Reduced serum concentration is permissive for increased in vitro endocrine differentiation from murine embryonic stem cells

Improvement of isolated caprine islet survival and functionality in vitro by enhancing of PDX1 gene expression

BACKGROUND

Dead islets replaced with viable islets are a promising offer to restore normal insulin production to a person with diabetes. The main reason for establishing a new islet source for transplantation is the insufficiency of human donor pancreas while using xenogeneic islets perhaps assists this problem. The expression of PDX1 is essential for the pancreas expansion. In mature β-cells, PDX1 has several critical roles such as glucose sensing, insulin synthesis, and insulin secretion. In this study, we aimed to evaluate the expression of pancreatic duodenal homeobox-1 (PDX1) in treated caprine islets in culture and to assess the protective effects of antioxidant factors on the PDX1 gene in cultured caprine islets.

MATERIALS AND METHODS

Purified islets were treated with serum-free, serum, IBMX, tocopherol, or IBMX and tocopherol media. Quantitative polymerase chain reaction and Western blotting were carried out to compare the expression levels of PDX1 in treated purified islets cultured with different media.

RESULTS

Islets treated with IBMX/tocopherol exhibited the highest fold change in the relative expression of PDX1 on day 5 post-treatment (relative expression: 6.80±2.08), whereas serum-treated islets showed the lowest fold changes in PDX1 expression on day 5 post-treatment (0.67±0.36), as compared with the expression on day 1 post-treatment. Insulin production and viability tests of purified islets showed superiority of islet at supplemented serum-free media with IBMX/tocopherol compared to other cultures (53.875%±1.59%).

CONCLUSIONS

Our results indicated that supplemented serum-free medium with tocopherol and IBMX enhances viability and PDX1 gene expression compared to serum-added and serum-free media.

Ectopic Ptf1a expression in murine ESCs potentiates endocrine differentiation and models pancreas development in vitro

Besides its role in exocrine differentiation, pancreas-specific transcription factor 1a (PTF1a) is required for pancreas specification from the foregut endoderm and ultimately for endocrine cell formation. Examining the early role of PTF1a in pancreas development has been challenging due to limiting amounts of embryonic tissue material for study. Embryonic stem cells (ESCs) which can be differentiated in vitro, and without limit to the amount of experimental material, can serve as a model system to study these early developmental events. To this end, we derived and characterized a mouse ESC line with tetracycline-inducible expression of PTF1a (tet-Ptf1a mESCs). We found that transient ectopic expression of PTF1a initiated the pancreatic program in differentiating ESCs causing cells to activate PDX1 expression in bud-like structures resembling pancreatic primordia in vivo. These bud-like structures also expressed progenitor markers characteristic of a developing pancreatic epithelium. The epithelium differentiated to generate a wave of NGN3+ endocrine progenitors, and further formed cells of all three pancreatic lineages. Notably, the insulin+ cells in the cultures were monohormonal, and expressed PDX1 and NKX6.1. PTF1a-induced cultures differentiated into significantly more endocrine and exocrine cells and the ratio of endocrine-to-exocrine cell differentiation could be regulated by retinoic acid (RA) and nicotinamide (Nic) signaling. Moreover, induced cultures treated with RA and Nic exhibited a modest glucose response. Thus, this tet-Ptf1a ESC-based in vitro system is a valuable new tool for interrogating the role of PTF1a in pancreas development and in directing differentiation of ESCs to endocrine cells.

Directed pancreatic acinar differentiation of mouse embryonic stem cells via embryonic signalling molecules and exocrine transcription factors

Pluripotent embryonic stem cells (ESC) are a promising cellular system for generating an unlimited source of tissue for the treatment of chronic diseases and valuable in vitro differentiation models for drug testing. Our aim was to direct differentiation of mouse ESC into pancreatic acinar cells, which play key roles in pancreatitis and pancreatic cancer. To that end, ESC were first differentiated as embryoid bodies and sequentially incubated with activin A, inhibitors of Sonic hedgehog (Shh) and bone morphogenetic protein (BMP) pathways, fibroblast growth factors (FGF) and retinoic acid (RA) in order to achieve a stepwise increase in the expression of mRNA transcripts encoding for endodermal and pancreatic progenitor markers. Subsequent plating in Matrigel® and concomitant modulation of FGF, glucocorticoid, and folllistatin signalling pathways involved in exocrine differentiation resulted in a significant increase of mRNAs encoding secretory enzymes and in the number of cells co-expressing their protein products. Also, pancreatic endocrine marker expression was down-regulated and accompanied by a significant reduction in the number of hormone-expressing cells with a limited presence of hepatic marker expressing-cells. These findings suggest a selective activation of the acinar differentiation program. The newly differentiated cells were able to release α-amylase and this feature was greatly improved by lentiviral-mediated expression of Rbpjl and Ptf1a, two transcription factors involved in the maximal production of digestive enzymes. This study provides a novel method to produce functional pancreatic exocrine cells from ESC.