Adult stem cells as a renewable source of insulin-producing cells.

Diabetes mellitus is a metabolic disorder resulting from an inadequate mass of insulin-producing pancreatic beta cells. The replacement or restoration of damaged beta cells would be considered the optimal therapeutic options. Islet transplantation seems to be a promising approach for replacement therapy; however, the main obstacle is the shortage of organ donors. As mature beta cells have been shown to be difficult to expand in vitro, regeneration of beta cells from embryonic or adult stem cells or pancreatic progenitor cells is an attractive method to restore the islet cell mass. So far, multiple studies using various strategies have shown direct differentiation of stem and progenitor cells toward insulin-producing cells. The important issue to be solved is how to differentiate these cells into mature functional insulin-producing cells. Further research is required to understand how endogenous beta cells differentiate and to develop methods to regenerate enough functional beta cells for clinically applicable therapies for diabetes.