Direct lineage conversion of adult cells is a promising approach for regenerative medicine. A major challenge of lineage conversion is to generate specific cell subtypes. The pancreatic islets contain three major hormone-secreting endocrine subtypes: insulin+ β-cells, glucagon+ α-cells, and somatostatin+ δ-cells. We previously reported that a combination of three transcription factors, Ngn3, Mafa, and Pdx1, directly reprograms pancreatic acinar cells to β-cells. We now show that acinar cells can be converted to δ-like and α-like cells by Ngn3 and Ngn3+Mafa respectively. Thus, three major islet endocrine subtypes can be derived by acinar reprogramming. Ngn3 promotes establishment of a generic endocrine state in acinar cells, and also promotes δ-specification in the absence of other factors. δ-specification is in turn suppressed by Mafa and Pdx1 during α- and β-cell induction. These studies identify a set of defined factors whose combinatorial actions reprogram acinar cells to distinct islet endocrine subtypes in vivo.
In mammals, the pancreas is responsible for controlling blood sugar by secreting insulin from specialized β-cells. Other cells in the pancreas, called δ-cells and α-cells, secrete other hormones to assist the β-cells. Diabetes is caused when this system breaks down: either the body attacks its own β-cells (type I diabetes), or the body stops responding properly to insulin (type II).
Type I diabetes is usually treated with insulin injections, but there is increasing interest in the possibility of replacing the defective β-cells instead. Building on previous work in which a fourth type of pancreatic cell, called an acinar cell, was reprogrammed to become a β-cell, Li et al. have now shown that the same technique can be used to produce α- and δ-cells as well. Just as the reprogrammed β-cells secreted insulin, like real β-cells, the reprogrammed α- and δ-cells also behaved like real α- and δ-cells.
The reprogramming technique relies on using a combination of three transcription factors—which are called Ngn3, Pdx1 and Mafa—to treat the acinar cells from mice. Previously, it was shown that using a combination of all three transcription factors reprogrammed the acinar cells to become β-cells. Now, Li et al. show that the Ngn3 transcription factor on its own appears to suppress certain genes that are usually expressed in acinar cells, and goes on to cause the acinar cells to become δ-cells. However, a combination of Ngn3 and Mafa produces a mixture of α- and δ-cells. The next challenge is to adapt this reprogramming technique to generate different types of hormone secreting cells from human tissue sources in order to explore its therapeutic potential.