diseases and damages to the eyes.
Another treatment that is currently under clinical trials is islet transplantation. Islet cell from cadaveric donors were transplanted into diabetic patients to replace the damaged islet cells and produce insulin. However, the lack of donors and chronic immune response set limit to this treatment method. Nevertheless, this treatment suggests that the regeneration of islet β-cells may be the key to treating type I diabetes.
Methods and Results
In this research, Tateishi et al. harvested human skin fibroblasts and generated iPSCs using the four transcription factors from Yamanaka et al.’s research (Oct3, Sox2, Klf-4, c-Myc) and some other growth factors. The iPSCs were then cultured and underwent a 4-stage differentiation process. In each stage, different growth factors were supplied to the culture media. The factors used to facilitate differentiation and the formation of islet-like cell clusters included basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and insulin-like growth factor II (IGF-II).
At the end of the 4-stage differentiation process, islet-like insulin-secreting cells formed from iPSCs. Figure 2 illustrates the expression of gene markers of two lines of iPSCs during the four stages. These gene markers (Foxa2, Sox17, Pdx1) indicate different cell lineage during differentiation. By stage 4 (Figure 2 k-p, i-r), the iPSCs expressed islet-specific proteins such as C-peptide. C-peptide is a linker protein that helps with the folding of insulin. When insulin is producd, C-peptide is cleaved and released. Therefore, the presence of C-peptide in iPSC media indicated the secretion of insulin.
Tests were also performed to study the iPSC-derived islet-like cell function. When different concentration of glucose was dosed, theses cells secreted more insulin in response to a higher glucose level and less at lower glucose concentration. However, the insulin production of iPSC-derived islet-like cells were lower than that of adult islet cells.
Conclusion
This study proved the potential of generating insulin-secreting islet-like cells from human fibroblast-derived iPSC. The islet-like cells were able to respond to different glucose levels by secreting insulin accordingly. However, although the iPSC-derived islet-like cells were similar to adult islet cells in morphology and genetic expressions, their ability to secrete insulin was significantly lower than that of mature islet cells. Therefore, this study suggests that iPSC may be a promising cell source for the regeneration of islet cells. However, further studies are required to improve the differentiation and culture of iPSCs into islet-like cells.
Clinical Implications
The paper discussed above was published in 2008. Currently, more research are being done to improve the method for the generation of iPSC-derived islet-like cells in a hope to increase the efficiency of cell culture and differentiation and to improve the insulin-secreting ability of these cells. iPSC-derived islet-like cells, if proved efficacious, may become a substitute to the islet transplantation treatment. Instead of transplanting islet cells from a foreign body, patient-specific islet cells can be produced from the patient’s fibroblast and implanted into his or her body for insulin production.
If you would like to read more about iPSC-based therapy for diabetes, please see the reference for papers and websites for more information.
Reference
http://www.diabetes.org/diabetes-basics/statistics/
Figure 1 credit to <http://www.closerlookatstemcells.org/stem-cells-and-medicine/diabetes#stem-cell-potential-diabetes>
Tateishi, K., He, J., Taranova, O., Liang, G., Dalessio, A. C., & Zhang, Y. (2008). Generation of Insulin-secreting Islet-like Clusters from Human Skin Fibroblasts. Journal of Biological Chemistry, 283(46), 31601-31607. doi:10.1074/jbc.m806597200
<http://www.jbc.org/content/283/46/31601.long>
Figure 2 credit to this paper
https://www.youtube.com/watch?v=MGL6km1NBWE
https://en.wikipedia.org/wiki/Diabetes_mellitus#Pathophysiology
Figure 2: Gene expression during the 4-stage differentiation process
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