A fishing expedition for antidiabetic drugs : identifying new avenues to stimulate beta-cell regeneration

Abstract

All types of diabetes are characterized by loss of the insulin-producing β-cells that reside in the pancreas. While current treatments can manage the disease, there is still no cure available. Understanding and promoting endogenous β-cell regeneration is an attractive approach that can lead to an eventual cure for diabetes. This thesis aims to discover new molecular pathways that can promote β-cell regeneration by using mainly the zebrafish model system, which can spontaneously regenerate its β-cells following injury.

In Papers I & II, we performed a transcriptomics profiling of the microenvironment of the zebrafish regenerating islet using microarray and RNA-Seq technologies respectively and we coupled this profile with in vivo genetic screens. We aimed to identify upregulated genes that code for secreted proteins that when overexpressed in the same zebrafish model could stimulate β-cell regeneration at supraphysiological levels. In Paper I, we found that by overexpressing igfbp1a, we promoted transdifferentiation of pancreatic a-cells to β-cells. This phenotype was conserved in mouse and human islet cultures suggesting that the pathway could translate to mammals. In Paper II, we showed that folr1 overexpression stimulated β- cell regeneration in the zebrafish through differentiation of duct-residing pancreatic progenitors. The observed phenotype was mediated through membrane-bound folr1 and treatment with folinic acid, a ligand of folr1, increased β-cell formation in zebrafish and pig islet cultures. Overall, these two in vivo genetic screens uncovered two important pathways stimulating β-cell regeneration in a variety of experimental models.

In Paper III, we aimed to identify the target of CID661578 a potent small molecule that potentiates β-cell regeneration in zebrafish. Experimentally, we combined a modified yeast-2- chemical screen together with in vivo zebrafish genetic models and uncovered MNK2 as the molecular target of CID661578. Mechanistically, CID661578 boosted protein translation by binding and removing MNK2 from the translation initiation complex as shown by in vitro biochemical and in vivo zebrafish experiments. In summary, this work ascribes a new role for the translation initiation complex in β-cell regeneration. In Paper IV, we characterized the liver to pancreas interaction following β-cell injury with the aim to identify secreted proteins/metabolites from the liver that stimulate β-cell regeneration. By performing a genetic screen in zebrafish larvae, we revealed a role for molybdenum metabolism in stimulating β-cell regeneration.

Overall, the work performed in this thesis identified four new molecular pathways that could stimulate β-cell regeneration in an array of experimental models that could be further advanced as potential diabetes therapies.