Optimization of activin-A: a breakthrough in differentiation of human induced pluripotent stem cell into definitive endoderm

Low concentrations of saracatinib promote definitive endoderm differentiation through inhibition of FAK-YAP signaling axis

Optimizing the efficiency of definitive endoderm (DE) differentiation is necessary for the generation of diverse organ-like structures. In this study, we used the small molecule inhibitor saracatinib (SAR) to enhance DE differentiation of human embryonic stem cells and induced pluripotent stem cells. SAR significantly improved DE differentiation efficiency at low concentrations. The interaction between SAR and Focal Adhesion Kinase (FAK) was explored through RNA-seq and molecular docking simulations, which further supported the inhibition of DE differentiation by p-FAK overexpression in SAR-treated cells. In addition, we found that SAR inhibited the nuclear translocation of Yes-associated protein (YAP), a downstream effector of FAK, which promoted DE differentiation. Moreover, the addition of SAR enabled a significant reduction in activin A (AA) from 50 to 10 ng/mL without compromising DE differentiation efficiency. For induction of the pancreatic lineage, 10 ng/ml AA combined with SAR at the DE differentiation stage yielded a comparative number of PDX1+/NKX6.1+ pancreatic progenitor cells to those obtained by 50 ng/ml AA treatment. Our study highlights SAR as a potential modulator that facilitates the cost-effective generation of DE cells and provides insight into the orchestration of cell fate determination.

Reduction of Activin A gives rise to comparable expression of key definitive endoderm and mature beta cell markers

Aim: Cell therapies for diabetes rely on differentiation of stem cells into insulin-producing cells, which is complex and expensive. Our goal was to evaluate production costs and test ways to reduce it. Methods: Cost of Goods (COGs) analysis for differentiation was completed and the effects of replacement or reduction of the most expensive item was tested using qRT-PCR, immunohistochemistry, flow cytometry along with glucose-stimulated insulin release. Results: Activin A (AA) was responsible for significant cost. Replacement with small molecules failed to form definitive endoderm (DE). Reducing AA by 50% did not negatively affect expression of beta cell markers. Conclusion: Reduction of AA concentration is feasible without adversely affecting DE and islet-like cell differentiation, leading to significant cost savings in manufacturing.

A Comparative Study of Endoderm Differentiation Between Activin A and Small Molecules

Small molecules such as ROCK inhibitors (Fasudil) and inducer of definitive endoderm 1 (IDE1) can promote differentiation of definitive endoderm, but their effects remain controversial. Therefore, we attempted to verify the effect of these small molecules on promoting definitive endoderm differentiation and found that Fasudil or IDE1 alone could not achieve a similar effect as activin A. On the contrary, CHIR99021 could efficiently promote definitive endoderm differentiation. Nearly 43.4% of experimental cells were SRY-box transcription factor 17 (SOX17)-positive under the synergistic effect of IDE1 and CHIR99021, but its ability to differentiate towards definitive endoderm was still insufficient. Transcriptional analysis and comparison of IDE1 and CHIR99021 synergistic groups (IC) and activin A and CHIR99021 synergistic groups (AC) showed significantly down-regulated definitive endoderm markers in the IC group compared with those in the AC group and the differences between the two groups were mainly due to bone morphogenetic proteins (BMP4) and fibroblast growth factor 17 (FGF17). Further single-cell transcriptome analysis revealed lower expression of BMP4 in SOX17-positive populations, while mothers against decapentaplegic homolog (SMAD) protein translation signal and FGF17 in the AC group were higher than that in the IC group. Western blot analysis showed a significant difference in levels of p-SMAD2/3 between AC and IC groups, which suggests that regulating p-SMAD2/3 may provide a reference to improve the differentiation of definitive endoderm.

