Reversible expansion of pancreatic islet progenitors derived from human induced pluripotent stem cells

Importance of multiple endocrine cell types in islet organoids for type 1 diabetes treatment

Almost 50 years ago, scientists developed the bi-hormonal abnormality hypothesis, stating that diabetes is not caused merely by the impaired insulin signaling. Instead, the presence of inappropriate level of glucagon is a prerequisite for the development of type 1 diabetes (T1D). It is widely understood that the hormones insulin and glucagon, secreted by healthy β and α cells respectively, operate in a negative feedback loop to maintain the body's blood sugar levels. Despite this fact, traditional T1D treatments rely solely on exogenous insulin injections. Furthermore, research on cell-based therapies and stem-cell derived tissues tends to focus on the replacement of β cells alone. In vivo, the pancreas is made up of 4 major endocrine cell types, that is, insulin-producing β cells, glucagon-producing α cells, somatostatin-producing δ cells, and pancreatic polypeptide-producing γ cells. These distinct cell types are involved synergistically in regulating islet functions. Therefore, it is necessary to produce a pancreatic islet organoid in vitro consisting of all these cell types that adequately replaces the function of the native islets. In this review, we describe the unique function of each pancreatic endocrine cell type and their interactions contributing to the maintenance of normoglycemia. Furthermore, we detail current sources of whole islets and techniques for their long-term expansion and culture. In addition, we highlight a vast potential of the pancreatic islet organoids for transplantation and diabetes research along with updated new approaches for successful transplantation using stem cell-derived islet organoids.

Ngn3-Positive Cells Arise from Pancreatic Duct Cells

The production of pancreatic β cells is the most challenging step for curing diabetes using next-generation treatments. Adult pancreatic endocrine cells are thought to be maintained by the self-duplication of differentiated cells, and pancreatic endocrine neogenesis can only be observed when the tissue is severely damaged. Experimentally, this can be performed using a method named partial duct ligation (PDL). As the success rate of PDL surgery is low because of difficulties in identifying the pancreatic duct, we previously proposed a method for fluorescently labeling the duct in live animals. Using this method, we performed PDL on neurogenin3 (Ngn3)-GFP transgenic mice to determine the origin of endocrine precursor cells and evaluate their potential to differentiate into multiple cell types. Ngn3-activated cells, which were marked with GFP, appeared after PDL operation. Because some GFP-positive cells were aligned proximally to the duct, we hypothesized that Ngn3-positive cells arise from the pancreatic duct. Therefore, we next developed an in vitro pancreatic duct culture system using Ngn3-GFP mice and examined whether Ngn3-positive cells emerge from this duct. We observed GFP expressions in ductal organoid cultures. GFP expressions were correlated with Ngn3 expressions and endocrine cell lineage markers. Interestingly, tuft cell markers were also correlated with GFP expressions. Our results demonstrate that in adult mice, Ngn3-positive endocrine precursor cells arise from the pancreatic ducts both in vivo and in vitro experiments indicating that the pancreatic duct could be a potential donor for therapeutic use.

Differentiation of Human-Induced Pluripotent Stem Cell-Derived Endocrine Progenitors to Islet-like Cells Using a Dialysis Suspension Culture System

The production of functional islet-like cells from human-induced pluripotent stem cells (hiPSCs) is a promising strategy for the therapeutic use and disease modeling for type 1 diabetes. However, the production cost of islet-like cells is extremely high due to the use of expensive growth factors for differentiation. In a conventional culture method, growth factors and beneficial autocrine factors remaining in the culture medium are removed along with toxic metabolites during the medium change, and it limits the efficient utilization of those factors. In this study, we demonstrated that the dialysis suspension culture system is possible to reduce the usage of growth factors to one-third in the differentiation of hiPSC-derived endocrine progenitor cells to islet-like cells by reducing the medium change frequency with the refinement of the culture medium. Furthermore, the expression levels of hormone-secretion-related genes and the efficiency of differentiation were improved with the dialysis suspension culture system, possibly due to the retaining of autocrine factors. In addition, we confirmed several improvements required for the further study of the dialysis culture system. These findings showed the promising possibility of the dialysis suspension culture system for the low-cost production of islet-like cells.

CD82 is a marker to isolate β cell precursors from human iPS cells and plays a role for the maturation of β cells

Generation of pancreatic β cells from pluripotent stem cells is a key technology to develop cell therapy for insulin-dependent diabetes and considerable efforts have been made to produce β cells. However, due to multiple and lengthy differentiation steps, production of β cells is often unstable. It is also desirable to eliminate undifferentiated cells to avoid potential risks of tumorigenesis. To isolate β cell precursors from late stage pancreatic endocrine progenitor (EP) cells derived from iPS cells, we have identified CD82, a member of the tetraspanin family. CD82⁺ cells at the EP stage differentiated into endocrine cells more efficiently than CD82^- EP stage cells. We also show that CD82⁺ cells in human islets secreted insulin more efficiently than CD82^- cells. Furthermore, knockdown of CD82 expression by siRNA or inhibition of CD82 by monoclonal antibodies in NGN3⁺ cells suppressed the function of β cells with glucose-stimulated insulin secretion, suggesting that CD82 plays a role in maturation of EP cells to β cells.

Harnessing Proliferation for the Expansion of Stem Cell-Derived Pancreatic Cells: Advantages and Limitations

Restoring the number of glucose-responsive β-cells in patients living with diabetes is critical for achieving normoglycemia since functional β-cells are lost during the progression of both type 1 and 2 diabetes. Stem cell-derived β-cell replacement therapies offer an unprecedented opportunity to replace the lost β-cell mass, yet differentiation efficiencies and the final yield of insulin-expressing β-like cells are low when using established protocols. Driving cellular proliferation at targeted points during stem cell-derived pancreatic progenitor to β-like cell differentiation can serve as unique means to expand the final cell therapeutic product needed to restore insulin levels. Numerous studies have examined the effects of β-cell replication upon functionality, using primary islets in vitro and mouse models in vivo, yet studies that focus on proliferation in stem cell-derived pancreatic models are only just emerging in the field. This mini review will discuss the current literature on cell proliferation in pancreatic cells, with a focus on the proliferative state of stem cell-derived pancreatic progenitors and β-like cells during their differentiation and maturation. The benefits of inducing proliferation to increase the final number of β-like cells will be compared against limitations associated with driving replication, such as the blunted capacity of proliferating β-like cells to maintain optimal β-cell function. Potential strategies that may bypass the challenges induced by the up-regulation of cell cycle-associated factors during β-cell differentiation will be proposed.