Redefining the signaling pathways from pluripotency to pancreas development: In vitro β-cell differentiation.

Pancreatic β-cells are destroyed by the immune system, in type 1 diabetes (T1D) and are impaired by glucose insensitivity in type 2 diabetes (T2D). Islet-cells transplantation is a promising therapeutic approach based on in vitro differentiation of pluripotent stem cells (PSCs) to insulin-producing cells (IPCs). According to evolutionary stages in β-cell development, there are several distinct checkpoints; each one has a unique characteristic, including definitive endoderm (DE), primitive gut (PG), posterior foregut (PF), pancreatic epithelium (PE), endocrine precursor (EP), and immature β-cells up to functional β-cells. A better understanding of the gene regulatory networks (GRN) and associated transcription factors in each specific developmental stage, guarantees the achievement of the next successful checkpoints and ensures an efficient β-cell differentiation procedure. The new findings in signaling pathways, related to the development of the pancreas are discussed here, including Wnt, Activin/Nodal, FGF, BMP, retinoic acid (RA), sonic hedgehog (Shh), Notch, and downstream regulators, required for β-cell commitment. We also summarized different approaches in the IPCs protocol to conceptually define a standardized system, leading to the creation of a reproducible method for β-cell differentiation. To normalize blood glucose level in diabetic mice, the replacement therapy in the early differentiation stage, such as EP stages was associated with better outcome when compared with the fully differentiated β-cells' graft.