Regeneration of Pancreatic Cells Using Optimized Nanoparticles and l-Glutamic Acid-Gelatin Scaffolds with Controlled Topography and Grafted Activin A/BMP4

Regeneration of insulin-producing cells (IPCs) from induced pluripotent stem cells (iPSCs) under controlled conditions has a lot of promise to emulate the pancreatic mechanism in vivo as a foundation of cell-based diabetic therapy. l-Glutamic acid-gelatin scaffolds with orderly pore sizes of 160 and 200 μm were grafted with activin A and bone morphogenic proteins 4 (BMP4) to differentiate iPSCs into definitive endoderm (DE) cells, which were then guided with fibroblast growth factor 7 (FGF7)-grafted retinoic acid (RA)-loaded solid lipid nanoparticles (FR-SLNs) to harvest IPCs. Response surface methodology was adopted to optimize the l-glutamic acid-to-gelatin ratio of scaffolds and to optimize surfactant concentration and lipid proportion in FR-SLNs. Experimental results of immunofluorescence, flow cytometry, and western blots revealed that activin A (100 ng/mL)-BMP4 (50 ng/mL)-l-glutamic acid (5%)-gelatin (95%) scaffolds provoked the largest number of SOX17-positive DE cells from iPSCs. Treatment with FGF7 (50 ng/mL)-RA (600 ng/mL)-SLNs elicited the highest number of PDX1-positive β-cells from differentiated DE cells. To imitate the natural pancreas, the scaffolds with controlled topography were appropriate for IPC production with sufficient insulin secretion. Hence, the current scheme using FR-SLNs and activin A-BMP4-l-glutamic acid-gelatin scaffolds in the two-stage differentiation of iPSCs can be promising for replacing impaired β-cells in diabetic management.

Mitochondrial homeostasis regulates definitive endoderm differentiation of human pluripotent stem cells

Cellular organelles play fundamental roles in almost all cell behaviors. Mitochondria have been reported to be functionally linked to various biological processes, including reprogramming and pluripotency maintenance. However, very little about the role of mitochondria has been revealed in human early development and lineage specification. Here, we reported the characteristics and function of mitochondria during human definitive endoderm differentiation. Using a well-established differentiation system, we first investigated the change of mitochondrial morphology by comparing undifferentiated pluripotent stem cells, the intermediate mesendoderm cells, and differentiated endoderm cells, and found that mitochondria were gradually elongated and matured along differentiation. We further analyzed the expression pattern of mitochondria-related genes by RNA-seq, indicating that mitochondria became active during differentiation. Supporting this notion, the production of adenosine triphosphate (ATP) and reactive oxygen species (ROS) was increased as well. Functionally, we utilized chemicals and genome editing techniques, which could interfere with mitochondrial homeostasis, to determine the role of mitochondria in human endoderm differentiation. Treatment with mitochondrial inhibitors, or genetic depletion of mitochondrial transcription factor A (TFAM), significantly reduced the differentiation efficiency of definitive endoderm. In addition, the defect in endoderm differentiation due to dysfunctional mitochondria could be restored to some extent by the addition of ATP. Moreover, the clearance of excessive ROS due to dysfunctional mitochondria by N-acetylcysteine (NAC) improved the differentiation as well. We further found that ATP and NAC could partially replace the growth factor activin A for definitive endoderm differentiation. Our study illustrates the essential role of mitochondria during human endoderm differentiation through providing ATP and regulating ROS levels, which may provide new insight for metabolic regulation of cell fate determination.

Differentiation of Human Wharton's Jelly Mesenchymal Stem Cells into SOX17 Expressing Cells Using a Wnt/ß-catenin Pathway Agonist on Polylactic Acid/Chitosan Nanocomposite Scaffold

Objective

The β-catenin signaling pathway promises the potential for differentiation of stem cells into definitive endoderm (DE) cells as precursors of beta cells. Therefore, it can be considered as an inducer for cell replacement therapies in diabetes. The main goal of this research is to successfully culture and induce differentiation of human Wharton's jelly mesenchymal stem cells (hWJMSCs) into Sox17-expressing cells using a Wnt/β-catenin pathway agonist (SKL2001) plus nanoparticles on a polylactic acid/chitosan (PLA/Cs) nanocomposite scaffold.

Materials and Methods

In this experimental study, the nanocomposite was prepared through an electrospinning method and hWJMSCs were isolated through an explant technique. The morphology and the cell viability were evaluated by scanning electron microscopy (SEM) and 3-(4, 5- Dimethylthiazol-2)-2, 5-diphenyltetrazolium bromide (MTT) assay. Here, we present two differentiation protocols: the first one is induction with SKL2001; and the second one is with a combination of SKL2001 and zinc oxide nanoparticles (nZnO). Real-time quantitative reverse transcription (QRT-PCR) and immunocytochemistry analysis are carried out to examine the expression of specific markers in the differentiated cells.

Results

The nanocomposite had appropriate biocompatibility for cell adhesion and growth. While the hWJMSCs cultured on the PLA/Cs scaffolds differentiated into DE cells in the presence of SKL2001, introducing nZnO to their environment increased the differentiation process. Analyses of DE-specific markers including SOX17, FOXA2, and gooscoid (GSC) genes in mRNA level, indicated significantly high levels of expression in the SKL2001/nZnO group, followed by SKL2001 group compared to the control.

Conclusion

Our results show the beneficial effects of the Wnt/β-catenin pathway agonist in three-dimensional (3D) cultures in cell replacement therapy for diabetes.

Toward Xeno-Free Differentiation of Human Induced Pluripotent Stem Cell-Derived Small Intestinal Epithelial Cells

The small intestinal epithelium has an important role in nutrition, but also in drug absorption and metabolism. There are a few two-dimensional (2D) patient-derived induced pluripotent stem cell (iPSC)-based intestinal models enabling easy evaluation of transcellular transport. It is known that animal-derived components induce variation in the experimental outcomes. Therefore, we aimed to refine the differentiation protocol by using animal-free components. More specifically, we compared maturation of 2D-cultured iPCSs toward small intestinal epithelial cells when cultured either with or without serum, and either on Geltrex or on animal-free, recombinant laminin-based substrata. Differentiation status was characterized by qPCR, immunofluorescence imaging, and functionality assays. Our data suggest that differentiation toward definitive endoderm is more efficient without serum. Both collagen- and recombinant laminin-based coating supported differentiation of definitive endoderm, posterior definitive endoderm, and small intestinal epithelial cells from iPS-cells equally well. Small intestinal epithelial cells differentiated on recombinant laminin exhibited slightly more enterocyte specific cellular functionality than cells differentiated on Geltrex. Our data suggest that functional small intestinal epithelial cells can be generated from iPSCs in serum-free method on xeno-free substrata. This method is easily converted to an entirely xeno-free method.

Evaluation of Autophagy Process in Differentiation of Human Induced Pluripotent Stem Cells toward Insulin Producing Cells

Background

Autophagy is an intracellular self-degradative homeostasis process which eliminates undesirable and harmful macromolecules and organelles. Autophagy is also involved in self-renewal and differentiation of induced pluripotent stem cell (iPSCs).

Objective

In this study, we investigated the expression profile of autophagy marker genes in human iPSCs during their differentiation induction toward insulin producing β-like cells.

Methods

Human iPSC line, R1-hiPSC1, was used for differentiation induction toward β-like cells. The mRNA expression of Nanog, OCT4 (pluripotency markers), SOX17, FOXA2 (endodermic markers), PTF1A, NKX6.1 (exocrine/endocrine determinants), and PDX1 were measured during differentiation stages. Autophagy was monitored by genes expression study of four autophagy markers, MAP1LC3B, BECN1, SQSTM1/P62 and ATG5, along with protein expression profile of LC3b-II during differentiation stages.

Results

The mRNA expression measurement of pluripotency, endoderm and exocrine/endocrine marker genes confirmed that hiPSCs skipped pluripotency, differentiated into endoderm, passed through the pancreatic lineage commitment stage and successfully generated insulin producing β-like cells. Expression profile of autophagy genes during differentiation stages indicated the decreased expression levels at the early stages (EB and MEI) and then increased at the definitive endoderm stages (DEI 1, DEI 2 and DE) followed by a subtractive pattern toward the end of differentiation. The results of protein expression of LC3b-II were consistent with gene expression data.

Conclusion

This study demonstrated the high contribution of key autophagy genes/proteins during the differentiation of hiPSC toward β-like cells. The enhanced autophagy levels were a prominent feature of early stages of differentiation and DE rather than the later stages.